Enhanced Cancer Theranostics with Self-Assembled, Multilabeled siRNAs

A knockdown gene approach identifies an insect vector membrane protein with leucin-rich repeats as one of the receptors for the VmpA adhesin of flavescence dorée phytoplasma

Introduction

The adhesion of flavescence dorée phytoplasma to the midgut epithelium cells of their insect vectors is partially mediated by the variable membrane protein A (VmpA), an adhesin which shows lectin properties. In order to identify the insect receptor for VmpA, we identified Euscelidius variegatus cell proteins interacting with recombinant VmpA-His6.

Methods

The E. variegatus proteins were identified by mass spectrometry analysis of VmpA-E. variegatus protein complexes formed upon in vitro interaction assays. To assess their impact in VmpA binding, we reduced the expression of the candidate genes on E. variegatus cells in culture by dsRNA-mediated RNAi. The effect of candidate gene knockdown on VmpA binding was measured by the capacity of E. variegatus cells to bind VmpA-coated fluorescent beads.

Results and discussion

There were 13 candidate proteins possessing potential N-glycosylation sites and predicted transmembrane domains selected. The decrease of expression of an unknown transmembrane protein with leucine-rich repeat domains (uk1_LRR) was correlated with the decreased adhesion of VmpA beads to E. variegatus cells. The uk1_LRR was more expressed in digestive tubes than salivary glands of E. variegatus. The protein uk1_LRR could be implicated in the binding with VmpA in the early stages of insect infection following phytoplasmas ingestion.

Bifunctional Au-templated RNA nanoparticles enable direct cell uptake detection and GRP75 knockdown in prostate cancer

Nucleic acids templated on gold (Au) surfaces have led to a wide range of functional materials ranging from microarrays, sensors and probes in addition to drug delivery and treatment. In this application, we describe a simple and novel method for templating amino-functionalized RNA onto Au surfaces and their self-assembly into small, discrete nanoparticles. In our method, sample hybridization with a complementary RNA strand with and without a fatty acid (palmitamide) appendage produced functionalized double-stranded RNA on the Au surface. The resulting Au-functionalized RNA particles were found to be stable under reducing conditions according to UV-Vis spectroscopy. Sample characterization by DLS and TEM confirmed self-assembly into primarily small (∼10-40 nm) spherical shaped nanoparticles expected to be amenable to cell biology. However, fluorescence emission (λexc: 350 nm, λem: 650 nm) revealed radiative properties which limited cell uptake detection. Introduction of FITC within the Au-functionalized RNA particles produced a bifunctional probe, in which FITC fluorescence emission (λexc: 494 nm, λem: 522 nm) facilitated cell uptake detection, in a time-dependent manner. The dual encapsulation-release profiles of the FITC-labeled Au-functionalized RNA particles were validated by time-dependent UV-Vis spectroscopy and spectrofluorimetry. These experiments respectively indicated an increase in FITC absorption (λabs: 494 nm) and fluorescence emission (λem: 522 nm) with increased sample incubation times, under physiological conditions. The release of Au-functionalized siRNA particles in prostate cancer (PC-3) cells resulted in concomitant knockdown of GRP75, which led to detectable levels of cell death in the absence of a transfection vector. Thus, the formulation of stable, small and discrete Au-functionalized RNA nanoparticles may prove to be valuable bifunctional probes in the theranostic study of cancer cells.

Size Matters: Arginine-Derived Peptides Targeting the PSMA Receptor Can Efficiently Complex but Not Transfect siRNA

Oligoarginine sequences conjugated to a short cancer-targeting peptide (CTP) selective for the prostate-specific membrane antigen (PSMA) receptor was developed for selective small interfering RNA (siRNA) delivery to a human metastatic/castration-resistant prostate cancer (PCa) cell line, which expresses PSMA on the surface. The PSMA-Rn (n = 6 and 9) peptides were synthesized by solid-phase peptide synthesis, characterized by liquid chromatography-mass spectrometry (LC-MS) and condensed with glucose-regulated protein (GRP)-silencing siRNAs. Native gels showed formation of stable CTP:siRNA ionic complexes. Furthermore, siRNA release was effected by heparin competition, supporting the peptides' capabilities to act as condensing and releasing agents. However, dynamic light scattering (DLS) and transmission electron microscopy (TEM) studies revealed large anionic complexes that were prone to aggregation and limited cell uptake for RNAi activity. Taken together, these data support the notion that the development of efficient peptide-based siRNA delivery systems is in part contingent on the formulation of discrete nanoparticles that can effectively condense and release siRNA in cells.

Solid phase synthesis and self-assembly of higher-order siRNAs and their bioconjugates

New methods for the synthesis of higher-order siRNA motifs and their bioconjugates have recently gained widespread attention in the development of new and improved gene therapeutics. Our efforts aim to produce new chemical tools and protocols for the generation of modified siRNAs that screen for important oncogene targets as well as silence their activity for effective gene therapy in cancer models. More specifically, we have developed an efficient solution-phase synthesis for the production of a ribouridine branchpoint synthon that can be effectively incorporated by solid phase synthesis within higher-order RNA structures, including those adopting V-, and Y- and >-< shape RNA templates. Self-assembly of complementary RNA to the template strands produced higher-order siRNA nanostructures that were characterized by a combination of PAGE, DLS, and TEM techniques. In an effort to extend the repertoire of functionally diverse siRNAs, we have also developed solid phase bioconjugation strategies for incorporating bio-active probes such as fatty acid appendages and fluorescent reporters. Taken together, these methods highlight the ability to generate higher-order siRNAs and their bioconjugates for exploring the influence of modified siRNA structure on anti-cancer activity.