Anti-OX40, Cyclophosphamide (CTX) and Radiation in Patients With Progressive Metastatic Prostate Cancer

Anti-OX40 will be administered intravenously at 0.4 mg/kg on days 4, 6 and 8 of the study. The total anti-OX40 dose will be reconstituted in 100 ml 0.9% saline and infused over no more than 60 minutes intravenously. A single-use non-pyrogenic durapore membrane low protein binding filter (e.g.: Braun 1.2 micron air eliminating filter or equivalent) shall be used to filter the study product in the line between infusion bag and patient.

8.0 Gy in 1 fraction to a maximum of three bone metastatic deposits will be administered on Day 4 of treatment. Imaging such as bone scan, MRI, CT scan, or radiograph must identify the target lesion as consistent with metastatic disease. Any bone lesion that is inducing pain or where there may be a clinical concern for potential pathological fracture will be selected over asymptomatic lesions.

CTX will be administered on day 1 (Friday only) at a dose determined by cohort assignment. The drug should be diluted per institutional standards. An added dose of IV fluids may help prevent bladder toxicity. In this protocol, CTX will be administered intravenously over 30 - 60 minutes.