Resistance to Paclitaxel in a Cisplatin-Resistant Ovarian Cancer Cell Line Is Mediated by P-Glycoprotein

Abstract

The IGROVCDDP cisplatin-resistant ovarian cancer cell line is also resistant to paclitaxel and models the resistance phenotype of relapsed ovarian cancer patients after first-line platinum/taxane chemotherapy. A TaqMan low-density array (TLDA) was used to characterise the expression of 380 genes associated with chemotherapy resistance in IGROVCDDP cells. Paclitaxel resistance in IGROVCDDP is mediated by gene and protein overexpression of P-glycoprotein and the protein is functionally active. Cisplatin resistance was not reversed by elacridar, confirming that cisplatin is not a P-glycoprotein substrate. Cisplatin resistance in IGROVCDDP is multifactorial and is mediated in part by the glutathione pathway and decreased accumulation of drug. Total cellular glutathione was not increased. However, the enzyme activity of GSR and GGT1 were up-regulated. The cellular localisation of copper transporter CTR1 changed from membrane associated in IGROV-1 to cytoplasmic in IGROVCDDP. This may mediate the previously reported accumulation defect. There was decreased expression of the sodium potassium pump (ATP1A), MRP1 and FBP which all have been previously associated with platinum accumulation defects in platinum-resistant cell lines. Cellular localisation of MRP1 was also altered in IGROVCDDP shifting basolaterally, compared to IGROV-1. BRCA1 was also up-regulated at the gene and protein level. The overexpression of P-glycoprotein in a resistant model developed with cisplatin is unusual. This demonstrates that P-glycoprotein can be up-regulated as a generalised stress response rather than as a specific response to a substrate. Mechanisms characterised in IGROVCDDP cells may be applicable to relapsed ovarian cancer patients treated with frontline platinum/taxane chemotherapy.

P-glycoprotein Mediates Drug Resistance via a Novel Mechanism Involving Lysosomal Sequestration

“…8C). Finally, it is notable that no significant alteration in cytotoxicity of the non-Pgp substrates cisplatin or carboplatin (32) were observed by lysosomotropic weak bases, regardless of Pgp expression (Fig. 9).…”

Carboplatin and taxol resistance develops more rapidly in functional BRCA1 compared to dysfunctional BRCA1 ovarian cancer cells

“…Western blotting was performed as per the method used by (Stordal et al 2012). Primary and secondary antibodies used are listed in supplementary material, Table S2.…”

“…Analysis of total cellular levels of glutathione (GSH) was carried out as per the method by (Stordal et al 2012) which was adapted from (Suzukake et al 1982). Plates were read and kinetics measured using the FLUOstar OPTIMA (BMG LABTECH) multifunctional microplate reader (405nM at 30°C).…”

“…These proteins may instead be relocated to different parts of the cell causing a resistance phenotype. An increase of ATP7A and ATP7B in the cellular membrane or a relocation of CTR1 to the golgi apparatus may lead to platinum resistance without a change in protein expression (Stordal et al 2012).…”

Reduced accumulation of platinum drugs is not observed in drug-resistant ovarian cancer cell lines derived from cisplatin-treated patients

“…Studies in mice have demonstrated that Pt concentrations in tumor tissue do not correlate with tumor regression activity [27]. It is interesting to note that drug-resistant cells from taxane-naïve patients were hypersensitive to taxanes [28]. This is reflective of the clinical finding that survival was prolonged in relapsed patients receiving platinum plus paclitaxel versus platinum alone [29].…”