In vivo Studies on Pharmacokinetics, Toxicity and Immunogenicity of Polyelectrolyte Nanocapsules Functionalized with Two Different Polymers: Poly-L-Glutamic Acid or PEG

Background

The functionalization of a nanoparticle surface with PEG (polyethylene glycol) is an approach most often used for extending nanomaterial circulation time, enhancing its delivery and retention in the target tissues, and decreasing systemic toxicity of nanocarriers and their cargos. However, because PEGylated nanomedicines were reported to induce immune response including production of anti-PEG antibodies, activation of the complement system as well as hypersensitivity reactions, hydrophilic polymers other than PEG are gaining interest as its replacement in nanomaterial functionalization. Here, we present the results of in vivo evaluation of polyelectrolyte nanocapsules with biodegradable, polyelectrolyte multilayer shells consisting of poly-l-lysine (PLL) and poly-l-glutamic (PGA) acid as a potential drug delivery system. We compared the effects of nanocapsules functionalized with two different “stealth” polymers as the external layer of tested nanocapsules was composed of PGA (PGA-terminated nanocapsules, NC-PGA) or the copolymer of poly-l-lysine and polyethylene glycol (PEG-terminated nanocapsules, NC-PEG).

Methods

Nanocapsules pharmacokinetics, biodistribution and routes of eliminations were analysed postmortem by fluorescence intensity measurement. Toxicity of intravenously injected nanocapsules was evaluated with analyses of blood morphology and biochemistry and by histological tissue analysis. DNA integrity was determined by comet assay, cytokine profiling was performed using flow cytometer and detection of antibodies specific to PEG was performed by ELISA assay.

Results

We found that NC-PGA and NC-PEG had similar pharmacokinetic and biodistribution profiles and both were eliminated by hepatobiliary and renal clearance. Biochemical and histopathological evaluation of long-term toxicity performed after a single as well as repeated intravenous injections of nanomaterials demonstrated that neither NC-PGA nor NC-PEG had any acute or chronic hemato-, hepato- or nephrotoxic effects. In contrast to NC-PGA, repeated administration of NC-PEG resulted in prolonged increased serum levels of a number of cytokines.

Conclusion

Our results indicate that NC-PEG may cause undesirable activation of the immune system. Therefore, PGA compares favorably with PEG in equipping nanomaterials with stealth properties. Our research points to the importance of a thorough assessment of the potential influence of nanomaterials on the immune system.

C1q-Mediated Complement Activation and C3 Opsonization Trigger Recognition of Stealth Poly(2-methyl-2-oxazoline)-Coated Silica Nanoparticles by Human Phagocytes

Poly(2-methyl-2-oxazoline) (PMOXA) is an alternative promising polymer to poly(ethylene glycol) (PEG) for design and engineering of macrophage-evading nanoparticles (NPs). Although PMOXA-engineered NPs have shown comparable pharmacokinetics and in vivo performance to PEGylated stealth NPs in the murine model, its interaction with elements of the human innate immune system has not been studied. From a translational angle, we studied the interaction of fully characterized PMOXA-coated vinyltriethoxysilane-derived organically modified silica NPs (PMOXA-coated NPs) of approximately 100 nm in diameter with human complement system, blood leukocytes, and macrophages and compared their performance with PEGylated and uncoated NP counterparts. Through detailed immunological and proteomic profiling, we show that PMOXA-coated NPs extensively trigger complement activation in human sera exclusively through the classical pathway. Complement activation is initiated by the sensing molecule C1q, where C1q binds with high affinity ( K_d = 11 ± 1 nM) to NP surfaces independent of immunoglobulin binding. C1q-mediated complement activation accelerates PMOXA opsonization with the third complement protein (C3) through the amplification loop of the alternative pathway. This promoted NP recognition by human blood leukocytes and monocyte-derived macrophages. The macrophage capture of PMOXA-coated NPs correlates with sera donor variability in complement activation and opsonization but not with other major corona proteins, including clusterin and a wide range of apolipoproteins. In contrast to these observations, PMOXA-coated NPs poorly activated the murine complement system and were marginally recognized by mouse macrophages. These studies provide important insights into compatibility of engineered NPs with elements of the human innate immune system for translational steps.