Thymidylate Synthase Inhibitor Research Articles

Exposure-response analysis of Raltitrexed assessing liver toxicity.

Raltitrexed (RTX) is a thymidylate synthase inhibitor with large pharmacokinetics (PK) variability that can be administered in case of 5-fluorouracil (5FU) intolerance or dihydropyrimidine dehydrogenase deficiency. While it is a more potent thymidylate synthase inhibitor than 5FU, RTX failed to replace this drug for colorectal cancer patients, mainly due to its toxicity at the recommended dose of 3 mg/m2 every 3 weeks. However, every 2 weeks administration at 2 mg/m2 demonstrated a favourable toxicity profile. We performed a randomized crossover comparative population PK study between every 2 weeks TOMOX (RTX 2 mg/m2 ) and every 3 weeks TOMOX (RTX 3 mg/m2 ). A three-compartment model and a proportional error model best describe the data. Creatinine clearance and sex, but not body surface area (BSA), were covariates of RTX clearance leading to decrease of its interindividual variability of 28%. Weight and body surface area were covariates of central and peripheral volumes of distribution, respectively, leading to decreases of interindividual variability of 34.6% and 100%, respectively. In contrast to the dose, AUC was a good predictor of liver toxicity (P = 0.006, OR = 3.91, 95%CI = [1.48-10.34]). Using covariates to compute individual clearance and a threshold AUC (1.639, determined in this study), a covariates-based dose was calculated, leading to less variability in AUC than observed with the actual BSA-based or fixed doses. These results advocate for the use of creatinine clearance and sex to determine the RTX dose instead of BSA.

Multiaction Platinum(IV) Prodrug Containing Thymidylate Synthase Inhibitor and Metabolic Modifier against Triple-Negative Breast Cancer.

Multifunctional platinumIV anticancer prodrugs have the potential to enrich the anticancer properties and overcome the clinical problems of drug resistance and side effects of platinumII anticancer agents. Herein, we develop dual and triple action platinumIV complexes with targeted and biological active functionalities. One complex (PFL) that consists of cisplatin, tegafur, and lonidamine exhibits strong cytotoxicity against triple negative breast cancer (TNBC) cells. Cellular uptake and distribution studies reveal that PFL mainly accumulates in mitochondria. As a result, PFL disrupts the mitochondrial ultrastructure and induces significant alterations in the mitochondrial membrane potential, which further leads to an increase in production of reactive oxygen species (ROS) and a decrease in ATP synthesis in MDA-MB-231 TNBCs. Western blot analysis reveals the formation of ternary complex of thymidylate synthase, which shows the intracellular conversion of tegafur into 5-FU after its release from PFL. Furthermore, treatment with PFL impairs the mitochondrial function, leading to the inhibition of glycolysis and mitochondrial respiration and induction of apoptosis through the mitochondrial pathway. The RNA-sequencing experiment shows that PFL can perturb the pathways involved in DNA synthesis, DNA damage, metabolism, and transcriptional activity. These findings demonstrate that PFL intervenes in several cellular processes including DNA damage, thymidylate synthase inhibition, and perturbation of the mitochondrial bioenergetics to kill the cancer cells. The results highlight the significance of a triple-action prodrug for efficient anticancer therapy for TNBCs.

Chemistry of Fluorinated Pyrimidines in the Era of Personalized Medicine.

We review developments in fluorine chemistry contributing to the more precise use of fluorinated pyrimidines (FPs) to treat cancer. 5-Fluorouracil (5-FU) is the most widely used FP and is used to treat > 2 million cancer patients each year. We review methods for 5-FU synthesis, including the incorporation of radioactive and stable isotopes to study 5-FU metabolism and biodistribution. We also review methods for preparing RNA and DNA substituted with FPs for biophysical and mechanistic studies. New insights into how FPs perturb nucleic acid structure and dynamics has resulted from both computational and experimental studies, and we summarize recent results. Beyond the well-established role for inhibiting thymidylate synthase (TS) by the 5-FU metabolite 5-fluoro-2′-deoxyuridine-5′-O-monophosphate (FdUMP), recent studies have implicated new roles for RNA modifying enzymes that are inhibited by 5-FU substitution including tRNA methyltransferase 2 homolog A (TRMT2A) and pseudouridylate synthase in 5-FU cytotoxicity. Furthermore, enzymes not previously implicated in FP activity, including DNA topoisomerase 1 (Top1), were established as mediating FP anti-tumor activity. We review recent literature summarizing the mechanisms by which 5-FU inhibits RNA- and DNA-modifying enzymes and describe the use of polymeric FPs that may enable the more precise use of FPs for cancer treatment in the era of personalized medicine.

Development of a novel thymidylate synthase (TS) inhibitor capable of up-regulating P53 expression and inhibiting angiogenesis in NSCLC

IntroductionThe development of a new type of Thymidylate synthase (TS) inhibitor that could inhibit cancer cells' proliferation and anti-angiogenesis is of great significance for cancer's clinical treatment. ObjectivesOur research hopes to develop a TS inhibitor that is more effective than the current first-line clinical treatment of pemetrexed (PTX) and provide a new reference for the clinical treatment of non-small cell lung cancer (NSCLC). MethodsWe obtained a series of novel TS inhibitors by chemical synthesis. Moreover, TS assay and molecular docking to verify the target compound's inhibitory mode. Use MTT assay, colony-forming assay, flow cytometry, and western blot to verify the compound's inhibitory effect on cancer cell proliferation and its mechanism; and explore the compound’s effect on angiogenesis in vitro and in vivo. Further, explore the hit compound's anti-cancer ability through the xenograft tumor model and the orthotopic cancer murine model. ResultsA series of N-(3-(5-phenyl-1,3,4-oxadiazole-2-yl) phenyl)-2,4-dihydroxypyrimidine-5-sulfamide derivatives were synthesized as TS inhibitors for the first time. All target compounds significantly inhibited hTS enzyme activity and demonstrated significant antitumor activity against five cancer cell lines. Notably, 7f had a high selectivity index (SI) and unique inhibitory effects on eight NSCLC cells. In-depth research indicated that 7f could induce apoptosis by the mitochondrial pathway in A549 and PC-9 cells through the upregulation of wild-type P53 protein expression. Additionally, 7f was shown to inhibit angiogenesis in vitro and in vivo. In vivo studies, compared to PTX, 7f significantly inhibited tumor growth in A549 cell xenografts and had a higher therapeutic index (TGI). Moreover, 7f could prolong the survival of the orthotopic lung cancer murine model more effectively than PTX. ConclusionThe anti-angiogenic effect of 7f provides a new reference for the development of TS inhibitors and the clinical treatment of NSCLC.

Detection of a G-Quadruplex as a Regulatory Element in Thymidylate synthase for Gene Silencing Using Polypurine Reverse Hoogsteen Hairpins.

Thymidylate synthase (TYMS) enzyme is an anti-cancer target given its role in DNA biosynthesis. TYMS inhibitors (e.g., 5-Fluorouracil) can lead to drug resistance through an autoregulatory mechanism of TYMS that causes its overexpression. Since G-quadruplexes (G4) can modulate gene expression, we searched for putative G4 forming sequences (G4FS) in the TYMS gene that could be targeted using polypurine reverse Hoogsteen hairpins (PPRH). G4 structures in the TYMS gene were detected using the quadruplex forming G-rich sequences mapper and confirmed through spectroscopic approaches such as circular dichroism and NMR using synthetic oligonucleotides. Interactions between G4FS and TYMS protein or G4FS and a PPRH targeting this sequence (HpTYMS-G4-T) were studied by EMSA and thioflavin T staining. We identified a G4FS in the 5’UTR of the TYMS gene in both DNA and RNA capable of interacting with TYMS protein. The PPRH binds to its corresponding target dsDNA, promoting G4 formation. In cancer cells, HpTYMG-G4-T decreased TYMS mRNA and protein levels, leading to cell death, and showed a synergic effect when combined with 5-fluorouracil. These results reveal the presence of a G4 motif in the TYMS gene, probably involved in the autoregulation of TYMS expression, and the therapeutic potential of a PPRH targeted to the G4FS.

Development and optimization of dual drug-loaded nanoparticles for the potent anticancer effect on renal carcinoma

The present study was focused on developing nanoparticles (NPs) loaded with dual drug conjugate (DDC) for the enhanced anti-tumor activity and reduced resistance against renal cancer cells. Gemcitabine (GT), a nucleoside analog, and 5-Fluorouracil (5FU), an anti-metabolite of thymidylate synthase inhibitor, were conjugated using succinyl chloride (SC). The conjugate GT–SC–5FU was confirmed by 1H NMR and mass spectroscopy (MS). DDC was then loaded onto bovine serum albumin NPs and the formulated NPs were characterized for surface morphology, particle size, zeta potential and PDI. In-vitro drug release and cytotoxicity studies were also performed. Furthermore, the apoptosis study was conducted in zebrafish embryos. Our results demonstrated that DDC was successfully synthesized and the structural conformation of the conjugate (GT–SC–5FU) was confirmed by 1H NMR and MS. DDC-loaded NPs showed smooth-surfaced spherical shaped particles with the following physicochemical properties: mean particle size of 142.5 nm, polydispersity index of 0.195, the zeta potential of −24.6 mV, and percentage entrapment efficiency of 90.46%. Also, the formulated NPs sustained drug release for up to 72 h. In-vitro cytotoxicity studies emphasized the superior anti-cancer activity of DDC-loaded NPs against the RCC cell line, compared to either pure or physical mixture of GT and 5FU. Furthermore, DDC-loaded NPs exerted a potent apoptotic response in the zebrafish embryos model, compared to free DDC or pure drugs. Collectively, our results suggest that the prepared DDC-loaded NPs might represent a promising therapeutic option for conquering renal carcinoma.

Alvaxanthone, a Thymidylate Synthase Inhibitor with Nematocidal and Tumoricidal Activities.

With the aim to identify novel inhibitors of parasitic nematode thymidylate synthase (TS), we screened in silico an in-house library of natural compounds, taking advantage of a model of nematode TS three-dimensional (3D) structure and choosing candidate compounds potentially capable of enzyme binding/inhibition. Selected compounds were tested as (i) inhibitors of the reaction catalyzed by TSs of different species, (ii) agents toxic to a nematode parasite model (C. elegans grown in vitro), (iii) inhibitors of normal human cell growth, and (iv) antitumor agents affecting human tumor cells grown in vitro. The results pointed to alvaxanthone as a relatively strong TS inhibitor that causes C. elegans population growth reduction with nematocidal potency similar to the anthelmintic drug mebendazole. Alvaxanthone also demonstrated an antiproliferative effect in tumor cells, associated with a selective toxicity against mitochondria observed in cancer cells compared to normal cells.

Thymidylate synthase inhibitor raltitrexed can induce high levels of DNA damage in MYCN-amplified neuroblastoma cells.

MYCN gene amplification is consistently associated with poor prognosis in patients with neuroblastoma, a pediatric tumor arising from the sympathetic nervous system. Conventional anticancer drugs, such as alkylating agents and platinum compounds, have been used for the treatment of high‐risk patients with MYCN‐amplified neuroblastoma, whereas molecule‐targeting drugs have not yet been approved. Therefore, the development of a safe and effective therapeutic approach is highly desired. Although thymidylate synthase inhibitors are widely used for colorectal and gastric cancers, their usefulness in neuroblastoma has not been well studied. Here, we investigated the efficacies of approved antifolates, methotrexate, pemetrexed, and raltitrexed (RTX), on MYCN‐amplified and nonamplified neuroblastoma cell lines. Cell growth‐inhibitory assay revealed that RTX showed a superior inhibitory activity against MYCN‐amplified cell lines. We found no significant differences in the protein expression levels of the antifolate transporter or thymidylate synthase, a primary target of RTX, among the cell lines. Because thymidine supplementation could rescue the RTX‐induced cell growth suppression, the effect of RTX was mainly due to the reduction in dTTP synthesis. Interestingly, RTX treatments induced single‐stranded DNA damage response in MYCN‐amplified cells to a greater extent than in the nonamplified cells. We propose that the high DNA replication stress and elevated levels of DNA damage, which are a result of deregulated expression of MYCN target genes, could be the cause of increased sensitivity to RTX.

Inhibition of Cyclooxygenase-2 and Thymidylate Synthase by Dietary Sphingomyelins: Insights from DFT and Molecular Docking Studies

Inhibition of cyclooxygenase-2 (COX-2) and thymidylate Synthase (TS) enzymes play prominent chemopreventive and chemotherapeutic roles in colorectal cancer studies. Basic computational investigation on the inhibition of these enzymes by sphingomyelin (SM) derivatives was carried out in silico using Density Functional Theory (DFT) and molecular docking studies. Interactions between SM with unsaturated fatty acids, COX-2 and TS were compared with that of 5-Fluorouracil (5-FU) and Celecoxib, the standard anti-colorectal cancer drugs. The results showed that SM with alpha-linoleic acid derivative possesses the highest HOMO (-4.70 eV) and lowest LUMO (0.09 eV) energies, which may enhance their interactions with their target receptors. All SM molecules, irrespective of the fatty acid nature have lower binding affinities, (ΔG = -5.5 to - 6.8 kcal/mol) against COX-2 than Celecoxib (-10.1 kcal/mol), indicating that the standard COX-2 inhibitor is much stronger than the natural SM. However, some of the natural SM are stronger inhibitors of thymidylate synthase than the standard drug, 5-FU, with SM having alpha-linoleic acid derivative (ΔG = - 6.2 kcal/mol) higher than 5-FU (ΔG = -5.28 kcal/mol), but lower than that of the active drug metabolite, 5-FdUMP (ΔG = - 7.4 kcal/mol). These ligand-protein interactions were all feasible and spontaneous.

Intratumoral exposure levels of pentaglutamated pemetrexed following treatment with LEAF-1401 and pemetrexed.

3524 Background: The activity of pemetrexed is highly dependent on the intracellular enzyme folypolyglutamate synthase (FPGS) which adds glutamates to pemetrexed and yields very potent pemetrexed polyglutamates. Pemetrexed pentaglutamate (tetraglutamated pemetrexed) is 80-fold more potent than pemetrexed in inhibiting thymidylate synthase. Yet it is a poor drug candidate because it cannot readily cross the negatively charged cell membrane due to its own negative charge. We are developing LEAF-1401, a novel nanoliposomal encapsulation of gamma L-pentaglutamated pemetrexed. Because liposomes can readily be taken up by tumor cells, for its anti-tumor effect, LEAF-1401 can directly deliver pentaglutamated pemetrexed into tumor cells, bypassing the need for transmembrane folate carriers and FPGS which are both downregulated in resistant tumors. Methods: To measure drug levels in tumor, blood and various tissues (biodistribution), in vivo testing of LEAF-1401 and pemetrexed was conducted in a CT-26 murine colorectal carcinoma xenograft model. Animals were treated with a single dose of either LEAF-1401 (80mg/kg; equivalent to 32 mg/kg pemetrexed) or pemetrexed (118mg/kg). Tumor growth inhibition and clinical assessments were conducted. Animals were sacrificed: 5 mice per timepoint in each group and tumor, blood, liver, spleen and other tissues were harvested. Pentaglutamated pemetrexed levels were quantitatively analyzed by LC/MS/MS. Results: Compared to pemetrexed, LEAF-1401 treatment resulted in a 19-fold increase in exposure levels of pentaglutamated pemetrexed in the tumor and significant tumor growth inhibition. Plasma levels of pentaglutamated pemetrexed were high with LEAF-1401, but undetectable with pemetrexed. Like other liposomes, LEAF-1401 also resulted in accumulation of pentaglutamated pemetrexed in the liver and spleen (See Table below). Treatment appeared to be generally well tolerated. Conclusions: LEAF-1401, given at approximately a quarter of the equivalent pemetrexed dose, resulted in a 19-fold increase in pentaglutamate pemetrexed in tumor tissue compared to regular pemetrexed. LEAF-1401 represents a promising new class of novel nanoliposomal antifolates, that enhance the intratumoral delivery of potent polyglutamate antifolates, and improve antitumor activity while retaining an acceptable safety profile. [Table: see text]

A phase I trial a FR alpha targeted thymidylate synthase inhibitor CT900 exploring four schedules of treatment in expansion cohorts of patients with high-grade serous ovarian cancer.

6043 Background: CT900 (BTG945/ONX-0801) is a novel small molecule that binds to folate receptor alpha (FRα), is internalized and causes cytotoxicity by thymidylate synthase inhibition. Methods: The aims of the expansion cohorts were to determine toxicity, response rates and correlation of the response to FRα expression in patients with HGSOC (NCT02360345). Four expansion cohorts were studied which included: schedule A (6 mg/m2/q every 2 weeks), schedule B (12 mg/m2/q every 2 weeks), schedule C (12 mg/m2/q every 2 weeks with 12 mg dexamethasone IV and 8 mg of dexamethasone for 2 days) and schedule D (12 mg/m2/q every 3 weeks). Response rates were assessed by RECIST V1.1 and GCIG CA125 response criteria. Patients who were withdrawn for reasons other than toxicity within 8 weeks (cohorts A, B, C) and 12 weeks (cohort D) were not assessable for efficacy. FRα expression was quantified using immunohistochemistry. Results: A total of 67 patients were treated in the 4 cohorts (14, 25, 15 and 13 for cohorts A, B, C and D). The median age was 62 (IQR 57 - 68) and the median lines of previous treatment was 5 (range 1 to 13). A majority of patients were platinum resistant. The most common toxicities across all expansion cohorts were: fatigue (51%), nausea (36%), anemia (27%), fever (25%), AST elevation (21%), most of which were grade 1 - 2. Toxicity of special interest included radiological changes of pneumonitis and was 15% in all cohorts (7%, 16%, 27% and 8% in cohorts A, B, C and D, respectively). These changes were grade 1 - 2 in all but one case. RECIST response rates in evaluable patients across the different cohorts were: A 1/8 (13%), B 6/21 (29%), C 5/12 (42%) and D 2/12 (17%). FRα expression in archival tumor tissue was measured in 59/67 patients. Expression was found to be high/medium in 43/59 (73%), low in 7/59 (12%) and negative/very low in 9/59 (15%). In patients with high/medium FRα expression, the RECIST response rates in different cohorts were: A 0/9 (0%), B 6/16 (38%), C 4/12 (33%) and D 1/6 (17%). The CA125 response rate in all patients within cohort B was 13/25 (52%) and 10/16 (63%) in patients with high/medium FRα expression. Conclusions: CT900 has shown clinical activity in patients with heavily pre-treated platinum-resistant, high/medium FRα expressing HGSOC. Based on toxicity and efficacy, the schedule of 12 mg/m2/q2 weekly (schedule B) is the recommended phase II dose for further evaluation in patients with relapsed high/medium FRα expressing HGSOC. Clinical trial information: NCT02360345.

Bevacizumab plus S-1 and raltitrexed for refractory metastatic colorectal cancer.

e16024 Background: There are lack of effective drugs and regimens for refractory metastatic colorectal cancer (mCRC), especially in China. Dihydropyrimidine dehydrogenase (DPD) is the rate limiting enzyme of 5-FU catabolic pathway. Thymidylate synthase (TS) is the target of 5-FU anti-tumor mechanism. Several studies have shown the up-regulation of the two enzymes after the use of 5-FU in colorectal cancer, which may be closely related to the 5-FU resistance. The preliminary research of our center has shown the efficacy and safety of S-1 (containing a DPD inhibitor) plus raltitrexed (a TS inhibitor) in refractory mCRC. The aim of this study is to evaluate the efficacy and safety of bevacizumab plus S-1 and raltitrexed for patients with mCRC after failure to fluoropyrimidine, irinotecan and oxaliplatin. Methods: This study is a one-center, single-arm, prospective phase II trial, being carried out in the Cancer Center, West China Hospital, Sichuan University, China. The patients who have progressed after the treatment of fluoropyrimidine, irinotecanand oxaliplatin, have at least one measurable lesion according to RECIST 1.1 criteria were enrolled. Patients receive bevacizumab 7.5mg/kg and raltitrexed 3 mg/m2 on days 1 plus S-1 80, 100 or 120 mg/d according to body-surface area on days 1 through 14 of a 21-day cycle. Primary endpoint was objective response rate (ORR). Secondary endpoints included progression-free survival (PFS), overall survival (OS) and toxicity. Results: From Sep 2015 to Nov 2019, 44 patients were enrolled. By Feb 5, 2020, eleven patients were alive. Tumor response evaluation was available in 44 patients at the time of the analysis. There was no complete response, ORR was 15.9%(7/14) and disease control rate was 54.5%(24/44). mPFS and mOS were 110 days (95% confidence interval, 65.0-155.0) and 367 days (95% confidence interval, 310.4-423.6). The most common adverse events were bone marrow depression, dysfunction of digestive system abnormality of liver function and bleeding. Most of these adverse events were mild to moderate. Conclusions: Bevacizumab plus S-1 and raltitrexed further showed its moderate effect for refractory mCRC. Most of the adverse effects were mild to moderate, which could be well controlled. This combined regimen is worthy of further study as third or later line therapy in mCRC. Clinical trial information: ChiCTR1900020485 .

Dysregulated Pyrimidine Biosynthesis Contributes to 5-FU Resistance in SCLC Patient-Derived Organoids but Response to a Novel Polymeric Fluoropyrimidine, CF10.

Chemo-immunotherapy is central to the treatment of small cell lung cancer (SCLC). Despite modest progress made with the addition of immunotherapy, current cytotoxic regimens display minimal survival benefit and new treatments are needed. Thymidylate synthase (TS) is a well-validated anti-cancer drug target, but conventional TS inhibitors display limited clinical efficacy in refractory or recurrent SCLC. We performed RNA-Seq analysis to identify gene expression changes in SCLC biopsy samples to provide mechanistic insight into the potential utility of targeting pyrimidine biosynthesis to treat SCLC. We identified systematic dysregulation of pyrimidine biosynthesis, including elevated TYMS expression that likely contributes to the lack of efficacy for current TS inhibitors in SCLC. We also identified E2F1-3 upregulation in SCLC as a potential driver of TYMS expression that may contribute to tumor aggressiveness. To test if TS inhibition could be a viable strategy for SCLC treatment, we developed patient-derived organoids (PDOs) from human SCLC biopsy samples and used these to evaluate both conventional fluoropyrimidine drugs (e.g., 5-fluorouracil), platinum-based drugs, and CF10, a novel fluoropyrimidine polymer with enhanced TS inhibition activity. PDOs were relatively resistant to 5-FU and while moderately sensitive to the front-line agent cisplatin, were relatively more sensitive to CF10. Our studies demonstrate dysregulated pyrimidine biosynthesis contributes to drug resistance in SCLC and indicate that a novel approach to target these pathways may improve outcomes.

On a New Proposed Mechanism of 5-Fluorouracil-Mediated Cytotoxicity

The major molecular mode of action of the cytotoxic drug 5-fluorouracil (5-FU) is generally considered to result from thymidylate synthase inhibition. Recent findings relating to the function of the human uracil-5 methyltransferase (U5MT), TRMT2A, and its interaction with 5-FU metabolites incorporated within tRNAs, lead to an additional hypothesis that is proposed here.

Landscape of combination therapy trials in breast cancer brain metastasis.

Combination therapy has become a cornerstone in cancer treatment to potentiate therapeutic effectiveness and overcome drug resistance and metastasis. In this work, we explore combination trials in breast cancer brain metastasis (BCBM), highlighting deficiencies in trial design and underlining promising combination strategies. On October 31, 2019, we examined ClinicalTrials.gov for interventional and therapeutic clinical trials involving combination therapy for BCBM, without limiting for date or location. Information on trial characteristics was collected. Combination therapies used in trials were analyzed and explored in line with evidence from the medical literature. Sixty-five combination therapy trials were selected (n = 65), constituting less than 0.7% of all breast cancer trials. Most trials (62%) combined ≥2 chemotherapeutic agents. Chemotherapy with radiation was main-stay in 23% of trials. Trastuzumab was mostly used in combination (31%), followed by lapatinib (20%) and capecitabine (15%). Common strategies involved combining tyrosine kinase inhibitors with thymidylate synthase inhibitors (6 trials), dual HER-dimerization inhibitors (3 trials), microtubule inhibitors and tyrosine kinase inhibitors (3 trials), and HER-dimerization inhibitors and tyrosine kinase inhibitors (3 trials). The combination of tucatinib and capecitabine yielded the highest objective response rate (83%) in early phase trials. The triple combination of trastuzumab, tucatinib and capecitabine lowered the risk of disease progression or death by 52% in patients with HER2-positive BCBM. Combining therapeutic agents based on biological mechanisms is necessary to increase the effectiveness of available anti-cancer regimens. Significant survival benefit has yet to be achieved in future combination therapy trials. Enhancing drug delivery through blood-brain barrier permeable agents may potentiate the overall therapeutic outcomes.

Structural analysis of a shrimp thymidylate synthase reveals species-specific interactions with dUMP and raltitrexed

Thymidylate synthase (TS) is a key enzyme in the de novo biosynthesis of thymidine monophosphate, serving as a well-known drug target in chemotherapy against cancers and infectious diseases. Additional to its clinical value, TS is supposed to be a promising drug target in aquatic-disease control. To facilitate designing pathogen-specific TS inhibitors for shrimp-disease control, we report the crystal structures of TS from Litopenaeus vannamei (LvTS) in the apo form, LvTS-dUMP complex and LvTS-dUMP-raltitrexed complex at 2.27 A, 1.54 A, and 1.56 A resolution, respectively. LvTS shares a similar fold with known TSs, existing as a dimer in the crystal. The apo LvTS and LvTS-dUMP take an open conformation, and raltitrexed binding induces structural changes into a closed conformation in LvTS-dUMP-raltitrexed. Compared to those in other known TS-dUMP-raltitrexed complexes with the closed conformation, the C-terminal loop in LvTS-dUMP-raltitrexed shifts its position away from the bound raltitrexed; the distance between C6 of dUMP and Sγ of the catalytic cysteine is obviously longer than that in the known TS structures with closed conformations, resembling that in the TS structures with open conformations. Other species-specific interactions with dUMP and raltitrexed are also observed. Therefore, LvTS-dUMP-raltitrexed adopts a loosely closed conformation with structural features intermediate between the closed and the open conformations that were reported in other TSs. Our study provides the first crustcean TS structure, and reveals species-specific interactions between TSs and the ligands, which would facilitate designing pathogen-specific TS inhibitors for shrimp-disease control.

Plasma deoxyuridine levels in metastatic colorectal cancer (mCRC) patients and clinical response after 5FU based therapy in combination with arfolitixorin.

185 Background: 5-Fluorouracil (5FU) is one of the most commonly used cancer drugs. FdUMP is a metabolite from 5FU which inhibits thymidylate synthase (TS). TS inhibition causes a rise in the intracellular pool of the natural TS substrate dUMP leading to increased global levels of deoxyuridine (dUR). In order to increase TS inhibition, 5FU is combined with folates, usually leucovorin (LV). However, LV needs enzymatic conversion to become active. The LV conversion capacity differs between patients, with the consequence that many patients will have a reduced effect of 5FU-based treatment. Arfolitixorin is a biologically active folate, 5,10-methylenetetrahydrofolate, which doesn´t need enzymatic conversion; hence it could potentially be more efficacious. Methods: ISO-CC-005 is a phase I/II safety and tolerability study in mCRC patients receiving 5FU/arfolitixorin alone or in combination with irinotecan or oxaliplatin ± bevacizumab. Efficacy was evaluated as Overall Response Rate (ORR) after 4 cycles of chemotherapy. A LC-MS/MS method was developed for quantification of plasma dUr and 5FU. Blood samples were collected before and 24 h after 5FU administration at the first (C1) and fourth (C4) treatment cycle (n = 33). The C4/C1 ratio for dUr and 5FU, respectively, were calculated.The clinical response, which is an ordered categorical data, was modelled using nominal logistic regression using the ratio C4/C1 and the absolute values C1 and C4 as explanatory variables. Results: A positive correlation between dUr and 5FU levels was seen (r = 0.89, p = 0.0011) at C4. The C4/C1 ratio for dUr and 5FU in plasma correlated positively (r = 0.95, p = 0.0001). A positive correlation was also found between arfolitixorin dose and plasma levels of dUr (r = 0.44, p = 0.016) at C1, but not at C4. In the model test, the C4/C1 dUr ratio, as well as the individual dUr levels at C1 and C4, had a highly significant effect on ORR (p = 0.0075). Conclusions: The results demonstrate that the arfolitixorin dose has an impact on plasma levels of dUr and also on clinical response. dUr could potentially be an early surrogate marker for TS inhibition in mCRC patients treated with 5FU/arfolitixorin. Clinical trial information: NCT02244632.

NuTide: 302—A phase Ib study of the ProTide NUC-3373 in combination with standard therapies in advanced colorectal cancer.

TPS274 Background: Although 5-FU-based regimens such as FOLFOX and FOLFIRI remain the cornerstone of treatment for patients (pts) with colorectal cancer (CRC), their clinical utility is limited by resistance mechanisms and toxicity. Anti-cancer activity of 5-FU is dependent on conversion to an active metabolite, fluorodeoxyuridine-monophosphate (FUDR-MP), which binds to and inhibits thymidylate synthase (TS), a critical enzyme in de novo nucleotide synthesis and cell survival. However, due to multiple limitations including: reliance on enzymatic activation; catabolism by dihydropyrimidine dehydrogenase (DPD) and a short plasma half-life, 5-FU is not efficiently converted to FUDR-MP. NUC-3373, a phosphoramidate transformation of FUDR-MP, was designed to bypass the key resistance mechanisms that limit the clinical utility of 5-FU. NUC-3373 demonstrated a favorable PK/PD profile and promising efficacy signals in the first-in-human study (NuTide:301) in pts with advanced solid tumors. NUC-3373 has a longer plasma t1/2 (9.7 hours) than 5-FU (8-14 minutes) and generates high intracellular levels of FUDR-MP (Ghazaly et al ESMO, 2017). TS is efficiently inhibited and sequestered into TS-ternary complexes, depleting the pool of deoxythymidine monophosphate (dTMP) within 2-4 hours. Methods: NuTide:302 is a three-part, Phase Ib study in pts with advanced CRC who have relapsed after ≥2 prior lines of 5-FU-containing therapies. Primary objective is to identify a RP2D of NUC-3373 when administered weekly and q2w in combination with standard agents used in CRC treatment. Secondary objectives include safety, PK/PD and anti‐tumor activity. In Part 1, patients are receiving NUC-3373 with leucovorin (LV) to determine if LV augments TS inhibition. In Part 2, NUC-3373 (±LV) will be administered in dose escalating cohorts, in a modified 3+3 design, with either oxaliplatin (NUFOX) or irinotecan (NUFIRI). In Part 3, the NUFOX and NUFIRI regimens selected in Part 2 will be combined with biologics targeting VEGF or EGFR pathways. To date, 22 pts have received study treatment. Recruitment is ongoing in the US and Europe. Clinical trial information: NCT03428958.

Drugging Protein-Protein Interfaces of a Supramolecular Assembly as a Means to Overcome Resistance to Active Site Thymidylate Synthase Inhibitors

Drugging Protein-Protein Interfaces of a Supramolecular Assembly as a Means to Overcome Resistance to Active Site Thymidylate Synthase Inhibitors

Systemic delivery of aptamer-drug conjugates for cancer therapy using enzymatically generated self-assembled DNA nanoparticles.

Aptamer-drug conjugates (ApDCs) are promising anticancer therapeutics with cancer cell specificity. However, versatile in vivo applications of ApDCs are hampered by their limited serum stability and inability to reach the tumour upon systemic administration. Here, we describe DNA nanoparticles of ApDCs as a platform for tumour-targeted systemic delivery of ApDCs. DNA nanoparticles of approximately 75 nm size were fabricated by self-assembly of a polymerised floxuridine (FUdR)-incorporated AS1411 aptamer produced via rolling circle amplification. The DNA nanoparticles of ApDCs showed highly efficient cancer cell uptake, enhanced serum stability, and tumour-targeted accumulation. These properties could be successfully utilised for tumour-specific apoptotic damage by ApDCs, leading to significant suppression of tumour growth without considerable systemic toxicity. Molecular analysis revealed that the enhanced anticancer potency was due to the synergic effect induced by the simultaneous activation of p53 by AS1411 and the inhibition of thymidylate synthase by FUdR, respectively, both of which were generated from the DNA nanoparticles. We therefore expect that the DNA nanoparticles of ApDCs can be a promising platform for tumour-targeted delivery of various nucleoside-incorporated ApDCs to treat cancer.