Last night I received an alert from Medivation announcing that an article would be published in today's online The Lancet regarding their prostate cancer agent, MDV3100.  Sure enough, here's the article:

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Although the trial is an early phase I/II study, encouraging antitumour effects were reported in 140 men, of whom 65 were chemotherapy naïve.  Time to disease progression (TTP) was 47 weeks, which is decent considering the men in the study were all castration resistant and likely had advanced disease.  

Obviously, it is too early to tell yet quite what Medivation and Astellas have here, but to put things in context, docetaxel (Taxotere), was approved for hormone refractory prostate cancer (HRPC) with prednisone in androgen independent (hormone refractory) metastatic prostate cancer with a median overall survival of 18.9 months (approx. 85 weeks) in a large phase III trial. 

We must also remember that in another more recent trial, it was demonstrated that men who received cabazitaxel (sanofi-aventis' follow on taxane to docetaxel) lived a median of 15.1 months (68 weeks), compared with 12.7 months (57 weeks) for those who receive mitoxantrone, a difference that was statistically significant.

That said, the side effect profile of chemotherapy is certainly not benign, with significant risk of myelosuppression and infectious complications.

However, what was encouraging about the Medivation trial was early Kaplan Meier response curves, which demonstrated those men who had no previous chemotherapy generally did better than those who received it in terms of both PSA and radiological progression.

At the AACR Molecular Targets meeting last November, Charles Sawyers gave a keynote talk on prostate cancer and looked at the various opportunities for investigating new therapeutics in clinical trials for prostate cancer.  He suggested that circulating tumour cells (CTCs) might be a more useful marker for disease status than PSA.  In The Lancet study, the authors noted that:

"We recorded early post-treatment conversions from unfavourable to favourable in 75% of patients not exposed to chemotherapy and in 37% of those who were exposed. Decreases in PSA were generally associated with parallel falls (or no progression) in CTCs, but this finding was not consistent, suggesting that these measures assess different aspects of the malignant process. PSA decreases might in some cases be an indicator of the mechanism of action of MDV3100 as an androgen-receptor antagonist rather than an actual antitumour effect. However, the benefit of MDV3100 on several assessments, including CTCs and radiological time to progression, suggest that MDV3100 does have a true antitumour effect."

The other interesting observation that Sawyers made was that traditionally, early prostate disease is treated with oral hormonal therapies and once castration resistance sets in, the patient is referred to an oncologist for consideration of chemotherapeutic options.  With the advent of new therapies with different MOAs in development such as MDV3100, abiraterone (Cougar/J&J) and Provenge (Dendreon), the lives of men with prostate cancer can potentially be extended further before stage IV metastases sets in. 

At AACR last November, Sawyers also discussed the importance of androgen receptor signalling in the disease (previously discussed here with simple models) and the data from this trial seem to bear out his elegant theory.  I'd like to see more analysis though and learn whether those men who had AR amplified prostate cancer did better on MDV3100 than those who did not?

All in all, this is an exciting time for men with prostate cancer.  Dendreon's Provenge may well be the first new drug that fits between the hormonal therapies and chemotherapy, since the FDA PDUFA date is May 1st, although since that is a Saturday, we may well here the Go/No Go news on Friday 30th April.  

In the meantime, the annual AACR meeting in DC this weekend can't come soon enough!
Scher, H., Beer, T., Higano, C., Anand, A., Taplin, M., Efstathiou, E., Rathkopf, D., Shelkey, J., Yu, E., & Alumkal, J. (2010). Antitumour activity of MDV3100 in castration-resistant prostate cancer: a phase 1–2 study The Lancet DOI: 10.1016/S0140-6736(10)60172-9