Mode of photoexcited C60 fullerene involvement in potentiating cisplatin toxicity against drug-resistant L1210 cells

Introduction: C-60 fullerene has received great attention as a candidate for biomedical applications. Due to unique structure and properties, C-60 fullerene nanoparticles are supposed to be useful in drug delivery, photodynamic therapy (PDT) of cancer, and reversion of tumor cells' multidrug resistance. The aim of this study was to elucidate the possible molecular mechanisms involved in photoexcited C-60 fullerene-dependent enhancement of cisplatin toxicity against leukemic cells resistant to cisplatin. Methods: Stable homogeneous pristine C-60 fullerene queous colloid solution (10(-4)M, purity 99.5%) was used in the study. The photoactivation of C-60 fullerene accumulated by L1210R cells was done by irradiation in microplates with light-emitting diode lamp (420-700 nm light, 100 mW.cm(2)). Cells were further incubated with the addition of Cis-Pt to a final concentration of 1 mu g/mL. Activation of p38 MAPK was visualized by Western blot analysis. blow cytometry was used for the estimation of cells distribution on cell cycle. Mitochondrial membrane potential (Delta psi(m)) was estimated with the use of fluorescent potential-sensitive probe TMRE (Tetra methyl rho damine Ethyl Ester). Results: Cis-Pt applied alone at 1 mu g/mL concentration failed to affect mitochondrial membrane potential in L1210R cells or cell cycle distribution as compared with untreated cells. Activation of ROS-sensitive proapoptotic p38 kinase and enhanced content of cells in subG1 phase were detected after irradiation of L1210R cells treated with 10(-5)M C-60 fullerene. Combined treatment with photoexcited C-60 fullerene and Cis-Pt was followed by the dissipation of Delta psi(m) in at early-term period, blockage of cell transition into S phase, and considerable accumulation of cells in proapoptotic subG1 phase at prolonged incubation. Conclusion: The effect of the synergic cytotoxic activity of both agents allowed to suppose that photoexcited C-60 fullerene promoted Cis-Pt accumulation in leukemic cells resistant to Cis-Pt. The data obtained could be useful for the development of new approaches to overcome drug-resistance of leukemic cells.