FS-108

Inhibition of heat shock protein (Hsp90) has been proven to be effective in overriding primary and acquired resistance of kinase inhibitors. In this study, we investigated the role of FS-108, a newly developed Hsp90 inhibitor, to overcome gefitinib resistance in EGFR mutant non-small cell lung cancer cells.

Cell proliferation was assessed using the SRB assay. Cell cycle distribution and apoptosis were analyzed by flow cytometry. Protein expression was examined by Western blotting. The in vivo effectiveness of FS-108 was determined in an NCI-H1975 subcutaneous xenograft model.

FS-108 triggered obvious growth inhibition in gefitinib-resistant HCC827/GR6, NCI-H1650 and NCI-H1975 cells through inducing G₂/M phase arrest and apoptosis. FS-108 treatment resulted in a remarkable degradation of key client proteins involved in gefitinib resistance and further abrogated their downstream signaling pathways. Interestingly, FS-108 alone exerted an identical or superior effect on circumventing gefitinib resistance compared to combined kinase inhibition. Finally, the ability of FS-108 to overcome gefitinib resistance in vivo was validated in an NCI-H1975 xenograft model.

FS-108 is a powerful agent that impacts the survival of gefitinib-resistant cells in vitro and in vivo through targeting Hsp90.

Fourteen of 21 naturally-occurring amino acids competitively inhibited the utilization of tryptophan for growth by an indole- or tryptophan-requiring strain of N. crassa (FS-108).Included in the group competitive with indole or tryptophan were: phenylalanine, leucine, methionine, norvaline, tyrosine, α-aminobutyric acid, norleucine, alanine, valine, glycine, threonine, serine, isoleucine, and asparagine.Growth on indole was neither enhanced nor inhibited by amino acids other than tryptophan.The uptake of tryptophan from the medium was inhibited by phenylalanine.The effects of amino acids on growth of this strain in media containing tryptophan can be explained by an inhibition of tryptophan uptake from the medium.