Tao Osgood

Abstract The prosurvival BCL2 family member MCL1 is frequently dysregulated in cancer. To overcome the significant challenges associated with inhibition of MCL1 protein–protein interactions, we rigorously applied small-molecule conformational restriction, which culminated in the discovery of AMG 176, the first selective MCL1 inhibitor to be studied in humans. We demonstrate that MCL1 inhibition induces a rapid and committed step toward apoptosis in subsets of hematologic cancer cell lines, tumor xenograft models, and primary patient samples. With the use of a human MCL1 knock-in mouse, we demonstrate that MCL1 inhibition at active doses of AMG 176 is tolerated and correlates with clear pharmacodynamic effects, demonstrated by reductions in B cells, monocytes, and neutrophils. Furthermore, the combination of AMG 176 and venetoclax is synergistic in acute myeloid leukemia (AML) tumor models and in primary patient samples at tolerated doses. These results highlight the therapeutic promise of AMG 176 and the potential for combinations with other BH3 mimetics. Significance: AMG 176 is a potent, selective, and orally bioavailable MCL1 inhibitor that induces a rapid commitment to apoptosis in models of hematologic malignancies. The synergistic combination of AMG 176 and venetoclax demonstrates robust activity in models of AML at tolerated doses, highlighting the promise of BH3-mimetic combinations in hematologic cancers. See related commentary by Leber et al., p. 1511. This article is highlighted in the In This Issue feature, p. 1494

We recently reported the discovery of AM-8553 (1), a potent and selective piperidinone inhibitor of the MDM2–p53 interaction. Continued research investigation of the N-alkyl substituent of this series, focused in particular on a previously underutilized interaction in a shallow cleft on the MDM2 surface, led to the discovery of a one-carbon tethered sulfone which gave rise to substantial improvements in biochemical and cellular potency. Further investigation produced AMG 232 (2), which is currently being evaluated in human clinical trials for the treatment of cancer. Compound 2 is an extremely potent MDM2 inhibitor (SPR KD = 0.045 nM, SJSA-1 EdU IC50 = 9.1 nM), with remarkable pharmacokinetic properties and in vivo antitumor activity in the SJSA-1 osteosarcoma xenograft model (ED50 = 9.1 mg/kg).

Structure-based rational design led to the discovery of novel inhibitors of the MDM2-p53 protein-protein interaction. The affinity of these compounds for MDM2 was improved through conformational control of both the piperidinone ring and the appended N-alkyl substituent. Optimization afforded 29 (AM-8553), a potent and selective MDM2 inhibitor with excellent pharmacokinetic properties and in vivo efficacy.

p53 is a critical tumor suppressor and is the most frequently inactivated gene in human cancer. Inhibition of the interaction of p53 with its negative regulator MDM2 represents a promising clinical strategy to treat p53 wild-type tumors. AMG 232 is a potential best-in-class inhibitor of the MDM2-p53 interaction and is currently in clinical trials. We characterized the activity of AMG 232 and its effect on p53 signaling in several preclinical tumor models. AMG 232 binds the MDM2 protein with picomolar affinity and robustly induces p53 activity, leading to cell-cycle arrest and inhibition of tumor cell proliferation. AMG 232 treatment inhibited the in vivo growth of several tumor xenografts and led to complete and durable regression of MDM2-amplified SJSA-1 tumors via growth arrest and induction of apoptosis. Therapeutic combination studies of AMG 232 with chemotherapies that induce DNA damage and p53 activity resulted in significantly superior antitumor efficacy and regression, and markedly increased activation of p53 signaling in tumors. These preclinical data support the further evaluation of AMG 232 in clinical trials as both a monotherapy and in combination with standard-of-care cytotoxics.