A 3-Part, Phase 2 Study of Bezuclastinib (CGT9486), an Oral, Selective, and Potent KIT D816V Inhibitor, in Adult Patients with Nonadvanced Systemic Mastocytosis (NonAdvSM)

▪ Systemic mastocytosis (SM) is characterized by mast cell infiltration of ≥ 1 extracutaneous organs and encompasses a spectrum of diagnoses that can range from a non-advanced to advanced disease (Shomali et al, 2018). There are two nonadvanced variants of SM: indolent systemic mastocytosis (ISM), which accounts for approximately 85% and smoldering systemic mastocytosis (SSM), which includes about 5% of the general SM population (Cohen et al, 2014, Jennings et al, 2014). ISM is characterized by 0 or 1 B-findings and SSM by 2 or more B findings and absence of organ damage or an associated hematologic neoplasm (Gotlib et al, 2018). There are currently no approved therapies to treat the underlying disease of ISM or SSM. Although anti-mediator therapies (e.g. anti-H1 and H2 antihistamines, leukotriene receptor antagonists, cromolyn sodium, corticosteroids) are used to control symptoms such as anaphylaxis, GI intolerance, and flushing to improve quality of life, their effectiveness and tolerability are variable. Many patients experience a persistently high symptom burden despite maximized anti-mediator therapies. Because the molecular pathogenesis of SM is driven by KIT D816V mutations in 95% of patients (Garcia-Montero et al, 2006, Jara-Acevedo et al, 2015, Vaes et al, 2017), other agents targeting this mutated kinase have been used to treat the spectrum of SM variants; however, toxicities such as cognitive impairment, GI effects, intracranial hemorrhage, and edema may limit dosing and thus efficacy. In addition to targeting KIT D816V, bezuclastinib was designed to avoid other closely related kinases with known liabilities, such as PDGFRα, PDGFRβ, wild-type KIT, VEGFR2 (KDR), and CSF1R (FMS). Furthermore, bezuclastinib has demonstrated minimal brain penetration and no CNS toxicities have been identified in preclinical studies. Preliminary clinical activity with bezuclastinib has been observed in patients with advanced solid tumors or locally advanced, unresectable, or metastatic gastrointestinal stromal tumor (GIST). A reduction in KIT exon 17 mutational burden was observed in patients treated with bezuclastinib. This reduction was temporally associated with a reduction in tumor burden supporting bezuclastinib as an active therapy in KIT-driven diseases (Wagner et al, 2018). This is a multi-center, Phase 2, double blind, placebo-controlled, 3-part clinical study to evaluate the safety, efficacy, and biomarker correlates (e.g. bone marrow mast cell percentage,