A Phase 1a/b Dose Escalation Study of the Mutation Agnostic BTK/FLT3 Inhibitor Luxeptinib (CG-806) in Patients with Relapsed or Refractory B-Cell Malignancies

INTRODUCTION: Luxeptinib (CG-806) is a potent, non-covalent oral inhibitor of BTK and FLT3. It suppresses BCR signaling pathways (LYN, SYK, BTK, AKT, ERK) and other oncogenic pathways in cell lines and primary CLL cells, kills malignant B-cells insensitive to ibrutinib or venetoclax at low nM concentrations, and shows enhanced activity in combination with venetoclax. Luxeptinib is currently being evaluated in a Phase 1a/b trial in patients with relapsed or refractory B-cell malignancies (NCT03893682).

AIMS: Primary objectives are to assess the safety and tolerability of luxeptinib and determine the recommended expansion dose for future clinical trials in patients with R/R CLL/SLL or B-NHL. Key secondary objectives include elucidation of the pharmacokinetic (PK) and pharmacodynamic (PD) characteristics, and evidence of antitumor activity.

METHODS: Luxeptinib is administered continuously as oral capsules BID in 28-day cycles, in ascending cohorts of 3 patients. Treatment emergent adverse events (TEAEs) and tumor responses are evaluated per disease specific guidelines.

RESULTS: As of June 7, 2021, a total of 23 patients (median age 64.0 years, 11 CLL/SLL, 4 follicular lymphoma (FL), 1 Richter's transformation lymphoma, 2 Waldenstrom's macroglobulinemia (WM), 2 mantle cell lymphoma, 3 diffuse large B cell lymphoma (DLBCL)) with a median of 3 prior systemic regimens (range of 1 - 12) have been treated with luxeptinib at doses of 150 mg (n=1), 300 mg (n=1), 450 mg (n=9), 600 mg (n=4) and 750 mg (n=8). Drug related grade ≥ 3 TEAEs included neutropenia (n=5, 21.7%), leukocytosis (n=2, 8.7%), decreased white blood cell count, decreased platelet count, anemia, increased alanine aminotransferase, diarrhea, hypertension, and headache (n=1, 4.3 % each). One patient, who experienced progressive hypertension before receiving luxeptinib, developed grade 1 hypertension during screening evolving to grade 2 prior to dosing on C1D1, experienced grade 4 hypertension after luxeptinib treatment at 750 mg BID for 5 days. While this was considered a DLT per protocol, luxeptinib plasma levels in this patient were lower than those observed in patients at this and lower dose levels, and no drug-related hypertension has been observed in any other patient treated to date. The average steady-state (C _min) plasma levels of luxeptinib in patients treated with 750 mg BID were > 1µM and were sustained over multiple cycles. PD analysis demonstrated that C _min of luxeptinib in the plasma of patients treated with doses of 300 mg or higher significantly reduced levels of phosphorylated BTK, SYK, ERK and FLT3 in EOL-1 reporter cells in a plasma inhibitor activity assay, demonstrating multi-target engagement. Response evaluations were available for 12 patients who had at least one imaging study or IgM measurements (WM patients) after starting treatment. Eight out of these 12 patients had various reductions of lesion size or IgM measurements compared to baseline (3 SLL, 2 FL, 1 CLL, 1 WM and 1 DLBCL), demonstrating anti-tumor activity. FDG PET-CT scans in one FL patient, who had 2 prior regimens, revealed lesion growth during treatment with luxeptinib at 450 mg BID for 7 cycles. After dose-escalation to 600 mg BID in Cycle 8, lesion measurements demonstrated continuous reduction. By C15D1, target lesions decreased by 42.5% and 11.3% when compared with peak tumor size and baseline measurements, respectively. One WM patient in Cohort 5 (750 mg BID), who had 2 prior regimens including ibrutinib, has had a 24.9% reduction in IgM level by C3D1 compared with baseline as her best response so far.

CONCLUSIONS: Luxeptinib has a favorable safety profile in patients treated with 150 mg to 600 mg BID over multiple cycles. A single apparent DLT (grade 4 hypertension in one patient with pre-existing hypertension) led to expansion of the 750 mg dose level to 6 patients. Pharmacodynamic studies documented inhibition of SYK, BTK and ERK in the BCR signaling pathway. Anti-tumor activity was observed in multiple B-NHL subtypes and CLL/SLL patients. Enrollment of patients with R/R CLL/SLL and B-NHL at dose level 5 (750 mg) is ongoing and updated clinical data will be presented at the meeting.