DNA minivectors may provide new gene therapy tool

From The Labs by By Ruth SoRelle, M.P.H.

Dr. Lynn Zechiedrich

Dr. Lynn Zechiedrich

A long-standing barrier to successful gene therapy in humans has been the lack of a non-toxic and effective tool or vector to carry the gene into the cell.

Now a Baylor College of Medicine researcher and her colleagues think they may have a solution – at least in the quest for a way to silence cancer genes. Their invention consists of tiny wound-up circular bits of DNA that carry a short “hairpin” of RNA.

The researchers from BCM and The Methodist Hospital Research Institute called them Minivectors™ in a report that appears in a recent issue of the journal Gene Therapy. Because the tool has yet to be used in human studies, Dr. Lynn Zechiedrich, associate professor of molecular virology and microbiology at BCM and one of the report’s senior authors is hesitant to claim victory.

“In the best case scenario, it could prove a valuable therapeutic tool that can work on cells that are difficult to manipulate. This may help clinicians treat some diseases,” she said.

Avoids toxicity of viruses

Minivector DNA avoids the toxicity of viruses, lasts longer than plasmids (large DNA circles containing bacterial sequences) and survives and continues gene delivery longer than small interfering RNAs (siRNA), currently used to silence the genes in the laboratory research setting. Plasmids are as much as 10 times larger than Minivectors, and siRNAs, while small, are too unstable in blood to translate to patient treatment.

“Plasmids are too large and toxic,” said Zechiedrich. “Smaller is better. Also, deleting toxic bacterial sequences from the tiny circles prevents bad side effects.”

Lymphoma

One disease that might be targeted by the Minivector DNA is lymphoma, the fifth most common cancer in the United States. A type called anaplastic large cell lymphoma is the most common T-cell lymphoma in children and the second most common aggressive systemic T-cell lymphoma in adults. Doctors treat it with a specific regimen of a cocktail of many anti-cancer drugs.

“Because this regimen can cause side effects, researchers are seeking a specific therapeutic approach,” said Dr. Youli Zu, associate professor in The Methodist Hospital Research Institute and a senior author of the report. However, while he has been able to suppress the growth of lymphoma with siRNA in animals, he has found siRNA to be unstable in blood, extremely limiting its value as a treatment.

Zechiedrich and Zu found that the Minivectors are stable in human blood for at least 48 hours, compared to only half an hour for siRNA and two hours for plasmids.

In addition, Minivectors are highly effective in taking the DNA into lymphoma cells, specifically shutting down cellular cancer genes, and action that resulted in death of the lymphoma cells.

Advance gene-targeting therapy

“Clinically, Minivectors should advance gene-targeting therapy specific for lymphoma, as well as other types of tumors, with little or no side effects on normal tissue in cancer patients,” said Zu.

“Using these Minivectors will be trickier in diseases of organs that are not as easily accessed as blood, but we are working on that now,” said Zechiedrich.

Minivectors are measured in nanometers and consist of no more than a few hundred DNA base pairs. They are highly effective in taking the DNA into cells and also very efficient in silencing the targeted genes. In this case, they target cancer genes.

The postdoctoral fellows who carried out this research are Dr. Nianxi Zhao of The Methodist Hospital Research Institute and Dr. Jonathan M. Fogg of BCM.

Funding for this work came from the National Institutes of Health, The Methodist Hospital Research Institute, and the Burroughs Wellcome Fund.

Source – From The Labs