Phase 1 Study of Weekly Vincristine Sulfate (VCR) Liposomes Injection (VSLI, Marqibo^™) Plus Dexamethasone in Adults with Relapsed or Refractory Acute Lymphoblastic Leukemia (ALL)

Novel formulations of standard chemotherapy allowing increased drug delivery without additional toxicity may improve outcomes for patients with relapsed or refractory acute lymphoblastic leukemia (ALL). Vincristine sulfate liposomes injection (VSLI, Marqibo^®) is VCR encapsulated in sphingomyelin (55%)/cholesterol (45%) nanoparticle liposomes called Optisomes^™. Pharmacokinetic studies have shown that the altered distribution and elimination phases of VSLI may lead to increased VCR exposure compared to traditional VCR, and may account for the increased efficacy observed in preclinical models. Activity of VCR is dose and time-dependent, but neurotoxicity limits dosing to 1.4 mg/m² (capped at 2.0 mg). VSLI, however, may be given without dose capping. We conducted a phase 1, open-label, dose-escalation study of VSLI in adults with relapsed or refractory ALL to determine the safety, maximum tolerated dose (MTD), and activity of this formulation. Subjects received VSLI intravenously weekly at doses of 1.5, 1.825, 2.0, 2.25 or 2.4 mg/m². Dexamethasone 40 mg was given days 1–4 and 11–14 of each 4 week cycle. Thirtysix eligible subjects, all of whom had been previously treated with VCR, received at least 1 dose of VSLI. All were Philadelphia chromosome negative except for one. Median number of doses received for all subjects was 4; total medium cumulative dose was 9.09 mg/m² (19.20 mg). 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 observed in 1 subject each at the 2.4 mg/m² dose level. The most common toxicities (constipation [67%], fatigue [61%], pyrexia [50%], anemia [50%], peripheral neuropathy [50%; mostly grade 1–2]) were as expected. Complete response (CR) was achieved in 7 of 36 (19%) subjects based on intent to treat analysis (Table). Overall response rate (including 1 PR) was 22%. Four subjects (11%) achieved hematologic improvement, 13 (36%) had stable disease, and 9 (25%) progressed. CR rate was 29% for the 7 subjects treated with VSLI as second salvage. Five of 7 subjects who achieved CR were able to undergo allogeneic stem cell transplant (SCT). In conclusion, VSLI appears to be an effective therapeutic option which may permit potentially curative SCT. A phase 2 international multi-center trial of single agent VSLI in subjects with relapsed ALL is currently accruing.

Table. VSLI Clinical Activity (CR) by Dose Level and Salvage Status