Onco Chat

What's in Placebos: Who knows? Analysis of randomized, controlled trials

Background: No regulations govern placebo composition. The composition of placebos can influence trial outcomes and merits reporting.

Purpose: To assess how often investigators specify the composition of placebos in randomized, placebo-controlled trials.

Data Sources: 4 English-language general and internal medicine journals with high impact factors.

Study Selection: 3 reviewers screened titles and abstracts of the journals to identify randomized, placebo-controlled trials published from January 2008 to December 2009.

Data Extraction: Reviewers independently abstracted data from the introduction and methods sections of identified articles, recording treatment type (pill, injection, or other) and whether placebo composition was stated. Discrepancies were resolved by consensus.

Data Synthesis: Most studies did not disclose the composition of the study placebo. Disclosure was less common for pills than for injections and other treatments (8.2% vs. 26.7%; P = 0.002).

Limitation: Journals with high impact factors may not be representative.

Conclusion: Placebos were seldom described in randomized, controlled trials of pills or capsules. Because the nature of the placebo can influence trial outcomes, placebo formulation should be disclosed in reports of placebo-controlled trials.

via www.annals.org

 

Thanks to Bruce Lehr of the Big Red Biotech Blog for bringing this topic to my attention.

In many trials of new drugs in development such as cardiovascular, dermatology, neuroscience etc, the test agent is typically compared to a placebo with a similar formulation such as a pill, topical cream etc, but as the journal points out, rarely is the composition defined in detail. 

This is not surprising, as the authors of the paper reported that they found that only a paltry 8.2% of the 86 studies they looked at actually stated clearly what the contents of the placebo were.

Does it matter?

Well, you might think it's just a 'sugar pill', but as this article in the LA Times noted, some placebos in cardiovascular trials might consist of olive oil or other polyunsaturated oils, thereby potentially reducing cholesterol and heart disease. Certainly something to think about, as they may have unexpected effects.

Although most cancer clinical trials are typically comparing a new treatment to the standard of care, often placebo is used in the comparator combination. A recent example is the abiraterone trial reported last week at ESMO in men with advanced, castration resistant prostate cancer after prior docetaxel therapy. The study compared abiraterone (a pill) with prednisone (a steroid) to placebo (pill) plus prednisone. Based on the information provided in clinicaltrials.gov, it isn't clear what the placebo actually was.

I liked the quote from the authors in the LA Times article above:

"Perfect placebo is not the aim, rather, we seek to ensure that its composition is disclosed."

Given the placebo could have unexpected effects or at least have an impact, perhaps we should start disclosing what's actually in them.

#ESMO 2010 round-up #3

Back from Milan and ESMO 2010, I thought it would be a good idea to quick a final quick overview of some of the early data from phase II trials that look interesting and might be worth watching as the research evolves (in no particular order).

1. Addition of cetuximab to cisplatin increased survival in triple negative breast cancer

Jose Baselga presented the results of a multi-centre randomised trial (from Spain, Belgium, Austria, Portugal, the UK and Israel) that compared the combination of cetuximab (Erbitux) with cisplatin versus cisplatin alone in 173 women with triple negative breast cancer (TNBC).

Although the overall response rate (ORR) trended in favour of the combination (20.0 vs 10.3%), the result did not meet the pre-specified assumptions. Interestingly though, the progression-free survival (PFS) showed a significant improvement with the addition of cetuximab (3.7 vs 1.5 months, P<0.03). Two months doesn't seem much, but in an advanced, highly aggressive disease, it may represent a disproportionally large improvement.

I'm not sure why cisplatin was chosen as a comparator, especially as TNBC is a particularly hard subset to treat, but the trial is ongoing to determine overall survival and a phase III study will likely evolve to determine if the results are repeatable in a larger population.

2. GSK2118436 in advanced melanoma with brain mets looks promising in a phase I/II study

By promising, I mean this was a very small cohort of patients who saw some early and unexpected evidence of tumour shrinkage in brain mets that had evolved from primary melanoma. The scans shown by the presenter, Georgina Long, from the Melanoma Institute Australia and Westmead Hospital in Sydney actually gave me goosebumps and it wasn't the chill in the room. You just don't expect to see such noticeable shrinkage with a single agent in this setting because this is a horrid, aggressive disease that has a nasty tendency to metastasize easily.

What was interesting about this study is that GSK2118436 is a BRAF inhibitor that also specifically targets V600E, similarly to Plexxikon/Roche's PLX4032. In both cases, they bind to the protein and shut down signaling activity. Although the trial is very early, since it looked at 3 different cohorts, the small subset with brain mets (n=10) were what caught everyone in the audience's attention, although good responses were also seen in the advanced melanoma group without brain mets.

To put the results in context, all 10 patients experienced some control of their brain mets, with 9 of the 10 patients having reductions in the overall size of their tumours. The overall reductions ranged from 20-100% of brain metastases that were 3mm or larger in diameter before treatment.

That just doesn't happen with advanced melanoma with brain mets... at least, I've never seen such dramatic responses before.

The big questions for me are how long will the responses be durable before resistance sets in and how soon is a larger scale trial going to get up and running? This is a very promising and most unexpected development that is worth following.

Dr Long summed it up very nicely:

“The ability to inhibit oncogenic BRAF is the most important development in the history of drug treatment of melanoma.”

3. ARQ-197 continues to show positive results in NSCLC

In this presentation, the final results of the phase II trial in non-small cell lung cancer (NSCLC) were discussed. We've covered this promising agent, ARQ-197 (ArQule/Daiichi Sankyo), a small molecule c-MET inhibitor, before on this blog.

A final analysis looked at the complete results in more depth. Patients treated with ARQ 197 plus erlotinib (Tarceva) developed new metastases in a median time of 7.3 months compared with 3.6 months for patients treated with erlotinib plus placebo.

What I found interesting in this study was that this effect was more pronounced among patients with non-squamous (NS) histology, since the median time to develop new metastases was 11.0 months in the ARQ 197 plus erlotinib arm compared to 3.6 months for those treated with the control arm (erlotinib plus placebo). I'm not sure why the NS over squamous histology should matter, but they clearly benefitted more.

The sponsors, ArQule and Daiichi Sankyo, have announced that they plan to pursue a phase III trial in this setting. It would, however, be nice to see an analysis of any lung biopsies collected to see if there are any relevant biomarkers that would explain the differences in histology and responders, otherwise many physicians may see this as an incremental improvement, if confirmed in a larger trial. Were thre any differences in people who were EGFR mutation or MET positive, for example?

There was certainly some energetic discussion in the Q&A, with tough questions asked of the speaker regarding why go ahead with a phase III study given a small benefit and why use OS when PFS is small and complicated by crossover, all very fair questions. Like many, I'd really like to see more granular analysis of who is responding to this agent and why before rushing into a phase III trial that may see a disappearing of any positive signal when investigator bias is eliminated in a larger randomised trial.

4. METMAB showed promising results in a subset of lung cancer patients

In the same session, David Spiegel presented the data from a phase II study with a different c-MET inhibitor. Here, patients with advanced NSCLC (n=128) were randomly assigned to receive either erlotinib plus METMAb (Roche/Genentech), a monoclonal antibody that binds specifically to the MET receptor on cancer cells or a control arm (erlotinib plus placebo).

The reason for the interest in c-MET inhibitors is that MET activation has been implicated in the resistance of lung cancers to EGFR inhibitors such as erlotinib. The big question is therefore whether a combination of the two would overcome resistance or not, thereby prolonging life.

In this study, participants were tested for mutations in the EGFR gene and also for expression of MET in tumour samples. 

The results were interesting - 51% of patients whose tumours expressed MET and those who received METMAb plus erlotinib had better OS and longer PFS than those who received erlotinib plus placebo.

Furthermore, in the subset of MET+ patients, adding METMAb to erlotinib nearly halved the risk of disease progression or death during the study compared to those treated with erlotinib plus placebo. In addition, patients whose tumours did not express MET protein appeared to do worse when treated with the METMAb/erlotinib combination, suggesting that the biomarker may be able to determine who is more likely to respond to therapy.

This is good news if it is repeatable in a phase III trial and show durable efficacy with good tolerability, because then potentially, oncologists would be able to screen and preselect patients for treatment with METMab rather than expose all patients to the systemic side effects without hope of it working.

Last but not least, there was some updated information on the novel trastuzumab-DM1 (T-DM1) combination therapy (Roche/Genentech).

4. T-DM1 continues to show solid results in metastatic breast cancer

Edith Perez presented the results of a phase II study looking at first line treatment with a new combination agent, trastuzumab-DM1 or T-DM1, in metastatic breast cancer.

As far as I know, T-DM1 is the first of a new type of cancer therapy known as an antibody-drug conjugate. Basically, it binds together two existing cancer drugs with the aim of delivering both drugs specifically to cancer cells, ie trastuzumab (Herceptin), an approved monoclonal antibody that targets the protein HER2 and DM1, a chemotherapy agent that targets microtubules. The goal of the new combination is too see if cardiotoxicity, a common problem associated with standard anthracycline therapy, is reduced and if efficacy is subsequently improved.

Women with breast cancer were randomised to treatment with either trastuzumab plus the chemotherapy drug docetaxel, or T-DM1. All 137 participants had HER2-positive metastatic cancer, with no prior chemotherapy for their metastatic disease.

The good news is that the early results demonstrated that T-DM1 has good anti-tumour activity as well as much lower toxicity when evaluated side by side to standard therapy.

After a median of approx 6 months of follow up, the overall response rate of in women who received T-DM1 was 48% compared with 41% in the control arm (trastuzumab plus docetaxel). The rates of clinically relevant adverse events were also significantly lower in the T-DM1 arm (37%) compared to the rate in women given traztuzumab plus docetaxel (75%).

Overall, I think the slight improvement in ORR was more than compensated by the dramatic improvement in side effects, which ultimately affect a patient's quality of life when undergoing cancer treatment. According to my chicken scratch notes from the session, cardiotoxicity and myelosuppression were both much improved in the T-DM1 arm over standard therapy.

Perez noted that the final analysis of the PFS data is expected in 2Q 2011, which I'm sure will be eagerly awaited based on the encouraging early data, although feeling better is one thing, but ultimately the sine qua non is will the women live longer?

All in all, I'm glad I trekked all the way to Milan for ESMO. There was more positive and promising early data than expected and aside from the repetitive blister walks, it was an enjoyable event. It was also nice to catch up with some friends in person and meet several readers of this blog who kindly came up and introduced themselves - I hope you all enjoyed the conference as much as I did!

What's hot in molecular diagnostics and biomarkers? #aacrMD #2

At the AACR meeting on Molecular Diagnostics and Cancer Therapeutics meeting in Denver, there was quite a bit of interesting scientific data coming out on cancer biology and biomarkers, so here is a quick synopsis of what appealed to me:

1. IGF-1R is over expressed in a subset of triple negative breast cancers (TNBC)

This presentation, from Witkiewicz et al., was interesting because they showed that IGF-1R might be a useful prognostic biomarker in TNBC. Usually, TNBC, which occurs in 15-20% of all breast cancers and is associated with a poorer prognosis, so finding a subgroup that might actually do better could be useful. Gene amplification was seen in 23% of the cases investigated. Caution must be exercised here, however, just because something is over expressed or amplified, does not mean that it is mutated, and therefore a potential druggable target with a therapeutic as we saw with the negative phase III results with figitumumab, an IGF-1R inhibitor in lung cancer.

What I would like to know though, is how many women with TNBC also have the BRCA1 or 2 mutation and have amplified IGF-1R? We know that targeting a cancer with one drug at one or two mutations in solid tumours has modest effects. But what if we target several things with a combination therapy, for a specific subset, then that might possibly yield different results altogether.

2. Molecular biomarker analysis using circulating tumour cells (CTCs)

Siminder Atwal, a Genentech scientist, presented her work on CTCs, with the idea of determining whether they could be used as a predictive biomarker by correlating CTCs with HER2 status in archival tumour samples. CTC's in theory should match tumour biopsies since they are cells that have shed from the primary tumour.  The Genentech scientists found that they were indeed correlated, with a high concordance (95%) using the CellSearch system. Of course, EpCAM expression can vary in some tumour types, complicating analysis and interpretation, but it looks like they saw some early hints that molecular biomarker status in CTCs are indeed reflecive of the biomarker status in patient tumours.

Predictive biomarkers allow us test whether a patient is likely to benefit from a given treatment, so the obvious and leading question is whether this work could be extended to look at eg CTC's in colorectal, lung or breast cancers to determine whether a patient is more likely to respond to bevacizumab (Avastin) or not. It would probably be easier in breast (lots of biopsy samples) and colorectal (lots of surgery providing samples).

At the moment, there is no way of telling who is most likely to respond to Avastin, so a predictive biomarker test would be really useful for clinicians before deciding on treatment, rather than having to expose thousands of patients to the systemic side effects. Given that the FDA have to make a decision by the year end on the full approval of Avastin in breast cancer, it is a shame that they likely won't have this sort of data to help guide a decision.  

3. BRCA1 mutations in prostate cancer

Gerhardt Attard gave an enlightening talk entitled, "Circulating tumor cells: Potential uses, pitfalls and challenges in their use as pharmacodynamic markers" but what struck me was not so much the fascinating information about CTCs as his mention that a subset of prostate cancer patients have the BRCA1 mutation. They tested the impact of olaparib, a small molecule PARP inhibitor from AstraZeneca, and found that all three responded.

A study open for men with prostate cancer and either BRCA1 or 2 mutations is currently recruiting patients. Given the interest with PARP inhibitors in breast and ovarian cancers, I'll be following this development with great interest.

What's hot in molecular diagnostics and biomarkers? AACR #1

One of the biggest challenges with Vascular Endothelial Growth Factor (VEGF) therapy to date has been the singular lack of either predictive or prognostic biomarkers.

This means that we have no idea which patients are most likely to respond to therapy (ie predictive) when selecting either a monoclonal antibody (eg bevacizumab) or a small molecule tyrosine kinase (eg sorafenib, sunitinib or pazopanib), nor do we will know what their likely prognostic outcome might be in terms of survival.

In an ideal world, we would be able to predetermine and monitor therapy for specific subtypes, thereby avoiding exposing thousands of patients to the systemic effects (and costs) of a drug that may not work for them.

Of course, we all know that developing biomarkers is:

1. not easy
2. could be rather expensive

I was therefore greatly cheered while at the AACR meeting Denver on Molecular Diagnostics and Cancer Therapeutics last week to come across a little gem of a poster from the scientists at AVEO Pharmaceuticals.

AVEO ($AVEO), a biotech based in Boston, are developing an oral VEGF inhibitor called tivozanib, currently in phase III for renal cell cancer, and appear to have developed a method to predict which patients are more likely to respond to the compound. Whoa!

I've been watching this company for a couple of years now and have been impressed with what I see so far. Two years ago I met their CMO Bill Slichenmyer over lunch at the AACR meeting in Denver when he was at Merrimack Pharma and kept track of what was happening at AVEO when he moved there. Both companies have interesting technology platforms and smart scientists.

Aside from the poster, AVEO's head of translational medicine, Murray Robinson, also presented the data during an oral session. What was particularly interesting was that the findings were not what one might expect - at all. They wondered if the potential biomarker they identified in animal studies might be reproduced in humans.

AVEO found their biomarker by inserting specific oncogenes and other engineered genes altered in numerous cancer types into the tissue of animals then studying the variety of tumours that were produced. One example of this approach was to genetically alter the HER2 gene, resulting in tumours that naturally expressed different pathways for growth.

They then looked at 600 tumour samples in clinical trials across eight different tumour types and realised that essentially the same biomarker identified in their breast tumour model was indeed associated with clinical activity in a set of kidney tumour patients from a previous Phase II kidney cancer trial. This biomarker was associated with white blood immune cells that are recruited into the tumour to produce angiogenic growth factors and leads to intrinsic resistance to tivozanib.

I confess to being kind of awed by this sort of research.

For some time, clinicians have been grumbling about not having a biomarker for Avastin, Sutent or Nexavar to better help choose which patients would be most likely to respond, thereby avoiding the need to treat everyone to gain a benefit in a few. Here we have three big pharma companies and no biomarker. A little biotech comes along with some smart ideas, a rational approach to the problem and some creative thinking to developing a biomarker for their compound, which is not yet on the market.

Of course, this biomarker is specific to AVEO's tivozanib, as no work has been completed to show that the myeloid component they identified is relevant in the others.

The good thing is that it's now the first biomarker associated with a VEGF therapy.

The bad news is that we will have to wait a little longer to see if the results of the phase III trials in kidney cancer are good enough for approval, but hopefully that won't be too long now.

Imagine one step further.  

Currently, the FDA is reviewing Roche's Avastin in breast cancer and deciding whether or not to withdraw the application given the marginal data currently available from trials such as AVADO. Suppose Roche/Genentech had a biomarker that was relative to Avastin and could be helpful for either prognostic or better still, predictive purposes? Then you could actually make better use of the drug based on a biomarker.

Before anyone in big pharma jumps up and down and starts moaning about the cost and the difficulty, take a look at AVEO's logical, sensible technical approach to the problem. You realise that what we really need is more imagination and creativity in R&D and less objections to progress.

Now suppose the biomarker AVEO identified in their breast cancer models turns out to be useful in breast cancer for women on their compound? If you can clearly show an association between different subsets, who is likely to develop resistance and who is more likely to respond, plus better outcomes, what's not to like?  The overall response rates will be higher in some subsets and lower in others, rather than a crapshoot of "well, it helps some women" or how about the vague "many women clearly benefitted". Great, but which ones and why?

In my opinion, AVEO have done a great job identifying a relevant biomarker for their compound which may actually increase rather than lessen the chances of successful approval down the road.

May the force be with them!

 

Biomarkers in cancer research - thoughts from AACR in Denver

This week I'm adjusting to the high altitude of Denver while at the American Association of Cancer Research (AACR) meeting on molecular diagnostics and cancer therapeutics. It's a great little meeting, networking opportunities are excellent and I'm learning a lot about what new cutting edge ideas are being explored.

I will be doing some highlights from each day series later in the week once I've had time to process all the information, as there is a lot to digest here.

What is interesting though, is to look at big picture trends, both in academia and basic research and also what industry are doing in their research teams, since these ideas may well get incorporated into early phase I clinical trials for validation and pilot purposes. More about this later in the week.

Although a lot of the attendees are from the diagnostics end of the business (either academic or industry), there are quite a few serious researchers and thinkers here too. Gordon Mills from MD Anderson gave one of the best talks I've seen at an opening session in a long while. David Parkinson from Nodality also laid out a strategic and thoughtful overview of how things are currently, and how they will continue to change in cancer research with new approaches. 

One thing really struck me here in Denver. While outsiders and FDA become more paranoid about conflicts of interest, it is clear to me that what we actually need is closer and more collaborative relationships between basic and clinical research in order to translate the knowledge and ideas into practice or the clinic more quickly.  To do this requires fresh ideas, a fresh approach and better communication and collaboration. 

By collaboration, I don't just mean between academia and industry, but between labs and between companies, rather than competition. Increasingly, I'm seeing smart researchers presenting data that was generated on behalf of several groups, often in different cities or even countries, each providing different skills and expertise to the research. This used to happen sporadically between friends and former colleagues, but now it's starting to become more commonplace. It's a good sign and a great way to synergies resources and bring more expertise to projects.

Industry are typically very slow to change and tend to see other companies as rivals rather than for collaborative purposes, which is a great shame given that we're all working towards the same goal: fight cancer. 

That said, there are some exciting new, albeit subtle changes afoot. When I think of cancer research, the first two industry research powerhouses I think of are Genentech, who have traditional sought strong relationships with academia and Novartis, who have the Novartis Institute for Biomedical Research (NIBR) and the Genomics Institute of the Novartis Research Foundation (GNF).  

More recent examples include Novartis and GSK, who appear to have been collaborating on research projects and the other major one that surprised many was the Merck-Astra-Zeneca hookup on specific, but related compounds with relevant cancer pathways.

Which brings me to Gordon Mills stirring talk on Monday evening. He made the case that this is the time for systems biology to make it's mark. Rather than looking at adding in a targeted therapy eg an EGFR, a MEK or whatever inhibitor (TKI or monoclonal antibody) to shut off one particular piece of a complex pathway, we need to start looking at a broader concept, which he called 'pathwayness'. That is, we have learned that cancer biology is highly complex and shutting off one aberrant or overexpressed protein, won't shut down the whole engine because either the cancer adapts or other parts continue to function and drive the tumour's survival.

For me, what was spooky about this well thought and well argued talk was that it was eerily similar as a concept to what Frank McCormack was describing earlier this year using PI3K as an example. Both McCormack and Mills are probably ahead of their time.

What we need to see is industry listening to what they have to say and start to think more strategically about what to do with all the inhibitors we already have out there for the 12 critical cancer drivers that Bert Vogelstein discussed at AACR earlier this year.  

Mills argued cogently that we actually have many of the potential tools we need to take a deeper systems biology approach to personalized medicine and by looking at each patients cancer biology we could potential develop a treatment approach relevant to them. He called this 'listening to what the patient tells us'.

This reminded me that recently, there was an article in Forbes about why personalized medicine is bunk, written by a MD at a VC firm. The article annoyed me, mainly for it's lack of critical thinking, fair balance or even a basic understanding of what is happening in medicine and clinical research. Rather than vent in the comments, I turned up at this AACR meeting and was greatly reassured that cancer research is in good hands and we have many excellent people and resources focused on the whole concept of matching treatment to a patients tumour. It will happen. In many ways the revolution has already begun; we just need to get better at it. Every failure tells us something new and important about what to do next.

We have the tools, but there are also a lot of hurdles and challenges to be addressed along the way, not least the regulatory side of things and a different way of thinking about testing and validating the ideas in clinical trials. The good news is that there is much needed activity going on behind the scenes at the policy level, as witnessed by the Cancer Caucus in DC today, where Harold Varmus is kicking off a new era at the NCI. I'm hopeful that the think tank will have open minds and the passion to change the way we think about cancer research.

 

AACR Molecular Diagnostics conference, Denver, CO

This week I'll be at the AACR conference on Molecular Diagnostics, which promises to be an interesting and informative meeting if it lives up to it's lofty goals:

"This meeting will explore the promise of this biologically based approach to therapeutic development and clinical investigations, review the current state of accomplishments in these areas, and discuss solutions to some of the challenges as well as the resulting future advancements."

You can find out more about the program here.

If you're at the meeting, do say hello and introduce yourself, I'm looking forward to catching up with old friends and meet some new people too.

Watch out for some synopses and summaries from the meeting here on the blog later this week.

Meanwhile, if you have any burning questions, please feel free to add them in the comments below or email me directly and I'll do my best to answer.

Angiogenesis, angiopoeitin and Glioblastoma Multiforme (GBM)

Read and writing about malignant brain cancers, gliomas or glioblastoma multiforme (GBM) always makes me sad as life span from diagnosis is often only a year. Over the last decade we have seen many advances in surgery, radiation, chemotherapy and targeted therapies in many cancers, yet this one remains largely immune to significant progress.

Background

Angiogenesis inhibitors targeting the VEGF signaling pathway have been shown to be effective both in preclinical cancer models and in clinical trials. This has led to the approval of several agents targeting VEGF in cancer, including bevacizumab (Avastin), sorafenib (Nexavar) and sunitinib (Sutent). To date, bevacizumab, has been approved for the treatment of relapsed glioblastomas in the US, at a dose of 10 mg/kg IV every 2 weeks. The approval in GBM was based on objective response rate, not survival.

There have been concerns in the past about the use of anti-angiogenic therapy (see references below) with malignant gliomas, principally malignant progression of the tumours with increased local invasion and distant metastasis. In other words, the cancer become more aggressive, which is not a good thing.  Still, the concerns and risk involved must be balanced with the severity of the disease and relatively poor prognosis. Development of resistance is also an ongoing problem.

This morning though, I was a little more cheered about the topic after someone kindly sent me a new clinical paper on angiogenesis and GBM.  

Angiogenesis 

Brunkhorst et al., (2010) looked more closely at the mechanisms underlying tumour angiogenesis, principally angiopoeitins, and found some interesting relationships:

"We establish that Ang-4 is upregulated in human GBM tissues and cells. We show that, like endothelial cells, human GBM cells express Tie-2 RTK."

In simple terms, angiopoietins (Ang-1, Ang-2, and Ang-4) are the ligands of the Tie-2 receptor tyrosine kinase (RTK). More details can be found in an excellent review of angiopoietins and Tie2 in a review by Huang et al., (2010).  While the roles of Ang-1 and Ang-2 are reasonably well known, little is understood about the role of Ang-4, so Brunkhorst et al., set out to research this in more detail.

What they found was really interesting:

"Our results establish the novel effects of Ang-4 on tumor angiogenesis and GBM progression and suggest that this pro-GBM effect of Ang-4 is mediated by promoting tumor angiogenesis and activating Erk1/2 kinase in GBM cells.

Together, our results suggest that the Ang-4–Tie-2 functional axis is an attractive therapeutic target for GBM."

The pipeline

There aren't too many inhibitors of Tie-2 in development, as this is a relatively new area of research.  That said, I did find a couple in my database:

• ARRY-614 (Array): inhibits p38, Abl, Tie2 and VEGFR2, research in MDS
• XL-184 (Exelixis): inhibits VEGFR-2, MET, c-KIT, FLT-3, and Tie2
• ABT-869/linifarnib (Abbott): Inhibits VEGF, FLT3, Tie2, c-FMS, PDGF, c-kit
• AP-24534/ponatinib (Ariad): inhibits BCR-ABL, FLT3, VEGFR, FGFR, Tie2 
• AMG-386 (Amgen): inhibits angiopoeitin 1 and 2, thus Tie2 is indirectly inhibited.

Insights

Regarding the relationship between angiopoetin and Tie2, Herbst et al., summarised it succinctly:

"AMG 386 is an investigational peptide-Fc fusion protein (ie, peptibody) that inhibits angiogenesis by preventing the interaction of angiopoietin-1 and angiopoietin-2 with their receptor, Tie2."

Mita et al., (2010) have generated some initial research looking at this compound in a catch-all phase I trial in advanced solid tumours with the standard combinations and dose finding approach. It's too early to say whether the agent will pan out, but some evidence of anti-tumour activity was seen.

In the original article on GBM and angiopoeitins, Brunckhorst et al., (2010) demonstrated that Ang-4 promotes GBM progression by promoting tumour angiogenesis. What was also clear from their data is that Ang-4 seems to display a more potent proangiogenic activity than Ang-1.  

More importantly, they found that GBM cells express Tie-2 and thus there may be a novel role for Ang-4 in promoting Erk1/2 kinase activation in GBM cells and in enhancing GBM cell viability.

Clearly, we still have a long way to go in figuring out the precise details around the broader angiogenesis process involved in tumour growth and development, but expanding the potential targets beyond VEGF into angiopoeitins, Tie2 and even platelet derived growth factor (PDGF), fibroblast growth factor (FGFR) and others will hopefully yield some productive bench to bedside success in the near future. 

 

References

Brunckhorst, M., Wang, H., Lu, R., & Yu, Q. (2010). Angiopoietin-4 Promotes Glioblastoma Progression by Enhancing Tumor Cell Viability and Angiogenesis Cancer Research, 70 (18), 7283-7293 DOI: 10.1158/0008-5472.CAN-09-4125

Verhoeff, J., van Tellingen, O., Claes, A., Stalpers, L., van Linde, M., Richel, D., Leenders, W., & van Furth, W. (2009). Concerns about anti-angiogenic treatment in patients with glioblastoma multiforme BMC Cancer, 9 (1) DOI: 10.1186/1471-2407-9-444

Pàez-Ribes, M., Allen, E., Hudock, J., Takeda, T., Okuyama, H., Viñals, F., Inoue, M., Bergers, G., Hanahan, D., & Casanovas, O. (2009). Antiangiogenic Therapy Elicits Malignant Progression of Tumors to Increased Local Invasion and Distant Metastasis Cancer Cell, 15 (3), 220-231 DOI: 10.1016/j.ccr.2009.01.027

Herbst, R., Hong, D., Chap, L., Kurzrock, R., Jackson, E., Silverman, J., Rasmussen, E., Sun, Y., Zhong, D., Hwang, Y., Evelhoch, J., Oliner, J., Le, N., & Rosen, L. (2009). Safety, Pharmacokinetics, and Antitumor Activity of AMG 386, a Selective Angiopoietin Inhibitor, in Adult Patients With Advanced Solid Tumors Journal of Clinical Oncology, 27 (21), 3557-3565 DOI: 10.1200/JCO.2008.19.6683

Mita, A., Takimoto, C., Mita, M., Tolcher, A., Sankhala, K., Sarantopoulos, J., Valdivieso, M., Wood, L., Rasmussen, E., Sun, Y., Zhong, Z., Bass, M., Le, N., & LoRusso, P. (2010). Phase 1 Study of AMG 386, a Selective Angiopoietin 1/2-Neutralizing Peptibody, in Combination with Chemotherapy in Adults with Advanced Solid Tumors Clinical Cancer Research, 16 (11), 3044-3056 DOI: 10.1158/1078-0432.CCR-09-3368

Huang, H., Bhat, A., Woodnutt, G., & Lappe, R. (2010). Targeting the ANGPT–TIE2 pathway in malignancy Nature Reviews Cancer, 10 (8), 575-585 DOI: 10.1038/nrc2894

MET and KRAS amplification mediate resistance to MET inhibitors

Here's an interesting paper that was just published in Cancer Research that describes some factors driving acquired resistance to MET inhibition with small molecules.

MET inhibitors have gained a lot of attention recently (see Comoglio et al's review in the references for a good overview) and we have covered this topic a few times on this blog both in terms of the biology and also on promising inhibitors such as ArQule/DaiichiSankyo's ARQ-197, which is the leading compound in this field.

Acquired resistance is a common and limiting problem for chronic therapy with many tyrosine kinase inhibitors (TKI), not just MET inhibitors. After initial excitement at seeing some responses though, they appear to stop working. The big question is why, and what underlying mechanisms may be at play?

Of course, while the issue may be a universal one, the resistance mechanisms are not and will differ with each class of TKI and potentially even tumour types or combinations.

Background

The MET gene is disregulated in a number of different tumour types and those cells exhibiting MET amplification may offer a suitable target for drug inhibition.  Doing so results in impairment of cell growth and apoptosis.

You can read more about the biology of the c-MET pathway here.

Acquired Resistance to MET

In this important research, the authors decided to see if they could define some of the underlying mechanisms of MET resistance:

"To predict mechanisms of acquired resistance, we generated resistant cells by treating MET-addicted cells with increasing concentrations of the MET small-molecule inhibitors PHA-665752 or JNJ38877605."

The results?

They found that cells progressively amplified KRAS, which resulted in increased expression and activation of wild-type (wt) KRAS and in activation of the mitogenactivated protein kinase (MAPK) pathway:

"We show that amplification of wt MET and KRAS is found in cells of diverse histotypes, resistant to different inhibitors.

Moreover, unexpectedly, we observed that resistance to treatment was reversible and that the alterations leading to resistance were lost after drug withdrawal."

This is a very important finding because it may well be helpful for designing future clinical studies, either in combination or in sequence, to reduce the potential for resistance emerging with MET inhibitors, thereby improving the potential for better long term outcomes with treatment.

"Our results suggest that MET and KRAS amplification is a general mechanism of resistance to specific MET inhibitors given that similar results were observed with two small inhibitors and in different cell lines of different histotypes."

Impact

My favourite part of this story was not just the identification of potential mechanisms of MET resistance, but some hints of how the learnings from the data could be applied:

"Because specific anti-RAS drugs are not available, we tested the ability of compounds acting downstream RAS (such as U0126, PD325901, and sorafenib) to impair cell viability. We observed that cells resistant to MET inhibitors that underwent KRAS amplification are indeed sensitive to these drugs."

Clearly, our ability to not only predict potential mechanisms of resistance, but also devise strategies for overcoming or preventing it, is crucial for improved clinical development with these agents as well as providing a clear rationale for other inhibitors still in research.

Where there's a viable target, there's a way forward.

 

References

Cepero, V., Sierra, J., Corso, S., Ghiso, E., Casorzo, L., Perera, T., Comoglio, P., & Giordano, S. (2010). MET and KRAS Gene Amplification Mediates Acquired Resistance to MET Tyrosine Kinase Inhibitors Cancer Research DOI: 10.1158/0008-5472.CAN-10-0436

Comoglio, P., Giordano, S., & Trusolino, L. (2008). Drug development of MET inhibitors: targeting oncogene addiction and expedience Nature Reviews Drug Discovery, 7 (6), 504-516 DOI: 10.1038/nrd2530

Incyte's INCB018424 looks promising in myelofibrosis

Just before the American Society of Hematology (ASH) meeting last December, I posted an overview of the JAK2 pathway and pipeline inhibitors in development. Things have changed a bit since then, with TargeGen's inhibitor, TG101348, being licensed by sanofi-aventis and the advent of new phase I/II data being published this week in the New England Journal of Medicine on the leading compound in this category, INCB018424 (Incyte/Novartis).

Background

I loved this simple overview from Verstovsek et al., which is hard to improve on for simplicity and logic:

"Myelofibrosis is a Philadelphia chromosome–negative myeloproliferative neoplasm associated with cytopenias, splenomegaly, poor quality of life, and shortened survival. About half of patients with myelofibrosis carry a gain-of-function mutation in the Janus kinase 2 gene (JAK2 V617F) that contributes to the pathophysiology of the disease. INCB018424 is a potent and selective Janus kinase 1 (JAK1) and JAK2 inhibitor."

Here's what the pathway looks like, for those interested:

Source: Cell Signal

Currently, there are no approved therapies for the treatment of myelofibrosis, so using a targeted inhibitor is a worthwhile approach to determine whether any clinical benefit will result.

The Patients

In this study, patients were preselected for one of the following characteristics:

• JAK2 V617F−positive or JAK2 V617F−negative primary myelofibrosis
• post–essential thrombocythemia myelofibrosis
• post–polycythemia vera myelofibrosis.

In all, 153 patients were given INCB018424 as oral therapy for a median duration of more than 14.7 months.  The initial dose-escalation phase established 25 mg twice daily or 100 mg once daily as maximum tolerated dose (MTD).

Additional doses were also examined, with a clear rationale emerging for a 15 mg twice daily starting dose.

The Results

Skimming through the results section, my attention was immediately drawn to the following:

"61 of 140 patients with an enlarged spleen at study entry (44%) had an objective response (clinical improvement), based on a reduction of 50% or more in palpable splenomegaly within the first 3 months after therapy."

Interestingly, the response rates were highest in patients who took their therapy BID, whereas none of the patients who took INCB018424 once daily showed any clinical improvement.

The researchers went onto note:

"A total of 28 patients who received 25 mg twice daily or 15 mg twice daily (the most active regimens for splenomegaly reduction) were transfusion-dependent at enrollment. After a median treatment duration of 12 weeks, 4 patients (14%) had transfusion independence (clinical improvement according to the International Working Group) for a median duration of 20 months."

One of the many problems people with myelofibrosis experience is a poor quality of life, so it was reassuring to see some real improvement in practical real life tests.

A small proportion of the patients underwent the 6-minute walk test, with the following improvement in their ability to walk as follows:

• 34 m after 1 month
• 57 m after 3 months
• 71 m after 6 months

I couldn't find the baseline, but we can reasonably assume that it was 34 m or less, judging from this positive trend.

When considering the patients with (n=61) and without (n=11) the JAK2 V617F mutation, there was no difference in response between the groups in the patients who received the most effective doses (ie 15 mg twice daily or 25 mg twice daily). The response rates were 51% and 45%, respectively.

In addition, people with primary myelofibrosis (n=37) had a response rate of 49%, while those with polycythemia vera (n=22), 45%, suggesting that the overall response rates were in the general 45-51% range, irrespective of the type of myelofibrosis.

With regards to serious adverse events, 59 people were affected by JAK2 therapy, of whom 12 had serious adverse events that were considered to be at least possibly related to treatment. Additionally, 3 patients had transformation to AML, but whether this was treatment related, or part of the natural disease progression, wasn't clear from the article.

Insights

The improvements in clinical benefit (response rates, reduction in splenomegaly and exercise endurance) look promising enough for phase III trials to begin. Understanding the mechanisms behind the inflammatory responses and reduction in splenomegaly will be important as more research is undertaken.

In the previous post on JAK2, we discussed how inhibiting JAK2 may influence or block cytokine signalling, which is thought to be responsible for the myelofibrosis. In this study, normalisation of the inflammatory cytokines was noted with INCB018424, suggesting that JAK1 and JAK2 inhibitors may possibly have clinical efficacy in inflammatory diseases such as rheumatoid arthritis (RA).  

Indeed, a trial with another JAK2 inhibitor, INCB028050, from Incyte is ongoing in RA and has already completed recruitment.  The results from this trial may offer proof of concept for JAK2 and cytokine normalisation in inflammatory disease.

The future though, may well involve some form of combination rather than single agent therapy, as the accompanying editorial pointed out:

"One disappointing finding in the trial was the minimal effect on the burden of the V617F-mutated clone; however, this was not entirely unexpected considering the lack of specificity of INCB018424 for mutated protein. Yet, one may question whether the disappearance of the V617F-mutated clone is a reasonable end point for JAK1 and JAK2 inhibitors without causing excessive toxicity, given the essential role of JAK1 and JAK2 in the normal immune system and hematopoiesis."

It is very good news to see that a single agent JAK2 inhibitor has some early efficacy, so we can hope that the phase III trials (COMFORT I and II) will also be positive and confirm the initial phase II results when the data is available in the first half of 2011. In the long run, though, combination approaches may well produce even better outcomes.

 

References

Vannucchi, A. (2010). From Palliation to Targeted Therapy in Myelofibrosis New England Journal of Medicine, 363 (12), 1180-1182 DOI: 10.1056/NEJMe1005856

Verstovsek, S., Kantarjian, H., Mesa, R., Pardanani, A., Cortes-Franco, J., Thomas, D., Estrov, Z., Fridman, J., Bradley, E., Erickson-Viitanen, S., Vaddi, K., Levy, R., & Tefferi, A. (2010). Safety and Efficacy of INCB018424, a JAK1 and JAK2 Inhibitor, in Myelofibrosis New England Journal of Medicine, 363 (12), 1117-1127 DOI: 10.1056/NEJMoa1002028

 

PIK3CA, MEK and mutant KRAS in cancer

One of the current challenges with developing new targeted agents in oncology is the tendency to rush various agents, whether monoclonal antibodies (mAB) or tyrosine kinase inhibitors (TKIs) into the clinic before we know how they might best work or in what potential combinations based on the precise underlying biology.

Another challenge I see is old school chemotherapy approaches permeating new development thinking. By this, I mean the traditional concept of testing therapies in advanced, metastatic and highly refractory disease where the tumour burden is high and the chances of getting a decent response is low.

This is one reason I love the I-SPY neoadjuvant concept in breast cancer. Testing a range of compounds prior to surgery based on the potential drivers of the cancer will let us know very early which agents are working or not and which could potentially be selected for subsequent adjuvant treatment after surgery.

Background

Recently, I reading a couple of papers (see references below) on phase I and II trials with a MEK inhibitor (PD-0325901), but it was a little bit with a sinking feeling because the trial design was rather old fashioned and traditional, ie take a bunch of solid tumours in phase I, see what (mixed) signals you get:

"PD-0325901 showed preliminary clinical activity. The maximum tolerated dose, based on first cycle dose-limiting toxicities, was 15 mg BID continuously. However, 10 and 15 mg BID continuous dosing and 10 mg BID 5 days on/2 days off schedules were associated with delayed development of RVO; thus, further enrollment to this trial was stopped."

Where RVO was retinal vein occlusion.

Next, do a phase II in a big (ie large potential patient numbers), advanced, metastatic and highly refractory cancer.  Predictably, the results were unsurprising:

"PD-0325901 did not meet its primary efficacy end point."

If we looked at those results in isolation, we might be tempted to dismiss the idea that the MEK inhibitor doesn't work and abandon it.

A different way of thinking

That said, I was much more encouraged by another article from another group that looked at the problem completely differently with exactly the same MEK agent.  If you think about it, a focused sniper rifle strategy is often going to be more effective than a bludgeoning blunderbuss.

They looked at the basic evidence that:

"Mutational activation of PIK3CA, which commonly co-occurs with KRAS mutation, provides resistance to MEK inhibition through reactivation of AKT signaling"

And then set out to look at this relationship more clearly in animal models:

"to determine the MEK dependence of tumors with mutational activation of the pathway. These studies indicate that many KRAS mutant tumor cell lines are, contrary to the prevailing view, sensitive to the MEK inhibitor PD0325901, and hence, dependent on the RAF/MEK/ERK signaling arm.

Resistance to MEK inhibitors in the relevant cell lines is not an intrinsic feature of KRAS oncogenic function but instead mutational activation of PIK3CA is present in most, but not all, MEK resistant KRAS mutant cancers."

It's hard to argue with that logical approach.

Findings

The article is well worth reading and nicely put together, but here are the main findings of the research:

1. A subset of KRAS mutant cells depends on MEK/ERK signaling
2. Coexistent KRAS and PIK3CA mutations prevent cyclin D degradation and sensitivity to MEK inhibition
3. Selective knockout of mutant PIK3CA allele confers MEK/ERK dependence
4. Sustained cyclin D expression and bypass of MEK inhibitor–induced G1 arrest correlates with MEK antagonist efficacy
5. Combined inhibition of both MEK/ERK and PI3K/AKT pathways suppresses the growth of tumors with coexisting KRAS and PIK3CA mutations

 

Implications for the future

The thoughtful approach behind Halilovic et al's data is particularly interesting:

"Mutational activation of KRAS is a common event in human tumors. Identification of the key signaling pathways downstream of mutant KRAS is essential for our understanding of how to pharmacologically target these cancers in patients.

We show that PD0325901, a small-molecule MEK inhibitor, decreases MEK/ERK pathway signaling and destabilizes cyclin D1, resulting in significant anticancer activity in a subset of KRAS mutant tumors in vitro and in vivo."

KRAS mutant tumours are particularly relevant to colorectal cancer.  Recently, we have seen that patients with colorectal cancer who have wild type, but not mutant, KRAS are more much more likely to respond to treatment with EGFR therapy ie Erbitux and Vectibix, allowing for careful patient selection and exposure.

What about melanoma where mutant RAS may stop the activity of RAS inhibitor such as PLX4032? Could adding a MEK inhibitor help overcome the problem in some cases, or perhaps that would be too simple? We don't know, but I'd love to see some research data in appropriate xenograft models in this area.

The problem is that there is currently no therapeutic agent that directly inhibits KRAS function, so the Halilovi data have very important implications for tumours driven by mutant RAS.

What the new data tells us:

"These data suggest that tumors with both KRAS and phosphoinositide 3-kinase mutations are unlikely to respond to the inhibition of the MEK pathway alone but will require effective inhibition of both MEK and phosphoinositide 3-kinase/AKT pathway signaling."

Bingo!  Now that's a much more elegant approach to defining which patient populations are most likely to respond based on preclinical research before attempting clinical trials and randomly exposing patients who had no hope of responding to the systemic side effects of a treatment.  

Personally, I would dearly love to see more clinical trial selection based on logical, well researched preclinical data rather than a scattergun let's hope and see approach.

We need to get smarter and faster at well designed research that points us in the right direction to increase the chances of better success and improved outcomes.  It will also conserve precious R&D dollars and focus it where it's needed most.

 

References

Halilovic, E., She, Q., Ye, Q., Pagliarini, R., Sellers, W., Solit, D., & Rosen, N. (2010). PIK3CA Mutation Uncouples Tumor Growth and Cyclin D1 Regulation from MEK/ERK and Mutant KRAS Signaling Cancer Research, 70 (17), 6804-6814 DOI: 10.1158/0008-5472.CAN-10-0409

Haura, E., Ricart, A., Larson, T., Stella, P., Bazhenova, L., Miller, V., Cohen, R., Eisenberg, P., Selaru, P., Wilner, K., & Gadgeel, S. (2010). A Phase II Study of PD-0325901, an Oral MEK Inhibitor, in Previously Treated Patients with Advanced Non-Small Cell Lung Cancer Clinical Cancer Research, 16 (8), 2450-2457 DOI: 10.1158/1078-0432.CCR-09-1920

LoRusso, P., Krishnamurthi, S., Rinehart, J., Nabell, L., Malburg, L., Chapman, P., DePrimo, S., Bentivegna, S., Wilner, K., Tan, W., & Ricart, A. (2010). Phase I Pharmacokinetic and Pharmacodynamic Study of the Oral MAPK/ERK Kinase Inhibitor PD-0325901 in Patients with Advanced Cancers Clinical Cancer Research, 16 (6), 1924-1937 DOI: 10.1158/1078-0432.CCR-09-1883

Selective cell death mediated by small conditional RNAs

Cancer cells are characterized by genetic mutations that deregulate cell proliferation and suppress cell death. To arrest the uncontrolled replication of malignant cells, conventional chemotherapies systemically disrupt cell division, causing diverse and often severe side effects as a result of collateral damage to normal cells. Seeking to address this shortcoming, we pursue therapeutic regulation that is conditional, activating selectively in cancer cells.

via www.pnas.org

This was an interesting paper that caught my eye in PNAS last night.  Further reading demonstrated that the process uses small RNA molecules. The idea behind this approach was that the small RNA molecules can be programmed to attack only specific cancer cells; then, by changing shape, those molecules cause the cancer cells to self-destruct.

Normal cells die after a period of time and are replaced by new ones, a process called programmed cell death or apoptosis.  In a tumour, the cells continue to proliferate and form a mass, growing new blood vessels to feed the structure via angiogenesis.  

One of the things that has absorbed researchers for years is how to stop that process and induce cell death in cancer cells without killing a lot of normal cells at the same time.  To do this, we need to find ways of distinguishing cancerous from normal cells, thereby inducing a more targeted and selective approach to destruction and reducing unwanted side effects.  ]

This is not as easy as it sounds though!

In the PNAS study, the researchers took small conditional RNAs, which are less than 30 base pairs in length and are hairpin shaped molecules as shown in the photo below.

The press release from Caltech described the concept as thus:

"The researchers' method involves the use of two different varieties of small conditional RNA. One is designed to be complementary to, and thus to bind to, an RNA sequence unique to a particular cancer cell—say, the cells of a glioblastoma, an aggressive brain tumor.

In order to bind to that cancer mutation, the RNA hairpin must open—changing the molecule from one form into another—which, in turn, exposes a sequence that can spontaneously bind to the second type of RNA hairpin. The opening of the second hairpin then reveals a sequence that binds to the first type of hairpin, and so on. 

In this way, detection of the RNA cancer marker triggers the self-assembly of a long double-stranded RNA polymer."

Essentially, this is a clever way to use small conditional RNAs to the trick cancer cells into self-destructing by selectively forming long double-stranded RNA polymers that mimic viral RNA.

The researchers tested the RNA concept in the lab in xenograft models derived from three types of cancers: glioblastoma, prostate carcinoma, and Ewing's sarcoma so far, with some success:

"The molecules caused a 20- to 100-fold drop in the numbers of cancer cells containing the targeted RNA cancer markers, but no measurable reduction in cells lacking the markers."

Now clearly this approach has a long way to go before we see it in clinical trials, but there's nothing like starting off your day with exciting new technology approaches that may have application in the near future.

We need more creative research like this in oncology!

 

Photo Credit: Caltech

 

Venkataraman, S., Dirks, R., Ueda, C., & Pierce, N. (2010). Selective cell death mediated by small conditional RNAs Proceedings of the National Academy of Sciences DOI: 10.1073/pnas.1006377107

Wnt signaling and cancer

In April at the AACR annual meeting, Bert Vogelstein talked about 12 critically aberrant pathways in cancer and we have talked about a few of these on this blog this year. Today, I want to take a look at another one of those key pathways, Wnt (pron. wint).

Background

Wnt is well known for it's network of proteins playing key roles in both development and cancer.  In simple terms, the process begins when Wnt proteins bind to cell-surface receptors of the Frizzled family, causing the receptors to activate the Dishevelled (dvl) family proteins, leading to a change in the amount of B-catenin that reaches the nucleus.

The basic pathway is described in the schematic below:

Source: Cell Signal

Previously, we have discussed the simplicity of Hh signalling driving medulloblastoma and KRAS mutations (WT, wild-type) being critical for deciding EGFR therapy in colorectal cancer, but in pancreatic ductal adenocarcinoma (PDAC) things are a lot more complex.  Morris et al., noted that:

"Analysis of PDAC mouse models driven by targeted pancreatic expression of oncogenic KRAS suggest that both temporal and spatial control of Hh and Wnt–B-catenin activity are involved in specifying a cell lineage that can progress to PDAC."

For those of you interested in more detailed biology associated with PDAC, I urge you to check out Hezel et al's excellent review on the topic (see reference link below).

Wnt–B-catenin signalling in PDAC

An interesting observation in the literature is that the KRAS mutation is nearly universal (>95%) in human PDAC. Furthermore, Morris et al., observed that:

"Wnt–β-catenin signalling is frequently activated in PDAC and contributes to tumour cell proliferation and biology.  Genetic models that allow Wnt–β-catenin deregulation reveal that this pathway can transform pancreatic cells but is insufficient to drive PDAC initiation."

So what else is going on?

In their review, the authors specifically look at:

• the ability of KRAS to alter cell fate in the pancreas
• how the timing and location of Hh and Wnt–B-catenin signalling contribute to PDAC development.

It's well worth a read with lots of helpful schematic diagrams to illustrate the underlying biology.

Clearly, we have a long way to go before we know more about the molecular basis of what is happening in this disease.  Some of the many factors that still need to be elucidated include:

• which components of the complex pathway are activated in cancer
• how they interact
• whether there are differences in the tumour epithelium and the microenvironment
• determine which Hh and B-catenin targets are ‘mission critical’ for maintaining proliferation, viability and differentiation
• how can we block the critical signalling proteins?

Wnt in multiple Myeloma

Other research has focused on the role of Wnt in multiple myeloma (see Guiliani et al., in the references).  Their results results supported the link between the production of Wnt antagonists by multiple myeloma cells and the presence of bone lesions in multiple myeloma patients. They also demonstrated that myeloma cells do not inhibit canonical Wnt signaling in human bone microenvironment.

Targeting different parts of the Wnt pathway has, however, produced some interesting results. Studies with an orally bioavailable GSK-3a/B dual inhibitor increased markers of cellular differentiation in vitro and bone mass in vivo, proving that we have much to learn about this complex pathway before a likely pharmacologic agent will emerge commercially.

Wnt inhibitors in the pipeline

While several inhibitors of Notch and Hedgehog pathways have reached the clinical trial stage, drugable targets for Wnt inhibitors seem to have have proven elusive so far. I haven't come across too many agents inhibiting Wnt, although I was amused to hear from a friend that one is called Soggy-1.  

The Novartis Institute of Biomedical Research (NIBR) reported on XAV939 in a Nature article.  XAV939 selectively inhibits B-catenin-mediated transcription and acts via tankyrase inhibition. Huang et al., (2009) succinctly noted:

"The development of targeted Wnt pathway inhibitors has been hampered by the limited number of pathway components that are amenable to small molecule inhibition."

Given that few first generation inhibitors hit the mark first time, we may have to test quite a few different generations of Wnt inhibitors or even inhibitors of different parts of the pathway in combination, before a successful strategy finally emerges from R&D pipelines in the future.

 

Morris JP 4th, Wang SC, & Hebrok M (2010). KRAS, Hedgehog, Wnt and the twisted developmental biology of pancreatic ductal adenocarcinoma. Nature reviews. Cancer PMID: 20814421

Giuliani, N., Morandi, F., Tagliaferri, S., Lazzaretti, M., Donofrio, G., Bonomini, S., Sala, R., Mangoni, M., & Rizzoli, V. (2007). Production of Wnt Inhibitors by Myeloma Cells: Potential Effects on Canonical Wnt Pathway in the Bone Microenvironment Cancer Research, 67 (16), 7665-7674 DOI: 10.1158/0008-5472.CAN-06-4666

Hezel, A. (2006). Genetics and biology of pancreatic ductal adenocarcinoma Genes & Development, 20 (10), 1218-1249 DOI: 10.1101/gad.1415606

Huang, S., Mishina, Y., Liu, S., Cheung, A., Stegmeier, F., Michaud, G., Charlat, O., Wiellette, E., Zhang, Y., Wiessner, S., Hild, M., Shi, X., Wilson, C., Mickanin, C., Myer, V., Fazal, A., Tomlinson, R., Serluca, F., Shao, W., Cheng, H., Shultz, M., Rau, C., Schirle, M., Schlegl, J., Ghidelli, S., Fawell, S., Lu, C., Curtis, D., Kirschner, M., Lengauer, C., Finan, P., Tallarico, J., Bouwmeester, T., Porter, J., Bauer, A., & Cong, F. (2009). Tankyrase inhibition stabilizes axin and antagonizes Wnt signalling Nature, 461 (7264), 614-620 DOI: 10.1038/nature08356

Mechanisms of castration resistance in prostate cancer

Over the last few weeks I've received quite a few questions relating to castration resistance and how it happens.  After all, while we have several therapies now approved once androgen deprivation therapy (ADT) fails, if we could keep men hormone sensitive for longer, then overall outcomes would likely improve.

Writing about prostate cancer is always a tough topic for me after my Dad passed away 10 years ago from the disease. He was sadly diagnosed in stage IV so there wasn't much that could be done really. It took only 18 months or so for a series of hormone therapies to fail and he developed castration resistant prostate cancer (CRPC). He subsequently declined chemotherapy on the grounds that he wanted to go with dignity on his own terms, nor did he want to put my Mother through hell either.  I rather respect that kind of mature and sensible approach in the face of a very difficult situation.

Ever since then though, I've always wondered what could we do inhibit androgen receptor (AR) signalling better and how could we improve on the therapies we have?After all, bicalutamide and similar therapies are not particularly effective agents because eventually, they all stop working and cycling through multiple therapies is very much the norm.

A new paper in Clinical Cancer Research attracted my attention recently (see journal link below).  The authors took a look at various possible methods of castration resistance and defined the main ones from the literature as:

"(i) AR activation by androgens converted from adrenal androgens or synthesized intratumorally via the de novo route

(ii) hypersensitivity of ARs due to overexpression of AR proteins and/or changes in cofactor expression levels

(iii) promiscuous activation of AR signaling by various ligands following AR mutation

(iv) constitutive activation of AR signaling by truncated ARs lacking ligand-binding domains."

A prior article by Harris et al., in Nature Reviews Urology defined 6 potential pathways slightly differently, including:

"(1) Tissue and tumoral steroidogenesis contribute to synthesis of testosterone and DHT, and might lead to persistence of tissue-level androgen despite castration.

(2) Mutations in the AR allow activation by alternate ligands or increased affinity for androgens.

(3) Amplification increases AR abundance.

(4) Ligandindependent activation of AR through ligand-independent modifications or cross-talk with other pathways, including phosphorylation of AR leading to hypersensitization and increased nuclear translocation.

(5) Change in the balance of coactivators and corepressors augment AR activity.

(6) Bypass pathways functioning independently of AR activity through upregulation of antiapoptotic molecules, such as Bcl-2."

These were also described graphically in the following picture, with the source referenced below:

Source: Medscape

A lot of people have been asking how the 17,20 lyase inhibitors work. 17,20-lyase is essential for androgen and testosterone synthesis in both the adrenal glands and CRPC tissue, so the inhibitors have been developed to target this mechanism in both organs.

There are a number of 17,20 inhibitor in the oncology R&D pipeline including:

1. abiraterone (J&J/Centocor) - phase III
2. TAK-700 (Millennium-Takeda) - phase II
3. TOK-001 (Tokai) - phase I/II

However, resistance to these therapies have already been observed in clinical trials, so while they may inhibit AR signalling for a period, they may not be the final answer.

The other drug in development that has garnered a lot of attention is MDV2100 (Medivation and Astellas).  This agent works via a completely different mechanism. Rather than acting through the adrenal cortex or CRPC tissues, it may operate in the cell nucleus on the AR regulated genes, essentially acting through the “intracrine” production of androgens from adrenal androgen or intratumorally, blocking the the interaction between androgens and AR.  The first generation agents such as bicalutamide, flutamide and nilutamide are not very effective because they have agonistic activity for CRPC so what is needed is a drug with more complete antagonist AR activity, especially against mutant ARs that develop over time.

What is particularly interesting in the new agents being developed to target advanced prostate cancer is what a poor marker of activity PSA is.  New studies with circulating tumour cells (CTC's) may well ultimately help us learn more about the underlying biology of the disease.

I'm also looking forward to hearing more about TMPRRS2-ERG, a recently discovered fusion by Tomlins et al., (2005) of an androgen-controlled serine protease, TMPRSS2, and the erythroblast transformation-specific (ETS) family gene ERG by chromosomal rearrangement. Together with phosphoinositide-3 kinase (PI3K), this fusion gene is now thought to be involved in the pathogenesis and progression of prostate cancer.

The authors noted:

"By using fluorescence in situ hybridization, we demonstrated that 23 of 29 prostate cancer samples harbor rearrangements in ERG or ETV1."

Once you have a fusion gene identified, you have a potentially druggable target that may play a causal role in cancer.  It will be interesting to see if what happens with this and how long it takes for a new agent to hit clinical trials targeting this aberration in prostate cancer.  

Maybe there is already one out there and I missed it!?

 

References:

Yamaoka M, Hara T, & Kusaka M (2010). Overcoming persistent dependency on androgen signaling after progression to castration-resistant prostate cancer. Clinical cancer research : an official journal of the American Association for Cancer Research, 16 (17), 4319-24 PMID: 20647476

Harris, William P, Mostaghel, Elahe A, Nelson, Peter S, & Montgomery, Bruce (2009). Androgen deprivation therapy: progress in understanding mechanisms of resistance and optimizing androgen depletion nature clinical practice UROLOGY, 6 (2), 76-85 DOI: 10.1038/ncpuro1296

Tomlins, SA, Rhodes, DR, & Perner, S (2005). Recurrent fusion of TMPRSS2 and ETS transcription factor genes in prostate cancer. Science, 310, 644-648 DOI: 10.1126/science.1117679

FDA rejects the Roche Immunogen T-DM1 accelerated approval filing

Interesting news arrived in my email box this morning:

"Roche (SIX: RO, ROG; OTCQX: RHHBY) today announced that the U.S. Food and Drug Administration (FDA) issued a Refuse to File letter for accelerated approval for the company’s trastuzumab-DM1 (T-DM1) Biologics License Application (BLA). As planned Roche will continue with its ongoing Phase III EMILIA registration study. Roche will continue to work with the FDA and expects a global regulatory submission of T-DM1 mid 2012.

The BLA submitted in July 2010 requested accelerated approval for T-DM1 based on the results of a single-arm Phase II study, which showed T-DM1 shrank tumors in one-third of women with advanced HER2 positive breast cancer, who had received on average seven prior medicines, including two HER2 targeted agents."

There was a lot of excitement around the initial phase II results (one third of the women experienced tumour shrinkage, for example).  Yet, to much surprise, the application was rejected:

"In their review of the BLA, FDA stated the T-DM1 trials did not meet the standard for accelerated approval because all available treatment choices approved for metastatic breast cancer, regardless of HER2 status, had not been exhausted in the study population."

At first reading of the press release, my thoughts centred around:

1. How could the FDA possibly reject such an application?
2. Was an SPA agreed up front?

The first question is easy to be indignant about, but what criteria were used for the trial and what does the data actually show?

Looking at the available clinical trials for T-DM1, this one looks most likely as 100 patients were required and the inclusion criteria stated:

• HER2-positive disease
• Metastatic breast cancer
• Disease progression on the last chemotherapy regimen received in the metastatic setting
• Prior treatment with an anthracycline, trastuzumab, a taxane, lapatinib, and capecitabine in the neoadjuvant, adjuvant, locally advanced, or metastatic setting and prior treatment with at least two lines of therapy (a line of therapy can be a combination of two agents or single-agent chemotherapy) in the metastatic setting
• At least two lines of anti-HER2 therapy must have been given in the metastatic setting as monotherapy or combined with chemotherapy or hormonal therapy. The HER2-targeted agent can include trastuzumab, lapatinib, or an investigational agent with HER2-inhibitory activity.

There are only two approved treatments for HER2-positive breast cancer, trastuzumab and lapatinib, plus others in clinical trials, eg pertuzumab, which was also allowed as one of the prior therapies.  All patients appear to have been refractory to at least two of these drugs, most likely trastuzumab and lapatinib.

The prior chemotherapies included anthracyclines, taxanes and capecitabine, which is quite heavy pre-treatment and includes all of the considered standards of care for several lines of therapy.  Indeed, the results of the trial presented at the San Antonio Breast Cancer Symposium last December showed that the average number of prior treatments in the metastatic setting was 7.

The others that could be used in the treatment of breast cancer include nab-paclitaxel (Abraxane), which I'm assuming would be covered in the taxane group and ixabepilone (Ixempra), an epothilone approved in by the FDA for metastatic breast cancer following progression on a taxane and anthracyclines, with or without capecitabine.

Ixabepilone is not a taxane or an anthracycline and therefore technically not covered in the inclusion criteria as a prior therapy, although some of the women would likely have received it, but not all.  It is, however, a taxane-like compound in that it targets the microtubules, as described in the PI:

"Ixabepilone is a semi-synthetic analog of epothilone B. Ixabepilone binds directly to B-tubulin subunits on microtubules, leading to suppression of microtubule dynamics. Ixabepilone suppresses the dynamic instability of aB-II and aB-III microtubules."

If that was the criteria for rejecting the trial as not truly refractory in a very heavily pre-treated setting, I would be surprised.  It's a bit of a technicality and nit-picking. Ixabepilone is not a commonly preferred treatment at all and BMS reported very low sales in 2009.  Most US physicians appear to prefer the well established taxanes such as paclitaxel, docetaxel and nab-paclitaxel rather than a synthetic taxane-like agent and probably consider it as a last resort. It is used as a standalone therapy in the refractory/salvage setting.

However, we're talking about a potential indication for a targeted agent that inhibits HER2 dimerization not a chemotherapy, so I would have thought that most of the important bases were covered by including the most common chemotherapies, trastuzumab and lapatinib in the inclusion criteria.

With regards to the latter question, Twitter chat this morning suggested that no, an SPA wasn't formally agreed upon, but Roche held discussions with the FDA that led them to file for accelerated approval. Thanks to Adam Feuerstein of The Street for being the first to answer that question.

My general opinion is that if you have an agreed Special Protocol Assessment (SPA) and meet the defined targets, it's much easier to move forward and gain approval. If you don't, things may turn into a crapshoot and it can go either way.  And that seems to be what has happened here.

The other factor that comes into play in this discussion is the ongoing discussion of the accelerated approval for Avastin in metastatic breast cancer and the overwhelming negative ODAC opinion last month.  That will not have helped, although one would like to think it shouldn't influence any decision making at the FDA.  We would probably be naive to think otherwise given the full protocol included PFS rather than OS as the endpoint.

To be fair, Roche appear to be addressing this issue, in their announcement this morning:

"Roche will amend the Phase III randomized EMILIA study in order to rigorously evaluate overall survival in addition to progression-free survival and will submit data from EMILIA to support a global regulatory submission in mid 2012."

Overall, I think it's a disappointing decision by the FDA given the heavily pre-treated population and lack of options for women who are refractory to both trastuzumab and lapatinib. Chemotherapy has not been shown to be particularly effective in HER2 disease, and by then the women generally have a poor prognosis. When you look again at the SABCS data, you find an objective response rate (ORR) of approximately 30% and a clinical benefit rate of around 40%, which is quite startling in a heavily pre-treated group.

Meanwhile, for now we'll have to wait another two years to see what the survival data looks like.  That's a rather long time for women who have failed Herceptin and Tykerb to wait for a drug that appears to have significant activity.

{UPDATE: I posted this analysis in a hurry, uncaffeinated, and in a rush to head out to a meeting.  Of course, one remembers later that SPA's apply to phase III not phase II trials, so a formal agreement wouldn't apply here. Thanks also to the two people who gently reminded me of this. Usually though, there are some discussions with FDA around the trial design for accelerated review. Essentially, in layman terms, it means patients are refractory to existing treatments for the disease concerned. Note that Roche, in their press release defined it as, "Consideration by the FDA for accelerated approval requires recognition of a defined patient population of unmet need (a life-threatening disease with limited treatment choices)." It looks like the FDA are applying it more strictly to ALL therapies, although the number of women who might have taken ixabepilone AND be HER2-positive will likely be miniscule.  I would still maintain that refractory to all available HER2 therapies and most chemotherapies apply for the majority in this case.}

New potential targets in ovarian cancer?

Treatment for ovarian cancer hasn't changed much in the last ten years, reflecting the lack of biomarkers and biochemical targets for the disease. Chemotherapy with a platinum (carboplatin or cisplatin) and a taxane (paclitaxel or docetaxel) has therefore formed the bedrock of therapy, along with other options such as gemcitabine or pemetrexed, as illustrated in the latest NCCN Guidelines.

The good news is that the use of paclitaxel-based combination chemotherapy has been shown to increase progression free survival (PFS) and overall survival (OS) in women with primary peritoneal or ovarian cancers.

While a proportion of ovarian cancers have been shown to be highly chemosensitive, a large number unfortunately fail to respond to primary taxane therapy, leading to the emergence of resistant disease.

The big unanswered questions are therefore why does this happen and what can be done about it to improve outcomes and overall prognosis?

It was with great interest that I read about the findings of a new study just published in Cancer Cell from researchers at MD Anderson (see e-link in the references below).  According to the MD Anderson news alert:

"For the first time, Salt Inducible Kinase 2 (SIK2) has been found to play a critical role in cell division and to regulate the response of some ovarian cancers to chemotherapy."

It's not often when you see the mention of both a potential target and prognostic/predictive biomarker mentioned in the same sentence as ovarian cancer, so this is huge news!  The press release went on to claim:

"Researchers found that depleting SIK2 from ovarian cancers sensitized the cancer cells to paclitaxel, a commonly prescribed chemotherapeutic agent that inhibits cell division, making the drug more effective in stopping the cancer's growth. Levels of the SIK2 protein are increased in approximately 30 percent of ovarian cancers and are associated with poorer survival in women with the disease."

The researchers analysed nearly 780 pools of siRNAs to identify proteins that alter sensitivity to paclitaxel. They found that SIK2 regulates sensitivity to paclitaxel and prevents cell division. This means that SIK2 may offer a useful therapeutic target for pipeline drugs to be developed in ovarian cancer.

What was even more fascinating was that another related article on ovarian cancer from Bast's group appeared in the same journal. In essence, they used siRNA-loaded nanoparticles to stifle a protein, Zeste homolog 2 (EZH2), which is associated with poor survival. This resulted in inhibition of angiogenesis (formation of new blood vessels) to the tumour and caused a steep reduction in the tumour burden in a mouse model of ovarian cancer.

In this study, the authors looked at human 180 ovarian cancer tumours and found that the protein was overexpressed in the tumour samples (66%) and in the endothelial cells (67%). It is relevant to note that endothelial cells line the inside of blood vessels and play a crucial role in angiogenesis.

In practice, they found that women with increased EZH2 levels in their tumours had a median survival of 2.5 years compared to 7.33 years for those without. Looking at overexpression in the endothelial cells, the difference was 2.33 years versus 8.33 years for those with normal levels.

Like me, you're probably wondering how these nanoparticles work.  According to MD Anderson:

"The nanoparticles accumulate in the cancer cell and vasculature passively as they circulate in the blood stream. Chitosan nanoparticles are so small that they can flow through tiny holes in the tumor vasculature. They also accumulate in other organs, so the researchers are working to add a targeting molecule that will limit nanoparticle uptake to tumors and their vasculature."

Targeting EZH2 may have application beyond ovarian cancer, since it been associated with the progression and spread of bladder, breast, prostate and gastric cancers and cancer of the pharynx.

All in all, a really interesting pair of papers from Bast's group, which may have clinical promise and real application to the future treatment of ovarian cancer.

 

Ahmed, A., Lu, Z., Jennings, N., Etemadmoghadam, D., Capalbo, L., Jacamo, R., Barbosa-Morais, N., Le, X., Vivas-Mejia, P., & Lopez-Berestein, G. (2010). SIK2 Is a Centrosome Kinase Required for Bipolar Mitotic Spindle Formation that Provides a Potential Target for Therapy in Ovarian Cancer Cancer Cell, 18 (2), 109-121 DOI: 10.1016/j.ccr.2010.06.018

Lu, C., Han, H., Mangala, L., Ali-Fehmi, R., Newton, C., Ozbun, L., Armaiz-Pena, G., Hu, W., Stone, R., & Munkarah, A. (2010). Regulation of Tumor Angiogenesis by EZH2 Cancer Cell, 18 (2), 185-197 DOI: 10.1016/j.ccr.2010.06.016