Clinical Evaluation of an Innovative PSMA-targeted Radiotherapy, CTT1403, in Prostate Cancer

PROJECT ABSTRACT Prostate-Specific Membrane Antigen (PSMA) is an ideal tumor biomarker as it is expressed on andgt;90% of all prostate cancers and expression increases as the cancer progresses. Cancer Targeted Technology (CTT) has developed a unique phosphoramidate-based scaffold that binds irreversibly to PSMA leading to andgt; 90% rapid internalization and selective accumulation in tumor cells. With previous SBIR grant support, CTT created an 18F- labeled PET diagnostic imaging agent, CTT1057, and in Aug 2017 completed a Phase I clinical trial in patients with metastatic prostate cancer. CTT1057 demonstrated significant uptake in PSMA-avid bone and visceral lesions with far greater specificity and sensitivity than standard of care scans. In Jan 2018, CTT licensed this PET imaging agent to Advanced Accelerator Applications/Novartis. Prostate cancer is radiosensitive, but only Radium-223, which is neither specific nor selective, has been commercialized as a radiotherapeutic for advanced stage disease. Under an additional SBIR Phase I/II fast track contract, CTT modified the original CTT1057 PSMA-binding scaffold to develop a specific and potent companion therapeutic, CTT1403, radiolabeled with 177Lu. CTT1403, unlike other PSMA-targeting agents under development, is highly innovative in that it binds irreversibly to PSMA and uses an albumin-binding motif to dramatically slow clearance, resulting in an unprecedented tumor uptake of andgt;80% injected dose/g of tumor tissue and a significant survival advantage in animal models. Under the SBIR Phase II contract, GMP-manufacturing, radiolabeling and IND- enabling pharmacology, dosimetry and initial animal safety studies were completed. An FDA pre-IND meeting was held, and the IND will be filed Q4 2018. The objective of this SBIR Phase IIB application is to support the first in human Phase 1 clinical trial of CTT1403 and to position the drug for further clinical development and rapid commercialization. Specific aims: AIM 1: Phase 1 clinical trial of CTT1403 in metastatic castration-resistant prostate cancer (mCRPC), assessing safety and initial efficacy: CTT will conduct an accelerated dose escalation/expansion trial in patients with mCRPC. Increased uptake of the albumin-binding, PSMA-targeted, 177Lu-labeled CTT1403 drug is hypothesized to translate into a meaningful survival advantage. AIM 2: Assess GLP late radiation safety: CTT will evaluate long term tolerance of repeat-dose CTT1403 in dogs to meet FDA late radiation safety recommendations prior to start of Phase 2 trials. AIM 3: Process development in support of further clinical development: CTT will develop and scale CTT1403 manufacturing methods in support of multiple dose trials. This innovative work harnesses the ideal performance of a cell-penetrating irreversible small-molecule PSMA-targeted drug that uses albumin binding to increase circulation half-life and tumor targeting and decrease renal toxicity. CTT1403 should have considerable significance for metastatic prostate cancer therapy by reducing toxic side effects in a patient population with a substantial unmet need.PROJECT NARRATIVE This grant proposes the development and characterization of an innovative Prostate Specific Membrane Antigen (PSMA)-targeted peptidomimetic 177Lu-radiotherapy, CTT1403, that can be specifically delivered to tumor cells and released over time as a result of an albumin-binding moiety. The work will assess the safety and initial efficacy of CTT1403 in a first in human Phase 1 study in late stage castration-resistant prostate cancer, and will further set the groundwork for subsequent clinical studies.