Replacing one amino acid increases the effectiveness of gene therapy by hundreds of times
Scientists at the University of Florida, working under the guidance of Professor Arun Srivastava, have developed a new version of the adeno-associated virus, almost 30 times more effective than viral vectors traditionally used in gene therapy.
Adeno-associated viruses are considered optimal vectors for gene therapy, because they are able to infect cells without causing disease. However, trillions of viral particles are needed to successfully deliver a therapeutic gene to the cell nucleus.
Based on their own data and the results obtained by other groups, the authors explain this by the fact that the body is not only trying to get rid of viruses with the help of the immune system, but also by the processes occurring after the penetration of viral particles into the cytoplasm of the cell, as a result of which most of them do not reach the nucleus.
The cell mistakes the particles of the adenoassociated virus for its own abnormal proteins and places them inside membrane organelles – proteasomes that break down cellular debris.
The researchers claim that the amino acid tyrosine, which is part of the shell of viral particles, is to blame for this.
The composition of tyrosine includes a hydroxyl group that attracts phosphates contained in the cytoplasm of the cell. The addition of a phosphate ion to a hydroxyl group is a signal to the proteasome about the need to eliminate debris.
The proteins of the shell of the adenoassociated virus contain several tyrosine molecules. The authors created several viral vectors, in each of which one of the tyrosine molecules was replaced by another amino acid – phenylalanine, which differs from tyrosine only in the absence of hydroxyl grouping. The gene of blood clotting factor IX, which is absent in the body of patients with hemophilia B, was also embedded in all vectors.
In experiments using tissue samples, the efficiency of one of the new vectors within 48 hours was 11 times higher than the standard. The results obtained in experiments on mice exceeded all expectations: two weeks after the injection of one of the new vectors, the expression of the therapeutic gene was 29 times higher than when a 10 times higher dose of the standard vector was administered.
The authors believe that this effect is due to the fact that due to the absence of tyrosine, the virus more often avoids phosphorylation and reaches the nucleus. They are currently working on creating an "ideal vector" devoid of all seven tyrosine molecules. Plans for the future also include joint testing of vectors on dogs with hemophilia with specialists from the University of North Carolina and, if positive results are obtained, conducting clinical trials.
In addition to increasing efficiency, the improved vector will reduce the cost of gene therapy, because, according to scientists, about 100 billion new vectors are required to obtain a therapeutic effect compared to 10 trillion standard viral particles.
Portal "Eternal youth" www.vechnayamolodost.ru based on the materials of the University of Florida
22.05.2008