Mei-Chu Lo

Structure-based design of novel inhibitors of the MDM2-p53 interaction.

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.

Discovery of AMG 232, a Potent, Selective, and Orally Bioavailable MDM2–p53 Inhibitor in Clinical Development

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).

Rational Design and Binding Mode Duality of MDM2–p53 Inhibitors

Structural analysis of both the MDM2-p53 protein-protein interaction and several small molecules bound to MDM2 led to the design and synthesis of tetrasubstituted morpholinone 10, an MDM2 inhibitor with a biochemical IC50 of 1.0 μM. The cocrystal structure of 10 with MDM2 inspired two independent optimization strategies and resulted in the discovery of morpholinones 16 and 27 possessing distinct binding modes. Both analogues were potent MDM2 inhibitors in biochemical and cellular assays, and morpholinone 27 (IC50 = 0.10 μM) also displayed suitable PK profile for in vivo animal experiments. A pharmacodynamic (PD) experiment in mice implanted with human SJSA-1 tumors showed p21(WAF1) mRNA induction (2.7-fold over vehicle) upon oral dosing of 27 at 300 mg/kg.

Selective and potent morpholinone inhibitors of the MDM2-p53 protein-protein interaction.

We previously reported the discovery of AMG 232, a highly potent and selective piperidinone inhibitor of the MDM2-p53 interaction. Our continued search for potent and diverse analogues led to the discovery of novel morpholinone MDM2 inhibitors. This change to a morpholinone core has a significant impact on both potency and metabolic stability compared to the piperidinone series. Within this morpholinone series, AM-8735 emerged as an inhibitor with remarkable biochemical potency (HTRF IC50 = 0.4 nM) and cellular potency (SJSA-1 EdU IC50 = 25 nM), as well as pharmacokinetic properties. Compound 4 also shows excellent antitumor activity in the SJSA-1 osteosarcoma xenograft model with an ED50 of 41 mg/kg. Lead optimization toward the discovery of this inhibitor as well as key differences between the morpholinone and the piperidinone series will be described herein.

Novel Inhibitors of the MDM2-p53 Interaction Featuring Hydrogen Bond Acceptors as Carboxylic Acid Isosteres.

We previously reported the discovery of potent and selective morpholinone and piperidinone inhibitors of the MDM2-p53 interaction. These inhibitors have in common a carboxylic acid moiety that engages in an electrostatic interaction with MDM2-His96. Our continued search for potent and diverse inhibitors led to the discovery of novel replacements for these acids uncovering new interactions with the MDM2 protein. In particular, using pyridine or thiazole as isosteres of the carboxylic acid moiety resulted in very potent analogues. From these, AM-6761 (4) emerged as a potent inhibitor with remarkable biochemical (HTRF IC50 = 0.1 nM) and cellular potency (SJSA-1 EdU IC50 = 16 nM), as well as favorable pharmacokinetic properties. Compound 4 also shows excellent antitumor activity in the SJSA-1 osteosarcoma xenograft model with an ED50 of 11 mg/kg. Optimization efforts toward the discovery of these inhibitors as well as the new interactions observed with the MDM2 protein are described herein.

Preclinical Evaluation of AMG 925, a FLT3/CDK4 Dual Kinase Inhibitor for Treating Acute Myeloid Leukemia

Acute myeloid leukemia (AML) remains a serious unmet medical need. Despite high remission rates with chemotherapy standard-of-care treatment, the disease eventually relapses in a major proportion of patients. Activating Fms-like tyrosine kinase 3 (FLT3) mutations are found in approximately 30% of patients with AML. Targeting FLT3 receptor tyrosine kinase has shown encouraging results in treating FLT3-mutated AML. Responses, however, are not sustained and acquired resistance has been a clinical challenge. Treatment options to overcome resistance are currently the focus of research. We report here the preclinical evaluation of AMG 925, a potent, selective, and bioavailable FLT3/cyclin-dependent kinase 4 (CDK4) dual kinase inhibitor. AMG 925 inhibited AML xenograft tumor growth by 96% to 99% without significant body weight loss. The antitumor activity of AMG 925 correlated with the inhibition of STAT5 and RB phosphorylation, the pharmacodynamic markers for inhibition of FLT3 and CDK4, respectively. In addition, AMG 925 was also found to inhibit FLT3 mutants (e.g., D835Y) that are resistant to the current FLT3 inhibitors (e.g., AC220 and sorafenib). CDK4 is a cyclin D–dependent kinase that plays an essential central role in regulating cell proliferation in response to external growth signals. A critical role of the CDK4–RB pathway in cancer development has been well established. CDK4-specific inhibitors are being developed for treating RB-positive cancer. AMG 925, which combines inhibition of two kinases essential for proliferation and survival of FLT3-mutated AML cells, may improve and prolong clinical responses. Mol Cancer Ther; 13(4); 880–9. ©2014 AACR.

Discovery of AM-7209, a Potent and Selective 4-Amidobenzoic Acid Inhibitor of the MDM2-p53 Interaction.

Structure-based rational design and extensive structure-activity relationship studies led to the discovery of AMG 232 (1), a potent piperidinone inhibitor of the MDM2-p53 association, which is currently being evaluated in human clinical trials for the treatment of cancer. Further modifications of 1, including replacing the carboxylic acid with a 4-amidobenzoic acid, afforded AM-7209 (25), featuring improved potency (KD from ITC competition was 38 pM, SJSA-1 EdU IC50 = 1.6 nM), remarkable pharmacokinetic properties, and in vivo antitumor activity in both the SJSA-1 osteosarcoma xenograft model (ED50 = 2.6 mg/kg QD) and the HCT-116 colorectal carcinoma xenograft model (ED50 = 10 mg/kg QD). In addition, 25 possesses distinct mechanisms of elimination compared to 1.

Discovery of Potent and Simplified Piperidinone-Based Inhibitors of the MDM2-p53 Interaction.

Continued optimization of the N-substituent in the piperidinone series provided potent piperidinone-pyridine inhibitors 6, 7, 14, and 15 with improved pharmacokinetic properties in rats. Reducing structure complexity of the N-alkyl substituent led to the discovery of 23, a potent and simplified inhibitor of MDM2. Compound 23 exhibits excellent pharmacokinetic properties and substantial in vivo antitumor activity in the SJSA-1 osteosarcoma xenograft mouse model.

Optimization beyond AMG 232: discovery and SAR of sulfonamides on a piperidinone scaffold as potent inhibitors of the MDM2-p53 protein-protein interaction.

We recently reported on the discovery of AMG 232, a potent and selective piperidinone inhibitor of the MDM2-p53 interaction. AMG 232 is being evaluated in human clinical trials for cancer. Continued exploration of the N-alkyl substituent of this series, in an effort to optimize interactions with the MDM2 glycine-58 shelf region, led to the discovery of sulfonamides such as compounds 31 and 38 that have similar potency, hepatocyte stability and rat pharmacokinetic properties to AMG 232.

Abstract 3663: Discovery of sulfonamide-piperidinones as potent inhibitors of the MDM2-p53 protein-protein interaction

The p53 tumor suppressor is controlled by MDM2, which binds p53 and negatively regulates its transcriptional activity and stability. Many tumors overproduce MDM2 to impair p53 function. Therefore, restoration of p53 activity by inhibiting p53-MDM2 binding represents an attractive, novel approach to cancer therapy. We previously reported the discovery of AM-8553, a potent and selective piperidinone inhibitor of the MDM2-p53 interaction (Rew et al. J. Med. Chem. 2012, 55, 4936). We report here continued optimization of the N-alkyl substituent of this series, focused in particular on a previously underutilized interaction in a shallow cleft on the MDM2 surface that led to the discovery of a variety of extremely potent sulfonamides such as 14 with an IC50 of 5.3 nM in the cell proliferation assay. The compound 14 interacts specifically with the p53-binding pocket of MDM2 and releases the p53 protein from negative control. Treatment of cancer cells expressing wild-type p53 with sulfonamide 14 stabilizes p53 and activates the p53 pathway, leading to cell cycle arrest and apoptosis. The compound 14 showed excellent efficacy and caused tumor regression in the SJSA-1 tumor xenograft model. Citation Format: Zhihong Li, Jiasheng Fu, Yosup Rew, Michael W. Gribble, Jude Canon, Ada Chen, John Eksterowicz, Xin Huang, Lixia Jin, Mei-Chu Lo, Lawrence R. McGee, Tao Osgood, Anne Y. Saiki, Paul Shaffer, Daqing Sun, Sarah Wortman, Qiuping Ye, Dongyin Yu, Xiaoning Zhao, Jing Zhou, Jonathan D. Oliner, Steve H. Olson, Julio C. Medina. Discovery of sulfonamide-piperidinones as potent inhibitors of the MDM2-p53 protein-protein interaction. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3663. doi:10.1158/1538-7445.AM2015-3663