The current doctrine of drug delivery requires the solubilization of the drug substance before delivery can occur. In the treatment of disease, the efficacy of many drugs is limited by poor solubility and severe side effects. After decades of research in drug delivery, almost all possible solubilization methods have already been identified. Targeted delivery, i.e., chemically linking a ligand to the delivery vehicle in order to spare normal cells and to kill targeted cells, such as cancer cells and tumors, has been tested. Despite these efforts, it is still very difficult to deliver drugs to specifically targeted sites.
The synthesis of ligand-conjugated systems can be difficult. It is even more difficult to achieve targeted drug delivery, while maintaining the solubility of insoluble drugs. One common strategy is to conjugate ligand molecules, which bind to specific receptors on the target cell surface, into the drug delivery system. This often requires the chemical linkage between a ligand and the polymer carrier that encapsulates the anticancer drug. One of the few such systems is based on liposomes, or micelles. However, these bioconjugates polymeric systems are complex and challenging to synthesize. Moreover, it is often difficult to maintain the integrity of the delicate delivery system during storage. Delivery systems are delicate and fragile, particularly during systemic circulation. In addition, every delivery vehicle works on its own, surrounded and solvated by the solvent (i.e., water). As a result, the amount of drug which eventually reaches each targeted cell may be considerably limited. For targeted delivery of bioimaging and radiotherapy agents, it is even more critical for the collective emission of radiation by a cluster of radioisotopes to occur. However, current delivery platforms do not satisfy these requirements.
Thus, there is a need for a delivery system which can target specific disease and/or imaging sites, while still avoiding the problems associated with lack of solubility and efficacy associated with current drug delivery models.