Carfilzomib, An Irreversible Proteasome Inhibitor, Induces Long-Term Growth Inhibition of Mantle Cell Lymphoma In Vivo,

Abstract 3740

Mantle cell lymphoma (MCL) is an aggressive B-cell lymphoma with poor clinical outcome, thus, novel therapeutic agents are urgently needed. The proteasome inhibitors are small molecular agents which show significant anti-tumor effect in patients with relapsed/refractory MCL. Carfilzomib, an irreversible proteasome inhibitor with selectivity for the chymotrypsin-like active site, inhibits the proliferation of MCL cells in vitro, as well as the reversible proteasome inhibitor bortezomib. Unlike bortezomib, carfilzomib is good-tolerated and does not induce severe neuropathy in patients. Therefore, carfilzomib can be used in higher dose than bortezomib in vivo. Our study was undertaken to evaluate the therapeutic efficacy of carfilzomib on MCL cells both in vitro and in vivo compared with bortezomib. Four human MCL cell lines, MINO, Jeko-1, MAVER, and NCEB-1, freshly isolated primary MCL cells from the patients with relapsed/refractory MCL, were treated with carfilzomib or bortezomib. A ³H-thymidine incorporation assay showed that both carfilzomib and bortezomib displayed the same dose-dependent manner in inducing growth inhibition of the MCL cells. Similarly, flow cytometry analysis with fluorescence-labeled Annexin V and propidium iodide showed that carfilzomib induced apoptosis of MCL cells in the same dose-dependent manner with bortezomib. However, under the tolerable dose of each of the two proteasome inhibitors, they had different therapeutic effect in a MCL-bearing mouse model established in severe combined immunodeficient (SCID) mice. MINO cells (5 × 10⁶) were inoculated subcutaneously into the right flank of SCID mice. Three weeks later, after palpable tumors developed, mice were treated intravenously with carfilzomib (5 mg/kg) on day 1 and day2, for 5 cycles, or treated intraperitoneally with bortezomib (1 mg/kg) on days 1, 4, 7 and 10, per 21 days. Tumor growth was almost abrogated after treatment with carfilzomib compared with bortezomib, and the survival time of tumor-bearing mice was significantly prolonged in the carfilzomib-treated mice versus bortezomib-treated mice. Notably, Increasing the frequency or dose of bortezomib treatment was unable because the mice were too suffered in toxicity to tolerate the treatment. Western blot analysis showed that carfilzomib induced apoptosis in caspase-dependent manner as well as bortezomib. Carfilzomib inhibited the phosphorylation of IκB, STAT3, and AKT and irreversibly blocked the release of NFκB to nuclei. In conclusion, carfilzomib displays the same anti-tumor effect and mechanism with bortezomib on MCL cells in vitro. However, carfilzomib but not bortezomib is well tolerated without severe side effect in vivo. Carfilzomib significantly inhibits tumor growth and prolongs survival indicating that carfilzomib is a potential agent in MCL chemotherapy.