In the peripheral blood leukocytes (PBLs) from the carriers of the human T-lymphotropic virus type-1 (HTLV-1) or the patients with
adult T-cell leukemia (ATL),
nuclear factor kappaB (NF-κB)-mediated antiapoptotic signals are constitutively activated primarily by the HTLV-1-encoded
oncoprotein Tax. Tax interacts with the I κB
kinase regulatory subunit NEMO (NF-κB essential modulator) to activate NF-κB, and this interaction is maintained in part by a
molecular chaperone,
heat-shock protein 90 (HSP90), and its co-chaperone cell division cycle 37 (CDC37). The
antibiotic geldanamycin (GA) inhibits HSP90's
ATP binding for its proper interaction with client
proteins. Administration of a novel water-soluble and less toxic GA derivative, 17-dimethylaminoethylamino-17-demethoxygeldanamycin hydrochloride (17-DMAG), to Tax-expressing ATL-transformed cell lines, C8166 and MT4, induced significant degradation of Tax.
17-DMAG also facilitated growth arrest and cellular apoptosis to C8166 and MT4 and other ATL cell lines, although this treatment has no apparent effects on normal PBLs.
17-DMAG also downregulated Tax-mediated intracellular signals including the activation of NF-κB,
activator protein 1 or HTLV-1 long terminal repeat in Tax-transfected HEK293 cells.
Oral administration of
17-DMAG to ATL model mice xenografted with lymphomatous transgenic Lck-Tax (Lck proximal promoter-driven Tax transgene) cells or HTLV-1-producing
tumor cells dramatically attenuated aggressive infiltration into multiple organs, inhibited de novo viral production and improved survival period. These observations identified
17-DMAG as a promising candidate for the prevention of ATL progression.