Vaccine/androgen ablation combination found safe

A combination vaccine and androgen ablation therapy is showing promise in some patients with prostate cancer.

In a phase II clinical trial, men with advanced prostate cancer (as evidenced by two rising PSA values and no visible metastasis) whose cancer is resistant to hormone therapy and who had either surgery or radiation were recruited from member institutions in the ECOG-ACRIN (Eastern Cooperative Oncology Group-American College of Radiology Imaging Network) Cancer Research Group. In their work, which was published online in European Urology (Jan. 12, 2015), the authors examined two different experimental treatment options.

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In step one, patients were treated with PROSTVAC-V/TRICOM and PROSTVAC-F/TRICOM. PROSTVAC-V is derived from a vaccinia virus that was used to vaccinate against smallpox. This virus is modified to produce a PSA protein that helps focus the body’s immune response to the PSA in the prostate tumor. In addition, it is modified to produce three other proteins that help increase an immune cell’s ability to destroy its target (TRICOM).

PROSTVAC-F is made from the fowlpox virus and contains the same genetic material as PROSTAC-V, but is given multiple times to further boost the body’s immune system.

Patients were given one cycle of PROSTVAC-V/TRICOM followed by PROSTVAC-F/TRICOM for subsequent cycles in combination with granulocyte macrophage colony-stimulating factor, a protein that normally increases the amount of certain white blood cells and make them more active. When in drug form, it is used to boost the body’s immune system to fight off disease.

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After 6 months from first treatment, 25 of 40 eligible patients (63%) were found to have no disease progression and experienced minimal toxicity. Median pre-treatment PSA velocity was 0.13 log (PSA)/month as compared to median post-registration (6 months) velocity of 0.09 log (PSA)/month, an improvement in PSA doubling time from 5.3 months to 7.7 months.

Step two included the addition of hormone therapy (androgen ablation) to the PROSTVAC-VF/TRICOM combination. In the 27 patients eligible for this step, 20 (74%) experienced a complete response at 7 months.

“Previous studies by the ECOG-ACRIN Cancer Research Group and others have shown it is optimal to explore agents like PROSTVAC that harness the body’s own defenses in shutting down cancer. With our current findings demonstrating the safe use of combination vaccine therapy earlier in the course of prostate cancer progression, we are laying the groundwork for future immunotherapy options for this patient population,” said lead author Robert S. DiPaola, MD, of Rutgers Cancer Institute of New Jersey, New Brunswick, in a press release from that institution.

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