Effects of interferon‐gamma and its interaction with retinoic acid on human neuroblastoma differentiation

Differentiation‐promoting effects of interferon‐gamma (IFN‐γ), both alone and in combination with retinoic acid RA), were studied on the human neuroblastoma cell line, LA‐N‐5. The results show that IFN‐γ inhibited the growth and induced morphological differentiation in a dose‐ and time‐dependent manner with measurable effects appearing at 20–40 IU/ml after 3 to 4 days of treatment in vitro. Acetylcholinesterase activity, used as a biochemical index of neuroblastoma differentiation, increased up to 2.5‐fold in the presence of IFN‐γ with a half maximal concentration of approximately 100 IU/ml. Concomitantly, modest IFN‐induced increases (≤2‐fold) in choline acetyltransferase (ChAT) and tyrosine hydroxylase (TH) activities were seen. Combination treatment of cells with IFN‐γ and RA resulted in synergistic effects on morphological differentiation, growth inhibition and induction of ChAT. Reversal of IFN‐γ's ability to influence neuroblastoma cell growth as well as potentiate the anti‐tumor effects of RA was obtained in the presence of an antibody against the IFN‐γ receptor, implying receptor‐mediated physiological events. Taken together, these data confirm the differentiating effects of IFN‐γ on human neuroblastoma cells and suggest that combination therapy with RA may be beneficial in the treatment of this disease.