Stable XIAP knockdown in HCT116 colon cancer cells

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. Human HCT116 colon cancer cell lines were transfected with either XIAP (X) or luciferase (L) shRNA. The expression profiles of both were compared at early (p4) and late (p8) passage.