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

Posts tagged ‘Androgen Receptor Signaling’

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.


Prostate cancer is the second leading cause of cancer death in men, so it was good news this morning when Medivation & Astellas issued a press release that showed positive data from the phase 3 AFFIRM trial for MDV3100.

MDV3100 produced a 4.8-month advantage in median overall survival compared to placebo.

The estimated median survival for men treated with MDV3100 was 18.4 months compared with 13.6 months for men treated with placebo.

MDV3100 provided a 37 percent reduction in risk of death compared to placebo (Hazard Ratio=0.631).

To put the 4.8 month survival advantage in context, this compares favorably with 3.9 months for abiraterone (Hazard Ratio =0.646), in the COU-AA-301 trial.

Positive data was expected given the sound scientific rationale behind MDV3100 and the preliminary data (abstract 4501) presented at the ASCO annual meeting this year. J Clin Oncol 29: 2011 (suppl; abstr 4501).

The drug has a high affinity for the androgen receptor (AR) that is highly expressed on prostate cancer cells.  You can read an excellent interview on Pharma Strategy Blog with Charles Sawyers, who was one of the co-inventors.

MDV3011 blocks the androgen receptor (AR) from moving into the nucleus and activating growth genes and is a more complete inhibitor of AR than bicalutamide.

One hot topic of conversation at ASCO was the potential to combine MDV3100 (androgen receptor blocker) with abiraterone acetate (Zytiga) (androgen synthesis inhibitor), thereby shutting down upstream and downstream activity of the driving receptor in advanced prostate cancer.  The scientific rationale for this appears sound, so it is likely that a combination clinical trial may well be done to test this hypothesis at some point in the future.

MDV3100 has a significant advantage over abiraterone acetate (Zytiga) in that concomitant steroids are not required. Daily steroids have their side effects.  Urologists in particular will be attracted to MDV3100 and its ease of use.

Clinical trials in prostate cancer are ongoing with a multitude of new emerging therapies including TAK-700, Cabozantinib (XL184), radium-223 chloride (Alpharadin), BPX-101, Prostvac-VF, ipilumumab, Custirsen (OGX-011), dasatinib (Sprycel), lenalidomide (Revlimid) and ARN-509 to name but a few.

It is a therapeutic area with a lot going on after very little activity for a decade. The positive interim data for MDV3100 announced today is good news for prostate cancer patients, and we await presentation of the data next year.

Medivation and Astellas plan to hold a pre-NDA meeting with the U.S. Food and Drug Administration (FDA) in early 2012, so US approval could be possible later next year.

The Oncologist Journal of the Society for Translational Oncology (STO) has published a video recording on prostate cancer that is well worth watching for those with an interest in this area.

At their Sept 8, 2011 CME symposium held in Belfast, a roundtable was held entitled “Prostate Cancer: Progress & Promise.”

Moderated by Bruce A. Chabner (Mass General/Harvard), the panelists were Joe O’Sullivan (Queen’s University, Belfast), Johann De Bono (The Institute for Cancer Research) and David Waugh (Queen’s University, Belfast).

Professor de Bono in the video comments that”

“with regards to our dream of eventually treating men with prostate cancer without castrating them, which must be our ultimate goal and curing them of cancer. I think we will have to focus on for example drugs targeting ERG or ERG signaling.”

Chabner then asks the good question of whether ERG is a druggable target?

To which De Bono replies that you can drug ERG by inhibiting PARP and references a paper by the Chinnaiyan group published in the May 2011 issue of Cancer Cell.

PARP inhibition represents an interesting area of prostate cancer research.

If you would like to know more, Sally Church, PhD has written about this on Pharma Strategy Blog.  See posts on “TMPRSS2: ERG may be a more useful marker than PSA in prostate cancer” and “Personalized Therapy for Prostate Cancer – is it possible?

In the STO video, De Bono discusses why he would like to replace bone scans in prostate cancer with another imaging modality that more accurately reflects the activity of the disease. Future possibilities include use of diffusion weighted magnetic resonance imaging and novel PET tracers.

There’s also a good discussion about Alpharadin for those interested in some anecdotal commentary on experiences with it.

Another notable comment by De Bono is his belief that “taxanes work in prostate cancer primarily by targeting androgen receptor signaling.” Taxanes have typically been thought to target mitosis.

De Bono goes on to say that clinical trial data being submitted for publication shows that patients who are refractory to abiraterone, are also refractory to docetaxel when they progress on it.  The suggestion is that there may be cross resistance between abiraterone and taxanes with a subgroup of patients who just don’t do well on androgen receptor (AR) targeting drugs.  The reason for this isn’t yet clear.

A new phase 2 clinical trial is starting soon that will look at the sequencing of abiraterone and cabazitaxel.  One group will receive abiraterone followed by cabazitaxel, the other cabazitaxel followed by abiraterone.

The Belfast STO symposium was the second in a three part series. The next one will be held during ASCO GU in San Francisco next year.

Another potentially useful meeting in this area is the February 2012 AACR workshop on “Advances in Prostate Cancer Research” chaired by Arul Chinnaiyan & Charles Sawyers.

Prostate cancer remains an exciting therapeutic area to watch with tremendous progress and promise of late.

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