Design, Synthesis, and In Vitro and In Vivo Evaluation of Cereblon Binding Bruton's Tyrosine Kinase (BTK) Degrader CD79b Targeted Antibody-Drug Conjugates

Antibody-drug conjugates (ADCs) are an established modality that allow for targeted delivery of a potent molecule, or payload, to a desired site of action. ADCs, wherein the payload is a targeted protein degrader, are an emerging area in the field. Herein we describe our efforts of delivering a Bruton's tyrosine kinase (BTK) bifunctional degrader 1 via a CD79b mAb (monoclonal antibody) where the degrader is linked at the ligase binding portion of the payload via a cleavable linker to the mAb. The resulting CD79b ADCs, 3 and 4, exhibit in vitro degradation and cytotoxicity comparable with that of 1, and ADC 3 can achieve more sustained in vivo degradation than intravenously administered 1 with markedly reduced systemic exposure of the payload.

Discovery of a novel 2-aminopyrazine-3-carboxamide as a potent and selective inhibitor of Activin Receptor-Like Kinase-2 (ALK2) for the treatment of fibrodysplasia ossificans progressiva

Inhibition of mutant activin A type-1 receptor ACVR1 (ALK2) signaling by small-molecule drugs is a promising therapeutic approach to treat fibrodysplasia ossificans progressiva (FOP), an ultra-rare disease leading to progressive soft tissue heterotopic ossification with no curative treatment available to date. Here, we describe the synthesis and in vitro characterization of a novel series of 2-aminopyrazine-3-carboxamides that led to the discovery of Compound 23 showing excellent biochemical and cellular potency, selectivity over other BMP and TGFβ signaling receptor kinases, and a favorable in vitro ADME profile.

Abstract LB140: CNS penetrant, irreversible inhibitors potently inhibit the family of allosteric oncogenic EGFR mutants expressed in GBM and demonstrate efficacy in patient-derived xenograft models

Oncogenic EGFR mutations occur in approximately 50% of glioblastomas (GBM) and largely reside in the extracellular domain. Prior attempts to reposition current generation EGFR inhibitors to treat GBM likely failed due to poor brain penetration and an inability to potently target the full spectrum of oncogenic mutations. As EGFR oncogenic mutations are found to be co-expressed in many GBMs, it is important that an inhibitor be broadly active against the entire family of relevant EGFR mutants. Additionally, a successful inhibitor would require a pharmacokinetic (PK) profile that allows for sufficient penetration of the blood brain barrier to elicit robust target engagement of the brain tumor. Using these design principles, we designed a series of highly potent molecules exemplified by BDTX-507. This molecule is an irreversible inhibitor of EGFR with antiproliferative IC50's less than 10 nM against the spectrum of GBM-relevant EGFR mutations. PK/PD studies demonstrated sustained pERK suppression exceeding 24 hours following a single QD dose. Furthermore, when dosed in GBM xenografts, including an intracranial Viii PDX (GBM6), robust tumor regressions and improved survival were observed. Emerging from this series were two advanced compounds, BDTX-700 and BDTX-1535, which also demonstrated potent inhibition of the GBM EGFR spectrum, selectivity v. wild-type EGFR, and an excellent CNS PK profile. BDTX-1535 is currently being evaluated in IND-enabling studies for future clinical evaluation in GBM patients.

Citation Format: Matthew O'Connor, Matt Lucas, Darlene Romashko, Sara Rasmussen, Tai-An Lin, Nigel Waters, Raffaele Fiorenza, Iwona Wrona, Deborah Chen, Theodore Nicolaides, David R. Raleigh, Tomoko Ozawa, George Trainor, Luca Arista, Alexander Flohr, Giorgio Ottaviani, Chris Roberts, Elizabeth Buck. CNS penetrant, irreversible inhibitors potently inhibit the family of allosteric oncogenic EGFR mutants expressed in GBM and demonstrate efficacy in patient-derived xenograft models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr LB140.

EXTH-59. POTENT, SELECTIVE, AND BRAIN PENETRANT INHIBITORS OF EXTRACELLULAR DOMAIN EGFR ONCOGENIC MUTANTS EXPRESSED IN GBM DEMONSTRATE EFFICACY IN AN INTRACRANIAL PATIENT DERIVED XENOGRAFT MODEL

EGFR mutations identified in glioblastomas (GBM) occur nearly exclusively at the allosteric extracellular domain (ECD) and constitutively activate oncogenic signaling. Despite wide success in treating tumors expressing EGFR catalytic site mutants, no drug has demonstrated clinical utility against tumors expressing the extracellular domain EGFR mutants. We demonstrate that the family of ECD mutations are not only co-expressed in GBM, but that they all activate the oncogene through a similar disulfide bond-mediated receptor dimerization mechanism. This dimerization occurs independent of ligands and renders the Locked-dimer (LoDi)-EGFR insensitive to agents that target the EGFR kinase domain mutants in NSCLC. The kinase conformation induced by these ECD mutations seen in glioblastomas is both oncogenic and altered from kinase domain mutations, thus necessitating a new approach to targeting. By screening against cells expressing LoDi-EGFR mutants, we have identified the first inhibitors that potently and selectively target LoDi-EGFR mutants versus both canonical active site oncogenic mutants and wild type EGFR. Through an optimization effort, we have identified a novel family of potent and selective LoDi-EGFR mutant inhibitors that effectively penetrate the blood brain barrier (BBB) following oral dosing in preclinical studies. A leading exemplar, BDTX-GBM-001, inhibits the 5 major LoDi-EGFR mutants expressed in GBM with antiproliferative potency of ~10 nM while showing favorable selectivity versus the human kinome. When dosed orally in the intracranial GBM6 patient derived xenograft model at 50, 30, and 15 mg/kg, a dose responsive decrease in tumor growth, as well as a statistically significant increase in survival, were observed. These data support the continued evaluation of rationally designed BBB penetrant inhibitors selectively targeting the common LoDi-EGFR mutants and enable the first chance to fully test the clinical hypothesis of EGFR driver mutants in GBM.

Multifunctional Carrier Based on Halloysite/Laponite Hybrid Hydrogel for Kartogenin Delivery

A novel carrier system based on halloysite nanotubes (HNT), for the potential intraarticular delivery of kartogenin (KGN) by means laponite (Lap) hydrogel (HNT/KGN/Lap), is developed. The drug was first loaded into HNT, and the hybrid composite obtained was used as filler for laponite hydrogel. Both the filler and the hydrogel were thoroughly investigated by several techniques and the hydrogel morphology was imaged by transmission electron microscopy. Furthermore, the gelating ability of laponite in the presence of the filler and the rheological properties of the hybrid hydrogel were also investigated. The kinetic release of kartogenin from HNT and HNT/Lap hybrid hydrogel was studied both in physiological conditions and in ex vivo synovial fluid. In the last case, the kinetic results highlighted that HNT carrier can effectively release KGN in a sustained manner for at least 38 days. Finally, a preliminary biological assays showed that the HNT/KGN/Lap hybrid hydrogel did not exhibit any cytotoxic effect.

Structural States of RORγt: X-ray Elucidation of Molecular Mechanisms and Binding Interactions for Natural and Synthetic Compounds

The T-cell-specific retinoic acid receptor (RAR)-related orphan receptor-γ (RORγt) is a key transcription factor for the production of pro-inflammatory Th17 cytokines, which are implicated in the pathogenesis of autoimmune diseases. Over the years, several structurally diverse RORγt inverse agonists have been reported, but combining high potency and good physicochemical properties has remained a challenging task. We recently reported a new series of inverse agonists based on an imidazopyridine core with good physicochemical properties and excellent selectivity. Herein we report eight new X-ray crystal structures for different classes of natural and synthetic compounds, including examples selected from the patent literature. Analysis of their respective binding modes revealed insight into the molecular mechanisms that lead to agonism, antagonism, or inverse agonism. We report new molecular mechanisms for RORγt agonism and propose a separation of the inverse agonists into two classes: those that act via steric clash and those that act via other mechanisms (for the latter, co-crystallization with a co-activator peptide and helix 12 in the agonist position is still possible). For the non-steric clash inverse agonists, we propose a new mechanism ("water trapping") which can be combined with other mechanisms (e.g., close contacts with H479). In addition, we compare the interactions made for selected compounds in the "back pocket" near S404 and in the "sulfate pocket" near R364 and R367. Taken together, these new mechanistic insights should prove useful for the design and optimization of further RORγt modulators.

Pyrrolo[3,4-c]pyridine-1,3(2H)-diones: A Novel Antimycobacterial Class Targeting Mycobacterial Respiration

High-throughput screening of a library of small polar molecules against Mycobacterium tuberculosis led to the identification of a phthalimide-containing ester hit compound (1), which was optimized for metabolic stability by replacing the ester moiety with a methyl oxadiazole bioisostere. A route utilizing polymer-supported reagents was designed and executed to explore structure-activity relationships with respect to the N-benzyl substituent, leading to compounds with nanomolar activity. The frontrunner compound (5h) from these studies was well tolerated in mice. A M. tuberculosis cytochrome bd oxidase deletion mutant (ΔcydKO) was hyper-susceptible to compounds from this series, and a strain carrying a single point mutation in qcrB, the gene encoding a subunit of the menaquinol cytochrome c oxidoreductase, was resistant to compounds in this series. In combination, these observations indicate that this novel class of antimycobacterial compounds inhibits the cytochrome bc1 complex, a validated drug target in M. tuberculosis.

G-protein-coupled bile acid receptor 1 (GPBAR1, TGR5) agonists reduce the production of proinflammatory cytokines and stabilize the alternative macrophage phenotype

GPBAR1 (also known as TGR5) is a G-protein-coupled receptor (GPCR) that triggers intracellular signals upon ligation by various bile acids. The receptor has been studied mainly for its function in energy expenditure and glucose homeostasis, and there is little information on the role of GPBAR1 in the context of inflammation. After a high-throughput screening campaign, we identified isonicotinamides exemplified by compound 3 as nonsteroidal GPBAR1 agonists. We optimized this series to potent derivatives that are active on both human and murine GPBAR1. These agonists inhibited the secretion of the proinflammatory cytokines TNF-α and IL-12 but not the antiinflammatory IL-10 in primary human monocytes. These effects translate in vivo, as compound 15 inhibits LPS induced TNF-α and IL-12 release in mice. The response was GPBAR1 dependent, as demonstrated using knockout mice. Furthermore, agonism of GPBAR1 stabilized the phenotype of the alternative, noninflammatory, M2-like type cells during differentiation of monocytes into macrophages. Overall, our results illustrate an important regulatory role for GPBAR1 agonists as controllers of inflammation.