Arachidonic acid (AA) metabolizing enzymes and peroxisome proliferator-activated receptors (PPARs) have been shown to regulate the growth of epithelial cells. We have previously reported that exposure to the 5-lipoxygenase activating protein-directed inhibitor MK886 but not the cyclooxygenase inhibitor, indomethacin, reduced growth, increased apoptosis, and up-regulated PPARA and ; expression in breast cancer cell lines. In the present study, we explore approaches to maximizing the proapoptotic effects of PPAR; on lung cancer cell lines. Non-small-cell cancer cell line A549 revealed dosedependent PPAR; reporter activity after treatment with MK886. The addition of indomethacin in combination with MK886 further increases reporter activity. We also show increased growth inhibition and up-regulation of apoptosis after exposure to MK886 alone, or in combination with indomethacin and the PPAR ligand, 15-deoxy-# 12,14 -prostaglandin J 2 compared with single drug exposures on the adenocarcinoma cell line A549 and small-cell cancer cell lines H345, N417, and H510. Real-time PCR analyses showed increased PPAR mRNA and retinoid X receptor (RXR)A mRNA expression after exposure to MK886 and indomethacin in a time-dependent fashion. The results suggest that the principal proapoptotic effect of these drugs may be mediated through the known antiproliferative effects of the PPAR;-RXR interaction. We therefore explored a three-drug approach to attempt to maximize this effect. The combination of low-dose MK886, ciglitazone, and 13-cis-retinoic acid interacted at least in a superadditive fashion to inhibit the growth of lung cancer cell lines A549 and H1299, suggesting that targeting PPAR; and AA action is a promising approach to lung cancer growth with a favorable therapeutic index. (Cancer Res 2005; 65(10): 4181-90)
The small molecular inhibitor MK886 is known to block 5-lipoxygenase-activating protein ALOX5AP and shows antitumor activity in multiple human cell lines. The broad antitumor therapeutic window reported in vivo for MK886 in rodents supports further consideration of this structural class. Better understanding of the mode of action of the drug is important for application in humans to take place. Affymetrix microarray study was conducted to explore MK886 pharmacologic mechanism. Ingenuity Pathway Analysis software was applied to validate the results at the transcriptional level by putting them in the context of an experimental proteomic network. Genes most affected by MK886 included actin B and focal adhesion components. A subsequent National Cancer Institute-60 panel study, RT-PCR validation followed by confocal microscopy, and Western blotting also pointed to actin B down-regulation, filamentous actin loss, and disorganization of the transcription machinery. In agreement with these observations, MK886 was found to enhance the effect of UV radiation in H720 lung cancer cell line. In light of the modification of cytoskeleton and cell motility by lipid phosphoinositide 3-kinase products, MK886 interaction with actin B might be biologically important. The low toxicity of MK886 in vivo was modeled and explained by binding and transport by dietary lipids. The rate of lipid absorbance is generally higher for tumors, suggesting a promise of a targeted liposome-based delivery system for this drug. These results suggest a novel antitumor pharmacologic mechanism.
The binding of nitric oxide to ferric and ferrous Chromatium vinosum cytochrome c' was studied. The extinction coefficients for the ferric and ferrous nitric oxide complexes were measured. A binding model that included both a conformational change and dissociation of the dimer into subunits provided the best fit for the ferric cytochrome c' data. The NO (nitric oxide) binding affinity of the WT ferric form was found to be comparable to the affinities displayed by the ferric myoglobins and hemoglobins. Using an improved fitting model, positive cooperativity was found for the binding of NO to the WT ferric and ferrous forms, while anticooperativity was the case for the Y16F mutant. Structural explanations accounting for the binding are proposed. The NO affinity of ferrous cytochrome c' was found to be much lower than the affinities of myoglobins, hemoglobins, and pentacoordinate heme models. Structural factors accounting for the difference in affinities were analyzed. The NO affinity of ferrous cytochrome c' was found to be in the range typical of receptors and carriers. In addition, cytochrome c' was found to react with cytosolic light-irradiated membranes in the presence of succinate and carbon monoxide. With these results, a biochemical model of cytochrome c' functioning as a nitric oxide carrier was proposed.
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