New Type Of Hsp90 Inhibitors Resisting Gastric Cancer And High-throughput Screening Mechanism Research Eif4e Inhibitors And Its Antitumor Effect

Heat shock protein90(Hsp90) is a molecular chaperone engaging in multiple cellular signaling by stabilizing oncoproteins (e.g., Akt and c-Raf) in tumor cells. Whereas Hsp90inhibitors such as17-AAG exert promising antitumor effects in clinical trials, current efforts focus on developing agents targeting Hsp90with improved efficacy and lower toxicity. Using a fluorescence polarization assay, over a hundred of synthetic small molecules were screened and a resorcinol derivative LD053that bound the Hsp90ATP-binding pocket effectively was identified. The binding of LD053to Hsp90dissociated the co-chaperone protein cdc37from Hsp90, resulting in destabilization of Akt and c-Raf and subsequent inhibition of PI3K/Akt and c-Raf/Mek/Erk signaling in BGC823gastric cancer cells. As a consequence, LD053decreased cancer cell viability and induced apoptosis evidenced by increased subGO/G1cell population and increased cleavage of caspase3and PARP. Interestingly, normal human cells appeared insensitive to LD053treatments. Consistent with its in vitro anticancer activities, LD053significantly inhibited growth of BGC823xenografts in nude mice without apparent body weight loss. These results thus demonstrate that LD053is a novel Hsp90inhibitor and has potential to be used to treat gastric cancer. Recent studies have demonstrated that cap-dependent translation initiated by the eIF4F complex is required for expression of a variety of oncogenic proteins including c-Myc, survivin, Cyclin D1, Mcl-1, VEGF. It is thus not surprising that cap-dependent translation is often elevated in human cancers. As a major component of the eIF4F initiation complex, eukaryotic translation initiation factor4E (eIF4E) is the rate-limiting factor for cap-dependent translation initiation and frequently overexpressed in cancers due to gene amplification and transcriptional upregulation. Down-regulation of eIF4E expression by siRNA or anti-sense oligonucleotides was shown to inhibit cancer cell growth and promote apoptosis without apparent toxicity. These results have generated increasing interests in the discovery of novel molecules targeting eIF4E-driven translation-initiation apparatus. Based on FRT-mediated homologous recombination, we developed a luciferase-based reporter assay that can be used to screen for small molecules inhibitory for eIF4E expression in a high-throughput manner. We screened the NCI Diversity-Set chemical library, and identified a small molecule, referred to as48F10, that significantly decreased the eIF4E mRNA level at lower micromolar concentrations in several kinds of breast cancer cells. As a consequence, this small molecule decreased the eIF4E protein level dose dependently, leading to reduced expression of survivin, cyclin D1, Mcl-1and c-Myc. Moreover, we found that this novel eIF4E inhibitor inhibited breast cancer cell growth and induced apoptosis sharply evidenced by increased cleavage of caspase3and PARP.48F10thus represents a novel class of eIF4E inhibitors that suppress cap-dependent translation through inhibiting eIF4E expression.