Protein kinase B inhibitors

Other azepane derivatives of interest include some protein kinase B inhibitors <2004JME1375>, and 3-(acylamino)-azepan-2-ones as metabolically-resistant broad spectrum chemokine inhibitors <2005JME867>. 

Protein kinase B uses ATP to phosphorylate other enzymes. Controlling protein kinase B is a method of influencing many cellular processes, including cell division in cancer cells. A virtual screen for protein kinase B inhibitors started with an x-ray structure of protein kinase B bound to AMP-PNP (10.32), an unreactive analog of ATP, and a peptide substrate (Figure 10.8). A collection of... 

Chiral Lewis bases catalyse hydrosilylation of (V-(l,2-diarylethylidene)-arylamines in CH2CI2 using HSiCl3 to form the corresponding 1,2-diarylethanamines in yields up to 99% and up to 98% ee. One of the products has been employed in the synthesis of a protein kinase B inhibitor. 

Lali, F. V., Hunt, A. E., Turner, S. J., and Foxwell, B. M. (2000). The pyridinyl imidazole inhibitor SB203580 blocks phosphoinositide-dependent protein kinase activity, protein kinase B phosphorylation, and retinoblastoma hyperphosphorylation in interleukin-2-stimulated T cells independendy ofp38 mitogen-activated protein kinase. J. Biol. Chem. 275, 7395-7402. 

Rotenberg, S.A., Calogeropoulou, T., Jaworski, J., Weinstein, I.B., and Rideout, D.A. (1991) Self-assembling protein kinase C inhibitor. Proc. Natl. Acad. Sci. USA 88, 2490-2494. 

An application of this synthetic strategy by the same group led to the development of a series of potent and selective allosteric Akt (protein kinase B/PKB) kinase inhibitors that induced apoptosis in tumor cells and inhibited Akt phosphorylation in vivo (Scheme 6.261) [451]. 

Figure 6.14. Kinetics of 02 secretion by activated neutrophils. Neutrophil suspensions (5 x 10s/ml) were suspended in RPMI 1640 medium containing 75 /JM cytochrome c. In (b) and (d), suspensions contained 100 nM staurosporine. At time zero, suspensions in (a) and (b) were stimulated by the addition of 1 /iM fMet-Leu-Phe, whilst suspensions in (c) and (d) were stimulated by the addition of 0.1 fi g/ml PM A. Reference cuvettes were identical to the sample cuvettes, but additionally contained 30 jUg/ml SOD. The bar marker represents a A4 of 0.03 in (a) and (b), or 0.08 in (c) and (d). Similar results were obtained using the more specific protein kinase C inhibitor, bisindolylmaleimide.

It is known that protein kinase C can phosphorylate a number of key oxidase components, such as the two cytochrome b subunits and the 47-kDa cytoplasmic factor. This process is prevented by protein kinase C inhibitors such as staurosporine (although it is now recognised that this inhibitor is not specific for protein kinase C), which also inhibits the respiratory burst activated by agonists such as PMA. However, when cells are stimulated by fMet-Leu-Phe, translocation of pAl-phox to the plasma membrane can occur even if protein kinase C activity is blocked - that is, phosphorylation is not essential for the translocation of this component in response to stimulation by this agonist. Similarly, the kinetics of phosphorylation of the cytochrome subunits do not follow the kinetics of oxidase activation, and protein kinase C inhibitors have no effect on oxidase activity elicited by some agonists -for example, on the initiation of the respiratory burst elicited by agonists such as fMet-Leu-Phe (Fig. 6.14). Furthermore, the kinetics of DAG accumulation do not always follow those of oxidase activity. Hence, whilst protein kinase C is undoubtedly involved in oxidase activation by some agonists, oxidase function is not totally dependent upon the activity of this kinase. 

Triciribine, also known as Akt/protein kinase B signaling inhibitor-2 (API-2) compound 52, Fig. 9), was identified by screening the National Cancer Institute Diversity Set chemical library (1992 compounds). The screen was performed using a cell-based proliferation assay with PKB/1 transformed NIH3T3 cells, and triciribine scored positive in this assay with an IC50 value of 50 nM [ 196]. Although the compound blocks the cellular phosphorylation... 

Chambers TC, Zheng B, Kuo JF (1992) Regulation by phorbol ester and protein kinase C inhibitors, and by a protein phosphatase inhibitor (okadaic acid) of P-glycoprotein phosphorylation and relationship to drug accumulation in multidrug-resistant human KB cells. Mol Pharmacol 41 1008-1015... 

B-Cell epitope mapping (foot-and-mouth disease, TMV antigen, shrimp allergen) T-Cell epitope mapping (type 1 diabetes, alloreactive T-cell) protein kinase substrate/inhibitor (protein kinase I) MHC class I molecule binding peptides and epitope mapping for monoclonal and polyclonal antibodies. 

The regulation of eNOS activity by phosphorylation is a well documented subject as the eNOS protein possess several consensus sequences for phosphorylation by protein kinase A (PKA), protein kinase C (PKC), protein kinase B (Akt/PKB) and AMP-activated protein kinase (AMPK). The eNOS enzyme has been reported to be phosphorylated on threonine, serine and t50 osine residues in response to various agonists. Many studies have shown that phosphorylation of eNOS on serine 1177 leads to an activation of eNOS [26-29], whereas phosphorylation on threonine 495 inactivates eNOS as this site is in the Ca Vcalmodulin binding domain [26]. Fleming et al. (2001) demonstrated that bradykinin (100 nM) increased eNOS activity in both porcine coronary artery endothelial cells (PCAE) and HUVEC via dephosphorylation of threonine 495 and phosphorylation of serine 1177 [30]. The bradykinin-induced phosphorylation of serine 1177 was abolished in the presence of a calmodulin dependent kinase II inhibitor whilst the dephosphorylation of threonine 495 was abolished by a protein phosphatase I inhibitor [30]. Harris et al. (2001) documented in BAEC that bradykinin (1 pM)-induced eNOS activity was mediated by activation of Akt/PKB [31] (see section 1.2.2) resulting in NOS phosphorylation at serine 1179 (bovine sequence) and a de-phosphorylation at threonine 497 mediated by calcineurin phosphatase. Typically, phosphorylation of eNOS at either of these sites is coordinated with dephosphorylation at the alternate site. 

Zimmermann ML, Sneden AT. Vanicosides A and B, protein kinase C inhibitors from Polygonum pensylvanicum. J Nat Prod 1994 57(2) 236-42. 

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