Effect of a photoactivated rhodium complex in melanoma

cis-Dichlorobis (3,4,7,8-tetramethyl-1,10-phenanthroline) rhodium(III) chloride (OCTBP) is an octahedral complex that has been shown to react with nucleic acids when irradiated with light. Earlier studies on its phototoxicity toward human esophageal, bladder, pancreas, and colon cancer cells have been extended to in-vitro and in-vivo evaluation of its effect on malignant melanoma cells using the 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium proliferation assay and xenograft model of melanoma. Tumor volume and the percentage of tumor growth delay were used to assess the antitumor effect of light-activated OCTBP. Terminal deoxynucleotidyl transferase dUTP nick-end labeling assays and immunohistochemistry were also performed on tumor tissue samples. Photoactivated OCTBP was found to inhibit melanoma cell growth by 40% at 100 μmol/l concentration. Phototherapy with OCTBP was most efficacious with optimal percentage treated/control values observed early in the course of the experiment. At the end of the experiment (60 days), there was a 50% tumor inhibition compared with vehicle or drug controls. OCTBP treatment resulted in a tumor growth delay of 16 days (tumor growth of 24%) compared with the untreated control, whereas cisplatin resulted in 10 days tumor growth delay. This antitumor activity was found to be closely associated with the induction of apoptosis. The use of photoactivated OCTBP as an adjuvant therapy for the treatment of melanoma may provide a new targeted therapy to prevent progression of this disease.