Calixarene-Guest Complexes: The Next Innovation in Delivery of Drugs and Biologics

Calixarenes are third generation of macrocyclic molecules with excellent biocompatibility currently being researched extensively for their diverse potential as therapeutic candidates and for delivery of drugs and biologics. This review discusses the unique structural features which allow them to selectively bind to a wide variety of guest molecules within their hydrophobic cavity, as well as complex with other molecules on their upper and lower rims to enable their application for encapsulation of drugs for targeted and controlled release, molecular carriers for antigens and nucleic acids, and as biomedical sensors. The calixarenes’ unique host–guest chemistry enables encapsulation of lipophilic drugs in the latter's cavity, while the head groups and side chains on the upper and lower rim can be functionalized readily with various targeting moieties as peptides and biological ligands which specifically recognize and bind to cancer cells via surface receptors. The design of calixarene constructs help incorporation of multiple functionalities into a single platform. This active targeting approach enhances the accumulation of the drug at the tumor site while reducing its distribution in healthy tissues, thereby minimizing side effects. Ongoing research in exploration and optimization of calixarenes for application as targeted drug and gene delivery agents has been discussed.