From Adversaries to Allies: Bacteria and viruses are two improbable but powerful weapons being tested in the targeted war on cancer.
Cancer cells are clever. Researchers characterize them as wily, smart, sneaky, and stubborn. But what cancer cells are not is impervious to damage and even death by targeted assault, which is why chemo- and radiation therapies can be so effective: They use chemical concoctions and X-rays, gamma rays, or charged particles to directly attack tumors. Yet those treatments cannot distinguish between cancerous and healthy cells, and ensuring they hit only their intended marks is challenging even with focused radiation. Further, the side effects that accompany both therapies are legion. Excising tumors also has mixed success, since any stray cells left behind can and often do regenerate. With human cancers having such extensive heterogeneity, it is unlikely there will ever be a single agent or even two that will eradicate all of them.
One novel option, immunotherapy, engages the body’s own immune system to confront the disease. Immunotherapeutic drugs attach to cancer cells, rendering them visible to the immune system, or block growth signals that would otherwise allow tumors to increase in size. The earliest studies proved successful in treating breast cancer and non-Hodgkin’s lymphoma, and in March of this year the first immunotherapeutic drug to treat a pediatric cancer—neuroblastoma, which develops from immature nerve cells—was approved by the U.S. Food and Drug Administration.
“Immunotherapy is very exciting, but it is not perfect yet,” says Robert Seeger, MD, director of the Cancer Research Program, Saban Research Institute, Children’s Hospital Los Angeles. “None of this is a 100-percent cure. There are all kinds of escape mechanisms; cancer is pretty sharp. Nevertheless, immunotherapy is now one of the components of treatment for some cancers.”
Researchers have taken a further step that happens to resurrect an approach that had been ignored for some 60-plus years: bacteriolytic therapy. The use of bacteria to destroy a tumor often triggers an immune response that in turn decimates any related tumors elsewhere in the body, largely by exploiting a tumor’s weakness. Solid tumors grow quickly and need a steady blood supply that provides both oxygen and nutrients for their cells to survive and thrive. But it is not uncommon to find that when a tumor grows large enough, the associated blood supply is unable to keep up developmentally, resulting in hypoxia, or very low oxygen, at the tumor’s core. In some tumors, those core cells will die without oxygen and nutrients, and this results in necrotic areas that are usually surrounded by hypoxic pockets where the cells are alive but no longer growing. Chemotherapy and radiation have little effect in this situation because the former needs blood to carry it into the tumor cells and the latter requires oxygen.
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