Abstract
Nitric oxide (NO) is a ubiquitous gas that can be endogenously formed to play several physiological roles in the body. These roles could be potentiated for therapeutic use; however, because of the volatility of the NO, a donor must be created to stabilise the molecule. Many donors have been created but faced several limitations, such as the lack of biostability, non-specific targeting, and the quick diffusion rate of NO itself. Based on the structure of s-nitrosothiols (RSNOs), tert-dodecane S-nitrosothiol (tDodSNO) was created to overcome these limitations. With increased hydrophobicity, photosensitivity, and improved efficacy compared to other RSNOs, tDodSNO has excellent potential in the future of NO therapeutics. Additionally, the cytotoxicity effect of NO donors, commonly seen in NO overproduction, makes tDodSNO a prominent candidate in photodynamic therapy. However, what is still unknown about this thiol-based donor is what happens to the thiyl radical once NO is liberated. Therefore, the current study investigates the significance of the thiyl radical by comparing free tDodSNO to encapsulated SMA-tDodSNO. Assuming the thiyl radical remains trapped, any discrepancy in efficacy could be attributed to the thiyl radical. Previous research has also shown that tDodSNO and SMA-tDodSNO share similar stability and NO release kinetics and that, when photoactivated, significantly reduced the half-life of the donor. Therefore, as a secondary objective, the half-lives of tDodSNO and SMA-tDodSNO at increasing intensity of photoactivation were determined and correlated to donor efficacy. NONOates were used as a comparison due to their well-established half-lives and metabolism-free mechanism of NO release. The results from this study showed that SMA-tDodSNO has a significantly faster half-life when compared to tDodSNO, shown to be significantly more cytotoxic in A549 lung cancer cells, with a marked increase in reactive nitrogen species (RNS) accumulation, as well as indicative effects on mitochondrial membrane potential. None of these was observed in tDodSNO. The study also showed that the half-life of a NO donor does not dictate the efficacy of the donor with DEA NONOate producing similar cytotoxicity and RNS generation and spermine NONOate despite their significant difference in half-lives.