Distinct binding and signaling activity of Acthar Gel compared to other melanocortin receptor agonists.

PURPOSE: To compare the binding and agonistic activity of Acthar® Gel and synthetic melanocortin receptor (MCR) agonists and examine how the activity of select agonists affects the in vivo production of corticosterone. MATERIALS AND METHODS: In vitro binding was determined using concentration-dependent displacement of the ligand [125I]Nle4, D-Phe7-α-melanocyte-stimulating hormone (α-MSH) on cells expressing MC1R, MC3R, MC4R, or MC5R. Functional activity was determined using a time-resolved fluorescence cyclic adenosine monophosphate (cAMP) assay in cells expressing MC1R, MC2R, MC3R, MC4R, or MC5R. In vivo corticosterone analyses were performed by measuring plasma corticosterone levels in Sprague Dawley rats. RESULTS: Acthar Gel and synthetic MCR agonists exhibited the highest binding at MC1R, lowest binding at MC5R, and moderate binding at MC3R and MC4R. Acthar Gel stimulated the production of cAMP in all 5 MCR-expressing cell lines, with MC2R displaying the lowest level of full agonist activity, 3-, 6.6-, and 10-fold lower than MC1R, MC3R, and MC4R, respectively. Acthar Gel was a partial agonist at MC5R. The synthetic MCR agonists induced full activity at all 5 MCRs, with the exception of α-MSH having no activity at MC2R. Acthar Gel treatment had less of an impact on in vivo production of corticosterone compared with synthetic ACTH1-24 depot. CONCLUSIONS: Acthar Gel bound to and activated each MCR tested in this study, with partial agonist activity at MC5R and the lowest level of full agonist activity at MC2R, which distinguished it from synthetic MCR agonists. The minimal activity of Acthar Gel at MC2R corresponded to lower endogenous corticosteroid production.

PAS kinase drives lipogenesis through SREBP-1 maturation.

Elevated hepatic synthesis of fatty acids and triglycerides, driven by hyperactivation of the SREBP-1c transcription factor, has been implicated as a causal feature of metabolic syndrome. SREBP-1c activation requires the proteolytic maturation of the endoplasmic-reticulum-bound precursor to the active, nuclear transcription factor, which is stimulated by feeding and insulin signaling. Here, we show that feeding and insulin stimulate the hepatic expression of PASK. We also demonstrate, using genetic and pharmacological approaches, that PASK is required for the proteolytic maturation of SREBP-1c in cultured cells and in the mouse and rat liver. Inhibition of PASK improves lipid and glucose metabolism in dietary animal models of obesity and dyslipidemia. Administration of a PASK inhibitor decreases hepatic expression of lipogenic SREBP-1c target genes, decreases serum triglycerides, and partially reverses insulin resistance. While the signaling network that controls SREBP-1c activation is complex, we propose that PASK is an important component with therapeutic potential.

Leukotrienes, but not angiotensin II, are involved in the renal effects elicited by the prolonged cyclooxygenase-2 inhibition when sodium intake is low.

It is known that cyclooxygenase-2 (COX-2) inhibition elicits significant renal hemodynamics alterations when sodium intake is low. However, the mechanisms involved in these renal changes are not well known. Our objective was to evaluate the role of angiotensin II and 5-lipooxygenase-derived metabolites in the renal effects induced by prolonged COX-2 inhibition when sodium intake is low. Conscious dogs were treated during 7 days with a COX-2 inhibitor (1 mg·kg·d, SC75416), and either a vehicle, an AT1 receptor antagonist (0.4 mg · kg · d, candesartan) or a selective 5-lipooxygenase inhibitor (PF-150, 20 and 60 mg · kg · d). The administration of SC75416 alone induced significant changes in renal blood flow (219 ± 14 to 160 ± 10 mL/min), glomerular filtration rate (51 ± 2 to 42 ± 3 mL/min), and plasma potassium (pK) (4.3 ± 0.1 to 4.6 ± 0.1 mEq/L). Similar decrements in renal blood flow (27%) and glomerular filtration rate (20%) and a similar increment in pK (7%) were found when SC75416 was administered in candesartan-pretreated dogs. However, SC75416 administration did not elicit significant changes in renal hemodynamics and pK in dogs pretreated with each dose of PF-150. Our data suggest that leukotrienes but not angiotensin II are involved in the renal effects induced by COX-2 inhibition when sodium intake is low.

Discovery and SAR of PF-4693627, a potent, selective and orally bioavailable mPGES-1 inhibitor for the potential treatment of inflammation.

Inhibition of mPGES-1, the terminal enzyme in the arachidonic acid/COX pathway to regulate the production of pro-inflammatory prostaglandin PGE2, is considered an attractive new therapeutic target for safe and effective anti-inflammatory drugs. The discovery of a novel series of orally active, selective benzoxazole piperidinecarboxamides as mPGES-1 inhibitors is described. Structure-activity optimization of lead 5 with cyclohexyl carbinols resulted in compound 12, which showed excellent in vitro potency and selectivity against COX-2, and reasonable pharmacokinetic properties. Further SAR studies of the benzoxazole ring substituents lead to a novel series of highly potent compounds with improved PK profile, including 23, 26, and 29, which were effective in a carrageenan-stimulated guinea pig air pouch model of inflammation. Based on its excellent in vitro and in vivo pharmacological, pharmacokinetic and safety profile and ease of synthesis, compound 26 (PF-4693627) was advanced to clinical studies.

A novel autotaxin inhibitor reduces lysophosphatidic acid levels in plasma and the site of inflammation.

Autotaxin is the enzyme responsible for the production of lysophosphatidic acid (LPA) from lysophosphatidyl choline (LPC), and it is up-regulated in many inflammatory conditions, including but not limited to cancer, arthritis, and multiple sclerosis. LPA signaling causes angiogenesis, mitosis, cell proliferation, and cytokine secretion. Inhibition of autotaxin may have anti-inflammatory properties in a variety of diseases; however, this hypothesis has not been tested pharmacologically because of the lack of potent inhibitors. Here, we report the development of a potent autotaxin inhibitor, PF-8380 [6-(3-(piperazin-1-yl)propanoyl)benzo[d]oxazol-2(3H)-one] with an IC(50) of 2.8 nM in isolated enzyme assay and 101 nM in human whole blood. PF-8380 has adequate oral bioavailability and exposures required for in vivo testing of autotaxin inhibition. Autotaxin's role in producing LPA in plasma and at the site of inflammation was tested in a rat air pouch model. The specific inhibitor PF-8380, dosed orally at 30 mg/kg, provided >95% reduction in both plasma and air pouch LPA within 3 h, indicating autotaxin is a major source of LPA during inflammation. At 30 mg/kg PF-8380 reduced inflammatory hyperalgesia with the same efficacy as 30 mg/kg naproxen. Inhibition of plasma autotaxin activity correlated with inhibition of autotaxin at the site of inflammation and in ex vivo whole blood. Furthermore, a close pharmacokinetic/pharmacodynamic relationship was observed, which suggests that LPA is rapidly formed and degraded in vivo. PF-8380 can serve as a tool compound for elucidating LPA's role in inflammation.

Pharmacology of PF-4191834, a novel, selective non-redox 5-lipoxygenase inhibitor effective in inflammation and pain.

5-Lipoxygenase (LOX) is an important arachidonic acid-metabolizing enzyme producing leukotrienes and other proinflammatory lipid mediators with potent pathophysiological functions in asthma and other inflammatory diseases. 4-(3-(4-(1-Methyl-1H-pyrazol-5-yl)phenylthio)phenyl)-tetrahydro-2H-pyran-4-carboxamide (PF-4191834) is a novel, selective non-redox 5-lipoxygenase inhibitor effective in inflammation and pain. In vitro and in vivo assays were developed for the evaluation of a novel 5-LOX inhibitor using conditions of maximal enzyme activity. PF-4191834 exhibits good potency in enzyme- and cell-based assays, as well as in a rat model of acute inflammation. Enzyme assay results indicate that PF-4191834 is a potent 5-LOX inhibitor, with an IC(50) = 229 +/- 20 nM. Furthermore, it demonstrated approximately 300-fold selectivity for 5-LOX over 12-LOX and 15-LOX and shows no activity toward the cyclooxygenase enzymes. In addition, PF-4191834 inhibits 5-LOX in human blood cells, with an IC(80) = 370 +/- 20 nM. This inhibitory concentration correlates well with plasma exposures needed for in vivo efficacy in inflammation in models of inflammatory pain. The combination of potency in cells and in vivo, together with a sustained in vivo effect, provides PF-4191834 with an overall pharmacodynamic improvement consistent with once a day dosing.

Biochemical, cellular, and anti-inflammatory properties of a potent, selective, orally bioavailable benzamide inhibitor of Rho kinase activity.

Rho kinase, is the most widely studied downstream effector of the small Rho GTPase RhoA. Two Rho kinase isoforms have been described and are frequently referred to in the literature as ROCK1 and ROCK2. The RhoA-Rho kinase pathway has been implicated in the recruitment of cellular infiltrates to disease loci in a number of preclinical animal models of inflammatory disease. In this study, we used biochemical enzyme assays and a cellular target biomarker assay to define PF-4950834 [N-methyl-3-{[(4-pyridin-4-ylbenzoyl)amino]methyl}benzamide] as an ATP-competitive, selective Rho kinase inhibitor. We further used PF-4950834 to study the role of Rho kinase activation in lymphocyte and neutrophil migration in addition to the endothelial cell-mediated expression of adhesion molecules and chemokines, which are essential for leukocyte recruitment. The inhibitor blocked stromal cell-derived factor-1alpha-mediated chemotaxis of T lymphocytes in vitro and the synthesis of vascular cell adhesion molecule-1 and intercellular adhesion molecule-1 in activated human endothelial cells in vitro. The secretion of chemokines interleukin-8 and monocyte chemoattractant protein-1 was also inhibited in activated endothelial cells. In addition, when dosed orally, the compound potently inhibited neutrophil migration in a carrageenan-induced acute inflammation model. In summary, we have used a pharmacologic approach to link Rho kinase activation to multiple phenotypes that can contribute to leukocyte infiltration. Inhibition of this pathway therefore could be strongly anti-inflammatory and provide therapeutic benefit in chronic inflammatory diseases.

Distinction of microsomal prostaglandin E synthase-1 (mPGES-1) inhibition from cyclooxygenase-2 inhibition in cells using a novel, selective mPGES-1 inhibitor.

Inflammation-induced microsomal prostaglandin E synthase-1 (mPGES-1) is the terminal enzyme that synthesizes prostaglandin E(2) (PGE(2)) downstream of cyclooxygenase-2 (COX-2). The efficacy of nonsteroidal anti-inflammatory drugs and COX-2 inhibitors in the treatment of the signs and symptoms of osteoarthritis, rheumatoid arthritis and inflammatory pain, largely attributed to the inhibition of PGE(2) synthesis, provides a rationale for exploring mPGES-1 inhibition as a potential novel therapy for these diseases. Toward this aim, we identified PF-9184 as a novel mPGES-1 inhibitor. PF-9184 potently inhibited recombinant human (rh) mPGES-1 (IC(50)=16.5+/-3.8nM), and had no effect against rhCOX-1 and rhCOX-2 (>6500-fold selectivity). In inflammation and clinically relevant biological systems, mPGES-1 expression, like COX-2 expression was induced in cell context- and time-dependent manner, consistent with the kinetics of PGE(2) synthesis. In rationally designed cell systems ideal for determining direct effects of the inhibitors on mPGES-1 function, but not its expression, PF-9184 inhibited PGE(2) synthesis (IC(50) in the range of 0.5-5 microM in serum-free cell and human whole blood cultures, respectively) while sparing the synthesis of 6-keto-PGF(1alpha) (PGF(1alpha)) and PGF(2alpha). In contrast, as expected, the selective COX-2 inhibitor, SC-236, inhibited PGE(2), PGF(1alpha) and PGF(2alpha) synthesis. This profile of mPGES-1 inhibition, distinct from COX-2 inhibition in cells, validates mPGES-1 as an attractive target for therapeutic intervention.

CJ-13610, an orally active inhibitor of 5-lipoxygenase is efficacious in preclinical models of pain.

Zileuton, a redox and iron chelator 5-lipoxygenase (5-LOX) inhibitor and, leukotriene receptor antagonists are presently used clinically in the long term treatment of asthma. Recent data implicate 5-LOX pathway in pain signaling. We report 5-LOX expression in the central nervous system (CNS) and analyze the pain efficacy of a new class of non redox, non iron chelating 5-LOX inhibitor. CJ-13610, 4-(3-(4-(2-methyl-1H-imidazol-1-yl) phenylthio) phenyl)-tetrahydro-2H-pyran-4-carboxamide, demonstrated antihyperalgesic activity in inflammatory pain models including the acute carrageenan model and the chronic inflammatory model using complete Freund's adjuvant. Following complete Freund's adjuvant stimulus leukotrieneB(4) concentration in the brain was elevated (9+/-1 ng/g, mean+/-S.E.M.) by about 3 times that of the control group (3+/-0.11, mean+/-S.E.M.). Hyperalgesia and leukotrieneB(4) concentration were both reversed following CJ-13610 treatment. Furthermore, we demonstrate CJ-13610 efficacy against osteoarthritis like pain using the rat medial meniscal transection model. CJ-13610 at oral doses of 0.6, 2 and 6 mg/kg/day reversed two modalities of pain in this model; tactile allodynia and weight bearing differential. Taken together, these data suggest that 5-LOX pathway and the leukotriene products are important mediators of pain.

A rat air pouch model for evaluating the efficacy and selectivity of 5-lipoxygenase inhibitors.

The 5-lipoxygenase (5-LOX) pathway has been associated with a variety of inflammatory diseases including asthma, atherosclerosis, rheumatoid arthritis, pain, cancer and liver fibrosis. Several classes of 5-LOX inhibitors have been identified, but only one drug, zileuton, a redox inhibitor of 5-LOX, has been approved for clinical use. To better evaluate the efficacy of 5-LOX inhibitors for pharmacological intervention, a rat model was modified to test the in vivo efficacy of 5-LOX inhibitors. Inflammation was produced by adding carrageenan into a newly formed air pouch and prostaglandins produced. While macrophages and neutrophils are present in the inflamed pouch, little 5-LOX products are formed. Cellular 5-LOX activation was obtained by adding calcium ionophore (A23187) into the pouch thus providing a novel model to evaluate the efficacy and selectivity of 5-LOX inhibitors. Also, we described modifications to the in vitro 5-LOX enzyme and cell assays. These assays included a newly developed fluorescence-based enzyme assay, a 5-LOX redox assay, an ex vivo human whole blood assay and an IgE-stimulated rat mast cell assay, all designed for maximal production of leukotrienes. Zileuton and CJ-13,610, a competitive, non-redox inhibitor of 5-LOX, were evaluated for their pharmacological properties using these assays. Although both compounds achieved dose-dependent inhibition of 5-LOX enzyme activity, CJ-13,610 was 3-4 fold more potent than zileuton in all-assays. Evaluation of 5-LOX metabolites-by LC/MS/MS and ELISA confirmed that both compounds selectively inhibited all products downstream of 5-hydroperoxy eicosatetraenoic acid (5-HPETE), including 5-oxo-6,8,11,14-eicosatetraenoic acid (5-oxoETE), without inhibition of 12-lipoxygenase (12-LOX), 15-lipoxygenase (15-LOX), or cyclooxygenase (COX) products. In the rat air pouch model, oral dosing of CJ-13,610 and zileuton resulted in selective inhibition 5-LOX activity from pouch exudate and ex vivo rat whole blood with similar potency to in vitro assay. These data show that the rat air pouch model is a reliable and useful tool for evaluating in vivo efficacy of 5-LOX inhibitors and may aid in the development of the next generation of 5-LOX inhibitors, such as the non-redox inhibitors similar to CJ-13,610.

Enzymologic and pharmacologic profile of loxoprofen sodium and its metabolites.

We investigated the mechanism of inhibition of loxoprofen sodium, a non-steroidal anti-inflammatory drug (NSAID), and its active metabolite (loxoprofen-SRS) on cyclooxygenase (COX). In in vitro assays, loxoprofen sodium appeared inactive against recombinant human COX-1 and COX-2, whereas loxoprofen-SRS inhibited both. In the investigation of kinetic behavior, loxoprofen-SRS showed time-dependent inhibition for both isozymes. Human whole blood assay also showed that loxoprofen-SRS possesses the profile of a non-selective inhibitor for COX. In a rat air pouch model, oral administration of loxoprofen sodium lowered prostaglandin (PG) E2 in both fluid exudates of the inflammatory pouch and stomach tissue with ED50 values of 2.0 and 2.1 mg/kg, respectively. Additionally, platelet thromboxane B2 production was also inhibited by loxoprofen sodium (ED50 of 0.34 mg/kg). In a rat carrageenan-induced paw edema model, loxoprofen sodium dose-dependently reduced the paw edema, accompanied by a decrease in PGE2 content in inflamed paw exudates. These findings suggest that the COX inhibitory activity of loxoprofen sodium is attributable to its active metabolite, loxoprofen-SRS, and that loxoprofen-SRS shows non-selective inhibition for COX.

COX-2 inhibitors and genetic background reduce mammary tumorigenesis in cyclooxygenase-2 transgenic mice.

Cyclooxygenase-2 (COX-2) overexpression is a widely recognized feature of human breast cancer and inhibitors of the enzyme have antitumor effects in a subset of tumor settings. Previously, we demonstrated that direct overexpression of COX-2 under control of the mammary-specific MMTV promoter/enhancer, was itself oncogenic and lead to the induction of mammary tumors in multiparous, outbred CD1 mice. In the present study, we provide evidence that COX-2 dependent tumor progression can also be studied in FVB/N, an inbred strain widely used for analysis of breast cancer progression. In these mice, the human COX-2 transgene was strongly induced during pregnancy/lactation and mammary tumors developed after multiple pregnancies. However, crossing the COX-2 FVB/N mice with the C57BL6 strain resulted in loss of the mammary tumorigenic phenotype despite the fact that the human COX-2 gene was induced. Treatment of the COX-2 transgenic mice in the FVB/N strain with celecoxib (1600 ppm), a COX-2 selective inhibitor, resulted significant reduction in tumor size and multiplicity when compared to transgenic mice fed with control chow. SC-560 (20 ppm), a COX-1 selective inhibitor did not have significant effect on tumorigenesis. These studies suggest that FVB/N is a susceptible mouse strain well suited to the study of COX-2 mediated tumor progression and may provide a tool for the identification of interacting genes and therapeutic treatments for this clinically important target.

Valdecoxib: assessment of cyclooxygenase-2 potency and selectivity.

The discovery of a second isoform of cyclooxygenase (COX) led to the search for compounds that could selectively inhibit COX-2 in humans while sparing prostaglandin formation from COX-1. Celecoxib and rofecoxib were among the molecules developed from these efforts. We report here the pharmacological properties of a third selective COX-2 inhibitor, valdecoxib, which is the most potent and in vitro selective of the marketed COX-2 inhibitors that we have studied. Recombinant human COX-1 and COX-2 were used to screen for new highly potent and in vitro selective COX-2 inhibitors and compare kinetic mechanisms of binding and enzyme inhibition with other COX inhibitors. Valdecoxib potently inhibits recombinant COX-2, with an IC(50) of 0.005 microM; this compares with IC values of 0.05 microM for celecoxib, 0.5 microM for rofecoxib, and 5 microM for etoricoxib. Unique binding interactions of valdecoxib with COX-2 translate into a fast rate of inactivation of COX-2 (110,000 M/s compared with 7000 M/s for rofecoxib and 80 M/s for etoricoxib). The overall saturation binding affinity for COX-2 of valdecoxib is 2.6 nM (compared with 1.6 nM for celecoxib, 51 nM for rofecoxib, and 260 nM for etoricoxib), with a slow off-rate (t(1/2) approximately 98 min). Valdecoxib inhibits COX-1 in a competitive fashion only at very high concentrations (IC(50) = 150 microM). Collectively, these data provide a mechanistic basis for the potency and in vitro selectivity of valdecoxib for COX-2. Valdecoxib showed similar activity in the human whole-blood COX assay (COX-2 IC(50) = 0.24 microM; COX-1 IC(50) = 21.9 microM). We also determined whether this in vitro potency and selectivity translated to significant potency in vivo. In rats, valdecoxib demonstrated marked potency in acute and chronic models of inflammation (air pouch ED(50) = 0.06 mg/kg; paw edema ED(50) = 5.9 mg/kg; adjuvant arthritis ED(50) = 0.03 mg/kg). In these same animals, COX-1 was spared at doses greater than 200 mg/kg. These data provide a basis for the observed potent anti-inflammatory activity of valdecoxib in humans.

Inhibition of cyclooxygenase-2 by celecoxib reverses tumor-induced wasting.

There have been a number of reports suggesting inhibition of prostaglandin production may impact tumor-mediated wasting and levels of associated humoral factors such as hypercalcemia. These reductions were achieved using traditional nonsteroidal anti-inflammatory drugs (NSAIDs), which are often contraindicated in cancer patients. This is especially true during chemotherapeutic regimens due to concerns of bleeding from gastrointestinal and hematopoietic toxicities associated with inhibition of the housekeeping cyclooxygenase enzyme COX-1. Here, we report that celecoxib, one of the new class of selective COX-2 inhibitors, has the potential to reverse tumor-mediated wasting and associated humoral factors such as interleukin (IL)-6 and hypercalcemia in preclinical models of cachexia. Tumor bearing mice in late stage cachexia regained weight within days of the start of celecoxib treatment. Two models were tested. The first was the Colon 26 (Col26) syngeneic murine model that induces high levels of circulating IL-6 and hypercalcemia. The second was the human head and neck 1483 HNSCC xenograft model, which is less inflammatory and produces less prostaglandin than Col26. Despite the observation that no significant impact on tumor growth was observed between vehicle and celecoxib-treated animals over the course of the studies, celecoxib rapidly reversed weight loss in both cachectic models. With the added safety of celecoxib over traditional NSAIDs, these results suggest a possible therapeutic use for celecoxib for treating tumor-mediated wasting.

Synergy between celecoxib and radiotherapy results from inhibition of cyclooxygenase-2-derived prostaglandin E2, a survival factor for tumor and associated vasculature.

Previous work has demonstrated that selective cyclooxygenase-2 (COX-2) inhibitors can act synergistically with radiotherapy to improve tumor debulking and control in preclinical models. The underlying mechanism of this remarkable activity has not yet been determined. Here, we report that radiation can elevate intratumoral levels of COX-2 protein and its products, particularly prostaglandin E(2) (PGE(2)). Furthermore, inhibition of COX-2 activity or neutralization of PGE(2) activity enhances radiotherapy even in tumors where COX-2 expression is restricted to the tumor neovasculature. Direct assessment of vascular function by direct contrast enhancement-magnetic resonance imaging showed that the combination of radiation and celecoxib lead to enhanced vascular permeability. These observations suggest that an important mechanism of celecoxib-induced radiosensitization involves inhibition of COX-2-derived PGE(2), thus removing a survival factor for the tumor and its vasculature.

The cyclooxygenase-2 inhibitor, celecoxib, prevents the development of mammary tumors in Her-2/neu mice.

Evidence is now available showing that cyclooxygenase (COX)-2, which is involved in prostaglandin production, is overexpressed in many types of tumors including breast. Several reports have indicated that HER-2/neu-positive breast tumors are associated with an increased amount of COX-2 protein. In this study, we evaluated the effectiveness of the select COX-1 and COX-2 inhibitors in preventing mammary tumor development in HER-2/neu transgenic mice. At 4 weeks of age, female HER-2/neu mice were fed a #5020 rodent diet supplemented with 900 ppm celecoxib, a COX-2 inhibitor, 64 ppm of SC560, a COX-1 inhibitor, or the unsupplemented #5001 diet (control). The incidence of mammary tumors was significantly lower in the celecoxib-fed mice (71%; P = 0.001 versus control) than in the control mice (95%) or in the SC560-fed mice (91%). Celecoxib-treated mice also developed fewer tumors (1.3 +/- 1.1 SD; P = 0.039 versus control) than the control mice (2.2 +/- 1.2) or the SC560 treated mice (2.3 +/- 1.3). The median time to tumor development was 266 days in the control group versus 291 days in the celecoxib-treated group (P = 0.003 versus control). Lung metastasis was also reduced by treatment with celecoxib. The COX-1 inhibitor SC560 had no protective effect. The protection offered by celecoxib was associated with significantly lower concentrations of prostacyclin and prostaglandin E(2) in mammary tumors and their adjacent mammary glands. Our findings provide additional preclinical evidence to support the clinical studies to investigate the potential effectiveness of COX-2 inhibitors in protecting woman who are at high risk for breast cancer.

Chemotherapeutic efficacy of topical celecoxib in a murine model of ultraviolet light B-induced skin cancer.

Over a million nonmelanoma skin cancer cases will be reported in the United States this year alone. Currently the primary form of treatment for these types of skin tumors is excision. However, excision of the initial lesion may not be curative because almost 50% of patients with one nonmelanoma skin cancer lesion develop another tumor within the next 5 yr at the site or adjacent to the site of excision. As with other types of epithelial based cancers, there is mounting evidence for the role of cyclooxygenase-2 (COX-2) and its products, particularly prostaglandin E(2) (PGE(2)), in the development of nonmelanoma skin cancer. To avoid the excision process, the present study was designed to evaluate the possible chemotherapeutic effect of directly treating established tumors with a topical formulation of the specific COX-2 inhibitor celecoxib. Skh/hr hairless mice were irradiated three times per wk for 16 wk to induce tumor formation. The mice were then divided into two groups and treated topically with either 500 microg celecoxib or the vehicle for 6 wk. Our results demonstrated that although topical treatment with celecoxib was not able to induce regression of established tumors, it did prevent new tumor formation after the onset of photocarcinogenesis. Although further studies are warranted, these data suggest that topical celecoxib treatment may prove to be effective in preventing the recurrence of tumors at the site of nonmelanoma skin cancer excision.

Inhibition of cutaneous ultraviolet light B-mediated inflammation and tumor formation with topical celecoxib treatment.

Inflammation, which includes the release of growth factors, proinflammatory cytokines and prostaglandins, the infiltration and activation of inflammatory cells, and the induction of oxidative DNA damage, is known to play a role in cancer development. The combination of damage to the skin resulting from chronic ultraviolet light B (UVB) exposure itself and the inflammatory response it induces is a major source of skin cancer development. Cyclooxygenase-2 (COX-2), an inflammatory enzyme responsible for the production of prostaglandins, is now implicated in the development of epithelial cancers, including squamous cell carcinoma in the skin. Previous work conducted in our laboratory has shown that topical treatment with celecoxib following UVB irradiation inhibits several parameters of acute inflammation, including vascular permeability, the infiltration and activation of neutrophils, and the production of prostaglandin E(2) (PGE(2)). The present studies expanded these observations, demonstrating the ability of topical celecoxib to inhibit acute oxidative damage. In addition, long-term studies illustrate the effectiveness of topical treatment with this drug in reducing chronic inflammation and UVB-induced papilloma/carcinoma formation. This data provides compelling evidence to explore the clinical efficacy of topically applied COX-2 inhibitors for the prevention of human skin cancers.

Direct evidence for a role of cyclooxygenase 2-derived prostaglandin E2 in human head and neck xenograft tumors.

Both nonsteroidal anti-inflammatory drugs (NSAIDs) and cyclooxygenase (COX) 2-selective inhibitors such as celecoxib are being reported as having potent anticancer activity in laboratory models. Several reports have suggested that the mechanism of action of these agents in reducing tumor volume/burden is unrelated to their inhibition of prostaglandin synthesis. Many in vitro reports use supraphysiological concentrations of these drugs to demonstrate COX-independent activities on apoptosis or proliferation. In vivo, most murine tumor models express COX-2 only in the vasculature and stroma, unlike human tumors that also express COX-2 in the tumor cells. In general, these models have the limitation of having no measurable, COX-2-derived, prostaglandins, the inhibition of which correlates with antitumor efficacy. We report here that 1483 human head and neck xenograft tumors express COX-2 similar to the pattern observed in human solid tumors and that COX-2 activity produces high levels of prostaglandin E2 (PGE2). Inhibition of COX-2 by celecoxib resulted in loss of intratumor PGE2 levels and reduced tumor growth in a dose-dependent manner. In contrast, a selective COX-1 inhibitor, SC-560, did not measurably reduce tumor prostaglandin levels or tumor growth despite the presence of COX-1 in the host and tumor cells. Celecoxib-treated tumors showed reduced proliferation and increased apoptosis of both tumor and stromal cells compared with vehicle controls. Specific inhibition of PGE2 activity by a neutralizing antibody mimicked the reduced tumor growth observed after celecoxib treatment, suggesting growth is PGE2 mediated. These data indicate that a major antitumor mechanism of action of celecoxib is inhibition of COX-2-derived prostaglandins, particularly PGE2, and suggest celecoxib as a novel therapeutic agent for human head and neck cancer.

Cyclooxygenase-2 inhibition with celecoxib enhances antitumor efficacy and reduces diarrhea side effect of CPT-11.

Combining anticancer drugs with different mechanisms of action has the potential to enhance antitumor effect. CPT-11 (Camptosar, irinotecan), a topoisomerase I inhibitor, has been shown to be highly effective in the treatment of a variety of cancers. However, its clinical usage is often complicated by late diarrhea. A number of studies have shown that cyclooxygenase (COX)-2 is overexpressed in many forms of human tumors, suggesting that COX-2 inhibition may be useful in the treatment of cancer. In this study, we used two mouse tumor models (HT-29 and colon-26 cells) to evaluate the effect of combining CPT-11 with celecoxib on tumor growth. We also assessed the involvement of COX-2 in the pathogenesis of CPT-11-induced late diarrhea using a rat model. Results indicate that celecoxib enhances the antitumor effect of CPT-11 and reduces the severity of late diarrhea in a dose-dependent manner. The extended benefits of combining celecoxib with CPT-11 may significantly improve the outcome of cancer patients.