In contrast to AUY922, the exposure of 5b on the K562 cells did not induce the expression of Hsp70, Hsp40, and Hsp27 involved in HSR (Figure ). Exposure of 5b to the leukemic cell lines (K562, KCL22 and HL60) inhibited their proliferation (SI Figure ) and induced apoptosis in a caspase 3/7 enzyme-dependent assay, with induction of approximately two-to eight-fold increase of apoptotic cells, in accordance to the reference Hsp90 CTD-targeting inhibitor, novobiocin (NB) (SI Figure ).