Studies have shown that cancer tumors with cells low in oxygen often survive and continue to grow despite the treatments thrown at them. Early results from clinical studies suggest that a method of identifying these hypoxic tumors developed by a scientist at the University of North Carolina can lead to a greater understanding of treatment resistance. The method may also help doctors more effectively predict the outcome of cancer therapies.
"For many years it's been known that cancerous tumors that have low amounts of oxygen are relatively resistant to the effects of radiation treatment," said Mahesh Varia, MD, professor of radiation oncology at UNC-CH. "More recently we have learned that some hypoxic tumors are resistant to chemotherapy, and that patients treated surgically who have hypoxic tumors also do less well than patients with normally oxygenated tumors."
But of the methods available for identifying tumor hypoxia, only one does so on the cellular level that's significantly the most advanced in its clinical work. Moreover, it is highly accurate and does not require probing the patient's tumor directly during a complicated procedure. This is the pimonidazole hypoxia marker invented by UNC scientist, James A. Raleigh, PhD, professor of radiation oncology.
"When we started at UNC in 1988, the idea was to measure the amount of hypoxia in human tumors because that would predict which patients were going to do poorly after radiation. So this was a predictive assay to begin with," he said. "We spent a number of years proving it out in the laboratory and with animals in a veterinary setting and found it was feasible and low-tech."
The FDA has since given the go-ahead for testing it in human tumors as a diagnostic tool. In the test, the chemical pimonidazole is injected into the patient. As it circulates throughout the body, it binds only to cells that have low oxygen concentrations. The tumor is then biopsied, usually the next day. Using special antibodies to pimonidazole that Raleigh developed and patented, tumor cells bound to the chemical can be detected by a laboratory immunoassay. Essentially, the test identifies the antibodies, which serve as markers for hypoxic cells.
In Boston, MA, October 23, at the annual meeting of the American Society for Therapeutic Radiology and Oncology, Varia will present UNC research that highlights the value of this marker for delving into the role of hypoxia in tumor physiology factors associated with tumor aggressiveness and treatment resistance. Among the factors studied were cell proliferation, growth of new blood vessels (angiogenesis), and gene expression of metallothionein (MT), an oxygen-regulated cellular protein that protects against chemotherapy and radiation. Because it's based on biopsied tissue, Raleigh's pimonidazole method for detecting hypoxia also allows scientists to focus on these and other factors in the same micro-regional tumor anatomy. "Our interest in tumor hypoxia is twofold: One, if these tumors don't do as well with radiation, chemotherapy or surgery, then it's important that we assess the hypoxia before we embark on treatment," Varia said. "The other important interest is in finding out why these hypoxic tumors are behaving badly? That's the thrust of this particular presentation."
Tumors from 36 patients were studied: 20 had cancers of the cervix and head and neck, 16 with breast cancer. Three or four random biopsy samples were obtained from each tumor and tested for hypoxia and the factors in aggressiveness and treatment resistance.
"So we looked at our biopsy samples, looked at hypoxia and looked at markers of cell proliferation. We did not see a correlation," Varia said. Nor was an association between tumor hypoxia and angiogenesis.
Varia, Raleigh and their collaborators are now are looking for links between hypoxia and other factors, including gene expression of the protein MT. In terms of that protein, Raleigh points out that in more than two-thirds of the tumor samples MT was expressed in proliferating cells but not in hypoxic cells.
"This, even though when you take cells in the test tube and expose them to hypoxia metallothionein production is induced. So there's something about human tumors which changes the way gene expression operates. And it's different from what we see in test tubes and in mouse tumors," Raleigh said.
"Our suspicion is that under condition of tumor hypoxia, somewhere along the molecular pathway gene expression is either up-regulated or down-regulated. We are going to investigate this," Varia said.
"What we're demonstrating here is a valuable approach to studying the mechanisms of hypoxia-associated poor prognosis," Varia added. "We're very interested in the translational aspect, taking findings from the laboratory into the clinic. And we appreciate the patients' participation in this type of research that advances our understanding of cancer and provides leads for better cancer treatment."
According to Raleigh, tumors from more than 200 patients around the world are being tested for hypoxia using his method. Beyond cancer treatment planning, clinical investigators at UNC and elsewhere are looking at the hypoxia marker for studying alcohol-associated liver damage, wound healing, and liver transplant success.
"It's a very novel tool that can be applied not only in cancer research but widely in medical investigations," Raleigh noted.
UNC-CH School of Medicine
Media note: Contact Dr. Varia at 919-966-7700 (varia@med.unc.edu).
Mon.10/23-Wed.10/25, Varia can be reached in Boston at 617-954-3616.
Contact Dr. Raleigh at 919-966-7710 (raleigh@radonc.unc.edu)
UNC Medical School contact: Les Lang, 919-843-9687 (llang@med.unc.edu).