Tanespimycin (17-AAG) is a potent HSP90 inhibitor with an IC50 of 5 nM, having a 100-fold higher binding affinity for tumour cell derived HSP90 than normal cell derived HSP90[1][5]. Tanespimycin depletes cellular STK38/NDR1 and reduces STK38 kinase activity. Tanespimycin also downregulates the stk38 gene expression[3].