A water soluble analogue of the diterpenoid triepoxide triptolide isolated from the Chinese herb Tripterygium wilfordii Hook F with potential antineoplastic activity. Upon intravenous administration, the triptolide analogue inhibits heat shock protein 70 (HSP70) and prevents HSP70-mediated inhibition of apoptosis. This leads to both the induction of apoptosis and a reduction of cancer cell growth. HSP70, a molecular chaperone upregulated in various cancer cells, plays a key role in the inhibition of caspase-dependent and -independent apoptosis.