Discovery and Preclinical Pharmacology of NX-2127, an Orally Bioavailable Degrader of Bruton's Tyrosine Kinase with Immunomodulatory Activity for the Treatment of Patients with B Cell Malignancies.

Bruton's tyrosine kinase (BTK), a member of the TEC family of kinases, is an essential effector of B-cell receptor (BCR) signaling. Chronic activation of BTK-mediated BCR signaling is a hallmark of many hematological malignancies, which makes it an attractive therapeutic target. Pharmacological inhibition of BTK enzymatic function is now a well-proven strategy for the treatment of patients with these malignancies. We report the discovery and characterization of NX-2127, a BTK degrader with concomitant immunomodulatory activity. By design, NX-2127 mediates the degradation of transcription factors IKZF1 and IKZF3 through molecular glue interactions with the cereblon E3 ubiquitin ligase complex. NX-2127 degrades common BTK resistance mutants, including BTKC481S. NX-2127 is orally bioavailable, exhibits in vivo degradation across species, and demonstrates efficacy in preclinical oncology models. NX-2127 has advanced into first-in-human clinical trials and achieves deep and sustained degradation of BTK following daily oral dosing at 100 mg.

Kinase-impaired BTK mutations are susceptible to clinical-stage BTK and IKZF1/3 degrader NX-2127.

Increasing use of covalent and noncovalent inhibitors of Bruton's tyrosine kinase (BTK) has elucidated a series of acquired drug-resistant BTK mutations in patients with B cell malignancies. Here we identify inhibitor resistance mutations in BTK with distinct enzymatic activities, including some that impair BTK enzymatic activity while imparting novel protein-protein interactions that sustain B cell receptor (BCR) signaling. Furthermore, we describe a clinical-stage BTK and IKZF1/3 degrader, NX-2127, that can bind and proteasomally degrade each mutant BTK proteoform, resulting in potent blockade of BCR signaling. Treatment of chronic lymphocytic leukemia with NX-2127 achieves >80% degradation of BTK in patients and demonstrates proof-of-concept therapeutic benefit. These data reveal an oncogenic scaffold function of mutant BTK that confers resistance across clinically approved BTK inhibitors but is overcome by BTK degradation in patients.