Abstract 4556: NOSH-aspirin is a potent inhibitor of colon cancer cell growth: effects of positional isomerism.

Abstract Background: We recently reported the synthesis of NOSH-aspirin, a novel hybrid capable of releasing both nitric oxide (NO) and hydrogen sulfide (H2S). In NOSH-aspirin, the two moieties that release NO and H2S are covalently linked at the 1, 2 positions of acetyl salicylic acid, ie ortho-NOSH-aspirin. Here we compared the cell growth inhibitory properties of ortho-NOSH-aspirin to that of the 1,3 (meta-NOSH-aspirin) and the 1,4 (para-NOSH-aspirin) positional isomers. We also incorporated electron donating/withdrawing groups about the bezyl ring in order to evaluate the effect of substitution on stability and biological activity of these novel compounds. Methods: Cell line: HT-29 and HCT 15 human colon adenocarcimoa; Cell growth: MTT; Cell cycle phase distribution: Flow cytometry; Apoptosis: subdiploid (sub-G0/G1) peak in DNA content histograms; Proliferation: PCNA; ROS: measured hydrogen peroxide and super oxide by flow cytometry using DCFDA and DHE dyes. Results: All positional isomers of NOSH-aspirin were potent growth inhibitors of both cell lines. The IC50s for growth inhibition in nM at 24h were, HT-29: ortho-NOSH-ASA (0.04 ± 0.011), meta-NOSH-ASA (0.24 ± 0.11), para-NOSH-ASA (0.46 ± 0.17); significance between the groups were: o vs m P>0.05, o vs p P<0.01, m vs p P>0.05; HCT 15: ortho-NOSH-ASA (0.062 ± 0.006), meta-NOSH-ASA (0.092 ± 0.004), para-NOSH-ASA (0.37 ± 0.04); significance between the groups were: o vs m P>0.05, o vs p P<0.001, m vs p P<0.001. Electron donating/withdrawing groups significantly affected these IC50s. All positional isomers qualitatively had similar effects on proliferation, apoptosis, and caused G0/G1 cell cycle arrest in both colon cancer cell lines. The underlying mechanism for these observations appeared to be mediated through generation of intracellular H2O2 and superoxide anions as pretreatment of cells with N-acetylcysteine, partially blocked these effects. Conclusions: Positional isomerism affects the potency of NOSH-aspirin and offers a platform for drug design. Further, NOSH-aspirin merits further evaluation as an anti-cancer agent. Citation Format: Erin K. Eschbach, Andrew C. MacKessack-Leitch, Federica Vannini, Ravinder Kodela, Mitali Chattopadhyay, Khosrow Kashfi. NOSH-aspirin is a potent inhibitor of colon cancer cell growth: effects of positional isomerism. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4556. doi:10.1158/1538-7445.AM2013-4556