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Although an accumulating body of evidence indicates that levels of prostaglandin E2 (PGE2) in human and rodent colon cancers are higher than those in surrounding normal tissues, the precise contribution of PGE2 to the process of colon cancer development has still been unclear. Therefore, we designed a study using a well-established azoxymethane (AOM)-induced colon carcinogenesis in male F344 rat model to investigate whether administration of exogenous PGE2 has a real impact on colon carcinogenesis. Intraperitoneal PGE2 injections (7.7 µg) once a week for 25 weeks significantly increased the AOM-induced colon tumor incidence (percent rats with tumors, 92 versus 53%, P < 0.05), especially adenocarcinomas (92 versus 47%, P < 0.05), and multiplicity (number of tumors per rat, 2.8 versus 1.0, P < 0.05). PGE2 treatment significantly increased 5-bromo-2′-deoxyuridine (BrdUrd) labeling index (11.8 versus 9.7%, P < 0.05) and reduced apoptotic index (0.34 versus 0.53%, P < 0.05) in colon cancers induced by AOM. PGE2 exhibits its physiological functions through binding to E-prostanoid (EP) membrane receptors EP1-4. All four types of EP receptors were detected in AOM-induced colon cancers using reverse transcription-polymerase chain reaction (RT-PCR). Our results provide evidence that PGE2 enhances colon carcinogenesis through induction of cell proliferation and reduction of apoptosis. [ABSTRACT FROM AUTHOR]

We report a subharmonic (frequency-divide-by-2) optical parametric oscillator (OPO) with a continuous wavelength span of 3 to 12 µm (-37 d B level) that covers most of the molecular rovibrational "signature" region. The key to obtaining such a wide spectral span is the use of an OPO with a minimal dispersion-through the choice of intracavity elements, the use of all gold-coated mirrors, and a special "injector" mirror. The system delivers up to 245 mW of the average power with the conversion efficiency exceeding 20% from a 2.35 µm Kerr-lens mode-locked pump laser.

Aberrant sphingolipid metabolism has been reported to promote breast cancer progression. Sphingosine kinase 1 (SphK1) is a key metabolic enzyme for the formation of pro-survival S1P from pro-apoptotic ceramide. The role of SphK1 in breast cancer has been well studied in estrogen receptor (ER)-positive breast cancer; however, its role in human epidermal growth factor 2 (HER2)-positive breast cancer remains unclear. Here, we show that genetic deletion of SphK1 significantly reduced mammary tumor development with reduced tumor incidence and multiplicity in the MMTV-neu transgenic mouse model. Gene expression analysis revealed significant reduction of claudin-2 (CLDN2) expression in tumors from SphK1 deficient mice, suggesting that CLDN2 may mediate SphK1's function. It is remarkable that SphK1 deficiency in HER2-positive breast cancer model inhibited tumor formation by the different mechanism from ER-positive breast cancer. In vitro experiments demonstrated that overexpression of SphK1 in ER-/PR-/HER2+ human breast cancer cells enhanced cell proliferation, colony formation, migration and invasion. Furthermore, immunostaining of SphK1 and CLDN2 in HER2-positive human breast tumors revealed a correlation in high-grade disease. Taken together, these findings suggest that SphK1 may play a pivotal role in HER2-positive breast carcinogenesis. Targeting SphK1 may represent a novel approach for HER2-positive breast cancer chemoprevention and/or treatment., (© The Author(s) 2017. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.)

Accumulating evidence suggests that the sphingosine kinase 1 (SphK1)/sphingosine 1-phosphate (S1P) pathway plays a pivotal role in colon carcinogenesis. Our previous studies indicate that the SphK1/S1P pathway mediates colon carcinogenesis at least by regulating cyclooxygenase 2 (COX-2) expression and prostaglandin E2 (PGE2) production. However, the mechanisms by which this pathway regulates colon carcinogenesis are still unclear. First, we show that SphK1 deficient mice significantly attenuated azoxymethane (AOM)-induced colon carcinogenesis as measured by colon tumor incidence, multiplicity, and volume. We found that AOM activates peritoneal macrophages to induce SphK1, COX-2, and tumor necrosis factor (TNF)-α expression in WT mice. Interestingly, SphK1 knockout (KO) mice revealed significant reduction of COX-2 and TNF-α expression from AOM-activated peritoneal macrophages, suggesting that SphK1 regulates COX-2 and TNF-α expression in peritoneal macrophages. We found that inoculation of WT peritoneal macrophages restored the carcinogenic effect of AOM in Sphk1 KO mice as measured by aberrant crypt foci (ACF) formation, preneoplastic lesions of colon cancer. In addition, downregulation of SphK1 only in peritoneal macrophage by short hairpin RNA (shRNA) reduced the number of ACF per colon induced by AOM. Intraperitoneal injection of sphingolipids demonstrates that S1P enhanced AOM-induced ACF formation, while ceramide inhibited. Finally, we show that SphK inhibitor SKI-II significantly reduced the number of ACF per colon. These results suggest that SphK1 expression plays a pivotal role in the early stages of colon carcinogenesis through regulating COX-2 and TNF-α expression from activated peritoneal macrophages., (© The Author 2017. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.)

Background: Magnesium (Mg 2+ ) is an essential cation implicated in carcinogenesis, solid tumor progression and metastatic potential. The Transient Receptor Potential Melastatin Member 7 (TRPM7) is a divalent ion channel involved in cellular and systemic Mg 2+ homeostasis. Abnormal expression of TRPM7 is found in numerous cancers, including colon, implicating TRPM7 in this process., Methods: To establish a possible link between systemic magnesium (Mg 2+ ) status, the Mg 2+ conducting channel TRPM7 in colon epithelial cells, and colon carcinogenesis, in vitro whole-cell patch clamp electrophysiology, qPCR, and pharmacological tools were used probing human colorectal adenocarcinoma HT-29 as well as normal primary mouse colon epithelial cells. This was extended to and combined with aberrant crypt foci development in an azoxymethane-induced colorectal cancer mouse model under hypomagnesemia induced by diet or pharmacologic intervention., Results: We find that TRPM7 drives colon cancer cell proliferation in human HT-29 and expresses in normal primary mouse colon epithelia. This is linked to TRPM7's dominant role as Mg 2+ transporter, since high extracellular Mg 2+ supplementation cannot rescue inhibition of cell proliferation caused by suppressing TRPM7 either genetically or pharmacologically. In vivo experiments in mice provide evidence that the specific TRPM7 inhibitor waixenicin A, given as a single bolus injection, induces transient hypomagnesemia and increases intestinal absorption of calcium. Repeated injections of waixenicin A over 3 weeks cause hypomagnesemia via insufficient Mg 2+ absorption by the colon. However, neither waixenicin A, nor a diet low in Mg 2+ , affect aberrant crypt foci development in an azoxymethane-induced colorectal cancer mouse model., Conclusion: Early stage colon cancer proceeds independent of systemic Mg 2+ status and TRPM7, and waixenicin A is a useful pharmacological tool to study of TRPM7 in vitro and in vivo.

Background: Accumulating evidence suggests that sphingosine kinase 1 (SphK1)/sphingosine 1-phosphate pathway plays a pivotal role in colon carcinogenesis., Methods: To further support the evidence, we investigated the effects of SphK1 using three separate animal models: SphK1 knockout mice, SphK1 overexpressing transgenic mice, and SphK1 overexpression in human colon cancer xenografts. Using azoxymethane (AOM, colon carcinogen), we analyzed colon tumor development in SphK1 KO and SphK1 overexpression in intestinal epithelial cells regulated by a tet-on system. Then, we analyzed subcutaneous tumor growth using xenografts of HT-29 human colon cancer cell. Finally, immunohistochemical analyses for SphK1 and COX-2 were performed on human colon cancer tissue microarray., Results: SphK1 KO mice, compared to wild-type mice, demonstrated a significant inhibition in colon cancer development induced by AOM (58.6% vs. 96.4%, respectively, P < 0.005). Tumor multiplicity (1.00 vs. 1.64 per colon, respectively, P < 0.05) and tumor volume (14.82 mm 3 vs. 29.10 mm 3 , P < 0.05) were both significantly reduced in SphK1 KO mice compared to wild-type mice. Next, SphK1 overexpression in HT-29 enhanced tumor growth as compared to GFP control in nude mice (229.5 mm 3 vs. 90.9 mm 3 , respectively, P < 0.05). Furthermore, overexpression of SphK1 in intestinal epithelial cells significantly enhances AOM-induced colon tumor formation (P < 0.05). Lastly, SphK1 and COX-2 intensity tended to reduce overall survival of late stage colon cancer patients., Conclusions: SphK1 expression regulates the early stage of colon carcinogenesis and tumor growth, thus inhibition of SphK1 may be an effective strategy for colon cancer chemoprevention.

Alterations in sphingolipid metabolism, especially ceramide and sphingosine 1-phosphate, have been linked to colon cancer, suggesting that enzymes of sphingolipid metabolism may emerge as novel regulators and targets in colon cancer. Neutral ceramidase (nCDase), a key enzyme in sphingolipid metabolism that hydrolyzes ceramide into sphingosine, is highly expressed in the intestine; however, its role in colon cancer has not been defined. Here we show that molecular and pharmacological inhibition of nCDase in colon cancer cells increases ceramide, and this is accompanied by decreased cell survival and increased apoptosis and autophagy, with minimal effects on noncancerous cells. Inhibition of nCDase resulted in loss of β-catenin and inhibition of ERK, components of pathways relevant for colon cancer development. Furthermore, inhibition of nCDase in a xenograft model delayed tumor growth and increased ceramide while decreasing proliferation. It is noteworthy that mice lacking nCDase treated with azoxymethane were protected from tumor formation. Taken together, these studies show that nCDase is pivotal for regulating initiation and development of colon cancer, and these data suggest that this enzyme is a suitable and novel target for colon cancer therapy.-García-Barros, M., Coant, N., Kawamori, T., Wada, M., Snider, A. J., Truman, J.-P., Wu, B. X., Furuya, H., Clarke, C. J., Bialkowska, A. B., Ghaleb, A., Yang, V. W., Obeid, L. M., Hannun, Y. A. Role of neutral ceramidase in colon cancer., (© FASEB.)

Sphingosine kinase 1 (SK1), one of two SK enzymes, is highly regulated and has been shown to act as a focal point for the action of many growth factors and cytokines. SK1 leads to generation of sphingosine-1-phosphate (S1P) and potentially the activation of S1P receptors to mediate biologic effects. Our previous studies implicated SK1/S1P in the regulation of inflammatory processes, specifically in inflammatory bowel disease (IBD). These studies were conducted using a total body knockout mouse for SK1 and were unable to determine the source of SK1/S1P (hematopoietic or extra-hematopoietic) involved in the inflammatory responses. Therefore, bone marrow transplants were performed with wild-type (WT) and SK1-/- mice and colitis induced with dextran sulfate sodium (DSS). Irrespective of the source of SK1/S1P, bone marrow or tissue, DSS induced colitis in all mice; however, mice lacking SK1 in both hematopoietic and extra-hematopoietic compartments exhibited decreased crypt damage. Systemic inflammation was assessed, and mice with WT bone marrow demonstrated significant neutrophilia in response to DSS. In the local inflammatory response, mice lacking SK1/S1P in either bone marrow or tissue exhibited decreased induction of cytokines and less activation of STAT3 (signal transducer and activator of transcription 3). Interestingly, we determined that extra-hematopoietic SK1 is necessary for the induction of cyclooxygenase 2 (COX2) in colon epithelium in response to DSS-induced colitis. Taken together our data suggest that hematopoietic-derived SK1/S1P regulates specific aspects of the systemic inflammatory response, while extra-hematopoietic SK1 in the colon epithelium is necessary for the autocrine induction of COX2 in DSS-induced colitis.

Background: Head and neck squamous cell carcinoma (HNSCC) is characterized by aggressive loco-regional invasion. Sphingosine kinase1 (SphK1), an enzyme in sphingolipid metabolism, is emerging as a key player in HNSCC pathology. The observation that SphK1 is overexpressed in all HNSCC stages and is associated with depth of tumor invasion, metastasis and clinical failure underscores the importance of SphK1 in HNSCC pathology. Still, the mechanisms underlying SphK1 regulation of invasion have not been delineated. Therefore, we sought to mechanistically describe how SphK1 regulates invasion in HNSCC., Methods: Invasion assays were used to measure invasive ability of SphK1 overexpressing human tongue squamous cell carcinoma (SCC-25 cells). Western blotting, quantitative qPCR, ELISA and zymography were used to measure the effect of SphK1 and sphingosine 1-phoshate receptor 1 (S1P1) on invasion measures, MMP-2/9, E-cadherin, EGFR, IL-6/STAT3, in SCC-25 cells., Results: SphK1 expression is elevated in cells with an invasive phenotype as compared to non-invasive phenotype. We show SphK1 overexpression increased EGF-induced EGFR/ERK and AKT activity, increased matrix metalloproteinase (MMP)-2/9 mRNA and reduced E-cadherin. SphK1 overexpression also increased IL-6 concentration and EGF-induced STAT3 phosphorylation, exemplifying that SphK1 modulates IL-6/STAT3 signaling. Notably, we show that S1P1 knockdown reduced IL-6/STAT3 signaling, representing another pathway by which SphK1/S1P regulates invasion., Conclusions: Taken together, our data suggest that SphK1 sits at the hub of multiple key signaling cascades, all which have been implicated in the regulation of invasiveness, making SphK1 an attractive target for the development of HNSCC therapies.

Head and neck squamous cell carcinoma (HNSCC) has a high reoccurrence rate and an extremely low survival rate. There is limited availability of effective therapies to reduce the rate of recurrence, resulting in high morbidity and mortality of advanced cases. Late presentation, delay in detection of lesions, and a high rate of metastasis make HNSCC a devastating disease. This review offers insight into the role of sphingosine kinase-1 (SphK1), a key enzyme in sphingolipid metabolism, in HNSCC. Sphingolipids not only play a structural role in cellular membranes, but also modulate cell signal transduction pathways to influence biological outcomes such as senescence, differentiation, apoptosis, migration, proliferation, and angiogenesis. SphK1 is a critical regulator of the delicate balance between proliferation and apoptosis. The highest expression of SphK1 is found in the advanced stage of disease, and there is a positive correlation between SphK1 expression and recurrent tumors. On the other hand, silencing SphK1 reduces HNSCC tumor growth and sensitizes tumors to radiation-induced death.  Thus, SphK1 plays an important and influential role in determining HNSCC proliferation and metastasis. We discuss roles of SphK1 and other sphingolipids in HNSCC development and therapeutic strategies against HNSCC.

Accumulating evidence suggests that sphingosine kinase 1 (SphK1) plays a key role in carcinogenesis by regulating cyclooxygenase-2 (COX-2) expression. Recent clinical studies have revealed that COX-2 inhibitors cause adverse cardiovascular side effects, likely due to inhibition of prostacyclin (PGI(2)). In this work, we investigated the roles of SphK1 inhibition on blood pressure (BP). The results show that lack of SphK1 expression did not exacerbate angiotensin II (Ang II)-induced acute hypertension, whereas celecoxib, a COX-2 inhibitor, augmented and sustained higher BP in mice. Interestingly, SphK1-knockout mice inhibited prostaglandin E(2) (PGE(2)) but not PGI(2) production in response to Ang II, whereas celecoxib blocked both PGE(2) and PGI(2) production. Mechanistically, SphK1 down-regulation by siRNA in human umbilical vein endothelial cells decreased cytokine-induced PGE(2) production primarily through inhibition of microsomal PGE synthase-1 (mPGES-1), not COX-2. SphK1 down-regulation also decreased MKK6 expression, which phosphorylates and activates P38 MAPK, which, in turn, regulates early growth response-1 (Egr-1), a transcription factor of mPGES-1. Together, these data indicate that SphK1 regulates PGE(2) production by mPGES-1 expression via the p38 MAPK pathway, independent of COX-2 signaling, in endothelial cells, suggesting that SphK1 inhibition may be a promising strategy for cancer chemoprevention with lack of the adverse cardiovascular side effects associated with coxibs.

The present study explored the preventive effects of perilla oil, rich in α-linolenic acid, in rodent models of colon tumorigenesis. Six-week-old male F344 rats were fed diets containing 5% corn oil or 10 or 20% perilla oil. Colonic aberrant crypt foci (ACF) were induced by azoxymethane (AOM) and colonic ACF were evaluated. In familial adenomatous polyposis mode, APC(min) mice fed with 20% corn oil or perilla oil for 80 days and intestines were evaluated for polyps. Multiple colonic mucosal and polyp samples were assayed for the expression and activity of cyclooxygenase COX-isoforms. Dietary perilla oil produced a dose-dependent inhibition of AOM-induced colonic ACF formation (by 35-53%, P < 0.01-0.005) and reduced the number of foci with ≥ 4 crypts/focus (by 38-50%, P < 0.01-0.001) in F344 rats. Dietary perilla oil significantly inhibited development of small intestinal (>69%, P < 0.0001) and colon tumors (>52%, P < 0.03) in APC(min) mice. Administration of perilla oil produced lower levels of type-2 prostaglandins (38-53%) from COX-activities in polyps of APC(min) mice. These observations demonstrate that dietary perilla oil rich in ω-3 fatty acids possesses preventive activity against intestinal neoplastic lesions, both in FAP in genetically-predisposed tissues, as well as against chemically induced preneoplastic lesions in the colon.

Sphingolipids are emerging as important mediators of immune and inflammatory responses. We have previously demonstrated that sphingosine-1-phosphate (S1P) and its synthetic enzyme sphingosine kinase-1 (SK1) play an important role in inflammatory bowel disease. S1P generation is dependent on SK phosphorylation of sphingosine. Generation of sphingosine results only from the breakdown of ceramide by ceramidases (CDase). In this study, we set out to determine the role of neutral CDase (nCDase) in S1P generation and inflammatory bowel disease. To this end, we established nCDase expression is increased in patients with ulcerative colitis. Using the dextran sulfate sodium (DSS)-induced colitis model, we determined nCDase activity increased in colon epithelium, but not submucosa, in wild-type (WT) mice. Following DSS, ceramide levels were elevated in colon epithelium from WT and nCDase(-/-) mice, while S1P levels were significantly elevated only in the epithelium of nCDase(-/-) mice. Similarly, cyclooxygenase-2 (Cox-2) levels were significantly elevated only in the epithelium of nCDase(-/-) mice. Neutral CDase(-/-) mice also exhibited higher endotoxin levels in circulation, as well as higher circulating levels of S1P. This increase in S1P in nCDase(-/-) mice was accompanied by a marked leukocytosis, most notably circulating neutrophils and lymphocytes. Taken together these data demonstrate that loss of nCDase results in an unexpected increase in S1P generation in inflammation, and suggests that nCDase may actually protect against inflammation., (Published by Elsevier Inc.)

Mechanisms by which cancer cells communicate with the host organism to regulate lung colonization/metastasis are unclear. We show that this communication occurs via sphingosine 1-phosphate (S1P) generated systemically by sphingosine kinase 1 (SK1), rather than via tumour-derived S1P. Modulation of systemic, but not tumour SK1, prevented S1P elevation, and inhibited TRAMP-induced prostate cancer growth in TRAMP(+/+) SK1(-/-) mice, or lung metastasis of multiple cancer cells in SK1(-/-) animals. Genetic loss of SK1 activated a master metastasis suppressor, Brms1 (breast carcinoma metastasis suppressor 1), via modulation of S1P receptor 2 (S1PR2) in cancer cells. Alterations of S1PR2 using pharmacologic and genetic tools enhanced Brms1. Moreover, Brms1 in S1PR2(-/-) MEFs was modulated by serum S1P alterations. Accordingly, ectopic Brms1 in MB49 bladder cancer cells suppressed lung metastasis, and stable knockdown of Brms1 prevented this process. Importantly, inhibition of systemic S1P signalling using a novel anti-S1P monoclonal antibody (mAb), Sphingomab, attenuated lung metastasis, which was prevented by Brms1 knockdown in MB49 cells. Thus, these data suggest that systemic SK1/S1P regulates metastatic potential via regulation of tumour S1PR2/Brms1 axis., (Copyright © 2012 EMBO Molecular Medicine.)

The bioactive sphingolipids including, ceramide, sphingosine, and sphingosine-1-phosphate (S1P) have important roles in several types of signaling and regulation of many cellular processes including cell proliferation, apoptosis, senescence, angiogenesis, and transformation. Recent accumulating evidence suggests that ceramide- and S1P-mediated pathways have been implicated in cancer development, progression, and chemotherapy. Ceramide mediates numerous cell-stress responses, such as induction of apoptosis and cell senescence, whereas S1P plays pivotal roles in cell survival, migration, and inflammation. These sphingolipids with opposing roles can be interconverted within cells, suggesting that the balance between them is related to cell fate. Importantly, these sphingolipids are metabolically related through actions of enzymes including ceramidases, ceramide synthases, sphingosine kinases, and S1P phosphatases thereby forming a network of metabolically interrelated bioactive lipid mediators whose importance in normal cellular function and diseases is gaining appreciation. In this review, we summarize involvement of sphingolipids and their related enzymes in pathogenesis and therapy of cancer and discuss future directions of sphingolipid field in cancer research.

It is important to identify novel and effective targets for cancer prevention and therapy against head and neck squamous cell carcinoma (HNSCC), one of the most lethal cancers. Accumulating evidence suggests that the bioactive sphingolipids, such as sphingosine-1-phosphate (S1P) and its generating enzyme, sphingosine kinase 1 (SphK1) play pivotal roles in several important biological functions including promoting tumor growth and carcinogenesis. However, roles of SphK1/S1P in HNSCC development and/or progression have not been defined previously. Therefore, in this study, we first analyzed the expression of SphK1 in human HNSCC tumor samples and normal head & neck tissues (n = 78 and 17, respectively) using immunohistochemistry. The data showed that SphK1 is overexpressed in all of the HNSCC tumors tested (stages I-IV). We next investigated whether SphK1 is necessary for HNSCC development. To define the role of SphK1/S1P in HNSCC development, we utilized 4-nitroquinoline-1-oxide (4-NQO)-induced HNSCC model in wild-type mice compared with SphK1(-/-) knockout (KO) mice. Remarkably, we found that the genetic loss of SphK1, which reduced S1P generation, significantly prevented 4-NQO-induced HNSCC carcinogenesis, with decreased tumor incidence, multiplicity, and volume when compared with controls. Moreover, our data indicated that prevention of 4-NQO-induced HNSCC development in SphK1(-/-) KO mice might be associated with decreased cell proliferation, increased levels of cleaved (active) caspase 3, and downregulation of phospho (active) AKT expression. Thus, these novel data suggest that SphK1/S1P signaling may play important roles in HNSCC carcinogenesis, and that targeting SphK1/S1P might provide a novel strategy for chemoprevention and treatment against HNSCC.

Bioactive sphingolipids play key roles in the regulation of several fundamental biological processes such as proliferation, apoptosis and transformation. The recent development of genetically engineered mouse (GEM) models has enabled the study of functional roles of sphingolipids in normal development and disease. In this chapter, we review the phenotypes of GEM models (knockout mice) that lack sphingolipid metabolism-related enzymes, discuss what we have learned from animal models and describe future directions of animal models in sphingolipid research.

Accumulating evidence suggests that cyclooxygenase-2 (COX-2) and prostaglandin E(2) (PGE(2)) may play an important role in colon carcinogenesis. Thus, blockage of this pathway may be a suitable strategy for colon cancer chemoprevention. Recent clinical studies suggest that COX-2 inhibitors cause adverse cardiovascular effects due to prostacyclin (PGI(2)) inhibition. To test our hypothesis that inhibition of PGE(2) signaling through E-prostanoid (EP) receptors may offer a safer cardiovascular profile than COX-2 inhibition, we analyzed expression of 6-keto PGF(1alpha), a hydrated form of PGI(2) and PGI(2) synthase, which was stimulated with cytokines in human umbilical vein endothelial cells (HUVECs) treated with the EP(1) receptor antagonist ONO-8711 or the COX-2 inhibitor celecoxib. ONO-8711 did not inhibit both 6-keto PGF(1alpha) production and PGIS expression, whereas celecoxib did in HUVECs. ONO-8711 also inhibited cytokine-induced tissue factor expression in HUVECs. These results suggest that ONO-8711 may be a safer chemopreventive agent with respect to cardiovascular events.

Sphingosine kinase 1 (SphK1) phosphorylates sphingosine to form sphingosine-1-phosphate (S1P) and is a critical regulator of sphingolipid-mediated functions. Cell-based studies suggest a tumor-promoting function for the SphK1/S1P pathway. Also, our previous studies implicated the SphK1/S1P pathway in the induction of the arachidonic acid cascade, a major inflammatory pathway involved in colon carcinogenesis. Therefore, we investigated whether the SphK1/S1P pathway is necessary for mediating carcinogenesis in vivo. Here, we report that 89% (42/47) of human colon cancer samples stained positively for SphK1, whereas normal colon mucosa had negative or weak staining. Adenomas had higher expression of SphK1 vs. normal mucosa, and colon cancers with metastasis had higher expression of SphK1 than those without metastasis. In the azoxymethane (AOM) murine model of colon cancer, SphK1 and S1P were significantly elevated in colon cancer tissues compared to normal mucosa. Moreover, blood levels of S1P were higher in mice with colon cancers than in those without cancers. Notably, SphK1(-/-) mice subjected to AOM had significantly less aberrant crypt foci (ACF) formation and significantly reduced colon cancer development. These results are the first in vivo evidence that the SphK1/S1P pathway contributes to colon carcinogenesis and that inhibition of this pathway is a potential target for chemoprevention.

The bioactive lipid sphingosine-1-phosphate (S1P) is emerging as an important mediator of immune and inflammatory responses. S1P formation is catalyzed by sphingosine kinase (SK), of which the SK1 isoenzyme is activated by tumor necrosis alpha (TNF-alpha). SK1 has been shown to be required for mediating TNF-alpha inflammatory responses in cells, including induction of cyclooxygenase 2 (COX-2). Because TNF-alpha and COX-2 are increased in patients with inflammatory bowel disease (IBD), we investigated the role of SK1 in a murine model of colitis. SK1(-/-) mice treated with dextran sulfate sodium (DSS) had significantly less blood loss, weight loss, colon shortening, colon histological damage, and splenomegaly than did wild-type (WT) mice. In addition, SK1(-/-) mice had no systemic inflammatory response. Moreover, WT but not SK1(-/-) mice treated with dextran sulfate sodium had significant increases in blood S1P levels, colon SK1 message and activity, and colon neutrophilic infiltrate. Unlike WT mice, SK1(-/-) mice failed to show colonic COX-2 induction despite an exaggerated TNF-alpha response; thus implicating for the first time SK1 in TNF-alpha-mediated COX-2 induction in vivo. Inhibition of SK1 may prove to be a valuable therapeutic target by inhibiting systemic and local inflammation in IBD.

Poor oral bioavailability has been a major limitation for the successful use of dietary flavonoids as cancer chemopreventive agents. In this study, we examined fully methylated flavones as promising improved agents. In the human oral SCC-9 cancer cells, 5,7-dimethoxyflavone and 5,7,4'-trimethoxyflavone were both 10 times more potent inhibitors of cell proliferation (IC(50) values 5-8 microM) than the corresponding unmethylated analogs chrysin and apigenin. Flow cytometry indicated that both methylated flavones arrested the SCC-9 cells in the G1 phase with a concomitant decrease in the S phase, dramatically different from the unmethylated analogs, which promoted G2/M phase arrest. Both methylated compounds inhibited the proliferation of two other cancer cell lines with very little effect on two immortalized normal cell lines. Examination of additional flavone structures indicated that methylated flavones in general have antiproliferative properties. Finally, we demonstrated that 5,7-dimethoxyflavone, in contrast to its unmethylated analog chrysin, was well absorbed and had high oral bioavailability as well as tissue accumulation in vivo in the rat. Thus, fully methylated flavones appear to have great potential as cancer chemopreventive/chemotherapeutic agents, in particular in oral cancer.

Sphingolipids are well established effectors of signal transduction downstream of the tumor necrosis factor (TNF) receptor. In a previous study, we showed that the sphingosine kinase/sphingosine 1-phosphate (S1P) pathway couples TNF receptor to induction of the cyclooxygenase 2 gene and prostaglandin synthesis (Pettus, B. J., Bielawski, J., Porcelli, A. M., Reames, D. L., Johnson, K. R., Morrow, J., Chalfant, C. E., Obeid, L. M., and Hannun, Y. A. (2003) FASEB J. 17, 1411-1421). In this study, the requirement for acid sphingomyelinase and sphingomyelin metabolites in the TNFalpha/prostaglandin E(2) (PGE(2)) pathway was investigated. The amphiphilic compound desipramine, a frequently employed inhibitor of acid sphingomyelinase (ASMase), blocked PGE(2) production. However, the action of desipramine was independent of its action on ASMase, since neither genetic loss of ASMase (Niemann-Pick fibroblasts) nor knockdown of ASMase using RNA interference affected TNFalpha-induced PGE(2) synthesis. Further investigations revealed that desipramine down-regulated acid ceramidase (AC), but not sphingosine kinase, at the protein level. This resulted in a time-dependent drop in sphingosine and S1P levels. Moreover, exogenous administration of either sphingosine or S1P rescued PGE(2) biosynthesis after desipramine treatment. Interestingly, knockdown of endogenous AC by RNA interference attenuated cyclooxygenase 2 induction by TNFalpha and subsequent PGE(2) biosynthesis. Taken together, these results define a novel role for AC in the TNFalpha/PGE(2) pathway. In addition, the results of this study warrant careful reconsideration of desipramine as a specific inhibitor for ASMase.

Sphingosine kinase 1 (SK1) phosphorylates sphingosine to form sphingosine 1-phosphate (S1P), which has the ability to promote cell proliferation and survival and stimulate angiogenesis. The SK1/S1P pathway also plays a critical role in regulation of cyclooxygenase-2 (COX-2), a well-established pathogenic factor in colon carcinogenesis. Therefore, we examined the expression of SK1 and COX-2 in rat colon tumors induced by azoxymethane (AOM) and the relationship of these two proteins in normal and malignant intestinal epithelial cells. Strongly positive SK1 staining was found in 21/28 (75%) of rat colon adenocarcinomas induced by AOM, whereas no positive SK1 staining was observed in normal mucosa. The increase in SK1 and COX-2 expression in AOM-induced rat colon adenocarcinoma was confirmed at the level of mRNA by real-time RT-PCR. In addition, it was found that 1) down-regulation of SK1 in HT-29 human colon cancer cells by small interfering RNA (siRNA) decreases COX-2 expression and PGE2 production; 2) overexpression of SK1 in RIE-1 rat intestinal epithelial cells induces COX-2 expression; and 3) S1P stimulates COX-2 expression and PGE2 production in HT-29 cells. These results suggest that the SK1/S1P pathway may play an important role in colon carcinogenesis, in part, by regulating COX-2 expression and PGE2 production.

The ability of pro-inflammatory cytokines such as interleukin-1beta (IL-1beta) to induce the major inflammatory mediator prostaglandin (PG) E(2) depends on the activation of two rate-limiting enzymes, phospholipase A(2) (PLA(2)) and cyclooxygenase 2 (COX-2). PLA(2) acts to generate arachidonic acid, which serves as the precursor substrate for COX-2 in the metabolic pathway leading to PGE(2) production. However, less is known about the mechanisms that coordinate the regulation of these two enzymes. We have provided prior evidence that sphingosine kinase 1 and its bioactive lipid product sphingosine-1-phosphate (S1P) mediate the effects of cytokines on COX-2 induction, whereas ceramide kinase and its distinct product, ceramide-1-phosphate (C1P), are required for the activation and translocation of cPLA(2) (FASEB J 17:1411-1421. 2003; J Biol Chem 278:38206-38213, 2003; J Biol Chem 279:11320-11326, 2004). Herein, we show that these two pathways are independent but coordinated, resulting in synergistic induction of PGE(2). Moreover, the combination of both S1P and C1P recapitulates the temporal and spatial activation of cPLA(2) and with COX-2 seen IL-1beta. Taken together, the results provide, for the first time, a mechanism that assures the coordinate expression and activation in time and space of COX-2 and cPLA(2), assuring maximal production of PGE(2).

Prostaglandin E(2) exerts its biological activity through binding to its membrane receptors, E-prostanoid (EP) receptors. Our previous finding that lack of EP(1) receptor inhibits the early stages of colon carcinogenesis led us to investigate whether EP(1) receptor deficiency reduces colon cancer development induced by azoxymethane (AOM) using EP(1) receptor knockout mice. At 6 weeks of age 33 homozygous EP(1)-deficient (EP(1)(-/-)) mice and 28 wild-type (EP(1)(+/+)) mice were given i.p. AOM (10 mg/kg body wt) once a week for 6 weeks. At 56 weeks of age all animals were killed and intestinal tumors were examined. The results clearly indicated that lack of EP(1) receptor significantly reduced colon cancer incidence (27 versus 57%, P < 0.05) and multiplicity (0.30 versus 0.76, P < 0.05) as well as tumor volume (12.2 versus 75.6 mm(3), P < 0.05). In EP(1)(-/-) mice, silver stained nucleolar organization region protein count as cell proliferation marker was significantly reduced (1.35 versus 2.17, P < 0.001) and apoptosis was significantly increased (0.685 versus 0.077, P < 0.001) in colon tumors induced by AOM compared with those in EP(1)(+/+) mice. We confirmed that EP(1) receptor mRNA was overexpressed in colon cancers of EP(1)(+/+) mice using reverse transcription-polymerase chain reaction. These results provide strong evidence that the EP(1) receptor is of major importance for colon cancer development and it could be a new target for a mechanism-based chemoprevention strategy against colon cancer development.

A novel mutagenic compound, 9-(4'-aminophenyl)-9H- pyrido[3,4-b]indole (aminophenylnorharman, APNH), is shown to be formed by the in vitro enzymatic reaction of 9H-pyrido[3,4-b]indole (norharman) and aniline. APNH generates DNA adducts (dG-C8-APNH), and is potently genotoxic to bacteria and mammalian cells. APNH has also been demonstrated to be formed in vivo from norharman and aniline, and suggested to be a new type of endogenous mutagenic compound. To determine its carcinogenic activity, long-term administration of APNH was investigated in 93 male and 90 female F344 rats. Rats were fed diets containing 0, 20 or 40 p.p.m. from 7 weeks of age. All animals were killed after 85 weeks treatment and necropsy was performed. Hepatocellular carcinomas (HCCs) were induced at incidences of 10 and 79% in male rats fed 20 and 40 p.p.m. APNH, and 34% in female rats fed 40 p.p.m. of APNH, respectively. In addition, colon adenocarcinomas were found at incidences of 3 and 9% in male rats, and 4 and 13% in female rats fed 20 and 40 p.p.m. of APNH, respectively. Other tumors, including thyroid carcinomas and mononuclear cell leukemia, were also seen in rats fed APNH. Polymerase chain reaction-single strand conformation polymorphism analysis revealed beta-catenin gene mutations in 24% of HCCs and K-ras, beta-catenin and Apc gene mutations were found in 22, 44 and 33% of colon cancers induced by APNH, respectively. Most mutations occurred at G:C base pairs. beta-Catenin protein accumulations in the nucleus and cytoplasm were also revealed in both liver and colon tumors. Thus, APNH induced liver and colon cancers with K-ras, beta-catenin and Apc gene mutations in F344 rats.

Background and Aims: Involvement of prostaglandin E(2) (PGE(2)) receptors EP(1), EP(2), and EP(4) in the formation of aberrant crypt foci (ACF) and/or intestinal polyps has been suggested. In contrast, EP(3) appears to have no influence on the early stages of colon carcinogenesis. In the present study, we examined expression of PGE(2) receptor subtypes EP(1), EP(2), EP(3), and EP(4) in normal colon mucosa and colon cancers, and assessed the contribution of EP(3) to colon cancer development., Methods: mRNA expression of PGE(2) receptor subtypes EP(1), EP(2), EP(3), and EP(4) in normal colon mucosa and colon cancers in azoxymethane (AOM) treated mice and rats, and in humans, were examined by reverse transcription-polymerase chain reaction (RT-PCR), quantitative real time RT-PCR, and immunohistochemical analyses. Evaluation of the role of EP(3) was performed by intraperitoneal injection of AOM, using EP(3) receptor knockout mice. Effects of EP(3) receptor activation on cell growth of human colon cancer cell lines were examined using ONO-AE-248, an EP(3) selective agonist. Moreover, EP(3) expression in colon cancer cell lines was analysed with or without 5-aza-2'-deoxycytidine (5-aza-dC) treatment., Results: Expression levels of EP(1) and EP(2) mRNA were increased in cancer tissues. EP(4) mRNA was constantly expressed in normal mucosa and cancers. In contrast, expression of EP(3) mRNA was markedly decreased in colon cancer tissues, being 5% in mice, 9% in rats, and 28% in humans compared with normal colon mucosa, analysed by quantitative real time RT-PCR. Immunohistochemical staining demonstrated the rat EP(3) receptor protein to be expressed in epithelial cells of normal mucosa and some parts of small carcinomas but hardly detectable in large carcinomas of the colon. Colon cancer development induced by AOM in EP(3) receptor knockout mice was enhanced compared with wild-type mice, with a higher incidence of colon tumours (78% v 57%) and mean number of tumours per mouse (2.17 (0.51) v 0.75 (0.15); p<0.05). Expression of EP(3) mRNA was detected in only one of 11 human colon cancer cell lines tested. Treatment with 5 microM of an EP(3) selective agonist, ONO-AE-248, resulted in a 30% decrease in viable cell numbers in the HCA-7 human colon cancer cell line in which EP(3) was expressed. Treatment with 5-aza-dC restored EP(3) expression in CACO-2, CW-2, and DLD-1 cells but not in WiDr cells, suggesting involvement of hypermethylation in the downregulation of EP(3) to some extent., Conclusion: The PGE(2) receptor subtype EP(3) plays an important role in suppression of cell growth and its downregulation enhances colon carcinogenesis at a later stage. Hypermethylation of the EP(3) receptor gene could occur and may contribute towards downregulating EP(3) expression to some extent in colon cancers.

The Long-Evans Cinnamon (LEC) rat, an animal model for Wilson's disease, is an inbred mutant strain, which because of the genetic copper metabolism disorder develops hepatitis approximately 4 months after birth, followed by chronic hepatitis later in life, and eventually all of the surviving animals from liver injury and hepatitis develop spontaneous hepatocellular carcinomas. This animal model also shows that the generation of reactive oxygen species and the accumulation of oxidative damage in the liver DNA has significantly increased over the lifetime of LEC versus the wild-type Long-Evans Agouti (LEA) rats. Thus, the LEC rats having this genetically induced oxidative condition are proved to be very useful model for the study of endogenous DNA lesions and their relation to spontaneous carcinogenesis. In this study, we tested the hypothesis that differences do exist between these two rat strains in respect to their capacity to repair oxidative DNA base modification, which could explain the elevation of endogenous oxidative damage in the LEC rat liver DNA. We found that both the activity and expression at the protein and RNA levels of major DNA glycosylases, endonuclease III and 8-oxoguanine DNA-glycosylase, which initiate the excision and repair of oxidized bases, were significantly altered during the acute (16-18 weeks) and early chronic (24 weeks) phases of hepatitis. Enzyme levels were restored in the later period of chronic hepatitis (week 40) in the LEC rat liver as compared with the age-matched LEA rats. This early reduction in the capacity to repair oxidative DNA base damage could have contributed to the accumulation of mutagenic adducts in liver DNA. These findings show for the first time in an animal model that acute hepatitis impairs the repair of oxidative DNA base damage and strongly suggest that the repair of endogenous DNA adducts plays a critical role in the development of spontaneous hepatocellular carcinoma in LEC rats.

The multistage model of colon carcinogenesis is well established in both humans and experimental animals, and aberrant crypt foci (ACF) are generally assumed to be putative preneoplastic lesions of the colon. However, morphological analyses of ACF have suggested that they are highly heterogeneous in nature and their role in tumorigenesis is still controversial. To better understand the biological significance of ACF in carcinogenesis, morphological and genetic analyses were performed using a rat colon cancer model induced by a food-borne colon carcinogen, 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP). ACF of different sizes were collected at weeks 6, 18, 25, and 32 after three cycles of 2-week PhIP feeding (400 ppm in diet) with 4-week intervals on a high-fat diet, and a total of 110 ACF, representing approximately three-quarters of the total ACF, were subjected to histological evaluation. Thirty (27%) were diagnosed as dysplastic ACF, based on cytological and structural abnormalities of crypts. Dysplastic ACF were detected even at week 6 (0.4 per rat), and the numbers increased slightly at later time points, being 0.8, 1.4, and 0.8 per rat at weeks 18, 25, and 32, respectively. The sizes of these dysplastic ACF varied widely from 1 to 16 crypts and 50% (15 of 30) were composed of less than 4 crypts. Immunohistochemical analysis revealed that 83% (25 of 30) of dysplastic ACF demonstrated beta-catenin accumulation; 22 only in the cytoplasm and 3 in both the cytoplasm and nucleus, the latter manifesting a higher grade of dysplasia as compared with the former. Seven dysplastic ACF harbored beta-catenin mutations at codon 32, 34, or 36 in exon 2, and one had an Apc mutation at the boundary of intron 10 and exon 11. Mutations at these sites were also commonly found in colon tumors induced by PhIP. The results of our present study indicate that dysplastic ACF, which accounted for approximately one-fourth of the total ACF, are preneoplastic lesions of colon cancers induced by PhIP in rats.

Although an accumulating body of evidence indicates that levels of prostaglandin E(2) (PGE(2)) in human and rodent colon cancers are higher than those in surrounding normal tissues, the precise contribution of PGE(2) to the process of colon cancer development has still been unclear. Therefore, we designed a study using a well-established azoxymethane (AOM)-induced colon carcinogenesis in male F344 rat model to investigate whether administration of exogenous PGE(2) has a real impact on colon carcinogenesis. Intraperitoneal PGE(2) injections (7.7 micro g) once a week for 25 weeks significantly increased the AOM-induced colon tumor incidence (percent rats with tumors, 92 versus 53%, P < 0.05), especially adenocarcinomas (92 versus 47%, P < 0.05), and multiplicity (number of tumors per rat, 2.8 versus 1.0, P < 0.05). PGE(2) treatment significantly increased 5-bromo-2'-deoxyuridine (BrdUrd) labeling index (11.8 versus 9.7%, P < 0.05) and reduced apoptotic index (0.34 versus 0.53%, P < 0.05) in colon cancers induced by AOM. PGE(2) exhibits its physiological functions through binding to E-prostanoid (EP) membrane receptors EP(1-4). All four types of EP receptors were detected in AOM-induced colon cancers using reverse transcription-polymerase chain reaction (RT-PCR). Our results provide evidence that PGE(2) enhances colon carcinogenesis through induction of cell proliferation and reduction of apoptosis.