title: Smac/DIABLO enhances the therapeutic potential of chemotherapeutic drugs and irradiation, and sensitizes TRAIL-resistant breast cancer cells.
abstract: BACKGROUND
  Drug resistance is a major concern in cancer therapy. Here, we investigate the clinical potential of the second mitochondria-derived activator of caspase (Smac/DIABLO) in enhancing the apoptosis-inducing potential of commonly used anticancer drugs (paclitaxel, doxorubicin, etoposide, tamoxifen), irradiation and TRAIL in breast carcinoma.
  
  
  METHODS
  Breast cancer cells were overexpressed with Smac/DIABLO gene (full-length or Delta55 Smac/DIABLO) or treated with Smac/DIABLO peptide to enhance the apoptosis-inducing potential of chemotherapeutic drugs and irradiation, and sensitize TRAIL-resistant cells. Cell viability and apoptosis were measured by XTT assay and DAPI staining, respectively. Protein-protein interaction was determined by immunoprecipitation followed by the Western blot analysis.
  
  
  RESULTS
  Overexpression of Smac/DIABLO gene (full-length or Delta55 Smac/DIABLO) or treatment with Smac/DIABLO peptide enhances apoptosis induced by paclitaxel, doxorubicin, etoposide, tamoxifen, and irradiation in breast cancer cells. Overexpression of Smac/DIABLO resulted in an increased interaction of Smac/DIABLO with IAPs, which correlated with an increase in caspase-3 activity and apoptosis. Furthermore, Smac/DIABLO sensitized TRAIL-resistant breast cancer cell lines to undergo apoptosis through caspase-3 activation. These data suggest that apoptotic events down-stream of mitochondria were intact in TRAIL-resistant cells since ectopic expression of Smac/DIABLO or pretreatment of cells with Smac/DIABLO peptide completely restored TRAIL sensitivity.
  
  
  CONCLUSIONS
  The ability of Smac/DIABLO agonists to enhance the apoptosis-inducing potential of chemotherapeutic drugs and irradiation, and sensitize TRAIL-resistant tumor cells suggests that Smac/DIABLO may induce fundamental alterations in cell signaling pathways. Thus, Smac/DIABLO agonists can be used as promising new candidates for cancer treatment by potentiating cytotoxic therapies.
authors.affiliation: Department of Oncology, The Sidney Kimmel Comprehensive Cancer Center at Johns Hopkins, Baltimore, MD 21231, USA. tfandy@jhu.edu
authors.forename: Tamer E
authors.initials: TE
authors.lastname: Fandy
authors.forename: Sharmila
authors.initials: S
authors.lastname: Shankar
authors.forename: Rakesh K
authors.initials: RK
authors.lastname: Srivastava
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects; D001943:Breast Neoplasms / Q000235:genetics / Q000378:metabolism* / Q000473:pathology*; D053148:Caspase 3 / Q000378:metabolism; D045744:Cell Line, Tumor; D024161:Collagen Type XI / Q000378:metabolism; D019008:Drug Resistance, Neoplasm / Q000187:drug effects / Q000528:radiation effects; D004789:Enzyme Activation / Q000187:drug effects; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism*; D024101:Mitochondrial Proteins / Q000235:genetics / Q000378:metabolism*; D017319:Photosensitizing Agents / Q000494:pharmacology*; D011485:Protein Binding; D053221:TNF-Related Apoptosis-Inducing Ligand / Q000378:metabolism*
chemical_list: D000970:Antineoplastic Agents; D024161:Collagen Type XI; D047908:Intracellular Signaling Peptides and Proteins; D024101:Mitochondrial Proteins; D017319:Photosensitizing Agents; D053221:TNF-Related Apoptosis-Inducing Ligand; D053148:Caspase 3