Cdc7 Kinase Inhibitors Research Articles

Antiproliferative Activity of Cephalotaxus Esters: Overcoming Chemoresistance.

Omacetaxine, a semisynthetic form of Homoharringtonine (HHT), was approved for the treatment of Chronic Myeloid Leukemia (CML). Previously, we have published the synthesis of this natural alkaloid and three of its derivatives: Deoxyharringtonine (DHT), Deoxyhomoharringtonine (DHHT), and Bis(demethyl)-deoxyharringtonine (BDHT), and reported its refractory activity against the HL-60/RV+ cells over-expressing P-glycoprotein 1 (MDR1). In this study, we have explored the extent of this resistance by first expanding the panel of established cell lines and using a panel of 21 leukemia patient-derived primary cells. Herein, we have reported consistent resistance to HTT of K562-derived cells and to mitoxantrone of MES-SA/MX2-derived cells; all of them have been found to overexpress MDR1, while we have found U87MG-ABCG2 and H69AR cells to be very sensitive to HTT. In contrast, DHT, DHHT, and BDHT seemingly overcame this resistance due to the changes made to the acyl chain of HTT, rendering the derivatives less susceptible to efflux. Surprisingly, the leukemia primary cells were very sensitive to HHT and its derivatives with low nanomolar potencies, followed by a new class of CDC7 kinase inhibitors, the anthracycline class of topoisomerase inhibitors, the DNA intercalator actinomycin-D, and the vinca alkaloid class of microtubule inhibitors. The mechanism of cell death induced by HTT and DHHT was found to be mediated via caspase 3 cleavage, leading to apoptosis. Taken together, our results confirm that HHT is a substrate for MDR1. It opens the door to a new opportunity to clinically evaluate HHT and its derivatives for the treatment of AML and other cancers.

ATR Restrains DNA Synthesis and Mitotic Catastrophe in Response to CDC7 Inhibition

DNA replication initiates from multiple origins, and selective CDC7 kinase inhibitors (CDC7is) restrain cell proliferation by limiting origin firing. We have performed a CRISPR-Cas9 genome-wide screen to identify genes that, when lost, promote the proliferation of cells treated with sub-efficacious doses of a CDC7i. We have found that the loss of function of ETAA1, an ATR activator, and RIF1 reduce the sensitivity to CDC7is by allowing DNA synthesis to occur more efficiently, notably during late S phase. We show that partial CDC7 inhibition induces ATR mainly through ETAA1, and that if ATR is subsequently inhibited, origin firing is unleashed in a CDK- and CDC7-dependent manner. Cells are then driven into a premature and highly defective mitosis, a phenotype that can be recapitulated by ETAA1 and TOPBP1 co-depletion. This work defines how ATR mediates the effects of CDC7 inhibition, establishing the framework to understand how the origin firing checkpoint functions.

Discovery of a Novel, Highly Potent, and Selective Thieno[3,2-d]pyrimidinone-Based Cdc7 Inhibitor with a Quinuclidine Moiety (TAK-931) as an Orally Active Investigational Antitumor Agent.

In our pursuit of developing a novel, potent, and selective cell division cycle 7 (Cdc7) inhibitor, we optimized the previously reported thieno[3,2-d]pyrimidinone analogue I showing time-dependent Cdc7 kinase inhibition and slow dissociation kinetics. These medicinal chemistry efforts led to the identification of compound 3d, which exhibited potent cellular activity, excellent kinase selectivity, and antitumor efficacy in a COLO205 xenograft mouse model. However, the issue of formaldehyde adduct formation emerged during a detailed study of 3d, which was deemed an obstacle to further development. A structure-based approach to circumvent the adduct formation culminated in the discovery of compound 11b (TAK-931) possessing a quinuclidine moiety as a preclinical candidate. In this paper, the design, synthesis, and biological evaluation of this series of compounds will be presented.

Abstract LB-288: CDC7 kinase inhibition by SRA141 induces a potentially novel caspase-dependent tumor cell apoptosis associated with altered DNA replication and cell cycle dynamics

Abstract DNA replication is a tightly regulated process required for faithful duplication of the genome. Previous research in lower eukaryotes has demonstrated a requisite role for the CDC7 protein kinase in DNA replication origin firing through phosphorylation of the MCM2-7 helicase complex. Owing to its overexpression in various neoplasms, CDC7 has emerged as an attractive target for cancer treatment. We previously reported that SRA141, a potent and selective CDC7 inhibitor, is cytotoxic to multiple tumor cell lines in vitro and demonstrates robust anti-tumor efficacy in colorectal and leukemia xenograft models. Here, we explored the effects of SRA141 on DNA replication and cell cycle dynamics and how these effects relate to the mechanism of SRA141-induced cell death in colorectal cancer cell lines. SRA141 treatment caused a complete inhibition of MCM2 phosphorylation and reduced overall cellular DNA synthesis within 3 hours, with the greatest effects observed in late S-phase. Unexpectedly, DNA combing experiments indicated that SRA141 caused a 70-90% increase in the rate of replication fork progression. These findings suggest that SRA141 may indeed limit origin firing, but this effect is compensated for in part by increased replication fork rates. Despite delay, nucleotide analog pulse-chase experiments indicated that SRA141 treated cells ultimately finished S phase and transitioned into mitosis. In contrast to other reports, no evidence of replication fork collapse was observed, indicating that the main mechanism of SRA141 cytotoxicity is not mediated through replication fork collapse. Intriguingly, some of the most pronounced effects of SRA141 treatment were on progression through M phase, as evidenced by an accumulation of mitotic cells and increased Cyclin B levels following treatment. Moreover, inhibition of Aurora B kinase, which regulates mitotic progression, strongly synergized with SRA141 in caspase-dependent cancer cell killing. Taken together, our findings indicate that the mechanism of cytotoxicity of CDC7 inhibitors is distinct from agents that cause replication fork collapse or inhibit CDKs, and thus may define a new class of cancer therapeutic agents that synergize with drugs that target certain mitotic pathways. Citation Format: Veena Jagannathan, Snezana Milutinovic, Ryan Hansen, Bryan Strouse, Christian Hassig, Eric Brown. CDC7 kinase inhibition by SRA141 induces a potentially novel caspase-dependent tumor cell apoptosis associated with altered DNA replication and cell cycle dynamics [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr LB-288.

Identification of Novel Cdc7 Kinase Inhibitors as Anti-Cancer Agents that Target the Interaction with Dbf4 by the Fragment Complementation and Drug Repositioning Approach.

BackgroundCdc7-Dbf4 is a conserved serine/threonine kinase that plays an important role in initiation of DNA replication and DNA damage tolerance in eukaryotic cells. Cdc7 has been found overexpressed in human cancer cell lines and tumor tissues, and the knockdown of Cdc7 expression causes an p53-independent apoptosis, suggesting that Cdc7 is a target for cancer therapy. Only a handful Cdc7 kinase inhibitors have been reported. All Cdc7 kinase inhibitors, including PHA-767491, were identified and characterized as ATP-competitive inhibitors. Unfortunately, these ATP-competitive Cdc7 inhibitors have no good effect on clinical trial.MethodsHere, we have developed a novel drug-screening platform to interrupt the interaction between Cdc7 and Dbf4 based on Renilla reniformis luciferase (Rluc)-linked protein-fragment complementation assay (Rluc-PCA). Using drug repositioning approach, we found several promising Cdc7 inhibitors for cancer therapy from a FDA-approved drug library.FindingsOur data showed that dequalinium chloride and clofoctol we screened inhibit S phase progression, accumulation in G2/M phase, and Cdc7 kinase activity. In addition, in vivo mice animal study suggests that dequalinium chloride has a promising anti-tumor activity in oral cancer. Interestingly, we also found that dequalinium chloride and clofoctol sensitize the effect of platinum compounds and radiation due to synergistic effect. In conclusion, we identified non-ATP-competitive Cdc7 kinase inhibitors that not only blocks DNA synthesis at the beginning but also sensitizes cancer cells to DNA damage agents.InterpretationThe inhibitors will be a promising anti-cancer agent and enhance the therapeutic effect of chemotherapy and radiation for current cancer therapy.FundThis work was supported by grants from the Ministry of Science and Technology, Ministry of Health and Welfare, and National Health Research Institutes, Taiwan.

Uncoupling fork speed and origin activity to identify the primary cause of replicative stress phenotypes

In growing cells, DNA replication precedes mitotic cell division to transmit genetic information to the next generation. The slowing or stalling of DNA replication forks at natural or exogenous obstacles causes “replicative stress” that promotes genomic instability and affects cellular fitness. Replicative stress phenotypes can be characterized at the single-molecule level with DNA combing or stretched DNA fibers, but interpreting the results obtained with these approaches is complicated by the fact that the speed of replication forks is connected to the frequency of origin activation. Primary alterations in fork speed trigger secondary responses in origins, and, conversely, primary alterations in the number of active origins induce compensatory changes in fork speed. Here, by employing interventions that temporally restrict either fork speed or origin firing while still allowing interrogation of the other variable, we report a set of experimental conditions to separate cause and effect in any manipulation that affects DNA replication dynamics. Using HeLa cells and chemical inhibition of origin activity (through a CDC7 kinase inhibitor) and of DNA synthesis (via the DNA polymerase inhibitor aphidicolin), we found that primary effects of replicative stress on velocity of replisomes (fork rate) can be readily distinguished from primary effects on origin firing. Identifying the primary cause of replicative stress in each case as demonstrated here may facilitate the design of methods to counteract replication stress in primary cells or to enhance it in cancer cells to increase their susceptibility to therapies that target DNA repair.

Abstract 3073: Potential predictive biomarkers of clinical responses for a novel CDC7-selective inhibitor TAK-931

Abstract Cell division cycle 7 (CDC7) is a serine/threonine kinase, which plays important roles in initiation of DNA replication by phosphorylating MCM2. Kinase activity of CDC7 is controlled by its binding protein DBF4 in a cell-cycle dependent manner. Here we developed a potent CDC7 inhibitor TAK-931 (IC50< 0.3 nM) as a cancer therapeutic drug candidate, which exhibits a time-dependent ATP-competitive kinetics to its ATP-binding pocket. The selectivity studies using the 308 kinases revealed >120-fold selectivity of TAK-931 for CDC7 kinase inhibition compared to other kinase inhibitions. Treatment with TAK-931 suppressed the cellular MCM2 phosphorylation at Ser40, resulting in a delayed S phase progression, checkpoint activation, apoptosis, and potent growth suppression in various cancer cell lines. Furthermore, oral administration of TAK-931 as a single agent caused a significant antitumor activity in multiple xenograft models which include both cell line-based xenografts and patient-derived xenograft (PDX) models. These results demonstrate that TAK-931 is a highly potent and selective inhibitor of CDC7 kinase, and causes a potent antiproliferation both in vitro and in vivo studies using various cancer cells. Next, to identify potential predictive biomarkers to guide patient-selection strategies, in vitro cell panel screening of TAK-931 using was tested for its ability to antiproliferation in 246 cell lines, which includes both solid and hematological cancer cells. TAK-931 inhibited proliferation of multiple cancer cell lines, with mean concentration producing a half-maximal response (EC50) values ranging from 29.1 nM to > 30 μM (median = 554.5 nM). While the wide range of TAK-931 antiproliferative spectrum was observed, neither doubling speed nor CDC7 expression profile did predict tTAK-931 sensitivity in cancer cell lines. A correlative study of the tumor genetic mutations in relation to antiproliferative activity that KRAS mutant cancer cells were more sensitive to TAK-931 compared to KRAS non-mutant cell lines (p<0.05). We also confirmed this KRAS-associated antiproliferative effect of TAK-931 in the SW48 isogenic cell lines of KRAS mutations (G12V, G13D). The ectopic expressions of G12V- and G13D-KRAS mutations increased the TAK-931 sensitivity compared to the KRAS-wild parental SW48 cell line. Given that KRAS mutations are frequently detected in clinical pancreatic tumors, we next conducted in vivo efficacy studies using pancreatic PDX models. Consistent to our hypothesis from in vitro studies, KRAS-mutant pancreatic PDX tumors were more sensitive to TAK-931 than the KRAS-wild pancreatic tumors; all KRAS-mutant pancreatic PDX models we tested exhibited >60% TGI. Our findings suggest that the KRAS-mutant pancreatic tumors could be the potential candidate for the TAK-931 target indication. Citation Format: Kenichi Iwai, Tadahiro Nambu, Osamu Kurasawa, Noriko Uchiyama, Ryo Dairiki, Yukiko Yamamoto, Satoru Nishizawa, Mengkun Zhang, Yuko Ishii, Huifeng Niu, Akihiro Ohashi. Potential predictive biomarkers of clinical responses for a novel CDC7-selective inhibitor TAK-931 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3073. doi:10.1158/1538-7445.AM2017-3073

DNA Replication Dynamics and Cellular Responses to ATP Competitive CDC7 Kinase Inhibitors.

The CDC7 kinase, by phosphorylating the MCM DNA helicase, is a key switch for DNA replication initiation. ATP competitive CDC7 inhibitors are being developed as potential anticancer agents; however how human cells respond to the selective pharmacological inhibition of this kinase is controversial and not understood. Here we have characterized the mode of action of the two widely used CDC7 inhibitors, PHA-767491 and XL-413, which have become important tool compounds to explore the kinase's cellular functions. We have used a chemical genetics approach to further characterize pharmacological CDC7 inhibition and CRISPR/CAS9 technology to assess the requirement for kinase activity for cell proliferation. We show that, in human breast cells, CDC7 is essential and that CDC7 kinase activity is formally required for proliferation. However, full and sustained inhibition of the kinase, which is required to block the cell-cycle progression with ATP competitor compounds, is problematic to achieve. We establish that MCM2 phosphorylation is highly sensitive to CDC7 inhibition and, as a biomarker, it lacks in dynamic range since it is easily lost at concentrations of inhibitors that only mildly affect DNA synthesis. Furthermore, we find that the cellular effects of selective CDC7 inhibitors can be altered by the concomitant inhibition of cell-cycle and transcriptional CDKs. This work shows that DNA replication and cell proliferation can occur with reduced CDC7 activity for at least 5 days and that the bulk of DNA synthesis is not tightly coupled to MCM2 phosphorylation and provides guidance for the development of next generation CDC7 inhibitors.

2-Aminomethylthieno[3,2-d]pyrimidin-4(3H)-ones bearing 3-methylpyrazole hinge binding moiety: Highly potent, selective, and time-dependent inhibitors of Cdc7 kinase

In order to increase the success rate for developing new Cdc7 inhibitors for cancer therapy, we explored a new chemotype which can comply with the previously-constructed pharmacophore model. Substitution of a pyridine ring of a serendipitously-identified Cdc7 inhibitor 2b with a 3-methylpyrazole resulted in a 4-fold increase in potency and acceptable kinase selectivity, leading to the identification of thieno[3,2-d]pyrimidin-4(3H)-one as an alternative scaffold. Structure-activity relationship (SAR) study revealed that incorporation of a substituted aminomethyl group into the 2-position improved kinase selectivity. Indeed, a pyrrolidinylmethyl derivative 10c was a potent Cdc7 inhibitor (IC50=0.70nM) with high selectivity (Cdk2/Cdc7≥14,000, ROCK1/Cdc7=200). It should be noted that 10c exhibited significant time-dependent Cdc7 inhibition with slow dissociation kinetics, cellular pharmacodynamic (PD) effects, and COLO205 growth inhibition. Additionally, molecular basis of high kinase selectivity of 10c is discussed by using the protein structures of Cdc7 and Cdk2.

Discovery of novel furanone derivatives as potent Cdc7 kinase inhibitors

Cdc7 is a serine-threonine kinase and plays a conserved and important role in DNA replication, and it has been recognized as a potential anticancer target. Herein, we report the design, synthesis and structure-activity relationship of novel furanone derivatives as Cdc7 kinase inhibitors. Compound 13 was identified as a strong inhibitor of Cdc7 with an IC50 value of 0.6 nM in the presence of 1 mM ATP and showed excellent kinase selectivity. In addition, it exhibited slow off-rate characteristics, which may offer advantages over known Cdc7 inhibitors in its potential to yield prolonged inhibitory effects in vivo. Compound 13 potently inhibited Cdc7 activity in cancer cells, and effectively induced cell death.

Cdc7 is a potent anti-cancer target in pancreatic cancer due to abrogation of the DNA origin activation checkpoint.

PurposeCdc7 is a serine/threonine kinase which is responsible for the ‘firing’ of replication origins leading to initiation of DNA replication. Inhibition or depletion of Cdc7 in normal cells triggers a DNA origin activation checkpoint causing a reversible G1 arrest. Here we investigate Cdc7 as a novel therapeutic target in pancreatic cancer.Experimental designCdc7 target validation was performed by immunoexpression profiling in a cohort of 73 patients with pancreatic adenocarcinoma including 24 controls. Secondly Cdc7 kinase was targeted in Capan-1 and PANC-1 pancreatic cancer cell line models using either an siRNA against Cdc7 or alternatively a small molecule inhibitor (SMI) of Cdc7 (PHA-767491).ResultsCdc7 was significantly overexpressed in pancreatic adenocarcinoma compared to benign pancreatic tissue (median LI 34.3% vs. 1.3%; P<0.0001). Cdc7 knockdown using siRNA in Capan-1 and PANC-1 cells resulted in marked apoptotic cell death when compared with control cells. A prominent sub-G1 peak was seen on flow cytometry (sub-G1 51% vs. 3% and 45% vs. 0.7% in Capan-1 and PANC-1 cells, respectively). Annexin V labelling confirmed apoptosis in 64% vs. 11% and 75% vs. 8%, respectively. Western blotting showed cleavage of PARP-1 and caspase-3 and presence of γH2A.X. TUNEL assay showed strong staining in treated cells. These results were mirrored following Cdc7 kinase inhibition with PHA-767491.ConclusionsOur findings show that Cdc7 is a potent anti-cancer target in pancreatic adenocarcinoma and that Cdc7 immunoexpression levels might be used as a companion diagnostic to predict response to therapeutic siRNAs or SMIs directed against this kinase.

Studies on the IC50 of Trisubstituted Thiazoles as Cdc7 Kinase Inhibitors

In this study, a nonlinear quantitative structure-activity relationship model for the prediction of the IC50 of trisubstituted thiazoles as Cdc7 kinase inhibitors was developed by the gene expression programming (GEP). This model is based on five descriptors which were selected from the descriptors' pool by heuristic method (HM). GEP rendered a good correlation between the experimental and predicted log (IC50) values with a correlation coefficient and a mean error of 0.85 and 0.22 for the training set, 0.84 and 0.39 for the testing set, respectively. The results indicate that this QSAR model has good predictive capability and it points to further optimization opportunities for Cdc7 kinase inhibitors.

Molecular Modeling Studies of Trisubstituted Thiazoles as Cdc7 Kinase Inhibitors through 3D‐QSAR and Molecular Docking Simulation

The cell division cycle 7 (Cdc7) is a serine‐threonine protein kinase which plays an essential role in replication and initiation of DNA synthesis. Overexpression of the Cdc7 in various tumor growths and in cell proliferation makes it a novel target for cancer therapy. In the present study, we have performed 3D quantitative structure–activity relationship (3D‐QSAR) studies on a series of trisubstituted thiazole derivatives targeting Cdc7 kinase. Reasonable CoMFA (q 2 = 0.838, NOC = 5, r 2 = 0.984) and CoMSIA (q 2 = 0.875, NOC = 6, r 2 = 0.979) models were developed. All the developed models were validated using an external validation test set, leave‐out‐five, bootstrapping, progressive samplings, and rm 2 metrics. Both the models exhibited acceptable values on all validation techniques and hence were considered to be robust and predictive. Molecular docking study revealed the crucial interaction of the most active compound (compound 49) with the conserved active site residues. Our results are in line with the previous studies. Contour map analysis revealed the important insights that would help in increasing the potency of the compounds. From these results, we could suggest that bulky positive substitutions are favored in the R2 position of the phenyl ring. Hydrogen‐bond acceptor groups in the R1 position could increase the activity. Hydrogen‐bond donor groups are favored near the amino group of R3 position. Long substitution in the R3 position will reduce the activity and must be avoided. Our results could be used to design more potent trisubstituted thiazole derivative of Cdc7 kinase inhibitors in future.

Human Multipotent Adult Progenitor Cells Effectively Reduce GVHD While Preserving Graft-Versus-Leukemia Activity after Allogeneic BMT

S158 dependent caspase-3 activation, and apoptotic cell death in cells exposed to the compounds. In vivo dose-dependent anti-tumor activity of 747 and 777 has been shown in both mouse models of ALL and AML. In addition, biomarker development and the mechansim of cancer cell selectivity with these compunds will be discussed. In all studies, MSK-777 was found to be at least a log more efficacious and therefore was chosen as the lead candidate to continue preclinical and clinical development. Conclusions: Cdc7 kinase inhibition is a novel and efficacious mode of therapy for the hematologic malignancies. MSK-777 is expected to enter Phase I clinical trials in early 2014.

Synthesis and structure–activity relationship of trisubstituted thiazoles as Cdc7 kinase inhibitors

The Cell division cycle 7 (Cdc7) protein kinase is essential for DNA replication and maintenance of genome stability. We systematically explored thiazole-based compounds as inhibitors of Cdc7 kinase activity in cancer cells. Our studies resulted in the identification of a potent, selective Cdc7 inhibitor that decreased phosphorylation of the direct substrate MCM2 in vitro and in vivo, and inhibited DNA synthesis and cell viability in vitro.

3D-QSAR Modeling Studies on Pyrrolopyridinone Derivatives as Inhibitors of Cdc7 Kinase

The cell division cycle 7 (Cdc7) is a serine threonine kinase that is a key regulator of the S-phase of the cell cycle, known to promote the activation of DNA replication origins in eukaryotic organisms. Cdc7 has recently emerged as an attractive target for the development of novel Cdc7 small-molecule inhibitors for cancer treatment. In this paper, we have applied 3D-QSAR mod r2 eling to develop the structure-activity correlation of pyrrolopyridinone derivatives based on Cdc7 inhibitors. The study has resulted in two types of satisfactory 3D-QSAR models, including the CoMFA model (q2= 0.633, r2 = 0.871) and CoMSIA model (q2 = 0.587, r2 = 0.757), for predicting the biological activity of new compounds. The contour maps obtained from the 3D-QSAR models help to better interpret the structure-activity relationship. The satisfactory results suggest that the developed 3D-QSAR models are advisable to offer utility in predicting the activity and guiding the rational design of novel Cdc7 inhibitors with desired activity. Keywords: Cdc7, Pyrrolopyridinone, 3D-QSAR, CoMFA, CoMSIA, Molecules Models.

Preclinical research in treatment of pancreatic cancer.

Pancreatic adenocarcinoma is an aggressive type of malignancy and remains a treatment-refractory cancer. Because of the few treatment options, understanding of the molecular mechanisms is necessary, for new drugs be developed against molecular targets. Two of the novel, promising regimens against molecular targets, NVP-BEZ235 and MSK-777, were examined in three preclinical studies performed in human pancreatic cell lines and mouse models and presented in the 2013 ASCO Annual Meeting. Two of the studies evaluated the role of NVP-BEZ235, an oral phosphatidylinositol-3-kinase (PI3K) inhibitor, in pancreatic cancer treatment, alone and in combination with nab-paclitaxel (Abstract #e15007) or gemcitabine (Abstract #e15070). The third study presents the effectiveness of the novel cell division cycle 7 (Cdc7) kinase inhibitor, MSK-777 (Abstract #e15059). All studies demonstrated promising results and further investigation is ongoing.

Cdc7 inhibition as a novel approach for pancreas cancer therapy.

e15059 Background: Pancreatic cancer is the fourth leading cause of cancer death in the USA. In 2012, 43,920 people will be diagnosed and 37,390 people will die of this disease. 95% of tumors reveal loss of the p16 protein, a regulator of the G1 to S phase transition. Cdc7 is a conserved kinase required for the initiation of DNA replication, is a target of the S-phase checkpoint, and has a role in controlling the DNA damage response. Downregulation of Cdc7 kinase activity resulted in slowing of S-phase and cell cycle arrest followed by accumulation of DNA damage. Cdc7 has been shown to be over-expressed in many different tumors including the majority of solid and liquid tumors. In our laboratory a novel natural product small molecule inhibitor (MSK-777) has been identified, developed and shown to be efficacious in cell based cytotoxicity assays and multiple animal models of cancer. Methods: We have examined the efficacy of Cdc7 kinase inhibition as a therapeutic approach for pancreatic cancer by examining the sensitivity of MSK-777 in Capan-1, BxPC3, and PANC-1 cell lines. These cells were treated with MSK-777, control (DMSO), or hydroxyurea and collected for viable cell counts, fluorescence-activated cell sorting (FACS), and western blotting. Results: Cell viability analyses revealed that MSK-777 had a dramatic effect after 24 hours, reducing cell viability to less then 20% in BxPC3 cells. FACS results demonstrated that MSK-777 exposure resulted in cell cycle arrest at G1/S in Capan-1 and PANC-1 cells by 48 hours while BxPC3 cells showed a significant sub-G1 population by 24 hours, indicating apoptotic cell death. Western blotting showed that in BxPC3 cells phosphorylation of the mini-chromosome maintenance 2 protein (Mcm2) disappeared by 24 hours, indicating inactivation of the helicase that unwinds the strands of DNA during replication. Western blots of Capan-1 and PANC-1 cells showed lower levels of phosphorylated Mcm2 by 48 hours. Conclusions: We are currently examining the efficacy of MSK-777 in mouse models of orthotopically injected pancreatic cancer cells. Based on these collective results, inhibition of Cdc7 kinase activity with MSK-777 represents a novel and promising therapy for this deadly disease.

Cdc7-dependent and -independent phosphorylation of Claspin in the induction of the DNA replication checkpoint

Claspin is a critical mediator protein in the DNA replication checkpoint, responsible for ATR-dependent activation of the effector kinase Chk1. Cdc7, an essential kinase required for the initiation of DNA replication, can also interact with and phosphorylate Claspin. In this study we use small-molecule inhibitors of Cdc7 kinase to further understand the relationship between Cdc7, Claspin and Chk1 activation. We demonstrate that inhibition of Cdc7 kinase delays HU-induced phosphorylation of Chk1 but does not affect the maintenance of the replication checkpoint once it is established. We find that while chromatin association of Claspin is not affected by Cdc7 inhibition, Claspin phosphorylation is attenuated following HU treatment, which may be responsible for the altered kinetics of HU-induced Chk1 phosphorylation. We demonstrate that Claspin is an in vitro substrate of Cdc7 kinase, and using mass-spectrometry, we identify multiple phosphorylation sites that help to define a Cdc7 phosphorylation motif. Finally, we show that the interaction between Claspin and Cdc7 is not dependent on Cdc7 kinase activity, but Claspin interaction with the DNA helicase subunit Mcm2 is lost upon Cdc7 inhibition. We propose Cdc7-dependent phosphorylation regulates critical protein-protein interactions and modulates Claspin’s function in the DNA replication checkpoint.

Abstract 711: Small molecule compounds that target cell division cycle 7 (Cdc7) kinase inhibit cell proliferation and tumor growth.

Abstract Cdc7 is an essential, serine/threonine protein kinase that activates the initiation of DNA synthesis at replication origins. Cdc7 also promotes cell cycle checkpoint activation in response to replication stress. As a key regulator of S phase entry and progression, Cdc7 kinase is a potential target for cancer therapy, with a distinct mechanism of action from known drugs that inhibit DNA replication. Following a high throughput screen for inhibitors of Cdc7 kinase activity, we investigated structure-activity relationships of azole-based compounds and optimized the compounds for potency and pharmacokinetic properties. Here we present the characterization of one of these compounds as a potent, selective, bioavailable Cdc7 kinase inhibitor. In cells, Cdc7 inhibition decreases MCM2 phosphorylation and DNA synthesis, causes DNA damage, and slows S phase progression. Cdc7 inhibition also induces chromosome missegregation leading to cell lethality in vitro and tumor growth inhibition in vivo. Cdc7 inhibition provides a new approach to target cancers, either as a single agent or in combination with chemotherapy. Citation Format: Julie Bailis, Li Fang, Jessica Orf, Scott Heller, Tammy Bush, Matthew Bourbeau, Sonia Escobar, Michael Frohn, Paul Harrington, Faye Hsieh, Alexander Pickrell, Kelvin Sham, Aaron Siegmund, Helming Tan, Leeanne Zalameda, John Allen, Dineli Wickramasinghe. Small molecule compounds that target cell division cycle 7 (Cdc7) kinase inhibit cell proliferation and tumor growth. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 711. doi:10.1158/1538-7445.AM2013-711