RO5353

RO5353 is an excellent probe to study the in vitro and in vivo biology of p53-MDM2 inhibition. It is potent, has excellent cellular selectivity and robust in-vivo efficacy at a dose (10 mg/kg) that is well-tolerated in mice. Although characterization of the activities of this compound against other proteins (e.g., kinase or other protein family selectivity panels) has not been described, the structural complexity of the probe and the fact that there is rich SAR around this compound reduces the likelihood that off-target activities will be significant, as compared to its potent 7 nM inhibitory activity against p53-MDM2. Moreover, the mode of action as an inhibitor of a highly specific protein-protein interaction also renders confounding off-target activity in intact biological systems fairly unlikely.

RO5353 is potent against MDM2 (7 nM), showing equipotency (7 nM) in antiproliferative assays with multiple WT p53 cells lines (i.e., the expected on-target pharmacology). The average antiproliferative activity in two mutant p53 cell lines was ~7 uM, suggesting a concentration at which off-target pharmacology can be expected. The individual IC₅₀'s for those  two cell lines were not reported, so a top concentration of 7 uM should probably not be approached. It is unknown if RO5353 has any off-target activities <7 uM. RO5353 has moderate PK and achieved complete tumor regression of a human tumor xenograft in male mice at 10 mg/kg oral (with statistically signficant reduction in tumor burden at 3 mg/kg) with chronic dosing over 3-4 weeks. Ortholog potency was not reported, so it is unclear what dose is necessary to study mouse MDM2 pharmacology in vivo. Significant hematologic toxicities were observed in humans with a related molecule, RG7112, which should be considered if chronically dosing animals. Two related compounds, RO8994 and RO2468, show tumor stasis or regression at 3 mg/kg, likely owing to improved DNAUC, so if material supply is a concern for in vivo studies, those two molecules could be considered. The overall balance of reasonable PK, cell potency and the window over general cytotoxicity puts RO5353 as the likely best tool for MDM2.