AF64A-induced changes in N-myc expression in the LA-N-2 human neuroblastoma cell line are modulated by choline and hemicholinium-3.

Due to AF64A's structural similarity to choline, AF64A can selectively affect cholinergic neurons, which possess a high affinity choline transport system for acetylcholine synthesis. The mechanism by which AF64A selectively produces its cytotoxic effect is unknown. However, based on previous studies that demonstrate that DNA lesions produced by AF64A caused premature termination of N-myc transcription in vitro, it is possible that AF64A may affect the transcription of genes necessary for developmental maintenance in cholinergic cells. Using the LA-N-2 cells as a model to study the effects of AF64A in a purely cholinergic system, we investigated the effects of AF64A on the expression of the N-myc gene and monitored cell growth. AF64A produced a maximal decrease in N-myc mRNA with a return to steady state levels at later time points. Moreover, a decrease in cell numbers in AF64A-treated cells was observed, and these cells did not double in number at their respective doubling time as compared to control. In other studies, a causal relationship between a reduction in N-myc and an inhibition of cell growth and replication has been reported. While these studies do not allow us to conclude that AF64A is specific for N-myc, the data do, nevertheless, suggest that AF64A affects cell growth and/or replication by down-regulating the expression of N-myc which is involved in differentiation and cell growth in neuroblastomas. Presence of choline or hemicholinium-3 prevented the AF64A-induced decrease of N-myc levels by competing with, or inhibiting the choline transport mechanism by which AF64A enters the cell, respectively.