Methotrexate-based PROTACs as DHFR-specific chemical probes
Sandeep Rana, Patricia Dranchak, Jayme L. Dahlin, Laurence Lamy, Wenqing Li, Erin Oliphant, Jonathan H. Shrimp, Girish H. Rajacharya, Ravi Tharakan, David O. Holland, Apryl S. Whitten, Kelli M. Wilson, Pankaj K. Singh, Scott K. Durum, Dingyin Tao, Ganesha Rai, James Inglese
Abstract
Methotrexate (MTX) is a tight-binding dihydrofolate reductase (DHFR) inhibitor, used as both an antineoplastic and immunosuppressant therapeutic. MTX, like folate undergoes folylpolyglutamate synthetase-mediated γ-glutamylation, which affects cellular retention and target specificity. Mechanisms of MTX resistance in cancers include a decrease in MTX poly-γ-glutamylation and an upregulation of DHFR. Here, we report a series of potent MTX-based proteolysis targeting chimeras (PROTACs) to investigate DHFR degradation pharmacology and one-carbon biochemistry. These on-target, cell-active PROTACs show proteasome- and E3 ligase-dependent activity, and selective degradation of DHFR in multiple cancer cell lines. By comparison, treatment with MTX increases cellular DHFR protein expression. Importantly, these PROTACs produced distinct, less-lethal phenotypes compared to MTX. The chemical probe set described here should complement conventional DHFR inhibitors and serve as useful tools for studying one-carbon biochemistry and dissecting complex polypharmacology of MTX and related drugs. Such compounds may also serve as leads for potential autoimmune and antineoplastic therapeutics.