Endogenous anti-tumorigenic nitro-fatty acids inhibit the ubiquitin-proteasome system by directly targeting the 26S proteasome

Nitro-fatty acids (NFAs) are endogenous lipid mediators causing a spectrum of anti-inflammatory effects by covalent modification of key proteins within inflammatory signaling pathways. Recent animal models of solid tumors have helped demonstrate their potential as anti-tumorigenic therapeutics. This study evaluated the anti-tumorigenic effects of NFAs in colon carcinoma cells and other solid and leukemic tumor cell lines. NFAs inhibited the ubiquitin-proteasome system (UPS) by directly targeting the 26S proteasome, leading to polyubiquitination and inhibition of the proteasome activities. UPS suppression induced the unfolded protein response, resulting in tumor cell death. The NFA-mediated effects were substantial, specific, and enduring, representing a unique mode of action for UPS suppression. This study provides mechanistic insights into the biological actions of NFAs as possible endogenous tumor-suppressive factors, indicating that NFAs might be key structures for designing a novel class of direct proteasome inhibitors.

The fourth vaccination with a non-SARS-CoV-2 variant adapted vaccine fails to increase the breadth of the humoral immune response

Escape mutations in the spike protein of SARS-CoV-2 are a major reason for Omicron breakthrough infections. After basal vaccination only very low titers of Omicron neutralizing antibodies are present. However, booster vaccinations induce higher titers against the Omicron variant. The neutralization of the Delta and Omicron variants by sera obtained 6 months after 3rd vaccination and 2 weeks or 6 months after 4th vaccination with a monovalent RNA vaccine (Spikevax) was analyzed. It was observed for the Omicron variant that 6 months after the fourth vaccination, the titer returns to the same very low neutralizing capacity as 6 months after the third vaccination. The Delta variant neutralizing capacity wanes with a comparable kinetic although the titers are higher as compared to the Omicron variant. This indicates that the fourth vaccination with a monovalent vaccine based on the ancestral isolate neither affects the kinetic of the waning nor the breadth of the humoral response.

An increase in Semaphorin 3A biases the axonal direction and induces an aberrant dendritic arborization in an in vitro model of human neural progenitor differentiation

Background

Semaphorins (Sema) belong to a large family of repellent guidance cues instrumental in guiding axons during development. In particular, Class 3 Sema (Sema 3) is among the best characterized Sema family members and the only produced as secreted proteins in mammals, thereby exerting both autocrine and paracrine functions. Intriguingly, an increasing number of studies supports the crucial role of the Sema 3A in hippocampal and cortical neurodevelopment. This means that alterations in Sema 3A signaling might compromise hippocampal and cortical circuits and predispose to disorders such as autism and schizophrenia. Consistently, increased Sema 3A levels have been detected in brain of patients with schizophrenia and many polymorphisms in Sema 3A or in the Sema 3A receptors, Neuropilins (Npn 1 and 2) and Plexin As (Plxn As), have been associated to autism.

Results

Here we present data indicating that when overexpressed, Sema 3A causes human neural progenitors (NP) axonal retraction and an aberrant dendritic arborization. Similarly, Sema 3A, when overexpressed in human microglia, triggers proinflammatory processes that are highly detrimental to themselves as well as NP. Indeed, NP incubated in microglia overexpressing Sema 3A media retract axons within an hour and then start suffering and finally die. Sema 3A mediated retraction appears to be related to its binding to Npn 1 and Plxn A2 receptors, thus activating the downstream Fyn tyrosine kinase pathway that promotes the threonine-serine kinase cyclin-dependent kinase 5, CDK5, phosphorylation at the Tyr15 residue and the CDK5 processing to generate the active fragment p35.

Conclusions

All together this study identifies Sema 3A as a critical regulator of human NP differentiation. This may imply that an insult due to Sema 3A overexpression during the early phases of neuronal development might compromise neuronal organization and connectivity and make neurons perhaps more vulnerable to other insults across their lifespan.

Antibody response to SARS-CoV-2 for more than one year - kinetics and persistence of detection are predominantly determined by avidity progression and test design

BACKGROUND

Antibody detection of SARS-CoV-2 requires an understanding of its variation, course, and duration.

METHODS

Antibody response to SARS-CoV-2 was evaluated over 5-430 days on 828 samples across COVID-19 severity levels, for total antibody (TAb), IgG, IgA, IgM, neutralizing antibody (NAb), antibody avidity, and for receptor-binding-domain (RBD), spike (S), or nucleoprotein (N). Specificity was determined on 676 pre-pandemic samples.

RESULTS

Sensitivity at 30-60 days post symptom onset (pso) for TAb-S/RBD, TAb-N, IgG-S, IgG-N, IgA-S, IgM-RBD, and NAb was 96.6%, 99.5%, 89.7%, 94.3%, 80.9%, 76.9% and 92.8%, respectively. Follow-up 430 days pso revealed: TAb-S/RBD increased slightly (100.0%); TAb-N decreased slightly (97.1%); IgG-S and IgA-S decreased moderately (81.4%, 65.7%); NAb remained positive (94.3%), slightly decreasing in activity after 300 days; there was correlation with IgG-S (Rs = 0.88) and IgA-S (Rs = 0.71); IgG-N decreased significantly from day 120 (15.7%); IgM-RBD dropped after 30-60 days (22.9%). High antibody avidity developed against S/RBD steadily with time in 94.3% of patients after 430 days. This correlated with persistent antibody detection depending on antibody-binding efficiency of the test design. Severe COVID-19 correlated with earlier and higher antibody response, mild COVID-19 was heterogeneous with a wide range of antibody reactivities. Specificity of the tests was ≥99%, except for IgA (96%).

CONCLUSION

Sensitivity of anti-SARS-CoV-2 assays was determined by test design, target antigen, antibody avidity, and COVID-19 severity. Sustained antibody detection was mainly determined by avidity progression for RBD and S. Testing by TAb and for S/RBD provided the highest sensitivity and longest detection duration of 14 months so far.

Persistence of infectious SARS-CoV-2 particles for up to 37 days in patients with mild COVID-19

BACKGROUND

People suffering from COVID-19 are typically considered non-infectious 14 days after diagnosis if symptoms have disappeared for at least 48 h. We describe three patients who independently acquired their infection. These three patients experienced mild COVID-19 and completely recovered symptomatically within 10 days, but remained PCR-positive in deep pharyngeal samples for at least 38 days. We attempted to isolate virus from pharyngeal swabs to investigate whether these patients still carried infectious virus.

METHODS

Infectious virus was amplified in Vero E6 cells and characterized by electron microscopy and WGS. The immune response was investigated by ELISA and peptide arrays.

RESULTS

In all three cases, infectious and replication-competent virus was isolated and amplified in Vero E6 cells. Virus replication was detected by RT-PCR and immunofluorescence microscopy. Electron microscopy confirmed the formation of intact SARS-CoV-2 particles. For a more detailed analysis, all three isolates were characterized by whole-genome sequencing (WGS). The sequence data revealed that the isolates belonged to the 20A or 20C clade, and two mutations in ORF8 were identified among other mutations that could be relevant for establishing a long-term infection. Characterization of the humoral immune response in comparison to patients that had fully recovered from mild COVID-19 revealed a lack of antibodies binding to sequential epitopes of the receptor-binding domain (RBD) for the long-term infected patients.

CONCLUSION

Thus, a small portion of COVID-19 patients displays long-term infectivity and termination of quarantine periods after 14 days, without PCR-based testing, should be reconsidered critically.

Systemic TLR2 Antibody Application in Renal Ischaemia and Reperfusion Injury Decreases AKT Phosphorylation and Increases Apoptosis in the Mouse Kidney

Acute kidney injury remains an important cause of renal dysfunction. In this context, Toll-like receptors have been demonstrated to play a critical role in the induction of innate and inflammatory responses. Among these, Toll-like receptor 2 (TLR2) is constitutively expressed in tubular epithelial cells (TECs) of the kidney and is also known to mediate ischaemia reperfusion (IR) injury. Adult male C57BL/6JRj mice were randomized into seven groups (n = 8): a non-operative control group (CTRL) and six interventional groups in which mice were subjected to a 30 min. bilateral renal ischaemia. Immediately before reperfusion, mice were treated either with saline or with TLR2 antibody (clone T2.5) and harvested after ischaemia and reperfusion for 3, 24 and 48 hr. Analysed kidney homogenates of TLR2 antibody-treated mice displayed significantly decreased levels of TLR2 protein after 3 hr of IR compared to saline-treated mice. Accordingly, the degree of AKT phosphorylation was significantly decreased after 3 hr of IR compared to saline-treated animals. TUNEL staining revealed significantly higher apoptosis rates in TLR2 antibody-treated animals compared to saline-treated mice after 3 and 24 hr of IR. Further, a positive correlation between TLR2 protein expression and phosphorylation of AKT as well as a negative correlation with the number of TUNEL-positive cells could be observed. Inhibition of TLR2 and its signalling pathway by a single application of TLR2 antibody results in reduced phosphorylation of AKT and consecutively increased apoptosis.

Cysteinyl leukotriene-receptor-1 antagonists interfere with PGE2 synthesis by inhibiting mPGES-1 activity

Because of their favourable safety profile and beneficial anti-inflammatory properties, the CysLT1 receptor antagonists (LTRA), montelukast, zafirlukast and pranlukast are approved for the treatment of asthma and are frequently prescribed as add-on therapeutics to reduce the amount of inhaled glucocorticoids and β2-agonists. There is evidence that some of these anti-inflammatory properties might be of a secondary nature and therefore, unrelated to the CysLT1 antagonism. Here, we show that LTRA inhibit PGE2 formation in cytokine-stimulated Hela and A549 carcinoma cells and in lipopolysaccharide (LPS)-stimulated human leukocyte preparations (IC50∼20μM). Neither expression of enzymes involved in PGE2 synthesis nor arachidonic acid release and COX activities were inhibited by the compounds. In contrast, mPGES-1 activity was suppressed at low micromolar levels (IC50 between 2 and 4μM). This suppression was specific for PGE2 synthesis, since PGD2 and PGI2 levels in LPS-stimulated leukocyte preparations were not negatively affected. PGF2α levels were concomitantly inhibited, probably due to its direct synthesis from PGE2. Several major conclusions can be drawn from this study: (A) clinical trials investigating elevated doses of the compounds are helpful to confirm suppression of PGE2 synthesis in vivo; (B) studies investigating the role of CysLTs in cell culture or animal models of inflammation and cancer have to be reassessed carefully, if higher doses of LTRA were applied or serum levels in cell culture assays were low; and (C) LTRA may serve as new scaffolds for the development of potent, selective and well tolerated mPGES-1 inhibitors.

Molecular pharmacological profile of a novel thiazolinone-based direct and selective 5-lipoxygenase inhibitor

BACKGROUND AND PURPOSE

The potency of many 5-lipoxygenase (5-LOX) inhibitors depends on the cellular peroxide tone and the mechanism of 5-LOX enzyme activation. Therefore, new inhibitors that act regardless of the mode of enzyme activation need to be developed. Recently, we identified a novel class of thiazolinone-based compounds as potent 5-LOX inhibitors. Here, we present the molecular pharmacological profile of (Z)-5-(4-methoxybenzylidene)-2-(p-tolyl)-5H-thiazol-4-one, compound C06.

EXPERIMENTAL APPROACH

Inhibition of 5-LOX product formation was determined in intact cells [polymorphonuclear leukocytes (PMNL), rat basophilic leukaemia-1, RAW264.7] and in cell-free assays [homogenates, 100, 000×g supernatant (S100), partially purified 5-LOX] applying different stimuli for 5-LOX activation. Inhibition of peroxisome proliferator-activated receptor (PPAR), cytosolic phospholipase A(2) (cPLA(2) ), 12-LOX, 15-LOX-1 and 15-LOX-2 as well as cyclooxygenase-2 (COX-2) were measured in vitro.

KEY RESULTS

C06 induced non-cytotoxic, direct 5-LOX inhibition with IC(50) values about 0.66 µM (intact PMNL, PMNL homogenates) and approximately 0.3 µM (cell-free PMNL S100, partially purified 5-LOX). Action of C06 was independent of the stimulus used for 5-LOX activation and cellular redox tone and was selective for 5-LOX compared with other arachidonic acid binding proteins (PPAR, cPLA(2) , 12-LOX, 15-LOX-1, 15-LOX-2, COX-2). Experimental results suggest an allosteric binding distinct from the active site and the C2-like domain of 5-LOX.

CONCLUSIONS AND IMPLICATIONS

C06 was identified as a potent selective direct 5-LOX inhibitor exhibiting a novel and unique mode of action, different from other established 5-LOX inhibitors. This thiazolinone may possess potential for intervention with inflammatory and allergic diseases and certain types of cancer.

A pirinixic acid derivative (LP105) inhibits murine 5-lipoxygenase activity and attenuates vascular remodelling in a murine model of aortic aneurysm

BACKGROUND AND PURPOSE Arachidonic acid derivatives play a central role in inflammation processes. Arachidonic acid is metabolized by several enzymes, particularly cyclooxygenases (COX), 5-lipoxygenase (5-LOX) and microsomal prostaglandin E-synthase-1 (mPGES-1) to pro-inflammatory mediators. EXPERIMENTAL APPROACH We determined the effect of LP105, a pirinixic acid derivative which acts as inhibitor of 5-LOX, COX and mPGES-1, on aortic aneurysm development in mice and on 5-LOX activity in murine monocytes. KEY RESULTS In a monocyte cell line (RAW264.7), LP105 inhibited 5-LOX in whole cells (IC(50) : 1-3 µM) and in supernatants (IC(50) : ∼10 µM). Oral administration of LP105 to mice resulted in therapeutic tissue and plasma levels. Aortic aneurysms were induced in ApoE(-/-) mice by angiotensin II (AngII) and LP105 (5 mg·day(-1) per animal) was co-administered to a subgroup. Compared with animals receiving AngII alone, the LP105+AngII group showed a lower heart rate, a trend towards reduced heart to body weight ratio but similar hypertensive responses. AngII alone significantly increased aortic weight and diameter but co-treatment with LP105+AngII prevented these changes. LC/MS-MS studies revealed increased 15-hydroxytetraenoic acid (15-HETE) and 14,15-epoxyeicosatrienoic acid (14,15-EET) plasma levels in LP105-treated animals. In the murine kidney, mRNAs of EET-generating or metabolizing enzymes and of 5-LOX and 15-LOX were unaffected by LP105. LP105 also did not inhibit the EET-metabolizing soluble epoxide hydrolase. CONCLUSIONS AND IMPLICATIONS LP105 was a potent inhibitor of monocyte 5-LOX and reduced AngII-induced vascular remodelling in mice. A shift of arachidonic acid metabolism to the protective EET pathway may contribute to the beneficial effects of LP105.

Effects of celecoxib on prostanoid biosynthesis and circulating angiogenesis proteins in familial adenomatous polyposis

Vascular cyclooxygenase (COX)-2-dependent prostacyclin (PGI(2)) may affect angiogenesis by preventing endothelial activation and platelet release of angiogenic factors present in platelet α-granules. Thus, a profound inhibition of COX-2-dependent PGI(2) might be associated with changes in circulating markers of angiogenesis. We aimed to address this issue by performing a clinical study with celecoxib in familial adenomatous polyposis (FAP). In nine patients with FAP and healthy controls, pair-matched for gender and age, we compared systemic biosynthesis of PGI(2), thromboxane (TX) A(2), and prostaglandin (PG) E(2), assessing their urinary enzymatic metabolites, 2,3-dinor-6-keto PGF(1α) (PGI-M), 11-dehydro-TXB(2) (TX-M), and 11-α-hydroxy-9,15-dioxo-2,3,4,5-tetranor-prostane-1,20-dioic acid (PGE-M), respectively. The impact of celecoxib (400 mg b.i.d. for 7 days) on prostanoid biosynthesis and 14 circulating biomarkers of angiogenesis was evaluated in FAP. Intestinal tumorigenesis was associated with enhanced urinary TX-M levels, but unaffected by celecoxib, suggesting the involvement of a COX-1-dependent pathway, presumably from platelets. This was supported by the finding that in cocultures of a human colon adenocarcinoma cell line (HT-29) and platelets enhanced TXA(2) generation was almost completely inhibited by pretreatment of platelets with aspirin, a preferential inhibitor of COX-1. In FAP, celecoxib profoundly suppressed PGE(2) and PGI(2) biosynthesis that was associated with a significant increase in circulating levels of most proangiogenesis proteins but also the antiangiogenic tissue inhibitor of metalloproteinase 2. Urinary PGI-M, but not PGE-M, was negatively correlated with circulating levels of fibroblast growth factor 2 and angiogenin. In conclusion, inhibition of tumor COX-2-dependent PGE(2) by celecoxib may reduce tumor progression. However, the coincident depression of vascular PGI(2), in a context of enhanced TXA(2) biosynthesis, may modulate the attendant angiogenesis, contributing to variability in the chemopreventive efficacy of COX-2 inhibitors such as celecoxib.

Inhibition of microsomal prostaglandin E2 synthase-1 as a molecular basis for the anti-inflammatory actions of boswellic acids from frankincense

BACKGROUND AND PURPOSE

Frankincense, the gum resin derived from Boswellia species, showed anti-inflammatory efficacy in animal models and in pilot clinical studies. Boswellic acids (BAs) are assumed to be responsible for these effects but their anti-inflammatory efficacy in vivo and their molecular modes of action are incompletely understood.

EXPERIMENTAL APPROACH

A protein fishing approach using immobilized BA and surface plasmon resonance (SPR) spectroscopy were used to reveal microsomal prostaglandin E(2) synthase-1 (mPGES1) as a BA-interacting protein. Cell-free and cell-based assays were applied to confirm the functional interference of BAs with mPGES1. Carrageenan-induced mouse paw oedema and rat pleurisy models were utilized to demonstrate the efficacy of defined BAs in vivo.

KEY RESULTS

Human mPGES1 from A549 cells or in vitro-translated human enzyme selectively bound to BA affinity matrices and SPR spectroscopy confirmed these interactions. BAs reversibly suppressed the transformation of prostaglandin (PG)H(2) to PGE(2) mediated by mPGES1 (IC(50) = 3-10 µM). Also, in intact A549 cells, BAs selectively inhibited PGE(2) generation and, in human whole blood, β-BA reduced lipopolysaccharide-induced PGE(2) biosynthesis without affecting formation of the COX-derived metabolites 6-keto PGF(1α) and thromboxane B(2) . Intraperitoneal or oral administration of β-BA (1 mg·kg(-1) ) suppressed rat pleurisy, accompanied by impaired levels of PGE(2) and β-BA (1 mg·kg(-1) , given i.p.) also reduced mouse paw oedema, both induced by carrageenan.

CONCLUSIONS AND IMPLICATIONS

Suppression of PGE(2) formation by BAs via interference with mPGES1 contribute to the anti-inflammatory effectiveness of BAs and of frankincense, and may constitute a biochemical basis for their anti-inflammatory properties.

5-lipoxygenase: underappreciated role of a pro-inflammatory enzyme in tumorigenesis

Leukotrienes constitute a group of bioactive lipids generated by the 5-lipoxygenase (5-LO) pathway. An increasing body of evidence supports an acute role for 5-LO products already during the earliest stages of pancreatic, prostate, and colorectal carcinogenesis. Several pieces of experimental data form the basis for this hypothesis and suggest a correlation between 5-LO expression and tumor cell viability. First, several independent studies documented an overexpression of 5-LO in primary tumor cells as well as in established cancer cell lines. Second, addition of 5-LO products to cultured tumor cells also led to increased cell proliferation and activation of anti-apoptotic signaling pathways. 5-LO antisense technology approaches demonstrated impaired tumor cell growth due to reduction of 5-LO expression. Lastly, pharmacological inhibition of 5-LO potently suppressed tumor cell growth by inducing cell cycle arrest and triggering cell death via the intrinsic apoptotic pathway. However, the documented strong cytotoxic off-target effects of 5-LO inhibitors, in combination with the relatively high concentrations of 5-LO products needed to achieve mitogenic effects in cell culture assays, raise concern over the assignment of the cause, and question the relationship between 5-LO products and tumorigenesis.

5-Lipoxygenase inhibitors induce potent anti-proliferative and cytotoxic effects in human tumour cells independently of suppression of 5-lipoxygenase activity

BACKGROUND AND PURPOSE

Certain 5-lipoxygenase (5-LO) inhibitors exhibit anti-carcinogenic activities against 5-LO overexpressing tumour types and cultured tumour cells. It has been proposed therefore that 5-LO products significantly contribute to tumour cell proliferation. To date, the relationship between the inhibitory mechanisms of 5-LO inhibitors, which vary widely, and tumour cell viability has not been evaluated. This study addresses the anti-proliferative and cytotoxic potency of a number of 5-LO inhibitors with different inhibitory mechanisms in 5-LO-positive and 5-LO-negative tumour cells.

EXPERIMENTAL APPROACH

Cell viability was measured by the WST-1 assay; cell proliferation was assessed using the bromodeoxyuridine (BrdU) incorporation assay. Cell death was analysed by annexin V staining, Western blot analysis of PARP (poly ADP-ribose polymerase) cleavage and a cytotoxicity assay. 5-LO product formation was quantified by a 5-LO activity assay.

KEY RESULTS

The common 5-LO inhibitors AA-861, Rev-5901 and MK-886 induced cytotoxic and anti-proliferative effects in 5-LO-positive Capan-2 pancreatic cancer cells; BWA4C and CJ-13,610 only caused anti-proliferative effects, while zileuton failed to impair cell viability. Moreover, the concentrations of the 5-LO inhibitors required to induce anti-proliferation and cytotoxicity highly exceeded those for suppression of 5-LO. Supplementation with mitogenic 5-LO products failed to protect Capan-2 cells from the effects of 5-LO inhibitors. Finally, the cytotoxic and anti-proliferative 5-LO inhibitors also potently reduced the viability of 5-LO-deficient tumour cell lines (HeLa, Panc-1 and U937).

CONCLUSIONS AND IMPLICATIONS

Certain 5-LO inhibitors cause cytotoxic and anti-proliferative effects independently of suppression of 5-LO activity. Thus, the role of 5-LO overexpression in tumour cell viability remains unclear and requires further elucidation.

Cyclooxygenase-2 (COX-2)-independent anticarcinogenic effects of selective COX-2 inhibitors

Nonsteroidal antiinflammatory drugs (NSAIDs) appear to reduce the risk of developing cancer. One mechanism through which NSAIDs act to reduce carcinogenesis is to inhibit the activity of cyclooxygenase-2 (COX-2), an enzyme that is overexpressed in various cancer tissues. Overexpression of COX-2 increases cell proliferation and inhibits apoptosis. However, selective COX-2 inhibitors can also act through COX-independent mechanisms. In this review, we describe the COX-2-independent molecular targets of these COX-2 inhibitors and discuss how these targets may be involved in the anticarcinogenic activities of these selective COX-2 inhibitors. We also compare the concentrations of these inhibitors used in in vitro and in vivo experiments and discuss the implications of the in vitro studies for clinical management of cancer with these drugs.

Targeting the beta-catenin/APC pathway: a novel mechanism to explain the cyclooxygenase-2-independent anticarcinogenic effects of celecoxib in human colon carcinoma cells

Celecoxib, a cyclooxygenase-2 (COX-2) selective nonsteroidal anti-inflammatory drug, is a new anticarcinogenic agent. Its antitumor effects depend on the one hand on its COX-2-inhibiting potency, but on the other hand on COX-2-independent mechanisms, which until now have not been fully understood. Here, we investigated whether celecoxib has an impact on the APC/beta-catenin pathway, which has been shown to play a pivotal role in the development of various cancers, especially of the colon. After only 2 h of treatment of human Caco-2 colon carcinoma cells with 100 muM celecoxib, we observed a rapid translocation of beta-catenin from its predominant membrane localization to the cytoplasm. Inhibition of the glycogen-synthase-kinase-3beta (GSK-3beta) by LiCl prevented this celecoxib-induced translocation, suggesting that phosphorylation of beta-catenin by the GSK-3beta kinase was essential for this release. Furthermore, the cytosolic accumulation was accompanied by a rapid increase of beta-catenin in the nuclei, starting already 30 min after celecoxib treatment. The DNA binding activity of beta-catenin time dependently decreased 2 h after celecoxib treatment. After this cellular reorganization, we observed a caspase- and proteasome-dependent degradation of beta-catenin after 8 h of drug incubation. Celecoxib-induced beta-catenin degradation was also observed in various other tumor cell lines (HCT-116, MCF-7, and LNCAP) but was not seen after treatment of Caco-2 cells with either the anticarcinogenic nonsteroidal anti-inflammatory drug R-flurbiprofen or the highly COX-2-selective inhibitor rofecoxib. These findings indicate that the anticarcinogenic effects of celecoxib can be explained, at least partly, by an extensive degradation of beta-catenin in human colon carcinoma cells.

Cyclooxygenase-2 (COX-2)-dependent and -independent anticarcinogenic effects of celecoxib in human colon carcinoma cells

Celecoxib, a selective cyclooxygenase-2 (COX-2) inhibitor, is the only non-steroidal anti-inflammatory drug so far which has been approved by the FDA for adjuvant treatment of patients with familial adenomatous polyposis. The molecular mechanism responsible for the anticarcinogenic effects of celecoxib is still not fully understood. To investigate the extent to which the anticarcinogenic effect of celecoxib depends on COX-2 expression, we transfected human colon carcinoma cells (Caco-2) with the human COX-2 cDNA, in both sense and in antisense orientation, to generate cells which either overexpress COX-2 (human COX-2-sense, hCOX-2-s), express no COX-2 (human COX-2-antisense, hCOX-2-as) or express only very small amounts of COX-2 (control cells). Treatment of these cells with celecoxib dose-dependently (0-100microM) reduced cell survival which was accompanied by an induction of a G(0)/G(1) phase block and apoptosis. The effect of celecoxib treatment on both, cell survival and induction of apoptosis in hCOX-2-as cells was less marked than in the COX-2-expressing cells. Apoptosis was accompanied by an activation of caspase-3 and caspase-9 and cytochrome c release. In contrast, we observed no difference in sensitivity with regard to the induction of a cell cycle block between the different cell clones. The G(0)/G(1) phase block caused by celecoxib correlated with a decrease in expression levels of cyclin A and cyclin B1 and an increase in the expression of the cell cycle inhibitory proteins p21(Waf1) and p27(Kip1) irrespective of the type of cell used. These data indicate that apoptosis-inducing effects of celecoxib partly depend on COX-2 expression of the cells, whereas induction of a cell cycle block occurred COX-2 independently. Thus, the anticarinogenic effects of celecoxib can be explained by both COX-2-dependent and -independent mechanisms.