Biotech Strategy Blog

Commentary on Science, Innovation & New Products with a focus on Oncology, Hematology & Cancer Immunotherapy

Posts tagged ‘cabozantinib XL184’

Maha Hussain MB ChB is Professor of Medical Oncology at the University of Michigan.  She is an international expert into genitourinary malignancies with a focus on clinical research into prostate and bladder cancer.

Cabozantinib is a new drug in development by Exelixis for multiple indications.  It captured a lot of attention at the ASCO 2011 annual meeting last year, when Dr Hussain presented data from a phase 2 prostate cancer trial that showed a dramatic improvement in bone scans and pain reduction in those men receiving it.

Unlike other new prostate cancer drugs such as abiraterone (Zytiga) or MDV3100 that target the androgen receptor, cabozantinib is a multi-kinase inhibitor of MET and VEGFR.  It has both an anti-tumor effect and an effect on bone metabolism.

At the AACR Advances in Prostate Cancer Research conference last month, chaired by Charles Sawyers (MSKCC) and Arul Chinnayan (Michigan), Dr Hussain gave a presentation on “Cabozantinib (XL-184) and prostate cancer: preclinical and clinical profile of a novel agent.”

I was privileged to have the opportunity to interview Dr Hussain by phone recently and obtain her insight into cabozantinib as a potential new treatment for prostate cancer.

We covered a lot of ground, too much for one blog post, so I’ve broken down the interview into segments that I will be posting separately.

Cabozantinib & Pain

As many readers will be aware, one of the dramatic results presented at ASCO last year, was the impact that cabozantinib had on pain.

AACR-Molecular-Targets-2011-Cabozantinib-Pain-DataAt the AACR Molecular Targets meeting in San Francisco last November, further pain data was presented by Howard Scher’s group at Memorial Sloan-Kettering Cancer Center. They showed in a non-randomized phase 2 trial that:

Cabozantinib treatment resulted in high rates of pain improvement and analgesic reduction or discontinuation in patients with moderate to severe pain at baseline

–  Rapid and durable pain relief

–  Pain relief observed regardless of prior lines of therapy

–  Improvement in pain accompanied by reduced interference with sleep and daily activity

Exelixis has since moved forward with clinical trials focusing on prostate cancer pain.

Pain response is the primary outcome in the phase III trial (COMET-2) of cabozantinib (XL184) Versus Mitoxantrone Plus Prednisone in Men With Previously Treated Symptomatic Castration-resistant Prostate Cancer (COMET-2 trial formerly known as XL184-306). Overall survival is a secondary endpoint.

The challenge with using pain as a primary endpoint is that all the advanced prostate cancer drugs that have recently been approved by the FDA such as cabazitaxel (Jevtana), abiraterone (Zytiga), and those for whom approval is expected, such as MDV3100 and radium-223 (Alpharadin), have all shown an improvement in overall survival.

I was, therefore, interested to hear Dr Hussain’s perspective on cabozantinib and its effect on pain in prostate cancer.

BSB: Can pain be a surrogate for survival that regulatory agencies might accept?

Dr Hussain: Honestly, I am not the expert on what the regulatory agencies will do. I know what they have done and I would say that pain has been an indication for regulatory approval of prostate cancer. That’s a long story, it’s an old story. Mitoxantrone was approved based on pain, so I don’t think that is going to be an issue.

Whether it is a surrogate for survival remains to be seen, and to be honest with you, I think that it may not be if you are really using it in far advanced cancer. As we have seen with mitoxantrone, it didn’t seem to make an impact on survival and it is really more about disease progression and pain and quality of life type issues. 

I am not aware of a trial that has been done with a primary endpoint being pain, and another key primary endpoint or a secondary endpoint being survival, that has been positive.  Having said that, I think in my view, it is a mistake to just focus on the pain. 

Pain, as far as I can tell from our experience and others, it’s very late in the setting of the disease by a nowadays standard. I would argue that using this drug as a pain only type drug, you could do it cheaper and less toxic with other agents, with morphine for example. 

My point here is, I go back and say to focus it on pain only, my average patient is interested in living longer, not just in controlling their pain. 

You can hear more about this in the SoundCloud audio clip below.  Prostate cancer patients are not just interested in “how will this drug make me feel,” but also “will I live longer?”  Click here if you can’t see the audio file.

Dr Hussain: My point is in a perfect world if the drug delivers, the importance is going to be a totality of effect, that is prolonging life and improving quality of life overall.

BSB: Thank you

The next installment of the Biotech Strategy Blog interview with Dr Hussain will focus on the clinical significance of the dramatic bone scans seen with cabozantinib.

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The recent AACR-NCI-EORTC Molecular Targets and Cancer Therapeutics international conference in San Francisco was an informative meeting.

What I particularly liked was the strategic overview that took place in many of the plenary sessions.

As an example, Johann de Bono, Professor of Experimental Cancer Medicine at The Institute of Cancer Research/The Royal Marsden in London highlighted the potential drug development targets based on prostate cancer biology:

  • Androgen Receptor (AR)
  • Heat Shock Proteins (Hsp)
  • Signaling: HER3, MET, IGF-1R, CCL2, IL-6, Src
  • PI3K/AKT/TOR signaling
  • PARP and BRCAness
  • Estrogen receptor (ER)
  • c-MYC & CHK1

His presentation discussed the possible therapeutic approaches, and complexity involved in developing novel targeted therapies for prostate cancer.

This is something that I expect we will hear more of at the AACR special conference on Advances in Prostate Cancer Research early next year.

In particular, de Bono discussed drug development strategies to target androgen receptor signaling, and some of the future challenges including:

  • Proving to the regulatory authorities that circulating tumor cell (CTC) count falls are a robust immediate endpoint of overall survival
  • Developing improved imaging for bone metastases

As a side note, there were several posters for cabozantinib (XL184) at the meeting (available on the Exelixis website), including preliminary research on computer-aided quantitative bone scan assessment.

However, as de Bono mentioned in his presentation, “diffusion weighted MRI shows hot spots not detected by bone scans.”

2010 and 2011 were good years for prostate cancer drugs, and with new approvals for MDV3100 and radium-223 (Alpharadin) expected, 2012 is set to be another “grand cru” year, to paraphase Bertrand Tombal.

If you were not able to make it to San Francisco for the Molecular Targets and Cancer Therapeutics conference, webcasts of many sessions will be available on the AACR site.

 

There has been a lot of negative publicity around Dendreon and sipuleucel-T (Provenge) recently, and the lack of a clear mechanism of action remains a concern to many.

Irrespective of the company’s commercial performance, sipuleucel-T remains an FDA approved therapeutic cancer vaccine that provides a benefit to some patients.  It provided a proof-of-concept that immunotherapy can offer a survival advantage, albeit for a median of 4.1 months in asymptomatic advanced prostate cancer.

Dendreon is learning the hard way the failings in its commercial strategy, and no doubt these will be absorbed by others with other therapeutic vaccines in development.

Which brings me to an interesting paper published online first on November 8, 2011 in the American Association for Cancer Research journal, Clinical Cancer Research.

NCI-SEM-Picture-Breast-Cancer-Cell

Researchers from the National Cancer Institute (NCI) published data from a small pilot trial showing a clinical response to a poxviral vaccine (PANVAC) in metastatic breast cancer and ovarian cancer patients.

Twenty six patients were in involved in the pilot NCI trial with PANVAC, a recombinant poxviral vaccine expressing the tumor-associated antigens (TAA), carcinoembryonic antigen (CEA) and mucin-1 (MUC-1).

The results showed a median overall survival of 13.7 months in the 12 breast cancer patients with four patients having stable disease, and one patient on study for 37 months.  One patient had a 17% reduction in mediastinal mass.

In ovarian cancer, median overall survival for the 14 patients treated was 15.0 months.

This is promising early stage data in very sick patients. Mahsa Mohebtash and colleagues conclude in their paper that:

“Some patients who had limited tumor burden with minimal prior chemotherapy seemed to benefit from the vaccine. Further studies to confirm these results are warranted.”

Immunotherapy holds a lot of promise.  Research suggests that cancer vaccines once they have provoked a response may improve a patients’ response to subsequent therapies through enhanced T-cell response.

The NCI researchers in their paper noted that time to progression and tumor shrinkage may not be good endpoints for evaluating immunotherapies given that it can take a few months for the optimal result after vaccination and there is often little impact on the tumor size, as judged by classical RECIST measurement.

Instead, overall survival (OS) should be considered a more relevant endpoint.  Sipuleucel-T failed to show a benefit in progression free survival (PFS), but did show an impact on OS. In prostate cancer, OS remains the gold standard for regulatory approval, which is why Exelixis recently took a hit for not making this the primary endpoint in their phase III trial (306) for cabozantinib (XL184).

There are several challenges to consider with vaccine therapies:

  • How do we identify upfront which patients are most likely to respond to the vaccine?
  • The ideal setting is likely to be adjuvant rather than metastatic disease, but these trials will take a very long time and significant funding to come to fruition.
  • Cancer vaccines may allow some patients to live longer, but they have yet to show any meaningful benefit in other clinical measures such as bone pain, symptoms etc.
  • There are fewer side effects, but how do we evaluate how well patients are doing without clinically validated surrogate markers to aid in assessment?

This early research with a vaccine in breast and ovarian cancer, albeit on a very small number of patients, adds further support to the notion that vaccines may offer treatment benefits in the future.

We still, however, have a long way to go in understanding how best to use immunotherapy effectively and incorporate it into clinical treatment guidelines.  We should also be wary of false hope and hype – I look forward to following the progress of PANVAC going forward.

ResearchBlogging.orgMohebtash, M., Tsang, K., Madan, R., Huen, N., Poole, D., Jochems, C., Jones, J., Ferrara, T., Heery, C., Arlen, P., Steinberg, S., Pazdur, M., Rauckhorst, M., Jones, E., Dahut, W., Schlom, J., & Gulley, J. (2011). A Pilot Study of MUC-1/CEA/TRICOM Poxviral-Based Vaccine in Patients with Metastatic Breast and Ovarian Cancer Clinical Cancer Research, 17 (22), 7164-7173 DOI: 10.1158/1078-0432.CCR-11-0649

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