In our previous study, xenogeneic mouse neuroblastoma cells bearing the POM
C gene, the precursor of ACTH and beta-endorphin, were implanted within pol
ymer capsules into the CSF space of rats. Although ACTH and beta-endorphin
were secreted, we were not able to control the amounts or times of hormone
release. A promoter that is inducible by administration of tetracycline der
ivatives (Tet) was linked to the POMC gene to control its gene expression (
Neuro2A-Tet-On-POMC; NTP). The results showed that POMC gene expression in
the implanted encapsulated NTP cells could be regulated in a dose-dependent
manner by Tet administration to the hosts. However, no analysis of gene co
ntrol with the Tet-On system over a long period has been performed. In this
study, encapsulated NTP cells were treated in vitro with doxycycline (Dox)
(1.0, 10, 100, 1000 ng/ml) continuously for a month. On day 4, the amount
of ACTH secretion was dependent on the Dox dose. But in the course of the e
xperiment, the difference of ACTH secretion among those treated with Dox 10
, 100, and 1000 ng/ml was eliminated. On the other hand, NTP cells, which w
ere treated with Dox (1000 ng/ml) just on days 7, 14, 21, and 28, secreted
almost the same amount of ACTH in 24 h. From these results, for clinical us
e, an NTP cell line that secretes enough opiate to reduce pain sensitivity
without Dox should be established, and Dox could then be administered if ne
cessary.