Thermo-responsive targeting of polymeric micelles by controlling the cellular uptake based on the change of their surface arginine density.

Stimulus-responsive nanocarriers are good candidates for targeted drug delivery. Herein, inspired by the existence of a clear threshold number of arginine residues in oligoarginines for cell-penetrating peptide (CPP) activity, we developed a strategy to control the CPP activity by changing the local arginine density for thermo-responsive targeting. We constructed polymeric micelles whose shell consists of a thermo-responsive polymer based on N-isopropylacrylamide, with a low density of arginine moieties (named Arg-TRM). At physiological temperature (37 °C), internalization of Arg-TRM into cells was small and comparable to that of micelle without arginine. In contrast, upon heating at 42 °C, the arginine density on the micellar surface was increased by thermo-responsive shrinkage of the shell, thereby switching on the CPP activity and enabling efficient cellular uptake. The response of Arg-TRM at 42 °C occurred within a few minutes and the intracellular uptake was rapidly enhanced from 5 min after the heating. This response was transient, thus enabling reversible control of the enhancement by heating. As proof-of-concept, we show that intravenously administered Arg-TRM was effectively accumulated in one ear of a normal mouse by local heating. These results indicate that Arg-TRM is a promising drug carrier for on-demand targeted drug delivery in response to mild external heating.