Enhanced potency of 9- cis versus all- trans-retinoic acid to induce the differentiation of human neuroblastoma cells

Abstract

All- trans-retinoic acid (ATRA) has been shown to be one of the most potent chemical inducers of human neuroblastoma differentiation. The recent discovery that the stereoisomer of ATRA, 9- cis-retinoic acid (9- cis-RA), binds to both the retinoic acid and retinoid X series of receptors prompted us to evaluate the ability of this compound to promote differentiation of this cell type. Using the LA-N-5 cell line, we have now determined that 9- cis-RA can induce the differentiation of human neuroblastoma cells as evidenced by dose-dependent inhibition of cell proliferation, neurite outgrowth, increased acetylcholinesterase activity, and reduction of N-myc mRNA expression. In comparing the effects of 9- cis-RA to ATRA, we found that while both compounds induced qualitatively similar cholinergic (versus adrenergic) features in LA-N-5 cells, 9- cis-RA was 5-to-10-fold more potent than ATRA in its antiproliferative and differentiation activity. These results were supported by transient transfection experiments utilizing chloramphenicol acetyltransferase (CAT) plasmid constructs containing a retinoic acid responsive regulatory element which showed a 2-to 3-fold increase in reporter gene activity induced with 9- cis-RA over that seen with ATRA at pharmacologically relevant retinoid concentrations (>10 −8 M). Furthermore we have determined that 9- cis-RA can significantly enhance mRNA levels of the nuclear retinoic acid receptors α and β in LA-N-5 cells. Taken together, these findings have established the ability of 9- cis-RA to induce neuroblastoma differentiation and suggest that this retinoic acid isomer may have better therapeutic characteristics than ATRA.