On January 19, 2021 Molecular Templates, Inc. (Nasdaq: MTEM, "Molecular Templates," "MTEM" or "the Company"), a clinical-stage biopharmaceutical company focused on the discovery and development of proprietary targeted biologic therapeutics, engineered toxin bodies (ETBs), reported that the U.S. Food and Drug Administration (FDA) has accepted its Investigational New Drug (IND) application for MT-6402, a next-generation ETB targeting PD-L1 that is enabled with MTEM’s antigen seeding technology (AST) (Press release, Molecular Templates, JAN 19, 2021, View Source [SID1234574098]). ETBs enabled with AST have dual mechanisms of action that include the enzymatic destruction of ribosomes and the delivery of viral class I antigens into the targeted tumor to be processed and presented on its cell surface to induce an antigen specific immune response. MTEM expects to start dosing enrolled subjects in a first-in-human Phase 1 study in relapsed/refractory patients with PD-L1-positive solid tumors in 2Q21.

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The Phase 1 study is planned as a multi-center, open-label, dose escalation and dose expansion trial in the United States and outside of the United States. Patients with confirmed PD-L1 expressing tumors or confirmed PD-L1 expression in the tumor microenvironment will be eligible to screen for enrollment in the clinical trial. Following determination of the maximum tolerated dose (MTD) or recommended Phase 2 dose, expansion cohorts are planned to study MT-6402 as a monotherapy in tumor-specific and tumor-agnostic cohorts.

"We are excited to be advancing MT-6402, a third generation ETB, into the clinic for the treatment of patients with PD-L1-positive cancers. MT-6402 utilizes both our proprietary de-immunized toxin scaffold and antigen seeding technology," said Eric Poma, Ph.D., CEO and CSO of Molecular Templates. "The PD-1/PD-L1 axis is central to many tumors and targeting that axis with a new mechanism of action has an opportunity to provide meaningful benefit to patients. We look forward to providing an update on the Phase 1 study by year-end 2021."

About MT-6402

MT-6402 is an ETB consisting of a single chain variable fragment (scFv) with affinity for PD-L1, fused to the enzymatically active de-immunized Shiga-like toxin-A subunit (SLTA) and a class I antigen derived from the human cytomegalovirus (HCMV) pp65 protein. MT-6402 was designed to induce potent anti-tumor effects via PD-L1 targeting through multiple mechanisms that may overcome the limitations of the PD-L1 antibodies. In MTEM’s preclinical studies, MT-6402 was found to specifically bind and kill both tumor and immune PD-L1 expressing cells in a manner consistent with SLTA mediated cellular cytotoxicity through ribosomal inactivation, independent of checkpoint inhibition. Additionally, MT-6402 alters the immunophenotype of targeted cells by delivering foreign class I antigen from CMV for presentation in complex with MHC class I, which may provoke a CMV-specific immune response against the targeted cells. Third, MT-6402 may rehabilitate the tumor microenvironment (TME) and allow for immune recognition of tumors by destroying PD-L1-expressing immune cells in the TME through ribosomal inactivation.