Efficient active transport of gene nanocarriers to the cell nucleus

Abstract

The intracellular transport of therapeutic gene carriers is poorly understood, limiting the rational design of efficient new vectors. We used live-cell real-time multiple particle tracking to quantify the intracellular transport of hundreds of individual nonviral DNA nanocarriers with 5-nm and 33-ms resolution. Unexpected parallels between several of nature's most efficient DNA viruses and nonviral polyethylenimine͞DNA nanocomplexes were revealed to include motor protein-driven transport through the cytoplasm toward the nucleus on microtubules. Active gene carrier transport led to efficient perinuclear accumulation within minutes. The results provide direct evidence to dispute the common belief that the efficiency of nonviral gene carriers is dramatically reduced because of the need for their relatively slow random diffusion through the cell cytoplasm to the nucleus and, instead, focuses the attention of rational carrier design on overcoming barriers downstream of perinuclear accumulation. G ene delivery to the cell nucleus has been implicated as the Achilles' heel of gene therapy (1). Synthetic, nonviral DNA delivery systems have been used to improve the transfer of foreign genetic material into cells, both in vitro (2) and in vivo (3). However, without evolution working to carefully hone and optimize the delivery process, manmade delivery vectors suffer from lower efficiencies compared with nature's DNA viruses. Despite this drawback, reduced immunogenicity, improved safety, and the ability to carry larger DNA loads make nonviral carriers attractive for gene therapy (4, 5). For scientists and engineers to ''evolve'' synthetic vectors into more efficient gene delivery vehicles, the key steps in the transfection process where viral systems show superior efficiency must first be identified.Investigation of the intracellular trafficking of DNA carriers promises to improve the efficiency of nonviral delivery vectors by determining the rate-limiting steps of gene transfection, thereby allowing for the development of strategies to overcome these barriers (6-8). Currently, the transport of nonviral DNA carriers through the cytoplasm is poorly characterized, but is thought to be inefficient and potentially rate limiting because of their need to ''randomly migrate'' to the nucleus (9). Confocal microscopy has been used to study intracellular trafficking of nonviral systems (6, 10, 11), allowing the locations of complexes at discrete times to be determined, yielding an insightful but qualitative description of the transport process. Fluorescence recovery after photobleaching has recently been used to quantify overall ''effective diffusion'' rates of DNA molecules in the cytoplasm (12). With this ensemble-averaged technique, however, information associated with individual DNA carriers [the rates of individual particle movements, the mode of transport (e.g., random versus directed or active), and the trajectory and directionality of the transport] remains a black box. To achieve single-particle resolution at the nanometer ...

Quantitating intracellular transport of polyplexes by spatio-temporal image correlation spectroscopy

“…The velocity component, the major determinant of directed motion at short times, is not significantly different among the polyplexes at short times. Aside from the nominal diameter, it is the characteristics of the endosome, powered by kinesin and dynein, that primarily determine diffusion and velocity (4,30,35). Based on the average velocity measurements and effective diffusion constants for the values, we estimate that motor activity increases slightly with increasing endosome size.…”

“…However, only a few studies of cytoplasmic transport have focused on quantitative biophysical parameters such as effective diffusion constants or transport velocities (4)(5)(6). Most experiments measuring these parameters have focused on examining small injected oligonucleotides or proteins (7)(8)(9)(10)(11).…”

“…Understanding such nonviral gene delivery (one type of vector that involves the combination of synthetic polymers and nucleic acids to form particles called polyplexes and is used here) requires knowledge of how they behave within cells, including the mechanisms involved in polyplex trafficking such as endocytosis, cytoplasmic transport, endosomal escape, and nuclear localization (1)(2)(3). Recent reports have indicated the presence of significant bottlenecks in the delivery process, especially problems with endosomal escape (4). Measuring these dynamics, especially transport parameters, is important for understanding both how such delivery methods compare with viruses and how to improve their efficiencies.…”

A biophysical model of intracellular distribution and perinuclear accumulation of particulate matter

“…Once entered the cells, the intracellular traffic and distribution of substances that do not follow the endocytotic pathway are related to aspecific movements or microtubule-based active mechanisms [2,3].…”

Methods to determine the interactions of micro- and nanoparticles with mucus

“…The group has also used MPT to quantify, for example, the intracellular transport of non-viral polyethyleneimine/DNA nano-sized polyplexes [45].…”