The Effects Of Carotenoids On Multidrug Resistance Of Cancer Cells And Its Mechanism

Aim A selection of carotenoids (β-carotene, crocin, retinoic acid, canthaxanthin, and fucoxanthin) was investigated whether they are substrates of P-gp, and if they can reverse MDR in resistant Caco-2and CEM/ADR5000cells as compared to the sensitive parent cell line CCRF-CEM.Methods The effects of the carotenoids on MDR activity in Caco-2cells were determined by incubating the cells with fluorescent substrates Rho123, calcein-AM, and doxorubicin, which are readily effluxed. The cytotoxicity of carotenoids and chemotherapeutic drugs was investigated using the MTT assay. The combinations of carotenoids with chemotherapeutical drugs were investigated in Caco-2cells.Drug interactions were evaluated by using combination index analysis (CI), isobologram (IB), medium effect equation (r-value), and reversal ratio calculations.Real time RT-PCR was carried out to quantify the mRNA level of MDR1in Caco-2after treatment for48h with40μM of selected carotenoids.Results The carotenoids increased accumulation of these P-gp substrates in a dose-dependent manner indicating that they themselves also function as substrates. Fucoxanthin and canthaxanthin (50-100μM) produced a3-5-fold higher retention of the fluorescent probes than the known competitive inhibitor verapamil. Carotenoids showed a low cytotoxicity in cells with MDR with IC50values between100and200μM. The combination of carotenoids with eight structurally different cytotoxic agents synergistically enhanced their cytotoxicity in Caco-2cells, probably by inhibiting the function of the ABC transporters. For example, fucoxanthin synergistically enhanced the cytotoxicity of5-FU53.37-fold, of vinblastine51.01-fold, and of etoposide12.47-fold. RT-PCR was applied to evaluate the mRNA levels of P-gp in Caco-2cells after treatment with carotenoids. Fucoxanthin and canthaxanthin significantly decreased P-gp levels to12%and24%, respectively as compared to untreated control levels (p<0.001).Conclusion This study implies that carotenoids may be utilised as chemosensitisers, especially as adjuvants in chemotherapy.