December 13, 2024
Author(s): Kristi Rosa
The investigative BET inhibitor JAB-8263 was found to be well tolerated and to demonstrate preliminary efficacy in patients with myelofibrosis, according to data from a phase 1/2 study (NCT04686682) presented during the 2024 ASH Annual Meeting.1
Any treatment-emergent adverse effects (TEAEs) occurred in 93.8% of those who received the agent at any dose level (n = 16), with 37.5% experiencing grade 3 or higher TEAEs and 25.0% experiencing a serious TEAEs. Treatment-related AEs (TRAEs) occurred in 87.5% of patients, with 31.3% experiencing grade 3 or higher TRAEs, and 18.8% experiencing serious TRAEs. TRAEs led to dose interruption and reduction for 43.8% and 25.0% of patients, respectively. One patient experienced a TRAE that led to discontinuation of JAB-8263. No treatment-related events proved to be fatal.
Notably, 1 dose-limiting toxicity occurred in a patient who received the agent at a dose of 0.4 mg; this patient experienced grade 3 increases in alanine and aspartate aminotransferase levels.
In all evaluable patients (n = 13), the mean spleen volume reduction (SVR) was –19.95% (range, –39.4% to 3.6%) at week 24 and –26.16% (range, 56.6% to –11.0%) at best response. Notably, 2 patients achieved an SVR of 35% or higher, and 1 patient experienced an SVR of –34.9%. Moreover, at week 24, 60% of 10 patients had a tumor symptom score reduction of at least 50% (TSS50). Two of 8 patients who had received JAK inhibitors experienced a best response of SVR of –41.2% and 34.9%, respectively. Moreover, 50% of 6 evaluable patients who had received JAK inhibitors achieved TSS50 at week 24.
“JAB-8263 at 0.125 mg [once daily to] 0.3 mg [once daily] was well tolerated…Hematological and gastrointestinal AEs are mild with JAB-8263 continuous dosing [compared with] other BET inhibitors,” Junyuan Qi, MD, of the Institute of Hematology and Blood Disease Hospital, Chinese Academy of Medical Sciences, in Tianjin, China, and coauthors, wrote in the poster of the data. “The preliminary efficacy data in myelofibrosis for JAB-8263 monotherapy is promising. Most patients showed spleen reduction and TSS reduction.”
The early-phase study enrolled patients with confirmed primary myelofibrosis (PMF), post–polycythemia vera myelofibrosis (PV-MF), or post–essential thrombocytopenia myelofibrosis (ET-MF). Patients were at least 18 years of age, had spleen volume of at least 450 cm3, a Dynamic International Prognostic Score (DIPSS) of at least intermediate-1, and an ECOG performance status up to 2.
The median age in the 16 total patients was 62 years (range, 36-69) and 56.3% were female. All patients were Asian. Regarding ECOG performance status, 31.3% had a status of 0, 62.5% had a status of 1, and 6.3% had a status of 2. Regarding disease subtype, 68.8% of patients had PMF, 18.8% had PV-MF, and 12.5% had ET-MF. Half of patients had prior exposure to a JAK inhibitor. Most patients had a JAK2 mutation (93.8%). Regarding DIPSS, 68.8% had intermediate-1 disease and 25.0% had intermediate-2 disease. The median time since initial diagnosis was 13.5 months (range, 0.9-76.6).