ZR-75-1 human breast cancer cells: expression of inducible nitric oxide synthase and effect of tamoxifen and phorbol ester on nitric oxide production

Gasotransmitters in the tumor microenvironment: Impacts on cancer chemotherapy (Review)

Nitric oxide, carbon monoxide and hydrogen sulfide are three endogenous gasotransmitters that serve a role in regulating normal and pathological cellular activities. They can stimulate or inhibit cancer cell proliferation and invasion, as well as interfere with cancer cell responses to drug treatments. Understanding the molecular pathways governing the interactions between these gases and the tumor microenvironment can be utilized for the identification of a novel technique to disrupt cancer cell interactions and may contribute to the conception of effective and safe cancer therapy strategies. The present review discusses the effects of these gases in modulating the action of chemotherapies, as well as prospective pharmacological and therapeutic interfering approaches. A deeper knowledge of the mechanisms that underpin the cellular and pharmacological effects, as well as interactions, of each of the three gases could pave the way for therapeutic treatments and translational research.

Screening of Hibiscus and Cinnamomum Plants and Identification of Major Phytometabolites in Potential Plant Extracts Responsible for Apoptosis Induction in Skin Melanoma and Lung Adenocarcinoma Cells

Carcinogenesis is a major concern that severely affects the human population. Owing to persistent demand for novel therapies to treat and prohibit this lethal disease, research interest among scientists is drawing its huge focus toward natural products, as they have minimum toxicity comparable with existing treatment methods. The plants produce secondary metabolites, which are known to have the anticancer potential for clinical drug development. Furthermore, the use of nanocarriers could boost the solubility and stability of phytocompounds to obtain site-targeting delivery. The identification of potential phytochemicals in natural compounds would be beneficial for the synthesis of biocompatible nanoemulsions. The present study aimed to investigate the potential cytotoxicity of ethanol extracts of Hibiscus syriacus and Cinnamomum loureirii Nees plant parts on human skin melanoma (G361) and lung adenocarcinoma (A549) cells. Importantly, biochemical analysis results showed the presence of high phenol (50-55 µgGAE/mg) and flavonoids [42-45 µg quercetin equivalents (QE)/mg] contents with good antioxidant activity (40-58%) in C. loureirii Nees plants extracts. This plant possesses potent antiproliferative activity (60-90%) on the malignant G361 and A549 and cell lines correlated with the production of nitric oxide. Especially, C. loureirii plant extracts have major metabolites that exhibit cancer cell death associated with cell cycle arrest. These findings support the potential application of Cinnamomum for the development of therapeutic nanoemulsion in future cancer therapy.

Antiproliferative activity and nitric oxide production of a methanolic extract of Fraxinus micrantha on Michigan Cancer Foundation-7 mammalian breast carcinoma cell line

AIM

Methanolic extract of a Fraxinus micrantha (MeFM) was evaluated for antiproliferative activity in vitro using Michigan Cancer Foundation-7 (MCF-7) breast carcinoma cell line. This plant was selected and studied for naturally available bioactive compound as different synthetic drugs available for cancer treatment has certain limitations and side effects.

MATERIALS AND METHODS

The anti-proliferative activity of a methanolic extract from the aerial parts of F. micrantha was assessed on MCF-7 breast cancer cell line using 3(4,5-dimethylthiazol-2-yl)2,5-diphenyl-tetrazolium bromide assay. Furthermore, to understand the mechanism of anti-proliferation, production of nitric oxide (NO) and DNA fragmentation was also determined on MCF-7 cells. Different phytoconstituents of the extract were determined qualitatively based on various biochemical assays.

RESULTS

The results demonstrated anti-proliferative activity of an MeFM in a concentration and time-dependent manner. The percentage viability determined was 31.24% at 125 µg/ml as compared to 80.46% in negative control group. An MeFM has also shown NO production in a concentration (0.2-125 µg/ml) and time-dependent manner (24-48 h). DNA fragmentation studies showed that a methanolic extract was causing DNA fragmentation thus inducing apoptosis in MCF-7 breast carcinoma cells. Biochemical analysis result showed the presence of flavonoids, polyphenols, and sterols in an MeFM.

CONCLUSION

In conclusion, F. micrantha possesses potent anti-proliferative activity on the malignant MCF-7 cell line which is correlated with the production of NO and DNA fragmentation. Further studies are required to identify, isolate, and characterize the phytochemicals present in the methanolic extract that might have antiproliferative potential in the treatment of different cancer conditions.

Dynamic interplay between nitration and phosphorylation of tubulin cofactor B in the control of microtubule dynamics

Tubulin cofactor B (TCoB) plays an important role in microtubule dynamics by facilitating the dimerization of alpha- and beta-tubulin. Recent evidence suggests that p21-activated kinase 1 (Pak1), a major signaling nodule in eukaryotic cells, phosphorylates TCoB on Ser-65 and Ser-128 and plays an essential role in microtubule regrowth. However, to date, no upstream signaling molecules have been identified to antagonize the functions of TCoB, which might help in maintaining the equilibrium of microtubules. Here, we discovered that TCoB is efficiently nitrated, mainly on Tyr-64 and Tyr-98, and nitrated-TCoB attenuates the synthesis of new microtubules. In addition, we found that nitration of TCoB antagonizes signaling-dependent phosphorylation of TCoB, whereas optimal nitration of TCoB requires the presence of functional Pak1 phosphorylation sites, thus providing a feedback mechanism to regulate phosphorylation-dependent MT regrowth. Together these findings identified TCoB as the third cytoskeleton protein to be nitrated and suggest a previously undescribed mechanism, whereby growth factor signaling may coordinately integrate nitric oxide signaling in the regulation of microtubule dynamics.

Structural and functional diversity in heme monooxygenases

Recent advances in understanding structure-function relationships in cytochrome P450 (P450), nitric-oxide synthase (NOS), and heme oxygenase are summarized. Of particular importance is the role that dynamics plays in P450 function, where the active site undergoes large open/close motions to enable substrates to bind and products to leave. In sharp contrast, the heme-containing active site of NOS is rigid and remains relatively exposed compared with P450s. This difference in dynamics and active site exposure requires that the O(2) activation machinery operate somewhat differently in P450 and NOS. Owing to the open NOS active site, the NOS-oxy complex could be subject to nonspecific protonation that short-circuits the normal reaction path. One working hypothesis holds that NOS recruited the cofactor, tetrahydrobiopterin, to bind near the heme for very rapid coupled electron/proton transfer to the oxy complex, which avoids indiscriminate reaction with bulk solvent. Despite these differences, P450, NOS, and also heme oxygenase use a very similar network of H-bonded water molecules in the active site that are required for oxygen activation. Both P450 and NOS are important drug targets. With NOS, the structural basis for isoform-selective inhibition by a class of dipeptide inhibitors has been worked out, thus providing the basis for structure-based drug design.

Lipopolysaccharide and inflammatory cytokines cause an inducible nitric oxide synthase-dependent bladder smooth muscle fibrotic response

PURPOSE

Bladder wall fibrosis is a sequela of recurrent urinary tract infection (UTI). Inducible nitric oxide synthase (iNOS) has been shown to mediate the fibrotic response to inflammation in other tissues. We determined if iNOS could be involved in the fibrotic response to recurrent UTI.

MATERIALS AND METHODS

Human bladder smooth muscle cells (SMC) were treated with bacterial lipopolysaccharides (LPS) and a mixture of inflammatory cytokines. The level of collagen type III, and the levels of iNOS mRNA, protein and activity were determined. The effect of the iNOS inhibitor aminoguanidine on collagen type III expression was then assessed.

RESULTS

Expression of collagen type III, iNOS mRNA and iNOS protein as well as iNOS activity were increased in bladder SMC treated with the combination of LPS and cytokines. The increase in collagen type III expression was inhibited by pretreatment of cells with aminoguanidine.

CONCLUSIONS

LPS and inflammatory cytokines induce collagen type III expression in an iNOS dependent manner in human bladder SMC. This finding suggests that iNOS may be a critical mediator of the bladder wall fibrotic response to chronic UTI and iNOS inhibitors may be of therapeutic value in patients with chronic UTI.

Cyclosporin A enhances the apoptotic effects of N-(4-hydroxyphenyl)retinamide in breast cancer cells

4HPR, an analogue of ATRA, effectively induces growth inhibition and apoptosis in breast cancer cell lines and animal models but is ineffective against advanced human breast tumors. Different compounds, including tamoxifen, are currently being tested to increase 4HPR efficacy in the clinic. Here, we report that cyclosporin A selectively increases the ability of 4HPR, but not ATRA, to induce growth inhibition and apoptosis in ER(+) and ER(-) breast cancer cell lines. Increased apoptosis by the 4HPR and cyclosporin A combination was correlated with increased production of the free radical nitric oxide. Thus, the 4HPR and cyclosporin A combination may potentially be a novel therapeutic modality against breast tumors.

Reduced expression of endothelial and inducible nitric oxide synthase in a human breast cancer cell line which has acquired estrogen independence

We have recently reported the presence of inducible nitric oxide synthase (iNOS) in the human breast cancer cell line ZR-75-1. The purpose of the present study was to examine differences in expression of endothelial (eNOS) and inducible nitric oxide synthase in normal human mammary epithelial cells (HMEC) compared with two variants of the ZR-75-1 cell line. One variant has acquired estrogen independence, the other has acquired resistance to tamoxifen. Immunohistochemical investigations demonstrated that 100% of HMEC cells staining positive for both eNOS and iNOS. ZR-75-1 cells showed 100% staining for eNOS and 52% positive staining for iNOS. There was no difference in staining between the parent cell line and cells which had acquired resistance to tamoxifen (ZR-75-9a1). However, in the breast cancer cell line which had acquired estrogen independence (ZR-PR-LT), less than 5% of cells exhibited positive staining for eNOS and staining for iNOS was undetectable. L-Arginine increased NO production in both ZR-75-9a1 and ZR-PR-LT cells. Progesterone was able to down regulate NO production in both ZR-75-1 and ZR-75-9a1 cells and this effect was reversible by RU486. These results support the suggestion that loss of NOS expression may be associated with the progression of breast cancers.

Divergent effect of taxol on proliferation, apoptosis and nitric oxide production in MHH225 CD34 positive and U937 CD34 negative human leukaemia cells

Paclitaxel (Taxol) has been shown to be clinically effective in treatment of patients with breast and ovarian cancer. It has also shown promising results in various other solid tumours. Paclitaxel has induced apoptosis in the G2/M phase of the cell cycle in both HL-60 and U937 human leukaemia cells. A recent study has shown a dose-dependent cytotoxicity for both taxanes: paclitaxel (taxol) and docetaxel (Taxotere) on fresh leukaemia cells in primary culture from 16 ALL and four AML patients and proposed their use in treatment of acute leukaemia patients. AML is a heterogeneous disease in which malignant transformation and disease progression occur at the level of CD34 positive cells. Also, the multi-drug resistance gene product, P-glycoprotein is expressed only in CD34 positive AML cells. Therefore, an in vitro evaluation of the efficacy of paclitaxel, a P-glycoprotein substrate, in CD34 positive AML cells is warranted before considering its clinical use in acute leukaemia patients. Since all in vitro studies of paclitaxel reported so far have involved only CD34 negative (HL-60, U937, K562) human AML cells, the aim of the present study was to evaluate paclitaxel efficacy against CD34 positive AML cells. The IC50 of paclitaxel for apoptosis was significantly higher in MHH225 CD34 positive cells (12 +/- 2 microM) than in U937 CD34 negative cells (1.7 +/- 0.2 microM), P < 0.001. Paclitaxel has a significantly weaker cytotoxic effect on CD34 positive AML cells. One log higher concentration of paclitaxel was required in MHH225 CD34 positive AML cells to achieve the same apoptosis level achieved in U937 CD34 negative leukaemia cells. Also, at the high concentration achievable in vivo: 10 microM paclitaxel, only half the MHH225 CD34 positive AML cells were apoptotic versus 72% of U937 CD34 negative leukaemia cells. Clearly, paclitaxel has only weak or modest in vitro efficacy compared with several conventional anti-leukaemia drugs used in AML treatment. The present results support the poor level of in vivo induction of apoptosis achieved during a phase I clinical study with paclitaxel therapy in 26 leukaemia patients. Also, the present results have shown a significant increase in nitric oxide production during paclitaxel-induced apoptosis in U937 monocytic leukaemia cells, confirming the vital role of nitric oxide in mediating paclitaxel-induced apoptosis by monocytic cells. In conclusion, the present study has demonstrated a clear difference between the effect of paclitaxel on CD34 negative and CD34 positive AML cells. Given its poor performance in the phase I clinical study of 26 acute leukaemia patients and the present weak in vitro cytotoxic effect, it is unlikely that paclitaxel will have a role in the treatment of acute leukaemia. Also, the present study emphasises the need to use CD34 positive AML cells such as MHH225 rather than the unsuitable lineage-specific CD34 negative cells such as HL-60 or U937 for in vitro pre-clinical screening of potential novel effective anti-leukaemia agents.