Importance Many cancer subtypes, including KIT-mutant gastrointestinal stromal tumors (GISTs), are driven by activating mutations in tyrosine kinases and may initially respond to kinase inhibitors but frequently relapse owing to outgrowth of heterogeneous subclones with resistance mutations. KIT inhibitors commonly used to treat GIST (eg, imatinib and sunitinib) are inactive-state (type II) inhibitors. Objective To assess whether combining a type II KIT inhibitor with a conformation-complementary, active-state (type I) KIT inhibitor is associated with broad mutation coverage and global disease control. Design, Setting, and Participants A highly selective type I inhibitor of KIT, PLX9486, was tested in a 2-part phase 1b/2a trial. Part 1 (dose escalation) evaluated PLX9486 monotherapy in patients with solid tumors. Part 2e (extension) evaluated PLX9486-sunitinib combination in patients with GIST. Patients were enrolled from March 2015 through February 2019; data analysis was performed from May 2020 through July 2020. Interventions Participants received 250, 350, 500, and 1000 mg of PLX9486 alone (part 1) or 500 and 1000 mg of PLX9486 together with 25 or 37.5 mg of sunitinib (part 2e) continuously in 28-day dosing cycles until disease progression, treatment discontinuation, or withdrawal. Main Outcomes and Measures Pharmacokinetics, safety, and tumor responses were assessed. Clinical efficacy end points (progression-free survival and clinical benefit rate) were supplemented with longitudinal monitoring of KIT mutations in circulating tumor DNA. Results A total of 39 PLX9486-naive patients (median age, 57 years [range, 39-79 years]; 22 men [56.4%]; 35 [89.7%] with refractory GIST) were enrolled in the dose escalation and extension parts. The recommended phase 2 dose of PLX9486 was 1000 mg daily. At this dose, PLX9486 could be safely combined with 25 or 37.5 mg daily of sunitinib continuously. Patients with GIST who received PLX9486 at a dose of 500 mg or less, at the recommended phase 2 dose, and with sunitinib had median (95% CI) progression-free survivals of 1.74 (1.54-1.84), 5.75 (0.99-11.0), and 12.1 (1.34-NA) months and clinical benefit rates (95% CI) of 14% (0%-58%), 50% (21%-79%), and 80% (52%-96%), respectively. Conclusions and Relevance In this phase 1b/2a nonrandomized clinical trial, type I and type II KIT inhibitors PLX9486 and sunitinib were safely coadministered at the recommended dose of both single agents in patients with refractory GIST. Results suggest that cotargeting 2 complementary conformational states of the same kinase was associated with clinical benefit with an acceptable safety profile. Trial Registration ClinicalTrials.gov Identifier: NCT02401815.

Abstract Bromodomain and extra-terminal (BET) family proteins are key regulators of gene expression in cancer. Herein, we utilize BRD4 profiling to identify critical pathways involved in pathogenesis of chronic lymphocytic leukemia (CLL). BRD4 is overexpressed in CLL and is enriched proximal to genes upregulated or de novo expressed in CLL with known functions in disease pathogenesis and progression. These genes, including key members of the B-cell receptor (BCR) signaling pathway, provide a rationale for this therapeutic approach to identify new targets in alternative types of cancer. Additionally, we describe PLX51107, a structurally distinct BET inhibitor with novel in vitro and in vivo pharmacologic properties that emulates or exceeds the efficacy of BCR signaling agents in preclinical models of CLL. Herein, the discovery of the involvement of BRD4 in the core CLL transcriptional program provides a compelling rationale for clinical investigation of PLX51107 as epigenetic therapy in CLL and application of BRD4 profiling in other cancers. Significance: To date, functional studies of BRD4 in CLL are lacking. Through integrated genomic, functional, and pharmacologic analyses, we uncover the existence of BRD4-regulated core CLL transcriptional programs and present preclinical proof-of-concept studies validating BET inhibition as an epigenetic approach to target BCR signaling in CLL. Cancer Discov; 8(4); 458–77. ©2018 AACR. This article is highlighted in the In This Issue feature, p. 371

Next-generation RAF inhibitors that inhibit oncogenic BRAF without inducing paradoxical pathway activation in cells with mutant RAS might yield improved safety and more durable efficacy.

Abstract Pancreatic cancer is a deadly malignancy in need of effective treatments. The most common driving oncogenes in pancreatic cancer – KRAS, p53, SMAD4, CDKN2A and CTNNB1 – historically have been difficult drug targets to modulate pharmacologically. An alternative approach could be to target regulators of tumor-stroma interactions. Pancreatic cancer invasion into neural tissue precedes tumor expansion. This perineural invasion is strongly associated with neural hypertrophy, pain and poor survival, and neurotrophins and their receptors (TRKs) are key suspects in mediating this process. At the same time, infiltrating macrophages are an additional component of the tumor microenvironment that supports tumor growth, invasion and inflammation, and the receptor for CSF-1 (FMS) is a key mediator of the function and survival of these macrophages. Both TRKs and FMS are transmembrane proteins with tyrosine kinase activities that can be inhibited with small molecule agents. We have developed a series of TRK/FMS dual inhibitors to target cancers that exhibit both neural and inflammatory components. These compounds inhibit biochemical TRK and FMS kinases with IC50<20nM and inhibit the proliferation of BaF3 cells engineered to express active TRK and FMS with IC50<50nM. In counterscreens across a broad kinase panel, these inhibitors are highly selective against non-target kinases. The lead compounds show good oral bioavailability in pharmacokinetic tests. Utilizing the engineered BaF3-TRK and BaF3-FMS cells injected into mice as pharmacology models, the lead candidates show growth inhibition of >80% at doses of 20 mg/kg qd, and without body weight changes, showing that efficacy is not due to nonspecific toxicity. In a mouse Complete Freund's Adjuvant (CFA) model, robust efficacy was demonstrated in readouts of paw edema, thermal hyperalgesia and mechanical allodynia, showing that these compounds reduce swelling and pain. In the TRK-driven SK-N-SH xenograft model, tumor growth reduction of >50% was observed. These compounds also showed anti-tumor efficacy of >40% in an orthotopic Panc-1 (pancreatic cancer) model. Evaluation of compound effects on perineural invasion and inflammation is ongoing. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 553. doi:10.1158/1538-7445.AM2011-553

Selective inhibitors of BRAF such as vemurafenib (PLX4032) and GSK2118436 show remarkable efficacy in melanoma patients with tumors harboring BRAF V600 mutations. However these compounds paradoxically activate the MAPK pathway in RAS-mutant cells and are associated clinically with appearance of skin tumors such as cutaneous squamous cell carcinomas (cuSCC), particularly of the keratoacanthoma subtype. Here we further investigated the molecular links between BRAF inhibitor treatment and skin neoplasm. In soft agar, BRAF inhibitors induced growth of HRAS-mutant cuSCC B9 cells via upregulation of several EGFR ligands. The EGFR inhibitor Tarceva antagonized this transforming effect. The “Paradox Breakers,” a class of BRAF inhibitors recently discovered at Plexxikon, did not activate the MAPK pathway in cells with RAS mutation or EGFR family kinase activation and failed to upregulate EGFR ligands or induce soft agar growth of B9 cells. Also when tested in vivo, subcutaneous B9-tumor growth was accelerated by a structural analog (PLX4720) of vemurafenib but not by an equally effective BRAF inhibitor of the Paradox Breaker class. Taken together, a novel mechanism responsible for BRAF inhibitor-induced cuSCC was uncovered. Our data suggest that combination treatment of EGFR inhibitors with BRAF inhibitors might prevent skin tumor growth and that Paradox Breakers represent a new generation of BRAF inhibitors that have fewer unwanted side effects and the potential for greater clinical efficacy. 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 A229.

This work presents a method to utilize the ever-expanding corporate collections of CYP450 inhibition data to forecast the future risk of compounds not yet synthesized. The global/local fusion method differs from existing QSAR methods, in that each prediction is derived from a custom-built QSAR model, constructed on-the-fly, using a customized training set assembled for each prediction. It uses a consensus of global and local descriptor-based models along with pharmacophore-based fingerprint similarity to form a prediction and to assess the uncertainty of the prediction on a case-by-case basis. We also present a new forward prediction testing and validation scheme in which the corporate dataset is split chronologically, and predictions for a molecule are based on the pool of existing data available before the molecule is registered and tested. The validation accuracy of the CYP2D6 and CYP3A4 models approaches the underlying accuracy of the data, about 0.4 log IC50 units standard error (or nearly 70% r(2) correlation) for the most confident predictions, and extends to about 0.6 log IC50 units standard error (or under 30% r(2) correlation) for the least confident predictions. As a classification model for CYP2D6 and CYP3A4 activity, the validation accuracy is about 79% for predicted actives and 85% for predicted inactives, which is consistent with existing published models.

We recently developed a global-local fusion model for CYP450 predictions. This model has the advantages of both global and local models. The expected error of the model is also estimated that helps to qualify the reliability of the predictions. It is described how different potential errors in QSAR model generation and prediction were averted and how the method was applied in an industrial environment.

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This paper describes the development of a set of new 2D fingerprints for the purposes of virtual screening in a pharmaceutical environment. The new fingerprints are based on established ones: the changes in their design included the introduction of overlapping pharmacophore feature types, feature counts for pharmacophore and structural fingerprints, as well as changes in the resolution in property description for property fingerprints. The effects of each of these changes on virtual screening performance were monitored using two types of training sets, emulating different stages in the drug discovery process. The results demonstrate that these changes all lead to an improvement in virtual screening performance.