Cell-based drug carriage of nanoformulated drugs and proteins has shown promise in early efforts aimed to improve central nervous system (CNS) drug delivery. Specifically, it is one promising avenue for translational research efforts seeking ways to combat the ravages of neurodegenerative disease [1
]. The system rests in the abilities of blood borne macrophages to carry a range of neuroprotective, immune modulatory, and antimicrobial drugs, acting as Trojan horses, to cross the blood brain barrier (BBB) and affecting ongoing disease at action sites [2
]. Specific drug carriage inside inflammatory cells rests with commonalities of inflammatory processes that underlie degenerative, infectious, and metabolic disorders of the CNS that include Alzheimer’s and Parkinson’s diseases (AD and PD), amyotrophic lateral sclerosis, Prion disease, meningitis, encephalitis, multiple sclerosis, hepatic encephalopathy, and human immunodeficiency virus (HIV)-associated neurocognitive impairment (HAND) [6
]. Such CNS inflammation is characterized by chemokine and cytokine-mediated leukocyte recruitment to the site of disease by processes involving macrophage diapedesis and chemotaxis [7
]. Importantly, macrophages also have a high rate of endocytosis that allows them to efficiently accumulate micro- and nanoparticles within intracytoplasmic endosomes and release them through processes that include exocytosis. All these features make blood borne and tissue macrophages attractive candidates for cell-mediated delivery of drugs and therapeutic proteins. Particularly, redox enzymes, which are known to inactivate reactive oxygen species (ROS) and reduce inflammation at the site of action, can be carried by into a diseased inflamed brain.
Recently our laboratories developed novel CNS drug delivery systems using macrophages for delivery of the antioxidant enzyme, catalase, in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model of PD [8
]. For this system, nanoformulated catalase was obtained by coupling the enzyme to a cationic block copolymer, polyethyleneimine-poly(ethylene glycol), leading to a polyion complex micelle. Using macrophages as a carrier for therapeutic proteins offers several advantages to combat CNS disease including: i) prolonged plasma drug levels; ii) time-controlled release of the cell loaded drug; iii) targeted drug transport to the site of disease; and iv) diminished drug immunogenicity. Indeed, our previous works has demonstrated that BMM loaded with nanoformulated catalase and injected into MPTP-intoxicated mice reduce neuroinflammation and attenuate nigrostriatal degeneration [9
In attempts to improve upon what was previously done we theorized that appropriate drug nanoformulations for cell-mediated delivery could be best designed by optimization of loading capacity, enabling sustained release, and realizing efficient preservation of drug activity within the cell-carriers. Indeed, size, charge and shape of nanoformulated antiretroviral drugs were shown important for macrophage-based delivery in treating ongoing HIV-1 disease [1
]. Similar results were reported for the monocytes and neutrophil-mediated delivery of the liposome-encapsulated antifungal agent, chloroquine, against C. neoformans
infection in the mouse brain [5
]. In particular, cell-carriers showed preferential uptake of liposomes containing negatively charged lipids, such as phosphatidylserine [3
], over liposomes that contain only neutral lipids, such as phosphatidylcholine. In addition, cytotoxicity of nanocontainers, as well as their ability to protect the drug inside cell-carriers, is also determined by their composition and structure [1
The present study serves to optimize cell mediated enzyme delivery for therapeutic gain by improving the preparation and characterization of polyion complexes obtained by coupling catalase to different block copolymers. This consisted of: a) ionic block (positively-charged: polyethyleneimine- (PEI), or poly(L-lysine)- (PL); or negatively-charged: poly(L-glutamic acid)- (PGLU); and b) non-ionic block, poly(ethylene glycol)- (PEG). Electrostatic interactions between catalase and the charged copolymer block resulted in the formation of a insoluble polyion core, while a PEG corona provided stability of nanoparticles in water solutions. Effects of the length, charge and structure (linear or branched) of the ionic block on the nanozyme cytotoxicity, kinetics of uptake and release, and ability to protect enzymatic activity inside the host cells were examined. In addition, polymers with the similar ionic blocks (PEI or PL) but without PEG block were used to evaluate the role of PEG corona. All together, the incorporation of catalase in a BIC with cationic block copolymers, polyethyleneimine-poly(ethylene glycol) (PEI50-PEG), or poly(L-lysine)-poly(ethylene glycol) (PL50-PEG), resulted in formulations with optimal protection and sustained enzyme release of active catalase from macrophage carriers.