Invading target cells: multifunctional polymer conjugates as therapeutic nucleic acid carriers

Multifunctional peptide-conjugated nanocarriers for pulp regeneration in a full-length human tooth root

Dental pulp is a highly vascularized tissue, situated in an inextensible environment surrounded by rigid dentinal walls. The pulp receives its blood supply solely from the small apical foramen of a tooth root. Due to the unique anatomy that controls nutrition supply, regeneration of pulp tissue in a full-length tooth root has long been a challenge in regenerative endodontics. In this study, we designed and synthesized a multifunctional peptide-conjugated, pH-sensitive, non-viral gene vector for fast revascularization and pulp regeneration in a full-length human tooth root. The multifunctional peptide was designed to have distinctive features, including a cell-penetrating peptide to enhance cellular uptake, a nuclear localization signal peptide to assist in the translocation of an angiogenic gene into the nucleus, and a fluorescent tryptophan residue to visualize and quantify the transfection efficiency. Furthermore, a pH-sensitive dimethylmaleic anhydride (DMA) was integrated with the multifunctional peptide to enhance the transfected gene complex to escape from endosomes/lysosomes after internalization. In vitro experiments showed that the multifunctional non-viral gene vector significantly increased internalization and gene transfection efficiency as well as reduced cytotoxicity. After dental pulp stem cells (DPSCs) were transfected with the multifunctional gene vector/pVEGF complexes, the expression of VEGF from the DPSCs was upregulated for more than eight folds, which in turn greatly enhanced endothelial cell migration and vascular-like tube formation. Six weeks after implantation, the VEGF-transfected DPSCs accelerated new blood vessel formation and the regenerated pulp tissue occupied most of the area in the canal of a full-length human tooth root. The multifunctional peptide conjugated non-viral gene delivery is a safe and effective approach for regenerative endodontics. STATEMENT OF SIGNIFICANCE: Pulp regeneration in a full-length tooth root canal has long been a challenge in regenerative endodontics. This is due to the unique root anatomy that allows the blood supply of the tooth root only from a small apical foramen (< 1 mm), leading to a severe barrier for revascularization during pulp regeneration. In this work, we designed a multifunctional peptide-conjugated, pH-sensitive, non-viral gene vector to address this challenge. Our work shows that the peptide-conjugated system was an excellent carrier for fast revascularization and pulp tissue regeneration in a full-length toot root. This study will interest the multidisciplinary readership in gene delivery, biomaterials, and dental/craniofacial tissue engineering community.

Improving the efficacy of liposome-mediated vascular gene therapy via lipid surface modifications

BACKGROUND

We have previously defined mechanisms of intimal hyperplasia that could be targets for molecular therapeutics aimed at vascular pathology. However, biocompatible nanocarriers are needed for effective delivery. Cationic liposomes (CLPs) have been demonstrated as effective nanocarriers in vitro. However, in vivo success has been hampered by cytotoxicity. Recently, neutral PEGylated liposomes (PLPs) have been modified with cell-penetrating peptides (CPPs) to enhance cellular uptake. We aim to establish CPP-modified neutral liposomes as viable molecular nanocarriers in vascular smooth muscle cells.

METHODS

CLPs, PLPs, and CPP-modified PLPs (R8-PLPs) were assembled with short interfering RNA (siRNA) via ethanol injection. Characterization studies determined liposomal morphology, size, and charge. siRNA encapsulation efficiency was measured via RiboGreen assay. Vascular smooth muscle cells were exposed to equal lipid/siRNA across all groups. Rhodamine-labeled liposomes were used to quantify cell association via fluorometry, live/dead dual stain was used to measure cytotoxicity, and gene silencing was measured by quantitative polymerase chain reaction.

RESULTS

R8-PLPs exhibited increased encapsulation efficiency equivalent to CLPs. PLPs and R8-PLP-5 mol% and R8-PLP-10 mol% had no cytotoxic effect. CLPs demonstrated significant cytotoxicity. R8-PLP-5 mol% and R8-PLP-10 mol% exhibited increased cell association versus PLPs. R8-PLP-10 mol% resulted in significant gene silencing, in a manner dependent on lipid-to-siRNA load capacity.

CONCLUSIONS

The negligible cytotoxicity and enhanced cellular association and gene silencing capacity exhibited by R8-PLPs reveal this class of liposomes as a candidate for future applications. Further modifications for optimizing R8-PLPs are still warranted to improve efficacy, and in vivo studies are needed for translational development. However, this could prove to be an optimal nanocarrier for vascular gene therapeutics.

Comparative analysis of polymers for short interfering RNA delivery in vascular smooth muscle cells

The use of short interfering RNA (siRNA) to degrade messenger RNA in the cell cytoplasm and transiently attenuate intracellular proteins shows promise in the inhibition of vascular pathogenesis. However, a critical obstacle for therapeutic application is a safe and effective delivery system. Biodegradable polymers are promising alternative molecular carriers for genetic material. Here, we aim to perform a comparative analysis of poly(B-amino ester) (PBAE) and polyethylenimine (PEI) polymers in their efficacy for vascular smooth muscle cell transfection using siRNA against the glyceraldehyde 3-phosphate dehydrogenase (GAPDH) housekeeping gene as our test target.

METHODS

Human aortic smooth muscle cells (HASMC) were transfected in vitro with polymers conjugated to GAPDH or negative control (NC) siRNAs. Increasing siRNA:polymer ratios were tested for optimal transfection efficiency. DharmaFECT2 chemical transfection complexes were used for comparative analysis. Live/dead dual stain was used to measure cell viability, and GAPDH gene silencing was measured by quantitative polymerase chain reaction normalized to 18S.

RESULTS

The highest rate of PEI-mediated silencing was achieved with a 9μL polymer:220 pmol/mL siRNA conjugate (16 ± 2% expression versus NC; n = 6). Comparable PBAE-mediated silencing could be achieved with a 1.95μL polymer:100 pmol/mL siRNA conjugate (10 ± 1% expression versus NC; n = 5). Transfection using PEIs resulted in silencing equivalent to other methods but with less efficiency and increased cell toxicity at 24h polymer exposure. Decreasing PEI exposure time to 4 h resulted in similar silencing efficacy (21 ± 9% expression versus NC, n = 6) with an improved toxicity profile.

CONCLUSIONS

Polymeric bioconjugates transfected HASMCs in a manner similar to chemical complexes, with comparable cell toxicity and silencing efficiency. PEI bioconjugates demonstrated silencing equivalent to PBAE bioconjugates, although less efficient in terms of required polymer concentrations. Given the cost-to-benefit difference between the assayed polymers, and PEI's ability to transfect HASMCs within a short duration of exposure with an improved toxicity profile, this study shows that PEI bioconjugates are a potential transfection agent for vascular tissue. Future studies will expand on this method of gene therapy to validate delivery of gene-specific inhibitors aimed at attenuating smooth muscle cell proliferation, adhesion, and migration. These studies will lay the framework for our future experimental plans to expand on this method of gene therapy for in vivo transfection in animal models of vascular disease.

Surface modification and endothelialization of biomaterials as potential scaffolds for vascular tissue engineering applications

This review highlights the recent developments of surface modification and endothelialization of biomaterials in vascular tissue engineering applications.