Novel targets for sensitizing breast cancer cells to TRAIL‐induced apoptosis with siRNA delivery

Tumor necrosis factor‐related apoptosis‐inducing ligand (TRAIL) induces apoptosis in variety of cancer cells without affecting most normal cells, which makes it a promising agent for cancer therapy. However, TRAIL therapy is clinically not effective due to resistance induction. To identify novel regulators of TRAIL that can aid in therapy, protein targets whose silencing sensitized breast cancer cells against TRAIL were screened with an siRNA library against 446 human apoptosis‐related proteins in MDA‐231 cells. Using a cationic lipopolymer (PEI‐αLA) for delivery of library members, 16 siRNAs were identified that sensitized the TRAIL‐induced death in MDA‐231 cells. The siRNAs targeting BCL2L12 and SOD1 were further evaluated based on the novelty and their ability to sensitize TRAIL induced cell death. Silencing both targets sensitized TRAIL‐mediated cell death in MDA‐231 cells as well as TRAIL resistant breast cancer cells, MCF‐7. Combination of TRAIL and siRNA silencing BCL2L12 had no effect in normal human umbilical vein cells and human bone marrow stromal cell. The silencing of BCL2L12 and SOD1 enhanced TRAIL‐mediated apoptosis in MDA‐231 cells via synergistically activating capsase‐3 activity. Hence, here we report siRNAs targeting BCL2L12 and SOD1 as a novel regulator of TRAIL‐induced cell death in breast cancer cells, providing a new approach for enhancing TRAIL therapy for breast cancer. The combination of siRNA targeting BCL2L12 and TRAIL can be a highly effective synergistic pair in breast cancer cells with minimal effect on the non‐transformed cells.