ATTENUATED SALMONELLA-TYPHIMURIUM CONTAINING INTERLEUKIN-2 DECREASES MC-38 HEPATIC METASTASES - A NOVEL ANTITUMOR AGENT

Currently there is no long-term effective treatment for unresectable h epatic malignancies Salmonella sp. are known to naturally track to the liver during active infection. To develop a biological vector for del ivery of Interleukin-2 (IL-2) to the liver for anti-tumor purposes, th e avirulent and highly immunogenic chi 4550 strain of Salmonella typhi murium was used as a vector for IL-2. The gene for human IL-2 was clon ed into plasmid pYA292 (renamed pIL-2) and inserted into the attenuate d Salmonella typhimurium and renamed [chi 4550 (pIL-2)]. This transfor mant was found to produced biologically active IL-2 demonstrated by NK cell activation in a 4 hour chromium release cytotoxicity assay. To d etermine anti-tumor potential, MCA-38 murine adenocarcinoma cells were injected intrasplenically into C57BL/6 mice to produce hepatic metast ases and metastases were subsequently enumerated after 12 days. Statis tical significance was determined by ANOVA with Fisher's test for sign ificance. 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 salmo nella demonstrated persistent colonization for up to 4 weeks. No obser vable toxicity was seen to either IL-2 or salmonella. These studies de monstrate that the chi 4550(pIL2) is a novel form of in vivo biotherap y which produces biologically active IL-2 and employs the oral route o f administration to stimulate an immune response against malignancy in the liver.