Thermal shift assay: CTD or NTD of r-Hsp90α (5 µM) protein and the indicated concentrations of the inhibitors were mixed together in the assay buffer (1X PBS, pH = 7.5) and were incubated for 2h. Then, 6X SYPRO Orange dye (Sigma-Aldrich) was added to the mixture (20 µl), which binds to the exposed hydrophobic residues of unfolded protein (during thermal exposure) and thereby showing an increase fluorescence. 96-well polymerase chain reaction (PCR) plates, and a PCR system (BioRad, CFX Connect™ Real-time system) were used to heat the samples from room temperature to 95 °C in increments of 0.5 °C for 10 seconds, with excitation wavelength at 470 nm and emission wavelength at 570 nm. For determination of protein melting temperature values (Tm), melting curve for each data set was analysed by GraphPad Prism 8.0.2 and fitted with the sigmoidal Boltzmann fit. Melting temperatures without the inhibitors were used as control.