Fisetin was previously reported to induce the p53-mediated apoptotic pathway in human renal carcinoma cells . Yet, the underlying mechanism and direct connection to SUMO1 has not been described to date. Numerous studies indicate that sumoylation is elevated in tumor cells in comparison to normal cells . In colon cancer patients, it was shown that the combined elevated expression of SUMO1 and p53 leads to increased metastasis, and moreover, p53 is predominantly sumoylated in colon cancer cell lines . Fisetin has also been shown to exert its anti-cancer effect by inducing cell cycle arrest and apoptosis in bladder cancer cells through activation of p53 . Our study demonstrates that fisetin treatment inhibits p53 sumoylation, suggesting a molecular mechanism underlying fisetin action. It was previously shown that p53 sumoylation promotes nuclear export and thus inactivation of p53-mediated apoptosis . Overall, our findings suggest a potential use for fisetin and its mimetics as novel p53 sumoylation inhibitors in cancer treatment.