Abstract 1306: SEL120, a potent and specific inhibitor of CDK8 induces complete remission in human patient derived xenograft models of acute myeloid leukemia

Cyclin-dependent kinase 8 inhibitors (CDK8i) have anti-cancer activity in human acute myeloid leukaemia (AML) cell lines both in vitro and in vivo. Activity of CDK8i often involves deregulation of super-enhancer-associated genes in AML cell lines. Previous studies established SEL120 as a specific CDK8 inhibitor active in AML cells with increased STAT1/5 signalling pathways. Differential gene expression analysis demonstrated high enrichment of leukaemia stem cell (LSC) signatures in responding cells, linked to resistance to standard therapies and relapsed disease. Cells sensitive to SEL120 treatment were positive for CD34 and negative for lineage commitment surface markers. SEL120 markedly reduced STAT5 phosphorylation on serine 726 (STAT5 pS726) in sensitive cell lines. Prolonged SEL120 treatment led to significant downregulation of CD34 and induction of lineage commitment markers. Transcriptomic analysis revealed that SEL120 regulated many genes involved in differentiation and apoptosis. We observed synergistic effects of SEL120 with standard of care cytotoxic drugs such as cytarabine. Treatment of AML cells with cytarabine spared many CD34+ cells, which could be effectively eradicated by subsequent treatment with SEL120. Many cell lines which were resistant to SEL120 treatment could be sensitized by concomitant treatment with BH3 mimetic agent ABT-199. Combination of both compounds resulted in potent induction of apoptosis in AML cells in vitro and in vivo. Treatment of mice bearing subcutaneously implanted human leukaemia cell lines resulted in significant tumour growth inhibition, whereas cotreatment with ABT-199 led to complete regressions at doses which were vey well tolerated by animals. Next we have selected patient derived primary AML cells using gene expression signatures identifying SEL120 -responder cell lines. In these cells SEL120 significantly reduced viability, induced apoptosis and lineage commitment. Further, the same cells were implanted into NOD scid gamma mice. Animals succumbed to AML, diagnosed by a significant presence of human CD45/CD34 positive leukaemia cells in a peripheral blood and splenomegaly. Stand-alone treatment with SEL120 resulted in the complete remission of AML cells in a peripheral blood and bone marrow, and reduced spleen weight, without symptoms of compound-related toxicity. These results validate SEL120 as a promising agent in the treatment of AML.

Citation Format: Milena Mazan, Eliza Majewska, Michal Mikula, Katarzyna Wiklik, Michal Combik, Aniela Golas, Magdalena Masiejczyk, Elzbieta Fiedor, Anna Polak, Magdalena Cybulska, Aleksandra Grochowska, Michal Kopczynski, Urszula Kuklinska, Zuzanna Sandowska-Markiewicz, Malgorzata Statkiewicz, Agnieszka Paziewska, Michalina Dabrowska, Arkadiusz Bialas, Maciej Mikulski, Renata Windak, Jerzy Ostrowski, Przemyslaw Juszczynski, Krzysztof Brzozka, Tomasz Rzymski. SEL120, a potent and specific inhibitor of CDK8 induces complete remission in human patient derived xenograft models of acute myeloid leukemia [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 1306.

Microenvironment-induced PIM kinases promote CXCR4-triggered mTOR pathway required for chronic lymphocytic leukaemia cell migration

Lymph node microenvironment provides chronic lymphocytic leukaemia (CLL) cells with signals promoting their survival and granting resistance to chemotherapeutics. CLL cells overexpress PIM kinases, which regulate apoptosis, cell cycle and migration. We demonstrate that BCR crosslinking, CD40 stimulation, and coculture with stromal cells increases PIMs expression in CLL cells, indicating microenvironment‐dependent PIMs regulation. PIM1 and PIM2 expression at diagnosis was higher in patients with advanced disease (Binet C vs. Binet A/B) and in those, who progressed after first‐line treatment. In primary CLL cells, inhibition of PIM kinases with a pan‐PIM inhibitor, SEL24‐B489, decreased PIM‐specific substrate phosphorylation and induced dose‐dependent apoptosis in leukaemic, but not in normal B cells. Cytotoxicity of SEL24‐B489 was similar in TP53‐mutant and TP53 wild‐type cells. Finally, inhibition of PIM kinases decreased CXCR4‐mediated cell chemotaxis in two related mechanisms‐by decreasing CXCR4 phosphorylation and surface expression, and by limiting CXCR4‐triggered mTOR pathway activity. Importantly, PIM and mTOR inhibitors similarly impaired migration, indicating that CXCL12‐triggered mTOR is required for CLL cell chemotaxis. Given the microenvironment‐modulated PIM expression, their pro‐survival function and a role of PIMs in CXCR4‐induced migration, inhibition of these kinases might override microenvironmental protection and be an attractive therapeutic strategy in this disease.

SEL120-34A is a novel CDK8 inhibitor active in AML cells with high levels of serine phosphorylation of STAT1 and STAT5 transactivation domains

Inhibition of oncogenic transcriptional programs is a promising therapeutic strategy. A substituted tricyclic benzimidazole, SEL120-34A, is a novel inhibitor of Cyclin-dependent kinase 8 (CDK8), which regulates transcription by associating with the Mediator complex. X-ray crystallography has shown SEL120-34A to be a type I inhibitor forming halogen bonds with the protein's hinge region and hydrophobic complementarities within its front pocket. SEL120-34A inhibits phosphorylation of STAT1 S727 and STAT5 S726 in cancer cells in vitro. Consistently, regulation of STATs- and NUP98-HOXA9- dependent transcription has been observed as a dominant mechanism of action in vivo. Treatment with the compound resulted in a differential efficacy on AML cells with elevated STAT5 S726 levels and stem cell characteristics. In contrast, resistant cells were negative for activated STAT5 and revealed lineage commitment. In vivo efficacy in xenotransplanted AML models correlated with significant repression of STAT5 S726. Favorable pharmacokinetics, confirmed safety and in vivo efficacy provide a rationale for the further clinical development of SEL120-34A as a personalized therapeutic approach in AML.

Abstract 4087: Development of a potent, dual pan-PIM/FLT3 inhibitor for the treatment of heme malignancies

Despite huge effort spent on understanding the pathogenesis of acute myeloid leukemia (AML), current standards of care are still based on the same chemotherapy agents as two decades ago - combinational treatment of cytarabine with an anthracycline. Fms-like tyrosine kinase 3 internal tandem duplication (FLT3-ITD) is one of the most common genetic lesions in AML. Although FLT3 inhibitors initially exhibit clinical activity, resistance to treatment inevitably occurs within months. PIM kinases are thought to be major drivers of the resistance phenotype and their inhibition in relapsed samples restores cell sensitivity to FLT3 inhibitors. Thus, simultaneous PIM and FLT3 inhibition represents a promising strategy in AML therapy. Selvita has developed a potent and selective first-in-class, dual PIM/FLT3 kinase inhibitor, the SEL24-B489 compound, and profiled its activity for in vitro and in vivo AML models showing significantly broader anti-tumor activity of SEL24-B489 than selective FLT3-ITD or PIM inhibitors. We compared SEL24-B489 head-to-head with a selective PIM inhibitor (AZD1208) and a selective FLT3-ITD inhibitor (AC220) in a panel of AML cell lines with FLT3-ITD or unmutated kinase (FLT3-WT) as well as peripheral AML cells and CD34+ bone marrow blasts. SEL24-B489 exhibited a significantly broader activity, irrespective of FLT3 status, than either of the selective inhibitors. Since PIM kinases have emerged as important mediators of FLT3-inhibitor resistance, we hypothesized that the dual specificity of SEL24-B489 might overcome the phenotype of resistance. We utilized previously developed MOLM-14 cells transduced with either FLT3-WT or FLT3 alleles containing TKD point mutations to show that neither of the these mutations decreased the cellular sensitivity to SEL24-B489. Higher cellular activity and biomarker response of SEL24-B489 than competitive inhibitors was shown by inhibition of specific biomarkers such as S6 and STAT5 phosphorylation at nanomolar concentrations in both FLT3-ITD positive and FLT3-WT cell lines in vitro. We have also demonstrated SEL24-B489 superior potency of SEL24-B489 in xenograft models in vivo. Consistent with the experiments in vitro showing marked synergy between SEL24-B489 and AraC, a combination of these agents resulted in almost completely blocked tumor growth in vivo. Most importantly, SEL24-B489 has been selected as a clinical candidate and is currently in phase I clinical trials.

Citation Format: Wojciech Czardybon, Renata Windak, Aniela Gołas, Michał Gałęzowski, Aleksandra Sabiniarz, Izabela Dolata, Magdalena Salwińska, Paweł Guzik, Magdalena Zawadzka, Ewelina Gabor-Worwa, Bożena Winnik, Małgorzata Żurawska, Ewa Kolasińska, Ewelina Wincza, Marta Bugaj, Monika Danielewicz, Grzegorz Dubin, Ewa Jabłońska, Maciej Szydłowski, Tomasz Sewastianik, Bartosz Puła, Anna Szumera-Ciećkiewicz, Monika Prochorec-Sobieszek, Elżbieta Mądro, Ewa Lech-Marańda, Krzysztof Warzocha, Jerome Tamburini, Przemysław Juszczyński, Krzysztof Brzózka. Development of a potent, dual pan-PIM/FLT3 inhibitor for the treatment of heme malignancies [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 4087. doi:10.1158/1538-7445.AM2017-4087

Abstract C194: Repression of tumor survival pathways by novel and selective inhibitors of MNK1 and MNK2 kinases in cancer

Herewith, we report development of small molecule inhibitors of MNK1 and MNK2 kinases and their cellular activity. MNK1 and 2 are MAP kinase-interacting kinases are activated by RAS and MAPK signaling pathways, and are involved in regulation of translation. Both kinases phosphorylate translation initiation factor eIF4e on a conserved serine 209. eIF4E can contribute to the oncogenic transformation both in vitro and in vivo and is highly expressed in diverse types of cancer. Interestingly, mice that lack both Mnk1 and Mnk2 do not have any apparent phenotype. Recently first dual MNK1/MNK2 inhibitors have entered clinical trials as a combinational therapy with docetaxel in NSCLC.

SEL201 is a series of small molecule inhibitors which inhibit activity of both MNK1 and MNK2 in a low nM range and high selectivity confirmed in kinome panels. Analysis of SEL201 cellular activity indicated potent inhibition of eIF4e Ser209 in vitro in cancer cells and in vivo after oral administration in xenograft tumors. Repressed phosphorylation of eIF4e resulted in impaired translation of several proteins involved in metastasis and activation of immune cells. High potency, selectivity and favorable ADME/PK profile indicates that SEL201 inhibitors would be useful tools in probing molecular consequences of eIF4e Ser209 inhibition in cancer cells. SEL201 in vitro and in vivo activities on viability and metastasis will be presented in cellular and in vivo models of solid tumors and hematological malignancies. SEL201 series is further developed as a cancer therapy with a good therapeutic window.

Citation Format: Tomasz Rzymski, Agnieszka Dreas, Ewelina Wincza, Charles-Henry Fabritius, Urszula Kulesza, Katarzyna Kucwaj- Brysz, Mariusz Milik, Aniela Gołas, Renata Windak, Eliza Żyłkiewicz, Anna Wróbel, Maciej Sułkowski, Krzysztof Brzózka. Repression of tumor survival pathways by novel and selective inhibitors of MNK1 and MNK2 kinases in cancer. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr C194.

Abstract 5394: First-in-class dual PIM/FLT3 kinase inhibitor SEL24-B489 for the treatment of hematological malignancies

Despite huge effort spent on understanding acute myeloid leukemia (AML), current standards of care are still based on the same chemotherapy agents as two decades ago - typically based on cytarabine chemotherapy with an anthracycline. Although patients aged <60 years may achieve remission to induction therapy, most patients will relapse. One of primary reasons for that is high heterogeneity of the disease. Recently one of the most extensively investigated approaches to the treatment of AML, are targeted therapies, especially inhibition of certain kinases. Probably mostly investigated up to date are inhibitors of FLT3 with most advanced clinical compound - AC220 (Quizartinib). FLT3 inhibitors are very effective in killing cancer lines with a major drawback of the therapy being fast development of resistance.

PIM kinases are expressed in various cancers including AML but also other liquid tumors as well as in some solid tumors. Inhibition of PIM kinases which are downstream in the FLT3 signaling cascade have already shown influence on cancer cell survival. In addition there are great hopes related to the fact that PIM kinases were shown to contribute in resistance to FLT3 inhibitors. This leads to the conclusion that combined inhibition of PIM and FLT3 may be a rational strategy.

Selvita has developed series of inhibitors combining activity against PIM and FLT3 kinases. Selected clinical candidate SEL24-B489 - has shown excellent anticancer efficacy. It is active against broad panel of AML cell lines and primary blasts, but also against other hematological cancers: DLBCL, CLL, HL - both in vitro on cell lines, patient samples and in vivo. Head to head comparison of SEL24-B489 with PIM (AZD1208) and FLT3 (AC220) inhibitors currently in clinical development will be presented. Comparison shows strong activity of SEL24-B489 against broader panel of cell lines in vitro and in vivo (in xenograft models) than AZD1208 or AC220. SEL24-B489 is currently in preclinical development and details of toxicology profile will also be discussed.

Citation Format: Krzysztof Brzózka, Wojciech Czardybon, Aniela Gołas, Renata Windak, Michał Gałęzowski, Ewelina Gabor-Worwa, Bożena Winnik, Agnieszka Przybyłowicz, Maciej Szydłowski, Emilia Białopiotrowicz, Tomasz Sewastianik, Elżbieta Mądro, Ewa Lech-Marańda, Krzysztof Warzocha, Przemysław Juszczyński. First-in-class dual PIM/FLT3 kinase inhibitor SEL24-B489 for the treatment of hematological malignancies. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 5394. doi:10.1158/1538-7445.AM2015-5394

Abstract 1663: Selective CDK8 inhibitor SEL120-34A alters expression of interferon-related DNA damage resistance signature genes in colorectal cancer

CDK8 (cyclin-dependent kinase 8) is a kinase component of a multi - protein Mediator complex, involved in transcription control. Several studies indicated that high overexpression and activity of CDK8 could be a driver of malignant progression in colorectal cancer (CRC). Herewith we present molecular insights into mechanism of action of SEL120-34A - a selective small molecule inhibitor of CDK8 kinase. Biochemical and binding studies indicated that SEL120-34A selectively binds and inhibits enzymatic activity of CDK8 in the low nM range. Recently CDK8 has been described as a regulator of STAT1 activity in NK cells where by phosphorylating STAT1 serine 727 (Ser727) influences a possible immunoescape mechanism in various cancers. Consistently, SEL120-34A and other recently reported selective CDK8 inhibitors could repress phosphorylation of STAT1 at a Ser727 at low nM concentrations in cancer cells without any significant changes on tyrosine sites directly regulated by JAK kinases. SEL120-34A inhibited expression of several STAT1 dependent genes in CRC cell lines, stimulated by various cytokines and growth factors. These results were further corroborated with specific CDK8 siRNA knockdown experiments and chromatin immunoprecipitation studies showing CDK8 occupancy on promoters of SEL120-34A regulated genes. In order to better characterize in vivo mechanism of action, mice bearing HCT116 and Colo205 xenograft tumors were treated with SEL120-34A and gene expression changes were measured with microarrays in excised tumors. In animals treated with the CDK8 inhibitor a dose dependent repression of STAT1 Ser727 was observed. The functional analyses of significantly (adj. p. value < 0.05) altered genes with Gene Ontology revealed that those with reduced expression belong to interferon I pathway and type I interferon-mediated signaling pathway terms. This subset of STAT regulated genes was further characterized as an interferon-related DNA damage resistance signature (IRDS) - a prosurvival pathway which correlated strongly with resistance to radiation and chemotherapy in various tumors. Consistently, SEL120-34A has shown very potent cytotoxic synergy with standard of care drugs in CRC, particularly in cells stimulated with interferons. Taken together, for the first time we have shown that selective CDK8 inhibitors are potent regulators of STAT related - IRDS signaling pathway in vitro and in vivo. In addition to previously reported stand-alone efficacy of CDK8 inhibitors in vivo, we provide also a combination treatment rationale for CRC.

Citation Format: Tomasz Rzymski, Michał Mikula, Małgorzata Szajewska-Skuta, Eliza Zyłkiewicz, Łukasz Sapała, Izabela Dolata, Agata Kitlińska, Krzysztof Goryca, Aleksandra Grochowska, Aleksandra Cabaj, Agnieszka Dreas, Katarzyna Kucwaj, Artur Białas, Adam Radzimierski, Aniela Gołas, Renata Windak, Jerzy Ostrowski, Krzysztof Brzózka. Selective CDK8 inhibitor SEL120-34A alters expression of interferon-related DNA damage resistance signature genes in colorectal cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1663. doi:10.1158/1538-7445.AM2015-1663

Abstract 755: Repression of tumor survival pathways by novel and selective inhibitors of MNK1 and MNK2 kinases in glioblastoma and colorectal cancer

Herewith, we report development of small molecule inhibitors of MNK1 and MNK2 kinases and their cellular activity. MNK1 and 2 are MAP kinase-interacting kinases that are activated by RAS and MAPK signaling pathways and are involved in regulation of translation. Both kinases phosphorylate translation initiation factor eIF4e on a conserved serine 209 residue. eIF4E can contribute to the oncogenic transformation both in vitro and in vivo and is highly expressed in various tumor types. Interestingly, mice that lack both MNK1 and MNK2 do not have any apparent phenotype, which is promising for the therapeutic window of MNK1/2 inhibitors. SEL201 is a series of small molecule inhibitors which inhibit activity of both MNK1 and MNK2 in a low nM range. Selected compounds were tested on the kinome panels and indicated MNK1 and MNK2 as primary kinase targets. SEL201 compounds caused dose dependent inhibition of phosphorylation of eIF4e at Ser209 in various cancer cell lines at concentrations <100nM, which were lower when compared with other reported MNK1/2 inhibitors such as Cercosporamid and CGP57380. Consistently, potent inhibition of eIF4e Ser209 was observed also in vivo after oral administration of the inhibitors in xenograft models. High potency, selectivity and favorable ADME/PK profile indicates that SEL201 inhibitors would be useful tools in probing molecular consequences of eIF4e Ser209 inhibition in cancer cells alone and in combination with other inhibitors targeting PI3K/mTOR or RAS/MEK pathway. SEL201 in vitro and in vivo activities on viability and metastasis will be presented in cellular and in vivo models of colorectal cancer and glioblastoma. SEL201 series is further developed as a promising anticancer therapy with potentially wide therapeutic window.

Citation Format: Tomasz Rzymski, Malgorzata Szajewska-Skuta, Adrian Zarebski, Kamil Sitarz, Lukasz Sapala, Malgorzata Zurawska, Magdalena Salwinska, Renata Windak, Ewa Trebacz, Joanna Daniel-Wojcik, Radoslaw Obuchowicz, Bozena Winnik, Ewelina Wincza, Urszula Kulesza, Katarzyna Kucwaj-Borysz, Mariusz Milik, Agnieszka Dreas, Krzysztof Brzozka. Repression of tumor survival pathways by novel and selective inhibitors of MNK1 and MNK2 kinases in glioblastoma and colorectal cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 755. doi:10.1158/1538-7445.AM2014-755

Abstract 1749: Preclinical characterization of SEL24-B489, a dual PIM/FLT3 inhibitor for the treatment of hematological malignancies

PIM kinases represent an emerging therapeutic target in multiple hematological malignancies, as exemplified by currently ongoing phase I clinical trials by Astra Zeneca (AZD1208) and Novartis (LGH447) in acute myeloid leukemia and multiple myeloma. Selvita has developed a potent and selective dual PIM/FLT3 mutant kinase inhibitor - SEL24-B489 showing high inhibitory activity on all three PIM kinase isoforms and FLT3 kinase mutants. We have previously reported that PIM kinases are important downstream effectors of FLT3 signaling and play a crucial role in cell survival and inhibition of apoptosis upon expression. Due to heterogeneous nature of AML, dual inhibition of FLT3 mutant kinase and PIM kinases led to improved efficacy of our compound in comparison to selective inhibitors of either PIM of FLT3 kinases.

Herewith, we would like to report further progress of characterizing the B489 inhibitor beyond AML. We assessed PIM kinase expression levels in a panel of lymphoid malignancies and found that PIM1 and PIM2 exhibit high expression levels in a fraction of mantle cell lymphoma (MCL), diffuse large-B-cell lymphoma (DLBCL), follicular lymphoma (FL), Hodgkin's lymphoma (HL), chronic lymphocytic leukemia (CLL) and mucosa associated lymphoid tissue-type (MALT) lymphoma cell lines and primary tumors . High levels of PIM kinases were associated with certain established adverse prognostic factors and clinical outcome of the patients and correlated with aggressiveness of the disease in some of these tumors. Inhibition of PIM kinases with tool inhibitors was shown to influence cellular proliferation and, translational inhibition of 4EBP1 as reported in the literature. In addition, SEL24-B489 inhibited NFκB activity and decreased CXCR4 expression. Comparison of SEL24-B489 to competitive PIM inhibitors revealed higher cellular activity and biomarker response, as shown by inhibition of phospho-S6 phosphorylation in sub-microM concentrations. The presented data will further validate SEL24-B489 as a successful example of rational drug design and present a promising therapeutic approach in multiple hematological malignancies, both stand alone and in combination with standard of care and targeted therapies in clinical development.

Citation Format: Wojciech Czardybon, Renata Windak, Izabela Dolata, Magdalena Salwińska, Maciej Szydlowski, Tomasz Sewastianik, Emilia Białopiotrowicz, Elżbieta Mądro, Ewa Lech-Marańda, Bożena K. Budziszewska, Katarzyna Borg, Przemysław Juszczynski, Krzysztof D. Brzózka. Preclinical characterization of SEL24-B489, a dual PIM/FLT3 inhibitor for the treatment of hematological malignancies. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1749. doi:10.1158/1538-7445.AM2014-1749

Abstract C257: Preclinical development of a potent dual PIM/FLT3 mutant kinase inhibitor for the treatment of AML and other hematological malignancies

Despite an evolving understanding of acute myeloid leukemia (AML), a group of heterogeneous diseases with a common feature of abnormal levels of myeloblasts in bone marrow and in circulation, the current standard of care including chemotherapy and allogeneic hematopoietic stem cell transplantation results in less than 40 % cure rate with little progress over the last decades. One of the most extensively investigated approaches in targeted therapy of AML are FLT3 inhibitors that address the population of patients harboring FLT3 mutations that result in high relapse rate and decreased overall survival when compared to patients lacking such mutations. Therefore inhibition of the constitutively active mutants of FLT3 is a promising therapeutic approach. Unfortunately, the clinical development of selective or multitargeted FLT3 inhibitors turned out to result in rapid, but very transient responses followed by disease progression. One of the main reasons for development of resistance was selection of clones harboring both ITD and tyrosine kinase mutations (TKD). In parallel, the role of PIM kinases, especially PIM1 in FLT3 mediated leukemogenesis attracted attention of the pharmaceutical industry with currently two phase I programs targeting PIM kinases in hematological malignancies. PIM kinases are important downstream effectors of FLT3 signaling and play a crucial role in cell survival and inhibition of apoptosis upon expression. For that reason, PIM kinases represent an emerging therapeutic target class in AML with promising preliminary data from clinical trials. Due to the heterogeneous nature of AML, dual inhibition of FLT3 mutant kinase and PIM kinases could lead to improved efficacy and constitute a promising approach to overcome rapid resistance development to targeted therapies. Selvita has developed a potent and selective dual PIM/FLT3 mutant kinase inhibitor - SEL24-B489 which is highly active in in vitro and in vivo AML models. The compound shows high inhibitory activity against mutated FLT3 (FLT3-ITD and TKD mutations such as D835H, D835Y, N841I) and all three PIM kinase isoforms, comparable to activity of selective inhibitors of FLT3 (A220) and PIM (AZD1208). A head to head comparison of SEL24-B489 in cellular models reveals high activity across tested cellular AML models and biomarker inhibition in line with the expected kinase activity profile. Most importantly, SEL24-B489 showed strong synergistic effect in combination with the current standard of care in AML - cytarabine, and with other targeted inhibitors in advanced clinical development. The activity of B489 in vivo in xenograft models of AML and lymphomas after oral administration was higher than compared to selective PIM inhibitor and led to remissions in certain models. SEL24-B489 is a successful example of rational drug design and is currently in preclinical development. It represents a promising therapeutic approach which addresses alternative survival pathways downstream of FLT3 in addition to the activity on resistant FLT3 mutant kinases, which hopefully will translate into improved survival of AML patients in clinical trials.

Citation Information: Mol Cancer Ther 2013;12(11 Suppl):C257.

Citation Format: Wojciech Czardybon, Michal Galezowski, Pawel Guzik, Magdalena Zawadzka, Renata Windak, Izabela Dolata, Magdalena Salwińska, Radoslaw Obuchowicz, Krzysztof D. Brzózka. Preclinical development of a potent dual PIM/FLT3 mutant kinase inhibitor for the treatment of AML and other hematological malignancies. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr C257.

The AP-1 transcription factor c-Jun prevents stress-imposed maladaptive remodeling of the heart

Systemic hypertension increases cardiac workload and subsequently induces signaling networks in heart that underlie myocyte growth (hypertrophic response) through expansion of sarcomeres with the aim to increase contractility. However, conditions of increased workload can induce both adaptive and maladaptive growth of heart muscle. Previous studies implicate two members of the AP-1 transcription factor family, junD and fra-1, in regulation of heart growth during hypertrophic response. In this study, we investigate the function of the AP-1 transcription factors, c-jun and c-fos, in heart growth. Using pressure overload-induced cardiac hypertrophy in mice and targeted deletion of Jun or Fos in cardiomyocytes, we show that c-jun is required for adaptive cardiac hypertrophy, while c-fos is dispensable in this context. c-jun promotes expression of sarcomere proteins and suppresses expression of extracellular matrix proteins. Capacity of cardiac muscle to contract depends on organization of principal thick and thin filaments, myosin and actin, within the sarcomere. In line with decreased expression of sarcomere-associated proteins, Jun-deficient cardiomyocytes present disarrangement of filaments in sarcomeres and actin cytoskeleton disorganization. Moreover, Jun-deficient hearts subjected to pressure overload display pronounced fibrosis and increased myocyte apoptosis finally resulting in dilated cardiomyopathy. In conclusion, c-jun but not c-fos is required to induce a transcriptional program aimed at adapting heart growth upon increased workload.

Abstract 696: Development of selective CDK8 inhibitors for colorectal cancer and mantle cell lymphoma treatment

CDK8 is a kinase component of the mediator complex which functions as a bridge between a basal transcriptional machinery and specific transcription factors. CDK8 is amplified and differentially expressed in colorectal cancer and in certain hematological malignancies such as mantle cell lymphomas. Cells that express elevated CDK8 levels are highly dependent on its expression for proliferation. Here we report development of first-in-class selective inhibitors CDK8. Compounds from the SEL120 series have binding affinities towards CDK8 in the low nM range. Results from the kinome panel indicated that selectivity of SEL120 compounds was comparable with some of the most selective clinical kinase inhibitors. SEL120 compounds reduced viability of mantle cell lymphoma and colorectal cancer cell lines, with particularly good activity in cell lines overexpressing CDK8 and with G13D mutation in KRAS. Slightly lower sensitivity was observed for cells with mutated P53 and other mutations in KRAS/BRAF pathway. In contrast to pan-CDK inhibitors with main target activity on CDK9, treatment with SEL120 compounds did not repress phosphorylation of PolII and did not cause global transcriptional shutdown. Selective inhibition of CDK8 was sufficient to inhibit both paracrine and autocrine activities of cancer cells and stimulated normal cells. Production of proinflammatory cytokines, such as IL6 was repressed by SEL120 compounds in normal and cancer cells stimulated by sub-optimal doses of chemotherapeutics. SEL120 also reduced both murine and human IL6 in blood of mice bearing human xenograft models. Oral administration of SEL120 revealed favorable pharmacokinetics profile and strong, dose dependent potency in colon cancer mouse xenograft models. Presented data validate inhibition of CDK8 as a promising strategy for anticancer treatment, particularly for CRC and mantle cell lymphomas resistant to current treatments.

Citation Format: Tomasz Rzymski, Adrian Zarebski, Renata Windak, Karolina Krawczynska, Ewa Trebacz, Agnieszka Dreas, Katarzyna Kucwaj, Karolina Osowska, Marek Cholody, Paulina Szczepanska, Jakub Woyciechowski, Radosław Obuchowicz, Magdalena Salwińska, Joanna Fogt, Malgorzata Zurawska, Arkadiusz Białas, Katarzyna Wiklik, Mariusz Milik, Angelo Sanzone, Adam Radzimierski, Krzysztof Brzózka. Development of selective CDK8 inhibitors for colorectal cancer and mantle cell lymphoma treatment. [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 696. doi:10.1158/1538-7445.AM2013-696

Abstract 3245: Identification of potent, dual PIM/FLT3 kinase inhibitors for AML treatment

Acute myeloid leukemia (AML) is a highly heterogeneous disease with numerous signaling pathways that contribute to its pathogenesis. Advances in our understanding of molecular mechanisms of AML pathogenesis and prognosis so far did not translate into significant clinical improvements. AML is still the highest unmet medical need within hematological malignancies area, particularly in case of the elderly patients. FLT3 inhibitors were investigated in the recent years as possible therapeutic agents, however to date the clinical trials of FLT3 inhibitors have yielded disappointing results. On the other hand, PIM kinases have been identified in the last years as critical downstream components of FLT3 signaling, especially in the case of oncogenic FLT3 mutants. PIM kinases are being overexpressed in a range of hematopoietic malignancies and solid cancers and the overexpression of PIMs is associated with a poor prognosis and decreased survival of patients suffering from cancer. In many cases also, PIM overexpression was associated with development of drug resistance. As dual and simultaneous inhibition of various pathway components is an emerging therapeutic idea, exemplified by several compounds in development for cancer treatment, we have developed a series of dual PIM/FLT3 small molecule inhibitors to investigate this concept. Similarly to examples of small molecule inhibitors from the JAK/STAT or PI3K/AKT pathways, where compounds are being developed as a way to improve efficacy, resistance development and overcoming the negative feedback loops, often seen after single target inhibition, we have observed increased potency of compounds developed in this series of dual PIM/FLT3 inhibitors. Synthesized inhibitors showed higher activity towards mutated FLT3 (FLT3-ITD and other FLT3 mutants) than wild type kinase and the selectivity profile on a panel of 450 kinases was comparable to best clinical examples of kinase inhibitors. In contrast to selective PIM inhibitors, the treatment with dual PIM/FLT3 inhibitors showed potent apoptosis induction as a results of Erk and S6 phosphorylation inhibition. The in vitro activity in FTL3-ITD positive cells was also confirmed in vivo in a PK/PD xenograft experiment, where sustained biomarker inhibition was observed already after single compounds administration. Oral administration of dual PIM/FLT3 inhibitors led to potent effect in vivo and in certain cases also to remissions in subcutaneous xenograft models. Observed activity profile and synergistic effects observed with other targeted therapies and standard of care compounds, makes dual PIM/FLT3 inhibitors an exciting approach for treatment of FLT3-mutant positive AML patients with high chances of clinical success.

Citation Format: Wojciech Czardybon, Michal Galezowski, Renata Windak, Magdalena Salwińska, Izabela Dolata, Ewa Trebacz, Radosław Obuchowicz, Pawel Guzik, Magdalena Zawadzka, Ewelina Wincza, Katarzyna Wiklik, Mariusz Milik, Malgorzata Zurawska, Karolina Krawczynska, Krzysztof Brzózka. Identification of potent, dual PIM/FLT3 kinase inhibitors for AML treatment. [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 3245. doi:10.1158/1538-7445.AM2013-3245

A VLP-based vaccine against interleukin-1α protects mice from atherosclerosis

Interleukin (IL)-1α is a potent proinflammatory cytokine that has been implicated in the development of atherosclerosis. We investigated whether a vaccine inducing IL-1α neutralizing antibodies could interfere with disease progression in a murine model of atherosclerosis. We immunized Apolipoprothin E (ApoE)-deficient mice with a vaccine (IL-1α-C-Qβ) consisting of full-length, native IL-1α chemically conjugated to virus-like particles derived from the bacteriophage Qβ. ApoE(-/-) mice were administered six injections of IL-1α-C-Qβ or nonconjugated Qβ over a period of 160 days while being maintained on a western diet. Atherosclerosis was measured in the descending aorta and in cross-sections at the aortic root. Macrophage infiltration in the aorta was measured using CD68. Expression levels of VCAM-1, ICAM-1, and MCP-1 were quantified by RT-PCR. Immunization against IL-1α reduced plaque progression in the descending aorta by 50% and at the aortic root by 37%. Macrophage infiltration in the aorta was reduced by 22%. Inflammation was also reduced in the adventitia, with a decrease of 54% in peri-aortic infiltrate score and reduced expression levels of VCAM-1 and ICAM-1. Active immunization targeting IL-1α reduced both the inflammatory reaction in the plaque as well as plaque progression. In summary, vaccination against IL-1α protected ApoE(-/-) mice against disease, suggesting that this may be a potential treatment option for atherosclerosis.

Abstract 3845: Antitumor activity of SEL120: An orally available dual inhibitors of Haspin/CDK9, for standalone and combination therapy with AuroraB inhibitors in solid tumors and hematopoietic malignancies

The mitotic machinery is a validated target for potential drug therapies in cancer. However, anti-mitotic agents are not without complications from various side effects, notably neurological and hematological toxicities. There is much interest in identifying new drug targets in mitosis which could lead to safer and more efficacious treatments of cancer. Recently, Haspin has been identified as another important kinase involved in mitosis. Similar to other mitotic kinases such as Polo-like kinase-1 and the Aurora kinases, inhibition of Haspin represents a novel approach in anti-mitotic cancer therapeutics. In this study we report the development of SEL120, series of novel ATP competitive inhibitors of Haspin kinase. These compounds have binding affinities towards Haspin kinase in the low nM range. Several compounds in the series exerted significant activity on CDK9 (selectively over other CDK kinases), a part of positive transcription elongation factor b (P-TEFb) involved in the expression of survival proteins during progression of cancer. SEL120 inhibited proliferation and clonogenic survival of a number of tumor cell lines with particularly good cytostatic activity in colon, lung (NSCLS) and B cell lymphoma cell lines. The only substrate of Haspin reported in literature to date is histone H3. During mitosis Haspin targets a single site in this protein, namely threonine at position T3 (H3T3ph). By using siRNA, we have confirmed that Thr3 phosphorylation of histone H3 could be completely repressed by the knockdown of Haspin in HCT116 colon and A549 (NSCLC) lung cancer cell lines. We also consistently observed decreased phosphorylation of histone H3 (Thr3) in both synchronized and asynchronous cell lines treated with SEL120 inhibitor. In addition SEL120-1 treatment decreased levels of CDK9 biomarkers- phosphorylation of pol II CTD (Ser2) and expression of the pro-survival protein Mcl-1 Treatment with SEL120 consistently resulted in mitotic cell cycle arrest in A549 cell line confirming inhibition of Haspin as the mechanism of action. Remarkably, inhibitory activity on CDK9 correlated with levels of cell death. Furthermore, co-administration of SEL120 with an AuroraB inhibitors, resulted in strong synergistic cytostatic effects. Treatment with both compounds increased the number of cells arrested in mitosis, notably without any signs of polyploidy typically observed after inhibition of AuroraB. Oral administration of SEL120 (25mg/kg BID) revealed excellent potency in colon and B-cell lymphoma xenograft models. Analysis of pharamcokinetic, ADMET and histopathological parameters afforded encouraging results towards potential development of new therapeutics emerging from our SEL120 program.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3845. doi:1538-7445.AM2012-3845

Abstract 2826: Preclinical development of a Pim kinase inhibitor for cancer treatment

Pim kinases were identified as the crucial downstream effectors various important oncogenes like Jak, FLT3 or Ras kinases. Multiple targets phosphorylated by Pim kinases, such as 4EBP1, p21Waf, p27KIP1, c-Myc or CXCR4 play important roles in intracellular signaling and contribute to pathways involved in cell survival, proliferation, stress response and cellular motility. Moreover, the significance and relevance of Pim kinases as valid therapeutic targets is further confirmed by their expression levels in variety of cancer types, especially in various types of lymphomas, leukemias or myelomas. For example Pim kinase overexpression contributes to the development of diffuse large B cell lymphoma, mantle cell lymphoma, B-cell chronic lymphocytic leukemia and FLT3-mediated acute myelogenous leukemia. As members of the family, Pim-1, Pim-2 and Pim-3 were shown to be prevent apoptosis, promote protein translation and cell survival thereby enhancing proliferation of malignant cells, Pim kinases emerged as a novel and interesting target with significant potential for therapeutic intervention in cancer. In the current study we are reporting the results of a second generation small molecule Pim kinase inhibitors that were developed by Selvita and results for the best characterized potent Pim kinase inhibitor developed so far. The small molecule inhibitors exert high potency in vitro both on all three Pim kinases as well as on a large panel of cancer cell lines. Mechanism of action for selected compounds was confirmed both in vitro in variety of cell lines and in vivo in xenograft models by downregulation of c-Myc and 4EBP1 phosphorylation inhibition. Selected compounds were tested in a range of combinations with standard anti-cancer therapeutics in both leukemias and solid tumor cell lines and showed potent synergistic effects. Strong synergies were observed particularly in combination with targeted therapies like the PI3K/Akt pathway inhibitors or Jak kinase inhibitors. Data will be presented on in vivo efficacy of lead compounds examined in xenograft models. Additionally, the results of safety assessment of the lead compound will be presented revealing preferable safety profile with no effect on ion channel mediated cardiotoxicity and favorable pharmacokinetic profile. Taken together, presented data will further support the rationale of using Pim kinase inhibition as a novel approach to standalone cancer therapy, and in combination with other targeted and cytotoxic therapies, especially to overcome developing drug resistance.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2826. doi:1538-7445.AM2012-2826

Abstract B242: Antitumor activity of SEL120: An orally available small-molecule inhibitor of Haspin kinase for standalone and combination therapy with AuroraB inhibitors in colorectal cancer

The mitotic machinery is a validated target for potential drug therapies in cancer. Anti-mitotic drugs like vinca alkaloids and taxanes interfering with microtubules are important classes of chemotherapeutical agents. However, these agents are not without complications from various side effects, notably neurological and hematological toxicities. There is much interest in identifying new drug targets in mitosis which could lead to safer and more efficacious treatments of cancer. Recently, Haspin has been identified as another important kinase involved in mitosis. Similar to other mitotic kinases such as Polo-like kinase-1 and the Aurora kinases, inhibition of Haspin represents a novel approach in anti-mitotic cancer therapeutics.

In this study we report the development of SEL120, a novel ATP competitive inhibitor of Haspin kinase. These small-molecule compounds have binding affinities towards Haspin kinase in the low nM range. SEL120 inhibited proliferation and clonogenic survival of a number of tumor cell lines with particularly good cytostatic activity in colon, lung (NSCLS) and B cell lymphoma cell lines.

The only substrate of Haspin reported in literature to date is histone H3. During mitosis Haspin targets a single site in this protein, namely threonine at position T3 (H3T3ph). By using siRNA, we have confirmed that Thr3 phosphorylation of histone H3 could be completely repressed by the knockdown of Haspin in HCT116 colon and A549 (NSCLC) lung cancer cell lines. We also consistently observed decreased phosphorylation of histone H3 (Thr3) in both synchronized and asynchronous cell lines treated with SEL120 inhibitor. Haspin-depleted cells were arrested in the prometaphase as a result of chromosome alignment defects and activation of the mitotic checkpoint. Treatment with SEL120 consistently resulted in mitotic cell cycle arrest in HCT116 and A549 cell lines confirming inhibition of Haspin as the mechanism of action. Furthermore, co-administration of SEL120 with an AuroraB inhibitor, AZD1152, resulted in strong synergistic cytostatic effects. Treatment with both compounds increased the number of cells arrested in mitosis, notably without any signs of polyploidy (cells with >4n) typically observed after inhibition of AuroraB.

Oral administration of SEL120 (25mg/kg BID) revealed excellent potency in the HCT116 xenograft model; observed tumor growth inhibition was over 80%. Analysis of pharamcokinetic, ADMET and histopathological parameters afforded encouraging results towards potential development of new therapeutics emerging from our SEL120 program. Presented data validates Haspin as a promising target for anticancer treatments, particularly for colon cancer, lung cancer and lymphomas.

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 B242.

Abstract A243: Novel Pim kinase inhibitors for treatment of hematological malignancies and solid tumors

The family of Pim kinases emerged as a novel and interesting target with significant potential for therapeutic intervention in cancer. All three members of the family Pim-1, Pim-2 and Pim-3 were shown to be prevent apoptosis, promote protein translation and cell survival thereby enhancing proliferation of malignant cells. Pim kinases seem to be crucial downstream effectors various important oncogenes like Jak, Flt3 or Ras kinases. Multiple targets phosphorylated by Pim kinases play important roles in intracellular signaling and contribute to pathways involved in cell survival, proliferation, stress response and cellular motility. Moreover, the significance and relevance of Pim kinases as valid therapeutic targets is further confirmed by their expression levels in variety of cancer types of both hematological origin. For example Pim kinase overexpression contributes to the development of diffuse B cell lymphoma, mantle cell lymphoma, B-cell chronic lymphocytic leukemia and Flt3-mediated acute myelogenous leukemia. Interestingly, accumulating literature data point towards emerging role of Pim kinases also in development of malignancies that originate from epithelial cells, especially gastric, colon and hepatocellular cancers, but also prostate and pancreatic cancers.

In this study we are reporting the results for novel small molecule Pim kinase inhibitors that were developed by Selvita. in Currently, we are performing a lead optimization program of novel, small molecule pan-Pim kinase inhibitors. Compounds developed within the SEL24 series exert high potency in vitro both on all three Pim kinases as well as on a large panel of cancer cell lines. Among synthesized compounds we have identified most selective Pim kinase inhibitors described so far with selectivity scores on a panel of 290 kinases inhibited over 90% at 1 μM concentration was equal to 1.8%. Mechanism of action for selected compounds was confirmed both in vitro in variety of cell lines and in vivo in xenograft models by downregulation of c-Myc and 4EBP1 phosphorylation inhibition. Further experiments indicated that our compounds induced both apoptotic cell death and cell cycle arrest at G0/G1, consistently with the predicted Pim kinase inhibition phenotype. SEL24 compounds showed mostly synergistic effects in a range of combinations with standard anti-cancer therapeutics in both leukemias and solid tumor cell lines. Strong synergies were observed not only for cytotoxic agents like docetaxel, gemcitabine or cyratabine, but also for targeted therapies like the PI3K/Akt pathway inhibitors or Jak kinase inhibitors. Data will be presented on in vivo efficacy of SEL24 lead compounds examined in xenograft models of leukemias, lymphomas and solid tumors (lung and colon cancer). Apart from excellent efficacy in in vivo xenograft models, SEL24 compounds show preferable safety profile with no effect on ion channel mediated cardiotoxicity and favorable pharmacokinetic profile. Taken together, presented data supports the rationale of using Pim kinase inhibition as a novel approach to standalone cancer therapy, and in combination with other targeted and cytotoxic therapies, especially to overcome developing drug resistance.

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 A243.

Effects of copper supplementation on the structure and content of elements in kidneys of mosaic mutant mice

Menkes disease is an effect of ATP7A gene mutation in humans, coding the Cu-ATP-ase which is essential in intestinal copper absorption and its subsequent transfer to circulation. This mutation results in a deficiency of copper in all tissues except the epithelia of intestine and kidney tubules. Subcutaneous injection of copper ions is the main therapy for Menkes patients. Mosaic (Atp7a(mo-ms)) mice closely simulate the situation in Menkes disease. The aim of this study was to evaluate the changes in structure and element content in kidneys of mosaic mice after copper supplementation. Hematoxylin-eosin staining was used to analyze tissue morphology and atomic absorption spectrometry to estimate Cu and Zn content. X-ray microanalysis was performed to measure Na, Mg, P, Cl, and K content in the cells of the proximal and distal tubules. Copper administration lengthened the lifespan of the mutants but led to its high accumulation and results in severe kidney damage. Karyomegalia, necrosis of tubular and Bowman's capsule epithelium, lesions, and atrophy of glomeruli were observed in the treated mutants. Copper treatment afterwards led to sclerosis of glomeruli and tubules enhanced proliferation of epithelial cells and formation of both polycystic and papillary carcinoma patterns in kidney. We suggest that copper excess may impair the activity of Na(+)/K(+) ATP-ase in renal tubules of ms/- males. The content of Mg, P, and Cl in kidneys in mutants was also changed after copper administration.

Activation of a HIF1alpha-PPARgamma axis underlies the integration of glycolytic and lipid anabolic pathways in pathologic cardiac hypertrophy

Development of cardiac hypertrophy and progression to heart failure entails profound changes in myocardial metabolism, characterized by a switch from fatty acid utilization to glycolysis and lipid accumulation. We report that hypoxia-inducible factor (HIF)1alpha and PPARgamma, key mediators of glycolysis and lipid anabolism, respectively, are jointly upregulated in hypertrophic cardiomyopathy and cooperate to mediate key changes in cardiac metabolism. In response to pathologic stress, HIF1alpha activates glycolytic genes and PPARgamma, whose product, in turn, activates fatty acid uptake and glycerolipid biosynthesis genes. These changes result in increased glycolytic flux and glucose-to-lipid conversion via the glycerol-3-phosphate pathway, apoptosis, and contractile dysfunction. Ventricular deletion of Hif1alpha in mice prevents hypertrophy-induced PPARgamma activation, the consequent metabolic reprogramming, and contractile dysfunction. We propose a model in which activation of the HIF1alpha-PPARgamma axis by pathologic stress underlies key changes in cell metabolism that are characteristic of and contribute to common forms of heart disease.

Regulation of PKD by the MAPK p38delta in insulin secretion and glucose homeostasis

Dysfunction and loss of insulin-producing pancreatic β cells represent hallmarks of diabetes mellitus. Here, we show that mice lacking the mitogen-activated protein kinase (MAPK) p38δ display improved glucose tolerance due to enhanced insulin secretion from pancreatic β cells. Deletion of p38δ results in pronounced activation of protein kinase D (PKD), the latter of which we have identified as a pivotal regulator of stimulated insulin exocytosis. p38δ catalyzes an inhibitory phosphorylation of PKD1, thereby attenuating stimulated insulin secretion. In addition, p38δ null mice are protected against high-fat-feeding-induced insulin resistance and oxidative stress-mediated β cell failure. Inhibition of PKD1 reverses enhanced insulin secretion from p38δ-deficient islets and glucose tolerance in p38δ null mice as well as their susceptibility to oxidative stress. In conclusion, the p38δ-PKD pathway integrates regulation of the insulin secretory capacity and survival of pancreatic β cells, pointing to a pivotal role for this pathway in the development of overt diabetes mellitus.