Yujun Zhao

Small-Molecule Inhibitors of the MDM2–p53 Protein–Protein Interaction (MDM2 Inhibitors) in Clinical Trials for Cancer Treatment

Design of small-molecule inhibitors (MDM2 inhibitors) to block the MDM2–p53 protein–protein interaction has been pursued as a new cancer therapeutic strategy. In recent years, potent, selective, and efficacious MDM2 inhibitors have been successfully obtained and seven such compounds have been advanced into early phase clinical trials for the treatment of human cancers. Here, we review the design, synthesis, properties, preclinical, and clinical studies of these clinical-stage MDM2 inhibitors.

A potent small-molecule inhibitor of the MDM2-p53 interaction (MI-888) achieved complete and durable tumor regression in mice.

We previously reported the discovery of a class of spirooxindoles as potent and selective small-molecule inhibitors of the MDM2-p53 interaction (MDM2 inhibitors). We report herein our efforts to improve their pharmacokinetic properties and in vivo antitumor activity. Our efforts led to the identification of 9 (MI-888) as a potent MDM2 inhibitor (Ki = 0.44 nM) with a superior pharmacokinetic profile and enhanced in vivo efficacy. Compound 9 is capable of achieving rapid, complete, and durable tumor regression in two types of xenograft models of human cancer with oral administration and represents the most potent and efficacious MDM2 inhibitor reported to date.

Diastereomeric spirooxindoles as highly potent and efficacious MDM2 inhibitors.

Small-molecule inhibitors that block the MDM2-p53 protein-protein interaction (MDM2 inhibitors) are being intensely pursued as a new therapeutic strategy for cancer treatment. We previously published a series of spirooxindole-containing compounds as a new class of MDM2 small-molecule inhibitors. We report herein a reversible ring-opening-cyclization reaction for some of these spirooxindoles, which affords four diastereomers from a single compound. Our biochemical binding data showed that the stereochemistry in this class of compounds has a major effect on their binding affinities to MDM2, with >100-fold difference between the most potent and the least potent stereoisomers. Our study has led to the identification of a set of highly potent MDM2 inhibitors with a stereochemistry that is different from that of our previously reported compounds. The most potent compound (MI-888) binds to MDM2 with a Ki value of 0.44 nM and achieves complete and long-lasting tumor regression in an animal model of human cancer.

SAR405838: An Optimized Inhibitor of MDM2–p53 Interaction That Induces Complete and Durable Tumor Regression

Blocking the oncoprotein murine double minute 2 (MDM2)-p53 protein-protein interaction has long been considered to offer a broad cancer therapeutic strategy, despite the potential risks of selecting tumors harboring p53 mutations that escape MDM2 control. In this study, we report a novel small-molecule inhibitor of the MDM2-p53 interaction, SAR405838 (MI-77301), that has been advanced into phase I clinical trials. SAR405838 binds to MDM2 with K(i) = 0.88 nmol/L and has high specificity over other proteins. A cocrystal structure of the SAR405838:MDM2 complex shows that, in addition to mimicking three key p53 amino acid residues, the inhibitor captures additional interactions not observed in the p53-MDM2 complex and induces refolding of the short, unstructured MDM2 N-terminal region to achieve its high affinity. SAR405838 effectively activates wild-type p53 in vitro and in xenograft tumor tissue of leukemia and solid tumors, leading to p53-dependent cell-cycle arrest and/or apoptosis. At well-tolerated dose schedules, SAR405838 achieves either durable tumor regression or complete tumor growth inhibition in mouse xenograft models of SJSA-1 osteosarcoma, RS4;11 acute leukemia, LNCaP prostate cancer, and HCT-116 colon cancer. Remarkably, a single oral dose of SAR405838 is sufficient to achieve complete tumor regression in the SJSA-1 model. Mechanistically, robust transcriptional upregulation of PUMA induced by SAR405838 results in strong apoptosis in tumor tissue, leading to complete tumor regression. Our findings provide a preclinical basis upon which to evaluate SAR405838 as a therapeutic agent in patients whose tumors retain wild-type p53.

Enantioselective Cationic Polyene Cyclization vs Enantioselective Intramolecular Carbonyl−Ene Reaction

This paper describes highly efficient catalytic enantioselective cationic polyene cyclization and catalytic enantioselective intramolecular carbonyl-ene reaction in good to high yields with high enantioselectivities. The intimate relationship and mechanistic differences between the two enantioselective reactions were studied in detail. In addition, the cyclization products are versatile and useful building blocks for natural products and pharmaceuticals syntheses.

Targeting the MDM2-p53 Protein-Protein Interaction for New Cancer Therapeutics

The p53 tumor suppressor protein is a transcriptional factor that plays a key role in regulation of several cellular processes, including the cell cycle, apoptosis, DNA repair, and angiogenesis. The murine double minute 2 (MDM2) protein is the primary cellular inhibitor of p53, functioning through direct interaction with p53. Design of non-peptide, small-molecule inhibitors that block the MDM2-p53 interaction has been sought as an attractive strategy to activate p53 for the treatment of cancer and other human diseases. In recent years, major advances have been made in the design of small-molecule inhibitors of the MDM2-p53 interaction in recent years, and several compounds have moved into advanced preclinical development or clinical trials. In this chapter, we will highlight these advances in the design and development of MDM2 inhibitors, and discuss lessons learned from these efforts.

Structure-Based Design of γ-Carboline Analogues as Potent and Specific BET Bromodomain Inhibitors.

Small-molecule inhibitors of bromodomain and extra terminal proteins (BET), including BRD2, BRD3, and BRD4 proteins have therapeutic potential for the treatment of human cancers and other diseases and conditions. In this paper, we report the design, synthesis, and evaluation of γ-carboline-containing compounds as a new class of small-molecule BET inhibitors. The most potent inhibitor (compound 18, RX-37) obtained from this study binds to BET bromodomain proteins (BRD2, BRD3, and BRD4) with Ki values of 3.2-24.7 nM and demonstrates high selectivity over other non-BET bromodomain-containing proteins. Compound 18 potently and selectively inhibits cell growth in human acute leukemia cell lines harboring the rearranged mixed lineage leukemia 1 gene. We have determined a cocrystal structure of 18 in complex with BRD4 BD2 at 1.4 Å resolution, which provides a solid structural basis for the compounds high binding affinity and for its further structure-based optimization. Compound 18 represents a promising lead compound for the development of a new class of therapeutics for the treatment of human cancer and other conditions.

Hepatic TRAF2 Regulates Glucose Metabolism Through Enhancing Glucagon Responses

Obesity is associated with intrahepatic inflammation that promotes insulin resistance and type 2 diabetes. Tumor necrosis factor receptor–associated factor (TRAF)2 is a key adaptor molecule that is known to mediate proinflammatory cytokine signaling in immune cells; however, its metabolic function remains unclear. We examined the role of hepatic TRAF2 in the regulation of insulin sensitivity and glucose metabolism. TRAF2 was deleted specifically in hepatocytes using the Cre/loxP system. The mutant mice were fed a high-fat diet (HFD) to induce insulin resistance and hyperglycemia. Hepatic glucose production (HGP) was examined using pyruvate tolerance tests, 2H nuclear magnetic resonance spectroscopy, and in vitro HGP assays. The expression of gluconeogenic genes was measured by quantitative real-time PCR. Insulin sensitivity was analyzed using insulin tolerance tests and insulin-stimulated phosphorylation of insulin receptors and Akt. Glucagon action was examined using glucagon tolerance tests and glucagon-stimulated HGP, cAMP-responsive element–binding (CREB) phosphorylation, and expression of gluconeogenic genes in the liver and primary hepatocytes. Hepatocyte-specific TRAF2 knockout (HKO) mice exhibited normal body weight, blood glucose levels, and insulin sensitivity. Under HFD conditions, blood glucose levels were significantly lower (by >30%) in HKO than in control mice. Both insulin signaling and the hypoglycemic response to insulin were similar between HKO and control mice. In contrast, glucagon signaling and the hyperglycemic response to glucagon were severely impaired in HKO mice. In addition, TRAF2 overexpression significantly increased the ability of glucagon or a cAMP analog to stimulate CREB phosphorylation, gluconeogenic gene expression, and HGP in primary hepatocytes. These results suggest that the hepatic TRAF2 cell autonomously promotes hepatic gluconeogenesis by enhancing the hyperglycemic response to glucagon and other factors that increase cAMP levels, thus contributing to hyperglycemia in obesity.

Discovery of a Small-Molecule Degrader of Bromodomain and Extra-Terminal (BET) Proteins with Picomolar Cellular Potencies and Capable of Achieving Tumor Regression

The bromodomain and extra-terminal (BET) family proteins, consisting of BRD2, BRD3, BRD4, and testis-specific BRDT members, are epigenetic “readers” and play a key role in the regulation of gene transcription. BET proteins are considered to be attractive therapeutic targets for cancer and other human diseases. Recently, heterobifunctional small-molecule BET degraders have been designed based upon the proteolysis targeting chimera (PROTAC) concept to induce BET protein degradation. Herein, we present our design, synthesis, and evaluation of a new class of PROTAC BET degraders. One of the most promising compounds, 23, effectively degrades BRD4 protein at concentrations as low as 30 pM in the RS4;11 leukemia cell line, achieves an IC50 value of 51 pM in inhibition of RS4;11 cell growth and induces rapid tumor regression in vivo against RS4;11 xenograft tumors. These data establish that compound 23 (BETd-260/ZBC260) is a highly potent and efficacious BET degrader.

Bioinspired polyene cyclization promoted by intermolecular chiral acetal-SnCl4 or chiral N-acetal-TiCl4: investigation of the mechanism and identification of the key intermediates.

New strategies using chiral acetal or chiral mixed-acetal in the presence of Lewis acids (SnCl4 or TiCl4) to promote polyene cyclization reaction are described. Acetal-promoted and mixed-acetal-promoted polyene cyclization products are very versatile and can easily be converted into various optically active tricyclic and tetracyclic terpenoids. One of the derivatives of the cyclization products was obtained up to 96% ee after a single recrystallization. In addition, an oxocarbenium intermediate was found to be responsible for the good asymmetric selectivity for this type of reaction.