Tuning G-Quadruplex Nanostructures with Lipids. Towards Designing Hybrid Scaffolds for Oligonucleotide Delivery

Lipid and Peptide-Oligonucleotide Conjugates for Therapeutic Purposes: From Simple Hybrids to Complex Multifunctional Assemblies

Antisense and small interfering RNA (siRNA) oligonucleotides have been recognized as powerful therapeutic compounds for targeting mRNAs and inducing their degradation. However, a major obstacle is that unmodified oligonucleotides are not readily taken up into tissues and are susceptible to degradation by nucleases. For these reasons, the design and preparation of modified DNA/RNA derivatives with better stability and an ability to be produced at large scale with enhanced uptake properties is of vital importance to improve current limitations. In the present study, we review the conjugation of oligonucleotides with lipids and peptides in order to produce oligonucleotide conjugates for therapeutics aiming to develop novel compounds with favorable pharmacokinetics.

Properties of Parallel Tetramolecular G-Quadruplex Carrying N-Acetylgalactosamine as Potential Enhancer for Oligonucleotide Delivery to Hepatocytes

The development of oligonucleotide conjugates for in vivo targeting is one of the most exciting areas for oligonucleotide therapeutics. A major breakthrough in this field was the development of multifunctional GalNAc-oligonucleotides with high affinity to asialoglycoprotein receptors (ASGPR) that directed therapeutic oligonucleotides to hepatocytes. In the present study, we explore the use of G-rich sequences functionalized with one unit of GalNAc at the 3'-end for the formation of tetrameric GalNAc nanostructures upon formation of a parallel G-quadruplex. These compounds are expected to facilitate the synthetic protocols by providing the multifunctionality needed for the binding to ASGPR. To this end, several G-rich oligonucleotides carrying a TGGGGGGT sequence at the 3'-end functionalized with one molecule of N-acetylgalactosamine (GalNAc) were synthesized together with appropriate control sequences. The formation of a self-assembled parallel G-quadruplex was confirmed through various biophysical techniques such as circular dichroism, nuclear magnetic resonance, polyacrylamide electrophoresis and denaturation curves. Binding experiments to ASGPR show that the size and the relative position of the therapeutic cargo are critical for the binding of these nanostructures. The biological properties of the resulting parallel G-quadruplex were evaluated demonstrating the absence of the toxicity in cell lines. The internalization preferences of GalNAc-quadruplexes to hepatic cells were also demonstrated as well as the enhancement of the luciferase inhibition using the luciferase assay in HepG2 cell lines versus HeLa cells. All together, we demonstrate that tetramerization of G-rich oligonucleotide is a novel and simple route to obtain the beneficial effects of multivalent N-acetylgalactosamine functionalization.

Parallel G-quadruplex Structures Increase Cellular Uptake and Cytotoxicity of 5-Fluoro-2'-deoxyuridine Oligomers in 5-Fluorouracil Resistant Cells

Fluoropyrimidines, such as 5-fluorouracil (5-FU) and related prodrugs have been considered first-line chemotherapy agents for the treatment of colorectal cancer. However, poor specificity and tumor cell resistance remain major limiting bottlenecks. G-quadruplexes, have been suggested as preferred nanostructures for enhancing cellular uptake mediated by G-quadruplex binding proteins which are abundant at the membranes of some tumor cells. In the current study, we propose a new strategy to deliver 5-fluoro-2′-deoxyuridine (5-FdU) monophosphate, the main active drug from 5-FU derivatives that may circumvent the cellular mechanisms of FU-resistant cancer cells. Two G-quadruplexes delivery systems containing four and six G-tetrads ((TG₄T) and (TG₆T)) linked to a FdU oligonucleotide were synthesized. Biophysical studies show that the G-quadruplex parallel structures are not affected by the incorporation of the 5 units of FdU at the 5’-end. Internalization studies confirmed the ability of such G-quadruplex nanostructures to facilitate the transport of the FdU pentamer and increase its cytotoxic effect relative to conventional FU drug in FU-resistant colorectal cancer cells. These results suggest that FdU oligomers linked to G-quadruplex parallel sequences may be a promising strategy to deliver fluoropyrimidines to cancer cells.