AZD4320, A Dual Inhibitor of Bcl-2 and Bcl-xL, Induces Tumor Regression in Hematologic Cancer Models without Dose-limiting Thrombocytopenia.

PURPOSE: Targeting Bcl-2 family members upregulated in multiple cancers has emerged as an important area of cancer therapeutics. While venetoclax, a Bcl-2-selective inhibitor, has had success in the clinic, another family member, Bcl-xL, has also emerged as an important target and as a mechanism of resistance. Therefore, we developed a dual Bcl-2/Bcl-xL inhibitor that broadens the therapeutic activity while minimizing Bcl-xL-mediated thrombocytopenia. EXPERIMENTAL DESIGN: We used structure-based chemistry to design a small-molecule inhibitor of Bcl-2 and Bcl-xL and assessed the activity against in vitro cell lines, patient samples, and in vivo models. We applied pharmacokinetic/pharmacodynamic (PK/PD) modeling to integrate our understanding of on-target activity of the dual inhibitor in tumors and platelets across dose levels and over time. RESULTS: We discovered AZD4320, which has nanomolar affinity for Bcl-2 and Bcl-xL, and mechanistically drives cell death through the mitochondrial apoptotic pathway. AZD4320 demonstrates activity in both Bcl-2- and Bcl-xL-dependent hematologic cancer cell lines and enhanced activity in acute myeloid leukemia (AML) patient samples compared with the Bcl-2-selective agent venetoclax. A single intravenous bolus dose of AZD4320 induces tumor regression with transient thrombocytopenia, which recovers in less than a week, suggesting a clinical weekly schedule would enable targeting of Bcl-2/Bcl-xL-dependent tumors without incurring dose-limiting thrombocytopenia. AZD4320 demonstrates monotherapy activity in patient-derived AML and venetoclax-resistant xenograft models. CONCLUSIONS: AZD4320 is a potent molecule with manageable thrombocytopenia risk to explore the utility of a dual Bcl-2/Bcl-xL inhibitor across a broad range of tumor types with dysregulation of Bcl-2 prosurvival proteins.

Towards the next generation of dual Bcl-2/Bcl-xL inhibitors.

Structural modifications of the left-hand side of compound 1 were identified which retained or improved potent binding to Bcl-2 and Bcl-xL in in vitro biochemical assays and had strong activity in an RS4;11 apoptotic cellular assay. For example, sulfoxide diastereomer 13 maintained good binding affinity and comparable cellular potency to 1 while improving aqueous solubility. The corresponding diastereomer (14) was significantly less potent in the cell, and docking studies suggest that this is due to a stereochemical preference for the RS versus SS sulfoxide. Appending a dimethylaminoethoxy side chain (27) adjacent to the benzylic position of the biphenyl moiety of 1 improved cellular activity by approximately three-fold, and this activity was corroborated in cell lines overexpressing Bcl-2 and Bcl-xL.

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 aminopiperidine-based Smac mimetics as IAP antagonists.

A series of structurally unique Smac mimetics that act as antagonists of inhibitor of apoptosis proteins (IAPs) has been discovered. While most previously described Smac mimetics contain the proline ring (or a similar cyclic motif) found in Smac, a key feature of the compounds described herein is that this ring has been removed. Despite this, compounds in this series potently bind to cIAP1 and elicit the expected phenotype of cIAP1 inhibition in cancer cells. Marked selectivity for cIAP1 over XIAP is observed for these compounds, which is attributed to a slight difference in the binding groove between the two proteins and the resulting steric interactions with the inhibitors. XIAP binding can be improved by constraining the inhibitor so that these unfavorable steric interactions are minimized.

Discovery of Disubstituted Imidazo[4,5-b]pyridines and Purines as Potent TrkA Inhibitors.

Trk receptor tyrosine kinases have been implicated in cancer and pain. A crystal structure of TrkA with AZ-23 (1a) was obtained, and scaffold hopping resulted in two 5/6-bicyclic series comprising either imidazo[4,5-b]pyridines or purines. Further optimization of these two fusion series led to compounds with subnanomolar potencies against TrkA kinase in cellular assays. Antitumor effects in a TrkA-driven mouse allograft model were demonstrated with compounds 2d and 3a.

Theraputic targeting of Trk supresses tumor proliferation and enhances cisplatin activity in HNSCC.

Head and neck squamous cell carcinoma (HNSCC) is a biologically aggressive disease that has been modestly impacted by improvements in therapeutic strategies. Several lines of evidence support the role of TrkB for invasion and metastasis in various solid tumor models, and we have shown an important function of this receptor in HNSCC tumor biology. Therapeutic modulation of TrkB function has been supported in the literature by the development of small molecule inhibitors (SMI) with minimal success. To assess the validity of targeting TrkB in HNSCC, we tested a novel agent, AZ64 and show significant dose and time-dependent inhibition of cellular proliferation in cell lines. Genetic studies revealed the specificity of this compound for the TrkB receptor, as exposure of cells that had genetic suppression of TrkB did not demonstrate abrogated oncogenic signaling. We next assessed the impact of AZ64 as a chemotherapy-sensitizer and identified an enhancement of cisplatin-mediated anti-proliferation across all cell lines. We then demonstrated that AZ64 can overcome chemotherapy resistance in a novel model of cisplatin resistance in HNSCC. Modulation of the pro-oncogenic STAT3 and Src pathways was identified, suggesting molecular mechanisms of action for AZ64. In this study, we demonstrate the feasibility of targeting TrkB and suggest a novel approach for the treatment of some chemotherapy-resistant HNSCC.

Identification and preclinical characterization of AZ-23, a novel, selective, and orally bioavailable inhibitor of the Trk kinase pathway.

Tropomyosin-related kinases (TrkA, TrkB, and TrkC) are receptor tyrosine kinases that, along with their ligands, the neurotrophins, are involved in neuronal cell growth, development, and survival. The Trk-neurotrophin pathway may also play a role in tumorigenesis through oncogenic fusions, mutations, and autocrine signaling, prompting the development of novel Trk inhibitors as agents for cancer therapy. This report describes the identification of AZ-23, a novel, potent, and selective Trk kinase inhibitor. In vitro studies with AZ-23 showed improved selectivity over previous compounds and inhibition of Trk kinase activity in cells at low nanomolar concentrations. AZ-23 showed in vivo TrkA kinase inhibition and efficacy in mice following oral administration in a TrkA-driven allograft model and significant tumor growth inhibition in a Trk-expressing xenograft model of neuroblastoma. AZ-23 represents a potent and selective Trk kinase inhibitor from a novel series with the potential for use as a treatment for cancer.

Identification of 4-aminopyrazolylpyrimidines as potent inhibitors of Trk kinases.

The design, synthesis and biological evaluation of a series of 4-aminopyrazolylpyrimidines as potent Trk kinase inhibitors is reported. High-throughput screening identified a promising hit in the 4-aminopyrazolylpyrimidine chemotype. Initial optimization of the series led to more potent Trk inhibitors. Further optimization using two strategies resulted in significant improvement of physical properties and led to the discovery of 10z (AZ-23), a potent, orally bioavailable Trk A/B inhibitor. The compound offers the potential to test the hypothesis that modulation of Trk activity will be of benefit in the treatment of cancer and other indications in vivo.