Comparative study of the sensitivities of cancer cells to doxorubicin, and relationships between the effect of the drug-efflux pump P-gp

Multi-drug resistance (MDR) of cancers to chemotherapy including doxorubicin (DOX) is mediated by several factors. To design an effective therapy for the treatment of chemotherapy-resistant cancers, it is essential to explore the elements responsible for mediating MDR. However, exploring these factors in detail in a wide range of tumor types is challenging as several critical analytical steps are involved. Here, we demonstrated the way of exploring the factors mediating MDR in the tumor types without performing the analysis at the molecular level of cells. The sensitivities of 15 different types of cancer cells to DOX were evaluated, and the role of P-glycoprotein (P-gp), one of the major efflux-pumps, was explored. A correlation curve was developed between the intracellular amounts of DOX and the sensitivities of cells, and, based on this correlation, the cells were classified in response to the involvement of P-gp that mediates MDR. P-gp plays an active role in mediating MDR of cancer cells where a correlation between the sensitivities of cells and the accumulated DOX exists. In contrast, in cells that show a resistance to DOX but whose sensitivities are independent of the amount of accumulated drug, it was reasonably presumed that mechanisms other than P-gp are likely to be involved in mediating MDR. Based on the correlation between the availability of a drug and cell sensitivity, it would be reasonable to explore the factors governing cancer MDR, which is essential in designing an effective therapeutic approach for treating chemotherapy-resistant cancers using chemotherapeutic drugs.