Combination Therapy of PPARgamma Ligands and Inhibitors of Arachidonic Acid in Lung Cancer

Nicotinamide N-methyltransferase upregulation contributes to palmitate-elicited peroxisome proliferator-activated receptor transactivation in hepatocytes

Peroxisome proliferator-activated receptor γ (PPARγ) plays a pivotal role in regulating lipid metabolism and hepatic PPARγ transactivation contributes to fatty liver development. Fatty acids (FAs) are well-known endogenous ligands for PPARγ. Palmitate, a 16-C saturated FA (SFA) and the most abundant SFA in human circulation, is a strong inducer of hepatic lipotoxicity, a central pathogenic factor for various fatty liver diseases. In this study, using both alpha mouse liver 12 (AML12) and primary mouse hepatocytes, we investigated the effects of palmitate on hepatic PPARγ transactivation and underlying mechanisms, as well as the role of PPARγ transactivation in palmitate-induced hepatic lipotoxicity, all of which remain ambiguous currently. Our data revealed that palmitate exposure was concomitant with both PPARγ transactivation and upregulation of nicotinamide N-methyltransferase (NNMT), a methyltransferase catalyzing the degradation of nicotinamide, the predominant precursor for cellular NAD+ biosynthesis. Importantly, we discovered that PPARγ transactivation by palmitate was blunted by NNMT inhibition, suggesting that NNMT upregulation plays a mechanistic role in PPARγ transactivation. Further investigations uncovered that palmitate exposure is associated with intracellular NAD+ decline and NAD+ replenishment with NAD+-enhancing agents, nicotinamide and nicotinamide riboside, obstructed palmitate-induced PPARγ transactivation, implying that cellular NAD+ decline resulted from NNMT upregulation represents a potential mechanism behind palmitate-elicited PPARγ transactivation. At last, our data showed that the PPARγ transactivation marginally ameliorated palmitate-induced intracellular triacylglycerol accumulation and cell death. Collectively, our data provided the first-line evidence supporting that NNMT upregulation plays a mechanistic role in palmitate-elicited PPARγ transactivation, potentially through reducing cellular NAD+ contents.NEW & NOTEWORTHY Hepatic PPARγ transactivation contributes to fatty liver development. Saturated fatty acids (SFAs) induce hepatic lipotoxicity. Here, we investigated whether and how palmitate, the most abundant SFA in the human blood, affects PPARγ transactivation in hepatocytes. We reported for the first time that upregulation of nicotinamide N-methyltransferase (NNMT), a methyltransferase catalyzing the degradation of nicotinamide, the predominant precursor for cellular NAD+ biosynthesis, plays a mechanistic role in regulating palmitate-elicited PPARγ transactivation through reducing intracellular NAD+ contents.

Pyrrolizines: Design, synthesis, anticancer evaluation and investigation of the potential mechanism of action

A novel set of pyrrolizine-5-carboxamides has been synthesized and evaluated for their anticancer potential against human breast MCF-7, lung carcinoma A549 and hepatoma Hep3B cancer cell lines. Compound 10c was the most active against MCF-7 with IC₅₀ value of 4.72µM, while compound 12b was the most active against A549 and Hep3B cell lines. Moreover, kinases/COXs inhibition and apoptosis induction were suggested as potential molecular mechanisms for the anticancer activity of the novel pyrrolizines based on their structural features. The new compounds significantly inhibited COX-1 and COX-2 with IC₅₀ values in the ranges of 5.78-11.96µM and 0.1-0.78µM, respectively with high COX-2 selectivity over COX-1. Interestingly, the most potent compound in MTT assay, compound 12b, exhibited high inhibitory activity against COX-2 with selectivity index (COX-1/COX-2)>100. Meanwhile, compound 12b displayed weak to moderate inhibition of six kinases with inhibition% (7-20%) compared to imatinib (inhibition%=1-38%). The results of cell cycle analysis, annexin V PI/FITC apoptosis assay and caspase-3/7 assay revealed that compound 12b has the ability to induce apoptosis. The docking results of compound 12b into the active sites of COXs, ALK1 and Aurora kinases indicated that it fits nicely inside their active sites. Overall, the current study highlighted the significant anticancer activity of the newly synthesized pyrrolizines with a potential multi-targeted mechanism which could serve as a base for future studies and further structural optimization into potential anticancer agents.

Licofelone abolishes survival of carcinogenic fibroblasts by inducing apoptosis

Dual inhibitors of cyclooxygenase (COX) and lipoxygenase (LOX) pathways of arachidonic acid metabolism prevent cancer development and induce apoptosis. One of the most promising compounds that blocks both of these pathways is licofelone. We questioned whether licofelone affects the survival and/or promotes apoptosis of H-ras transformed rat embryonic fibroblast (5RP7) cells in vitro. Using 5-fluorouracil (5-FU) and colchicine as positive controls, we determined cell viability with 3-3-(4,5-D-methylthiazol-2-yl)-2,5-diphenyltetrazolium bromide, thyazolyl blue (MTT), apoptosis with flow cytometry and activity of caspase enzyme with real-time reverse transcription polymerase chain reaction (PCR). Compared to the control, all used six doses (10, 50, 100, 150, 250 and 250 µM) of 5-FU, colchicine and licofelone, which were cytotoxic and reduced the number of H-Ras transformed 5RP7 cells by as much as 78, 72 and 92%, respectively. In addition, we found that 150, 200 and 250 µM of licofelone induced apoptosis and necrosis of H-Ras transformed 5RP7 cells in a dose- and time-dependent manner. Each three tested drugs at 250 µM also increased the level of caspase-3 enzyme up to 5-fold. Although colchicine was effective in inducing early apoptosis, licofelone had much more capacity to induce the total of early plus late apoptosis by approximately 96% in cells after 48 hours. The present study reveals the possibility that licofelone posseses strong dose- and time-dependent anticancer and apoptotic properties on carcinogenic fibroblasts.

Cyclooxygenases and lipoxygenases in cancer

Cancer initiation and progression are multistep events that require cell proliferation, migration, extravasation to the blood or lymphatic vessels, arrest to the metastatic site, and ultimately secondary growth. Tumor cell functions at both primary or secondary sites are controlled by many different factors, including growth factors and their receptors, chemokines, nuclear receptors, cell-cell interactions, cell-matrix interactions, as well as oxygenated metabolites of arachidonic acid. The observation that cyclooxygenases and lipoxygenases and their arachidonic acid-derived eicosanoid products (prostanoids and HETEs) are expressed and produced by tumor cells, together with the finding that these enzymes can regulate cell growth, survival, migration, and invasion, has prompted investigators to analyze the roles of these enzymes in cancer progression. In this review, we focus on the contribution of cyclooxygenase- and lipoxygenase-derived eicosanoids to tumor cell function in vitro and in vivo and discuss hope and tribulations of targeting these enzymes for cancer prevention and treatment.