Dose-Dependent Doxycycline-Mediated Adrenocorticotropic Hormone Secretion from Encapsulated Tet-On Proopiomelanocortin Neuro2A Cells in the Subarachnoid Space

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Abstract
We previously reported that polymer-encapsulated mouse neuroblastoma cells that are capable of secreting β-endorphin may reduce pain sensitivity in rats after capsule implantation into the cerebrospinal fluid (CSF)-filled subarachnoid space of the spinal cord. The neuroblastoma cells carry the proopiomelanocortin (POMC) gene that encodes the precursor of adrenocorticotropic hormone (ACTH) and β-endorphin. To control the expression of these hormones in the present study, a promoter that is inducible by administration of tetracycline derivatives such as doxycycline (Dox) was linked to the POMC gene. Encapsulated cells in the CSF space of rats stimulated by four intraperitoneal doses of Dox responded with ACTH expression as determined in a subsequence 36-hr in vitro incubation. The amount of ACTH released was dependent on the in vivo Dox dose. These findings indicate that gene expression in xenogeneic cells in the CSF space can be manipulated by injection of a relatively innocuous drug, and suggest that this system may be applicable to cell transplantation therapy in patients with central nervous system diseases that require temporary control of ligand delivery. In our previous study, xenogeneic mouse neuroblastoma cells bearing the proopiomelanocortin (POMC) gene, the precursor of adenocorticotropic hormone (ACTH) and β-endorphin, were implanted within polymer capsules into the cerebrospinal fluid (CSF) space of rats. Although adrenocorticotropic hormone (ACTH) and β-endorphin were secreted, we were not able to control the amount or time course of hormone release. In this study, a promoter that is inducible by administration of tetracycline (Tet) derivatives was linked to the POMC gene for control of gene expression. The results showed that POMC gene expression in the implanted encapsulated cells could be regulated in a dose-dependent manner by Tet administration to the hosts. Withdrawal of Tet led to a rapid reduction in POMC expression as indexed by in vitro ACTH release. Our results suggest that Tet-inducible gene expression may be promising for cell therapy in patients with central nervous system diseases that require regulated delivery of specific substance.