Genomic targeting and genetic conversion in cancer therapy

A number of cellular transformations are due, in large part, to a single base mutation that alters the function of the expressed protein. Similarly, alterations in the DNA sequence of a gene involved in cell proliferation can have a significant effect on the viability of particular cells, Thus, the capacity to modulate the base sequence of such a gene would be a useful tool for cancer therapeutics. We have developed an experimental strategy that centers around site-specific DNA base mutation or correction using a unique chimeric oligonucleotide. This chimeric molecule has demonstrated higher recombinogenic activities than identical oligonucleotides containing only DNA residues, both in vitro and in vivo. The chimeric molecule is designed to hybridize to a target site within the genome and induce a single base mismatch at the residue targeted for mutation. The DNA structure created at this site is recognized by the host cell's repair system which mediates the correction reaction. The bcr-abl fusion gene, the product of a translocation between human chromosomes 9 and 22, and the cause of chronic myelogenous leukemia (CML) can be targeted for gene correction. This fusion gene is a good choice because (1) it is a unique target in CML; (2) it is a single copy target; (3) the DNA sequence of the fusion gene is unique. The goal of such experiments is to knock-out the fusion gene by changing a glutamine or lysine codon into a stop codon through a chimeric directed DNA repair system.