Role of acidic cell organelles in the higher nonmelanoma retention of melanoma markers based on N-(2-dialkylaminoethyl)benzamides and the cytotoxicity of alkylating benzamides.

Melanoma markers based on both N-(2-dialkylaminoethyl)benzamides and lysosomotropic agents comprise a N-(2-dialkylaminoethyl)aminocarbamoyl pharmacophore, suggesting that benzamides and lysosomotropic probes should show affinity to melanoma and acidic cell organelles. We prepared novel fluorescent N-(2-dialkylaminoethyl)benzamides to prove this presumption. Lysosomotropic probes showed a melanin affinity comparable to benzamides. Lysosomal markers and benzamides colocalized in acidic organelles. Various nonmelanoma cell lines showed equal benzamide uptake and retention compared with melanoma cells. In nonmelanoma cells the amount of retained benzamides correlates with the number of acidic cell organelles. Benzamides almost completely failed to accumulate in melanoma cells with neutralized acidic organelles but normal melanin content. In melanoma retention of benzamides, acidic cell organelles are the main determinant. N-(2-dialkylaminoethyl)benzamides are lysosomotropic probes with high accumulation in nonmelanoma tumors with many acidic cell organelles. Alkylating benzamides were reported previously to show a melanoma unselective, in general enhanced cytotoxicity. Alkylating benzamides can act as lysosomotropic detergents or as DNA alkylators. The ability of alkylating benzamides to disrupt the membrane of lysosomes and cause liberation of lysosomal-trapped fluorescent dyes was demonstrated by fluorescence microscopy. Whether they act as an alkylating agent or a lysosomotropic detergent in a specific cell line is dependent on the amount of acidic cell organelles. In cell lines with small amounts of acidic cell organelles alkylating benzamides act as alkylating agents, whereas in cell lines with many acidic cell organelles they act as lysosomotropic detergents. In cell lines with high amounts of acidic cell organelles they do not reach the nucleus.