Novel half-sandwich rhodium(III) and iridium(III) photosensitizers for dual chemo- and photodynamic therapy

Background and objective: Photodynamic therapy has emerged as a promising treatment for cancer and other malignancies. Design of photosensitizers with two different action mechanisms may be an essential strategy for the improvement of the efficacy of phototherapeutic drugs. The objective of this study was to evaluate the anticancer photo- and chemocytotoxic effects of the novel half-sandwich rhodium(III) and iridium(III) photosensitizers. Materials and methods: A series of novel half-sandwich Cp*-Rh(III) and Cp*-Ir(III) complexes containing 9-anthraldehyde thiosemicarbazones, (Cp*)M(L)Cl (M = Rh or Ir, L = 9-anthraldehyde thiosemicarbazones), were compared for cell uptake and photo- and chemocytotoxic effects against human prostate carcinoma (PC3) and human ovarian carcinoma (SKOV3) cell lines. Results: Cp*-Ir(III) complexes, (Cp*)Ir(L)Cl, showed remarkable phototoxic behavior against human ovarian adenocarcinoma SKOV3 cells (IC50 = 2.7 and 2.3 mu M, respectively, lambda(irr) > 400 nm), as well as the 7.4 and 5.3-fold lower toxicity in the dark, implying possibility of dual action as chemo- and phototherapeutic agents. Conclusion: The complexes, which present a synergistic effect with good properties of both the Cp*-Rh(III) and Cp*-Ir(III) chemotherapeutic effect and the anthracene photodynamic therapy efficiency, show great potential as a new generation of light activated dual-action anticancer agents for photodynamic therapy.