Design, synthesis and biological application of affinity-based small molecular probe for Hsp90 endoplasmic reticulum paralogue of Grp94

Glucose-regulated protein 94(Grp94), an endoplasmic reticulum resident Hsp90 paralog, has a limited set of client proteins. Selective inhibition of Grp94 has emerged as a new direction for the development of drugs targeting the Hsp90 chaperone system. Now Grp94-Probe, an affinity-based probe of Grp94, was designed and synthesized based on DDO-5813, a most potent Grp94-selective inhibitor we found previously. Using fluorescence polarization(FP)assay and double staining assay with ER-Red in cells, we confirmed the binding of Grp94-Probe with ER Grp94. The FR results showed that the probe exhibited high affinity for Grp94^N(EC₅₀=117. 9 nmol/L)without exhibiting obvious Hsp90α inhibition, Moreover, as a fluorescence probe molecule, Grp94-Probe could better distinguish the inhibitory activity of compounds for Grp94^N. The results of fluorescence analysis in cells showed that Grp94-Probe could co-stain with ER-Red in the endoplasmic reticulum, and the fluorescence did not decay rapidly with time after 4 h of staining, which further indicated the binding of Grp94-Probe with Grp94 in cells. This Grp94 selective probe can be further used for biology evaluation of Grp94 inhibitor and exploration of Grp94 biological functions.