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A new study sheds light on a mechanism involved in the pathological destruction of bone tissue caused by metastatic prostate cancer. The findings provide critical insight into the process of cancer-driven bone destruction and identify a treatment that may interrupt bone disease caused by the spread of prostate cancer. The research is published in the May issue of Cancer Cell.
The spread of cancer to other body regions is the primary cause of death from prostate cancer. The most common place for prostate cancer to metastasize is the bone, causing intense pain, pathological fracture, and immobility. At the current time, treatment options for patients with bone metastases are limited. Drs. Mitsuru Futakuchi and Rakesh Singh from the University of Nebraska Medical Center and Lynn Matrisian of Vanderbilt University used a new rodent model that mimics the changes to bone that occur following prostate cancer metastasis. Transplantation of prostate tumor tissue onto bone surfaces provided a histological picture similar to human prostate cancers growing in the bone. The goal of the study was to look for mechanisms that drive the behavior of this disease, with the hope of discovering new therapeutic targets.
The researchers identified genes that are expressed in the tumor-bone interface but not in the tumor alone. Several genes that play a role in bone physiology were abnormally regulated, including the gene for MMP-7. MMP-7 is an enzyme that regulates communication between the tumor and surrounding normal tissue by processing cytokines and growth factors to active forms, and which has been shown to be involved in the invasion and spread of several cancers. Cells called osteoclasts at the tumor-bone interface were observed to secrete MMP-7. Osteoclasts break down bone as part of normal bone remodeling, but are overactive in cancerous bone, leading to excessive bone destruction. The researchers found that MMP-7 cleaved a molecule called RANKL into a soluble form that promoted osteoclast activation and bone degradation. Mice deficient in MMP-7 had little to no soluble RANKL and exhibited substantially reduced prostate cancer-induced bone degradation compared to control mice expressing MMP-7.
The researchers conclude that MMP-7 plays a major role in prostate cancer-driven osteolysis and that the mechanism of MMP-7 action involves cleavage of RANKL to a soluble form that promotes osteoclast activation and pathological bone breakdown. "Our results make MMP-7 an attractive therapeutic target for the control of cancer-induced bone osteolysis," suggests Dr. Futakuchi.
The researchers include Conor C. Lynch, Heath B. Acuff, Michelle D. Martin, Tracy C. Vargo-Gogola, Jennifer L. Begtrup, Todd E. Peterson, Barbara Fingleton, and Lynn M. Matrisian of Vanderbilt University; Atsuya Hikosaka, Noriyasu Kawai, Tomoyuki Shirai of Nagoya City University Medical School; Rakesh K. Singh, of the University of Nebraska Medical Center; and Mitsuru Futakuchi of Nagoya City University Medical School and University of Nebraska Medical Center. This work was supported by a grant from the NIH, Grants-in-Aid for Cancer Research from the Ministry of Education, Culture, Sports, Science, and Technology and the Ministry of Health, Labor, and Welfare, Japan, a Grant-in-aid from the Ministry of Health, Labor and Welfare for the Second-Term Comprehensive 10-Year Strategy for Cancer Control, Japan, and a grant from the Society for Promotion of Pathology of Nagoya, Japan. C.C.L. is supported by a grant awarded by the Susan G. Komen Breast Cancer Foundation.
Lynch, C.C., Hikosaka, A., Acuff, H.B., Martin, M.D., Kawai, N., Singh, R.K. Vargo-Gogola, T.C., Begtrup, J.L., Peterson, T.E. Fingleton, B., Shirai, T., Matrisian, L.M., and Futakuchi, M. (2005). MMP-7 promotes prostate cancer-induced osteolysis via the solubilization of RANKL. Cancer Cell 7, 485–496. www.cancercell.org
Journal
Cancer Cell