A quantitativeex vivostudy of the interactions between reconstituted high-density lipoproteins and human leukocytes

Deciphering the monocyte-targeting mechanisms of PEGylated cationic liposomes by investigating the biomolecular corona

Cationic liposomes specifically target monocytes in blood, rendering them promising drug-delivery tools for cancer immunotherapy, vaccines, and therapies for monocytic leukaemia. The mechanism behind this monocyte targeting ability is, however, not understood, but may involve plasma proteins adsorbed on the liposomal surfaces. To shed light on this, we investigated the biomolecular corona of three different types of PEGylated cationic liposomes, finding all of them to adsorb hyaluronan-associated proteins and proteoglycans upon incubation in human blood plasma. This prompted us to study the role of the TLR4 co-receptors CD44 and CD14, both involved in signalling and uptake pathways of proteoglycans and glycosaminoglycans. We found that separate inhibition of each of these receptors hampered the monocyte uptake of the liposomes in whole human blood. Based on clues from the biomolecular corona, we have thus identified two receptors involved in the targeting and uptake of cationic liposomes in monocytes, in turn suggesting that certain proteoglycans and glycosaminoglycans may serve as monocyte-targeting opsonins. This mechanistic knowledge may pave the way for rational design of future monocyte-targeting drug-delivery platforms.

Pitfalls and opportunities in quantitative fluorescence-based nanomedicine studies - A commentary

Fluorescence-based techniques are prevalent in studies of nanomedicine-targeting to cells and tissues. However, fluorescence-based studies are rarely quantitative, thus prohibiting direct comparisons of nanomedicine-performance across studies. With this Commentary, we aim to provoke critical thinking about experimental design by treating some often-overlooked pitfalls in 'quantitative' fluorescence-based experimentation. Focusing on fluorescence-labeled nanoparticles, we cover mechanisms like solvent-interactions and fluorophore-dissociation, which disqualify the assumption that 'a higher fluorescence readout' translates directly to 'a better targeting efficacy'. With departure in recent literature, we propose guidelines for circumventing these pitfalls in studies of tissue-accumulation and cell-uptake, thus covering fluorescence-based techniques like bulk solution fluorescence measurements, fluorescence microscopy, flow cytometry, and infrared fluorescence imaging. With this, we hope to lay a foundation for more 'quantitative thinking' during experimental design, enabling (for example) the estimation and reporting of actual numbers of fluorescent nanoparticles accumulated in cells and organs.

Reconstituted high density lipoprotein (rHDL), a versatile drug delivery nanoplatform for tumor targeted therapy

rHDL is a synthesized drug delivery nanoplatform exhibiting excellent biocompatibility, which possesses most of the advantages of HDL. rHDL shows almost no toxicity and can be degraded to non-toxic substances in vivo. The severe limitation of the application of various antitumor agents is mainly due to their low bioavailability, high toxicity, poor stability, etc. Favorably, antitumor drug-loaded rHDL nanoparticles (NPs), which are known as an important drug delivery system (DDS), help to change the situation a lot. This DDS shows an outstanding active-targeting ability towards tumor cells and improves the therapeutic effect during antitumor treatment while overcoming the shortcomings mentioned above. In the following text, we will mainly focus on the various applications of rHDL in tumor targeted therapy by describing the properties, preparation, receptor active-targeting ability and antitumor effects of antineoplastic drug-loaded rHDL NPs.

Effect of apoA-I PEGylation on the Biological Fate of Biomimetic High-Density Lipoproteins

Biomimetic high-density lipoproteins (b-HDL) have in the past two decades been applied for various drug delivery applications. As b-HDL inherently have relatively long circulation half-life and high tumor accumulation, this has inspired researchers to use b-HDL to selectively deliver drugs to tumors. PEGylation of the b-HDL has been pursued to increase the circulation half-life and therapeutic efficacy even further. The b-HDL consist of lipids stabilized by a protein/peptide scaffold, and while PEGylation of the scaffold has been shown to greatly increase the circulation half-life of the scaffold, the effect of PEGylation of the lipids is much less significant. Still, it remains to be evaluated how the biological fate, including cellular uptake, biodistribution, and circulation half-life, of the b-HDL lipids is affected by PEGylation of the b-HDL scaffold. We studied this with apolipoprotein A-I (apoA-I)-based b-HDL and mono-PEGylated b-HDL (PEG b-HDL) both in vitro and in vivo. We found that PEGylation of the b-HDL scaffold only seemed to have minimal effect on the biological fate of the lipids. Both b-HDL and PEG b-HDL overall shared similar biological fates, which includes cellular uptake through the scavenger receptor class B type 1 (SR-BI) and relatively high tumor accumulation. This highlights that b-HDL are dynamic particles, and the biological fates of the b-HDL components (lipids and scaffold) can differ. A phenomenon that may also apply for other multicomponent nanoparticles.

A systematic review of the biodistribution of biomimetic high-density lipoproteins in mice

For the past two decades, biomimetic high-density lipoproteins (b-HDL) have been used for various drug delivery applications. The b-HDL mimic the endogenous HDL, and therefore possess many attractive features for drug delivery, including high biocompatibility, biodegradability, and ability to transport and deliver their cargo (e.g. drugs and/or imaging agents) to specific cells and tissues that are recognized by HDL. The b-HDL designs reported in the literature often differ in size, shape, composition, and type of incorporated cargo. However, there exists only limited insight into how the b-HDL design dictates their biodistribution. To fill this gap, we conducted a comprehensive systematic literature search of biodistribution studies using various designs of apolipoprotein A-I (apoA-I)-based b-HDL (i.e. b-HDL with apoA-I, apoA-I mutants, or apoA-I mimicking peptides). We carefully screened 679 papers (search hits) for b-HDL biodistribution studies in mice, and ended up with 24 relevant biodistribution profiles that we compared according to b-HDL design. We show similarities between b-HDL biodistribution studies irrespectively of the b-HDL design, whereas the biodistribution of the b-HDL components (lipids and scaffold) differ significantly. The b-HDL lipids primarily accumulate in liver, while the b-HDL scaffold primarily accumulates in the kidney. Furthermore, both b-HDL lipids and scaffold accumulate well in the tumor tissue in tumor-bearing mice. Finally, we present essential considerations and strategies for b-HDL labeling, and discuss how the b-HDL biodistribution can be tuned through particle design and administration route. Our meta-analysis and discussions provide a detailed overview of the fate of b-HDL in mice that is highly relevant when applying b-HDL for drug delivery or in vivo imaging applications.

Head-to-Head Comparison of the Penetration Efficiency of Lipid-Based Nanoparticles into Tumor Spheroids

Most tumor-targeted drug delivery systems must overcome a large variety of physiological barriers before reaching the tumor site and diffuse through the tight network of tumor cells. Many studies focus on optimizing the first part, the accumulation of drug carriers at the tumor site, ignoring the penetration efficiency, i.e., a measure of the ability of a drug delivery system to overcome tumor surface adherence and uptake. We used three-dimensional (3D) tumor spheroids in combination with light-sheet fluorescence microscopy in a head-to-head comparison of a variety of commonly used lipid-based nanoparticles, including liposomes, PEGylated liposomes, lipoplexes, and reconstituted high-density lipoproteins (rHDL). Whilst PEGylation of liposomes only had minor effects on the penetration efficiency, we show that lipoplexes are mainly associated with the periphery of tumor spheroids, possibly due to their positive surface charge, leading to fusion with the cells at the spheroid surface or aggregation. Surprisingly, the rHDL showed significantly higher penetration efficiency and high accumulation inside the spheroid. While these findings indeed could be relevant when designing novel drug delivery systems based on lipid-based nanoparticles, we stress that the used platform and the detailed image analysis are a versatile tool for in vitro studies of the penetration efficiency of nanoparticles in tumors.