Robert Epple

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.

Inhibitors of cathepsin s

Cathepsin B is an abundant and ubiquitously expressed cysteine peptidase of the papain family. It is involved in many physiological processes, such as remodeling of the extracellular matrix (wound healing), apoptosis, and activation of thyroxine and renin. In addition to its physiological roles, cathepsin B is important in many pathological processes, such as inflammation, parasite infection and cancer, where it is highly up-regulated. In cancer patients, elevated cathepsin B activity correlates to poor therapy outcome. Therefore, it is not surprising that the use of cathepsin B inhibitors reduces both tumor cell motility and invasiveness in vitro. This review summarizes recent developments in cathepsin B inhibition. To date, numerous protein inhibitors of cathepsin B have been described, some of which are of endogenous origin and function as regulators of cathepsin B activity in the cell, such as the cystatins. In addition, some exogenous protein inhibitors of cathepsin B have been isolated from various natural sources, and the use of X-ray crystal structures of cathepsin B complexed with such protein inhibitors has resulted in the design and synthesis of many new small-molecular-weight compounds as inhibitors of cathepsin B. These synthetic compounds generally contain an electrophilic functionality that reacts with cathepsin B. In the present review, these inhibitors are divided according to their mechanisms of action, as reversible and irreversible, and then further subdivided into groups for their full descriptions.

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.

Novel Bisaryl Substituted Thiazoles and Oxazoles as Highly Potent and Selective Peroxisome Proliferator-Activated Receptor δ Agonists

The discovery, synthesis, and optimization of compound 1 from a high-throughput screening hit to highly potent and selective peroxisome proliferator-activated receptor delta (PPARdelta) agonists are reported. The synthesis and structure-activity relationship in this series are described in detail. On the basis of a general schematic PPAR pharmacophore model, scaffold 1 was divided into headgroup, linker, and tailgroup and successively optimized for PPAR activation using in vitro PPAR transactivation assays. A (2-methylphenoxy)acetic acid headgroup, a flexible linker, and a five-membered heteroaromatic center ring with two hydrophobic aryl substituents were required for efficient and selective PPARdelta activation. The fine-tuning of these aryl substituents led to an array of highly potent and selective compounds such as compound 38c, displaying an excellent pharmacokinetic profile in mouse. In an in vivo acute dosing model, selected members of this array were shown to induce the expression of pyruvate dehydrogenase kinase-4 (PDK4) and uncoupling protein-3 (UCP3), genes that are known to be involved in energy homeostasis and regulated by PPARdelta in skeletal muscle.

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.

Discovery of structurally novel, potent and orally efficacious GPR119 agonists.

Screening hit 5 was identified in a biochemical screen for GPR119 agonists. Compound 5 was structurally novel, displayed modest biochemical activity and no oral exposure, but was structurally distinct from typical GPR119 agonist scaffolds. Systematic optimization led to compound 36 with significantly improved in vitro activity and oral exposure, to elevate GLP1 acutely in an in vivo mouse model at a dose of 10mg/kg.

Novel tricyclic pyrazolopyrimidines as potent and selective GPR119 agonists

Systematic SAR optimization of the GPR119 agonist lead 1, derived from an internal HTS campaign, led to compound 29. Compound 29 displays significantly improved in vitro activity and oral exposure, leading to GLP1 elevation in acutely dosed mice and reduced glucose excursion in an OGTT study in rats at doses ⩾10 mg/kg.

Abstract 2585: Discovery of a potent covalent mutant-selective EGFR inhibitor - the journey from high throughput screening to EGF816

Epidermal growth factor receptor (EGFR) is a validated therapeutic target for lung cancer. First and second generation EGFR inhibitors (e.g., gefitinib, erlotinib and afatinib) have revolutionized treatment paradigms of non-small cell lung cancer (NSCLC) patients with oncogenic EGFR mutations. The use of EGFR tyrosine kinase inhibitors (TKI) provides superior efficacy compared to chemotherapy in patients with EGFR L858R or exon 19 deletion tumors. However, resistance inevitably develops after 8-12 months of treatment; most commonly via a secondary T790M point mutation at the gatekeeper residue of EGFR. Furthermore, responses are hindered due to treatment intolerance in the form of rash and diarrhea that are mediated by simultaneous inhibition of wild-type (WT) EGFR at doses required for mutant EGFR suppression. To overcome these limitations, we initiated a project to identify mutant-selective EGFR inhibitors that potently inhibit both activating and T790M resistance EGFR mutations while sparing WT EGFR. In this presentation, we report our medicinal chemistry approach and optimization that led to the discovery of EGF816, a selective and potent covalent mutant-selective EGFR inhibitor with single digit nanomolar cellular target modulation on both activating and T790M resistance mutations. In addition, we will also report validated clinical efficacy data from the first patient treated with EGF816. Citation Format: Gerald Lelais, Robert Epple, Pierre-Yves Michellys, Thomas H. Marsilje, Yun Long, Matthew McNeill, Bei Chen, Wenshuo Lu, Badry Bursulaya, Michael DiDonato, Yong Jia, Shailaja Kasibhatla, Chun Li, Igor Matushansky, Steven Bender. Discovery of a potent covalent mutant-selective EGFR inhibitor - the journey from high throughput screening to EGF816. [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 2585. doi:10.1158/1538-7445.AM2015-2585