A stiff punishment for tumors

Cancer The behavior of tumor cells is regulated not only by their own biology, but also by interactions with their microenvironment. A key part of the microenvironment is the extracellular matrix, which typically has a greater stiffness in tumors than in surrounding normal tissues. Exploiting this difference, Liu et al. engineered mechanoresponsive mesenchymal stem cells to act as vehicles for cancer drug delivery in a mouse model. The engineered stem cells accumulated in tumors, delivering the first half of a two-part cancer therapy: the enzyme cytosine deaminase. Subsequently, the drug 5-fluorocytosine was delivered systemically, and the cytosine deaminase present in the tumor environment activated the drug to supply local anticancer therapy with no off-target damage. Sci. Transl. Med. 9 , eaan2966 (2017).