Novel 4,5,6,7-tetrahydropyrazolo[1,5-a]pyridine fused chlorins as very active photodynamic agents for melanoma cells.

The development of new stable 4,5,6,7-tetrahydropyrazolo[1,5-a]pyridine-fused chlorins with high absorption properties at 650 nm, and their impressive photosensitizer ability against melanotic and amelanotic cancer cells is described. Comparison between a diester-substituted chlorin with the corresponding dihydroxymethyl derivative demonstrated that the increased hydrophilicity of the latter is crucial to ensure nanomolar activity against melanoma cells. The new photosensitizer leads to death of human melanoma cells being both apoptosis and necrosis in equal parts involved in the treatment response. The dihydroxymethyl-chlorin was particularly active against human melanocytic melanoma A375 cells, which can be viewed as a solution to overcome the resistance of melanotic melanoma to photodynamic therapy.