Tumour-targeted delivery of TRAIL using Salmonella typhimurium enhances breast cancer survival in mice

Abstract

BACKGROUND: An effective cancer therapeutic must selectively target tumours with minimal systemic toxicity. Expression of a cytotoxic protein using Salmonella typhimurium would enable spatial and temporal control of delivery because these bacteria preferentially target tumours over normal tissue. METHODS: We engineered non-pathogenic S. typhimurium to secrete murine TNF-related apoptosis-inducing ligand (TRAIL) under the control of the prokaryotic radiation-inducible RecA promoter. The response of the RecA promoter to radiation was measured using fluorometry and immunoblotting. TRAIL toxicity was determined using flow cytometry and by measuring caspase-3 activation. A syngeneic murine tumour model was used to determine bacterial accumulation and the response to expressed TRAIL. RESULTS: After irradiation, engineered S. typhimurium secreted TRAIL, which caused caspase-3-mediated apoptosis and death in 4T1 mammary carcinoma cells in culture. Systemic injection of Salmonella and induction of TRAIL expression using 2 Gy g-irradiation caused a significant delay in mammary tumour growth and reduced the risk of death by 76% when compared with irradiated controls. Repeated dosing with TRAIL-bearing Salmonella in conjunction with radiation improved the 30-day survival from 0 to 100%. CONCLUSION: These results show the pre-clinical utility of S. typhimurium as a TRAIL expression vector that effectively reduces tumour growth and extends host survival.

Targeting Tumors with Salmonella Typhimurium - Potential for Therapy

“…It is envisaged that specific anti-cancer molecules delivered by S. Typhimurium can be used to target the outer regions of the tumor with the bacteria invading deep within the tumor, penetrating regions of the tumor architecture that conventional therapies cannot reach [12,32]. One of the key challenges with conventional chemotherapy is delivery of potentially toxic agents to the appropriate areas of the tumor while preventing damage to healthy tissue.…”

“…Inducible gene promoters offer a solution that is presently employed. Detection of small molecules by the bacteria, or irradiation at the point where expression is required, have both been used successfully in vivo along with the use of pro-drugs introduced at the tumor site for conversion into an anticancer agent by the bacteria upon contact [13,32,33]. recA, the radiation inducible promoter, was linked to tumor necrosis factor (TNF)-related apoptosis inducing ligand (TRAIL) to control its expression by Salmonella during infection of tumors [32].…”

“…The metabolism of S. Typhimurium has been exploited to attenuate the strains used in cancer therapy, manipulating the bacteria so that they grow only at tumor sites. Metabolic genes have been removed from S. Typhimurium, such as purI in the [32,34,59] Antibiotic sensitivity Salmonella can be easily removed following treatment with antibiotics Native cytotoxicity Ability of the bacteria to produce virulence factors that leads to cytotoxicity and attract immune cells to the tumors helps in further tumor regression [50,60] Post delivery detection Engineered Salmonella expresses fluorescent proteins that offers the ability to be externally detected [47,61,62,63] mutant strain VNP20009, rendering the mutant bacterium auxotrophic for certain compounds that are found in very high concentrations at tumor sites, in this case purines [23]. Such genetic engineering, forces migration of S. Typhimurium towards tumors in order to survive and results in the bacteria accumulating at the tumor site at over a 1,000 times higher levels than in normal tissue [24].…”

Quorum-sensing Salmonella selectively trigger protein expression within tumors

“…Current cancer chemotherapeutic regimens have limited efficacy due to therapeutic resistance and systemic toxicity (1)(2)(3), which prevents the use of more aggressive dosage schemes (4). Salmonella are capable of overcoming these limitations because they preferentially accumulate in tumors, actively penetrate tumor tissue, and can be engineered to produce anticancer drugs in situ (5)(6)(7)(8)(9)(10)(11). Salmonella that only activate drug expression in tumors and not healthy tissue will reduce toxicity and allow for the use of more aggressive therapeutics.…”

“…Precise triggering of expression can boost drug concentration within tumors while minimizing harmful side effects (6). Salmonella can be engineered to induce protein expression in response to molecular triggers, radiation, or hypoxia (6,11,(13)(14)(15)(16)(17)(18).…”