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Novel Anti-Sense Drug Lowers PSA Levels and Delays Disease Progression in a Phase II Clinical Trial for Men with Advanced Prostate Cancer

From this year’s European Society for Medical Oncology (ESMO) Congress in Vienna September 28-October 2, 2012

Abstract Title: A Randomized Phase II Study of OGX-427 plus Prednisone (P) vs. P Alone in Patients (PTS) with Metastatic Castration Resistant Prostate Cancer (CRPC).

October 04, 2012 -- Heat shock proteins (Hsp) are a class of proteins that become especially active when cells are stressed or exposed to attack or invasion such as from cancer cell proliferation. A specific heat shock protein, known as Hsp27, has multiple functions in the body, one of which is to “chaperone” or assist certain proteins that are implicated in cancer cell proliferation in body tissues. Phase II clinical trial data presented this week at the annual European Society for Medical Oncology (ESMO) Congress in Vienna, demonstrated that a pharmacological inhibitor of Hsp27 slowed disease progression in men with an advanced form of metastatic prostate cancer, dubbed castration-resistant prostate cancer (CRPC), known for its resistance to androgen deprivation therapy. This data provides clinical evidence that targeting Hsp27 may be beneficial to men battling this form of prostate cancer and that the compound used in the clinical trial (OGX-427) may move into Phase III clinical trials for further testing.

In the Phase II clinical trial, 64 men with treatment-resistant prostate cancer—also known as castration-resistant prostate cancer (CRPC)—were given either the Hsp27 inhibitor OGX-427 and prednisone, or prednisone alone. The primary goal of the study was to evaluate disease progression in both sets of men 12 weeks into the study.

At week twelve, 77 percent of the men who received OGX-427 + prednisone were found to have stable disease, that is, their disease had not progressed. Only 40 percent of the men who received prednisone alone were found to be progression free. (Because patient recruitment to clinical trials occurs in stages, only 42 of the 64 patients enrolled in the trial were ready for this interim 12 week analysis.)

The study also evaluated other outcomes at the 12-week mark, such as declines in prostate specific antigen (PSA) and tumor cells found in blood circulation, both presumed measures of disease extent. Half of the men given Hsp27 inhibitor OGX-427 experienced PSA declines of 50 percent or greater compared to only 20 percent of men on prednisone alone achieving those levels of PSA declines. In addition, levels of tumor cells found in systemic circulation dropped to a greater degree in men who received OGX-427.

“The mechanism of action Hsp27 protein plays in prostate cancer is not well understood,” said Dr. Philip Kantoff, the director of The Lank Center for Genitourinary Oncology, and chief of the division of solid tumor oncology at the Dana-Farber Cancer Institute, who was not involved in the study. However, by targeting Hsp27 with an anti-sense molecule (OGX-427) that lowers the amount of the protein, and in turn, seeing PSA levels drop significantly in half of the men given the drug, suggests targeting Hsp27 is promising, said Kantoff.

“Whether this will translate into meaningful clinical benefit awaits a Phase III study,” said Kantoff.

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