Phase I Study of a Novel Oral Janus Kinase 2 Inhibitor, SB1518, in Patients With Relapsed Lymphoma: Evidence of Clinical and Biologic Activity in Multiple Lymphoma Subtypes

Abstract

The Janus kinase 2/signal transducers and activators of transcription (JAK2/STAT) pathway plays an important role in the pathogenesis of hematologic malignancies. We conducted a phase I dose-finding and pharmacokinetic/pharmacodynamic study of SB1518, a potent JAK2 inhibitor, in patients with relapsed lymphoma. Patients with relapsed or refractory Hodgkin or non-Hodgkin lymphoma of any type except Burkitt's or CNS lymphoma were enrolled. Patient cohorts received escalating doses of SB1518 orally once daily for 28-day cycles. Response was evaluated after 8 weeks. Thirty-four patients received doses of 100 to 600 mg/d. The maximum tolerated dose was not reached. Treatment was well tolerated, with mostly grade 1 and 2 toxicities. Gastrointestinal toxicities were the most common treatment-related events. Cytopenias were infrequent and modest. Pharmacologically active concentrations were achieved at all doses. Dose-related linear increases in area under the concentration-time curve were seen on day 1, with no significant accumulation on day 15. Mean terminal half-life was 1 to 4 days, and mean time to peak concentration ranged from 5 to 9 hours. SB1518 inhibited JAK2 signaling at 4 hours postdose at all levels. Increases in fms-like tyrosine kinase-3 (FLT-3) ligand, reflecting FLT-3 inhibition, were seen in most patients. There were three partial responses (≥300 mg/d) and 15 patients with stable disease (SD), with most responses lasting longer than 2 months. Seven of 13 SDs had tumor reductions of 4% to 46%. SB1518 has encouraging activity in relapsed lymphoma, providing the first proof-of-principle of the potential therapeutic value of targeting the JAK/STAT pathway in lymphoma in the clinical setting.