Geldanamycin-FITC, a Geldanamycin fluorescent probe, can be used in a fluorescence polarization assay for HSP90 inhibitors. Geldanamycin-FITC also can be used for detection of cell surface HSP90[1][2][3].
The HSP90 inhibitor Geldanamycin, when conjugated with FITC (GA-FITC) is cell-membrane impermeable, binding only cell surface HSP90 and inhibiting its functions but having no effect on cytosolic HSP90[3].
[1]. Kim J, et al. Development of a fluorescence polarization assay for the molecular chaperone Hsp90. J Biomol Screen. 2004;9(5):375‐381.
[2]. Posfai D, et al. Identification of Hsp90 Inhibitors with Anti-Plasmodium Activity. Antimicrob Agents Chemother. 2018;62(4):e01799-17. Published 2018 Mar 27.
[3]. Imai T, et al. Heat shock protein 90 (HSP90) contributes to cytosolic translocation of extracellular antigen for cross-presentation by dendritic cells. Proc Natl Acad Sci U S A. 2011;108(39):16363‐16368.