Tumor-specific Cytotoxic Activity of 1,2,3,4-Tetrahydroisoquinoline Derivatives against Human Oral Squamous Cell Carcinoma Cell Lines

The tumor-specific cytotoxicity and the type of cell death induced by thirty-eight newly synthesized tetrahydroisoquinoline derivatives in human oral squamous cell carcinoma cell lines were investigated. 6,7-Dimethoxy-3,4-dihydroisoquinolin-2(1H)-yl)(3,4-dimethoxyphenyl) methanone that has bulky substituents (such as 3,4-dimethoxybenzoyl group) (TQ9) and ethyl 2-benzyloxycarbonyl-1,2,3,4-tetrahydroisoquinoline-1-carboxylate that has ethoxycarbonyl group and benzyloxycarbonyl group (TD13) showed the highest tumor-specific cytotoxicity (TS=12.5 and 5.3, respectively). This supports the importance of molecular size for the cytotoxicity induction. TQ9 induced internulceosomal DNA fragmentation and caspase-3 activation only marginally in HL-60 cells, whereas it enhanced the formation of acidic organelles (stained with acridine orange) without induction of DNA fragmentation or caspase-3 activation in human squamous cell carcinoma cell lines (HSC-2, HSC-4), suggesting the induction of autophagy in the latter cells.