Phytochemicals induce apoptosis by modulation of nitric oxide signaling pathway in cervical cancer cells

Nitric Oxide (NO) is produced by NO synthases (NOS) and is a key signaling molecule that regulates tumorigenesis, both aiding and alleviating it. Elevated NO levels are cytotoxic to cancer cells, making NOS an important target for cancer treatment. In the present study, the modulatory effects of the phytochemicals, quercetin, sulforaphane, genistein, and epigallocatechin-3-gallate on NO pathway and apoptosis were shown in HeLa cervical cancer cells.

Fluorescent microscopy and flow cytometry were used to assess apoptosis. A Griess assay was used to quantitatively measure NO, quantitative PCR array was used to assess the expression levels of genes involved in the NO signaling pathway, and immunocytochemistry was used to determine NOS protein expression. The functional association among the modulated genes was evaluated using network biology analysis, gene set enrichment, and KEGG pathway analysis.

Treatment with the phytochemicals elevated NO levels in HeLa cells and modulated various genes involved in nitric oxide biosynthesis, superoxide metabolism, and oxidative stress, including NOS1, NOS2, NOS3, ALOX12, and SOD2, with a concomitant increase in NOS2 and NOS3 protein expression levels; also, the phytochemicals were found to induce apoptosis.

These results suggest that the phytochemical-induced cell death is partially attributed to the activation of the NO pathway and upregulation of pro-oxidant ROS generators. Further experimental studies are required to explore this mechanistic association of NO signaling pathway activation and induction of apoptosis in other types of cancer.