Synthesis and SAR of inhibitors of protein kinase CK2: novel tricyclic quinoline analogs.

Protein kinase CK2 is a potential drug target for many diseases including cancer and inflammation disorders. The crystal structure of clinical candidate CX-4945 1 with CK2 revealed an indirect interaction with the protein through hydrogen bonding between the NH of the 3-chlorophenyl amine and a water molecule. Herein, we investigate the relevance of this hydrogen bond by preparing several novel tricyclic derivatives lacking a NH moiety at the same position. This SAR study allowed the discovery of highly potent CK2 inhibitors.

Pre-clinical characterization of CX-4945, a potent and selective small molecule inhibitor of CK2 for the treatment of cancer.

In this article we describe the preclinical characterization of 5-(3-chlorophenylamino) benzo[c][2,6]naphthyridine-8-carboxylic acid (CX-4945), the first orally available small molecule inhibitor of protein CK2 in clinical trials for cancer. CX-4945 was optimized as an ATP-competitive inhibitor of the CK2 holoenzyme (Ki = 0.38 nM). Iterative synthesis and screening of analogs, guided by molecular modeling, led to the discovery of orally available CX-4945. CK2 promotes signaling in the Akt pathway and CX-4945 suppresses the phosphorylation of Akt as well as other key downstream mediators of the pathway such as p21. CX-4945 induced apoptosis and caused cell cycle arrest in cancer cells in vitro. CX-4945 exhibited a dose-dependent antitumor activity in a xenograft model of PC3 prostate cancer model and was well tolerated. In vivo time-dependent reduction in the phosphorylation of the biomarker p21 at T145 was observed by immunohistochemistry. Inhibition of the newly validated CK2 target by CX-4945 represents a fresh therapeutic strategy for cancer.

Novel potent pyrimido[4,5-c]quinoline inhibitors of protein kinase CK2: SAR and preliminary assessment of their analgesic and anti-viral properties.

We describe the discovery of novel potent substituted pyrimido[4,5-c]quinoline ATP-competitive inhibitors of protein kinase CK2. A binding model of the inhibitors with the protein was elaborated on the basis of SAR and revealed various modes of interaction with the hinge region. Representative analog 14k (CK2 IC(50)=9 nM) showed anti-viral activity at nanomolar concentrations against HIV-1. Orally available compound 7e (CK2 IC(50)=3 nM) reduced pain in the phase II of a murine formalin model. These preliminary data confirm that properly optimized CK2 inhibitors may be used for anti-viral and pain therapy.

Potent, orally active corticotropin-releasing factor receptor-1 antagonists containing a tricyclic pyrrolopyridine or pyrazolopyridine core.

Two new classes of tricyclic-based corticotropin-releasing factor (CRF(1)) receptor-1 antagonists were designed by constraining known 1H-pyrrolo[2,3-b]pyridine and 1H-pyrazolo[3,4-b]pyridine ligands. Pyrrole- and pyrazole-based molecules 19g and 22a, respectively, were discovered that potently bind the recombinant CRF(1) receptor (K(i) = 3.5, 2.9 nM) and inhibit adrenocorticotropic hormone (ACTH) release from rat pituitary cell culture (IC(50) = 14, 6.8 nM). These compounds show good oral bioavailabity (F = 24%, 7.0%) and serum half-lives in rats (t(1/2) = 6.3, 12 h) and penetrate the rat brain ([brain]/[plasma] = 0.27, 0.52) but tend toward large volumes of distribution (V(D) = 38, 44 L kg(-1)) and rapid clearances (CL = 70, 43 mL min(-1) kg(-1)). When given orally, both the pyrazole and the pyrrole leads dose-dependently inhibit stress-induced ACTH release in vivo. ACTH reductions of 84-86% were observed for 30 mg kg(-1) doses.

Discovery of CX-6258. A Potent, Selective, and Orally Efficacious pan-Pim Kinases Inhibitor.

Structure-activity relationship analysis in a series of 3-(5-((2-oxoindolin-3-ylidene)methyl)furan-2-yl)amides identified compound 13, a pan-Pim kinases inhibitor with excellent biochemical potency and kinase selectivity. Compound 13 exhibited in vitro synergy with chemotherapeutics and robust in vivo efficacy in two Pim kinases driven tumor models.

Discovery of CX-5461, the First Direct and Selective Inhibitor of RNA Polymerase I, for Cancer Therapeutics.

Accelerated proliferation of solid tumor and hematologic cancer cells is linked to accelerated transcription of rDNA by the RNA polymerase I (Pol I) enzyme to produce elevated levels of rRNA (rRNA). Indeed, upregulation of Pol I, frequently caused by mutational alterations among tumor suppressors and oncogenes, is required for maintenance of the cancer phenotype and forms the basis for seeking selective inhibitors of Pol I as anticancer therapeutics. 2-(4-Methyl-[1,4]diazepan-1-yl)-5-oxo-5H-7-thia-1,11b-diaza-benzo[c]fluorene-6-carboxylic acid (5-methyl-pyrazin-2-ylmethyl)-amide (CX-5461, 7c) has been identified as the first potent, selective, and orally bioavailable inhibitor of RNA Pol I transcription with in vivo activity in tumor growth efficacy models. The preclinical data support the development of CX-5461 as an anticancer drug with potential for activity in several types of cancer.

Inhibition of RNA polymerase I as a therapeutic strategy to promote cancer-specific activation of p53.

Increased transcription of ribosomal RNA genes (rDNA) by RNA Polymerase I is a common feature of human cancer, but whether it is required for the malignant phenotype remains unclear. We show that rDNA transcription can be therapeutically targeted with the small molecule CX-5461 to selectively kill B-lymphoma cells in vivo while maintaining a viable wild-type B cell population. The therapeutic effect is a consequence of nucleolar disruption and activation of p53-dependent apoptotic signaling. Human leukemia and lymphoma cell lines also show high sensitivity to inhibition of rDNA transcription that is dependent on p53 mutational status. These results identify selective inhibition of rDNA transcription as a therapeutic strategy for the cancer specific activation of p53 and treatment of hematologic malignancies.

Targeting RNA polymerase I with an oral small molecule CX-5461 inhibits ribosomal RNA synthesis and solid tumor growth.

Deregulated ribosomal RNA synthesis is associated with uncontrolled cancer cell proliferation. RNA polymerase (Pol) I, the multiprotein complex that synthesizes rRNA, is activated widely in cancer. Thus, selective inhibitors of Pol I may offer a general therapeutic strategy to block cancer cell proliferation. Coupling medicinal chemistry efforts to tandem cell- and molecular-based screening led to the design of CX-5461, a potent small-molecule inhibitor of rRNA synthesis in cancer cells. CX-5461 selectively inhibits Pol I-driven transcription relative to Pol II-driven transcription, DNA replication, and protein translation. Molecular studies demonstrate that CX-5461 inhibits the initiation stage of rRNA synthesis and induces both senescence and autophagy, but not apoptosis, through a p53-independent process in solid tumor cell lines. CX-5461 is orally bioavailable and demonstrates in vivo antitumor activity against human solid tumors in murine xenograft models. Our findings position CX-5461 for investigational clinical trials as a potent, selective, and orally administered agent for cancer treatment.

Discovery and SAR of 5-(3-chlorophenylamino)benzo[c][2,6]naphthyridine-8-carboxylic acid (CX-4945), the first clinical stage inhibitor of protein kinase CK2 for the treatment of cancer.

Herein we chronicle the discovery of CX-4945 (25n), a first-in-class, orally bioavailable ATP-competitive inhibitor of protein kinase CK2 in clinical trials for cancer. CK2 has long been considered a prime cancer drug target because of the roles of deregulated and overexpressed CK2 in cancer-promoting prosurvival and antiapoptotic pathways. These biological properties as well as the suitability of CK2's small ATP binding site for the design of selective inhibitors, led us to fashion novel therapeutic agents for cancer. The optimization leading to 25n (K(i) = 0.38 nM) was guided by molecular modeling, suggesting a strong binding of 25n resulting from a combination of hydrophobic interactions, an ionic bridge with Lys68, and hydrogen bonding with the hinge region. 25n was found to be highly selective, orally bioavailable across species (20-51%) and efficacious in xenograft models. The discovery of 25n will allow the therapeutic targeting of CK2 in humans for the first time.

CX-4945, an orally bioavailable selective inhibitor of protein kinase CK2, inhibits prosurvival and angiogenic signaling and exhibits antitumor efficacy.

Malignant transformation and maintenance of the malignant phenotype depends on oncogenic and non-oncogenic proteins that are essential to mediate oncogene signaling and to support the altered physiologic demands induced by transformation. Protein kinase CK2 supports key prosurvival signaling pathways and represents a prototypical non-oncogene. In this study, we describe CX-4945, a potent and selective orally bioavailable small molecule inhibitor of CK2. The antiproliferative activity of CX-4945 against cancer cells correlated with expression levels of the CK2α catalytic subunit. Attenuation of PI3K/Akt signaling by CX-4945 was evidenced by dephosphorylation of Akt on the CK2-specific S129 site and the canonical S473 and T308 regulatory sites. CX-4945 caused cell-cycle arrest and selectively induced apoptosis in cancer cells relative to normal cells. In models of angiogenesis, CX-4945 inhibited human umbilical vein endothelial cell migration, tube formation, and blocked CK2-dependent hypoxia-induced factor 1 alpha (HIF-1α) transcription in cancer cells. When administered orally in murine xenograft models, CX-4945 was well tolerated and demonstrated robust antitumor activity with concomitant reductions of the mechanism-based biomarker phospho-p21 (T145). The observed antiproliferative and anti-angiogenic responses to CX-4945 in tumor cells and endothelial cells collectively illustrate that this compound exerts its antitumor effects through inhibition of CK2-dependent signaling in multiple pathways. Finally, CX-4945 is the first orally bioavailable small molecule inhibitor of CK2 to advance into human clinical trials, thereby paving the way for an entirely new class of targeted treatment for cancer.