Chelerythrine exerts its anticancer activity by stabilizing G-quadruplex structure as well as by inhibition of protein kinase C. The RT-PCR experiment in combination with luciferase assay showed that Chelerythrine treatment to MCF7 breast cancer cells highly down regulated the transcript level of VEGFA, BCL2 and KRAS genes, suggesting that arresting of promoter G-quadruplex structures resulting the repression of transcription of these genes at nanomolar level. The gene discussed is KRAS; the disease is breast cancer.