Antje Margret Wengner

BAY 1000394, a Novel Cyclin-Dependent Kinase Inhibitor, with Potent Antitumor Activity in Mono- and in Combination Treatment upon Oral Application

Deregulated activity of cyclin-dependent kinases (CDK) results in loss of cell-cycle checkpoint function and increased expression of antiapoptotic proteins, which has been directly linked to the molecular pathology of cancer. BAY 1000394 inhibits the activity of cell-cycle CDKs CDK1, CDK2, CDK3, CDK4, and of transcriptional CDKs CDK7 and CDK9 with IC50 values in the range between 5 and 25 nmol/L. Cell proliferation was inhibited at low nanomolar concentration in a broad spectrum of human cancer cell lines. In cell-based assays, the inhibition of phosphorylation of the CDK substrates retinoblastoma protein, nucleophosmin, and RNA polymerase II was shown. Cell-cycle profiles were consistent with inhibition of CDK 1, 2, and 4 as shown in cell-cycle block and release experiments. The physicochemical and pharmacokinetic properties of BAY 1000394 facilitate rapid absorption and moderate oral bioavailability. The compound potently inhibits growth of various human tumor xenografts on athymic mice including models of chemotherapy resistance upon oral dosing. Furthermore, BAY 1000394 shows more than additive efficacy when combined with cisplatin and etoposide. These results suggest that BAY 1000394 is a potent pan-CDK inhibitor and a novel oral cytotoxic agent currently in phase I clinical trials. Mol Cancer Ther; 11(10); 2265–73. ©2012 AACR.

The Lab Oddity Prevails: Discovery of Pan-Cdk Inhibitor (R)- S-Cyclopropyl-S-(4-{[4-{[(1R,2R)-2-Hydroxy-1-Methylpropyl]Oxy}-5-(Trifluoromethyl)Pyrimidin-2-Yl]Amino}Phenyl)Sulfoximide (Bay 1000394) for the Treatment of Cancer.

Lead optimization of a high‐throughput screening hit led to the rapid identification of aminopyrimidine ZK 304709, a multitargeted CDK and VEGF‐R inhibitor that displayed a promising preclinical profile. Nevertheless, ZK 304709 failed in phase I studies due to dose‐limited absorption and high inter‐patient variability, which was attributed to limited aqueous solubility and off‐target activity against carbonic anhydrases. Further lead optimization efforts to address the off‐target activity profile finally resulted in the introduction of a sulfoximine group, which is still a rather unusual approach in medicinal chemistry. However, the sulfoximine series of compounds quickly revealed very interesting properties, culminating in the identification of the nanomolar pan‐CDK inhibitor BAY 1000394, which is currently being investigated in phase I clinical trials.

Novel Mps1 Kinase Inhibitors with Potent Antitumor Activity.

Monopolar spindle 1 (Mps1) has been shown to function as the key kinase that activates the spindle assembly checkpoint (SAC) to secure proper distribution of chromosomes to daughter cells. Here, we report the structure and functional characterization of two novel selective Mps1 inhibitors, BAY 1161909 and BAY 1217389, derived from structurally distinct chemical classes. BAY 1161909 and BAY 1217389 inhibited Mps1 kinase activity with IC50 values below 10 nmol/L while showing an excellent selectivity profile. In cellular mechanistic assays, both Mps1 inhibitors abrogated nocodazole-induced SAC activity and induced premature exit from mitosis (“mitotic breakthrough”), resulting in multinuclearity and tumor cell death. Both compounds efficiently inhibited tumor cell proliferation in vitro (IC50 nmol/L range). In vivo, BAY 1161909 and BAY 1217389 achieved moderate efficacy in monotherapy in tumor xenograft studies. However, in line with its unique mode of action, when combined with paclitaxel, low doses of Mps1 inhibitor reduced paclitaxel-induced mitotic arrest by the weakening of SAC activity. As a result, combination therapy strongly improved efficacy over paclitaxel or Mps1 inhibitor monotreatment at the respective MTDs in a broad range of xenograft models, including those showing acquired or intrinsic paclitaxel resistance. Both Mps1 inhibitors showed good tolerability without adding toxicity to paclitaxel monotherapy. These preclinical findings validate the innovative concept of SAC abrogation for cancer therapy and justify clinical proof-of-concept studies evaluating the Mps1 inhibitors BAY 1161909 and BAY 1217389 in combination with antimitotic cancer drugs to enhance their efficacy and potentially overcome resistance. Mol Cancer Ther; 15(4); 583–92. ©2016 AACR.

Abstract 836: ATR inhibitor BAY 1895344 shows potent anti-tumor efficacy in monotherapy and strong combination potential with the targeted alpha therapy Radium-223 dichloride in preclinical tumor models

The integrity of the genome of eukaryotic cells is secured by complex signaling pathways, known as DNA damage response (DDR). Recognition of DNA damage activates DDR pathways resulting in cell cycle arrest, induction of DNA repair, or cell death. Proteins that directly recognize aberrant DNA structures recruit and activate kinases of the DDR pathway, such as ATR (ataxia telangiectasia and Rad3-related). ATR responds to a broad spectrum of DNA damage, including double-strand breaks (DSB) and lesions derived from interference with DNA replication as well as increased replication stress. Therefore, inhibition of ATR kinase activity could be the basis for a novel anti-cancer therapy in tumors with increased DNA damage, deficiency in DNA damage repair or replication stress. Radium-223 dichloride (Xofigo®) is the first and only approved targeted alpha therapy so far. It is indicated for the treatment of patients with castration-resistant prostate cancer (CRPC), symptomatic bone metastases and no known visceral metastatic disease, based on improvement of overall survival. It exhibits strong cytotoxic effects on adjacent cells via the induction of DNA DSB. Here, we disclose for the first time the structure and functional characterization of the novel ATR kinase inhibitor BAY 1895344. In vitro, BAY 1895344 is a selective low-nanomolar inhibitor of ATR kinase activity, potently inhibiting proliferation of a broad spectrum of human tumor cell lines (median IC50 of 78 nM). A clear separation between highly sensitive (IC50 Our findings validate the concept of synthetic lethality of genetically determined DNA repair deficiency and ATR blockade by demonstrating strong monotherapy efficacy of the highly potent ATR inhibitor BAY 1895344 in a variety of tumor indications. Furthermore, the mechanism-based combination potential of DNA damage induction by Radium-223 with BAY 1895344 creates a powerful new treatment option for CRPC patients with bone metastases. The start of clinical investigation of BAY 1895344 is planned early 2017. Citation Format: Antje Margret Wengner, Gerhard Siemeister, Ulrich Luecking, Julien Lefranc, Philip Lienau, Gesa Deeg, Eleni Lagkadinou, Li Liu, Sven Golfier, Christoph Schatz, Arne Scholz, Franz von Nussbaum, Michael Brands, Dominik Mumberg, Karl Ziegelbauer. ATR inhibitor BAY 1895344 shows potent anti-tumor efficacy in monotherapy and strong combination potential with the targeted alpha therapy Radium-223 dichloride in preclinical tumor models [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 836. doi:10.1158/1538-7445.AM2017-836

Abstract 3883: Pharmacologic profile of the oral novel pan-CDK inhibitor BAY 1000394 in chemosensitive and chemorefractory tumor models

We report on the pharmacological profile of the novel pan-CDK inhibitor BAY 1000394. Loss of cell cycle control and increased resistance to apoptosis represent major hallmarks of cancer. Cyclin-dependent kinases (CDKs) belong to a family of serine/threonine kinases which associate with an activating cyclin regulatory subunit. Cell cycle CDKs 1, 2, 4 & 6 are required for the correct timing and order of the events of the cell division cycle, whereas non-cell cycle CDKs 7 and 9 have been shown to be involved in gene transcription via regulation of RNA polymerase II activity. Deregulated CDK activity results in loss of cell cycle checkpoint function and increased expression of anti-apoptotic proteins, which has been directly linked to the molecular pathology of cancer. BAY 1000394 is a nanomolar pan CDK inhibitor (IC 50 s : CDK1/CycB, 7 nM; CDK2/CycE, 9 nM; CDK4/CycD1, 11 nM; CDK9/CycT1, 50 of 16 nM (8-37 nM). The cellular activity of BAY 1000394 was independent of the presence of functional p53 or retinoblastoma (Rb) tumor suppressor proteins. BAY 1000394 induced disappearance of the hyperphosphorylated form of Rb protein in MCF7 and HCT116 tumor cells indicating intracellular inhibition of CDK2 and CDK4. Furthermore, the compound inhibited the phosphorylation of the mitotic CDK1 substrate protein nucleophosmin in HeLa cells. Cell cycle profiles of BAY 1000394 treated HeLa cells were consistent with inhibition of CDK 1, 2 and 4 as demonstrated in cell cycle block and release experiments. A robust decrease of viability of non-proliferating peripheral blood mononuclear cells isolated from a B-CLL patient (EC 50 : 15 nM) was observed and indicated inhibition of intracellular CDK9. Oral dosing of BAY 1000394 at various schedules (QD or BID x 2 and 5 days off) potently inhibited growth of human cervical HeLa-MaTu xenograft tumors in a dose-dependent manner. The MTD for BAY 1000394 was found to be 2.0 mg/kg on QD schedule and 2.5 mg/kg on a BID intermittent schedule. At these two doses and schedules tumor growth inhibition (TGI) of 104% and 106% was achieved in this model. A single oral dose of 2.0 mg/kg of BAY 1000394 resulted in complete suppression of the hyperphosphorylated form of Rb protein in HeLa-MaTu tumor tissue for at least 7 hrs. BAY 1000394 was also highly efficacious in a paclitaxel-refractory HeLa-MaTu-ADR Res xenograft model, and in a cisplatin-refractory A2780-Cis human ovarian xenograft model. Furthermore, the growth of human colorectal HCT116 tumors in nude rats treated on once daily (QD) or on intermittent (BID x 2 and 5 days off) schedules was strongly inhibited (TGI of 85 - 88%). In conclusion, BAY 1000394 is a highly potent oral pan-CDK inhibitor with a pharmacological profile suggesting activity in a broad range of histological tumor subtypes. 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 3883.

Abstract 4538: BAY 1112054, a highly selective, potent and orally available inhibitor of PTEFb/CDK9, shows convincing anti-tumor activity

The family of cyclin-dependent kinase (CDK) proteins consists of multiple cell cycle regulating CDK members as well as members involved in the regulation of gene transcription like CDK9/PTEFb (positive transcription elongation factor b). Inhibition of PTEFb and its direct downstream target RNA polymerase II is thought to cause rapid depletion of short-lived mRNA transcripts of important survival proteins like c-myc and Mcl-1 and thereby to induce growth delay and apoptosis in addicted tumor cells. In contrast to pan-CDK inhibitiors which are currently evaluated in Phase I and II clinical trials, PTEFb selective inhibitors have not been explored for clinical utility. BAY 1112054 is a potent and highly selective PTEFb-kinase inhibitor with low nanomolar activity against PTEFb/CDK9 and an at least 50-fold selectivity against other CDKs in enzymatic assays. Furthermore, BAY 1112054 shows a favourable selectivity against non-CDK kinases in vitro. The compound exhibits broad anti-proliferative activity against a panel of tumor cell lines with sub-micromolar IC-50 values. In line with the proposed mode of action, a concentration-dependent inhibition of the phosphorylation of the RNA polymerase II was observed in A549 tumor cells. This inhibition was accompanied by a reduction of intracellular Mcl-1 protein levels. Furthermore, BAY 1112054 increased DNA fragmentation in synchronized HeLa cells upon compound treatment for 24 hours. BAY 1112054 showed convincing in vivo efficacy at tolerated doses in two xenograft models in mice. Once daily oral treatment led to complete tumor stasis in established MOLM-13 AML xenografts. Pharmacokinetic analysis revealed that unbound plasma levels were 8 to 12 hours above the cellular IC50 in this model. In vivo efficacy and tolerability of the once daily po schedule of BAY 1112054 was confirmed in NCI-H82 SCLC xenografts. Xenografted tumors of this model showed lower levels of RNA polymerase II phosphorylation and Mcl-1 upon treatment with BAY 1112054. In conclusion, our data provides in vitro and in vivo proof of concept for BAY 1112054, a potent and highly selective inhibitor of PTEFb/CDK9 with first-in-class potential, and warrant further clinical evaluation of PTEFb selective inhibitors for the treatment of cancers addicted to the transcription of short-lived anti-apoptotic survival proteins. Citation Format: Arne Scholz, Ulrich Lucking, Gerhard Siemeister, Philip Lienau, Knut Eis, Antje Wengner, Kirstin Petersen, Ulf Bomer, Peter Nussbaumer, Axel Choidas, Gerd Ruhter, Jan Eickhoff, Carsten Schultz-Fademrecht, Bert Klebl, Stuart Ince, Franz von Nussbaum, Dominik Mumberg, Michael Brands, Karl Ziegelbauer. BAY 1112054, a highly selective, potent and orally available inhibitor of PTEFb/CDK9, shows convincing anti-tumor activity. [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 4538. doi:10.1158/1538-7445.AM2014-4538

Abstract 983: Identification of potent, highly selective and orally available ATR inhibitor BAY 1895344 with favorable PK properties and promising efficacy in monotherapy and combination in preclinical tumor models

The integrity of the genome of eukaryotic cells is secured by complex signaling pathways, known as DNA damage response (DDR). Recognition of DNA damage activates DDR pathways resulting in cell cycle arrest, suppression of general translation, induction of DNA repair, cell survival or even cell death. Proteins that directly recognize aberrant DNA structures recruit and activate kinases of the DDR pathway, such as ATR (ataxia telangiectasia and Rad3-related). ATR responds to a broad spectrum of DNA damage, including double-strand breaks (DSB) and lesions derived from interference with DNA replication as well as increased replication stress (e.g. in oncogene-driven tumor cells). Therefore, inhibition of ATR kinase activity could be the basis for a novel anti-cancer therapy in tumors with increased DNA damage, deficiency in DNA damage repair or replication stress. Herein we report the identification of the potent, highly selective and orally available ATR inhibitor BAY 1895344 by a collaborative effort involving medicinal chemistry, pharmacology, DMPK and computational chemistry. The chemical structures of lead compound BAY-937 and clinical candidate BAY 1895344 as well as the main SAR trends within this novel class of naphthyridine derivatives will be disclosed for the first time. The novel lead compound BAY-937 revealed promising inhibition of ATR (IC50 = 78 nM) and high kinase selectivity in vitro. In cellular mechanistic assays BAY-937 inhibited hydroxyurea-induced H2AX phosphorylation (IC50 = 380 nM) demonstrating the anticipated mode of action. Moreover, BAY-937 was shown to inhibit proliferation of a variety of tumor cell lines with low- to sub-micromolar IC50 values. In initial xenograft studies, BAY-937 revealed moderate activity in monotherapy and in combination with cis-platin. However, BAY-937 also revealed low aqueous solubility, low bioavailability (rat) and activity in the hERG patch clamp assay. Extensive lead optimization efforts led to the identification of the novel, orally available ATR inhibitor BAY 1895344. In vitro, BAY 1895344 was shown to be a very potent and highly selective ATR inhibitor (IC50 = 7 nM), which potently inhibits proliferation of a broad spectrum of human tumor cell lines (median IC50 = 78 nM). In cellular mechanistic assays BAY 1895344 potently inhibited hydroxyurea-induced H2AX phosphorylation (IC50 = 36 nM). Moreover, BAY 1895344 revealed significantly improved aqueous solubility, bioavailability across species and no activity in the hERG patch-clamp assay. BAY 1895344 also demonstrated very promising efficacy in monotherapy in DNA damage deficient tumor models as well as combination treatment with DNA damage inducing therapies. The start of clinical investigation of BAY 1895344 is planned for early 2017. Citation Format: Ulrich T. Luecking, Julien Lefranc, Antje Wengner, Lars Wortmann, Hans Schick, Hans Briem, Gerhard Siemeister, Philip Lienau, Christoph Schatz, Benjamin Bader, Gesa Deeg, Franz von Nussbaum, Michael Brands, Dominik Mumberg, Karl Ziegelbauer. Identification of potent, highly selective and orally available ATR inhibitor BAY 1895344 with favorable PK properties and promising efficacy in monotherapy and combination in preclinical tumor models [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 983. doi:10.1158/1538-7445.AM2017-983

Abstract 341: Preclinical mode of action and anti-tumor efficacy of the selective MKNK1 inhibitor BAY 1143269 in NSCLC models

MKNK1 (MAP kinase-interacting serine/threonine-protein kinase, also known as Mnk1) is activated by the mitogen-activated protein kinases ERK1/2 and p38. Thus, MKNK1 signaling is involved in the cellular response to environmental stress factors and cytokines. Of particular interest, MKNK1 kinase regulates mRNA translation by phosphorylating the translation initiation factor eIF4E (eukaryotic translation initiation factor 4E), known to be critical for malignant transformation but shown to be dispensable for translation in normal cells. Phosphorylated eIF4E levels were found to be elevated in several cancer tissues, including lung cancer. MKNK1 is also involved in resistance mechanisms to cancer therapeutics. Thus, the inhibition of MKNK1 activity may provide an innovative approach for anti-cancer therapy, and in particular for lung cancer, the main cancer-related cause of death worldwide. BAY 1143269 is a potent and selective MKNK1 inhibitor and inhibits eIF4E phosphorylation and reduces MKNK1-regulated translational downstream targets in non-small cell lung cancer (NSCLC) cell lines. In this study, BAY 1143269-mediated effects on molecular mechanisms in lung cancer models were analyzed. Epithelial-mesenchymal transition (EMT) is associated with the pathogenesis of numerous lung diseases including cancer progression, metastasis and resistance. BAY 1143269 reduced expression of EMT key regulators like Snail1 and cellular junction components, as well as reduced TGFβ1-induced EMT. Accumulating evidence suggests a role for proinflammatory cytokines in the development and progression of cancer; increased serum concentrations of cytokines like interleukin 6 (IL-6) are associated with diminished lung cancer survival rates. BAY 1143269 reduced the secretion of several proinflammatory cytokines, including TNFα and IL-6 in whole blood, and affected IFN-stimulated gene expression in cell lines. Consistent with the observed effects in vitro, BAY 1143269 showed significant anti-tumor effects in vivo in cell line as well as patient derived NSCLC xenograft models in monotherapy. In combination with chemotherapeutics approved for treatment of NSCLC, BAY 1143269 improved anti-tumor effects in comparison to chemotherapy alone. In conclusion, BAY 1143269 has the potential to provide therapeutic benefit in NSCLC. A phase I study of BAY 1143269 in combination with docetaxel for subjects with advance solid tumors is ongoing (NCT02439346). Citation Format: Susann Santag, Franziska Siegel, Antje M. Wengner, Claudia Lange, Ulf Boemer, Knut Eis, Florian Puehler, Martin Michels, Franz von Nussbaum, Karl Ziegelbauer, Dominik Mumberg, Kirstin Petersen. Preclinical mode of action and anti-tumor efficacy of the selective MKNK1 inhibitor BAY 1143269 in NSCLC models. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 341.

Abstract 3090: Novel Mps1 kinase inhibitors with potent anti-tumor activity

Proceedings: AACR 106th Annual Meeting 2015; April 18-22, 2015; Philadelphia, PA Cell cycle deregulation represents one of the hallmarks of cancer and consequently cell cycle arrest is the predominant mode of action for a number of antimitotic cancer drugs (e.g. taxanes and vinca alkaloids). Targeted disruption of the cell cycle checkpoint offers a novel approach to cancer treatment since tumor cells will not arrest in mitosis despite DNA damage or unattached/misattached chromosomes resulting in aneuploidy and cell death. Mps1, a mitotic kinase that is overexpressed in several human cancers, has been shown to function as the key kinase which activates the spindle assembly checkpoint (SAC) to secure proper distribution of chromosomes to daughter cells. Here, we disclose for the first time the structure and functional characterization of two novel Mps1 inhibitors, BAY 1161909 and BAY 1217389, derived from structurally distinct chemical classes. BAY 1161909 and BAY 1217389 inhibited Mps1 kinase activity with IC50 values below 10 nM while showing an excellent selectivity profile against a broad panel of kinases. In cellular mechanistic assays, BAY 1161909 and BAY 1217389 abrogated nocodazole-induced SAC activity, inducing premature exit from mitosis (“mitotic breakthrough”), which results in multinuclearity and tumor cell death. Both compounds efficiently inhibited tumor cell proliferation in vitro (IC50 values in low nanomolar range), showing a similar inhibitory pattern in a broad panel of tumor cell lines. In vivo, the Mps1 inhibitors BAY 1161909 and BAY 1217389 achieved moderate efficacy in monotherapy in tumor xenograft studies (tumor growth inhibition ∼ 50%). However, according to its unique mode of action, when combined with paclitaxel, at the maximum tolerated dose, low doses of Mps1 inhibitor reduced paclitaxel-induced mitotic arrest in line with weakening of SAC activity. Consequently, combination therapy strongly improved efficacy over paclitaxel or Mps1 inhibitor mono-treatment in a broad range of xenograft models including those being intrinsically paclitaxel-insensitive as well as those with acquired paclitaxel resistance. Both Mps1 inhibitors showed good tolerability without adding toxicity to paclitaxel monotherapy. Our findings validate the innovative concept of SAC abrogation and justify clinical proof of concept studies evaluating Mps1 inhibitors BAY 1161909 and BAY 1217389 in combination with antimitotic cancer drugs in order to enhance their efficacy and potentially overcome resistance. BAY 1161909 is currently in a phase I clinical trial ([NCT02138812][1]), start of clinical investigation of BAY 1217389 is planned. To our knowledge BAY 1161909 and BAY 1217389 are the first Mps1 inhibitors in clinical trials. Citation Format: Antje Margret Wengner, Gerhard Siemeister, Marcus Koppitz, Volker Schulze, Dirk Kosemund, Ulrich Klar, Detlef Stoeckigt, Roland Neuhaus, Philip Lienau, Benjamin Bader, Stefan Prechtl, Olaf Doehr, Marian Raschke, Oliver von Ahsen, Cem Elbi, Ingmar Bruns, Martin Michels, Bertolt Kreft, Franz von Nussbaum, Michael Brands, Dominik Mumberg, Karl Ziegelbauer. Novel Mps1 kinase inhibitors with potent anti-tumor activity. [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 3090. doi:10.1158/1538-7445.AM2015-3090 [1]: /lookup/external-ref?link_type=CLINTRIALGOV&access_num=NCT02138812&atom=%2Fcanres%2F75%2F15_Supplement%2F3090.atom

Abstract 4540: SAC abrogation by MPS1 kinase inhibition: preclinical proof of concept of a novel approach to tumor treatment

Cell cycle deregulation represents one of the classical hallmarks of cancer and consequently cell cycle arrest is the predominant mode of action of a number of antimitotic cancer drugs (e.g. taxanes and vinca alkaloids). Targeted disruption of the cell cycle checkpoint offers a novel approach to cancer treatment: driving tumor cells into cell division despite DNA damage or unattached/misattached chromosomes resulting in a lethal degree of DNA damage or aneuploidy. MPS1, a mitotic kinase that is overexpressed in several human cancers, has been shown to function as the key kinase which activates the spindle assembly checkpoint (SAC) to secure proper distribution of chromosomes to daughter cells. Here, we report the identification and functional characterization of novel inhibitors of MPS1 from two structurally unrelated chemical classes. In biochemical assays, these molecules inhibited the kinase activity of MPS1 with IC50 values in the single digit nanomolar range and have shown an exquisite selectivity against a panel of kinases. In cellular assays the compounds were able to abrogate nocodazole-induced SAC, to reduce time in mitosis, to induce multinuclearity and apoptotic cell death, and to inhibit tumor cell proliferation with IC50 values in the low nanomolar range. In combination experiments MPS1 inhibitors showed cooperativity with low concentrations of paclitaxel. MPS1 inhibitors showed limited efficacy in monotherapy (T/C ca. 0.6) in tumor xenograft studies. However, when combined with paclitaxel dosed at the maximal tolerated dose, low doses of MPS1 inhibitor strongly improved efficacy over paclitaxel or MPS inhibitor monotreatment in intrinsically paclitaxel-insensitive xenograft models. The combination treatment was well tolerated. These results validate the concept of SAC abrogation preclinically and pave the way to a clinical proof of concept. Citation Format: Dominik Mumberg, Gerhard Siemeister, Antje M. Wengner, Marcus Koppitz, Volker Schulze, Benjamin Bader, Stefan Prechtl, Bertolt Kreft, Karl Ziegelbauer. SAC abrogation by MPS1 kinase inhibition: preclinical proof of concept of a novel approach to tumor treatment. [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 4540. doi:10.1158/1538-7445.AM2014-4540