Chemical probe development versus drug development.

Phosphatases as a class of proteins have recently attracted significant attention from the pharmaceutical industry. As our knowledge of this diverse family of proteins has grown, the relationship between phosphatases and human disease has clearly been established, with model systems proving much validation for the potential of some members of this family to be candidate drug targets. This, coupled with the fact that there have been a flood of successful drug development efforts over the past 10 years targeting protein kinases, has led some to propose that phosphatases as a class of enzymes might be equally as rich a source of drug targets as kinases. However to date there remain relatively few molecules targeting protein phosphatases in clinical development. This is less a reflection of their importance in key processes associated with disease, but rather seems to reflect inherent issues with developing drugs for many members of this family. This seems especially so for intracellular phosphatases where the development of selective, potent cell penetrant molecules with good drug-like properties has proven a formidable challenge. This chapter provides a brief outline of the two major processes that have resulted in the existing armament of chemical modulators of protein phosphatases, namely, chemical probe development and drug development. These two processes initially seem to be rather similar and while they do overlap, the stated goals of the two approaches at project initiation are distinct.