Atiprimod Inhibits Growth of Mantle Cell Lymphoma In Vitro and In Vivo and Induces Apoptosis Via Activation of the Mitochondrial Pathway.

Mantle cell lymphoma (MCL) has poor outcome and is a therapeutic challenge. Atiprimod, a cationic amphiphilic compound, inhibits the proliferation of most human tumor cell lines. Our study was undertaken to evaluate the therapeutic efficacy of Atiprimod on MCL cells and elucidate the mechanism by which it induces cell apoptosis. Four human MCL cell lines, SP53, MINO, Grant 519, and Jeko-1; freshly isolated primary MCL cells from three MCL patients; and normal peripheral blood mononuclear cells (PBMCs) from five healthy donors were treated with Atiprimod. A ³H-thymidine incorporation assay showed that Atiprimod not only inhibited the growth of the MCL cell lines SP53, MINO, Grant 519, and Jeko-1, but also freshly isolated patient MCL cells in a dose-dependent manner. Interestingly, Atiprimod also inhibited the proliferation of PHA-, PMA/ionomycin-, or anti-CD3 mAb/anti-CD28 mAb-activated, but not resting PBMCs from healthy donors. Flow cytometry analysis with fluorescence-labeled Annexin V and propidium iodide showed that Atiprimod induced apoptosis in both the cell lines and primary MCL cells in time-dependent and dose-dependent manners. Notably, Atiprimod did not induce apoptosis of normal T cells and B cells. Atiprimod was also effective and therapeutic in a MCL mouse model established in severe combined immunodeficient (SCID) mice. SP53 cells (5 × 10⁶) were inoculated subcutaneously into the right leg of SCID mice. Three weeks later, after palpable tumors developed, mice were treated intraperitoneally with either vehicle alone (PBS) or Atiprimod (25 mg/kg per day) for 6 consecutive days. Tumor growth was significantly inhibited after Atiprimod treatment compared with vehicle control, and the survival time of tumor-bearing mice was significantly prolonged in the treatment group. Western blot analysis showed that apoptosis of MCL cells was induced through the activation of caspase-9, caspase-3, and PARP pathway. Furthermore, the expression of phosphorylated Bcl-2, Bax, Bad, Bax-xL, and cytochrome C was increased in Atiprimod-treated MCL cells. Pretreatment of cells with caspase-9 inhibitor (z-LEHD) or pan-caspase inhibitor (z-VAD) but not caspase-8 inhibitor (z-IETD) completely blocked Atiprimod-induced apoptosis. In conclusion, Atiprimod inhibits growth and induces apoptosis of MCL cells in vitro and in vivo. Cell apoptosis was induced via activation of the mitochondrial signaling pathway. The therapeutic efficacy of Atiprimod on MCL cells in the mouse model supports the use of Atiprimod as a potential agent in MCL chemotherapy.