Polymeric nanovehicles for anticancer drugs with triggering release mechanisms

To maximize the efficacy of anticancer drugs and minimize untoward side effects such as nonspecific toxicity and the development of multi-drug resistance, nano-sized drug delivery systems have been revolutionized by introducing triggering mechanisms for drug release. This will increase the feasibility of obtaining local high-dose therapy in cancerous tissues and at intracellular compartments. Such technology requires highly sophisticated strategies and systems which perform the desired chemical/physical functions depending on the triggering signals. This review introduces and summarizes several design principles using representative examples such as nanosystems responsive to acidic pH (i.e., tumor extracellular pH and endosomal pH), hyperthermic conditions, ultrasound, and specific enzymes.