Quantifying the heterogeneity of enzymatic dePEGyaltion of liposomal nanocarrier systems

Nanotherapeutic Heterogeneity: Sources, Effects, and Solutions

Nanomaterials have revolutionized medicine by enabling control over drugs' pharmacokinetics, biodistribution, and biocompatibility. However, most nanotherapeutic batches are highly heterogeneous, meaning they comprise nanoparticles that vary in size, shape, charge, composition, and ligand functionalization. Similarly, individual nanotherapeutics often have heterogeneously distributed components, ligands, and charges. This review discusses nanotherapeutic heterogeneity's sources and effects on experimental readouts and therapeutic efficacy. Among other topics, it demonstrates that heterogeneity exists in nearly all nanotherapeutic types, examines how nanotherapeutic heterogeneity arises, and discusses how heterogeneity impacts nanomaterials' in vitro and in vivo behavior. How nanotherapeutic heterogeneity skews experimental readouts and complicates their optimization and clinical translation is also shown. Lastly, strategies for limiting nanotherapeutic heterogeneity are reviewed and recommendations for developing more reproducible and effective nanotherapeutics provided.

Micro- and nanochamber array system for single enzyme assays

Arrays of small reaction containers, ranging from 624 femtoliters (10-15 L) to 270 attoliters (10-18 L), for capturing a single enzyme molecule and measuring the activity were developed along with a new reversible sealing system based on a pneumatic valve actuator made of polydimethylsiloxane (PDMS). The valve was actuated by PBS solution, effectively preventing evaporation of the solution from the micro- and nanochambers and allowing the assay to be performed over a long period of time. The hydrolysis rates of β-D-galactosidase (β-gal), kcat, were decreased according to the decrease of the chamber size, and the overall tendency seems to be symmetrically related to the specific surface area of the chambers even under the prevented condition of non-specific adsorption. The spatial localization of the protons in the chambers, which might could affect the dissociation state of the proteins, was also investigated to explain the decrease in the hydrolysis rate. The developed chamber system developed here may be useful for artificially reproducing the confined intracellular environment and molecular crowding conditions.

Drug Delivery Systems with a “Tumor-Triggered” Targeting or Intracellular Drug Release Property Based on DePEGylation

Coating nanosized anticancer drug delivery systems (DDSs) with poly(ethylene glycol) (PEG), the so-called PEGylation, has been proven an effective method to enhance hydrophilicity, aqueous dispersivity, and stability of DDSs. What is more, as PEG has the lowest level of protein absorption of any known polymer, PEGylation can reduce the clearance of DDSs by the mononuclear phagocyte system (MPS) and prolong their blood circulation time in vivo. However, the “stealthy” characteristic of PEG also diminishes the uptake of DDSs by cancer cells, which may reduce drug utilization. Therefore, dynamic protection strategies have been widely researched in the past years. Coating DDSs with PEG through dynamic covalent or noncovalent bonds that are stable in blood and normal tissues, but can be broken in the tumor microenvironment (TME), can achieve a DePEGylation-based “tumor-triggered” targeting or intracellular drug release, which can effectively improve the utilization of drugs and reduce their side effects. In this review, the stimuli and methods of “tumor-triggered” targeting or intracellular drug release, based on DePEGylation, are summarized. Additionally, the targeting and intracellular controlled release behaviors of the DDSs are briefly introduced.

Unravelling Heterogeneities in Complement and Antibody Opsonization of Individual Liposomes as a Function of Surface Architecture

Coating nanoparticles with poly(ethylene glycol) (PEG) is widely used to achieve long-circulating properties after infusion. While PEG reduces binding of opsonins to the particle surface, immunogenic anti-PEG side-effects show that PEGylated nanoparticles are not truly "stealth" to surface active proteins. A major obstacle for understanding the complex interplay between opsonins and nanoparticles is the averaging effects of the bulk assays that are typically applied to study protein adsorption to nanoparticles. Here, a microscopy-based method for directly quantifying opsonization at the single nanoparticle level is presented. Various surface coatings are investigated on liposomes, including PEG, and show that opsonization by both antibodies and complement C3b is highly dependent on the surface chemistry. It is further demonstrated that this opsonization is heterogeneous, with opsonized and non-opsonized liposomes co-existing in the same ensemble. Surface coatings modify the percentage of opsonized liposomes and/or opsonin surface density on the liposomes, with strikingly different patterns for antibodies and complement. Thus, this assay provides mechanistic details about opsonization at the single nanoparticle level previously inaccessible to established bulk assays.