Selective expression of transgene using hypoxia-inducible trans-splicing group I intron ribozyme

Low oxygen conditions, termed hypoxia, can affect cell survivals. Cells may adapt to hypoxic conditions through hypoxia response elements (HRE) such as erythropoietin enhancer or phosphoglycerate kinase element. Hypoxic conditions usually appear in solid tumors, and can cause resistance to radiotherapy or chemotherapy. In this study, a genetic approach based upon Tetrahymena group I ribozyme was developed, which can address the challenges induced by a hypoxic microenvironment. To this end, human telomerase reverse transcriptase (hTERT) targeting trans-splicing ribozymes whose expression and activity were induced by HRE under hypoxia were constructed. Luciferase reporter assay showed induction of the transgene to increase due to the hypoxia-inducible ribozymes through a specific trans-splicing reaction in hTERT-expressing cells under hypoxic conditions. Increase in the transgene expression was mainly due to the increased trans-splicing reaction through a concurrent increase of the ribozyme expression level. Moreover, hypoxia-inducible ribozyme with herpes simplex virus thymidine kinase as the 3'exon effectively induced cell death when treated with ganciclovir under both hypoxic and normoxic conditions. These results indicated that the trans-splicing ribozyme could be a target-specific and efficacious anti-cancer tool to overcome resistance to radio- and chemotherapy under hypoxic conditions.