Protein kinase family inhibitor selectivity

One of the current approaches to the treatment of cancer involves the disruption of kinase activity and signal transduction pathways. For example, protein kinase C (PKC) plays a crucial role in signal transductions, cellular proliferation, and differentiation. PKC is the term for a whole family of cytosolic serine/threonine kinases. Phenylamino-pyrimidines like 3- 4-[2-(3-chlorophenylamino)-pyrimidin-4-yl]pyridin-2-yl-amino propanol (159, CGP 60474) represent a promising class of inhibitors of PKC with a high degree of selectivity versus other serine/threonine and tyrosine kinases and show competitive kinetics relative to ATP. Analogs of CGP 60474 were synthesized as useful models for the evaluation of structure-activity relationships of phenylamino-pyrimidine-type protein kinase C inhibitors. 

In mammalian cells, there are multiple forms of enzymes within the same family, e.g., protein kinase C, phospholipase C, and caspase. A selective assay system would be instrumental in such cases to advance understanding of the respective role for each form within the same enzyme family. An example for design of a selective assay system for the superfamily of phospholipase A2 is provided in this chapter. Such a selective assay system may play a signihcant enabling role for PLA2 and other enzyme families in the discovery of inhibitors relevant to the treatment of pathologies involving those enzymes. 

The probes of this type were shown to selectively label at least 75% of human kinases in crude cell lysates, thus demonstrating their selectivity and promiscuity for kinases [101]. As a follow up, the labeled kinases were subjected to proteolytic digestion, and the biotinylated peptides purified on avidin beads and analyzed by LC-MS/MS. This analysis demonstrated that the site of probe labeling was indeed the conserved active-site lysine as predicted. In contrast to the promiscuity demonstrated by the acyl phosphate probes, several selective covalent inhibitors of protein kinases have been used as ABPP probes. Wortmannin is a natural product derived from the fungus Penicillium funiculosum. It is a potent and specific covalent inhibitor of phosphoinositide 3-kinase (PI3K) and the PI3K-related kinase (PIKK) families [102, 103]. The use of natural products in relation to ABPP is covered by Breinbauer et al. [104]. 

A method of treating aberrant cellular proliferation disorders by the selective inhibition of the tyrosine family of protein kinases (TrkA, TrkB, and TrkC) using oxindole derivatives is described. This novel chemical art is an improvement over the existing treatment agents in that the materials are selective tyrosine kinase inhibitors and are prepared in one step. 

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