Tetracycline analogues (doxycycline and COL‐3) induce caspase‐dependent and ‐independent apoptosis in human colon cancer cells

Abstract

Tetracycline analogues (TCNAs) possess cytotoxic activities as well as matrix metalloproteinase (MMP) inhibitory properties. Previously, we demonstrated that doxycycline (DOXY) could induce apoptosis in human HT29 colon cancer cells. In present study, the molecular apoptotic mechanisms induced by two kinds of TCNAs, designated as DOXY and COL-3 (chemically modified tetracycline-3; 6-demethyl, 6-deoxy, 4-dedimethylamino tetracycline), were evaluated in cultured HT29 cells. Both TCNAs inhibited the proliferation of 6 different colorectal cancer cell lines in a dose-dependent manner. Especially, COL-3 had a stronger effect on cancer cells than DOXY. Apoptotic changes were actually observed by 10 lg/ml COL-3 and 20 lg/ml DOXY in a timedependent manner. COL-3 produced the increase in cytosolic cytochrome c and the loss of mitochondrial membrane potential after 3 hr treatment, and thereafter activated caspases. In case of DOXY, these changes were observed after 24 hr. Bax translocation was not a prerequisite for cytochrome c releasing in COL-3 treatment. Pretreated pancaspase inhibitor (Z-VAD-FMK) reduced COL-3 and DOXY mediated apoptosis up to 81.3 and 35.3%, as compared with nontreated cells, respectively. These data indicated that TCNAs could induce mitochondria-mediated apoptosis through both caspase-dependent and -independent pathway. In fact, endonuclease G and apoptosis-inducing factor were released into cytosol after the treatment of TCNAs, which indicated that caspase-independent apoptotic pathway is also one of the key mechanisms for the treatment of TCNAs. Taken together, we believe that TCNAs could have strong potentials for clinical application in treating colorectal cancers and improve cancer chemotherapy. ' 2005 Wiley-Liss, Inc.Key words: apoptosis; mitochondria; colorectal cancer; doxycycline; COL-3The tetracyclines (TCNs) were discovered in the 1940s as broad-spectrum antibiotics, with wide spread activities against bacteria, chlamydiae, mycoplasmas, rickettsiae and also protozoan parasites. 1 The bacteriostatic activity of TCNs lies in their capacity to inhibit protein synthesis by preventing the binding of aminoacyl t-RNA to ribosome. 2 Because of the similarity between the prokaryotic protein synthesis machinery and that of eukaryotic mitochondria, TCNs are believed to be able to interfere with mitochondrial protein synthesis in mammalian cells. 3 In addition, the selective permeability of different mammalian cells to TCNs leads to the hypothesis that these agents could be used to achieve cell proliferation arrest and applied to the treatment of malignancies. 4 From the perspective of clinical application, renewed interest in TCNs has recently grown because of their unique abilities to inhibit matrix metalloproteinases (MMPs) activities 5 and cell proliferation in several types of malignancies, including melanoma, 6 osteosarcoma, 7 prostate, 8 breast 9,10 and colorectal cancers. 11 Moreover, some of tetracycline analogues (TCNAs) have been reported to act as apoptotic inducers. 12-16 Although thes...

Recent advances in MMP inhibitor design

“…Recent pharmacological evaluation of the tetracycline mechanism Fig. 12 Chemically modified tetracycline MMP inhibitor is consistent with diminution of MMP-9 expression and activity, and also inhibition of downstream caspase, growth factor, and kinase activities, in both cancer and neurological models [207][208][209][210][211][212]. Tetracycline-dependent reduction in reactive oxygen may contribute to the lowered MMP expression [213,214].…”

Tetracyclines increase lipid phosphate phosphatase expression on plasma membranes and turnover of plasma lysophosphatidate

“…The bacteriostatic activity is caused by preventing the binding of aminoacyl tRNA to ribosomes, which is necessary for protein synthesis ( 31 ). It is also well documented that tetracyclines inhibit matrix metalloproteinase (MMP) activities ( 32 ).…”

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