Increased sensitivity to gemcitabine of P-glycoprotein and multidrug resistance-associated protein-overexpressing human cancer cell lines

0.05), respectively. P-glycoprotein and MRP1 overexpression possibly caused a cellular stress resulting in increased gemcitabine metabolism and sensitivity, while reversal of collateral gemcitabine sensitivity by verapamil also suggests a direct relation between the presence of membrane efflux pumps and gemcitabine sensitivity

Paclitaxel alters the expression and specific activity of deoxycytidine kinase and cytidine deaminase in non-small cell lung cancer cell lines

<p>Abstract</p> <p>Background</p> <p>We observed that paclitaxel altered the pharmacokinetic properties of gemcitabine in patients with non-small cell lung cancer (NSCLC) and limited the accumulation of gemcitabine and its metabolites in various primary and immortalized human cells. Therefore, we classified the drug-drug interaction and the effects of paclitaxel on deoxycytidine kinase (dCK) and cytidine deaminase (CDA) in three NSCLC cell lines. These enzymes are responsible for the metabolism of gemcitabine to its deaminated metabolite dFdU (80% of the parent drug) and the phosphorylated metabolites dFdCMP, dFdCDP and dFdCTP. These metabolites appear to relate to sensitivity and tolerability of gemcitabine based on previous animal and laboratory studies.</p> <p>Methods</p> <p>Three immortalized human cells representative of the most common histological subtypes identified in patients with advanced NSCLC were exposed to the individual drugs or combinations to complete a multiple drug effect analysis. These same cell lines were exposed to vehicle-control or paclitaxel and the mRNA levels, protein expression and specific activity of dCK and CDA were compared. Comparisons were made using a two-tailed paired t-test or analysis of variance with a P value of < 0.05 considered significant.</p> <p>Results</p> <p>The multiple drug effect analysis indicated synergy for H460, H520 and H838 cells independent of sequence. As anticipated, paclitaxel-gemcitabine increased the number of G2/M cells, whereas gemcitabine-paclitaxel increased the number of G0/G1 or S cells. Paclitaxel significantly decreased dCK and CDA mRNA levels in H460 and H520 cells (40% to 60%, P < 0.05) and lowered dCK protein (24% to 56%, P < 0.05) without affecting CDA protein. However, paclitaxel increased both dCK (10% to 50%) and CDA (75% to 153%) activity (P < 0.05). Paclitaxel caused substantial declines in the accumulation of the deaminated and phosphorylated metabolites in H520 cells (P < 0.05); the metabolites were not measurable in the remaining two cell lines. The ratio of dCK to CDA mRNA levels corresponded to the combination index (CI) estimated for sequential paclitaxel-gemcitabine.</p> <p>Conclusion</p> <p>In summary, paclitaxel altered the mRNA levels and specific activity of dCK and CDA and these effects could be dependent on histological subtype. More cell and animal studies are needed to further characterize the relationship between mRNA levels and the overall drug-drug interaction and the potential to use histological subtype as a predictive factor in the selection of an appropriate anticancer drug regimen.</p

Application of ProTide Technology to Gemcitabine: A Successful Approach to Overcome the Key Cancer Resistance Mechanisms Leads to a New Agent (NUC-1031) in Clinical Development

Gemcitabine is a nucleoside analogue commonly used in cancer therapy but with limited efficacy due to a high susceptibility to cancer cell resistance. The addition of a phosphoramidate motif to the gemcitabine can protect it against many of the key cancer resistance mechanisms. We have synthesized a series of gemcitabine phosphoramidate prodrugs and screened for cytostatic activity in a range of different tumor cell lines. Among the synthesized compounds, one in particular (NUC-1031, 6f) was shown to be potent in vitro. Importantly, compared with gemcitabine, 6f activation was significantly less dependent on deoxycytidine kinase and on nucleoside transporters, and it was resistant to cytidine deaminase-mediated degradation. Moreover, 6f showed a significant reduction in tumor volumes in vivo in pancreatic cancer xenografts. The ProTide 6f is now in clinical development with encouraging efficacy signals in a Phase I/II study, which strongly supports the ProTide approach to generate promising new anticancer agents

Metabolism and accumulation of the lipophilic deoxynucleoside analogs elacytarabine and CP-4126

Cytarabine (ara-C) and gemcitabine (dFdC) are commonly used anticancer drugs, which depend on the equilibrative (ENT) and concentrative-nucleoside-transporters to enter the cell. To bypass transport-related drug resistance, lipophilic derivatives elacytarabine (CP-4055), ara-C-5′elaidic-acid-ester, and CP-4126, (CO 1.01) gemcitabine-5′elaidic-acid-ester, were investigated for the entry into the cell, distribution, metabolism and retention. The leukemic CEM-cell-line and its deoxycytidine-kinase deficient variant (CEM/dCK-) were exposed for 30 and 60 min to the radiolabeled drugs; followed by culture in drug-free medium in order to determine drug retention in the cell. The cellular fractions were analyzed with thin-layer-chromatography and HPLC. Elacytarabine and CP-4126 were converted to the parent compounds both inside and outside the cell (35–45%). The ENT-inhibitor dipyridamole did not affect their uptake or retention. Inside the cell Elacytarabine and CP-4126 predominantly localized in the membrane and cytosolic fraction, leading to a long retention after removal of the medium. In contrast, in cells exposed to the parent drugs ara-C and dFdC, intracellular drug concentration increased during exposure but decreased to undetectable levels after drug removal. In the dCK- cell line, no metabolism was observed. The concentrations of ara-CTP and dFdCTP reached a peak at the end of the incubation with the drugs, and decreased after drug removal; peak levels of dFdCTP were 35 times higher than ara-CTP and was retained better. In contrast, after exposure to elacytarabine or CP-4126, ara-CTP and dFdCTP levels continued to increase not only during exposure but also during 120 min after removal of the elacytarabine and CP-4126. Levels of ara-CTP and dFdCTP were higher than after exposure to the parent drugs. In conclusion, the lipophilic derivatives elacytarabine and CP-4126 showed a nucleoside-transporter independent uptake, with long retention of the active nucleotides. These lipophilic nucleoside analogues are new chemical entities suitable for novel clinical applications