Dr. Weeks’ Comment: Any pediatrician knows that tetracycline mottles bone in general and teeth in particular in developing kids so it is rarely used BUT – now this part requires thinking so bear with me – I have long used tetracycline to inhibit bone metastatic process since this is a centisble* treatment which, despite not being the standard of care) can be used to prevent or treat bone metastatic disease. Consider the risk benefit ratio and ask your doctor to prescribe tetracycline or doxycycline if you are concerned about cancer in your bones. And the does does not need to high since “the effective concentrations are relatively high for plasma, but are clinically achievable in the bone, since tetracyclines are osteotropic.”
*i.e. safe, effective and cost-effective
Anticancer Drugs. 2003 Nov;14(10):773-8.
Doxycycline and other tetracyclines in the treatment of bone metastasis.
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.
Use of tetracycline as an inhibitor of matrix metalloproteinase activity secreted by human bone-metastasizing cancer cells.
Bone metastases are a common complication in prostate and breast cancer patients. It leads to extensive morbidity and eventually mortality. Matrix metalloproteinases are implicated in various steps of development of metastasis, through their ability to degrade the extracellular matrix. Increased matrix metalloproteinase activity of tumor cells has been associated with a higher metastatic potential. Inhibitors of metalloproteinases have been shown to effectively reduce or prevent the formation of metastases. The family of tetracyclines is able to inhibit matrix metalloproteinase activity through chelation of the zinc ion at the active site of the enzyme. Using tumor cell lines relevant to bone metastases, i.e. PC-3, MDA-MB-231, Hs696, B16/F1, we showed that tetracycline and derivatives of tetracycline, namely doxycycline and minocycline, also induced cytotoxicity. The effective concentrations are relatively high for plasma, but are clinically achievable in the bone, since tetracyclines are osteotropic. All four bone-metastasizing tumor cells produced and secreted various matrix metalloproteinases. Doxycycline was able to inhibit the activity of 72- and 92-kDa type IV collagenase secreted by bone-metastasizing cells by 79-87%. These characteristics could make tetracycline a unique candidate as a therapeutic agent to prevent bone metastases in cancer patients with a high likelihood for development of bone metastasis. Studies using animal models of experimental bone metastasis will be necessary to confirm this.
Inhibition of tumor cell invasiveness by chemically modified tetracyclines.
COLO 205 is a cell line derived from a human colon carcinoma with high degradative activity towards extracellular matrix (ECM). It has been shown that COLO 205 cells produce matrix metalloproteinases (MMPs). MMPs are a family of enzymes known to degrade components of the ECM and have been implicated in tumor invasion. In the present study, we have analyzed the multiple effects of chemically modified tetracyclines (CMTs) on the expression and activity of MMPs secreted by COLO 205 cells in vitro with the aim of evaluating these compounds for potential use in management of invasive tumors. Because COLO 205 cells can degrade an interstitial ECM in serum-free medium in vitro, we have been able to compare the effects of the tetracyclines on this measure of invasive activity with their effects on proteinase expression and activity. We demonstrate here that one of the chemically modified tetracyclines, 6-deoxy-6-demethyl-4-de(dimethylamino)tetracycline (CMT-3) can effectively inhibit ECM degradation mediated by COLO 205 cells or their conditioned medium. Gelatin zymography and immunoblots show that CMT-3 has the ability to inhibit release of MMP-2 into conditioned medium as well as to inhibit MMP-2 gelatinolytic activity, which correlates with the results from ECM degradation assays. On the basis of our findings with COLO 205 cells we have expanded our evaluation of the tetracyclines to include effects on a genetically engineered line of MDA-MB-231 breast tumor cells overexpressing MMP-9 at levels over tenfold those of the parent cell line, and on three human prostate tumor cell lines, LNCaP, DU-145, and PC-3. We show here that CMT-3 displays multiple modes of action: inhibiting MMP activity, reducing levels of MMP expression, and exhibiting selective cytotoxicity towards some of the tumor cell lines.
Cytotoxic activity and inhibition of tumor cell invasion by derivatives of a chemically modified tetracycline CMT-3 (COL-3).
Tetracyclines such as chlortetracycline and doxycycline with antimicrobial activity were reported to possess cytostatic and cytotoxic activity against mammalian tumor cells, often at high doses. Non-antimicrobial chemically modified tetracyclines (CMTs), with limited systemic toxicity but with significant tumor cell toxicity and antimetastatic activity, are attractive for long term treatment for cancer. We recently reported one such CMT, 6-deoxy,6-demethyl 4-dedimethylamino tetracycline (CMT-3) is a potent anti-tumor and anti-metastatic drug. Here we report on the anti-cell proliferation and anti-invasive activity of five nitro derivatives of CMT-3 (CMT-3N). All the five CMT-3Ns (CMT-302, CMT-303, CMT-306, CMT-308 and CMT-316) inhibited in vitro cell proliferation of prostate cancer cells. The 50% growth inhibition concentration (IC(50)) of CMT-3Ns was similar to that of CMT-3. Although CMT-3 was by far the most potent anti-cell proliferation drug, all CMT-3Ns except CMT-303 and CMT-308 had similar anti-cell proliferation activity (IC(50): 2.5 -5.7 microg/ml). IC(50)s for CMT-303 and CMT-308 were approximately 8.1 and -12.4 microg/ml, respectively. Activity against tumor cell invasion was tested in vitro using the Matrigel invasion assay. All CMT-3Ns had similar anti- invasive activity. While cytotoxic activity of CMT-3 was strongly associated with cell death-effector caspase activation, mitochondrial permeablization and apoptosis, the CMT-3Ns weakly induced apoptosis and did not activate Caspase-3. However, the CMT-3Ns were able to induce mitochondrial permeabilization. This dichotomous mechanism of cytotoxic activity of CMTs may have significance in their selection for clinical application.