Salvage therapeutic options are limited for multiple myeloma (MM) patients who relapse after autologous hematopoietic stem cell transplantation (ASCT). A second ASCT using a different conditioning regimen may provide long-term disease control. We report efficacy and safety of daily intravenous busulfan (IV Bu) conditioning given with bortezomib for second ASCT.
In this prospective, multicenter, Phase IIa study, thirty MM patients who relapsed ≥ 1 year after initial ASCT and were candidates for second ASCT were enrolled at eleven centers in the US and Canada. Patients received a test dose of IV Bu (0.8 mg/kg) over 2 hours between Days -12 and -9 prior to ASCT. Pharmacokinetic (PK) analysis from test dose determined Bu exposure as area under the concentration-time curve (AUC). This analysis was used to determine individualized Bu PK-directed dosing for the conditioning regimen in order to achieve a total regimen AUC of 20,000 mM*min. IV Bu was administered over 3 hours once daily from Day -5 to Day -2. Confirmatory PK analysis was conducted in all patients on Day -5. Bu doses were adjusted on Days -3 and -2, if needed. Bortezomib (1.3 mg/m2 QD) was administered as an IV bolus injection on Day -1. Disease response was evaluated prior to the ASCT and at 3 and 6 months post-transplant, based on the International Myeloma Working Group uniform response criteria in 2006.
Median age at second ASCT was 59 years (range: 48–73). All patients had previously been treated with bortezomib (86.7%), thalidomide (46.7%), and/or lenalidomide (66.7%). All subjects underwent first ASCT with high-dose melphalan. Median time from first ASCT to second ASCT was 28.0 months (range: 12–119). The disease status at second ASCT was seven very good partial response (VGPR; 23.3%), twelve partial response (PR; 40.0%), two stable disease (SD; 6.7%); and nine progressive disease (PD; 30.0%).
The most common grade 3 or 4 adverse event (CTCAE v3.0) was febrile neutropenia in 15 patients (50.0%), followed by stomatitis in 13 patients (43.3%), nausea in four (13.3%) and hypokalemia in three (10.0%). One transplant-related death due to pulmonary complications was reported for a patient with Parkinsonism on post-transplant Day 20. There was no instance of seizure, worsening neuropathy, or hepatic veno-occlusive disease (VOD) meeting the Baltimore criteria.
28 patients had evaluable disease response at least at one time point after second ASCT. Disease response at 3 months were two complete responses (CR; 6.7%), five VGPR (16.7%), four PR (13.3%), eight SD (26.7%), nine PD (30.0%), and two cases without evaluable assessment (6.7%). Two patients who achieved CR at 3 months had PD and VGPR prior to ASCT, respectively. Disease response at 6 months were one stringent CR (sCR; 3.3%), one CR (3.3%), four VGPR (13.3%), seven SD (23.3%), fourteen PD (46.7%), and three cases without evaluable assessment (10.0%). Median progression-free survival was 191 days, while median overall survival has not been reached yet.
40.0% (n=12/30) of patients had AUC outside the expected range from pre-transplant test dose, 0.8 mg/kg of IV Bu: eleven cases with AUC <1,000 μM*min and one case with AUC >1,500 μM*min. If only weight was used (e.g. 3.2 mg/kg daily) to determine the dose without considering difference in individual busulfan metabolism, this 40% would have been dosed outside the total target AUC range. Based on test PK, IV Bu dosing for conditioning was individualized ranging between 1.99 and 4.73 mg/kg, which resulted in 93.3% of patients (n=28/30) falling between 16,000 and 24,000 μM*min as a total target AUC without any further dose alteration during conditioning. Only 2 patients (6.7%) needed dose reduction on Days -3 and -2. Mean Bu clearance for test dose and on Day -5 were comparable, 3.00 and 2.92 ml/min/kg, respectively.
A new combination of IV Bu and bortezomib had acceptable safety profile after second ASCT, and induced approximately 20% VGPR or better responses at 6 months in heavily treated myeloma patients.
Pre-transplant PK guided individually optimized dosing in more than 90% of patients. PK-directed dose adjustment of IV Bu might substantially reduce the hepatic VOD risk.
Stadtmauer:Millenium: Consultancy, Speakers Bureau; Celgene: Consultancy, Speakers Bureau. Off Label Use: IV busulfan and bortezomib-based conditioning regimen prior to transplant for myeloma. Freytes:Otsuka Pharmaceuticals: Research Funding. Shaughnessy:Otsuka: Honoraria, Speakers Bureau. White:Otsuka: Honoraria, 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 Pharmaceutical Development & Commercialization, Inc: Consultancy. Elekes:Otsuka Pharmaceutical Development & Commercialisation., Inc.: Employment. Kato:Otsuka Pharmaceutical Development & Commercialization, Inc.: Employment. Reece:Otsuka: Honoraria, Research Funding; Janssen: Consultancy, Honoraria, Research Funding; Celgene: Consultancy, Honoraria, Research Funding; Bristol Myers Squibb: Honoraria, Research Funding; Novartis: Honoraria, Research Funding; Millinneum Pharmaceuticals: Research Funding; Merck: Consultancy, Honoraria, Research Funding.
Asterisk with author names denotes non-ASH members.