Safety of PK-Guided IV Bu Cy VP-16 Preparative Regimen Prior to Autologous Hematopoietic Stem Cell Transplantation for Lymphoma: Findings From a Multi-Center Phase II Study in North America

Published reports indicate that oral or intravenous (IV) busulfan in combination with cyclophosphamide and VP-16 (BuCyVP-16) is an effective conditioning regimen with acceptable safety profile for lymphoma patients prior to autologous hematopoietic stem cell transplantation (ASCT). Since the therapeutic window of Bu is narrow, it is important to standardize the systemic exposure during conditioning. Although the IV formulation of Bu eliminates the problem of variable drug absorption, unpredictable systemic exposure can still occur due to interpatient differences in Bu clearance. Therefore, tighter control of systemic Bu exposure using pharmacokinetics (PK) may lead to improved efficacy and further decrease in toxicity. The aim of this multi-center, single-arm, Phase II study was to prospectively evaluate the safety and efficacy of IV BuCyVP-16 regimen in lymphoma patients undergoing ASCT, after optimizing Bu exposure using PK-directed dosing.

Patients with chemosensitive, relapsed or primary-refractory Hodgkin and B-cell non-Hodgkin lymphoma undergoing the first ASCT received a test dose of IV Bu (0.8 mg/kg) given as a 2-hour infusion 11 to 14 days before transplant. Bu exposure was determined as area under the concentration-time curve (AUC) using six serial blood samples after the test dose administration. Doses for the conditioning regimen were then calculated to result in total AUC (conditioning + test) of 20,000 mM*min. One-fourth of the resulting calculated Bu dose was given as a 3-hour infusion on Day -8, followed by a second, confirmatory PK analysis. The same daily Bu dose was administered on the next 3 days, unless the confirmatory PK analysis showed that this would result in total AUC outside the target range (>24,000 mM*min or <16,000 mM*min), in which case the subsequent dosing was further adjusted. VP-16 (1.4 g/m²) was administered on Day -4, followed by 2.5 g/m²/day of Cy on Days -3 and -2. Transplant-related mortality (TRM), defined by death from any cause other than disease progression, was monitored throughout the trial. After median 2 years of follow-up, the outcomes will be compared with a BEAM regimen control group from the CIBMTR registry, using pre-specified matching criteria.

A total of 202 subjects with Hodgkin (n=65) and non-Hodgkin lymphoma (n=137) were enrolled from 32 centers in the US and Canada.

196 subjects had both test PK and confirmatory PK results. Test PK demonstrated that 36.2% (n=71) of the patients had exposure outside of expected range (1,250 μM*min ± 20%): higher AUC (>1,500 μM*min) in five patients (2.6 %) and lower AUC (<1,000 μM*min) in 66 (33.7%). These would have been dosed outside the total target AUC range if dose was not individualized based on test PK. Mean Bu clearances were comparable between test and Day -8 PK, 3.04 ± 0.48 ml/min/kg and 3.03 ± 0.49 ml/min/kg, respectively. Accordingly, 94.9 % of patients (n=186) fell within the target range (AUC, 20,000 μM*min ± 20%), using consistent doses on Days -8 through -5. The other ten patients (5.1%) required dose alteration for the last two days of conditioning due to clearance changes between test PK and confirmatory PK (Day -8): a dose reduction in eight patients (4.1%) and a dose increase in two (1.0%).

An early subset-analysis by age in June 2011 revealed that 4 of 18 subjects older than 65 years suffered TRM. Consequently, the protocol was amended to lower the inclusion age limit to 65. The final TRM at day 100 was 4/18 (22.2% [95%CI; 6.4–47.6%]) for patients older than 65 years and 5/184 (2.7% [95%CI; 0.9–6.2%]) for those 65 years old or younger. PK results indicated no extraordinary Bu exposure in TRM cases. The most frequently observed grade ≥ 3 adverse events (CTCAE ver. 3.0) were febrile neutropenia 55.1 % (Grade 3: 52.2%; Grade 4: 2.9%; no Grade 5), stomatitis 37.7% (all Grade 3 events) and nausea 9.7% (all Grade 3 events). No case of hepatic veno-occlusive disease (HVOD) meeting Baltimore criteria was reported.

A pre-conditioning test dose estimated individual PK parameters and accurately predicted Day-8 PK in 95% of the subjects. This strategy personalized the dosing for optimal Bu exposure preventing the Bu overexposure or underexposure that would have occurred in over a third of patients. The toxicity of PK-guided IV BuCyVP-16 preparative regimen was low for patients younger than 66 years of age. This approach resulted in no incidence of HVOD.

Costa:Otsuka: Research Funding. Off Label Use: Off label use of busulfan in non hodgkin and hodgkin lymphoma. Waller:Outsuka: Research Funding. Freytes:Otsuka Pharmaceuticals: Research Funding. Shea:Otsuka : Research Funding. Rodriguez:Otsuka: Consultancy, Research Funding, Speakers Bureau; Millennium: Research Funding, Speakers Bureau; Celgene: Consultancy, Speakers Bureau; SOBI: Consultancy, Speakers Bureau. Sun:Otsuka Pharmaceutical Development & Commercialization, Inc.: Employment. Armstrong:Otsuka: Employment. Smith:Otsuka America Pharmaceuticals Inc: Consultancy. Elekes:Otsuka Pharmaceutical Development & Commercialization, Inc.: Employment. Kato:Otsuka Pharmaceutical Development & Commercialization, Inc.: Employment. Vaughan:Pierre Fabre: Honoraria.