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Retinoic acid (RA) induced concentration-dependent morphologic differentiation and growth inhibition in the LA-N-1 human neuroblastoma cell line. Time course studies demonstrated a significant increase in the formation of long neurites in LA-N-1 cultures within 48 hours of RA addition; maximum expression of differentiation occurred at approximately 4 days. This differentiation profile corresponded to a detectable decrease in 3Hthymidine incorporation at 48 hours and complete inhibition of cell growth after 3-4 days. The RA-induced morphologic differentiation and growth inhibition persisted despite removal of the drug. A soft agar assay system showed that RA also inhibited the ability of LA-N-1 cells to form anchorage-independent colonies and induced morphologic differentiation in colonies that did develop. These findings suggest that RA promoted the differentiation of LA-N-1 neuroblastoma cells, resulting in an altered expression of the malignant phenotype.
Neil Sidell (Thu,) studied this question.