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Yoko Yoshida, Atsuko Kasai, Takeshi Izuhara, Kengo Sumi, Masaki Hori, Hiroyoshi Hidaka; An anti-glaucoma agent, H-1129, binds to middle domain of Hsp90. Invest. Ophthalmol. Vis. Sci. 2012;53(14):5018.
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© ARVO (1962-2015); The Authors (2016-present)
Our novel isoquinolinesulfonamide, H-1129, which produced intraocular pressure (IOP) lowering effect, was first reported (ARVO2012 abstract Hidaka et al.) to bind Hsp90 (heat shock protein 90). To investigate the target protein of H-1129, we screened binding proteins of H-1129 by using Drug-Western method. We also determined binding site of H-1129 on Hsp90. Many Hsp90 inhibitors have already been reported to be anti-cancer agents (17-AAG, 17-DMAG, BIIB021 and NVP-AUY922) (Oncol Rep, 23: 1483-1492, 2010; Curr Opin Pharmacol, 8: 370-374, 2008). We tried to explain why these Hsp90 binding anti-cancer agents could not reduce IOP.
Binding proteins of H-1129 was screened by Drug-Western method established by Hidaka and his associates (Mol Pharmacol, 55: 356-363, 1999). H-1129 labeled with FLAG peptide was used for detection of binding H-1129 to Hsp90. ELISA (Enzyme-linked immunosorbent assay) was employed for measurement of binding affinity of H-1129 to Hsp90. Various fragments of Hsp90 with different length were prepared from E.coli.
Hsp90α was found to be a target of H-1129 by Drug-Western method. The binding site of H-1129 was identified at middle domain of Hsp90. On the other hand, anti-cancer agents such as 17-AAG, 17-DMAG, BIIB021 and NVP-AUY922, were reported to bind N-terminal. The effect of these anti-cancer agents on IOP was examined by using rabbits. Single administration of all anti-cancer agents used failed to reduce IOP by 1.0%.
H-1129 binding domain to Hsp90α is completely different from the binding site of anti-cancer agents. Consistent with this difference, any anti-cancer drugs which we tested cannot lower IOP of rabbits. N-terminal of Hsp90 contained ATP-binding site, but middle domain was not related to direct binding of ATP. It was reported that middle domain was essential for the binding to glucocorticoid receptor (Proc Natl Acad Sci USA, 90: 11424-11428, 1993; Mol Cell Biol, 15: 3917-3925, 1995). It is likely that H-1129 produces IOP lowering effect through Hsp90.
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