The p53 tumor suppressor induces cell growth arrest and apoptosis in response to DNA damage or stress. And inactivation of the p53 pathway plays an indispensable role in tumor survival. Approximately p53 mutations resulting in loss of its function account for 50% human cancers. And the wild-type p53, present in the remaining 50% of malignancies, is downregulated by the MDM2 oncoprotein via a direct protein-protein interaction. Subsequently, MDM2 inhibits p53 activity by blocking p53 mediated transactivation, inducing nuclear export of p53. Additionally, it acts as E3 ubiquitin ligase targeting both itself and p53 for the degradation by the 26S proteasome. Since all of these mechanisms can be blocked by neutralizing the MDM2-p53 interaction, MDM2-p53 interaction inhibitors have been considered as a promising strategy to reactivate the p53 pathway in wild-type p53 tumors over the last two decades.
Among the reported MDM2-p53 interaction inhibitors, AMG 232 is a potent, selective and orally available inhibitor of p53-MDM2 interaction, with an IC50 of 0.6 nM. AMG 232 binds to MDM2 with a Kd of 0.045 nM.
In vitro, AMG 232 (10 μM) induces p53 signaling and inhibits tumor cell proliferation in three p53 wild-type tumor cell lines (SJSA-1, HCT116, and ACHN). AMG 232 also potently inhibits proliferation of non-MDM2-amplified HCT116 colorectal cells in the BrdU assay (IC50=10 nM).
In vivo, AMG 232 (10, 25, 75 mg/kg, p.o.) activates p53 pathway activity in vivo. AMG 232 (100 mg/kg, p.o.) results in 86% TGI compared with control, and the ED50 is 31 mg/kg in the HCT116 colorectal cancer model (KRAS mutant), and results in 97% TGI, with an ED50 of 18 mg/kg in an A375sq2 BRAF-mutant melanoma model. Additionally, it exhibits low clearance and moderate to high oral bioavailability in mice, rats and monkeys (>42%), but high clearance and low oral exposure in dogs (18%). AMG 232 displays robust tumor growth inhibition compared to the vehicle, with an ED50 of 9.1 mg/kg q.d. AMG 232 causes a dose-dependent tumor growth inhibition with an ED50 of 16 mg/kg.