Tumor-Targeted Salmonella Expressing Cytosine Deaminase as an Anticancer Agent

Abstract

The study was designed to evaluate whether TAPET-CD, an attenuated strain of Salmonella typhimurium ex pressing Escherichia coli cytosine deaminase (CD), was capable of converting nontoxic 5-fluorocytosine (5-FC) to the active antitumor agent 5-fluorouracil (5-FU). The antitumor effect of TAPET-CD plus 5-FC against subcutaneously implanted colon tumors was also evaluated. TAPET-CD was given to tumor-bearing mice by a single bolus intravenous administration followed with 5-FC by intraperitoneal administration. TAPET-CD accumulated in tumors at levels 1000-fold higher than that in normal tissues and high levels of 5-FU were de growth by 88%-96%, compared to TAPET-CD alone, which inhibited tumor growth by 38%-79%. These data suggest that tumor-targeting Salmonella could be used to deliver prodrug-converting enzyme selectively to tumors and produced anti-tumor effects when the corresponding prodrug was also given. These studies demonstrate the potential use of attenuated Salmonella as a tumor-selective protein delivery vector.

Non-invasive 19F MR spectroscopy of 5-fluorocytosine to 5-fluorouracil conversion by recombinant Salmonella in tumours

“…This 19 F MRS analysis revealed the absence of 5-FU and only small amounts of catabolites in the liver, at least up to 2 h after the in vivo measurements. Our results agree with the observations made by King et al, (2002) using high-performance liquid chromatography. The difference between the small catabolite levels in our study and the large levels usually found with conventional 5-FU chemotherapy, is obvious for two reasons: (1) it is expected that the 'leakage' of 5-FU from the tumour microenvironment into the systemic circulation is poor (eg, indirectly shown by Wallace et al, 1994), and (2) this type of conversion occurs mainly in the liver and little FBAL enters the systemic circulation (discussed by eg, Prior et al, 1990).…”

“…Using in vitro analysis of bacterial lysates, we also clearly demonstrated the positive correlation between the number of TAPET-CD and the amount of 5-FC that is converted to 5-FU for a given incubation period. Second, the TAPET-CD persist in the tumours without the need for a repeat injection, similar to the findings of King et al, (2002) and Mei et al, (2002). Indeed, in the present study, the production of 5-FU after the i.p.…”

“…This suggests that MRS may be useful for monitoring therapy with TAPET-CD/5-FC since it allows repetitive examinations without the need to interfere with the microenvironment. The use of non-pathogenic strains of bacteria to transfer effector genes and therapeutic proteins selectively to the tumour microenvironment is being intensively investigated (Minton et al, 1995;Zheng et al, 2000;Theys et al, 2001;King et al, 2002;Liu et al, 2002). Based on the promising preclinical in vitro and in vivo data, including the positive safety profile, the application of the attenuated Salmonella strain (both i.tu.…”

“…Previous results showed that recombinant bacteria can be used as a delivery vector to transfer CDase selectively to the compromised intratumoural microenvironment. The tumour-selective applicability of this strategy has recently been demonstrated in vitro and in vivo with non-pathogenic clostridia (Minton et al, 1995;Fox et al, 1996;Theys et al, 2001) and attenuated Salmonella Typhimurium (msbB À ,purI À strain; Vion Pharmaceuticals Inc.) (Low et al, 1999;Lee et al, 2001;King et al, 2002;Mei et al, 2002). Since such bacteria-based vectors are tumour selective, the enzyme/prodrug system may provide maximal tumour dosing with prolonged drug presence and circumvent treatment-limiting side effects (reviewed by Aghi et al, 2000).…”

Pilot trial of genetically modified, attenuated Salmonella expressing the E. coli cytosine deaminase gene in refractory cancer patients

“…19,20,24 CD is an enzyme found in both bacteria and fungi, but not in mammalian cells. It converts 5-fluorocytosine (5-FC), an antifungal agent with limited systemic toxicity, to 5-fluorouracil (5-FU).…”