Targeted anticancer effect through microRNA-181a regulated tumor-specific hTERT replacement.

We previously generated a group I intron-based ribozyme that can reprogram human telomerase reverse transcriptase (hTERT) RNA to stimulate transgene activity in cancer cells expressing the target RNA via an accurate and specific trans-splicing reaction. One of the major concerns of the hTERT RNA targeting anti-cancer approach is the potential side effects to hTERT(+) hematopoietic stem cell-derived blood cells. Thus, here we modified the ribozyme by inserting target sites against microRNA-181a, which is a blood cell-specific microRNA, downstream of its 3' exon. The specificity of transgene induction and anticancer activity in hTERT(+) cancer cells improved significantly with the modified ribozyme, resulting in selective targeting of hTERT(+) cancer cells, but not hematopoietic cells even if they are hTERT-positive. Importantly, the trans-splicing reaction of the microRNA-regulated ribozyme worked equally well in a nude mouse model of hepatocarcinoma-derived intrasplenic carcinomatosis, inducing highly specific expression of a therapeutic transgene and efficiently regressing hTERT-positive liver tumors with minimal liver toxicity when systemically delivered with an adenoviral vector encoding the ribozyme. These results suggest that a combined approach of microRNA regulation with targeted RNA replacement is more useful for effective anti-cancer treatment.