Endocytosis of Nanomedicines

TLDR: This review describes the current experimental tools to study endocytosis of nanomedicines and provides specific examples from recent literature and the authors' own work on endocyTosis of Nanomedicine.

About: This article is published in Journal of Controlled Release.The article was published on 2010-08-03 and is currently open access. It has received 1819 citations till now.

Figures

Fig. 1. Different mechanisms of endocytosis. There are multiple pathways for cellular entry o evolving [11,12]. In all cases the initial stage of endocytosis proceeds from the plasmamembr The second stage often involves sorting of the cargo through endosomes. It is followed by extracellular milieu or delivered across cells (not shown). The figure is a simplified represent phagocytosis and CME are presented in Figs. 3 and 5. Abbreviations are: CCV, clathrin coat compartment; GPI, glycophosphatidylinositol, MVB, multivesicular body.

Fig. 6. Pathways of intracellular trafficking of cl-micelles in normal and cancer epithelial cells. The cl-micelles carrying a drug, doxorubucin (Dox), in normal epithelial cells were shown to sequester at the apical surface of the cell membrane near the TJs. However, during cancer progression the TJs are lost. As a result the cancer epithelial cells internalize the cl-micelles through caveolae. The cl-micelles are then routed to the lysosomes where the drug is released through a pH-dependent mechanism. The released drug accumulates in the nucleus and kills the cancer cells.

Fig. 10. Targeting of stimuli-sensitive double-targeted liposome to tumors. A. The surface of the drug-loaded liposome ismodifiedwith a cell-penetratingpeptide (CPP) attached via relatively short PEG chains. This peptide is masked by long PEG chains anchored to the liposome surface via pH-sensitive cleavable links. Some of the long PEG chains are decoratedwith theantibodyspecific to the tumorantigen. Theantibody is exposed and can bind with the antigen at the tumor cell surface. B. Inside the acidic microenvironment of the tumor the long PEG chains and the antibody conjugates are detached from the liposome resulting in exposure of the CPP. The CPP interacts with the cell membrane and facilitates endocytosis of the drug-loaded liposomes into tumor cells.

Fig. 9. DNA delivery to the nucleus. 1). PEI/DNA complexes internalize into cells utilizing actin-dependent pathway. 2). The endosomes containing PEI/DNA complexes travel inside the cytoplasm along the microtubules and reach the perinuclear space where the DNA is released through an unknownmechanism. 3). An alternativemechanismmay involve direct release of PEI/DNA complex from endosomal/lysosomal compartments, followed by the transportof the complex through thecytoplasmand to thenucleus. 4). TheDNA import to the nucleus can be enhanced by activating cellular signaling by Pluronic® block copolymers. In this case Pluronics® bindwith the cellmembranes and activate phosphorylation of IκB by an IκB-kinase (not shown). Thephosphorylated IκBdissociates from its complexwithNFκB. The released active NFκB enhances transport of DNA into nucleus in a promoter-dependent fashion.

Fig. 7. Cellular entry of PRINT nano- and microparticles. PRINT nanoparticles of all shapes utilize multiple pathways to gain cellular entry including CME (1), caveolaemediated endocytosis (2) and, to a lesser extent, macropinocytosis (3). The shape of the particles appears to be important in regulating the rate of their cellular entry (not shown). Cube-shaped PRINT microparticles also utilize multiple routes of cellular entry but their macropinocytosis appears to be the most prominent.

Fig. 3. Stagesofphagocytosis ofparticles. 1)Particlesundergorecognition in thebloodstream through opsonization i.e. adsorption of proteins (immunoglubulins (Ig) G (and M), complement components (C3, C4, C5); blood serumproteins (including laminin,fibronectin, etc.). 2) Opsonized particles attach onto the cellmembrane through receptors present on the cell surfaceof aphagocyte. 3)Theparticles are ingested intophagosomes. 4)Thephagosomes mature, fuse with lysosomes and become acidified, leading to the enzyme-rich phagolysosomes where the particles are prone to degradation.

Frequently asked questions

Q1. What are some of the characterized CPPs?

Some of the best characterized CPPs are TAT peptide, penetratin, transportan, poly-arginine, rabies virus glycoprotein (RVG) peptide, etc. 

Q2. What are the components of the caveolae endocyticmachinery?

Other components of the caveolae endocyticmachinery include proteins like cavin, which induces membrane curvature, dynamin, which enables vesicle scission, as well as vesicle-associated membrane protein (VAMP2) and synaptosome-associated protein (SNAP), which mediate subsequent vesicle fusion, etc. [57,58]. 

Q3. What is the role of the receptor in the formation of membrane ruffles?

The receptor activationmediates a signaling cascade that leads to changes in the actin cytoskeleton and triggers formation of membrane ruffles. 

Q4. What is the definitive characteristic of caveolae?

The definitive characteristic of caveolae is the presence of the hairpinlike membrane protein, caveolin-1, which is necessary for biogenesis of caveolae. 

Q5. What is the common reason why negative charged nanomaterials are more likely to enter cells?

Since cell membranes are generally negatively charged, it is widely believed that negatively charged nanomaterials should internalize slower compared to their positively charged counterparts. 

Q6. What other ligands were used to enhance the delivery of nanoparticles?

In addition to CPPs, various other ligands were used to enhance cellular delivery of both nanoparticles and water-soluble polymers. 

Q7. What are the main types of particles that can induce the ruffling behavior?

Many particles like bacteria, apoptotic bodies, necrotic cells and viruses can induce the ruffling behavior independently of the growth factors, and internalize in macropinosomes [24]. 

Q8. What is the role of dendrimers in the development of drugs?

Dendrimers are repeatedly branched, monodisperse and usually highly symmetric compounds, which have been widely researched for delivery of therapeutic and diagnostic agents [84]. 

Q9. What is the effect of the interplay between nanomaterials and cells?

The complex interplay of nanomaterial-cell interactions results in intracellular sortingof nanomaterials towardsdifferentdestinations and canmediate activation of cellular signaling. 

Q10. What are the key parameters that determine the intracellular entry of nanomedicines?

Based on examples reported one can conclude that charge, shape, material composition, and surface chemistry are critical physicochemical parameters that determine cellular entry of nanomedicines through definitive endocytic route(s). 

Q11. What is the effect of the acylating of amino groups on the charge of the nano?

when the charge of these materials was inverted to negative (−34 mV) by acylating their amino groups their entry became negligible. 

Q12. What is the role of lysosomes in the release of cytotoxic drugs?

Somematerials like cl-micelles canbe routed to lysosomes and employ lysosomal pH as a trigger for release of a cytotoxic drug precisely within the cancer cells [26]. 

Q13. What is the importance of understanding the cell biology and its relation to nanomaterials science?

in-depth understanding of the cell biology and it's relation to nanomaterials science is most critical for advancement of this area of nanomedicine and drug delivery. 

Q14. Why do caveolae have their hallmark flask shape?

Due to this protein caveolae assume their hallmark flaskshaped structure (60–80 nm) and can engulf cargo molecules, which bind to caveolae surface. 

Q15. What is the effect of the Pluronics® on the delivery of the naked DNA?

the interest in the effects of the Pluronics® on gene delivery has been recently propelled by findings that these copolymers can greatly enhance the delivery of the naked DNA in vivo [101].