Thymidylate synthase inhibitors

An insight into thymidylate synthase inhibitor as anticancer agents: an explicative review

Cancer, a widespread challenge to global health, remains a puzzle of intricate molecular dynamics. This review article delves into the mystery of cancer, with a keen focus on understanding the contributory role of thymidylate synthase (TS) in cancer. TS, a vital enzyme in DNA synthesis and repair, emerges as a significant player in the narrative of cancer development. The conversion of deoxyuridine monophosphate (dUMP) to deoxythymidine monophosphate (dTMP) is a major step in producing DNA. Numerous malignancies, including those of the breast, colon, lung, and ovary, have been linked to dysregulation of TS activity. Overexpression or mutations of TS lead to uncontrolled cell proliferation and tumorigenesis molecular interactions and signalling pathways involving TS come under scrutiny, revealing the nuanced connections that propel its involvement in cancer progression. Beyond overexpression and mutations, there emerges a subtle layer of regulation that involves microRNAs (miRNAs). These tiny particles attach to the TS messenger RNA, causing translational repression or its degradation, which in turn affects TS activity. Moving towards the therapeutic realm, thymidylate synthase inhibition acts as a promising anti-cancer strategy. Targeting TS with small-molecule inhibitors could provide a novel approach to treat various cancers. By reducing the number of available nucleotides, TS inhibition would slow down or halt cancer cell division, thus depriving the tumor of the building blocks required for its proliferation and growth. The aim is to assess the viability and effectiveness of targeting TS to halt or slow down cancer progression. There is growing evidence that, in comparison to traditional TS inhibitors, few novel antifolate TS inhibitors are effective against a wider variety of neoplasms, such as lung carcinomas. It has been discovered that TS inhibitors increase cancer tissues' sensitivity to chemotherapy and radiation, increasing their vulnerability to these treatments. This article aims to provide a comprehensive insight into TS, examining its cellular details, detailing the heterocyclic moieties and molecular foundations, and providing a promising future outlook.

Recent Advances in the Development of "Curcumin Inspired" Compounds as New Therapeutic Agents

Despite a huge body of research in the past two decades investigating the antioxidant, antiinflammatory, anti-microbial, and anti-carcinogenic properties of curcumin (CUR), a CUR-based antitumor drug is yet to be developed. Lack of success in achieving this goal stems from CUR's unfavorable biophysicochemical features, particularly poor solubility, low bioavailability, and rapid metabolism, coupled with a complex biological profile making it difficult to determine its mechanism of action. A significant body of literature aimed at improving its physicochemical properties through synthesis or by designing delivery methods has been published, and the progress in these areas has been reviewed. The present review aims to summarize recent progress in the synthesis of structurally diverse "curcumin-inspired" compounds along with computational docking and bioassay studies, through which a number of promising analogs have been identified that warrant further study.

Folate pathway modulation in Rhipicephalus ticks in response to infection

Folate pathways components were demonstrated to be present in RNA-sequencing data obtained from uninfected and pathogen-infected Rhipicephalus ticks. Here, PCR and qPCR allowed the identification of folate-related genes in Rhipicephalus spp. ticks and in the tick cell line IDE8. Genes coding for GTP cyclohydrolase I (gch-I), thymidylate synthase (ts) and 6-pyrovoyltetrahydropterin (ptps) were identified. Differential gene expression was evaluated by qPCR between uninfected and infected samples of four biological systems, showing significant upregulation and largest fold-change for the gch-I gene in the majority of the biological systems, supporting the selection for functional analysis by RNAi silencing. Efficient knockdown of the gch-I gene in uninfected and Ehrlichia canis-infected IDE8 cells showed no detectable impact on the capacity of the bacteria to invade or replicate in the tick cells. Overall, this work demonstrated an increase in the expression of some folate-related genes, though not always statistically significantly, in the presence of infection, suggesting gene expression modulation of these pathways, either as a tick response to an invader or manipulation of the tick cell machinery by the pathogens to their advantage. This discovery points to folate pathways as interesting targets for further studies.

Targeting plant DIHYDROFOLATE REDUCTASE with antifolates and mechanisms for genetic resistance

The folate biosynthetic pathway and its key enzyme dihydrofolate reductase (DHFR) is a popular target for drug development due to its essential role in the synthesis of DNA precursors and some amino acids. Despite its importance, little is known about plant DHFRs, which, like the enzymes from the malarial parasite Plasmodium, are bifunctional, possessing DHFR and thymidylate synthase (TS) domains. Here using genetic knockout lines we confirmed that either DHFR-TS1 or DHFR-TS2 (but not DHFR-TS3) was essential for seed development. Screening mutated Arabidopsis thaliana seeds for resistance to antimalarial DHFR-inhibitor drugs pyrimethamine and cycloguanil identified causal lesions in DHFR-TS1 and DHFR-TS2, respectively, near the predicted substrate-binding site. The different drug resistance profiles for the plants, enabled by the G137D mutation in DHFR-TS1 and the A71V mutation in DHFR-TS2, were consistent with biochemical studies using recombinant proteins and could be explained by structural models. These findings provide a great improvement in our understanding of plant DHFR-TS and suggest how plant-specific inhibitors might be developed, as DHFR is not currently targeted by commercial herbicides.

Structural analyses of human thymidylate synthase reveal a site that may control conformational switching between active and inactive states

Thymidylate synthase (TS) is the sole enzyme responsible for de novo biosynthesis of thymidylate (TMP) and is essential for cell proliferation and survival. Inhibition of human TS (hTS) has been extensively investigated for cancer chemotherapy, but several aspects of its activity and regulation are still uncertain. In this study, we performed comprehensive structural and biophysical studies of hTS using crystallography and thermal shift assay and provided the first detailed structural information on the conformational changes induced by ligand binding to the hTS active site. We found that upon binding of the antifolate agents raltitrexed and nolatrexed, the two insert regions in hTS, the functions of which are unclear, undergo positional shifts toward the catalytic center. We investigated the inactive conformation of hTS and found that the two insert regions are also involved in the conformational transition between the active and inactive state of hTS. Moreover, we identified a ligand-binding site in the dimer interface, suggesting that the cavity in the dimer interface could serve as an allosteric site of hTS to regulate the conformational switching between the active and inactive states. On the basis of these findings, we propose a regulatory mechanism of hTS activity that involves allosteric regulation of interactions of hTS with its own mRNA depending on cellular demands for TMP.

Novel developments in the use of antimetabolites

Antimetabolites are the most widely used and most efficacious group of anticancer drugs. Antimetabolites are also the oldest rationally designed anticancer drugs, targeted against RNA and DNA, and can, therefore, be considered as the first generation of targeted drugs. Unfortunately, resistance often develops, leading to the design of new antimetabolites, which either have a novel mechanism of action, bypass resistance or in combination enhance the effect of other drugs, such as another antimetabolite, other DNA, or protein kinase targeted anticancer drugs. Several novel antimetabolites are in clinical development. The cytidine-analog fluorocyclopentenylcytosine (RX-3117) is active in gemcitabine-resistant tumors and is activated by uridine-cytidine-kinase, can be incorporated into RNA and DNA and can downregulate DNA-methyltransferase-1. TAS-114 is a new generation dUTPase inhibitor. dUTPase normally prevents incorporation of dUTP and of the 5FU-nucleotide FdUTP into DNA. However, inhibition of dUTPase will enhance their incorporation, thereby increasing thymine-less cell-death. The formulation TAS-102 (trifluorothymidine and thymidine-phosphorylase-inhibitor) acts by incorporation into DNA and has shown efficacy in tumors progressing on 5FU therapy. Gemcitabine and cytarabine prodrugs were tested in model systems and have entered clinical evaluation. The elaidic-acid prodrugs of gemcitabine (CP-4126, CO101) and cytarabine (elacytarabine) failed in randomized Phase III studies. Two other gemcitabine prodrugs LY2334737 (gemcitabine with a valproic acid at the 5'-position) and NUC1031 (a 5'-arylphosphoamidate prodrug, with a side-chain at the 5'-phosphate) are in early clinical development. In summary, several novel antimetabolites show promise in clinical development, either because of a novel mechanism of action, or clever combination or by innovative prodrug design.

Differential activation of cell death and autophagy results in an increased cytotoxic potential for trifluorothymidine compared to 5-fluorouracil in colon cancer cells

Trifluorothymidine (TFT) is part of the oral drug formulation TAS-102. Both 5-fluorouracil (5-FU) and TFT can inhibit thymidylate synthase and be incorporated into DNA. TFT shows only moderate cross-resistance to 5-FU. Therefore, we examined whether mechanistic differences in cell death could underlie their different modes of action in colorectal cancer cell lines (WiDR, Lovo92 and Colo320). Drug cytotoxicity was determined by SRB- and clonogenic assays, cell death by flow cytometry (PI and annexin V), caspase cleavage by Western blotting and activity assays and in vivo activity in the hollow fiber assay. The IC(50) values of TFT were 1-6 fold lower than for 5-FU, and clonogenic survival was less than 0.9% at 3 muM TFT, while 2-20% of the cells still survived after 20 muM 5-FU. In general, TFT was a more potent inducer of apoptosis than 5-FU, although the contribution of caspases varied between the used cell lines and necrosis-like cell death was detected. Accordingly, both drugs induced caspase (Z-VAD) independent cell death and lysosomal cathepsin B was involved. Activation of autophagy recovery mechanisms was only triggered by 5-FU, but not by TFT as determined by LC3B expression and cleavage. Inhibition of autophagy by 3-MA in 5-FU exposed cells reduced cell survival. Also, in vivo TFT (as TAS-102) caused more cell death than a 5-FU formulation. We conclude that TFT and 5-FU induce cell death via both caspase-dependent and independent mechanisms. The TFT was more potent than 5-FU, because it induces higher levels of cell death and does not elicit an autophagic survival response in the cancer cell lines. This provides a strong molecular basis for further application of TFT in cancer therapy.

Thymidylate synthetase allelic imbalance in clear cell renal carcinoma

PURPOSE

To investigate the allelic status of the thymidylate synthetase (TYMS) gene, located at chromosome band 18p11.32, in renal cell carcinoma (RCC). TYMS is a key target of the 5-fluorouracil (5-FU)-based class of drugs, frequently considered in combination therapies in advanced RCC. TYMS variants, such as the TYMS polymorphic 5'-untranslated region variable number tandem repeat sequence (VNTR), are under investigation to guide 5-FU treatment. Yet, no information is available with regard to changes in TYMS allele frequencies in RCC malignances.

METHODS

Blood and matched tumor samples were collected from 41 histological proven clear cell RCC affected patients (30 males, 11 females.). TYMS VNTR genotype was first determined in blood to identify heterozygotes employing PCR techniques. To evaluate for allelic imbalance, fragment analysis was performed both in blood and matched tumor DNA of the heterozygote patients. Microsatellite analysis, employing the markers D18S59 and D18S476 mapping, respectively, at the TYMS locus (18p11.32) and 1.5 Mb downstream of the TYMS gene sequence (18p11.31), was performed to confirm TYMS allelic imbalance in tumors.

RESULTS

Germ-line TYMS VNTR distribution was: 2R/2R (19.5%), TYMS 2R/3R (36.6%) and TYMS 3R/3R (43.9%). Allelic imbalance for the TYMS tandem repeat region was detected in 26.6% of the heterozygote patients. Microsatellite analysis confirmed the allelic imbalance detected by TYMS VNTR analysis and revealed that the overall frequence of allelic imbalance of chromosome band 18p11.32 was 35%, while the overall allelic imbalance of chromosome band 18p11.31 was 28%.

CONCLUSIONS

By focusing on the TYMS polymorphic variants in renal cancer, we here provide evidence, to our knowledge, for the first time showing loss of 18p11.32 and 18p11.31 in renal cell carcinomas. As allelic imbalances involving TYMS locus may be an important variable affecting 5-FU responsiveness, this study may contribute to explain different responses of advanced RCC in combined chemotherapeutic regimens incorporating fluoropyridines.