verlukast and Colonic-Neoplasms

We have recently shown that drug conjugation catalysed by UDP-glucuronosyltransferases (UGTs) functions as an intrinsic mechanism of resistance to the topoisomerase I inhibitors 7-ethyl-10-hydroxycamptothecin and NU/ICRF 505 in human colon cancer cells and now report on the role of drug transport in this mechanism. The ability of transport proteins to recognise NU/ICRF 505 as a substrate was evaluated in model systems either transfected with breast cancer-resistance protein 1 (Bcrp1), multidrug-resistance protein 2 (Mrp2) or Mrp3, or overexpressing MRP1 or P-170 glycoprotein. Results from chemosensitivity assays suggested that NU/ICRF 505 was not a substrate for any of the above proteins. In drug accumulation studies in human colon cancer cell lines NU/ICRF 505 was taken up avidly and retained in cells lacking UGTs (HCT116), whereas, following equally rapid uptake, it was cleared rapidly from cells displaying UGT activity (HT29) as glucuronide metabolites. HT29 cells were shown to express MRP1 and 3, but not P-170 glycoprotein, MRP2 or breast cancer-resistance protein. The major glucuronide of NU/ICRF 505 inhibited ATP-dependent transport of estradiol 17-beta-glucuronide in Sf9 insect cell membrane vesicles containing MRP1 or MRP3, while co-incubation of HT29 cells with the MRP antagonist, MK571, significantly restored intracellular concentrations of NU/ICRF 505. These data lead us to conclude that the presence of a glucuronide transporter is essential for glucuronidation to represent a major de novo resistance mechanism and that UGTs will contribute more as a primary resistance mechanism when the parent drug (e.g. NU/ICRF 505) is not itself recognised by transport proteins.

Topics: Anthraquinones; Antigens, CD; Antineoplastic Agents, Phytogenic; Biological Transport; Camptothecin; Carrier Proteins; Colonic Neoplasms; Drug Interactions; Drug Resistance; Glucuronides; HT29 Cells; Humans; Irinotecan; Membrane Glycoproteins; Membrane Transport Proteins; Multidrug Resistance-Associated Protein 2; Multidrug Resistance-Associated Proteins; Propionates; Quinolines; Tetraspanin 29; Tumor Cells, Cultured; Tyrosine

Regulation of capacitative Ca(2+) entry was studied in two different multidrug resistance (MDR) protein (MRP1) overexpressing cell lines, HT29(col) and GLC4/ADR. MRP1 overexpression was accompanied by a decreased response to thapsigargin. Moreover, inhibition of capacitative Ca(2+) entry by D, L-threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol (PDMP) was abolished in MRP1 overexpressing cells. Both PDMP and the MRP1 inhibitor MK571 greatly reduced InsP(3)-mediated (45)Ca(2+) release from intracellular stores in HT29 cells. Again, these effects were virtually abolished in HT29(col) cells. Our results point to a modulatory role of MRP1 on intracellular calcium concentration ([Ca(2+)](i)) homeostasis which may contribute to the MDR phenotype.

Topics: Adenocarcinoma; ATP-Binding Cassette Transporters; Calcium; Calcium Radioisotopes; Colonic Neoplasms; Gene Expression; Homeostasis; Humans; Inositol 1,4,5-Trisphosphate; Morpholines; Multidrug Resistance-Associated Proteins; Propionates; Quinolines; Thapsigargin; Tumor Cells, Cultured

We have obtained a novel multidrug resistant cell line, derived from HT29 G(+) human colon carcinoma cells, by selection with gradually increasing concentrations of the anti-mitotic, microtubule-disrupting agent colchicine. This HT29(col) cell line displayed a 25-fold increase in colchicine resistance and exhibited cross-resistance to doxorubicin, VP16, vincristine and taxol. Immunoblotting, combined with RT-PCR showed that the multidrug resistance phenotype was conferred by specific overexpression of the multidrug resistance protein 1. Confocal scanning laser microscopy revealed that multidrug resistance protein 1 specifically localized in the plasma membrane of HT29(col) cells. In a functional assay, using the fluorescent multidrug resistance protein 1 substrate 5-carboxyfluorescein, an increased efflux activity of HT29(col) cells was measured, as compared to the wild-type HT29 G(+) cells. MK571, a specific inhibitor of multidrug resistance protein 1, blocked the 5-carboxyfluorescein efflux, but only partially reversed resistance to colchicine, indicating that additional multidrug resistance mechanisms operate in HT29(col) cells. In conclusion, these results show for the first time overexpression of a functional multidrug resistance protein 1 under colchicine pressure, indicating that colchicine is not a P-glycoprotein-specific substrate. Colchicine-induced overexpression of multidrug resistance protein 1 is accompanied by a changed sphingolipid composition, i.e., enhanced levels of glucosylceramide and galactosylceramide. In addition, ceramide, a lipid messenger molecule involved in apoptosis-related signal transduction processes, was much more abundant in HT29(col) cells, which is indicative of a stress response.

Topics: Antineoplastic Agents; ATP-Binding Cassette Transporters; Cell Survival; Ceramides; Colchicine; Colonic Neoplasms; Dose-Response Relationship, Drug; Doxorubicin; Drug Resistance, Multiple; Etoposide; Fluoresceins; Galactosylceramides; Glucosylceramides; HT29 Cells; Humans; Immunoblotting; Immunohistochemistry; Microscopy, Confocal; Microtubules; Mitosis; Multidrug Resistance-Associated Proteins; Paclitaxel; Propionates; Quinolines; Signal Transduction; Sphingolipids; Vincristine