RITA is anti-tumor agent that binds wild-type p53 (Kd = 1.5 nM) preventing p53-MDM2 (HDM2) interaction. Induces p53 accumulation and stimulates apoptosis in tumor cell lines expressing wild-type p53 in vitro and in vivo. Inhibits HPV-E6-mediated proteasomal degradation. RITA is well tolerated in mice after intraperitoneal administration, with no observable weight loss at doses up to 10 mg/kg during 1 month. After five injections of 0.1 mg/kg of RITA, the growth of the HCT116 tumors is suppressed by 40%, without apparent effects on the HCT116 TP53-/- tumors. At a dose of 1 or 10 mg/kg, RITA shows strong antitumor activity. Five 1 mg/kg injections of RITA results in a more than twofold decrease in the growth rate of p53-positive xenografts without any effect on p53-null xenografts. HCT116 tumors are 90% smaller in mice treated with 10 mg/kg of RITA than in control untreated mice. RITA inhibits the tumor growth in a wild-type p53−dependent manner.