Molecular Templates, Inc. announced that the first patient has been dosed in the Phase 1 clinical trial evaluating MT-8421, a novel engineered toxin body targeting CTLA-4, for the treatment of advanced solid tumors. The Phase 1 study is a multi-center open-label, dose-escalation, dose-expansion, and a first-in-human study designed to evaluate the safety, tolerability, pharmacokinetics (PK), pharmacodynamics (PD), and the preliminary efficacy of MT-8421. The study will enroll adult patients with tumors where CTLA-4 inhibitors have been proven to provide benefit and in other select tumor types known to frequently have an immune rich tumor microenvironment (?TME?).

This will include melanoma, hepatocellular carcinoma (HCC), non-small cell lung cancer (NSCLC), renal cell carcinoma (RCC), Microsatellite Instability-High (MSI-H) /Mismatch Repair Deficient (dMMR) cancer, mesothelioma, esophageal squamous cell carcinoma (ESCC), squamous cell carcinoma of the head and neck (SCCHN), urothelial carcinoma, and cervical carcinoma. Approximately 24-30 patients are anticipated to enroll in Part A dose escalation with a starting dose of 32 mcg/kg. MT-8421, along with MT-6402 (PD-L1 Targeting ETB with Antigen Seeding Technology), represents its unique approach to immuno-oncology based on dismantling the TME through direct cell-kill of tumor and immune cells and not only the blocking of ligand-ligand interactions seen with current antibody therapeutics. The ETB approach includes potent destruction of CTLA4+ regulatory T cells (?Tregs?) via enzymatic ribosome destruction, and the mechanism of cell kill is independent of TME. MT-8421 preferentially destroys high CTLA4 expressing Tregs in the TME relative to peripheral Tregs which are lower CTLA4 expressing.