siRNA-Mediated Down-Regulation of P-glycoprotein in a Xenograft Tumor Model in NOD-SCID Mice
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The efficacy of chemotherapy is decreased due to over-expression of the drug transporter P-glycoprotein (P-gp). This study was conducted to determine the feasibility of down-regulating tumor P-gp levels with non-viral siRNA delivery in order to sensitize the tumors to drug therapy.
P-gp over-expressing MDA435/LCC6 MDR1 cells were used to establish xenografts in NOD-SCID mouse. Cationic polymers polyethylenimine (PEI) and stearic acid-substituted poly-L-lysine (PLL-StA) were formulated with P-gp- specific siRNAs and delivered intratumorally to explore the feasibility of P-gp down-regulation in tumors. Intravenous Doxil™ was administered to investigate tumor growth.
PEI and PLL-StA effectively delivered siRNA to MDA435/LCC6 MDR1 cells in vitro to reduce P-gp expression for 3 days. Intratumoral injection of siRNA with the carriers resulted in 60-80% and 20–32% of siRNA retention in tumors after 24 and 96 hr, respectively. This led to ~29.0% and ~61.5% P-gp down-regulation with PEI- and PLL-StA-mediated siRNA delivery, respectively. The P-gp down-regulation by intratumoral siRNA injection led to better response to systemic Doxil™ treatment, resulting in slowed tumor growth in originally doxorubicin-resistant tumors.
Effective P-gp down-regulation was feasible with polymeric siRNA delivery in a xenograft model, resulting in an enhanced response to the drug therapy.
KEY WORDSmultidrug resistance non-viral siRNA delivery P-glycoprotein polymeric biomaterials xenograft
Hank’s Balanced Salt Solution
multi-drug resistance gene 1 expressing cells
non-obese/severe combined immunodeficient
stearic acid substituted poly-L-lysine
short interfering RNA
ACKNOWLEDGMENTS & DISCLOSURES
Financial support for this project was provided by the Natural Sciences and Engineering Council of Canada (NSERC) and Canadian Institutes of Health Research (CIHR). Equipment support was provided by the Alberta Heritage Foundation for Medical Research (AHFMR) and Alberta Advanced Education & Technology. We thank Ms. Vanessa Incani for preparing the lipid-substituted PLL-StA, and Dr. Richard Clarke (Georgetown University, DC, USA) for the cell line used for this study.
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