Search

Human nucleoside transporter (NT) complementary DNAs (cDNAs) was cloned and sequenced by polymerase chain reaction (PCR) amplification of human Na+-nucleoside cotransporter (hCNT1) from human kidney cDNA library. The isolated human kidney cDNAs that encode structural and functional hCNT1a and hCNT1b in rat kidney Na+-dependent NT rCNT1 exhibited different amino acid sequences. However, both human NT isoforms mediated Na+-dependent fluxes of uridine and adenosine indicating the presence of similar nucleoside transport activity.

Abstract Background Gemcitabine, a deoxycytidine nucleoside analog, is the current standard chemotherapy used as first-line treatment for patients with locally advanced or metastatic cancer of the pancreas, and extends life survival by 5.7 months. Advanced pancreatic cancer thus remains a highly unmet medical need and new therapeutic agents are required for this patient population. Troxacitabine (Troxatyl™) is the first unnatural L-nucleoside analog to show potent preclinical antitumor activity and is currently under clinical investigation. Troxacitabine was recently evaluated as a first-line therapy in 54 patients with advanced adenocarcinoma of the pancreas and gave comparable overall results to those reported with gemcitabine in recently published randomized trials. Methods The human pancreatic adenocarcinoma cell lines, AsPC-1, Capan-2, MIA PaCa-2 and Panc-1, were exposed to troxacitabine or gemcitabine alone or in combination, for 72 h, and the effects on cell growth were determined by electronic particle counting. Synergistic efficacy was determined by the isobologram and combination-index methods of Chou and Talalay. Mechanistic studies addressed incorporation of troxacitabine into DNA and intracellular levels of troxacitabine and gemcitabine metabolites. For in vivo studies, we evaluated the effect of both drugs, alone and in combination, on the growth of established human pancreatic (AsPC-1) tumors implanted subcutaneously in nude mice. Statistical analysis was calculated by a one-way ANOVA with Dunnett as a post-test and the two-tailed unpaired t test using GraphPad prism software. Results Synergy, evaluated using the CalcuSyn Software, was observed in all four cell-lines at multiple drug concentrations resulting in combination indices under 0.7 at Fa of 0.5 (50% reduction of cell growth). The effects of drug exposures on troxacitabine and gemcitabine nucleotide pools were analyzed, and although gemcitabine reduced phosphorylation of troxacitabine when cells were exposed at equal drug concentrations, there was no effect on phosphorylated pools at drug combinations that were synergistic. The amount of troxacitabine incorporated into DNA was also not affected by the presence of gemcitabine. In vivo testing against a human pancreatic (AsPC-1) xenograft mouse tumor model indicated that both drugs were more than additive at well-tolerated doses and schedule. The biological basis for this synergy is unclear as we did not observe changes in apoptosis, DNA repair, troxacitabine incorporation into DNA or troxacitabine metabolism in the presence of gemcitabine. Conclusion These data, together with phase I clinical data showing tolerability of both agents when combined, suggest combination therapy with troxacitabine and gemcitabine warrants further evaluation in advanced pancreatic cancer patients.

We previously identified a novel breast cancer susceptibility variant on chromosome 4q31.22 locus (rs1429142) conferring risk among women of European ancestry. Here, we report replication of findings, validation of the variant in diverse populations and fine‐mapping of the associated locus in Caucasian population. The SNP rs1429142 (C/T, minor allele frequency 18%) showed association for the overall breast cancer risk in Stages 1–4 (n = 4,331 cases/4271 controls; p = 4.35 × 10−8; odds ratio, ORC‐allele,1.25), and an elevated risk among premenopausal women (n = 1,503 cases/4271 controls; p = 5.81 × 10−10; ORC‐allele 1.40) in European populations. SNP rs1429142 was associated with premenopausal breast cancer risk in women of African (T/C; p‐value 1.45 × 10−02; ORC‐allele 1.2) but not from Chinese ancestry. Fine‐mapping of the locus revealed several potential causal variants which are present within a single association signal, revealed from the conditional regression analysis. Functional annotation of the potential causal variants revealed three putative SNPs rs1366691, rs1429139 and rs7667633 with active enhancer functions inferred based on histone marks, DNase hypersensitive sites in breast cell line data. These putative variants were bound by transcription factors (C‐FOS, STAT1/3 and POL2/3) with known roles in inflammatory pathways. Furthermore, Hi‐C data revealed several short‐range interactions in the fine‐mapped locus harboring the putative variants. The fine mapped locus was predicted to be within a single topologically associated domain, potentially facilitating enhancer–promoter interactions possibly leading to the regulation of nearby genes. What's new? To date, genome‐wide association studies have addressed familial or postmenopausal breast cancer susceptibility variants. However, genetic predisposition for sporadic premenopausal breast cancer risk is unknown. This study reports a novel variant (at 4q31.22) associated with elevated risk for premenopausal breast cancer among women from European and African ancestry. The fine‐mapped locus was predicted to be within a single topologically associated domain, potentially facilitating enhancer‐promoter interactions leading to the regulation of nearby genes. [ABSTRACT FROM AUTHOR]

Various studies are conducted to study the specific mutations observed in the transmembrane helix 8 of the human concentrative [Na.sub.+]/nucleoside contransporter hCNT1. The analysis reveals that the residues of hCNT1 exhibits uridine-protectable inhibition by p-chloromercuribenzene sulfonate, as they occupy the positions close to the nucleoside translocation pore.

Protein-ligand binding affinities and stoichiometries are determined by measuring changes in protein intrinsic fluorescence. A direct value that confirms the formation of a ternary complex involving a polynucleotide kinase and an oligonucleotide and supports a reaction mechanism in which ATP and DNA bind simultaneously to the enzyme is presented.