Carriers Break Barriers in Drug Delivery: Endocytosis and Endosomal Escape of Gene Delivery Vectors

Abstract

ConspectusOver the past decades, major efforts were undertaken to develop devices on a nanoscale level for the efficient and nontoxic delivery of molecules to tissues and cells, for the purpose of either diagnosis or treatment of disease. The application of such devices in drug delivery has proven to be beneficial for matters as diverse as drug solubility, drug targeting, controlled drug release, and transport of drugs across cellular barriers. Multiple nanotherapeutics have been approved for clinical treatment, and more products are being evaluated in preclinical and clinical trials. However, many biological barriers hinder the medical application of nanocarriers. There are two main classes of barriers that need to be overcome by drug nanocarriers: extracellular and intracellular barriers, both of which may capture and/or destroy therapeutics before they reach their target site. This Account discusses major biological barriers that are confronted by nanotherapeutics, following their systemic administration, focusing on cellular entry and endosomal escape of gene delivery vectors. The use of pH-responsive materials to overcome the endosomal barrier is addressed.Historically, cell biologists have studied the interaction between cells and pathogens in order to unveil the mechanisms of endocytosis and cell signaling. Meanwhile, it is becoming clear that cells may respond in similar ways to artificial drug delivery systems and, consequently, that knowledge on the cellular response against both pathogens and nanoparticulate systems will aid in the design of improved nanomedicine. A close collaboration between bioengineers and cell biologists will promote this development. At the same time, we have come to realize that tools that we use to study fundamental cellular processes, including metabolic inhibitors of endocytosis and overexpression/downregulation of proteins, may cause changes in cellular physiology. This calls for the implementation of refined methods to study nanocarrier–cell interactions, as is discussed in this Account.Finally, recent papers on the dynamics of cargo release from endosomes by means of live cell imaging have significantly advanced our understanding of the transfection process. They have initiated discussion (among others) on the limited number of endosomal escape events in transfection, and on the endosomal stage at which genetic cargo is most efficiently released. Advancements in imaging techniques, including super-resolution microscopy, in concert with techniques to label endogenous proteins and/or label proteins with synthetic fluorophores, will contribute to a more detailed understanding of nanocarrier-cell dynamics, which is imperative for the development of safe and efficient nanomedicine.

An Elucidative Review to Analytically Sieve the Viability of Nanomedicine Market

“…The use of nanomedicines either directly as therapeutic agents or as drug delivery agents (nanocarriers), active implants, contrasting agents for bioimaging and diagnostics, drug encapsulates, gene delivery systems and tissue engineering has brought immense impetus to pharmaceutical and medical research [17]. In the last decade, the scientific community expressed a high commitment to exploring the medical application of nanotechnolgy through an exponential rise in the number of research articles and review papers [18].…”

Efficient Polymer-Mediated Delivery of Ribonucleoprotein Payloads Through Combinatorial Design & Parallelized Experimentation

“…The tendency of the hit formulation to form polyplexes larger than 100 nm in radius, has interesting implications for cellular internalization and nuclear accumulation. 52 While particles smaller than 100 nm in radius exhibit a preference for clathrin-mediated pathways, larger particles are internalized via caveolar pathways, which permit polyplexes to traverse the cytosol and enter the nucleus while avoiding lysosomal interrogation. 19,53 In addition, physical aspects of bolus transfection cannot be overlooked: upon introduction into the cell culture media, bulkier polyplexes will settle to the surface of adherent monolayer cultures faster than smaller polyplexes.…”

Nanoscopy for endosomal escape quantification

“…Although various NP formulations have been marketed (16,17), achieving efficient intracellular delivery still remains a significant challenge (18)(19)(20)(21)(22). One of the main culprits is that the majority of NP -once taken up via endocytosis -are unavoidably distributed to endocytic vesicles.…”

“…Mechanisms through which NP -and more importantly the therapeutic cargo -can escape these degrading vesicles have become the subject of intense research over the past decades (19,20,24,32). Inspired by the innate ability of bacterial toxins and viruses to escape endosomal vesicles, various hypothetical endosomal escape mechanisms have been proposed and reviewed in literature, such as: the "proton sponge" effect, membrane fusion, pore formation, membrane disruption, and vesicle budding and collapse (24,27,(32)(33)(34)(35)(36).…”