Breast Tumor Xenografts In Mice Research Articles

Promising Perspectives of the Antiproliferative GPER Inverse Agonist ERα17p in Breast Cancer.

The estrogen receptor α (ERα) corresponds to a large platform in charge of the recruitment of a panel of molecules, including steroids and related heterocyclic derivatives, oligonucleotides, peptides and proteins. Its 295-311 region is particularly targeted by post-translational modifications, suggesting that it could be crucial for the control of transcription. In addition to anionic phospholipids, the ERα 295-311 fragment interacts with Ca2+-calmodulin, the heat shock protein 70 (Hsp70), ERα and possibly importins. More recently, we have demonstrated that it is prone to interacting with the G-protein-coupled estrogen receptor (GPER). In light of these observations, the pharmacological profile of the corresponding peptide, namely ERα17p, has been explored in breast cancer cells. Remarkably, it exerts apoptosis through GPER and induces a significant decrease (more than 50%) of the size of triple-negative breast tumor xenografts in mice. Herein, we highlight not only the promising therapeutic perspectives in the use of the first peptidic GPER modulator ERα17p, but also the opportunity to modulate GPER for clinical purposes.

Imaging-Guided Evaluation of the Novel Small-Molecule Benzosuberene Tubulin-Binding Agent KGP265 as a Potential Therapeutic Agent for Cancer Treatment.

Simple SummaryVascular-disrupting agents promise significant therapeutic efficacy against solid tumors by selectively damaging tumor-associated vasculature. Dynamic BLI and oxygen-enhanced multispectral optoacoustic tomography (OE-MSOT) were used to compare vascular shutdown following administration of KGP265. BLI signal and vascular oxygenation response (ΔsO2) to a gas breathing challenge were both significantly reduced within 2 h indicating vascular disruption, which continued over 24 h. Twice-weekly doses of KGP265 caused a significant growth delay in MDA-MB-231 human breast tumor xenografts and 4T1 syngeneic breast tumors growing orthotopically in mice.The selective disruption of tumor-associated vasculature represents an attractive therapeutic approach. We have undertaken the first in vivo evaluation of KGP265, a water-soluble prodrug of a benzosuberene-based tubulin-binding agent, and found promising vascular-disrupting activity in three distinct tumor types. Dose escalation in orthotopic MDA-MB-231-luc breast tumor xenografts in mice indicated that higher doses produced more effective vascular shutdown, as revealed by dynamic bioluminescence imaging (BLI). In syngeneic orthotopic 4T1-luc breast and RENCA-luc kidney tumors, dynamic BLI and oxygen enhanced multispectral optoacoustic tomography (OE-MSOT) were used to compare vascular shutdown following the administration of KGP265 (7.5 mg/kg). The BLI signal and vascular oxygenation response (ΔsO2) to a gas breathing challenge were both significantly reduced within 2 h, indicating vascular disruption, which continued over 24 h. A correlative histology confirmed increased necrosis and hemorrhage. Twice-weekly doses of KGP265 caused significant growth delay in both MDA-MB-231 and 4T1 breast tumors, with no obvious systemic toxicity. A combination with carboplatin produced significantly greater tumor growth delay than carboplatin alone, though significant carboplatin-associated toxicity was observed (whole-body weight loss). KGP265 was found to be effective at low concentrations, generating long-term vascular shutdown and tumor growth delay, thus providing strong rationale for further development, particularly in combination therapies.

Enhancement of Radiotherapy with Human Mesenchymal Stem Cells Containing Gold Nanoparticles.

Radiotherapy is a common approach for the treatment of a wide variety of cancer types. Available data indicate that nanoparticles can enhance the effect of radiotherapy. We report the use of human mesenchymal stem cells to selectively deliver gold nanoparticles (GNPs) to MDA-MB-231 breast tumor xenografts in mice for the purpose of enhancing the effect of radiation therapy. Targeted delivery of GNPs to the tumor site, followed by irradiation of the tumor, enabled control of tumor growth. The results indicate that tumor-selective GNP delivery by human mesenchymal stem cells may represent a viable way to enhance the effectiveness of radiotherapy.

Urokinase-type plasminogen activator receptor inhibits apoptosis in triple-negative breast cancer through miR-17/20a suppression of death receptors 4 and 5.

Dissection and understanding of the molecular pathways driving triple-negative breast cancer (TNBC) are urgently needed to develop efficient tailored therapies. Aside from cell invasion and metastasis, the urokinase-type plasminogen activator receptor (uPAR) has been linked to apoptosis resistance in breast tumors. We explored the mechanism of uPAR-disrupted apoptosis in breast cancer. We found that depletion of uPAR by RNAi increases death receptor 4 (DR4) and death receptor 5 (DR5) expression and triggers TRAIL-induced apoptosis in TNBC cells. The microRNAs miR-17-5p and miR-20a inhibit cell apoptosis via suppression of DR4/DR5. We provide evidence that uPAR enhances miR-17-5p/20a expression through upregulation of c-myc. Blocking miR-17-5p/20a with antagomiRNA suppressed the growth of uPAR-overexpressing breast tumor xenografts in mice. These results indicate that uPAR suppresses cell apoptosis by inhibiting the c-myc-miR-17/5p/20a-DR4/DR5 pathway. Therapy directed at uPAR-induced miR-17/20a is a potential option for breast cancer and TNBC.

Abstract 3859: Peptidomimetic Src kinase inhibitor KX-01 sensitizes estrogen receptor α-negative breast tumor xenografts to tamoxifen by inducing ERα re-expression

Abstract Unlike breast cancer that is positive for estrogen receptor α (ERα) or amplified/overexpressed HER2/neu, there are no targeted therapies for triple negative breast cancer (TNBC). ERα is silenced in TNBC through epigenetic changes including DNA methylation and histone acetylation. Restoring ERα expression in TNBC tumors may sensitize patients to endocrine therapy. Expression of c-Src kinase and ERα are inversely correlated in breast cancer suggesting that c-Src inhibition may lead to re-expression of ERα in TNBC. KX-01 is a peptide substrate targeted Src kinase/pretubulin inhibitor in clinical trials for solid tumors. At low dose, KX-01 is an effective Src kinase inhibitor in breast tumor xenografts in mice, but does not affect microtubules. MDA-MB-231 and MDA-MB-468 TNBC xenografts in NUDE mice were treated with low dose (1 mg/kg b.wt. BID) KX-01 for 40 days. KX-01 treatment decreased Src kinase activity in tumors and increased ERα mRNA and protein. Immunohistochemistry and Western blot demonstrated that the epithelial markers progesterone receptor and E-cadherin were increased, whereas the mesenchymal markers vimentin and nuclear β-catenin were decreased, suggesting a mesenchymal to epithelial transition (MET) in the tumors. At the ERα promoter in MDA-MB-231 tumors, KX-01 treatment led to enrichment of transcriptionally active (acetyl-H3, acetyl-H3Lys9) chromatin marks. There was no change in ERα promoter methylation as assessed by methylation PCR analysis and bisulfite sequencing. KX-01 treatment did not alter histone deacetylase 1 (HDAC1) levels or activity in tumors, but did result in HDAC1 dissociation from the ERα promoter, and a concomitant recruitment of RNA Polymerase II as assessed by chromatin immunoprecipitation (ChIP). Tamoxifen-resistant MDA-MB-231 xenografts in NUDE mice were treated with vehicle, tamoxifen alone (5 mg pellet; 60 day release), KX-01 alone (1 mg/kg b.wt. BID), or KX-01 + tamoxifen for 40 days. KX-01 alone and KX-01 + tamoxifen reduced tumor volume by 59% and 70%, respectively, compared to vehicle. Tumor volume for the KX-01 + tamoxifen group was significantly reduced compared to the KX-01 alone group (P = .023), and tumor weight of the KX-01 + tamoxifen group was 32% lower compared to the KX-01 alone group (P< 0.01). Only the KX-01 + tamoxifen group exhibited reduced levels of ERα targets pS2, c-Myc and cyclin D1 indicating that estradiol signaling was attenuated by tamoxifen only in tumors treated with KX-01. In MDA-MB-468 tumors, tamoxifen alone (10 mg pellet; 60 day release) and KX-01 alone (1 mg/kg b.wt. BID) had no effect on tumor volume compared to vehicle, but KX-01 + tamoxifen reduced tumor volume 67% compared to vehicle (P = 0.0025). Collectively, these data demonstrate that the peptidomimetic Src inhibitor KX-01 can restore ERα expression in TNBC through changes in histone acetylation that sensitize TNBC tumors to endocrine therapy (tamoxifen). Citation Format: Murali Anbalagan, Mei Sheng, Brian Fleischer, David Hangauer, Brian G. Rowan. Peptidomimetic Src kinase inhibitor KX-01 sensitizes estrogen receptor α-negative breast tumor xenografts to tamoxifen by inducing ERα re-expression. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 3859.

Inhibition of cancer cell proliferation and breast tumor targeting of pHLIP-monomethyl auristatin E conjugates.

Localized delivery is vital for the successful development of novel and effective therapeutics for the treatment of cancer. The targeting and delivery described herein is based on the pH (low) insertion peptide (pHLIP), a unique delivery peptide that can selectively target tumors in mice and translocate and release cargo molecules intracellularly based solely on the low extracellular pH intrinsic to cancer cells. In this study, we investigate the efficacy of pHLIP to target and deliver the highly potent and clinically validated microtubule inhibitor monomethyl auristatin E (MMAE) to cancer cells and breast tumors. We show that pHLIP-MMAE conjugates induce a potent cytotoxic effect (>90% inhibition of cell growth) in a concentration- and pH-dependent manner after only 2 h incubation without any apparent disruption of the plasma membrane. pHLIP-MMAE conjugates exhibit between an 11- and 144-fold higher antiproliferative effect at low pH than that at physiological pH and a pronounced pH-dependent cytotoxicity as compared to that of free drug. Furthermore, we demonstrate that a pHLIP-MMAE drug conjugate effectively targets triple-negative breast tumor xenografts in mice. These results indicate that pHLIP-based auristatin conjugates may have an enhanced therapeutic window as compared to that of free drug, providing a targeting mechanism to attenuate systemic toxicity.

Synaptojanin 2 is a druggable mediator of metastasis and the gene is overexpressed and amplified in breast cancer.

Amplified HER2, which encodes a member of the epidermal growth factor receptor (EGFR) family, is a target of effective therapies against breast cancer. In search for similarly targetable genomic aberrations, we identified copy number gains in SYNJ2, which encodes the 5'-inositol lipid phosphatase synaptojanin 2, as well as overexpression in a small fraction of human breast tumors. Copy gain and overexpression correlated with shorter patient survival and a low abundance of the tumor suppressor microRNA miR-31. SYNJ2 promoted cell migration and invasion in culture and lung metastasis of breast tumor xenografts in mice. Knocking down SYNJ2 impaired the endocytic recycling of EGFR and the formation of cellular lamellipodia and invadopodia. Screening compound libraries identified SYNJ2-specific inhibitors that prevented cell migration but did not affect the related neural protein SYNJ1, suggesting that SYNJ2 is a potentially druggable target to block cancer cell migration.

Abstract 3801: Small molecule inhibitor of Stat3 induces antitumor cell effects in vitro and antitumor effects in vivo against human glioma or breast cancer model

Abstract Aberrant activation of signal transducer and activator of transcription 3 (Stat3) is prevalent in many human cancers. Compelling evidence shows that constitutively-active Stat3 constitutes a point of convergence in oncogenic tyrosine kinase signaling, functioning as a master regulator of events crucial for tumorigenesis and malignant progression. We show herein that the small-molecule, SH5-07 abrogates constitutive activation of Stat3 and Stat3-dependent functions in human glioma and breast cancer cells. SH5-07 inhibits in vitro Stat3 DNA-binding activity with an IC50 value of 3.9 μM. Treatment of human glioma U251MG and breast cancer MDA-MB-231 cells that harbor aberrantly-active Stat3 with low micromolar SH5-07 blocks Stat3 phosphorylation, DNA-binding, and transcriptional activities in a time and dose-dependent manner. By contrast, SH5-07 shows little or no effect on the induction of pJAK2, pSrc, pErk1/2, and pShc in glioma and breast cancer cells. SH5-07 preferentially inhibited viability of human glioma and breast cancer cells that harbor aberrant Stat3 activity, with IC50 of 1.1-5.2 µM, compared to IC50 of 6.0-10.8 µM for cells that do not. Inhibition of aberrantly-active Stat3 by SH5-07 preferentially suppresses the anchorage-dependent and independent growth, induces apoptosis, and blocks migration and invasion in vitro of human glioma and breast cancer cells that harbor constitutively-active Stat3. Moreover, oral administration of SH5-07 inhibits the growth of human breast tumor xenografts in mice. Data together indicates SH5-07 is a promising small-molecule Stat3 inhibitor and a suitable drug candidate for clinical development. Citation Format: Peibin Yue, Francisco Lopez-Tapia, Marcus Tius, James Turkson. Small molecule inhibitor of Stat3 induces antitumor cell effects in vitro and antitumor effects in vivo against human glioma or breast cancer model. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3801. doi:10.1158/1538-7445.AM2014-3801

Structure Activity Relationships of N-linked and Diglycosylated Glucosamine-Based Antitumor Glycerolipids

1-O-Hexadecyl-2-O-methyl-3-O-(2'-amino-2'-deoxy-β-d-glucopyranosyl)-sn-glycerol (1) was previously reported to show potent in vitro antitumor activity on a range of cancer cell lines derived from breast, pancreas and prostate cancer. This compound was not toxic to mice and was inactive against breast tumor xenografts in mice. This inactivity was attributed to hydrolysis of the glycosidic linkage by glycosidases. Here three N-linked (glycosylamide) analogs 2–4, one triazole-linked analog 5 of 1 as well as two diglycosylated analogs 6 and 7 with different stereochemistry at the C2-position of the glycerol moiety were synthesized and their antitumor activity against breast (JIMT-1, BT-474, MDA-MB-231), pancreas (MiaPaCa2) and prostrate (DU145, PC3) cancer cell lines was determined. The diglycosylated analogs 1-O-hexadecyl-2(R)-, 3-O-di-(2'-amino-2'-deoxy-β-d-glucopyranosyl)-sn-glycerol (7) and the 1:1 diastereomeric mixture of 1-O-hexadecyl-2(R/S), 3-O-di-(2'-amino-2'-deoxy-β-d-glucopyranosyl)-sn-glycerol (6) showed the most potent cytotoxic activity at CC50 values of 17.5 µM against PC3 cell lines. The replacement of the O-glycosidic linkage by a glycosylamide or a glycosyltriazole linkage showed little or no activity at highest concentration tested (30 µM), whereas the replacement of the glycerol moiety by triazole resulted in CC50 values in the range of 20 to 30 µM. In conclusion, the replacement of the O-glycosidic linkage by an N-glycosidic linkage or triazole-linkage resulted in about a two to three fold loss in activity, whereas the replacement of the methoxy group on the glycerol backbone by a second glucosamine moiety did not improve the activity. The stereochemistry at the C2-position of the glycero backbone has minimal effect on the anticancer activities of these diglycosylated analogs.

Heptamethine cyanine based 64Cu-PET probe PC-1001 for cancer imaging: Synthesis and in vivo evaluation

Development of a heptamethine cyanine based tumor-targeting PET imaging probe for noninvasive detection and diagnosis of breast cancer. Tumor-specific heptamethine-cyanine DOTA conjugate complexed with Cu-64 (PC-1001) was synthesized for breast cancer imaging. In vitro cellular uptake studies were performed in the breast cancer MCF-7 and noncancerous breast epithelial MCF-10A cell lines to establish tumor specificity. In vivo time-dependent fluorescence and PET imaging of breast tumor xenografts in mice were performed. Blood clearance, biodistribution, and tumor-specific uptake and plasma binding of PC-1001 were quantified. Tumor histology (H&E staining) and fluorescence imaging were examined. PC-1001 displayed similar fluorescence properties (ε=82,880cm(-1)M(-1), Ex/Em=750/820nm) to the parental dye. Time-dependent cellular accumulation indicated significantly higher probe uptake (>2-fold, 30min) in MCF-7 than MCF-10A cells and the uptake was observed to be mediated by organic anion transport peptides (OATPs) system. In vivo studies revealed that PC-1001 has desirable accumulation profile in tumor tissues, with tumor versus muscle uptake of about 4.3 fold at 24h and 5.8 fold at 48h post probe injections. Blood half-life of PC-1001 was observed to be 4.3±0.2h. Microscopic fluorescence imaging of harvested tumor indicated that the uptake of PC-1001 was restricted to viable rather than necrotic tumor cells. A highly efficient tumor-targeting PET/fluorescence imaging probe PC-1001 is synthesized and validated in vitro in MCF-7 breast cancer cells and in vivo in mice breast cancer xenograft model.

Abstract B8: Selective inhibition of Stat3 Tyr705 phosphorylation inhibits angiogenesis in breast cancer xenografts.

Abstract Signal transducer and activator of transcription 3 (Stat3) is recruited, via its SH2 domain, to phosphotyrosine residues on growth factor and IL-6 family receptors at which time it is phosphorylated on Tyr705 by Janus kinases, Src, or the kinase activity of the receptor. Phosphorylation of Tyr705 (pStat3) leads to dimerization, translocation to the nucleus, and transcription of downstream genes. Stat3 is activated in several human cancers and is considered a drug target. Starting with pTyr-Leu-Pro-Gln, we have been developing phosphopeptide mimics to target the SH2 domain with the goal of blocking recruitment to receptors to uncouple Stat3 from its signaling role. We have developed cell-permeable, phosphatase-stable prodrugs that inhibit constitutive and IL-6-stimulated Tyr705 phosphorylation at concentrations of 0.5 − 1 μM in a variety of human cancer cell lines. They are selective for Stat3 over Stat1, Stat5, Src, and PI3K. At 5 μM they are not cytotoxic to a panel of human cancer cell lines. Higher concentrations lead to off-target effects and cytotoxicity. Recent reports indicate that Ser727 phosphorylated Stat3 participates in electron transfer in the mitochodria and unphosphorylated Stat3 participates with NF-κB-mediated transcription. As opposed to Stat3 knockdown techniques which cannot discriminate the multiple roles of Stat3, our prodrugs are potential tools to selectively probe Stat3 phosphorylation. Both intra-tumoral and intra-peritoneal administration of our lead prodrug, PM-73G, resulted in reduction of orthotopic breast tumor xenografts in mice. There was no evidence of apoptosis, reduction of cyclin D1 or survivin. Treated tumors exhibited significant reduction in microvessel density. Thus, selectively inhibiting Tyr705 phosphorylation is a potential antiangiogenic treatment modality. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr B8.

Abstract 1983: A cell-permeable Stat3 SH2 domain mimetic inhibitor of Stat3 activation inhibits growth of human breast tumor xenografts

Abstract Human tumors harbor multiple molecular aberrations that have become the driving force for uncontrolled cell proliferation and survival, and other tumor-associated processes. Constitutive activation of the Signal Transducer and Activator of Transcription (Stat) 3 protein is a frequent occurrence in many human cancers, including breast cancer. Given the role of aberrant Stat3 activity in human tumors, small-molecule Stat3 inhibitors would be useful novel therapeutics and tools for probing Stat3-mediated tumor processes. We herein report that a 28-mer peptide, SPI, composed of the amino acid residues 588-615 of the Stat3 SH2 domain, replicates Stat3 biochemical properties and functions as a Stat3 inhibitor. Studies show SPI and Stat3 (or Stat3 SH2 domain) both bind with similar affinities to known Stat3-binding phosphotyrosine (pY) peptide motifs, including the epidermal growth factor receptor (EGFR) peptides, pY1068EGFR and pY1086EGFR, and the high-affinity, interleukin-6 receptor (IL-6R)/gp130-derived peptide, GpYLPQTV-NH2. Consequently, SPI potently and selectively inhibits Stat3 SH2 domain:pY interactions and disrupts the binding of Stat3 to the IL-6R/gp130 peptide, GpYLPQTV-NH2. Fluorescence imaging studies show SPI is cell membrane-permeable. Treatment with SPI of malignant cells that harbor aberrant Stat3 activity resulted in the selective inhibition of constitutive Stat3 phosphorylation, and of Stat3 DNA-binding and transcriptional activities. By contrast, similar treatments have little or no effects on the induction of the Stat1, Stat5, and Erk1/2MAPK pathways in malignant cells or in EGF-stimulated fibroblasts. In contrast to normal cells, human breast, pancreatic, prostate, and non-small cell lung cancer cells harboring constitutively-active Stat3 are highly sensitive to SPI and undergo extensive morphology changes, concomitant with the loss of viability and apoptosis. Significantly, treatment with SPI or its inverse sequence version strongly inhibited the growth of human breast tumor xenografts in mice, which is associated with the down-regulation of the expression of the known Stat3-regulated genes, Cyclin D1, Bcl-xL and Survivin. Our study identifies SPI as a novel molecular probe for interrogating Stat3 signaling and that functions as a selective Stat3 inhibitor, which induces antitumor response in vivo. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 1983. doi:10.1158/1538-7445.AM2011-1983

S-Gal, a novel 1H MRI reporter for beta-galactosidase.

Reporter genes and associated enzyme activity are becoming increasingly significant for research in vivo. The lacZ gene and beta-galactosidase (beta-gal) expression have long been exploited as reporters of biologic manipulation at the molecular level, and a noninvasive detection strategy based on proton MRI is particularly attractive. 3,4-Cyclohexenoesculetin beta-D-galactopyranoside (S-Gal) is a commercial histologic stain, which forms a black precipitate in the presence of beta-gal and ferric ions, suggesting potential detectability by MRI. Generation of the precipitate is now shown to cause strong T(2)* relaxation, revealing beta-gal activity. A series of tests with the enzyme in vitro and with tumor cells shows that this approach can be used as an assay for beta-gal activity. Proof of principle is shown in human breast tumor xenografts in mice. Upon direct injection of a mixture of 3,4-cyclohexenoesculetin beta-D-galactopyranoside and ferric ammonium citrate, intense contrast was observed immediately in MCF7-lacZ tumors, but not in wild-type tumors. 3,4-Cyclohexenoesculetin beta-D-galactopyranoside activation in combination with ferric ions introduces a novel approach for assaying enzyme activity by MRI in vivo.

Abstract 3244: Combination of COX-2 inhibitor Celebrex with androgen deprivation synergistically inhibits tumor growth in a syngeneic mouse model of prostate cancer

Abstract Prostate cancer (PC) is the most common solid tumor in men in the United States. Effective treatment options include surgery and radiation therapy for localized tumors, whereas advanced cancer is treated by androgen deprivation. Unfortunately, most patients with metastatic prostate cancer will eventually relapse into a hormone-independent cancer that is notoriously resistant to chemotherapy. Thus, more effective therapeutic strategies are needed to improve this outcome, which leads to about 30 000 deaths every year. Nonsteroidal anti-inflammatory drugs (NSAIDs) have shown efficacy for the prevention or the treatment of several human cancers. Among them, specific COX-2 inhibitors have received particular attention because COX-2 is overexpressed in many epithelial tumors, including prostate, and because a number of studies have shown that they slow the growth of colon, lung and breast tumor xenografts in mice. In addition, COX-2 inhibitors have potent antitumor activity in prostate cancer both in vitro and in vivo. Celebrex (Celecoxib), the only COX-2 inhibitor still approved for clinical use, is being evaluated in clinical trials for the treatment of localized or advanced prostate cancer. In this study, we observed that celebrex in combination with androgen deprivation inhibits tumor growth much more efficiently that either treatment alone. A syngeneic pseudo-orthotropic mouse model and Intravital Microscopy (IVM) were used to measure several parameters of tumor progression and study the effect of Celebrex combined with androgen deprivation. Androgen-dependent TRAMP-C2 mouse prostate cancer cells were co-implanted with prostate tissue into the dorsal skinfold chamber of syngeneic C57Bl/6 mice. Mice were subjected to surgical or hormonal castration, alone or in combination with Celebrex. Tumor growth, apoptosis, mitosis and angiogenesis were measured. We observed that Celebrex alone inhibited tumor growth with no evidence of apoptosis but most likely through growth arrest during mitosis. Interestingly, Celebrex alone had no effect on angiogenesis. Castration alone had a significant angiostatic effect but tumor growth was inhibited only by 20%. In contrast, the combination of castration and Celebrex inhibited tumor growth by 65% and resulted in both increased apoptosis and increased mitotic arrest. Conclusion: our study provides evidence that Celebrex treatment of prostate cancer-bearing mice results in a lower proliferative rate in tumors. In addition, Celebrex potentiates the effect of castration to inhibit tumor growth in vivo. We propose therefore that administration of Celebrex during androgen deprivation may be more efficient than androgen deprivation alone and warrants further study. Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3244.