Abstract 1742: Inhibition of BET signaling leads to reversible GATA1-associated repression of hematopoietic progenitors: translation from preclinical assessment to clinical development

Bromodomain and extraterminal (BET) proteins recognize acetylated lysine residues for the purpose of transcriptional regulation of genes, including those involved in stem cell renewal and oncogenes such as MYC. Inhibition of BET proteins BRD2, BRD3, BRD4, and BRDT represents a promising treatment option for patients with cancer. However, little is known about the consequence of BET inhibition on normal stem cell renewal processes, such as hematopoiesis. This study explored the mechanistic effects of BET inhibition on bone marrow (BM) hematopoiesis. Rats treated with BET inhibitors JQ1, BMS-X, or BMS-986158 for 4 days in vivo showed dose-dependent pan-cellular BM atrophy and reduction of hematopoietic progenitors of myeloid and erythroid lineage (combination of anti-rat CD45, CD11b, anti-granulocyte, CD71, anti-erythroid, and CD90 via flow cytometry) and consequential reductions in circulating platelet and reticulocyte counts, with complete reversibility within 10 days of stopping treatment with BET inhibitors. Primary rat BM stem and progenitor cells treated with BET inhibitors in vitro were evaluated with the colony-forming unit assay and resulted in dose-dependent reduction of multiple lineage progenitor colonies, especially the erythroid and megakaryocyte lineages. To further elucidate pathways involved in BET-related BM atrophy, erythropoiesis and thrombopoiesis genes regulated by GATA1, a BRD-associated transcription factor, from rat BM, as well as rat and human whole-blood samples exposed to BET inhibitor(s) were evaluated via RNAseq and RT-PCR. Dose-dependent responses in genes involved in erythropoiesis (Alas2, ABCme, PBG-D, HMBS) and thrombopoiesis (NFE2, PF4, GP1Bb, MPL) were observed after 4 days of treatment with BMS-986158. In a clinical trial (NCT02419417), patients with solid tumors treated with BMS-986158 demonstrated reversible thrombocytopenia and downregulation of NFE2, PF4, and HMBS expression, similar to that observed in rats. GATA1 was also downregulated in rat BM, with target engagement in rat and human demonstrated by the induction of HEXIM1 transcription, a pharmacodynamic (PD) biomarker of growth inhibition and apoptosis induced by BRD4 inhibition. Overall, our results suggest inhibition of BET signaling causes target-related, dose-dependent repression of hematopoietic progenitors through alterations of GATA1-associated erythropoiesis and thrombopoiesis regulation in rat BM and human blood samples, and these effects are reversible on cessation of BET inhibitor treatment. This is the first in vivo study demonstrating the mechanism of BET inhibition resulting in GATA1-associated repression of hematopoietic progenitors that is correlated to clinical pharmacokinetics and PD (Chen X, et al. AACR 2020) and is translatable from preclinical evaluation to clinical experience.

Citation Format: Cindy Zhang, Ke Xu, Julie Panzica-Kelly, Jennifer Price, Denise Bounous, Shodeinde Coker, Kezi Unsal-Kacmaz, Danielle Greenawalt, Ashvinikumar Gavai, Ronald Fleming, Karen Augustine-Rauch, Richard Westhouse. Inhibition of BET signaling leads to reversible GATA1-associated repression of hematopoietic progenitors: translation from preclinical assessment to clinical development [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 1742.

Abstract B284: Discovery of imidazopyridazinecarbonitriles as potent, selective inhibitors of CK2

Casein kinase 2 (CK2) is a serine/threonine kinase that has been implicated in the regulation of a number of oncogenic or tumor suppressor proteins. CK2 activity has been shown to be elevated in numerous studies in a variety of cancer types. CK2 has been shown to phosphorylate numerous cellular proteins. Among the proteins regulated directly or indirectly by CK2 phosphorylation are oncogenes and tumor suppressor proteins including beta-catenin, c-Myc, PML, and PTEN as well as proteins directly involved in cell cycle, apoptosis, and transcriptional regulation. The plethora of CK2 substrates and their participation in various cellular processes is a major confounding factor in understanding the role of CK2 in oncogenesis. Unlike other kinase targets that participate in relatively linear growth factor signaling pathways, CK2 appears to function more “laterally,” across many important signaling pathways to promote growth and survival of cancer cells. It is clear from numerous studies using siRNA as well as small molecule CK2 inhibitors that cancer cells are highly dependent upon CK2 for growth and survival. As a result, new small molecule inhibitors of CK2 may provide useful tools for probing CK2 biology and may also provide therapeutic benefits against several cancer types. Herein, we report our efforts toward the identification of CK2 inhibitors based on an imidazopyridazine carbonitrile scaffold. Lead compounds from this series demonstrate low nanomolar CK2 biochemical potency, while achieving excellent selectivity versus the majority of kinases in the human kinome. The development of structure-activity relationships and the establishment of a strong correlation between biochemical potency, inhibition of cellular protein target phosphorylation and anti-proliferative effects in targeted cancer cell lines will be presented. In addition, the optimization of pharmacokinetic properties resulting in compounds with excellent in vivo exposure has allowed for the investigation of CK2 inhibition in a pharmacodynamic model. Finally, our efforts to elucidate pathway effects mediated by CK2 in model colon cancer cell lines, including gene expression profiling using advanced small molecules leads, will be disclosed.

Citation Information: Mol Cancer Ther 2013;12(11 Suppl):B284.

Citation Format: Brian Fink, Ashvinikumar Gavai, Soong-Hoon Kim, Yufen Zhao, Ashok Purandare, Gregory Vite, John Tokarski, Chiang Yu, Benjamin Henley, Joseph Fargnoli, Heshani Desilva, Petra Ross-MacDonald, Brent Rupnow, Tai W. Wong. Discovery of imidazopyridazinecarbonitriles as potent, selective inhibitors of CK2. [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 B284.

Design and synthesis of 4-[3,5-dioxo-11-oxa-4,9-diazatricyclo[5.3.1.0(2,6)]undec-4-yl]-2-trifluoromethyl-benzonitriles as androgen receptor antagonists

A novel series of 4-[3,5-dioxo-11-oxa-4,9-diazatricyclo[5.3.1.0(2,6)]undec-4-yl]-2-trifluoromethyl-benzonitriles has been synthesized. The ability of these compounds to act as antagonists of the androgen receptor was investigated and several were found to have potent activity in vitro and in vivo.

Arylpropanolamines: Selective β3 agonists arising from strategies to mitigate phase I metabolic transformations

Utilization of N-substituted-4-hydroxy-3-methylsulfonanilidoethanolamines 1 as selective beta(3) agonists is complicated by their propensity to undergo metabolic oxidative N-dealkylation, generating 0.01-2% of a very potent alpha(1) adrenergic agonist 2. A summary of the SAR for this hepatic microsomal conversion precedes presentation of strategies to maintain the advantages of chemotype 1 while mitigating the consequences of N-dealkylation. This effort led to the identification of 4-hydroxy-3-methylsulfonanilidopropanolamines 15 for which the SAR for the unique stereochemical requirements for binding to the beta adrenergic receptors culminated in the identification of the potent, selective beta(3) agonist 15f.

5-((4-Aminopiperidin-1-yl)methyl)pyrrolotriazine dual inhibitors of EGFR and HER2 protein tyrosine kinases

Pyrrolotriazine dual EGFR/HER2 kinase inhibitors with a 5-((4-aminopiperidin-1-yl)methyl) solubilizing group were found to be superior to analogs with previously reported C-5 solubilizing groups. New synthetic methodology was developed for the parallel synthesis of C-4 analogs with the new solubilizing group. Interesting new leads were evaluated in tumor xenograft models and the C-4 aminofluorobenzylindazole, 1c, was found to exhibit the best antitumor activity. It is hypothesized that this solubilizing group extends into the ribose-phosphate portion of the ATP binding pocket and enhances the binding affinity of the inhibitor.

Novel C-5 aminomethyl pyrrolotriazine dual inhibitors of EGFR and HER2 protein tyrosine kinases

Novel C-5 aminomethyl pyrrolotriazines were prepared and optimized for dual EGFR and HER2 protein tyrosine kinase inhibition. The homopiperazine, 1p, emerged as a key lead and it showed promising oral efficacy in EGFR and dual EGFR/HER2 driven human tumor xenograft models. It is hypothesized that the C-5 homopiperazine side chain binds in the ribose-phosphate portion of the ATP binding pocket.

New C-5 substituted pyrrolotriazine dual inhibitors of EGFR and HER2 protein tyrosine kinases

Novel C-5 substituted pyrrolotriazines were optimized for dual EGFR and HER2 protein tyrosine kinase inhibition. The lead compound exhibited promising oral efficacy in both EGFR and HER2 driven human tumor xenograft models. It is hypothesized that its C-5 morpholine side chain binds in the ribose phosphate portion of the ATP binding pocket.

Novel cytokine release inhibitors. Part IV: analogs of podocarpic acid

Podocarpic acid derivatives as cytokine (IL-1beta) release inhibitors are discussed.

Novel cytokine release inhibitors. Part III: Truncated analogs of tripterine

Truncated analogs of tripterine as cytokine (IL-1 alpha, IL-1 beta, TNF-alpha, IL-6, and IL-8) release inhibitors are discussed.