Conversion to the terminally differentiated state during treatment of NG108-15 neural tumor cells with 1-beta-D-arabinofuranosylcytosine in defined medium.

Differentiation of cells of the neural tumor hybrid cloned cell line NG108-15 begins stochastically upon transfer to a serum-free defined medium (A. Krystosek, J. Cell. Physiol., 125: 319-329, 1985). Such cultures in N2 medium contain both proliferating and neurite-forming cells (which are not mutally exclusive subpopulations). Addition of 1-beta-D-arabinofuranosylcytosine (ara-C) to NG108-15 cells in N2 medium yielded cultures with a highly differentiated appearance. Investigation of the nature of this effect revealed that ara-C did not increase the probability that cells would enter the differentiation pathway; it did, however, completely abolish proliferation. The early kinetics of neurite formation were similar in control and treated cultures. This was followed by a phase in which ara-C-treated cells underwent continuous rapid maturation including normalization of nucleolar features. Loss of proliferative potential of treated cells was tested in a drug-free serum challenge protocol. Permanently postmitotic cells (i.e., cells which failed to divide even once) were shown to accumulate with time of ara-C pretreatment; this represented 59% of total cells at day 3 and 94% at day 7 of treatment. Thus, the bulk of the population can commit to terminal differentiation. Even among the minority of cells capable of 1-2 rounds of division in the challenge incubation, cessation of proliferation was more likely than continuous colonial growth, suggesting that a profound phenotypic alteration had occurred. The results show that advanced morphological maturation and the step(s) of terminal neuronal differentiation can be achieved in this cell line in response to a cancer chemotherapeutic agent and that this drug is a more complete inducer than compounds which modulate the cyclic AMP system.