A benzoquinone antineoplastic antibiotic derived from the antineoplastic antibiotic geldanamycin. Tanespimycin binds to and inhibits the cytosolic chaperone functions of heat shock protein 90 (HSP90). HSP90 maintains the stability and functional shape of many oncogenic signaling proteins; the inhibition of HSP90 promotes the proteasomal degradation of oncogenic signaling proteins that may be overexpressed by tumor cells. or A substance being studied in the treatment of cancer. It is made from an antibiotic called geldanamycin. Tanespimycin helps cause the breakdown of certain proteins in the cell, and may kill cancer cells. It is a type of antineoplastic antibiotic and a type of HSP90 inhibitor. Also called 17-AAG and 17-N-allylamino-17-demethoxygeldanamycin.