Selective killing of cancer cells based on loss of heterozygosity and normal variation in the human genome: A new paradigm for anticancer drug therapy

Most drugs for cancer therapy are targeted to relative differences in the b iological characteristics of cancer cells and normal cells. The therapeutic index of such drugs is theoretically limited by the magnitude of such diff erences, and most anticancer drugs have considerable toxicity to normal cel ls. Here we describe a new approach for developing anticancer drugs. This a pproach, termed variagenic targeting, exploits the absolute difference in t he genotype of normal cells and cancer cells arising from normal gene seque nce Variation in essential genes and loss of heterozygosity (LOH) occurring during oncogenesis. The technology involves identifying genes that are: 1) essential for cell survival; 2) are expressed as multiple alleles in the n ormal population because of the presence of one or more nucleotide polymorp hisms; and 3) are frequently subject to LOH in several common cancers. An a llele-specific drug inhibiting the essential gene remaining in cancer cells would be lethal to the malignant cell and would have minimal toxicity to t he normal heterozygous cell that retains the drug-insensitive allele. With antisense oligonucleotides designed to target two alternative alleles of re plication protein A, 70-kDa subunit (RPA70) we demonstrate in vitro selecti ve killing of cancer cells that contain only the sensitive allele of the ta rget gene without killing cells expressing the alternative RPA70 allele. Ad ditionally, we identify several other candidate genes for variagenic target ing. This technology represents a new approach for the discovery of agents with high therapeutics indices for treating cancer and other proliferative disorders.