Interferon-gamma cooperates with retinoic acid and phorbol ester to inducedifferentiation and growth inhibition of human neuroblastoma cells

The prognosis of patients with advanced stages of neuroblastoma with N-myc amplification remains poor despite escalated therapy, a situation that has called for alternative therapeutic approaches. Neuroblastoma cells, which r epresent immature peripheral neuronal cells, treated with certain physiolog ic and nonphysiologic agents such as retinoic acid (RA), phorbol esters and interferons (IFN) in vitro undergo cellular differentiation and stop to di vide, a process that mimics normal neuronal development. Such "differentiat ion therapy" using RA after autologous bone marrow transplantation has rece ntly given encouraging results in neuroblastoma patients with advanced dise ase. Considering approaches for improved differentiation therapy, we invest igated possible synergistic effects of combining agents known to influence neuroblastoma growth and differentiation in vitro. Our results show that co mbined treatment with IFN-gamma and RA or the phorbol ester 12-O-tetradecan oyl-phorbol acetate (TPA) had synergistic or enhancing effects on morpholog ic differentiation and neurite outgrowth in 5 of 5 neuroblastoma cell lines , 3 of which expressed very high levels of N-myc mRNA due to N-myc amplific ation. The combinations RA+IFN-gamma or TPA+IFN-gamma also enhanced induced growth inhibition in all 5 cell lines, in several cases resulting in compl ete growth arrest under conditions where cells stimulated with either agent alone continued to grow. The phenotypic effects of the combined RA+IFN-gam ma or TPA+IFN-gamma treatments were in most, but not all, investigated case s accompanied by moderate reductions in N-myc expression, suggesting that t he cooperative signals may counteract N-Myc activity at several levels. The cooperativity between IFN-gamma and other differentiation signals may be r elevant for approaches to improve the therapy for high-risk neuroblastoma w ith N-myc-amplification. (C) 2001 Wiley-Liss, Inc.