High Dose Intravenous Busulfan (BU) and Melphalan (MEL) Followed by Bortezomib (BTZ) as Conditioning with Autologous Peripheral Blood Stem Cell Transplantation (ASCT) for Patients with Multiple Myeloma (MM)

Overall survival for patients with MM has improved significantly over the past 10 years primarily as a result of novel therapeutics. High dose therapy with ASCT continues to be an effective modality but the progression-free survival following ASCT has improved minimally over the same period of time due to a continued reliance on single agent melphalan. Many chemotherapy/chemoradiotherapy regimens have been used in preparation for stem cell transplantation. However, no regimen has proven superior to high dose melphalan 200 mg/ m2 (MEL 200) which is considered the standard conditioning for patients with MM with relatively predictable results. In order to improve progression free survival (PFS) and overall survival (OS), continued efforts in developing effective preparative regimens are needed. Busulfan is an alkylating agent that affects cells in an AUC-dependent manner. Recent data suggests that the combination of BU and MEL delivers better PFS compared to MEL 200 alone (Grande and Lahuerta; PETHEMA, 36th EBMT meeting. Vienna 2010). Moreover, the addition of bortezomib following MEL 200 appears to increase the VGPR rate when compared to historical cohort receiving MEL 200 alone (Lonial, et al; Blood. ASH Annual Meeting Abstracts, Nov 2008; 112: 3332). Furthermore, the recently published IFM trial of MEL 200 plus BTZ also demonstrated superior response rates and PFS compared to historical controls (Roussel et al Blood. 2010;115:32-7).

The combination of intravenous BU and MEL followed by BTZ (BuMelVel) will be an effective preparative regimen with acceptable toxicity for patients with MM.

Patients received intravenous BU 130 mg/kg over 3 hours daily × 4 days from D-6 to D-3. Based on the pharmacokinetics of the first two doses, the subsequent 2 doses were adjusted to achieve an AUC of 20,000 mMol-min (5,000 mMol-min/day). MEL was administered at 140 mg/ m2 IV over 15–30 minutes on day -2. Bortezomib was administered IV push over 3–5 seconds on day -1. Bortezomib administration followed a phase I dose escalation design starting at 1.0 mg/m2 for the first cohort; then, 1.3 mg/m2 for the second cohort; then, 1.6 mg/m2/kg for the 3^rd cohort and subsequent subjects at the 3^rd dose level if no limiting toxicity was observed. Autologous stem cell infusion occurred on day 0.

20 patients have been enrolled to date, with 19 evaluable for toxicity and 13 for response assessment at D +100. The median age is 61 (47 - 69). The median time for engraftment for ANC ≥ 500 and plts ≥ 20, was 10 days. The median length of stay (LOS) was 18 days (16 – 21 days). 12 patients required a median of 2 units of PRBC and 16 patients required a median of 1 platelet transfusion. PRBC and PLT transfusions as well as LOS are not significantly different to what has been observed at our institution with MEL 200 (2 PRBC, 2 RD PLT transfusions, and 15 days LOS, respectively). All patients responded including: 77% ≥ VGPR and 54% nCR, CR, or sCR. The most common grade ≥ 3 toxicities were neutropenic fever (n = 11), mucositis (n = 9), and hypophosphatemia (n = 7). Three patients developed reversible transaminitis. One patient developed Clostridium difficile colitis and Klebsiella pneumonia UTI. Another patient developed E. coli UTI. No cases of VOD or interstitial pneumonitis were observed. There were no treatment related deaths and no re-admissions post discharge.

BuMelVel proved to be an effective preparative regimen with ≥ VGPR and nCR/CR/sCR of 77% and 54%, respectively, as compared to responses reported with MEL/BTZ (70% and 32%, respectively); and to MEL 200 alone (43% and 11%, respectively) by Roussel et al. Furthermore, BuMelVel had an acceptable toxicity profile without any cases of VOD or interstitial pneumonitis, and mucositis/infections incidence and severity are comparable to our institutional experience with MEL 200. Therefore, the regimen of BuMelVel may lead to improvements in PFS and OS, critical criteria to improve the outcomes of patients with MM. These promising results will be further evaluated in a planned Phase III clinical trial with MEL 200.

Rodriguez:Otsuka: Consultancy, Research Funding, Speakers Bureau; Millennium: Consultancy, Speakers Bureau; Celgene: Speakers Bureau. Kaufman:Celgene, Millenium: Consultancy; Celgene, Merck: Research Funding. Lonial:Millennium: Consultancy, Research Funding; Celgene: Consultancy, Research Funding; Novartis: Consultancy, Research Funding; BMS: Consultancy, Speakers Bureau. Vesole:Celgene: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Millenium: Speakers Bureau.