Promiscuous kinases

Non-selective PKB inhibitors have been extensively used as tool compounds to elucidate the role of this kinase in the biology of human cancers. Thus, PKB isoforms are potently inhibited by promiscuous kinase inhibitors like staurosporine (compound 22, Fig. 5 IC50 = 48 to 11 nM for PKBa) [131-133] and derivatives thereof (e.g., compound 23, Fig. 5) [134]. Another example of a potent and non-selective pan-PKB inhibitor is Ro-31-8220 (compound 24, Fig. 5), a PKC inhibitor (IC50 = 10 nM) [135] that also interferes with PKB kinase activity (IC50 = 240 nM for PKBa). 

Where a preferential enzyme substrate, e.g. for a protein kinase, is to be enriched, it is only the modified (e.g. phosphorylated phage, Ref. 42) phage which is selected. This modified ligand phage can, for instance, be enriched on an antibody, which can be immobilized in vast excess. In this case the enzyme need only be present in trace catalytic amounts, and indeed a limiting concentration of the enzyme is necessary to distinguish the preferred substrate for promiscuous kinases [43],... 

Zhang X, Crespo A, Femindez A (2008) Trung promiscuous kinase inhibitors into safer drugs. Trends Biotechnol 26 295-300... 

The safety of less selective dmgs, and especially that of promiscuous kinase inhibitors, is often addressed by assessing the full extent of their cross-reactivity [19], This assessment has been facilitated by novel high-throughput screening... 

Several researchers have exploited the wealth of crystal structures of kinase inhibitor complexes to build protein-based pharmacophores for this target class (20). Aronov and Murcko (21) considered the crystal structures of four promiscuous kinase inhibitors, i.e., inhibitors with an affinity of at least 2 pM on five representative kinases. After aligning the structures of the four proteins, they assigned pharmacophoric features to the bound inhibitors, which led to the identification of five clusters of pharmacophoric features. These served to define a five point pharmacophore for kinase frequent hitters (Fig. la). This pharmacophore could discriminate frequent hitters from selective kinase inhibitors. Recently, McGregor (22) aligned 220 kinase crystal structures from the PDB and assigned one of seven possible pharmacophoric types to each atom of the bound ligands. 

Fig. 1. Pharmacophores for (a) promiscuous kinase inhibitors, (b) type II kinase inhibitors.

In vitro glycorandomization (TVG) is a chemoenzymatic method that uses substrate-flexible anomeric sugar kinases and Ntfs to convert diverse sugars into their NDP-activated forms [21], The ability to enhance the promiscuity of these two... 

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 response of cytosolic kinases to the input signal can be regulated by monomeric G proteins. An example is the control of the Raf-1 kinase in the MAP kinase cascade by the GTP/GDP on/off switch function of Ras. Signals passing through the Ras control point can be routed in different directions. The right of way is controlled by kinases. The specificity of the kinases overrules the coupling promiscuity of Ras, and other linkers. 

---