(560d) Acid-Degradable Polyketal Nanoparticles Carrying MnSOD siRNA to Restore Intrinsic Apoptosis in Tamoxifen-Resistant Breast Cancer Cells

Drug-resistance in cancer cells is a major cause of cancer relapse and eventually leads to failure of chemotherapy. RNA interference (RNAi) has been suggested to be a promising treatment option for supporting chemotherapy. RNAi can restore cancer cells’ sensitivity towards chemotherapeutic drugs by silencing the proteins responsible for increased resistance. Specifically, manganese superoxide dismutase (MnSOD), an enzyme which converts DNA-damaging reactive oxygen species (ROS) to less harmful ROS, has been known to be up-regulated in tamoxifen-resistant breast cancer cells. By silencing MnSOD, intrinsic apoptosis pathways can be recovered and re-sensitize cells to tamoxifen.

Despite immense potential, RNAi therapy is limited due to delivery issues especially for invivo applications. In order to develop safe and efficient siRNA carriers for invivo applications, an acid-degradable polyketal (PK) layer was introduced to poly(amidoamine) (PAMAM)/siRNA dendriplexes via surface-initiated photo-polymerization. The PK layer is hypothesized to provide the protection of siRNA as well as avoid detrimental aggregation in serum. An acid-degradable PK layer can also promote efficient escape from endosomal compartments. Photo-polymerization enables simple tuning of the shell thickness, thereby offering control over release kinetics.

siRNA-PAMAM/PK core-shell nanoparticles (NPs) were prepared with MnSOD-specific siRNAs. Resulting NPs showed narrow size distribution and avoided aggregation in serum contrary to dendriplex cores. Core-shell structure provided protection of siRNA from biological macromolecules and stimuli-responsive release. Intracellular trafficking by confocal laser scanning microscopy showed efficient release from endosomal compartments as hypothesized. Invitro transfection in tamoxifen-resistant breast cancer cell line MCF7-BK-TR demonstrated that delivery of MnSOD-siRNA resulted in knockdown of MnSOD levels and reversed tamoxifen-resistance. Moreover, inclusion of NPs in the transplanted tamoxifen-resistant tumor model significantly suppressed the growth of the tumor. Recovery of apoptotic activity in tumors treated with NPs was confirmed by Annexin-V staining, TUNEL staining, and cleaved Caspase-7 immuno-blotting.

In conclusion, acid-degradable polyketal nanoparticles were prepared to complex and protect siRNA from biological macromolecules and promote efficient intracellular trafficking. Our novel in vivo model with tamoxifen-resistant breast cancer demonstrates the reversal of drug resistance by MnSOD knockdown, proving the pre-clinical significance of this study.