Benjamin Fisher

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).

An expeditious synthesis of the MDM2-p53 inhibitor AM-8553.

The development of the structurally complex MDM2/p53 inhibitor AM-8553 was impeded by the low yield of the initial synthesis. A second generation synthesis is described that features a Noyori dynamic kinetic resolution, a highly diastereoselective allylation, and a novel oxazoline-assisted piperidinone forming reaction to provide AM-8553 in 35.6% yield and 11 steps.

Discovery and in Vivo Evaluation of the Potent and Selective PI3Kδ Inhibitors 2-((1S)-1-((6-Amino-5-cyano-4-pyrimidinyl)amino)ethyl)-6-fluoro-N-methyl-3-(2-pyridinyl)-4-quinolinecarboxamide (AM-0687) and 2-((1S)-1-((6-Amino-5-cyano-4-pyrimidinyl)amino)ethyl)-5-fluoro-N-methyl-3-(2-pyridinyl)-4-quinolinecarboxamide (AM-1430)

Optimization of the potency and pharmacokinetic profile of 2,3,4-trisubstituted quinoline, 4, led to the discovery of two potent, selective, and orally bioavailable PI3Kδ inhibitors, 6a (AM-0687) and 7 (AM-1430). On the basis of their improved profile, these analogs were selected for in vivo pharmacodynamic (PD) and efficacy experiments in animal models of inflammation. The in vivo PD studies, which were carried out in a mouse pAKT inhibition animal model, confirmed the observed potency of 6a and 7 in biochemical and cellular assays. Efficacy experiments in a keyhole limpet hemocyanin model in rats demonstrated that administration of either 6a or 7 resulted in a strong dose-dependent reduction of IgG and IgM specific antibodies. The excellent in vitro and in vivo profiles of these analogs make them suitable for further development.

Abstract 2351: CDK4/FLT3 dual inhibitors as potential therapeutics for acute myeloid leukemia.

CDK4 is a cyclin D dependent kinase that promotes cell cycle progression in a broad range of tumor types by phosphorylating the tumor suppressor retinoblastoma protein (Rb) and releasing transcription factor E2F. Critical involvement of the cyclin D-CDK4-Rb pathway in carcinogenesis is strongly supported by a large amount of genetic evidence. In addition, promoter methylation with consequent silencing of expression of the CDK4 inhibitor, p15, has been reported in 44-60% of acute myeloid leukemia (AML) patients. It is also well established that constitutive activation of the tyrosine kinase FLT3 via mutation contributes to the development of AML, with 30% of AML carrying such activating mutations. FLT3 tyrosine kinase inhibitors used as single agents reduce peripheral blood and bone marrow blasts in only a minority of AML patients, and the effect tends to be transient. This may be due to insufficient FLT3 inhibition, the selection of drug-resistant clones, or the independence of the cell on FLT3 signaling for proliferation and survival. In preclinical models, a synergistic effect of CDK4 inhibition and FLT3 inhibition resulting in increased apoptosis of AML cell lines was reported (Wang et al., Blood, 2007). From a HTS hit through SAR optimization led to AM-5992, a potent and orally bioavailable dual inhibitor of CDK4 and FLT3 including all FLT3 mutants reported to date. AM-5992 inhibits the proliferation of a panel of human tumor cell lines including MDA-MB-435(Rb+), colo-205(Rb+), U937(FLT3WT) and induced cell death in MOLM13(FLT3ITD), MV4-11(FLT3ITD), and even in MOLM13(FLT3ITD, D835Y) which exhibits resistance to a number of FLT3 inhibitors currently under clinical development. In mouse models of leukemia using cells with the FLT3ITD mutation, AM-5992 treatment at 150 mpk qd on days 6-16 after leukemia cell injection significantly reduced the leukemia burden and prolonged survival 11 days over that of vehicle controls. Collectively, these data support the hypothesis that simultaneously inhibition of CDK4 and FLT3 may improve the durability of clinical response in AML; and consequently that this hypothesis should be tested in the clinic. Citation Format: Zhihong Li, Kang Dai, Kathleen Keegan, Ji Ma, Mark Ragains, Jacob Kaizerman, Dustin McMinn, Jiasheng Fu, Benjamin Fisher, Michael Gribble, Lawrence R. McGee, John Eksterowicz, Cong Li, Lingming Liang, Margaret Weidner, Justin Huard, Robert Cho, Timothy Carlson, Grace M. Alba, David Hollenback, John Hill, Darrin Beaupre, Alexander Kamb, Dineli Wickramasinghe, Julio C. Medina. CDK4/FLT3 dual inhibitors as potential therapeutics for acute myeloid leukemia. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2351. doi:10.1158/1538-7445.AM2013-2351