Polysaccharide-based Polyion Complex Micelles as New Delivery Systems for Hydrophilic
Cationic Drugs

Polyion complex (PIC) micelles have emerged as promising delivery systems of ionic hydrophilic drugs. It was the aim of this study to develop dextran-based PIC micelles for the delivery of hydrophilic cationic drugs using a new family of carboxymethyldextranblock- poly(ethylene glycol) (CMD-PEG) copolymers. Four CMD-PEG copolymers were prepared: (i) two copolymers identical in terms of the length of CMD and PEG blocks, but different in terms of the charge density of the CMD block; and (ii) two copolymers in which the charged block is the same, but the PEG block is of different molecular weight. The micellization of CMD-PEG copolymers and drug delivery aspects of the resulting micelles were evaluated using different cationic drugs: diminazene (DIM), a model cationic drug, minocycline hydrochloride (MH), a semisynthetic tetracycline antibiotic with promising neuroprotective properties and different aminoglycoside antibiotics. The cytotoxicity of CMD-PEG copolymers was evaluated in different cell lines using MTT and Alamar blue assays. CMD-PEG micelles encapsulating different drugs were characterized using different techniques, such as 1H NMR spectroscopy, dynamic light scattering (DLS), and isothermal titration calorimetry (ITC). The pattern of drug release and pharmacological activity of micelles-encapsulated drugs were also evaluated. The CMD-PEG copolymers did not induce cytotoxicity in human hepatocytes and murine microglia (N9) in concentrations as high as 15 mg/mL after incubation for 24 h. Electrostatic interactions between CMD-PEG copolymers and different cationic drugs triggered the formation of PIC micelles with a CMD/drug core and a PEG corona. The properties of DIM/CMD-PEG micelles were strongly dependent on the degree of carboxymethylation of the CMD block. Micelles of CMD-PEG copolymers having degree of carboxymethylation ≥ 60%, incorporated up to 64 wt% DIM, resisted salt-induced disintegration in solutions up to 400 mM NaCl and sustained DIM release under physiological conditions (pH 7.4, 150 mM NaCl). In contrast, micelles of CMD-PEG of degree of carboxymethylation ~ 30% had lower drug content (~ 40 wt% DIM) and disintegrated at lower salt concentration (∼ 100 mM NaCl). The CMD-PEG copolymer that showed the most satisfactory micellar properties, in terms of high drug loading capacity, sustained drug release and micelles stability was selected as a potential delivery system of minocycline hydrochloride (MH) and different aminoglycosides. CMD-PEG micelles encapsulating either MH or aminoglycosides had small size (< 200 nm in diameter), high drug loading capacity (≥ 50 wt% drug) and sustained drug release. These micelles were stable in aqueous solution for up to one month, after freeze drying and in the presence of bovine serum albumin. Furthermore, the micelles protected MH against degradation in aqueous solutions. Micelles-encapsulated drugs maintained their pharmacological activity where MH micelles reduced lipopolysaccharides-induced inflammation in murine microglia (N9) cells. And aminoglycosides micelles were able to kill a test micro-organism (E. coli X-1 blue strain) in culture. Aminoglycosides/CMD-PEG micelles were unstable under physiological conditions. Micelle properties were greatly enhanced by hydrophobic modification of CMD-PEG. Thus, aminoglycosides/dodecyl-CMD-PEG micelles showed smaller size and better stability under physiological conditions. The results obtained in this study show that CMD-PEG copolymers are promising delivery systems for cationic hydrophilic drugs.

Keyphrases: Minocycline, Neuro-inflammation, Aminoglycosides, Dextran, Hydrophilic drugs, Polyion complex micelles, Diminazene, Minocycline, Micelles stability, Aminoglycosides, Neuroinflammation