Retrovirus-mediated expression of an artificial β-endorphin precursor in primary fibroblasts

Peptides are of potential interest in the field of gene therapy but require modification by genetic engineering to facilitate their secretion. Amino terminal addition of a signal peptide is not always sufficient to achieve this goal, as found in this study for β-endorphin. To overcome this problem, addition of the pre-pro-sequence of mouse nerve growth factor to β- endorphin was tested. Retrovirus-mediated expression of a hybrid construct of the pre-pro-sequence of nerve growth factor and human β-endorphin in primary fibroblasts resulted in the secretion of β-endorphin immunoreactivity at a rate of 620 pg/h/10⁶ cells. Analysis of the secreted β-endorphin immunoreactivity with reverse-phase HPLC, immunoassays using three different antibodies, and an assay for the specific displacement of [³H][D-Ala²,N- MePhe⁴,Gly-ol⁵]enkephalin from μ-opioid receptors suggests that the pre- pro-sequence is cleaved off from the pre-pro-sequence/β-endorphin construct prior to secretion, resulting in bona fide β-endorphin. Transplantation of β-endorphin-secreting cells into brain or spinal cord may provide a gene therapy approach for the treatment of chronic, opioid-sensitive pain states.