Relationship between Electrochemical Parameters, Cytotoxicity Data against Cancer Cells of 3-Thio-Substituted Nor-Beta-Lapachone Derivatives. Implications for Cancer Therapy

Electrochemical methods are powerful in the characterization and design of redox-modulating agents. We, herein, report the electrochemical investigation, in aprotic medium, of eleven synthetic 3-thio-substituted-nor-beta-lapachones, along with the determination of cytotoxic activity and correspondent selectivity index, against several cancer cell lines and one normal cell. Four of the quinones are novel compounds. The redox behavior is representative of two independent systems: the easy reduction of the quinone moiety and, at far more negative potential, the reductive cleavage of the C-S-C bonding; and the anodic part controlled by the oxidation of the sulfur moiety. The compounds have shown relevant cytotoxic activity, with emphasis on 3-phenyl-thio-2,2-dimethyl-2,3-dihydronaphtho[1,2-b]furan-4,5-dione (compound 2), which mechanism of molecular action was shown to be related to reactive oxygen species (ROS) release. Despite the absence of a linear correlation, there is a trend: the majority of the thionaphthoquinones, with values of first wave reduction potential, less negative than -0.65 V, were active. The less electrophilic compound (3-(cyclohexylthio)-2,2-dimethyl-2,3-dihydronaphtho[1,2-b]furan-4,5-dione, cyclohexyl derivative) is also the less cytotoxic toward cancer cells. Agents containing chalcogens and quinones can be used to attack entities with a disturbed redox balance.