Cellular Pharmacodynamics of a Novel Pyrrolo[3,2-]pyrimidine Inhibitor Targeting Mitochondrial and Cytosolic One-Carbon Metabolism.

Folate-dependent one-carbon (C1) metabolism is compartmentalized in the mitochondria and cytosol and is a source of critical metabolites for proliferating tumors. Mitochondrial C1 metabolism including serine hydroxymethyltransferase 2 (SHMT2) generates glycine for de novo purine nucleotide and glutathione biosynthesis and is an important source of NADPH, ATP, and formate, which affords C1 units as 10-formyl-tetrahydrofolate and 5,10-methylene-tetrahydrofolate for nucleotide biosynthesis in the cytosol. We previously discovered novel first-in-class multitargeted pyrrolo[3,2-]pyrimidine inhibitors of SHMT2 and de novo purine biosynthesis at glycinamide ribonucleotide formyltransferase and 5-aminoimidazole-4-carboxamide ribonucleotide formyltransferase with potent in vitro and in vivo antitumor efficacy toward pancreatic adenocarcinoma cells. In this report, we extend our findings to an expanded panel of pancreatic cancer models. We used our lead analog [(4-(4-(2-amino-4-oxo-3,4-dihydro-5-pyrrolo[3,2-]pyrimidin-5-yl)butyl)-2-fluorobenzoyl)-l-glutamic acid] to characterize pharmacodynamic determinants of antitumor efficacy for this series and demonstrated plasma membrane transport into the cytosol, uptake from cytosol into mitochondria, and metabolism to polyglutamates in both cytosol and mitochondria. Antitumor effects of downstream of SHMT2 and purine biosynthesis included suppression of mammalian target of rapamycin signaling, and glutathione depletion with increased levels of reactive oxygen species. Our results provide important insights into the cellular pharmacology of novel pyrrolo[3,2-]pyrimidine inhibitors as antitumor compounds and establish as a unique agent for potential clinical application for pancreatic cancer, as well as other malignancies. SIGNIFICANCE STATEMENT: This study establishes the antitumor efficacies of novel inhibitors of serine hydroxymethyltransferase 2 and of cytosolic targets toward a panel of clinically relevant pancreatic cancer cells and demonstrates the important roles of plasma membrane transport, mitochondrial accumulation, and metabolism to polyglutamates of the lead compound to drug activity. We also establish that loss of serine catabolism and purine biosynthesis resulting from treatment impacts mammalian target of rapamycin signaling, glutathione pools, and reactive oxygen species, contributing to antitumor efficacy.