Otmar Schaaf

Structure-Based Design of an in Vivo Active Selective BRD9 Inhibitor

Components of the chromatin remodelling switch/sucrose nonfermentable (SWI/SNF) complex are recurrently mutated in tumors, suggesting that altering the activity of the complex plays a role in oncogenesis. However, the role that the individual subunits play in this process is not clear. We set out to develop an inhibitor compound targeting the bromodomain of BRD9 in order to evaluate its function within the SWI/SNF complex. Here, we present the discovery and development of a potent and selective BRD9 bromodomain inhibitor series based on a new pyridinone-like scaffold. Crystallographic information on the inhibitors bound to BRD9 guided their development with respect to potency for BRD9 and selectivity against BRD4. These compounds modulate BRD9 bromodomain cellular function and display antitumor activity in an AML xenograft model. Two chemical probes, BI-7273 (1) and BI-9564 (2), were identified that should prove to be useful in further exploring BRD9 bromodomain biology in both in vitro and in vivo settings.

A Novel RAF Kinase Inhibitor with DFG-Out–Binding Mode: High Efficacy in BRAF-Mutant Tumor Xenograft Models in the Absence of Normal Tissue Hyperproliferation

BI 882370 is a highly potent and selective RAF inhibitor that binds to the DFG-out (inactive) conformation of the BRAF kinase. The compound inhibited proliferation of human BRAF–mutant melanoma cells with 100× higher potency (1–10 nmol/L) than vemurafenib, whereas wild-type cells were not affected at 1,000 nmol/L. BI 882370 administered orally was efficacious in multiple mouse models of BRAF-mutant melanomas and colorectal carcinomas, and at 25 mg/kg twice daily showed superior efficacy compared with vemurafenib, dabrafenib, or trametinib (dosed to provide exposures reached in patients). To model drug resistance, A375 melanoma–bearing mice were initially treated with vemurafenib; all tumors responded with regression, but the majority subsequently resumed growth. Trametinib did not show any efficacy in this progressing population. BI 882370 induced tumor regression; however, resistance developed within 3 weeks. BI 882370 in combination with trametinib resulted in more pronounced regressions, and resistance was not observed during 5 weeks of second-line therapy. Importantly, mice treated with BI 882370 did not show any body weight loss or clinical signs of intolerability, and no pathologic changes were observed in several major organs investigated, including skin. Furthermore, a pilot study in rats (up to 60 mg/kg daily for 2 weeks) indicated lack of toxicity in terms of clinical chemistry, hematology, pathology, and toxicogenomics. Our results indicate the feasibility of developing novel compounds that provide an improved therapeutic window compared with first-generation BRAF inhibitors, resulting in more pronounced and long-lasting pathway suppression and thus improved efficacy. Mol Cancer Ther; 15(3); 354–65. ©2016 AACR.

BI 885578, a Novel IGF1R/INSR Tyrosine Kinase Inhibitor with Pharmacokinetic Properties That Dissociate Antitumor Efficacy and Perturbation of Glucose Homeostasis.

Inhibition of the IGF1R, INSRA, and INSRB receptor tyrosine kinases represents an attractive approach of pharmacologic intervention in cancer, owing to the roles of the IGF1R and INSRA in promoting cell proliferation and survival. However, the central role of the INSRB isoform in glucose homeostasis suggests that prolonged inhibition of this kinase could result in metabolic toxicity. We describe here the profile of the novel compound BI 885578, a potent and selective ATP-competitive IGF1R/INSR tyrosine kinase inhibitor distinguished by rapid intestinal absorption and a short in vivo half-life as a result of rapid metabolic clearance. BI 885578, administered daily per os, displayed an acceptable tolerability profile in mice at doses that significantly reduced the growth of xenografted human GEO and CL-14 colon carcinoma tumors. We found that treatment with BI 885578 is accompanied by increases in circulating glucose and insulin levels, which in turn leads to compensatory hyperphosphorylation of muscle INSRs and subsequent normalization of blood glucose within a few hours. In contrast, the normalization of IGF1R and INSR phosphorylation in GEO tumors occurs at a much slower rate. In accordance with this, BI 885578 led to a prolonged inhibition of cell proliferation and induction of apoptosis in GEO tumors. We propose that the remarkable therapeutic window observed for BI 885578 is achieved by virtue of the distinctive pharmacokinetic properties of the compound, capitalizing on the physiologic mechanisms of glucose homeostasis and differential levels of IGF1R and INSR expression in tumors and normal tissues. Mol Cancer Ther; 14(12); 2762–72. ©2015 AACR.

A comprehensive pharmacokinetic/pharmacodynamics analysis of the novel IGF1R/INSR inhibitor BI 893923 applying in vitro, in vivo and in silico modeling techniques

PurposeBI 893923 is a novel IGF1R/INSR tyrosine kinase inhibitor demonstrating anti-tumor efficacy and good tolerability. We aimed to characterize the relationship between BI 893923 plasma concentration, tumor biomarker modulation, tumor growth and hyperglycemia in mice using in silico modeling analyses.MethodsIn vitro molecular and cellular assays were used to demonstrate the potency and selectivity of BI 893923. Diverse in vitro DMPK assays were used to characterize the compound’s drug-like properties. Mice xenografted with human GEO tumors were treated with different doses of BI 893923 to demonstrate the compound’s efficacy, biomarker modulation and tolerability. PK/PD analyses were performed using nonlinear mixed-effects modeling.ResultsBI 893923 demonstrated potent and selective molecular inhibition of the IGF1R and INSR and demonstrated attractive drug-like properties (permeability, bioavailability). BI 893923 dose-dependently reduced GEO tumor growth and demonstrated good tolerability, characterized by transient hyperglycemia and normal body weight gain. A population PK/PD model was developed, which established relationships between BI 893923 pharmacokinetics, hyperglycemia, pIGF1R reduction and tumor growth.ConclusionBI 893923 demonstrates molecular properties consistent with a highly attractive inhibitor of the IGF1R/INSR. A generic PK/PD model was developed to support preclinical drug development and dose finding in mice.

Discovery of novel amino-pyrimidine inhibitors of the insulin-like growth factor 1 (IGF1R) and insulin receptor (INSR) kinases; parallel optimization of cell potency and hERG inhibition

The insulin-like growth factor-1 receptor (IGF1R) and closely related insulin receptor (INSR) are receptor tyrosine kinases which have been postulated to play a role in the tumorigenesis of certain cancers. Strategies for inhibiting oncogenic signalingvia the IGF1R and INSR include IGF1R antibodies, IGF1/2 antibodies and dual IGF1R/INSR tyrosine kinase inhibitors (TKIs). IGF1R/INSR TKIs linsitinib (OSI-906) and BMS-754807 have progressed to phase II/III clinical studies in cancer patients. We describe here our efforts to develop small molecule dual inhibitors of the IGF1R/INSR receptor kinases based on an amino-pyrimidine structural class. Our main focus was the parallel optimization of cellular potency and off target activity (principally hERG inhibition) through modulation of physicochemical properties and introduction of key structural motifs using a matched molecular pairs approach and hERG homology model.

Abstract 4558: In vitro and in vivo characterization of the PD-1 targeting antibody BI 754091

The programmed cell death-1 (PD-1) receptor provides inhibitory checkpoint signals to activated T cells upon binding to its ligands, PD-L1 and PD-L2, which are expressed on antigen-presenting cells and cancer cells leading to suppression of T-cell effector function and tumor immune evasion. Blockade of the PD-1 axis using either anti-PD-1 or anti-PD-L1 approved monoclonal antibodies (mAbs) results in improved T-cell effector function and anti-tumor immune responses. Durable tumor responses occur in 15-30% of cancer patients. BI 754091, a humanized IgG4 mAb with high affinity against hPD-1 blocks the interaction between PD-1 and PD-L1 or PD-L2. BI 754091 was characterized in a panel of binding, blocking and functional cell-based assays. In addition, efficacy and safety was assessed in mice and in cynomolgus monkeys, respectively. The ability of BI 754091 to stimulate cytokine production in exhausted human T cells in vitro was tested in an autologous assay system with antigen-specific memory CD4+ T cells being re-stimulated by antigen-pulsed dendritic cells in the presence of BI 754091 or isotype control. Under these assay conditions the majority of T cells co-expressed the exhaustion markers PD-1 and LAG-3 on their surface. Furthermore, PD-L1 and PD-L2 were expressed on the dendritic cells. At the end of the experiment supernatants were harvested and analyzed for IFNγ secretion as a measure for T-cell activation. BI 754091 showed a potent dose dependent T-cell activation. The average fold increase of IFNγ was 7.9 as compared to isotype control, with an average EC50 of 0.9 nM. The in vivo activity of BI 754091 was determined in MC-38 tumor-bearing mice, using a mouse strain where parts of the extracellular domain of murine PD-1 was replaced by the corresponding human PD-1 domain (C57BL/6NTac-PDCD1tm(PDCD1)Arte mice). A dose of 10 mg/kg BI 754091, given either as single treatment or in a twice weekly schedule, induced significant tumor growth inhibition (median TGI of 83% and 90%, respectively) and complete responses (CRs) in some tumors (3 CRs out of 10 and 2 CRs out of 10, respectively). BI 754091 binds to PD-1 from cynomolgus monkeys with comparable affinities as to human PD-1, thus allowing pharmacokinetic and toxicological assessment in this species. Repeated high doses of BI 754091 were well tolerated without adverse immune-related effects. BI 754091 is currently undergoing clinical investigations (NCT02952248). Citation Format: Markus Zettl, Melanie Wurm, Otmar Schaaf, Inigo Tirapu, Sven Mostbock, Markus Reschke, Stephan-Michael Schmidbauer, Lee Frego, Ivo C. Lorenz, Michael Thibodeau, Diann Blanset, Elisa Oquendo Cifuentes, Jurgen Moll, Norbert Kraut, Eric Borges, Anne Vogt, Jonathon Sedgwick, Irene C. Waizenegger. In vitro and in vivo characterization of the PD-1 targeting antibody BI 754091 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4558.

Abstract 2344: Modeling 1st- and 2nd-line therapy of BRAF mutant melanoma using a novel BRAF inhibitor with DFG-out binding mode.

Proceedings: AACR 104th Annual Meeting 2013; Apr 6-10, 2013; Washington, DC The BRAF inhibitor vemurafenib (VEM) was approved for treatment of patients with BRAFV600E melanoma based on an ORR of 48% and a PFS of 5.3 months. Phase III data reported for the BRAF inhibitor dabrafenib (DAB) as well as the MEK inhibitor trametinib (TRA) in BRAFmut melanoma indicate similar outcomes. Phase I/II data published recently for a combination of DAB and TRA suggest improved efficacy compared with single-agent therapy; nevertheless, the short duration of responses even for the combination points to an urgent need for further improvement. BI 882370, a potent and selective B/CRAF inhibitor, binds to the DFG-out (inactive) conformation of BRAF, whereas VEM as well as DAB occupy the DFG-in (active) conformation. BI 882370 inhibited proliferation of BRAFmut melanoma cell lines with about 100x higher potency (EC50 1 - 10 nM) than VEM; BRAFwt cell lines were not affected at 1 μM. For studies in nude mouse xenograft models, VEM and DAB were dosed to provide exposures achieved in patients; TRA was used at the MTD for mice, resulting in exposures at or above the exposures tolerated by humans. In the G361 melanoma model (BRAFV600E), 1st line treatment with 25 mg/kg BI 882370 administered twice daily (bid) resulted in partial regression of all tumors, superior to results achieved by VEM, DAB as well as their combination. To model clinical resistance, a large cohort of A375 melanoma (BRAFV600E) bearing mice was treated with VEM; without exception, all tumors responded with partial regression and their median volume reached a nadir on day 11. Thereafter, the majority of tumors resumed growth in spite of continued treatment, whereas tumors in a subset of animals regressed further. Progressing tumors were randomized to 2nd line therapy on day 36 (median volume 280 mm3). TRA did not show any efficacy in this resistant population. BI 882370 induced tumor regression, however, resistance developed within 3 weeks. BI 882370 in combination with TRA resulted in more pronounced regressions and resistance was not observed until the end of the experiment, 6 weeks after initiation of 2nd line therapy. Importantly, in multiple in vivo studies performed to date, mice treated with BI 882370 at doses of 25 mg/kg bid for several weeks did not show any body weight loss or clinical signs of intolerability. Mice treated for 2 weeks were euthanized and major organs subjected to histological analysis. No changes were observed in any of the animals; in particular, there was no evidence for epidermal hyperplasia. Further, a pilot study in male rats dosed at 25 mg/kg bid for 2 weeks did not result in any toxicologically relevant findings in terms of clinical chemistry, hematology, pathology and toxicogenomics of liver and skin. Our results suggest that compared to 1st generation BRAF inhibitors, BI 882370 may provide an improved therapeutic window, enabling more pronounced and longer-lasting pathway suppression and thus resulting in improved efficacy. Citation Format: Irene C. Waizenegger, Anke Baum, Heinz Stadtmuller, Steffen Steurer, Gerd Bader, Pilar Garin-Chesa, Norbert Schweifer, Andreas Bernthaler, Christian Haslinger, Otmar Schaaf, Sien Mousa, Florian Colbatzky, Gunther R. Adolf. Modeling 1st- and 2nd-line therapy of BRAF mutant melanoma using a novel BRAF inhibitor with DFG-out binding mode. [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 2344. doi:10.1158/1538-7445.AM2013-2344