In recent years, Salmonella has tainted foods including spinach, peanut butter and eggs, sickening thousands of people in the process. But researchers hope that these microbes will make headlines for a better reason: curing cancer. They want to harness Salmonella’s special ability to thrive in oxygen-deprived conditions to target regions of solid tumors that are normally immune to conventional therapies. Elie Dolgin reports.

A tumor extracted from a patient can look deceptively homogenous. Pink and fleshy, it appears be a bundle of cells that are all alike. In reality, these cancerous lumps are anything but uniform. The reason for this has to do with the evolution of the malicious mass: as solid tumors grow unchecked, they expand so fast that their cores become dark slums where essential nutrients are scarce. The dying, oxygen-starved cells at the tumor center collapse in on themselves, their nuclei shrivel up and they die, turning the blackened tissue at the center soft and squishy. In contrast, cancer cells at the periphery of the tumor are continuously bathed in nutrients from the surrounding blood supply, so they maintain their strength and vibrancy.

“It’s like a jelly donut,” says Neil Lindeman, a pathologist at the Brigham and Women’s Hospital in Boston. And, as in these treats, the gooey tumor center might be the sweet spot that researchers hoping to eradicate cancer are seeking.

Blood vessels inside tumors typically penetrate only a few cell layers deep, making it difficult for most chemotherapy agents to reach the surviving cancer cells hiding beneath the surface. Although these hard-to-reach cells are often on their way to joining the dead mass of cells at the tumor center, before that happens they often wreak havoc on the body. In fact, the cells that manage to survive in the core often adapt to hardship and become even more resilient and dangerous. Thus, researchers have long sought better ways to infiltrate the tumor’s inner sanctum.

Instead of searching for small-molecule drugs that might passively enter tumors through the bloodstream, now a handful of researchers have been advancing a radically different approach: they plan to engineer bacteria that can colonize tumors, destroying them from the inside out.

“This is the only way to treat solid tumors effectively because of the ability of bacteria to actively penetrate tumors,” says Neil Forbes, a chemical engineer at the University of Massachusetts–Amherst who has studied this approach.

(Click here to continue reading.)

Image by Eric Collins