Delivery of antisense oligonucleotides for splice-correction of androgen receptor pre-mRNA in castration-resistant prostate cancer models using cell-penetrating peptides

BACKGROUND

Cell-penetrating peptides (CPPs) are a promising approach for delivering antisense oligonucleotides (AONs) as they form nanosized complexes through noncovalent interactions that show efficient cellular uptake. Previously, we have designed an AON system to correct splicing of the androgen receptor (AR) pre-mRNA, thereby preventing the generation of the splice variant AR-V7 mRNA. AON-mediated knockdown of AR-V7 resulted in inhibition of androgen-independent cell proliferation. In this study, we evaluated the CPP-mediated delivery of this AON into castration-resistant prostate cancer cell line models 22Rv1, DuCaP (dura mater cancer of the prostate), and VCaP (vertebral cancer of the prostate).

METHODS

Nanoparticles (polyplexes) of AONs and CPPs were formed through rapid mixing. The impact of the peptide carrier, the formulation parameters, and cell incubation conditions on cellular uptake of fluorescently labeled AONs were assessed through flow cytometry. The cytotoxic activity of these formulations was measured using the CellTiter-Glo cell viability assay. The effectivity of CPP-mediated delivery of the splice-correcting AON-intronic splicing enhancer (ISE) targeting the ISE in the castration-resistant prostate cancer (CRPC)-derived 22Rv1, DuCaP, and VCaP cells was determined by measuring levels of AR-V7 mRNA normalized to those of the human heterochromatin protein 1 binding protein 3 (HP1BP3). Western blot analysis was used to confirm AR-V7 downregulation at a protein level. The cellular distribution of fluorescently labeled AON delivered by a CPP or a transfection reagent was determined through confocal laser scanning microscopy.

RESULTS

The amphipathic and stearylated CPP PepFect 14 (PF14) showed higher uptake efficiency than arginine-rich CPPs. Through adjustment of formulation parameters, concentration and incubation time, an optimal balance between carrier-associated toxicity and delivery efficiency was found with a formulation consisting of an amino/phosphate ratio of 3, 0.35 μM AON concentration and 30 min incubation time of the cells with polyplexes. Cellular delivery of AON-ISE directed against AR pre-mRNA achieved significant downregulation of AR-V7 by 50%, 37%, and 59% for 22Rv1, DuCaP, and VCaP cells, respectively, and reduced androgen-independent cell proliferation of DuCaP and VCaP cells.

CONCLUSIONS

This proof-of-principle study constitutes the basis for further development of CPP-mediated delivery of AONs for targeted therapy in prostate cancer.

Use of PepFect14 and siRNA for Targeted Gene Silencing in Human Embryonic Stem Cells

The unique properties of human embryonic stem (hES) cells render them invaluable for many scientific and clinical endeavors. Wider application of hES cells requires a comprehensive understanding of their biology that can be dissected using RNA interference-based gene silencing. However, commonly used transfection methods to deliver nucleic acids into a cell often lead to differentiation of hES cells. For that reason, effective transfection technique with minimal side effects is essential for studying and employing hES cells. Here, we describe a CPP-based method for targeted gene silencing in hES cells using siRNA complexed with PepFect 14 (PF14). This approach results in effective downregulation of mRNA and protein levels of a target gene without adverse effects on cell viability and pluripotency.

Targeted gene silencing in human embryonic stem cells using cell-penetrating peptide PepFect 14

Background

Human embryonic stem (hES) cells serve as an invaluable tool for research and future medicine, but their transfection often leads to unwanted side effects as the method itself may induce differentiation. On the other hand, RNA interference (RNAi)-based targeted gene silencing is a quick, cost-effective, and easy-to-perform method to address questions regarding the function of genes, especially when hypomorphic knockdowns are needed. Therefore, effective transfection method with minimal side effects is essential for applying RNAi to hES cells. Here, we report a highly promising approach for targeted gene silencing in hES cells with siRNA complexed with cell-penetrating peptide PepFect 14 (PF14). This strategy provides researchers with efficient tool for unraveling the functions of genes or addressing the differentiation of pluripotent stem cells.

Methods

We present a method for delivery of siRNA into hES cells with cell-penetrating peptide PF14. Accordingly, hES cells were transfected in ROCK inhibitor containing medium for 24 h right after EDTA passaging as small cell clumps. Fluorescently labeled siRNA and siRNAs targeting OCT4 or beta-2-microglobulin (B2M) mRNA sequences were used to evaluate the efficiency of transfection and silencing. Analyses were performed at various time points by flow cytometry, RT-qPCR, and immunofluorescence microscopy.

Results

Effective downregulation of OCT4 in 70% of treated hES cells at protein level was achieved, along with 90% reduction at mRNA level in bulk population of cells. The applicability of this low-cost and easy-to-perform method was confirmed by inducing silencing of another target not associated with hES cell pluripotency (B2M). Furthermore, we discovered that downregulation of OCT4 induces neuroectodermal differentiation accompanied by reduced expression of B2M during early stage of this lineage.

Conclusions

The results demonstrate PF14 as a promising tool for studying gene function and regulatory networks in hES cells by using RNAi.

Electronic supplementary material

The online version of this article (10.1186/s13287-019-1144-x) contains supplementary material, which is available to authorized users.