OBJECTIVES: The contribution of overexpressed microRNA-21 and -221 (miR-21 and 
miR-221) to the malignant phenotype was determined by inhibiting these miRNAs 
using antisense oligonucleotides.
METHODS: The effects of antisense to miR-21 and miR-221 on cell proliferation, 
cell cycle arrest, induction of apoptosis, combinatorial effects with 
gemcitabine, and effects on target protein levels were studied.
RESULTS: Low nanomolar concentrations of both antisense oligonucleotides reduced 
proliferation of pancreatic cancer cell lines. Reduced proliferation was less 
pronounced in the normal ductal epithelial cell line human pancreatic 
Nestin-expressing cell or in pancreatic cancer cell lines exposed to an 
irrelevant control oligonucleotide. Inhibition of miR-21 and miR-221 increased 
the amount of apoptosis in HS766T cells by 3- to 6-fold compared with the 
control oligonucleotide. HS766T cells exposed to miR-21 antisense resulted in 
cell cycle arrest (G1 phase). Protein levels of tumor suppressor targets of the 
miRNAs were increased by antisense to miR-21 (PTEN and RECK) and miR-221 (p27). 
Antisense to miR-21 and miR-221 sensitized the effects of gemcitabine, and the 
antisense-gemcitabine combinations were synergistic at high fraction affected.
CONCLUSIONS: We demonstrate that antisense to miR-21 and miR-221 results in 
significant cell killing under various conditions and that antisense 
oligonucleotides targeted to miRNA represents a potential new therapy for 
pancreatic cancer.