Functional Loss of the Reduced Folate Carrier Enhances the Antitumor Activities of Novel Antifolates with Selective Uptake by the Proton-Coupled Folate Transporter
Functional Loss of the Reduced Folate Carrier Enhances the Antitumor Activities of Novel Antifolates with Selective Uptake by the Proton-Coupled Folate Transporter
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DOI：
10.1124/mol.112.079004
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发表时间：
2012-10-01
影响因子：
3.6
通讯作者：
Matherly, Larry H.
中科院分区：
文献类型：
--
作者：
Desmoulin, Sita Kugel;Wang, Lei;Matherly, Larry H.
质子偶联叶酸转运体（PCFT）将具有四个或三个桥碳的6-取代吡咯[2,3-d]嘧啶硫代抗叶酸盐[化合物1 （C1）和化合物2 (C2)]摄取到实体肿瘤中，代表了一种利用酸性肿瘤微环境的新型治疗策略。虽然这些化合物不是叶酸载体（RFC）的底物，但RFC的表达可能通过影响细胞四氢叶酸（THF）辅助因子池来改变药物疗效，这些辅助因子池可以竞争多谷氨酰化和/或结合细胞内酶靶点。包括野生型（WT）和R5 (RFC-null) HeLa细胞在内的人类肿瘤细胞表达高水平的PCFT蛋白。C1和C2对R5细胞增殖的抑制作用是WT细胞或RFC转染的R5细胞的3 ~ 4倍。在WT和R5细胞中，C1和C2的转运几乎相同，这表明亚系之间药物敏感性的差异与PCFT转运无关。与WT细胞相比，R5细胞中由[H-3]5-甲酰基THF衍生的稳态细胞内[H-3]THF辅助因子在R5细胞中减少，C1和C2加重了这种影响。尽管C1和C2多谷氨酸在WT和R5细胞中积累到相似的水平，但多谷氨酸在最长链长度形式的分布上存在差异。在严重联合免疫缺陷小鼠中，C1和C2对皮下R5肿瘤的抗肿瘤作用大于对WT肿瘤的抗肿瘤作用，证实了体外观察到的侧边药物敏感性。因此，具有pcft选择性细胞摄取的实体肿瘤靶向抗叶酸药应该对缺乏RFC功能的肿瘤具有增强的活性，反映了THF辅助因子池的收缩。
Uptake of 6-substituted pyrrolo[2,3-d] pyrimidine thienoyl antifolates with four or three bridge carbons [compound 1 (C1) and compound 2 (C2), respectively] into solid tumors by the proton-coupled folate transporter (PCFT) represents a novel therapeutic strategy that harnesses the acidic tumor microenvironment. Although these compounds are not substrates for the reduced folate carrier (RFC), the major facilitative folate transporter, RFC expression may alter drug efficacies by affecting cellular tetrahydrofolate (THF) cofactor pools that can compete for polyglutamylation and/or binding to intracellular enzyme targets. Human tumor cells including wild-type (WT) and R5 (RFC-null) HeLa cells express high levels of PCFT protein. C1 and C2 inhibited proliferation of R5 cells 3 to 4 times more potently than WT cells or R5 cells transfected with RFC. Transport of C1 and C2 was virtually identical between WT and R5 cells, establishing that differences in drug sensitivities between sublines were independent of PCFT transport. Steady-state intracellular [H-3]THF cofactors derived from [H-3]5-formyl-THF were depleted in R5 cells compared with those in WT cells, an effect exacerbated by C1 and C2. Whereas C1 and C2 polyglutamates accumulated to similar levels in WT and R5 cells, there were differences in polyglutamyl distributions in favor of the longest chain length forms. In severe combined immunodeficient mice, the antitumor efficacies of C1 and C2 were greater toward subcutaneous R5 tumors than toward WT tumors, confirming the collateral drug sensitivities observed in vitro. Thus, solid tumor-targeted antifolates with PCFT-selective cellular uptake should have enhanced activities toward tumors lacking RFC function, reflecting contraction of THF cofactor pools.