Cyclodextrin-based host-guest supramolecular nanoparticles for delivery: from design to applications.

CONSPECTUS: Efficient assembly in host-guest interactions is crucial to supramolecular nanotechnology. Cyclodextrins (CDs), which possess a hydrophilic exterior surface and hydrophobic interior cavity on the truncated cone, improve the biocompatibility of nanodelivery systems, and hence, supramolecular approaches utilizing CDs can improve and expand the design and applications of functional delivery systems. Owing to good inclusion ability, αCD and βCD are commonly used in the design and construction of supramolecular structures. In this Account, we describe the design strategies to adopt CDs in host-guest delivery systems. Modification of CDs with polymers is popular in current research due to the potential benefits rendered by cationic protection and improved capability. While the process has only minor influence on the host characteristics of the CD cavity, the interaction between the CD and the guest moiety imparts new attributes to the nanosystems with guest-decorated functional groups such as adamantyl poly(ethylene glycol) (PEG) for coating protection, hybrid guests for conformational flexibility, and adamantyl prodrugs for drug delivery. Some specific agents form inclusion complexes with the polymerized βCDs directly and core-shell nanoparticles with hydrophobic cores and are usually created to carry insoluble drugs while the hydrophilic shells offer protection. These unique designs provide the means to practically adapt special characteristics for additional functions or co-delivery. In order to be accepted clinically, delivery systems need to possess extra functions such as controlled particle size, biodegradability, controlled release, and targeted delivery to overcome the hurdles in delivery. These features can be added to biomaterials by self-assembly of functional groups facilitated by the host-guest interactions. Size control by hybridization of switchable polymer compartments in supramolecular structures contributes to the biodistribution utility and biodegradability by incorporating the moieties with hydrolyzable connections and enhancing intracellular degradation and clearance. Controlled release by application of responsive structures like molecular gatings eased by the host-guest interaction can be triggered by the tumor microenvironment at extreme pH and temperature or by external stimuli such as light. Along with the binding selectivity and controlled release, the host-guest nanoparticles show enhanced efficacy in delivery especially to tumors. Recent developments in supramolecular co-delivery systems are described in this Account. Nanoparticles can be designed to carry adamantyl prodrugs and therapeutic nucleotides to tumors so that the released drugs and gene expression synergistically inhibit malignant tissue growth. Optimization of nanoparticle delivery systems by multifunctional transitions yields better biocompatibility and controlled response, and such novel designs will expedite in vivo applications. Hence, multifunctional CD-based host-guest supramolecular nanoparticles with co-delivery ability are expected to have many potential clinical applications.