The purpose of this study is to determine the therapeutic activity of different concentrations of PRX302 at increasing volumes and/or number of deposits per gram of prostate. Therapeutic activity will be determined based on changes in PSA levels, PSA velocity, PSA doubling time and tumor burden following treatment.

Inclusion Criteria:

• Completed a full course of radiation therapy for prostate cancer at least 2 years before enrollment.
• Biochemical failure at screening as determined by either the ASTRO or the Phoenix definitions.
• At least 5 available PSA readings after completion of radiation therapy and prior to screening.
• PSA level of not greater than 10 ng/mL.
• PSA doubling time of at least 9 months at screening.
• Biopsy-proven recurrent localized prostate cancer.
• Tumor stage T1C to T2C.
• Prostate volume estimated at 40 mL or less as determined by TRUS.
• ECOG performance score 0 to 2.
• Serum testosterone of at least 1 ng/dL.

Exclusion Criteria:

• Prior history of metastatic prostate cancer.
• Salvage external beam therapy and/or salvage brachytherapy prior to enrollment.
• Biological, immunological, chemotherapeutic treatment or cryotherapy after completing radiation.
• Androgen ablation therapy within 12 months prior to enrollment.
• Recurrence of prostate cancer within 18 months of definitive primary radiotherapy.
• Other medication for prostate cancer.
• Presence of active malignancy other than prostate cancer.
• Treatment with other investigational therapies within 12 months prior to enrolment.
• Presence of a chronic indwelling Foley catheter for obstructive uropathy.
• Previous transurethral resection of the prostate (TURP), transurethral resection of the bladder neck, photo-selective vaporization of the prostate (PVP) or other resection surgery in the urinary tract.
• Previous treatment with PRX302.
• Any evidence of metastatic disease on bone scan, CT or magnetic resonance imaging (MRI) within 3 months prior to enrollment.