Hongbin Yuan

Apogossypol derivatives as antagonists of antiapoptotic Bcl-2 family proteins

Guided by a combination of nuclear magnetic resonance binding assays and computational docking studies, we synthesized a library of 5,5′ substituted Apogossypol derivatives as potent Bcl-XL antagonists. Each compound was subsequently tested for its ability to inhibit Bcl-XL in an in vitro fluorescence polarization competition assay and exert single-agent proapoptotic activity in human cancer cell lines. The most potent compound BI79D10 binds to Bcl-XL, Bcl-2, and Mcl-1 with IC50 values of 190, 360, and 520 nmol/L, respectively, and potently inhibits cell growth in the H460 human lung cancer cell line with an EC50 value of 680 nmol/L, expressing high levels of Bcl-2. BI79D10 also effectively induces apoptosis of the RS11846 human lymphoma cell line in a dose-dependent manner and shows little cytotoxicity against bax−/−bak−/− mouse embryonic fibroblast cells, in which antiapoptotic Bcl-2 family proteins lack a cytoprotective phenotype, implying that BI79D10 has little off-target effects. BI79D10 displays in vivo efficacy in transgenic mice, in which Bcl-2 is overexpressed in splenic B cells. Together with its improved plasma and microsomal stability relative to Apogossypol, BI79D10 represents a lead compound for the development of novel apoptosis-based therapies for cancer. [Mol Cancer Ther 2009;8(4):904–13]

Design, Synthesis, and Structure-Activity Relationship of Substrate Competitive, Selective, and in Vivo Active Triazole and Thiadiazole inhibitors of the c-Jun N-Terminal Kinase

We report comprehensive structure-activity relationship studies on a novel series of c-Jun N-terminal kinase (JNK) inhibitors. The compounds are substrate competitive inhibitors that bind to the docking site of the kinase. The reported medicinal chemistry and structure-based optimizations studies resulted in the discovery of selective and potent thiadiazole JNK inhibitors that display promising in vivo activity in mouse models of insulin insensitivity.

Identification of Inhibitors of NOD1-Induced Nuclear Factor-κB Activation

NOD1 (nucleotide-binding oligomerization domain 1) protein is a member of the NLR (NACHT and leucine rich repeat domain containing proteins) protein family, which plays a key role in innate immunity as a sensor of specific microbial components derived from bacterial peptidoglycans and induction of inflammatory responses. Mutations in NOD proteins have been associated with various inflammatory diseases that affect NF-κB (nuclear factor κB) activity, a major signaling pathway involved in apoptosis, inflammation, and immune response. A luciferase-based reporter gene assay was utilized in a high-throughput screening program conducted under the NIH-sponsored Molecular Libraries Probe Production Center Network program to identify the active scaffolds. Herein, we report the chemical synthesis, structure–activity relationship studies, downstream counterscreens, secondary assay data, and pharmacological profiling of the 2-aminobenzimidazole lead (compound 1c, ML130) as a potent and selective inhibitor of NOD1-induced NF-κB activation.

Small-Molecule IAP Antagonists Sensitize Cancer Cells to TRAIL-Induced Apoptosis: Roles of XIAP and cIAPs

TNF-related apoptosis-inducing ligand (TRAIL) is a promising anticancer agent because it shows apoptosis-inducing activity in transformed, but not in normal, cells. As with most anticancer agents, however, its clinical use is restricted by either inherent or acquired resistance by cancer cells. We demonstrate here that small-molecule SMAC mimetics that antagonize the inhibitor of apoptosis proteins (IAP) potently sensitize previously resistant human cancer cell lines, but not normal cells, to TRAIL-induced apoptosis, and that they do so in a caspase-8–dependent manner. We further show that the compounds have no cytotoxicity as single agents. Also, we demonstrate that several IAP family members likely participate in the modulation of cellular sensitivity to TRAIL. Finally, we note that the compounds that sensitize cancer cells to TRAIL are the most efficacious in binding to X-linked IAP, and in inducing cellular-IAP (cIAP)-1 and cIAP-2 degradation. Our studies thus describe valuable compounds that allow elucidation of the signaling events occurring in TRAIL resistance, and demonstrate that these agents act as potent TRAIL-sensitizing agents in a variety of cancer cell lines. Mol Cancer Ther; 13(1); 5–15. ©2013 AACR.

Synthesis and evaluation of Apogossypol Atropisomers as Potential Bcl-xL Antagonists

Anti-apoptotic Bcl-2 family proteins such as Bcl-2 and Bcl-X(L) have been recently validated as targets for the discovery of novel anti-cancer agents. We previously reported that racemic (+/-) Apogossypol, a semi-synthetic compound derived from the natural product Gossypol, binds and inhibits Bcl-2 and Bcl-X(L)in vitro and in cell. Given that (+) and (-) Gossypol display different proapoptotic activities, here we report on the synthesis of (+) and (-) Apogossypol and the evaluation of their in vitro and cellular activity.

Design, synthesis and evaluation of monovalent Smac mimetics that bind to the BIR2 domain of the anti-apoptotic protein XIAP

We report the systematic rational design and synthesis of new monovalent Smac mimetics that bind preferentially to the BIR2 domain of the anti-apoptotic protein XIAP. Characterization of compounds in vitro (including 9i; ML101) led to the determination of key structural requirements for BIR2 binding affinity. Compounds 9h and 9j sensitized TRAIL-resistant breast cancer cells to apoptotic cell death, highlighting the value of these probe compounds as tools to investigate the biology of XIAP.

Structure-activity relationship studies of a novel series of anthrax lethal factor inhibitors.

We report on the identification of a novel small molecule inhibitor of anthrax lethal factor using a high-throughput screening approach. Guided by molecular docking studies, we carried out structure-activity relationship (SAR) studies and evaluated activity and selectivity of most promising compounds in in vitro enzyme inhibition assays and cellular assays. Selected compounds were further analyzed for their in vitro ADME properties, which allowed us to select two compounds for further preliminary in vivo efficacy studies. The data provided represents the basis for further pharmacology and medicinal chemistry optimizations that could result in novel anti-anthrax therapies.

Inhibition of Hematopoietic Protein Tyrosine Phosphatase Augments and Prolongs ERK1/2 and p38 Activation

The hematopoietic protein tyrosine phosphatase (HePTP) is implicated in the development of blood cancers through its ability to negatively regulate the mitogen-activated protein kinases (MAPKs) ERK1/2 and p38. Small-molecule modulators of HePTP activity may become valuable in treating hematopoietic malignancies such as T cell acute lymphoblastic leukemia (T-ALL) and acute myelogenous leukemia (AML). Moreover, such compounds will further elucidate the regulation of MAPKs in hematopoietic cells. Although transient activation of MAPKs is crucial for growth and proliferation, prolonged activation of these important signaling molecules induces differentiation, cell cycle arrest, cell senescence, and apoptosis. Specific HePTP inhibitors may promote the latter and thereby may halt the growth of cancer cells. Here, we report the development of a small molecule that augments ERK1/2 and p38 activation in human T cells, specifically by inhibiting HePTP. Structure-activity relationship analysis, in silico docking studies, and mutagenesis experiments reveal how the inhibitor achieves selectivity for HePTP over related phosphatases by interacting with unique amino acid residues in the periphery of the highly conserved catalytic pocket. Importantly, we utilize this compound to show that pharmacological inhibition of HePTP not only augments but also prolongs activation of ERK1/2 and, especially, p38. Moreover, we present similar effects in leukocytes from mice intraperitoneally injected with the inhibitor at doses as low as 3 mg/kg. Our results warrant future studies with this probe compound that may establish HePTP as a new drug target for acute leukemic conditions.

Discovery of 2-(5-nitrothiazol-2-ylthio)benzo[d]thiazoles as novel c-Jun N-terminal kinase inhibitors.

A new series of 2-thioether-benzothiazoles has been synthesized and evaluated for JNK inhibition. The SAR studies led to the discovery of potent, allosteric JNK inhibitors with selectivity against p38.

BI-69A11-mediated inhibition of AKT leads to effective regression of xenograft melanoma

The AKT/PKB pathway plays a central role in tumor development and progression and is often up‐regulated in different tumor types, including melanomas. We have recently reported on the in silico approach to identify putative inhibitors for AKT/PKB. Of the reported hits, we selected BI‐69A11, a compound which was shown to inhibit AKT activity in in vitro kinase assays. Analysis of BI‐69A11 was performed in melanoma cells, a tumor type that commonly exhibits up‐regulation of AKT. Treatment of the UACC903 human melanoma cells, harboring the PTEN mutation, with BI‐69A11 caused efficient inhibition of AKT S473 phosphorylation with concomitant inhibition of AKT phosphorylation of PRAS40. Treatment of melanoma cells with BI‐69A11 also reduced AKT protein expression, which coincided with inhibition of AKT association with HSP‐90. BI‐69A11 treatment not only caused cell death of melanoma, but also prostate tumor cell lines. Notably, the effect of BI‐69A11 on cell death was more pronounced in cells that express an active form of AKT. Significantly, intra‐peritoneal injection of BI‐69A11 caused effective regression of melanoma tumor xenografts, which coincided with elevated levels of cell death. These findings identify BI‐69A11 as a potent inhibitor of AKT that is capable of eliciting effective regression of xenograft melanoma tumors.