Listeria bacteria lethal to metastatic prostate cancer cells

Researchers have leveraged Listeria bacteria to launch a selective attack on metastatic prostate cancer, according to a study published April 23 in Proceedings of the National Academy of Sciences. The technique has the potential to launch a new era in the treatment of metastatic prostate cancer, the research team said in a press release.

The impetus for the current project was the observation that an attenuated form of Listeria can target cancer cells and bypass normal cells. That’s because the tumor environment suppresses the immune response and allows the bacteria to survive in the tumor cells.

In the next step, researchers used Listeria to transport an anticancer agent to tumors in the lab. The current study took the process further and applied the radioimmunotherapy technique in a mouse model.

Claudia Gravekamp, PhD, of Albert Einstein College of Medicine in New York City, and colleagues paired the radioactive isotope rhenium with attenuated Listeria. The agent was injected into mice with metastatic prostate cancer once daily for seven days. After seven days without treatment, the mice received four additional daily injections.

After 21 days, metastatic lesions were reduced by 90 percent in treated mice compared with untreated mice. The researchers observed that the radioisotope honed in on metastases and less abundantly to primary tumors but bypassed normal tissues. No side effects were observed in treated mice.

“At this point, we can say that we have a therapy that is very effective for reducing metastasis in mice,” Gravekamp said in the release. “Our goal is to clear 100 percent of the metastases, because every cancer cell that stays behind can potentially form new tumors.”

Potential strategies for achieving improved clearance of metastatic cells include: fine-tuning the treatment schedule, increasing the radiation dose and adding additional drugs to the cocktail.

The researchers’ next step is assessing the impact of the treatment on survival.

For more about targeted radiotherapy, please read "Theranostics Sets the Stage for Personalized Medicine," in Health Imaging.