Phase 1 multicenter study of vincristine sulfate liposomes injection and dexamethasone in adults with relapsed or refractory acute lymphoblastic leukemia

BACKGROUND: Dose intensification of chemotherapy has improved outcome for younger adults with de novo acute lymphoblastic leukemia (ALL). Novel formulations of standard chemotherapy agents may further reduce the incidence of disease recurrence after frontline chemotherapy. Vincristine (VCR) sulfate liposomes injection (VSLI) is a sphingomyelin/cholesterol nanoparticle encapsulated VCR formulation that improves the pharmacokinetic profile of VCR without augmenting neurotoxicity. METHODS: A phase 1 trial of weekly, intravenous VSLI at 1.5 mg/m², 1.825 mg/m², 2.0 mg/m ², 2.25 mg/m², or 2.4 mg/m² was conducted to determine the maximum tolerated dose (MTD) using a standard, 3+3 dose-escalation design. Dexamethasone (40 mg) was given on Days 1 through 4 and on Days 11 through 14 of each 4-week cycle. RESULTS: Thirty-six adults with relapsed/refractory ALL, all previously treated with conventional VCR, received at least 1 dose of VSLI. The MTD of VSLI was 2.25 mg/m² based on dose-limiting toxicities of grade 3 motor neuropathy, grade 4 seizure, and grade 4 hepatotoxicity in 1 patient each at the 2.4 mg/m² dose level. The most common toxicities attributed to VSLI included peripheral neuropathy (55%) and constipation (53%). A complete response (CR) was achieved in 7 of 36 patients (19%) based on an intent-totreat analysis; the CR rate was 29% for the 14 patients who underwent therapy as their first salvage attempt. Four of 7 patients who achieved a CR underwent subsequent allogeneic stem cell transplantation in remission. CONCLUSIONS: In this study, VSLI plus dexamethasone appeared to be an effective salvage therapy option for relapsed/refractory ALL. A phase 2, international, multicenter clinical trial assessing the efficacy of single-agent VSLI as second salvage therapy for patients with previously treated ALL is underway.