Light-emitting microbes promising for cancer detection

Light-emitting bacteria and viruses localize to tumors when injected into animal models of cancer, without causing bacteremia or viremia, according to an article in the February 8th online issue of Nature Biotechnology.

Although microbes are known to home in on tumors, this is the first study to demonstrate in real time the spatiotemporal progression of infections in live animals with implanted tumors, note Dr. Aladar A. Szalay of Loma Linda University, California and colleagues. This was made possible by transforming the bacteria with plasmids encoding a luciferase or a fluorescent protein gene.Intravenous injection of vaccinia virus and Escherichia coli and attenuated strains of Vibrio cholerae, Salmonella typhimurium and Listeria monocytogenes showed tumor-specific localization. No mutations were required for tumor-specific entry and replication. In healthy animals, the organisms were cleared within days.Only established tumors, regardless of size, were capable of protecting bacteria from immune clearance, the researchers found. This was true for implanted human prostate carcinoma, murine bladder carcinoma, human mammary carcinoma and human fibrosarcoma. After combined injection of bacteria and vaccinia, both organisms accumulated and replicated in the same tumor.Metastatic tumors as small as 0.5 mm?, normally difficult to detect, were illuminated.This technique seems to be equally effective in immunocompetent and immunocompromised animals, and for syngeneic and allogeneic tumors, the authors note. “These systems,” they conclude, “may be applied to the detection of tumors and metastases and may allow the development of tumor-specific gene therapy protocols.” (Source: Nature Biotech 2004: Reuters Health: February 9, 2004: Oncolink)