Azobenzenes are a class of photoswitchable molecules and are used in photopharmalogical applications for their reversible photoisomerization, as described in the previous section. An example of a photoswitchable molecule that uses azobenzene is phototrexate. Phototrexate is an inhibitor of human dihydrofolate reductase and is an analogue of methotrexate, a chemotherapy agent. When in its photoactive cis form, phototrexate has been shown to be a potent antifolate and is relatively inactive when in the trans form. The azologization, or incorporation of azobenzene, of methotrexate allows for control of cytotoxic activity and is considered a step forward in developing targeted anticancer drugs with localized efficacy.