A polymeric micelle is a macromolecular assembly that forms typically from AB type of block copolymers and that has a spherical inner core and an outer shell as shown in Figure 1. Polymeric micelle carriers have been actively studied for targeting of anti-cancer drugs to solid tumors. Since polymeric micelles can be formed through various cohesive interactions such as hydrophobic and ionic interactions, various chemical species including hydrophobic organic compounds and metal ions can be incorporated into polymeric micelles. Therefore, polymeric micelle carriers can deliver both contrast agents for diagnosis and drugs for chemotherapy.
In this paper, we like to talk on two topics of the polymeric micelle carrier systems. First, we like to show contrast agent targeting to two therapeutic sites, solid tumors and brain ischemic stroke sites. Secondary, we talk on immunological responses to multiple injections of polymeric micelle carriers, since these immunological issues are more important in non-cytotoxic contrast agent targeting than in targeting of cytotoxic anti-cancer drugs. (The immunological responses are greatly suppressed by injections of cytotoxic drugs.) An immunological response, accelerated blood clearance (ABC) phenomenon, is well known for PEG-coated liposomes. Our polymeric micelle carriers also possess PEG as the outer shell. Since the ABC phenomenon greatly influences targeting functions of carrier systems, studies on polymeric micelles' ABC phenomenon are of great importance. Interestingly, the polymeric micelles showed no or low ABC phenomenon. This is a clear contrast to PEG-coated liposomes that strongly exhibit the ABC phenomenon. This interesting difference in the ABC phenomenon behaviors is considered to result from differences in chemical structures of the interface between PEG and the other component. This fact stresses on an importance of chemistry in biomedical applications.