Inhibition of prostaglandin-degrading enzyme 15-PGDH rejuvenates aged muscle mass and strength.

Treatments are lacking for sarcopenia, a debilitating age-related skeletal muscle wasting syndrome. We identifed increased amounts of 15-hydroxyprostaglandin dehydrogenase (15-PGDH), the prostaglandin E2 (PGE2)-degrading enzyme, as a hallmark of aged tissues, including skeletal muscle. The consequent reduction in PGE2 signaling contributed to muscle atrophy in aged mice and results from 15-PGDH-expressing myofibers and interstitial cells, such as macrophages, within muscle. Overexpression of 15-PGDH in young muscles induced atrophy. Inhibition of 15-PGDH, by targeted genetic depletion or a small-molecule inhibitor, increased aged muscle mass, strength, and exercise performance. These benefits arise from a physiological increase in PGE2 concentrations, which augmented mitochondrial function and autophagy and decreased transforming growth factor-ß signaling and activity of ubiquitin-proteasome pathways. Thus, PGE2 signaling ameliorates muscle atrophy and rejuvenates muscle function, and 15-PGDH may be a suitable therapeutic target for countering sarcopenia.

Early pregnancy loss in 15-hydroxyprostaglandin dehydrogenase knockout (15-HPGD-/-) mice due to requirement for embryo 15-HPGD activity.

Prostaglandins (PGs) have critical signaling functions in a variety of processes including the establishment and maintenance of pregnancy, and the initiation of labor. Most PGs are non-enzymatically degraded, however, the two PGs most prominently implicated in the termination of pregnancy, including the initiation of labor, prostaglandin E2 (PGE2) and prostaglandin F2α (PGF2α), are enzymatically degraded by 15-hydroxyprostaglandin dehydrogenase (15-HPGD). The role of PG metabolism by 15-HPGD in the maintenance of pregnancy remains largely unknown, as direct functional studies are lacking. To test the hypothesis that 15-PGDH-mediated PG metabolism is essential for pregnancy maintenance and normal labor timing, we generated and analyzed pregnancy in 15-HPGD knockout mice (Hpgd-/-). We report here that pregnancies resulting from matings between 15-HPGD KO mice (Hpgd-/- X Hpgd-/-KO mating) are terminated at mid gestation due to a requirement for embryo derived 15-HPGD. Aside from altered implantation site spacing, pregnancies from KO matings look grossly and histologically normal at days post coitum (dpc) 6.5 and 7.5 of pregnancy. However, virtually all of these pregnancies are resorbed by dpc 8.5. This resorption is preceded by elevation of PGF2∝ but is not preceded by a decrease in circulating progesterone, suggesting that pregnancy loss is a local inflammatory phenomenon rather than a centrally mediated phenomena. This pregnancy loss can be temporarily deferred by indomethacin treatment, but treated pregnancies are not maintained to term and indomethacin treatment increases maternal mortality. We conclude that PG metabolism to inactive products by embryo derived 15-HPGD is essential for pregnancy maintenance in mice, and may serve a similar function during human pregnancy.

TISSUE REGENERATION. Inhibition of the prostaglandin-degrading enzyme 15-PGDH potentiates tissue regeneration.

Agents that promote tissue regeneration could be beneficial in a variety of clinical settings, such as stimulating recovery of the hematopoietic system after bone marrow transplantation. Prostaglandin PGE2, a lipid signaling molecule that supports expansion of several types of tissue stem cells, is a candidate therapeutic target for promoting tissue regeneration in vivo. Here, we show that inhibition of 15-hydroxyprostaglandin dehydrogenase (15-PGDH), a prostaglandin-degrading enzyme, potentiates tissue regeneration in multiple organs in mice. In a chemical screen, we identify a small-molecule inhibitor of 15-PGDH (SW033291) that increases prostaglandin PGE2 levels in bone marrow and other tissues. SW033291 accelerates hematopoietic recovery in mice receiving a bone marrow transplant. The same compound also promotes tissue regeneration in mouse models of colon and liver injury. Tissues from 15-PGDH knockout mice demonstrate similar increased regenerative capacity. Thus, 15-PGDH inhibition may be a valuable therapeutic strategy for tissue regeneration in diverse clinical contexts.

Novel contraceptive targets to inhibit ovulation: the prostaglandin E2 pathway.

BACKGROUND: Prostaglandin E2 (PGE2) is an essential intrafollicular regulator of ovulation. In contrast with the one-gene, one-protein concept for synthesis of peptide signaling molecules, production and metabolism of bioactive PGE2 requires controlled expression of many proteins, correct subcellular localization of enzymes, coordinated PGE2 synthesis and metabolism, and prostaglandin transport in and out of cells to facilitate PGE2 action and degradation. Elevated intrafollicular PGE2 is required for successful ovulation, so disruption of PGE2 synthesis, metabolism or transport may yield effective contraceptive strategies. METHODS: This review summarizes case reports and studies on ovulation inhibition in women and macaques treated with cyclooxygenase inhibitors published from 1987 to 2014. These findings are discussed in the context of studies describing levels of mRNA, protein, and activity of prostaglandin synthesis and metabolic enzymes as well as prostaglandin transporters in ovarian cells. RESULTS: The ovulatory surge of LH regulates the expression of each component of the PGE2 synthesis-metabolism-transport pathway within the ovulatory follicle. Data from primary ovarian cells and cancer cell lines suggest that enzymes and transporters can cooperate to optimize bioactive PGE2 levels. Elevated intrafollicular PGE2 mediates key ovulatory events including cumulus expansion, follicle rupture and oocyte release. Inhibitors of the prostaglandin-endoperoxide synthase 2 (PTGS2) enzyme (also known as cyclooxygenase-2 or COX2) reduce ovulation rates in women. Studies in macaques show that PTGS2 inhibitors can reduce the rates of cumulus expansion, oocyte release, follicle rupture, oocyte nuclear maturation and fertilization. A PTGS2 inhibitor reduced pregnancy rates in breeding macaques when administered to simulate emergency contraception. However, PTGS2 inhibition did not prevent pregnancy in monkeys when administered to simulate monthly contraceptive use. CONCLUSION: PTGS2 inhibitors alone may be suitable for use as emergency contraceptives. However, drugs of this class are unlikely to be effective as monthly contraceptives. Inhibitors of additional PGE2 synthesis enzymes or modulation of PGE2 metabolism or transport also hold potential for reducing follicular PGE2 and preventing ovulation. Approaches which target multiple components of the PGE2 synthesis-metabolism-transport pathway may be required to effectively block ovulation and lead to the development of novel contraceptive options for women. Therapies which target PGE2 may also impact disorders of the uterus and could also have benefits for women's health in addition to contraception.

Biosynthesis and degradation of canine placental prostaglandins: prepartum changes in expression and function of prostaglandin F2α-synthase (PGFS, AKR1C3) and 15-hydroxyprostaglandin dehydrogenase (HPGD).

There is no distinct explanation of the mechanism for the prepartal prostaglandin F2alpha (PGF2alpha) increase in pregnant dogs. Although the PGF2alpha-synthase (PGFS [AKR1C3]) mRNA expression and localization profiles have been previously investigated in canine utero/placental compartments, the availability and biochemical activity of the PGFS (AKR1C3) protein remain unknown. In order to better understand the regulation of canine uterine PGF2alpha availability and eventual prepartum release in luteolytic amounts in dogs, canine-specific PGFS (AKR1C3) and 15-hydroxyprostaglandin dehydrogenase (HPGD) antibodies were generated and used to characterize the expression, cellular localization, and biochemical properties of PGFS (AKR1C3) and HPGD in the utero/placental compartments and corpus luteum throughout pregnancy and at prepartum luteolysis. PGFS (AKR1C3) expression was weak or absent in luteal samples. Uterine PGFS (AKR1C3) was up-regulated postimplantation and declined prepartum. The utero/placental expression of PGFS (AKR1C3) was identified in the superficial uterine glands throughout gestation and in the trophoblast cells within the feto-maternal contact zone during placentation, suggesting a possible role for PGFS (AKR1C3) in the trophoblast invasion. Utero-placental HPGD was up-regulated until postimplantation, lower at midgestation, and greatly suppressed at prepartum. Expression was routinely identified in the endometrial surface and glandular epithelia, and positive signals were also observed in the trophoblast cells at the feto-maternal contact zone. The biochemical activity of recombinant PGFS (AKR1C3) and HPGD was confirmed after its expression in a heterologous system. The colocalization of HPGD with PGFS (AKR1C3) expression suggests a modulatory role for HPGD as a gatekeeper of the supply of prostaglandin in the pregnant canine uterus.

The bioreductive prodrug PR-104A is activated under aerobic conditions by human aldo-keto reductase 1C3.

PR-104, currently in phase II clinical trials, is a phosphate ester pre-prodrug which is converted in vivo to its cognate alcohol, PR-104A, a prodrug designed to exploit tumor hypoxia. Bioactivation occurs via one-electron reduction to DNA crosslinking metabolites in the absence of oxygen. However, certain tumor cell lines activate PR-104A in the presence of oxygen, suggesting the existence of an aerobic nitroreductase. Microarray analysis identified a cluster of five aldo-keto reductase (AKR) family members whose expressions correlated with aerobic metabolism of PR-104A. Plasmid-based expression of candidate genes identified aldo-keto reductase 1C3 as a novel nitroreductase. AKR1C3 protein was detected by Western blot in 7 of 23 cell lines and correlated with oxic PR-104A metabolism, an activity which could be partially suppressed by Nrf2 RNAi knockdown (or induced by Keap1 RNAi), indicating regulation by the ARE pathway. AKR1C3 was unable to sensitize cells to 10 other bioreductive prodrugs and was associated with single-agent PR-104 activity across a panel of 9 human tumor xenograft models. Overexpression in two AKR1C3-negative tumor xenograft models strongly enhanced PR-104 antitumor activity. A population level survey of AKR1C3 expression in 2,490 individual cases across 19 cancer types using tissue microarrays revealed marked upregulation of AKR1C3 in a subset including hepatocellular, bladder, renal, gastric, and non-small cell lung carcinoma. A survey of normal tissue AKR1C3 expression suggests the potential for tumor-selective PR-104A activation by this mechanism. These findings have significant implications for the clinical development of PR-104.

Type 5 17beta-hydroxysteroid dehydrogenase (AKR1C3) contributes to testosterone production in the adrenal reticularis.

CONTEXT: The human adrenal gland produces small amounts of testosterone that are increased under pathological conditions. However, the mechanisms through which the adrenal gland produces testosterone are poorly defined. OBJECTIVE: Our objective was to define the role of type 5 17beta-hydroxysteroid dehydrogenase (AKR1C3) in human adrenal production of testosterone. DESIGN AND METHODS: Adrenal vein sampling was used to confirm ACTH stimulation of adrenal testosterone production. Adrenal expression of AKR1C3 was studied using microarray, quantitative real-time RT-PCR, and immunohistochemical analyses. AKR1C3 knockdown was accomplished in cultured adrenal cells (H295R) using small interfering RNA, followed by measurement of testosterone production. RESULTS: Acute ACTH administration significantly increased adrenal vein testosterone levels. Examination of the enzymes required for the conversion of androstenedione to testosterone using microarray analysis, quantitative real-time RT-PCR, and immunohistochemistry demonstrated that AKR1C3 was present in the adrenal gland and predominantly expressed in the zona reticularis. Decreasing adrenal cell expression of AKR1C3 mRNA and protein inhibited testosterone production in the H295R adrenal cell line. CONCLUSIONS: The human adrenal gland directly secretes small, but significant, amounts of testosterone that increases in diseases of androgen excess. AKR1C3 is expressed in the human adrenal gland, with higher levels in the zona reticularis than in the zona fasciculata. AKR1C3, through its ability to convert androstenedione to testosterone, is likely responsible for adrenal testosterone production.

Inactivation of the anticancer drugs doxorubicin and oracin by aldo-keto reductase (AKR) 1C3.

Resistance towards anticancer drugs is a general problem upon chemotherapy. Among the mechanisms of resistance, metabolic inactivation by carbonyl reduction is a major cause of chemotherapy failure that applies to drugs bearing a carbonyl moiety. Oracin is a promising anticancer drug which is presently in phase II clinical trials. Pharmacokinetic studies have revealed that oracin undergoes metabolic inactivation by carbonyl reduction. In the present study, we provide evidence that AKR1C3, a member of the aldo-keto reductase (AKR) superfamily, catalyzes the inactivation of oracin. Moreover, AKR1C3 does also mediate C13 carbonyl reduction of doxorubicin to its inactive hydroxy metabolite doxorubicinol. Doxorubicinol, however, has also been considered responsible for the cardiomyopathy observed upon doxorubicin chemotherapy. Since AKR1C3 is overexpressed in hormone-dependent malignancies like prostate and breast cancer, coadministration of AKR1C3 inhibitors might enhance the chemotherapeutic efficacy of oracin and doxorubicin, and simultaneously reduce the risk of cardiomyopathy upon doxorubicin treatment.

15-Hydroxyprostaglandin dehydrogenase is a target of hepatocyte nuclear factor 3beta and a tumor suppressor in lung cancer.

The forkhead transcription factor hepatocyte nuclear factor 3beta (HNF3beta) is essential in foregut development and the regulation of lung-specific genes. HNF3beta expression leads to growth arrest and apoptosis in lung cancer cells and HNF3beta is a candidate tumor suppressor in lung cancer. In a transcriptional profiling study using a conditional cell line system, we now identify 15-PGDH as one of the major genes induced by HNF3beta expression. 15-PGDH is a critical metabolic enzyme of proliferative prostaglandins, an antagonist to cyclooxygenase-2 and a tumor suppressor in colon cancer. We confirmed the regulation of 15-PGDH expression by HNF3beta in a number of systems and showed direct binding of HNF3beta to 15-PGDH promoter elements. Western blotting of lung cancer cell lines and immunohistochemical examination of human lung cancer tissues found loss of 15-PGDH expression in approximately 65% of lung cancers. Further studies using in vitro cell-based assays and in vivo xenograft tumorigenesis assays showed a lack of in vitro but significant in vivo tumor suppressor activity of 15-PGDH via an antiangiogenic mechanism analogous to its role in colon cancer. In summary, we identify 15-PGDH as a direct downstream effector of HNF3beta and show that 15-PGDH acts as a tumor suppressor in lung cancer.

Loss of 15-hydroxyprostaglandin dehydrogenase expression disrupts urothelial differentiation.

OBJECTIVES: Urothelial differentiation is essential for the maintenance of urinary bladder function. We explored the expression and function of 15-hydroxyprostaglandin dehydrogenase (PGDH) during urothelial differentiation. METHODS: We evaluated expression of PGDH by Northern and Western blotting and immunostaining in human urothelial cultures, cell lines, and tissues. We determined enzymatic function using enzyme-linked immunosorbent assay. Small inhibitory ribonucleic acids were used to inhibit PGDH expression in human bladder cancer cells. RESULTS: We found PGDH messenger ribonucleic acid was increased in an in vitro model of human urothelial differentiation by Northern blotting. Western blotting of human bladder cancer cell lines showed expression in the well-differentiated RT4 cells and no expression in poorly differentiated UC3 cells. Immunostaining showed that PGDH expression increased with differentiation in normal bladder urothelium. The enzyme was functional in the well-differentiated RT4 human bladder cancer cell line. Inhibition of PGDH expression resulted in disruption of E-cadherin expression at cell-cell contacts in well-differentiated RT4 bladder cancer cells. CONCLUSIONS: These studies indicate that PGDH expression is associated with urothelial differentiation, and loss of PGDH expression results in disruption of urothelial differentiation.

NAD+-dependent 15-hydroxyprostaglandin dehydrogenase regulates levels of bioactive lipids in non-small cell lung cancer.

Elevated levels of procarcinogenic prostaglandins (PG) are found in a variety of human malignancies including non-small cell lung cancer (NSCLC). Overexpression of cyclooxygenase-2 and microsomal prostaglandin synthase 1 occurs in tumors and contributes to increased PG synthesis. NAD+-dependent 15-hydroxyprostaglandin dehydrogenase (15-PGDH), the key enzyme responsible for metabolic inactivation of PGs, is down-regulated in various malignancies. The main objective of this study was to elucidate the effect of loss of 15-PGDH on levels of bioactive lipids in NSCLC. We found that levels of cyclooxygenase-2 and microsomal prostaglandin synthase 1 were commonly increased whereas the amount of 15-PGDH was frequently decreased in NSCLC compared with adjacent normal lung. Reduced expression of 15-PGDH occurred in tumor cells and was paralleled by decreased 15-PGDH activity in tumors. Amounts of PGE1, PGE2, and PGF(2alpha), known substrates of 15-PGDH, were markedly increased whereas levels of 13,14-dihydro-15-keto-PGE2, a catabolic product of PGE2, were markedly reduced in NSCLC compared with normal lung. Complementary in vitro and in vivo experiments were done to determine whether these changes in PG levels were a consequence of down-regulation of 15-PGDH in NSCLC. Similar to NSCLC, amounts of PGE1, PGE2, and PGF(2alpha) were markedly increased whereas levels of 13,14-dihydro-15-keto-PGE2 were decreased in the lungs of 15-PGDH knockout mice compared with wild-type mice or when 15-PGDH was silenced in A549 lung cancer cells. Collectively, these data indicate that 15-PGDH is commonly down-regulated in NSCLC, an effect that contributes to the accumulation of multiple bioactive lipids in NSCLC.

15-Hydroxyprostaglandin dehydrogenase is an in vivo suppressor of colon tumorigenesis.

15-Hydroxyprostaglandin dehydrogenase (15-PGDH) is a prostaglandin-degrading enzyme that is highly expressed in normal colon mucosa but is ubiquitously lost in human colon cancers. Herein, we demonstrate that 15-PGDH is active in vivo as a highly potent suppressor of colon neoplasia development and acts in the colon as a required physiologic antagonist of the prostaglandin-synthesizing activity of the cyclooxygenase 2 (COX-2) oncogene. We first show that 15-PGDH gene knockout induces a marked 7.6-fold increase in colon tumors arising in the Min (multiple intestinal neoplasia) mouse model. Furthermore, 15-PGDH gene knockout abrogates the normal resistance of C57BL/6J mice to colon tumor induction by the carcinogen azoxymethane (AOM), conferring susceptibility to AOM-induced adenomas and carcinomas in situ. Susceptibility to AOM-induced tumorigenesis is mediated by a marked induction of dysplasia, proliferation, and cyclin D1 expression throughout microscopic aberrant crypt foci arising in 15-PGDH null colons and is concomitant with a doubling of prostaglandin E(2) in 15-PGDH null colonic mucosa. A parallel role for 15-PGDH loss in promoting the earliest steps of colon neoplasia in humans is supported by our finding of a universal loss of 15-PGDH expression in microscopic colon adenomas recovered from patients with familial adenomatous polyposis, including adenomas as small as a single crypt. These models thus delineate the in vivo significance of 15-PGDH-mediated negative regulation of the COX-2 pathway and moreover reveal the particular importance of 15-PGDH in opposing the neoplastic progression of colonic aberrant crypt foci.

Aldo-keto reductase (AKR) 1C3: role in prostate disease and the development of specific inhibitors.

Human aldo-keto reductases (AKR) of the 1A, 1B, 1C and 1D subfamilies are involved in the pre-receptor regulation of nuclear (steroid hormone and orphan) receptors by regulating the local concentrations of their lipophilic ligands. AKR1C3 is one of the most interesting isoforms. It was cloned from human prostate and the recombinant protein was found to function as a 3-, 17- and 20-ketosteroid reductase with a preference for the conversion of Delta4-androstene-3,17-dione to testosterone implicating this enzyme in the local production of active androgens within the prostate. Using a validated isoform specific real-time RT-PCR procedure the AKR1C3 transcript was shown to be more abundant in primary cultures of epithelial cells than stromal cells, and its expression in stromal cells increased with benign and malignant disease. Using a validated isoform specific monoclonal Ab, AKR1C3 protein expression was also detected in prostate epithelial cells by immunoblot analysis. Immunohistochemical staining of prostate tissue showed that AKR1C3 was expressed in adenocarcinoma and surprisingly high expression was observed in the endothelial cells. These cells are a rich source of prostaglandin G/H synthase 2 (COX-2) and vasoactive prostaglandins (PG) and thus the ability of recombinant AKR1C enzymes to act as PGF synthases was compared. AKR1C3 had the highest catalytic efficiency (kcat/Km) for the 11-ketoreduction of PGD2 to yield 9alpha,11beta-PGF2 raising the prospect that AKR1C3 may govern ligand access to peroxisome proliferator activated receptor (PPARgamma). Activation of PPARgamma is often a pro-apoptotic signal and/or leads to terminal differentiation, while 9alpha,11beta-PGF2 is a pro-proliferative signal. AKR1C3 is potently inhibited by non-steroidal anti-inflammatory drugs suggesting that the cancer chemopreventive properties of these agents may be mediated either by inhibition of AKR1C3 or COX. To discriminate between these effects we developed potent AKR1C inhibitors based on N-phenylanthranilic acids that do not inhibit COX-1 or COX-2. These compounds can now be used to determine the role of AKR1C3 in producing two proliferative signals in the prostate namely testosterone and 9alpha,11beta-PGF2.

Tibolone metabolism in human liver is catalyzed by 3alpha/3beta-hydroxysteroid dehydrogenase activities of the four isoforms of the aldo-keto reductase (AKR)1C subfamily.

Tibolone [[7alpha,17alpha]-17-hydroxy-7-methyl-19-norpregn-5(10)-en-20-yn-3-one] is used to treat climacteric symptoms and prevent osteoporosis. It exerts tissue-selective effects via site-specific metabolism into 3alpha- and 3beta-hydroxymetabolites and a Delta4-isomer. Recombinant human cytosolic aldo-keto reductases 1C1 and 1C2 (AKR1C1 and AKR1C2) produce 3beta-hydroxytibolone, and the liver-specific AKR1C4 produces predominantly 3alpha-hydroxytibolone. These observations may account for the appearance of 3beta-hydroxytibolone in target tissues and 3alpha-hydroxytibolone in the circulation. Using liver autopsy samples (which express AKR1C1-AKR1C4), tibolone was reduced via 3alpha- and 3beta-hydroxysteroid dehydrogenase (HSD) activity. 3beta-Hydroxytibolone was exclusively formed in the cytosol and was inhibited by the AKR1C2-specific inhibitor 5beta-cholanic acid-3alpha, 7alpha-diol. The cytosolic formation of 3alpha-hydroxytibolone was inhibited by an AKR1C4-selective inhibitor, phenolphthalein. The ratio of these stereoisomers was 4:1 in favor of 3beta-hydroxytibolone. In HepG2 cell cytosol and intact cells (which do not express AKR1C4), tibolone was exclusively reduced to 3beta-hydroxytibolone and was blocked by the AKR1C1-AKR1C3 inhibitor flufenamic acid. In primary hepatocytes (which express AKR1C1-AKR1C4), time-dependent reduction of tibolone into 3beta- and 3alpha-hydroxytibolone was observed again in a 4:1 ratio. 3beta-HSD activity was inhibited by both 5beta-cholanic acid-3alpha,7alpha-diol and flufenamic acid, implicating a role for AKR1C2 and AKR1C1. By contrast, the formation of 3alpha-hydroxytibolone was exclusively inhibited by phenolphthalein implicating AKR1C4 in this reaction. 3beta- and 3alpha-Hydroxytibolone were rapidly metabolized into polar metabolites (>85%). The formation of minor amounts of tibolone was also observed followed by AKR1C-catalyzed epimerization. The low hepatic formation of 3alpha-hydroxytibolone suggests that AKR1C4 is not the primary source of this metabolite and instead it maybe formed by an intestinal or enterobacterial 3alpha-HSD.

The two-step model of prostaglandin signal termination: in vitro reconstitution with the prostaglandin transporter and prostaglandin 15 dehydrogenase.

Termination of prostaglandin (PG) signaling has been proposed to involve carrier-mediated uptake across the plasma membrane followed by cytoplasmic oxidation. Here, we tested this hypothesis directly by coexpressing the PG uptake carrier prostaglandin transporter (PGT) in various cell types with and without human PG 15 dehydrogenase (PG15DH). In HeLa cells, which express neither PGT nor PG15DH, exogenously added PGE2 or PGF2alpha were rapidly oxidized to the 13, 14-dihydro, 15-keto metabolites only when PGT and PG15DH were coexpressed, directly confirming the two-step hypothesis. Cells expressing PG15DH that were broken open formed more PG metabolites than cells in which the PGs could gain access to PG15DH only via PGT. Similar results were obtained using the human prostate cancer cell line LNCaP, in which endogenous PG15DH is induced after exposure to dihydrotestosterone. Because PGT in vivo is expressed in renal collecting duct epithelia, we also expressed PGT in Madin-Darby canine kidney cells grown on filters, where it mediated both the active uptake of PGE2 across the apical membrane and the transepithelial transport of PGE2 to the basolateral compartment. When PG15DH was coexpressed with PGT in these epithelial monolayers, about half of the PGE2 taken up apically was oxidized to 13, 14-dihydro, 15-keto-PGE2, which in turn exited the cells nondirectionally into both the apical and basolateral compartments. Our data represent reconstitution of the longstanding model of PG metabolism consisting of sequential carrier-mediated PG uptake, cytoplasmic oxidation, and diffusional efflux of the PG metabolite.

Tumor growth inhibition by indomethacin in a mouse model of human medullary thyroid cancer: implication of cyclooxygenases and 15-hydroxyprostaglandin dehydrogenase.

Medullary thyroid cancer (MTC) is a C cell neoplasm-secreting calcitonin. Surgery remains the only treatment as the primary tumor and metastases resist radio- and chemotherapies. MTC produces high amounts of prostaglandins (PGs). Nonsteroidal antiinflammatory drugs have an antitumoral effect, generally related to the decrease of PG levels. We assessed the therapeutic potential of indomethacin in a model of human (TT cells) tumors in nude mice. Indomethacin (1.5 or 2.0 mg/kg body weight.d for 7 wk) inhibited tumor volume by 49 or 77%, respectively, and decreased the plasma level of CT. Although the terminal deoxynucleotidyltransferase-mediated deoxyuridine triphosphate nick end labeling method revealed few apoptotic nuclei, the number of proliferating cells was significantly decreased (Ki-67 antigen study). Immunological effector recruitment and vascular network was not modified by treatment. The inducible synthesis enzyme, cyclooxygenase-2 (COX-2), was revealed only in infiltrating cells, both in treated and control tumors. The expression of the constitutive synthesis enzyme COX-1 was diminished, and the expression of 15-prostaglandin dehydrogenase, the key enzyme catabolizing PGs, was increased in treated tumors. Thus, our results demonstrated the potential of indomethacin, inhibitor of COX-1 and COX-2, to prevent MTC growth. The synthesis enzyme, COX-1, and the catabolism enzyme 15-prostaglandin dehydrogenase, could be involved in MTC development.