Abstract 4541: The design, synthesis and evaluation of selective FR α and β substrates with potent GARFTase inhibitory activity as antitumor agents

Abstract

Abstract Glycinamide ribonucleotide formyl transferase (GARFTase) catalyzes the first of two formyl transfer steps in the de novo purine biosynthetic pathway. Potent inhibitors of GARFTase and de novo purine biosynthesis have shown promise as antitumor drugs. However, a lack of selectivity and toxicity has been a major hurdle for GARFTase inhibitors as cancer chemotherapeutic agents. We recently reported a series of thieno[2,3-d]pyrimidine classical antifolates that are specifically taken up by the folate receptor (FR) and inhibit FR expressing tumor cells at nanomolar IC50 values (IC50= 4.9 nM in human KB tumor cells, IC50= 5.9 nM in human IGROV1 tumor cells,). GARFTase was confirmed as the target. Notably, the thieno[2,3-d]pyrimidine antifolates are unique and distinct from all other classical antifolates evaluated, including pemetrexed (PMX), raltitrexed (RTX), and methotrexate (MTX) in that they are neither substrates for reduced folate carrier (RFC) nor for the proton-coupled folate transporter (PCFT). This characteristic results in selective targeting of FR-expressing cells, without toxicity to normal cells that express RFC. To further investigate the structural requirements of antifolates with respect to FR substrate activity, a series of four 2-amino-4-oxo-6-substituted thieno[2,3-d]pyrimidines with different aryl side chains were synthesized. This afforded potent antitumor agents with increased inhibitory activity against FRα expressing tumor cells (IC50= 2 nM in human KB tumor cells) 2.5- fold more potent than the lead benzoyl compound. In addition, these thieno[2,3-d]pyrimidines were specific for FRα and were not transported by RFC or PCFT and indicated that the nature of the bicyclic scaffold is an important structural determinant for transport specificity. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4541.