Mitochondrial-targeted fatty acid analog induces apoptosis with selective loss of mitochondrial glutathione in promyelocytic leukemia cells

Inclusion of the in-chain sulfur in 3-thiaCTU increases the efficiency of mitochondrial targeting and cell killing by anticancer aryl-urea fatty acids

Mitochondria in tumor cells are functionally different from those in normal cells and could be targeted to develop new anticancer agents. We showed recently that the aryl-ureido fatty acid CTU is the prototype of a new class of mitochondrion-targeted agents that kill cancer cells by increasing the production of reactive oxygen species (ROS), activating endoplasmic reticulum (ER)-stress and promoting apoptosis. However, prolonged treatment with high doses of CTU were required for in vivo anti-tumor activity. Thus, new strategies are now required to produce agents that have enhanced anticancer activity over CTU. In the present study we prepared a novel aryl-urea termed 3-thiaCTU, that contained an in-chain sulfur heteroatom, for evaluation in tumor cell lines and in mice carrying tumor xenografts. The principal finding to emerge was that 3-thiaCTU was several-fold more active than CTU in the activation of aryl-urea mechanisms that promoted cancer cell killing. Thus, in in vitro studies 3-thiaCTU disrupted the mitochondrial membrane potential, increased ROS production, activated ER-stress and promoted tumor cell apoptosis more effectively than CTU. 3-ThiaCTU was also significantly more active than CTUin vivo in mice that carried MDA-MB-231 cell xenografts. Compared to CTU, 3-thiaCTU prevented tumor growth more effectively and at much lower doses. These findings indicate that, in comparison to CTU, 3-thiaCTU is an aryl-urea with markedly enhanced activity that could now be suitable for development as a novel anticancer agent.

Anti-tumor activities of lipids and lipid analogues and their development as potential anticancer drugs

Lipids have the potential for development as anticancer agents. Endogenous membrane lipids, such as ceramides and certain saturated fatty acids, have been found to modulate the viability of tumor cells. In addition, many tumors over-express cyclooxygenase, lipoxygenase or cytochrome P450 enzymes that mediate the biotransformation of ω-6 polyunsaturated fatty acids (PUFAs) to potent eicosanoid regulators of tumor cell proliferation and cell death. In contrast, several analogous products from the biotransformation of ω-3 PUFAs impair particular tumorigenic pathways. For example, the ω-3 17,18-epoxide of eicosapentaenoic acid activates anti-proliferative and proapoptotic signaling cascades in tumor cells and the lipoxygenase-derived resolvins are effective inhibitors of inflammatory pathways that may drive tumor expansion. However, the development of potential anti-cancer drugs based on these molecules is complex, with in vivo stability a major issue. Nevertheless, recent successes with the antitumor alkyl phospholipids, which are synthetic analogues of naturally-occurring membrane phospholipid esters, have provided the impetus for development of further molecules. The alkyl phospholipids have been tested against a range of cancers and show considerable activity against skin cancers and certain leukemias. Very recently, it has been shown that combination strategies, in which alkyl phospholipids are used in conjunction with established anticancer agents, are promising new therapeutic approaches. In future, the evaluation of new lipid-based molecules in single-agent and combination treatments may also be assessed. This could provide a range of important treatment options in the management of advanced and metastatic cancer.

Lipid analogues as potential drugs for the regulation of mitochondrial cell death

The mitochondrion plays an important role in the production of energy as ATP, the regulation of cell viability and apoptosis, and the biosynthesis of major structural and regulatory molecules, such as lipids. During ATP production, reactive oxygen species are generated that alter the intracellular redox state and activate apoptosis. Mitochondrial dysfunction is a well-recognized component of the pathogenesis of diseases such as cancer. Understanding mitochondrial function, and how this is dysregulated in disease, offers the opportunity for the development of drug molecules to specifically target such defects. Altered energy metabolism in cancer, in which ATP production occurs largely by glycolysis, rather than by oxidative phosphorylation, is attributable in part to the up-regulation of cell survival signalling cascades. These pathways also regulate the balance between pro- and anti-apoptotic factors that may determine the rate of cell death and proliferation. A number of anti-cancer drugs have been developed that target these factors and one of the most promising groups of agents in this regard are the lipid-based molecules that act directly or indirectly at the mitochondrion. These molecules have emerged in part from an understanding of the mitochondrial actions of naturally occurring fatty acids. Some of these agents have already entered clinical trials because they specifically target known mitochondrial defects in the cancer cell.

Cyclic AMP induces IPC leukemia cell apoptosis via CRE-and CDK-dependent Bim transcription

The IPC-81 cell line is derived from the transplantable BNML model of acute myelogenic leukemia (AML), known to be a reliable predictor of the clinical efficiency of antileukemic agents, like the first-line AML anthracycline drug daunorubicin (DNR). We show here that cAMP acted synergistically with DNR to induce IPC cell death. The DNR-induced death differed from that induced by cAMP by (1) not involving Bim induction, (2) being abrogated by GSK3β inhibitors, (3) by being promoted by the HSP90/p23 antagonist geldanamycin and truncated p23 and (4) by being insensitive to the CRE binding protein (CREB) antagonist ICER and to cyclin-dependent protein kinase (CDK) inhibitors. In contrast, the apoptosis induced by cAMP correlated tightly with Bim protein expression. It was abrogated by Bim (BCL2L11) downregulation, whether achieved by the CREB antagonist ICER, by CDK inhibitors, by Bim-directed RNAi, or by protein synthesis inhibitor. The forced expression of BimL killed IPC-81_WT cells rapidly, Bcl2-overexpressing cells being partially resistant. The pivotal role of CREB and CDK activity for Bim transcription is unprecedented. It is also noteworthy that newly developed cAMP analogs specifically activating PKA isozyme I (PKA-I) were able to induce IPC cell apoptosis. Our findings support the notion that AML cells may possess targetable death pathways not exploited by common anti-cancer agents.

Tetradecylthioacetic acid inhibits proliferation of human SW620 colon cancer cells--gene expression profiling implies endoplasmic reticulum stress

Background

Previous reports have shown an antiproliferative effect of the synthetic, 3-thia fatty acid tetradecylthioacetic acid (TTA) on different cancer cells in vitro and in vivo. The mechanisms behind the observed effects are poorly understood. We therefore wanted to explore the molecular mechanisms involved in TTA-induced growth inhibition of the human colon cancer cell line SW620 by gene expression profiling.

Methods

An antiproliferative effect of TTA on SW620 cells in vitro was displayed in real time using the xCELLigence System (Roche). Affymetrix gene expression profiling was performed to elucidate the molecular mechanisms behind the antiproliferative effect of TTA. Changes in gene expression were verified at protein level by western blotting.

Results

TTA reduced SW620 cell growth, measured as baseline cell index, by 35% and 55% after 48 h and 72 h, respectively. We show for the first time that TTA induces an endoplasmic reticulum (ER) stress response in cancer cells. Gene expression analysis revealed changes related to ER stress and unfolded protein response (UPR). This was verified at protein level by phosphorylation of eukaryote translation initiation factor 2 alpha (eIF2α) and downstream up-regulation of activating transcription factor 4 (ATF4). Transcripts for positive and negative cell cycle regulators were down- and up-regulated, respectively. This, together with a down-regulation of Cyclin D1 at protein level, indicates inhibition of cell cycle progression. TTA also affected transcripts involved in calcium homeostasis. Moreover, mRNA and protein level of the ER stress inducible C/EBP-homologous protein (CHOP), Tribbles homolog 3 (Drosophila) (TRIB3) and CCAAT/enhancer binding protein beta (C/EBPβ) were enhanced, and the C/EBPβ LIP/LAP ratio was significantly increased. These results indicate prolonged ER stress and a possible link to induction of cell death.

Conclusion

We find that TTA-induced growth inhibition of SW620 cells seems to be mediated through induction of ER stress and activation of the UPR pathway.

The apoptosis-inducing activity towards leukemia and lymphoma cells in a cyanobacterial culture collection is not associated with mouse bioassay toxicity

Cyanobacteria (83 strains and seven natural populations) were screened for content of apoptosis (cell death)-inducing activity towards neoplastic cells of the immune (jurkat acute T-cell lymphoma) and hematopoetic (acute myelogenic leukemia) lineage. Apoptogenic activity was frequent, even in strains cultured for decades, and was unrelated to whether the cyanobacteria had been collected from polar, temperate, or tropic environments. The activity was more abundant in the genera Anabaena and Microcystis compared to Nostoc, Phormidium, Planktothrix, and Pseudanabaena. Whereas the T-cell lymphoma apoptogens were frequent in organic extracts, the cell death-inducing activity towards leukemia cells resided mainly in aqueous extracts. The cyanobacteria were from a culture collection established for public health purposes to detect toxic cyanobacterial blooms, and 54 of them were tested for toxicity by the mouse bioassay. We found no correlation between the apoptogenic activity in the cyanobacterial isolates with their content of microcystin, nor with their ability to elicit a positive standard mouse bioassay. Several strains produced more than one apoptogen, differing in biophysical or biological activity. In fact, two strains contained microcystin in addition to one apoptogen specific for the AML cells, and one apoptogen specific for the T-cell lymphoma. This study shows the potential of cyanobacterial culture collections as libraries for bioactive compounds, since strains kept in cultures for decades produced apoptogens unrelated to the mouse bioassay detectable bloom-associated toxins.

Marine benthic diatoms contain compounds able to induce leukemia cell death and modulate blood platelet activity

In spite of the high abundance and species diversity of diatoms, only a few bioactive compounds from them have been described. The present study reveals a high number of mammalian cell death inducing substances in biofilm-associated diatoms sampled from the intertidal zone. Extracts from the genera Melosira, Amphora, Phaeodactylum and Nitzschia were all found to induce leukemia cell death, with either classical apoptotic or autophagic features. Several extracts also contained inhibitors of thrombin-induced blood platelet activation. Some of this activity was caused by a high content of adenosine in the diatoms, ranging from 0.07 to 0.31 μg/mg dry weight. However, most of the bioactivity was adenosine deaminase-resistant. An adenosine deaminase-resistant active fraction from one of the extracts was partially purified and shown to induce apoptosis with a distinct phenotype. The results show that benthic diatoms typically found in the intertidal zone may represent a richer source of interesting bioactive compounds than hitherto recognized.

Connexin-based signaling in acute myelogenous leukemia (AML)

Normal and malignant hematopoiesis are regulated by intercellular communication in the hematopoietic microenvironments, and both soluble mediators as well as direct cell-cell contact play important functional roles. Gap junctions are complex membrane structures that transfer molecules between neighboring cells and thereby alter intracellular signaling and metabolism. The gap junction building blocks, the connexins, are also involved in gap junction-independent intercellular communication by forming hemichannels that transfer substances between the intra- and extracellular spaces. Connexins are furthermore involved in cell regulation as single molecules by modulating intracellular pathways and possibly gene transcription. The role of connexins in leukemogenesis and leukemic cell functions are not well characterized. In this review, we describe the known effects of gap junctions and connexins in acute myelogenous leukemia and the diverse potential of connexins in acute myelogenous leukemia chemosensitivity, intracellular signaling and cell death regulation.

Protein kinase A activators and the pan-PPAR agonist tetradecylthioacetic acid elicit synergistic anti-leukaemic effects in AML through CREB

Targeting of signal transduction pathways and transcriptional regulation represents an attractive approach for less toxic anti-leukaemic therapy. We combined protein kinase A (PKA) activation with a pan-peroxisome proliferator-activated receptor (PPAR) activator tetradecylthioacetic acid, resulting in synergistic decrease in viability of AML cell lines. PKA isoform II activation appeared to be involved in inhibition of proliferation but not induction of apoptosis in HL-60 cells. Inhibition of CREB function protected against this anti-leukaemic effect with higher efficiency than enforced Bcl-2 expression. Preclinical studies employing the rat AML model Brown Norwegian Myeloid Leukaemia also indicated anti-leukaemic activity of the combination therapy in vivo. In conclusion, combined PKA and pan-PPAR activation should be explored further to determine its therapeutic potential.

Isomer-specific effects of conjugated linoleic acid on gene expression in RAW 264.7

Conjugated linoleic acid (CLA) is a mixture of dietary fatty acids that has various beneficial effects including decreasing cancer, atherosclerosis, diabetes and inflammation in animal models. Some controversy exists on the specific isomers of CLA that are responsible for the benefits observed. This study was conducted to examine how different CLA isomers regulate gene expression in RAW 264.7. A mouse macrophage cell line, RAW 264.7, was treated with five different CLA isomers (9E,11E-, 9Z,11E-, 9Z,11Z-, 10E,12Z- and 11Z,13E-CLA). Gene expression microarrays were performed, and several significantly regulated genes of interest were verified by a real-time polymerase chain reaction (PCR). Examination of the biological functions of various significantly regulated genes by the five CLA isomers showed distinct properties. Isomers 9E,11E-, 9Z,11Z-, 10E,12Z- and 11Z,13E-CLA decreased production of proinflammatory cytokines such as interleukin (IL)-1alpha, IL-1beta and IL-6. Many of CLA's effects are believed to be mediated by the fatty acid receptors such as the peroxisome proliferator-activated receptors (PPAR) and retinoid-X-receptors (RXR). Using PPAR and RXR specific antagonists and coactivator recruitment assays, it was evident that multiple mechanisms were responsible for gene regulation by CLA isomers. Coactivator recruitment by CLA isomers showed their distinct properties as selective receptor modulators for PPARgamma and RXRalpha. These studies demonstrate distinct isomer differences in gene expression by CLA and will have important ramifications for determining the potential therapeutic benefit of these dietary fatty acids in prevention of inflammation-related diseases.

A bioactively modified fatty acid improves survival and impairs metastasis in preclinical models of acute leukemia

PURPOSE

Polyunsaturated fatty acids (PUFA) and the sulfur-substituted fatty acid tetradecylthioacetic acid (TTA) inhibit proliferation and induce apoptosis in lymphoma and leukemic cell lines, but it is unknown if they can modify leukemogenesis in the intact organism.

EXPERIMENTAL DESIGN

We now examined the effects of PUFA and TTA in rats transplanted with either acute promyelocytic leukemia or acute T-cell leukemia. The rats were randomized to isoenergetic diets containing either lard (control), omega3 (n-3) PUFA, or TTA.

RESULTS

Whereas TTA prolonged survival (P < 0.05) in both types of rat leukemia, n-3 PUFA had no significant effect compared with controls. Only TTA inhibited (P < 0.05) leukemic infiltration in the bone marrow and spleen, probably due to apoptosis of the leukemic cells. Plasma metalloproteinase activity, a marker of metastatic activity, was significantly reduced in TTA-fed rats only.

CONCLUSIONS

Dietary intake of TTA, but not of n-3 PUFA, in rats with acute leukemia, prolonged their survival. TTA intake was also associated with reduced leukemic cell burden as well as diminished extramedullar dissemination. TTA represents a modified fatty acid that exerts unique effects on malignant hematopoietic cells, and the present study indicates that TTA may have a therapeutic potential in patients with acute leukemias.

Targeting mitochondria in the treatment of human cancer: a coordinated attack against cancer cell energy metabolism and signalling

Mitochondria have major roles in bioenergetics and vital signalling of the mammalian cell. Consequently, these organelles have been implicated in the process of carcinogenesis, which includes alterations of cellular metabolism and cell death pathways. Multiple molecular routes of malignant transformation appear to result in the common ability of many tumours to take up large amounts of glucose. This metabolic twist has been explained by phenomena such as aerobic glycolysis and impaired mitochondrial function, and is linked to tumour growth potential via major cellular signalling pathways. This paper reviews the literature on central mechanisms through which energy metabolism merges with growth, proliferation and death signalling, which tend to include mitochondria at some level. These processes can potentially be targeted by pharmacological agents for therapeutic and chemosensitising purposes.

The antimicrobial peptide, lactoferricin B, is cytotoxic to neuroblastoma cellsin vitro and inhibits xenograft growthin vivo

Antimicrobial peptides have been shown to exert cytotoxic activity towards cancer cells through their ability to interact with negatively charged cell membranes. In this study the cytotoxic effect of the antimicrobial peptide, LfcinB was tested in a panel of human neuroblastoma cell lines. LfcinB displayed a selective cytotoxic activity against both MYCN-amplified and non-MYCN-amplified cell lines. Non-transformed fibroblasts were not substantially affected by LfcinB. Treatment of neuroblastoma cells with LfcinB induced rapid destabilization of the cytoplasmic membrane and formation of membrane blebs. Depolarization of the mitochondria membranes and irreversible changes in the mitochondria morphology was also evident. Immuno- and fluorescence-labeled LfcinB revealed that the peptide co-localized with mitochondria. Furthermore, treatment of neuroblastoma cells with LfcinB induced cleavage of caspase-6, -7 and -9 followed by cell death. However, neither addition of the pan-caspase inhibitor, zVAD-fmk, or specific caspase inhibitors could reverse the cytotoxic effect induced by LfcinB. Treatment of established SH-SY-5Y neuroblastoma xenografts with repeated injections of LfcinB resulted in significant tumor growth inhibition. These results revealed a selective destabilizing effect of LfcinB on two important targets in the neuroblastoma cells, the cytoplasmic- and the mitochondria membrane.

Is targeted chemotherapy an alternative to immunotherapy in chronic lymphocytic leukemia?

Although molecular remission is now detected, it is still unknown whether we have the tools to cure B cell chronic lymphocytic leukemia (referred to as CLL). Nonetheless, several new therapeutic approaches have been introduced in cancer therapy during the last decade, including antiangiogenic therapy, apoptosis-inducing treatment and inhibition of heat shock proteins, farnesyl transferase, tyrosine kinases and proteasomes. These modalities may also be considered in CLL, but additional experimental characterization is required. Further characterization and development of CLL animal models should be a part of this preclinical work (especially xenografting in NOD/SCID animals, but also murine leukemia) to allow a more extensive evaluation prior to clinical trials. Animal models are particularly important for preclinical comparison of pharmacological effects between different disease compartments and for in vivo evaluation of antileukemic immune reactivity. However, T cell targeting therapy seems to have several advantages in comparison to other approaches: (1) based on the current clinical experience one would expect low toxicity for several of these strategies, especially vaccine treatment; (2) several studies have demonstrated that autologous T cells can recognize CLL cells; (3) experimental and clinical evidence suggests that immunotherapy can be combined with chemotherapy. Thus, T cell therapy has a relatively strong scientific basis that justifies further clinical studies of immunotherapy in CLL. Although several of the new pharmacological agents seem to have immunosuppressive effects, at least some of them (e.g. heat shock protein 90 inhibitors, proteasome inhibitors, inhibition of angiogenesis) appear to affect T cells only at relatively high concentrations and may thus be used in combination with immunotherapy.

Antiinflammatory Effects of Tetradecylthioacetic Acid Involve Both Peroxisome Proliferator–Activated Receptor α–Dependent and –Independent Pathways

OBJECTIVE

Tetradecylthioacetic acid (TTA) is a hypolipidemic antioxidant with immunomodulating properties involving activation of peroxisome proliferator-activated receptors (PPARs). Human endothelial cells express PPARs. We hypothesized that TTA could modulate endothelial cell activation at least partly through PPAR-related mechanisms.

METHODS AND RESULTS

We explored this hypothesis by different experimental approaches involving both in vitro studies in human endothelial cells (HUVECs) and in vivo studies in humans and PPAR-alpha-/- mice. Our main findings were as follows: (1) TTA suppressed the tumor necrosis factor alpha-induced expression of vascular cell adhesion molecule 1 (VCAM-1) and interleukin 8 (IL-8) in HUVECs. (2) No TTA-mediated attenuation of VCAM-1 and chemokine expression was seen in the liver of PPAR-alpha-/- mice. (3) Whereas TTA markedly enhanced PPAR-alpha-target genes in the liver of wild-type, but not of PPAR-alpha-/-, mice, no such effect on PPAR-alpha-target genes was seen in HUVECs. (4) The relevance of our findings to human disease was suggested by a TTA-mediated downregulation of serum levels of soluble VCAM-1 and IL-8 in psoriasis patients.

CONCLUSIONS

We show that TTA has the ability to attenuate tumor necrosis factor alpha-mediated endothelial cell activation, further supporting antiinflammatory effects of this fatty acid, possibly involving both PPAR-alpha-dependent and -independent pathways.

Modified fatty acids and their possible therapeutic targets in malignant diseases

Fatty acids and other lipids have multiple roles in the cell, functioning as structural components, participating in intracellular signalling and serving as metabolic fuel. Various compounds that influence cellular lipid metabolism can reduce the growth of malignant cells, and dietary as well as pharmacological strategies for modulating lipid metabolism have therefore been suggested as possible approaches for cancer prevention and treatment. By chemically modifying fatty acids (e.g., butyrates, retinoids), new potential anticancer agents have been produced that possess increased metabolic stability and more specific and potent biological activity compared to the natural fatty acids. Possible therapeutic targets for such modified fatty acids include: i) Histone deacetylase; ii) nuclear hormone receptors (retinoid receptors), peroxisome proliferator-activated receptors; iii) cyclooxygenase-2; iv) intracellular signalling involving protein farnesylation and Ras activation; and v) various mitochondrial functions. Although several fatty acid derivatives have been thoroughly investigated in experimental models, clinical data on toxicity and pharmacological interactions are not available for the majority of these agents. However, several promising novel compounds are now being evaluated in preclinical and early clinical studies, and future research will hopefully reveal new formulations and therapy schedules that will improve the outcome of patients with malignant disorders.