Carfilzomib Exerts Anti-Neoplastic Activity in Waldenstrom Macroglobulinemia.

Proteasome inhibition represents a valid therapeutical approach in several tumors and its use has been validated in Waldenstrom's macroglobulinemia (WM), where single-agent Bortezomib has been successfully tested in phase 2 clinical trials. Nevertheless, a significant fraction of patients relapse, or develop significant toxicity due to high toxicity in non-transformed cells. Therefore preclinical evaluation of new proteasome inhibitor with a more selective inhibition of neoplastic cells is needed in order to increase efficacy and improve patient outcome. We tested Carfilzomib, a tetrapeptide epoxyketone selective inhibitor of the chymotrypsin-like activity of the immunoproteasome and constitutive proteasome in WM.

WM and IgM secreting low-grade lymphoma cell lines (BCWM.1, MEC1, RL) were used. Expression of imunoproteasome and constitutive proteasome subunits (beta1, beta2, beta5; LMP2, MECL1, LMP7) were detected primary WM cells and cell lines by an ELISA-based assay. Cytotoxicity and DNA synthesis were measured by thymidine uptake and MTT, respectively. Cell signaling and apoptotic pathways were determined by Western Blot. Determination of the additive or synergistic effect of drugs combination was calculated using the CalcuSyn software based on the Chou-Talalay method.

Primary CD19 bone-marrow derived WM cells express higher level of the immunopreoteasome as compared to the constitutive proteasome. Carfilzomib inhibited the chymotrypsin-like activity of both the immunoproteasome (LMP7) and the constitutive proteasome (beta5) and in WM cells, in a dose-dependent manner; leading to inhibition of proliferation (IC50: 5nM; 48h) and induction of cytotoxicity (IC50: 7.5nM; 48h) in WM cells. Carfilzomib mediated apoptosis in WM by increasing PARP-, caspase-9- and -3-cleavage; as well as by inducing activation of c-jun-N-terminal kinase and ER-stress in a dose-dependent manner. Moreover, combination of Carfilzomib and bortezomib induced synergistic cytotoxicity in WM cells, as shown by enhanced PARP-, caspase-9- and -3-cleavage; and synergy in inhibiting the chymotrypsin-like activity of the immunoproteasome and constitutive proteasome.

Taken together, these findings provide the pre-clinical rational for testing Carfilzomib in Waldenstrom Macroglobulinemia.

Aujay:Proteolix: Employment, Equity Ownership. Demo:Proteolix: Employment, Equity Ownership. Ghobrial:Millennium: Honoraria, Research Funding, Speakers Bureau; Celgene: Consultancy, Honoraria, Speakers Bureau; Novartis: Honoraria, Speakers Bureau.