Biodegradable polymeric nanocarriers have emerged as one of the most promising platforms for targeted tumor therapy owing to their prolonged circulation time

enhanced accumulation in tumors

decreased adverse effects

improved drug bioavailability

and in vivo biodegradability. However

their therapeutic outcomes are far from optimal partially owing to inefficient and slow intracellular release of drugs at pathological sites. The development of stimuli-responsive nanocarriers that achieve fast drug release at the target site has received great interests. Notably

glutathione(GSH)concentration in tumor tissue and especially inside tumor cells varies from 2 to 10mM

which is about 100~1000 times higher than that in body fluids and extracellular matrices(2~10μM). Taking advantage of the high reducing potential

various reduction-sensitive polymeric nanocarriers have been fabricated for triggered anticancer drug release in tumor tissues and tumor cells. These reduction-sensitive nanocarriers have displayed several unique merits:(1)they have good stability under physiological conditions;(2)they show fast response to intracellular reducing environment

resulting in efficient intracellular drug release;(3)no extra instrument is required. This review highlights the construction and applications of various bioreducible biodegradable polymeric nanocarriers

including bioreducible biodegradable polymeric micelles

polymersomes

and nanogels.