Because E. coli beta-glucuronidase can hydrolyze SN-38G to SN-38 about 250-fold faster than murine beta-glucuronidase (Fig. 8A), we anticipated that bacterial-mediated delivery of E. coli beta-glucuronidase to tumors would greatly enhance the antitumor activity of CPT-11 based on our previous studies in which we showed that ectopic expression or viral-mediated expression of murine beta-glucuronidase on tumor cells resulted in intratumoral conversion of SN-38G to SN-38, thereby increasing the antitumor activity of CPT-11 in mouse models of human cancer [4,36,37]. The gene discussed is GUSB; the disease is cancer.