Thomas H. Marsilje

Synthesis, structure-activity relationships, and in vivo efficacy of the novel potent and selective anaplastic lymphoma kinase (ALK) inhibitor 5-chloro-N2-(2-isopropoxy-5-methyl-4-(piperidin-4-yl)phenyl)-N4-(2-(isopropylsulfonyl)phenyl)pyrimidine-2,4-diamine (LDK378) currently in phase 1 and phase 2 clinical trials.

The synthesis, preclinical profile, and in vivo efficacy in rat xenograft models of the novel and selective anaplastic lymphoma kinase inhibitor 15b (LDK378) are described. In this initial report, preliminary structure-activity relationships (SARs) are described as well as the rational design strategy employed to overcome the development deficiencies of the first generation ALK inhibitor 4 (TAE684). Compound 15b is currently in phase 1 and phase 2 clinical trials with substantial antitumor activity being observed in ALK-positive cancer patients.

Overcoming EGFR(T790M) and EGFR(C797S) resistance with mutant-selective allosteric inhibitors

EGFR tyrosine kinase inhibitors (TKIs) gefitinib, erlotinib and afatinib are approved treatments for non-small cell lung cancers harboring activating mutations in the EGFR kinase1,2, but resistance arises rapidly, most frequently due to the secondary T790M mutation within the ATP-site of the receptor.3,4 Recently developed mutant-selective irreversible inhibitors are highly active against the T790M mutant5,6, but their efficacy can be compromised by acquired mutation of C797, the cysteine residue with which they form a key covalent bond7. All current EGFR TKIs target the ATP-site of the kinase, highlighting the need for therapeutic agents with alternate mechanisms of action. Here we describe rational discovery of EAI045, an allosteric inhibitor that targets selected drug-resistant EGFR mutants but spares the wild type receptor. A crystal structure shows that the compound binds an allosteric site created by the displacement of the regulatory C-helix in an inactive conformation of the kinase. The compound inhibits L858R/T790M-mutant EGFR with low-nanomolar potency in biochemical assays, but as a single agent is not effective in blocking EGFR-driven proliferation in cells due to differential potency on the two subunits of the dimeric receptor, which interact in an asymmetric manner in the active state8. We observe dramatic synergy of EAI045 with cetuximab, an antibody therapeutic that blocks EGFR dimerization9,10, rendering the kinase uniformly susceptible to the allosteric agent. EAI045 in combination with cetuximab is effective in mouse models of lung cancer driven by L858R/T790M EGFR and by L858R/T790M/C797S EGFR, a mutant that is resistant to all currently available EGFR TKIs. More generally, our findings illustrate the utility of purposefully targeting allosteric sites to obtain mutant-selective inhibitors.

EGF816 Exerts Anticancer Effects in Non–Small Cell Lung Cancer by Irreversibly and Selectively Targeting Primary and Acquired Activating Mutations in the EGF Receptor

Non-small cell lung cancer patients carrying oncogenic EGFR mutations initially respond to EGFR-targeted therapy, but later elicit minimal response due to dose-limiting toxicities and acquired resistance. EGF816 is a novel, irreversible mutant-selective EGFR inhibitor that specifically targets EGFR-activating mutations arising de novo and upon resistance acquisition, while sparing wild-type (WT) EGFR. EGF816 potently inhibited the most common EGFR mutations L858R, Ex19del, and T790M in vitro, which translated into strong tumor regressions in vivo in several patient-derived xenograft models. Notably, EGF816 also demonstrated antitumor activity in an exon 20 insertion mutant model. At levels above efficacious doses, EGF816 treatment led to minimal inhibition of WT EGFR and was well tolerated. In single-dose studies, EGF816 provided sustained inhibition of EGFR phosphorylation, consistent with its ability for irreversible binding. Furthermore, combined treatment with EGF816 and INC280, a cMET inhibitor, resulted in durable antitumor efficacy in a xenograft model that initially developed resistance to first-generation EGFR inhibitors via cMET activation. Thus, we report the first preclinical characterization of EGF816 and provide the groundwork for its current evaluation in phase I/II clinical trials in patients harboring EGFR mutations, including T790M.

NMR structural studies of interactions of a small, nonpeptidyl tpo mimic with the thrombopoietin receptor extracellular Juxtamembrane and transmembrane domains

Thrombopoietin (Tpo) is a glycoprotein growth factor that supports hematopoietic stem cell survival and expansion and is the principal regulator of megakaryocyte growth and differentiation. Several small, nonpeptidyl molecules have been identified as selective human Tpo receptor (hTpoR) agonists. To understand how the small molecule Tpo mimic SB394725 interacts and activates hTpoR, we performed receptor domain swap and mutagenesis studies. The results suggest that SB394725 interacts specifically with the extracellular juxtamembrane region (JMR) and the transmembrane (TM) domain of hTpoR. Solution and solid-state NMR structural studies using a peptide containing the JMR-TM sequences showed that this region of hTpoR, unexpectedly, consists of two α-helices separated by a few nonhelical residues. SB394725 interacts specifically with His-499 in the TM domain and a few distinct residues in the JMR-TM region and affects several specific C-terminal TM domain residues. The unique structural information provided by these studies both sheds light on the distinctive mechanism of action of SB394725 and provides valuable insight into the mechanism of ligand-induced cytokine receptor activation.

Discovery and biological evaluation of benzo[a]carbazole-based small molecule agonists of the thrombopoietin (Tpo) receptor

A novel series of benzo[a]carbazole-based small molecule agonists of the thrombopoietin (Tpo) receptor is reported. Starting from a 3.4 microM high throughput screen hit, members of this series have been identified which are full agonists with functional potency <50 nM and oral bioavailability in mice.

Discovery of (R,E)-N-(7-Chloro-1-(1-[4-(dimethylamino)but-2-enoyl]azepan-3-yl)-1H-benzo[d]imidazol-2-yl)-2-methylisonicotinamide (EGF816), a Novel, Potent, and WT Sparing Covalent Inhibitor of Oncogenic (L858R, ex19del) and Resistant (T790M) EGFR Mutants for the Treatment of EGFR Mutant Non-Small-Cell Lung Cancers.

Over the past decade, first and second generation EGFR inhibitors have significantly improved outcomes for lung cancer patients with activating mutations in EGFR. However, both resistance through a secondary T790M mutation at the gatekeeper residue and dose-limiting toxicities from wild-type (WT) EGFR inhibition ultimately limit the full potential of these therapies to control mutant EGFR-driven tumors and new therapies are urgently needed. Herein, we describe our approach toward the discovery of 47 (EGF816, nazartinib), a novel, covalent mutant-selective EGFR inhibitor with equipotent activity on both oncogenic and T790M-resistant EGFR mutations. Through molecular docking studies we converted a mutant-selective high-throughput screening hit (7) into a number of targeted covalent EGFR inhibitors with equipotent activity across mutants EGFR and good WT-EGFR selectivity. We used an abbreviated in vivo efficacy study for prioritizing compounds with good tolerability and efficacy that ultimately led to the selection of 47 as the clinical candidate.

Optimization of small molecule agonists of the thrombopoietin (Tpo) receptor derived from a benzo[a]carbazole hit scaffold

The lead optimization of a novel series of benzo[a]carbazole-based small molecule agonists of the thrombopoietin (Tpo) receptor is reported. The chemical instability of the dihydro-benzo[a]carbazole lead 2 was successfully addressed in the design and evaluation of compounds which also demonstrated improved potency compared to 2. Members of the scaffold have been identified which are full agonists that demonstrate cellular functional potency <50 nM. Analog 21 demonstrates equivalent efficacy in the human megakaryocyte differentiation (CFU-mega) assay compared to Eltrombopag.

Identification and characterization of small molecule modulators of the Epstein-Barr virus-induced gene 2 (EBI2) receptor.

Oxysterols have recently been identified as natural ligands for a G protein-coupled receptor called EBI2 (aka GPR183) ( Nature 2011 , 475 , 524 ; 519 ). EBI2 is highly expressed in immune cells ( J. Biol. Chem. 2006 , 281 , 13199 ), and its activation has been shown to be critical for the adaptive immune response and has been genetically linked to autoimmune diseases such as type I diabetes ( Nature 2010 , 467 , 460 ). Here we describe the isolation of a potent small molecule antagonist for the EBI2 receptor. First, we identified a small molecule agonist NIBR51 (1), which enabled identification of inhibitors of receptor activation. One antagonist called NIBR127 (2) was used as a starting point for a medicinal chemistry campaign, which yielded NIBR189 (4m). This compound was extensively characterized in binding and various functional signaling assays. Furthermore, we have used 4m to block migration of a monocyte cell line called U937, suggesting a functional role of the oxysterol/EBI2 pathway in these immune cells.

Abstract B232: Activity of a potent and selective phase I ALK inhibitor LDK378 in naive and crizotinib-resistant preclinical tumor models.

A c-MET/ALK kinase inhibitor crizotinib has demonstrated significant activity in lung cancer patients with EML4-ALK in clinical studies. However relapse (or acquired resistance) has also been reported. We have developed crizotinib resistant tumor models and used the models to evaluate the ALK inhibitor LDK378. LDK378 is a potent and selective ALK inhibitor that does not cross react with c-MET. In a mouse xenograft tumor model derived from the EML4-ALK+ lung cancer cell line NCI-H2228, LDK378 caused complete tumor regression when dosed orally at 25 mg/kg/day. After tumor bearing animals had been treated with LDK378 at 50 mg/kg/day for 14 days, remission was maintained for more than 4 months. In several NCI-H2228 tumor models that were induced to become resistant to crizotinib, LDK378 demonstrated efficacy at 50 mg/kg/day. Based on 4-wk GLP toxicology studies the drug exposure associated with this dose is predicted to be below the exposure at the MTD in humans. ALK resistance mutations reported in crizotinib relapsed patients were also found in the crizotinib resistant NCI-H2228 tumor models. The results from these preclinical studies suggest that LDK378 may be active in crizotinib-relapsed patients. A phase I clinical study of LDK378 has recently begun in both crizotinib-relapsed and crizotinib-naive patients. 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 B232.

Optimisation of a 5-[3-phenyl-(2-cyclic-ether)-methyl-ether]-4-aminopyrrolopyrimidine series of IGF-1R inhibitors

Taking the pyrrolopyrimidine derived IGF-1R inhibitor NVP-AEW541 as the starting point, the benzyl ether back-pocket binding moiety was replaced with a series of 2-cyclic ether methyl ethers leading to the identification of novel achiral [2.2.1]-bicyclic ether methyl ether containing analogues with improved IGF-1R activities and kinase selectivities. Further exploration of the series, including a fluorine scan of the 5-phenyl substituent, and optimisation of the sugar-pocket binding moiety identified compound 33 containing (S)-2-tetrahydrofuran methyl ether 6-fluorophenyl ether back-pocket, and cis-N-Ac-Pip sugar-pocket binding groups. Compound 33 showed improved selectivity and pharmacokinetics compared to NVP-AEW541, and produced comparable in vivo efficacy to linsitinib in inhibiting the growth of an IGF-1R dependent tumour xenograft model in the mouse.