Alexander Hird

Discovery of novel benzylidene-1,3-thiazolidine-2,4-diones as potent and selective inhibitors of the PIM-1, PIM-2, and PIM-3 protein kinases.

Novel substituted benzylidene-1,3-thiazolidine-2,4-diones (TZDs) have been identified as potent and highly selective inhibitors of the PIM kinases. The synthesis and SAR of these compounds are described, along with X-ray crystallographic, anti-proliferative, and selectivity data.

Inhibition of Mcl-1 through covalent modification of a noncatalytic lysine side chain

Targeted covalent inhibition of disease-associated proteins has become a powerful methodology in the field of drug discovery, leading to the approval of new therapeutics. Nevertheless, current approaches are often limited owing to their reliance on a cysteine residue to generate the covalent linkage. Here we used aryl boronic acid carbonyl warheads to covalently target a noncatalytic lysine side chain, and generated to our knowledge the first reversible covalent inhibitors for Mcl-1, a protein-protein interaction (PPI) target that has proven difficult to inhibit via traditional medicinal chemistry strategies. These covalent binders exhibited improved potency in comparison to noncovalent congeners, as demonstrated in biochemical and cell-based assays. We identified Lys234 as the residue involved in covalent modification, via point mutation. The covalent binders discovered in this study will serve as useful starting points for the development of Mcl-1 therapeutics and probes to interrogate Mcl-1-dependent biological phenomena.

Discovery of a Novel Class of Dimeric Smac Mimetics as Potent IAP Antagonists Resulting in a Clinical Candidate for the Treatment of Cancer (AZD5582)

A series of dimeric compounds based on the AVPI motif of Smac were designed and prepared as antagonists of the inhibitor of apoptosis proteins (IAPs). Optimization of cellular potency, physical properties, and pharmacokinetic parameters led to the identification of compound 14 (AZD5582), which binds potently to the BIR3 domains of cIAP1, cIAP2, and XIAP (IC50 = 15, 21, and 15 nM, respectively). This compound causes cIAP1 degradation and induces apoptosis in the MDA-MB-231 breast cancer cell line at subnanomolar concentrations in vitro. When administered intravenously to MDA-MB-231 xenograft-bearing mice, 14 results in cIAP1 degradation and caspase-3 cleavage within tumor cells and causes substantial tumor regressions following two weekly doses of 3.0 mg/kg. Antiproliferative effects are observed with 14 in only a small subset of the over 200 cancer cell lines examined, consistent with other published IAP inhibitors. As a result of its in vitro and in vivo profile, 14 was nominated as a candidate for clinical development.

Discovery of novel hedgehog antagonists from cell-based screening: Isosteric modification of p38 bisamides as potent inhibitors of SMO

Cell-based subset screening of compounds using a Gli transcription factor reporter cell assay and shh stimulated cell differentiation assay identified a series of bisamide compounds as hedgehog pathway inhibitors with good potency. Using a ligand-based optimization strategy, heteroaryl groups were utilized as conformationally restricted amide isosteres replacing one of the amides which significantly increased their potency against SMO and the hedgehog pathway while decreasing activity against p38α kinase. We report herein the identification of advanced lead compounds such as imidazole 11c and 11f encompassing good p38α selectivity, low nanomolar potency in both cell assays, excellent physiochemical properties and in vivo pharmacokinetics.

Structure Based Design of Non-Natural Peptidic Macrocyclic Mcl-1 Inhibitors

Mcl-1 is a pro-apoptotic BH3 protein family member similar to Bcl-2 and Bcl-xL. Overexpression of Mcl-1 is often seen in various tumors and allows cancer cells to evade apoptosis. Here we report the discovery and optimization of a series of non-natural peptide Mcl-1 inhibitors. Screening of DNA-encoded libraries resulted in hit compound 1, a 1.5 μM Mcl-1 inhibitor. A subsequent crystal structure demonstrated that compound 1 bound to Mcl-1 in a β-turn conformation, such that the two ends of the peptide were close together. This proximity allowed for the linking of the two ends of the peptide to form a macrocycle. Macrocyclization resulted in an approximately 10-fold improvement in binding potency. Further exploration of a key hydrophobic interaction with Mcl-1 protein and also with the moiety that engages Arg256 led to additional potency improvements. The use of protein-ligand crystal structures and binding kinetics contributed to the design and understanding of the potency gains. Optimized compound 26 is a <3 nM Mcl-1 inhibitor, while inhibiting Bcl-2 at only 5 μM and Bcl-xL at >99 μM, and induces cleaved caspase-3 in MV4-11 cells with an IC50 of 3 μM after 6 h.

Small molecule inhibitor of apoptosis proteins antagonists: a patent review

Introduction: The family of inhibitor of apoptosis proteins (IAPs) plays a key role in the suppression of proapoptotic signaling; hence, a small molecule that disrupts the binding of IAPs with their functional partner should restore apoptotic response to proapoptotic stimuli in cells. The continued publication of new patent applications of IAP antagonists over the past 4 years is a testament to the continued interest surrounding the IAP family of proteins. Areas covered: This review summarizes the IAP antagonist patent literature from 2010 to 2014. Monovalent and bivalent Smac mimetics will be covered as well as two new developments in the field: IAP antagonists coupled to or merged with other targeted agents and new BIR2 selective IAP antagonists. Expert opinion: In addition to the well-explored scaffolds for monovalent and bivalent Smac-mimetics, some companies have taken more drastic approaches to explore new chemical space – for example, fragment-based approaches and macrocyclic inhibitors. Furthermore, other companies have designed compounds with alternative biological profiles – tethering to known kinase binding structures, trying to target to the mitochondria or introducing selective binding to the BIR2 domain. An overview of the status for the four small molecule IAP antagonists being evaluated in active human clinical trials is also provided.

Abstract DDT01-02: AZD5991: A potent and selective macrocyclic inhibitor of Mcl-1 for treatment of hematologic cancers

Mcl-1, a member of the Bcl/Mcl family, is a key protein involved in evasion of apoptosis in a wide variety of tumors. Its amplification and overexpression have also been implicated in innate and acquired resistance to anticancer drugs. Mcl-1 is capable of preventing induction of apoptosis, both by binding and inactivating the pro-apoptotic executioner Bcl-2 protein, Bak, as well as by sequestering other pro-apoptotic BH3-only proteins such as Bim and Noxa. AZD5991 is a rationally designed macrocycle with sub-nanomolar affinity for Mcl-1. It demonstrates all the hallmarks of a true Mcl-1 inhibitor: 1. potent, selective, and rapid apoptosis in Mcl-1-dependent cell lines (e.g., GI50 as low as 10 nM in multiple myeloma cell lines); 2. loss of activity upon overexpression of Bcl-xL or siRNA-mediated knockout of Bak; 3. Mcl-1:Bak complex disruption as demonstrated by co-immunoprecipitation. AZD5991 is active in vivo, with complete (100%) tumor regression demonstrated in several mouse xenograft models after a single tolerated dose. We have also demonstrated synergistic in vivo efficacy in combination with standard-of-care agents. Analysis of ex vivo activity in primary samples from leukemia patients indicates that a high percentage of leukemia patients should respond to drug treatment, which supports our plan for a phase I trial of AZD5991 in patients with hematologic cancers. Citation Format: Alexander W. Hird, J. Paul Secrist, Ammar Adam, Matthew A. Belmonte, Eric Gangl, Frank Gibbons, David Hargreaves, Jeffrey W. Johannes, Stephen L. Kazmirski, Jason G. Kettle, Stephen E. Kurtz, Michelle L. Lamb, Martin J. Packer, Bo Peng, Craig R. Stewart, Jeffrey W. Tyner, Wenzhan Yang, Qing Ye, XiaoLan Zheng, Edwin A. Clark. AZD5991: A potent and selective macrocyclic inhibitor of Mcl-1 for treatment of hematologic cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr DDT01-02. doi:10.1158/1538-7445.AM2017-DDT01-02

Structure-based design and synthesis of tricyclic IAP (Inhibitors of Apoptosis Proteins) inhibitors

The design and synthesis of a series of novel tricyclic IAP inhibitors is reported. Rapid assembly of the core tricycle involved two key steps: Rh-catalyzed hydrogenation of an unsaturated bicyclic ring system and a Ru-catalyzed ring closing alkene metathesis reaction. The final Smac mimetics bind to cIAP1 and XIAP BIR3 domains and elicit the desired phenotype in cellular proliferation assays. Dimeric IAP inhibitors were found to possess nanomolar potency in a cellular proliferation assay and favourable in vitro drug-like properties.

Adventures in Scaffold Morphing: Discovery of Fused Ring Heterocyclic Checkpoint Kinase 1 (CHK1) Inhibitors

Checkpoint kinase 1 (CHK1) inhibitors are potential cancer therapeutics that can be utilized for enhancing the efficacy of DNA damaging agents. Multiple small molecule CHK1 inhibitors from different chemical scaffolds have been developed and evaluated in clinical trials in combination with chemotherapeutics and radiation treatment. Scaffold morphing of thiophene carboxamide ureas (TCUs), such as AZD7762 (1) and a related series of triazoloquinolines (TZQs), led to the identification of fused-ring bicyclic CHK1 inhibitors, 7-carboxamide thienopyridines (7-CTPs), and 7-carboxamide indoles. X-ray crystal structures reveal a key intramolecular noncovalent sulfur-oxygen interaction in aligning the hinge-binding carboxamide group to the thienopyridine core in a coplanar fashion. An intramolecular hydrogen bond to an indole NH was also effective in locking the carboxamide in the preferred bound conformation to CHK1. Optimization on the 7-CTP series resulted in the identification of lead compound 44, which displayed respectable drug-like properties and good in vitro and in vivo potency.

Correction to “Structure Based Design of Non-Natural Peptidic Macrocyclic Mcl-1 Inhibitors”

[This corrects the article DOI: 10.1021/acsmedchemlett.6b00464.].