C 2011 American Chemical Society

espite numerous advances over the past several decades, effective can-cer chemotherapy remains challeng-ing. The generalized toxicity of many drugs makes it difficult to achieve therapeutic concentrations without severe systemic side effects. Nanocarriers are being devel-oped that address these issues by selec-tively delivering drugs to tumor sites. Some designs take advantage of the enhanced permeability of vasculature in the tumor vicinity to promote passive accumulation of drug nanocarriers that are too large to otherwise leave the circulation. Others seek to endow a nanocarrier with the adde