AttenuatedSalmonella typhimuriumContaining Interleukin-2 Decreases MC-38 Hepatic Metastases: A Novel Anti-tumor Agent

Abstract

Currently, there is no long-term effective treatment for unresectable hepatic malignancies. Salmonella sp. are known to naturally track to the liver during active infection. To develop a biological vector for delivery of Interleukin-2 (IL-2) to the liver for anti-tumor purposes, the avirulent and highly immunogenic chi 4550 strain of Salmonella typhimurium was used as a vector for IL-2. The gene for human IL-2 was cloned into plasmid pYA292 (renamed pIL-2) and inserted into the attenuated Salmonella typhimurium and renamed [chi 4550 (pIL-2)]. This transformant was found to produced biologically active IL-2 demonstrated by NK cell activation in a 4 hour chromium release cytotoxicity assay. To determine anti-tumor potential, MCA-38 murine adenocarcinoma cells were injected intrasplenically into C57BL/6 mice to produce hepatic metastases and metastases were subsequently enumerated after 12 days. Statistical significance was determined by ANOVA with Fisher's test for significance. Hepatic metastases enumerated by blinded observers revealed that the mean number of metastases was 106.4 in control mice, 103.7 in mice gavage fed attenuated salmonella without IL-2 [chi 4550(pYA292)], and 44.3 in mice fed the chi 4550(pIL2); (ANOVA: p < 0.01). Culture of livers and spleens in mice administered a single gavage dose of salmonella demonstrated persistent colonization for up to 4 weeks. No observable toxicity was seen to either IL-2 or salmonella. These studies demonstrate that the chi 4550(pIL2) is a novel form of in vivo biotherapy which produces biologically active IL-2 and employs the oral route of administration to stimulate an immune response against malignancy in the liver.

Attenuated Salmonella typhimurium with IL-2 Gene Reduces Pulmonary Metastases in Murine Osteosarcoma

“…Individual drugs have been ineffective in treating pulmonary metastases [31], and combined therapy has not substantially altered the course of disease in patients who present with detectable pulmonary osteosarcoma metastases, as the 5-year survival rate continues to hover around 30% [9,11,37]. Our previous research demonstrates an antitumor effect in a variety of animal cancer models associated with oral dosing of attenuated Salmonella typhimurium with and without a truncated gene for human IL-2 [1,7,8,27,29,33]. This project represents the early assessment of S. typhimurium in an osteosarcoma pulmonary metastatic model.…”

“…In these studies, NK cell populations appear largely responsible for the decrease in tumor burden in salmonella-treated animals [7,8,27,29,33]. We sought to determine whether previous antitumor mechanisms of SalpIL2 could be applied to an experimental model of metastatic osteosarcoma.…”

“…Other experimental metastasis models utilizing SalpIL2 demonstrate NK expansion and involvement [7,8,27,29,33], implicating NK cell receptor involvement in the antitumor mechanism. Future studies within this model are focusing on the prophylactic use of SalpIL2 in metastatic osteosarcoma, local tumor/NK cell interaction, and the systemic cytokine response to tumor and SalpIL2.…”

“…We recently demonstrated a single oral dose of an attenuated Salmonella typhimurium genetically engineered with a gene for a truncated human interleukin-2 (SalpIL2) substantially reduces unresectable adenocarcinoma metastases to the liver in experimental treatment and prophylactic mouse models [7,8,27,29,33]. In addition, SalpIL2 reduces the volume and mass of retroperitoneal neuroblastoma tumors in an experimental murine treatment model [1].…”

Targeting Tumors with Salmonella Typhimurium - Potential for Therapy

“…Other approaches employ S. Typhimurium to deliver cytokines to the tumor site in an attempt to activate immune cells or elicit an immune response against the tumor [8,10,35,36,37,38,39]. Antigens have also been linked to bacterial toxins that are highly immunogenic to sensitize the immune system against cancer cell antigens [10,40].…”