Molecular analysis of the effects of Piroxicam and Cisplatin on mesothelioma cells growth and viability

Nonsteroidal anti-inflammatory drugs (NSAIDs) have been proposed for prevention and treatment of a variety of human cancers. Piroxicam, in particular, has been recently shown to exert significant anti-tumoral activity in combination with cisplatin (CDDP) on mesothelioma cells. However, the mechanisms through which NSAIDs regulate the cell cycle as well as the signal pathways involved in the growth inhibition, remain unclear. In the present study, using two mesothelioma cell lines, MSTO-211H and NCI-H2452, we have investigated the influence of piroxicam alone and in association with CDDP on proliferation, cell cycle regulation and apoptosis. In both cell lines a significant effect on cell growth inhibition, respect to the control, was observed with all the drugs tested. Moreover, treatment with piroxicam or CDDP alone altered the cell cycle phase distribution as well as the expression of some cell cycle regulatory proteins in both cell lines. These effects were increased, even if in a not completely overlapping manner, after treatment with the association of piroxicam and CDDP. In particular, the two drugs in NCI cell line had a synergistic effect on apoptosis, probably through activation of caspase 8 and caspase 9, while the most evident targets among the cell cycle regulators were cyclin D1 and p21waf1. These results suggest that the association of piroxicam and CDDP specifically triggers cell cycle regulation and apoptosis in different mesothelioma cell lines and may hold promise in the treatment of mesothelioma.


Background
Nonsteroideal anti-inflammatory drugs (NSAIDs) are commonly used as anti-inflammatory and analgesic drugs. However, several epidemiological studies have found that treatment with NSAIDs is associated with a reduced risk for cancer [1,2]. Since then, the antineoplas-tic effects of NSAIDs have been evaluated in many randomized clinical trials [3][4][5][6][7][8]. NSAIDs inhibit cyclooxygenases (COX-1 and COX-2), key enzymes in arachidonic acid metabolism, which catalyze an intermediate step in the production of prostaglandins, prostacyclins and thromboxanes [9]. Although COX-1 is constitutively expressed in many tissues, COX-2 is detected negligibly in most tissues but can be induced by cytokines and stress in various cell types. In several cancers COX-2 is overexpressed and this over-expression appears to be involved in the development of cancer by promoting cell division [10,11], inhibiting apoptosis [12,13], altering cell adhesion and enhancing neovascularization [14][15][16]. The inhibition of COX-2 by NSAIDs blocks these activities and, thus, may account for the anti-carcinogenic effects of these drugs. However, NSAIDs can also act through COX-independent mechanisms and each NSAID appears to have its own, more or less specific, COX-independent target [17,18]. Recently, an overexpression of COX-2 has been demonstrated in malignant mesothelioma [19][20][21] and this has provided the rationale to explore the use of COX inhibitors for the prevention and/or treatment of this tumour.
Malignant mesothelioma (MM) is one of the most lethal human tumours, which incidence is expected to increase in Europe within the next 20 years [22]. Prognosis is poor and patients have a median survival of few months in either treated or untreated cases [23,24]. Mesothelioma represents a therapeutic problem since it is resistant to radiation, chemotherapy or surgical resection. Recent randomized studies on treatment of mesothelioma with combined chemotherapy demonstrate a survival benefit when a combination of cisplatin and antifolate drugs has been used [25,26]. Moreover, the combination of chemotherapy followed by surgery supplemented by postoperative radiotherapy in cases of incomplete resection, seems to be a promising treatment [27]. Unfortunately, none of these forms of treatment has significant impact on the progression and the outcome of mesothelioma and new therapeutic approaches must be investigated for a more successful treatment of this disease. Recently, the antitumour effects of NSAIDs have been studied on in vitro and in vivo experimental MM models. In particular, NS398 has produced a significant reduction of proliferation level in MM cell lines established and derived from previously untreated patients [28] and celecoxib has proved to be efficient in inhibiting mesothelioma cell growth [29] In a previous work we have demonstrated a significant anti-proliferative effect of piroxicam in two mesothelioma cell lines (MSTO-211H and NCI-H2452), not expressing COX-2, treated with piroxicam alone or in combination with CDDP [30]. The combination of the two drugs resulted in a synergistic effect, suggesting that piroxicam sensitizes mesothelioma cells to CDDP cytotoxicity. This result was confirmed also in vivo, by using a mesothelioma flank tumour model and a mesothelioma orthotopic tumour model [30].
In this work we have investigated the molecular mechanisms of cell cycle perturbation caused by piroxicam, CDDP and their association in two mesothelioma cell lines MSTO-211H and NCI-H2452. The resulting knowledge of the biological events elicited by these drugs in exerting their anti-tumour effects, could represent the basis for identifying specific molecular target of mesothelioma cells and for leading to advances in therapy.

Reagents
Piroxicam (FELDENE; Pfizer, New York, NY) was supplied as a 60 mmol/L injectable solution and CDDP (Pharmacia-Italia, Nerviano, MI, Italy) as a 50 mmol/L injectable solution. Primary mouse monoclonal antibody against human p27 Kip1 (p27) and primary rabbit polyclonal antibody against human p21 waf1 (p21) were supplied by S. Cruz Biotechnology, Inc. Santa Cruz, CA, U.S.A.. Anti cyclin D1 (Cyc D1) monoclonal antibody was supplied by Cell signalling Technology, Inc. Danvers, MA, U.S.A. and anti cyclin A (Cyc A) monoclonal antibody by Calbiochem, EMD Chemicals, Inc. La Jolla CA, U.S.A. Anti actin monoclonal antibody was supplied by SIGMA, Saint Louis, Missouri, U.S.A. and anti COX-2 monoclonal antibody by Cayman Chemical, Ann Arbor, MI, U.S.A. Horseradish peroxidase-conjugated secondary antibodies were supplied from Santa Cruz Biotechnology, Inc. Santa Cruz, CA, U.S.A., and ECL and Super ECL Western blotting detection reagents from Amersham-Pharmacia, Uppsala, Sweden.

Cell lines
The human mesothelioma cell lines MSTO-211H (MSTO) and NCI-H2452 (NCI) were purchased from the American Type Culture Collection (Rockville, MD). Cells were cultured as monolayers in flasks using American Type Culture Collection complete growth medium in a humidified atmosphere containing 5% CO 2 at 37°C.

Cell growth
Cells were treated as mentioned above and were counted 3, 6, 24 and 48 hours after beginning of treatment. Experiments were repeated in triplicate and media values were calculated. Cell growth was expressed as percent of control (untreated cells) and was compared between different treatment groups by Bonferroni test. P values < 0.05 was regarded as statistically significant. SPSS software (version 14.00, SPSS, Chicago) was used for statistical analysis.

Cell cycle analysis on cancer cells
Unsynchronized cells in the mid log phase were seeded at a density of 10 6 in T25 flasks. After 16 hours, cells were treated with piroxicam and/or CDDP, as described in the previous section. At 24 and 48 hours, adherent and floating cells were harvested, resuspended in staining solution containing propidium iodide (50 µg/ml), RNAse A, sodium citrate (0.1%), NP40 (0.1%) in PBS 1×, and incubated for 30 minutes in the dark. Cell cycle distribution of 20.000 cells was analyzed with a FACScalibur flow cytometer (Becton Dickinson, Franklin Lakes, NJ) by ModFit version 3 Technology (Verity) as previously reported [31,32]. Pre-G1 picks were analysed as indicative of sub-G1 apoptotic population. All the experiments were performed at least 3 times and values were expressed in mean ± SD.

Caspase 3, 8 and 9 assays
Caspase activity was detected within whole living cells using BIOMOL and B-BRIDGE Kits supplied with cell-permeable fluorescent substrates. The fluorescent substrates for caspase 3, 8 and 9 were respectively FAM-DEVD-FMK, FAM-LETD-FMK, FAM-LEHD-FMK. Cells were washed twice in cold PBS and incubated for 1 h in ice with the corresponding substrates as recommended by suppliers. Cells were analysed after washing using the CellQuest software applied to a FACScalibur (BD). Experiments were performed in triplicate and values were expressed in mean ± SD.

Protein analysis by western blotting
Cell lysates were prepared by treating cells with ice-cold lysis buffer (Roche Applied Science, Mannheim, Germany) for 20 minutes followed by centrifugation at 4°C for 15 minutes. 40 µg of proteins were separated on 10% SDS-PAGE gels and then transferred on polyvinylidene fluoride (PVDF) membrane. For p21 and Cyc D1 detection in NCI were used 80 µg of proteins. Membranes were incubated with specific antibodies diluted 1:250 (p21, p27 and Cyc A), 1:500 (anti Cyc D1) and 1:1,000 (anti COX-2). Probing with anti-actin antibody diluted 1:10,000 was used to normalize the sample loading. Horseradish peroxidase-conjugated secondary antibodies were used at 1:3,000 dilution. Antibody reaction was visualized using ECL and Super ECL Western blotting detection reagents. The experiments were done in triplicate with comparable results and electrophoretic bands were analyzed by Scion Image program.

Prostaglandin E2 assay
Prostaglandin E2 levels were detected in medium from cell culture by using the Correlate-EIA High Sensitivity Prostaglandin E2 Enzyme Immunoassay kit from Assay Designs (Ann Arbor, MI).

Effects of piroxicam alone and in combination with CDDP on mesothelioma cells growth
To determine the effects of piroxicam alone or in combination with CDDP on cellular growth, MSTO and NCI cells were treated with the two drugs (as described in Methods) for different times. Cell growth was assessed by cell counts using as control the untreated cells (Fig 1). In both cell lines a significant effect on cell growth inhibition, respect to the control, was observed at 24 and 48 hours with all the drugs tested. Interestingly, in MSTO the combination of piroxicam and CDDP resulted in a stronger growth inhibition, respect to the other treatments, at 3 and 6 hours.

COX-2 and prostaglandin E2 protein expression levels in the MSTO and NCI cell line
In order to determine if some of the anti-proliferative effects of piroxicam were due to its role as COX inhibitor, COX-2 protein levels in MSTO and NCI cells were assessed by western blot. Both mesothelioma cell lines expressed not detectable level of COX-2 ( fig. 2). As positive controls, a human prostate cancer cell line (PC3) lysate expressing high levels of COX-2 [30], a human osteosarcoma cell line (U-2 OS) lysate expressing low levels [unpublished results], and ovine COX-2 standard were used. The not detectable expression of COX-2 was further confirmed by the lack of detectable levels of prostaglandin E2 in cell medium analyzed (detection limit for the used kit was 8 to 10 pg/ml) (data not shown).

Effects of piroxicam alone and in combination of CDDP on Cell Cycle Phase Distribution
To dissect the effects on cell cycle distribution of the treatment with piroxicam and/or CDDP, we performed FACS analysis ( fig. 3). Cells were treated with piroxicam and/or CDDP for 24 and 48 hours. Cell cycle analysis on MSTO ( fig. 3 left panel) showed that piroxicam was able to induce only a mild alteration, in particular a decrease in the S and an increase in the G1 phase of the cell cycle. On the other hand, CDDP treatment induced a significant block of the cells in S phase at 24 hours that, subsequently, evolves in part in apoptosis and in part into G2/ M phase. Cell cycle analysis on NCI ( fig. 3 right panel), on the other hand, showed that piroxicam was not able to induce a significant modification in the cell cycle distribution, except for a slight increase in the apoptosis fraction. CDDP, on the contrary, caused, as in MSTO, an increase in the S and apoptotic fractions, while it determined a complete disappearance of cells in G2/M phase.
The results obtained with the combination of the two drugs showed a stronger and sinergic induction of apoptosis respect to single treatment in both cell lines.

Piroxicam and CDDP treatment induces caspase activation
In order to deeply investigate the apoptotic pathways activated by the two drugs, we monitored the enzymatic activity of the initiator caspases 8 and 9 and of the effector caspase 3 using flow cytometry technology ( fig. 4). When apoptosis was analysed by caspase 9 and 8 activity in MSTO and NCI, we observed that, in both cell lines, caspase 9 was activated more in presence of the double treatment, which thereby showed at least an additive effect in induction of cell death. On the other hand, caspase 8 was significantly activated in MSTO by both the single drugs and their combination in a similar manner, whereas in NCI all treatments only produced a slight increase. Aiming to understand the effects of these initiatior caspase activations, we tested the activity of the effector caspase 3 in these conditions. As shown in fig. 4, we detected in NCI an increased activation by the combined treatment, whereas MSTO seems more directly sensitive to the CDDP treatment alone. The effects of treatments in NCI is in agreement with the hypothesis that piroxicam and CDDP cooperates for the induction of apoptosis via caspase 8, 9 and 3.

Effects of piroxicam alone and in combination with CDDP on cell cycle regulatory proteins
To identify the molecular pathways targeted by the two drugs, the expression levels of several cell cycle regulatory  6), after treatment with piroxicam or CDDP. Interestingly, in NCI cell line the effect on p21 was more evident when a combination of CDDP and piroxicam was used.

Inhibition of MSTO (left panel) and NCI (right panel) by piroxicam and/or CDDP
No appreciable changes were observed in the levels of Cyc A and p27 in both mesothelioma cell lines with all the different drug treatments (data not shown).

Discussion
MM is an insidious tumor with a dismal prognosis. Due to the low incidence of the disease, only few randomized studies have been performed to date. The reported response rates to the different therapeutic protocols ranged from 10 to 45% with no clear advantage in terms of survival that is between 4 and 12 months [25,33]. Various drugs have been tested in different combinations so far; among the most commonly employed are doxorubicin, cyclophosphamide, CDDP, carboplatin, gemcitabine, and pemetrexed. Recently, a benefit in response rate was observed with a combination of premetrexed and cisplatin and, similarly, by adding raltitrexed to cisplatin alone [25,26]. However, new and more effective chemotherapic drugs are urgently required for a more successful treatment of this deadly disease.
Cancer, indeed, is viewed now not only as being the consequence of uncontrolled proliferation, but is also considered to be the result of an altered balance between cell proliferation and cell apoptosis. Therefore, therapies combining abrogation of cell cycle checkpoints and enhancement of the cell death mechanisms should be investigated in MM.
Our previous studies demonstrated that piroxicam induced a significant inhibition of proliferation in two mesothelioma cell lines (MSTO and NCI). Moreover, we demonstrated a marked tumour growth inhibition and an extended survival of mice treated with a combination of piroxicam and CDDP in peritoneal mesotheliomas induced by MSTO intra-peritoneal injection [30]. Intrigued by the possible convergent activities exerted by CDDP and piroxicam, we studied the effects of those treatments in single dosage or in combination on cell growth in NCI and MSTO cells. Our data suggest that piroxicam has anti-proliferative effects in both cell lines, a finding that is consistent with data from the literature showing that piroxicam may target multiple component of the molecular machinery regulating cell cycle. Moreover, in MSTO, piroxicam in association with CDDP caused a stronger growth inhibition at 3 and 6 hours respect to the single drug treatments. Based on the fact that in both cell lines the level of COX-2 is very low and PGE2 is undetectable, we assume that piroxicam in these cells exerts its anti-proliferative activity via COX-2/prostaglandin E2independent mechanisms. These data confirm recent reports that some of the anti-proliferative and anti-neoplastic effects of NSAIDs are independent of the inhibition of COX enzymes [34][35][36]. For example, in colon carcinoma the regulation by NSAIDs of the molecular pathways of cellular proliferation includes modulation of Ras and MAP Kinase signal transduction pathways, nuclear factor kB protein activation and cyclin expression [37][38][39][40]. Moreover, the treatment of human colon carcinoma cells either with indomethacin or aspirin results in a decrease in β-catenin/TCF transcriptional activity and cyclin D1 expression [41].
To dissect the effects on cell cycle distribution and apoptosis of the treatment with piroxicam and/or CDDP, we performed FACS analysis. This analysis demonstrated that the combination of the two drugs is able to perturb the cell cycle regulation of the mesothelioma cells in a not completely overlapping manner in the two cell lines. In particular, in MSTO cells the combination of the two drugs was very effective in causing an important increase of apoptotic fraction essentially due to CDDP action. Probably, the slight increase of apoptotic index between CDDP alone and the combined treatment is not a consequence of a direct action of piroxicam on cell cycle distri-Effects of piroxicam alone and in combination with CDDP on cell cycle regulatory proteins Figure 5 Effects of piroxicam alone and in combination with CDDP on cell cycle regulatory proteins. CycD1 was analysed by western blotting in MSTO (left side) and NCI (right side) treated with piroxicam and/or CDDP for different times. Electrophoretic bands were analyzed using Scion Image program. Experiments were repeated in triplicate and media values and standard deviations were calculated. CTRL = control; P = piroxicam; C = CDDP.
bution but is the result of a sensibilization of cells to CDDP action, as we previously demonstrated [30]. On the other hand, in NCI cells there is an important synergic effect on apoptosis. In this last case the better efficacy of the combined treatment could be correlated with the increase of the three analyzed caspases. This is in agreement with the hypothesis that piroxicam and CDDP cooperate for the induction of apoptosis via caspase 8, 9 and 3 activation in NCI cells. Nevertheless, the greater sensitivity of the MSTO cell line to apoptosis induced by the single CDDP is in line with the higher caspase 8 and 9 activation.
Our data support previous observations [30,42,43] of a synergistic effect of piroxicam, when used in combination with CDDP on cell cycle regulation and apoptosis. Inter-estingly, the specific check-points affected by this treatment are not overlapping in different cell lines, this demonstrating that the effects of piroxicam could be on multiple targets. In our experimental model, when we looked at the molecular regulators of cell cycle, we detected in MSTO and NCI a significant down-regulation of Cyc D1 and in NCI an up-regulation of p21 expression level. These effects are consistent with the results of growth inhibition described above. Interestingly, our research group has recently demonstrated that p21 expression is correlated with prognosis in mesothelioma patients, thus further confirming the key role played by this molecule in mesothelioma progression [44,46]. Nevertheless, genomic and proteomic technologies should be used to confirm and better analyze the molecular effects demonstrated by our biochemical approach.
Effects of piroxicam alone and in combination with CDDP on cell cycle regulatory proteins Figure 6 Effects of piroxicam alone and in combination with CDDP on cell cycle regulatory proteins. p21 was analysed by western blotting in MSTO (left side) and NCI (right side) treated with piroxicam and/or CDDP for different times. Electrophoretic bands were analyzed using Scion Image program. Experiments were repeated in triplicate and media values and standard deviations were calculated. CTRL = control; P = piroxicam; C = CDDP.

Conclusion
Piroxicam is a widely used, well tolerated, easily administrable medication that could be readily associated not only to CDDP but also to a broad spectrum of chemotherapy and immunotherapy agents to improve efficacy of therapeutic protocols for mesothelioma. Our data support the hypothesis that piroxicam could sensitize mesothelioma cells to cisplatin treatment by acting on several molecular pathways. Indeed, careful molecular dissection of the molecular pathways elicited or turned off by piroxicam treatment should be better carried on by genomic and proteomic experimental approaches in order to more clearly define the most suitable targets of this drug and, eventually, propose the use of piroxicam in clinical trial setting, even if the cardiac risks associated with COXinhibitors should be considered.