Not all gene products are, in the argot, “drugable”. And this is where the economics comes in.
Todd Golub of the Broad Institute, in Cambridge, Massachusetts, reckons drug firms have got rather lazy about pursuing leads. For example, many oncogenes, as those whose breakage causes cancer are known, encode proteins called kinases. These are enzymes which are involved in intracellular signalling pathways. A lucky break some years ago revealed a systematic way of attacking kinases with small molecules that block their activation. Researchers with putative anti-kinase drugs are thus welcomed by venture-capital firms. The odds of success are understood and the time to market is tolerable. That is in marked contrast to, say, drugs that might control transcription factors. A failed transcription-factor gene is as common a cause of cancer as a failed kinase gene. Transcription factors, though, are not regarded as drugable. No systematic way of dealing with them has yet been discovered.
The Economist, "Biology 2.0," Link.