Design and optimisation of dendrimer-conjugated Bcl-2/xL inhibitor, AZD0466, with improved therapeutic index for cancer therapy.

Dual Bcl-2/Bcl-xL inhibitors are expected to deliver therapeutic benefit in many haematological and solid malignancies, however, their use is limited by tolerability issues. AZD4320, a potent dual Bcl-2/Bcl-xL inhibitor, has shown good efficacy however had dose limiting cardiovascular toxicity in preclinical species, coupled with challenging physicochemical properties, which prevented its clinical development. Here, we describe the design and development of AZD0466, a drug-dendrimer conjugate, where AZD4320 is chemically conjugated to a PEGylated poly-lysine dendrimer. Mathematical modelling was employed to determine the optimal release rate of the drug from the dendrimer for maximal therapeutic index in terms of preclinical anti-tumour efficacy and cardiovascular tolerability. The optimised candidate is shown to be efficacious and better tolerated in preclinical models compared with AZD4320 alone. The AZD4320-dendrimer conjugate (AZD0466) identified, through mathematical modelling, has resulted in an improved therapeutic index and thus enabled progression of this promising dual Bcl-2/Bcl-xL inhibitor into clinical development.

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.

Multiscale Model Identifies Improved Schedule for Treatment of Acute Myeloid Leukemia In Vitro With the Mcl-1 Inhibitor AZD5991.

Anticancer efficacy is driven not only by dose but also by frequency and duration of treatment. We describe a multiscale model combining cell cycle, cellular heterogeneity of B-cell lymphoma 2 family proteins, and pharmacology of AZD5991, a potent small-molecule inhibitor of myeloid cell leukemia 1 (Mcl-1). The model was calibrated using in vitro viability data for the MV-4-11 acute myeloid leukemia cell line under continuous incubation for 72 hours at concentrations of 0.03-30 µM. Using a virtual screen, we identified two schedules as having significantly different predicted efficacy and showed experimentally that a "short" schedule (treating cells for 6 of 24 hours) is significantly better able to maintain the rate of cell kill during treatment than a "long" schedule (18 of 24 hours). This work suggests that resistance can be driven by heterogeneity in protein expression of Mcl-1 alone without requiring mutation or resistant subclones and demonstrates the utility of mathematical models in efficiently identifying regimens for experimental exploration.

Biomarker-driven strategy for MCL1 inhibition in T-cell lymphomas.

There is a pressing need for more effective therapies to treat patients with T-cell lymphomas (TCLs), including first-line approaches that increase the response rate to cyclophosphamide, adriamycin, vincristine, and prednisone (CHOP) chemotherapy. We characterized the mitochondrial apoptosis pathway in cell lines and patient-derived xenograft (PDX) models of TCL and assessed the in vitro efficacy of BH3 mimetics, including the BCL2 inhibitor venetoclax, the BCL2/BCL-xL inhibitor navitoclax, and the novel MCL1 inhibitor AZD5991. The abundance of antiapoptotic BCL2 family members based on immunoblotting or RNA transcript levels correlated poorly with the activity of BH3 mimetics. In contrast, the functional approach BH3 profiling reliably predicted sensitivity to BH3 mimetics in vitro and in vivo. We used BH3 profiling to select TCL PDX that were dependent on MCL1. Mice xenografted with these PDX and treated with AZD5991 had markedly improved survival. The combination of AZD5991 and CHOP achieved synergy based on survival improvement beyond a mathematical "sum of benefits" model. Thus, MCL1 inhibition is a promising strategy as both a single agent and in combination with chemotherapy for patients with TCL and functional dependence on MCL1.

Discovery of Mcl-1-specific inhibitor AZD5991 and preclinical activity in multiple myeloma and acute myeloid leukemia.

Mcl-1 is a member of the Bcl-2 family of proteins that promotes cell survival by preventing induction of apoptosis in many cancers. High expression of Mcl-1 causes tumorigenesis and resistance to anticancer therapies highlighting the potential of Mcl-1 inhibitors as anticancer drugs. Here, we describe AZD5991, a rationally designed macrocyclic molecule with high selectivity and affinity for Mcl-1 currently in clinical development. Our studies demonstrate that AZD5991 binds directly to Mcl-1 and induces rapid apoptosis in cancer cells, most notably myeloma and acute myeloid leukemia, by activating the Bak-dependent mitochondrial apoptotic pathway. AZD5991 shows potent antitumor activity in vivo with complete tumor regression in several models of multiple myeloma and acute myeloid leukemia after a single tolerated dose as monotherapy or in combination with bortezomib or venetoclax. Based on these promising data, a Phase I clinical trial has been launched for evaluation of AZD5991 in patients with hematological malignancies (NCT03218683).

Delayed and Prolonged Histone Hyperacetylation with a Selective HDAC1/HDAC2 Inhibitor.

The identification and in vitro and in vivo characterization of a potent SHI-1:2 are described. Kinetic analysis indicated that biaryl inhibitors exhibit slow binding kinetics in isolated HDAC1 and HDAC2 preparations. Delayed histone hyperacetylation and gene expression changes were also observed in cell culture, and histone acetylation was observed in vivo beyond disappearance of drug from plasma. In vivo studies further demonstrated that continuous target inhibition was well tolerated and efficacious in tumor-bearing mice, leading to tumor growth inhibition with either once-daily or intermittent administration.

Molecular and biologic analysis of histone deacetylase inhibitors with diverse specificities.

Histone deacetylase inhibitors (HDACi) are anticancer agents that induce hyperacetylation of histones, resulting in chromatin remodeling and transcriptional changes. In addition, nonhistone proteins, such as the chaperone protein Hsp90, are functionally regulated through hyperacetylation mediated by HDACis. Histone acetylation is thought to be primarily regulated by HDACs 1, 2, and 3, whereas the acetylation of Hsp90 has been proposed to be specifically regulated through HDAC6. We compared the molecular and biologic effects induced by an HDACi with broad HDAC specificity (vorinostat) with agents that predominantly inhibited selected class I HDACs (MRLB-223 and romidepsin). MRLB-223, a potent inhibitor of HDACs 1 and 2, killed tumor cells using the same apoptotic pathways as the HDAC 1, 2, 3, 6, and 8 inhibitor vorinostat. However, vorinostat induced histone hyperacetylation and killed tumor cells more rapidly than MRLB-223 and had greater therapeutic efficacy in vivo. FDCP-1 cells dependent on the Hsp90 client protein Bcr-Abl for survival, were killed by all HDACis tested, concomitant with caspase-dependent degradation of Bcr-Abl. These studies provide evidence that inhibition of HDAC6 and degradation of Bcr-Abl following hyperacetylation of Hsp90 is likely not a major mechanism of action of HDACis as had been previously posited.

Exploring the pharmacokinetic properties of phosphorus-containing selective HDAC 1 and 2 inhibitors (SHI-1:2).

We report the preparation and structure-activity relationships of phosphorus-containing histone deacetylase inhibitors. A strong trend between decreasing phosphorus functional group size and superior mouse pharmacokinetic properties was identified. In addition, optimized candidates showed tumor growth inhibition in xenograft studies.

SAR profiles of spirocyclic nicotinamide derived selective HDAC1/HDAC2 inhibitors (SHI-1:2).

A potent family of spirocyclic nicotinyl aminobenzamide selective HDAC1/HDAC2 inhibitors (SHI-1:2) is profiled. The incorporation of a biaryl zinc-binding motif into a nicotinyl scaffold resulted in enhanced potency and selectivity versus HDAC3, but also imparted hERG activity. It was discovered that increasing polar surface area about the spirocycle attenuates this liability. Compound 12 induced a 4-fold increase in acetylated histone H2B in an HCT-116 xenograft model study with acute exposure, and inhibited tumor growth in a 21-day efficacy study with qd dosing.

Combination therapy of established cancer using a histone deacetylase inhibitor and a TRAIL receptor agonist.

Histone deacetylase inhibitors (HDACi) and agents such as recombinant tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) and agonistic anti-TRAIL receptor (TRAIL-R) antibodies are anticancer agents that have shown promise in preclinical settings and in early phase clinical trials as monotherapies. Although HDACi and activators of the TRAIL pathway have different molecular targets and mechanisms of action, they share the ability to induce tumor cell-selective apoptosis. The ability of HDACi to induce expression of TRAIL-R death receptors 4 and 5 (DR4/DR5), and induce tumor cell death via the intrinsic apoptotic pathway provides a molecular rationale to combine these agents with activators of the TRAIL pathway that activate the alternative (death receptor) apoptotic pathway. Herein, we demonstrate that the HDACi vorinostat synergizes with the mouse DR5-specific monoclonal antibody MD5-1 to induce rapid and robust tumor cell apoptosis in vitro and in vivo. Importantly, using a preclinical mouse breast cancer model, we show that the combination of vorinostat and MD5-1 is safe and induces regression of established tumors, whereas single agent treatment had little or no effect. Functional analyses revealed that rather than mediating enhanced tumor cell apoptosis via the simultaneous activation of the intrinsic and extrinsic apoptotic pathways, vorinostat augmented MD5-1-induced apoptosis concomitant with down-regulation of the intracellular apoptosis inhibitor cellular-FLIP (c-FLIP). These data demonstrate that combination therapies involving HDACi and activators of the TRAIL pathway can be efficacious for the treatment of cancer in experimental mouse models.

Phenylglycine and phenylalanine derivatives as potent and selective HDAC1 inhibitors (SHI-1).

An HTS screening campaign identified a series of low molecular weight phenols that showed excellent selectivity (>100-fold) for HDAC1/HDAC2 over other Class I and Class II HDACs. Evolution and optimization of this HTS hit series provided HDAC1-selective (SHI-1) compounds with excellent anti-proliferative activity and improved physical properties. Dose-dependent efficacy in a mouse HCT116 xenograft model was demonstrated with a phenylglycine SHI-1 analog.

Exploration of the internal cavity of histone deacetylase (HDAC) with selective HDAC1/HDAC2 inhibitors (SHI-1:2).

We report herein the initial exploration of novel selective HDAC1/HDAC2 inhibitors (SHI-1:2). Optimized SHI-1:2 structures exhibit enhanced intrinsic activity against HDAC1 and HDAC2, and are greater than 100-fold selective versus other HDACs, including HDAC3. Based on the SAR of these agents and our current understanding of the HDAC active site, we postulate that the SHI-1:2 extend the existing HDAC inhibitor pharmacophore to include an internal binding domain.

Amino acid derivatives as histone deacetylase inhibitors.

Ongoing clinical studies indicate that inhibitors of Class I and Class II histone deacetylase (HDAC) enzymes show great promise for the treatment of cancer. Zolinza (SAHA, Zolinza) was recently approved by the FDA for the treatment of the cutaneous manifestations of cutaneous T-cell lymphoma. As a part of an ongoing effort to identify novel small molecules to target these important enzymes, we have prepared several classes of amino acid-derived HDAC1 inhibitors. The design rationale and in vitro activity against the HDAC1 enzyme and HCT116 cell line are described in this letter.

Optimization of biaryl Selective HDAC1&2 Inhibitors (SHI-1:2).

A class of biaryl benzamides was identified and optimized as selective HDAC1&2 inhibitors (SHI-1:2). These agents exhibit selectivity over class II HDACs 4-7, as well as class I HDACs 3 and 8; providing examples of selective HDAC inhibitors for the HDAC isoforms most closely associated with cancer. The hypothesis for the increased selectivity is the binding of a pendant aromatic group in the internal cavity of the HDAC1&2 enzymes. SAR development based on an initial lead led to a series of potent and selective inhibitors with reduced off-target activity and tumor growth inhibition activity in a HCT-116 xenograft model.

Quantitative analysis of histone deacetylase-1 selective histone modifications by differential mass spectrometry.

Inhibitors of class 1 and class 2 histone deacetylase (HDAC) enzymes have shown antitumor activity in human clinical trials. More recently, there has been interest in developing subtype-selective HDAC inhibitors designed to retain anticancer activity while reducing potential side effects. Efforts have been initiated to selectively target HDAC1 given its role in tumor proliferation and survival. The development of HDAC1-specific inhibitors will require the identification of HDAC1-selective pharmacodynamic markers that correlate closely with HDAC1-inhibition in vitro and in vivo. Existing histone markers of HDAC target engagement were developed using pan-HDAC inhibitors and do not necessarily represent robust readouts for isoform-specific inhibitors. Therefore, we have initiated a proteomic approach to identify readouts for HDAC1 inhibition. This approach involves the use of differential mass spectrometry (dMS) to identify post-translational changes in histones by profiling histone-enriched cellular fractions treated with various HDAC inhibitors. In this study, we profiled histones isolated from the HCT116 human colon cancer cell line that have been treated with compounds from multiple chemical classes that are specific for HDAC1; HDAC1 and 3; and HDAC1, 3, and 6 enzymes. In two independent experiments, we identified 24 features that correlated with HDAC1-inhibition. Among the peptides modulated by HDAC1-selective inhibitors were Ac-H2B-K5 from histone H2B, and Ac-H3-K18 from histone H3. Commercially available antibodies to specific histone acetyl-lysine residues were used to confirm that these peptides also provide pharmacodynamic readouts for HDAC1-selective inhibitors in vivo and in vitro. These results show the utility of dMS in guiding the identification of specific readouts to aid in the development of HDAC-selective inhibitors.

Phase 1 study of the histone deacetylase inhibitor vorinostat (suberoylanilide hydroxamic acid [SAHA]) in patients with advanced leukemias and myelodysplastic syndromes.

Vorinostat (suberoylanilide hydroxamic acid, SAHA) is a histone deacetylase inhibitor active clinically in cutaneous T-cell lymphoma and preclinically in leukemia. A phase 1 study was conducted to evaluate the safety and activity of oral vorinostat 100 to 300 mg twice or thrice daily for 14 days followed by 1-week rest. Patients with relapsed or refractory leukemias or myelodysplastic syndromes (MDS) and untreated patients who were not candidates for chemotherapy were eligible. Of 41 patients, 31 had acute myeloid leukemia (AML), 4 chronic lymphocytic leukemia, 3 MDS, 2 acute lymphoblastic leukemia, and 1 chronic myelocytic leukemia. The maximum tolerated dose (MTD) was 200 mg twice daily or 250 mg thrice daily. Dose-limiting toxicities were fatigue, nausea, vomiting, and diarrhea. Common drug-related adverse experiences were diarrhea, nausea, fatigue, and anorexia and were mild/moderate in severity. Grade 3/4 drug-related adverse experiences included fatigue (27%), thrombocytopenia (12%), and diarrhea (10%). There were no drug-related deaths; 7 patients had hematologic improvement response, including 2 complete responses and 2 complete responses with incomplete blood count recovery (all with AML treated at/below MTD). Increased histone acetylation was observed at all doses. Antioxidant gene expression may confer vorinostat resistance. Further evaluation of vorinostat in AML/MDS is warranted.

The discovery of 6-amino nicotinamides as potent and selective histone deacetylase inhibitors.

This communication highlights the development of a nicotinamide series of histone deacetylase inhibitors within the benzamide structural class. Extensive exploration around the nicotinamide core led to the discovery of a class I selective HDAC inhibitor that possesses excellent intrinsic and cell-based potency, acceptable ancillary pharmacology, favorable pharmacokinetics, sustained pharmacodynamics in vitro, and achieves in vivo efficacy in an HCT116 xenograft model.

Benzo[b]thiophene-based histone deacetylase inhibitors.

Benzo[b]thienyl hydroxamic acids, a novel class of histone deacetylase (HDAC) inhibitors, were identified via a targeted screen of small molecule hydroxamic acids. Various substitutions were explored in the C5- and C6-positions of the benzo[b]thiophene core to characterize SAR and develop optimal inhibitors. It was determined that substitution at the C6-position of the benzo[b]thiophene core with a three-atom spacer yielded optimal HDAC1 inhibition and anti-proliferative activity in murine erythroleukemia (SC-9) cells.

Aminosuberoyl hydroxamic acids (ASHAs): a potent new class of HDAC inhibitors.

Histone deacetylase (HDAC) inhibitors that target Class I and Class II HDACs are currently in advanced clinical trials for the treatment of cancer. Vorinostat (Zolinza, SAHA) is a hydroxamic acid approved for the treatment of patients with cutaneous T-cell lymphoma who have progressive, persistent or recurrent disease on or following two systemic therapies. As part of an on-going effort to better understand the nature of the HDAC enzyme/inhibitor interaction and design highly effective HDAC inhibitors, we herein report the design, synthesis and HDAC inhibitory activity of a vorinostat-derived series of substrate-based HDAC inhibitors.

Phase I study of an oral histone deacetylase inhibitor, suberoylanilide hydroxamic acid, in patients with advanced cancer.

PURPOSE: To determine the safety, dosing schedules, pharmacokinetic profile, and biologic effect of orally administered histone deacetylase inhibitor suberoylanilide hydroxamic acid (SAHA) in patients with advanced cancer. PATIENTS AND METHODS: Patients with solid and hematologic malignancies were treated with oral SAHA administered once or twice a day on a continuous basis or twice daily for 3 consecutive days per week. Pharmacokinetic profile and bioavailibity of oral SAHA were determined. Western blots and enzyme-linked immunosorbent assays of histones isolated from peripheral-blood mononuclear cells (PBMNCs) pre and post-therapy were performed to evaluate target inhibition. RESULTS: Seventy-three patients were treated with oral SAHA and major dose-limiting toxicities were anorexia, dehydration, diarrhea, and fatigue. The maximum tolerated dose was 400 mg qd and 200 mg bid for continuous daily dosing and 300 mg bid for 3 consecutive days per week dosing. Oral SAHA had linear pharmacokinetics from 200 to 600 mg, with an apparent half-life ranging from 91 to 127 minutes and 43% oral bioavailability. Histones isolated from PBMNCs showed consistent accumulation of acetylated histones post-therapy, and enzyme-linked immunosorbent assay demonstrated a trend towards a dose-dependent accumulation of acetylated histones from 200 to 600 mg of oral SAHA. There was one complete response, three partial responses, two unconfirmed partial responses, and 22 (30%) patients remained on study for 4 to 37+ months. CONCLUSIONS: Oral SAHA has linear pharmacokinetics and good bioavailability, inhibits histone deacetylase activity in PBMNCs, can be safely administered chronically, and has a broad range of antitumor activity.