Cancer cells, compared with normal cells, are under oxidative stress associated with the increased generation of reactive oxygen species (ROS) including H 2 O 2 and are also susceptible to further ROS insults. Cancer cells adapt to oxidative stress by upregulating antioxidant systems such as glutathione to counteract the damaging effects of ROS. Therefore, the elevation of oxidative stress preferentially in cancer cells by depleting glutathione or generating ROS is a logical therapeutic strategy for the development of anticancer drugs. Here we report a dual stimuli-responsive hybrid anticancer drug QCA, which can be activated by H 2 O 2 and acidic pH to release glutathione-scavenging quinone methide and ROS-generating cinnamaldehyde, respectively, in cancer cells. Quinone methide and cinnamaldehyde act in a synergistic manner to amplify oxidative stress, leading to preferential killing of cancer cells in vitro and in vivo. We therefore anticipate that QCA has promising potential as an anticancer therapeutic agent.

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A main challenge in the development of anticancer drugs that eradicate cancer cells specifically with minimal toxicity to normal cells is to identify the cancer-specific properties. Cancer cells sustain a higher level of reactive oxygen species, owing to metabolic and signaling aberrations and unrestrained growth. Cancer cells are also furnished with a powerful reducing environment, owing to the overproduction of antioxidants such as glutathione (GSH). Therefore, the altered redox balance is probably the most prevailing property of cancer cells distinct from normal cells, which could serve as a plausible therapeutic target. In this work, we developed a GSH-depleting pro-oxidant, benzoyloxy dibenzyl carbonate, termed B2C, which is capable of rapidly declining GSH and elevating oxidative stress to a threshold level above which cancer cells cannot survive. B2C was designed to release quinone methide (QM) that rapidly depletes GSH through esterase-mediated hydrolysis. B2C was able to rapidly deplete GSH and induce an overwhelming level of oxidative stress in cancer cells, leading to mitochondrial disruption, activation of procaspase-3 and PARP-1, and cleavage of Bcl-2. In the study of tumor xenograft models, intravenously injected B2C caused apoptotic cell death in tumors and significantly suppressed tumor growth. These findings provide a new insight into the design of more effective anticancer drugs, which exploit altered redox balance in cancer cells.