SYNTHETIC RIBOZYMES USED IN MEDICINE
Ribozymes are beginning to be used in medical applications. Researchers studying AIDS have derived a hammerhead ribozyme that can inhibit HIV replication. This engineered ribozyme was in clinical trials as of 2006. It is administered by expressing the ribozyme gene in a viral vector. The vector is transfected into peripheral blood T lymphocytes from HIV-infected patients. It is hoped that the expressed ribozyme will cleave the RNA version of the HIV genome, thus preventing replication of the HIV virus.
Another ribozyme has been developed to cleave an RNA virus, hepatitis C virus (HCV). HCV is the leading cause of chronic hepatitis, and no vaccine is available. Various engineered ribozymes have been identified that can efficiently cleave HCV RNA, but these studies are still in vitro. The engineered ribozymes have worked efficiently in cell culture where liver cells from infected individuals have been harvested and grown in dishes, but they have not yet been tested directly in patients.
The clinical use of ribozymes has many of the same obstacles as for any new drug. Each new ribozyme must be delivered to the correct location and expressed in cells that are diseased. Each ribozyme must be stable and resistant to degradation. In this regard, many engineered ribozymes contain modified bases, which prevent degradation by cellular endonucleases. Finally, the ribozyme must not have any deleterious side effects. High specificity to their target provides ribozymes with more potential than many preexisting therapies. For example, chemotherapy of cancer patients kills any rapidly dividing cells, not just the cancerous cells. This is why chemotherapy patients lose their hair. Ribozymes recognize one specific target mRNA; therefore, ribozyme treatments may avoid side effects seen in chemotherapy treatments.