Biodegradable Inorganic Nanovector : Passive versus Active Tumor Targeting in siRNA Transportation
Nano-sized layered double hydroxide (LDH), as a new vehicle for gene therapy, could encapsulate DNA, target tumor tissues and eventually transport therapeutic DNA into cells. The LDH vectors could transport therapeutic DNA strands, such as anti-sense or siRNA into cancerous cells and inhibit their growth
Gene therapy delivers helpful gene or repaired DNA sequences to cells. As a viral vector, viruses were frequently used, since they could be grafted to cells and inject DNA, but they were known to trigger the immune response of body. And if it were out of luck, the tragic consequences might occur as well-known by Jesse Gelsinger, who died during a trial of gene therapy. It has been, therefore, highly required to find some alternative vectors instead of viral ones, and several attempts were made for non-viral vectors based on organic molecules and polymers, but these seemed to be not to work as well.
Now, Prof. Jin-Ho Choy and his colleagues at Ewha Womans University propose a totally new type of non-viral vector. They develop a materials based on magnesium and aluminium hydroxide into anionic clays called “layered double hydroxides(LDHs)”. Between the layers are negatively charged ions such as carbonate, nitrate, and chloride depending upon synthetic condition, and these can be replaced with negatively charged molecules like DNA by ion exchange reaction.
The LDH nanoparticles with an average size of 100 nm can be considered as the potential drug delivery carrier with targeting functions to overcome drug resistance, since the cellular uptake mechanism of drug and/or gene is completely different from that of LDH vector due to its specific clathrin-mediated endocytosis. And the cellular uptake rate of LDH is remarkably high compared to that of other carriers. In addition, the cells repel negatively charged molecules with their similarly charged cell membranes, and the LDH layers, however, shield DNA from these opposing forces, helping it to permeate through the cell membrane. Once inside the cell, the outer LDH layers start to dissolve to expose the DNA. The dissolved LDH vector is not toxic, since the dissolved magnesium and aluminium species are common ions, those which are abundant in our body.
In order to improve the therapeutic efficacy, drug or gene molecules must be target-delivered to malignant tissues or cells with passive and active targeting strategy.
The present platform technology for nano-drug delivery system (nano-DDS) represents a paradigm shift for non-viral vector. Prof. Choy’s group demonstrated the anionic clay vectors in two experiments in cell culture lines and the others in animal models for a long time. In the first, they showed how the fluorescent molecules with LDH nano-vector could be efficiently permeated inside the cell. In the second, they demonstrated how to encapsulate a DNA sequence designed to impede a specific gene of leukaemia cells grown in the laboratory into LDH. According to the cell viability test for the DNA-LDH nanohybrid, the growth of the cancerous cells was strongly reduced by 65 %.
But Prof. Choy was still cautious, because there were many reports as if the gene transfer was enhanced in vitro. And therefore, no one will take note if not the new technique works when used in living animals. And therefore, in the third, they modified the surface of LDH nanoparticles by conjugating a cancer overexpressing receptor, folic acid, with a targeting ligand (FALDH) in order to induce active targeting function, and they were able to finally demonstrate the active and passive targeting functions of LDH nanohybrid particles not only in vitro but also in vivo by either EPR (Enhanced Permeability and Retention) effect and clathrin-mediated endocytosis or folate receptor-mediated endocytosis. Transfected into KB cells or injected into xenograft mice, it was evidenced that siSurvivin-FA-LDH could result in an excellent effect of gene silencing at mRNA and protein levels in vitro, and eventually achieve a 3.0-fold better inhibition in tumor growth than siSurvivin-LDH in vivo (Figure 1). Such an antitumor effect could be explained by the fact that siSurvivin molecules could be more targeted (1.2-fold higher) to tumor tissues, compared to other organs.
These rationally designed LDH carriers and their drug delivery hybrids are chemically well-defined based on novel synthetic strategy, and their particle sizes can easily be controlled in a nanoscale, to maximize the passive targeting function based on EPR effect. Moreover, their external surface can also be modified with antibodies and tumor-targeting ligands to enhance the active targeting function, etc., depending on the research goal desired.
Thus, there would be no doubt that advanced or novel nano-DDSs will be the most important challenge in nanomedicine for the healthcare of human beings in the future.
NOTE: This work has been selected as a back cover paper and hot paper in the issue of Angewandte Chemie International Edition (Figure 2).
Figure 1. In vivo antitumor effect: tumor growth inhibition (n = 6 per group). Tumor volumes were measured at 2-day interval. Tumor sizes are presented in the format of mean ± standard error (SE) (single asterisk (*) represents p < 0.05 versus siSurvivin-LDH treated group and double asterisk (**) represents p < 0.01 versus PBS-treated group) (inset photo shows the data for mice after 18 days).
Figure 2. Cover of the journal of Angewandte Chemie International Edition (Vol. 55, issue 14).
* Related Article
“Biodegradable Inorganic Nanovector : Passive versus Active Tumor Targeting in siRNA Transportation” Angewandte Chemie International Edition, 24 March, 2016, Vol. 55, P. 4582-4586