Drug target validation: Hitting the target

Abstract

or the pharmaceutical industry, the Human Genome Project has proved to be both a blessing and a curse. Where potential drug targets were once hard to come by, the industry is now awash with them. This has left researchers with the unenviable challenge of sifting through the data in search of the elusive proteins that are instrumental in human disease. Akin to seeking a needle in a haystack, this herculean task has boosted the importance of rapid screening technologies. Of the roughly 35,000 genes in the human genome, only a few have known functions. So the task of identifying and verifying a positive lead is key to effective drug development. Drugs fail in the clinic for two basic reasons: they either don't work or they prove to be unsafe. "Both of these are often the direct result of sloppy early target validation," says David Szymkowski, director of biotherapeutics at the biopharmaceutical company Xencor in Monrovia, California. Validation is a crucial step in the drugdiscovery process. Most drugs are inhibitors that block the action of a particular target drug target validation technology feature Hitting the target For any protein, it is not guaranteed that all of its isoforms will have the same function, so it is important to work out which forms are valid drug targets. Many proteins are expressed as different isoforms as a result of alternative splicing of the precursor messenger RNAs (mRNAs) and post-translational modifications. Techniques such as gene knockouts effectively remove all isoforms, but manipulation of mRNA with antisense technology or RNA interference (see 'The silent treatment', page 343) cannot distinguish between isoforms that differ in their post-translational modifications. To overcome this problem, biotechnology company Sangamo BioSciences in Richmond, California, has developed a system that allows the expression of endogenous genes to be altered in cells or whole-animal models. It uses zinc-finger transcription factors in which the DNA-recognition domain is coupled to a functional domain that allows the expression of the target gene to be up-or downregulated. The advantage of this method over gene knockouts or transgenes is that the expression levels of all the isoforms of an endogenous target gene can be specifically manipulated. This technique has been used by a group including researchers at Sangamo and Frank Giordano at Yale University to investigate the growth of blood vessels by activating the endogenous expression of vascular endothelial growth factor (VEGF). The team found that all isoforms of VEGF are needed to stimulate the growth of blood vessels that do not leak (E. J. Rebar et al. Nature Med. 8, 1427-1432; 2002). Casey Case of Sangamo is excited by what he sees as the growing awareness of the biological importance of alternative mRNA splicing. "Conventional overexpression methods for target validation miss the biological consequences of this important phenomenon," he says. Another approach to the problem has been developed by Xerion Pharmaceuticals in Martinsried, Germany. I...

Therapeutic Targets: Progress of Their Exploration and Investigation of Their Characteristics

“…Where potential targets were once hard to come by, the industry is now awash with them. This has left drug discovery communities with the difficult task of shifting through the gene data to find novel targets (Debouck and Metcalf, 2000;Smith, 2003). Genomics approaches such as large-scale gene expression analysis, functional screens in model organisms, genome scans for disease susceptibility genes, and the search for new members of effective drug target classes have enabled the finding of countless candidates for many diseases (Sanseau, 2001;Desany and Zhang, 2004;Dohrmann, 2004).…”

The Pharmacology and Function of Receptors for Short-Chain Fatty Acids

“…Target validation is an essential step in drug-development studies and assists in defining the physiologic role(s) of a GPCR and its importance in pathophysiologic conditions, with the aim of developing a pipeline of potential therapeutic medicines (Smith, 2003). Among several approaches, validation of a GPCR can be achieved by using ligands that selectively perturb the target of interest in vitro and/or in vivo.…”

Therapeutic targeting in the silent era: advances in non-viral siRNA delivery

“…The discovery of gene silencing by RNA interference (RNAi) has revolutionarised this area and presents new opportunities for the successful achievement of gene-based therapies. Moreover, modern biomedical research heavily depends on genomic and proteomic strategies that help uncover disease mechanisms and detect potential target genes relevant to the disease pathology [2] . Therapeutic targets identified from the use of such high-throughput technologies warrant comprehensive in vivo validation of their aetiological role in the disease [3] .…”