pH-Responsive Polymeric siRNA Carriers Sensitize Multidrug Resistant Ovarian Cancer Cells to Doxorubicin via Knockdown of Polo-like Kinase 1

Abstract

Small interfering RNA (siRNA)-based therapies have great potential for the treatment of debilitating diseases such as cancer, but an effective delivery strategy for siRNA is elusive. Here, pH-responsive complexes were developed for the delivery of siRNA in order to sensitize drug-resistant ovarian cancer cells (NCI/ADR-RES) to doxorubicin. The electrostatic complexes consisted of a cationic micelle used as a nucleating core, siRNA, and a pH-responsive endosomolytic polymer. Cationic micelles were formed from diblock copolymers of dimethylaminoethyl methacrylate (pDMAEMA) and butyl methacrylate (pDbB). The hydrophobic butyl core mediated micelle formation while the positively-charged pDMAEMA corona enabled siRNA condensation. To enhance cytosolic delivery through endosomal release, a pH-responsive copolymer of poly(styrene-alt-maleic anhydride) (pSMA) was electrostatically complexed with the positively-charged siRNA/micelle to form a ternary complex. Complexes exhibited size (30–105 nm) and charge (slightly positive) properties important for endocytosis and were found to be non-cytotoxic and mediate uptake in >70% of ovarian cancer cells after 1 hour of incubation. The pH-responsive ternary complexes were used to deliver siRNA against polo-like kinase 1 (plk1), a gene upregulated in many cancers and responsible for cell cycle progression, to ovarian cancer cell lines. Treatment resulted in ∼50% reduction of plk1 gene expression in the drug-resistant NCI/ADR-RES ovarian cancer cell model and in the drug-sensitive parental cell line, OVCAR8. This knockdown functionally sensitized NCI/ADR-RES cells to doxorubicin at levels similar to OVCAR8. Sensitization occurred through a p53 signaling pathway, as indicated by caspase 3/7 upregulation following plk1 knockdown and doxorubicin treatment, and this effect could be abrogated using a p53 inhibitor. To demonstrate the potential for dual delivery from this polymer system, micelle cores were subsequently loaded with doxorubicin and utilized in ternary complexes to achieve cell sensitization through simultaneous siRNA and drug delivery from a single carrier. These results show knockdown of plk1 results in sensitization of multidrug resistant cells to doxorubicin, and this combination of gene silencing and small molecule drug delivery may prove useful to achieve potent therapeutic effects.

Downregulation of HNF1 homeobox B is associated with drug resistance in ovarian cancer

“…In addition to the pathways in cancer and pathways related to specified cancers (such as prostate and colorectal cancer), 4 pathways including ErbB signaling, focal adhesion, apoptosis and p53 signaling were enriched, suggesting that HNF1B may contribute to drug resistance in ovarian cancer via those pathways. ErbB signaling (91), focal adhesion (92,93), apoptosis (94,95) and p53 signaling (96,97) have been reported to associate with drug resistance in ovarian cancer. For example, miR-21 regulates drug resistance via apoptosis and cellular survival pathways (94), and loss of DOK2 induces carboplatin resistance in ovarian cancer via suppression of apoptosis (98).…”

Systemic delivery of therapeutic small interfering RNA using a pH-triggered amphiphilic poly-l-lysine nanocarrier to suppress prostate cancer growth in mice

“…This is mainly due to poor endosomal escape (pH 5-6.5), and subsequent degradation of the nucleic acid cargo in the late lysosomes (pH ~4.5) by a variety of degradative enzymes (Dominska and Dykxhoorn 2010). It has been recently reported that fusogenic/synthetic peptides and pH-sensitive moieties can be attached to various polymers to assist endosomal escape ( [Meyer et al, 2009], [Hatakeyama et al, 2009], [Carmona et al, 2009] and [Benoit et al, 2010]). These compounds are normally pHtriggered amphiphiles that undergo a surface change in the acidic environment, leading to the release of nanoparticles into the cytoplasm.…”

FOXM1 overexpression is associated with cisplatin resistance in non-small cell lung cancer and mediates sensitivity to cisplatin in A549 cells via the JNK/mitochondrial pathway

“…Evidence suggests that ATM and p53 coordinately regulated FoxM1 to modulate responses and resistance to epirubicin in breast cancer [19]. It has been shown that PLK1 plays a role in DNA damage recognition with homologous recombination repair and has been involved in multidrug resistance [44][45][46]. Based on the interaction between FoxM1 and its downstream genes, FoxM1 could be used as a therapeutic target to overcome acquired resistance to chemotherapy.…”