Abstract B190: Pharmacokinetics of the AKT inhibitor CCT128930 from dried blood spots sampled from caudal bleeding compared with conventional cardiac puncture

There has been much increase in the use of blood spots in recent years as a result of the ease of storage and transport of blood dried on cards compared with frozen plasma. In preclinical studies in oncology, mice are the model used for therapy experiments and blood spots allow full pharmacokinetic (PK) studies in 3–4 animals versus 21–27 for conventional plasma pharmacokinetics analysis, saving animals and decreasing compound usage. We here apply the blood spots technology to the early pharmacokinetic analysis of the AKT inhibitor CCT128930 dosed i.v. at 10mg/kg and bled from the tail vein.

The PK are very reproducible between individual mice and the blood levels are not affected by the type of anticoagulant used (heparin or EDTA) or by use of the FTA-DMPK card. CCT128930 shows a blood clearance of 0.092L/h (<liver blood flow) and volume of distribution of 140mL. However, the PK parameters evaluated in blood water by conventional methods (cardiac puncture) differ significantly to those from the blood spot experiments. The overall blood clearance is 1.6-fold higher following blood measurement in samples taken by cardiac puncture versus serial tail bleed. The 6h post-dosing concentrations of CCT128930 following caudal sampling are 10-fold higher than that measured after cardiac puncture although there is no difference in Cmax. These data suggest that the serial bleeding from the tail vein affects the PK parameters of this compound compared with conventional bleeding. We have used blood spots extensively in our drug discovery programs checking the 6h sample versus conventional cardiac bleed and this strategy has allowed us to save over 50% of animals in the last year in our preclinical PK evaluations.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr B190.

The 2,11-cyclized cembranoids: cladiellins, asbestinins, and briarellins (period 1998-2010)

The 2,11-cyclized cembranoids are isolated from marine invertebrates of Octocorallia species. They are a very interesting class of natural products sharing a common oxatricyclo[6.6.1.0(2,7)]pentadecane core and carrying a varied substituent pattern. This review presents their structural diversity along with the reported biological activities. The 2,11-cyclized cembranoids were comprehensively reviewed previously in 1998, and this contribution will serve as an update of that work. Since 1998 a number of structural assignments of the isolated products have been revised, some as a result of total synthesis efforts. The chemical reactivity of several of the natural compounds has been studied, and the relevance of these findings to the biosynthesis or the generation of isolation artifacts is discussed. The wide range of biological activities displayed by the 2,11-cyclized cembranoids justifies the interest shown within the synthetic chemistry community and suggests that this class of natural products remains a fruitful area for future synthetic and biological research.

Checkpoint kinase inhibitors: a patent review (2009 - 2010)

INTRODUCTION

Cells that suffer DNA damage activate the checkpoint kinases CHK1 and CHK2, which signal to initiate repair processes, limit cell-cycle progression and prevent cell replication, until the damaged DNA is repaired. Due to their potential application as novel anticancer therapies, inhibitors of CHK1 and CHK2 have become the focus of numerous drug discovery projects.

AREAS COVERED

This patent review examines the chemical structures and biological activities of recently reported CHK1 and CHK2 inhibitors. The chemical abstract and patent databases SciFinder and esp@cenet were used to locate patent applications that were published between September 2008 and December 2010, claiming chemical structures for use as CHK1 or CHK2 inhibitors.

EXPERT OPINION

This is an exciting time for checkpoint kinase inhibitors, with several currently in Phase I or II clinical trials. Many of the CHK1 inhibitors contained within this patent review have shown preclinical efficacy in combination with DNA-damaging chemotherapies. CHK1 inhibitors have recently been demonstrated to be efficacious as single agents in preclinical models of tumors with constitutive activation of CHK1 or high intrinsic DNA damage due to replication stress. The level of newly published patent applications covering CHK1 and CHK2 inhibitors remains high and a diverse range of scaffolds has been claimed.

CCT241533 is a potent and selective inhibitor of CHK2 that potentiates the cytotoxicity of PARP inhibitors

CHK2 is a checkpoint kinase involved in the ATM-mediated response to double-strand DNA breaks. Its potential as a drug target is still unclear, but inhibitors of CHK2 may increase the efficacy of genotoxic cancer therapies in a p53 mutant background by eliminating one of the checkpoints or DNA repair pathways contributing to cellular resistance. We report here the identification and characterization of a novel CHK2 kinase inhibitor, CCT241533. X-ray crystallography confirmed that CCT241533 bound to CHK2 in the ATP pocket. This compound inhibits CHK2 with an IC(50) of 3 nmol/L and shows minimal cross-reactivity against a panel of kinases at 1 μmol/L. CCT241533 blocked CHK2 activity in human tumor cell lines in response to DNA damage, as shown by inhibition of CHK2 autophosphorylation at S516, band shift mobility changes, and HDMX degradation. CCT241533 did not potentiate the cytotoxicity of a selection of genotoxic agents in several cell lines. However, this compound significantly potentiates the cytotoxicity of two structurally distinct PARP inhibitors. Clear induction of the pS516 CHK2 signal was seen with a PARP inhibitor alone, and this activation was abolished by CCT241533, implying that the potentiation of PARP inhibitor cell killing by CCT241533 was due to inhibition of CHK2. Consequently, our findings imply that CHK2 inhibitors may exert therapeutic activity in combination with PARP inhibitors.

Preclinical pharmacology, antitumor activity, and development of pharmacodynamic markers for the novel, potent AKT inhibitor CCT128930

AKT is frequently deregulated in cancer, making it an attractive anticancer drug target. CCT128930 is a novel ATP-competitive AKT inhibitor discovered using fragment- and structure-based approaches. It is a potent, advanced lead pyrrolopyrimidine compound exhibiting selectivity for AKT over PKA, achieved by targeting a single amino acid difference. CCT128930 exhibited marked antiproliferative activity and inhibited the phosphorylation of a range of AKT substrates in multiple tumor cell lines in vitro, consistent with AKT inhibition. CCT128930 caused a G(1) arrest in PTEN-null U87MG human glioblastoma cells, consistent with AKT pathway blockade. Pharmacokinetic studies established that potentially active concentrations of CCT128930 could be achieved in human tumor xenografts. Furthermore, CCT128930 also blocked the phosphorylation of several downstream AKT biomarkers in U87MG tumor xenografts, indicating AKT inhibition in vivo. Antitumor activity was observed with CCT128930 in U87MG and HER2-positive, PIK3CA-mutant BT474 human breast cancer xenografts, consistent with its pharmacokinetic and pharmacodynamic properties. A quantitative immunofluorescence assay to measure the phosphorylation and total protein expression of the AKT substrate PRAS40 in hair follicles is presented. Significant decreases in pThr246 PRAS40 occurred in CCT128930-treated mouse whisker follicles in vivo and human hair follicles treated ex vivo, with minimal changes in total PRAS40. In conclusion, CCT128930 is a novel, selective, and potent AKT inhibitor that blocks AKT activity in vitro and in vivo and induces marked antitumor responses. We have also developed a novel biomarker assay for the inhibition of AKT in human hair follicles, which is currently being used in clinical trials.

Aminopyrazine inhibitors binding to an unusual inactive conformation of the mitotic kinase Nek2: SAR and structural characterization

We report herein the first systematic exploration of inhibitors of the mitotic kinase Nek2. Starting from HTS hit aminopyrazine 2, compounds with improved activity were identified using structure-based design. Our structural biology investigations reveal two notable observations. First, 2 and related compounds bind to an unusual, inactive conformation of the kinase which to the best of our knowledge has not been reported for other types of kinase inhibitors. Second, a phenylalanine residue at the center of the ATP pocket strongly affects the ability of the inhibitor to bind to the protein. The implications of these observations are discussed, and the work described here defines key features for potent and selective Nek2 inhibition, which will aid the identification of more advanced inhibitors of Nek2.

Structure-based design of potent and selective 2-(quinazolin-2-yl)phenol inhibitors of checkpoint kinase 2

Structure-based design was applied to the optimization of a series of 2-(quinazolin-2-yl)phenols to generate potent and selective ATP-competitive inhibitors of the DNA damage response signaling enzyme checkpoint kinase 2 (CHK2). Structure-activity relationships for multiple substituent positions were optimized separately and in combination leading to the 2-(quinazolin-2-yl)phenol 46 (IC(50) 3 nM) with good selectivity for CHK2 against CHK1 and a wider panel of kinases and with promising in vitro ADMET properties. Off-target activity at hERG ion channels shown by the core scaffold was successfully reduced by the addition of peripheral polar substitution. In addition to showing mechanistic inhibition of CHK2 in HT29 human colon cancer cells, a concentration dependent radioprotective effect in mouse thymocytes was demonstrated for the potent inhibitor 46 (CCT241533).

Identification by high-throughput screening of viridin analogs as biochemical and cell-based inhibitors of the cell cycle-regulated nek2 kinase

Nek2 is a serine/threonine protein kinase that localizes to the centrosome and is implicated in mitotic regulation. Overexpression of Nek2 induces premature centrosome separation and nuclear defects indicative of mitotic errors, whereas depletion of Nek2 interferes with cell growth. As Nek2 expression is upregulated in a range of cancer cell lines and primary human tumors, inhibitors of Nek2 may have therapeutic value in cancer treatment. The authors used a radiometric proximity assay in a high-throughput screen to identify small-molecule inhibitors of Nek2 kinase activity. The assay was based on the measurement of the radiolabeled phosphorylated product of the kinase reaction brought into contact with the surface of wells of solid scintillant-coated microplates. Seventy nonaggregating hits were identified from approximately 73,000 compounds screened and included a number of toxoflavins and a series of viridin/wortmannin-like compounds. The viridin-like compounds were >70-fold selective for Nek2 over Nek6 and Nek7 and inhibited the growth of human tumor cell lines at concentrations consistent with their biochemical potencies. An automated mechanism-based microscopy assay in which centrosomes were visualized using pericentrin antibodies confirmed that 2 of the viridin inhibitors reduced centrosome separation in a human tumor cell line. The data presented show that pharmacological inhibition of Nek2 kinase results in the expected phenotype of disruption to centrosome function associated with growth inhibition and further supports Nek2 as a target for cancer drug discovery.

Probing the probes: fitness factors for small molecule tools

Chemical probes for interrogating biological processes are of considerable current interest. Cell permeable small molecule tools have a major role in facilitating the functional annotation of the human genome, understanding both physiological and pathological processes, and validating new molecular targets. To be valuable, chemical tools must satisfy necessary criteria and recent publications have suggested objective guidelines for what makes a useful chemical probe. Although recognizing that such guidelines may be valuable, we caution against overly restrictive rules that may stifle innovation in favor of a "fit-for-purpose" approach. Reviewing the literature and providing examples from the cancer field, we recommend a series of "fitness factors" to be considered when assessing chemical probes. We hope this will encourage innovative chemical biology research while minimizing the generation of poor quality and misleading biological data, thus increasing understanding of the particular biological area, to the benefit of basic research and drug discovery.

Creating an antibacterial with in vivo efficacy: synthesis and characterization of potent inhibitors of the bacterial cell division protein FtsZ with improved pharmaceutical properties

3-Methoxybenzamide (1) is a weak inhibitor of the essential bacterial cell division protein FtsZ. Alkyl derivatives of 1 are potent antistaphylococcal compounds with suboptimal drug-like properties. Exploration of the structure−activity relationships of analogues of these inhibitors led to the identification of potent antistaphylococcal compounds with improved pharmaceutical properties.

Abstract 3503: CCT241533 is a novel, potent and selective inhibitor of CHK2 and potentiates the cellular effects of PARP inhibitors

CHK2 is a checkpoint kinase involved in the ATM-mediated response to double stranded DNA breaks (DSB). Detection of DSB by the MRE11-RAD50-NBS1 (MRN) complex leads to activation of ataxia telangiectasia mutated (ATM) kinase, which can then phosphorylate CHK2 on threonine 68. This facilitates CHK2 to dimerisation and autophosphorylation in trans at threonine 383/387, resulting in full activation and subsequent phosphorylation in cis at serine 516, a biomarker read out of CHK2 activation. Once activated, CHK2 phosphorylates a range of targets involved in DNA damage repair, cell cycle arrest and apoptosis.

It has been suggested that inhibitors of CHK2 may increase the efficacy of genotoxic cancer therapies. However, the evidence so far is inconsistent. We have therefore developed a CCT241533, a potent and selective inhibitor of CHK2, as a molecular tool and potential therapeutic agent (the structure will be disclosed in the presentation). The co-crystal structure of CCT241533 bound to the kinase domain of CHK2 confirms that the compound binds the ATP binding pocket. CCT241533 inhibits CHK2 with an IC50 of 3 nM and shows minimal inhibitory activity against a panel of known kinases at 1 μM, including CHK1 (IC50 = 245 nM). We show that CCT241533 blocks CHK2 activity in three human tumor cell lines (HT29, HeLa, MCF7) in which we have confirmed functional activation of CHK2. We also show that CCT241533 potentiates the growth inhibitory effect of two structurally distinct Poly (ADP-ribose) polymerase (PARP) inhibitors in p53 defective human cancer cells. We further demonstrate that this cellular effect correlates with inhibition of PARP inhibitor-mediated induction of CHK2 activity, as assessed by the phospho-serine 516 biomarker and CHK2 mobility shift. This adds strength to the conclusion that the potentiation between the two compounds is due to their effects on CHK2.

To summarize, we have developed a potent and selective CHK2 inhibitor and show, for the first time, potentiation between CHK2 inhibition and PARP inhibition.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3503.

Abstract 3518: Preclinical pharmacology of the novel, potent & selective CHK1 inhibitor SAR-020106

Genotoxic antitumor agents continue to be the mainstay of current cancer chemotherapy. These drugs cause DNA damage and activate numerous cell cycle checkpoints facilitating DNA repair and the maintenance of genomic integrity. Most human tumors lack functional p53 and consequently have compromized G1/S checkpoint control. This has led to the hypothesis that S and G2/M checkpoint abrogation may selectively enhance genotoxic cell killing in a p53 deficient background, as normal cells would be rescued at the G1/S checkpoint. CHK1 is a serine/threonine kinase associated with DNA damage linked S and G2/M checkpoint control. SAR-020106 (the structure will be shown on the poster) is an ATP competitive, potent and selective CHK1 inhibitor with an IC50 of 13.3nM on the isolated human enzyme. This compound abrogates an etoposide-induced G2 arrest with an IC50 of 55nM in HT29 cells, and significantly enhances the cell killing of gemcitabine and SN38 by 3.0 to 29-fold in a number of colon tumor lines in vitro and in a p53 dependent fashion. Biomarker studies have shown that SAR-020106 inhibits cytotoxic drug induced autophosphorylation of CHK1 at S296 and blocks phosphorylation of CDK1 at Y15 in a dose-dependent fashion both in vitro and in vivo. Cytotoxic drug combinations were associated with increased γH2AX and PARP cleavage consistent with SAR-020106 enhanced DNA damage and tumor cell death. Irinotecan and gemcitabine antitumor activity was enhanced by SAR-020106 in vivo with minimal toxicity. Orally bioavailable analogues of SAR-02106 are currently under development. In conclusion SAR-020106 represents a novel class of CHK1 inhibitors which can enhance antitumor activity with selected anticancer drugs in vivo and may therefore have clinical utility.

Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3518.

Abstract 4481: First report of preclinical pharmacology of two novel potent AKT inhibitors and development of pharmacodynamic (PD) biomarkers in tumor and surrogate tissue

Deregulated AKT signalling is implicated in cancer. The preclinical characterization of AKT inhibitors and development of PD biomarkers are vital prior to clinical trials. Invasive techniques for clinical PD analyses pose ethical and logistical issues, hence hair follicles may represent a non-invasive option. The pyrazole AT7867 and pyrrolopyrimidine CCT128930 are novel ATP-competitive AKT inhibitors from different chemical series developed at The Institute of Cancer Research in collaboration with Astex Therapeutics (Cambridge, UK).

AT7867 and CCT128930 have IC50 values against AKT2 of 17nM and 6nM respectively. Growth inhibitory IC50 (GI50) values were 2.4μM and 6.3μM in PTEN-null U87MG glioblastoma cells as measured by SRB assay. Cellular studies of both compounds in U87MG cells were carried out by Meso Scale Discovery (MSD) ELISA, western blot (WB) and immunofluorescence. These showed an initial induction of phosphorylated (p) Ser473 AKT as expected with ATP-competitive AKT inhibitors, and inhibition of downstream AKT targets, including pSer9 GSK-3β, pThr246 PRAS40, pSer127 YAP and pSer235/236 S6RP, indicating AKT pathway blockade. Interestingly, CCT128930 inhibited phosphorylation of AKT targets GSK-3β, S6RP and PRAS40 at lower concentrations (0.5-1µM), compared to AT7867 (5-10µM) in U87MG cells. Phosphorylation was also inhibited at earlier time points with equipotent doses (3XGI50) of CCT128930 versus AT7867. CCT128930 also caused a predominant G0/G1 phase arrest, while AT7867 resulted in a predominant G2 arrest in U87MG cells at equipotent doses (3XGI50), using BrdU and PI staining and flow cytometry. We report for the first time in vivo efficacy with intraperitoneally (ip) or orally administered AT7867 in PTEN-null MES-SA uterine sarcoma and U87MG mouse xenograft models; and ip administered CCT128930 in HER2-overexpressing BT474 breast cancer and U87MG xenografts, which correlated with in vivo pharmacokinetics (PK) and PD biomarker modulation of pSer9 GSK-3β and pSer235/236 S6RP using WB and MSD.

Hair follicles were developed as a robust surrogate PD biomarker, with pThr246 PRAS40 as a PD readout. This assay was validated with healthy volunteer hair follicles, which were treated ex vivo with CCT128930. A significant decrease in pThr246 PRAS40 (p<0.001) relative to total PRAS40 was observed with immunofluorescence, which was quantified using INCell Translator software. This assay is currently being utilized as a PD readout in the MK2206 Phase I AKT inhibitor trial, and will be used in future clinical studies of ATP-competitive AKT inhibitors.

In conclusion, by employing an integrated PK and PD biomarker-driven drug discovery strategy, we have developed 2 novel and potent AKT inhibitors with antitumor activity, and have validated a robust surrogate biomarker assay for AKT inhibition for use in clinical trials.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4481.

Abstract 2677: A detailed analysis of protein binding and biological activity of methoxy-substituted resorcinylic isoxazole amide HSP90 inhibitors

The molecular chaperone Heat Shock Protein 90 (HSP90) has emerged as an exciting biological target in cancer therapy. HSP90 regulates the conformation, stability and activity of several client proteins such as ERBB2, BRAF, CRAF, AKT and mutant p53, many of which are associated with the six hallmarks of cancer. Inhibition of HSP90 results in the degradation of these clients by the 26S proteasome, leading to cell cycle arrest and apoptosis. Resorcinylic isoxazole amide HSP90 inhibitors show considerable promise and NVP-AUY922 is currently in Phase I clinical trials. Our previous studies have reported that one or both of the phenolic groups on the resorcinol ring are important for HSP90 inhibitory activity (Brough et al J Med Chem 51 196-218 2008). To explore the mechanisms underlying the importance of the phenol groups on protein binding and biological activity, a series of monomethoxy- and dimethoxy-substituted resorcinylic 5′-ethyl isoxazole amides were synthesized and compared with the 2′,4′-dihydroxy compound by protein X-ray crystal structure and biological techniques. The most potent HSP90 inhibitors in this series in terms of binding to the HSP90 target and inhibiting cancer cell proliferation was the 2′,4′-dihydroxy-5′ethyl isoxazole CCT239215, followed by the 2′-hydroxy-4′methoxy-5′ethyl isoxazole CCT078722. In contrast, 2′,4′-dimethoxy and 2′-methoxy, 4′-hydroxy derivatives showed no binding to HSP90 or antiproliferative activity. This structure-activity relationship was also maintained with respect to biomarkers of HSP90 target inhibition, as measured by depletion of HSP90 client proteins and induction of HSP72. In HCT116 human colon cells treatment with 350nM of CCT239215 and CCT078722 for 4hr caused a loss of HSP90 from P23 immunoprecipitates, demonstrating dissociation between P23 and HSP90, thereby confirming on-target effects. No dissociation was observed with the inactive 2′-methoxy, 4′-hydroxy or 2′,4′-dimethoxy analogs. These results confirm that the hydroxy group at the 2′ position on the resorcinol ring is crucial for HSP90 inhibitory activity. X-ray crystal structures showed that for CCT078722, the 4′-methoxy group of the resorcinol ring disrupts the hydrogen bonding that is seen with 2′,4′-dihydroxy CCT239215 and with the clinical candidate NVP-AUY922, and instead is involved in van der Waals contacts. Thus the results provide a structural explanation for the reduced but still significant activity of the 2′-methoxy-subtituted analog and the lack of activity of the 2′,4′-dimethoxy-substituted compound.

Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2677.

Discovery of 4-amino-1-(7H-pyrrolo[2,3-d]pyrimidin-4-yl)piperidine-4-carboxamides as selective, orally active inhibitors of protein kinase B (Akt)

Protein kinase B (PKB or Akt) is an important component of intracellular signaling pathways regulating growth and survival. Signaling through PKB is frequently deregulated in cancer, and inhibitors of PKB therefore have potential as antitumor agents. The optimization of lipophilic substitution within a series of 4-benzyl-1-(7H-pyrrolo[2,3-d]pyrimidin-4-yl)piperidin-4-amines provided ATP-competitive, nanomolar inhibitors with up to 150-fold selectivity for inhibition of PKB over the closely related kinase PKA. Although active in cellular assays, compounds containing 4-amino-4-benzylpiperidines underwent metabolism in vivo, leading to rapid clearance and low oral bioavailability. Variation of the linker group between the piperidine and the lipophilic substituent identified 4-amino-1-(7H-pyrrolo[2,3-d]pyrimidin-4-yl)piperidine-4-carboxamides as potent and orally bioavailable inhibitors of PKB. Representative compounds modulated biomarkers of signaling through PKB in vivo and strongly inhibited the growth of human tumor xenografts in nude mice at well-tolerated doses.

The preclinical pharmacology and therapeutic activity of the novel CHK1 inhibitor SAR-020106

Genotoxic antitumor agents continue to be the mainstay of current cancer chemotherapy. These drugs cause DNA damage and activate numerous cell cycle checkpoints facilitating DNA repair and the maintenance of genomic integrity. Most human tumors lack functional p53 and consequently have compromised G(1)-S checkpoint control. This has led to the hypothesis that S and G(2)-M checkpoint abrogation may selectively enhance genotoxic cell killing in a p53-deficient background, as normal cells would be rescued at the G(1)-S checkpoint. CHK1 is a serine/threonine kinase associated with DNA damage-linked S and G(2)-M checkpoint control. SAR-020106 is an ATP-competitive, potent, and selective CHK1 inhibitor with an IC(50) of 13.3 nmol/L on the isolated human enzyme. This compound abrogates an etoposide-induced G(2) arrest with an IC(50) of 55 nmol/L in HT29 cells, and significantly enhances the cell killing of gemcitabine and SN38 by 3.0- to 29-fold in several colon tumor lines in vitro and in a p53-dependent fashion. Biomarker studies have shown that SAR-020106 inhibits cytotoxic drug-induced autophosphorylation of CHK1 at S296 and blocks the phosphorylation of CDK1 at Y15 in a dose-dependent fashion both in vitro and in vivo. Cytotoxic drug combinations were associated with increased gammaH2AX and poly ADP ribose polymerase cleavage consistent with the SAR-020106-enhanced DNA damage and tumor cell death. Irinotecan and gemcitabine antitumor activity was enhanced by SAR-020106 in vivo with minimal toxicity. SAR-020106 represents a novel class of CHK1 inhibitors that can enhance antitumor activity with selected anticancer drugs in vivo and may therefore have clinical utility.

Abstract C208: CCT129254 (AT11854) is a well tolerated, orally bioavailable inhibitor of AKT/PKB with pharmacodynamic and antitumor activity in a range of xenograft models

The PI3K/AKT/mTOR pathway is the most frequently deregulated pathway in human cancer. The serine/threonine kinase AKT (PKB), a member of the AGC family of protein kinases, is central to this pathway and is considered an important target for cancer therapy. However, the development of well tolerated, orally bioavailable inhibitors of catalysis targeting this enzyme has proved challenging and there are currently no such agents that have progressed to phase II clinical studies. We have characterised the pharmacodynamic and anti-tumor activity of CCT129254, a small molecule inhibitor of AKT. CCT129254 was well tolerated when dosed chronically at up to 200 mg/kg qd in nude mice. Acute doses of 100–200 mg/kg CCT129254 caused dose-dependent transient elevations of blood glucose concentration and inhibition of AKT substrate phosphorylation in xenografts. An acute dose of 200 mg/kg qd CCT129254 significantly reduced pGSK3 for >6h in U87-MG xenografts, and this pharmacodynamic activity correlated with plasma drug concentration. Moreover, chronic dosing of CCT129254 caused a dose-dependent inhibition of tumor growth in this model. Chronic once daily dosing of CCT129254 significantly inhibited tumor growth in 14 of 16 other xenograft models, including breast, prostate, lung, ovarian, kidney and colon. The highest single agent activity was seen in two breast cancer xenografts (BT474c and HCC-1954). Significant activity was also seen in the gefitinib-resistant NCI-H1975 NSCLC model with respectively activating and resistance L858R and T790M mutations in EGFR. Increased efficacy is also seen when CCT129254 is combined with the cytotoxic agents cisplatin, doxorubicin and taxotere in xenograft models. CCT129254 exemplifies an oral, well tolerated inhibitor of AKT catalysis with the potential to inhibit the growth of a wide range of solid tumors both as monotherapy and in combination with cytotoxic agents.

Citation Information: Mol Cancer Ther 2009;8(12 Suppl):C208.

Identification and characterisation of 2-aminopyridine inhibitors of checkpoint kinase 2

5-(Hetero)aryl-3-(4-carboxamidophenyl)-2-aminopyridine inhibitors of CHK2 were identified from high throughput screening of a kinase-focussed compound library. Rapid exploration of the hits through straightforward chemistry established structure-activity relationships and a proposed ATP-competitive binding mode which was verified by X-ray crystallography of several analogues bound to CHK2. Variation of the 5-(hetero)aryl substituent identified bicyclic dioxolane and dioxane groups which improved the affinity and the selectivity of the compounds for CHK2 versus CHK1. The 3-(4-carboxamidophenyl) substituent could be successfully replaced by acyclic omega-aminoalkylamides, which made additional polar interactions within the binding site and led to more potent inhibitors of CHK2. Compounds from this series showed activity in cell-based mechanistic assays for inhibition of CHK2.