Binding kinase inhibitors

The fact that the aliosterically preferred conformation may be relatively rare in the library of conformations available to the receptor may have kinetic implications. Specifically, if the binding site for the modulator appears only when the preferred conformation is formed spontaneously, then complete conversion to alios terically modified receptor may require a relatively long period of equilibration. For example, the allosteric p38 MAP kinase inhibitor BIRB 796 binds to a conformation of MAP kinase requiring movement of a Phe residue by 10 angstroms (so-called out conformation). The association rate for this modulator is 8.5 x 105 M-1 s-1, 50 times slower than that required for other inhibitors (4.3 x 107 M 1 s-1). The result is that while other inhibitors reach equilibrium within 30 minutes, BIRB 376 requires 2 full hours of equilibration time [8],... 

The most extensive development of pharmacological inhibitors of MAPK cascades members has been for p38 (Table 1) [3]. Small-molecule inhibitors have been developed for two p38 isoforms (a and (3). Pyridinyl imidazole compounds have been known to block inflammation since the early 1970s. Structural analyses have revealed that p38 kinase inhibitors binds to the ATP-binding pocket of p38 thereby acting as competitive inhibitors. The p38 kinase inhibitor SB202190 is able to bind both the low-activity nonphosphorylated... 

Poorly soluble brickdust compounds are not preferentially selected for by HTS as is the case with greaseballs. However, brickdust compounds are extremely common in certain popular current era targets, e.g. the ATP competitive hinge region binding site in protein kinase inhibitors. 

Fig. 1.6 The increase in potency of a 1.3 mM p38 a protein kinase-binding fragment inhibitor identified by X-ray screening through the major changes made to the chemical series to exploit key binding features within the active site.

Gleevec ) is a tyrosine kinase inhibitor used as first-line therapy in the majority of patients with CML. As a potent tyrosine kinase inhibitor, imatinib inhibits phosphorylation of various proteins involved in cell proliferation. Imatinib works by binding to the ATP-binding pocket of BCR-ABL.7 The drug induces complete hematologic responses in more than 95% of patients and complete cytogenetic responses in about 80% of patients in chronic phase.8 Most patients have traces of the disease when measured by RT-PCR and are not cured of their disease. 

The unbound fraction of the epidermal growth factor receptor tyrosine kinase inhibitor gefitinib has been extensively studied in cancer patients [39]. The drug was found to bind to serum albumin, oq-acid glycoprotein, and red blood cells with a mean unbound fraction of 3.4% which was constant over 28 days of dosing. Unbound fraction ranged from 2.2% to 5.4% and was inversely correlated with pre-treatment levels of oq-acid glycoprotein. 

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