Mean tumor fluorescence from groups of three mice treated with E. coli (lux/βG) was significantly greater when FDGlcU was directly injected into tumors as opposed to after i.v, administration (Fig. 9B), suggesting that systemically administered FDGlcU was less able to come into contact with beta-glucuronidase in E. coli as opposed to beta-glucuronidase expressed in cancer cells after administration of Ad/mβG. Here, GUSB is linked to cancer.