LAUSR

One-carbon (C1) metabolism supports a number of physiological and pathophysiological processes ranging from stem cell renewal to cancer progression. Clinically used antifolates are transported into both tumor and normal cells by the ubiquitously expressed reduced folate carrier (RFC). Uptake of targeted agents via tumor-specific folate receptors (FRs) over RFC would permit tumor-selectivity, while limiting dose-limiting toxicities associated with standard chemotherapy. Serine catabolism in mitochondria is the major source of glycine and C1 units for cytosolic biosynthesis, preserves redox balance and minimizes reactive oxygen species, and is an important source of ATP. Among the mitochondrial C1 enzymes, serine hydroxymethyltransferase 2 (SHMT2) and 5,10-methylene tetrahydrofolate (me-THF) dehydrogenase 2 (MTHFD2) are highly expressed in tumors versus normal tissues. SHMT2 has been suggested to be an important oncodriver. However, there are no clinically relevant inhibitors of these enzymes. To generate potential inhibitors of these enzymes, we synthesized 5-substituted pyrrolo[3,2- d ]pyrimidine analogs as structural hybrids of cytotoxic 5-substituted pyrrolo[2,3- d ]pyrimidines and me-THF. The 5-substituted pyrrolo[3,2- d ] pyrimidine with a four carbon bridged phenyl side chain AGF300 afforded selective uptake via FRα over RFC, with inhibition of mitochondrial C1 metabolism and de novo purine biosynthesis, resulting in inhibition of KB human tumor cell proliferation. Inhibition of KB cells by AGF300 was reversed by glycine and adenosine. As previous studies of related 5-substituted pyrrolo[2,3- d ]pyrimidines established that the nature and length of the bridge plays an important role in determining tumor cell potency and transport selectivity, we replaced the carbon adjacent to the phenyl ring in AGF300 with heteroatoms, including O ( AGF323 ), S ( AGF346 ) or NH ( AGF350 ). These compounds were tested as growth inhibitors against engineered Chinese hamster ovary (CHO) cells singly expressing human FRα (RT16) or RFC (PC43-10). Incorporation of the O, S and NH in the pyrrolo[3,2- d ]pyrimidine analogs preserved excellent inhibition of FRα-containing CHO cells (IC 50 s of 57 nM, 77 nM and 50 nM, respectively); there was no inhibition of cells with RFC uptake up to 1000 nM. AGF323 , AGF346 and AGF350 inhibited proliferation of KB cells which was reversed by excess glycine and adenosine. This establishes that for AGF323 , AGF346 and AGF350 , both mitochondrial and cytosolic C1 metabolism were inhibited. The development of novel compounds targeting mitochondrial and cytosolic C1 pathways with tumor-selective uptake is highly significant in that this would overcome the drawbacks of currently used cytotoxic agents for cancer. Citation Format: Nian Tong, Khushbu Shah, Aleem Gangjee, Carrie O’Connor, Adrianne W. Porvirk, Aamod Dekhne, Zhanjun Hou, Larry H. Matherly. Multi-targeted novel 5-substituted pyrrolo[3,2- d ]pyrimidines with tumor-selective targeting and inhibition of cytosolic de novo purine biosynthesis and mitochondrial one-carbon metabolism [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 789.