Acid-induced Growth Inhibition Research Articles

Two-tiered mutualism improves survival and competitiveness of cross-feeding soil bacteria

Metabolic cross-feeding is a pervasive microbial interaction type that affects community stability and functioning and directs carbon and energy flows. The mechanisms that underlie these interactions and their association with metal/metalloid biogeochemistry, however, remain poorly understood. Here, we identified two soil bacteria, Bacillus sp. BP-3 and Delftia sp. DT-2, that engage in a two-tiered mutualism. Strain BP-3 has low utilization ability of pyruvic acid while strain DT-2 lacks hexokinase, lacks a phosphotransferase system, and is defective in glucose utilization. When strain BP-3 is grown in isolation with glucose, it releases pyruvic acid to the environment resulting in acidification and eventual self-killing. However, when strain BP-3 is grown together with strain DT-2, strain DT-2 utilizes the released pyruvic acid to meet its energy requirements, consequently rescuing strain BP-3 from pyruvic acid-induced growth inhibition. The two bacteria further enhance their collective competitiveness against other microbes by using arsenic as a weapon. Strain DT-2 reduces relatively non-toxic methylarsenate [MAs(V)] to highly toxic methylarsenite [MAs(III)], which kills or suppresses competitors, while strain BP-3 detoxifies MAs(III) by methylation to non-toxic dimethylarsenate [DMAs(V)]. These two arsenic transformations are enhanced when strains DT-2 and BP-3 are grown together. The two strains, along with their close relatives, widely co-occur in soils and their abundances increase with the soil arsenic concentration. Our results reveal that these bacterial types employ a two-tiered mutualism to ensure their collective metabolic activity and maintain their ecological competitive against other soil microbes. These findings shed light on the intricateness of bacterial interactions and their roles in ecosystem functioning.

Phytohormone ethylene mediates oligogalacturonic acid-induced growth inhibition in tomato etiolated seedlings

Plant growth and immunity are tightly interconnected. Oligogalacturonic acids (OGs) are pectic fragments and have been well investigated in plant immunity as a damage-associated molecular pattern. However, little is known regarding how OGs affect plant growth. Here, we reveal that OGs inhibit the growth of intact etiolated seedling by using the horticultural crop tomato as a model. This inhibitory effect is partially suppressed by the action of ethylene biosynthesis inhibitors, or the gene silencing of SlACS2, an essential rate-limiting enzyme for ethylene biosynthesis, suggesting that SlACS2-mediated ethylene production promotes OG-induced growth inhibition. Furthermore, OGs treatment elevates the SlACS2 protein phosphorylation, and its decrease by the kinase inhibitor K252a partially rescue OG-induced growth inhibition, indicating that SlACS2 phosphorylation involves in OG-induced growth inhibition. Moreover, the mitogen-activated protein kinase SlMPK3 could be activated by OGs treatment and can directly phosphorylate SlACS2 in vitro, and the bimolecular fluorescence complementation combining with the yeast two-hybrid assay shows that SlMPK3 interacts with SlACS2, indicating that SlMPK3 may participate in modulating the OG-induced SlACS2 phosphorylation and growth inhibition. Our results reveal a regulatory mechanism at both the transcriptional and post-transcriptional levels by which OGs inhibit the growth of intact plant seedlings.

The Acid-Base Equilibrium of Pyrazinoic Acid Drives the pH Dependence of Pyrazinamide-Induced Mycobacterium tuberculosis Growth Inhibition.

Pyrazinamide, a first-line antibiotic used against Mycobacterium tuberculosis, has been shown to act in a pH-dependent manner in vitro. Why pyrazinamide, an antitubercle prodrug discovered more than 65 years ago, exhibits this pH-dependent activity was unclear. Upon entering mycobacterial cells, pyrazinamide is deamidated to pyrazinoate by an enzymatic process and exists in an acid-base equilibrium with pyrazinoic acid. Thus, the effects of total pyrazinoic acid (pyrazinoic acid + pyrazinoate) on M. tuberculosis growth, pH homeostasis, and proton motive force over a range of pH values found in host tissues were investigated. Although M. tuberculosis was able to maintain pH homeostasis over an external pH range of 7.0 to 5.5, total pyrazinoic acid induced growth inhibition increased as culture medium pH was decreased from 7.3 to 6.4. Consistent with growth inhibition, total pyrazinoic acid increased both acidification of the bacterial cytoplasm and dissipation of membrane potential as the environmental pH decreased when added to the bacterial suspensions. The results suggest pyrazinoic acid is the active form of the drug, which acts as an uncoupler of proton motive force, likely a protonophore, providing a mechanistic explanation for the pH dependence of the drug activity.

Molecular mechanisms of gallic acid-induced growth inhibition, apoptosis, and necrosis in hypertrophic scar fibroblasts

AimsTo explore the effect and molecular mechanism of gallic acid (GA) on the cytostatic and cytotoxicity of hypertrophic scar fibroblasts (HSFs). Materials and methodsHSFs were treated with a serial dose of GA for indicated time. The cytostatic and cytotoxicity of GA were evaluated by microscopy, trypan blue exclusion assay and LDH releasing. The mechanisms of GA-induced cytostatic were examined by cell cycle distribution assay and the expression of cell cycle-relative protein. GA-elicited apoptosis were verified by TUNEL assay, mitochondria membrane potential, caspase activity and the expression of apoptosis-relative protein. GA-induced necrosis was confirmed by lysosome rupture using acridine orange stain. Various blockers, including intracellular calcium chelator; BAPTA-AM, IP3R blocker; 2-APB, calpain inhibitor, ALLM and ALLN were used to address the signaling cascade in GA-induced HSF necrosis. Key findingsGA-induced growth inhibition, apoptosis, and necrosis in HSFs depend on increasing dose. HSFs treated with GA at non-cytotoxic concentrations (50 to 75μM) significant increased both the S- and G2/M-phase HSFs population, and this event was accompanied with down-regulation of cyclin A, cyclin B, CDK1 and CDK2. Incubation of HSFs with 100–150μM of GA induced apoptosis through Bcl2/Bax-mitochondrial-dependent pathway. While the concentrations up to 200μM of GA that elicited necrosis via a calcium/calpain I/lysosome rupture signaling axis. Interestingly, GA at 200μM did not harm to keratinocyte. SignificanceThese results revealed that GA might have the potential to be developed as a treatment for patients with hypertrophic scar.

Valproic acid sensitizes human glioma cells to gefitinib-induced autophagy.

Autophagy and apoptosis represent important cellular processes involved in cancer cell killing mechanisms. Epidermal growth factor receptor inhibitor gefitinib and valproic acid have been implicated in the treatment of malignancies including glioma involving autophagic and apoptotic mechanisms. Therefore, it is interesting to investigate whether a combination of gefitinib and valproic acid shows better cancer cell killing effect on human glioma cells. We found that a nontoxic concentration of valproic acid sensitized U87 and T98G glioma cells to gefitinib cytotoxicity by inhibiting cell growth and long-term clonogenic survival. The augmented consequences were accompanied by the formation of autophagic vacuoles, conversion of microtubule-associated protein-1 light chain 3-II (LC3-II), and degradation of p62. Autophagy inhibitor 3-methyladenosine and chloroquine and genetic silencing of LC3 but not broad-spectrum caspase inhibitor attenuated gefitinib/valproic acid-induced growth inhibition. Gefitinib/valproic acid-induced autophagy was accompanied by the activation of liver kinase-B1 (LKB1)/AMP-activated protein kinase (AMPK)/ULK1. Silencing of AMPK and ULK1 suppressed gefitinib/valproic acid-induced autophagy and growth inhibition. Mechanistic studies showed that gefitinib/valproic acid increased intracellular reactive oxygen species generation and N-acetyl cysteine attenuated gefitinib/valproic acid-caused autophagy and growth inhibition. In addition to demonstrating the autophagic mechanisms of gefitinib/valproic acid, the results of this study further suggest that intracellular oxidative stress and the LKB1/AMPK signaling might be a potential target for the development of therapeutic strategy against glioma.

Zoledronic acid affects the cytotoxic effects of Chlamydia pneumoniae and the modulation of cytokine production in human osteosarcoma cells

Chlamydia pneumoniae is an obligate intracellular Gram-negative bacterium that causes persistent infections with a tendency to chronicize, which might motivate the resistance of chlamydiae to some commonly used antibiotics. The bisphosphonates are an emerging class of drugs mostly used in the palliative care of cancer patients to inhibit proliferation and metastasis of cancer cells but their role in modulating immune responses remains unknown. We investigated the in vitro activity of a highly potent bisphosphonate, zoledronic acid, on the cytotoxic effects of C. pneumoniae in human SaOS-2 osteoblast-like cells and the consequent immune response carried out by this cell line. We have reported that zoledronic acid showed a significant anti-proliferative effect on SaOS-2 cell line infected by C. pneumoniae in a time- and dose-dependent manner. We have also found that zoledronic acid induced growth inhibition of C. pneumoniae. Our data showed that C. pneumoniae-infection of SaOS-2 cells induced a significant gene expression of proinflammatory cytokines TNF-α, IL-6, IL-8 and IL-12, detected by RT-PCR, and confirmed by protein release assay. Our results demonstrated that zoledronic acid could facilitate C. pneumoniae-mediated immune response, thus reprofiling this traditional anti-tumor drug as a novel immune regulator in promoting host defense against C. pneumoniae infection.

Gambogic acid induces growth inhibition and differentiation via upregulation of p21waf1/cip1 expression in acute myeloid leukemia cells

Gambogic acid (GA) is the major active ingredient of gamboges, a brownish to orange resin product from Garcinia hanburyi tree in Southeast Asia. This compound exhibits anti-cancer effect on solid tumors. In this study, we investigated the effects of GA on the growth and differentiation of acute myeloid leukemia cells by growth-inhibition detection, morphological changes observation, nitroblue tetrazolium reduction, and the expression of the relative cell-surface differentiation markers. The results showed that GA could inhibit cell growth and promote differentiation in U937 and HL-60 cells. In addition, GA upregulated the expression of p21waf1/cip1 in the two cell lines. Finally, downregulating the p21waf1/cip1 expression with small interfering RNA partially blocked GA-induced cell growth inhibition and differentiation. These results of this study revealed that GA may be used as one of the investigational drugs for acute myeloid leukemia.

Linoleic Acid-Induced Growth Inhibition of Human Gastric Epithelial Adenocarcinoma AGS Cells is Associated with Down-Regulation of Prostaglandin E2 Synthesis and Telomerase Activity.

Linoleic acid is the most abundant polyunsaturated fatty acid in human nutrition and found in most vegetable oils and certain food products. In the present study, we investigated the effects of linoleic acid on the growth of human epithelial adenocarcinoma AGS cells. MTT assay, flow cytometry, RT-PCR and Western-blot analyses were used to investigate the effects and underlying mechanisms of linoleic acid on AGS cells. The effects of this compound were also tested on prostaglandin E2 (PGE2) production and telomerase activity. Our data indicated that growth inhibition of AGS cells by linoleic acid treatment was associated with induction of apoptosis. Linoleic acid treatment decreased the expression levels of the cyclooxygenase (COX)-2 mRNA and protein without causing significant changes in the COX-1 levels, which was correlated with the inhibition of PGE2 synthesis. Linoleic acid treatment also decreased the expression of human telomerase reverse transcriptase (hTERT), a main determinant of the telomerase enzymatic activity, and activity of telomerase, with inhibiting the expression of c-myc in a concentration-dependent manner. Taken together, our results indicate that linoleic acid inhibits the production of PGE2 and activity of telomerase by suppressing COX-2 and hTERT expression.

Gambogic acid induces EGFR degradation and Akt/mTORC1 inhibition through AMPK dependent-LRIG1 upregulation in cultured U87 glioma cells

Glioblastoma multiforme (GBM) is the most common malignant tumor in adults’ central nervous system (CNS). The development of novel anti-cancer agents for GBM is urgent. In the current study, we found that gambogic acid induced growth inhibition and apoptosis in cultured U87 glioma cells, which was associated with Akt/mTORC1 (mTOR complex 1) signaling in-activation. To restore Akt activation by introducing a constitutively active (CA) Akt attenuated gambogic acid-induced cytotoxicity against U87 cells. For mechanism study, we found that gambogic acid induced LRIG1 (leucine-rich repeat and Ig-like domain-containing-1) upregulation, which was responsible for EGFR (epidermal growth factor receptor) degradation and its downstream Akt/mTORC1 inhibition. Further, we provided evidence to support that AMPK (AMP-activated protein kinase) activation mediated gambogic acid-induced LRIG1 upregulation, U87 cell apoptosis and growth inhibition, while AMPK inhibition by shRNA or compound C reduced gambogic acid-induced EGFR/Akt inhibition and cytotoxicity in U87 cells. We here proposed novel signaling mechanism mediating gambogic acid-induced cytotoxic effects in glioma cells.

Abstract 3296: KLF9, a differentiation-associated transcription factor, suppresses Notch1 signaling and inhibits glioblastoma-initiating stem cells

Abstract Tumor-initiating stem cells (alternatively called cancer stem cells, CSCs) are a subpopulation of tumor cells that plays unique roles in tumor propagation, therapeutic resistance and tumor recurrence. It is becoming increasingly important to understand the molecular signaling that regulates the self-renewal and differentiation of CSCs. Transcription factors are critical for the regulation of normal and neopolastic stem cells. The Krüppel-like family of transcription factors (KLFs) consists of 17 evolutionarily conserved zinc finger containing proteins with diverse regulatory functions. KLFs bind to GC-GT rich sites in gene promoter and enhancer regions and are known to contextually regulate the growth, proliferation, and differentiation of cells including non-neoplastic stem cells and cancer cells. Here, we examined the expression and function of KLF transcription factors in human glioblastoma (GBM)-drived neurosphere lines and low passage primary GBM-derived neurospheres that are enriched for tumor-initiating stem cells. We identify KLF9 as a relatively unique differentiation-induced transcription factor in GBM-derived neurospheres. KLF9 knockdown rescues GBM-derived neurospheres from Retinoic -acid-induced growth inhibition and differentiation. KLF9 induction is shown to induce neurosphere cell differentiation, inhibit neurosphere formation and deplete neurospheres of CD133+ stem-like cells. KLF9 induction also inhibits the growth of tumor xenografts established from GBM-derived neurospheres. We also show that KLF9 regulates GBM neurosphere cells by binding to the Notch1 promoter and suppressing Notch1 expression and downstream signaling. We compared the KLF9 expression between human GBM tumors and non-neoplastc human specimens. KLF9 is down regulated in human GBM tumors relative to normal brain. Our findings expand the role of KLF family members in stem cell and cancer biology, support KLF9 as a regulator of GBM malignancy, and as a potential biomarker and target for cancer therapeutics. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 3296. doi:10.1158/1538-7445.AM2011-3296

Oleic acid inhibits stearic acid-induced inhibition of cell growth and pro-inflammatory responses in human aortic endothelial cells

Saturated fatty acids (SFAs), significant components of both enteral/parenteral nutritional formulations (including diet), are linked to cardiovascular disease complications, such as atherosclerosis. We investigated whether oleic acid (C18:1n-9) reduces the growth inhibitory and pro-inflammatory effects of the stearic acid (C18:0) in human aortic endothelial cells (HAEC). Stearic acid induced growth inhibition at concentrations less than 50 μM, whereas higher concentrations invoked cytotoxicity. Stearic acid-induced growth inhibition and cytotoxic effects were eradicated upon cosupplementation with oleic acid (25 μM). Oleic acid (as low as 5 μM) also inhibited the stearic acid-induced increase in intercellular adhesion molecule-1 (ICAM-1) expression. Stearic acid-induced phosphorylation of nuclear factor-kappa B (NF-κB), a transcriptional regulator of ICAM-1, was also reduced by oleic acid. HAECs supplemented with either stearic or oleic acid resulted in cellular incorporation of C18:0 and C18:1n-9, respectively. Stearic acid primarily incorporated into phospholipids without increasing the total fatty acid content in HAECs. In contrast, oleic acid, with or without stearic acid, incorporated into both phospholipids and triglycerides, with a significant increase in total fatty acid amounts in triglycerides. Our data suggest that oleic acid has the ability to reduce the inflammatory effects of long-chain SFAs in HAECs through reducing cellular stearic acid incorporation and NF-κB activation.

The histone deacetylase inhibitor suberoylanilide hydroxamic acid induces growth inhibition and enhances taxol-induced cell death in breast cancer

The histone deacetylase inhibitor (HDACi) suberoylanilide hydroxamic acid (SAHA) enhances taxol-induced antitumor effects against some human cancer cells. The aim of this study is to investigate whether SAHA can enhance taxol-induced cell death against human breast cancer cells and to illustrate the mechanism in detail. A panel of eight human breast cancer cell lines and an immortalized human breast epithelial cell line were used to determine the inhibitory effects of SAHA, taxol, or their combination by MTT assay. The effects of SAHA with or without taxol on cell cycle distributions, apoptosis, and protein expressions were also examined. The inhibitory effects on tumor growth were characterized in vivo in BALB/c nude mice bearing a breast cancer xenograft model. Taxol-resistant and multi-resistant breast cancer cells were as sensitive to SAHA as taxol-sensitive breast cancer cells. A dose-dependent synergistic growth inhibition was found in all the tested breast cancer cell lines treated with the SAHA/taxol combinations. The synergetic effect was also observed in the in vivo xenograft tumor model. The cell cycle analysis and apoptosis assay showed that the synergistic effects resulted from enhanced G2/M arrest and apoptosis. SAHA increased the anti-tumor effects of taxol in breast cancer in vitro and in vivo. The combination of SAHA and taxol may have therapeutic potential in the treatment of breast cancer.

Olfactomedin 4 Mediates All-Trans Retinoic Acid Induced Growth Inhibition, Differentiation and Apoptosis in Myeloid Leukemia Cells and Inhibits 4E-BP1 Phosphorylation.

Abstract 2395Poster Board II-372 Introduction:All-trans retinoic acid (ATRA) has been shown to induce cellular differentiation and growth inhibition of acute promyelocytic leukemia cells. Clinical application of ATRA has proved extremely successful in inducing clinical remission in most acute promyelocytic leukemia patients. Although the mechanisms of retinoid-dependent gene transcription regulation are well understood, the target genes that mediate retinoid-induced biological responses still remain to be defined. Olfactomedin 4 (OLFM4, also called hGC-1 and GW112) is a member of olfactomedin-related glycoprotein family. It is constitutively expressed in myeloid cells and gastrointestinal tract. It has been recently reported that OLFM4 expression is up-regulated in stomach and colon cancer patients. The purpose of this study is to examine its expression in myeloid leukemia patients, its regulation by ATRA and potential biological functions in myeloid leukemia. Results:1) In this study, we found that OLFM4 expression was up-regulated in the peripheral leukocytes of chronic myeloid leukemia patients (91%, 22 cases) and acute myeloid leukemia patients (30%, 10 cases). OLFM4 expression in accelerated phase of chronic myeloid leukemia patients was significantly higher than that in chronic phase. 2) We identified that OLFM4 is a novel target gene of retinoic acids in myeloid leukemia cells. Treatment of HL-60 cells with ATRA and 9-cis-RA induced OLFM4 expression. The expression level of OLFM4 is correlated with the myeloid cell differentiation stage. Deletion analysis led to the identification of a positive retinoic acid response element (DR5) and a negative response element (DR1) within OLFM4 promoter. Furthermore, electrophoretic mobility-shift assays and transfection study in COS-7 cells demonstrated that RARα/RXRα binds to the DR5 site and mediates ATRA induced transactivation of OLFM4 promoter. 3) We showed that OLFM4 over-expression in HL-60 cells lead to growth inhibition, differentiation and apoptosis and potentates ATRA mediated these effects. Conversely, silencing of endogenous OLFM4 by lentiviral shRNA against OLFM4 in AML-193 cells reduces ATRA induced growth inhibition, differentiation and apoptosis. 4) We further investigated the molecular mechanism that OLFM4 is involved in leukemia cell growth and differentiation. We found that over-expression of OLFM4 in HL60 cells inhibited ATRA induced phosphorylation of translation repressor 4E-BP1. This inhibitory effect was further confirmed in 293T cells, in which over-expression of OLFM4 inhibits 4E-BP1 phosphorylation at all four phosphorylation sites (Thr37/46, Thr70 and Ser65). Application of lentiviral shRNA against OLFM4 in AML-193 increased phosphorylation of 4E-BP1 compared with control shRNA. Over-expression of OLFM4 in HL60 cells does not affect phosphorylation of Akt, p70S6 kinase, GSK3β and ERK1/2 . Conclusion:1) OLFM4 expression is up-regulated in chronic and acute myeloid leukemia patients and is correlated with the stage of chronic myeloid leukemia. 2) OLFM4 is a novel target gene of retinoic acids. RARα/RXRα binds to the DR5 site of OLFM4 promoter and mediates the ATRA induced transactivation of OLFM4. 3) OLFM4 mediates ATRA induced growth inhibition, differentiation and apoptosis of myeloid leukemia cells. 4) OLFM4 acts an inhibitor of 4E-BP1 phosphorylation down stream of Akt and mTOR, suggesting OLFM4 may inhibit protein synthesis that is observed with the differentiation of myeloid leukemia cells. Our results suggest that OLFM4 up-regulation in the leukocytes of leukemia patients might have a feedback effect to restrain cell growth, and induce differentiation and apoptosis rather than act as an initiator of leukemiagenesis. As OLFM4 is a secreted glycoprotein, it could represent a promising therapeutic agent in the treatment of myeloid leukemia patients. The effect of purified OLFM4 on leukemia cells is currently under investigation. Disclosures:No relevant conflicts of interest to declare.

The Histone Deacetylase Inhibitor Suberoylanilide Hydroxamic Acid Induces Growth Inhibition and Enhances Gemcitabine-Induced Cell Death in Pancreatic Cancer

Pancreatic cancer is an aggressive human malignancy that is generally refractory to chemotherapy. Histone deacetylase inhibitors are novel agents that modulate cell growth and survival. In this study, we sought to determine whether a relatively new histone deacetylase inhibitor, suberoylanilide hydroxamic acid (SAHA), inhibits pancreatic cancer cell growth. The effects of SAHA on the growth of three pancreatic cancer cell lines (BxPC3, COLO-357, and PANC-1) were examined with respect to cell cycle progression, p21 induction and localization, and interactions with the nucleoside analogue gemcitabine. SAHA induced a G(1) cell cycle arrest in BxPC-3 cells and COLO-357 cells but not in PANC-1 cells. This arrest was dependent, in part, on induction of p21 by SAHA, as p21 was not induced in PANC-1 cells, and knockdown of p21 using small interfering RNA oligonucleotides nearly completely suppressed the effects of SAHA on cell cycle arrest in COLO-357 and partly attenuated the effects of SAHA in BxPC-3. COLO-357 and BxPC-3 cells, but not PANC-1 cells, were also sensitive to gemcitabine. In the gemcitabine-resistant PANC-1 cells, a 48-h cotreatment with SAHA rendered the cells sensitive to the inhibitory and proapoptotic effects of gemcitabine. An additive effect on growth inhibition by SAHA and gemcitabine was observed in COLO-357 and BxPC-3 cells. Moreover, analysis of p21 distribution in COLO-357 cells revealed that SAHA induced the cytoplasmic localization of both p21 and phospho-p21. These data indicate that SAHA exerts proapoptotic effects in pancreatic cancer cells, in part, by up-regulating p21 and sequestering it in the cytoplasm, raising the possibility that SAHA may have therapeutic potential in the treatment of pancreatic cancer.

Modulation of the Cell Cycle and Induction of Apoptosis in Human Cancer Cells by Synthetic Bile Acids

In this paper, we will outline the current understanding of cell cycle modulation and induction of apoptosis in cancer cells by natural and synthetic bile acid. Bile acid homeostasis is tightly regulated in health, and their cellular and tissue concentrations are restricted. However, when pathophysiological processes impair their biliary secretion, hepatocytes are exposed to elevated concentrations of bile acids which trigger cell death. In this context, we developed several newly synthesized bile acid derivatives. These synthetic bile acids modulated the cell cycle and induced apoptosis in several human cancer cells similar to natural bile acids. In human breast and prostate cancer cells with different tumor suppressor p53 status, synthetic bile acid-induced growth inhibition and apoptosis were associated with up-regulation of Bax and p21(WAF1/CIP1) via a p53-independent pathway. In Jurkat human T cell leukemia cells, the synthetic bile acids induced apoptosis through caspase activation. In addition to this, the synthetic bile acids induced apoptosis in a JNK dependent manner in SiHa human cervical cancer cells, via induction of Bax and activation of caspases in PC3 prostate cancer cells and induction of G1 phase arrest in the cell cycle in HT29 colon cancer cells. Moreover, they induced apoptosis in four human glioblastoma multiform cell lines (i.e., U-118MG, U-87MG, T98G, and U-373MG) and one human TE671 medulloblastoma cells. In addition to this, a chenodeoxycholic acid derivative, called HS-1200, significantly decreased the growth of TE671 medulloblastoma tumor size and increased life span in non-obese diabetic and severe combined immunodeficient (NOD/SCID) mice. Therefore, these new synthetic bile acids, which are novel apoptosis mediators, might be applicable to the treatment of various human cancer cells.

Docosahexaenoic acid inhibits cancer cell growth via p27Kip1, CDK2, ERK1/ERK2, and retinoblastoma phosphorylation

Docosahexaenoic acid (DHA), a PUFA of the n-3 family, inhibited the growth of FM3A mouse mammary cancer cells by arresting their progression from the late-G(1) to the S phase of the cell cycle. DHA upregulated p27(Kip1) levels by inhibiting phosphorylation of mitogen-activated protein (MAP) kinases, i.e., ERK1/ERK2. Indeed, inhibition of ERK1/ERK2 phosphorylation by DHA, U0126 [chemical MAPK extracellularly signal-regulated kinase kinase (MEK) inhibitor], and MEK(SA) (cells expressing dominant negative constructs of MEK) resulted in the accumulation of p27(Kip1). MAP kinase (MAPK) inhibition by DHA did not increase p27(Kip1) mRNA levels. Rather, this fatty acid stabilized p27(Kip1) contents and inhibited MAPK-dependent proteasomal degradation of this protein. DHA also diminished cyclin E phosphorylation, cyclin-dependent kinase-2 (CDK2) activity, and phosphorylation of retinoblastoma protein in these cells. Our study shows that DHA arrests cell growth by modulating the phosphorylation of cell cycle-related proteins.

Mechanisms of omega-3 fatty acid-induced growth inhibition in MDA-MB-231 human breast cancer cells

The omega-3 fatty acids, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), inhibit the growth of human breast cancer cells in animal models and cell lines, but the mechanism by which this occurs is not well understood. In order to explore possible mechanisms for the modulation of breast cancer cell growth by omega-3 fatty acids, we examined the effects of EPA and DHA on the human breast cancer cell line MDA-MB-231. Omega-3 fatty acids (a combination of EPA and DHA) inhibited the growth of MDA-MB-231 cells by 30-40% (p<0.05) in both the presence and absence of linoleic acid, an essential omega-6 fatty acid. When provided individually, DHA was more potent than EPA in inhibiting the growth of MDA-MB-231 cells (p<0.05). EPA and DHA treatment decreased tumor cell proliferation (p<0.05), as estimated by decreased [methyl-(3)H]-thymidine uptake and expression of proliferation-associated proteins (proliferating cell nuclear antigen, PCNA, and proliferation-related kinase, PRK). In addition, EPA and DHA induced apoptosis, as indicated by a loss of mitochondrial membrane potential, increased caspase activity and increased DNA fragmentation (p<0.05). Cells incubated with omega-3 fatty acids demonstrated decreased Akt phosphorylation, as well as NFkappaB DNA binding activity (p<0.05). The results of this study indicate that omega-3 fatty acids decrease cell proliferation and induce apoptotic cell death in human breast cancer cells, possibly by decreasing signal transduction through the Akt/NFkappaB cell survival pathway.

Mechanisms of nordihydroguaiaretic acid-induced growth inhibition and apoptosis in human cancer cells

Lipoxygenase metabolites of arachidonic acid can act as growth promoting factors for various cancer cell lines. Here we demonstrate that the 5-lipoxygenase inhibitor nordihydroguaiaretic acid potently inhibits anchorage-independent growth of human pancreatic and cervical cancer cells in soft agar and delays growth of pancreatic and cervical tumours established in athymic mice. Furthermore, nordihydroguaiaretic acid induces apoptosis of these cancer cells in vitro and in vivo. Potential mechanisms mediating these effects of nordihydroguaiaretic acid were examined. Nordihydroguaiaretic acid had no inhibitory effect on growth and survival signals such as tyrosine phosphorylation of the epidermal growth factor receptor or basal and growth factor-stimulated activities of extracellular signal-regulated kinase 1/2, p70s6k and AKT but selectively inhibited expression of cyclin D1 in the cancer cells. In addition, treatment with nordihydroguaiaretic acid lead to a disruption of the filamentous actin cytoskeleton in human pancreatic and cervical cancer cells which was accompanied by the activation of Jun-NH2-terminal kinase and p38mapk. Similar effects were obtained by treatment of the cancer cells with cytochalasin D. These results suggest that nordihydroguaiaretic acid induces anoikis-like apoptosis as a result of disruption of the actin cytoskeleton in association with the activation of stress activated protein kinases. In conclusion, nordihydroguaiaretic acid could constitute a lead compound in the development of novel therapeutic agents for various types of cancer.

Mechanisms of nordihydroguaiaretic acid-induced growth inhibition and apoptosis in human cancer cells

Mechanisms of nordihydroguaiaretic acid-induced growth inhibition and apoptosis in human cancer cells

Mechanisms of nordihydroguaiaretic acid-induced growth inhibition and apoptosis in human cancer cells.

Lipoxygenase metabolites of arachidonic acid can act as growth promoting factors for various cancer cell lines. Here we demonstrate that the 5-lipoxygenase inhibitor nordihydroguaiaretic acid potently inhibits anchorage-independent growth of human pancreatic and cervical cancer cells in soft agar and delays growth of pancreatic and cervical tumours established in athymic mice. Furthermore, nordihydroguaiaretic acid induces apoptosis of these cancer cells in vitro and in vivo. Potential mechanisms mediating these effects of nordihydroguaiaretic acid were examined. Nordihydroguaiaretic acid had no inhibitory effect on growth and survival signals such as tyrosine phosphorylation of the epidermal growth factor receptor or basal and growth factor-stimulated activities of extracellular signal-regulated kinase 1/2, p70s6k and AKT but selectively inhibited expression of cyclin D1 in the cancer cells. In addition, treatment with nordihydroguaiaretic acid lead to a disruption of the filamentous actin cytoskeleton in human pancreatic and cervical cancer cells which was accompanied by the activation of Jun-NH2-terminal kinase and p38mapk. Similar effects were obtained by treatment of the cancer cells with cytochalasin D. These results suggest that nordihydroguaiaretic acid induces anoikis-like apoptosis as a result of disruption of the actin cytoskeleton in association with the activation of stress activated protein kinases. In conclusion, nordihydroguaiaretic acid could constitute a lead compound in the development of novel therapeutic agents for various types of cancer.British Journal of Cancer (2002) 86, 1188–1196. DOI: 10.1038/sj/bjc/6600186 www.bjcancer.com© 2002 Cancer Research UK