PHASE I STUDY OF COMBINED VIRAL & SUICIDE GENE THERAPIES

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Although conventional therapies for prostate cancer (surgery and radiation therapy) produce a high rate of cure for patients with early stage disease, a significant fraction of these cancers recur and each therapy results in high morbidity. The prognosis for androgen-independent prostate cancer is much worse, as there is no effective treatment and a vast majority of these patients eventually succumb to the disease. There is a real need to develop new therapies that would reduce the morbidity associated with conventional therapies, decrease the incidence of local tumor recurrence, and improve the outlook for recurrent and androgen-independent cancer. Up to 80 percent of prostate cancer patients who received radiation therapy as their primary treatment will fail biochemically (develop a rising PSA) within 5 years and 65 percent will die within 10 years. Unfortunately, limited therapeutic options exist for such patients. Our research program has developed a novel, trimodal gene therapy approach for the treatment of prostate cancer. Our approach utilizes a lytic, replication-competent adenovirus (Ad5-CD/TKrep) to selectively and efficiently deliver a pair of therapeutic "suicide" genes to prostate tumors. Preclinical studies in animals have demonstrated that the Ad5-CD/TKrep virus itself generates a potent anti-tumor effect. The therapeutic efficacy of Ad5- CD/TKrep viral therapy can be enhanced significantly by invoking two suicide gene systems (CD/5-FC and HSV-1 TK/GCV), which render malignant cells sensitive to specific pharmacological agents and sensitizes them to radiation. Our research efforts are currently at the cusp of preclinical/phase I clinical studies. A phase I study that will evaluate the toxicity and efficacy of Ad5-CD/TKrep viral therapy concomitant with double prodrug therapy in men with local recurrence of prostate cancer following radiotherapy has been approved by our Institutional Review Boards (IRB), and an Investigational New Drug (IND) application has been submitted to the U.S. Food and Drug Administration (FDA). The specific aims of this proposal are to evaluate the toxicity and efficacy of Ad5-CD/TKrep viral therapy concomitant with double prodrug therapy in patients with local recurrence of prostate cancer following radiation therapy. A dose escalation study will be performed on 12 patients (4 patients/dose) using 10e9 to 10e12 viral particles (vp) per dose to determine the maximum tolerable dose (MTD) that can be safely administered to humans. Clinical response will be assessed during follow-up by serial measurements of serum PSA levels, and by assessing the presence of tumor by digital rectal exam (DRE), transrectal ultrasound (TRUS), and needle biopsy of the prostate. This research may lead to a safe and effective therapy for men with localized prostate cancer.