Bone marrow stromal-derived interleukin-6 (IL-6) stimulates proliferation and survival of neuroblastoma cells in the bone marrow microenvironment

Proc Amer Assoc Cancer Res, Volume 47, 2006 3977 Neuroblastoma is the second most common solid tumor of childhood and often metastasizes to the bone marrow and the bone. We have previously shown that in the bone marrow, human neuroblastoma cells can activate osteoclasts by stimulating the production of IL-6, a pleiotropic cytokine implicated in angiogenesis and bone metastasis, by bone marrow mesenchymal stem cells (BM-MSC). Here we have evaluated whether IL-6 could also have a paracrine effect on neuroblastoma cells. An analysis of the expression of IL-6 and its receptor (IL-6R) in neuroblastoma cell lines indicated an absence of expression of IL-6 in 4 out of 5 cell lines examined, but the presence of a functional IL-6 receptor complex including the ligand binding membranous gp80 (α-chain subunit) and the common signal transducing protein gp130 (β-chain subunit) in 4 cell lines (CHLA-255, CHLA-171, SMS-SAN and SK-N-BE2). Treatment of neuroblastoma cells expressing the receptor complex with recombinant human IL-6 (rhIL-6) resulted in activation of STAT-3 and MAPK as demonstrated by a dose dependent (10-30 ng/ml) increase in STAT-3 phosphorylation at Tyr705 and P44/42 MAPK (Erk1/Erk2) phosphorylation within 15-30 minutes after stimulation. This effect was enhanced by the addition of soluble IL-6R and inhibited in the presence of a neutralizing antibody against IL-6R. rhIL-6 stimulated the proliferation of CHLA-255 neuroblastoma cells that expressed a functional receptor complex in a dose dependent manner (0.001-10 ng/ml), both in the presence or absence of serum but not the proliferation of NB19 neuroblastoma cells that did not express a functional receptor complex. This stimulatory effect on proliferation was inhibited by treatment with the MAPK inhibitor PD98059 (100 μM), indicating the involvement of MAPK in IL6-mediated proliferation. We observed that rhIL-6 protected CHLA-255 cells from VP-16 induced apoptosis. Further evidence for a role of IL-6 in neuroblastoma progression was obstained by documenting higher levels of IL-6 in the serum of children with neuroblastoma that had metastasized to the bone. The data indicate that the ability of neuroblastoma cells to stimulate the production of IL-6 by BM-MSC in the bone marrow microenvironment, in addition to activating osteoclasts and promoting bone formation of osteolytic lesions, provides them with a proliferative and survival advantage. Therefore blocking IL-6 may be a valuable approach in the treatment of neuroblastoma bone metastasis because of its dual effect on osteoclasts and tumor cells.