Cytosine Arabinoside Differentially Alters Survival and Neurite Outgrowth of Neuronal PC12 Cells

Jason Y. Chang * and Scott Brown +
*Department of Anatomy, University of Arkansas for Medical Sciences, Little Rock, AR, 72205; +Department of Biology, Hendrix College, Conway, AR, 72032
Received 7 December 1995. Available online 22 April 2002

Summary
This study tries to understand the mechanism for the negative effects of an anticancer drug- AraC- on the viability of PC12 neural cells. It concludes that AraC does not interfere with the NGF signaling pathway- a pathway which leads to neurite growth. Yet AraC shows a time-dependant effect on the viability of these cells.

Background
Cytosine arabinoside (AraC) is a potent antimitotic agent commonly used as an anticancer drug. However, high dosage of this drug comes with severe neurotoxic effects. Due to the fact that neural cells are generally post-mitotic cells, the reasoning and process for this neuronal dysfunction is unclear.
PC12 cells are tumor cells; therefore, they grow continuously under normal culture conditions. Once PC12 cells are treated with NGF, they become post-mitotic cells and exhibit the normal morphology of neural cells similar to sympathetic neurons.

Results
1. AraC does not block the NGF signal pathway for neurite growth after one day:
Neuronal PC12 cells were obtained by being treated with NGF for 10 days. The neuronal PC12 cells were then cultured in plates: A. With NGF in the media, B. With no NGF yet with NGF antibodies, C. With NGF as well as AraC (Figure 1). The viability tests of MTT showed that the plate with NGF (B) is the only one that does not have NGF signaling while the presence of NGF with or without AraC shows the same amount of NGF signaling.

Figure 1.

2. Dose- and time-response of AraC on the viability of neuronal and regular PC12 cells.
The results show the low sensitivity of neuronal PC12 cells to large amounts of AraC (Figure 2A). However there is a large reduction of viability for regular PC12 tumor cells (e.i. PC12 cells not treated with NGF) after the exposure to low amounts of AraC (Figure 2B).

Figure 2.

3. Some neuroprotective agents could increase the viability of neuronal PC12 cells treated with AraC:
Several different neuroprotective agents were examined. Out of these only Aurintricarboxylic acid (ATA) and KCI could enhance the viability of neuronal PC12 cells. The 25um of Aurintricarboxylic acid (ATA) could increase the viability of neuronal PC12 cells treated with 100uM of Arac from 50% to 80%. Moreover, 30um of KCI could increase the viability of such cells to about 85%.

Discussion
NGF converts PC12 tumor cells into post-mitotic cells, so this could partially be a reason for the lower sensitivity of neuronal PC12 cells to AraC. However, NGF has shown to protect the viability of many other neuronal cells against AraC, cells which are already post-mitotic. This suggests that NGF does not increase the viability of neural PC12 cells against AraC merely due to its ability to introduce the post-mitotic phenotype. Moreover the nuclear staining with bisbenzimide indicated the nuclei condensation of some neuronal PC12 cells- this event usually indicates the neuronal programmed cell death. However, since only some cells showed the programmed cell death, apoptosis cannot be introduced as the main reason for the effects of AraC on neuronal PC12 cells. Overall there is a distinction between the neurite growth and the nerve growth factor mechanism.