Histone deacetylase inhibitors and retinoic acids inhibit growth of human neuroblastoma in vitro

Background. Neuroblastoma is a common childhood cancer with a poor overall prognosis. Retinoic acids (RAs) have been studied as a potential therapy, s howing promise in recurrent disease. The histone deacetylase inhibitor (HDA CI) M-carboxycinnamic acid bishydroxamide (CBHA) is another potential thera py, which we recently described. Combinations of RAs and HDACIs currently u nder investigation display synergy in certain neoplasms. In this study, we evaluate the effect of combinations of RAs and HDACIs on human neuroblastom a cells. Procedure. Established cell lines were cultured in increasing conc entrations of HDACIs, RAs, and combinations thereof. Following exposure, vi able cell number was quantified by trypan blue dye exclusion on a hemacytom eter. Cell cycle analysis was performed by propidium iodide staining and FA GS. Results. All assayed HDACIs and RAs decreased viable cell number. Lower concentrations of each agent were effective when the two were combined. Th e primary reason for decreased cell number appears to be apoptosis followin g HDACI exposure and G1 arrest following RA exposure. Both effects are seen with cotreatment. Caspase inhibition abrogates the apoptotic response. Con clusions. CBHA causes apoptosis of human neuroblastoma in vitro, an effect that can add to the effects of RA. HDACIs and RAs inhibit neuroblastoma in significantly lower concentrations when used together than when used indivi dually. Combination therapy may improve the ultimate efficacy while reducin g the side effects of these agents in clinical use. (C) 2000 Wiley-Liss, In c.