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

Contrasting effects of aspirin on prostate cancer cells: suppression of proliferation and induction of drug resistance

BACKGROUND

Aspirin is widely used as a preventive measure against occlusive vascular diseases. Since the age group in which aspirin use has become prevalent is similar to the one presenting with prostate cancer, we decided to examine the potential effects of aspirin on prostate cancer.

METHODS

We studied the effects of plasma-attainable concentrations of aspirin (0.5-2 mM) on the human prostate cancer cell lines LNCaP, PC-3, and DU 145, employing cytotoxicity assays and flow cytometric analyses.

RESULTS

Incubation with aspirin for 3 days reduced cellular proliferation by up to 35-55% in each cell line studied, but induced a tripling of the percentage of cells expressing P-glycoprotein (an efflux pump conferring multidrug resistance) only in the LNCaP cells. Both effects were dose-dependent. The effect on P-glycoprotein expression was reflected in the induction of resistance against adriamycin cytotoxicity. Furthermore, this protective effect of aspirin was reversed by a specific P-glycoprotein inhibitor, PSC833. The cellular expression of P-glycoprotein returned to normal within 3 days following the removal of aspirin. Aspirin did not affect the cell cycle distribution of LNCaP cells.

CONCLUSIONS

This study suggests that aspirin enhances the ability of androgen-responsive prostate cancer cells to resist chemotherapeutic drugs. These findings could potentially have significant clinical ramifications for prostate cancer patients taking aspirin shortly before or during chemotherapeutic sessions.

Inhibition of rat colon tumors by sulindac and sulindac sulfone is independent of K-ras (codon 12) mutation

Nonsteroidal anti-inflammatory drug (NSAID) use reduces the risk of colorectal cancer by 40-50%. Previous studies suggest that effective inhibition of colorectal cancer by NSAIDs may be dependent on the presence or absence of a K-ras mutation. This study was aimed at determining the relationship between inhibition of colorectal cancer by sulindac and sulindac sulfone and the presence of activating K-ras mutations in the 1,2-dimethylhydrazine dihydrochloride rat model. Sulindac (20 mg x kg(-1) x day(-1)), sulindac sulfone (40 mg x kg(-1) x day(-1)), or vehicle was administered orally to male Sprague-Dawley rats for a 4-wk period beginning 20 wk after tumor induction. Tumor number and volume were measured before treatment by laparotomy and colonoscopy and again after treatment. Sulindac and sulindac sulfone treatment significantly reduced the number and volume of colorectal tumors compared with control rats. For K-ras (codon 12) mutation detection, frozen tumor tissue was collected at the endpoint. We found K-ras codon 12 mutations in 11 of 21 (52%) control tumors. The proportion of tumors with K-ras mutations in the sulindac-treated group [5 of 8 (62%); odds ratio = 1.51 (95% confidence interval = 0.29, 8.33)] and the proportion of sulindac sulfone-treated tumors [9 of 14 (64%); odds ratio = 1.63 (95% confidence interval = 0.41, 6.66)] were not significantly different from controls. Tumor inhibition did not correlate with K-ras (codon 12) mutation status, which suggests that the mechanism of inhibition of rat colorectal cancer by sulindac and sulindac sulfone is independent of K-ras mutation.

Cancer chemoprevention through interruption of multistage carcinogenesis. The lessons learnt by comparing mouse skin carcinogenesis and human large bowel cancer

Whilst in the early stages, neoplastic development is predominantly triggered by environmental genotoxic and non-genotoxic carcinogens, tumour progression becomes more and more autonomous at later stages. In this context a dysregulation of arachidonic acid metabolism seems to play a disastrous role. Conversely, non-steroidal anti-inflammatory drugs (NSAIDs) rank among the most potent and most promising agents for cancer chemoprevention probably because of their ability to inhibit prostaglandin biosynthesis, in particular, at the level of the 'pro-inflammatory' enzyme cyclooxygenase-2 (COX-2). A pathological overexpression of COX-2 resulting in excessive prostaglandin production has been found already in early stages of carcinogenesis and seems to be a consistent feature of neoplastic development in a wide variety of tissues. COX-2 overexpression is thought to occur along signalling pathways of inflammation and tissue repair which become activated in the course of tumour promotion and, due to autocrine and auto-stimulatory mechanisms, finally lead to some autonomy of tumour development (self-promotion). Prostaglandins formed along a dysregulated COX pathway have been shown to mediate tumour promotion in animal experiments and may play a role, in addition, in other processes involved in tumour growth such as angiogenesis, metastasis and immunosuppression. Moreover, genotoxic byproducts such as organic free radicals, reactive oxygen species and malondialdehyde produced in the course of prostanoid biosynthesis may contribute to genetic instability (mutator phenotype) of neoplastic cells thereby promoting malignant progression. Such mixtures of physiologically highly active mediators and genotoxic byproducts are, in addition, formed along the various lipoxygenase-catalysed pathways of arachidonic acid metabolism some of which also become dysregulated during tumour development and, therefore, provide novel targets of future chemopreventive approaches.

Is inhibition of cyclooxygenase required for the chemopreventive effect of NSAIDs in colon cancer? A model reconciling the current contradiction

NSAIDs are powerful chemopreventive agents for colon cancer, but their mechanism of action remains unknown. Their best recognized pharmacological property is inhibition of the enzyme cyclooxygenase (COX), which catalyzes the synthesis of prostaglandins; however, additional effects are well documented. Current studies on the mechanism of the chemopreventive effect of NSAIDs lead to two contradictory conclusions: NSAIDs prevent colon cancer either by inhibiting the activity of COX, or through mechanisms that do not require COX inhibition. To resolve this apparent conflict, after examining several alternatives, we propose a model, which assumes that both mechanisms are correct but that they exert their effect either on different steps of the multistep process of colon carcinogenesis or on different control mechanisms. This postulated dual action of NSAIDs may explain their remarkable effectiveness in colon cancer prevention. Unraveling these mechanistic details can be very rewarding for the design of more refined approaches to cancer chemoprevention and for a deeper understanding of colorectal carcinogenesis.

Sodium salicylate inhibits proliferation and induces G1 cell cycle arrest in human pancreatic cancer cell lines

The mutations most common in pancreatic cancer decrease the ability to control G1 to S cell cycle progression and cellular proliferation. In colorectal cancer cells, nonsteroidal anti-inflammatory drugs inhibit proliferation and induce cell cycle arrest. We examined whether sodium salicylate, an aspirin metabolite, could inhibit proliferation in human pancreatic cancer cell lines (BxPC3 and Panc-1). Quiescent cells were treated with medium containing 10% fetal calf serum, with or without salicylate. Cellular proliferation was measured by MTT assay and bromodeoxyuridine incorporation. The fractions of cells in G0/G1, S, and G2/M phases of the cell cycle were quantitated by fluorescence-activated cell sorting. Results were compared between groups by two-tailed t test. Cyclin D1 expression was determined by Western blot analysis and prostaglandin E2 expression by enzyme-linked immunosorbent assay. Serum-starved cells failed to proliferate, with most arrested in the G1 phase. Salicylate significantly inhibited serum-induced progression from G1 to S phase, cellular proliferation, and the expression of cyclin D1. The concentrations at which 50% of serum-induced proliferation was inhibited were 1.2 mmol/L (Panc-1) and 1.7 mmol/L (BxPC3). The antiproliferative effect of sodium salicylate was not explained by inhibition of prostaglandin E2 production. This study provides further evidence in a noncolorectal cancer model for the antineoplastic effects of nonsteroidal anti-inflammatory drugs.

Specific inhibition of cyclooxygenase 2 restores antitumor reactivity by altering the balance of IL-10 and IL-12 synthesis

Cyclooxygenase-2 (COX-2), the enzyme at the rate-limiting step of prostanoid production, has been found to be overexpressed in human lung cancer. To evaluate lung tumor COX-2 modulation of antitumor immunity, we studied the antitumor effect of specific genetic or pharmacological inhibition of COX-2 in a murine Lewis lung carcinoma (3LL) model. Inhibition of COX-2 led to marked lymphocytic infiltration of the tumor and reduced tumor growth. Treatment of mice with anti-PGE2 mAb replicated the growth reduction seen in tumor-bearing mice treated with COX-2 inhibitors. COX-2 inhibition was accompanied by a significant decrement in IL-10 and a concomitant restoration of IL-12 production by APCs. Because the COX-2 metabolite PGE2 is a potent inducer of IL-10, it was hypothesized that COX-2 inhibition led to antitumor responses by down-regulating production of this potent immunosuppressive cytokine. In support of this concept, transfer of IL-10 transgenic T lymphocytes that overexpress IL-10 under control of the IL-2 promoter reversed the COX-2 inhibitor-induced antitumor response. We conclude that abrogation of COX-2 expression promotes antitumor reactivity by restoring the balance of IL-10 and IL-12 in vivo.

Monocytically differentiating HL60 cells proliferate rapidly before they mature

1alpha,25-Dihydroxyvitamin D(3) (D(3)) provokes growth arrest and monocytic differentiation in myeloid cells. Although it is usually assumed that the cellular events leading to growth arrest start within one cell cycle of D(3) addition, there is also evidence that D(3) provokes the expression of proliferation-related genes and accelerates cell division. Herein we clarify the relationship between proliferation and maturation in differentiating HL60 cells. Cells were cultured singly, D(3) was added at various stages of the cell cycle, the progeny were counted, and the proportions of mature monocytes were determined. Initially, the D(3)-treated cells proliferated at an accelerated rate, and they matured only later. If cells encountered D(3) early in G1 they divided two to four times before maturing, and if they encountered D(3) later in the cell cycle they underwent an extra division. Indomethacin slows HL60 cell multiplication by prolonging G1, and when these slower-growing cells were exposed to D(3), they matured after the usual period but underwent one division less than indomethacin-free cells. Contrary to common assumptions, we conclude that promyeloid cells do not initiate growth arrest or monocytic maturation immediately after exposure to D(3). Instead, an encounter with D(3) early in G1 sets in train a complex differentiation program. This consists of 2-3 days of rapid proliferation-probably employing cell cycles with a shortened G1 phase-that is followed by growth arrest and maturation. As a result, a single D(3)-treated promyeloid cell gives rise to 10 or more mature monocytes. These observations not only explain why "differentiating" cells express proliferation-related characteristics soon after D(3) addition, but they also show that the process of D(3)-induced monocytic differentiation is much more complex than has previously been realized.

Selective cyclo-oxygenase-2 inhibitors aggravate ischaemia-reperfusion injury in the rat stomach

1. Effects of indomethacin, the selective cyclo-oxygenase (COX)-2 inhibitors NS-398 and DFU, and dexamethasone on gastric damage induced by 30 min ischaemia followed by 60 min reperfusion (I-R) were investigated in rats. Modulation of gastric levels of COX-1 and COX-2 mRNA by I-R was evaluated using Northern blot and reverse transcription-polymerase chain reaction. 2. I-R-induced gastric damage was dose-dependently aggravated by administration of indomethacin (1 - 10 mg kg(-1)), NS-398 (0.4 - 4 mg kg(-1)) or DFU (0.02 - 2 mg kg(-1)) as assessed macroscopically and histologically. 3. Likewise, administration of dexamethasone (1 mg kg(-1)) significantly increased I-R damage. 4. Low doses of 16, 16-dimethyl-prostaglandin(PG)E(2), that did not protect against ethanol-induced mucosal damage, reversed the effects of the selective COX-2 inhibitors, indomethacin and dexamethasone. 5. I-R had no effect on gastric COX-1 mRNA levels but increased COX-2 mRNA levels in a time-dependent manner. Dexamethasone inhibited the I-R-induced expression of COX-2 mRNA. 6. I-R was not associated with a measurable increase in gastric mucosal formation of 6-keto-PGF(1alpha) and PGE(2). PG formation was substantially inhibited by indomethacin (10 mg kg(-1)) but was not significantly reduced by NS-398 (4 mg kg(-1)), DFU (2 mg kg(-1)) or dexamethasone (1 mg kg(-1)). 7. The findings indicate that selective COX-2 inhibitors and dexamethasone markedly enhance gastric damage induced by I-R. Thus, whereas COX-2 has no essential role in the maintenance of gastric mucosal integrity under basal conditions, COX-2 is rapidly induced in a pro-ulcerogenic setting and contributes to mucosal defence by minimizing injury. This suggests that in certain situations selective COX-2 inhibitors may have gastrotoxic effects.

High expression of cyclooxygenase-2 in macrophages of human colonic adenoma

Cyclooxygenase (COX)-2 is a possible molecular target for suppression of colon carcinogenesis by non-steroidal anti-inflammatory drugs (NSAIDs). However, the expression of COX-2 in human colonic tumors during the adenoma-carcinoma sequence has not been elucidated. In the present study, we examined immuno-histochemically the expression and localization of the COX-2 protein in human colonic adenomas and cancers. Twelve human colonic adenomas and 9 advanced cancers were studied. Immunoreactive COX-2 was predominantly and strongly expressed in sub-epithelial interstitial cells broadly present in the surface area of adenomas. The staining pattern of macrophages was similar to that observed for COX-2 in adenomas. Adjacent normal colonic mucosa was negative for COX-2 expression. In contrast, COX-2 was relatively weakly expressed in both tumor cells and interstitial cells in advanced colon cancers. In conclusion, the target of NSAIDs in preventing colon carcinogenesis may be the COX-2 expressed in interstitial cells, possibly macrophages, of colonic adenomas.

PPARdelta is an APC-regulated target of nonsteroidal anti-inflammatory drugs

PPARB was identified as a target of APC through the analysis of global gene expression profiles in human colorectal cancer (CRC) cells. PPARdelta expression was elevated in CRCs and repressed by APC in CRC cells. This repression was mediated by beta-catenin/Tcf-4-responsive elements in the PPARdelta promotor. The ability of PPARs to bind eicosanoids suggested that PPARdelta might be a target of chemopreventive non-steroidal anti-inflammatory drugs (NSAIDs). Reporters containing PPARdelta-responsive elements were repressed by the NSAID sulindac. Furthermore, sulindac was able to disrupt the ability of PPARdelta to bind its recognition sequences. These findings suggest that NSAIDs inhibit tumorigenesis through inhibition of PPARdelta, the gene for which is normally regulated by APC.

Cyclooxygenase knockout mice: models for elucidating isoform-specific functions

The development of cyclooxygenase (COX) deficient mice has allowed investigation into the individual physiological roles of the COX-1 and COX-2 isoforms. In the following article, the phenotypes of the two Ptgs (genes coding for COX-1 and COX-2) knockouts are summarized, and recent studies to investigate the effects of COX deficiency on cancer susceptibility, inflammatory response, gastric ulceration, and female reproductive processes are discussed. Also, the development and potential uses of mice deficient in both COX isoforms and mice containing only a single copy of one isoform are discussed. Additionally, when the data permit, the effects of genetic ablation of COX activity are compared with those of pharmacological inhibition of COX activity by nonsteroidal anti-inflammatory drugs. The data suggest that prostaglandins derived via the individual COX isoforms have separate as well as common functions. However, for the maintenance of normal physiology, it appears that deficiency of COX-2 has more profound effects than deficiency of COX-1.

Lovastatin augments sulindac-induced apoptosis in colon cancer cells and potentiates chemopreventive effects of sulindac

BACKGROUND & AIMS

3-Hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase inhibitors (HRIs) were found incidentally to reduce new cases of colon cancer in 2 large clinical trials evaluating coronary events, although most patients in both treatment and control group were taking nonsteroidal anti-inflammatory drugs (NSAIDs). NSAIDs are associated with reduced colon cancer incidence, predominantly by increasing apoptosis. We showed previously that lovastatin induces apoptosis in colon cancer cells. In the present study we evaluated the potential of combining lovastatin with sulindac for colon cancer chemoprevention.

RESULTS

Lovastatin, 10-30 micromol/L, augmented sulindac-induced apoptosis up to 5-fold in 3 colon cancer cell lines. This was prevented by mevalonate (100 micromol/L) or geranylgeranylpyrophosphate (10 micromol/L) but not farnesylpyrophosphate (100 micromol/L), suggesting inhibition of geranylgeranylation of target protein(s) as the predominant mechanism. In an azoxymethane rat model of chemical-induced carcinogenesis, the total number of colonic aberrant crypt foci per animal (control, 161 +/- 11) and the number of foci with 4+ crypts (control, 40 +/- 4.5) decreased to 142 +/- 14 (NS) and 43 +/- 2.9 (NS), respectively, with 50 ppm lovastatin alone; to 137 +/- 5.4 (P = 0.053) and 36 +/- 2.1 (NS) with 80 ppm sulindac alone; and to 116 +/- 8.1 (P = 0.004) and 28 +/- 3.4 (P = 0.02) when 50 ppm lovastatin and 80 ppm sulindac were combined.

CONCLUSIONS

Addition of an HRI such as lovastatin may augment chemopreventive effects of NSAIDs or/and may allow lower, less toxic doses of these drugs to be used.

Sulindac derivatives inhibit growth and induce apoptosis in human prostate cancer cell lines

We examined the activity of two metabolites of sulindac (a nonsteroidal anti-inflammatory drug), sulindac sulfide and sulindac sulfone (exisulind, Prevatec), and a novel highly potent analog of exisulind (CP248) on a series of human prostate epithelial cell lines. Marked growth inhibition was seen with the BPH-1, LNCaP, and PC3 cell lines with IC50 values of about 66 microM, 137 microM, and 64 nM for sulindac sulfide, exisulind, and CP248, respectively. DNA flow cytometry and 4',6'-diamido-2-phenylindole (DAPI) staining indicated that these three compounds also induced apoptosis in all of these cell lines. Similar growth inhibition also was seen with the PrEC normal human prostate epithelial cell line, but these cells were resistant to induction of apoptosis at concentrations up to 300 microM, 1 mM, and 750 nM of sulindac sulfide, exisulind, and CP248, respectively. Derivatives of LNCaP cells that stably overexpress bcl-2 remained sensitive to growth inhibition and induction of apoptosis by these compounds. In vitro enzyme assays indicated that despite its high potency in inhibiting growth and inducing apoptosis, CP248, like exisulind, lacked cyclooxygenase (COX-1 and COX-2) inhibitory activity even at concentrations up to 10 mM. Moreover, despite variations of COX-1 and COX-2 expression, the three benign and malignant prostate cell lines showed similar sensitivity to growth inhibition and induction of apoptosis by these three compounds. Therefore, sulindac derivatives can cause growth inhibition and induce apoptosis in human prostate cancer cells by a COX-1 and -2 independent mechanism, and this occurs irrespective of androgen sensitivity or increased expression of bcl-2. These compounds may be useful in the prevention and treatment of human prostate cancer.

Sulindac inhibits activation of the NF-kappaB pathway

Sulindac is a non-steroidal anti-inflammatory agent that is related both structurally and pharmacologically to indomethacin. In addition to its anti-inflammatory properties, sulindac has been demonstrated to have a role in the prevention of colon cancer. Both its growth inhibitory and anti-inflammatory properties are due at least in part to its ability to decrease prostaglandin synthesis by inhibiting the activity of cyclooxygenases. Recently, we demonstrated that both aspirin and sodium salicylate, but not indomethacin, inhibited the activity of an IkappaB kinase beta (IKKbeta) that is required to activate the nuclear factor-kappaB (NF-kappaB) pathway. In this study, we show that sulindac and its metabolites sulindac sulfide and sulindac sulfone can also inhibit the NF-kappaB pathway in both colon cancer and other cell lines. Similar to our previous results with aspirin, this inhibition is due to sulindac-mediated decreases in IKKbeta kinase activity. Concentrations of sulindac that inhibit IKKbeta activity also reduce the proliferation of colon cancer cells. These results suggest that the growth inhibitory and anti-inflammatory properties of sulindac may be regulated in part by inhibition of kinases that regulate the NF-kappaB pathway.

Effects of nonsteroidal anti-inflammatory drugs and prostaglandins on osteoblastic functions

It has been reported that nonsteroidal anti-inflammatory drugs (NSAIDs) suppress bone repair and bone remodeling but only mildly inhibit bone mineralization at the earlier stage of the repair process. We proposed that the proliferation and/or the earlier stage of differentiation of osteoblasts may be affected by NSAIDs. This study was designed to investigate whether NSAIDs affect the proliferation and/or differentiation of osteoblasts and whether these effects are prostaglandin (PG) mediated. The effects of PGE1 and PGE2, indomethacin, and ketorolac on thymidine incorporation, cell count, intracellular alkaline phosphatase (ALP) activity, and Type I collagen content in osteoblast-enriched cultures derived from fetal calvaria were evaluated. The results showed that both PGs and NSAIDs inhibited DNA synthesis and cell mitosis in a time- and concentration-dependent manner. However, intracellular ALP activity and Type I collagen content were stimulated at an earlier stage of differentiation in osteoblasts. These results suggested that (i) the inhibitory effect of ketorolac on osteoblastic proliferation contributes to its suppressive effects on bone repair and remodeling in vivo; (ii) PGEs and NSAIDs may be involved in matrix maturation and biologic bone mineralization in the earlier stage of osteoblast differentiation; and (iii) the effects of ketorolac and indomethacin on cell proliferation and differentiation may not be through the inhibition of the synthesis of PGE1 or PGE2.

Malignant transformation and antineoplastic actions of nonsteroidal antiinflammatory drugs (NSAIDs) on cyclooxygenase-null embryo fibroblasts

In this study, we use primary embryonic fibroblasts derived from cyclooxygenase-deficient transgenic embryos to further investigate the role of the two cyclooxygenases, cyclooxygenase 1 (COX-1) and cyclooxygenase 2 (COX-2), in the process of neoplastic transformation. Cells with either, neither, or both of the cyclooxygenases were transformed by Ha-ras and/or SV40. Our results show that when a cyclooxygenase enzyme is present, the transformed cells have marked increases in COX-2 and/or COX-1 expression. Nevertheless, each type of cell, deficient in either or both cyclooxygenases, can be readily transformed at almost equal efficiency. Different nonsteroidal antiinflammatory drugs (NSAIDs) were used to examine their possible antineoplastic effects on the transformed cells, which have various levels of expression of COX-1 or COX-2. Our results show that NSAIDs suppress the colony formation in soft agar in a dosage-dependent manner in the absence of the cyclooxygenase(s). Thymidine incorporation and apoptosis analyses further demonstrate that the NSAIDs are effective in the cyclooxygenase-null cells. Our findings with cyclooxygenase knockout cells confirm recent reports that some of the antiproliferative and antineoplastic effects of NSAIDs are independent of the inhibition of either COX-1 or COX-2. They also show that transformation is independent of the status of cyclooxygenase expression, suggesting that the involvement of the cyclooxygenases in tumorigenesis may occur at later steps.

Inhibition of pristane-induced peritoneal plasmacytoma formation

While the mechanism of how Indo inhibits PCTGEN is not established, Several hypothetical explanations provide new potential experimental approaches. Indo may block production of cytokines such as Il-6 in accessory cells that are critical for B-cell growth, viability and maturation, or it may directly target B cells via PPAR-gamma receptors. The latter mode of action is described in other cell types but not yet defined in B cells.

Differential apoptosis by indomethacin in gastric epithelial cells through the constitutive expression of wild-type p53 and/or up-regulation of c-myc

Nonsteroidal anti-inflammatory drug (NSAID)-induced apoptosis is considered to be an important mechanism in the antineoplastic effects and damage produced by the drugs in the gastrointestinal tract. In this study, two different gastric cancer cell lines, MKN28 (mutant-type p53) and AGS (wild-type p53), were compared as to growth inhibition, apoptosis, and cell cycle and apoptosis-related gene expression in response to indomethacin treatment. Cell growth was measured by MTT (3-(4,5-dimethylthiazole-2-yl)-2,5-diphenyl tetrazolium bromide) assay. Apoptosis was characterized by acridine orange staining and DNA fragmentation, and cell cycle kinetics by flow cytometry. The mRNA and protein levels of p53, p21waf1/cip1, and c-myc were determined by Northern and Western blotting. The results showed that indomethacin initiated growth inhibition and apoptosis in both cell lines without cell cycle shifting. AGS cells were more sensitive to growth inhibitory activity and apoptosis of indomethacin than MKN28 cells. In MKN28 cells, the levels of p53, p21waf1/cip1, and c-myc mRNA remained unchanged over the 24-hr treatment with indomethacin, but the p53 protein level was elevated after 4 hr. There was no change in the p21waf1/cip1 and c-myc protein levels in the MKN28 cells. In AGS cells, a progressive increase in c-myc mRNA and protein levels was noted, while p53 and p21waf1/cip1 remained unchanged. It can be concluded that wild-type p53 and/or up-regulation of c-myc is associated with indomethacin-mediated differential apoptosis in gastric epithelial cells.

Selective potentiation of drug cytotoxicity by NSAID in human glioma cells: the role of COX-1 and MRP

Here, we report that nonsteroidal anti-inflammatory drugs (NSAID) enhance the cytotoxic effects of doxorubicin and vincristine in T98G human malignant glioma cells. The cytotoxicity of BCNU, cisplatin, VM26, camptothecin, and cytarabine is unaffected by NSAID. No free radical formation is induced by doxorubicin or vincristine in the absence or presence of NSAID. Doxorubicin and vincristine cytotoxicity in the absence or presence of NSAID are unaffected by free radical scavengers. Functional inhibitors of phospholipase A2 (PLA2), such as dexamethasone and quinacrine, do not mimick the effects of NSAID. T98G cells, but not LN-18, LN-229, LN-308, or A172 glioma cells, express cyclooxygenase (COX-1) and NSAID do not modulate drug cytotoxicity in the other cell lines, except T98G. Thus, augmentation of doxorubicin and vincristine cytotoxicity by NSAID correlates with COX-1 expression. However, ectopic expression of COX-1 in LN-229 cells does not induce the phenotype of T98G cells, indicating that COX-1 inhibition does not mediate the effects of NSAID on drug cytotoxicity. In contrast, a multidrug resistance (MDR) phenotype due to expression of the multidrug resistance-associated protein (MRP) is most prominent in T98G cells and is amenable to modulation by indomethacin, suggesting that inhibition of MRP is at least in partly responsible for the potentiation of doxorubicin and vincristine cytotoxicity by NSAID.

Nonsteroidal anti-inflammatory drugs attenuate epidermal growth factor-induced proliferation independent of prostaglandin synthesis inhibition

BACKGROUND

The mechanism(s) whereby nonsteroidal anti-inflammatory drugs (NSAIDs) attenuate colorectal tumor growth remains poorly understood. This study determined if NSAIDs decreased epidermal growth factor (EGF)-induced proliferation in human colonic tumor (Caco-2) cells and whether this process involved the inhibition of prostaglandin (PG) synthesis.

METHODS

Caco-2 cells were serum-starved (48 h) and subsequently treated (48 h) with either serum-free media or EGF (10 ng/ml) +/- physiologic and noninjurious (as determined by LDH release) concentrations of aspirin, indomethacin, and ibuprofen. PG synthesis was measured by EIA. Proliferation was quantitated with two assays: cellular protein and nucleic acid content.

RESULTS

NSAID treatment did not inhibit growth in cells treated with only serum-free media. Cells exposed to EGF demonstrated a significant increase in PGE2, protein, and nucleic acid. Levels of other eicosanoids (PGI2, TXA2) were minimal both before and after EGF treatment. Despite varying degrees of PGE2 inhibition, each NSAID group equally attenuated EGF-induced protein and nucleic acid synthesis. The correlation between PGE2 levels and protein (R2 = 0.56) or nucleic acid (R2 = 0.54) was poor. Finally, the addition of a physiologically appropriate concentration of exogenous PGE2 failed to reverse NSAID-induced growth inhibition.

CONCLUSION

These data suggest that NSAIDs, independent of PG synthesis inhibition, attenuate EGF-induced proliferation in Caco-2 cells. This may provide one explanation for how NSAIDs limit colonic neoplasia.

Sulindac sulfide, but not sulindac sulfone, inhibits colorectal cancer growth

Sulindac sulfide, a metabolite of the nonsteroidal antiinflammatory drug (NSAID) sulindac sulfoxide, is effective at reducing tumor burden in both familial adenomatous polyposis patients and in animals with colorectal cancer. Another sulindac sulfoxide metabolite, sulindac sulfone, has been reported to have antitumor properties without inhibiting cyclooxygenase activity. Here we report the effect of sulindac sulfone treatment on the growth of colorectal carcinoma cells. We observed that sulindac sulfide or sulfone treatment of HCA-7 cells led to inhibition of prostaglandin E2 production. Both sulindac sulfide and sulfone inhibited HCA-7 and HCT-116 cell growth in vitro. Sulindac sulfone had no effect on the growth of either HCA-7 or HCT-116 xenografts, whereas the sulfide derivative inhibited HCA-7 growth in vivo. Both sulindac sulfide and sulfone inhibited colon carcinoma cell growth and prostaglandin production in vitro, but sulindac sulfone had no effect on the growth of colon cancer cell xenografts in nude mice.

Metabolic targets of cancer chemoprevention: interruption of tumor development by inhibitors of arachidonic acid metabolism

Tumor promotion is understood as a process that favors the clonal outgrowth of single mutated (initiated) cells to premalignant lesions through co-mitogenic and anti-apoptotic effects. This process can be evoked by repeated induction of a regenerative tissue response as achieved either by irritation and wounding or by agents (tumor promoters) that interact with the corresponding pathways of cellular signaling. Metabolic processes regulated by such pathways and essential for tumor development are potential targets of cancer chemoprevention. Examples are provided by the expression of ornithine decarboxylase and the activation of eicosanoid formation from arachidonic acid. Arachidonic acid metabolism is a particularly attractive and important target of chemopreventive measures. Its induction is a characteristic response to tissue damage and irritation and an apparently critical event in epithelial tumor promotion. Inhibitors of eicosanoid formation, such as nonsteroidal anti-inflammatory drugs, rank among the most powerful chemopreventive agents in animal models and have been shown to halve the incidence of colorectal cancer in man. Recently, the role of cyclooxygenase-2 (COX-2)-catalyzed prostaglandin synthesis has been the subject of much attention. COX-2 is a typical 'emergency enzyme', since in most tissues it is transiently induced only in the course of repair and defense reactions. In epithelial neoplasia, i.e. in skin and colorectal tumors, the enzyme is constitutively overexpressed along different molecular pathways, and it seems to be critically involved in tumor promotion. Consequently, specific COX-2 inhibitors have been shown to exhibit considerable cancer chemopreventive potential. The putative role of other pathways of arachidonic acid metabolism in tumor promotion and malignant progression is presently under investigation.

Chemopreventive effect of N-(2-cyclohexyloxy-4-nitrophenyl)methane sulfonamide (NS-398), a selective cyclooxygenase-2 inhibitor, in rat colon carcinogenesis induced by azoxymethane

Non-steroidal anti-inflammatory drugs (NSAIDs) such as sulindac and indomethacin inhibit colon carcinogenesis, and selective cyclooxygenase (COX)-2 inhibitors are considered to be potential chemopreventive agents without the side effects of usual NSAIDs. We reported that NS-398, N-(2-cyclohexyloxy-4-nitrophenyl)methane sulfonamide, suppressed the formation of preneoplastic lesions, aberrant crypt foci (ACF), induced by azoxymethane (AOM) in a short-term assay of rat colon carcinogenesis. In this study, we examined the effects of long-term NS-398 administration on rat colon carcinogenesis. After three AOM treatments at weekly intervals, a dose of 10 mg/kg of NS-398 in 5% Arabic gum solution was administered by gavage three times per week in group 2 until the termination of the experiment. Rats in group 1 were fed in a basal diet and given 5% Arabic gum solution alone after AOM treatment. At 40 weeks after the first AOM treatment, all rats were killed and the whole intestines including colon were examined. While the incidences of whole intestinal and colon neoplasms in group 1 were 84.6% and 80.8%, respectively, those in group 2 (given NS-398) were 51.9% and 44.4% respectively (P=0.0177 and P=0.0103 by Fisher's exact test, respectively). The multiplicities in group 2 (0.67+/-0.78 and 0.48+/-0.58) were also decreased significantly compared with those (1.39+/-1.10 and 1.08+/-0.74) in group 1 (P<0.01 by Welch's method and P<0.002 by Student's t test, respectively). In immunohistochemistry for proliferative cell nuclear antigen (PCNA), the PCNA-stained cell index (7.40+/-0.5) in group 2 was significantly decreased from that in group 1 (14.03+/-0.82) (P<0.001 by Welch's method). The results suggest that NS-398, a selective COX inhibitor, has a chemopreventive activity against colon carcinogenesis without side-effects such as gastric ulceration.

Relationship of beta-catenin and Bcl-2 expression to sulindac-induced regression of intestinal tumors in Min mice

Non-steroidal anti-inflammatory drugs (NSAIDs) can cause regression of early intestinal tumors and although this is believed to involve cyclooxygenase-2 and apoptosis, the molecular mechanisms remain unclear. Cytoplasmic and nuclear beta-catenin are overexpressed in many of these lesions and Bcl-2, which inhibits apoptosis, may also be elevated during the course of intestinal tumorigenesis. We recently showed that sulindac causes regression of 70-80% of small intestinal tumors in Min/+ mice within 4 days, but does not have the same impact on colonic lesions; after 20 days of treatment the tumor load stabilizes at 10-20% of that in untreated animals. The aim of this study was to determine if NSAID-induced regression of intestinal adenomas might be associated with changes in beta-catenin or Bcl-2 expression. Intestinal tumors from Min/+ mice were harvested after treatment with sulindac for 2, 4 or 20 days and evaluated for expression of beta-catenin and Bcl-2 using immunohistochemistry. There was a > or = 50% decrease in beta-catenin (P = 0.001) and diminishing Bcl-2 (P = 0.019) in small intestinal tumors harvested between 2 and 4 days of treatment when compared with untreated controls. In contrast, small intestinal tumors from animals treated for 20 days were not significantly different from untreated controls. Colonic tumors expressed higher levels of Bcl-2 than those from the small intestine and did not show any significant changes in either Bcl-2 or beta-catenin expression after treatment. Results suggest that modulation of aberrant beta-catenin expression occurs during NSAID-induced regression of intestinal adenomas and that Bcl-2 may confer resistance to these effects.

Non-steroidal anti-inflammatory drug-induced apoptosis in gastric cancer cells is blocked by protein kinase C activation through inhibition of c-myc

Apoptosis plays a major role in gastrointestinal epithelial cell turnover, ulcerogenesis and tumorigenesis. We have examined apoptosis induction by non-steroidal anti-inflammatory drugs (NSAIDs) in human gastric (AGS) cancer cells and the role of protein kinase C (PKC) and apoptosis-related oncogenes. After treatment with aspirin or indomethacin, cell growth was quantified by MTT assay, and apoptosis was determined by acridine orange staining, DNA fragmentation and flow cytometry. The mRNA and protein of p53, p21waf1/cip1 and c-myc was detected by Northern and Western blotting respectively. The influence of PKC on indomethacin-induced apoptosis was determined by co-incubation of 12-O-tetradecanoylphorbol 13-acetate (TPA). The role of c-myc was determined using its antisense oligonucleotides. The results showed that both aspirin and indomethacin inhibited cell growth and induced apoptosis of AGS cells in a dose- and time-dependent manner, without altering the cell cycle. Indomethacin increased c-myc mRNA and protein, whereas p53 and p21wafl/cip1 were unchanged. Down-regulation of c-myc by its antisense oligonucleotides reduced apoptosis induction by indomethacin. TPA could inhibit indomethacin-induced apoptosis and accumulate cells in G2/M. Overexpression of c-myc was inhibited by TPA and p21waf1/cip1 mRNA increased. In conclusion, NSAIDs induce apoptosis in gastric cancer cells which may be mediated by up-regulation of c-myc proto-oncogene. PKC activation can abrogate the effects of NSAIDs by decreasing c-myc expression.

Exisulind (sulindac sulfone) suppresses growth of human prostate cancer in a nude mouse xenograft model by increasing apoptosis

OBJECTIVES

Recent studies have shown that Exisulind, a sulfone metabolite of the nonsteroidal anti-inflammatory drug (NSAID) sulindac, has inhibitory activity in vitro with cultured human prostate cancer cells. To determine whether this effect might be pharmacologically relevant in vivo, we tested whether Exisulind therapy could suppress the growth of human prostate cancer cells in a nude mouse xenograft model.

METHODS

Thirty athymic nude mice were injected subcutaneously in the flank with 1 x 10(7) LNCaP human prostate tumor cells. All mice received a control diet for 21 days. One group of mice was continued on this control diet for an additional 4 weeks, a second group was switched to a diet supplemented with 0.05% Exisulind (40% of maximal tolerated dose [MTD]), and a third group was switched to a diet supplemented with 0.1% Exisulind (80% MTD) for the additional 4 weeks. Tumor growth was measured through the 4-week test period, and subsequently tissue sections from the various groups were tested for apoptotic and dividing cells by quantified use of the TUNEL assay and a bromodeoxyuridine (BrdU) incorporation immunoassay.

RESULTS

Tumors grew by 158%, 24%, and 18% for the control and 0.05% and 0.1% Exisulind groups, respectively (P = 0.02) during the 4-week test period. Immunohistochemical studies on excised tumors showed an increased number of apoptotic bodies in the treated groups versus the control group (P<0.0001) but no change in the number of BrdU positive cells.

CONCLUSIONS

This is the first study to show a direct in vivo effect of an NSAID-derived drug, lacking cyclooxygenase inhibitory activity, in a xenograft model of prostate cancer. Clinical studies to evaluate the effects of Exisulind against prostate cancer in humans are warranted.

Selective inhibitors of cyclooxygenase-2: are they really effective, selective, and GI-safe?

Selective inhibitors of the "inducible" isoform of cyclooxygenase (COX-2) have been suggested to be effective analgesic and anti-inflammatory drugs while sparing the gastrointestinal (GI) tract of injury. There is some experimental and early clinical evidence to support this hypothesis. However, some important questions remain regarding the utility of selective COX-2 inhibitors. For example, estimates of the selectivity of COX-2 inhibitors based on in vitro studies are likely to be poor predictors of selectivity in vivo. Efficacy with selective blockade of COX-2 may be inferior to that achieved with combined inhibition of COX-1 and COX-2. Furthermore, in situations in which there is inflammation or ulceration in the GI tract, COX-2 produces prostaglandins that are essential for repair. In these circumstances, inhibition of COX-2 leads to delay of ulcer healing and exacerbation of inflammation. Some caution should therefore be exercised before the theory is fully accepted that selective COX-2 inhibitors are effective anti-inflammatory drugs that spare the GI tract of injury.

The effect of selective cyclooxygenase inhibitors on intestinal epithelial cell mitogenesis

INTRODUCTION

Previous research has demonstrated that nonsteroidal anti-inflammatory agents alter the incidence of colorectal cancer. It has been postulated that the response may be due to the effect of these agents on the activities of the cyclooxygenase (COX) enzymes. The COX enzymes catalyze the conversion of arachidonic acid to biologically active prostanoids. Two forms of COX have been identified. COX-1 is a constitutive enzyme, generally involved in cell functions, while COX-2 is commonly an enzyme which is inducible in response to various stimuli, including mitogens. Recently, specific inhibitors of COX-1 and COX-2 enzymes have been developed.

PURPOSE

The present study was undertaken to determine the effects of specific COX-1 and COX-2 inhibitors on the proliferation and the induction of apoptosis of intestinal epithelial cells.

METHODS

A continuously proliferating rat small intestinal cell line (IEC-18) and a mouse colon cancer cell line (WB-2054) were utilized for these experiments. The cells were placed in microwells with serum-free or serum-supplemented media. The effects of serum on proliferation were then evaluated in the presence of the COX-1 inhibitor, valerylsalicyclic acid (VSA), the COX-2 inhibitor, SC-58125, or indomethacin. The presence of COX-1 and COX-2 protein was evaluated by Western blotting. Proliferation of intestinal cells was quantitated by incorporation of [3H]thymidine into DNA and cell counting, and apoptosis was determined by evaluating cell attachment. COX activity was evaluated by prostaglandin E2 production measured by enzyme-linked immunoabsorbent assay (ELISA).

RESULTS

Western blotting of IEC-18 and WB-2054 cell protein demonstrated COX-1 enzyme in cells incubated in serum-free media with increased COX-1 expression produced by incubation in media supplemented with 10% serum. COX-2 enzyme was not demonstrated in serum-free media; however, it was present in cells maintained in 10% serum-supplemented media. Spontaneous DNA synthesis was present in both cell lines and serum increased proliferation. In both cell lines [3H]thymidine incorporation stimulated by serum was inhibited by the COX-2 inhibitor SC-58125, but not by the COX-1 inhibitor VSA. Both indomethacin and SC-58125 produced a dose-dependent increase in apoptotic ratios in both cell lines. PGE2 formation, stimulated by serum, was inhibited by SC-58125, VSA, and indomethacin.

CONCLUSION

A differential effect on intestinal cell mitogenesis was seen with different COX inhibitors. The COX-2 inhibitor, but not the COX-1 inhibitor, significantly inhibited [3H]thymidine incorporation in both cell types, suggesting COX-2 inhibitors may be specific inhibitors of normal epithelial cell proliferation and growth of malignant cells. SC-58125, a selective inhibitor of COX-2, has a potent apoptosis inducing effect. The inhibition of PGE2 production did not correlate with the inhibition of proliferation, suggesting the two processes are unrelated.

Combination oral antiangiogenic therapy with thalidomide and sulindac inhibits tumour growth in rabbits

Neovascularization facilitates tumour growth and metastasis formation. In our laboratory, we attempt to identify clinically available oral efficacious drugs for antiangiogenic activity. Here, we report which non-steroidal anti-inflammatory drugs (NSAIDs) can inhibit corneal neovascularization, induced by basic fibroblast growth factor (bFGF) or vascular endothelial growth factor (VEGF). This antiangiogenic activity may contribute to the known effects of NSAIDs on gastric ulcers, polyps and tumours. We found that sulindac was one of the most potent antiangiogenic NSAIDs, inhibiting bFGF-induced neovascularization by 50% and VEGF-induced neovascularization by 55%. Previously, we reported that thalidomide inhibited growth factor-induced corneal neovascularization. When we combined sulindac with thalidomide, we found a significantly increased inhibition of bFGF- or VEGF-induced corneal neovascularization (by 63% or 74% respectively) compared with either agent alone (P < 0.01). Because of this strong antiangiogenic effect, we tested the oral combination of thalidomide and sulindac for its ability to inhibit the growth of V2 carcinoma in rabbits. Oral treatment of thalidomide or sulindac alone inhibited tumour growth by 55% and 35% respectively. When given together, the growth of the V2 carcinoma was inhibited by 75%. Our results indicated that oral antiangiogenic combination therapy with thalidomide and sulindac may be a useful non-toxic treatment for cancer.

Prostaglandins in the stomach: an update

Prostaglandins (PGs) are responsible for regulation of various physiologic activities in many tissues and organs, including the stomach. Recent studies have shown new crucial roles of PGs in the stomach. Activation of inflammatory cytokines and neutrophils may cause acute gastric mucosal lesions and recurrence of ulcers, which are induced by noxious stimuli such as nonsteroidal antiinflammatory drugs (NSAIDs), stress and Helicobacter pylori (H. pylori). These phenomena are PG-dependent because exogenous PGs reverse them. PG deficiency and H. pylori may worsen the quality of ulcer healing in terms of inflammatory responses, which are related to future ulcer recurrence. Neutrophils, monocytes/macrophages, and adhesion molecules are involved in the mechanism of recurrence caused by inflammatory cytokines. PGs accelerate ulcer healing, possibly via angiogenesis, epithelial cell proliferation, production of growth factors such as hepatocyte growth factor and transforming growth factor beta, reconstruction of extracellular matrices, and suppression of inflammatory cell infiltration, in addition to gastroprotective mechanisms. The PG synthase cyclooxygenase (COX) has two forms, COX-1 and COX-2. COX-2, but not COX-1, contributes to ulcer healing. Moreover, recent studies suggest the involvement of COX-2 in development of gastric and colon carcinoma. This may be linked to the chemopreventive effect of NSAIDs.

Induction of apoptotic DNA fragmentation by nonsteroidal anti-inflammatory drugs in cultured rat gastric mucosal cells

Nonsteroidal anti-inflammatory drugs (NSAIDs) have been shown to cause apoptosis in several cell lines including transformed chicken embryo fibroblasts and human colon cancer cells. We herein report the apoptotic effect of NSAIDs in a non-transformed cell line derived from the rat gastric mucosa, RGMI (rat gastric mucosa cell first). 1-[p-Chlorobenzoyl]-5-methoxy-2-methylindole-3-acetic acid (indomethacin) and sodium 2-(2,6-dichloroanilino)phenylacetate (sodium diclofenac), potent and non-selective inhibitors of cyclooxygenase, were found to induce DNA fragmentation in RGM1 cells in a time- and concentration-dependent manner. The expression of mRNA for cyclooxygenase-2 was hardly detected in the intact cells but was clearly enhanced when the cells were incubated with the two NSAIDs. In contrast, the expression of mRNA for cyclooxygenase-1 was constitutive and was never affected by NSAIDs. The effect of [3,4-di(4-methoxyphenyl)-5-isoxazolyl] acetic acid (mofezolac), a potent and highly preferential inhibitor of cyclooxygenase-1, and N-[2-(cyclohexyloxy)-4-nitrophenyl]methanesulphonamide (NS-398), a selective inhibitor of cyclooxygenase-2, on DNA fragmentation and cyclooxygenase-2 mRNA expression was weak compared to the effect of indomethacin or sodium diclofenac. The DNA fragmentation induced by sodium diclofenac was hardly affected by the exogenous addition of 16,16-dimethyl prostaglandin E2 but was inhibited by caspase inhibitors such as Ac-YVAD-CHO and Ac-DEVD-CHO. The present data provide the first evidence that NSAIDs, such as indomethacin and sodium diclofenac, cause apoptotic DNA fragmentation in cultured gastric mucosal cells, and also indicate the involvement of caspases rather than the inhibition of cellular prostaglandin synthesis in the apoptotic process.

Rectal cancer after sulindac therapy for a sporadic adenomatous colonic polyp

Like adenomatous polyps in familial adenomatous polyposis, some sporadic colorectal polyps have been reported to regress in response to sulindac administration. However, a rapidly growing invasive rectal cancer developed in one of 15 patients with sulindac-treated sporadic adenomatous colorectal polyps 16 months after sulindac treatment. In this patient, both the adenomatous polyp that responded partially to sulindac and the rectal cancer developing after sulindac therapy showed immunostaining for cyclooxygenase-2. Although short term sulindac therapy seems to be able to cause some adenomatous colorectal polyps to regress, 4 months of sulindac therapy may not reliably prevent colorectal cancer development in these patients.

The effects of nonsteroidal anti-inflammatory drugs on immune functions of human peripheral blood mononuclear cells

It is generally accepted that the nonsteroidal anti-inflammatory drugs (NSAIDs) exhibit anti-inflammatory effects primarily through inhibition of prostaglandin (PG) synthesis. However, effects of NSAIDs on immune responses are not fully understood. This study investigated effects of indomethacin and a new NSAID (d-2-[4-(3-methyl-2-thienyl)phenyl]propionic acid, termed as M-5011 in this study) on cytokine production, lymphocyte proliferation, activities of natural killer (NK) and lymphokine activated killer (LAK) cells and secretion of immunoglobulin (Ig). Both indomethacin and M-5011 augmented interleukin (IL)-2 production, whereas they suppressed IL-6 production both at the protein and mRNA levels. These two NSAIDs augmented proliferation of phytohemagglutinin (PHA)-stimulated PBMC and enhanced NK and LAK cell activities. In contrast, indomethacin was more potent than M-5011 in inhibition of both PG synthesis and Ig secretions by pokeweed mitogen (PWM)-stimulated PBMC. These results suggest that these two NSAIDs equally augment cell-mediated immunity, whereas indomethacin was more potent than M-5011 in the inhibition of humoral immunity and PG synthesis.

Apoptosis induced by sulindac sulfide in epithelial and mesenchymal cells from human abdominal neoplasms

We investigated whether the therapeutic action of sulindac, used for the treatment of familial adenomatous polyposis, desmoid tumors, and against colon cancer, could be mediated by its active metabolite, sulindac sulfide, in cell growth and apoptosis on cell lines derived from abdominal neoplasms. Sulindac sulfide actions on cell growth and apoptosis were evaluated in epithelial human colon tumor 8 (HCT8) cell line and mesenchymal cell lines (bovine bone endothelial (BBE) cell line, desmoid tumor-derived cells, human colorectal cancer-derived fibroblasts). Sulindac sulfide (0.1-60 microg/ml) induced a dose-dependent inhibition of cell proliferation of all cell lines tested. Apoptosis was induced at doses of 20 and 40 microg/ml, respectively, in BBE and HCT8 cells with no effect on desmoid tumor cells and colorectal cancer-derived fibroblasts. Since mesenchymal cells respond to clinically effective concentrations of the compound, its preferential action on the stromal compartment of intestinal polyps, desmoid tumors and colon cancer can be proposed, with consequent regression of the tumor.

Clinical models of chemoprevention for colon cancer

Colon cancer is a common malignancy in the westernized world and is incurable in its advanced stages. This article summarizes the currently available information on colorectal cancer chemoprevention. A brief outline of the incidence and etiologic factors is followed by a discussion of the evidence on which chemopreventive strategies for colon cancer are modeled. This includes a description of the development of surrogate endpoint biomarkers and experimental models to study colorectal cancer chemopreventives, a review of the promising colorectal cancer chemopreventives, and a discussion of the issues to be addressed in the design of future chemoprevention trials. The article concludes with an emphasis on the development and validation of biomarkers and selection of high-risk cohorts using genetic and epidemiologic tools as the main goals of future colon cancer chemoprevention trials before large-scale, risk-reduction trials are conducted.

Aspirin suppresses the mutator phenotype associated with hereditary nonpolyposis colorectal cancer by genetic selection

Nonsteroidal anti-inflammatory drugs (NSAIDs) are well-known cancer preventives, which have been largely attributed to their antiproliferative and apoptosis-inducing activities. In this study, we show that microsatellite instability (MSI) in colorectal cancer cells deficient for a subset of the human mismatch repair (MMR) genes (hMLH1, hMSH2, and hMSH6), is markedly reduced during exposure to aspirin or sulindac [or Clinoril, which is chemically related to indomethacin (Indocin)]. This effect was reversible, time and concentration dependent, and appeared independent of proliferation rate and cyclooxygenase function. In contrast, the MSI phenotype of a hPMS2-deficient endometrial cancer cell line was unaffected by aspirin/sulindac. We show that the MSI reduction in the susceptible MMR-deficient cells was confined to nonapoptotic cells, whereas apoptotic cells remained unstable and were eliminated from the growing population. These results suggest that aspirin/sulindac induces a genetic selection for microsatellite stability in a subset of MMR-deficient cells and may provide an effective prophylactic therapy for hereditary nonpolyposis colorectal cancer kindreds where alteration of the hMSH2 and hMLH1 genes are associated with the majority of cancer susceptibility cases.

Expression of 15-lipoxygenase by human colorectal carcinoma Caco-2 cells during apoptosis and cell differentiation

We studied arachidonic acid metabolism and the expression of cyclooxygenase (Cox) and 15-lipoxygenase (15-LO) in the human colorectal carcinoma cell line, Caco-2, which undergo apoptosis and cell differentiation in the presence of sodium butyrate (NaBT). Caco-2 cells expressed very low levels of Cox-1 but highly expressed Cox-2. NaBT treatment shifted the arachidonic acid metabolites by cell lysates from prostaglandins to 15-hydroxyeicosatetraenoic acid, indicating the presence of a 15-LO. Linoleic acid, an excellent substrate for 15-LO, was metabolized poorly by the Caco-2 cells, but NaBT treatment shifted metabolism to 15-LO metabolite, 13(S)-hydroxyoctadecadienoic acid. Caco-2 cells expressed a 15-LO but only after treatment with NaBT, as determined by Northern blotting. Immunoblotting with anti-human 15-LO antibody detected a 72-kDa band in NaBT-treated Caco-2 cells. Expression of 15-LO mRNA was dependent on the duration of NaBT treatment, with the highest expression observed between 10 and 24 h. Results from expression and metabolism studies with arachidonic and linoleic acid cells indicated Cox-2 was responsible for the lipid metabolism in control cells, whereas 15-LO was the major enzyme responsible after NaBT induction of apoptosis and cell differentiation. The 15-LO in Caco-2 cells was characterized as human reticulocyte 15-LO by reverse transcription-polymerase chain reaction and restriction enzyme analysis. The expression of 15-LO and 15-hydroxyeicosatetraenoic acid or 13(S)-hydroxyoctadecadienoic acid formation correlates with cell differentiation or apoptosis in Caco-2 cells induced by NaBT. The addition of nordihydroguaiaretic acid, a lipoxygenase inhibitor, significantly increased NaBT-induced apoptosis, whereas the addition of indomethacin did not alter NaBT-induced apoptosis in the Caco-2 cells. However, indomethacin treatment decreased the expression of Cox-2 in NaBT-treated cells and significantly increased the expression of 15-LO during NaBT treatment. These studies suggest a role for 15-LO, in addition to Cox-2, in modulating NaBT-induced apoptosis and cell differentiation in human colorectal carcinoma cells.

Aspirin and Salicylate Induce Apoptosis and Activation of Caspases in B-Cell Chronic Lymphocytic Leukemia Cells

We analyzed the effect of aspirin, salicylate, and other nonsteroidal antiinflammatory drugs (NSAIDs) on the viability of B-chronic lymphocytic leukemia (B-CLL) cells. Aspirin induced a decrease in cell viability in a dose- and time-dependent manner. The mean IC50 for cells from 5 patients was 5.9 ± 1.13 mmol/L (range, 4.4 to 7.3 mmol/L). In some cases, 2.5 mmol/L aspirin produced an important cytotoxic effect after 4 days of incubation. No effect was observed with other NSAIDs, at concentrations that inhibit cyclooxygenase, such as ketorolac (10 μmol/mL), NS-398 (100 μmol/mL), or indomethacin (20 μmol/mL), thus suggesting the involvement of cyclooxygenase-independent mechanisms in aspirin-induced cytotoxicity. Salicylate also produced dose-dependent cytotoxic effects on B-CLL cells and the mean IC50 for cells from 5 patients was 6.96 ± 1.13 mmol/L (range, 5 to 7.8 mmol/L). Both aspirin and salicylate induced DNA fragmentation and the proteolytic cleavage of poly(ADP(adenosine 5′-diphosphate)-ribose) polymerase (PARP), demonstrating that both compounds induce apoptosis of B-CLL cells. Finally, inhibition of caspases by Z-VAD.fmk blocked proteolytic cleavage of PARP, DNA fragmentation, and cytotoxicity induced by aspirin. Mononuclear cells from normal donors showed a lower sensitivity than cells from B-CLL patients to aspirin as determined by analysis of cell viability. B and T lymphocytes from normal donors and T lymphocytes from CLL patients are more resistant to aspirin-induced apoptosis, as determined by analysis of phosphatidylserine exposure. These results indicate that aspirin and salicylate induce apoptosis of B-CLL cells by activation of caspases and that this activation involves cyclooxygenase-independent mechanisms.

© 1998 by The American Society of Hematology.

Aspirin and Salicylate Induce Apoptosis and Activation of Caspases in B-Cell Chronic Lymphocytic Leukemia Cells

We analyzed the effect of aspirin, salicylate, and other nonsteroidal antiinflammatory drugs (NSAIDs) on the viability of B-chronic lymphocytic leukemia (B-CLL) cells. Aspirin induced a decrease in cell viability in a dose- and time-dependent manner. The mean IC50 for cells from 5 patients was 5.9 ± 1.13 mmol/L (range, 4.4 to 7.3 mmol/L). In some cases, 2.5 mmol/L aspirin produced an important cytotoxic effect after 4 days of incubation. No effect was observed with other NSAIDs, at concentrations that inhibit cyclooxygenase, such as ketorolac (10 μmol/mL), NS-398 (100 μmol/mL), or indomethacin (20 μmol/mL), thus suggesting the involvement of cyclooxygenase-independent mechanisms in aspirin-induced cytotoxicity. Salicylate also produced dose-dependent cytotoxic effects on B-CLL cells and the mean IC50 for cells from 5 patients was 6.96 ± 1.13 mmol/L (range, 5 to 7.8 mmol/L). Both aspirin and salicylate induced DNA fragmentation and the proteolytic cleavage of poly(ADP(adenosine 5′-diphosphate)-ribose) polymerase (PARP), demonstrating that both compounds induce apoptosis of B-CLL cells. Finally, inhibition of caspases by Z-VAD.fmk blocked proteolytic cleavage of PARP, DNA fragmentation, and cytotoxicity induced by aspirin. Mononuclear cells from normal donors showed a lower sensitivity than cells from B-CLL patients to aspirin as determined by analysis of cell viability. B and T lymphocytes from normal donors and T lymphocytes from CLL patients are more resistant to aspirin-induced apoptosis, as determined by analysis of phosphatidylserine exposure. These results indicate that aspirin and salicylate induce apoptosis of B-CLL cells by activation of caspases and that this activation involves cyclooxygenase-independent mechanisms.

© 1998 by The American Society of Hematology.

Cyclooxygenase-independent chemoprevention with an aspirin derivative in a rat model of colonic adenocarcinoma

Aspirin decreases the risk of colorectal cancer, reportedly through suppression of cyclooxygenase (COX) activity. Using a rat model of colonic adenocarcinoma, we compared the chemopreventative effects of aspirin versus a nitric oxide-releasing derivative (NCX-4016) which does not inhibit COX. Beginning six weeks after intracolonic administration of trinitrobenzene sulfonic acid, the rats were given azoxymethane weekly (15 mg/kg i.p.) for 4 weeks. Over the same 4-week period, the rats were treated daily with vehicle, aspirin (10 mg/kg) or NCX-4016 (equimolar dose). Six weeks later, the number of aberrant crypt foci (an early preneoplastic lesion) were blindly counted by light microscopy. Effects of aspirin vs. NCX-4016 on COX-1 and COX-2 activity were compared, as was their analgesic activity. Rats receiving vehicle developed a mean of 856 +/- 260 aberrant crypt foci in the colon. Aspirin reduced the number of aberrant crypt foci by 64%, while NCX-4016 produced an 85% reduction. Aspirin, but not NCX-4016, markedly suppressed systemic COX-1 and COX-2 activity, and colonic prostaglandin synthesis. Despite not inhibiting COX, NCX-4016 exhibited comparable analgesic activity to aspirin. These results demonstrate that NCX-4016, a nitric oxide-releasing aspirin derivative, exhibited superior chemopreventative effects to aspirin in this model of colon cancer. This effect occurred independent of inhibition of COX-1 or COX-2.

Sulindac sulfide alters the expression of cyclin proteins in HT-29 colon adenocarcinoma cells

Sulindac sulfide (SS), the active metabolite of the colon cancer chemopreventive compound sulindac, inhibits the proliferation of HT-29 colon cancer cells mainly by inducing cell quiescence. We determined by bivariate flow-cytometric analysis both the DNA and cyclin protein content of individual cells. Thus, we assessed in detail the expression of several cyclins during the cell-cycle phases and demonstrated that SS (i) decreases the expression of cyclins B1 and E and (ii) increases the expression of cyclins D1, D2 and D3, particularly in the G1 phase of the cell cycle. SS-induced apoptotic cells expressed both E- and D-type cyclins but not cyclin B1. The changes in cyclin expression combined with reduced catalytic activity of cyclin-dependent kinases could explain in molecular terms the anti-proliferative effect of SS on HT-29 colon cancer cells. These changes may contribute to the chemopreventive effect of sulindac.

Nonsteroidal anti-inflammatory drugs, short-chain fatty acids, and reactive oxygen metabolism in human colorectal cancer cells

Nonsteroidal anti-inflammatory drugs (NSAIDs) and short-chain fatty acids are effective suppressors of colorectal cancer that may work in part by accentuating apoptosis of transformed cells. Since reactive oxygen species (ROS) can play an important role in regulating cell growth and cell death, we determined the effect of the NSAIDs indomethacin and salicylic acid, and the short-chain fatty acids butyrate and propionate on ROS metabolism in the HT-29 human colorectal carcinoma cell line. We find that all of these agents increase cellular peroxide generation, as determined by two independent assays. Arachidonic acid was also found to increase ROS generation, and could synergize with indomethacin in this reaction. The NSAIDs and short-chain fatty acids under study all possess a carboxyl group, and this carboxyl group is essential for salicylic acid's ability to increase ROS production. Although the two NSAIDs examined increase peroxide production, they were both found to suppress superoxide generation by vitamin K3 (menadione), a redox cycling compound similar to those found in the colon. The short-chain fatty acids did not have this activity. The ability of these NSAIDs and short-chain fatty acids to alter cellular ROS metabolism may contribute to their chemopreventive activity.

On the induction of cyclooxygenase-2, inducible nitric oxide synthase and soluble phospholipase A2 in rat mesangial cells by a nonsteroidal anti-inflammatory drug: the role of cyclic AMP

One of the challenges in the therapy with anti-inflammatory drugs is the avoidance of gastrointestinal side effects, which may be achieved by selective inhibition of cyclooxygenase (COX) -2. CGP 28238 is reported with these characteristics inhibiting selectively the COX-2 activity at nanomolar concentrations. However, we report here on a novel action of this compound uncovered during the application of higher concentrations. In rat mesangial cells, CGP 28238 induced the mRNA and the protein of COX-2 as well as those of inducible nitric oxide synthase and soluble phospholipase A2. In the case of COX-2, this stimulation had no effect on the production of COX-2 metabolites because of the effective blockade of the enzyme. In contrast, the level of NO produced by the cells increased in a concentration-dependent manner from 1.2 to 12.5 nmol of nitrite/3 x 10(5) cells. Furthermore, in combination with low doses of IL-1 CGP 28238 superinduced the formation of nitrite. The observed effects were independent of the inhibition of prostaglandin formation, as suggested by the failure of the potent COX inhibitor diclofenac to cause similar effects. Furthermore, the activity and expression of enzymes downstream of the COX step, such as prostacyclin synthase, were unaffected by CGP 28238. The inductive action of CGP 28238 could be blocked by inhibitors for tyrosine kinases and protein kinase A, such as genistein and KT5720, respectively. The increase in intracellular cAMP concentration in rat mesangial cells and the inhibition by CGP 28238 of phosphodiesterase 4 activity with an IC50 value of 23 muM gave a rationale to explain the underlying mechanisms for the induction of the inflammatory response genes COX-2, soluble phospholipase A2 and inducible NO synthase in rat mesangial cells.

A chelate theory for the mechanism of action of aspirin-like drugs

Two hundred years after the discovery of the pharmaceutical usefulness of aspirin, it and aspirin-like drugs, a family with an ever-increasing number of members, are an indispensable part of modern life. However, the question as to how these drugs work in the body has remained unsettled. It is postulated here that this group of drugs may exert their therapeutic (and adverse) effects by chelating various physiologically important metallic cations in the body. The chelate theory is supported by the vast majority, if not all, of the observations on these drugs made in the past.

Mechanisms underlying nonsteroidal antiinflammatory drug-mediated apoptosis

Nonsteroidal antiinflammatory drugs (NSAIDs) can inhibit colorectal tumorigenesis and are among the few agents known to be useful for the chemoprevention of neoplasia. Here, we show that the tumor suppressive effects of NSAIDs are not likely to be related to a reduction in prostaglandins but rather are due to the elevation of the prostaglandin precursor arachidonic acid (AA). NSAID treatment of colon tumor cells results in a dramatic increase in AA that in turn stimulates the conversion of sphingomyelin to ceramide, a known mediator of apoptosis. These results have significant implications for understanding and improving colon cancer chemoprevention.

Cyclooxygenase-2-selective antagonists do not inhibit growth of colorectal carcinoma cell lines

Non-steroidal anti-inflammatory drugs (NSAIDs) reduce the incidence of colorectal carcinoma. We now report that the potent cyclooxygenase-1 inhibitor indomethacin had no effect on the growth of human colorectal carcinoma cell lines in vitro at concentrations up to 30 microM. The selective cyclooxygenase-2 inhibitors L-745337 and NS-398 reduced cyclooxygenase activity, but had no effect on cell growth at concentrations as high as 100 microM. Our results provide direct evidence that inhibition of cyclooxygenase activity does not necessarily inhibit the growth of colorectal carcinoma cell lines and imply that the growth-inhibitory effects of NSAIDs in vitro are not mediated by inhibition of cyclooxygenases.

Effect of aspirin on induction of apoptosis in HT-29 human colon adenocarcinoma cells

Aspirin (ASA) and other nonsteroidal anti-inflammatory drugs (NSAIDs) inhibit colorectal tumorigenesis. Apoptosis is a critical determinant of tissue mass homeostasis and may play a role in carcinogenesis. We studied the effect of ASA on the survival of a human colon cancer cell line using more sensitive methods than we had applied previously. ASA induced apoptosis in HT-29 colon adenocarcinoma cells at concentrations > or =1 mM as established by: (a) morphological changes consistent with apoptosis in cells examined by fluorescence microscopy and semi-thin cell sections, and (b) DNA strand breaks: 45% of the cells were TdT-mediated dUTP nick end labeling (TUNEL) positive at 3 mM at 72 hr, and 70% were positive by the comet assay. Electron microscopy also confirmed the induction of apoptosis by ASA. ASA-induced apoptosis was not associated with: (a) a ladder pattern on genomic DNA electrophoresis, or (b) a subdiploid peak on flow cytometry. Apoptotic bodies were virtually absent on standard morphological assessments and only a few were detected on semi-thin sections. For the above reasons, this apoptosis induced by ASA is "atypical," and the unusual features of ASA-induced apoptosis, besides their taxonomic value, may offer clues to the mechanisms that control the process of apoptosis or perhaps the cancer chemopreventive properties of this compound. These findings demonstrate that ASA induces apoptosis in human colon cancer cells, bolstering the hypothesis that apoptosis may be a mechanism by which NSAIDs inhibit colon carcinogenesis. These findings should be examined in animal and/or clinical research studies in vivo.