Abstract B42: Molecular and cytogenetic characterization of novel multidrug-resistant human tumor cell lines

Abstract

Abstract Multidrug resistance (MDR) is the major cause of failure to a successful cancer treatment. Cancer cells manifesting MDR phenotype are cross-resistant to many structurally and functionally unrelated drugs. The purpose of this study was to establish in vitro models, i.e., resistant cell lines, to further investigate the mechanisms of MDR. We used the human colon cancer cell line DLD1 and the glioma cell line U87 to establish paclitaxel-resistant cell lines, DLD1 -TxR and U87-TxR, by continuous exposure to stepwise increasing concentrations of the drug. The newly established, DLD1 -TxR and U87-TxR cell lines showed extensive resistance to paclitaxel (301-fold and 103-fold respectively). They also demonstrated cross-resistance to other anticancer agents such as doxorubicin, epirubicin, vinblastin, and etoposide. Cytogenetic data based on inverted-DAPI Banding, demonstrated that both resistant cell lines retained several karyotypic characteristics of their sensitive counterparts and also acquired novel structural or numerical chromosomal aberrations that may be related to resistance to chemotherapy. Interestingly, while the dividing parental U87 cells were mainly near-tetraploid, chemoresistance in the U87-TxR cell line was accompanied by one level ploidy reduction as verified by the increased prevalence of near-diploid cell populations. In addition, the DLD1 -TxR cells showed an increase tendency to loose the Y chromosome. Gene expression analyses revealed a 4-fold increase in the level of mdr1 mRNA in DLD1 -TxR cells. U87-TxR cells demonstrated prominent mdr1 activity since the expression in parental cells was undetectable. In contrast, the level of mrp1 mRNA was 40% decreased in both resistant cell lines. The expression of other MDR-related genes, topo IIα, and lrp, was unaffected by paclitaxel resistance. Flow cytometry analyses showed that the accumulation of rhodamine in resistant cells DLD1 -TxR and U87-TxR was significantly lower than in their sensitive counterparts, 17-fold and 8-fold, respectively. These results indicate that P-gp, encoded by mdr1 gene, is significantly overexpressed in both resistant cell lines and may account for paclitaxel resistance. In conclusion, the two novel resistant cell lines, DLD1 -TxR and U87-TxR may serve as appropriate models for the study of the mechanisms of paclitaxel resistance offering novel insights into potential targets for overcoming MDR that would improve the response to chemotherapy and patient outcome. Citation Information: Clin Cancer Res 2010;16(14 Suppl):B42.