Rituximab (RTX), a chimeric anti-CD20 antibody, is associated with direct induction of apoptosis and antibody-dependent cell-mediated cytotoxicity (ADCC) with clinical efficacy in mantle cell lymphoma (MCL). Lenalidomide (LEN), a novel immunomodulatory agent, sensitizes tumor cells and enhances ADCC. Our study attempted to elucidate the mechanism of LEN-enhanced RTX-mediated cytotoxicity of MCL cells. We found that LEN and RTX induced growth inhibition of both cultured and fresh primary MCL cells. LEN enhanced RTX-induced apoptosis via upregulating phosphorylation of c-Jun N-terminal protein kinases (JNK), Bcl-2, Bad; increasing release of cytochrome-c; enhancing activation of caspase-3, -8, -9 and cleavage of PARP. Meanwhile, LEN activated NK cells and increased CD16 expression on CD56lowCD161 NK cells. Whole PBMCs but not NK cell-depleted PBMCs treated with LEN augmented 30% of RTX-dependent cytotoxicity. Daily treatment with LEN increased NK cells by 10-folds in SCID mice, and combination of LEN and RTX decreased tumor burden and prolonged survival of MCL-bearing SCID mice. Taken together, our study demonstrates that LEN plus RTX provides a synergistically therapeutic effect on MCL cells by enhancing apoptosis and RTX-dependent NK cell-mediated cytotoxicity and may be an optimal combination in the clinical trial of relapsed or refractory MCL.
1. LEN and RTX inhibit the growth of MCL cells
Effect of LEN and RTX on the growth of MCL cells. (A) MCL cell lines: SP53, MINO, and Grant 519 were treated with a concentration of 0–1,000 nM of LEN, or (B) with 0–20 mg/mL of RTX. (C) Freshly isolated primary MCL cells from three patients (PT1, PT2, PT3) treated with 0–1,000 nM of LEN. (D) Synergism after treatment with 100 nM of LEN and 10 mg/mL of RTX. Cells were cultured for 48 hr and the growth was assessed by 3 H-thymidine incorporation assay. Results of three independent experiments are shown. Figure 1
2. LEN enhances RTX-induced apoptosis of MCL cells, enhances RTX-induced JNK and mitochondrial apoptotic pathway, augments RTX-dependent NK cell-mediated cytotoxicity by increasing CD16 expression on CD56lowCD161 NK cells and inhibits the growth of MCL cells in SCID mice.
Lenalidomide, as a novel immunomodulatory agent, plus therapeutic antibodies displays synergistic effect with antibody-based therapy. Combination of LEN with humanized mAb significantly induces apoptosis and immune response against MM . In clinical trial, RTX induces high rates of remission in patients with B-cell lymphoma by mechanisms involving ADCC and apoptosis. Our results demonstrate that LEN not only enhanced RTX-induced apoptosis by upregulating RTX-triggered apoptotic proteins but also augmented RTX-dependent NK cellmediated cytotoxicity by increasing CD16 expression on CD56lowCD161 NK cells.