Description
X-linked inhibitor of apoptosis (XIAP) is the most potent endogenous caspase inhibitor preventing cell death via caspase-9, -7 and -3 (initiator and executioner caspase pathways). Using short hairpin RNA (shRNA) against XIAP, stably expressed in a parent HCT116 human colon cancer cell line, a series of clones have been developed. XIAP mRNA levels were established by RT-PCR, the four X (XIAP knockdown) clonal cell lines show 82-93% reduction in XIAP mRNA when compared to the four L (luciferase control) cell lines. Immunoblot analysis showed a 67-89% reduction in XIAP protein in X cell lines compared to L. RNA was analysed by microarray and XIAP knockdown was confirmed in 7 probe sets, there was no significant compensation of other IAP family members. XIAP knockdown induced a 2-fold increase in the basal level of apoptosis without modification of caspase 3/7 activity. Finally, XIAP knockdown sensitises cells to radiotherapy by 20%, to recombinant TRAIL by a 3-fold factor, and to paclitaxel and docetaxel by >2 fold factor. Future work should focus on targeted agents such as rhTRAIL in combination with strategies to down regulate XIAP. XIAP antisense is now in clinical development in oncology.