Abstract CK2 is a highly conserved, and constitutively active family of serine/threonine kinases abnormally elevated in a wide variety of cancers and linked to poor prognosis and disease progression. The enzymes form as hetero-tetrameric complexes comprised of two highly related catalytic subunits (α or α´) with two regulatory β subunits in various combinations and distributions, depending on cell type. While CK2 plays a role in normal growth and development, deregulation of the enzymes has been shown to promote and maintain a malignant phenotype through mechanisms in both the anti-apoptotic and the pro-proliferative signaling pathways. CK2 has been reported to modulate the activity of several oncogenic transcription factors including CREB, Myc, Jun and Fos. Studies with RNAi and small molecule compounds have demonstrated tumor cell dependence on CK2. We sought to identify potent CK2 inhibitors to probe the function of CK2 in cancer-linked pathways and for evaluation in CK2 dependent tumor xenograft models. Herein we report SAR studies in the imidazo[1,2-b]pyridazine chemotype leading to the discovery of BMS-595, a highly potent and selective ATP-competitive CK2 inhibitor with a commensurate level of cellular potency. BMS-595 demonstrates strong PK/PD correlations and robust, oral anti-tumor efficacy in CK2-driven xenograft models at tolerated doses. Citation Format: Christine M. Tarby, Liqi He, Brian E. Fink, Andrew Nation, Yufen Zhao, Soong-Hoon Kim, Libing Chen, John S. Tokarski, Chiang Yu, Jonathan G. Pabalan, Urvashi V. Roongta, Jonathan Lippy, Mary Obermeier, Paul A. Elzinga, Aberra Fura, Benjamin Henley, Joseph J. Fargnoli, William R. Foster, Ashvinikumar V. Gavai, Tai W. Wong, John T. Hunt, Gregory D. Vite, Ashok V. Purandare, Brent A. Rupnow. The identification of BMS-595, an orally active imidazo[1,2-b]pyridazine CK2 inhibitor with in vivo anti-tumor activity. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 5417. doi:10.1158/1538-7445.AM2015-5417

The CK2 protein kinases are a small family of two highly related serine/threonine kinases composed of two catalytic subunits, α and α’, and a single β subunit. Numerous substrates have been reported for CK2 and these proteins are known to participate in diverse cellular processes, including cell signaling, transcription, DNA repair, apoptosis regulation and tumor suppression. Elevated CK2 expression and kinase activity has been observed in many cancer types. Further, mRNA knockdown and enzyme inhibition studies have demonstrated that many cancer cell lines are dependent on CK2 for growth and survival. To further evaluate CK2 kinases as targets for therapeutic intervention in cancer, we identified BMS-595, a potent and selective, ATP-competitive CK2 inhibitor. BMS-595 inhibits the in vitro proliferation of human colorectal and lung cancer cell lines with IC50s ranging from less than 10 nM to greater than 1 μM. In sensitive cell lines, anti-proliferative effects of BMS-595 and structurally related analogs strongly correlated with cellular CK2 kinase inhibition. Oral administration of BMS-595 to mice bearing colorectal cancer and lung cancer xenografts demonstrated pharmacodynamic effects and robust efficacy at tolerated doses. These studies confirm the dependence of a subset of human colon and lung cancer cell lines on CK2 activity for growth and demonstrate that pharmacologic inhibition of CK2 can produce anti-tumor efficacy at tolerated doses. Citation Format: Brent A. Rupnow, Chiang Yu, Jonathan G. Pabalan, Urvashi V. Roongta, Jonathan S. Lippy, Ashok R. Dongre, Mary T. Obermeier, Aberra Fura, Paul A. Elzinga, Benjamin J. Henley, Joseph Fargnoli, Francis Y. Lee, William R. Foster, Christine M. Tarby, Brian E. Fink, John S. Tokarski, Ashvinikumar V. Gavai, Tai W. Wong, John T. Hunt, Gregory D. Vite, Ashok V. Purandare. Anti-tumor activity of BMS-595, a novel CK2 kinase inhibitor. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 5395. doi:10.1158/1538-7445.AM2015-5395

Abstract Over the past few years, a more detailed picture of the importance of metabolic pathways to the maintenance and progression of human cancers has begun to emerge. In particular, recent studies have implicated lipid biosynthesis and desaturation as a requirement for tumor cell survival. The endoplasmic reticulum-resident Stearoyl CoA Desaturase (SCD) is the rate limiting enzyme that catalyzes conversion of saturated fatty acids to monounsaturated fatty acids, a key step in the fatty acid metabolic network. In the studies reported here, we show that inhibition of SCD1 by siRNA or a small molecule antagonist results in strong induction of apoptosis and growth inhibition when tumor cells are cultured in reduced (2%) serum conditions but has little impact on cells cultured under normal (10%) serum conditions. Consistent with the observed dependence on SCD1, levels of SCD1 protein increased in response to decreasing serum levels. Both induction of SCD1 protein and sensitivity to growth inhibition by SCD1 inhibition could be reversed by supplementing growth media with unsaturated fatty acids. Transcription profiling of cells treated with an SCD inhibitor revealed strong induction of markers of endoplasmic reticulum stress. This finding was confirmed using siRNA specifically targeting SCD1. Underscoring its importance in cancer, SCD1 protein was found to be highly expressed in a large percentage of human cancer specimens. SCD inhibition resulted in tumor growth delay in a human gastric cancer xenograft model. Altogether, these results suggest that unsaturated fatty acids are required for tumor cell survival and that SCD may represent a viable target for the development of novel agents for cancer therapy. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4115. doi:1538-7445.AM2012-4115

Abstract Emerging literature suggests that metabolic pathways play an important role in the maintenance and progression of human cancers. In particular, recent studies have implicated lipid biosynthesis and desaturation as a requirement for tumor cell survival. In the studies reported here, we aimed to understand whether tumor cells require the activity of either human isoform of stearoyl-CoA-desaturase (SCD1 or SCD5) for survival. Inhibition of SCD1 by siRNA or a small molecule antagonist results in strong induction of apoptosis and growth inhibition, when tumor cells are cultured in reduced (2%) serum conditions, but has little impact on cells cultured in 10% serum. Depletion of SCD5 had minimal effects on cell growth or apoptosis. Consistent with the observed dependence on SCD1, but not SCD5, levels of SCD1 protein increased in response to decreasing serum levels. Both induction of SCD1 protein and sensitivity to growth inhibition by SCD1 inhibition could be reversed by supplementing growth media with unsaturated fatty acids, the product of the enzymatic reaction catalyzed by SCD1. Transcription profiling of cells treated with an SCD inhibitor revealed strong induction of markers of endoplasmic reticulum stress. Underscoring its importance in cancer, SCD1 protein was found to be highly expressed in a large percentage of human cancer specimens. SCD inhibition resulted in tumor growth delay in a human gastric cancer xenograft model. Altogether, these results suggest that desaturated fatty acids are required for tumor cell survival and that SCD may represent a viable target for the development of novel agents for cancer therapy. Mol Cancer Res; 9(11); 1551–61. ©2011 AACR.

N-Acyl-2-aminothiazoles with nonaromatic acyl side chains containing a basic amine were found to be potent, selective inhibitors of CDK2/cycE which exhibit antitumor activity in mice. In particular, compound 21 {N-[5-[[[5-(1,1-dimethylethyl)-2-oxazolyl]methyl]thio]-2-thiazolyl]-4-piperidinecarboxamide, BMS-387032}, has been identified as an ATP-competitive and CDK2-selective inhibitor which has been selected to enter Phase 1 human clinical trials as an antitumor agent. In a cell-free enzyme assay, 21 showed a CDK2/cycE IC50 = 48 nM and was 10- and 20-fold selective over CDK1/cycB and CDK4/cycD, respectively. It was also highly selective over a panel of 12 unrelated kinases. Antiproliferative activity was established in an A2780 cellular cytotoxicity assay in which 21 showed an IC50 = 95 nM. Metabolism and pharmacokinetic studies showed that 21 exhibited a plasma half-life of 5-7 h in three species and moderately low protein binding in both mouse (69%) and human (63%) serum. Dosed orally to mouse, rat, and dog, 21 showed 100%, 31%, and 28% bioavailability, respectively. As an antitumor agent in mice, 21 administered at its maximum-tolerated dose exhibited a clearly superior efficacy profile when compared to flavopiridol in both an ip/ip P388 murine tumor model and in a sc/ip A2780 human ovarian carcinoma xenograft model.

High throughput screening identified 2-acetamido-thiazolylthio acetic ester 1 as an inhibitor of cyclin-dependent kinase 2 (CDK2). Because this compound is inactive in cells and unstable in plasma, we have stabilized it to metabolic hydrolysis by replacing the ester moiety with a 5-ethyl-substituted oxazole as in compound 14. Combinatorial and parallel synthesis provided a rapid analysis of the structure-activity relationship (SAR) for these inhibitors of CDK2, and over 100 analogues with IC50 values in the 1-10 nM range were rapidly prepared. The X-ray crystallographic data of the inhibitors bound to the active site of CDK2 protein provided insight into the binding modes of these inhibitors, and the SAR of this series of analogues was rationalized. Many of these analogues displayed potent and broad spectrum antiproliferative activity across a panel of tumor cell lines in vitro. In addition, A2780 ovarian carcinoma cells undergo rapid apoptosis following exposure to CDK2 inhibitors of this class. Mechanism of action studies have confirmed that the phosphorylation of CDK2 substrates such as RB, histone H1, and DNA polymerase alpha (p70 subunit) is reduced in the presence of compound 14. Further optimization led to compounds such as water soluble 45, which possesses a favorable pharmacokinetic profile in mice and demonstrates significant antitumor activity in vivo in several murine and human models, including an engineered murine mammary tumor that overexpresses cyclin E, the coactivator of CDK2.