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Antiproliferative effect of growth hormone-releasing hormone (GHRH) antagonist on ovarian cancer cells… Guo, Jian; Schally, Andrew V; Zarandi, Marta; Varga, Jozsef; Leung, Peter C May 28, 2010

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Guo et al. Reproductive Biology and Endocrinology 2010, 8:54http://www.rbej.com/content/8/1/54Open AccessR E S E A R C HResearchAntiproliferative effect of growth hormone-releasing hormone (GHRH) antagonist on ovarian cancer cells through the EGFR-Akt pathwayJian Guo1,2, Andrew V Schally3, Marta Zarandi3, Jozsef Varga3 and Peter CK Leung*1AbstractBackground: Antagonists of growth hormone-releasing hormone (GHRH) are being developed for the treatment of various human cancers.Methods: MTT assay was used to test the proliferation of SKOV3 and CaOV3. The splice variant expression of GHRH receptors was examined by RT-PCR. The expression of protein in signal pathway was examined by Western blotting. siRNA was used to block the effect of EGFR.Results: In this study, we investigated the effects of a new GHRH antagonist JMR-132, in ovarian cancer cell lines SKOV3 and CaOV3 expressing splice variant (SV)1 of GHRH receptors. MTT assay showed that JMR-132 had strong antiproliferative effects on SKOV3 and CaOV3 cells in both a time-dependent and dose-dependent fashion. JMR-132 also induced the activation and increased cleaved caspase3 in a time- and dose-dependent manner in both cell lines. In addition, JMR-132 treatments decreased significantly the epidermal growth factor receptor (EGFR) level and the phosphorylation of Akt (p-Akt), suggesting that JMR-132 inhibits the EGFR-Akt pathway in ovarian cancer cells. More importantly, treatment of SKOV3 and CaOV3 cells with 100 nM JMR-132 attenuated proliferation and the antiapoptotic effect induced by EGF in both cell lines. After the knockdown of the expression of EGFR by siRNA, the antiproliferative effect of JMR-132 was abolished in SKOV3 and CaOV3 cells.Conclusions: The present study demonstrates that the inhibitory effect of the GHRH antagonist JMR-132 on proliferation is due, in part, to an interference with the EGFR-Akt pathway in ovarian cancer cells.BackgroundOvarian cancer is the second most common gynecologiccancer among women and ranks as the most commoncause of death from gynecologic malignancies in thewestern world [1]. Ovarian cancer is difficult to diagnoseat an early stage and most patients are discovered atadvanced stage due to lack of effective early screeningmethods [2]. Despite the use of cytoreductive surgery andsystemic chemotherapy, the metastatic disease remainsgenerally incurable with a 5-year survival rate of around40% for these patients [1]. Therefore, it is critical to intro-duce more effective therapeutic agents for the manage-ment of this malignancy.Antagonists of growth hormone-releasing hormone(GHRH) are being developed for the treatment of variouscancers [3,4]. Since 1994, many antagonistic analogs ofGHRH have been synthesized in the laboratories of oneof us [3]. GHRH antagonists were shown to inhibit theproliferation both in vivo and in vitro of various humancancers, including pancreatic [5], colorectal [6], prostatic[7-10], breast [11,12], renal [13], glioblastomas [14], oste-osarcomas and Ewing sarcomas [15,16], lung carcinomas[17,18], lymphomas [19], as well as ovarian [20] andendometrial cancer [21]. GHRH antagonists can suppresstumor growth by indirect and direct pathways. The indi-* Correspondence: peleung@interchange.ubc.ca1© 2010 Guo et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons At-tribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in anymedium, provided the original work is properly cited.rect action is mediated through the suppression of pro- Department of Obstetrics & Gynaecology, Child and Family Research Institute, UBC, Vancouver, CanadaFull list of author information is available at the end of the articleGuo et al. Reproductive Biology and Endocrinology 2010, 8:54http://www.rbej.com/content/8/1/54Page 2 of 11duction of the pituitary GH and hepatic insulin-likegrowth factor I (IGF-I), which results in growth inhibi-tion of some tumors [3,22,23]. However, much evidencefrom both in vivo and in vitro experiments shows thatGHRH antagonists can also directly suppress tumor cellsgrowth. Thus, the growth of various human cancers wassuppressed without any involvement of the hypothalamicGHRH/pituitary GH/hepatic IGF-I axis [3]. The effectoccurs through the disruption of the autocrine/paracrineproduction of IGF-I and/or IGF-II in tumors [3,24-26] byGHRH antagonists, or through the blockade of the stimu-latory loop formed by tumoral GHRH and its receptors intumors [3,27-34].Four splice variants (SVs) of GHRH receptors(GHRHR) have been demonstrated in various humancancers and cancer cell lines [3,27]. One of the four iso-forms, SV1 has the greatest structural similarity to thepituitary GHRHR and is probably the main SV that medi-ates the effects of GHRH and its antagonists in tumors[3,27-34].JMR-132 is a novel, highly potent GHRH antagonist.JMR-132 has been shown to inhibit human breast cancer[35,36], prostate cancer [37] and lung cancer [38,39], butthe effect on ovarian cancer cells has not been reportedso far. Knowledge about the mechanisms of GHRHantagonists involved in the antiproliferative effects,including apoptosis and cell circle arrest, is limited. Somerecent studies have shown that cAMP [40], PKC [41], p21[39] and p53 [42,43] may participate in mediating theeffect of GHRH antagonists on inhibition of proliferationand the induction of apoptosis.It has been also proposed that EGFR plays an importantrole in ovarian cancer, since this receptor is overex-pressed in nearly 75% of primary ovarian cancers [44].The over-expression of EGFR might be related toadvanced-stage disease and poor prognosis [45]. EGFRregulates essential cellular functions, including prolifera-tion, apoptosis, migration, and differentiation. Variousligands, such as EGF, amphiregulin (AR) and transform-ing growth factor-α (TGFα), are known to bind to EGFR,and will stimulate receptor homodimerization or het-erodimerization for initiation of signal transduction. Pub-lished data demonstrates that the effects of EGFRsignaling on cell proliferation and survival are mediatedby PI3K-Akt pathways. Activation of EGFR results in theactivation of the lipid kinase, PI3K, generating the secondmessenger phosphatidylinositol 3,4,5-trisphos-phate(PIP3), which in turn activates Akt [46]. Thus,EGFR signaling has become an important target in anti-cancer drug development due to its ability to suppressapoptosis and to control tumor cell proliferation andthe antiproliferative effect of GHRH antagonists [49,50],but it hasn't been reported in ovarian cancer cell lines byJMR-132 treatment.In this study, we for the first time demonstrate that theantiproliferative effect of JMR-132 in SKOV3 and CaOV3cells occurs through EGFR pathway-dependent down-regulation of the p-Akt level, and consequently leads tothe induction of cleaved caspase3, which indicate thatSKOV3 and CaOV3 cells have experienced apoptosis.Our work also suggests that JMR-132 could be useful inthe treatment of ovarian cancers.MethodsReagentsThe GHRH antagonist JMR-132 was synthesized in thelaboratories of one of us. Its structure is [PhAc0-Tyr1, D-Arg2, Phe(4-Cl)6, Ala8, Har9, Tyr(Me)10, His11, Abu15,His20, Nle27, D-Arg28, Har29] hGH-RH(1-29)NH2, whereAbu is α-aminobutyric acid, Har is homoarginine, Nle isnorleucine, PhAc is phenylacetyl and Tyr(Me) is o-meth-yltyrosine, as reported previously [3]. The PI3K inhibitorLY294002 and EGF were purchased from Sigma (St.Louis, MO, USA).Cell cultureHuman epithelial ovarian cancer cell lines SKOV3 andCaOV3 classified as adenocarcinomas were obtainedfrom the American Type Culture Collection (ATCC,Moanassas, USA). The cells were cultured in Dulbecco'sminimum essential medium (DMEM) (Invitrogen Inc.,Burlington, ON, Canada) supplemented with 10% fetalbovine serum (FBS) (HyClone Laboratories Inc., Logan,UT), 100 U/ml penicillin and 100 mg/ml streptomycin(Life Technologies, Inc., Rockville, MD, USA) and incu-bated at 37°C in a humidified incubator with 5% CO2. Thecells were grown to 80% confluence and incubated withserum free medium overnight before treatment withJMR-132, EGF and PI3K inhibitor LY294002.MTT assayCell viability was estimated by the [3-(4,5-dimethylthi-azol-2-yl)-2,5-diphenyltetrazoliumbromide] (MTT)(Sigma-Aldrich Corp.) assay. CaOV3 or SKOV3 cellswere seeded into 96-well dishes (SKOV3, 2 × 103 cells/well; CaOV3, 3 × 103 cells/well) with DMEM containing10% FBS. DMEM medium (180 ul) was added to eachwell. After 24 hours of incubation, the cells were treatedwith GHRH antagonist JMR-132 (100 nM), EGF (10 ng/ml) and PI3K inhibitor LY294002 (10 μM). The MTT col-orimetric assay was performed to detect tumor cell viabil-ity after 24 h, 48 h, 72 h and 96 h of incubation. The cellsmigration [47,48]. Previous in vivo studies in lung cancershowed that decreased EGFR level might be involved inwere then incubated at 37°C with 20 μl of MTT solution(5 mg/ml in PBS) for 4 h. The supernatants were removedGuo et al. Reproductive Biology and Endocrinology 2010, 8:54http://www.rbej.com/content/8/1/54Page 3 of 11and the cells were solubilized in DMSO (200 μl) for 15min. The OD at 490 nm was determined using an ELISAreader (Fisher Scientific Ltd., Ottawa, Canada).mRNA isolation and RT-PCRAfter treatment with JMR-132, the medium was removedfrom each culture dish and RNA was extracted using Tri-zol (Invitrogen). Total RNA (2 μg) was reverse-tran-scribed into first-strand cDNA (GEHealthcare Bio-Science, Piscataway NJ, USA) following the manufac-turer's protocol. The primer for the analysis of mRNAexpression of GHRH receptor SV1 has been described[28,29]. The primers used were 5'-CCT ACT GCC CTTAGG ATG CTG G-3' (sense) and 5'-GCA GTA GAGGAT GGC AAC AAT G-3' (antisense). The PCR condi-tions were 1 cycle at 95°C for 3 min, followed by 40 cyclesat 95°C for 30 s, 60°C for 30 s and 72°C for 60 s. Fourmicroliters of the PCR product were then used to per-form a second PCR. The primers used were 5'-GCA CCTTTG AAG CCA GAG AAG G-3' (sense) and 5'-CACGTG CCA GTG AAG AGC ACG G-3' (antisense). Theproduct length was 720 bp. The primers for humanGAPDH were 5'-ATGTTCGTCATGGGTGTGAACCA-3' (sense) and 5'-TGGCAGGTTTTTCTAGACGGCAG-3' (antisense). The cycling conditions were 94°C for 5 m,followed by 25 cycles of 94°C for 30 s, 55°C for 30 s and72°C for 60 s. The product length was 373 bp. The PCRproducts were electrophoresed on a 2% agarose gel,stained with ethidium bromide and visualized underultraviolet light.Western blottingThe cells were homogenized in RIPA lysis buffer contain-ing 50 nM Tris-HCl pH 7.4, 150 mM NaCl, 1% NonidetP-40 and 0.1% SDS, supplemented with protease inhibi-tors (PMSF) and phosphatase inhibitors (1 mM NaF).After centrifugation (12000 × g, 15 min), the superna-tants were collected and the protein concentrations weredetermined by spectrophotometer. After boiling at 98°Cfor 5 min, 50 μg of total protein per lane was added. Theproteins were separated by 8-10% SDS-PAGE and trans-ferred to a nitrocellulose membrane. The nitrocellulosesheet was incubated in 5% nonfat milk for 1 h at roomtemperature and then exposed to the primary antibodiesagainst caspase3, p-Akt, Akt, EGFR and β-actin (1:1000)at 4°C overnight. After three washes in TBS, the mem-branes were incubated with the correct peroxidase-con-jugated secondary antibodies for 1 h at room temperatureand washed again with TBS. The bands were visualizedwith Supersignal West Pico Chemiluminescent Substrate(Pierce Co., USA).used as a control. The siRNA transfection was performedaccording to the manufacturer's instructions (Invitrogen).Briefly, 24 hours before transfection, 6-well plates wereseeded with 1 × 104 cells per well in 2 ml of culturemedium. The cells were transfected with EGFR (100 nMfinal concentration) or scrambled siRNA with 1 ml oflipofectamine iMAX reagent according to the manufac-turer's protocol. 48 hours later, the cells were treated withJMR-132. For the MTT assay, the cells from the 6-wellplate were re-seeded in a 96-well plate 48 hours aftertransfection.Statistical analysisData were subjected to one-way ANOVA and differenceswere determined by Tukey's multiple comparison test.Each experiment was repeated three times. Data areshown as the means of three individual experiments andpresented as the mean ± SEM. P < 0.0 5 was consideredstatistically significant.ResultsThe expression of mRNA for GHRHR SV1 in SKOV3 and CaOV3 cellsPrevious studies showed that GHRHR SV1 was expressedin different cancer cells. As shown in Figure 1, mRNA forGHRHR SV1 was expressed in both SKOV3 and CaOV3cancer cells. LNCaP cells are androgen-sensitive humanprostate adenocarcinoma cells. It has been reported thatsplice variants 1(SV1) of GHRH receptors was expressedin LNCaP cells [27-29]. However, the level of GHRHRSV1 mRNA in SKOV3 and CaOV3 cells is lower than thatin LNCaP prostate cancer cells, which were used as a pos-itive control.The antiproliferative effect of JMR-132 on the SKOV3 and CaOV3 cell linesThe growth of the SKOV3 and CaOV3 cells was checkedby the MTT assay. As shown in Figure 2A and 2B, boththe treatment with a different dose per day of JMR-132In vitro transfection with small interfering RNAs (siRNAs)siRNAs targeting EGFR were synthesized by Invitrogen(Burlington, ON, Canada). In addition, a nonspecificscrambled siRNA was purchased from Invitrogen andFigure 1 The expression of mRNA for GHRHR SV1 in SKOV3 and CaOV3 human ovarian cancer cells. The prostate cancer cell line LN-CaP was used as a positive control. Human GAPDH was used as an in-ternal control.Guo et al. Reproductive Biology and Endocrinology 2010, 8:54http://www.rbej.com/content/8/1/54Page 4 of 11Figure 2 Antiproliferative effect of JMR-132 on SKOV3 and CAOV3 cells. SKOV3 (2000/well) and CaOV3 (3000/well) were treated with JMR-132 at a different dose (25, 50, 100 and 200 nM) per day for 2 days (A), (C) and with 100 nM JMR-132 per day for different periods of time (24, 48, 72 and 96 h) (B) (D). MTT assay showed that proliferation was inhibited in a dose (A) and time (B) dependent manner after JMR-132 treatment. * P < 0.05 com-pared to the no treatment group. The expression of cleaved caspase3 increased in a dose (C) and time (D) dependent manner. The results indicated that JMR-132 treatment induced apoptosis in these cells.Guo et al. Reproductive Biology and Endocrinology 2010, 8:54http://www.rbej.com/content/8/1/54Page 5 of 11for 2 days and treatment with 100 nM JMR-132 per dayfor 1 to 4 days resulted in a significant decrease in thegrowth of SKOV3 and CaOV3 cells compared to the con-trol group. However, the effect in SKOV3 cells was stron-ger than that in CaOV3 cells. The maximum inhibitionoccurred after continuous treatment for 4 days with 100nM JMR-132 and reached about 60% in SKOV3 cells.These data showed that JMR-132 can suppress growth ofSKOV3 and CaOV3 cells in a dose- and time-dependentmanner.To further clarify whether the antiproliferative effect isdue to growth inhibition or apoptosis induced in theSKOV3 and CaOV3 cells, we checked the expression ofcleaved caspase3 which is a known marker of apoptosis.As shown in Figure 2C and 2D, after treatment with JMR-132, the level of cleaved caspase3 obviously increased intime- and dose-dependent manner. As seen from growthinhibition in SKOV3 and CaOV3 cells, the increase in thelevel of cleaved caspase3 in SKOV3 cells was greater thanthat in CaOV3 cells. Thus apoptosis might contribute tothe antiproliferative effect induced by JMR-132 treatmentin SKOV3 and CaOV3 cells.Decrease in EGFR level after JMR-132 treatment in SKOV3 and CaOV3 cellsEGFR plays an important role in proliferation in cancerresearch. To determine whether the mechanism of theantiproliferative effect of JMR-132 is associated withEGFR, we studied the EGFR protein expression. Asshown in Figure 3, EGFR levels decreased significantly inSKOV3 and CaOV3 cells after 48 to 96 hours of treat-ment with 100 nM JMR-132. Our data indicated thereforethat EGFR might be involved in the regulation of theeffect of JMR-132.JMR-132 attenuates the effect of EGF-induced p-Akt activationTo characterize whether the antiproliferative effect isrelated to the decreased level of EGFR, we measuredEGFR downstream signaling by Western blotting of Aktand apoptotic-associated caspase3. We first confirmedthat EGF (10 ng/μl) induced p-Akt activation (Figure 4A).The treatment of SKOV3 and CaOV3 cells with JMR-132led to a decrease in p-Akt (Figure 4B), which suggestedthat the antiproliferative effect might result from thePI3K-Akt pathway. Using the PI3K-specific inhibitorLY294002 as a positive control, we treated the cells withJMR-132 alone or in combination with EGF and foundthat JMR-132 still inhibited p-Akt expression as com-pared to the control group. In addition, JMR-132 attenu-ated the EGF-induced increase in the p-Akt level. Ourresults indicate that the EGFR-Akt pathway plays a role inregulating the function of the GHRH antagonist JMR-132.JMR-132 abolishes the pro-proliferative and anti-apoptotic effect of EGFTo continue the investigation of the EGFR-Akt pathway,we examined the proliferation of SKOV3 and CaOV3cells after treatment with JMR-132 alone or in combina-tion with EGF. As shown in Figure 5A, the growth ofSKOV3 and CaOV3 cells was significantly inhibited aftertreatment with JMR-132 alone or in combination withEGF. The antiproliferative effect was stronger in SKOV3cells than in CaOV3 cells. We also examined the expres-sion of caspase3 in SKOV3 and CaOV3 cells after thesame treatment. Similar to the proliferation data, JMR-132 upregulated the level of cleaved caspase3, which sug-gested that apoptosis occurred. However, EGFR plays anantiapoptotic role and no cleaved caspase3 was inducedin the EGF treatment group. Interestingly, treatment withJMR-132 in combination with EGF again led to anincrease in the level of the cleaved caspase3. The apopto-sis data are consistent with the proliferation data, sug-gesting that the antiproliferative effect is mainly due tothe cells undergoing apoptosis and partially to the anti-proliferative effect of JMR-132 acting on the EGFR-Aktpathway.Lack of effect of treatment with JMR-132 after EGFR siRNA transfection in SKOV3 and CaOV3 cellsTo further confirm that EGFR is involved in mediatingthe function of JMR-132, we knocked down EGFR using100 nM EGFR siRNA. After transfection with 100 nMEGFR siRNA for 2 days, the EGFR expression was signifi-cantly decreased. Since we reseeded the cells in a 96-wellplate after stable EGFR siRNA transfection to examinethe cell proliferation with or without JMR-132 treatmentfor 2 and 4 days, we checked the long-term expression ofEGFR, which was still low (Figure 6A). In the MTT assay(Figure 6B), we found that the growth of SKOV3 andFigure 3 The expression of EGFR in SKOV3 and CaOV3 cells de-creased after JMR-132 treatment. The protein level of EGFR de- CaOV3 cells was inhibited after EGFR was knockeddown, which indicated that EGFR plays a major role incell proliferation. More importantly, no changes in prolif-creased after treatment with 100 nM JMR-132 per day for 2 and 4 days. β-actin was used as an internal control. The data are from one experi-ment and are representative of the three separate experiments.Guo et al. Reproductive Biology and Endocrinology 2010, 8:54http://www.rbej.com/content/8/1/54Page 6 of 11eration were detected after transfection with EGFRsiRNA, following JMR-132 treatment. However, therewas still an inhibitory effect of JMR-132 in the controlsiRNA transfection group. The same results were foundfor cleaved caspase3 expression in SKOV3 cells (Figure6C). These data suggest that the antiproliferative effect ofJMR-132 was reduced. Consistent with the results forthen examined the expression of cleaved caspase3 with orwithout JMR-132 treatment after knocking down EGFR,and no obvious changes between the two groups werefound. These data confirmed that the antiproliferativeeffect of JMR-132 is partially due to the decrease inEGFR. In addition, the effects on growth inhibition andapoptosis induction after JMR-132 treatment wereFigure 4 JMR-132 attenuated the effect of EGF-induced p-Akt activation. A. p-Akt was activated after EGF (10 ng/ul) treatment without changes in Akt. β-actin was used as an internal control. B. p-Akt expression decreased after treatment with 100 nM JMR-132 per day for 2 and 4 days without changes in Akt level. C. JMR-132 attenuated the effect of EGF-induced p-Akt expression. JMR-132 (100 nM) and PI3K specific inhibitor LY294002 (10 nM) were used separately to continuously treat SKOV3 and CaOV3 cells for 2 days. PI3K specific inhibitor LY294002 was used as a positive control. β-actin was used as an internal control. EGF was added 15 min prior to harvesting.proliferation, the level of cleaved caspase3 was slightlyincreased after knocking down EGFR, which indicatesthat a decrease in the EGFR level results in apoptosis. Wegreater in the EGFR siRNA group compared to the con-trol siRNA group, which confirmed the importance ofEGFR in cell proliferation.Guo et al. Reproductive Biology and Endocrinology 2010, 8:54http://www.rbej.com/content/8/1/54Page 7 of 11DiscussionSince 1994, various GHRH analogs with different struc-tural features, including GHRH agonists and antagonists,have been synthesized [3]. Many studies were performedon the effects of the GHRH antagonists on differentexperimental cancers or human cancer cell lines. It wasfound that the treatment with the GHRH antagonistsantagonists on the proliferation of ovarian cancer [3,20],the effects of GHRH antagonists on other aspects of can-cer phenomena, such as apoptosis, is poorly understood.It has been also shown that the GHRH antagonist JMR-132 had antiproliferative effects in lung, breast and pros-tate cancers [35-39], but the effect of JMR-132 on ovariancancer cell lines was not reported. Thus, we conductedFigure 5 JMR-132 abolished the pro-proliferative and anti-apoptotic effect of EGF. A. Using the MTT assay, it was determined that the growth of SKOV3 and CaOV3 cells was significantly inhibited after continuous treatment with 100 nM JMR-132 for 2 days in combination with EGF (10 μg/ml). Letters (a, b, c) between pairs indicate significant differences (P < 0.05). B. The expression of cleaved caspase3 increased during treatment with 100 nM JMR-132 per day for 2 days in combination with EGF (10 μg/ml). β-actin was used as an internal control. EGF was added 15 min prior to harvesting in (A) and (B).inhibit the growth of many human cancers, includingovarian cancer cell lines [3,20]. Although these observa-tions have demonstrated the inhibitory role of GHRHthe present study to examine the effect of JMR-132 ontwo ovarian cancer cell lines, SKOV3 and CaOV3, and toinvestigate the mechanisms involved.Guo et al. Reproductive Biology and Endocrinology 2010, 8:54http://www.rbej.com/content/8/1/54Page 8 of 11Previous studies showed that SV1 of GHRHR expressedin several cancers, may mediate the direct inhibitoryeffect of GHRH antagonists [3,27-34]. Here, we examinedthe expression of GHRHR SV1 in SKOV3 and CaOV3cancer cell lines. Our data are in agreement with previousstudies, indicating that GHRHR SV1 may play a func-tional role in regulating the effect of GHRH antagonists.The presence and the role of pituitary type of GHRHreceptor [3,17] in ovarian cancer lines was not investi-gated in this study.The effect of the GHRH antagonist JMR-132 on ovariancancer cells was primarily studied with the MTT assay.Treatment with JMR-132 significantly inhibited the pro-liferation of SKOV3 and CaOV3 ovarian cancer cell lines.We then considered whether this antiproliferative effectwas due to growth inhibition or apoptosis induction.132 induced an increase in activated caspase3 in a time-and dose-dependent manner, which indicates that thecells were undergoing apoptosis. Both cell cycle arrestand apoptosis lead to growth inhibition. We also lookedfor changes in the cell cycle phase using flow cytometry;the G1 phase showed no obviously increase (data notshown). Results from this study demonstrate that growthsuppression induced by JMR-132 treatment may be dueto promoting apoptosis, not by cell cycle arrest. In short,JMR-132 could activate and increase cleaved caspase3expression in ovarian cancer cells, which resulted inapoptosis, thus inhibiting the cell proliferation. There-fore, the apoptosis induced by JMR-132 treatment was amain contributor to proliferative inhibition.The overexpression of EGFR results in an increasedproliferation of solid tumors, including ovarian cancerFigure 6 No changes were detected after transfection with EGFR siRNA, either with or without JMR-132 treatment. A. EGFR was knocked down after transfection with EGFR siRNA for various periods of time. After transfection with 100 nM EGFR siRNA for 48 hours, we reseeded the cells for the MTT assay. Pretreatment: after cell reseeding; 48 and 96 hours: treatment with 100 nM JMR-132 per day for 2 and 4 days after cell reseeding. The EGFR expression was still lower when compared to the cells transfected with 100 nM control siRNA. B. No changes were found by the MTT assay after transfection with EGFR siRNA, with or without JMR-132 treatment. The cells (SKOV3 and CaOV3: 4000/well) were reseeded in a 96-well plate after trans-fection with control siRNA or EGFR siRNA for 2 days. After 2 and 4 days of treatment with 100 nM JMR-132, the MTT assay was performed. Letters (a, b, c) indicate significant differences (P < 0.05) between pairs. C. No changes were detected in cleaved caspase3 expression after transfection with EGFR siRNA, either with or without JMR-132 treatment in SKOV3 cells. After transfection with 100 nM EGFR siRNA for 48 hours, the SKOV3 cells were treated with 100 nM JMR-132 per day for 2 days. β-actin was used as an internal control.Cleaved caspase3, the large fragment (17-19 kDa) of acti-vated caspase3, results from pro-caspase3 (37KD) and isa known marker of apoptosis. It was observed that JMR-[45]. Moreover, EGFR expression correlates with tumorresistance to chemotherapy [45] and indicates a poorprognosis. Previous studies suggested that the antiprolif-Guo et al. Reproductive Biology and Endocrinology 2010, 8:54http://www.rbej.com/content/8/1/54Page 9 of 11erative effect of the GHRH antagonist might involveEGFR [49,50]. However, the molecular mechanisms link-ing GHRH antagonists to the EGFR pathway in ovariancancer cells were not well established. Our findingsshowed that the protein level of EGFR decreased afterJMR-132 treatment, which means that the antiprolifera-tive effect of JMR-132 might be associated with EGFR. Itis well known that the activation of EGFR leads to theactivation of PI3K, which in turn activates Akt, the maindownstream target, which appears to play various impor-tant roles in regulating cellular growth and apoptosis[48]. Therefore, to characterize the cell growth inhibitiondue to the decrease in EGFR protein, we measured EGFRdownstream signaling of the Akt pathway by Westernblotting. In accord with the decrease in EGFR level, treat-ment with JMR-132 induced a down-regulation of phos-phorylation of Akt. More importantly, JMR-132 couldattenuate the EGF-induced, upregulated p-Akt level. Itwas also observed that, treatment of SKOV3 and CaOV3cells with JMR-132 alone, as well as co-treatment withEGF or treatment with LY294002, a PI3K/Akt inhibitor,the pro-proliferative effect of EGF was all abolished byJMR-132. These results demonstrate that the down-regu-lation of the EGFR-Akt pathway which was induced byJMR-132 treatment results in inhibition of cell prolifera-tion. In addition, it was reported that Akt can directlyinhibit caspase9 and caspase3 to avoid apoptosis andcleaved caspase3 level was activated and increased bydecreased p-Akt level [51]. Then we examined the effectof EGFR-Akt pathway in apoptotic process. Similarresults were seen with cleaved caspase3 level. The expres-sion of cleaved caspase3 was still increased after treat-ment with JMR-132 in combination with EGF. JMR-132and EGF co-treatment were able to counter the EGF pro-tection of cells, which led to an increase in cleavedcaspase3, suggesting that apoptosis still occurred. Thedata demonstrate that down-regulation of the EGFR-Aktpathway induced by JMR-132 treatment is the main con-tributor in suppression of cell proliferation and inductionof apoptosis.These observations prompted us to investigate whetherthe antiproliferative effect of JMR-132 could be altered ifendogenous EGFR was eliminated. The results confirmedour hypothesis as there was no difference between thesiControl and siEGFR groups after treatment with JMR-132. The same findings were observed for cleavedcaspase3 expression. These data suggest that the antipro-liferative effect of JMR-132 is abolished if EGFR expres-sion is knocked down, confirming that theantiproliferative effect of JMR-132 is due to the reductionin EGFR. Thus, our findings indicate that the effect ofOf much interest was the observation of slowed growthand cleaved caspase 3 induction in SKOV3 and CaOV3cells after EGFR knock-down, which indicates that adecreased level of EGFR results in apoptosis anddecreased proliferation. Furthermore, the effects of JMR-132 growth inhibition in CaOV3 cells were higher in theEGFR siRNA group when compared to the control siRNAgroup after JMR-132 treatment. All these results point tothe critical role of EGFR in cell proliferation. Therefore,the inhibition of EGFR level by JMR-132 could be of sig-nificance in clinical treatment ovarian cancer.ConclusionsIn summary, we show here for the first time that theGHRH antagonist JMR-132 acts as an effective anti-pro-liferation agent in the ovarian cancer cell lines, SKOV3and CaOV3, by inducing apoptosis. Furthermore, we alsoshed light on the potential molecular mechanism of JMR-132, which may occur through partial suppression of theEGFR-Akt pathway.Competing interestsThe authors declare that they have no competing interests.Authors' contributionsJG designed the study and performed the experiments and participated in dis-cussion of the results and drafted the manuscript. AVS, MZ and JV provided thereagent of JMR-132, and were responsible for supervision of this work. PCKLwas responsible for the conception, design, discussion of the results, draftingand critical revision of the manuscript. All authors read and approved the finalmanuscript.AcknowledgementsThis work was supported by the Canadian Institutes of Health Research (PCKL), and in part by the Medical Research Service of the Veterans Affairs Department and the University of Miami Miller School of Medicine Departments of Pathol-ogy and Medicine Division of Hematology/Oncology (AVS).Author Details1Department of Obstetrics & Gynaecology, Child and Family Research Institute, UBC, Vancouver, Canada, 2School of Preclinical Medicine, Beijing University of Chinese Medicine, Beijing, China and 3Veterans Affairs Medical Center and Departments of Pathology and Medicine, Division of Hematology/Oncology, University of Miami Miller School of Medicine, Miami, FL 33125, USAReferences1. Jemal A, Siegel R, Ward E, Hao Y, Xu J, Thun MJ: Cancer statistics, 2009.  CA Cancer J Clin 2009, 59:225-249.2. Partridge EE, Barnes MN: Epithelial ovarian cancer: prevention, diagnosis, and treatment.  CA Cancer J Clin 1999, 49:297-320.3. Schally AV, Varga JL, Engel JB: Antagonists of growth-hormone-releasing hormone: an emerging new therapy for cancer.  Nat Clin Pract Endocrinol Metab 2008, 4:33-43.4. Gelato M: Growth hormone releasing hormone: clinical perspectives revisited.  Endocrinologist 2005, 15:159-164.5. Szepeshazi K, Schally AV, Groot K, Armatis P, Hebert F, Halmos G: Antagonists of growth hormone-releasing hormone (GH-RH) inhibit in vivo proliferation of experimental pancreatic cancers and decrease Received: 2 February 2010 Accepted: 28 May 2010 Published: 28 May 2010This article is available from: http://www.rbej.com/content/8/1/54© 2010 Guo et al; licensee BioMed Central Ltd. is an Op n Access article distributed un er the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.Reprodu tive Biology and Endocrinology 2010, 8:54JMR-132 on proliferation may partially be mediatedthrough the EGFR pathway.IGF-II levels in tumours.  Eur J Cancer 2000, 36:128-136.6. Szepeshazi K, Schally AV, Groot K, Armatis P, Halmos G, Herbert F, Szende B, Varga JL, Zarandi M: Antagonists of growth hormone-releasing Guo et al. Reproductive Biology and Endocrinology 2010, 8:54http://www.rbej.com/content/8/1/54Page 10 of 11hormone (GH-RH) inhibit IGF-II production and growth of HT-29 human colon cancers.  Br J Cancer 2000, 82:1724-1731.7. Jungwirth A, Schally AV, Pinski J, Halmos G, Groot K, Armatis P, Vadillo-Buenfil M: Inhibition of in vivo proliferation of androgen-independent prostate cancers by an antagonist of growth hormone-releasing hormone.  Br J Cancer 1997, 75:1585-1592.8. Lamharzi N, Schally AV, Koppan M, Groot K: Growth hormone-releasing hormone antagonist MZ-5-156 inhibits growth of DU-145 human androgen-independent prostate carcinoma in nude mice and suppresses the levels and mRNA expression of insulin-like growth factor II in tumors.  Proc Natl Acad Sci USA 1998, 95:8864-8868.9. Letsch M, Schally AV, Busto R, Bajo AM, Varga JL: Growth hormone-releasing hormone (GHRH) antagonists inhibit the proliferation of androgen-dependent and -independent prostate cancers.  Proc Natl Acad Sci USA 2003, 100:1250-1255.10. Stangelberger A, Schally AV, Varga JL, Zarandi M, Szepeshazi K, Armatis P, Halmos G: Inhibitory effect of antagonists of bombesin and growth hormone-releasing hormone on orthotopic and intraosseous growth and invasiveness of PC-3 human prostate cancer in nude mice.  Clin Cancer Res 2005, 11:49-57.11. Kahan Z, Varga JL, Schally AV, Rekasi Z, Armatis P, Chatzistamou L, Czompoly T, Halmos G: Antagonists of growth hormone-releasing hormone arrest the growth of MDA-MB-468 estrogen-independent human breast cancers in nude mice Breast.  Cancer Res Treat 2000, 60:71-79.12. Chatzistamou I, Schally AV, Varga JL, Groot K, Busto R, Armatis P, Halmos G: Inhibition of growth and metastases of MDA-MB-435 human estrogen-independent breast cancers by an antagonist of growth hormone-releasing hormone.  Anticancer Drugs 2001, 12:761-768.13. Jungwirth A, Schally AV, Pinski J, Groot K, Armatis P, Halmos G: Growth hormone-releasing hormone antagonist MZ-4-71 inhibits in vivo proliferation of Caki-I renal adenocarcinoma.  Proc Natl Acad Sci USA 1997, 94:5810-5813.14. Kiaris H, Schally AV, Varga JL: Antagonists of growth hormone-releasing hormone inhibit the growth of U-87MG human glioblastoma in nude mice.  Neoplasia 2000, 2:242-250.15. Pinski J, Schally AV, Groot K, Halmos G, Szepeshazi K, Zarandi M, Armatis P: Inhibition of growth of human osteosarcomas by antagonists of growth hormone-releasing hormone.  J Natl Cancer Inst 1995, 87:1787-1794.16. Braczkowski R, Schally AV, Plonowski A, Varga JL, Groot K, Krupa M, Armatis P: Inhibition of proliferation in human MNNG/HOS osteosarcoma and SK-ES-1 Ewing sarcoma cell lines in vitro and in vivo by antagonists of growth hormone-releasing hormone: effects on insulin-like growth factor II.  Cancer 2002, 95:1735-1745.17. Hohla F, Schally AV, Szepeshazi K, Varga JL, Buchholz S, Köster F, Heinrich E, Halmos G, Rick FG, Kannadka C, Datz C, Kanashiro CA: Synergistic inhibition of growth of lung carcinomas by antagonists of growth hormone-releasing hormone in combination with docetaxel.  Proc Natl Acad Sci USA 2006, 103:14513-8.18. Szereday Z, Schally AV, Varga JL, Kanashiro CA, Hebert F, Armatis P, Groot K, Szepeshazi K, Halmos G, Busto R: Antagonists of growth hormone-releasing hormone inhibit the proliferation of experimental non-small cell lung carcinoma.  Cancer Res 2003, 63:7913-7919.19. Keller G, Schally AV, Groot K, Toller GL, Havt A, Köster F, Armatis P, Halmos G, Zarandi M, Varga JL, Engel JB: Effective treatment of experimental human non-Hodgkin's lymphomas with antagonists of growth hormone-releasing hormone.  Proc Natl Acad Sci USA 2005, 102:10628-33.20. Chatzistamou I, Schally AV, Varga JL, Groot K, Armatis P, Busto R, Halmos G: Antagonists of growth hormone-releasing hormone and somatostatin analog RC-160 inhibit the growth of the OV-1063 human epithelial ovarian cancer cell line xenografted into nude mice.  J Clin Endocrinol Metab 2001, 86:2144-52.21. Engel JB, Keller G, Schally AV, Toller GL, Groot K, Havt A, Armatis P, Zarandi M, Varga JL, Halmos G: Inhibition of growth of experimental human endometrial cancer by an antagonist of growth hormone-releasing hormone.  J Clin Endocrinol Metab 2005, 90:3614-3621.antagonists indicative of interference with both IGF and EGF pathways.  Prostate 2000, 44:172-80.23. Jaffe CA, DeMott-Friberg R, Frohman LA, Barkan AL: Suppression of growth hormone (GH) hypersecretion due to ectopic GH-releasing hormone (GHRH) by a selective GHRH antagonist.  J Clin Endocrinol Metab 1997, 82:634-637.24. Szepeshazi K, Schally AV, Armatis P, Groot K, Hebert F, Feil A, Varga JL, Halmos G: Antagonists of GHRH decrease production of GH and IGF-I in MXT mouse mammary cancers and inhibit tumor growth.  Endocrinology 2001, 142:4371-8.25. Plonowski A, Schally AV, Letsch M, Krupa M, Hebert F, Busto R, Groot K, Varga JL: Inhibition of proliferation of PC-3 human prostate cancer by antagonists of growth hormone-releasing hormone: lack of correlation with the levels of serum IGF-I and expression of tumoral IGF-II and vascular endothelial growth factor.  Prostate 2002, 52:173-182.26. Rekasi Z, Varga JL, Schally AV, Halmos G, Armatis P, Groot K, Czompoly T: Antagonists of GHRH decrease production of GH and IGF-I in MXT mouse mammary cancers and inhibit tumor growth.  Endocrinology 2000, 141:2120-2128.27. Rekasi Z, Czompoly T, Schally AV, Halmos G: Isolation and sequencing of cDNAs for splice variants of growth hormone releasing hormone receptors from human cancers.  Proc Natl Acad Sci USA 2000, 97:10561-10566.28. Plonowski A, Schally AV, Busto R, Krupa M, Varga JL, Halmos G: Expression of growth hormone-releasing hormone (GHRH) and splice variants of GHRH receptors in human experimental prostate cancers Peptides.  2002, 23:1127-1133.29. Busto R, Schally AV, Varga JL, Garcia-Fernandez MO, Groot K, Armatis P, Szepeshazi K: The expression of growth hormonereleasing hormone (GHRH) and splice variants of its receptor in human gastroenteropancreatic carcinomas.  Proc Natl Acad Sci USA 2002, 99:11866-11871.30. Busto R, Schally AV, Braczkowski R, Plonowski A, Krupa M, Groot K, Armatis P, Varga JL: Expression of mRNA for growth hormone-releasing hormone and splice variants of GHRH receptors in human malignant bone tumors.  Regul Pept 2002, 108:47-53.31. Garcia-Fernandez MO, Schally AV, Varga JL, Groot K, Busto R: The expression of growth hormone-releasing hormone (GHRH) and its receptor splice variants in human breast cancer lines; the evaluation of signaling mechanisms in the stimulation of cell proliferation.  Breast Cancer Res Treat 2003, 77:15-26.32. Kiaris H, Schally AV, Busto R, Halmos G, Artavanis-Tsakonas S, Varga JL: Expression of a splice variant of the receptor for GHRH in 3T3 fibroblasts activates cell proliferation responses to GHRH analogs.  Proc Natl Acad Sci USA 2002, 99:196-200.33. Kiaris H, Chatzistamou I, Schally AV, Halmos G, Varga JL, Koutselini H, Kalofoutis A: Ligand-dependent and -independent effects of splice variant 1 of growth hormonereleasinghormone receptor.  Proc Natl Acad Sci USA 2003, 100:9512-9517.34. Barabutis N, Tsellou E, Schally AV, Kouloheri S, Kalofoutis A, Kiaris H: Stimulation of proliferation of MCF-7 breastcancer cells by a transfected splice variant of growth hormone releasing hormone receptor.  Proc Natl Acad Sci USA 2007, 104:5575-5579.35. Seitz S, Hohla F, Schally AV, Moder A, Engel JB, Horn F, Varga J, Zarandi M, Ortmann O, Köster F, Buchholz S: Inhibition of estrogen receptor positive and negative breast cancer cell lines with a growth hormone-releasing hormone antagonist.  Oncol Rep 2008, 20:1289-94.36. Buchholz S, Schally AV, Engel JB, Hohla F, Heinrich E, Koester F, Varga JL, Halmos G: Potentiation of mammary cancer inhibition by combination of antagonists of growth hormone-releasing hormone with docetaxel.  Proc Natl Acad Sci USA 2007, 104:1943-6.37. Barabutis N, Schally AV: Antioxidant activity of growth hormone-releasing hormone antagonists in LNCaP human prostate cancer line.  Proc Natl Acad Sci USA 2008, 105:20470-5.38. Barabutis N, Schally AV: Knocking down gene expression for growth hormone-releasing hormone inhibits proliferation of human cancer cell lines.  Br J Cancer 2008, 98:1790-6.39. Volakaki AA, Lafkas D, Kassi E, Schally AV, Papavassiliou AG, Kiaris H: 22. Plonowski A, Schally AV, Varga JL, Rekasi Z, Hebert F, Halmos G, Groot K: Potentiation of the inhibitory effect of growth hormone-releasing hormone antagonists on PC-3 human prostate cancer by bombesin Essential role of p21/waf1 in the mediation of the antiproliferative effects of GHRH antagonist JMR-132.  J Mol Endocrinol 2008, 41:389-92.Guo et al. Reproductive Biology and Endocrinology 2010, 8:54http://www.rbej.com/content/8/1/54Page 11 of 1140. Csernus V, Schally AV, Groot K: Antagonistic analogs of growth hormone releasing hormone (GHRH) inhibit cyclic AMP production of human cancer cell lines in vitro.  Peptides 1999, 20:843-50.41. Kanashiro CA, Schally AV, Zarandi M, Hammann BD, Varga JL: Suppression of growth of H-69 small cell lung carcinoma by antagonists of growth hormone releasing hormone and bombesin is associated with an inhibition of protein kinase C signaling.  Int J Cancer 2004, 112:570-6.42. Kanashiro CA, Schally AV, Groot K, Armatis P, Bernardino AL, Varga JL: Inhibition of mutant p53 expression and growth of DMS-153 small cell lung carcinoma by antagonists of growth hormone-releasing hormone and bombesin.  Proc Natl Acad Sci USA 2003, 100:15836-41.43. Zhao L, Yano T, Osuga Y, Nakagawa S, Oishi H, Wada-Hiraike O, Tang X, Yano N, Kugu K, Schally AV, Taketani Y: Cellular mechanisms of growth inhibition of human endometrial cancer cell line by an antagonist of growth hormone-releasing hormone.  Int J Oncol 2008, 32:593-601.44. Chan JK, Pham H, You XJ, Cloven NG, Burger RA, Rose GS, Van Nostrand K, Korc M, Disaia PJ, Fan H: Suppression of ovarian cancer cell tumorigenicity and evasion of Cisplatin resistance using a truncated epidermal growth factor receptor in a rat model.  Cancer Res 2005, 65:3243-3248.45. Berchuck A, Rodriguez GC, Kamel A, Dodge RK, Soper JT, Clarke-Pearson DL, Bast RC Jr: Epidermal growth factor receptor expression in normal ovarian epithelium and ovarian cancer. I. Correlation of receptor expression with prognostic factors in patients with ovarian cancer.  Am J Obstet Gynecol 1991, 164:669-674.46. Hackel PO, Zwick E, Prenzel N, Ullrich A: Epidermal growth factor receptors: critical mediators of multiple receptor pathways.  Curr Opin Cell Biol 1999, 11:184-18.47. Maihle NJ, Baron AT, Barrette BA, Boardman CH, Christensen TA, Cora EM, Faupel-Badger JM, Greenwood T, Juneja SC, Lafky JM, Lee H, Reiter JL, Podratz KC: EGF/ErbB receptor family in ovarian cancer.  Cancer Treat Res 2002, 107:247-258.48. Zhou C, Qiu L, Sun Y, Healey S, Wanebo H, Kouttab N, Di W, Yan B, Wan Y: Inhibition of EGFR/PI3K/AKT cell survival pathway promotes TSA's effect on cell death and migration in human ovarian cancer cells.  Int J Oncol 2006, 29:269-78.49. Kanashiro CA, Schally AV, Varga JL, Hammann B, Halmos G, Zarandi M: Antagonists of growth hormone releasing hormone and bombesin inhibit the expression of EGF/HER receptor family in H-69 small cell lung carcinoma.  M Cancer Lett 2005, 226:123-131.50. Kanashiro CA, Schally AV, Zarandi M, Hammann BD, Varga JL: Alterations of EGFR/HER, angiogenesis and apoptosis pathways after therapy with antagonists of growth hormone releasing hormone and bombesin in non-small cell lung cancer.  Int J Oncol 2007, 30:1019-28.51. Kermer P, Klöcker N, Labes M, Bähr M: Insulin-like growth factor-I protects axotomized rat retinal ganglion cells from secondary death via PI3-K-dependent Akt phosphorylation and inhibition of caspase-3 in vivo.  J Neurosci 2000, 20:722-728.doi: 10.1186/1477-7827-8-54Cite this article as: Guo et al., Antiproliferative effect of growth hormone-releasing hormone (GHRH) antagonist on ovarian cancer cells through the EGFR-Akt pathway Reproductive Biology and Endocrinology 2010, 8:54

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