Canine mammary carcinoma cell line are resistant to chemosensitizers: verapamil and cyclosporin A

Cancer chemotherapy can fail in many ways. One of the most significant is the development of multiple drug resistance (MDR), which constitutes a serious clinical problem. The development of MDR relates to the expression of a major membrane pump, P-glycoprotein (P-gp). Thus, currently one of the goals of experimental and clinical oncology is to decrease its activity. So far, many different P-gp inhibitors are available, but their efficacy is still questionable and requires further study. The aim of our study was to assess an impact of classical P-gp inhibitors (verapamil and cyclosporin A) in the reversion of multidrug resistance in canine mammary cancer cells. We used two cell lines isolated from mammary tumors and two cell lines isolated from their lung metastases. All of them showed P-gp over-expression confirmed using Real-time rt-PCR, Skan boolean AND R screening station and confocal microscopy. The FACS analysis showed that in three of the examined cell lines, treatment with verpamil/cyclosporin A was ineffective to reverse cancer chemoresistance. However, more studies in this field are required.