Treatment of experimental human breast cancer and lung cancer brain metastases in mice by macitentan, a dual antagonist of endothelin receptors, combined with paclitaxel

BACKGROUND

We recently demonstrated that brain endothelial cells and astrocytes protect cancer cells from chemotherapy through an endothelin-dependent signaling mechanism. Here, we evaluated the efficacy of macitentan, a dual endothelin receptor (ETAR and ETBR) antagonist, in the treatment of experimental breast and lung cancer brain metastases.

METHODS

The effect of macitentan on astrocyte- and brain endothelial cell-mediated chemoprotective properties was measured in cytotoxic assays. We compared survival of mice bearing established MDA-MB-231 breast cancer or PC-14 non-small cell lung cancer (NSCLC) brain metastases that were treated with vehicle, macitentan, paclitaxel, or macitentan plus paclitaxel. Cell division, apoptosis, tumor vasculature, and expression of survival-related proteins were assessed by immunofluorescent microscopy.

RESULTS

Cancer cells and tumor-associated endothelial cells expressed activated forms of AKT and MAPK in vehicle- and paclitaxel-treated groups in both metastasis models, but these proteins were downregulated in metastases of mice that received macitentan. The survival-related proteins Bcl2L1, Gsta5, and Twist1 that localized to cancer cells and tumor-associated endothelial cells in vehicle- and paclitaxel-treated tumors were suppressed by macitentan. Macitentan or paclitaxel alone had no effect on survival. However, when macitentan was combined with paclitaxel, we noted a significant reduction in cancer cell division and marked apoptosis of both cancer cells and tumor-associated endothelial cells. Moreover, macitentan plus paclitaxel therapy significantly increased overall survival by producing complete responses in 35 of 35 mice harboring brain metastases.

CONCLUSIONS

Dual antagonism of ETAR and ETBR signaling sensitizes experimental brain metastases to paclitaxel and may represent a new therapeutic option for patients with brain metastases.

The challenge of targeting metastasis

Metastases that are resistant to conventional therapy are the major cause of death from cancer. In most patients, metastasis has already occurred by the time of diagnosis. Thus, the prevention of metastasis is unlikely to be of therapeutic benefit. The biological heterogeneity of metastases presents a major obstacle to treatment. However, the growth and survival of metastases depend on interactions between tumor cells and host homeostatic mechanisms. Targeting these interactions, in addition to the tumor cells, can produce synergistic therapeutic effects against existing metastases.

Abstract PR05: Control of the melanoma metastatic phenotype by A-to-I microRNA editing

Although recent studies have shown that adenosine-to-inosine (A-to-I) RNA editing occurs in microRNAs, its effects on tumor growth and metastasis are not well understood. We present evidence of CREB-mediated low expression of ADAR1 in metastatic melanoma cell lines and tumor specimens. Re-expression of ADAR1 resulted in the suppression of melanoma growth and metastasis in vivo. Consequently, we identified 3 miRs (miR-455-5P, mir-378-3P, miR-324-5P) undergoing A-to-I editing in the low-metastatic melanoma cell lines but not in highly metastatic. One of these miRs, miR-455-5P has two A-to-I RNA editing sites. The biological function of edited miR-455-5P is different from the unedited form. Indeed, w.t. miR-455 promotes melanoma metastasis via inhibition of the tumor suppressor gene CPEB1 . Moreover, w.t. miR-455 enhances melanoma growth and metastasis in vivo while the edited form inhibits these features mainly by affecting the tumor microenvironment. TCGA analysis confirmed accumulation of wild-type miR-455 in metastatic melanoma lesions. These results demonstrate a previously unrecognized role of RNA editing in melanoma progression.

Citation Format: Einav Shoshan, Li Huang, Mayra E. Vasquez, Ho-Jeong Lee, Sun-Jin Kim, Cristina Ivan, George A. Calin, Anil K. Sood, Patrick Hwu, Jeffrey E. Gershenwald, Gal Markel, Isaiah J. Fidler, Menashe Bar-Eli. Control of the melanoma metastatic phenotype by A-to-I microRNA editing. [abstract]. In: Proceedings of the AACR Special Conference: Function of Tumor Microenvironment in Cancer Progression; 2016 Jan 7–10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2016;76(15 Suppl):Abstract nr PR05.

Abstract 2943: Hypoxia induced resistance to chemotherapy is regulated by the endothelin receptor axis

Introduction

Tumor cells growing in the brain are resistant to chemotherapy. We have recently demonstrated that the activation of the endothelin receptors A and B axis is involved in the induction of resistance to chemotherapy by primary brain tumor cells and by brain metastases. Treatment with a dual endothelin receptor antagonist in combination with chemotherapy produced significant therapy of orthotopically growing glioblastoma cells as well as breast cancer and lung cancer brain metastases. Since the milieu of tumors in the brain is hypoxic (0.5% - 1% O2), we investigated whether the chemo-resistance of the tumor cells is linked to hypoxia mediated activation of the endothelin receptor axis.

Materials and Methods Human glioma (LN229), breast cancer (MDA231), and lung adenocarcinoma (PC14) cell lines were cultured in DMEM supplemented with 5% FBS. The endothelin receptor A (ETAR) and/or B (ETBR) of cancer cells were knocked down by shRNA. ETAR and ETBR were activated by incubating the tumor cells with exogenous endothelin-1 for 15 minutes or blocked by treating the parental or engineered cells with ETAR-specific antagonist, BQ123 (100nM), and/or ETBR-specific antagonist, BQ788 (100nM), for 2 hours prior to the addition of paclitaxel (5ng/ml), temozolomide (100μg/ml) or cisplatinum (5μg/ml). The cultures were placed into incubators with an atmosphere of 20%, 6% or 1% oxygen for 48 hours

(MDA231 cells) or 72 hours (LN229 and PC14 cells). Tumor cells were then plated into 96-well plates to determine chemosensitivity by the MTT assay or into 6-well plates for western blots, or into chamber slides for immunohistochemical analyses. Expression of survival-related proteins such as pETAR, pETBR, pAkt, pMAPK, pNFκB, GSTA5, TWIST1 or Bcl2L1, were then determined.

Results Stimulation of parental MDA-231, PC-14, or LN229 cells with exogenous ET-1 induced significant resistance against all tested chemotherapeutic agents. The resistance was abolished only when both the ETAR and ETBR were antagonized by a combination of BQ123 and BQ788. Parental cells cultured under hypoxia were also significantly resistant to chemotherapy and treatment of these cells with BQ123 and BQ788 reversed this resistance. The effects of exogenous ET-1 on the induction of chemo-resistance or BQ123 and BQ788 on restoration of chemo-sensitivity were not found in any cancer cells devoid of ETAR and ETBR. In all cases, the chemo-resistance of tumor cells was associated with increased level of expression of proteins related to cell survival.

Conclusion These data suggest that the endothelin receptor axis plays a role in hypoxia induced resistance of cancer cells to chemotherapy. Additional studies are warranted to determine the functional changes of the endothelin receptor axis in hypoxia.

Citation Format: Hyun Kyung Yu, Ho Jeong Lee, Fahao Zhang, Qiuyu Wu, Isaiah J. Fidler, Sun Jin Kim. Hypoxia induced resistance to chemotherapy is regulated by the endothelin receptor axis. [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 2943.

Abstract 737: Transcriptome of glioma growing in the brain is simulated by tumor cells cultured under low oxygen pressure

Introduction

Studies using cultured tumor cells are frequently used to generate large scale data. However, the discrepancy between culture media conditions and host microenvironment factors prevent adequate translation to the clinical reality. Since culturing tumor cells in atmospheric oxygen pressure (20% O2) significantly differs from oxygen pressure within different organs (5-7% O2). We investigated whether the transcriptome of glioma cells cultured under oxygen concentration that is similar to the lesion in the brain (0.5-2% O2) can simulate the transcriptome of tumors growing in vivo.

Materials and Methods

Human glioma, LN229, cells were cultured in MEM supplemented with 10% FBS under 20%, 6% and 1% oxygen pressure. Glioma growing in the brain was established by stereotactic injection of 1×105 LN229 cells into the brain of nude mice, subcutaneous tumors were established by injection of 1×105 cells. Gene microarray was performed using Illumina Human HT-12_v4_BeadChip microarray and data were collected by using an Illumina bead Array Reader

confocal scanner (BeadStation 500GXDW; Illumina). Array data processing and analysis were performed using Illumina BeadStudio software. All statistical analysis was performed using BRB Arraytools Version 4.4.1 under the R language environment. Cluster analysis was performed and Heat Map was generated by Tree view.

Results

Brain and subcutaneous tumors were harvested 3 weeks post injection. RNA was extracted and processed for gene microarray that identified 2187 genes as brain specific transcriptome. Determination of common genes (same direction) between the transcriptome of glioma growing in the brain and cells growing in culture under 20%, 6%, and 1% O2 identified 23, 5, and 174 specific genes, respectively. Ingenuity pathway analysis and gene set enrichment analysis of the 174 common genes (from cells growing in 1% O2) revealed cluster of genes related to cancer and neurologic diseases, cell death/survival, cell-to-cell signaling. Up-regulation of genes associated with survival and resistance such as AKT, MAPK, NFêB1A, VEGF, and GSTA5 were also commonly identified in glioma growing in the brain and LN229 cells cultured under 1% oxygen.

Conclusion

Culturing glioma cells under different oxygen pressures induces different transcriptomes and cells cultured under 1% O2 express transcriptome most similar to cells growing in the brain. These data demonstrate that, to simulate clinical relevance, the oxygen tension of cultures should approximate those found in organs.

Citation Format: Ho Jeong Lee, Hyun Kyung Yu, Seung Wook Kim, Sung Il Choi, Junqin He, Isaiah J. Fidler, Sun Jin Kim. Transcriptome of glioma growing in the brain is simulated by tumor cells cultured under low oxygen pressure. [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 737.

The molecular biology of lung cancer brain metastasis: an overview of current comprehensions and future perspectives

Brain metastases occur in 20-40% of patients with advanced malignancies and lung cancer is one of the most common causes of brain metastases. The occurrence of brain metastases is associated with poor prognosis and high morbidity in patients with advanced lung cancer, even after intensive multimodal therapy. Progress in treating brain metastases has been hampered by a lack of model systems, a lack of human tissue samples, and the exclusion of brain metastatic patients from many clinical trials. While the biology of brain metastasis is still poorly understood, it is encouraging to see more efforts are beginning to be directed toward the study of brain metastasis. During the multi-step process of metastasis, functional significance of gene expressions, changes in brain vasculature, abnormal secretion of soluble factors and activation of autocrine/paracrine signaling are considered to contribute to the brain metastasis development. A better understanding of the mechanism of this disease will help us to identify the appropriate therapeutic strategies, which leads to circumvent brain metastases. Recent findings on the biology of lung cancer brain metastases and translational leads identified by molecular studies are discussed in this review.

Abstract 5463: Role of the endothelin axis in astrocyte and endothelial cell mediated chemoprotection of cancer cells

Background. Recent evidence suggests that astrocytes protect cancer cells from chemotherapy by stimulating the upregulation of anti-apoptotic genes in cancer cells. We investigated the possibility that activation of the endothelin axis orchestrates survival gene expression and chemoprotection in MDA-MB-231 breast cancer cells and H226 lung cancer cells.

Methods. Cancer cells, murine astrocytes, and murine fibroblasts were cultured in isolation and expression of endothelin (ET) peptides and ET receptors (ETAR and ETBR) was compared with expression on cancer cells and astrocytes (or cancer cells and fibroblasts) that were co-incubated for 48 hours. Type-specific endothelin receptor antagonists were used to evaluate the contribution of ETAR and ETBR to astrocyte-induced activation of the protein kinase B (AKT)/mitogen-activated protein kinase (MAPK) signal transduction pathways, anti-apoptotic gene expression, and chemoprotection of cancer cells. We also investigated the chemoprotective potential of brain endothelial cells and microglial cells.

Results. Gap junction signaling between astrocytes and MDA-MB-231 cancer cells stimulates upregulation of interleukin 6 (IL-6) and IL-8 expression in cancer cells, which increases ET-1 production from astrocytes and ET receptor expression on cancer cells. ET-1 signals for activation of AKT/MAPK and upregulation of survival proteins that protect cancer cells from taxol. Brain endothelial cell-mediated chemoprotection of cancer cells also involves endothelin signaling. Dual antagonism of ETAR and ETBR is required to abolish astrocyte- and endothelial cell-mediated chemoprotection.

Conclusions. Bidirectional signaling between astrocytes and cancer cells involves upregulation and activation of the endothelin axis, which protects cancer cells from cytotoxicity induced by chemotherapeutic drugs.

Citation Format: Mark S. Kim, Hyun Jin Choi, Ho-Jeong Lee, Junqin He, Qiuyu We, Robert R. Langley, Sin-Jin Kim, Isaiah J. Fidler. Role of the endothelin axis in astrocyte and endothelial cell mediated chemoprotection of cancer 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 5463. doi:10.1158/1538-7445.AM2015-5463

Abstract 5154: Diagnostic serum markers for metastatic brain tumors identified by cross-species hybridization of microarrays in animal models

Introduction: Cancer-related mortality of many tumors is due to development of metastasis to the brain with limited response to conventional therapies. Diagnosis of metastasis to the brain depends on symptoms or imaging techniques, which often fail to detect small brain lesions. Serologic markers enabling early diagnosis of metastatic brain tumors would therefore significantly improve clinical outcome. Using the cross-species hybridization of microarrays differentiating human from mouse gene signatures, we identified proteins significantly increased in brain metastases were detected in the sera of mice bearing human cancer metastases to the brain and determined whether these can be potentially diagnostic.

Materials and Methods: Human breast cancer (MDA-MB-231), lung cancer (PC-14), melanoma (A375), colon cancer (KM12), prostate cancer (PC-3P) and renal cancer (SN12) cells were implanted into relative primary and metastatic organs of nude mice. RNAs were extracted from tumor tissues and processed for differential hybridization of microarray. To identify genes differentially expressed in brain lesions, the random variance t test or one-way ANOVA was performed for the two-group or multi-group analysis, respectively. In the next set of experiments, we determined whether coded proteins differentially expressed in brain metastasis can be detected in the sera. MDA-MB-231 and PC-14 cells were implanted into mammary fat pad, lung or brain. Tumor tissues and sera were collected for immunohistochemical (IHC) analyses and antibody array with 13 available antibodies detecting proteins coded by genes differentially expressed in the brain metastases.

Results: In the first set of experiments, common 210 genes were identified to be differentially expressed in metastatic brain tumors, as compared with tumors growing in other organs such as mammary fat pad, lung, skin, cecum, prostate, kidney, and bone. Among the proteins coded by the 210 genes, 13 with commercially available antibodies were selected for validation. In the second set of experiments, IHC revealed that all these 13 proteins were expressed in metastasis produced by MDA-MB-231 and PC-14. Compared to sera of mice bearing primary tumors, elevated level of 10 proteins was detected in sera collected from mice with brain metastases.

Conclusion: These data demonstrated that cross-species differential hybridization of microarray with class comparison of gene expression using orthotopic animal is a novel approach to identify potential diagnostic serum markers for brain metastases. Studies to detect these proteins in the sera of patients with brain metastases are now planned.

Citation Format: Ho Jeong Lee, Sun Jin Kim, Hyun Kyung Yu, Seung Wook Kim, Qiuyu Wu, Junqin He, Isaiah J. Fidler. Diagnostic serum markers for metastatic brain tumors identified by cross-species hybridization of microarrays in animal models. [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 5154. doi:10.1158/1538-7445.AM2015-5154

Macitentan, a Dual Endothelin Receptor Antagonist, in Combination with Temozolomide Leads to Glioblastoma Regression and Long-term Survival in Mice

PURPOSE

The objective of the study was to determine whether astrocytes and brain endothelial cells protect glioma cells from temozolomide through an endothelin-dependent signaling mechanism and to examine the therapeutic efficacy of the dual endothelin receptor antagonist, macitentan, in orthotopic models of human glioblastoma.

EXPERIMENTAL DESIGN

We evaluated several endothelin receptor antagonists for their ability to inhibit astrocyte- and brain endothelial cell-induced protection of glioma cells from temozolomide in chemoprotection assays. We compared survival in nude mice bearing orthotopically implanted LN-229 glioblastomas or temozolomide-resistant (LN-229(Res) and D54(Res)) glioblastomas that were treated with macitentan, temozolomide, or both. Tumor burden was monitored weekly with bioluminescence imaging. The effect of therapy on cell division, apoptosis, tumor-associated vasculature, and pathways associated with cell survival was assessed by immunofluorescent microscopy.

RESULTS

Only dual endothelin receptor antagonism abolished astrocyte- and brain endothelial cell-mediated protection of glioma cells from temozolomide. In five independent survival studies, including temozolomide-resistant glioblastomas, 46 of 48 (96%) mice treated with macitentan plus temozolomide had no evidence of disease (P < 0.0001), whereas all mice in other groups died. In another analysis, macitentan plus temozolomide therapy was stopped in 16 mice after other groups had died. Only 3 of 16 mice eventually developed recurrent disease, 2 of which responded to additional cycles of macitentan plus temozolomide. Macitentan downregulated proteins associated with cell division and survival in glioma cells and associated endothelial cells, which enhanced their sensitivity to temozolomide.

CONCLUSIONS

Macitentan plus temozolomide are well tolerated, produce durable responses, and warrant clinical evaluation in glioblastoma patients.

Modulation of the cancer cell transcriptome by culture media formulations and cell density

We investigated how varying the composition of cell culture formulations and growing cancer cells at different densities might affect tumor cell genotype. Specifically, we compared gene expression profiles generated by human MDA‑MB‑231 breast cancer cells cultured in different media [minimum essential medium (MEM), Dulbecco's modified Eagle's medium (DMEM), or Roswell Park Memorial Institute (RPMI)‑1640 medium] containing different concentrations of fetal bovine serum (FBS) or different sera (equine or bovine) that were grown at different cell densities. More than 2,000 genes were differentially modulated by at least a 2‑fold difference when MDA‑MB‑231 cancer cells were 90% confluent and compared with cultures that were 50% confluent. Altering the concentration of serum produced an even more pronounced effect on MDA‑MB‑231 cancer cell gene expression in that 2,981 genes were differentially expressed in a comparison between cells cultured in 0.1% FBS and same cell density cultures that were maintained in 10% FBS. A comparison between MDA‑MB‑231 cancer cells that were 90% confluent in MEM, DMEM, or RPMI‑1640 media, all containing 10% FBS, resulted in 8,925 differentially expressed genes. Moreover, one‑quarter (25.6%) of genes from our genome‑wide expression analysis were expressed at significantly different levels by cells grown in MEM, DMEM, or RPMI‑1640 media. Genes associated with epithelial‑mes-enchymal transition (EMT) were among the genes that were differentially modulated by cells grown in different cell culture formulations and these genes were verified at the protein level. Collectively, these results underscore the importance of accurate reporting and maintenance of uniform culture conditions to ensure reproducible results.

Reduced adenosine-to-inosine miR-455-5p editing promotes melanoma growth and metastasis

Although recent studies have shown that adenosine-to-inosine (A-to-I) RNA editing occurs in microRNAs, its effects on tumor growth and metastasis are not well understood. We present evidence of CREB-mediated low expression of ADAR1 in metastatic melanoma cell lines and tumor specimens. Re-expression of ADAR1 resulted in the suppression of melanoma growth and metastasis in vivo. Consequently, we identified 3 miRs undergoing A-to-I editing in the low-metastatic melanoma but not in highly metastatic cell lines. One of these miRs, miR-455-5p has two A-to-I RNA editing sites. The biological function of edited miR-455-5p is different from the unedited form as it recognizes different set of genes. Indeed, w.t. miR-455-5p promotes melanoma metastasis via inhibition of the tumor suppressor gene CPEB1. Moreover, w.t. miR-455 enhances melanoma growth and metastasis in vivo while the edited form inhibits these features. These results demonstrate a previously unrecognized role of RNA editing in melanoma progression.

Gain of glucose-independent growth upon metastasis of breast cancer cells to the brain

Breast cancer brain metastasis is resistant to therapy and a particularly poor prognostic feature in patient survival. Altered metabolism is a common feature of cancer cells, but little is known as to what metabolic changes benefit breast cancer brain metastases. We found that brain metastatic breast cancer cells evolved the ability to survive and proliferate independent of glucose due to enhanced gluconeogenesis and oxidations of glutamine and branched chain amino acids, which together sustain the nonoxidative pentose pathway for purine synthesis. Silencing expression of fructose-1,6-bisphosphatases (FBP) in brain metastatic cells reduced their viability and improved the survival of metastasis-bearing immunocompetent hosts. Clinically, we showed that brain metastases from human breast cancer patients expressed higher levels of FBP and glycogen than the corresponding primary tumors. Together, our findings identify a critical metabolic condition required to sustain brain metastasis and suggest that targeting gluconeogenesis may help eradicate this deadly feature in advanced breast cancer patients.

Abstract 4878: Modification of gene expression in tumor cells by the culture microenvironment

Purpose: Since cell culture techniques were developed in 1950s, in vitro assays using monolayer cell cultures have played a major role in cancer research. Despite the absence of cross-talk between tumor cells and their respective host organ-microenvironment, data produced by in vitro assays have often been used to address challenge. However, the potential discrepancy between in vitro and in vivo mircoenvironments should not be overlooked. We have investigated the influence of culture conditions of the biology of tumor cells by comparing the genetic profiles of tumor cells growing in different culture conditions, such as culture media, sera, concentration of sera, and cell confluence.

Materials and Methods: We profiled the gene expression of human breast cancer tumor cells (MDA-MB-231) that were cultured for 48 hours under various culture conditions; in different media (MEM, DMEM, RPMI-1640), different sera (FBS, horse serum), different concentrations of FBS (10%, 0.1%), and different cell confluence (90%, 50%) using microarray analysis of total cellular RNA using an Illumina platform (human HT-12v12 expression beadchip)

Results: Upon analysis, 2,234 genes were differentially expressed among cultures with varied cell confluence, 2,981 genes differentially expressed in cultures with various FBS concentrations, 422 genes were differentially expressed in cells cultured with different sera, and 8,925 genes were differentially expressed in cells cultured with different media. Of 8,925 genes, 10 (ARHGEF6, CAPN3, COPG, DAMM2, GSTK1, PGM1, QPCT, QPRT, SLC1A4, and VAT1) were identified as commonly upregulated in confluent cultures, regardless of the media, as compared with sub-confluent cultures. In addition, 5 genes (IL7R, MPP4, NOP56, G3BP1 and IFP38) were identified as commonly downregulated in confluent cultures. Collectively, these data indicate that the gene expression profiles varied significantly across different cultures conditions.

Conclusion:These results demonstrated that even under commonly “simplified” culture conditions, gene expression profiles can significantly vary across cells exposed to different culture conditions. Some of these conditions parallel those found in vivo, i.e., sub-confluent versus confluent cultures, where cell division is more active in the former than the latter condition. The significant differences in gene expression by cells exposed to fetal bovine serum as compared to horse serum are likely caused by different levels of growth factors within the sera. Likewise, the different gene expressions in tumor cells growing in different media can be attributed to different levels of glucose and salts present. Collectively, our data indicate that any change in culture conditions can lead to significant changes in the gene expression of tumor cells. Hence, to obtain reproducible data, one must strictly adhere to specified experimental details.

Citation Format: Seung Wook Kim, Sun Jin Kim, Ho-jeong Lee, Junqin He, Qiuyu Wu, Erica J. Lawson, Isaiah J. Fidler. Modification of gene expression in tumor cells by the culture microenvironment. [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 4878. doi:10.1158/1538-7445.AM2014-4878

Abstract 3779: Treatment of experimental brain metastasis of human breast cancer by macitentan, a dual antagonist of endothelin receptors combined with paclitaxel

Purpose: Breast cancer is a leading cause of cancer-related mortality among women in the United States. The major cause of death is due to metastasis that is resistant to conventional therapy. The median survival of women with brain metastases is measured in months due to resistance to all standard therapies. Thus, the development of effective treatment options for these patients is mandatory. We have reported that astrocytes can protect tumor cells from chemotherapeutic drugs by a mechanism involving the phosphorylation of endothelin receptors on tumor cells (Kim et al, AACR, 2012). Moreover, we observed a heterogeneous expression of endothelin receptors A and B in clinical samples of breast cancer brain metastasis. We therefore examined whether blockade of the endothelin axis by using macitentan, a dual endothelin antagonist, combined with paclitaxel can produce therapeutic effects in an orthotopic model of human breast cancer brain metastasis.

Materials and Methods: Twenty thousand MDA-MB-231 human breast cancer cells were injected into the internal carotid artery of female nude mice to produce orthotopic brain metastasis. Two weeks later, the mice were randomized into 4 groups (n=10): (1) control group - mice receiving vehicle (p.o., daily; i.p. injection once per week); (2) paclitaxel group - mice receiving paclitaxel (8 mg/kg; i.p. injection once per week) and vehicle (p.o.; daily); (3) macitentan group - mice receiving macitentan (10 mg/kg; p.o.; daily) and vehicle (i.p. injection, once per week); and (4) paclitaxel plus macitentan group. Moribund mice were euthanized, days of survival were recorded, and the brains were harvested and processed for histology and immunohistochemical analyses. The study was repeated with luciferase-labeled MDA-MB-231 cells and produced similar therapeutic results supported by IVIS imaging.

Results: After 130-140 days of treatment, the survival was significantly higher in mice treated with the combination of paclitaxel and macitentan (80%) as compared with control (20%), paclitaxel (20%), and macitentan alone (40%) (p&lt;0.0001, log-rank test). Immunohistochemical analyses revealed that the phosphorylation of endothelin receptors A and B on tumor cells and tumor-associated endothelial cells were inhibited by macitentan. Treatment with macitentan also suppressed the expression of survival proteins such as pAKT, pMAPK, BCL2L1, TWIST1, and GSTA5 in tumor cells. More importantly, only the combination therapy induced significant apoptosis of tumor cells and tumor-associated endothelial cells and reduced the number of KI67 positive tumor cells. IVIS imaging confirmed regression of brain lesions.

Conclusion: Treatment with macitentan, a dual endothelin receptor antagonist, combined with paclitaxel leads to regression of experimental breast cancer brain metastasis and therefore should be considered for clinical development.

Citation Format: Ho Jeong Lee, Sun Jin Kim, Seung Wook Kim, Junqin He, Qiuyu Wu, Erica J. Lawson, Francois Lehembre, Urs Regenass, Isaiah J. Fidler. Treatment of experimental brain metastasis of human breast cancer by macitentan, a dual antagonist of endothelin receptors combined with paclitaxel. [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 3779. doi:10.1158/1538-7445.AM2014-3779

Hematogenous metastasis of ovarian cancer: rethinking mode of spread

Ovarian cancer has a clear predilection for metastasis to the omentum, but the underlying mechanisms involved in ovarian cancer spread are not well understood. Here, we used a parabiosis model that demonstrates preferential hematogenous metastasis of ovarian cancer to the omentum. Our studies revealed that the ErbB3-neuregulin 1 (NRG1) axis is a dominant pathway responsible for hematogenous omental metastasis. Elevated levels of ErbB3 in ovarian cancer cells and NRG1 in the omentum allowed for tumor cell localization and growth in the omentum. Depletion of ErbB3 in ovarian cancer impaired omental metastasis. Our results highlight hematogenous metastasis as an important mode of ovarian cancer metastasis. These findings have implications for designing alternative strategies aimed at preventing and treating ovarian cancer metastasis.

Role of the endothelin axis in astrocyte- and endothelial cell-mediated chemoprotection of cancer cells

BACKGROUND

Recent evidence suggests that astrocytes protect cancer cells from chemotherapy by stimulating upregulation of anti-apoptotic genes in those cells. We investigated the possibility that activation of the endothelin axis orchestrates survival gene expression and chemoprotection in MDA-MB-231 breast cancer cells and H226 lung cancer cells.

METHODS

Cancer cells, murine astrocytes, and murine fibroblasts were grown in isolation, and expression of endothelin (ET) peptides and ET receptors (ETAR and ETBR) compared with expression on cancer cells and astrocytes (or cancer cells and fibroblasts) that were co-incubated for 48 hours. Type-specific endothelin receptor antagonists were used to evaluate the contribution of ETAR and ETBR to astrocyte-induced activation of the protein kinase B (AKT)/mitogen-activated protein kinase (MAPK) signal transduction pathways, anti-apoptotic gene expression, and chemoprotection of cancer cells. We also investigated the chemoprotective potential of brain endothelial cells and microglial cells.

RESULTS

Gap junction signaling between MDA-MB-231 cancer cells and astrocytes stimulates upregulation of interleukin 6 (IL-6) and IL-8 expression in cancer cells, which increases ET-1 production from astrocytes and ET receptor expression on cancer cells. ET-1 signals for activation of AKT/MAPK and upregulation of survival proteins that protect cancer cells from taxol. Brain endothelial cell-mediated chemoprotection of cancer cells also involves endothelin signaling. Dual antagonism of ETAR and ETBR is required to abolish astrocyte- and endothelial cell-mediated chemoprotection.

CONCLUSIONS

Bidirectional signaling between astrocytes and cancer cells involves upregulation and activation of the endothelin axis, which protects cancer cells from cytotoxicity induced by chemotherapeutic drugs.

Exogenous expression of human SGLT1 exhibits aggregations in sodium dodecyl sulfate polyacrylamide gel electrophoresis

Sodium/glucose co-transporter 1 (SGLT1), which actively and energy-dependently uptakes glucose, plays critical roles in the development of various diseases including diabetes mellitus and cancer, and has been viewed as a promising therapeutic target for these diseases. Protein-protein interaction with EGFR has been shown to regulate the expression and activity of SGLT1. Exogenous expression of SGLT1 is one of the essential approaches to characterize its functions; however, exogenously expressed SGLT1 is not firmly detectable by Western blot at its calculated molecular weight, which creates a hurdle for further understanding the molecular events by which SGLT1 is regulated. In this study, we demonstrated that exogenous SGLT1 functions in glucose-uptake normally but is consistently detected near the interface between stacking gel and running gel rather than at the calculated molecular weight in Western blot analysis, suggesting that the overexpressed SGLT1 forms SDS-resistant aggregates, which cannot be denatured and effectively separated on SDS-PAGE. Co-expression of EGFR enhances both the glucose-uptake activity and protein level of the SGLT1. However, fusion with Flag or HA tag at its carboxy- but not its amino-terminus abolished the glucose-uptake activity of exogenous SGLT1 without affecting its protein level. Furthermore, the solubility of SGLT1 aggregates was not affected by other detergents but was partially improved by inhibition of o-link glycosylation. These findings suggested exogenous overexpression of SGLT1 can function normally but may not be consistently detectable at its formula weight due to its gel-shift behavior by forming the SDS-resistant aggregates.

Abstract 4951: The role of endothelin axis signaling pathway in astrocyte mediated chemoprotection of tumor cells

Purpose: More than 40% of patients with the breast cancer develop brain metastasis that are resistant to conventional chemotherapeutic agents. We have reported that reactive astrocytes establish gap junction communication channels with adjacent tumor cells and protect tumor cells from chemotherapy by up-regulation of survival genes in the tumor cells. We now report on the mechanism by which astrocytes up-regulate expression of the survival genes in tumor cells.

Materials and Methods: Human breast cancer cells, MDA-MB-231 cultured with murine astrocytes produce endothelin 1 (ET-1) leading to expression and activation of endothelin receptors (ETRs). Using small interfering RNA (siRNA) of ETAR and ETBR, and ETRs specific antagonists (BQ123, BQ788, and PD145065) demonstrated the correlation between the activation of the endothelin axis in tumor cells and the induction of survival genes (BCL2L1, GSTA5, and TWIST1) leading to chemoresistance.

Results: Co-culture of MDA-MB-231 cells and murine astrocytes induced up-regulation of ETRs (ETAR and ETBR) and activation of endothelin receptors axis in tumor cells as well as increased production of ET-1 by murine astrocytes. Activation of the ETRs by exogenous ET-1 up-regulated the expression of survival genes, such as BCL2L1, GSTA5 and TWIST1 via activation of phosphorylated AKT/MAPKinase signal transduction pathways, leading to resistance of tumor cells to several chemotherapeutic agents. Knockdown of both ETAR and ETBR by siRNAs or treatment of tumor cells with dual ETR inhibitor abolished the chemoprotection induced by astrocytes.

Conclusion: ET axis signaling pathway plays an essential role in astrocytes-mediated induction of chemoresistance of tumor cells by up-regulation of survival genes in tumor cells. Simultaneous blockade of both ETR can prevent tumor cells from developing resistance to chemotherapeutic agents.

Citation Format: Seung Wook Kim, Sun Jin Kim, Hyun Jin Choi, Ho-Jeong Lee, Junqin He, Qiuyu Wu, Erica J. Lawson, Isaiah J. Fidler. The role of endothelin axis signaling pathway in astrocyte mediated chemoprotection of tumor 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 4951. doi:10.1158/1538-7445.AM2013-4951

Abstract 5481: Therapy of human LN229 glioblastoma growing in the brain of nude mice by Macitentan, a dual endothelin receptor A and B antagonist, combined with Temozolomide

Purpose: We determined whether the blockade of endothelin receptor pathways can reverse the chemoprotection mediated by astrocytes and produce therapy of Human LN 229 Glioblastoma cells growing in the brain of nude mice treated with the dual endothelin receptor antagonist, Macitentan and Temozolomide (TMZ).

Materials and Methods: In the first set of experiments, murine astrocytes were cultured with tumor cells in the presence or absence of Macitentan and TMZ. For therapy studies the leuciferas labeled LN229 cells were implanted (stereotactically) into the brains of nude mice. The mice were ear tagged and imaged by IVIS spectrometer at multiple times. On day 24 the mice were randomized to receive vehicle, TMZ (p.o., 7.5mg/kg, one week on and two weeks off), Macitentan (p.o., 10mg/kg, daily) and Macitentan plus TMZ. Survival of mice was compared by Kaplan-Meyer curve (log-rank test) and immunohistochemical analyses were carried out for multiple markers.

Results: Simultaneous blocking of endothelin receptor A and B pathways reversed the in culture protection induced by astrocytes against TMZ (p&lt;0.05). Therapy with Macitentan and TMZ significantly prolonged the survival of mice (p&lt;0.0001) .The blockade of endothelin receptor A and B significantly decreased the level of expression of phosphorylated AKT and MAPK, and down-regulated the expression of BCL2L1, TWIST1 and GSTA5 in LN 229 cells growing in the brain. Proliferation of tumor cells and tumor-associated endothelial cells was significantly decreased. Moreover the apoptosis of LN229 cells was significantly increased in the brain of the combination treatment group.

Conclusion: Blockade of endothelin receptor A and B pathways by Macitentan combined with TMZ provides a new approach for the treatment of patients with Glioblastoma.

Citation Format: Sun Jin Kim, Seung Wook Kim, Hyun Jin Choi, Ho Jeong Lee, Francois Lehembre, Junqin He, Urs Regenass, Charles A Conrad, W.K. Yung, Isaiah J. Fidler. Therapy of human LN229 glioblastoma growing in the brain of nude mice by Macitentan, a dual endothelin receptor A and B antagonist, combined with Temozolomide. [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 5481. doi:10.1158/1538-7445.AM2013-5481

The biology of brain metastasis

BACKGROUND

It is estimated that at least 200 000 cases of brain metastases occur each year in the US, which is 10 times the number of patients diagnosed with primary brain tumors. Brain metastasis is associated with poor prognosis, neurological deterioration, diminished quality of life, and extremely short survival. Favorable interactions between tumor cells and cerebral microvascular endothelial cells encourage tumor growth in the central nervous system, while tumor cell interactions with astrocytes protect brain metastases from the cytotoxic effects of chemotherapy.

CONTENT

We review the pathogenesis of brain metastasis and emphasize the contributions of microvascular endothelial cells and astrocytes to disease progression and therapeutic resistance. Animal models used to study brain metastasis are also discussed.

SUMMARY

Brain metastasis has many unmet clinical needs. There are few clinically relevant tumor models and no targeted therapies specific for brain metastases, and the mean survival for untreated patients is 5 weeks. Improved clinical outcomes are dependent on an enhanced understanding of the metastasis-initiating population of cells and the identification of microenvironmental factors that encourage disease progression in the central nervous system.

Porous silicon nanocarriers for dual targeting tumor associated endothelial cells and macrophages in stroma of orthotopic human pancreatic cancers

Pancreatic cancer is a highly fatal disease characterized by a dominant stroma formation. Exploring new biological targets, specifically those overexpressed in stroma cells, holds significant potential for the design of specific nanocarriers to attain homing of therapeutic and imaging agents to the tumor. In clinical specimens of pancreatic cancer, we found increased expression of CD59 in tumor associated endothelial cells as well as infiltrating cells in the stroma as compared to uninvolved pancreas. We explored this dual targeting effect using orthotopic human pancreatic cancer in nude mice. By immunofluorescence analysis, we confirmed the increased expression of Ly6C, mouse homolog of CD59, in tumor associated endothelial cells as well as in macrophages within the stroma. We decorated the surface of porous silicon nanocarriers with Ly6C antibody. Targeted nanocarriers injected intravenously accumulated to tumor associated endothelial cells within 15min. At 4h after administration, 9.8±2.3% of injected dose/g tumor of the Ly6C targeting nanocarriers accumulated in the pancreatic tumors as opposed to 0.5±1.8% with non-targeted nanocarriers. These results suggest that Ly6C (or CD59) can serve as a novel dual target to deliver therapeutic agents to the stroma of pancreatic tumors.

Biological heterogeneity of cancer: implication to therapy

Despite significant improvements in diagnosis, surgical techniques, and advancements in general patient care, the majority of deaths from cancer are caused by the continuous growth of metastases that are resistant to conventional therapies. In a large number of cancer patients, metastasis may well have occurred by the time of diagnosis. The metastases can be located in different distant organs and in different regions within a single organ. The major obstacle for the eradication of metastases is the biologic heterogeneity of tumor cells that constitute primary cancers and metastases. Specifically, by the time of diagnosis, malignant neoplasms contain multiple cell populations with diverse biological heterogeneity in growth rate, karyotype, cell surface receptors, antigenicity, immunogenicity, maker enzymes, gene expression, sensitivity to different cytotoxic drugs, invasion, and metastasis. This biologic heterogeneity is not restricted to primary lesions. The cellular composition of metastases in the same organ or in different organs is heterogeneous, both within a single metastasis (intralesional heterogeneity) and among different metastases (interlesional heterogeneity). This heterogeneity is due to two major processes: the selective nature of the metastatic process, and the rapid evolution and phenotypic diversification of clonal tumor cell populations during progressive tumor growth resulting from inherent genetic and epigenetic instability of many clonal populations of tumor cells.

Abstract 2453: Overcoming transport barriers in liver metastasis with multi-stage nanovectors (MSV)

Liver metastasis occur in 30-70% of patients dying of various malignancies. In the case of metastatic breast cancer, 50% of the patients develop liver metastasis with median survival rate of only a few months and very rare 5-year survival. We hypothesized that the inefficiency in treatment of liver metastasis of breast tumors can be related to biophysical barriers in the tumor microenvironment preventing delivery of therapeutics to tumor loci. Our research focused on physical factors involved in the progression of liver metastasis and design of systems for targeted delivery of therapeutics. Multi-stage vectors (MSV) were previously reported to overcome sequential biophysical barriers and to efficiently carry therapeutic payload to the tumor microenvironment. The first stage porous silicon particles target tumor-associated endothelium or macrophages releasing second stage therapeutic nanoparticles in the close proximity to the tumor. The objectives of this work were to investigate: (1) in vivo barriers associated with drug delivery in breast tumor liver metastasis; (2) in vitro/in vivo interaction of MSV with macrophages; and (3) to perform initial therapeutic efficiency study with MSV loaded with Abraxane (albumin bound paclitaxel). Liver metastases were produced by intra-splenic injected of 4T1 breast cancer cells to balb/C mice. A small incision in the abdomen of the animals was made to expose the liver and the kinetics of distribution of tracers/MSV was recorded. Intravital microscopy was used to observe the distribution of tracers (MW 4 and 30KDa dextrans) and MSV particles. Macrophages and RBC were pre-labeled 4-48 hours prior to the experiment. For therapy experiment, 10-14 days following tumor inoculation mice were randomly divided in three groups: untreated, MSV-Abraxane treated and Abraxane treated. The mice were sacrificed on day 7 following the treatment and the number of metastasis and liver weight were recorded. From the intravital microscopy studies, it appears that liver metastasis of 4T1 tumors have insufficient functional vascularization, which can be the reason for inability to efficiently treat metastatic loci. Dextran −4KDs with nominal diameter of 2-3nm (similar to unbound chemotherapeutics) penetrate into the tumor but washed out within minutes, while dextran ∼30KdA (d=12nm) retain longer, but penetrate less due to the limited vascular permeability. MSV were efficiently Internalized by murine and human macrophages in vitro and by liver macrophages in vivo in the metastatic liver. MSV encapsulated Abraxane enabled an almost complete elimination of the metastatic loci, while Abraxane was not efficient. The initial therapy data suggest that MSV targeted macrophages in breast cancer liver metastasis enabling high concentrations of chemotherapeutic agents to accumulate in the tumor loci. This can be an efficient strategy for overcoming physical barriers in breast cancer liver metastasis.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2453. doi:1538-7445.AM2012-2453

Abstract 4283: Cross-species hybridization of microarrays for studying tumor transcriptome of brain metastasis

Although the importance of the cellular microenvironment (soil) during invasion and metastasis of cancer cells (seed) has been well-recognized, technical challenges have limited the ability to assess the influence of the microenvironment on cancer cells at the molecular level. Here, we show that an experimental strategy, competitive cross-species hybridization of microarray experiments, can characterize the influence of different microenvironments on cancer cells by independently extracting gene expression data of cancer and host cells when human cancer cells were xenografted into different organ sites of immunocompromised mice. Surprisingly, the analysis of gene expression data showed that the brain microenvironment induces complete reprogramming of metastasized cancer cells, resulting in a gain of neuronal cell characteristics and mimicking neurogenesis during development. We also show that epigenetic changes coincide with transcriptional reprogramming in cancer cells. These observations provide proof of principle for competitive cross-species hybridization of microarray experiments to characterize the effect of the microenvironment on tumor cell behavior

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4283. doi:1538-7445.AM2012-4283

P4-17-10: Insights into Mechanisms Involved in the Accumulation of Nanovectors within the Breast Cancer Brain Metastasis

Systemic chemotherapy for brain metastasis of breast cancer (BMBC) is considered to be inefficient. It is widely accepted in the literature that blood-brain-barrier (BBB) is responsible for clinical failures with the conventional chemotherapy. We hypothesized that nanovectors, therapeutic carriers with submicron dimensions, can be delivered to the brain tissue through a different pathway than molecular therapeutics. The objective of this study was to examine the accumulation of various intravenously injected nanovectors into the brain metastasis of breast and other cancers loci and to explore possible mechanisms involved.

Both human (MDAMB231) and mouse (4T1) breast cancer brain metastasis were evaluated. We also tested lung (3LL) and colon (CT26) originated cancers. Orthotopic brain tumors were produced either by intracarotid injection or stereotactic brain injection of cancer cells. When the animals became moribund, they were injected intravenously with one of the following nanovectors including fluorescently labeled PEGylated (100nm) and non-PEGylated (100nm, 250nm, 500nm) liposomes, disc-shape silicon particles (600, 1000nm in diameter). The accumulation of the nanovectors was compared to an unencapsulated fluorescent molecule. The accumulation of the nanovectors in the brain tumor tissue was evaluated through live animal imaging (IVIS) and immunohistochemical analysis. Immunohistochemical staining of endothelial cells and basal membrane markers was performed to determine the integrity of the tumor associated vasculature and the co-localization of the fluorescent nanovectors/molecules with tumor associated vasculature.

Interestingly, we have found that brain metastasis of different tumors (originated form breast, lung and colon cancers) possess dissimilar accumulation profiles for intravenously administered nanovectors. For example when comparing various tumor origins, 4T1 breast cancer originated brain tumors enabled the highest accumulation of the nanovectors as compared to CT26 and 3LL. On the other hand, free molecule accumulated into the 4T1 brain metastasis model to a much lower extend than in nanovector. Finally, the observed brain distribution of nanovectors corresponded well with impairment in vascular endothelium and basal membrane integrity shown in immunohistochemical analysis.

The results of our study point toward a possibility to treat specific patients with impaired BBB function with nanovector encapsulated chemotherapeutics based on the fact that their transport, accumulation and retention in the brain tissue are governed by different biological mechanisms, such as Enhanced Permeation and Retention (EPR) effect. These studies indicate that it is possible to cross the blood brain barrier, thus giving hope to patients with brain metastasis.

Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P4-17-10.

Selection of brain metastasis-initiating breast cancer cells determined by growth on hard agar

An approach that facilitates rapid isolation and characterization of tumor cells with enhanced metastatic potential is highly desirable. Here, we demonstrate that plating GI-101A human breast cancer cells on hard (0.9%) agar selects for the subpopulation of metastasis-initiating cells. The agar-selected cells, designated GI-AGR, were homogeneous for CD44(+) and CD133(+) and five times more invasive than the parental GI-101A cells. Moreover, mice injected with GI-AGR cells had significantly more experimental brain metastases and shorter overall survival than did mice injected with GI-101A cells. Comparative gene expression analysis revealed that GI-AGR cells were markedly distinct from the parental cells but shared an overlapping pattern of gene expression with the GI-101A subline GI-BRN, which was generated by repeated in vivo recycling of GI-101A cells in an experimental brain metastasis model. Data mining on 216 genes shared between GI-AGR and GI-BRN breast cancer cells suggested that the molecular phenotype of these cells is consistent with that of cancer stem cells and the aggressive basal subtype of breast cancer. Collectively, these results demonstrate that analysis of cell growth in a hard agar assay is a powerful tool for selecting metastasis-initiating cells in a heterogeneous population of breast cancer cells, and that such selected cells have properties similar to those of tumor cells that are selected based on their potential to form metastases in mice.

Abstract 601: Macitentan (ACT-064992), a tissue-targeting endothelin receptor antagonist enhances therapeutic efficacy of paclitaxel by modulating survival pathways in orthotopic models of metastatic human ovarian cancer

Introduction: In 2009, ovarian cancer was the leading cause of death from gynecologic cancer in the United States. Efforts to develop tools for early detection and therapeutic regimens to overcome drug resistance of the ovarian cancer have not made a significant achievement to prolong the median survial of the patients. Potential treatments for ovarian cancers that have become resistant to standard chemotherapies include modulators of tumor cell survival, such as endothelin receptor (ETR) antagonist. We investigated the therapeutic efficacy of the dual ETR antagonist, macitentan, on human ovarian cancer cells, SKOV3ip1 and IGROV1, growing orthotopically in nude mice.

Materials and Methods: Mice were injected with one million cells of SKOV3ip1 or IGROV1. Ten days later, mice with established disease were randomized into vehicle (control), paclitaxel (weekly, intraperitoneal injections), macitentan (daily oral administrations) or a combination of paclitaxel and macitentan treatment groups. After 4 weeks of treatment, mice were necropsied and tumor incidence, tumor weight, and incidence of ascites were recorded. Tumor tissues were processed for immunohistochemical analyses.

Results: Treatment with paclitaxel decreased tumor weight and volume of ascites. Combination therapy with macitentan and paclitaxel reduced tumor incidence and further reduced tumor weight and volume of ascites when compared with paclitaxel alone. Macitentan alone occasionally reduced tumor weight but alone had no effect on tumor incidence or ascites. Immunohistochemical analyses revealed that treatment with macitentan and macitentan plus paclitaxel inhibited the phosphorylation of ETRs and suppressed the survival pathways of tumor cells by decreasing the levels of pVEGFR2, pAkt, and pMAPK. The dose of macitentan necessary for inhibition of phosphorylation correlated with the dose required to increase antitumor efficacy of paclitaxel.

Conclusion: Treatment with macitentan enhanced the cytotoxicity mediated by paclitaxel as measured by the degree of apoptosis in tumor cells and tumor-associated endothelial cells. Collectively, these results show that administration of macitentan in combination with paclitaxel prevents the progression of ovarian cancer in the peritoneal cavity of nude mice in part by inhibiting survival pathways of both tumor cells and tumor-associated endothelial cells.

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 601. doi:10.1158/1538-7445.AM2011-601

The seed and soil hypothesis revisited--the role of tumor-stroma interactions in metastasis to different organs

The fact that certain tumors exhibit a predilection for metastasis to specific organs has been recognized for well over a century now. An extensive body of clinical data and experimental research has confirmed Stephen Paget's original "seed and soil" hypothesis that proposed the organ-preference patterns of tumor metastasis are the product of favorable interactions between metastatic tumor cells (the "seed") and their organ microenvironment (the "soil"). Indeed, many of the first-line therapeutic regimens, currently in use for the treatment of human cancer are designed to target cancer cells (such as chemotherapy) and also to modulate the tumor microenvironment (such as antiangiogenic therapy). While some types of tumors are capable of forming metastases in virtually every organ in the body, the most frequent target organs of metastasis are bone, brain, liver and the lung. In this review, we discuss how tumor-stromal interactions influence metastasis in each of these organs.

Formation of solid tumors by a single multinucleated cancer cell

BACKGROUND

Large multinucleated cells (MNCs) commonly exist in tumorigenic cancer cell lines that are used widely in research. However, the contributions of MNCs to tumorigenesis are unknown.

METHODS

In this study, MNCs were characterized in the murine fibrosarcoma cell line UV-2237 in vitro and in vivo at the single-cell level.

RESULTS

The authors observed that MNCs originated from a rare subpopulation of mononuclear cells and were positive for a senescent marker, β-galactosidase. In addition, MNCs were responsible for the majority of clonogenic activity when cultured in hard agar; they were more resistant to chemotherapeutic agents than mononuclear cells; they could undergo asymmetric division (producing mononuclear cells) and self-renewal in vitro and in vivo; and, most important; a single MNC produced orthotopic, subcutaneous tumors (composed mainly of mononuclear cells) that gave rise to spontaneous lung metastases in nude mice.

CONCLUSIONS

The current results indicated that the growth of MNCs may be arrested under stress and that MNCs are highly resistant to chemotherapy and can generate clonal, orthotopic, metastatic tumors.

In vivo evaluation of safety of nanoporous silicon carriers following single and multiple dose intravenous administrations in mice

Porous silicon (pSi) is being extensively studied as an emerging material for use in biomedical applications, including drug delivery, based on the biodegradability and versatile chemical and biophysical properties. We have recently introduced multistage nanoporous silicon microparticles (S1MP) designed as a cargo for nanocarrier drug delivery to enable the loaded therapeutics and diagnostics to sequentially overcome the biological barriers in order to reach their target. In this first report on biocompatibility of intravenously administered pSi structures, we examined the tolerability of negatively (-32.5±3.1mV) and positively (8.7±2.5mV) charged S1MP in acute single dose (10(7), 10(8), 5×10(8) S1MP/animal) and subchronic multiple dose (10(8) S1MP/animal/week for 4 weeks) administration schedules. Our data demonstrate that S1MP did not change plasma levels of renal (BUN and creatinine) and hepatic (LDH) biomarkers as well as 23 plasma cytokines. LDH plasma levels of 145.2±23.6, 115.4±29.1 vs. 127.0±10.4; and 155.8±38.4, 135.5±52.3 vs. 178.4±74.6 were detected in mice treated with 10(8) negatively charged S1MP, 10(8) positively charged S1MP vs. saline control in single and multiple dose schedules, respectively. The S1MPs did not alter LDH levels in liver and spleen, nor lead to infiltration of leukocytes into the liver, spleen, kidney, lung, brain, heart, and thyroid. Collectively, these data provide evidence of a safe intravenous administration of S1MPs as a drug delivery carrier.

Reactive astrocytes protect melanoma cells from chemotherapy by sequestering intracellular calcium through gap junction communication channels

Brain metastases are highly resistant to chemotherapy. Metastatic tumor cells are known to exploit the host microenvironment for their growth and survival. We report here that melanoma brain metastases are surrounded and infiltrated by activated astrocytes, and we hypothesized that these astrocytes can play a role similar to their established ability to protect neurons from apoptosis. In coculture experiments, astrocytes, but not fibroblasts, reduced apoptosis in human melanoma cells treated with various chemotherapeutic drugs. This chemoprotective effect was dependent on physical contact and gap junctional communication between astrocytes and tumor cells. Moreover, the protective effect of astrocytes resulted from their sequestering calcium from the cytoplasm of tumor cells. These data suggest that brain tumors can, in principle, harness the neuroprotective effects of reactive astrocytes for their own survival and implicate a heretofore unrecognized mechanism for resistance in brain metastasis that might be of relevance in the clinic.

The brain microenvironment and cancer metastasis

The process of metastasis consists of a series of sequential, selective steps that few cells can complete. The outcome of cancer metastasis depends on multiple interactions between metastatic cells and homeostatic mechanisms that are unique to one or another organ microenvironment. The specific organ microenvironment determines the extent of cancer cell proliferation, angiogenesis, invasion and survival. Many lung cancer, breast cancer, and melanoma patients develop fatal brain metastases that do not respond to therapy. The blood-brain barrier is intact in and around brain metastases that are smaller than 0.25 mm in diameter. Although the blood-brain barrier is leaky in larger metastases, the lesions are resistant to many chemotherapeutic drugs. Activated astrocytes surround and infiltrate brain metastases. The physiological role of astrocytes is to protect against neurotoxicity. Our current data demonstrate that activated astrocytes also protect tumor cells against chemotherapeutic drugs.

AACR centennial series: the biology of cancer metastasis: historical perspective

Metastasis resistant to therapy is the major cause of death from cancer. Despite almost 200 years of study, the process of tumor metastasis remains controversial. Stephen Paget initially identified the role of host-tumor interactions on the basis of a review of autopsy records. His "seed and soil" hypothesis was substantiated a century later with experimental studies, and numerous reports have confirmed these seminal observations. An improved understanding of the metastatic process and the attributes of the cells selected by this process is critical for the treatment of patients with systemic disease. In many patients, metastasis has occurred by the time of diagnosis, so metastasis prevention may not be relevant. Treating systemic disease and identifying patients with early disease should be our goal. Revitalized research in the past three decades has focused on new discoveries in the biology of metastasis. Even though our understanding of molecular events that regulate metastasis has improved, the contributions and timing of molecular lesion(s) involved in metastasis pathogenesis remain unclear. Review of the history of pioneering observations and discussion of current controversies should increase understanding of the complex and multifactorial interactions between the host and selected tumor cells that contribute to fatal metastasis and should lead to the design of successful therapy.

AACR centennial series: the biology of cancer metastasis: historical perspective

Metastasis resistant to therapy is the major cause of death from cancer. Despite almost 200 years of study, the process of tumor metastasis remains controversial. Stephen Paget initially identified the role of host-tumor interactions on the basis of a review of autopsy records. His "seed and soil" hypothesis was substantiated a century later with experimental studies, and numerous reports have confirmed these seminal observations. An improved understanding of the metastatic process and the attributes of the cells selected by this process is critical for the treatment of patients with systemic disease. In many patients, metastasis has occurred by the time of diagnosis, so metastasis prevention may not be relevant. Treating systemic disease and identifying patients with early disease should be our goal. Revitalized research in the past three decades has focused on new discoveries in the biology of metastasis. Even though our understanding of molecular events that regulate metastasis has improved, the contributions and timing of molecular lesion(s) involved in metastasis pathogenesis remain unclear. Review of the history of pioneering observations and discussion of current controversies should increase understanding of the complex and multifactorial interactions between the host and selected tumor cells that contribute to fatal metastasis and should lead to the design of successful therapy.

Abstract 3428: Astrocytes upregulate survival genes in tumor cells and induce protection from chemotherapy

Background. In the USA, more than 40% of cancer patients develop brain metastasis. The median survival of untreated patients is 1-2 months which may be extended to 6 months with conventional therapy. The resistance of tumor cells growing in the brain to chemotherapy has been attributed to the blood-brain barrier (BBB). Recent data, however, reveal that tumor cells growing in the brain release VEGF that leads to vascular permeability, ruling out that the BBB is a sole mechanism of drug resistance. Brain metastases are surrounded and infiltrated by activated astrocytes whose role in physiology is to protect neurons from toxicity. We became intrigued by the possibility that tumor cells exploit astrocytes for protection from apoptosis induced by chemotherapeutic drugs.

Material and Methods. Human breast cancer cells (MDA231) and human lung cancer cells (PC14Br4) were co-cultured with GFP-labeled murine astrocytes or NIH3T3 fibroblasts. Chemosensitivity assays against P-glycoprotein (P-gp)-1-associated chemotherapeutic agents, such as paclitaxel, adriamycin, vinblastine, and vincristine, or P-gp-1-dissociated agents such as 5-FU and cisplatinum, were performed by propidium iodide staining and FACS analysis. The development of tumor cell resistance from chemotherapeutic agents was correlated with gap junction communication and expression of survival genes. Identified genes were knocked-down by SiRNA and chemosensitivity was repeated for functional validation. Lastly, to confirm the influence of the microenvironment, tumor cells were first co-cultured with murine astrocytes or fibroblasts and then cultured with either murine astrocytes or fibroblasts. Chemosensitivity assays and gene arrays were performed.

Results. Direct cultures of murine astrocytes (but not fibroblasts) with human breast cancer cells or lung cancer cells protected the tumor cells against all tested chemotherapeutic agents, correlating with upregulation of survival genes including GSTA5, BCL2L1, and TWIST1, and activation of Akt and MAPK pathways in the tumor cells. The upregulation of the survival genes and consequent drug resistance were dependent on direct contact between the astrocytes and tumor cells through gap junctions. Knocking down the genes in the tumor cells using specific SiRNA rendered the tumor cells sensitive to the chemotherapeutic agents. The gene expression profiles and chemoresistance were transient, i.e., loss of direct contact of tumor cells with murine astrocytes resulted in loss of resistance and downregulation of the survival genes.

Conclusion. Our data clearly demonstrate that host cells, e.g., astrocytes, influence the biological behavior of tumor cells and reinforces the contention that successful therapy of brain metastasis requires targeting both tumor cells and the organ microenvironment.

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 3428.

ARD1 stabilization of TSC2 suppresses tumorigenesis through the mTOR signaling pathway

Mammalian target of rapamycin (mTOR) regulates various cellular functions, including tumorigenesis, and is inhibited by the tuberous sclerosis 1 (TSC1)-TSC2 complex. Here, we demonstrate that arrest-defective protein 1 (ARD1) physically interacts with, acetylates, and stabilizes TSC2, thereby repressing mTOR activity. The inhibition of mTOR by ARD1 inhibits cell proliferation and increases autophagy, thereby inhibiting tumorigenicity. Correlation between ARD1 and TSC2 abundance was apparent in multiple tumor types. Moreover, evaluation of loss of heterozygosity at Xq28 revealed allelic loss in 31% of tested breast cancer cell lines and tumor samples. Together, our findings suggest that ARD1 functions as an inhibitor of the mTOR pathway and that dysregulation of the ARD1-TSC2-mTOR axis may contribute to cancer development.

Generation of an immortalized astrocyte cell line from H-2Kb-tsA58 mice to study the role of astrocytes in brain metastasis

Astrocytes play a critical role in maintaining cerebral homeostasis and their dysregulation is thought to contribute to the pathogenesis of several diseases, including brain cancer and metastasis. Similar to the human disease, we found that lung and melanoma metastases in the mouse brain are accompanied by a reactive gliosis. To begin to study the biology of astrocytes and examine how these cells might contribute to metastasis formation and progression in the brain, we generated a conditionally immortal astrocyte cell line from H-2Kb-tsA58 mice. Astrocytes grown in culture expressed glial fibrillary acid protein (GFAP), glutamate receptor 1, and the N-methyl-D-aspartate (NMDA) receptor. Astrocytes also expressed the glial-specific transporters excitatory amino acid transporter 1 (EAAT1) and EAAT2. Astrocytes grown under permissive conditions (33 degrees C) expressed SV40 large T antigen and had a doubling time of 36 h, whereas expression of SV40 large T antigen was negligible in astrocytes grown at 37 degrees C for 72 h, which coincided with a plateau in cell division. In a co-culture assay with human lung adenocarcinoma cells (PC14-PE6), astrocytes activated programs in the tumor cells that signal for cell division and survival. Hence, the immortalized cell line will be useful for studying the role of astrocytes in disease processes in the brain, such as metastasis.

Circulating monocytes expressing CD31: implications for acute and chronic angiogenesis

To identify the roles of various circulating cells (eg, endothelial and/or stem and progenitor cells) in angiogenesis, we parabiosed a wild-type syngeneic mouse with a transgenic syngeneic green fluorescent protein mouse. Following the establishment of a common circulation between these parabionts, we investigated acute (7 to 10 days), subacute (2 to 3 weeks), and chronic (4 to 6 weeks) phases of angiogenesis in wild-type mice using wound healing, implanted gel foam fragments, and subcutaneous tumor assays, respectively. We found that under in vitro conditions, circulating murine monocytes expressed F4/80, CD31, and vascular endothelial growth factor receptor 2, but neither CD133 nor von Willebrand factor, whereas murine endothelial cells expressed CD31, vascular endothelial growth factor receptor 2, and von Willebrand factor, but neither CD133 nor F4/80. Immunofluorescence analysis revealed that green fluorescent protein-positive cells in the walls of new vessels in wounds, gel foam blocks, and tumors expressed both F4/80 and CD31, that is, macrophages. Pericytes, cells that express both CD31 and desmin, were found both in the walls of tumor-associated vessels and within tumors. Collectively, these data demonstrate that monocytes (ie, cells that express both CD31 and F4/80) may be recruited to the site of tissue injury and directly contribute to angiogenesis, reaffirming the close relationships between various cell types within the reticuloendothelial system and suggesting possible targets for anticancer treatments.

Transforming growth factor-beta2 is a molecular determinant for site-specific melanoma metastasis in the brain

Murine melanomas produce site-specific experimental brain metastases that reflect clinical reality. When injected into the internal carotid artery of mice, K-1735 melanoma cells produce metastatic lesions only in the brain parenchyma, whereas B16 melanoma cells and the somatic hybrid cells of B16 x K-1735 melanoma cells produce metastatic lesions only in the leptomeninges and ventricles. In the present study, we identified transforming growth factor-beta2 (TGF-beta2), an isoform of the TGF-beta family, as a molecular determinant of melanoma cell growth in the brain parenchyma. We found that the TGF-beta2 mRNA was highly expressed by the K-1735 cells, whereas the B16 cells or any B16 x K-1735 somatic cell-cell fusion hybrids have low expression. Transfection of the TGF-beta2 gene into B16 cells resulted in the production of microscopic metastatic lesions in the brain parenchyma, without a decrease in metastasis to the leptomeninges or ventricles. TGF-beta2 knockdown in the K-1735 melanoma cells significantly reduced metastasis to the brain parenchyma but did not induce metastasis to the leptomeninges or ventricles. These data show that TGF-beta2 expression by murine melanoma cells is necessary for the establishment and growth of metastases in the brain parenchyma.

Targeted induction of lung endothelial cell apoptosis causes emphysema-like changes in the mouse

Pulmonary gas exchange relies on a rich capillary network, which, together with alveolar epithelial type I and II cells, form alveolar septa, the functional units in the lung. Alveolar capillary endothelial cells are critical in maintaining alveolar structure, because disruption of endothelial cell integrity underlies several lung diseases. Here we show that targeted ablation of lung capillary endothelial cells recapitulates the cellular events involved in cigarette smoke-induced emphysema, one of the most prevalent nonneoplastic lung diseases. Based on phage library screening on an immortalized lung endothelial cell line, we identified a lung endothelial cell-binding peptide, which preferentially homes to lung blood vessels. This peptide fused to a proapoptotic motif specifically induced programmed cell death of lung endothelial cells in vitro as well as targeted apoptosis of the lung microcirculation in vivo. As early as 4 days following peptide administration, mice developed air space enlargement associated with enhanced oxidative stress, influx of macrophages, and up-regulation of ceramide. Given that these are all critical elements of the corresponding human emphysema caused by cigarette smoke, these data provide evidence for a central role for the alveolar endothelial cells in the maintenance of lung structure and of endothelial cell apoptosis in the pathogenesis of emphysema-like changes. Thus, our data enable the generation of a convenient mouse model of human emphysema. Finally, combinatorial screenings on immortalized cells followed by in vivo targeting establishes an experimental framework for discovery and validation of additional ligand-directed pharmacodelivery systems.

Dynamic change in phosphorylated platelet-derived growth factor receptor in peripheral blood leukocytes following docetaxel therapy predicts progression-free and overall survival in prostate cancer

In a placebo-controlled randomised study of the platelet-derived growth factor receptor (PDGFR) inhibitor imatinib mesylate and docetaxel in metastatic prostate cancer with bone metastases (n=116), no significant differences in progression-free and overall survival were observed. To evaluate pharmacodynamic correlates of outcomes, we assessed the association of plasma platelet-derived growth factor (PDGF) isoform kinetics and PDGFR inhibition with progression-free and overall survival by individual treatment arm. We found that in the docetaxel–placebo arm alone, the probability of decrease in PDGFR phosphorylation (Pr-Decr-pPDGFR) above 0.5 (vs ⩽0.5) was associated with a sharp increase in all measured plasma PDGF isoforms (P=0.006 for AA, 0.002 for BB, 0.045 for AB); a decreased median progression-free survival of 3.3 months vs 6.8 months (hazard ratio (HR) 2.5; P=0.006 in log-rank test) and an inferior median overall survival of 20 months vs >30 months (HR 3.1; P=0.04 in log-rank test). By contrast, in the docetaxel plus imatinib arm, the association of Pr-Decr-pPDGFR >0.5 with a rise in plasma PDGF isoform concentrations and inferior survival was not observed. The data suggest that dynamic changes in PDGFR phosphorylation in peripheral blood leukocytes predict docetaxel efficacy. Rising plasma PDGF concentrations may explain and/or mark docetaxel resistance. Validation and mechanistic studies addressing these unexpected findings should anticipate a confounding influence of concurrent PDGFR inhibitor therapy.

Modification of the primary tumor microenvironment by transforming growth factor alpha-epidermal growth factor receptor signaling promotes metastasis in an orthotopic colon cancer model

The transforming growth factor alpha (TGFalpha)/epidermal growth factor receptor (EGFR) signaling pathway appears to play a critical role in colon cancer progression, but the cellular and molecular mechanisms that contribute to metastasis remain unknown. KM12C colon cancer cell clones expressing high (C9) or negligible (C10) levels of TGFalpha were implanted into the cecal walls of nude mice. C9 tumors formed autocrine and paracrine EGFR networks, whereas C10 tumors were unable to signal through EGFR. The tumor microenvironment of C9, but not C10, contained cells enriched in vascular endothelial growth factor (VEGF) A, interleukin-8, and matrix metalloproteinases-2 and -9 and had a high vascular surface area. C9 tumors recruited a macrophage population that co-expressed F4/80 and lymphatic vessel endothelial hyaluronic acid receptor and produced VEGFC. The mean lymphatic density of C9 tumors was threefold higher than that of C10 tumors. C9, but not C10, tumor cells metastasized to regional lymph nodes in all mice and to the liver in 5 of 10 mice. Forced expression of TGFalpha in C10 tumor cells led to the generation of autocrine and paracrine EGFR signaling, macrophage recruitment, enhanced blood and lymphatic vascular surface areas, and increased lymphatic metastasis. Collectively, these data show that activation of TGFalpha-EGFR signaling in colon cancer cells creates a microenvironment that is conducive for metastasis, providing a rationale for efforts to inhibit EGFR signaling in TGFalpha-positive colon cancers.