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Sporadic gastrointestinal stromal tumors (GIST), characterized by activating mutations of KIT or PDGFRA, favorably respond to KIT inhibitory treatment but eventually become resistant. The development of effective salvage treatments is complicated by the heterogeneity of KIT secondary resistance mutations. Recently, additional mutations that independently activate KIT-downstream signaling have been found in pretreated patients—adding further complexity to the scope of resistance. We collected genotyping data for KIT from tumor samples of pretreated GIST, providing a representative overview on the distribution and incidence of secondary KIT mutations (n = 80). Analyzing next-generation sequencing data of 109 GIST, we found that 18% carried mutations in KIT-downstream signaling intermediates (NF1/2, PTEN, RAS, PIK3CA, TSC1/2, AKT, BRAF) potentially mediating resistance to KIT inhibitors. Notably, we found no apparent other driver mutations in refractory cases that were analyzed by whole exome/genome sequencing (13/109). Using CRISPR/Cas9 methods, we generated a panel of GIST cell lines harboring mutations in KIT, PTEN, KRAS, NF1, and TSC2. We utilized this panel to evaluate sapanisertib, a novel mTOR kinase inhibitor, as a salvage strategy. Sapanisertib had potent antiproliferative effects in all cell lines, including those with KIT-downstream mutations. Combinations with KIT or MEK inhibitors completely abrogated GIST-survival signaling and displayed synergistic effects. Our isogenic cell line panel closely approximates the genetic heterogeneity of resistance observed in heavily pretreated patients with GIST. With the clinical development of novel, broad spectrum KIT inhibitors, emergence of non-KIT–related resistance may require combination treatments with inhibitors of KIT-downstream signaling such as mTOR or MEK.

Supplemental Methods; Supplemental Figure S1: Cancer-related mutations in the DKTK-Master patient cohort; Supplemental Figure S2: T1-PTEN cells were treated with increasing concentrations of approved KIT-inhibitors for 72h and analyzed by SRB assay; Supplemental Figure S3: Dose-combination studies with sapanisertib

Purpose: KIT is the major oncogenic driver of gastrointestinal stromal tumors (GIST). Imatinib, sunitinib, and regorafenib are approved therapies; however, efficacy is often limited by the acquisition of polyclonal secondary resistance mutations in KIT, with those located in the activation (A) loop (exons 17/18) being particularly problematic. Here, we explore the KIT-inhibitory activity of ponatinib in preclinical models and describe initial characterization of its activity in patients with GIST.Experimental Design: The cellular and in vivo activities of ponatinib, imatinib, sunitinib, and regorafenib against mutant KIT were evaluated using an accelerated mutagenesis assay and a panel of engineered and GIST-derived cell lines. The ponatinib–KIT costructure was also determined. The clinical activity of ponatinib was examined in three patients with GIST previously treated with all three FDA-approved agents.Results: In engineered and GIST-derived cell lines, ponatinib potently inhibited KIT exon 11 primary mutants and a range of secondary mutants, including those within the A-loop. Ponatinib also induced regression in engineered and GIST-derived tumor models containing these secondary mutations. In a mutagenesis screen, 40 nmol/L ponatinib was sufficient to suppress outgrowth of all secondary mutants except V654A, which was suppressed at 80 nmol/L. This inhibitory profile could be rationalized on the basis of structural analyses. Ponatinib (30 mg daily) displayed encouraging clinical activity in two of three patients with GIST.Conclusion:Ponatinib possesses potent activity against most major clinically relevant KIT mutants and has demonstrated preliminary evidence of activity in patients with refractory GIST. These data strongly support further evaluation of ponatinib in patients with GIST. Clin Cancer Res; 20(22); 5745–55. ©2014 AACR.

Supplementary methods, patient information and figure legends

Supplementary Tables. Table S1. In Vitro Kinase IC50 Values (nM) for Native and Mutant Recombinant KIT. Table S2. Summary of Ba/F3 KIT Cell Lines Generated in this Study. Table S3. Summary of IC50 Viability Values in Ba/F3 KIT Cells. Table S4. Summary of KIT Driven Ba/F3 In Vivo Studies.

Supplementary Figures. Figure S1. Chemical structures of imatinib, sunitinib, regorafenib and ponatinib. Figure S2. Expression and activation of KIT in engineered Ba/F3 cells. Figure S3. Ponatinib inhibits the phosphorylation of exon 11primary activating, and secondary resistant mutant forms of KIT. Figure S4. Secondary mutants reduce ponatinib potency in Ex9 ins and V560D cell lines. Figure S5. Illustration of the optimal fit of ponatinib to KIT. Figure S6. Impact of compound treatment on KIT signaling in GIST-derived cell lines.

Mutated or amplified Her2 serves as a driver of non-small cell lung cancer or mediates resistance toward the inhibition of its family member epidermal growth factor receptor with small-molecule inhibitors. To date, small-molecule inhibitors targeting Her2 which can be used in clinical routine are lacking, and therefore, the development of novel inhibitors was undertaken. In this study, the well-established pyrrolopyrimidine scaffold was modified with structural motifs identified from a screening campaign with more than 1600 compounds, which were applied against wild-type Her2 and its mutant variant Her2-A775_G776insYVMA. The resulting inhibitors were designed to covalently target a reactive cysteine in the binding site of Her2 and were further optimized by means of structure-based drug design utilizing a set of obtained complex crystal structures. In addition, the analysis of binding kinetics and absorption, distribution, metabolism, and excretion parameters as well as mass spectrometry experiments and western blot analysis substantiated our approach.

Sporadic gastrointestinal stromal tumors (GIST), characterized by activating mutations of KIT or PDGFRA, favorably respond to KIT inhibitory treatment but eventually become resistant. The development of effective salvage treatments is complicated by the heterogeneity of KIT secondary resistance mutations. Recently, additional mutations that independently activate KIT-downstream signaling have been found in pretreated patients—adding further complexity to the scope of resistance. We collected genotyping data for KIT from tumor samples of pretreated GIST, providing a representative overview on the distribution and incidence of secondary KIT mutations (n = 80). Analyzing next-generation sequencing data of 109 GIST, we found that 18% carried mutations in KIT-downstream signaling intermediates (NF1/2, PTEN, RAS, PIK3CA, TSC1/2, AKT, BRAF) potentially mediating resistance to KIT inhibitors. Notably, we found no apparent other driver mutations in refractory cases that were analyzed by whole exome/genome sequencing (13/109). Using CRISPR/Cas9 methods, we generated a panel of GIST cell lines harboring mutations in KIT, PTEN, KRAS, NF1, and TSC2. We utilized this panel to evaluate sapanisertib, a novel mTOR kinase inhibitor, as a salvage strategy. Sapanisertib had potent antiproliferative effects in all cell lines, including those with KIT-downstream mutations. Combinations with KIT or MEK inhibitors completely abrogated GIST-survival signaling and displayed synergistic effects. Our isogenic cell line panel closely approximates the genetic heterogeneity of resistance observed in heavily pretreated patients with GIST. With the clinical development of novel, broad spectrum KIT inhibitors, emergence of non-KIT–related resistance may require combination treatments with inhibitors of KIT-downstream signaling such as mTOR or MEK.

Predictive markers; Sarcoma; Gastrointestinal stromal tumours Marcadores predictivos; Sarcoma; Tumores del estroma gastrointestinal Marcadors predictius; Sarcoma; Tumors estromals gastrointestinals Background Most patients with KIT-mutant gastrointestinal stromal tumours (GISTs) benefit from imatinib, but treatment resistance results from outgrowth of heterogeneous subclones with KIT secondary mutations. Once resistance emerges, targeting KIT with tyrosine kinase inhibitors (TKIs) sunitinib and regorafenib provides clinical benefit, albeit of limited duration. Methods We systematically explored GIST resistance mechanisms to KIT-inhibitor TKIs that are either approved or under investigation in clinical trials: the studies draw upon GIST models and clinical trial correlative science. We subsequently modelled in vitro a rapid TKI alternation approach against subclonal heterogeneity. Results Each of the KIT-inhibitor TKIs targets effectively only a subset of KIT secondary mutations in GIST. Regorafenib and sunitinib have complementary activity in that regorafenib primarily inhibits imatinib-resistance mutations in the activation loop, whereas sunitinib inhibits imatinib-resistance mutations in the ATP-binding pocket. We find that rapid alternation of sunitinib and regorafenib suppresses growth of polyclonal imatinib-resistant GIST more effectively than either agent as monotherapy. Conclusions Our data highlight that heterogeneity of KIT secondary mutations is the main mechanism of tumour progression to KIT inhibitors in imatinib-resistant GIST patients. Therapeutic combinations of TKIs with complementary activity against resistant mutations may be useful to suppress growth of polyclonal imatinib-resistance in GIST. This work was supported in part by an ASCO Young Investigator Award (CS), a Spanish Society of Medical Oncology Translational Award (CS), Río Hortega-ISCIII CM14/00241 (CS) FERO Foundation (CS), US National Institutes of Health grants 1P50CA127003 (GDD, ES, JAF), 1P50CA168512 (JAF, AME), GIST Cancer Research Fund (JAF, MCH), Life Raft Group (JAF, MCH, SB), V Foundation Translational Grant (MCH), VA Merit Review Award (2I01BX000338–05) (MCH) and the Deutsche Krebshilfe (SB). CS acknowledges to the Cellex Foundation for providing facilities and equipment.

We present inhibitors of drug resistant mutants of EGFR including T790M and C797S. In addition, we present the first X-ray crystal structures of covalent inhibitors in complex with C797S-mutated EGFR to gain insight into their binding mode., Precision medicine has revolutionized the treatment of patients in EGFR driven non-small cell lung cancer (NSCLC). Targeted drugs show high response rates in genetically defined subsets of cancer patients and markedly increase their progression-free survival as compared to conventional chemotherapy. However, recurrent acquired drug resistance limits the success of targeted drugs in long-term treatment and requires the constant development of novel efficient inhibitors of drug resistant cancer subtypes. Herein, we present covalent inhibitors of the drug resistant gatekeeper mutant EGFR-L858R/T790M based on the pyrrolopyrimidine scaffold. Biochemical and cellular characterization, as well as kinase selectivity profiling and western blot analysis, substantiate our approach. Moreover, the developed compounds possess high activity against multi drug resistant EGFR-L858R/T790M/C797S in biochemical assays due to their highly reversible binding character, that was revealed by characterization of the binding kinetics. In addition, we present the first X-ray crystal structures of covalent inhibitors in complex with C797S-mutated EGFR which provide detailed insight into their binding mode.

Korrektur zu 10.1038/s41416-019-0389-6

Targeting and stabilizing distinct kinase conformations is an instrumental strategy for dissecting conformation-dependent signaling of protein kinases. Herein the structure-based design, synthesis, and evaluation of pleckstrin homology (PH) domain-dependent covalent-allosteric inhibitors (CAIs) of the kinase Akt is reported. These inhibitors bind covalently to a distinct cysteine of the kinase and thereby stabilize the inactive kinase conformation. These modulators exhibit high potency and selectivity, and represent an innovative approach for chemical biology and medicinal chemistry research.

Proteinkinasen reprasentieren wichtige Knotenpunkte intrazellularer Signalwege und sind somit an vielen physiologischen und pathologischen Prozessen beteiligt. Konformations-abhangige Eigenschaften dienen hierbei der Feinregulation ihrer enzymatischen Aktivitat und Katalyse-unabhangigen Funktionen. Die Stabilisierung definierter Konformationen ermoglicht detaillierte Analysen solcher Konformations-abhangiger Funktionen. Hier beschreiben wir das strukturbasierte Design, die Synthese und die Charakterisierung Pleckstrin-Homologie(PH)-Domanen-abhangiger Akt-Inhibitoren, die einen neuartigen kovalent-allosterischen Bindungsmodus aufweisen. Durch die kovalente Modifizierung bestimmter Cysteine stabilisieren diese Molekule die inaktive Kinasekonformation irreversibel. Ihre betrachtliche Inhibitorwirkung und Selektivitat bezuglich verwandter Proteinkinasen machen sie zu einem neuartigen Hilfsmittel fur die Erforschung chemisch-biologischer und medizinischer Fragestellungen.

Purpose: KIT is the major oncogenic driver of gastrointestinal stromal tumors (GIST). Imatinib, sunitinib, and regorafenib are approved therapies; however, efficacy is often limited by the acquisition of polyclonal secondary resistance mutations in KIT, with those located in the activation (A) loop (exons 17/18) being particularly problematic. Here, we explore the KIT-inhibitory activity of ponatinib in preclinical models and describe initial characterization of its activity in patients with GIST. Experimental Design: The cellular and in vivo activities of ponatinib, imatinib, sunitinib, and regorafenib against mutant KIT were evaluated using an accelerated mutagenesis assay and a panel of engineered and GIST-derived cell lines. The ponatinib–KIT costructure was also determined. The clinical activity of ponatinib was examined in three patients with GIST previously treated with all three FDA-approved agents. Results: In engineered and GIST-derived cell lines, ponatinib potently inhibited KIT exon 11 primary mutants and a range of secondary mutants, including those within the A-loop. Ponatinib also induced regression in engineered and GIST-derived tumor models containing these secondary mutations. In a mutagenesis screen, 40 nmol/L ponatinib was sufficient to suppress outgrowth of all secondary mutants except V654A, which was suppressed at 80 nmol/L. This inhibitory profile could be rationalized on the basis of structural analyses. Ponatinib (30 mg daily) displayed encouraging clinical activity in two of three patients with GIST. Conclusion:Ponatinib possesses potent activity against most major clinically relevant KIT mutants and has demonstrated preliminary evidence of activity in patients with refractory GIST. These data strongly support further evaluation of ponatinib in patients with GIST. Clin Cancer Res; 20(22); 5745–55. ©2014 AACR.

The specific targeting of oncogenic mutant epidermal growth factor receptor (EGFR) is a breakthrough in targeted cancer therapy and marks a drastic change in the treatment of non-small cell lung cancer (NSCLC). The recurrent emergence of resistance to these targeted drugs requires the development of novel chemical entities that efficiently inhibit drug-resistant EGFR. Herein, we report the optimization process for a hit compound that has emerged from a phenotypic screen resulting in indazole-based compounds. These inhibitors are conformationally less flexible, target gatekeeper mutated drug-resistant EGFR-L858R/T790M, and covalently alkylate Cys797. Western blot analysis, as well as characterization of the binding kinetics and kinase selectivity profiling, substantiates our approach of targeting drug-resistant EGFR-L858R/T790M with inhibitors incorporating the indazole as hinge binder.

In modern cancer therapy, the use of small organic molecules against receptor tyrosine kinases (RTKs) has been shown to be a valuable strategy. The association of cancer cells with dysregulated signaling pathways linked to RTKs represents a key element in targeted cancer therapies. The tyrosine kinase mast/stem cell growth factor receptor KIT is an example of a clinically relevant RTK. KIT is targeted for cancer therapy in gastrointestinal stromal tumors (GISTs) and chronic myelogenous leukemia (CML). However, acquired resistance mutations within the catalytic domain decrease the efficacy of this strategy and are the most common cause of failed therapy. Here, we present the structure-based design and synthesis of novel type II kinase inhibitors to overcome these mutations in KIT. Biochemical and cellular studies revealed promising molecules for the inhibition of mutated KIT.

Targeting acquired drug resistance represents the major challenge in the treatment of EGFR-driven non-small-cell lung cancer (NSCLC). Herein, we describe the structure-based design, synthesis, and biological evaluation of a novel class of covalent EGFR inhibitors that exhibit excellent inhibition of EGFR-mutant drug-resistant cells. Protein X-ray crystallography combined with detailed kinetic studies led to a deeper understanding of the mode of inhibition of EGFR-T790M and provided insight into the key principles for effective inhibition of the recently discovered tertiary mutation at EGFR-C797S.

10518 Background: Resistance to kinase inhibitors is associated with a marked genomic heterogeneity of secondary mutations of KIT in metastatic GIST which is poorly represented in single tumor biop...

Mutations in the catalytic domain at the gatekeeper position represent the most prominent drug-resistant variants of kinases and significantly impair the efficacy of targeted cancer therapies. Understanding the mechanisms of drug resistance at the molecular and atomic levels will aid in the design and development of inhibitors that have the potential to overcome these resistance mutations. Herein, by introducing adaptive elements into the inhibitor core structure, we undertake the structure-based development of type II hybrid inhibitors to overcome gatekeeper drug-resistant mutations in cSrc-T338M, as well as clinically relevant tyrosine kinase KIT-T670I and Abl-T315I variants, as essential targets in gastrointestinal stromal tumors (GISTs) and chronic myelogenous leukemia (CML). Using protein X-ray crystallography, we confirm the anticipated binding mode in cSrc, which proved to be essential for overcoming the respective resistances. More importantly, the novel compounds effectively inhibit clinically relevant gatekeeper mutants of KIT and Abl in biochemical and cellular studies. © 2013 American Chemical Society.

Introduction: Gastrointestinal stromal tumors (GIST) are characterized by activating mutations of the KIT or PDGFRA receptor tyrosine kinases. Most patients respond to the KIT/PDGFRA inhibitor imatinib (IM) but eventually progress due to secondary resistance mutations in KIT. Development of salvage treatments is hampered by the genomic heterogeneity of resistance mutations as single KIT-inhibitory drugs do not inhibit all mutants. The PI3K pathway is strongly activated in GIST regardless of secondary KIT mutations and thus provides a rational target for therapeutic combinations. Rapamycin-analogues have yet shown limited clinical benefit in GIST but next-generation mTOR inhibitors have not been tested in GIST. Here we evaluated the effects of the novel mTOR inhibitor MLN0128 alone and in combination with other kinase inhibitors in GIST. Methods: Three IM-sensitive (IM-S; GIST-T1, GIST882, GIST430) and 2 IM-resistant (IM-R; GIST430/654, GIST48B) cell lines were studied. Cells were treated with MLN0128 alone and in combinations with KIT inhibitors (IM, sunitinib, regorafenib), MEK1/2 inhibitor trametinib, and everolimus. Cell viability was evaluated by Sulforhodamin B (SRB) assay after 3 or 6 days of treatment. Biological consequences of on KIT, KIT-dependent signaling intermediates and apoptosis were evaluated by immunoblotting. Results: In cell viability assays MLN0128 displayed IC50 values between 15nM (GIST-T1) and 30nM (GIST48B). Immunoblots revealed inhibition of phosphorylation of ribosomal protein S6 (as marker for mTOR activation) at 1nM with complete inhibition at 50-100nM in all cell lines. In contrast to everolimus, MLN0128 did also abrogate phosphorylation of 4E-BP1 at 50-100nM. At these concentrations we also observed strong inhibition of AKT phosphorylation (except in GIST48B), upstream of mTOR, while phosphorylation of KIT remained unchanged. A notable induction of ERK1/2 phosphorylation in response to MLN0128 treatment suggested a feedback loop activating the MEK/ERK signaling. Combinations of MLN0128 with the clinical MEK1/2 inhibitor trametinib as well as with different KIT inhibitors exhibited additive effects. Conclusions: MLN0128 has strong antiproliferative effects in IM-sensitive and IM-resistant cell lines in the low nanomolar range, including KIT-negative GIST. The distinct inhibitory profile, inhibition of AKT as well as 4E-BP1, suggests superior clinical efficacy compared to first- and second-generation rapalogues. Combinations with approved KIT and MEK inhibitors display additive effects and may represent a feasible clinical strategy, which warrants further investigation. Citation Format: Thomas Mühlenberg, Julia Ketzer, Jonathan A. Fletcher, Sebastian Bauer. Novel mTOR inhibitor MLN0128 inhibits imatinib-resistant GIST more potently than rapalogues by abrogating AKT and 4EBP1 activation. [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 377.