Hormone-Refractory Prostate Cancer

or Castrate-Resistant Prostate Cancer

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VACCINES FOR PROSTATE CANCER

 

Introduction

The FDA has approved Dendreon's Provenge vaccine and it is an available, proven treatment. The other vaccines currently in development are GVAX and Prostvac-VF. These two are briefly discussed here. Provenge is on its own page.

 

GVAX

May 3, 2010. Originally developed by Cell Genesys, it was bought out by BioSante last October.  BioSante plans new prostate cancer drug testing (or re-start testing almost two years after research was stopped -- it was put on hold in August 2008 because of a high number of deaths among patients taking the drug..) This is expected by YE2010, subject to regulatory approval. BioSante said it has started manufacturing new GVAX Prostate and is working to get the Food and Drug Administration to allow it to resume testing. It hopes to begin treating patients in a midstage clinical study in the beginning of the fourth quarter. This Vaccine was in phase III development.

 

PROSTVAC-VF

The most recent clinical trial results for this vaccine is a phase II trial whose purpose was to evaluate PROSTVAC-VF for safety and for prolongation of progression-free survival (PFS) and overall survival (OS). The trial was a randomized, controlled, and blinded phase II study. Details follow.
 

No. of patients: 125 randomly assigned. Patients had minimally symptomatic HRPC (mCRPC). Eighty-two patients received PROSTVAC-VF and 40 received control vectors (essentially a placebo). Patients were limited to those believed to have favorable risk features. Patients with visceral metastases or pain requiring opioid analgesics were excluded and they were required to have ECOG performance status of 0 or 1 as well as a Gleason score of ≤ 7 (2).

The vaccine: "PROSTVAC-VF comprises two recombinant viral vectors, each encoding transgenes for PSA, and three immune costimulatory molecules (B7.1, ICAM-1, and LFA-3). Vaccinia-based vector was used for priming followed by six planned fowlpox-based vector boosts. Patients were allocated (2:1) to PROSTVAC-VF plus granulocyte-macrophage colony-stimulating factor or to control empty vectors plus saline injections." Note that the viruses are the same cowpox virus that forms the basis of the smallpox vaccine and a bird virus called fowlpox. They are genetically engineered to carry prostate specific antigen or PSA, which is made only by prostate cells.

Progression Free Survival (PFS) - The primary end point.

  • similar in the two groups.

Overall Survival (OS) (evaluated 3 years post study),

  • PROSTVAC-VF patients had a better OS with 25 (30%) of 82 alive versus 7 (17%) of 40 controls, longer median survival by 8.5 months (25.1 v 16.6 months for controls). 

Conclusion: PROSTVAC-VF immunotherapy was well tolerated and associated with a 44% reduction in the death rate and an 8.5-month improvement in median OS in men with mCRPC. A larger phase III trial is needed.

Note: PROSTVAC-VF is being developed by BN ImmunoTherapeutics, a division of Danish biotech firm Bavarian Nordic (BAVA.CO).

References - Prostvac-VF

1. Philip W. Kantoff, Thomas J. Schuetz, Brent A. Blumenstein, L. Michael Glode, David L. Bilhartz, Michael Wyand, Kelledy Manson, Dennis L. Panicali, Reiner Laus, Jeffrey Schlom, William L. Dahut, Philip M. Arlen, James L. Gulley, Wayne R. Godfrey, Overall Survival Analysis of a Phase II Randomized Controlled Trial of a Poxviral-Based PSA-Targeted Immunotherapy in Metastatic Castration-Resistant Prostate Cancer, J. Clinical Oncology Jan 25 2010: doi:10.1200/JCO.2009.25.0597. 

2. EJ Small et al, Developing Immunotherapy As Legitimate Therapy for Patients with Prostate Cancer, J. Clin Oncology, vol 28, 2010, editorial.

 Author: Howard Hansen, last update 28 July 2010

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