Tumor Targeting with Novel 6-Substituted Pyrrolo 23-d Pyrimidine Antifolates with Heteroatom Bridge Substitutions Via Cellular Uptake by Folate Receptor α and the Proton-coupled Folate Transporter and Inhibition of De Novo Purine Nucleotide Biosynthesis

摘要

Targeted antifolates with heteroatom replacements of the carbon vicinal to the phenyl ring in >1 by N (>4), O (>8), or S (>9), or with N-substituted formyl (>5), acetyl (>6), or trifluoroacetyl (>7) moieties, were synthesized and tested for selective cellular uptake by folate receptor (FR) α and β or the proton-coupled folate transporter. Results show increased in vitro anti-proliferative activity toward engineered Chinese hamster ovary cells expressing FRs by >4–>9 over the CH2 analog >1. Compounds >4–>9 inhibited de novo purine biosynthesis and glycinamide ribonucleotide formyltransferase (GARFTase). X-ray crystal structures for >4 with FRα and GARFTase showed that the bound conformations of >4 required flexibility for attachment to both FRα and GARFTase. In mice bearing IGROV1 ovarian tumor xenografts, >4 was highly efficacious. Our results establish that heteroatom substitutions in the 3-atom bridge region of 6-substituted pyrrolo[2,3-d]pyrimidines related to >1 provide targeted antifolates that warrant further evaluation as anticancer agents.