Abstract 1483: MT-3724, an engineered toxin body targeting CD20 for non-Hodgkin's lymphoma

Abstract

Molecular Templates has developed engineered toxin bodies (ETBs), potent recombinant immunotoxins that combine the specificity of an antibody fragment with the powerful direct cytotoxicity of the Shiga-like toxin A subunit to specifically destroy target expressing cells. The use of other immunotoxins and antibody-drug conjugates is limited to targets with tumor-specific cell surface expression that efficiently internalize. The ETB scaffold has been designed to overcome this limitation and promote forced internalization of ETBs, a property that expands the potential targets to receptors with poor internalization kinetics. An additional benefit to ETBs is the mechanism of action (MOA) which is unique to that of other oncology treatments. CD20, a receptor that does not undergo rapid internalization, is a well characterized target for agents used to treat non-Hodgkin's lymphoma (NHL). Thus, successful CD20-targeted clinical strategies include monoclonal antibodies (mAbs) and radiolabeled mAbs that act on the cell surface. Molecular Templates’ lead compound, MT-3724, is a CD20-targeted ETB that has been engineered to force the rapid internalization of the immunotoxin after binding to CD20. MT-3724 has potent direct cell kill activity on CD20 positive lymphoma cells and is the first immunotoxin to CD20 to enter the clinic. The on-going phase I study being conducted at Memorial Sloan-Kettering Cancer Center, MD Anderson Cancer Center, and New York University Langone Medical Center has shown promising safety and efficacy in highly refractory NHL patients. Once MT-3724 is delivered to appropriate cells, the Shiga toxin A subunit inhibits protein synthesis and promotes apoptosis of tumor cells. The difference in MOA allows for activity in the refractory setting, where resistance to other treatments has emerged, and may also allow for combination therapy. Pre-clinical studies with immunomodulatory drugs (IMiDs), PI3K and Bcl-2 inhibitors that are used in treatment of NHL have shown promising results when combined with MT-3724. MT-3724 is a promising novel agent in the treatment of NHL and other CD20 positive hematological malignancies. Data around the internalization kinetics, enzymatic activity, and combination with other agents will be presented. Citation Format: Garrett L. Robinson, Sangeetha Rajagopalan, Brigitte Brieschke, Jennifer Erdman, Jane Neill, Rodney E. Flores-Lefranc, Julia Foree, William Null, Jensing Liu, Jack P. Higgins, Erin K. Willert. MT-3724, an engineered toxin body targeting CD20 for non-Hodgkin's lymphoma. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1483.

Safety and Efficacy of Engineered Toxin Body MT-3724 in Relapsed or Refractory B-cell Non-Hodgkin's Lymphomas and Diffuse Large B-cell Lymphoma

“…The study also included a dose expansion phase, which was added to address a potential interaction between circulating rituximab and MT-3724 efficacy ( 11 ). This additional dose-expansion evaluated safety and efficacy of MT-3724 in serum rituximab-negative patients with DLBCL treated at the MTD.…”

“…MT-3724, a novel ETB construct comprised of an anti-CD20 single-chain variable fragment genetically fused to SLT-A, is capable of binding to and forcing internalization of CD20, a cell surface protein that does not otherwise internalize; subsequently, MT-3724 is routed to the endoplasmic reticulum and induces potent direct cell kill via permanent inactivation of ribosomes ( 10 ). Preclinical in vitro studies have demonstrated that MT-3724 specifically targets and directly kills CD20 + cells, resulting in decreased tumor growth in the Daudi-Luc xenograft murine model ( 11 ).…”