RNA interference in the era of nucleic acid therapeutics

The guide-RNA sequence dictates the slicing kinetics and conformational dynamics of the Argonaute silencing complex

The RNA-induced silencing complex (RISC), which powers RNA interference (RNAi), consists of a guide RNA and an Argonaute protein that slices target RNAs complementary to the guide. We find that, for different guide-RNA sequences, slicing rates of perfectly complementary bound targets can be surprisingly different (>250-fold range), and that faster slicing confers better knockdown in cells. Nucleotide sequence identities at guide-RNA positions 7, 10, and 17 underlie much of this variation in slicing rates. Analysis of one of these determinants implicates a structural distortion at guide nucleotides 6-7 in promoting slicing. Moreover, slicing directed by different guide sequences has an unanticipated, 600-fold range in 3'-mismatch tolerance, attributable to guides with weak (AU-rich) central pairing requiring extensive 3' complementarity (pairing beyond position 16) to more fully populate the slicing-competent conformation. Together, our analyses identify sequence determinants of RISC activity and provide biochemical and conformational rationale for their action.

VAV1 as a putative therapeutic target in autoimmune and chronic inflammatory diseases

The guanine nucleotide exchange factor (GEF) VAV1, a previously 'undruggable' protein integral to T/B lymphocyte antigen-receptor signaling, promotes actin polymerization, immunological synapse formation, T cell activation and differentiation, and cytokine production. With the development of novel modalities for targeting proteins, we hypothesize that interventions targeting VAV1 will have therapeutic potential in T and T/B cell-mediated autoimmune and chronic inflammatory diseases. This opinion is supported by recent CRISPR-Cas9 studies showing VAV1 as a key positive regulator of T cell receptor (TCR) activation and cytokine production in primary human CD4+ and CD8+ T cells; data demonstrating that loss/suppression of VAV1 regulates autoimmunity and inflammation; and promising preclinical data from T and T/B cell-mediated disease models of arthritis and colitis showing the effectiveness of selective VAV1 targeting via protein degradation.

ROS-Responsive Ferrocenyl Amphiphilic PAMAM Dendrimers for On-Demand Delivery of siRNA Therapeutics to Cancer Cells

Small interfering RNA (siRNA) therapeutics, characterized by high specificity, potency, and durability, hold great promise in the treatment of cancer and other diseases. However, the clinic implementation of siRNA therapeutics critically depends on the safe and on-demand delivery of siRNA to the target cells. Here, we reported a family of ferrocenyl amphiphilic dendrimers (Fc-AmDs) for on-demand delivery of siRNA in response to the high ROS content in cancer cells. These dendrimers bear ROS-sensitive ferrocene moieties in the hydrophobic components and positively chargeable poly(amidoamine) dendrons as the hydrophilic entities, possessing favorable safety profiles and ROS responsive properties. One of these ferrocenyl amphiphilic dendrimers, Fc-C8-AmD 8A, outperforms in siRNA delivery, benefiting from its optimal balance of hydrophobicity and hydrophilicity. Its ROS feature facilitates specific and efficient disassembly of its complex with siRNA in ROS-rich cancer cells for effective siRNA delivery and gene silencing. Moreover, Fc-C8-AmD 8A also integrates the features and beneficial properties of both lipid and dendrimer vectors. Therefore, it represents a novel on-demand delivery system for cancer cell-specific siRNA delivery. This work opens new perspectives for designing self-assembly nanosystems for on-demand drug delivery.

The guide RNA sequence dictates the slicing kinetics and conformational dynamics of the Argonaute silencing complex

The RNA-induced silencing complex (RISC), which powers RNA interference (RNAi), consists of a guide RNA and an Argonaute protein that slices target RNAs complementary to the guide. We find that for different guide-RNA sequences, slicing rates of perfectly complementary, bound targets can be surprisingly different (>250-fold range), and that faster slicing confers better knockdown in cells. Nucleotide sequence identities at guide-RNA positions 7, 10, and 17 underlie much of this variation in slicing rates. Analysis of one of these determinants implicates a structural distortion at guide nucleotides 6-7 in promoting slicing. Moreover, slicing directed by different guide sequences has an unanticipated, 600-fold range in 3'-mismatch tolerance, attributable to guides with weak (AU-rich) central pairing requiring extensive 3' complementarity (pairing beyond position 16) to more fully populate the slicing-competent conformation. Together, our analyses identify sequence determinants of RISC activity and provide biochemical and conformational rationale for their action.

Direct Conjugation of Gallium-(III)-Corroles to Short Interfering RNA(siRNA) Providing Real-Time siRNA Imaging and Gene Silencing

Discovering new modifications for oligonucleotide therapeutics is essential for expanding its application to new targets and diseases. In this project, we focus on conjugating metaled ligands to short interfering RNAs (siRNAs) to investigate robust and simple conjugation methods for adding new properties such as real-time imaging to the siRNA. Here we report the chemical synthesis of novel Ga-(III)-corroles for their direct conjugation to siRNAs. Ga-(III)-corrole-siRNAs showed promising results when evaluated for gene silencing and live cell imaging. The knockdown activity of the firefly luciferase reporter gene was measured to evaluate gene silencing activity. Gene silencing studies from two 5'-Ga-(III)-labeled-siRNAs exhibited dose-dependent knockdown with IC50s of 812.7 and 451.4 pM, which is comparable to wild-type (IC50=439.7 pM) in the absence of red light, and IC50s of 562.9 and 354.5 pM, which is also comparable to wild-type (IC50=337.4 pM), in the presence of red light. In addition, imaging studies with Ga-(III)-corrole-modified siRNAs showed intense fluorescence in HeLa cells, highlighting that the Ga-(III)-corrole modification is an effective fluorophore for siRNA tracing and imaging. Moreover, the photodynamic activity of free base corrole vs the Ga-(III)-corrole was evaluated. Results show an increase of light cytotoxicity of the corrole ligand upon the addition of Ga-(III); however, no phototoxicity was observed when Ga-(III) ligands were linked to siRNA. In conclusion, Ga-(III)-corrole-siRNAs show promising results for applications in simultaneous real-time imaging and gene silencing.