The heat shock protein 90 (Hsp90) is a molecular chaperone that activates and maintains the biological functioning of several client proteins, many of which are associated with oncogenic signaling pathways. Its activity is driven by ATP and regulated by co-chaperones such as Hsp72. CCT018159 is a 3,4-diaryl pyrazoloresorcinol compound that inhibits the ATPase activity of Hsp90 with IC50 values of 3.2 and 6.6 µM for human Hsp90β and yeast Hsp90, respectively.At concentrations up to 100 µM, CCT018159 does not inhibit human Hsp72 ATPase or topoisomerase II, yet at 50 µM CCT018159 inhibits 13 out of a panel of 20 commonly studied kinases.In human tumor xenografts, such as SKMEL 28 melanoma cells, CCT018159 induces Hsp72 expression and decreases the expression of oncogenic client proteins such as C-RAF, ERBB2, and Cdk4.