NOSH-Aspirin Inhibits Colon Cancer Cell Growth: Effects Of Positional Isomerism

Abstract

Background: NOSH-aspirin, a novel hybrid that releases nitric oxide (NO) and hydrogen sulfide (H2S) was designed to overcome the potential side effects of aspirin. Aim: We compared the cell growth inhibitory properties of ortho-, meta-, and para-NOSH-aspirins. Effects of electron donating/withdrawing groups on the stability and biological activity of these novel compounds were also evaluated. Methods: Cell line: HT-29 (Cyclooxygenase, COX-1 & -2 expressing) and HCT 15 (COX null) 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: The IC50s for growth inhibition in µM 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 P0.05; 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<0.01, 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 ROS, as pretreatment of the cells with N-acetylcysteine, partially blocked these effects. Conclusions: Positional isomerism affects the potency of NOSH-aspirin. The effects appear to be COX independent.