TY - JOUR T1 - Therapeutic Targeting of a Novel 6-Substituted Pyrrolo [2,3-<em>d</em>]pyrimidine Thienoyl Antifolate to Human Solid Tumors Based on Selective Uptake by the Proton-Coupled Folate Transporter JF - Molecular Pharmacology JO - Mol Pharmacol SP - 1096 LP - 1107 DO - 10.1124/mol.111.073833 VL - 80 IS - 6 AU - Sita Kugel Desmoulin AU - Lei Wang AU - Eric Hales AU - Lisa Polin AU - Kathryn White AU - Juiwanna Kushner AU - Mark Stout AU - Zhanjun Hou AU - Christina Cherian AU - Aleem Gangjee AU - Larry H. Matherly Y1 - 2011/12/01 UR - http://molpharm.aspetjournals.org/content/80/6/1096.abstract N2 - 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. ER -