抗叶酸剂类抗肿瘤药物的研究进展*

抗叶酸剂通过抑制叶酸依赖性酶的生物活性，阻断核酸和某些氨基酸的生物合成，导致肿瘤细胞的死亡，在临床上用作抗肿瘤药物。现综述近年来以叶酸依赖性酶，如胸苷酸合酶和二氢叶酸还原酶为靶酶的抑制剂的分子设计及生物活性，同时还简要介绍了胸苷酸合酶和二氢叶酸还原酶双抑制剂的研究进展。     

脱氧胸苷酸合成酶抑制剂的设计和生化药理学前景

2′-脱氧胸苷酸(dTMP)合成酶(EC2.1.1.45)能将2′-脱氧尿苷酸(dUMP)还原甲基化,生成2′-脱氧胸苷酸,同时使5,10-甲撑-5,6,7,8-四氢叶酸(CH_2-H_4叶酸)转化成7,8-二氢叶酸(H_2叶酸);二氢叶酸还原酶则催化H_2叶酸转化成H_4叶酸,为继续合成dTMP所必需。因为dTMP合成酶是代表着dUMP+CH_2-H_4叶酸—→H_2叶酸+dTMP     

紫杉醇/卡铂联合贝伐珠单抗治疗培美曲塞失败/耐药后的肺腺癌10例效果观察

<正>培美曲塞能够抑制胸苷酸合成酶、二氢叶酸还原酶和甘氨酰胺核苷酸甲酰转移酶的活性,这些酶都是合成叶酸所必需的酶,参与胸腺嘧啶核苷酸和嘌吟核苷酸的生物再合成过程,培美曲塞通过运载叶酸的载体和细胞膜上的叶酸结合蛋     

雷替曲塞

结肠直肠癌(CRC)是世界上仅次于肺癌的第二位最常见的肿瘤,是导致患者死亡的主要原因之一。雷替曲塞为喹唑啉叶酸盐类似物,为新型水溶性胸苷酸合成酶(TS)抑制剂。胸苷酸合成酶是DNA合     

雷替曲塞

结肠直肠癌(CRC)是世界上仅次于肺癌的第二位最常见的肿瘤,是导致患者死亡的主要原因之一。雷替曲塞为喹唑啉叶酸盐类似物,为新型水溶性胸苷酸合成酶(TS)抑制剂。胸苷酸合成酶是DNA合成过程牛的关键酶之一,可将脱氧尿苷——磷酸     

叶酸依赖性酶抑制剂的抗肿瘤活性

 叶酸依赖性酶以四氢叶酸衍生物为辅酶,在细胞DNA的生物合成中发挥重要作用。叶酸依赖性酶抑制剂通过抑制叶酸依赖性酶与正常底物的结合,干扰一碳代谢与叶酸代谢,阻碍DNA的生物合成,从而导致肿瘤细胞死亡。作为抗肿瘤药物作用靶点的叶酸依赖性酶,主要包括二氢叶酸还原酶、胸苷酸合成酶、甘氨酰胺核糖核苷酸甲酰基转移酶和咪唑甲酰胺核苷酸甲酰转移酶等。本文根据酶的分类,综述近年来叶酸依赖性酶抑制剂的抗肿瘤药物的研究进展。     

抗生素Iclaprim

二氢叶酸还原酶（DHFR）是细菌存活所必需的酶，它参与四氢叶酸最初的合成以及由脱氧尿苷酸合成胸苷酸过程中再氧化后的再循环，因此已被鉴定为抗菌药物开发的靶点。在不同物种间，该酶的氨基酸序列存在显著差异，其在细菌和哺乳动物间的同源性小于30％，且细菌和哺乳动物间DHFR的活性部位有极大区别。因此，DHFR成为具潜在抗菌活性的强效和选择性抑制剂开发的一个极佳靶点。     

培美曲塞在肿瘤化疗治疗中的应用进展分析

培美曲塞是一种作用于叶酸代谢过程中多种靶点的抗肿瘤药物。其主要作用机制是抑制叶酸代谢过程中的胸苷酸合酶、二氢叶酸还原酶和甘氨酰胺核苷酸转甲酰酶,导致细胞不能复制,从而抑制肿瘤的生长。其能从多个途径达到抑制小细胞肺癌、胰腺癌和胃癌肿瘤细胞生长的目的,其副作用较轻,易于与其他化疗药物联合应用,以提高疗效。     

胸苷酸合成酶抑制剂的研究进展

胸苷酸合成酶(thymidylate synthase,TS)是DNA合成的关键酶,当胸苷酸合成酶受到抑制时会导致细胞因缺乏dTMP而使DNA合成受阻,进而导致细胞死亡.因此,多年来胸苷酸合成酶作为抗肿瘤药物研究的理想靶点,一直受到药物研发人员的广泛关注.近年来,已有多种胸苷酸合成酶抑制剂作为有效的抗肿瘤化合物被报道....     

叶酸拮抗剂的趋向——提高治疗指数与开发新类似物

叶酸拮抗剂是一类重要的药物,其功能是抗感染、抗肿瘤与抗炎症(表1)。它们作为抗感染的选择性机制已阐明,但作为抗癌与抗炎的选择机制则还不甚了了。迄今为止,已知它们都属二氢叶酸还原酶(DHFR)抑制剂,该酶是合成胸腺苷的关键性酶,因此对DNA的生物合成,至关重要。     

Comparison of the biological effects of selected 5,8-dideazafolate analogues with their 2-desamino counterparts

Three new 5,8-dideaza analogues of folic acid devoid of an amino group at position 2 have been prepared by using synthetic routes patterned after earlier methodologies. They were 2-desamino-5,8-dideazaisofolic acid, 2b, 2-desamino-10-thia-5,8-dideazafolic acid, 2c, and 2-desamino-10-oxa-5,8-dideazafolic acid, 2d. These compounds were found to be 4-6-fold more cytoxic toward L1210 leukemia cells than their 2-NH2 counterparts and to be poor inhibitors of mammalian thymidylate synthase. However, they were only 1.5-3-fold less inhibitory toward dihydrofolate reductase than the analogous compounds containing a 2-NH2 group. The known thymidylate synthase inhibitors 2-desamino-10-propargyl-5,8-dideazafolic acid and 10-propargyl-5,8-dideazafolic acid were included in this study for purposes of comparison.     

Folate analogues. 26. Syntheses and antifolate activity of 10-substituted derivatives of 5,8-dideazafolic acid and of the poly-gamma-glutamyl metabolites of N10-propargyl-5,8-dideazafolic acid (PDDF)

The poly-gamma-glutamyl derivatives of n10-propargyl-5,8-dideazafolic acid (PDDF) with a chain length of up to five glutamate residues were synthesized from N10-propargyl-5,8-dideazapteroic acid by the solid-phase procedure. These compounds were evaluated for their antifolate activity using folate-requiring microorganisms and intact and permeabilized L1210 cells and as inhibitors of dihydrofolate reductase and thymidylate synthase derived from L. casei. The polyglutamylated derivatives of PDDF (1) were more active than the parent compound in inhibiting the growth of L. casei, thymidylate synthesis in permeabilized L1210 cells, and L. casei thymidylate synthase. Two analogues of 5,8-dideazafolic acid (2 and 3), one with a 2-butyne and another with a cyclopropylmethyl substituent at N10, were also synthesized and evaluated for their antifolate activities using the above-mentioned test systems. They were considerably less active than PDDF or its polyglutamylated derivatives. N10-Propargyl-5,8-dideazapteroyl tri-, tetra-, and pentaglutamates were equipotent with 5-fluorodeoxyuridylate as inhibitors of thymidylate synthesis in permeabilized L1210 cells. The polyglutamyl metabolites of PDDF were shown to be the most potent antifolate inhibitors of L. casei and L1210 thymidylate synthases yet described.     

Role of antimetabolites of purine and pyrimidine nucleotide metabolism in tumor cell differentiation.

Transformed cells are characterized by imbalances in metabolic routes. In particular, different key enzymes of nucleotide metabolism and DNA biosynthesis, such as CTP synthetase, thymidylate synthase, dihydrofolate reductase, IMP dehydrogenase, ribonucleotide reductase, DNA polymerase, and DNA methyltransferase, are markedly up-regulated in certain tumor cells. Together with the concomitant down-modulation of the purine and pyrimidine degradation enzymes, the increased anabolic propensity supports the excessive proliferation of transformed cells. However, many types of cancer cells have maintained the ability to differentiate terminally into mature, non-proliferating cells not only in response to physiological receptor ligands, such as retinoic acid, vitamin D metabolites, and cytokines, but also following exposure to a wide variety of non-physiological agents such as antimetabolites. Interestingly, induction of tumor cell differentiation is often associated with reversal of the transformation-related enzyme deregulations. An important class of differentiating compounds comprises the antimetabolites of purine and pyrimidine nucleotide metabolism and nucleic acid synthesis, the majority being structural analogs of natural nucleosides. The CTP synthetase inhibitors cyclopentenylcytosine and 3-deazauridine, the thymidylate synthase inhibitor 5-fluoro-2'-deoxyuridine, the dihydrofolate reductase inhibitor methotrexate, the IMP dehydrogenase inhibitors tiazofurin, ribavirin, 5-ethynyl-1-beta-D-ribofuranosylimidazole-4-carboxamide (EICAR) and mycophenolic acid, the ribonucleotide reductase inhibitors hydroxyurea and deferoxamine, and the DNA polymerase inhibitors ara-C, 9-(2-phosphonylmethoxyethyl)adenine (PMEA), and aphidicolin, as well as several nucleoside analogs perturbing the DNA methylation pattern, have been found to induce tumor cell differentiation through impairment of DNA synthesis and/or function. Thus, by selectively targeting those anabolic enzymes that contribute to the neoplastic behavior of cancer cells, the normal cellular differentiation program may be reactivated and the malignant phenotype suppressed.     

Interconversion of tetrahydrofolate cofactors to dihydrofolate induced by trimetrexate after suppression of thymidylate synthase by fluorodeoxyuridine in L1210 leukemia cells.

Previous studies from this laboratory demonstrated that marked suppression of thymidylate synthase activity is required to slow the rate of interconversion of tetrahydrofolate cofactors to dihydrofolate when dihydrofolate reductase is blocked by an antifolate. This finding is due to the high catalytic activity of thymidylate synthase within cells in comparison to the tetrahydrofolate cofactor pool size. In the present study, we assessed the rate of resumption of thymidylate synthase catalytic activity in terms of [3H]deoxyuridine incorporation into DNA and dihydrofolate generation from tetrahydrofolate cofactors following exposure of cells to fluorodeoxyuridine. Log phase L1210 leukemia cells, incubated with fluorodeoxyuridine to abolish thymidylate synthase catalytic activity, were suspended into drug-free medium. Resumption of [3H]deoxyuridine incorporation into DNA was negligible; by 4 hr enzyme activity was still inhibited by approximately 98%. However, this was sufficient to interconvert all available tetrahydrofolate cofactors to dihydrofolate (T1/2 approximately 2 hr) when dihydrofolate reductase was inhibited by the lipophilic antifolate trimetrexate. Interconversion of tetrahydrofolate cofactors to dihydrofolate correlated with a decline, then cessation, of purine synthesis as measured by the incorporation of [14C]formate into purine bases. These data suggest that an earlier than previously expected depletion of tetrahydrofolate cofactors with consequent inhibition of purine and other folate-dependent synthetic processes is likely to occur when antifolates are administered after a fluoropyrimidine.     

Depletion of 5,10-methylenetetrahydrofolate and 10-formyltetrahydrofolate by methotrexate in cultured hepatoma cells.

The effect of the inhibition of dihydrofolate reductase by methotrexate on the cellular folates involved in de novo purine and thymidylate biosynthesis has been measured in H35 hepatoma cells grown in 4 microM folic acid or 20 nM folinic acid. The major cellular folate species in cells from medium with folate or folinate is 10-formyltetrahydrofolate (approximately 5 microM), with lesser amounts of 5,10-methylenetetrahydrofolate and tetrahydrofolate. Cultures were exposed to a pulse dose of methotrexate, resulting in the accumulation of nearly exclusively methotrexate polyglutamates (predominantly Glu3, Glu4, and Glu5), or a continuous exposure to the poorly glutamylated analog threo-4-fluoromethotrexate, resulting in 93% intracellular monoglutamate. At 4 hr and 18 hr after exposure to either compound there was extensive depletion of the reduced folate coenzymes, which generally corresponded to the extent of inhibition of glycine and deoxyuridine incorporation. This was accompanied by an increase of the cellular dihydrofolate and 10-formyldihydrofolate. In the H35 cells the effect of methotrexate polyglutamates on the reduced folate coenzyme pools was restricted to dividing cultures, because the reduced folate coenzymes were not depleted in confluent cultures. The results demonstrate that the methotrexate and methotrexate polyglutamates that initially accumulate within dividing H35 cells readily inhibit dihydrofolate reductase but are not adequate to inhibit thymidylate synthase and prevent the depletion of reduced folate coenzymes. Thus, inhibition of de novo glycine and deoxyuridine incorporation into DNA as a result of dihydrofolate reductase inhibitors appears to be closely related to a reduction in the intracellular concentration of 10-formyltetrahydrofolate and 5,10-methylenetetrahydrofolate, the respective folate coenzymes for de novo purine and thymidylate synthesis.     

Folate analogues. 25. Synthesis and biological evaluation of N10-propargylfolic acid and its reduced derivatives

N10-Propargylfolic acid (2), which is the closest pteridine analogue of the thymidylate synthase inhibitor N10-propargyl-5,8-dideazafolic acid (PDDF), was synthesized starting from diethyl [p-(N-propargylamino)benzoyl]-L-glutamate (5) and N-(3-bromo-2-oxopropyl)phthalimide (8). The 7,8-dihydro derivative of propargylfolic acid served as a synthetic substrate of Lactobacillus casei dihydrofolate reductase. Propargylfolic acid and its reduced derivatives were weak inhibitors of L. casei thymidylate synthase compared to PDDF. All derivatives of propargylfolate were active against the growth of Streptococcus faecium, but with the exception of 7,8-dihydropropargylfolic acid, all were inactive against L. casei. Although less potent than PDDF, marked inhibition of thymidylate synthase by 2 was observed in permeabilized L1210 cells.     

Folate analogues. 21. Synthesis and antifolate and antitumor activities of N10-(cyanomethyl)-5,8-dideazafolic acid

A close analogue of the antileukemic agent 5,8-dideaza-N10 propargylfolic acid (2) was synthesized by replacing the propargyl moiety of 2 with a cyanomethyl group. This compound, N10-(cyanomethyl)-5,8-dideazafolic acid (3), was evaluated for its antifolate and antitumor activities in several biological test systems. Alkylation of diethyl N-(4-aminobenzoyl)-L-glutamate with bromoacetonitrile gave diethyl N-[4-[(cyanomethyl)amino]benzoyl]-L-glutamate (7). Reaction of 7 with 2 amino-6-(bromomethyl)-4-hydroxyquinazoline (9) in dimethylacetamide gave the corresponding diethyl ester 11, which was hydrolyzed to the target compound 3. The known antileukemic agent 2 was also synthesized for comparative studies by employing a modified procedure, which resulted in a better yield of this product. Both compounds 2 and 3 were evaluated for their antifolate activities by using two folate-requiring microorganisms, Streptococcus faecium and Lactobacillus casei. They were further evaluated as inhibitors of thymidylate synthase and dihydrofolate reductase derived from the above organisms, as well as for their antitumor activity by using selected tumor cells in culture. Compound 2 was found to be as equally potent as methotrexate (MTX) against S. faecium, and it was an excellent inhibitor of L. casei thymidylate synthase. The cyanomethyl analogue 3 was less active than 2 in all the test systems, except the inhibition of dihydrofolate reductase.     

Potent activity of 5-fluoro-2'-deoxyuridine and related compounds against thymidine kinase-deficient (TK-) herpes simplex virus: targeted at thymidylate synthase

5-Fluorouracil, 5-fluorouridine (FUrd), 5-fluoro-2'-deoxyuridine (FdUrd), 5-fluorocytidine (FCyd), 5-fluoro-2'-deoxycytidine (FdCyd), 5-trifluoro-2'-deoxythymidine (F3dThd), and the 5'-monophosphates and 3',5'-cyclic monophosphates thereof were found to inhibit thymidine kinase-deficient (TK-) mutant strains of herpes simplex virus (HSV) at a much lower concentration than the wild-type (TK+) HSV strains. Other 5-substituted 2'-deoxyuridines that have previously been recognized as potent thymidylate synthase inhibitors behaved in a similar fashion. The activity of FdUrd, FdCyd, F3dThd, and their 3',5'-cyclic monophosphates against TK-HSV was readily reversed by 2'-deoxythymidine (dThd) but not by 2'-deoxyuridine (dUrd). These compounds also inhibited the incorporation of [6-3H]dUrd into DNA at a concentration which was up to 5 orders of magnitude lower than the concentration at which the incorporation of [methyl-3H] dThd was inhibited. Thus, while not being a target for the well established anti-HSV compounds in TK+HSV-infected cells, thymidylate synthase appears to be an important target in TK-HSV-infected cells. In addition to dTMP synthase, TK-HSV-infected cells appear to reveal other therapeutically exploitable targets such as OMP decarboxylase (towards pyrazofurin), CTP synthase (towards carbodine and its cyclopentenyl analogue), dihydrofolate reductase (towards methotrexate), and S-adenosylhomocysteine hydrolase (towards neplanocins).