retaspimycin hydrochloride (also known as ipi-504), a hydroquinone hydrochloride salt derivative of 17-aag, is a novel, potent and selective inhibitor of heat shock protein 90(hsp90) that binds to the amino-terminal atp/adp-binding site of hsp90. as a highly water-soluble version of 17-aag, ipi-504 (solubility > 200 mg/ml) does not need prior dissolution in organic solvents and hence can be delivered in high concentrations. once in the systemic circulation, ipi-504 is deprotonated and converted into the free base ipi-504 which is subsequently oxidized to 17-aag. ipi-504 potently inhibits proliferation in several tumor cell lines with 50% inhibition concentration ic50 values ranging from 10-40 nmol/l and has been used for the treatment of gastrointestinal stromal tumors, soft-tissue sarcomas and non-small cell lung cancer.britt erika hanson and david h vesole. retaspimycin hydrochloride (ipi-504): a novel heat shock protein inhibitor as an anticancer agent. expert opin. investi. drugs (2009) 18(9): 1375-1383david siegel, sundar jagannath, david h. vesole, ivan borello, amitabha mazumder, constantine mitsiades, jill goddard, joi dunbar, emmanuel normant, julian adams, david grayzel, kenneth c. anderson and paul richardson. a phase 1 study of ipi-504 (retaspimycin hydrochloride) in patients with relapsed or relapsed and refractory multiple myeloma. leukemia & lymphoma, 2011; 52(12): 2308-2315ching ching leow, jon chesebrough, karen t. coffman, christine a. fazenbaker, john gooya, david weng, steve coats, dowdy jackson, bahija jallal and yong chang. antitumor efficacy of ipi-504, a selective heat shock protein 90 inhibitor against human epidermal growth factor receptor 2-positive human xenograft models as a single agent and in combination with trastuzumab or lapatinib. mol cancer ther 2009; 8: 2131-2141
