Pilot Study of Hyperfractionated Dosing of Lutetium-177-Labeled Antiprostate-Specific Membrane Antigen Monoclonal Antibody J591 (177 Lu-J591) for Metastatic Castration-Resistant Prostate Cancer.

LESSONS LEARNED: Hyperfractionation of lutetium-177 (177 Lu)-J591 for patients with metastatic castration-resistant prostate cancer did not appear to have any additional advantage over the single dose 177 Lu-J591 or fractionated two-dose 177 Lu-J591 therapy. Definite conclusions were challenging because of the small sample size of this study, and so further studies are needed to evaluate the viability of the hypothesis. On the basis of available data, a registration study of 177 Lu-J591 (also known as TLX591) is planned and will use the two-dose fractionation schedule (Telix Pharma Q3 2019 update https://telixpharma.com/news-media/). BACKGROUND: Phase I and II single-dose studies of lutetium-177 (177 Lu)-J591, a radio-labeled antibody binding prostate-specific membrane antigen (PSMA), demonstrated safety and efficacy with dose response. Modest dose fractionation of 177 Lu-J591 (2 doses) has less myelosuppression per similar cumulative dose, allowing higher doses to be administered safely. We hypothesized that additional dose fractionation would allow a higher cumulative dose, potentially with less toxicity and more efficacy. METHODS: Men with progressive metastatic castration-resistant prostate cancer and adequate organ function were enrolled. 177 Lu-J591 was administered at 25 mCi/m2 every 2 weeks until the emergence of related grade 2 toxicity. 177 Lu-J591 imaging was performed and circulating tumor cell (CTC) counts were measured before and after treatment along with standard monitoring. RESULTS: Six subjects in a single cohort, with a median age of 68.6 years, were enrolled. Patients received three to six doses (cumulative 75-150 mCi/m2 ). Two (33%) patients had >30% prostate-specific antigen (PSA) decline and three (50%) had CTC count decline. Two (33%) experienced grade (Gr) 4 neutropenia (without fever), three (50%) had Gr 4 thrombocytopenia (without hemorrhage), and two (33%) required platelet transfusions. Following hematological improvement, two patients developed worsening cytopenia during prostate cancer progression; bone marrow biopsies revealed infiltrative tumor replacing normal marrow elements without myelodysplasia. Targeting of known disease sites was seen on planar imaging in all. CONCLUSION: Hyperfractionation of 177 Lu-J591 is feasible but does not seem to have significant advantages over the two-dose fractionation regimen.

Phase 1/2 study of fractionated dose lutetium-177-labeled anti-prostate-specific membrane antigen monoclonal antibody J591 (177 Lu-J591) for metastatic castration-resistant prostate cancer.

BACKGROUND: Prostate cancer is radiosensitive. Prostate-specific membrane antigen (PSMA) is selectively overexpressed on advanced, castration-resistant tumors. Lutetium-177-labeled anti-PSMA monoclonal antibody J591 (177 Lu-J591) targets prostate cancer with efficacy and dose-response/toxicity data when delivered as a single dose. Dose fractionation may allow higher doses to be administered safely. METHOD: Men with metastatic castration-resistant prostate cancer refractory to or refusing standard treatment options with normal neutrophil and platelet counts were enrolled in initial phase 1b dose-escalation cohorts followed by phase 2a cohorts treated at recommended phase 2 doses (RP2Ds) comprising 2 fractionated doses of 177 Lu-J591 2 weeks apart. 177 Lu-J591 imaging was performed after treatment, but no selection for PSMA expression was performed before enrollment. Phase 2 patients had circulating tumor cell (CTC) counts assessed before and after treatment. RESULTS: Forty-nine men received fractionated doses of 177 Lu-J591 ranging from 20 to 45 mCi/m2 ×2 two weeks apart. The dose-limiting toxicity in phase 1 was neutropenia. The RP2Ds were 40 mCi/m2 and 45 mCi/m2 ×2. At the highest RP2D (45 mCi/m2 ×2), 35.3% of patients had reversible grade 4 neutropenia, and 58.8% of patients had thrombocytopenia. This dose showed a greater decrease in prostate-specific antigen (PSA) levels and longer survival (87.5% with any PSA decrease, 58.8% with >30% decrease, 29.4% with >50% decrease; median survival, 42.3 months [95% confidence interval, 19.9-64.7]). Fourteen of 17 (82%) patients with detectable CTCs experienced a decrease in CTC count. Overall, 79.6% of patients had positive PSMA imaging; those with less intense PSMA imaging tended to have poorer responses. CONCLUSION: Fractionated administration of 177 Lu-J591 allowed higher cumulative radiation dosing. The frequency and depth of PSA decrease, overall survival, and toxicity (dose-limiting myelosuppression) increased with higher doses.

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 177Lu-J591 allows similar administered doses with less toxicity. This study (NCT00916123) was designed to determine the safety, DLT, and maximum tolerated dose of fractionated 177Lu-J591 administered concurrently with standard docetaxel. METHODS: Men with progressive mCRPC received docetaxel 75 mg/m2 every 3 weeks with escalating 2 fractionated doses of 177Lu-J591 (1.48 GBq/m2 up to max of 2.96 GBq/m2) with cycle 3. Cycle 4 of docetaxel was planned 6 weeks after cycle 3 to allow for recovery from 177Lu-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 177Lu-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/m2). 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 177Lu-J591. All patients had targeting of known sites of disease by planar 177Lu-J591 imaging. CONCLUSION: The combination of 177Lu-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.

Anti-PSMA/CD3 Bispecific Antibody Delivery and Antitumor Activity Using a Polymeric Depot Formulation.

Small therapeutic proteins represent a promising novel approach to treat cancer. Nevertheless, their clinical application is often adversely impacted by their short plasma half-life. Controlled long-term delivery of small biologicals has become a challenge because of their hydrophilic properties and in some cases their limited stability. Here, an in situ forming depot-injectable polymeric system was used to deliver BiJ591, a bispecific T-cell engager (BiTE) targeting both prostate-specific membrane antigen (PSMA) and the CD3 T-cell receptor in prostate cancer. BiJ591 induced T-cell activation, prostate cancer-directed cell lysis, and tumor growth inhibition. The use of diblock (DB) and triblock (TB) biodegradable polyethylene glycol-poly(lactic acid; PEG-PLA) copolymers solubilized in tripropionin, a small-chain triglyceride, allowed maintenance of BiJ591 stability and functionality in the formed depot and controlled its release. In mice, after a single subcutaneous injection, one of the polymeric candidates, TB1/DB4, provided the most sustained release of BiJ591 for up to 21 days. Moreover, the use of BiJ591-TB1/DB4 formulation in prostate cancer xenograft models showed significant therapeutic activity in both low and high PSMA-expressing tumors, whereas daily intravenous administration of BiJ591 was less efficient. Collectively, these data provide new insights into the development of controlled delivery of small therapeutic proteins in cancer. Mol Cancer Ther; 17(9); 1927-40. ©2018 AACR.

Induction of PSMA and Internalization of an Anti-PSMA mAb in the Vascular Compartment.

Angiogenesis is critical for tumor growth and survival and involves interactions between cancer and endothelial cells. Prostate-specific membrane antigen (PSMA/FOLH1) is expressed in the neovasculature of several types of cancer. However, the study of neovascular PSMA expression has been impeded as human umbilical vein endothelial cell (HUVEC) cultures are PSMA-negative and both tumor xenografts and patient-derived xenograft (PDX) models are not known to express PSMA in their vasculature. Therefore, PSMA expression was examined in HUVECs, in vitro and in vivo, and we tested the hypothesis that cancer cell-HUVEC crosstalk could induce the expression of PSMA in HUVECs. Interestingly, conditioned media from several cancer cell lines induced PSMA expression in HUVECs, in vitro, and these lines induced PSMA, in vivo, in a HUVEC coimplantation mouse model. Furthermore, HUVECs in which PSMA expression was induced were able to internalize J591, a mAb that recognizes an extracellular epitope of PSMA as well as nanoparticles bearing a PSMA-binding ligand/inhibitor. These findings offer new avenues to study the molecular mechanism responsible for tumor cell induction of PSMA in neovasculature as well as the biological role of PSMA in neovasculature. Finally, these data suggest that PSMA-targeted therapies could synergize with antiangiogenic and/or other antitumor agents and provide a promising model system to test therapeutic modalities that target PSMA in these settings. IMPLICATIONS: Cancer cells are able to induce PSMA expression in HUVECs, in vitro and in vivo, allowing internalization of PSMA-specific mAbs and nanoparticles bearing a PSMA-binding ligand/inhibitor. Mol Cancer Res; 14(11); 1045-53. ©2016 AACR.