Doxorubicin sensitizes Dex-sensitive (MM-1S) and Dex-resistant (MM-1R) cells, as well as Dox-sensitive (RPMI-8226/S) and Dox-resistant (Dox40) cells, to TRAIL.

MTT colorimetric assays demonstrate that pretreatment with Dox, as described in “Materials and methods,” enhances the TRAIL sensitivity of MM cells, including MM cells resistant to apoptosis induced by Dex (MM-1R) or Dox (Dox40).