Pancreatic cancer is the fourth leading cause of cancer deaths in the U.S.; each year 30,000 cases are diagnosed, and for the majority of patients the disease is incurable.
Using human cell lines, the researchers showed that pancreatic cancer growth can be arrested by chemically blocking a signaling pathway that previously had been known to be active in human embryonic development. Known as the Hedgehog pathway, this cascade of chemical steps allows proteins to pass along a signal that ultimately leads to changes in gene activity and has already been linked to several other types of cancer.
The research highlights the link between embryonic development and cancer. Proteins that normally regulate rapid growth in the embryo may often be responsible for the out-of-control cell divisions in cancer, the scientists say.
"Surgery has represented the only possible cure for pancreatic cancer patients," said Sarah P. Thayer, MD, PhD, of MGH, co-first and co-senior author of the paper. "However, the majority of patients are diagnosed at an incurable stage of their disease. We have been stymied by our inability to diagnose patients earlier and offer effective treatments."
Thayer deals principally with the surgical management of pancreatic cancer patients, and the disease is the main focus of her research.
Although much more work needs to be done to determine whether the research can be applied to clinical practice, "identifying the role of this pathway in pancreatic cancer offers hope for developing treatments," said Matthias Hebrok, PhD, assistant professor of medicine in UCSF's Diabetes Center. "It also underscores how studying organ development in embryos can provide clues to cancer, diabetes and other serious diseases." Hebrok is co-senior author on the paper.
"Our funding of this research emphasizes the importance of understanding the signals and genetic networks that regulate development of the pancreatic cells. These insights will prove relevant for activating beta cell regeneration, and for understanding how beta cell growth is disordered in pancreatic malignancies," said Richard Insel, MD, Vice President, Research, Juvenile Diabetes Research Foundation International.
Normally, Hedgehog proteins influence early development by binding to another protein on the cell surface, known as the Patched receptor. This union triggers a series of chemical changes, leading to gene activity in the nucleus. Mutations in the Hedgehog pathway are known to cause several types of cancer, and this research adds pancreatic cancer to the list of serious outcomes of aberrant Hedgehog activity.
In one part of the study, the scientists compared normal adult human pancreatic tissue to specimens from patients with pancreatic cancer. No Hedgehog protein was detected in the normal tissue, but it was found in 70 percent of precancerous and cancerous specimens. Furthermore, key genes in the Hedgehog pathway were also found to be overexpressed.
"Mis-expression of the Hedgehog pathway in transgenic mice resulted in the formation of abnormal pancreatic cells that resembled human precursor lesions, suggesting that this pathway may have a role in the initiation of this cancer," said Thayer, an instructor in surgery at Harvard Medical School. "However, its true role in pancreatic cancer remains to be determined."
The researchers also examined 26 human pancreatic cancer cell lines and found Hedgehog activity in all of them. When the Hedgehog pathway was blocked experimentally, the cancer was killed half of the time. Cancer-causing mutations "downstream" from the Hedgehog pathway may cause the other half of the cancers, the researchers think. The scientists then transplanted pancreatic cancer cells into mice, creating tumors. They injected the mice with an inhibitor of the Hedgehog pathway, which resulted in a 50 to 60 percent reduction in tumor size after seven days.
The research results -- death of tumor cells both in the Petri dish and in animals --suggest that this may one day hold promise as a treatment avenue, the researchers say.
Unfortunately, the inhibitor used in this research is not a practical drug for clinical use, they point out. But since abnormalities in Hedgehog expression have already been linked to gliomas, basal cell carcinoma and very recently, small cell lung cancer, university and commercial labs are screening for more effective Hedgehog blockers.
"If Hedgehog is involved in pancreatic cancer, these other blockers might offer a bright prospect in treating a disease that has eluded effective treatment up to now," Hebrok said.
A second paper in the same issue of Nature reports that Hedgehog signaling is active in pancreatic and other cancers along the gastrointestinal tract. These results provide further evidence that deregulation of this pathway is a more general phenomenon than previously anticipated.
Marina Pasca di Magliano, Ph.D., of the UCSF Diabetes Center, is co-first author on the paper with Thayer. Other UCSF co-authors are graduate students Patrick W. Heiser and Yan Ping Qi, of the Diabetes Center; and Stephan Grysin, PhD, and Martin McMahon, PhD, of the Cancer Research Institute. Co-authors at MGH and HMS are Drucilla Roberts, MD; Gregory Lauwers, MD; Corinne Nielsen, MS; Carlos Fernández-del Castillo, MD, Bozena Antoniu, MS; Vijay Yajnik, MD, Ph.D; and Andrew Warshaw, MD, professor and chair, Department of Surgery.
The research was supported by grants from the Lustgarten Foundation for Pancreatic Cancer Research, the National Institutes of Health, and the Juvenile Diabetes Research Foundation.