RITA p53 Activator

Inducer of DNA cross-links, not a DNA intercalator.

RITA shows a highly selective pattern of differential cytotoxic activity in the tumor cell lines, due to cellular accumulation to the cytosolic (S100) fraction. This compound also inhibits the growth of other renal cell lines including ACHN and UO-31 with IC50 of 13 μM and 37 μM, respectively. [1] It (10 nM) causes cell cycle arrest with accumulation of cells at the G2-M phase and induces DNA fragmentation and apoptosis at 100 nM, both with evaluated p53 protein levels. This chemical (30 nM) also induces both DNA-protein and DNA-DNA cross-links in A498 cells. Meanwhile it has no effects on top1-mediated relaxation of supercoiled SV40 DNA. [2] It significantly suppresses the growth of HCT116 cells (97%) but only slightly inhibits the growth of HCT116 TP53^-/- cells (13%). This compound is much more efficient at growth suppression in wild-type p53-expressing tumor cell lines than in cell lines lacking p53 and those expressing mutant p53. It binds full-length p53 but not glutathione S-transferase (GST) protein or HDM-2 (a key regulator of p53 is strongly supported by the rescue of embryonic lethality of MDM2). This chemical blocks p53−HDM-2 interaction and p53 ubiquitination. It substantially decreases the amount of HDM-2 that is co-precipitated with p53, although both proteins are upregulated. This compound prevents interactions between the purified GST-p53 and 6XHis-tagged His-HDM-2 proteins. [3] It is shown to induce apoptosis by promoting p53Ser46 phosphorylation. [4] This chemical induces activation of p53 in conjunction with up-regulation of phosphorylated ASK-1, MKK-4 and c-Jun. It induces the activation of JNK signaling. [5] But On the contrary, another results by nuclear magnetic resonance (NMR) show that it does not block the formation of the complex between p53 (residues 1-312) and the N-terminal p53-binding domain of MDM2 (residues 1-118), which is highly probable that the binding of this compound requires native conformation of p53. [6]

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 this compound, 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, it shows strong antitumor activity. Five 1 mg/kg injections of this chemical 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 it than in control untreated mice. This compound inhibits the tumor growth in a wild-type p53−dependent manner. [3]