Specialized transgenic mice, which contain the HBV in their DNA and which are chronic carriers of HBV, were treated with the tiny HBV-fighting packages. Clawson and co-workers chose the dosage and schedule of the drug delivery to the mice based on their cell culture work. Studies with the transgenic mice were performed with John Morrey, Ph.D., at Utah State, under the auspices of an NIH contract which supports testing of antiviral reagents.

The treatment effects were quite dramatic, Clawson said. We recorded a greater than 80 percent reduction in the HBV liver DNA, meaning far less virus was being produced, and staining for the virus using antibodies also showed a dramatic decrease in residual viral production. This is significant because there are so few examples of successful in vivo applications of ribozymes against bona fide naturally-occurring, disease-causing organisms.

Clawson believes this cassette is more effective than previous ones for a number of reasons. First, the best target sites were chosen using a library selection process. Second, the ribozyme cassette is engineered to cut itself into pieces, thereby freeing the HBV-targeted ribozymes from extraneous sequences that could interfere with their activity. In addition, Clawson ™s cassette included two distinct trans-acting ribozymes, whereas previous versions included only one. With two trans-acting hammerhead ribozymes in the SNIPAA cassette, twice the amount of medicine was present and was delivered over a longer period.

Co-authors on the study were: Wei-Hua Pan, Pin Xin, Departments of Pathology and Biochemistry and Molecular Biology, The Gittlen Cancer Research Institute, Penn State Milton S. Hershey Medical Center, and John D. Morrey, Institute for Antiviral Research, Utah State University.

This work was supported by a research and development contract with Biosan Laboratories/Hexal AG and by a contract from the National Institutes of Health.