Toxicology and Drug Delivery by Cucurbit[n]uril Type Molecular Containers

Abstract

Background

Many drug delivery systems are based on the ability of certain macrocyclic compounds – such as cyclodextrins (CDs) – to act as molecular containers for pharmaceutical agents in water. Indeed β-CD and its derivatives have been widely used in the formulation of hydrophobic pharmaceuticals despite their poor abilities to act as a molecular container (e.g., weak binding (K _a<10 ⁴ M ⁻¹) and their challenges toward chemical functionalization. Cucurbit[n]urils (CB[n]) are a class of molecular containers that bind to a variety of cationic and neutral species with high affinity (K _a>10 ⁴ M ⁻¹) and therefore show great promise as a drug delivery system.

Methodology

In this study we investigated the toxicology, uptake, and bioactivity of two cucurbit[n]urils (CB [5] and CB [7]) and three CB[n]-type containers (Pentamer 1, methyl hexamer 2, and phenyl hexamer 3). All five containers demonstrated high cell tolerance at concentrations of up to 1 mM in cell lines originating from kidney, liver or blood tissue using assays for metabolic activity and cytotoxicity. Furthermore, the CB [7] molecular container was efficiently internalized by macrophages indicating their potential for the intracellular delivery of drugs. Bioactivity assays showed that the first-line tuberculosis drug, ethambutol, was as efficient in treating mycobacteria infected macrophages when loaded into CB [7] as when given in the unbound form. This result suggests that CB [7]-bound drug molecules can be released from the container to find their intracellular target.

Conclusion

Our study reveals very low toxicity of five members of the cucurbit[n]uril family of nanocontainers. It demonstrates the uptake of containers by cells and intracellular release of container-loaded drugs. These results provide initial proof-of-concept towards the use of CB[n] molecular containers as an advanced drug delivery system.