Nanoparticles are expected to be applicable for the theranostics as a carrier of the diagnostic and therapeutic agents. Lactosome is a polymeric micelle composed of amphiphilic polydepsipeptide, poly(sarcosine)64-block-poly(l-lactic acid)30, which was found to accumulate in solid tumors through the enhanced permeability and retention effect. However, lactosome was captured by liver on the second administration to a mouse. This phenomenon is called as the accelerated blood clearance phenomenon. On the other hand, peptide-nanosheet composed of amphiphilic polypeptide, poly(sarcosine)60-block-(l-Leu-Aib)6, where the poly(l-lactic acid) block in lactosome was replaced with the (l-Leu-Aib)6 block, abolished the accelerated blood clearance phenomenon. The ELISA and in vivo near-infrared fluorescence imaging revealed that peptide-nanosheets did not activate the immune system despite the same hydrophilic block being used. The high surface density of poly(sarcosine) chains on the peptide-nanosheet may be one of the causes of the suppressive immune response. Copyright © 2014 European Peptide Society and John Wiley & Sons, Ltd.
Polymeric micelles and peptide-nanosheets were prepared with using amphiphilic block polymers having the same hydrophilic poly(sarcosine) block. The former generated anti-poly(sarcosine) IgM as a T-independent antigen, but the latter did not.