An orally bioavailable formulation of the ansamycin derivative 17-amino-17-demethoxygeldanamycin (17-AG) with potential antineoplastic activity. Oral Hsp90 inhibitor IPI-493 binds to and inhibits Hsp90, which may result the in growth inhibition in sensitive tumor cell populations. Hsp90, a 90 kDa molecular chaperone, may be highly expressed in tumor cells, playing a key role in the conformational maturation, stability and function of other substrate or "client" proteins within the cell; many of these client proteins are involved in signal transduction, cell cycle regulation and apoptosis, and may include kinases, transcription factors and hormone receptors.