Discovery and optimization of covalent Bcl-xL antagonists

Over the last ten years, targeted covalent inhibition has become a key discipline within medicinal chemistry research, most notably in the development of oncology therapeutics. One area where this approach is underrepresented, however, is in targeting protein-protein interactions. This is primarily because these hydrophobic interfaces lack appropriately located cysteine residues to allow for standard conjugate addition chemistry. Herein, we report our development of the first covalent inhibitors of the antiapoptotic protein B-cell lymphoma extra-large (Bcl-xL), utilizing a sulfonyl fluoride (SF) warhead to selectively covalently modify tyrosine 101 of the BH3 domain-binding groove. These compounds display time-dependent inhibition in a biochemical assay and are cellularly active (U266B1). In addition, compound 7 was further elaborated to generate a chemical-biology probe molecule, which may find utility in understanding the intricacies of Bcl-xL biology.

A study of the reactivity of S(VI)–F containing warheads with nucleophilic amino-acid side chains under physiological conditions

Profiling the reactivity and stability of S^VI–F warheads towards nucleophilic amino acids for the development of biochemical probe compounds.

Abstract 3769: Continuous, low intensity systemic dosing maximizes the therapeutic margin of Eg5/KSP inhibition in an orthotopic model of urothelial cell carcinoma

Urothelial Cell Carcinoma (UCC) is the fifth most common cancer, but no new generation molecularly targeted therapies have been registered to treat this disease. Non muscle-invasive bladder cancer can be treated by systemic or intravesical dosing routes. However, the urothelium is one of the most formidable permeability barriers in nature, and may limit the penetration of small molecules into tumour tissue from the intravesical location. Inhibitors of mitosis, including spindle proteins such as Eg5, are attractive targets for cancer therapy, but their efficacy when dosed systemically is severely limited by bone marrow toxicities such as neutropenia and thrombocytopenia. AZ9814, a very potent and selective small molecule inhibitor of Eg5, induces apoptosis and inhibits proliferation of UCC cells in culture with a GI50 of < 1 nM. We have developed an orthotopic model of bladder cancer in the nude rat coupled with a programmable mini-pump system to continuously infuse AZ9814 into the bladder, and compared the therapeutic index of this delivery route with systemic dosing schedules using intraperitoneal injection and continuous subcutaneous infusion using an osmotic mini-pump. Continuous intravesical infusion resulted in severe bladder toxicity including hydropic degeneration and ulceration of urothelium, mucosal erosion and bilateral hydronephrosis, with limited penetration of compound into the tumour, and no significant impact on tumour pharmacodynamics and growth. In contrast, continuous low intensity systemic dosing resulted in significant tumour pharamacodynamic activity and control of tumour growth, albeit with significant but non-lethal effects on bone marrow toxicity. Daily intraperitoneal injection of AZ9814 resulted in very modest anti-tumour effects which were limited by bone marrow toxicity. It is concluded that Eg5 inhibitors have potential to treat UCC, but continuous systemic infusion is the best dosing schedule to maximize therapeutic index.

Citation Format: Leigh Williams, Rebecca Ellston, Dawn Trueman, Helen Musgrove, Linette Ruston, Brian Aquila, Elizabeth Pease, Stephanie Klein, Barry R. Davies. Continuous, low intensity systemic dosing maximizes the therapeutic margin of Eg5/KSP inhibition in an orthotopic model of urothelial cell carcinoma. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 3769.

Abstract B100: Structure-based design of AZ7732 a novel in vivo active beta-alanine-derived pan-IAP inhibitor

Both monomeric and dimeric SMAC (Second Mitochondria-derived Activator of Caspaces) mimetics acting as IAP (Inhibitor of apoptosis proteins) anatgonists have been reported in the clinic as well as extensively in the literature (1). The first four amino acids in the N-terminal of SMAC (AVPI) are critical for binding to IAP proteins. Reported medicinal chemistry exploration of the AVPI template has primarily consisted of variation to the VPI position in the amino-terminal of the SMAC peptide. Structural illucidation of XIAP bound to IAP inhibitors has revealed a critical role for the alanine with dense hydrogen bonding, electrostatic and hydrophibic complementarity with the protein. To our knowledge, exploration of alanine modifications has been limited and generally led to significant reduction in potency. Using the molecular modeling software SuperStar(2), we investigated the publically available co-crystal structures of Smac-mimetics with cIAP1 and hypothesized that homologating the basic amine might be tolerated. Applying this strategy, we report on the successful transfer of a beta-alanine warhead to a number of monomeric scaffolds. The resulting novel monomers maintained cIAP1/2 potency albeit with a reduction in xIAP potency. We report here the first co-crystal structure of xIAP baculoviral IAP repeat 3 domain (BIR3) with a beta-alanine derived monomer. Examination of the binding site contacts in the co-crystal structure provided further insight into the optimization of the warhead. Herein we describe the synthesis, SAR and SPR of this novel warhead and the discovery of beta-alanine derived pan-IAP inhibitors. We show that the SAR can be transferred to dimers and is invariant to the position of dimerization. We report our efforts to optimize the series and mitigate Cyp3A4 inhibition. This work led to the discovery of AZ7732, a novel dimeric SMAC-mimetic; a pan inhibitor of IAPs (cIAP BIR3 IC50 = 12 nM, XIAP BIR3 IC50 = 13 nM, and XIAP BIR2 IC50 = 30 nM); potent in cells as a single agent (MDA-MB231 cIAP degradation IC50 = 0.2 nM, GI50 = 0.4 nM) and is synergistic in vitro in combination with gemcitabine. AZ7732 has favorable in vivo PK with physical properties suitable for IV dosing. AZ7732 is active in vivo as a single agent. Once weekly dosing in MDA-MB231 led to dose-dependent tumor growth inhibition with stasis achieved at 2.5 mpk, ¼ MTD.

In conclusion, Structure-based design and medicinal chemistry efforts have successfully identified novel monomeric and dimeric SMAC mimetics leading to the discovery of a novel in vivo active dimeric pan-IAP inhibitor.

(1) Fulda et al, Nat. Rev. Drug Disc., 11, 109-123, 2012.

(2) M. L. Verdonk, et al, J. Mol. Biol., 289, 1093-1108, 1999

Citation Information: Mol Cancer Ther 2013;12(11 Suppl):B100.

Citation Format: Jamal C. Saeh, Brian Aquila, Daniel Russell, Edward Hennessy, Alex Hird, Melissa Vasbinder, Andrew Ferguson, Bin Yang, Maureen Hattersley, Naomi Laing, Terry MacIntyre, Troy Patterson, Galina Repik, Michael Rooney, Haiyun Wang, Dave Witson, Li Sha, Donald Cook, Paula Lewis, John Lee, Danyang Li, Victor Kamhi, Vibha Oza, Charles Omer. Structure-based design of AZ7732 a novel in vivo active beta-alanine-derived pan-IAP inhibitor. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr B100.

Discovery of (+)-N-(3-aminopropyl)-N-[1-(5-benzyl-3-methyl-4-oxo-[1,2]thiazolo[5,4-d]pyrimidin-6-yl)-2-methylpropyl]-4-methylbenzamide (AZD4877), a kinesin spindle protein inhibitor and potential anticancer agent

Structure-activity relationship analysis identified (+)-N-(3-aminopropyl)-N-[1-(5-benzyl-3-methyl-4-oxo-[1,2]thiazolo[5,4-d]pyrimidin-6-yl)-2-methylpropyl]-4-methylbenzamide (AZD4877), from a series of novel kinesin spindle protein (KSP) inhibitors, as exhibiting both excellent biochemical potency and pharmaceutical properties suitable for clinical development. The selected compound arrested cells in mitosis leading to the formation of the monopolar spindle phenotype characteristic of KSP inhibition and induction of cellular death. A favorable pharmacokinetic profile and notable in vivo efficacy supported the selection of this compound as a clinical candidate for the treatment of cancer.