Effect of proteasome inhibitors on canine lymphoma cell response to CHOP chemotherapy in vitro

The standard treatment for canine lymphoma is the CHOP chemotherapy regimen. Proteasome inhibitors have been employed with CHOP for the treatment of human haematological malignancies but remain to be fully explored in canine lymphoma. We identified an association between poor response to CHOP chemotherapy and high mRNA expression levels of proteasomal subunits in a cohort of 15 canine lymphoma patients, and sought to determine the effect of proteasome inhibitors on the viability of a canine B-cell lymphoma cell line (CLBL-1). The aim of this study was to investigate whether proteasome inhibitors sensitize these cells to the CHOP agents doxorubicin, vincristine and cyclophosphamide (as 4-hydroxycyclophosphamide/4-HC). CLBL-1 cells were sensitive to proteasome inhibition by bortezomib and ixazomib. The IC50 of bortezomib was 15.1 nM and of ixazomib was 59.14 nM. Proteasome inhibitors plus doxorubicin had a synergistic effect on CLBL-1 viability; proteosome inhibitors plus vincristine showed different effects depending on the combination ratio, and there was an antagonistic effect with 4-HC. These results may have clinical utility, as proteasome inhibition could potentially be used with a synergizing CHOP compound to improve responsiveness to chemotherapy for canine lymphoma patients.

Cancer detection in clinical practice and using blood-based liquid biopsy: A retrospective audit of over 350 dogs

BACKGROUND

Guidelines-driven screening protocols for early cancer detection in dogs are lacking, and cancer often is detected at advanced stages.

HYPOTHESIS/OBJECTIVES

To examine how cancer typically is detected in dogs and whether the addition of a next-generation sequencing-based "liquid biopsy" test to a wellness visit has the potential to enhance cancer detection.

ANIMALS

Client-owned dogs with definitive cancer diagnoses enrolled in a clinical validation study for a novel blood-based multicancer early detection test.

METHODS

Retrospective medical record review was performed to establish the history and presenting complaint that ultimately led to a definitive cancer diagnosis. Blood samples were subjected to DNA extraction, library preparation, and next-generation sequencing. Sequencing data were analyzed using an internally developed bioinformatics pipeline to detect genomic alterations associated with the presence of cancer.

RESULTS

In an unselected cohort of 359 cancer-diagnosed dogs, 4% of cases were detected during a wellness visit, 8% were detected incidentally, and 88% were detected after the owner reported clinical signs suggestive of cancer. Liquid biopsy detected disease in 54.7% (95% confidence interval [CI], 49.5%-59.8%) of patients, including 32% of dogs with early-stage cancer, 48% of preclinical dogs, and 84% of dogs with advanced-stage disease.

CONCLUSIONS/CLINICAL IMPORTANCE

Most cases of cancer were diagnosed after the onset of clinical signs; only 4% of dogs had cancer detected using the current standard of care (i.e., wellness visit). Liquid biopsy has the potential to increase detection of cancer when added to a dog's wellness visit.

RNA-Seq analysis of gene expression in 25 cases of canine lymphoma undergoing CHOP chemotherapy

Objectives

Canine lymphoma, the most common hematological cancer in dogs, shares many molecular and clinical characteristics with human Non-Hodgkin lymphoma (NHL). The standard treatment for canine lymphoma is “CHOP” multiagent chemotherapy protocol consisting of Cyclophosphamide, Doxorubicin (Hydroxydaunorubicin), Vincristine (Oncovin™), and Prednisone. Approximately 70–85% of patients treated with CHOP achieve clinical remission. However, duration of remission varies and the majority of dogs eventually relapse. To identify possible biomarkers for patients failing to achieve remission, we performed RNA-Seq analysis on 25 cases of canine lymphoma obtained prior the start of their CHOP therapy regime and assessed gene expression associated with patient progression free survival (PFS).

Data description

The data consists of (1) raw RNA-Seq reads in 75 bp fastq format from fine needle aspirate samples of enlarged lymph nodes from canine patients with naturally occurring lymphoma; (2) Fragments Per Kilobase Million (FPKM) values for each sample; (3) raw transcript counts for each sample; (4) anonymized patient details including PFS; (5) heat map of gene expression and (6) Cox proportional hazard analysis showing significantly expressed genes. These data may be useful for comparative analysis of gene expression in human NHL and analysis of gene expression associated with disease outcome in canine lymphoma.

Beclin-1 is a novel predictive biomarker for canine cutaneous and subcutaneous mast cell tumors

Mast cell tumors (MCTs) are the most common skin tumor of the dog, and accurately predicting their clinical behavior is critical in directing patient therapy, as they range from benign lesions to a fatal systemic disease. Grading is useful for prognosis, but it cannot predict the behavior of all MCTs. We hypothesized that biomarker immunolabeling in tumor tissues would correlate with patient morbidity and mortality. A clinically annotated tissue microarray (TMA) of primary, recurrent, and metastatic (to lymph node) canine dermal and subcutaneous MCTs was created. Some dogs whose MCTs were included in the TMA did not receive adjunctive treatment after surgical excision of the MCT, whereas others were treated with one or a combination of chemotherapy, radiation, or oral toceranib. Immunohistochemistry for beclin-1, an autophagy protein, was performed followed by digital image analysis. Beclin-1 immunolabeling was higher in recurrent tumors (mean H-score 110.8) than primary MCTs (mean H-score 73.5), and highest in lymph node metastases (mean H-score 138.5) with a significant difference in means (P < .001). While beclin-1 level was not prognostic, it was strongly predictive for survival after adjunctive treatment; dogs with high beclin-1-expressing tumors showed poorer survival compared to those with low beclin-1-expressing tumors (HR = 5.7, P = .02), especially in Kiupel high-grade tumors (HR = 16.3, P = .01). Beclin-1 immunolabeling was the only significant predictive factor by multivariable analysis (P = .04). These findings may improve our ability to predict the response to adjunctive therapy. Importantly, these data suggest that autophagy inhibitors may be useful in improving response to treatment for dogs with high-grade MCTs.

RNA disruption indicates CHOP therapy efficacy in canine lymphoma

Background

Assessment of the efficacy of a multi-agent chemotherapy protocol in which cyclophosphamide, doxorubicin, vincristine and prednisone (CHOP) are administered in canine lymphoma is generally performed by physical measurement of lymph node diameter. However, no consistent correlation has been made with prognostic indicators and the length or absence of clinical remission based on lymph node size. RNA disruption measured mid-therapy has been correlated with increased disease-free survival in recent studies of human cancer and was assessed in this study of canine lymphoma patients. Fine needle aspirate samples were taken before treatment and at weeks 3, 6, and 11 of CHOP therapy. RNA was isolated from these samples and assessed using an Agilent Bioanalyzer. RNA disruption assay (RDA) analysis was performed on the data from the resulting electropherograms.

Results

An increased RNA disruption index (RDI) score was significantly associated with improved progression-free survival.

Conclusions

Predicting the risk of early relapse during chemotherapy could benefit veterinary patients by reducing ineffective treatment and could allow veterinary oncologists to switch earlier to a more effective drug regimen.

Metabolic reprogramming in the tumour microenvironment: a hallmark shared by cancer cells and T lymphocytes

Altered metabolism is a hallmark of cancers, including shifting oxidative phosphorylation to glycolysis and up-regulating glutaminolysis to divert carbon sources into biosynthetic pathways that promote proliferation and survival. Therefore, metabolic inhibitors represent promising anti-cancer drugs. However, T cells must rapidly divide and survive in harsh microenvironments to mediate anti-cancer effects. Metabolic profiles of cancer cells and activated T lymphocytes are similar, raising the risk of metabolic inhibitors impairing the immune system. Immune checkpoint blockade provides an example of how metabolism can be differentially impacted to impair cancer cells but support T cells. Implications for research with metabolic inhibitors are discussed.

Pilot assessment of vascular endothelial growth factor receptors and trafficking pathways in recurrent and metastatic canine subcutaneous mast cell tumours

Canine subcutaneous mast cell tumour (scMCT) shows less aggressive biological behaviour than cutaneous MCT. Vascular endothelial growth factor receptor 2 (VEGFR2) is expressed by neoplastic cells in canine scMCT, but the relevance of this signalling pathway for disease pathobiology is not clear. The objective of this study was to quantify VEGF‐A, VEGFR2, pVEGFR2, the VEGF co‐receptor Neuropilin 1 (NRP‐1) and the E3 ubiquitin protein ligase c‐Cbl in canine scMCT, and to evaluate their association with disease outcome. Immunohistochemical staining for biomarkers was quantified from 14 cases of canine scMCT using manual and computer‐assisted methods. Kaplan–Meier curves were generated for disease‐free survival (DFS) and compared using Mantel–Cox log‐rank analysis. Cases with high levels of neoplastic cell VEGFR2, pVEGFR2 or c‐CBL immunoreactivity had significantly reduced DFS. All cases displayed neoplastic cells positive for VEGF‐A, which was significantly associated with pVEGFR2 immunoreactivity. There were also significant positive correlations between VEGFR2 and pVEGFR2, and between c‐CBL and pVEGFR2 levels. This pilot study demonstrates the potential utility of these markers in a subset of scMCT in dogs.

Release of endothelial cell associated VEGFR2 during TGF-β modulated angiogenesis in vitro

Background

Sprouting angiogenesis requires vascular endothelial proliferation, migration and morphogenesis. The process is regulated by soluble factors, principally vascular endothelial growth factor (VEGF), and via bidirectional signaling through the Jagged/Notch system, leading to assignment of tip cell and stalk cell identity. The cytokine transforming growth factor beta (TGF-β) can either stimulate or inhibit angiogenesis via its differential surface receptor signaling. Here we evaluate changes in expression of angiogenic signaling receptors when bovine aortic endothelial cells were exposed to TGF-β1 under low serum conditions.

Results

TGF-β1 induced a dose dependent inhibition of tip cell assignment and subsequent angiogenesis on Matrigel, maximal at 5.0 ng/ml. This occurred via ALK5-dependent pathways and was accompanied by significant upregulation of the TGF-β co-receptor endoglin, and SMAD2 phosphorylation, but no alteration in Smad1/5 activation. TGF-β1 also induced ALK5-dependent downregulation of Notch1 but not of its ligand delta-like ligand 4. Cell associated VEGFR2 (but not VEGFR1) was significantly downregulated and accompanied by reciprocal upregulation of VEGFR2 in conditioned medium. Quantitative polymerase chain reaction analysis revealed that this soluble VEGFR2 was not generated by a selective shift in mRNA isoform transcription. This VEGFR2 in conditioned medium was full-length protein and was associated with increased soluble HSP-90, consistent with a possible shedding of microvesicles/exosomes.

Conclusions

Taken together, our results suggest that endothelial cells exposed to TGF-β1 lose both tip and stalk cell identity, possibly mediated by loss of VEGFR2 signaling. The role of these events in physiological and pathological angiogenesis requires further investigation.

Electronic supplementary material

The online version of this article (doi:10.1186/s12860-017-0127-y) contains supplementary material, which is available to authorized users.

KRAS Mutations in Canine and Feline Pancreatic Acinar Cell Carcinoma

Companion animals may serve as valuable models for studying human cancers. Although KRAS is the most commonly mutated gene in human ductal pancreatic cancers (57%), with mutations frequently occurring at codons 12, 13 and 61, human pancreatic acinar cell carcinomas (ACCs) lack activating KRAS mutations. In the present study, 32 pancreatic ACC samples obtained from 14 dogs and 18 cats, including seven metastases, were analyzed for six common activating KRAS mutations located in codons 12 (n = 5) and 13 (n = 1) using Sequenom MassARRAY. No KRAS mutations were found, suggesting that, similar to human pancreatic ACC, KRAS mutations do not play a critical role in feline or canine pancreatic ACC. Due to the similarity of the clinical disease in dogs and cats to that of man, this study confirms that companion animals offer potential as a suitable model for investigating this rare subtype of pancreatic carcinoma.

Solamargine triggers cellular necrosis selectively in different types of human melanoma cancer cells through extrinsic lysosomal mitochondrial death pathway

BACKGROUND

Previous reports showed that the Steroidal Glycoalkaloid Solamargine inhibited proliferation of non-melanoma skin cancer cells. However, Solamargine was not tested systematically on different types of melanoma cells and was not simultaneously tested on normal cells either. In this study we aimed to investigate the effect of Solamargine and the mechanism involved in inhibiting the growth of different types of melanoma cells.

METHODS

Solamargine effect was tested on normal cells and on another three melanoma cell lines. Vertical growth phase metastatic and primary melanoma cell lines WM239 and WM115, respectively and the radial growth phase benign melanoma cells WM35 were used. The half inhibitory concentration IC50 of Solamargine was determined using Alamarblue assay. The cellular and subcellular changes were assessed using light and Transmission Electron Microscope, respectively. The percentage of cells undergoing apoptosis and necrosis were measured using Flow cytometry. The different protein expression was detected and measured using western blotting. The efficacy of Solamargine was determined by performing the clonogenic assay. The data collected was analyzed statistically on the means of the triplicate of at least three independent repeated experiments using one-way ANOVA test for parametric data and Kruskal-Wallis for non-parametric data. Differences were considered significant when the P values were less than 0.05.

RESULTS

Hereby, we demonstrate that Solamargine rapidly, selectively and effectively inhibited the growth of metastatic and primary melanoma cells WM239 and WM115 respectively, with minimum effect on normal and benign WM35 cells. Solamargine caused cellular necrosis to the two malignant melanoma cell lines (WM115, WM239), by rapid induction of lysosomal membrane permeabilization as confirmed by cathepsin B upregulation which triggered the extrinsic mitochondrial death pathway represented by the release of cytochrome c and upregulation of TNFR1. Solamargine disrupted the intrinsic apoptosis pathway as revealed by the down regulation of hILP/XIAP, resulting in caspase-3 cleavage, upregulation of Bcl-xL, and Bcl2, and down regulation of Apaf-1 and Bax in WM115 and WM239 cells only. Solamargine showed high efficacy in vitro particularly against the vertical growth phase melanoma cells.

CONCLUSION

Our findings suggest that Solamargine is a promising anti-malignant melanoma drug which warrants further attention.

The effect of 3-bromopyruvate on human colorectal cancer cells is dependent on glucose concentration but not hexokinase II expression

Cancer cells heavily rely on the glycolytic pathway regardless of oxygen tension. Hexokinase II (HKII) catalyses the first irreversible step of glycolysis and is often overexpressed in cancer cells. 3-Bromopyruvate (3BP) has been shown to primarily target HKII, and is a promising anti-cancer compound capable of altering critical metabolic pathways in cancer cells. Abnormal vasculature within tumours leads to heterogeneous microenvironments, including glucose availability, which may affect drug sensitivity. The aim of the present study was to elucidate the mechanisms by which 3BP acts on colorectal cancer (CRC) cells with focus on the HKII/Akt signalling axis. High HKII-expressing cell lines were more sensitive to 3BP than low HKII-expressing cells. 3BP-induced rapid Akt phosphorylation at site Thr-308 and cell death via both apoptotic and necrotic mechanisms. Cells grown under lower glucose concentrations showed greater resistance towards 3BP. Cells with HKII knockdown showed no changes in 3BP sensitivity, suggesting the effects of 3BP are independent of HKII expression. These results emphasize the importance of the tumour microenvironment and glucose availability when considering therapeutic approaches involving metabolic modulation.

Abstract 4078: Investigating chemoresistance mechanisms in colorectal cancer stem cells

Treatment of advanced colorectal cancer (CRC) is impacted by a lack of selectivity, the development of drug resistance and overall tumour heterogeneity. Cancer stem cells (CSCs) are a subpopulation of tumour cells believed to be responsible for tumour recurrence due to their ability to self-renew, differentiate and evade current treatments. This project explores the responses of CRC CSCs to chemotherapy and aims to identify therapeutic targets of the CSC population. We used serial colonosphere culture to enrich for CSCs from two human CRC cell lines, HCT116 and SW480. Limiting dilution analysis showed that CSC enriched cell lines have significantly higher colonosphere formation ability compared to their respective parental cells. Further characterization of CSC cell lines was performed via qPCR and flow cytometry to determine the expression of colorectal CSC markers. A significant upregulation in CD166 and EpCAM gene expression was seen in HCT-CSC and SW-CSCs compared to parental cell lines. In vitro assays were used to determine cellular responses to three commonly employed chemotherapeutics, 5-fluorouracil, cisplatin and epirubicin. A limiting dilution analysis demonstrated that cells treated with chemotherapy for 48 hours had reduced colonosphere forming potential. Cell viability in response to chemotherapy was analyzed via PrestoBlue assays in both monolayer and 3D culture. CSC and parental cell lines responded similarly in a dose-dependent manner to treatment in monolayer, but CSC colonospheres were more resistant to high doses of chemotherapy than their respective parental cells. ABC transporter expression plays a major role in the development of multi-drug resistance so the expression of ABCB1, ABCC1 and ABCG2 was examined via qPCR. There was a significant upregulation in ABCB1 and ABCG2 in HCT-CSCs compared to HCT-P cells. SW-CSCs also had significant upregulation in ABCB1 compared to SW-P cells. Other resistance mechanisms may also be key targets for therapeutic intervention including the functional CSC marker aldehyde dehydrogenase (ALDH). The detoxification effects of ALDH could have a protective effect against the surges of reactive oxygen species resulting from chemotherapy treatment. The expression of ALDH and ABC transporter genes was also explored in response to chemotherapy. The goal of this project is to elucidate drug resistance mechanisms in colorectal CSCs, in order to target and eradicate the tumour cells responsible for metastases and recurrent disease. Our analysis demonstrates that colorectal CSCs possess heightened protective mechanisms in comparison to other cancer cells originating from the same tumour. Future experiments will further investigate these resistance mechanisms to determine their therapeutic potential.

Note: This abstract was not presented at the meeting.

Citation Format: Stacey J. Butler, Lisa Richardson, Nathan Farias, Brenda L. Coomber. Investigating chemoresistance mechanisms in colorectal cancer stem cells. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4078. doi:10.1158/1538-7445.AM2015-4078

The effects of folic acid on global DNA methylation and colonosphere formation in colon cancer cell lines

Folate and its synthetic form, folic acid (FA), are essential vitamins for the regeneration of S-adenosyl methionine molecules, thereby maintaining adequate cellular methylation. The deregulation of DNA methylation is a contributing factor to carcinogenesis, as alterations in genetic methylation may contribute to stem cell reprogramming and dedifferentiation processes that lead to a cancer stem cell (CSC) phenotype. Here, we investigate the potential effects of FA exposure on DNA methylation and colonosphere formation in cultured human colorectal cancer (CRC) cell lines. We show for the first time that HCT116, LS174T, and SW480 cells grown without adequate FA demonstrate significantly impaired colonosphere forming ability with limited changes in CD133, CD166, and EpCAM surface expression. These differences were accompanied by concomitant changes to DNA methyltransferase (DNMT) enzyme expression and DNA methylation levels, which varied depending on cell line. Taken together, these results demonstrate an interaction between FA metabolism and CSC phenotype in vitro and help elucidate a connection between supplemental FA intake and CRC development.

Pyruvate dehydrogenase kinase expression and metabolic changes following dichloroacetate exposure in anoxic human colorectal cancer cells

Dichloroacetate (DCA) is a small molecule that inhibits pyruvate dehydrogenase kinase (PDK) to constrain the aerobic glycolytic pathway observed in many cancer cells and effectively kill them with limited cytotoxicity on normal cells. We previously showed that DCA induced a cytoprotective effect in different human colorectal cancer (CRC) cell lines under anoxic conditions. In this study, we investigated the molecular and metabolic changes that may be providing this cytoprotection. The expression profiles of PDK isoforms in SW480 and LS174T cells along with subsequent changes in pyruvate dehydrogenase (PDH) phosphorylation were assessed following DCA exposure. Changes in mitochondrial activity and subsequent glucose consumption and lactate production were then examined. We show evidence of differential regulation in PDH phosphorylation between different human CRC cells leading to differences in mitochondrial activity following DCA exposure. However, these effects did not lead to significant changes in cellular metabolism nor growth. In conclusion, DCA may only be beneficial in treating a subset of tumor types based on their molecular profiles of different PDK isoforms.

Genome-wide analysis in human colorectal cancer cells reveals ischemia-mediated expression of motility genes via DNA hypomethylation

DNA hypomethylation is an important epigenetic modification found to occur in many different cancer types, leading to the upregulation of previously silenced genes and loss of genomic stability. We previously demonstrated that hypoxia and hypoglycaemia (ischemia), two common micro-environmental changes in solid tumours, decrease DNA methylation through the downregulation of DNMTs in human colorectal cancer cells. Here, we utilized a genome-wide cross-platform approach to identify genes hypomethylated and upregulated by ischemia. Following exposure to hypoxia or hypoglycaemia, methylated DNA from human colorectal cancer cells (HCT116) was immunoprecipitated and analysed with an Affymetrix promoter array. Additionally, RNA was isolated and analysed in parallel with an Affymetrix expression array. Ingenuity pathway analysis software revealed that a significant proportion of the genes hypomethylated and upregulated were involved in cellular movement, including PLAUR and CYR61. A Matrigel invasion assay revealed that indeed HCT116 cells grown in hypoxic or hypoglycaemic conditions have increased mobility capabilities. Confirmation of upregulated expression of cellular movement genes was performed with qPCR. The correlation between ischemia and metastasis is well established in cancer progression, but the molecular mechanisms responsible for this common observation have not been clearly identified. Our novel data suggests that hypoxia and hypoglycaemia may be driving changes in DNA methylation through downregulation of DNMTs. This is the first report to our knowledge that provides an explanation for the increased metastatic potential seen in ischemic cells; i.e. that ischemia could be driving DNA hypomethylation and increasing expression of cellular movement genes.

Immunohistological insight into the correlation between neuropilin-1 and epithelial-mesenchymal transition markers in epithelial ovarian cancer

The mechanism by which neuropilin-1 (NRP-1) induces malignancy in Epithelial Ovarian Cancer (EOC) is still unknown. This study is the first to demonstrate the relationship between NRP-1 expression and EMT markers vimentin, N-cadherin, E-cadherin and Slug. We used tissue microarrays containing the three main subtypes of EOC tumors: serous, mucinous cystadenocarcinoma and endometrioid adenocarcinoma and representative cases retrieved from our pathology archives. Immunohistochemistry was performed to detect the expression levels and location of NRP-1 and the aforementioned EMT proteins. NRP-1 was mainly expressed on cancer cells but not in normal ovarian surface epithelium (OSE). The Immunoreactive Scoring (IRS) values revealed that the expression of NRP-1, Slug and E-cadherin in the malignant subtypes of ovarian tissues was significantly higher (5.18 ± 0.64, 4.84 ± 0.7, 4.98 ± 0.68, respectively) than their expression in the normal and benign tissues (1.04 ± 0.29, 0.84 ± 0.68, 1.71 ± 0.66, respectively), with no significant differences among the studied subtypes. Vimentin was expressed in the cancer cell component of 43% of tumors and it was exclusively localized in the stroma of all mucinous tumors. The Spearman's rho value indicated that NRP-1 is positively related to the EMT markers E-cadherin and Slug. This notion might indicate that NRP-1 is a partner in the EMT process in EOC tumors.

Selenized milk casein in the diet of BALB/c nude mice reduces growth of intramammary MCF-7 tumors

BACKGROUND

Dietary selenium has the potential to reduce growth of mammary tumors. Increasing the Se content of cows' milk proteins is a potentially effective means to increase Se intake in humans. We investigate the effects of selenized milk protein on human mammary tumor progression in immunodeficient BALB/c nude mice.

METHODS

Four isonitrogenous diets with selenium levels of 0.16, 0.51, 0.85 and 1.15 ppm were formulated by mixing low- and high-selenium milk casein isolates with a rodent premix. MCF-7 cells were inoculated into the mammary fat pad of female BALB/c nude mice implanted with slow-release 17 β-estradiol pellets. Mice with palpable tumors were randomly assigned to one of the four diets for 10 weeks, during which time weekly tumor caliper measurements were conducted. Individual growth curves were fit with the Gompertz equation. Apoptotic cells and Bcl-2, Bax, and Cyclin D1 protein levels in tumors were determined.

RESULTS

There was a linear decrease in mean tumor volume at 70 days with increasing Se intake (P < 0.05), where final tumor volume decreased 35% between 0.16 and 1.15 ppm Se. There was a linear decrease in mean predicted tumor volume at 56, 63 and 70 days, and the number of tumors with a final volume above 500 mm3, with increasing Se intake (P < 0.05). This tumor volume effect was associated with a decrease in the proportion of tumors with a maximum growth rate above 0.03 day-1. The predicted maximum volume of tumors (Vmax) and the number of tumors with a large Vmax, were not affected by Se-casein. Final tumor mass, Bcl-2, Bax, and Cyclin D1 protein levels in tumors were not significantly affected by Se-casein. There was a significantly higher number of apoptotic cells in high-Se tumors as compared to low-Se tumors.

CONCLUSIONS

Taken together, these results suggest that turnover of cells in the tumor, but not its nutrient supply, were affected by dairy Se. We have shown that 1.1 ppm dietary Se from selenized casein can effectively reduce tumor progression in an MCF-7 xenograft breast cancer model. These results show promise for selenized milk protein as an effective supplement during chemotherapy.

Abstract 1852: Pyruvate dehydrogenase kinase expression and metabolic changes following dichloroacetate exposure in anoxia in human colorectal cancer cells

Introduction: While glycolysis is a suboptimal metabolic strategy used by cells under hypoxic conditions, many cancer cells preferentially utilize glycolysis for energy production in the presence of abundant oxygen, a phenomenon known as the “Warburg Effect”. Dichloroacetate (DCA) is a small molecule metabolic modulator that shifts cellular metabolism to glucose oxidation by inhibition of pyruvate dehydrogenase kinase (PDK), an enzymatic inhibitor of pyruvate dehydrogenase (PDH). Furthermore, DCA has been shown to induce apoptosis in cancer but not normal cells. Our previous work showed that some human colorectal cancer (CRC) cells are protected from anoxia-induced apoptosis upon exposure to DCA, through as yet unclear mechanisms.

Hypothesis: It is hypothesized that differential expression of PDK isoforms will correlate with the ability of different cancer cells to withstand the apoptotic effects of DCA in anoxia.

Methods: SW480, LS174T (CRC) and IEC-18 (normal intestinal epithelial) cell lines were exposed to 10 mM DCA in either normoxic (20% O2) or anoxic (&lt; 0.1% O2) conditions for 24 hours. Following treatment, expression of different PDK isoforms was determined through qRT-PCR and western blotting. Phosphorylation of PDH at Ser293 and Ser300 was assessed through western blotting. Glucose consumption and lactate production was determined using a colorimetric-based assay. Changes in mitochondrial function were quantified through Mitotracker staining and subsequent flow cytometry. Cell viability was assessed using the neutral red assay.

Results: In all three cell lines: A) PDK isoforms 1 and 3 are highly expressed relative to isoforms 2 and 4, B) DCA and/or anoxic treatment induced a greater effect on PDH phosphorylation at Ser300 than Ser293, and C) DCA had minimal effect on glucose consumption in either normoxia or anoxia.

Conclusions: Altered PDK expression and PDH activation may not fully explain the differences in resistance to DCA-induced apoptosis observed in human CRC cells. Investigating the mechanisms by which certain cancer cells are protected from DCA-induced apoptosis will lead to a better understanding of cancer metabolism and thus provide better therapeutic opportunities.

Citation Format: Nelson Ho, Brenda L. Coomber. Pyruvate dehydrogenase kinase expression and metabolic changes following dichloroacetate exposure in anoxia in human colorectal cancer cells. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1852. doi:10.1158/1538-7445.AM2013-1852

VEGFR2 expression and TGF-β signaling in initial and recurrent high-grade human glioma

OBJECTIVE

Bevacizumab has promising activity against glioma, although reasons for poor efficacy and variable response rates in certain patients are unclear. Vascular endothelial growth factor receptor 2 (VEGFR2) is heterogeneously expressed within the microvasculature of various malignancies. Moreover, transforming growth factor β (TGF-β), a negative prognostic factor for glioma, is intimately involved in angiogenesis including VEGFR2 regulation. Our objective was to associate expression of VEGFR2 and TGF-β activity with clinicopathological features of human glioma.

METHODS

Expression patterns determined by immunohistochemistry for VEGFR2 and phosphorylated Smad2 in human gliomas were compared to overall survival, progression-free survival (PFS), initial versus recurrent tumors and tumor grade.

RESULTS

Endothelial VEGFR2 expression was low or undetectable in normal tissue but the proportion of VEGFR2-positive vessels increased with tumor grade. Decreased PFS was associated with tumors whose vessels had increased proportions of VEGFR2 at recurrence. Neither parenchymal nor endothelial cell p-Smad2 was associated with tumor grade; however, the former was negatively correlated with overall survival in glioblastoma multiforme.

CONCLUSIONS

The molecular phenotype of the vasculature based on the status of VEGFR2 but not p-Smad2 is related to aspects of glioma progression and patient response. Changes in VEGFR2-positive vessels may account for variable therapeutic efficacy of anti-angiogenic agents.

Colorectal carcinoma cell production of transforming growth factor beta decreases expression of endothelial cell vascular endothelial growth factor receptor 2

BACKGROUND

Vascular endothelial growth factor (VEGF) signaling is a target for antiangiogenic cancer therapy. The authors have previously observed that up to 40% of vessels in colorectal carcinoma (CRC) tumors are negative for VEGF receptor 2 (VEGFR2) expression. Differential activity of transforming growth factor beta (TGF-β) is a potential contributor to this receptor heterogeneity because TGF-β contributes to both angiogenesis and CRC tumor progression.

METHODS

The authors analyzed VEGFR2 expression by Western blotting, and TGF-β expression in endothelial and CRC cell lines, respectively. In addition, they immunostained endothelial cells in CRC xenografts to find an association between VEGFR2 and TGF-β levels or activity.

RESULTS

In bovine aortic endothelial cells (BAECs), TGF-β1 significantly repressed VEGFR2 protein in a time-dependent and dose-dependent fashion (P < .05). Serum-free conditioned media from various malignant human CRC cell lines (HCT116, 379.2, Dks8, and DLD1) induced down-regulation of VEGFR2 in BAECs. This effect was proportional to the total levels of TGF-β1 and TGF-β2 and was blocked by SB-431542 and SD-208, TGF-β receptor I inhibitors. Immunofluorescence staining of subcutaneous mouse xenografts of HCT116, 379.2, Dks8, and SW480 cells revealed vessels with an inverse relationship between TGF-β activity and VEGFR2 expression. Oxygen and bone morphogenetic protein 9 levels were shown to modulate TGF-β-induced VEGFR2 down-regulation.

CONCLUSIONS

In combination with other factors, TGF-β may contribute to the vascular heterogeneity in human colorectal tumors.

Selenomethionine increases proliferation and reduces apoptosis in bovine mammary epithelial cells under oxidative stress

The decline in mammary epithelial cell number as lactation progresses may be due, in part, to oxidative stress. Selenium is an integral component of several antioxidant enzymes. The present study was conducted to examine the effect of oxidative stress and selenomethionine (SeMet) on morphology, viability, apoptosis, and proliferation of bovine mammary epithelial cells (BMEC) in primary culture. Cells were isolated from mammary glands of lactating dairy cows and grown for 3 d in a low-serum gel system containing lactogenic hormones and 0 or 100 μM H2O2 with 0, 10, 20, or 50 nM SeMet. Hydrogen peroxide stress increased intracellular H2O2 to 3 times control concentrations and induced a loss of cuboidal morphology, cell-cell contact, and viability of BMEC by 25%. Apoptotic cell number more than doubled during oxidative stress, but proliferating cell number was not affected. Supplementation with SeMet increased glutathione peroxidase activity 2-fold and restored intracellular H2O2 to control levels with a concomitant return of morphology and viability to normal. Apoptotic BMEC number was decreased 76% below control levels by SeMet and proliferating cell number was increased 4.2-fold. These findings suggest that SeMet modulated apoptosis and proliferation independently of a selenoprotein-mediated reduction of H2O2. In conclusion, SeMet supplementation protects BMEC from H2O2-induced apoptosis and increased proliferation and cell viability under conditions of oxidative stress.

VEGFR2 heterogeneity and response to anti-angiogenic low dose metronomic cyclophosphamide treatment

Background

Targeting tumor vasculature is a strategy with great promise in the treatment of many cancers. However, anti-angiogenic reagents that target VEGF/VEGFR2 signaling have met with variable results clinically. Among the possible reasons for this may be heterogeneous expression of the target protein.

Methods

Double immunofluorescent staining was performed on formalin-fixed paraffin embedded sections of treated and control SW480 (colorectal) and WM239 (melanoma) xenografts, and tissue microarrays of human colorectal carcinoma and melanoma. Xenografts were developed using RAG1^-/- mice by injection with WM239 or SW480 cells and mice were treated with 20 mg/kg/day of cyclophosphamide in their drinking water for up to 18 days. Treated and control tissues were characterized by double immunofluorescence using the mural cell marker α-SMA and CD31, while the ratio of desmin/CD31 was also determined by western blot. Hypoxia in treated and control tissues were quantified using both western blotting for HIF-1α and immunohistochemistry of CA-IX.

Results

VEGFR2 is heterogeneously expressed in tumor vasculature in both malignant melanoma and colorectal carcinoma. We observed a significant decrease in microvascular density (MVD) in response to low dose metronomic cyclophosphamide chemotherapy in both malignant melanoma (with higher proportion VEGFR2 positive blood vessels; 93%) and colorectal carcinoma (with lower proportion VEGFR2 positive blood vessels; 60%) xenografts. This reduction in MVD occurred in the absence of a significant anti-tumor effect. We also observed less hypoxia in treated melanoma xenografts, despite successful anti-angiogenic blockade, but no change in hypoxia of colorectal xenografts, suggesting that decreases in tumor hypoxia reflect a complex relationship with vascular density. Based on α-SMA staining and the ratio of desmin to CD31 expression as markers of tumor blood vessel functionality, we found evidence for increased stabilization of colorectal microvessels, but no such change in melanoma vessels.

Conclusions

Overall, our study suggests that while heterogeneous expression of VEGFR2 is a feature of human tumors, it may not affect response to low dose metronomic cyclophosphamide treatment and possibly other anti-angiogenic approaches. It remains to be seen whether this heterogeneity is partly responsible for the variable clinical success seen to date with targeted anti-VEGFR2 therapy.

Canine subcutaneous mast cell tumors: cellular proliferation and KIT expression as prognostic indices

Molecular assays are widely used to prognosticate canine cutaneous mast cell tumors (MCT). There is limited information about these prognostic assays used on MCT that arise in the subcutis. The aims of this study were to evaluate the utility of KIT immunohistochemical labeling pattern, c-KIT mutational status (presence of internal tandem duplications in exon 11), and proliferation markers--including mitotic index, Ki67, and argyrophilic nucleolar organizing regions (AgNOR)--as independent prognostic markers for local recurrence and/or metastasis in canine subcutaneous MCT. A case-control design was used to analyze 60 subcutaneous MCT from 60 dogs, consisting of 24 dogs with subsequent local recurrence and 12 dogs with metastasis, as compared to dogs matched by breed, age, and sex with subcutaneous MCT that did not experience these events. Mitotic index, Ki67, the combination of Ki67 and AgNOR, and KIT cellular localization pattern were significantly associated with local recurrence and metastasis, thereby demonstrating their prognostic value for subcutaneous MCT. No internal tandem duplication mutations were detected in exon 11 of c-KIT in any tumors. Because c-KIT mutations have been demonstrated in only 20 to 30% of cutaneous MCT and primarily in tumors of higher grade, the number of subcutaneous MCT analyzed in this study may be insufficient to draw conclusions on the role c-KIT mutations in these tumors.

Heterogeneity of vascular and progenitor cell compartments in tumours from MMTV-PyVmT transgenic mice during mammary cancer progression

Transgenic mice are important tools for our study of breast cancer pathobiology. In order to evaluate changes in cell phenotype with breast cancer progression, we examined vascular and progenitor cell characteristics in tumours derived from MMTV-PyVmT mice. We performed dual-immunofluorescence staining for Tie2, pTie2Y1100, VEGFR2 and PDGFR-β and the pan-endothelial marker PECAM-1 (CD31) in 39 tumours from MMTV-PyVmT transgenic mice grouped by nuclear grade and tumour morphology. Immunohistochemical staining for Aldh1a1 was performed in MMTV-PyVmT-derived tumours and in non-transgenic mouse mammary glands. Tumour blood vessels were heterogeneous in all samples analysed, with the proportion of Tie2-, pTie2 (Y1100)-, VEGFR2- and PDGFR-β-positive tumour blood vessels ranging from 18-98%, 7-40%, 19-86% and 16-94% respectively. We observed a statistically significant difference in vascular pTie2Y1100 levels between low-nuclear-grade tumours and intermediate-/high-nuclear-grade tumours (P=0.03) and an increase in the proportion of PDGFR-β-positive tumour blood vessels in tumours with high vs. Intermediate-nuclear grade tumours (P<0.01). Aldh1a1-positive mammary epithelial cells were observed in the terminal end buds of non-transgenic mammary glands and Aldh1a1-positive mammary tumour cells were observed in tumours from MMTV-PyVmT transgenic mice. We observed a decrease in the average number of Aldh1a1-positive cells in tumours with a non-invasive vs. solid morphology (P=0.03), and in the average number of Aldh1a1-positive mammary tumour cells in low vs. intermediate and low vs. High-nuclear grade tumours (P<0.001). Our findings suggest heterogeneous expression of several molecules important for tumour angiogenesis and tumour progression that are currently under investigation as therapeutic targets for metastatic breast cancer.

Sodium dichloroacetate (DCA) reduces apoptosis in colorectal tumor hypoxia

We examined the effect of hypoxia on apoptosis of human colorectal cancer (CRC) cells in vitro and in vivo. All cell lines tested were susceptible to hypoxia-induced apoptosis. DCA treatment caused significant apoptosis under normoxia in SW480 and Caco-2 cells, but these cells displayed decreased apoptosis when treated with DCA combined with hypoxia, possibly through HIF-1alpha dependent pathways. DCA treatment also induced significantly increased growth of SW480 tumor xenografts, and a decrease in TUNEL positive nuclei in hypoxic but not normoxic regions of treated tumors. Thus DCA is cytoprotective to some CRC cells under hypoxic conditions, highlighting the need for further investigation before DCA can be used as a reliable apoptosis-inducing agent in cancer therapy.

Molecular blockade of VEGFR2 in human epithelial ovarian carcinoma cells

Human epithelial ovarian cancer (EOC) is the most lethal neoplasm affecting the female genital tract, and is characterized by overexpression of vascular endothelial growth factor (VEGF) and growth as ascites. Anti-VEGF strategies are currently used in EOC therapy with promising results; however, molecular targeting of specific VEGF receptors on the cancer cells themselves has not been explored to date. We previously showed that activation of a VEGF/VEGFR2 signaling loop in EOC cells supports their survival in suspension, and short-term pharmacological inhibition of this loop increased EOC cell apoptosis in vitro. In this study, we stably knocked down VEGFR2 in OVCAR-3 and SKOV-3 EOC cells using short hairpin RNA (shRNA), an RNA interference strategy that could potentially overcome chemoresistance arising with angiogenic inhibitors. Unexpectedly, we observed an induction of more aggressive cellular behavior in transfected cells, leading to increased growth in mouse xenografts, enhanced accumulation of ascites, increased VEGF and neuropilin-1 (NRP-1) expression, and decreased expression of adhesion proteins, notably cadherins and integrins. Sonic hedgehog (SHH) pathways do not seem to be involved in the upregulation of NRP-1 message in VEGFR2 knockdown cells. Supporting our mouse model, we also found a significant increase in the ratio between NRP-1 and VEGFR2 with increasing tumor grade in 80 cases of human EOC. The change in EOC behavior that we report in this study occurred independent of the angiogenic response and shows the direct effect of VEGF blockade on the cancer cells themselves. Our findings highlight the possible confounding events that may affect the usefulness of RNAi in a therapeutic setting for disrupting EOC cell survival in ascites.

Modulation of the tumor suppressor protein alpha-catenin by ischemic microenvironment

Dysregulation or mislocalization of cell adhesion molecules and their regulators, such as E-cadherin, beta-catenin, and alpha-catenin, usually correlates with loss of polarity, dedifferentiation, invasive tumor growth, and metastasis. A subpopulation of alpha-catenin-negative cells within the DLD-1 colorectal carcinoma cell line causes it to display a heterogeneous morphological makeup, thus providing an excellent model system in which to investigate the role of alpha-catenin in tumorigenesis. We re-established expression of alpha-catenin protein in an alpha-catenin-deficient subpopulation of the DLD-1 cell line and used it to demonstrate that loss of alpha-catenin resulted in increased in vitro tumorigenic characteristics (increased soft agarose colony formation, clonogenic survival after suspension, and survival in suspension). When the cells were used to form tumor xenografts, those lacking alpha-catenin showed faster growth rates because of increased cellular cycling but not increased tumor microvascular recruitment. alpha-Catenin-expressing cells were preferentially located in well perfused areas of xenografts when tumors were formed from mixed alpha-catenin-positive and -negative cells. We therefore evaluated the role of the ischemic tumor microenvironment on alpha-catenin expression and demonstrated that cells lose expression of alpha-catenin after prolonged exposure in vitro to hypoglycemic conditions. Our findings illustrate that the tumor microenvironment is a potent modulator of tumor suppressor expression, which has implications for localized nutrient deficiency and ischemia-induced cancer progression.

Selenomethionine stimulates expression of glutathione peroxidase 1 and 3 and growth of bovine mammary epithelial cells in primary culture

This study examined the localization of cellular glutathione peroxidase (GPx1) and extracellular glutathione peroxidase (GPx3) in lactating mammary tissue and in primary cultures of bovine mammary epithelial cells (BMEC). The effect of selenium as selenomethionine (SeMet) on the growth and viability of BMEC and GPx protein expression and activity were also studied. Single mammary epithelial cells were recovered by serial collagenase/hyaluronidase digestion from lactating bovine mammary tissue and cultured in a low-serum collagen gel system enriched with lactogenic hormones and 0, 10, 20, or 50 nM SeMet. Positive immunostaining with anti-cytokeratin and bovine anti-casein confirmed the epithelial nature and differentiated state of BMEC. Addition of SeMet to media facilitated rapid confluence of BMEC and formation of dome structures. Immunohistochemical and immunocytochemical staining revealed that both GPx1 and GPx3 are synthesized by BMEC and localized in the cytoplasm and nucleus. Up to 50 nM SeMet linearly increased BMEC number and viability over 5 d of culture. Bovine mammary epithelial cells cultured in SeMet-supplemented medium also exhibited markedly elevated GPx activity and linear increases in abundance of GPx1 and GPx3 proteins. It is apparent that SeMet degradation to release Se for synthesis of selenoproteins is carried out by BMEC. Results indicate that bovine mammary epithelial cells express GPx1 and GPx3 in vivo and in vitro; SeMet enhances expression of these selenoproteins in vitro and the growth and viability of BMEC.

Autocrine VEGF-A/KDR loop protects epithelial ovarian carcinoma cells from anoikis

Epithelial ovarian carcinoma (EOC) patients are usually diagnosed at an advanced stage, characterized by interperitoneal carcinomatosis and production of large volumes of ascites. Vascular endothelial growth factor-A (VEGF-A) and its main signaling receptor VEGFR2 (KDR) are coexpressed in primary ovarian tumors, ascitic cells and metastases, suggesting the existence of an autocrine VEGF-A/KDR loop in EOC cells. In the present study, we examined this possibility and explored the role of this autocrine loop in protecting EOC cells from apoptosis under anchorage free growth conditions (anoikis). We found that 3 different EOC cell lines (Caov3, OVCAR3, SKOV3) express both VEGF-A and its receptors, including KDR. In these cells, KDR is constitutively phosphorylated and is detected both in the cell plasma membrane and in the nucleus. Treating EOC cells with specific internal inhibitors of KDR kinase activity or a VEGF-A neutralizing antibody abolished KDR autophosphorylation and resulted in significant increase in apoptosis when cells were grown in single-cell, anchorage-free conditions. By contrast, these blocking reagents had no effect on cell viability when EOC cells were grown in adhesive monolayers. In summary, our results indicate that an autocrine VEGF-A/KDR loop exists in EOC cells and that it plays a role in protecting the cells from anoikis. Our results imply that treating EOC patients with VEGF blocking agents may potentially reduce peritoneal dissemination by decreasing vascular permeability as well as inducing apoptosis of shed ovarian cancer cells in ascites.

Induction of DNA hypomethylation by tumor hypoxia

In cancer, the extensive methylation found in the bulk of chromatin is reduced, while the normally unmethylated CpG islands become hypermethylated. Regions of solid tumors are transiently and/or chronically exposed to ischemia (hypoxia) and reperfusion, conditions known to contribute to cancer progression. We hypothesized that hypoxic microenvironment may influence local epigenetic alterations, leading to inappropriate silencing and re-awakening of genes involved in cancer. We cultured human colorectal and melanoma cancer cell lines under severe hypoxic conditions, and examined their levels of global methylation using HPLC to quantify 5-methylcytosine (5-mC), and found that hypoxia induced losses of global methylation. This was more extensive in normal human fibroblasts than cancer cell lines. Cell lines from metastatic colorectal carcinoma or malignant melanoma were found to be markedly more hypomethylated than cell lines from their respective primary lesions, but they did not show further reduction of 5-mC levels under hypoxic conditions. To explore these epigenetic changes in vivo, we established xenografts of the same cancer cells in immune deficient mice. We used Hypoxyprobe to assess the magnitude of tissue hypoxia, and immunostaining for 5-mC to evaluate DNA methylation status in cells from different regions of tumors. We found an inverse relationship between the presence of extensive tumor hypoxia and the incidence of methylation, and a reduction of 5-mC in xenografts compared to the levels seen in the same cancer cell lines in vitro, verifying that methylation patterns are also modulated by hypoxia in vivo. This suggests that epigenetic events in solid tumors may be modulated by microenvironmental conditions such as hypoxia.

Heterogeneity of Tie2 expression in tumor microcirculation: influence of cancer type, implantation site, and response to therapy

To evaluate the expression of the Tie2/Tek tyrosine kinase receptor in tumor blood vessels, we examined Tie2lacZ(+)/RAG1(-) mice. There was considerable heterogeneity (Tie2-negative, Tie2-positive, or Tie2-composite blood vessels) in subcutaneous xenografts of human colorectal carcinoma (HCT116; 97.5% Tie2-positive vessels) versus human melanoma (WM115; 75.9% Tie2-positive vessels). Similar patterns of Tie2 expression occurred in abdominal metastases derived from the same cell lines. Immunostaining for endothelial markers and Tie2 revealed that endogenous protein levels corresponded with transgene activity. Endothelial cells were confirmed to be of mouse origin through triple immunofluorescence staining with mouse antiserum to human nuclei, isolectin GS-IB(4), and anti-Tie2. Similar Tie2 heterogeneity was observed in clinical specimens from a variety of human cancers, including malignant melanoma and colorectal carcinoma. We also examined the effect of Tek-Delta Fc anti-angiogenic therapy on tumor growth and Tie2 expression patterns in HCT116 and WM115 subcutaneous xenografts. Tek-Delta induced extensive tumor regression in HCT116 tumors and concomitant reductions in Tie2-expressing blood vessels. However, no significant responses were seen in Tek-Delta-treated WM115 tumors. Thus, vascular heterogeneity of Tie2 expression is cancer-type specific, suggesting that the tumor microenvironment and/or direct cancer cell interactions influence Tie2 endothelial expression.

Clopidogrel induced suppression of bovine platelet activation in vitro and a preliminary study of its effect on the development of Mannheimia haemolytica induced pneumonia

We report here on the influence of the platelet antagonist clopidogrel (Plavix) on bovine platelet function. We first evaluated the capacity of clopidogrel to inhibit adenosine diphosphate (ADP)-stimulated platelet function in the bovine species, using an ex vivo approach with blood from treated animals. Platelets isolated from treated calves displayed rapid and consistent reduction in function (aggregation, thromboxane production) upon ADP, but not platelet activating factor (PAF), stimulation. We then examined the possibility that clopidogrel could influence Mannheimia haemolytica pneumonia pathobiology using an experimental challenge model. We were unable to detect significant differences between clopidogrel treated and untreated animals when challenged with intra-tracheal inoculation of M. haemolytica. There was a trend towards inhibition of platelet degranulation in the affected regions of lungs from clopidogrel treated calves, and pre-treated challenged animals had similar amounts of fibrin deposition and enhanced fibrous tissue formation in their lungs when compared with control counterparts.

Ischemia-Induced K-ras Mutations in Human Colorectal Cancer Cells: Role of Microenvironmental Regulation of MSH2 Expression

Mutation of the K-ras gene is one of the most common genetic alterations in solid tumors, including colorectal cancer. The relatively late emergence of K-ras mutations in colorectal cancer is particularly striking in the class of mismatch repair-deficient tumors associated with early-onset microsatellite instability. We, therefore, tested the hypothesis that the microsatellite instability phenotype itself does not efficiently trigger K-ras mutations in colorectal cancer cells, but rather that tumor-associated microenvironmental conditions (e.g., hypoxia and hypoglycemia) contribute to this event by modulating genetic instability. We examined K-ras(G13D) mutation using PCR-RFLP analysis in two different microsatellite instability colorectal cancer cell lines (HCT116 and DLD-1) and their variants in which the mutant (but not the wild-type) K-ras allele has been genetically disrupted (Hkh-2 and Dks-8). We found K-ras(G13D) mutation to occur at far greater incidence in cells derived from xenografted tumors or exposed to conditions of combined hypoxia and hypoglycemia in vitro. Interestingly, this mutagenesis was neither enhanced by induced oxidative damage nor prevented by the antioxidant vitamin E. Moreover, the accumulation of K-ras mutations was paralleled by down-regulation of the key mismatch repair protein MSH2 in xenografted tumors, particularly in hypoperfused areas and under hypoglycemic conditions (in vitro). In contrast, the microsatellite stable colorectal cancer cell line Caco-2 neither accumulated K-ras mutations nor showed down-regulation of MSH2 under these conditions. Thus, our study suggests that ischemia may not simply select for, but can actually trigger, increased mutation rate in crucial colorectal cancer oncoproteins. This finding establishes a novel linkage between genetic instability, tumor ischemia, and genetic tumor progression and carries important implications for applying anticancer therapies involving tumor hypoxia (e.g., antiangiogenesis) in microsatellite instability cancers.

Microenvironmental influences on mutagenesis in mammary epithelial cells

Tumor progression may be viewed as an evolutionary process at the cellular level. Because blood supply to solid tumors is inadequate, the cancer cells face a hostile microenvironment characterized by hypoxia or anoxia, acidic extracellular pH and nutrient deficiencies. It has been proposed that these factors result in increased levels of spontaneous mutagenesis and thereby contribute to tumor progression. We have examined spontaneous mutagenesis in vitro and in vivo, using previously characterized cell lines (mammary epithelial cells [ME] and mammary fibroblast cells [MFib]) from the mammary gland of the BigBluetrade mark rat, carrying a transgene construct suitable for the detection of mutations. Cells were exposed in vitro to control conditions, low pH, or to glucose deprivation, under normoxic or hypoxic culture conditions, and were also grown as xenografted tumors in immune-deficient mice. We examined cell survival and mutant frequency/spectrum at the cII locus. Significant increases in mutant frequency were observed in ME cells exposed to hypoxia alone or in combination with no glucose; the latter condition also resulted in reduced clonogenic survival. Cells grown as xenografts and then recovered and expanded in culture also had elevated frequencies of spontaneous mutations. We observed a shift in the spontaneous mutation spectrum between the ME cells and the MET cells (cultured in vitro or isolated from mouse xenograft tumors). These results support the concept that the tumor microenvironment contributes to tumor progression by enhancing spontaneous mutagenesis, that different cell types from the same organ can respond differently to these stresses and that differences in microenvironment may influence the types of mutations that arise.

Oncogenic events regulate tissue factor expression in colorectal cancer cells: implications for tumor progression and angiogenesis

Tissue factor (TF) is the primary cellular initiator of blood coagulation and a modulator of angiogenesis and metastasis in cancer. Indeed, systemic hypercoagulability in patients with cancer and TF overexpression by cancer cells are both closely associated with tumor progression, but their causes have been elusive. We now report that in human colorectal cancer cells, TF expression is under control of 2 major transforming events driving disease progression (activation of K-ras oncogene and inactivation of the p53 tumor suppressor), in a manner dependent on MEK/mitogen-activated protein kinase (MAPK) and phosphatidylinositol 3'-kinase (PI3K). Furthermore, the levels of cell-associated as well as circulating (microvesicle-associated) TF activity are linked to the genetic status of cancer cells. Finally, RNA interference experiments suggest that TF expression is an important effector of the K-ras-dependent tumorigenic and angiogenic phenotype in vivo. Thus, this study establishes a causal link between cancer coagulopathy, angiogenesis, and genetic tumor progression.

Potential involvement of gelatinases and their inhibitors in Mannheimia haemolytica pneumonia in cattle

Mannheimia haemolytica infection of the lower respiratory tract of cattle results in a bronchofibrinous pneumonia characterized by massive cellular influx and lung tissue remodeling and scarring. Since altered levels of gelatinases and their inhibitors have been detected in a variety of inflammatory conditions and are associated with tissue remodeling, we examined the presence of gelatinases in lesional and nonlesional lung tissue obtained from calves experimentally infected with M. haemolytica. Lesional tissue had elevated levels of progelatinase A and B and active gelatinase A and B when compared with nonlesional tissue obtained from the same lung lobe. In vitro, M. haemolytica products stimulated production of gelatinase B, but not its activation, by bovine monocytes. Alveolar macrophages showed constitutive production of gelatinase B but no change in response to M. haemolytica products. Bovine neutrophils exposed to M. haemolytica products also released gelatinase B, and there was a significant increase in the activated form of this enzyme. These effects were virtually identical when recombinant O-sialoglycoprotease was used to stimulate these cells. M. haemolytica products also enhanced the expression by bovine monocytes and alveolar macrophages of the tissue inhibitor of metalloproteinase 1. Our results provide evidence that matrix metalloproteinases are activated in lung lesions from cattle with shipping fever and that M. haemolytica virulence products induce production, release, and especially activation of gelatinase B by bovine inflammatory cells in vitro.

Vascular endothelial growth factor and its receptor, Flk-1/KDR, are cytoprotective in the extravascular compartment of the ovarian follicle

Vascular endothelial growth factor (VEGF) is a potent mitogen and cytoprotective factor for vascular endothelial cells. Although VEGF is ubiquitously expressed, its role in nonvascular tissues is poorly understood. VEGF interacts with various cell surface receptors to mediate its cellular effects. It previously has been thought that the VEGF receptor Flk-1/KDR, its main signaling receptor, was expressed exclusively by endothelial cells. However, in the present study using bovine and rodent models, we demonstrate that VEGF and Flk-1/KDR are coexpressed in ovarian granulosa cells. VEGF and Flk-1/KDR mRNA and protein were both detectable in follicle tissue sections and in vitro cultured granulosa cells. Expression of both ligand and receptor increased in healthy follicles throughout follicular development. VEGF treatment of serum-starved and cytokine-exposed granulosa cells resulted in enhanced survival, and this cytoprotection was ameliorated when Flk-1/KDR signaling was inhibited. Reduced expression of Flk-1/KDR was also associated with the onset and progression of follicle atresia, suggesting involvement in follicular health in vivo. The results of this study demonstrate for the first time expression of Flk-1/KDR in ovarian granulosa cells and identify a novel extravascular role for VEGF and its receptor in ovarian function.

Angiogenesis and the role of epigenetics in metastasis

The major obstacle to devising effective ways to treat cancer is its heterogeneity and genetic instability. It was originally postulated that targeting the process of tumor angiogenesis could circumvent this problem, as it involves genetically stable epigenetically controlled host stroma. Thus, anti-angiogenic approaches should be applicable across various tumor types and organ sites, including metastases. However, early clinical experience with this therapy revealed unexpectedly distinct responses between different tumors and organ sites. Here we propose that the heterogeneity of pre-clinical and clinical results obtained with anti-angiogenic agents stems from the deep functional linkage that may exist between genetic and epigenetic tumor progression. Thus, epigenetic processes regulating tumor associated host blood vessels (such as tumor microenvironment) display unstable, heterogeneous and progressive characteristics to an extent comparable with (and causally linked to) the instability of the cancer cell genome. As well, many known epigenetic factors (such as hypoxia, inflammation, expression of growth factors, etc.) may have genetic causes and consequences (e.g., oncogene expression, loss of tumor suppressor genes). This reciprocal interrelationship and heterogeneity may translate into site and stage specific changes in angiogenesis regulation, and angiogenesis dependence, ultimately to changes in the metastatic ability/efficiency of cancer cells, even in the same patient. A better understanding of the linkage between genetic and epigenetic events in growth and metastasis of various cancers may result in more effective use of anti-angiogenic therapy in future.

Mutagenicity of the oral carcinogen 4-nitroquinoline-1-oxide in cultured BigBlue rat tongue epithelial cells and fibroblasts

Environmental carcinogen exposures contribute to the development of oral cancer and improved test systems for the analysis of such carcinogens are needed. We have previously isolated and characterized an epithelial cell line from the tongue of a BigBlue rat. Now, we have established an immortalized fibroblast cell line from the same organ. We exposed these cells to 4-nitroquinoline-1-oxide (NQO), a well-known experimental oral carcinogen in the rat and other species, and measured its cytotoxic and genotoxic (cII transgene mutagenesis) effects. Both cell lines were very sensitive to NQO toxicity and showed dose-dependent mutant frequency responses. At the highest NQO dose tested, 70 ng/ml, the mutant frequency was elevated more than eight-fold above background for the epithelial cells and more than 25-fold for the fibroblast cells. We examined cellular parameters which could affect glutathione-dependent detoxication of mutagens. Glutathione (GSH) contents of the two cell lines were similar. Glutathione transferase (GST) activities were measured with several substrates and were generally higher in the epithelial cells. Although multiple biochemical and biological characteristics of individual cell lines are likely to determine responses to mutagens, the greater sensitivity of the fibroblast cells to NQO mutagenicity is in accord with the lower GST activity and the lower DNA content of these cells. These new cell lines are suitable for in vitro testing of chemicals as possible oral mutagens and for studies of their biochemical mechanisms of action.

A paradigm for therapy-induced microenvironmental changes in solid tumors leading to drug resistance

Intrinsic alterations in the tumor microenvironment are known to contribute to various forms of drug resistance. For example, tumor hypoxia, due to abnormal or sluggish blood flow within areas of solid tumors, can result in both microenvironment-mediated radiation and chemotherapeutic drug resistance. In contrast, acquired resistance to chemotherapy is generally considered to be the result of the gradual selection of mutant subpopulations having genetic mutations and biochemical alterations responsible for the resistant phenotype. Here we present a paradigm for therapyinduced microenvironment-mediated acquired drug resistance. It is based on the results showing that tumor cells appear to be heterogeneous in their relative dependence on adjacent tumor-associated vasculature for survival. Some tumor cells are highly vessel dependent, whereas some are significantly less so, and thus can survive in more hypoxic regions of tumors, distal from such tumor vessels. Hence, it is possible that variant tumor cells that are less vessel dependent may therefore be selected for over time by successful antiangiogenic drug therapies. This results in loss of response or attenuated responses to the therapy. Preliminary evidence is summarized in support of this hypothesis, using paired human colon cancer (HCT116) cell lines that contain two copies of either the wild-type or the disrupted p53 tumor suppressor gene. The mutant cells were found to be less responsive to antiangiogenic therapy, compared to the wild-type cells, and could be progressively selected for in mixed cell populations. Because p53 inactivation can lead to resistance to hypoxia-mediated apoptosis, the results suggest that a protracted and successful antiangiogenic therapy may create more hypoxic tumor microenvironments, thereby creating the necessary conditions to accelerate the selection of mutant tumor cells that are more adept in surviving and growing in such environments. As such, consideration might be given to the combined use of bioreductive hypoxic cell cytotoxic drugs and angiogenesis inhibitors to prolong the efficacy of antiangiogenic therapeutics.

Possible mechanisms of acquired resistance to anti-angiogenic drugs: implications for the use of combination therapy approaches

The ultimate target of anti-angiogenic drugs is the genetically stable, activated endothelial cell of a newly forming tumor blood vessel, rather than the genetically unstable tumor cell population per se. This led to the notion that acquired resistance to such drugs may not develop as readily, if at all. While there is some evidence that this lack of resistance development may be the case for some direct-acting angiogenesis inhibitors, it is becoming apparent that resistance can develop over time to many types of angiogenesis inhibitors including, possibly, some direct inhibitors, especially when used as monotherapies. Possible mechanisms for such acquired or induced resistance include: (i) redundancy of pro-angiogenic growth factors when the drug used targets a single such growth factor or its cognate endothelial cell-associated receptor tyrosine kinase; (ii) the anti-apoptotic/pro-survival function of growth factors such as VEGF, which, in high local concentrations, can antagonize the pro-apoptotic effects of various angiogenesis inhibitors; (iii) epigenetic, transient upregulation, or induction, of various anti-apoptotic effector molecules in host-endothelial cells; and (iv) heterogeneous vascular dependence of tumor cell populations. It is suggested that long-term disease control with anti-angiogenic drugs can be best achieved by judicious combination therapy. In this regard, the great molecular diversity of anti-angiogenic drug targets, in contrast to chemotherapy, makes this a particularly attractive therapeutic option, especially when approved, commercially available drugs considered to have anti-angiogenic effects are used in such combination treatment strategies.

Effect of p53 status on tumor response to antiangiogenic therapy

The p53 tumor suppressor gene is inactivated in the majority of human cancers. Tumor cells deficient in p53 display a diminished rate of apoptosis under hypoxic conditions, a circumstance that might reduce their reliance on vascular supply, and hence their responsiveness to antiangiogenic therapy. Here, we report that mice bearing tumors derived from p53(-/-) HCT116 human colorectal cancer cells were less responsive to antiangiogenic combination therapy than mice bearing isogenic p53(+/+) tumors. Thus, although antiangiogenic therapy targets genetically stable endothelial cells in the tumor vasculature, genetic alterations that decrease the vascular dependence of tumor cells can influence the therapeutic response of tumors to this therapy.

2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP)-induced mutagenesis in cultured Big Blue rat mammary epithelial and fibroblast cells

Epithelial cells are the primary site of carcinogenesis in most tissues, including the mammary gland. As an alternative to the study of mutation induction in whole tissues in vivo, we have established Big Blue transgenic rat cell lines from the mammary epithelium (BBR/ME) and the mammary stroma (BBR/MFib), to permit a comparison of their mutagenic responses to carcinogens. We previously demonstrated their responsiveness to the alkylating agent N-ethyl-N-nitrosourea (ENU) (McDiarmid H et al. [2001]: Mutat Res 497:39-47). Here, we examined the responses of cultured epithelial and stromal cells to the protein pyrolysis product and mammary carcinogen 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP). Rat hepatic S9 was used as a source of bioactivation enzymes. Mutant induction (cII locus) and clonogenic survival were measured as a function of PhIP concentration. PhIP mutagenicity was observed in the fibroblast cells, but the greater toxicity of PhIP to the epithelial cells prevented a definitive evaluation of mutagenicity. Since PhIP may be detoxified by conjugation with glutathione, we measured glutathione levels and glutathione-S-transferase expression and activities in both cell lines. The epithelial cells had higher glutathione-S-transferase enzyme activity and protein expression than did the fibroblast cell line. Because the epithelial cells were more sensitive to toxicity, glutathione conjugation evidently plays only a minor role in PhIP toxicity and mutagenicity in our cell lines.

Epithelial and fibroblast cell lines cultured from the transgenic BigBlue rat: an in vitro mutagenesis assay

We have isolated, cultured, and immortalised three new BigBlue transgenic rat cell lines for the study of mutation induction in vitro. The two epithelial cell lines, from the mammary gland and oral cavity, were designated BBR/ME and BBR/OE, respectively, and the third is a mammary fibroblast line designated BBR/MFib. We have characterised these cell lines with respect to chromosome number and the expression of some cell-specific antigens. The clonogenic survival and cII transgene mutation induction responses of these three cell lines to N-ethyl-N-nitrosourea (ENU) treatment were determined. Both epithelial cell lines were much more sensitive to ENU toxicity than was the fibroblast cell line. However, all cell lines showed similar ENU dose-dependent increases in mutant frequency. We hope that cell lines such as these will extend the power of the BigBlue assay to in vitro studies.

Effects of relaxin on matrix remodeling enzyme activity of cultured equine ovarian stromal cells

Relaxin participates in extracellular matrix (ECM) remodeling in many reproductive organs, including the ovary, by regulating proteolytic enzyme activity. Accumulated evidence indicates this action of relaxin is involved in ovarian follicle development and ovulation. Equine follicles are embedded in cortex that is at the center of the ovary and they must expand/emigrate to the fossa, the only site in the ovary for ovulation. Due to the tremendous expansion of the follicle in this species, we hypothesized that ovarian stromal remodeling would be extensive. Therefore, cultured equine ovarian stromal cell (EOSC) lines were obtained from stroma at the apex of large follicles and the effects of relaxin on gelatinases A and B, tissue inhibitors of matrix metalloproteinases (TIMPs), plasminogen activators (PAs) and PA inhibitor-1 (PAI-1) activities were assessed. Our results showed that equine relaxin increased the activity of total gelatinase A (both pro forms and mature forms) and latent progelatinase B present in conditioned medium, latent progelatinase A present in cell extracts, and TIMP-1 and TIMP-2 present in conditioned medium. This study also revealed that equine relaxin increased the urokinase-type PA activity in conditioned medium and cell extracts, tissue-type PA activity in ECM and PAI-1 activity in conditioned medium. These results suggest that relaxin may contribute to equine follicle growth and migration, and facilitate ovulation by modulating the degradation of ECM in ovarian stromal tissue.

Neutrophil-platelet interactions and their relevance to bovine respiratory disease

Respiratory disease is a serious and significant health problem for the bovine industry. Classically, the clinical and research focus has been on the putative causative agents and conditions, and their interactions with host inflammatory cells, particularly alveolar macrophages and blood neutrophils. There is, currently, growing acceptance of the concept that blood platelets play a primary role in the inflammatory process. This review explores the implications of such pro-inflammatory activity, especially in the context of neutrophil-platelet interactions, and the species specificity of cellular responses. The relevance of these issues for the treatment and prevention of bovine respiratory disease is also discussed.