Phase I trial of docetaxel plus lutetium-177-labeled anti-prostate-specific membrane antigen monoclonal antibody J591 (177Lu-J591) for metastatic castration-resistant prostate cancer

Background: Docetaxel remains a standard of care for metatsatic castration resistant porstate cancer (mCRPC) and has radiosensitizing properties. The dose limiting toxicity (DLT) of radioimmunotherapy is myelosuppression; dose fractionation of Lu-177-J591 allows similar administered doses with less toxicity. This study (NCT00916123) was designed to determine the safety, DLT, and maximum tolerated dose of fractionated Lu-177-J591 administered concurrently with standard docetaxel. Methods: Men with progressive mCRPC received docetaxel 75 mg/m(2) every 3 weeks with escalating 2 fractionated doses of Lu-177-J591 (1.48 GBq/m(2) up to max of 2.96 GBq/m(2)) with cycle 3. Cycle 4 of docetaxel was planned 6 weeks after cycle 3 to allow for recovery from Lu-177-J591-associated hematologic toxicity. DLT was defined as delay in docetaxel > 3 weeks, prolonged myelosuppression or need for > 2 platelet transfusions, febrile neutropenia, or grade >= 3 nonhematological toxicity following Lu-177-J591. PSA was assessed prior to each cycle and serial computed tomography (CT) and bone scan were performed. Results: Fifteen men with progressive mCRPC received dose-escalated targeted radionuclide therapy in 4 cohorts up to the highest planned dose (2.96 GBq/m(2)). No DLT was seen at any dose level. Grade 4 neutropenia without fever occurred in 8 (53.5%) and thromboytopenia in 2 (13.3%), with 2 receiving prophylactic platelet transfusion. No grade >= 3 nonhematological toxicity was observed. 11 (73.3%) had > 50% PSA decline, with 78.6% having favorable circulating tumor cell counts after Lu-177-J591. All patients had targeting of known sites of disease by planar Lu-177-J591 imaging. Conclusion: The combination of Lu-177-J591 delivered as a single fractionated cycle with docetaxel/prednisone is feasible in patients with mCRPC. Without preselection for prostate-specific membrane antigen, accurate targeting of known sites of disease and a strong preliminary efficacy signal was observed. (C) 2020 The Author(s). Published by Elsevier Inc.