Bexarotene activates the p53/p73 pathway in human cutaneous T-cell lymphoma.

BACKGROUND: Bexarotene is the first synthetic retinoid X receptor-selective retinoid (rexinoid) approved for the treatment of cutaneous T-cell lymphoma (CTCL). However, little is known about the signalling pathways by which it exerts its anticarcinogenic effect. OBJECTIVES: To characterize the effects of bexarotene in CTCL cell lines and elucidate the underlying molecular pathways of its antineoplastic effect. METHODS: The cell lines Hut-78, HH and MJ were used. Cell viability was assessed with the XTT assay. The self-renewal potential of cells after bexarotene treatment was studied with the methylcellulose clonogenic assay. Flow cytometry was used to analyse the effects on cell cycle, Ki-67 expression and apoptosis induction. Cell cycle and apoptosis-related protein expression were determined by Western blot and immunofluorescence. RESULTS: Bexarotene induced a loss of viability and more pronounced inhibition of clonogenic proliferation in HH and Hut-78 cells, whereas the MJ line exhibited resistance. Bexarotene upregulated and activated Bax in sensitive lines, although not enough to signal significant apoptosis. Instead, all data point to the inhibition of proliferation, rather than apoptosis, as the main mechanistic action of the rexinoid. Bexarotene signals both G(1) and G(2)/M arrest by the modulation of critical checkpoint proteins. We further found that bexarotene activates p53 by phosphorylation at Ser15, which influences the binding of p53 to promoters for cell cycle arrest, induces p73 upregulation, and, in concordance, also modulates some p53/p73 downstream target genes, such as p21, Bax, survivin and cdc2. Bexarotene-mediated ataxia telangiectasia mutated protein (ATM) activation in all studied lines suggests that ATM is likely to be the p53/p73 upstream activator. CONCLUSIONS: Our data indicate for the first time that bexarotene exerts its effect in CTCL mainly by triggering the p53/p73-dependent cell cycle inhibition pathway, probably by upstream ATM activation. Therefore, bexarotene-modulated genes represent potential biomarkers to assess the response to treatment of patients with CTCL.

Metformin Induces Cell Cycle Arrest and Apoptosis in Drug-Resistant Leukemia Cells.

Recent epidemiological studies indicate that the antidiabetic drug metformin has chemosensitizing and chemopreventive effects against carcinogenesis. Here, we demonstrate that metformin exerts varying degrees of antitumor activity against human leukemia cells, as reflected by differences in growth inhibition, apoptosis, and alterations to metabolic enzymes. In metformin-sensitive cells, autophagy was not induced but rather it blocked proliferation by means of arresting cells in the S and G2/M phases which was associated with the downregulation of cyclin A, cyclin B1, and cdc2, but not that of cyclin E. In 10E1-CEM cells that overexpress Bcl-2 and are drug-resistant, the effect of metformin on proliferation was more pronounced, also inducing the activation of the caspases 3/7 and hence apoptosis. In all sensitive cells, metformin decreased the Δψ m and it modified the expression of enzymes involved in energy metabolism: PKCε (PKCepsilon) and PKCδ (PKCdelta). In sensitive cells, metformin altered PKCε and PKCδ expression leading to a predominance of PKCε over PKCδ which implies a more glycolytic state. The opposite occurs in the nonresponsive cells. In conclusion, we provide new insights into the activity of metformin as an antitumoral agent in leukemia cells that could be related to its capability to modulate energy metabolism.

Presence of laminin and 67KDa laminin-receptor on endothelial surface of lung capillaries. An immunocytochemical study.

The existence of cell surface-associated molecules has been claimed to play a major role in cellular recognition and interaction. In this respect, different tumor cell lines express laminin and its receptor, and this expression has been correlated with metastatic potential. In the present work, we have studied, by electron microscopic immunolabeling methods, the presence of laminin and 67KDa laminin-receptor on the surface of endothelial cells of lung blood capillaries. To label these molecules, we have developed an easy method in which the labeling is carried out "in situ", in previously excised lungs. The presence of both molecules was observed on the luminal surface of endothelial capillaries and, in many cases, gold particles were associated to small open vesicles of the endothelial cells. The results suggest that these molecules, traditionally associated to extracellular matrix, are also expressed in cellular surface of the lung vascular bed.

Laminin surface binding sites and metastatic potential of 3LL tumor cells, increased by indomethacin.

The level of laminin receptor expression on tumor cell surface has been correlated with the capacity of tumor cells to metastasize. In the present work we show that indomethacin treatment of a low metastatic 3LL tumor cells increases the ability of these cells to form lung metastasis and the binding of [125I] laminin on their cell surface. Scatchard analysis showed that the incubation with indomethacin (10(-7) M) for 48 h induced a specific increase of laminin binding sites on 3LL cell surface (1.5 fold per cell), presenting both a high and low affinity class of binding sites. On the other hand, indomethacin treatment (2 mg/kg weight) of tumor bearing mice increased the number of spontaneous metastatic nodules on the lung surface. Likewise, when 3LL tumor cells were incubated with indomethacin (10(-7) M) for 48 h, we observed an enhancement of lung metastatic nodules after intravenous injection of tumor cells. This last effect was partially reversed by peptides DPGYIGSR or YIGSR, corresponding to the active site at the B1 chain of laminin, with ability to bind the 67-kD laminin cell surface receptors. In summary, our results show that the increased attachment of 3LL tumor cells to laminin mediated by indomethacin is directly correlated with the metastatic activity of these cells, and suggests that the indomethacin effect on the metastatic potential could involve a modulation of laminin receptors on tumor cell surface.

Implication of mitochondria-derived ROS and cardiolipin peroxidation in N-(4-hydroxyphenyl)retinamide-induced apoptosis.

We have studied the effect of N-(4-hydroxyphenyl)retinamide on either malignant human leukaemia cells or normal cells and investigated its mechanism of action. We demonstrate that 4HPR induces reactive oxygen species increase on mitochondria at a target between mitochondrial respiratory chain complex I and II. Such oxidative stress causes cardiolipin peroxidation which in turn allows cytochrome c release to cytosol, caspase-3 activation and therefore apoptotic consumption. Moreover, this apoptotic pathway seems to be bcl-2/bax independent and count only on malignant cells but not normal nor activated lymphocytes.

Are laminin binding sites on tumor cell surface involved in the indomethacin-induced sensitivity to natural cytotoxic cells?

Prostaglandins are secreted by a variety of tumor cell lines. The prostaglandin synthesis inhibitor indomethacin (IND) inhibits 3LL tumor growth after both intramuscular or intrasplenic transplantation (45 and 72%, respectively). Moreover, when tumor cells were cultured with IND, the sensitivity of 3LL cells to natural cytotoxic (NC) effector cells was increased (30%) and a higher cytotoxicity was reached when both target and effector cells were treated. This effect was reversed partially or totally when the assay was performed in the presence of laminin or an octapeptide from the laminin B1 chain. In addition, we correlate the increased cytotoxicity mediated by IND with an enhanced ability of 3LL tumor cells to bind labeled laminin (55%). In summary, our results show that the blockage or modulation of cell surface laminin binding components could be directly correlated with the sensitivity of tumor target cells to be eliminated by way of natural cytotoxicity.

Efficacy of liposome-encapsulated indomethacin in response against metastatic 3LL and B16F1 tumor cells.

The ability of large liposomes to be taken up by tissue phagocytic cells, e.g., macrophages, has made it possible to increase the efficacy of several drugs as immunomodulating agents. In the present work, we have evaluated the effect of indomethacin, a prostaglandin synthesis inhibitor, both free and encapsulated in liposomes, on the spontaneous metastatic potential of 3LL and B16F1 tumor cells. Liposomes containing either carboxyfluorescein, indomethacin, or carboxyfluorescein plus indomethacin, were made in order to evaluate their in vitro plasma stability and in vivo clearance from the blood. The liposomes showed a high stability after 6 hours of plasma incubation and they were rapidly cleared in vivo. Liposomes encapsulating propidium iodide, a fluorescent DNA binding dye, were mainly taken up in vivo by hepatic and spleen macrophages 1 hour after intravenous injection, but not by lung macrophages. When C57BL/6 mice were intravenously inoculated with 10(5) 3LL or B16F1 tumor cells previously incubated with indomethacin (10(-7) M) for 48 hours, the number of experimental lung metastatic foci was increased with respect to their respective control groups. Also, in 3LL or B16F1 tumor-bearing mice, treatment with indomethacin (0.5 mg/kg weight/day) for 10 days enhanced the number of lung metastases, but not significantly. However, when mice received indomethacin encapsulated in liposomes, the number of metastases was significantly reduced. In addition, encapsulated indomethacin (0.5 mg/kg weight/day) inhibits prostaglandin E2 production by peritoneal and spleen macrophages, whereas no significant inhibitory effect was observed with control-liposomes or equivalent doses of free indomethacin. We conclude that intravenous administration of liposome-encapsulated indomethacin has an antimetastatic effect on tumor-bearing mice. Use of indomethacin in liposomes may avoid the stimulation of metastases observed when the drug is administered alone.

The role of cleavage of cell structures during apoptosis.

In this work we have studied the behavior of some cell structures, such as actin, tubulin and chromatin during apoptosis induced in F9 cells after retinoic acid treatment. In this experimental model, all defined steps of morphological changes described for apoptosis are observed. The correlation between a partial maintenance of F-actin and microtubular structures and the spatial distribution of F-actin suggests a possible relationship between this molecule and the characteristic shape changes observed in apoptosis. Additionally, the disposition of monomeric G-actin suggests a possible relationship between the fragmentation of this molecule and the cleavage of DNA. The analysis of the U2af1-rs1 specific sequence shows that the internucleosomal fragmentation observed in this gene is randomly produced during apoptosis and is not dependent of demethylation status. The results obtained confirm that specific cleavage of these cell structures is inherent to the development of the apoptotic process and do not exclude the possibility that proteolysis of key actin and/or tubulin molecules or the cleavage of specific chromatin sequences other than the ones analyzed here, could control the different phases of the apoptotic process.