RESUMEN
BACKGROUND/AIM: Despite improvements in cancer therapy, life expectancy after tumor recurrence remains low. Relapsed cancer is characterized by drug resistance, often mediated through overexpression of multidrug resistance (MDR) genes. Camellia sinensis non fermentatum extract is known for its anticancer properties in several cancer cell lines and might improve cancer therapy outcome after tumor recurrence. MATERIALS AND METHODS: Embryonal rhabdomyosarcoma cell lines, alveolar rhabdomyosarcoma cell lines and primary rhabdomyosarcoma MAST139 cells were used to test NPE® effects on cell viability in combination with chemotherapeutic agents. Cell viability was measured by the WST-1 assay and CV staining. Gene expression levels of chemotherapy-induced efflux pumps and their activity was assessed upon NPE® treatment by measuring doxorubicin retention through evaluation of the autofluorescence signal. RESULTS: Administration of increasing doxorubicin concentrations triggered immediate adaptation to the drug, which was surprisingly overcome by the addition of NPE®. Investigating the mechanism of immediate adaptation, MDR1 gene overexpression was observed upon doxorubicin treatment. Although NPE® did not alter pump gene expression, it was able to reduce pump activity, thus allowing the chemotherapeutic agent to stay inside the cells to exert its full anticancer activity. CONCLUSION: NPE® might improve chemotherapeutic treatment by re-sensitizing relapsed tumors to anticancer drugs. Fighting MDR represents the key to overcome tumor relapse and improve the overall survival of cancer patients.