N-acetylcysteine improves the inhibitory effect of Quercetin-rich onion extract on HT-29 and HCT-116 colorectal cancer migration and invasion through iNOS suppression

As colorectal cancer (CRC) usually presents at an advanced stage, it responds poorly to traditional surgery and chemoradiotherapy. Reactive oxygen species (ROSs) are a critical factor in cancer progression. Quercetin, a bioflavonoid derived from onion peel extract, provides great anti-oxidant and anti-cancer potential. Therefore, quercetin in combination with N-Acetylcysteine (NAC), a well-known anti-oxidant and adjuvant agent in cancer-chemotherapeutic drugs, was considered as a way of increasing treatment efficacy. Thus, this study aimed to evaluate the improvement effect of quercetin in combination with NAC in human CRC (HT-29 and HCT-116) cell progression, migration and invasion. Firstly, the effects of quercetin, NAC, and the combination of quercetin and NAC on cellular oxidants and glutathione levels were evaluated. Cell viability, anti-migrative activity and invasive activity were determined by MTT, wound healing, and Matrigel invasion tests, respectively. Then, the proteins involved in cell migration, invasion, and cellular oxidants were investigated. Moreover, the gene expression and overall survival were further validated by the GEPIA2 database. The results reveal that the combination was most effective in decreasing cellular oxidants and increasing glutathione levels, while there was a significant decrease in cancer cell migration and invasion involved in the suppression of iNOS, ICAM-1, and MMP-2 proteins. Furthermore, bioinformatic analysis verified that iNOS, ICAM-1, and MMP-2 were highly expressed in CRC tissue and also associated with a poor prognosis. This study demonstrated that Quercetin has higher efficacy when used in combination with NAC, representing a potential combination agent for anti-cancer drug development.