Wortmannin, PI3K inhibitor

Two well known and isoform unselective PI3K inhibitors are the fungal metabolite wortmannin (compound 7, Fig. 3) and LY294002 (compound 8, Fig. 3). These two compounds have served as powerful research tools for more than a decade to elucidate the role of PI3Ks in human tumorigenesis and evaluate the potential utility of PI3K inhibitors as cancer therapeutics. 

Using wortmannin as a model, broad-spectrum PI3K inhibitors with improved pharmaceutical properties and therapeutic indexes have been reported in recent pubhcations. PWT-458 (compound 10, Fig. 3), which is a pe-gylated derivative of wortmannin, was shown to inhibit PI3K signaling and hold a higher therapeutic index over its parent compoimd when used in sev-... 

Membrane activity is accompanied by cellular motility, characterized by extension and withdrawal of cell projections, unaccompanied by significant translational movement. Although this cellular motility program is initiated by MSP, it persists for at least 2 hr without a requirement for continuing MSP stimulation. This conclusion is based on the fact that MSP action is dependent on PI3K, and can be prevented by prior administration of the PI3K inhibitor wortmannin. However, once MSP induces the cellular motility pattern, addition of wortmannin has no effect. 

Due to the homology between PI3K and the PIKKs, most notably mTOR, many PI3K inhibitors also inhibit mTOR. Two prototypical PI3K inhibitors have been used extensively as pharmacological tools the natural product, irreversible inhibitor wortmannin ((38), Figure 6.16) and the reversible inhibitor LY294002 (40), a derivative of the natural product quercetin. 

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]. 

The first example of an irreversible inhibitor is the natural product Wortmannin, which was isolated from Penicillium wortmannii [30], Wortmannin effectively inhibits PI3K at low nanomolar concentration and was shown to be specific across a large panel of kinases [31]. Covalent attachment to PI3K occurs after attack by Lys-883, which is essential for phosphate transfer (see Section 7.2), at the furan ring of Wortmannin [32], Attack at this ring specifically occurs within the catalytic site of the PI3K kinase and is unaffected by nucleophiles in aqueous solution. 

Most PI3Ks (including Class 1 and Ig) are inhibited by a fungal toxin, wortmannin, and the structurally unrelated inhibitor LY294002. These compounds are potent inhibitors of chemoattractant-induced degranulation and oxidant production by neutrophils although phospholipase C activation and the cytosolic calcium increase are not... 

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