Sensitivity to Anticancer Agents and Resistance Mechanisms in Clear Cell Carcinoma of the Ovary

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Abstract
We conducted the present study to determine the chemoresistance mechanisms in clear cell carcinoma of the ovary (CCC). Five human CCC cell lines (HAC‐2, RMG‐I, RMG‐II, KK, and KOC‐7c) were used in this study. The sensitivity of the cells to the anticancer agents was determined by 3–(4,5–dimethylthiazol‐2‐yl)‐2,5‐diphenyltetrazolium bromide (MTT) assay and we assessed drug sensitivity by calculating assay area under the curve (AUC) for each agent. The expression of multi‐drug resistance genes (MDR‐1, MRP‐1, MRP‐2) was detected by reverse transcription‐polymerase chain reaction (RT‐PCR). Glutathione (GSH) concentration was measured by an enzymatic assay. Topoisomerase (topo) I activity was assayed in terms of relaxation of supercoiled plasmid substrate DNA. The IC50 to anticancer agents ranged widely. The assay AUC indicated that 3 of 5 cell lines (RMG‐I, RMG‐II, and KK) were sensitive to paclitaxel (PTX), 3 (HAC‐2, RMG‐I, and RMG‐II) were sensitive to 7–ethyl‐10‐hydroxycamptothecin (SN‐38), which is an active metabolite of camptothecin (CPT‐11), and only one (HAC‐2) was sensitive to cisplatin (CDDP). All cell lines were resistant to mitomycin‐C (MMC) and etoposide (VP‐16). The MRP‐1 gene was detected in all cell lines. Only one cell line showed both MRP‐2 and MDR‐1 gene expression. Except for HAC‐2 cells, expression of MRP genes was related to CDDP resistance, and MDR‐1 gene expression was associated with PTX resistance. GSH concentrations increased after exposure to CDDP or MMC in all cell lines. There was a significant correlation between topo‐I enzymatic activity and the response to SN‐38. The present study revealed several resistance mechanisms in CCC and the results suggested that PTX and CPT‐11 might be effective agents to treat CCC.

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