Chemically modified tetracyclines induce cytotoxic effects against J774 tumour cell line by activating the apoptotic pathway

Potent Anti-Inflammatory Effects of Tetracyclines on Human Eosinophils

Eosinophils are potent pro-inflammatory cells. Not only in allergic diseases but also in other diseases there is a need for treatment strategies to induce resolution of eosinophil-mediated inflammation. During the last years beneficial non-antibiotic activities of tetracyclines (TCNs) have been shown in different diseases in which eosinophils play a role, for example, asthma and bullous pemphigoid. The working mechanism of these effects remains to be clarified. Aim of the present study was to investigate the effects of TCNs on eosinophils. Flow cytometry analysis of apoptosis, mitochondrial membrane potential, activation of caspases, intracellular H₂O₂ and calcium, surface expression of eosinophil activation markers was performed in highly purified peripheral blood eosinophils of non-atopic donors. Tetracycline hydrochloride, minocycline and doxycycline significantly induced eosinophil apoptosis. All TCNs were able to significantly overcome the strong survival enhancing effects of pro-eosinophilic cytokines and staphylococcus aureus enterotoxins. Tetracycline hydrochloride induced eosinophil apoptosis was accompanied by intracellular production of hydrogen peroxide, loss of mitochondrial membrane potential and activation of caspases. Moreover, tetracycline hydrochloride significantly down regulated eosinophil surface expression of CD9 and CD45, and of the activation markers CD11b and CD69, but not of CD54, CD63, or CD95. Our data, propably for the first time, point to a potent anti-inflammatory role of TCNs on eosinophils.

Activation of c-Jun N-terminal kinase is essential for mitochondrial membrane potential change and apoptosis induced by doxycycline in melanoma cells

BACKGROUND AND PURPOSE

Tetracyclines were recently found to induce tumour cell death, but the early processes involved in this cytotoxic effect remain unclear.

EXPERIMENTAL APPROACH

Viability of human and mouse melanoma cells was determined by MTT assay and flow cytometry. Kinase/protein/caspase activation was measured by Western blotting and mitochondrial membrane potential (DeltaPsi(m)) was analyzed by fluorescence microscopy and flow cytometry.

KEY RESULTS

Human and mouse melanoma cells were treated with doxycycline or minocycline but only doxycycline was cytotoxic. This cell death (apoptosis) in A2058 cells involved activation of caspase-3, -7 and -9 and contributed to inhibition, by doxycycline, of matrix metalloproteinase (MMP) activity and migration of these cells. Doxycycline induced intra-cellular reactive oxygen species (ROS) production, apoptosis signal-regulated kinase 1 (ASK1), c-Jun N-terminal kinase (JNK) and p38 mitogen-activated protein kinase (MAPK) activation at an early stage of treatment and induced mitochondrial cytochrome c release into cytosol and DeltaPsi(m) change during apoptosis. The JNK inhibitor/small interference RNA inhibited doxycycline-induced JNK activation, DeltaPsi(m) change and apoptosis, but did not affect ASK1 activation, suggesting a role of ASK1 for JNK activation in melanoma cell apoptosis. Two ROS scavengers reduced doxycycline-induced JNK and caspase activation, and apoptosis. Taken together, the results suggest the involvement of a ROS-ASK1-JNK pathway in doxycycline-induced melanoma cell apoptosis.

CONCLUSIONS AND IMPLICATIONS

We have shown a promising cytotoxic effect of doxycycline on melanoma cells, have identified ROS and ASK1 as the possible initiators and have demonstrated that JNK activation is necessary for doxycycline-induced melanoma cell apoptosis.

Lowering the apoptotic threshold in colorectal cancer cells by targeting mitochondria

Background

Colorectal cancer is the third most-common cancer and the second most-common cause of cancer related death in UK. Although chemotherapy plays significant role in the treatment of colorectal cancer, morbidity and mortality due to drug resistance and cancer metastasis are yet to be eliminated. Recently, doxycycline has been reported to have cytotoxic and anti-proliferating properties in various cancer cells. In this study, whether doxycycline was apoptosis threshold lowering agent in colorectal cancer cells by targeting mitochondria was answered.

Results

This study showed dose-dependent cytotoxic effects of cisplatin, oxaliplatin and doxycycline in HT29 colorectal cancer cells. Doxycycline showed inhibition of cytochrome-c-oxidase activity in these cells over a time-period. The pre-treatment of doxycycline reported statistically significant increased cytotoxicity of cisplatin and oxaliplatin compared to cisplatin and oxaliplatin alone. The caspase studies revealed significantly less expression and activity of caspase 3 in HT29 cells pre-treated with doxycycline compared to the cells treated with cisplatin and oxaliplatin alone.

Conclusions

It was concluded that doxycycline lowered the apoptotic threshold in HT 29 cells by targeting mitochondria. This also raised possible caspase-independent mechanisms of apoptosis in HT29 cells when pre-treated with doxycycline however this needs further research work.

Fast and ultrafast spectroscopic investigation of tetracycline derivatives in organic and aqueous media

The photophysical properties of seven tetracycline derivatives (tetracycline, oxytetracycline, demeclocycline, chlortetracycline, doxycycline, minocycline and meclocycline) in organic solvents and aqueous solution were studied using steady-state absorption and fluorescence techniques and transient absorption spectroscopies with nanosecond and femtosecond time resolution. The molecular structure, solvent and pH effects on the optical properties of this class of pharmaceutically interesting compounds were investigated in detail. The investigation furnished a complete description of the nature, the spectral and kinetic properties of the excited states formed upon irradiation. All the tetracycline derivatives exhibited a similar behaviour, and the photophysics of these molecules is different in organic solvents and in aqueous medium, where they exhibit a significant pH dependence. In water, compared to organic solvents, these compounds showed a blue-shifted bathochromic absorption band, a red-shifted emission spectrum, an increased Stokes shift and a decreased fluorescence quantum yield. These findings, together with the overall investigated solvent effect, suggested that in aqueous solvent additional fast and non-radiative deactivation processes, responsible for the large Stokes Shift and for the reduced fluorescence efficiency, are present. In fact, in organic media just two transients were observed during the ultrafast time-resolved investigation: the vibrationally hot S(1) state which was quickly stabilized by solvent reorganization to the relaxed S(1) state. This state showed lifetimes of tens of picoseconds and relaxed by fluorescence and internal conversion. No longer-lived transients were detected. In aqueous solution the excited-state deactivation of tetracyclines was found to be more complicated. Different protonated and tautomeric forms of the S(1) state were detected: a component which showed decay times of tens of picoseconds and a component which was longer-lived. A significant pH effect on the nature and number of these components was found. In fact, a remarkable change in the Stokes shift and in the fluorescence efficiency was also observed on going from acidic to basic aqueous solutions. The most important variations in the absorption properties were found in the pH range in which the second acid-base equilibrium takes place. The tetracycline lowest excited triplet state was observed as a 'rest absorption' during the femtosecond-resolved measurements in aqueous solution; through the nanosecond-resolved laser flash photolysis study, lower-energy radical species were detected, characterized by lifetimes of tens of microseconds. The formation of these species may be involved in the observed phototoxicity of the tetracycline drugs.

Doxycycline enhances the Ras-MAPK signaling and proliferation of mouse thymic epithelial cells

Depletion of T-cell-dependent immunity is a major consideration for patients suffering from infections of human immunodeficiency virus (HIV), those undergoing organ transplantation, and those receiving anti-cancer chemotherapy and/or radiotherapy. In general, T-cell regeneration occurs in the thymus through thymopoiesis. We have found that doxycycline (Dox), a tetracycline derivative, enhances the proliferation of mouse thymic epithelial cells, which are unique in their capacity to support positive selection and are essential throughout the development of thymocytes. Cell cycle analysis indicates that the increased cell proliferation is due to a shortened G(0)/G(1) phase. To reveal the underlying mechanisms, we examined the expression of an array of molecules that regulate the cell cycle. The results show that in mouse thymic medullary-type epithelial cell line 1 (MTEC1) Dox leads to elevated levels of H-Ras, phosphorylated extracellular signal-regulated kinase 1/2 (p-ERK1/2), cyclin E, cyclin dependent kinase 4/2 (CDK4/CDK2), E2F3, and c-myc. These data, and the observation that the proliferation-enhancing effect is largely abolished following treatment with an ERK inhibitor support an active role of the Ras-ERK/mitogen-activated protein kinase (MAPK) signaling pathway. In conclusion, the present study reveals a new activity of an old family of antibiotics. The in vivo effect of Dox on immune reconstitution warrants further exploration.

Does doxycycline work in synergy with cisplatin and oxaliplatin in colorectal cancer?

BACKGROUND

In recent years, apart from antibacterial properties, doxycycline is reported to have cytotoxic and anti-proliferative actions in various cancers including colorectal cancer. Colorectal cancer constitutes one of the most common cancers in the western population. Apart from surgery, chemotherapy plays crucial role in the treatment of colorectal cancer. Cisplatin and oxaliplatin are most commonly used platinum compounds for the cancer chemotherapy. This study has looked for any impact of doxycycline on the cytotoxic effects of platinum compounds in colorectal cancer including its mechanisms of actions.

METHODS

HT 29 colorectal cancer cells were used for this study. These cells were treated with cisplatin and oxaliplatin with or without doxycycline treatment. The caspase 3 gene expression was quantitated by gel electrophoresis and qualitated by real time polymerase chain reactions. The caspase 3 activity was assessed in HT 29 cells with fluorescence kit.

RESULTS

The results revealed increased caspase 3 gene expressions and activities in HT 29 cells treated with cisplatin, oxaliplatin and doxycycline; however the combination of doxycycline with cisplatin and oxaliplatin did not report increased caspase 3 gene expressions and activity compared to cisplatin and oxaliplatin alone.

CONCLUSION

We concluded that doxycycline has role in apoptosis induction in the colorectal cancer. However, it did not show any synergy with platinum compounds in the colorectal cancer cells. This study also pointed towards possible caspase-independent actions of doxycycline with cisplatin and oxaliplatin. However, further work is required to underpin the mechanisms of actions of doxycycline.

Inhibition of smooth muscle cell proliferation by a chemically modified tetracycline

INTRODUCTION

Chemically modified tetracyclines (CMTs) are a group of nonantimicrobial derivatives of tetracycline, which exert antiproliferative and anticollagenolytic properties. The molecular mechanisms, however, are poorly understood.

MATERIALS AND METHODS

The effect of CMT-3 on cultured, subconfluent rat aortic smooth muscle cells (SMCs) was analyzed by [(3)H]-thymidine incorporation, counting cell numbers, and flow cytometry analysis.

RESULTS

CMT-3 inhibited the incorporation of [(3)H]-thymidine and reduced the cell number dose-dependently, with approximately 60% inhibition at the maximal CMT-3 concentration used (20 mumol/l). CMT-3 decreased the SMC proportion in S-phase and gradually increased the proportion at G2/M. Initially, the proportion of cells in G1-phase increased and then gradually decreased back to baseline as the CMT-3 concentration increased. CMT-3 treatment of confluent SMCs for 24 h did not induce apoptosis.

CONCLUSIONS

CMT-3 inhibited SMC proliferation by inducing cell cycle arrest at the G2/M restriction point. Nonetheless, CMT-3 did not induce SMC apoptosis.

The PVT-1 oncogene is a Myc protein target that is overexpressed in transformed cells

The human PVT-1 gene is located on chromosome 8 telomeric to the c-Myc gene and it is frequently involved in the translocations occurring in variant Burkitt's lymphomas and murine plasmacytomas. It has been proposed that PVT-1 regulates c-Myc gene transcription over a long distance. To get new insights into the functional relationships between the two genes, we have investigated PVT-1 and c-Myc expression in normal human tissues and in transformed cells. Our findings indicate that PVT-1 expression is restricted to a relative low number of normal tissues compared to the wide distribution of c-Myc mRNA, whereas the gene is highly expressed in many transformed cell types including neuroblastoma cells that do not express c-Myc. Reporter gene assays were used to dissect the PVT-1 promoter and to identify the region responsible for the elevated expression observed in transformed cells. This region contains two putative binding sites for Myc proteins. The results of transfection experiments in RAT1-MycER cells and chromatin immunoprecipitation (ChIP) assays in proliferating and differentiated neuroblastoma cells indicate that PVT-1 is a downstream target of Myc proteins.

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

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 mug/ml COL-3 and 20 mug/ml DOXY in a time-dependent 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.

Chemically modified tetracyclines induce apoptosis in cultured mast cells

Chemically modified tetracyclines are a group of non-antimicrobial tetracycline derivatives, which possess antiinflammatory, anticollagenolytic and antiproliferative properties. Here we studied the effects of four different chemically modified tetracyclines (CMT-1, CMT-3, CMT-8 and CMT-308) on proliferation and viability of cultured mouse and human mast cells. All studied CMTs (25 microM) effectively inhibited the viability and proliferation of human mast cell line (HMC-1) cells and mouse bone marrow derived mast cells (mBMMCs), as judged by trypan blue exclusion and by incorporation of [(3)H]thymidine. The antiproliferative effect of CMTs was not dependent on the stimulating growth factor, i.e. CMTs inhibited both IL-3 and c-kit ligand-induced proliferation of mBMMCs. The reduced viability of mast cells was due to induction of apoptosis, as indicated by the increased amount of apoptotic nucleosomes and the appearance of TUNEL positive cells in the presence of CMTs. The induction of apoptosis was further confirmed by showing that CMT-3 induces activation of caspase-3 and caspase-9 in HMC-1 cells. Additionally, CMT-3 induced downregulation of the expression of antiapoptotic Bcl-2 protein in HMC-1 cells. Compared to doxycycline, the antiproliferative and proapoptotic effects of different CMTs were clearly more pronounced. Of the studied CMTs, CMT-3 and CMT-8 appeared to be the most potent inhibitors of mast cell proliferation and survival. The present results show that CMTs have an antiproliferative and proapoptotic effect on both malignant and non-malignant mast cells. In conclusion, CMTs could offer a novel means to treat disorders with inappropriate expansion of mast cells, such as rheumatoid arthritis and systemic mast cell diseases.

Chemically modified tetracyclines as inhibitors of matrix metalloproteinases

Matrix metalloproteinases belong to a diverse group of enzymes that are not only involved in restructuring the extracellular matrix, but also play a major role in various pathophysiological conditions by virtue of their complicated expression, activation, and regulation processes. They have been widely implicated to function as major contenders in cancer progression, frequently due to their role in invasion, proliferation and metastasis. MMP inhibitors have been specifically designed to target these altered activities of MMPs, mostly by means of inhibiting their function and by diminishing their increased expression in various disease states, particularly cancer. Tetracyclines and chemically modified tetracyclines (CMTs) have been rationally designed to inhibit the activity of MMPs and thus decrease the potential risk of spread of tumor cells to distant sites by invasion and metastasis. Pre-clinical and early clinical data for one of these CMTs, COL-3 (formerly CMT-3) indicate considerable potential for this group of anticancer agents. Further testing and rational modifications of these CMT analogues might lead to new anticancer agents.

Chemically modified tetracyclines act through multiple mechanisms directly on osteoclast precursors

Chemically modified tetracyclines (CMTs) are thought to inhibit bone resorption primarily through their ability to inhibit matrix metalloproteinases (MMPs). We have previously demonstrated that some tetracycline compounds (TCs) induce apoptosis in mature rabbit osteoclasts and inhibit osteoclastic resorption in mouse osteoblast/marrow co-cultures in vitro. In this report, we now show that non-antibiotic analogues of doxycycline (CMT-3) and minocycline (CMT-8) are potent inhibitors of osteoclastogenesis in vitro from human peripheral blood mononuclear cells (PBMC) stimulated with macrophage colony stimulating factor (MCSF) and receptor activator of NF-kappaB ligand (RANKL), through an action that is independent of osteoblast-osteoclast interactions. Osteoclast formation over 20 days was completely abrogated when CMT-3 or CMT-8 were included in PBMC cultures at a concentration of 250 ng/ml, although doxycycline at this concentration reduced osteoclast formation to ca. 50% of control. CMT-3 and CMT-8 also significantly induced apoptosis over 24 h in mature osteoclasts generated over 20 days when added to cultures at 5 microg/ml or more. In a time-course experiment, apoptosis was evident after a delay of 1-2 h following treatment of mature osteoclasts with CMT-3 at 20 microg/ml. The broad-spectrum MMP inhibitor BB94 (Batimastat) did not recapitulate the apoptosis induced by CMT-3, even at a concentration where MMP-13 activity was completely inhibited. There was no evidence for an anabolic effect of any of the TCs on osteoblast lineage cells in a calcifying fibroblastic colony (CFU-f) formation assay, where CMT-3 partially inhibited CFU-f formation at 5 microg/ml. Our data indicate that inhibition of osteoclast formation and induction of osteoclast apoptosis are pharmacologically significant actions of CMTs in inhibiting bone resorption, and that osteoclast apoptosis cannot be attributed to the ability of CMTs to inhibit MMPs or to actions mediated by osteoblastic lineage cells.

Anti-inflammatory effects of annexin-1: stimulation of IL-10 release and inhibition of nitric oxide synthesis

Annexin-1 (ANX-1) is an anti-inflammatory protein induced by glucocorticoids. Like glucocorticoids, ANX-1 and derived peptides inhibit eicosanoid synthesis, block leukocyte migration and induce apoptosis of inflammatory cells. Cytokines may possess either pro-inflammatory, i.e. interleukin(IL)-1beta, tumor necrosis factor (TNF)-alpha, IL-12 or anti-inflammatory properties, i.e. IL-4, IL-10. The experiments described in the present study have been performed to answer the question whether the anti-inflammatory action of ANX-1 may be mediated, at least in part, by the release of IL-10. In macrophage (J774) cell line cultures primed with lipolysaccharide (LPS), recombinant ANX-1 stimulated IL-10 release in a dose- and time-dependent manner. In the same cells, the protein and its derived N-terminal peptide (amino acids 2-26) dose-dependently inhibited the release of nitric oxide (NO). Furthermore, both the whole protein and the peptide down-regulated the mRNA expression of the inducible nitric oxide sythase (iNOS). The peptide was also able to inhibit the expression of IL-12 mRNA. These results suggest that some of the anti-inflammatory effects of ANX-1 may be mediated by the release of IL-10, which, in turn, inhibits iNOS mRNA expression and, hence, NO release. In addition, ANX-1-stimulated IL-10 release may also be responsible for the inhibition of IL-12 mRNA expression and, consequently, IL-12 synthesis.