Nanoaggregates of a random amphiphilic polyanion to carry water-insoluble clofazimine in neutral aqueous media

Effects of Different Weak Small Organic Acids on Clofazimine Solubility in Aqueous Media

BACKGROUND/OBJECTIVES

Clofazimine (CFZ) is a Biopharmaceutics Classification System (BCS) II drug introduced in the US market in 1986 for the treatment of leprosy. However, CFZ was later withdrawn from the market due to its extremely low aqueous solubility and low absorption. In the literature, the intrinsic solubility of CFZ has been estimated to be <0.01 μg/mL, and solubilities of its different salt forms in simulated gastric and intestinal fluids are <10 µg/mL. These are extremely low solubilities for the dissolution of a drug administered orally at 100-200 mg doses.

METHODS

In the present investigation, seven weak organic acids (adipic, citric, glutaric, maleic, malic, succinic, and tartaric) were tested by determining the aqueous solubility of CFZ as the function of acid concentration to investigate whether any of the acids would lead to the supersolubilization of CFZ.

RESULTS

There were only minimal increases in solubilities when concentrations of acids in water were increased up to 2.4 M. The solubilities, however, increased to 0.32, 1.23, and 10.68 mg/mL, respectively, in 5 M solutions of tartaric, malic, and glutaric acids after equilibration for 24 h at 25 °C. Crystalline solids were formed after the equilibration of CFZ with all acids. Apparently, salts or cocrystals were formed with all acids, except for glutaric acid, as their melting endotherms in DSC scans were in the range of 207.6 to 248.5 °C, which were close to that of CFZ itself (224.8 °C). In contrast, the adduct formed with glutaric acid melted at the low temperature of 77 °C, and no other peak was observed at a higher temperature, indicating that the material converted to an amorphous state.

CONCLUSIONS

The increase in CFZ solubility to >10 mg/mL in the presence of 5 M glutaric acid could be called supersolubilization when compared to the intrinsic solubility of the basic drug. Such an increase in CFZ solubility and the conversion of the glutarate adduct to an amorphous state are being exploited to develop rapidly dissolving dosage forms.

Overcoming clofazimine intrinsic toxicity: statistical modelling and characterization of solid lipid nanoparticles

The aim of this work was to develop solid lipid nanoparticles (SLNs) loaded with clofazimine (CLZ) (SLNs-CLZ) to overcome its intrinsic toxicity and low water solubility, for oral drug delivery. A Box-Behnken design was constructed to unravel the relations between the independent variables in the selected responses. The optimized SLNs-CLZ exhibited the following properties: particle size ca 230 nm, zeta potential of -34.28 mV, association efficiency of 72% and drug loading of 2.4%, which are suitable for oral delivery. Further characterization included Fourier transformed infrared spectroscopy that confirmed the presence of the drug and the absence of chemical interactions. By differential scanning calorimetry was verified the amorphous state of CLZ. The storage stability studies ensured the stability of the systems over a period of 12 weeks at 4°C. In vitro cytotoxicity studies evidenced no effect of both drug-loaded and unloaded SLNs on MKN-28 gastric cells and on intestinal cells, namely Caco-2 and HT29-MTX cells up to 25 µg ml^-1 in CLZ. Free CLZ solutions exhibited IC₅₀ values of 16 and 20 µg ml^-1 for Caco-2 and HT29-MTX cells, respectively. It can be concluded that the optimized system, designed considering important variables for the formulation of poorly soluble drugs, represents a promising platform for oral CLZ delivery.

Complexation of clofazimine by macrocyclic cucurbit[7]uril reduced its cardiotoxicity without affecting the antimycobacterial efficacy

Cucurbit[7]uril (CB[7]) has recently attracted increasing attention in pharmaceutical sciences due to its great potential in improving the physicochemical properties and bioactivity of drug molecules. Herein, we have investigated the influence of CB[7]'s complexation on the solubility, antimycobacterial activity, and cardiotoxicity of a model anti-tuberculosis drug, clofazimine (CFZ), that has poor water-solubility and inherent cardiotoxicity. In our study, CFZ was found to be complexed by CB[7], in a 1 : 1 binding mode with a relatively strong binding affinity (in the order of magnitude of 10(4)-10(5) M(-1)), as determined by the phase solubility method via HPLC-UV analysis and (1)H NMR titration, as well as UV-visible spectroscopic titration, and further confirmed by electrospray ionization mass spectrometry (ESI-MS). Upon complexation, the solubility of virtually insoluble CFZ was significantly increased, reaching a concentration of up to approximately 0.53-fold of the maximum solubility of CB[7]. The inherent cardiotoxicity of CFZ was dramatically reduced to almost nil in the presence of CB[7]. Importantly, on the other hand, such a supramolecular complexation of the drug did not compromise its therapeutic efficacy, as shown by the antimycobacterial activities examined against Mycobacterium smegmatis, demonstrating the significant potential of CB[7] as a functional pharmaceutical excipient.

Self-assembly of random copolymers

Self-assembly of random copolymers has attracted considerable attention recently. In this feature article, we highlight the use of random copolymers to prepare nanostructures with different morphologies and to prepare nanomaterials that are responsive to single or multiple stimuli. The synthesis of single-chain nanoparticles from random copolymers and their potential applications are also discussed in some detail. We aim to draw more attention to these easily accessible copolymers, which are likely to play an important role in translational polymer research.

Solubilization of water-insoluble drugs due to random amphiphilic and degradable poly(dimethylmalic acid) derivatives

Amphotericin B (AmB) and clofazimine are potent drugs hindered by their low water solubilities and their toxicities. Carriers able to increase their apparent water solubilities are needed for these drugs and for other molecules with similar properties. Random amphiphilic copolymers derived from poly(dimethylmalic acid) were obtained using different hydrophobization ratios and side group sizes. Apparent water solubilities of pyrene, clofazimine, and AmB were increased up to 10 000, 20 000 and 1000 times, respectively, in aqueous solutions containing these polymers. The presence of sodium chloride in polymer solution increased pyrene solubility but decreased the solubilities of clofazimine and AmB, compared to the salt-free solutions. Synergy between hydrophobic and electrostatic interactions was observed for polar and cationic molecules. Degradation studies showed that the examined polymers were degradable, but none of them were totally degraded in 28 days. These polymers could be used as a new tool for drug solubilization.

Nanoaggregates of biodegradable amphiphilic random polycations for delivering water-insoluble drugs

Cationic amphiphilic random copolyesters were obtained by copolymerization of 5-Z-amino-δ-valerolactone and ε-caprolactone. The amino content of the final copolymers was controlled by the polymerization feed ratio and was in the range 10 to 100%. Copolymers solubility and aggregation behavior was assessed by conductometric and zeta potential analyses. A critical aggregation concentration of ca. 0.05% (w/v) was found for all water-soluble copolymers that formed nanoaggregates. Two populations were found to be present in equilibrium with hydrodynamic diameters in the range of 30-50 and 100-250 nm. The capacity to use the amphiphilic and cationic character of the nanoaggregates to encapsulate highly hydrophobic compounds was further investigated. Finally, copolymers hemo- and cytocompatibility were evaluated by hemagglutination, hemolysis, and cells proliferation tests. The results showed that the proposed cationic amphiphilic random copolyesters are biocompatible.