Arabinoxylan rice bran (MGN-3/Biobran) enhances natural killer cell-mediated cytotoxicity against neuroblastoma in vitro and in vivo.

BACKGROUND AIMS: Natural killer cell (NK) cytotoxic activity plays a major role in natural immunologic defences against malignancies. NK cells are emerging as a tool for adoptive cancer immunotherapies. Arabinoxylan rice bran (MGN-3/Biobran) has been described as a biological response modifier that can enhance the cytotoxic activity of NK cells. This study evaluated the effect of MGN-3/Biobran on NK cell activation, expansion and cytotoxicity against neuroblastoma cells. METHODS: NK cells were enriched with magnetic beads and stimulated with MGN-3/Biobran. NK cell activation was evaluated via analysis of their phenotype, and their expansion capability was tracked. The in vitro cytotoxic ability of the activated NK cells was tested against K562, Jurkat, A673, NB1691, A-204, RD and RH-30 cell lines and the in vivo cytotoxic ability against the NB1691 cell line. RESULTS: MGN-3/Biobran stimulation of NK cells induced a higher expression of the activation-associated receptors CD25 and CD69 than in unstimulated cells (P < 0.05). The expression of NKG2D, DNAM, NCRs and TLRs remained unchanged. Overnight MGN-3/Biobran stimulation increased NK cell cytotoxic activity against all cell lines tested in vitro and decelerated neuroblastoma growth in vivo. The mechanism is not mediated by lipopolysaccharide contamination in MGN-3/Biobran. Furthermore, the addition of MGN-3/Biobran promoted NK cell expansion and decreased T cells in vitro. CONCLUSIONS: Our data show that MGN-3/Biobran upregulates NK cell activation markers, stimulates NK cell cytotoxic activity against neuroblastoma in vitro and in vivo and selectively augments the expansion of NK cells. These results may be useful for future NK cell therapeutic strategies of the treatment of neuroblastoma.

Influence of Histone Deacetylase Inhibitors and DNA-Methyltransferase Inhibitors on the NK Cell-Mediated Lysis of Pediatric B-Lineage Leukemia.

Epigenetic drugs like histone deacetylase inhibitors (HDACi) and DNA-methyltransferase inhibitors (DNMTi) have been shown to be effective against a variety of tumor entities. Among different molecular anticancer activities of epigenetic active substances, up-regulation of natural killer (NK) cell ligands was described to contribute to an enhanced NK cell-mediated killing of tumor cell lines. So far, no data is available on this effect in childhood acute lymphoblastic leukemia. We investigated the effect of two HDACi [vorinostat, valproic acid (VPA)] and two DNMTi (azacytidine, decitabine) on the viability, expression of NK ligands, and NK susceptibility of the pre-B-cell-ALL cell line MHH-CALL-4. Whereas vorinostat, azacytidine, and decitabine directly reduced viability of the cell line, VPA had no direct cytotoxic effect. NKG2D-ligands were expressed only at very low levels and not affected by epigenetic treatment. Higher expression was found for the DNAM-1 ligands with significant up regulation of CD112 after treatment with VPA (p = 0.02). No significant increase in lysis mediated by resting NK cells could be observed, whereas incubation of target cells with decitabine resulted in a significant increase in lysis mediated by IL-2 activated NK cells (p = 0.0051, p = 0.06 for azacytidine). Vorinostat and VPA could increase the lysis by expanded NK cells which was statistically not significant due to high inter-individual variability. Furthermore, HDACi but not DNMTi reduced the NK-mediated lysis of MHH-CALL-4 after incubation of effector cells. In conclusion, there is a synergistic effect between epigenetic drugs and NK cells against MHH-CALL-4 which is not as strong as in other tumor entities. In situations where NK-mediated control of leukemia is assumed or wanted, a sophisticated combination of single epigenetic drugs and ex vivo expanded NK cells is needed to maximize the synergistic effect of both treatment strategies and DNMTIs may be preferred based on the direct inhibitory effect of HDACi on NK cell cytotoxicity.