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PD168393 is an irreversible kinase inhibitor of epidermal growth factor receptor (EGFR) with IC50 value of 0.70±0.09 nM and continued to have suppressed kinase activity after 8 hr in compound-free medium.[1]

The epidermal growth factor receptor (EGFR; ErbB-1; HER1 in humans) is the cell-surface receptor for members of the epidermal growth factor family (EGF-family) of extracellular protein ligands. Upon activation by its growth factor ligands, EGFR undergoes a transition from an inactive monomeric form to an active homodimer.[2] In addition to forming homodimers after ligand binding, EGFR may pair with another member of the ErbB receptor family to create an activated heterodimer. EGFR dimerization stimulates its intrinsic intracellular protein-tyrosine kinase activity. [3] As a result, autophosphorylation of several tyrosine (Y) residues in the C-terminal domain of EGFR occurs which elicits downstream activation and signaling by several other proteins that associate with the phosphorylated tyrosines through their own phosphotyrosine-binding SH2 domains. These downstream signaling proteins initiate several signal transduction cascades, principally the MAPK, Akt and JNK pathways, leading to DNA synthesis and cell proliferation.[4]

Mutations that lead to EGFR overexpression or overactivity have been associated with a number of cancers, thus many therapeutic approaches are aimed at the EGFR now. PD 168393 can poss a high specificity toward the EGFr with Cys-773 which  inhibit the EGFR tyrosine kinase, which is on the cytoplasmic side of the receptor. Without kinase activity, EGFR is unable to activate itself, which is a prerequisite for binding of downstream adaptor proteins. Ostensibly by halting the signaling cascade in cells that rely on this pathway for growth, tumor proliferation and migration is diminished.[5]

PD168393 can enhance paclitaxel-induced DNA fragmentation, sub-G1 fraction accumulation, mitochondrial membrane dysfunction, cytochrome C release, caspase-3 activation and eventually apoptosis in vitro by MTT assay and median-effect analysis. In conclusion, the combination of paclitaxel and PD168393 produced a profound synergistic growth inhibition of AIPC cells,resulting in clinical benefits and warrants further investigation.[6]

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