Preliminary Results from a Phase I Study of HMPL-523, a Selective Oral Syk Inhibitor, in Patients with Relapsed or Refractory Lymphoma

Background: Spleen tyrosine kinase (Syk) plays an integral role in B-cell receptor signaling critical in the development and survival of several subtypes of lymphoma. HMPL-523 is a selective, oral Syk inhibitor that has shown strong anti-tumor efficacy in xenograft models of B-cell and T-cell lymphoma. HMPL-523 had a manageable safety profile and demonstrated anti-tumor activity in a phase I study of lymphoma patients in China (NCT02857998). Here, we report the safety and preliminary anti-tumor activity of HMPL-523 in the dose escalation phase of a phase 1 study of relapsed/refractory lymphoma patients in the United States and Europe (NCT03779113).

Methods: The primary objectives of the phase I study were to evaluate the safety and tolerability of HMPL-523 and to determine the maximum tolerated dose (MTD)/recommended phase 2 dose (RP2D). Secondary objectives were to assess the pharmacokinetics (PK) and evaluate the preliminary efficacy of HMPL-523. Eligible patients had histologically confirmed lymphoma, exhausted all approved therapy options, and had good organ function, including creatinine clearance ≥ 40 ml/min by Cockcroft-Gault, absolute neutrophil count ≥ 1000/µL, platelet count ≥ 50,000/µL, and hemoglobin ≥ 8.0 g/dL. Dose escalation was performed according to a 3+3 study design. Treatment emergent adverse events (AEs) were assessed per NCI CTCAE v5.0. Treatment responses were assessed by Lugano criteria at weeks 8, 16, and 24, and then every 12 weeks. Patients received HMPL-523 treatment daily in 28-day cycles until disease progression or unacceptable toxicity.

Results: As of July 15, 2021, 21 patients had been enrolled and dosed with HMPL-523 at one of six dose levels (100 to 800 mg once daily). Baseline tumor subtypes included Hodgkin lymphoma (HL; n=5); diffuse large B-cell lymphoma (DLBCL; n=4); follicular lymphoma (FL; n=4); marginal zone lymphoma (MZL; n=2); and 1 patient each with mantle cell lymphoma (MCL), small lymphocytic lymphoma (SLL), peripheral T-cell lymphoma (PTCL), cutaneous T-cell lymphoma (CTCL), mixed HL/DLBCL, and Richter's transformation. Patients were predominantly Caucasian (90.5%) and male (71.4%). The median age was 61 years (range 27 to 89 years) and 71.4% had an ECOG performance status of 1. The median lines of prior therapy was 4 (range 2 to 17). The majority of patients had prior anti-CD20 antibody exposure (71.4%), and four patients (19%) received prior Bruton tyrosine kinase inhibitors.

Five patients continue to receive study treatment. The most frequently reported treatment emergent AEs were aspartate aminotransferase increase (23.8%), anemia (23.8%), neutropenia (19%), hyponatremia (19%), creatinine increase (19%), and nausea (19%). The most common grade ≥ 3 AEs were neutropenia (14.3%), hyponatremia (14.3%), and anemia (9.5%). Three dose limiting toxicities were observed: 1 in the 100 mg cohort (grade 3 confusion) and 2 in the 800 mg cohort (grade 3 fever and grade 3 alanine aminotransferase increase). The dose was deescalated to 700 mg, which was determined to be the MTD and RP2D.

Among 17 efficacy evaluable patients, 2 patients (1 HL, 1 FL) dosed at 600 mg and 800 mg (reduced to 600 mg due to toxicity) achieved complete response, and 1 patient (dose increased from 400 to 600 mg) achieved partial response (FL). Stable disease was observed in 5 (29.4%) patients (2 DLBCL, 1 MCL, 1 SLL, 1 PTCL). At steady state, HMPL-523 showed approximately dose proportional PK over the daily dose range of 100 to 700 mg.

Conclusions: HMPL-523 was well tolerated at all dose levels within the range of 100 mg to 700 mg and demonstrated proof of activity at dose levels of 400 mg or higher in heavily pre-treated patients. The dose expansion phase of the study will evaluate safety and efficacy in patients with multiple subtypes of B-cell and T-cell lymphoma at the RP2D of 700 mg. Updated safety, PK, and anti-tumor activity will be presented.