Linear-dendritic drug conjugates forming long-circulating nanorods for cancer-drug delivery.

Elongated micelles have many desirable characteristics for cancer-drug delivery, but they are difficult to obtain since amphiphilic polymers form such nanostructures only within narrow composition ranges depending on their own structures. Herein, we demonstrated a facile fabrication of different nanostructures via drug content-controlled self-assembly of amphiphilic linear-dendritic drug conjugates - using the number of the conjugated hydrophobic drug molecule camptothecin (CPT) to tailor the hydrophobicity of amphiphilic PEG-block-dendritic polylysine-CPT (PEG-xCPT) conjugates and thereby control their self-assembled nanostructures - nanospheres or nanorods of different diameters and lengths. The shape and size of the nanostructures were found to strongly affect their in vitro and in vivo properties, particularly the blood clearance kinetics, biodistribution and tumor targeting. The nanorods with medium lengths (<500 nm) had a much longer blood circulation and faster cellular uptake than the nanospheres or long nanorods. Thus, polymeric nanorods with proper lengths may be ideal nanocarriers capable of uniting the opposite requirements in cancer-drug delivery.