Alkylating benzamides with melanoma cytotoxicity

Radioiodinated N-(2-(diethylamino)ethyl)benzamides have recently been discovered as selective agents for melanotic melanoma and are used for scintigraphic imaging in nuclear medicine. Owing to the high binding capacity, benzamide derivatives conjugated with alkylating cytostatics were synthesized and tested for their potential for targeted drug delivery. Conjugates of chlorambucil with procainamide (1), diethylaminoethylamine (2) and 2-pyrrolidin-1-yl-ethylamine (3), as well as 4-(bis(2-chloroethyl)amino)- (6,7) and 4-(N,N-diethyltriazeno)-substituted (8-10) benzamides, were synthesized. Cell uptake studies with B16 melanoma cells revealed high uptake of radioiodinated 1 and 2, while radiolabelled chlorambucil was found to lack this characteristic. These results were confirmed by biodistribution studies in a mouse melanoma model. Viability measurements revealed that all chlorambucil-benzamide derivatives showed higher toxicity against B16 melanoma and SK-MEL-28 cells than did the parent chlorambucil itself, and that the triazene derivatives were more potent than dacarbazine, which is currently used as a standard cytostatic drug in melanoma therapy. Of all the compounds tested in this series, the triazenes 9 and 10 showed the most promising targeting effect. The toxicity of these compounds against hepatoma cells (MH3924A) and, to a lesser extent, against mouse fibroblast (NIH 3T3) and cervix carcinoma (HeLa) cells was also enhanced, but they were not as toxic as dacarbazine (HeLa). These findings support the concept of a selective, benzamide-mediated in vivo delivery of cytostatics in melanoma cells, leading to enhanced efficacy.