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Drug combination therapies are commonly used for the treatment of cancers to increase therapeutic efficacy, reduce toxicity, and decrease the incidence of drug resistance. Although drug combination therapies were originally devised primarily by empirical methods, the increased understanding of drug mechanisms and the pathways they modulate provides a unique opportunity to design combinations that are based on mechanistic rationale. We have identified protein kinase CK2 as a promising therapeutic target for combination therapy, because CK2 regulates not just one but many oncogenic pathways and processes that play important roles in drug resistance, including DNA repair, epidermal growth factor receptor signaling, PI3K/AKT/mTOR signaling, Hsp90 machinery activity, hypoxia, and interleukin-6 expression. In this article, we show that CX-4945, a clinical stage selective small molecule inhibitor of CK2, blocks the DNA repair response induced by gemcitabine and cisplatin and synergizes with these agents in models of ovarian cancer. Mechanistic studies show that the enhanced activity is a result of inactivation of XRCC1 and MDC1, two mediator/adaptor proteins that are essential for DNA repair and that require phosphorylation by CK2 for their function. These data position CK2 as a valid pharmacologic target for intelligent drug combinations and support the evaluation of CX-4945 in combination with gemcitabine and platinum-based chemotherapeutics in the clinical setting. Mol Cancer Ther; 11(4); 994–1005. ©2012 AACR.

PDF file - 148K, The effects of CK2, MDC1 or XRCC1 depletion by siRNA on Gamma-H2AX levels induced by cisplatin or gemcitabine.

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PDF file - 97K, Quantified western blots for Gamma-H2AX and cleaved PARP levels normalized to �eta-actin levels from cisplatin or gemcitabine combinations with CX-4945.

PDF file - 1.0MB, The global role of CK2 in DNA repair and cancer therapies that potentially rely on CK2 mediated repair mechanisms.

Supplementary Methods and Materials from Anticancer Activity of CX-3543: A Direct Inhibitor of rRNA Biogenesis

Supplementary Materials from Targeting RNA Polymerase I with an Oral Small Molecule CX-5461 Inhibits Ribosomal RNA Synthesis and Solid Tumor Growth

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.

Hallmark deregulated signaling in cancer cells drives excessive ribosome biogenesis within the nucleolus, which elicits unbridled cell growth and proliferation. The rate-limiting step of ribosome biogenesis is synthesis of rRNA (building blocks of ribosomes) by RNA Polymerase I (Pol I). Numerous kinase pathways and products of proto-oncogenes can up-regulate Pol I, whereas tumor suppressor proteins can inhibit rRNA synthesis. In tumorigenesis, activating mutations in certain cancer-associated kinases and loss-of-function mutations in tumor suppressors lead to deregulated signaling that stimulates Pol I transcription with resultant increases in ribosome biogenesis, protein synthesis, cell growth, and proliferation. Certain anticancer therapeutics, such as cisplatin and 5-fluorouracil, reportedly exert, at least partially, their activity through disruption of ribosome biogenesis, yet many prime targets for anticancer drugs within the ribosome synthetic machinery of the nucleolus remain largely unexploited. Herein, we describe CX-3543, a small molecule nucleolus-targeting agent that selectively disrupts nucleolin/rDNA G-quadruplex complexes in the nucleolus, thereby inhibiting Pol I transcription and inducing apoptosis in cancer cells. CX-3543 is the first G-quadruplex interactive agent to enter human clinical trials, and it is currently under evaluation against carcinoid/neuroendocrine tumors in a phase II clinical trial. [Cancer Res 2009;69(19):7653–61]

Drug combination therapies are commonly used for the treatment of cancers to increase therapeutic efficacy, reduce toxicity, and decrease the incidence of drug resistance. Although drug combination therapies were originally devised primarily by empirical methods, the increased understanding of drug mechanisms and the pathways they modulate provides a unique opportunity to design combinations that are based on mechanistic rationale. We have identified protein kinase CK2 as a promising therapeutic target for combination therapy, because CK2 regulates not just one but many oncogenic pathways and processes that play important roles in drug resistance, including DNA repair, epidermal growth factor receptor signaling, PI3K/AKT/mTOR signaling, Hsp90 machinery activity, hypoxia, and interleukin-6 expression. In this article, we show that CX-4945, a clinical stage selective small molecule inhibitor of CK2, blocks the DNA repair response induced by gemcitabine and cisplatin and synergizes with these agents in models of ovarian cancer. Mechanistic studies show that the enhanced activity is a result of inactivation of XRCC1 and MDC1, two mediator/adaptor proteins that are essential for DNA repair and that require phosphorylation by CK2 for their function. These data position CK2 as a valid pharmacologic target for intelligent drug combinations and support the evaluation of CX-4945 in combination with gemcitabine and platinum-based chemotherapeutics in the clinical setting. Mol Cancer Ther; 11(4); 994–1005. ©2012 AACR.

Ser/Thr protein kinase CK2 regulates multiple processes that play important roles in the sensitivity of cancer to epidermal growth factor receptor targeting therapeutics, including PI3K-Akt-mTOR signaling, Hsp90 activity, and inhibition of apoptosis. We hypothesized that top-down inhibition of EGFR, combined with lateral suppression of multiple oncogenic pathways by targeting CK2, would create a pharmacologic synthetic lethal event and result in an improved cancer therapy compared to EGFR inhibition alone. This hypothesis was tested by combining CX-4945, a first-in-class clinical stage inhibitor of CK2, with the EGFR tyrosine kinase inhibitor, erlotinib, in vitro and in vivo in models of non-small cell lung carcinoma, NCI-H2170, and squamous cell carcinoma, A431. Our results demonstrate that combination of CX-4945 with erlotinib results in enhanced attenuation of the PI3K-Akt-mTOR pathway. We also observed an increase in apoptosis, synergistic killing of cancer cells in vitro, as well as improved antitumor efficacy in vivo. Taken together, these data position CK2 as a valid pharmacologic target for drug combinations and support further evaluation of CX-4945 in combination with EGFR targeting agents.

Inflammatory breast cancer is driven by pro-angiogenic and pro-inflammatory cytokines. One of them Interleukin-6 (IL-6) is implicated in cancer cell proliferation and survival, and promotes angiogenesis, inflammation and metastasis. While IL-6 has been shown to be upregulated by several oncogenes, the mechanism behind this phenomenon is not well characterized. Here we demonstrate that the pleotropic Serine/Threonine kinase CK2 is implicated in the regulation of IL-6 expression in a model of inflammatory breast cancer. We used siRNAs targeted toward CK2 and a selective small molecule inhibitor of CK2, CX-4945, to inhibit the expression and thus suppress the secretion of IL-6 in in vitro as well as in vivo models. Moreover, we report that in a clinical trial, CX-4945 was able to dramatically reduce IL-6 levels in plasma of an inflammatory breast cancer patient. Our data shed a new light on the regulation of IL-6 expression and position CX-4945 and potentially other inhibitors of CK2, for the treatment of IL-6-driven cancers and possibly other diseases where IL-6 is instrumental, including rheumatoid arthritis.

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.

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.

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. Cancer Res; 70(24); 10288–98. ©2010 AACR.

The phosphatidylinositol 3-kinase (PI3K) pathway is activated in many human tumors and mediates processes such as cell proliferation, survival, adhesion, and motility. The natural product, wortmannin, has been widely used to study the functional consequences of PI3K inhibition in both normal and transformed cells in culture but is not a suitable cancer chemotherapeutic agent due to stability and toxicity issues. PX-866, an improved wortmannin analogue, displays significant antitumor activity in xenograft models. Here, we directly compare PX-866 and wortmannin in human cancer cell lines cultured in monolayer or as three-dimensional spheroids. Both PI3K inhibitors failed to inhibit monolayer cell growth at concentrations up to 100 nmol/L but strongly suppressed spheroid growth at low nanomolar concentrations, with PX-866 showing greater potency than wortmannin. Relative to wortmannin, PX-866 treatment results in a more sustained loss of Akt phosphorylation, suggesting that the increased potency of PX-866 is related to a more durable inhibition of PI3K signaling. PX-866 and wortmannin both inhibit spheroid growth without causing cytotoxicity, similar to known cytostatic agents, such as rapamycin. PX-866 also inhibits cancer cell motility at subnanomolar concentrations. These findings suggest that the antitumor activities of PX-866 stem from prolonged inhibition of the PI3K pathway and inhibition of cell motility. In addition, we propose that the use of three-dimensional tumor models is more predictive of in vivo growth inhibition by PI3K inhibitors in cancer cell lines lacking phosphatase and tensin homologue activity or expression. [Mol Cancer Ther 2007;6(9):2505–14]

Phosphoinositide 3-kinases (PI3-Ks) are an ubiquitous class of signaling enzymes that regulate diverse cellular processes including growth, differentiation, and motility. Physiological roles of PI3-Ks have traditionally been assigned using two pharmacological inhibitors, LY294002 and wortmannin. Although these compounds are broadly specific for the PI3-K family, they show little selectivity among family members, and the development of isoform-specific inhibitors of these enzymes has been long anticipated. Herein, we prepare compounds from two classes of arylmorpholine PI3-K inhibitors and characterize their specificity against a comprehensive panel of targets within the PI3-K family. We identify multiplex inhibitors that potently inhibit distinct subsets of PI3-K isoforms, including the first selective inhibitor of p110beta/p110delta (IC(50) p110beta=0.13 microM, p110delta=0.63 microM). We also identify trends that suggest certain PI3-K isoforms may be more sensitive to potent inhibition by arylmorpholines, thereby guiding future drug design based on this pharmacophore.

Platinum-based chemotherapeutics are commonly used to treat solid tumors but may be restricted in their application by dose limiting toxicity and inherent or acquired resistance. Because efficient DNA damage repair mechanisms contribute to resistance, targeting components of the repair machinery has emerged as a strategy to increase the effectiveness of these and other DNA-damaging anti-cancer drugs. Protein kinase CK2 is a serine/threonine kinase that has emerged as an attractive molecular target due to its overexpression in cancer and regulatory role in key cellular processes including the cell cycle, apoptosis and DNA damage repair. Multiple lines of evidence suggest an increasingly important role for CK2 in the DNA damage response, including the phosphorylation and activation of the mediator/adaptor proteins XRCC1 and MDC1. XRCC1 is an essential component for nucleotide excision repair which is the major repair pathway responsible for removing platinum adducts. MDC1 is the predominant γ-H2AX recognition factor in mammalian cells and is essential for homologous recombination repair. CX-4945 is a first-in-class, selective, oral inhibitor of CK2 currently in Phase 1 clinical trials. We sought to determine if inhibiting CK2 activity with CX-4945 would prevent phosphorylation of XRCC1 and MDC1 and potentiate the activity of platinum-based drugs by preventing DNA damage repair. Treatment of the ovarian cancer cell lines A2780 and SKOV3 with CX-4945 led to decreased phosphorylation of XRCC1 at the CK2 specific phosphorylation sites and reduced total XRCC1 protein levels. Likewise, immunoprecipitation of MDC1 from SKOV3 cells treated with CX-4945 revealed significant reductions in phosphorylation at the CK2 specific sites, while in A2780 cells MDC1 protein levels were decreased. The reduction of MDC1 protein levels was reproduced by CK2 siRNA, confirming that CK2 activity supports MDC1 expression levels. Combined treatment of A2780 cells with CX-4945 and cycloheximide revealed a faster rate of MDC1 degradation than with cycloheximide alone but did not affect MDC1 mRNA levels, indicating that CK2 regulates MDC1 protein stability. When combined with cisplatin, CX-4945 enhanced the activation of CHK2 and increased levels of γ-H2AX and cleaved PARP. In antiproliferative experiments, CX-4945 exhibited synergy with cisplatin in A2780 and SKOV3 cell lines. The combination of CX-4945 with cisplatin or carboplatin significantly enhanced antitumor activity in ovarian xenograft models and was well tolerated. Thus, the inhibition of CK2 by CX-4945 enhanced the antitumor activity of platinum agents by preventing DNA damage repair and inducing apoptosis. These data provide compelling preclinical support for pursuing CX-4945 in combination with platinum chemotherapy in the clinic. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 5494. doi:10.1158/1538-7445.AM2011-5494

Cancer is characterized by hyperactivation of ribosome biogenesis which depends on increased RNA Polymerase I (Pol I) transcription. Inhibition of Pol I transcription causes nucleolar stress that leads to the release of ribosomal proteins from the nucleolus into the nucleoplasm where they can sequester the p53 inhibitory protein MDM2, causing activation of p53 and induction of apoptosis. The inhibition of Pol I transcription as a therapeutic approach is significant because it impacts two critically balanced processes, proliferation and apoptosis, that regulate cancer cell survival. CX-5461 is a potent and selective inhibitor of Pol I transcription. CX-5461 acts at the initiation stage of Pol I transcription through the disruption of the SL1/rDNA complex. CX-5461 is non-genotoxic and does not inhibit DNA replication, protein translation or RNA Polymerase II transcription. We have previously demonstrated that CX-5461 triggers autophagic cell death in solid tumor cell lines and exhibits antitumor activity in xenograft models, highlighting the importance of Pol I transcription in cancer (Drygin et al. Cancer Res. in press). In preparation for clinical testing we sought to identify the most sensitive indications by evaluating CX-5461 against a panel of genetically diverse cancer cell lines. CX-5461 exhibited a broad range of antiproliferative activity with wild-type (wt) p53 cells derived from hematological malignancies being the most sensitive (median IC50 = 5 nM). Other cell types, i.e. p53 mutated hematological, p53wt and p53 mutated solid tumors were less sensitive to CX-5461 (median IC50s = 94, 164 and 265 nM respectively). In contrast, the median IC50 against normal cells was 5 uM indicating that CX-5461 selectively kills cancer cells. Further molecular characterization revealed that CX-5461 treatment of p53wt hematologic cancer cells inhibited rRNA synthesis, stabilized p53, activated p21, caused cell cycle arrest and induced apoptosis. Chemical inhibition of p53 prevented the induction of apoptosis indicating that CX-5461 acts through activation of p53. Interestingly, while p53 mutations impacted the activity of CX-5461, other genetic alterations known to silence p53 response, i.e. deletion of ARF, did not affect sensitivity to CX-5461 (Bywater et al. 2010 AACR Ann Met Proceedings). Activation of p53 has long been considered an attractive approach for treating cancers because of the surveillance function of p53 to remove abnormal cells via induction of apoptotic cell death. The fact that mutations or deletions of the p53 gene are relatively rare in hematological malignancies, coupled with our data that p53wt hematologic cancer cells are particularly sensitive to CX-5461 provides compelling rationale for evaluating CX-5461 in this patient population. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 4511. doi:10.1158/1538-7445.AM2011-4511

The epidermal growth factor receptor (EGFR) regulates several oncogenic signaling pathways including PI3K/AKT/mTOR, MEK/ERK, and STAT. A number of EGFR antagonists have been approved for treatment of late-stage tumors of epithelial origin. Despite these advances, there are several limitations to these therapies, including primary and acquired resistance, prompting the need to combine EGFR antagonists with agents that target pathways downstream of EGFR. CK2 modulates multiple pro-proliferative and pro-survival signals through many of these same signaling pathways, and co-overexpression of EGFR and CK2 has been frequently observed in solid tumors. Here we present the combination of EGFR-targeted agents with CX-4945, a first-in-class selective CK2 inhibitor currently under evaluation in a Phase I clinical trial. CK2 phosphorylates several key proteins at multiple levels within the PI3K/AKT/mTOR signaling pathway including AKT, PTEN, and p70S6K1. CK2 also regulates the Hsp90/Cdc37 machinery, whose clients include EGFR, AKT, and Src. We proposed that top-down inhibition of EGFR, combined with lateral inhibition of the PI3K/ATK/mTOR pathway by CX-4945, would result in an improved cancer therapy compared to EGFR antagonism alone. This hypothesis was tested in vitro and in vivo in A431 squamous cell carcinoma (SCC) and non-small cell lung carcinoma (NSCLC) models of various genetic backgrounds. Signaling pathways and induction of apoptosis were analyzed by western blot and cell proliferation was measured in a 96-hour cell viability assay. The combination of CX-4945 and erlotinib resulted in enhanced reduction in phosphorylation of AKT (T308), AKT (S473), PRAS40 (S246), mTOR (S2481), mTOR (S2448), p70S6K1 (T389), S6 (S235/6), S6 (240/4), and 4E-BP1 (T37/46), and decreased Mcl-1 levels. These effects were accompanied by decreased cell proliferation and synergistic induction of apoptosis. CX-4945 plus erlotinib exhibited enhanced antitumor activity in A431 SCC and NCI-H2170 NSCLC xenograft models; moreover, in the erlotinib-resistant NCI-H1975 NSCLC xenograft model, CX-4945 plus cetuximab resulted in enhanced efficacy. These data suggest that CX-4945 in combination with EGFR-targeted agents may improve clinical outcomes in patients with EGFR and CK2-driven cancers by inhibiting multiple nodes of the EGFR signaling pathway. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2560. doi:10.1158/1538-7445.AM2011-2560

Abstract 787 Multiple myeloma (MM) is an incurable malignancy characterized by infiltration of malignant plasma cells in the bone marrow. There are many subtypes of MM each of which relies on distinct oncogenic pathways. Oncogene addiction has been regarded as an Achilles' heel of cancer and has consequently been the focus of extensive efforts to design molecularly targeted anticancer therapies based on the premise that silencing an oncogene's expression will prove lethal in certain cancers. However, recent evidence suggests that MM may have a fatal vulnerability that is better described as non-oncogene addiction. Non-oncogenes do not directly transform cells but rather encode for normal cellular proteins that become overexpressed or otherwise deregulated in order to maintain oncogenic signaling. Protein kinase CK2 represents the prototypical non-oncogene. CK2 activity and expression levels are elevated in many cancers and it has been reported that MM cells rely on elevated CK2 for survival. CK2 is a highly conserved, constitutively active serine/threonine protein kinase that regulates multiple pathways important in MM including PI3K/AKT, JAK-STAT and NF-κB signaling cascades. Further, CK2 is elevated under hypoxic conditions regulating hypoxia-inducible transcription factor 1 alpha (HIF-1α) activity and other mediators of angiogenesis that are known to play an important role in MM pathogenesis. Given the generalized overexpression of CK2 in cancers, the central role of CK2 in multiple pro-survival pathways and the evidence that CK2 is an essential protein for MM cell survival, the development of selective CK2 inhibitors has emerged as an attractive targeted approach for the treatment of MM. Herein we describe CX-4945, a selective, orally bioavailable, small molecule inhibitor of CK2. CX-4945 is a potent, ATP-competitive inhibitor of both isoforms of the CK2 catalytic subunits CK2α and CK2α' with IC50 values of 1 nM. In a panel of 13 MM cell lines, CX-4945 exhibited a range of antiproliferative activity in the low micromolar range as measured by CellTiter-Glo® Luminescent Cell Viability Assay. Molecular characterization of the MM cell line panel revealed that on average CK2α mRNA levels and CK2α protein levels were elevated 9.5-fold and 14-fold, respectively, compared to normal CD138+ plasma cells. CX-4945 effectively reduced CK2 enzymatic activity in the MM cell lines. In immunoblots, the attenuation of PI3K/Akt signaling by CX-4945 was evidenced by dephosphorylation of Akt on the CK2-specific Ser129 site as well as the Ser473 and Thr308 sites. Further evidence of diminished Akt activity was demonstrated by decreased phosphorylation of the downstream Akt target protein p21 at Thr145. An additional biochemical consequence of CK2 inhibition was noted as CX-4945 selectively reduced phosphorylation of the p65 subunit of NF-κB at the CK2-specific Ser529 phosphorylation site but not at the S536 site. Moreover, CX-4945 inhibited the JAK/STAT pathway as demonstrated by the reduction in phosphorylation of regulatory sites on STAT3 (Tyr705) and JAK2 (Tyr1007/1008). PCR Arrays were used to analyze the global effect of CK2 inhibition on the NFκB and JAK/STAT mediated signal transduction pathways. Several key mediators, e.g. IL-6, CyclinD1, MYC, STAT1, STAT3, IFNγ, and IL-1R, were significantly downregulated upon treatment with CX-4945. Furthermore, CX-4945 reduced IL-6 secretion in a concentration dependent manner. In culture, MM cell lines have adapted to maintain HIF1α protein expression. CX-4945 effectively inhibited HIF1α expression and a well-known HIF1α transcriptional target, VEGF. Inhibition of CK2 by CX-4945 induced apoptosis in MM cells as shown by an increase in Caspase 3/7 activity and PARP cleavage. Interestingly, CX-4945 failed to induce apoptosis and had no effect on viability in the normal human-derived stromal cell line HS-5. These data lend further support to the CK2 non-oncogene addiction hypothesis in MM. A Phase 1 clinical trial evaluating CX-4945 as a single agent in solid tumors has already established a favorable pharmacokinetic, pharmacodynamic and safety profile. These findings, coupled with our preclinical data, suggest CX-4945 is a promising therapeutic agent for targeting aberrant CK2 activity in MM and a Phase 1 clinical trial in MM is underway. Disclosures: No relevant conflicts of interest to declare.

The PIM family of serine/threonine kinases are pro-proliferative kinases activated by multiple cytokines and growth factor signaling. The Pim kinases are unusual in that they are regulated primarily by transcription and not by membrane recruitment or phosphorylation like other serine/threonine kinases. Activated cytokine receptors recruit JAKs to induce STAT-dependent transcription of the Pim genes. They are proto-oncogenes and have been implicated in the process of lymphomagenesis and malignant transformation. Pim overexpression has been reported in diffuse B cell lymphoma, chronic lymphocytic leukemia, FLT3-mediated acute myelogenous leukemia and prostate cancer. Pim-2 is over expressed in leukemias and lymphomas, whereas Pim-3 overexpression has been observed in melanoma, pancreatic and gastric tumors. The recent reports of elevated levels of Pim-1 expression in human prostate tumor biopsies implicate the Pim family of protein kinases in the progression of human prostate tumors. Further, in transgenic animal models, Pim-1 expression has been shown to be elevated in prostate tumors that are caused by overexpression of the c-myc oncogene. Recent evidence reveals the overlapping and compensatory nature of Pim-1 and Pim-2 phosphorylation and highlights the importance of inhibiting all isoforms. The emerging role of the PIM kinase family in hematological malignancies and solid tumors and the druggable nature of their ATP binding pocket make them attractive targets for anticancer drug development. Utilizing a highly distinct molecular scaffold, CX-6258 was developed as a selective and potent small molecule pan-PIM kinase inhibitor. CX-6258 inhibits Pims 1, 2 and 3 with IC50 values in the low nanomolar range and high selectivity as evidenced in a screening panel of over 100 kinases. CX-6258 demonstrates potent in vitro antiproliferative activity, particularly in leukemia derived cell lines expressing the FLT3-ITD. Moreover, CX-6258 inhibits the phosphorylation of BAD and 4EBP1, known substrates for PIMs 1, 2 and 3. When delivered orally, this pan-Pim inhibitor is well tolerated and demonstrates potent antitumor activity in murine xenograft models of PIM driven cancer. Using CX-6258 as our “path finder” molecule, we have created four additional unique chemical scaffolds as pan-Pim inhibitors, and certain molecules from these scaffolds can inhibit Pims 1, 2 and 3 in the picomolar range while exhibiting no inhibitory activity of the Flt3 protein kinase. The in vivo and in vitro profiles of these chemically diverse series are indicative of an effective and potent anti-cancer mechanism mediated through the selective inhibition of PIM kinase activity. Together, these findings exemplify that we have created multiple proprietary chemical series of pan-Pim inhibitors exhibiting picomolar potency and discerning selectivity. Citation Information: Mol Cancer Ther 2009;8(12 Suppl):A246.

Akt, a critical protein kinase in the PI3K signaling pathway regulates multiple biological processes that are important in tumorigenesis. This “Master Regulator Kinase” is often hyperactivated in cancer through various mechanisms, including mutations or deletions in Akt, PI3K or PTEN tumor suppressor. The last decade witnessed the emergence of another “Master Regulator Kinase” - CK2. Like Akt, CK2 controls the growth, proliferation and survival of cancer cells. Ironically, CK2 regulates Akt through phosphorylation and down regulation of PTEN and via direct and specific phosphorylation of Akt at Ser129. This phosphorylation event by CK2 further stimulates the activity of Akt, thereby enhancing the “driver effect” of Akt in promoting oncogenic signaling. Unlike Akt, CK2 does not require phosphorylation for activation but rather its activity appears to be regulated through expression levels. Due to the unique shape of the ATP-binding site and an incomplete understanding of the regulation of CK2 expression, pharmacological targeting of CK2 has proven to be very challenging. To date only one small molecule inhibitor of CK2, CX-4945, has advanced into clinical development. Herein, we describe the pharmacological characterization of CX-4945, its impact on Akt signaling and implications for combination therapies. The high incidence of abnormalities found in the PI3K pathway in breast cancers and the distinct roles that CK2 and Akt play in this disease have made it an attractive tumor type to study the effects of CX-4945. A cell viability screen of 16 diverse but genetically well-characterized breast cancer lines revealed that cells carrying mutations causing Akt-activation were significantly more sensitive to CX-4945 than those that did not. Western blot analyses of these cell lines demonstrated good correlation between the phosphorylation of Akt at Ser129 and expression of catalytic subunits of CK2. Treatment with CX-4945 resulted in dramatic reductions of phosphorylation of Akt at Ser129 and reductions in phosphorylation of the downstream targets of Akt, e.g. p21. Upon combination of CX-4945 with inhibitors that targeted the PI3K/Akt pathway, we observed synergistic antiproliferative activity in breast cancer cells. Thus, evaluation of the effects of CX-4945 on the Akt pathway in breast cancer cell lines may allow for the identification of patient populations more sensitive to CX-4945 and guide the selection of more effective combination therapies for cancer patients. Citation Information: Mol Cancer Ther 2009;8(12 Suppl):C198.

Abstract 1726 Poster Board I-752 The PIM family of serine/threonine kinases are pro-proliferative kinases activated by multiple cytokines and growth factor signaling. The Pim kinases are unusual in that they are regulated primarily by transcription and not by membrane recruitment or phosphorylation like other serine/threonine kinases. Activated cytokine receptors recruit JAKs to induce STAT-dependent transcription of the Pim genes. They are proto-oncogenes and have been implicated in the process of lymphomagenesis and malignant transformation. Pim overexpression has been reported in diffuse B cell lymphoma, chronic lymphocytic leukemia, FLT3-mediated acute myelogenous leukemia and prostate cancer. Pim-2 is over expressed in leukemias and lymphomas, whereas Pim-3 overexpression has been observed in melanoma, pancreatic and gastric tumors. The recent reports of elevated levels of Pim-1 expression in human prostate tumor biopsies implicate the Pim family of protein kinases in the progression of human prostate tumors. Further, in transgenic animal models, Pim-1 expression has been shown to be elevated in prostate tumors that are caused by overexpression of the c-myc oncogene. Recent evidence reveals the overlapping and compensatory nature of Pim-1 and Pim-2 phosphorylation and highlights the importance of inhibiting all isoforms. The emerging role of the PIM kinase family in hematological malignancies and solid tumors and the druggable nature of their ATP binding pocket make them attractive targets for anticancer drug development Utilizing a highly distinct molecular scaffold, CX-6258 was developed as a selective and potent small molecule pan-PIM kinase inhibitor. CX-6258 inhibits Pims 1, 2 and 3 with IC50 values in the low nanomolar range and high selectivity as evidenced in a screening panel of over 100 kinases. CX-6258 demonstrates potent in vitro antiproliferative activity, particularly in leukemia derived cell lines expressing the FLT3-ITD. Moreover, CX-6258 inhibits the phosphorylation of BAD and 4EBP1, known substrates for PIMs 1, 2 and 3. When delivered orally, this pan-Pim inhibitor is well tolerated and demonstrates potent antitumor activity in murine xenograft models of PIM driven cancer. Using CX-6258 as our “path finder” molecule, we have created four additional unique chemical scaffolds as pan-Pim inhibitors, and certain of these scaffolds can inhibit Pims 1, 2 and 3 in the picomolar range while exhibiting no inhibitory activity of the Flt3 protein kinase. The in vivo and in vitro profiles of these chemically diverse series are indicative of an effective and potent anti-cancer mechanism mediated through the selective inhibition of PIM kinase activity. Together, these findings exemplify that we have created multiple proprietary chemical series of pan-Pim inhibitors exhibiting picomolar potency and high selectivity. Disclosures No relevant conflicts of interest to declare.

A series of viridin analogs was prepared from wortmannin by nucleophilic ring opening at C(20) and evaluated against the signaling kinases PI-3-kinase and mTOR. Several subnanomolar enzyme inhibitors with orders of magnitude selectivity for PI-3-kinase and strong cytotoxic activity against four cancer cell lines were identified. Among the ten most promising derivatives, six demonstrated lower liver toxicity and greater promise for inhibition of tumor cell growth than the lead structure wortmannin.