Bone is one of the most frequent sites for metastasis of breast and prostate cancers. Bone metastases are associated with pathologic changes in bone turnover and severe pain. The mechanisms that trigger these effects are not well understood, but it is postulated that tumour cells release factors which interfere with signalling processes critical to bone homeostasis. We have identified that several cancer cell lines known to cause bone disruption in animal models of bone metastasis appear to secrete glutamate into their extracellular environment in vitro. Although these cells also express specific glutamate receptors, the implications of this potentially disruptive chemical signal are discussed in relation to normal glutamate-dependent communication processes in bone and a possible mechanistic connection is made between tumour cell glutamate release and the development of pathological changes in bone turnover.
The tetracycline family includes tetracycline, doxycycline and minocycline, all of which have been used as antibiotics effectively for decades. New uses emerged for these compounds after their effect on mitochondrial function was discovered. Cytostatic and cytotoxic activity of these compounds was shown against cell lines of various tumor origins. In addition, tetracyclines and chemically modified tetracyclines inhibit the activity of several matrix metalloproteinases (MMPs). Given the importance of these enzymes in tumor cell invasion and metastatic ability, the potential use of tetracyclines in cancer therapy needed to be investigated. Col-3, a chemically modified tetracycline, is now the subject of clinical trials in cancer patients. However, the potential of tetracyclines in cancer therapy takes on an added dimension in the bone. MMPs have been shown to be important mediators of metastasis formation in the bone, contributing largely to the morbidity of breast cancer and prostate cancer patients. The natural osteotropism of tetracyclines would allow them to be highly effective in the inhibition of MMPs produced by osteoclasts or tumor cells in the bone. This hypothesis has now been confirmed by experimental evidence showing that doxycycline reduces tumor burden in a mouse model of breast cancer-derived osteolytic bone metastasis. This effect is likely due to a combination of multiple roles of doxycycline, including MMP inhibition and a negative effect on osteoclast differentiation and survival. These encouraging results have now paved the way for an ongoing trial of doxycycline in early combination therapy for breast cancer and prostate cancer patients.
Embryonal tumors, such as neuroblastoma, medulloblas-toma and Wilms' tumor, have their peak incidence in the first 4 years of life. These neoplasias exhibit genetic and clinical heterogeneity, but little is known about their molecular pathogenesis. Application of the differential-display PCR approach led to the identification of a gene, glypican 3 (GPC3), that is differentially expressed in cancer cells. Expression of this gene is usually limited to fetal mesodermal tissue, and its inactivation has been found to be responsible for the X-linked Simpson-Golabi-Behmel overgrowth syndrome. Here, we show that GPC3 mRNA is present in several neu-roblastomas and all Wilms' tumors tested to date but not in medulloblastoma. GPC3 was not expressed in normal kidney tissues obtained from the corresponding Wilms' tumor patients , suggesting that in these cancer cells expression was not repressed (or was activated). No correlation was found between expression of GPC3 and the known indicator of neuroblastoma prognosis MYCN mRNA. However, all samples that expressed GPC3 also expressed IGF-II, coding for a growth factor important in the survival and growth of many cancer types. Although the biological significance of this relationship remains unclear, our results suggest that GPC3 may be implicated in the development of embryonal tumors through a signaling pathway that appears to involve IGF-II.
Background: Prostate cancer progression to androgen independence is the primary cause of mortality by this tumor type. The IGF-1/IGF-1R axis is well known to contribute to prostate cancer initiation, but its contribution to invasiveness and the downstream signalling mechanisms that are involved are unclear at present.
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