Bortezomib in Combination with Melphalan in the Treatment of Relapsed or Refractory Multiple Myeloma: A Phase I/II Study.

Introduction: Bortezomib (VELCADE^®) is a proteasome inhibitor that has demonstrated durable responses as monotherapy for the treatment of pts with relapsed and refractory multiple myeloma. In vitro, bortezomib has been shown to restore melphalan sensitivity to melphalan-resistant cell lines (U266-LR7) and to synergize with melphalan in killing myeloma cells, thereby allowing the use of lower concentrations of melphalan (

Methods : Bortezomib 0.7 mg/m² was administered by IV push on days 1, 4, 8, and 11 in combination with oral melphalan (0.025, 0.05, 0.1, 0.15, 0.25 mg/kg) on days 1–4 every 4 weeks for up to 8 cycles to 3-pt cohorts with active progressive disease. In the absence of dose-limiting toxicity (DLT), bortezomib was increased to 1.0 mg/m² and melphalan co-administered using the original 5 escalating doses to subsequent cohorts.

Results : Twenty six pts (50% male, median age 55 years, range 33–90 years) have been accrued to the study. The myeloma subtypes include IgG (16/26), IgA (4/26), IgM (2/26) and light chain only (4/26). The median ß₂ microglobulin level was 5.0 mg/L (range 2.2–14 mg/L). In this heavily pretreated population (range 2–7 prior therapies), 12 patients received prior melphalan, 12 prior thalidomide, 7 prior CC-5013, 13 prior VAD, 2 prior bortezomib, and 8 prior autologous stem cell transplantation. Dose escalation has proceeded into the bortezomib 1.0 mg/m² + melphalan 0.10 mg/kg cohort. Toxicities have been manageable. One DLT, grade 4 anemia, was observed at bortezomib 1.0 mg/m² + melphalan 0.025 mg/kg, requiring expansion of that specific cohort. Grade 3 events were predominantly associated with myelosuppression (anemia, neutropenia, and thrombocytopenia) and were observed only among pts with baseline cytopenia. Among the 12 pts with baseline peripheral neuropathy (PN), symptoms worsened transiently in 1 pt, resolved in 1 pt, and remained stable in the other pts. Treatment-related PN (grade 1) developed de novo in 2 pts. Responses were observed in 67% (16/24 evaluable) of pts: 1 CR, 1 near CR, 6 PR, and 8 MR. The CR and near CR occurred in pts receiving bortezomib 1.0 mg/m² in combination with melphalan .025 mg/kg. PR or better was independent of prior type of therapy and was also observed among pts who had previously received melphalan or bortezomib. Median time to progression was 1-18 mo. Six active pts out of 26 total pts remain progression-free for 2-8+ mo.

Conclusion : Combination bortezomib plus oral melphalan is a promising regimen for the treatment of relapsed, refractory myeloma. The responses that were observed in pts who had previously received either drug serve as preliminary confirmation of preclinical evidence that the combination of low-dose bortezomib and melphalan has the capacity for chemosensitization and suggest possible synergy. Dose escalation with melphalan plus a fixed dose of bortezomib 1.0 mg/m² is continuing in order to explore the full potential of this combination.