First-in-Human Study of the Reversible BTK Inhibitor Nemtabrutinib in Patients with Relapsed/Refractory Chronic Lymphocytic Leukemia and B-Cell Non-Hodgkin Lymphoma

Nemtabrutinib is an orally bioavailable, reversible inhibitor of Bruton tyrosine kinase (BTK) and C481S mutant BTK. We evaluated the safety, pharmacology, and antitumor activity of nemtabrutinib in relapsed/refractory hematologic malignancies. Forty-eight patients with chronic lymphocytic leukemia (CLL), B-cell non-Hodgkin lymphoma (NHL), or Waldenström macroglobulinemia (WM), relapsed/refractory after ≥2 prior therapies were enrolled in the open-label, single-arm, phase I MK-1026-001 study (NCT03162536) to receive nemtabrutinib 5 to 75 mg once daily in 28-day cycles. Dose finding progressed using a 3 + 3 dose escalation design. Primary endpoints were safety and the recommended phase II dose (RP2D). Among 47 treated patients, 29 had CLL, 17 had NHL, and 1 had WM. Grade ≥3 treatment-emergent adverse events occurred in 37 (89%), most commonly neutropenia (11; 23.4%), febrile neutropenia (7; 14.9%), and pneumonia (7; 14.9%). The RP2D was 65 mg daily. An overall response rate of 75% was observed in patients with CLL at 65 mg daily.

SIGNIFICANCE

This first-in-human phase I study demonstrates the safety and preliminary efficacy of nemtabrutinib in patients with relapsed/refractory B-cell malignancies. These data support further exploration of nemtabrutinib in larger clinical studies. This article is featured in Selected Articles from This Issue, p. 5.

The BTK Inhibitor ARQ 531 Targets Ibrutinib-Resistant CLL and Richter Transformation

Targeted inhibition of Bruton tyrosine kinase (BTK) with the irreversible inhibitor ibrutinib has improved outcomes for patients with hematologic malignancies, including chronic lymphocytic leukemia (CLL). Here, we describe preclinical investigations of ARQ 531, a potent, reversible inhibitor of BTK with additional activity against Src family kinases and kinases related to ERK signaling. We hypothesized that targeting additional kinases would improve global inhibition of signaling pathways, producing more robust responses. In vitro treatment of patient CLL cells with ARQ 531 decreases BTK-mediated functions including B-cell receptor (BCR) signaling, viability, migration, CD40 and CD86 expression, and NF-κB gene transcription. In vivo, ARQ 531 was found to increase survival over ibrutinib in a murine Eμ-TCL1 engraftment model of CLL and a murine Eμ-MYC/TCL1 engraftment model resembling Richter transformation. Additionally, ARQ 531 inhibits CLL cell survival and suppresses BCR-mediated activation of C481S BTK and PLCγ2 mutants, which facilitate clinical resistance to ibrutinib.Significance: This study characterizes a rationally designed kinase inhibitor with efficacy in models recapitulating the most common mechanisms of acquired resistance to ibrutinib. Reversible BTK inhibition is a promising strategy to combat progressive CLL, and multikinase inhibition demonstrates superior efficacy to targeted ibrutinib therapy in the setting of Richter transformation. Cancer Discov; 8(10); 1300-15. ©2018 AACR. This article is highlighted in the In This Issue feature, p. 1195.

Abstract 1963: ARQ 531, a potent reversible BTK inhibitor, exhibits potent antitumor activity in ibrutinib-resistant diffuse large B-cell lymphoma

Background: B-cell receptor (BCR)-mediated signaling plays an important role in the pathogenesis of a subset of diffuse large B-cell lymphoma (DLBCL). Despite major advances in the treatment, ~40% of the relapsed/refractory DLBCL patients still experience early treatment failure after initial response to chemotherapy. ARQ 531, a reversible inhibitor of BTK and BTK-C481S mutant, also potently suppresses BCR signaling. Here we demonstrate that ARQ 531 targets additional kinases and suppresses multiple oncogenic pathways, this inhibitory potency is coupled to broad anti-tumor activity in DLBCL subtypes including tumors resistant to BCR targeted therapy.

Methods: Biochemical inhibition and broad kinase profiling were assessed using recombinant proteins. Binding kinetics and the residence time with BTK and BTK-C481S were measured by Surface Plasmon Resonance (SPR) assay. Binding mode of ARQ 531 with BTK was determined by protein crystallography. Pathway inhibition assessments, in vivo efficacy and in vivo target inhibition were performed in DLBCL tumor models derived from TMD8, SUDHL-4 and DOHH-2 cell lines.

Results: ARQ 531 potently inhibited BTK (IC50 = 0.85 nM), the binding potency was accompanied by long residence time (51 min). Crystal structure of BTK/ARQ 531 complex showed that ARQ 531 occupies the ATP-binding pocket. Kinase selectivity profile suggested that ARQ 531 inhibits sub-families of Tec, Src, Trk kinases. Significant anti-proliferative activity (GI50 = < 1µM) was observed in hematological malignant cell lines characterized by addiction to BTK signaling and primarily resistant to ibrutinib. Pathway inhibition analysis suggested that ARQ 531 targets multiple oncogenic signaling pathways in both ABC- and GCB-DLBCL cell lines. Unlike ibrutinib, ARQ 531 suppressed both the upstream activating signals (via inhibition of a select member of Src kinase family) and the downstream signaling pathways (via pAKT and pERK kinases). In GCB-DLBCL cell lines (SUDHL-4 and DOHH-2), ARQ 531 potently suppressed expression of anti-apoptotic c-Myc and BCL6 oncoproteins in a dose dependent fashion, and concomitantly induced apoptotic cleavage of PARP protein. In the ibrutinib-resistant SUDHL-4 mouse xenograft model, ARQ 531 potently suppressed tumor growth (>80% inhibition) compared to the control group when dosed orally at 75 mg/kg. Additionally, preliminary data suggest that ARQ 531 crosses the blood, brain-barrier.

Conclusion: ARQ 531 is a potent reversible inhibitor of BTK, its distinct kinase selectivity profile offers significant advantage for simultaneous inhibition of multiple therapeutically relevant targets. ARQ 531 attenuated the expression of key oncogenic drivers via inhibition of downstream BCR activating kinases. These results highlight the therapeutic potential of inhibition of BCR signaling inhibition by ARQ 531 in the treatment of DLBCL.

Citation Format: Sudharshan Eathiraj, Yi Yu, Ron Savage, Jennifer A. Woyach, Sean D. Reiff, Amy J. Johnson, Brian Schwartz. ARQ 531, a potent reversible BTK inhibitor, exhibits potent antitumor activity in ibrutinib-resistant diffuse large B-cell lymphoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1963.

Probing the metabotropic glutamate receptor 5 (mGlu₅) positive allosteric modulator (PAM) binding pocket: discovery of point mutations that engender a "molecular switch" in PAM pharmacology

Positive allosteric modulation of metabotropic glutamate receptor subtype 5 (mGlu₅) is a promising novel approach for the treatment of schizophrenia and cognitive disorders. Allosteric binding sites are topographically distinct from the endogenous ligand (orthosteric) binding site, allowing for co-occupation of a single receptor with the endogenous ligand and an allosteric modulator. Negative allosteric modulators (NAMs) inhibit and positive allosteric modulators (PAMs) enhance the affinity and/or efficacy of the orthosteric agonist. The molecular determinants that govern mGlu₅ modulator affinity versus cooperativity are not well understood. Focusing on the modulators based on the acetylene scaffold, we sought to determine the molecular interactions that contribute to PAM versus NAM pharmacology. Generation of a comparative model of the transmembrane-spanning region of mGlu₅ served as a tool to predict and interpret the impact of mutations in this region. Application of an operational model of allosterism allowed for determination of PAM and NAM affinity estimates at receptor constructs that possessed no detectable radioligand binding as well as delineation of effects on affinity versus cooperativity. Novel mutations within the transmembrane domain (TM) regions were identified that had differential effects on acetylene PAMs versus 2-methyl-6-(phenylethynyl)-pyridine, a prototypical NAM. Three conserved amino acids (Y658, T780, and S808) and two nonconserved residues (P654 and A809) were identified as key determinants of PAM activity. Interestingly, we identified two point mutations in TMs 6 and 7 that, when mutated, engender a mode switch in the pharmacology of certain PAMs.

Financial planning: a necessity for the '90s

The changing face of healthcare demands a long-range strategic financial planning system. Yet who's responsible? The chief information officer or the chief financial officer? Reiff and Nelson provide a framework for CIOs to understand their CFO's needs.

Evaluating strategic change using the microcomputer

To respond to the many strategic changes in health care, CFOs need to analyze and integrate volumes of information that organizations generate. The microcomputer-based strategic financial planning system brings together all the information that is generated from other decision-support systems with the organization and provides the CFO with concise, timely, and accurate analyses of the changes that are affecting their institutions. This system has been proven to be an efficient and effective means to consolidate and analyze strategic data.