Renal impairment is associated with poor prognosis in multiple myeloma (MM). This subgroup analysis of the phase 3 Assessment of Proteasome Inhibition for Extending Remissions (APEX) study of bortezomib vs high-dose dexamethasone assessed efficacy and safety in patients with relapsed MM with varying degrees of renal impairment (creatinine clearance (CrCl) o30, 30-50, 51-80 and 480 ml min À1). Time to progression (TTP), overall survival (OS) and safety were compared between subgroups with CrCl p50 ml min À1 (severe-to-moderate) and 450 ml min À1 (no/mild impairment). Response rates with bortezomib were similar (36-47%) and time to response rapid (0.7-1.6 months) across subgroups. Although the trend was toward shorter TTP/OS in bortezomib patients with severeto-moderate vs no/mild impairment, differences were not significant. OS was significantly shorter in dexamethasone patients with CrCl p50 vs 450 ml min À1 (P ¼ 0.003), indicating that bortezomib is more effective than dexamethasone in overcoming the detrimental effect of renal impairment. Safety profile of bortezomib was comparable between subgroups. With dexamethasone, grade 3/4 adverse events (AEs), serious AEs and discontinuations for AEs were significantly elevated in patients with CrCl p50 vs 450 ml min À1. These results indicate that bortezomib is active and well tolerated in patients with relapsed MM with varying degrees of renal insufficiency. Efficacy/safety were not substantially affected by severe-tomoderate vs no/mild impairment.

Bortezomib is a proteasome inhibitor for the treatment of relapsed/refractory multiple myeloma (MM). Mechanisms of resistance to Bortezomib are undefined. Myeloid cell leukemia-1 (Mcl-1) is an antiapoptotic protein, which protects tumor cells against spontaneous and chemotherapy-induced apoptosis. In MM, specific downregulation of Mcl-1 induces apoptosis. Here, we examined the role of Mcl-1 in Bortezomib- and doxorubicin-induced apoptosis. We demonstrate that Bortezomib, but not doxorubicin, triggers caspase-dependent generation of a 28 kDa Mcl-1-fragment, in several MM cell lines, including MM.1S cells. Conversely, transient transfection of MM.1S cells with a previously reported 28 kDa Mcl-1(128-350) fragment, but not with the Mcl-1(1-127) fragment, induces apoptosis. Therefore, both downregulation of full-length antiapoptotic Mcl-1, as well as Bortezomib-induced generation of Mcl-1(128-350) cleaved protein, contribute to MM cell apoptosis. To verify further these findings, we next compared effects triggered by Bortezomib, doxorubicin and melphalan in Mcl-1(wt/wt) and Mcl-1(Delta/null) murine embryonic fibroblasts (MEFs). Our results show that Bortezomib, but not doxorubicin or melphalan, triggers Mcl-1 cleavage in Mcl-1(wt/wt), but not Mcl-1(Delta/null) MEFs and induces sub-G(1) phase cells; caspase-3 and -9, and PARP cleavage as well as morphological signs of apoptosis. Taken together, these results support an important role of Mcl-1 and a Mcl-1 fragment in Bortezomib-induced cell death in general, and in MM in particular. To prevent relapse of MM in patients treated with Bortezomib, we therefore recommend the combination of Bortezomib with agents that induce MM cell death independent of Mcl-1.

No abstract

No abstract