Autophagy inhibition sensitizes multiple myeloma cells to 17-dimethylaminoethylamino-17-demethoxygeldanamycin-induced apoptosis

The Hsp90 inhibitor 17DMAG (17-dimethylaminoethylamino-17-demethoxygeldanamycin) is currently undergoing clinical trials as an antitumor drug. We show here that treatment of human multiple myeloma (MM) cells with 17DMAG induces mTOR inhibition and microtubule-associated protein light chain 3 (LC3) conversion (LC3-I to LC3-II), an indicator of autophagy. Interestingly, 17DMAG synergistically induces apoptosis through a mitochondria-operated pathway in the presence of the autophagy inhibitor 3-methyladenine (3-MA). Inhibition of autophagy by 3-MA facilitated caspase activation, cytochrome c release from mitochondria and poly (ADP-ribose) polymerase (PARP) cleavage in myeloma cells treated with 17DMAG. The potential use of Hsp90 and autophagy inhibitors combinations as a therapeutic tool in MM is further discussed in our work.