Faessel H M, Slocum H K, Jackson R C, Boritzki T J, Rustum Y M, Nair M G, Greco W R
Grace Cancer Drug Center and Department of Biomathematics, Roswell Park Cancer Institute, New York State Department of Health, Buffalo 14263, USA.
Cancer Res. 1998 Jul 15;58(14):3036-50.
The combined action among polyglutamylatable and nonpolyglutamylatable antifolates, directed against dihydrofolate reductase (DHFR), glycinamide ribonucleotide formyltransferase (GARFT), 5-aminoimidazole-4-carboxamide ribonucleotide formyltransferase (AICARFT), and thymidylate synthase (TS), in human ileocecal HCT-8 cells was examined in a 96-well plate growth inhibition assay (96-h continuous drug exposure). An interaction parameter, alpha, was estimated for each of 95 experiments by fitting a seven-parameter model to data with weighted nonlinear regression. In a representative experiment, raising the folic acid concentration in the medium dramatically increased the Loewe synergy for the combination of trimetrexate (TMTX) and the GARFT inhibitor AG2034 (from a mean alpha +/- SE of 1.50 +/- 0.25 at 2.3 microM folic acid to 146 +/- 20 at 78 microM folic acid). Enhancements were also found for combinations of TMTX with the GARFT inhibitors AG2032, Lometrexol, and LY309887, the AICARFT inhibitor AG2009, and the TS inhibitors LY231514 and Tomudex but not with the GARFT inhibitor LL95509 or with the TS inhibitors AG337, ZD9331, and BW1843U89. Replacing TMTX with methotrexate in two-drug mixtures decreased the intensity of Loewe synergy. Examination of isobolograms at different effect levels revealed informative reproducible changes in isobol patterns. No two-drug combinations among inhibitors of GARFT, AICARFT, and TS exhibited Loewe synergy at either 2.3 or 78 microM folic acid. Thus, the ideal requirement for the folic acid-enhanced synergy is that a nonpolyglutamylatable DHFR inhibitor be combined with a polyglutamylatable inhibitor of another folate-requiring enzyme. A hypothesis to explain this general phenomenon involves the critical role of folylpoly-gamma-glutamate synthetase and the effect of the DHFR inhibitor in decreasing the protection by folic acid of cells to the other antifolates.
在96孔板生长抑制试验（96小时持续药物暴露）中，研究了聚谷氨酰化和非聚谷氨酰化抗叶酸药物联合作用于人类回盲部HCT - 8细胞中针对二氢叶酸还原酶（DHFR）、甘氨酰胺核糖核苷酸甲酰基转移酶（GARFT）、5 - 氨基咪唑 - 4 - 甲酰胺核糖核苷酸甲酰基转移酶（AICARFT）和胸苷酸合成酶（TS）的情况。通过加权非线性回归将七参数模型拟合到数据中，对95个实验中的每一个实验估计了一个相互作用参数α。在一个代表性实验中，提高培养基中的叶酸浓度显著增加了三甲曲沙（TMTX）与GARFT抑制剂AG2034组合的洛氏协同作用（从2.3微摩尔叶酸时平均α±标准误为1.50±0.25增加到78微摩尔叶酸时的146±20）。还发现TMTX与GARFT抑制剂AG2032、洛美曲唑和LY309887、AICARFT抑制剂AG2009以及TS抑制剂LY231514和托姆德克斯的组合有增强作用，但与GARFT抑制剂LL95509或TS抑制剂AG337、ZD9331和BW1843U89的组合没有增强作用。在两药混合物中用甲氨蝶呤替代TMTX降低了洛氏协同作用的强度。在不同效应水平下检查等效线图揭示了等效线模式中信息丰富且可重复的变化。在2.3或78微摩尔叶酸时，GARFT、AICARFT和TS抑制剂之间的任何两药组合均未表现出洛氏协同作用。因此，叶酸增强协同作用的理想要求是将非聚谷氨酰化的DHFR抑制剂与另一种叶酸依赖性酶的聚谷氨酰化抑制剂联合使用。一个解释这一普遍现象的假说是，叶酰聚 - γ - 谷氨酸合成酶起关键作用，以及DHFR抑制剂在降低叶酸对细胞免受其他抗叶酸药物保护方面的作用。
