Effects of nonsteroidal anti-inflammatory drugs on proliferation and on induction of apoptosis in colon cancer cells by a prostaglandin-independent pathway

Dysregulation of integrin-linked kinase (ILK) signaling in colonic polyposis

Mutation of the adenomatous polyposis coli (APC) gene and the subsequent dysregulation of beta-catenin are well-documented abnormalities in familial adenomatous polyposis (FAP), as well as sporadic polyposis. Intriguingly, overexpression of the integrin-linked kinase (ILK) has been shown to modulate beta-catenin subcellular localization and function. However, the significance of this finding for human carcinogenesis remains unclear. Here, we report the increased biochemical activity and expression of ILK protein in polyps from FAP patients. Furthermore, dramatic increases in ILK immunoreactivity were observed in all abnormal crypts from sporadic polyps, when compared with the normal appearing crypts within the same resected specimens. As sulindac and aspirin are the two most important therapeutic/chemopreventative agents demonstrated in colorectal carcinogenesis, in both humans and animals, further investigation revealed that these non-steroidal anti-inflammatory drugs (NSAIDs) target ILK and ILK-mediated events in vivo. These include inhibition of, both the biochemical activation of ILK, inhibition of serine 9 GSK3beta phosphorylation and the enhancement of TCF-4 transcriptional activity. In conclusion, ILK protein hyperexpression appears to be an early event in colonic polyposis. Additionally, ILK signaling is shown to undergo modulation by sulindac (and aspirin) for the first time, indicating that it is likely to be one of the targets affected by these agents in vivo.

Polyamines and colon cancer

Colorectal cancer is a major health problem in the western world and is associated with significant morbidity and mortality. Diet makes a significant contribution to the disease, with high fat, low fibre diets correlating positively with a high incidence of colorectal cancer. Intracellular polyamine concentrations and ornithine decarboxylase activity are both increased in colorectal cancer tissue and in premalignant polyps. Measurement of the polyamine content of serum and urine of individuals has been proposed as a diagnostic marker of malignancy but a number of false positives make this idea untenable. There may, however, still be a role for the measurement of urinary polyamine content as a means of monitoring the efficacy of therapy. Inhibition of polyamine metabolism by polyamine analogues or by non-steroidal anti-inflammatory drugs may be useful in the chemotherapy and/or chemoprevention of colorectal cancer. Preliminary results suggest that a low polyamine diet might be helpful as part of a health care plan for cancer patients.

A cyclooxygenase-2 inhibitor (SC-58125) blocks growth of established human colon cancer xenografts

Selective COX-2 inhibitors reduce adenoma formation and cancer progression in rodent models of colorectal cancer. To assess the therapeutic activity of selective COX-2 inhibitors, we tested the effect of SC-58125 treatment on the growth of human colon carcinoma cells in nude mice. Delaying treatment by 2, 4, or 7 weeks following implantation of the carcinoma cells resulted in a significant inhibition of tumor growth. Furthermore, short-term (48 hours) treatment with SC-58125 was sufficient to attenuate tumor growth for up to 15 days. SC-58125 treatment did not alter the rate at which cells underwent apoptosis, but did result in a delayed progression through the cell cycle at the G(2)/M transition. Accordingly, p34(cdc2) protein levels and activity were decreased following SC-58125 treatment. We conclude that SC-58125 primarily exerts a cytostatic effect in vivo, which is likely to be mediated through inhibition of progression through the G(2)/M phase of the cell cycle.

Autophagy delays sulindac sulfide-induced apoptosis in the human intestinal colon cancer cell line HT-29

Autophagy is a major catabolic process allowing the renewal of intracellular organelles by which cells maintain their homeostasis. We have previously shown that autophagy is controlled by two transduction pathways mediated by a heterotrimeric Gi3 protein and phosphatidylinositol 3-kinase activities in the human colon cancer cell line HT-29. Here, we show that 3-methyladenine, an inhibitor of autophagy, increases the sensitivity of HT-29 cells to apoptosis induced by sulindac sulfide, a nonsteroidal anti-inflammatory drug which inhibits the cyclooxygenases. Similarly, HT-29 cells overexpressing a GTPase-deficient mutant of the G(alpha i3) protein (Q204L), which have a low rate of autophagy, were more sensitive to sulindac sulfide-induced apoptosis than parental HT-29 cells. In both cell populations we did not observe differences in the expression patterns of COX-2, Bcl-2, Bcl(XL), Bax, and Akt/PKB activity. However, the rate of cytochrome c release was higher in Q204L-overexpressing cells than in HT-29 cells. These results suggest that autophagy could retard apoptosis in colon cancer cells by sequestering mitochondrial death-promoting factors such as cytochrome c.

Prostaglandin inhibitors as tocolytic agents

Indomethacin, a nonspecific prostaglandin synthetase inhibitor, gained popularity several decades ago as a potent tocolytic agent. This popularity, however, was tempered by concerns over fetal and neonatal complications associated with its use. However, with better recognition of the safety limitations, there has been a renewed interest in using indomethacin for acute tocolysis. More recently, the tocolytic potential of cyclooxygenase-2 (COX-2) specific inhibitors has gained much interest as well as the theoretical minimization of side effects associated with these agents. This article reviews the pharmacology and efficacy of indomethacin and some of the newer cyclooxygenase-2 inhibitors, and discusses the potential adverse fetal and neonatal effects associated with their use. Guidelines will be presented that will assist theclinician in using indomethacin as an effective tocolytic while avoiding untoward effects.

Detection of differentially expressed genes in human colon carcinoma cells treated with a selective COX-2 inhibitor

Numerous reports suggest that use of nonsteroidal anti-inflammatory drugs (NSAIDs) decrease mortality from colorectal cancer. To better understand all of the mechanisms underlying this effect, the global pattern of gene expression in colon carcinoma cells following treatment with NS-398, a selective cyclo-oxygenase-2 inhibitor was evaluated. We utilized suppression subtractive hybridization combined with differential screening to identify genes whose expression was affected following treatment. Among the subtracted cDNA fragments confirmed as differentially expressed, there were two which are known to be involved in the regulation of cell adhesion (human FAT and proto-cadherin-7). We identified two other genes whose levels were decreased and these are known to be involved in the regulation of cell proliferation (cyclin K and p-100). We identified additional genes which are involved in different signaling pathways which regulate programmed cell death (Dynamin 2, Pdcd4 and LIP.1). These results provide evidence that some of the effects of NS-398 on carcinoma cells may be due to modulation of genes which regulate programmed cell death, cell proliferation and cell-cell communication. Additional studies are underway to determine the biological function of the novel genes that were identified.

Cyclooxygenase-2 as a target for prevention of colorectal cancer

COX-2 is an isoenzyme of cyclooxygenase that is increased in response to growth factors, cytokines, and other mitogenic stimuli. Upregulation of COX-2 gene expression and functional activity is an early event in colorectal tumor formation. The long-term use of cyclooxygenase inhibitors, such as aspirin and nonsteroidal anti-inflammatory drugs, is associated with a decreased rate of colorectal tumors. This observation holds across a range of experimental models, from animal genetic tumor models to large epidemiologic studies of human sporadic colorectal cancer. Selective inhibitors of COX-2 were primarily developed to treat COX-2-related inflammation with minimal side effects. These drugs, however, may also provide safe, effective chemoprevention of colorectal neoplasia.

Inhibitors of arachidonic acid metabolism potentiate tumour necrosis factor-alpha-induced apoptosis in HL-60 cells

We investigated whether and how could various modulators of arachidonic acid metabolism affect apoptosis induced by tumour necrosis factor-alpha (TNF-alpha) in human myeloid leukaemia HL-60 cells. These included arachinonyltrifluoromethyl ketone (AACOCF3; cytosolic phospholipase A2 inhibitor), indomethacin (cyclooxygenase inhibitor), MK-886 (3-[1-(4-chlorobenzyl)-3-t-butyl-thio-5-isopropylindol-2-yl]-2,2-dimethyl propanoic acid; 5-lipoxygenase-activating protein inhibitor), nordihydroguaiaretic acid (general lipoxygenase inhibitor), and arachidonic acid itself. Incubation of HL-60 cells with nordihydroguaiaretic acid resulted in apoptosis and it was characterised by mitochondria membrane depolarisation, release of cytochrome c from mitochondria into cytosol and activation of caspase-3. Indomethacin and nordihydroguaiaretic acid synergistically potentiated TNF-alpha-induced apoptosis, while arachidonic acid, AACOCF3 and MK-886 did not modulate its effects. Furthermore, indomethacin potentiated apoptosis in cells treated with a differentiating agent, all-trans retinoic acid, which induces resistance to TNF-alpha. However, the observed effects were probably not associated either with the cyclooxygenase- or lipoxygenase-dependent activities of indomethacin and nordihydroguaiaretic acid, respectively. Since indomethacin may reportedly activate peroxisome proliferator-activated receptors (PPARs), the effects of specific ligands of PPARs on apoptosis were studied as well. It was found that selective PPARs ligands had no effects on TNF-alpha-induced apoptosis. The findings suggest that arachidonic acid metabolism does not play a key role in regulation of apoptosis induced by TNF-alpha in the present model. Nevertheless, our data raise the possibility that indomethacin could potentially be used to improve the treatment of human myeloid leukaemia.

Evaluation of piroxicam for the treatment of oral squamous cell carcinoma in dogs

OBJECTIVE

To evaluate the use of piroxicam for the treatment of oral squamous cell carcinoma in dogs.

DESIGN

Prospective case series.

ANIMALS

17 dogs with measurable oral squamous cell carcinoma.

PROCEDURE

Dogs were treated with piroxicam at a dosage of 0.3 mg/kg (0.14 mg/lb) of body weight, PO, every 24 hours until progressive disease or unacceptable signs of toxicosis developed or the dog died.

RESULTS

One dog had a complete remission (maxillary tumor), and 2 dogs had partial remissions (lingual tumor and tonsillar tumor). An additional 5 dogs had stable disease, including 1 with a maxillary tumor, 2 with mandibular tumors, and 2 with tonsillar tumors. Variables associated with tumor response were not identified. Median and mean times to failure for the 3 dogs that had a remission were 180 and 223 days, respectively. Median and mean times to failure for the 5 dogs with stable disease were 102 and 223 days, respectively. Time to failure was positively associated with tumor response and negatively associated with tumor size. One dog had mild adverse gastrointestinal tract effects that resolved with the addition of misoprostol to the treatment regimen.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggest that piroxicam may be useful in the treatment of dogs with oral squamous cell carcinoma; response rate was similar to that reported for other cytotoxic treatments. Larger-scale studies are warranted to determine what role piroxicam may have, alone or in combination with other treatments, for the treatment of dogs with oral squamous cell carcinoma.

Differing mechanisms of inhibition of calcium increases in human uterine myocytes by indomethacin and nimesulide

OBJECTIVE

Indomethacin, an inhibitor of cyclooxygenase types 1 and 2, and nimesulide, a cyclooxygenase 2 selective inhibitor, are both well-known inhibitors of prostaglandin production. It has been assumed that the tocolytic mechanism of nimesulide and indomethacin is only through decreased prostaglandin production. The purpose of this study was to test the hypothesis that either nimesulide or indomethacin, or both, has a mechanism of action on human myocytes other than inhibition of prostaglandin production.

STUDY DESIGN

Human uterine myometrium was obtained from consenting patients during cesarean deliveries. Myocytes were cultured, plated, and loaded with a calcium-dependent fluorescent dye, calcium green 1. The relative concentrations of intracellular free calcium were determined by measurement of time-dependent fluorescence changes by means of a video fluorimeter. In all experiments, cells were stimulated with prostaglandin F2alpha, 30 micromol/L. Experiments were performed without pretreatment (control) or with pretreatment consisting of indomethacin, 10 micromol/L, or nimesulide, 30 micromol/L. The percentages of cells demonstrating calcium increases were counted and compared by means of the Fisher exact test. A P value =.05 was considered significant.

RESULTS

After prostaglandin F2alpha exposure, 33% of cells showed an increase in intracellular free calcium under control conditions. When pretreated with nimesulide, 39% of cells responded to prostaglandin F2alpha (P =.59). When pretreated with indomethacin, only 16% of cells responded to prostaglandin F2alpha (P =.019).

CONCLUSIONS

Pretreatment with nimesulide failed to reduce the fraction of cells that responded to prostaglandin F2alpha. In contrast, pretreatment with indomethacin significantly reduced the fraction of responding cells. These data suggest that, in vitro, indomethacin exhibits a mechanism of tocolysis other than inhibition of prostaglandin synthesis.

Non-steroidal anti-inflammatory drugs with activity against either cyclooxygenase 1 or cyclooxygenase 2 inhibit colorectal cancer in a DMH rodent model by inducing apoptosis and inhibiting cell proliferation

BACKGROUND

Standard non-steroidal anti-inflammatory drugs (NSAIDs) reduce the risk of colorectal cancer by 40-60% but the mechanism by which this occurs is uncertain. Selective cyclooxygenase 2 inhibitors are potentially ideal chemopreventive agents as they are less toxic than standard NSAIDs. No study has compared the efficacy of these drugs at clinically relevant doses in a tumour model.

AIMS

To assess the efficacy of a range of NSAIDs with varying activity against the two cyclooxygenase isoforms in a rodent colorectal carcinogen model at anti-inflammatory doses and to explore the effect of NSAIDs on the rate of tumour apoptosis and proliferation.

METHODS

Colorectal tumours were induced in six week old Sprague-Dawley rats with five weekly doses of 1,2 dimethylhydrazine. Test agents were: indomethacin 2 mg/kg/day, meloxicam 0.6 mg/kg/day, celecoxib 6 mg/kg/day, and sulindac sulphone 40 mg/kg/day. Sulindac was tested at its chemoprotective dose of 20 mg/kg/day. After 23 weeks the number and volume of tumours per animal were recorded. Histology was performed. Tumour apoptosis was quantified on haematoxylin-eosin sections. Tumour proliferation was quantified using an immunohistochemical stain for bromodexoyuridine incorporation.

RESULTS

Test agents effectively reduced the number and volume of tumours developing in the treatment period. In all groups there was an increase in the rate of tumour apoptosis and a reduced rate of proliferation.

CONCLUSIONS

These data suggest that the chemopreventive effect of NSAIDs is independent of their cyclooxygenase inhibitory profile. One potential mechanism for their action may be through induction of apoptosis and inhibition of proliferation.

The retinoid fenretinide inhibits proliferation and downregulates cyclooxygenase-2 gene expression in human colon adenocarcinoma cell lines

Fenretinide [N-(4-Hydroxyphenyl)retinamide, 4-HPR] (10(-10)-10(-6) M) treatment of HT-29 human colon cancer cells for 24-72 h significantly inhibited their growth. Using HCT-15 cells, 4-HPR had limited inhibitory effects on cell proliferation over the same concentration range and time period. The inhibitory effects of 4-HPR on cell growth in HT-29 cells were markedly reduced in the presence of exogenously added prostaglandins (PGs), suggesting a possible role for inhibition of PG synthesis as a mechanism for 4-HPR's antiproliferative effects. Inhibition of PGE(2) production was caused by 4-HPR in a concentration-dependent manner and decreased COX-2 but not COX-1 mRNA levels; this is the first indication that 4-HPR selectively inhibits COX-2 gene expression. Our findings suggest a possible mechanism for the chemopreventive and anti-proliferative effects of 4-HPR.

Acetaminophen selectively reduces glioma cell growth and increases radiosensitivity in culture

Glioblastoma multiforme (GBM) is a highly lethal brain cancer. Using cultures of rodent and human malignant glioma cell lines, we demonstrated that millimolar concentrations of acetylsalicylate, acetaminophen, and ibuprofen all significantly reduce cell numbers after several days of culture. However, their mechanisms of action may vary, as demonstrated by (1) differences in the morphological changes produced by these compounds; (2) varied responses to these drugs with respect to toxicity kinetics; and (3) respective rates of cell proliferation, DNA synthesis, and mitotic index. We studied the effects of acetaminophen on relative cell number further. Evidence is presented that acetaminophen induced cell death by an apoptotic mechanism after a brief burst of mitosis in which cell numbers increased transiently, followed by a reduction in cell number and an increase in DNA fragmentation, as evidenced by terminal deoxytransferase-mediated dUTP-biotin nick end labeling (TUNEL) analysis. Using cultures of adult human brain and embryonic rat brain, we demonstrated that glioma cells were several-fold more sensitive to acetaminophen than normal brain cells in culture. Finally, subtoxic doses of acetaminophen increased the sensitivity of the human glioma cells in culture to ionizing radiation. Taken together, these results suggest that acetaminophen may prove to be a useful therapeutic agent in the treatment of human brain tumors.

NF-kappaB, p38 MAPK and JNK are highly expressed and active in the stroma of human colonic adenomatous polyps

The factors that govern the progression from colonic adenomatous polyp to colon cancer are poorly understood. The observation that NSAIDs act as chemopreventative agents and reduce the size of colonic polyps suggests the involvement of inflammatory signalling, but inflammatory signalling in colonic polyps has not been studied. We investigated the expression of the active forms of NF-kappaB, JNK and p38 MAPK using immunohistochemistry with activation specific antibodies in human colonic adenomas. We show that active NF-kappaB is seen in stromal macrophages that also express COX-2 and TNF-alpha, active JNK is seen in stromal and intraepithelial T-lymphocytes and periendothelial cells of new blood vessels, and active p38 MAPK is most highly expressed in macrophages and other stromal cells. These results demonstrate the presence of active inflammatory signal transduction in colonic polyps and that these are predominantly in the stroma. In the case of NF-kappaB this coincides with the cellular localisation of COX-2. These results support evidence that NSAIDs may act through effects on stromal cells rather than epithelial cells.

The nonsteroidal anti-inflammatory drugs aspirin and indomethacin attenuate beta-catenin/TCF-4 signaling

Increasing epidemiological and experimental evidence implicates non-steroidal anti-inflammatory drugs (NSAIDs) as anti-tumorigenic agents. The precise mechanisms whereby NSAIDs exert their anti-neoplastic effects remain poorly understood. Studies from hereditary and sporadic colorectal cancer (CRC) patients suggest that NSAIDs may interfere with initiating steps of carcinogenesis, i.e. disturbances within the beta-catenin signaling pathway. We therefore investigated beta-catenin/TCF signaling in response to aspirin or indomethacin, respectively, in four CRC cell lines (SW948, SW480, HCT116, LoVo). Both, aspirin and indomethacin inhibited transcription of a beta-catenin/TCF-responsive reporter gene in a dose dependent manner. In addition, the beta-catenin/TCF transcriptional target cyclin D1 was downregulated by both drugs. Endogenous beta-catenin levels remained unaffected by either drug. Moreover, indirect immunofluorescence studies revealed no significant changes of subcellular beta-catenin localization in either cell line after NSAID treatment. Likewise, binding of the beta-catenin/TCF complex to its specific DNA-binding sites was not altered, as demonstrated by electrophoretic mobility shift assay (EMSA) of nuclear extracts derived from NSAID treated cells. These results strongly suggest that aspirin and indomethacin attenuate the transcription of beta-catenin/TCF-responsive genes, by modulating TCF activity without disrupting beta-catenin/TCF complex formation.

Cyclooxygenase-two (COX-2) modulates proliferation in aggressive fibromatosis (desmoid tumor)

Aggressive fibromatosis is a locally invasive soft tissue lesion. Seventy-five per cent of cases harbor a somatic mutation in either the APC or beta-catenin genes, resulting in beta-catenin protein stabilization. Cyclooxygenase-2 (COX-2) is an enzyme involved in prostaglandin synthesis that modulates the formation of colonic neoplasia, especially in cases due to mutations resulting in beta-catenin stabilization. Human aggressive fibromatoses and lesions from the Apc+/Apc1638N mouse (a murine model for Apc-driven fibromatosis) demonstrated elevated COX-2 levels. COX-2 blockade either by the selective agent DFU or by non-selective COX blocking agents results in reduced proliferation in human tumor cell cultures. Breeding mice with Cox-2-/- mice resulted in no difference in number of aggressive fibromatoses formed, but in a smaller tumor size, while there was a decrease in number of GI lesions by 50%. Mice fed various COX blocking agents also showed a decline in tumor size. COX-2 expression was regulated by tcf-dependent transcription in this lesion. COX-2 partially regulates proliferation due to beta-catenin stabilization in aggressive fibromatosis. Although COX blockade alone does not cause tumor regression, this data suggests that it may have a role as an adjuvant therapy to slow tumor growth in this lesion.

Peroxisome proliferator-activated receptors: roles in tumorigenesis and chemoprevention in human cancer

Peroxisome proliferator-activated receptors are nuclear receptors that were isolated for their ability to modulate lipid metabolism. Similar to other members of the nuclear receptor family, peroxisome proliferator-activated receptors bind ligand as heterodimers and exert their effects via transcriptional regulation through their DNA binding domains. During the past decade, it has become clear that peroxisome proliferator-activated receptors also contribute to a variety of different biologic processes, including atherosclerosis, insulin resistance, and more recently, cancer. In this review, we discuss the evidence for the different peroxisome proliferator-activated receptors' roles in tumorigenesis and also their potential application for the treatment and prevention of neoplastic diseases.

Growth-suppressive effect of non-steroidal anti-inflammatory drugs on 11 colon-cancer cell lines and fluorescence differential display of genes whose expression is influenced by sulindac

In addition to an anti-inflammatory effect, sulindac, one of the non-steroidal anti-inflammatory drugs (NSAIDs), has been shown to have a protective effect against the incidence and mortality of colorectal cancer. However, the molecular basis of its anti-proliferative function remains unclear. To investigate its molecular mechanism, we exposed 11 colon-cancer cell lines to NSAIDs such as aspirin, sulindac and the sulfide and sulfone metabolites of sulindac. Sensitivity to these drugs was dose- and time-dependent but varied from one cell line to another. Among the cell lines examined, sulindac showed a moderate anti-proliferative effect on HT-29 colon cancer cells and caused morphological changes, including an increase of cells with abnormal DNA content. We used the mRNA fluorescence differential display method with these cells to identify molecules that might contribute, through altered expression, to cellular changes in response to NSAIDs. Sixty-eight cDNA fragments were confirmed by RT-PCR to have significantly different expression levels following sulindac treatment. Thirty of these fragments proved to be novel cDNA sequences or identical to expressed sequence tags; the other 38 fragments were identical, or showed significant homology, to genes whose function was already known. Among the known genes differentially expressed in HT-29 cells after sulindac treatment were those encoding acetylglucosaminyltransferase, ferritin heavy chain, zinc finger protein 165, aldose reductase, carcinoembryonic antigen, aldoketoreductase, NF-kappaB-activating kinase, lysosome-associated protein, RhoE = 26 kDa GTPase homologue, NADH oxidoreductase, G/T mismatch bindingprotein, TM7SF3, ADP/ATP carrier-like protein and chromosome segregation protein. This variety among classes of proteins affected by sulindac in our experiments underscores the complexity of anti-proliferative mechanisms that may operate in colon-cancer cells treated with NSAIDs. Furthermore, identification of genes regulated by NSAIDs in colon-cancer cells should provide useful information to identify novel therapeutic targets for treatment and/or prevention of colon cancer.

Sulindac inhibits neointimal formation after arterial injury in wild-type and apolipoprotein E-deficient mice

Neointimal hyperplasia is a critical component of restenosis, a major complication of angioplasty and related therapeutic procedures. We studied the effects of hyperlipidemia and the nonsteroidal anti-inflammatory drugs, aspirin (acetyl-salicylic acid; ASA), and sulindac, on neointimal formation in a mouse femoral arterial injury model. At 2 months of age, normolipidemic, wild-type (WT), and hyperlipidemic, apolipoprotein E-deficient (apoE-/-) mice were divided into three treatment groups: Western-type diet (WD), WD + ASA (200 mg/kg food), and WD + sulindac (300 mg/kg food). After 1 week, mice underwent arterial injury and treatments were maintained for 4 weeks. Histomorphometry of the injured arteries showed striking effects of plasma cholesterol levels and drug treatment on neointimal hyperplasia. In the WD or WD + ASA groups, apoE-/- mice had twice the neointimal area than WT mice ( approximately 30,000 vs. 13,000 microm(2) per section; P < 0.0001). Compared with ASA or WD alone, sulindac treatment resulted in approximately 70% (P = 0.0001) and 50% (P = 0.01) reductions in the neointimal area in apoE-/- and WT mice, respectively. ASA, at a dose sufficient to inhibit platelet aggregation, did not affect neointimal formation in mice of either genotype. Evidence of macrophages was noted in the lesions of apoE-/- mice in the WD and WD + ASA groups, but remarkably, none was detectable with sulindac treatment, despite hyperlipidemia, suggesting early steps in the response to injury were abrogated. These results demonstrate sulindac reduces neointimal formation in both normolipidemic and hyperlipidemic settings and raise the possibility that similar benefits may be obtained in patients undergoing angioplasty and related procedures.

Aspirin induces apoptosis through release of cytochrome c from mitochondria

Nonsteroidal anti-inflammatory drugs (NSAID) reduce the risk for cancer, due to their antiproliferative and apoptosis-inducing effects. A critical pathway for apoptosis involves the release of cytochrome c from mitochondria, which then interacts with Apaf-1 to activate caspase proteases that orchestrate cell death. In this study we found that treatment of a human cancer cell line with aspirin induced caspase activation and the apoptotic cell morphology, which was blocked by the caspase inhibitor zVAD-fmk. Further analysis of the mechanism underlying this apoptotic event showed that aspirin induces translocation of Bax to the mitochondria and mitochondrial release of cytochrome into the cytosol. The release of cytochrome c from mitochondria was inhibited by overexpression of the antiapoptotic protein Bcl-2 and cells that lack Apaf-1 were resistant to aspirin-induced apoptosis. These data provide evidence that the release of cytochrome c is an important part of the apoptotic mechanism of aspirin.

[Non-steroidal anti-inflammatory agents with selective inhibitory activity on cyclooxygenase-2. Interest and future prospects]

INTRODUCTION

Non-steroidal anti-inflammatory drugs (NSAIDs) inhibit the production of primary prostanoids by blocking the access of arachidonic acid to the active site of the cyclooxygenases (COXs). Because the prostanoids produced by COX-1 appear to play a physiological role (protection of the gastric mucosa, platelet aggregation, vascular homeostasis, maintenance of renal sodium-water balance) while those produced by COX-2 seem mainly to intervene in the inflammatory response and in certain processes associated with cell proliferation, the hypothesis has been put forward that the NSAIDs that are selective COX-2 inhibitors should theoretically be capable of maintaining NSAID therapeutic properties but also have fewer adverse side effects due to the maintenance of prostaglandin production at normal physiological levels.

CURRENT KNOWLEDGE AND KEY POINTS

The hypothesis of COX isoenzyme selectivity has led to a proposed classification for COX inhibitors: 1) COX-1 selective inhibitors (low-dosage aspirin); 2) COX non-selective inhibitors (the majority of classified NSAIDs, which when administered over the long term, e.g., in cases of rheumatoid arthritis, cause duodenal ulcers in 20% of cases and gastric hemorrhage in 1-4% of cases/year); 3) COX-2 preferential inhibitors (meloxicam and nimesulide, which have fewer gastric side effects than standard NSAIDs, but which are not risk-free at high doses); 4) COX-2 selective inhibitors (celecoxib and rofecoxib). Preliminary clinical studies have shown that COX-2 selective inhibitors are as efficient as standard NSAIDs and have fewer adverse digestive side effects, thereby confirming the interest of this proposed classification. In the UK, the aforementioned studies have led to the commercialization of rofecoxib for the treatment of pain and osteoarthritis, while celecoxib has been introduced in medical practice in the USA and other countries for the treatment of rheumatoid arthritis and osteoarthritis.

FUTURE PROSPECTS AND PROJECTS

Various epidemiological and laboratory studies have indicated that NSAIDs may be able to reduce the risk of cancer (colorectal cancer in particular) and Alzheimer's disease due to their inhibitory activity on COXs, especially COX-2. The therapeutic contribution of COX-2 specific inhibitors has to be more fully evaluated, particularly as these agents could delay the healing of duodenal ulcers and interfere with several COX-2-induced physiological functions. It is therefore suggested that until further information becomes available, this new class of NSAIDs should be used with caution in certain patient populations.

Biochemistry of cyclooxygenase (COX)-2 inhibitors and molecular pathology of COX-2 in neoplasia

Several types of human tumors overexpress cyclooxygenase (COX) -2 but not COX-1, and gene knockout transfection experiments demonstrate a central role of COX-2 in experimental tumorigenesis. COX-2 produces prostaglandins that inhibit apoptosis and stimulate angiogenesis and invasiveness. Selective COX-2 inhibitors reduce prostaglandin synthesis, restore apoptosis, and inhibit cancer cell proliferation. In animal studies they limit carcinogen-induced tumorigenesis. In contrast, aspirin-like nonselective NSAIDs such as sulindac and indomethacin inhibit not only the enzymatic action of the highly inducible, proinflammatory COX-2 but the constitutively expressed, cytoprotective COX-1 as well. Consequently, nonselective NSAIDs can cause platelet dysfunction, gastrointestinal ulceration, and kidney damage. For that reason, selective inhibition of COX-2 to treat neoplastic proliferation is preferable to nonselective inhibition. Selective COX-2 inhibitors, such as meloxicam, celecoxib (SC-58635), and rofecoxib (MK-0966), are NSAIDs that have been modified chemically to preferentially inhibit COX-2 but not COX-1. For instance, meloxicam inhibits the growth of cultured colon cancer cells (HCA-7 and Moser-S) that express COX-2 but has no effect on HCT-116 tumor cells that do not express COX-2. NS-398 induces apoptosis in COX-2 expressing LNCaP prostate cancer cells and, surprisingly, in colon cancer S/KS cells that does not express COX-2. This effect may due to induction of apoptosis through uncoupling of oxidative phosphorylation and down-regulation of Bcl-2, as has been demonstrated for some nonselective NSAIDs, for instance, flurbiprofen. COX-2 mRNA and COX-2 protein is constitutively expressed in the kidney, brain, spinal cord, and ductus deferens, and in the uterus during implantation. In addition, COX-2 is constitutively and dominantly expressed in the pancreatic islet cells. These findings might somewhat limit the use of presently available selective COX-2 inhibitors in cancer prevention but will probably not deter their successful application for the treatment of human cancers.

Cyclooxygenase-2 expression in Helicobacter pylori-associated premalignant and malignant gastric lesions

Expression of cyclooxygenase-2 (COX-2) in various stages of the Helicobacter pylori-associated gastric carcinogenesis pathway has not been elucidated. We investigated the distribution and intensity of COX-2 expression in premalignant and malignant gastric lesions, and monitored the changes after H. pylori eradication. Gastric biopsies from H. pylori-infected patients with chronic active gastritis, gastric atrophy, intestinal metaplasia (IM), gastric adenocarcinoma, and noninfected controls were studied. Expression of COX-2 was evaluated by immunohistochemistry and in situ hybridization. Endoscopic biopsies were repeated 1 year after successful eradication of H. pylori in a group of IM patients for comparing COX-2 expression and progression of IM. In all H. pylori-infected patients, COX-2 expression was predominantly found in the foveolar and glandular epithelium and, to a lesser extent, in the lamina propria. In the noninfected group, only 35% of cases demonstrated weak COX-2 expression. Intensity of COX-2 was not significantly different between the chronic active gastritis, gastric atrophy, IM, and gastric adenocarcinoma groups. In 17 patients with IM, COX-2 expressions in the epithelial cells and stromal cells were reduced 1 year after H. pylori eradication. However, the changes in COX-2 expression did not correlate with progression/regression of IM. Both premalignant and malignant gastric lesions demonstrate strong COX-2 expression. Successful eradication of H. pylori leads to down-regulation of COX-2 expression but failed to reverse IM at 1 year.

The role of cyclooxygenase enzymes in the growth of human gall bladder cancer cells

Information suggests that the cyclooxygenase (COX) metabolites, the prostanoids, play a role in gall bladder physiology and disease. Non-steroidal anti-inflammatory drugs which inhibit COX enzymes have been shown in vivo and in vitro to alter the growth patterns of intestinal epithelial cells, and specific COX-2 inhibitors have been shown to decrease mitogenesis in intestinal epithelial cells. The present study was intended to evaluate the effect of specific COX inhibitors on the growth patterns of gall bladder cancer cells. Employing a human gall bladder cancer cell line, mitogenesis, apoptosis and prostaglandin E(2) (PGE(2)) formation were evaluated in response to serum and hepatocyte growth factor and transforming growth factor alpha stimulation in the presence and absence of specific COX-1 and -2 inhibitors. The effect of the mitogens on COX enzyme expression was also evaluated. Serum and the growth factors increased COX enzyme expression and mitogenesis, and decreased apoptosis as evaluated by the percentage of cells that were floating in culture media rather than attached. There was more DNA degradation in floating than in attached cells. The specific COX-2 inhibitor, but not the COX-1 inhibitor, decreased mitogenesis and increased gall bladder cell apoptosis as evaluated by the number of floating versus attached cells and the number of floating cells in the terminal phase of apoptosis or dead. The inhibition of mitogenesis and the increased apoptosis produced by the COX-2 inhibitor was associated with decreased PGE(2) production. The inhibition of replication of gall bladder cancer cells and the increase in apoptosis produced by the selective COX-2 inhibitor suggests that the COX enzymes and the prostanoids may play a role in the development of gall bladder cancer and that the COX-2 inhibitors may have a therapeutic role in the prevention of gall bladder neoplasms.

The Mom1AKR intestinal tumor resistance region consists of Pla2g2a and a locus distal to D4Mit64

The Mom1 (Modifier of Min-1) region of distal chromosome 4 was identified during a screen for polymorphic modifiers of intestinal tumorigenesis in ApcMin/+ mice. Here, we demonstrate that the Mom1AKR allele consists of two genetic components. These include the secretory phospholipase Pla2g2a, whose candidacy as a Mom1 resistance modifier has now been tested with several transgenic lines. A second region, distal to Pla2g2a, has also been identified using fine structure recombinants. Pla2g2aAKR transgenic mice demonstrate a modest resistance to tumorigenesis in the small intestine and a very robust resistance in the large intestine. Moreover, the tumor resistance in the colon of Pla2g2aAKR animals is dosage-dependent, a finding that is consistent with our observation that Pla2g2a is expressed in goblet cells. By contrast, mice carrying the distal Mom1 modifier demonstrate a modest tumor resistance that is confined to the small intestine. Thus, the phenotypes of these two modifier loci are complementary, both in their quantitative and regional effects. The additive effects and tight linkage of these modifiers may have been necessary for the initial identification of the Mom1 region.

Host cyclooxygenase-2 modulates carcinoma growth

Cyclooxygenase-2 (COX-2; Ptgs2) acts as a tumor promoter in rodent models for colorectal cancer, but its precise role in carcinogenesis remains unclear. We evaluated the contribution of host-derived COX-1 and COX-2 in tumor growth using both genetic and pharmacological approaches. Lewis lung carcinoma (LLC) cells grow rapidly as solid tumors when implanted in C57BL/6 mice. We found that tumor growth was markedly attenuated in COX-2(-/-), but not COX-1(-/-) or wild-type mice. Treatment of wild-type C57BL/6 mice bearing LLC tumors with a selective COX-2 inhibitor also reduced tumor growth. A decrease in vascular density was observed in tumors grown in COX-2(-/-) mice when compared with those in wild-type mice. Because COX-2 is expressed in stromal fibroblasts of human and rodent colorectal carcinomas, we evaluated COX-2(-/-) mouse fibroblasts and found a 94% reduction in their ability to produce the proangiogenic factor, VEGF. Additionally, treatment of wild-type mouse fibroblasts with a selective COX-2 inhibitor reduced VEGF production by 92%.

Non-steroidal anti-inflammatory drugs and apoptosis in the gastrointestinal tract: potential role of the pentose phosphate pathways

Non-steroidal anti-inflammatory drugs (NSAIDs) are among the most widely prescribed drugs, primarily for treatment of arthritis. NSAIDs can have two effects independent of their anti-inflammatory action. In the stomach and small bowel long term NSAID consumption can lead to ulceration, whereas in the colon NSAID use can regress existing tumours. In this review, we hypothesise that NSAID-induced damage occurs predominantly by promoting apoptosis, involving a number of mechanisms depending on the type and the redox state of the cell. In addition to inhibiting cyclooxygenase (COX) activity, this includes interfering with glucose metabolism through both arms of the pentose phosphate pathways and energy production via glycolysis and oxidative phosphorylation. Shifting the cellular balance from proliferation to apoptosis is probably the most important outcome by which NSAIDs exhibit their differing actions. Understanding how these different pathways can be reconciled and their contribution to the balance between cell birth and cell death is the challenge for the future. The pentose phosphate pathways may provide a pivotal point for understanding links between factors which alter proliferative activity (e.g. COXs), provide energy metabolism (particularly aerobic and anaerobic metabolism of glucose), and change the redox state of the cell leading to apoptosis.

Apoptosis induction and cyclooxygenase-2 regulation in human colorectal adenoma and carcinoma cell lines by the cyclooxygenase-2-selective non-steroidal anti-inflammatory drug NS-398

We determined the effect of the highly selective cyclooxygenase-2 (COX-2) inhibitor NS-398 on proliferation, apoptosis and COX-2 regulation in 3 pre-malignant human colorectal adenoma cell lines (RG/C2, AA/C1, RR/C1) and compared its effect on 3 colorectal carcinoma cell lines (HT29, KS, JW2). COX-2 protein was expressed in each cell line derived from an adenoma, thus providing evidence that COX-2 is expressed in the tumour cells themselves at an early stage in human colorectal adenoma formation. NS-398 (20 to 100 microM for 96 h) induced apoptosis and inhibited the proliferation of the adenoma cell lines. Of the 3 carcinoma lines, only HT29 expressed COX-2 protein, yet each line was similarly sensitive to NS-398. There was a positive correlation between overall sensitivity of the cell lines (determined by the attached cell yield) and sensitivity to NS-398-induced apoptosis, suggesting that apoptosis is the dominant anti-proliferative effect of NS-398. Two of the 3 adenoma cell lines (RG/C2, AA/C1) were less sensitive than the carcinoma cell lines. NS-398 up-regulated COX-2 protein expression in the HT29 and adenoma cell lines. This was studied further in HT29 cultures, where treatment with NS-398 inhibited COX-2 activity, reducing prostaglandin E(2) secretion. Here, neither the increase in COX-2 protein expression nor the anti-proliferative and apoptosis-inducing effect of NS-398 was prevented by addition of exogenous prostaglandin E(2). Apoptosis appears to be the dominant anti-proliferative effect of NS-398 and, in COX-2 expressing cells, may be mechanistically linked to the observed induction of COX-2 protein expression upon treatment with NS-398.

Effect of prostaglandin E(2) on the proliferation, Ca(2+) mobilization and cAMP in HT-29 human colon adenocarcinoma cells

Several lines of evidence suggest that non-steroidal antiinflammatory drugs (NSAIDs) have anticarcinogenic effects. The causal relationship linking the preventive effect of NSAIDs on colon cancer and the inhibition of prostaglandin synthesis is questioned by the contrasting results obtained by many laboratories. The experiments reported in this paper demonstrate that prostaglandin E(2) (PGE(2)) did not stimulate the proliferation in HT-29 human colon adenocarcinoma cells under several experimental conditions. Moreover, PGE(2) and 17-phenyl trinor prostaglandin E(2) (a specific agonist of EP1 receptors) did not increase intracellular Ca(2+) concentration. Finally, PGE(2) did not affect the intracellular cAMP and did not reduce the isoproterenol dependent increase in cAMP. These results indicate that in HT-29 cells: (1) proliferation is not directly sensitive to PGE(2); and (2) PGE(2) does not stimulate a signal transduction pathway leading to intracellular increase in cAMP or Ca(2+) mobilization. Therefore, other cell lines should be used to assess the direct role played by prostanoids in promoting cell proliferation in colon cancer.

Indomethacin induces apoptosis and inhibits proliferation in chronic myeloid leukemia cells

A nonsteroidal anti-inflammatory drug (NSAID)--indomethacin (IN), was found to induce apoptosis and inhibit proliferation of K562 cells and primary culture bone marrow cells from six chronic myelogenous leukemia (CML) patients. IN induced cells apoptosis and inhibited cells proliferation in a dose-and time-dependent manner, the optimum IN concentration and incubation time for eliciting these effects were 400 micromol/l and 72 h, respectively. A synergic effect on Vp-16 (2.5 microg/ml) induced apoptosis was observed when combined with 100 micromol/l IN in K562 cells. RT-PCR results showed that IN down-regulated Bcl-2 mRNA expression, and did not change Bax mRNA expression; Western blot results confirmed that IN inhibited Bcl-2 protein expression, no influence was found on the translative level of bax protein. Our study indicate that IN induce apoptosis of CML cells by down-regulating Bcl-2 expression partially, and there is a potential significance in the treatment of CML.

Lack of cyclooxygenase-2 activity in HT-29 human colorectal carcinoma cells

Induction of cyclooxygenase-2 (COX-2) is an early event in the sequence of polyp formation to colon carcinogenesis. COX-2 is at elevated levels in human colorectal cancers and in tumors and polyps of mouse models of colorectal cancer. Mutation of the adenomatous polyposis coli (APC) gene is the initial event leading to colorectal cancer. Colorectal cells in culture which express mutant APC are often used to examine the association of COX-2 expression and apoptosis. The expression of full-length APC in HT-29 cells, a human colorectal carcinoma cell line which normally expresses truncated APC and highly expresses COX-2, inhibits cell growth through increased apoptosis and results in a down-regulation of COX-2 protein. In this report, we examine whether down-regulation of COX-2 is directly linked to the increase in apoptosis observed in these HT-29-APC cells. We present evidence that COX-2 and apoptosis are not linked since COX-2, although expressed, is catalytically inactive. Interestingly, the COX-2 cloned from HT-29 cells is catalytically active when transfected into HCT-116 cells, a colorectal cell line which normally does not express COX-2, but is not active in the HT-29 cell line itself.

Discordant effect of aspirin and indomethacin on intestinal tumor burden in Apc(Min/+)mice

Epidemiologic and animal studies indicate that sustained use of non-steroidal anti-inflammatory drugs (NSAIDs) have a chemopreventive effect against the incidence of colorectal neoplasia and subsequent mortality. We previously demonstrated that sulindac significantly reduces intestinal tumor load in Apc(Min/+)mice and the tumor regression was not necessarily correlated with prostaglandin biosynthesis. In the present study, we further investigate the relationship of NSAID treatment and tumorigenesis in the Apc(Min/+)mouse model. We demonstrate that indomethacin (9 ppm) is a very potent chemopreventive agent, reducing tumor load by 85% and significantly inhibiting basal and ex vivo prostaglandin formation (P< 0.006 and P< 0.0001, respectively). Aspirin (400 ppm) has a similar impact on reducing prostaglandin levels, but in contrast to indomethacin, is uneffective in reducing the tumor load. The data indicate a discordance between the impact of different NSAIDs on tumorigenesis in Apc(Min/+)mice.

The cyclooxygenase-2 inhibitor celecoxib induces apoptosis by blocking Akt activation in human prostate cancer cells independently of Bcl-2

This study investigates the apoptotic activity of the cyclooxygenase-2 (COX-2) inhibitor celecoxib in prostate carcinoma cells. COX-2 is constitutively expressed in androgen-responsive LNCaP and androgen-nonresponsive PC-3 cells. Exposure of these cells to celecoxib induces characteristic features of apoptosis, including morphological changes, DNA laddering, and caspase-3 activation, whereas piroxicam, a COX-1-specific inhibitor, displays no appreciable effect on either cancer cell line even after prolonged exposure. Moreover, the potency of celecoxib in apoptosis induction is significantly higher than that of other COX-2 inhibitors examined despite the observation that these inhibitors exhibit similar IC(50) in COX-2 inhibition. It is noteworthy that normal human prostate epithelial cells, expressing a marginally detectable level of COX-2, are insensitive to the induction of apoptosis by celecoxib. These data suggest a correlation between COX-2 expression and sensitivity to the apoptotic effect of the COX-2 inhibitor. In an effort to delineate the underlying mechanism, we examined the effect of celecoxib on the expression of Bcl-2 as well as the activation of the key anti-apoptotic kinase Akt. In contrast to an earlier report that attributed the apoptotic activity of NS398 in LNCaP cells to Bcl-2 down-regulation, we provide evidence that the induction of apoptosis by celecoxib in LNCaP and PC-3 cells is independent of Bcl-2. First, treatment with celecoxib does not alter the cellular Bcl-2 level in both cell lines. Second, enforced Bcl-2 expression in PC-3 cells does not confer protection against the induction of apoptosis by celecoxib. Our data show that celecoxib treatment blocks the phosphorylation of Akt. This correlation is supported by studies showing that overexpression of constitutively active Akt protects PC-3 cells from celecoxib-induced apoptosis. Nevertheless, how celecoxib down-regulates Akt is not clear because the drug does not adversely affect phosphoinositide 3-kinase activity in vivo and okadaic acid, a protein phosphatase 2A inhibitor, cannot rescue the inhibition. In summary, our data demonstrate that inhibition of Akt activation may play a crucial role in the induction of apoptosis by celecoxib.

Review article: cyclooxygenase--a target for colon cancer prevention

Use of nonsteroidal anti-inflammatory drugs such as aspirin, which are known to inhibit cyclooxygenase activity, reduces the relative risk of colorectal cancer in humans by 40-50%. Animal and human studies have shown a 50-80% reduction in tumour multiplicity following treatment with a variety of nonsteroidal anti-inflammatory drugs. Two isoforms of cyclooxygenase have been described, cyclooxygenase-1 (COX-1) and cyclooxygenase-2 (COX-2). In 85% of colorectal adenocarcinomas taken from humans. COX-2 levels are 2-50-fold higher than levels in adjacent normal intestinal mucosa, while COX-1 levels are unchanged. These observations raise the question: Does COX-1 or COX-2 provide a useful target for prevention or treatment of colorectal cancer?

The role of COX-2 in intestinal cancer

Cyclooxygenase (COX), the key regulatory enzyme for prostaglandin synthesis is transcribed from two distinct genes. COX-1 is expressed constitutively in most tissues, and COX-2 is induced by a wide variety of stimuli and was initially identified as an immediate-early growth response gene. In addition, COX-2 expression is markedly increased in 85-90% of human colorectal adenocarcinomas, whereas COX-1 levels remain unchanged. Several epidemiological studies have reported a 40-50% reduction in the risk of developing colorectal cancer in persons who chronically take such nonsteroidal anti-inflammatory drugs (NSAIDs) as aspirin, which are classic inhibitors of cyclooxygenase. Genetic evidence also supports a role for COX-2, since mice null for COX-2 have an 86% reduction in tumor multiplicity in a background containing a mutated APC allele. These results strongly suggest that COX-2 contributes to the development of intestinal tumors and that inhibition of COX is chemo-preventative.

Cyclooxygenase-deficient mice. A summary of their characteristics and susceptibilities to inflammation and carcinogenesis

Cyclooxygenase (COX)-1- and COX-2-deficient mice have unique physiological differences that have allowed investigation into the individual biological roles of the COX isoforms. In the following, the phenotypes of the two COX knockout mice are summarized, and recent studies to investigate the effects of COX deficiency on inflammatory responses and cancer susceptibility are discussed. The data suggest that both isoforms have important roles in the maintenance of physiological homeostasis and that such designations as house-keeping and/or response gene may not be entirely accurate. Furthermore, data from COX-deficient mice indicate that both isoforms can contribute to the inflammatory response and that both isoforms have significant roles in carcinogenesis.

The effect of non-steroidal anti-inflammatory drugs on human colorectal cancer cells: evidence of different mechanisms of action

Non-steroidal anti-inflammatory drugs (NSAIDs) inhibit proliferation and induce apoptosis in human colorectal cancer cells in vitro. It remains unclear whether individual NSAIDs act by cyclooxygenase-2 (COX-2) inhibition and how NSAIDs exert their anti-proliferative effects. We investigated the effects of NS-398 (a selective COX-2 inhibitor), indomethacin (a non-selective COX inhibitor) and aspirin on four human colorectal cancer cell lines (HT29.Fu, HCA-7, SW480 and HCT116). NS-398 completely inhibited proliferation, induced G1 arrest and promoted apoptosis in COX-2-expressing cells (HT29.Fu and HCA-7). However, indomethacin had similar effects on all cells, regardless of COX-2 expression. NS-398 also had anti-proliferative activity on COX-2-negative cell lines (SW480 and HCT116). Aspirin inhibited proliferation of all cell lines but did not induce apoptosis. Indomethacin decreased beta-catenin protein expression in all cells (unlike NS-398 or aspirin). NSAIDs act on human colorectal cancer cells via different mechanisms. Decreased beta-catenin protein expression may mediate the anti-proliferative effects of indomethacin.

Nonsteroidal anti-inflammatory drugs attenuate proliferation of colonic carcinoma cells by blocking epidermal growth factor-induced Ca++ mobilization

Numerous studies suggest that nonsteroidal anti-inflammatory drugs (NSAIDs) inhibit colorectal carcinogenesis. We have previously reported that NSAIDs, in human colonic carcinoma cells (Caco-2), attenuate epidermal growth factor (EGF)-induced cellular proliferation through a process independent of their inhibitory effects on prostaglandin synthesis. Furthermore, separate studies have also suggested that NSAIDs inhibit EGF-induced store-operated Ca++ influx. Thus we developed the hypothesis that NSAIDs may limit the activity of EGF by altering intracellular Ca++ ([Ca++]i) mobilization. Serum-deprived Caco-2 cells were employed for all experimentation. [Ca++]i was measured with Fluo-3 and extracellular Ca++ influx was monitored by quenching Fluo-3 fluorescence with Mn++. Proliferation was quantitated with two assays: cellular nucleic acid and total protein content. Caco-2 cells exposed to EGF demonstrated an initial increase in [Ca++]i which was blocked by neomycin, an inhibitor of IPsubscript 3 generation, and the phospholipase C inhibitor U73122 but not U73343 (inactive control). This was followed by sustained extracellular Ca++ influx, which was attenuated with calcium-free buffer (-Ca++), the store- operated Ca++ channel blocker lanthanum, indomethacin, ibuprofen, and aspirin. In subsequent studies, cells were treated with either serum-free media or EGF +/- the aforementioned inhibitors, and again serum starved. Cells exposed to EGF +/- the inactive phospholipase C inhibitor U73343 demonstrated a significant increase in nucleic acid and protein. However, proliferation induced by EGF was not observed when [Ca++]i elevation was prevented by blocking either internal Ca++ store release via phospholipase C/IPsubscript 3 or sustained Ca++ influx through store-operated Ca++ channels. Sustained [Ca++]i elevation, as induced by EGF, appears to be required for mitogenesis. These data support our premise that one mechanism whereby NSAIDs may attenuate colonic neoplasia is by blocking EGF-induced Ca++ mobilization.