RT Journal Article SR Electronic T1 Therapeutic Targeting of a Novel 6-Substituted Pyrrolo [2,3-d]pyrimidine Thienoyl Antifolate to Human Solid Tumors Based on Selective Uptake by the Proton-Coupled Folate Transporter JF Molecular Pharmacology JO Mol Pharmacol FD American Society for Pharmacology and Experimental Therapeutics SP 1096 OP 1107 DO 10.1124/mol.111.073833 VO 80 IS 6 A1 Sita Kugel Desmoulin A1 Lei Wang A1 Eric Hales A1 Lisa Polin A1 Kathryn White A1 Juiwanna Kushner A1 Mark Stout A1 Zhanjun Hou A1 Christina Cherian A1 Aleem Gangjee A1 Larry H. Matherly YR 2011 UL http://molpharm.aspetjournals.org/content/80/6/1096.abstract AB The proton-coupled folate transporter (PCFT) is a proton-folate symporter with an acidic pH optimum. By real-time reverse transcription-polymerase chain reaction, PCFT was expressed in the majority of 53 human tumor cell lines, with the highest levels in Caco-2 (colorectal adenocarcinoma), SKOV3 (ovarian), and HepG2 (hepatoma) cells. A novel 6-substituted pyrrolo[2,3-d]pyrimidine thienoyl antifolate (compound 1) was used to establish whether PCFT can deliver cytotoxic drug under pH conditions that mimic the tumor microenvironment. Both 1 and pemetrexed (Pmx) inhibited proliferation of R1-11-PCFT4 HeLa cells engineered to express PCFT without the reduced folate carrier (RFC) and of HepG2 cells expressing both PCFT and RFC. Unlike Pmx, 1 did not inhibit proliferation of R1-11-RFC6 HeLa cells, which express RFC without PCFT. Treatment of R1-11-PCFT4 cells at pH 6.8 with 1 or Pmx inhibited colony formation with dose and time dependence. Transport of [3H]compound 1 into R1-11-PCFT4 and HepG2 cells was optimal at pH 5.5 but appreciable at pH 6.8. At pH 6.8, [3H]compound 1 was metabolized to 3H-labeled polyglutamates. Glycinamide ribonucleotide formyltransferase (GARFTase) in R1-11-PCFT4 cells was inhibited by 1 at pH 6.8, as measured by an in situ GARFTase assay, and was accompanied by substantially reduced ATP levels. Compound 1 caused S-phase accumulation and a modest level of apoptosis. An in vivo efficacy trial with severe combined immunodeficient mice implanted with subcutaneous HepG2 tumors showed that compound 1 was active. Our findings suggest exciting new therapeutic possibilities to selectively deliver novel antifolate drugs via transport by PCFT over RFC by exploiting the acidic tumor microenvironment.