Published in Cancer Detection and Prevention 2000; 24(Supplement 1).

Gene repair therapy with chimeric RNA-DNA oligonucleotides

RM Blaese MD

ValiGen, Newtown, PA 18940, USA,

Genes are the blueprints of life, containing all the information that directs the development and function of living organisms. Over the past decade we have seen the beginning of efforts to use the vast information contained in genes as a treatment for both inherited and acquired diseases. The original approach to gene therapy involved the delivery and insertion of copies of the entire gene into those cells affected by a gene defect or to cells where a new gene-directed function was desired (addition gene therapy). Because entire genes or even cDNAs are very large molecules, they are often incorporated into modified viruses to aid their delivery to the cell. These early generation viral delivery systems have several limitations and have not yet reached the level of activity needed to effectively treat most diseases. Therapy with genes requiring regulation that mirrors normal physiology has presented a particularly difficult problem for addition gene therapy. Similarly progress has been slow for disorders needing the therapeutic genes to be delivered to all affected cells (cancer) or to major internal organs (liver, lungs). A new approach to correcting diseases caused by defective genes is to repair the error or defect in the intrinsic gene rather than to add an entire new copy of that gene. Using a small RNA/DNA containing oligonucleotide (a chimeraplast) it is possible to specifically and permanently modify genomic DNA sequences to change, insert or delete specific nucleotides. Chimeraplasty, as the technique is called, is uses the cell's own DNA repair machinery to specifically change the spelling of genomic sequences as directed by the sequence of the added chimeraplast template (mismatch repair). Chimeraplasty has been used successfully to change DNA sequences in bacteria, yeast, plants, rodent and human cells. Using an anionic liposome formulated with galactose terminated galactocerebroside, high efficiency delivery of chimeraplasts to hepatocytes bearing the asialoglycoprotein receptor has been achieved by simple tail vein injection. To demonstrate that chimeraplasty could repair an inherited genetic defect affecting the liver, jaundiced Gunn rats with a defect in bilirubin conjugation were treated IV with a chimeraplast designed to insert a missing G at base position 1206 of the BUGT gene. Successful correction of this mutation was shown by Southern and Western blots, by a fall in serum bilirubin and by the appearance of conjugated bilirubin in the bile of these animals. Preparations are underway for a clinical trial testing this gene repair strategy in patients with Crigler-Najjar syndrome that should open the way to similar clinical trials for many other diseases with gene defects in the liver. Development of improved delivery systems to other organs and cell types should enable treatment of a much wider range of inherited and acquired disorders based in the genes.

For more information, contact

Paper presented at the International Symposium on Impact of Biotechnology on Cancer Diagnostic & Prognostic Indicators; Geneva, Switzerland; October 28 - 31, 2000; in the section on molecular detection & therapy.