Trifluoromethylated carboline compounds targeting DNA: Synthesis, binding and anti-proliferative effects on human cancer cell lines.

Three sets of carboline derived compounds were prepared by Pictet-Spengler cyclization. These tetrahydro β- and γ-carbolines have CF3 group with an additional amino alkyl chains (α- or δ-position) and guanidine alkyl chains (α-position), of varying length. Structure-activity relationship of these molecules with calf thymus DNA was emphasized by fluorescence, ITC, FTIR and viscosity. Binding with DNA resulted in dramatic enhancement and quenching in the fluorescence emission. Gamma-carboline analogs showed maximum DNA binding followed by beta-carboline compounds with amino alkyl chain and least with guanidine alkyl chain compounds. It decreased with increasing chain length. The bindings were entropically driven being more with guanidine alkyl chain analogs. Site preference and mode of binding with partial intercalation and external binding was supported by FTIR and viscosity. Cytotoxic potencies of the compounds were tested on seven different cancer cell lines. The smallest alkyl chain analog attached to gamma position, Comp3, showed maximum cytotoxicity with GI50 6.2 µM, against HCT-116 causing apoptosis, followed by the guanidine alkyl chain compounds, but amino alkyl chain compounds to beta position showed poor cytotoxicity. These results may be of prospective use in a framework to design novel carboline derivatives as antitumor drugs for improved therapeutic applications in future.