Naphthalimide derivatives such as mitonafide, a topoisomerase II inhibitor, have shown antitumor activity both in preclinical studies and in phase I and phase II clinical trials. However, it suffers from severe toxicity issues, especially central nervous system (CNS) toxicity. We have recently reported promising naphthalimide analogs designed by incorporating functional groups such as a isothiocyanate (ITC) group which is present in chemicals found in cruciferous vegetables, in place of N, N-dimethyl group in mitonafide. Some of these agents effectively induced apoptosis in melanoma cells and inhibited cell proliferation, and inhibited melanoma tumor growth by ∼60% without any apparent systemic toxicity issues. The ITC group was incorporated in the structure in an attempt to lower the toxicity associated with mitonafide and also because this functionality has been shown to block PI3K/Akt pathway which is activated in majority of cancer types; Akt3 is activated in 70% of sporadic melanomas. The idea was to generate a compound capable of inhibiting not only topoisomerase II similar to mitonafide but also PI3K kinase. In order to evaluate the underlying mechanism of action, we first evaluated topoisomerase-II inhibitory activity of agents relative to mitonafide to check if the new agents retained this property. Relaxation activity of DNA topoisomerase II was determined by measuring the conversion of supercoiled pBR322 plasmid DNA to its relaxed form. Our results indicate that the ITC analogs, NNITC-2 and NITC-6, exhibited significant inhibition for DNA-topoisomerase II similar to mitonafide. Interestingly, corresponding isoselenocyanate (ISC) analog NISC-6 was less effective compared to NITC-6 as a topoisomerase II inhibitor; NNISC-2 on the other hand was equally good as NNITC-2. Furthermore, to test our hypothesis that the addition of ITC group into the structure would make it capable of inhibiting PI3K/Akt pathway, we examined the ability of naphthalimide derivatives to inhibit the total cellular content of human Akt pathway proteins, by Western blot analysis using polyclonal antibodies, in human melanoma cancer cells (UACC903). UACC903 cells treated with ITC derivatives at 0.5, 1 and 5 μM, showed a rapid decrease in Akt pathway proteins level in a dose-dependent manner. In comparison, ISC analogs were less effective. Detailed results of these investigations will be presented.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1759. doi:1538-7445.AM2012-1759