Phenylalkyl isoselenocyanates vs phenylalkyl isothiocyanates: thiol reactivity and its implications.

Phenylalkyl isoselenocyanate (ISC) compounds were recently designed in our laboratory by incorporating the anticancer element selenium into a panel of phenylalkyl isothiocyanates (ITCs), known to have anticancer properties. A structural activity investigation was carried out to compare the ISC and ITC panels. Cell viability assay and Annexin V staining for apoptosis showed ISC compounds to be more potent in killing A549 lung adenocarcinoma cells. Both ITCs and ISCs were able to deplete reduced glutathione (GSH) in cells, ISCs more rapidly, but ITCs to a greater extent. ISC compounds had a higher rate of reaction to thiol (-SH) groups as determined by pseudo first order kinetics than the corresponding carbon chain length ITC. The equilibrium concentrations of the GSH and protein thiol conjugates did not differ significantly when comparing sulfur to selenium compounds of the same carbon chain length, and did follow the same trend of displaying decreasing reactivity with increasing carbon chain length for both ITCs and ISCs. Furthermore, only ITCs were able to induce cell cycle arrest, suggesting that protein targets inside the cell may differ for the S and Se panels. Finally, the panels were tested for their ability to redox cycle when reacted with GSH to form superoxide and other reactive oxygen species (ROS). ISC compounds showed a much greater ability to redox cycle than corresponding ITCs, and were able to induce higher levels of ROS in A549 cells. Also, the direct pro-apoptotic effects of ISCs and ITCs were inhibited by GSH and potentiated by depletion of intracellular GSH by buthionine sulfoximine. In conclusion, our studies suggest that the redox-cycling capabilities of ISCs and thus generation of higher levels of ROS may be contributing to the increased cytotoxicity of ISC compounds in A549 cells, compared to that of the corresponding ITCs.

Phenylbutyl isoselenocyanate modulates phase I and II enzymes and inhibits 4-(methylnitrosamino)-1-(3-pyridyl)- 1-butanone-induced DNA adducts in mice.

Lung cancer remains one of the most preventable forms of cancer with about 90% of cases attributed to cigarette smoking. Over the years, the development of chemopreventive agents that could inhibit, delay, or reverse the lung carcinogenesis process has been an active field of research, however, without much attainment. Through extensive structure-activity relationship studies, we recently identified a novel agent phenylbutyl isoselenocyanate (ISC-4), designed on the basis of naturally occurring isothiocyanates well known for their lung cancer prevention properties, as a potential chemopreventive agent. In this study, we used A/J mice to evaluate the lung cancer chemopreventive potential of ISC-4. A single intragastric dose of 1.25 µmol ISC-4 resulted in a time-dependent increase of selenium levels in serum, liver, and lung, suggesting that ISC-4 is orally bioavailable, a key requirement for a chemopreventive agent. This dose also resulted in a time-dependent inhibition of microsomal cytochrome P450 (Cyp450) activity and delayed increases in phase II UDP-glucuronyl transferase (Ugt) and glutathione-S-transferase (Gst) activity. ISC-4 was able to induce mRNA expression of Cyp, Ugt, and Gst enzyme isoforms in liver, but in lung, it inhibited Cyp isoforms while inducing Ugt and Gst isoforms. In addition, ISC-4 effectively inhibited methyl-DNA adduct formation in mice fed diet supplemented with ISC-4 for two weeks and then treated with the tobacco procarcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone. These results suggest that ISC-4 is a strong candidate for development as a chemopreventive agent.

Development of novel naphthalimide derivatives and their evaluation as potential melanoma therapeutics.

Synthesis and anti-melanoma activity of various naphthalimide analogs, rationally modified by introducing isothiocyanate (ITC) and thiourea (TU) functionalities, found in well-known anti-cancer agents, is described. The structure-activity relationship comparison of the novel agents in inhibiting cancer cell growth was evaluated in various melanoma cell lines. Both ITC and TU analogs effectively inhibited cell viability and induced apoptosis in various human melanoma cells. Nitro substitution and increase in alkyl chain length, in general, enhanced the apoptotic activity of ITC derivatives. All the new compounds were well tolerated when injected intraperitoneal (i.p.) in mice at effective doses at which both the ITC and TU derivatives inhibited melanoma tumor growth in mice following i.p. xenograft. The nitro substituted naphthalimide-ITC derivative 3d was found to be the most effective in inducing apoptosis, and in inhibiting melanoma cell and tumor growth.