Another branch of targeted therapies is the design of nanofactories that can be steered to specific locations in the body and there produce proteins and other drugs in response to local conditions or external commands. Early work in this field is underway: "Science is one step closer to producing drugs in the right place at the right time in the body, avoiding the collateral damage of untargeted treatments. Researchers [have] designed nanoparticles that can be stimulated via UV light to produce proteins on demand in vivo. The new method, which involves packaging the molecular machinery for making proteins into a membraned capsule, allows the researchers to spatially and temporally regulate protein production ... The scientists created the nano-sized 'protein factories' by using lipids to encapsulate polymerase and other machinery necessary for protein production from E. coli, along with a DNA plasmid containing a gene of interest. To block transcription until the right moment, they added a DNA 'photo-labile cage' to the plasmid - a small chemical that inhibits transcription but is cleaved by exposure to UV light. To test the principle in vivo, the researchers used luciferase as the reporter protein and injected mice with the nanovesicles. After zapping them with UV light at the site of injection, they were able to measure a local burst of luminescence. ... We have a long way to go still before we have a drug factory that will land in a target tissue to produce a drug of interest ... The study has proved the principle of the first step - getting the protein expressed on signal - but future research will need to ensure that the nanoparticles and the proteins they produce aren't toxic in the wrong place, and that they get to the right location. Targeting the nanoparticles to the appropriate tissues might be achieved by 'decorating' the surface of the vesicles with specific proteins."