BACKGROUNDDeath receptor therapy induces apoptosis in different tumors but pancreatic cancer is resistant to this therapy. We have shown how triptolide decreases apoptosis resistance in pancreatic cancer. We hypothesized that triptolide increases the effectiveness of death receptor therapy in pancreatic cancer. Our aims were to evaluate the effects of combined therapy with triptolide and anti-Death Receptor 5 Antibody (anti-DR5Ab) on a) cell viability and apoptosis and b) anti-apoptotic protein expression in pancreatic cancer cells.METHODS5 pancreatic cancer cell lines were exposed to triptolide (0-400 nM), anti-DR5Ab (0-100 ng/ml), or both (triptolide 100 nM + anti-DR5Ab 12.5 ng/ml). We assessed the effects of both drugs on cell viability, apoptosis, caspase-3, -8 and -9 activity, PARP and BID cleavage. XIAP protein levels were measured after 24 hours of treatment.RESULTSPancreatic cancer cells were resistant to anti-DR5Ab. Combined therapy decreased cell viability, triggered apoptosis and caspase -3, -8 and -9 activity in all cell lines(Table) PARP and BID cleavage were only seen in combined therapy. Triptolide decreased XIAP levels, an inhibitor of caspase -3 and -9.(Figure)CONCLUSIONSTriptolide decreased XIAP protein levels. Pancreatic cancer cells are resistant to anti-DR5Ab but combined therapy with triptolide and anti-DR5Ab triggers apoptosis because it induces both apoptotic pathways. This effect is seen in anti-DR5 resistant cell lines.

Table 1. Effect of Anti-DR5Ab and Triptolide on apoptosis and caspase activity on pancreatic cancer cells
Cell line	Control		Anti-DR5Ab		Triptolide		Combined Therapy
	Apoptosis	Caspase Activity#	Apoptosis	Caspase Activity#	Apoptosis	Caspase Activity#	Apoptosis	Caspase Activity#
MiaPaCa2	9±1.9	-	14±0.7	+	24±6.6	+	65±5.1*	+++
Panc-1	10±2.1	-	9±2	+	27±2.9	+	61±3.1*	+++
S2013	11.5±5.1	-	10.46±3.2	-	22.7±5.8	+	60.2±5.1*	+++
S2VP10	3±1.9	-	4±2.5	-	6±2.9	-	59±3.1*	+++
ASPC-1	9.64±1.9	-	11.5±1.3	-	10.6±2.7	-	37.2±0.7*	+++
n=4. *p<.0001 compared to control or each drug alone. Date expressed as mean ± SEM# n=3 Indicates caspase 3, 8 and 9 activity.