Bo R. Rueda

Induction of interleukin-8 preserves the angiogenic response in HIF-1alpha-deficient colon cancer cells.

Hypoxia inducible factor-1 (HIF-1) is considered a crucial mediator of the cellular response to hypoxia through its regulation of genes that control angiogenesis. It represents an attractive therapeutic target in colon cancer, one of the few tumor types that shows a clinical response to antiangiogenic therapy. But it is unclear whether inhibition of HIF-1 alone is sufficient to block tumor angiogenesis. In HIF-1α knockdown DLD-1 colon cancer cells (DLD-1HIF-kd), the hypoxic induction of vascular endothelial growth factor (VEGF) was only partially blocked. Xenografts remained highly vascularized with microvessel densities identical to DLD-1 tumors that had wild-type HIF-1α (DLD-1HIF-wt). In addition to the preserved expression of VEGF, the proangiogenic cytokine interleukin (IL)-8 was induced by hypoxia in DLD-1HIF-kd but not DLD-1HIF-wt cells. This induction was mediated by the production of hydrogen peroxide and subsequent activation of NF-κB. Furthermore, the KRAS oncogene, which is commonly mutated in colon cancer, enhanced the hypoxic induction of IL-8. A neutralizing antibody to IL-8 substantially inhibited angiogenesis and tumor growth in DLD-1HIF-kd but not DLD-1HIF-wt xenografts, verifying the functional significance of this IL-8 response. Thus, compensatory pathways can be activated to preserve the tumor angiogenic response, and strategies that inhibit HIF-1α may be most effective when IL-8 is simultaneously targeted.

CD133 Expression Defines a Tumor Initiating Cell Population in Primary Human Ovarian Cancer

Evidence is accumulating that solid tumors contain a rare phenotypically distinct population of cells, termed cancer stem cells (CSC), which give rise to and maintain the bulk of the tumor. These CSC are thought to be resistant to current chemotherapeutic strategies due to their intrinsic stem‐like properties and thus may provide the principal driving force behind recurrent tumor growth. Given the high frequency of recurrent metastasis associated with human ovarian cancer, we sought to determine whether primary human ovarian tumors contain populations of cells with enhanced tumor‐initiating capacity, a characteristic of CSC. Using an in vivo serial transplantation model, we show that primary uncultured human ovarian tumors can be reliably propagated in NOD/SCID mice, generating heterogeneous tumors that maintain the histological integrity of the parental tumor. The observed frequency of tumor engraftment suggests only certain subpopulations of ovarian tumor cells have the capacity to recapitulate tumor growth. Further profiling of human ovarian tumors for expression of candidate CSC surface markers indicated consistent expression of CD133. To determine whether CD133 expression could define a tumor‐initiating cell population in primary human ovarian tumors, fluorescence‐activated cell sorting (FACS) methods were employed. Injection of sorted CD133+ and CD133− cell populations into NOD/SCID mice established that tumor‐derived CD133+ cells have an increased tumorigenic capacity and are capable of recapitulating the original heterogeneous tumor. Our data indicate that CD133 expression defines a NOD/SCID tumor initiating subpopulation of cells in human ovarian cancer that may be an important target for new chemotherapeutic strategies aimed at eliminating ovarian cancer. STEM CELLS 2009;27:2875–2883

Redefining the relevance of established cancer cell lines to the study of mechanisms of clinical anti-cancer drug resistance

Although in vitro models have been a cornerstone of anti-cancer drug development, their direct applicability to clinical cancer research has been uncertain. Using a state-of-the-art Taqman-based quantitative RT-PCR assay, we investigated the multidrug resistance (MDR) transcriptome of six cancer types, in established cancer cell lines (grown in monolayer, 3D scaffold, or in xenograft) and clinical samples, either containing >75% tumor cells or microdissected. The MDR transcriptome was determined a priori based on an extensive curation of the literature published during the last three decades, which led to the enumeration of 380 genes. No correlation was found between clinical samples and established cancer cell lines. As expected, we found up-regulation of genes that would facilitate survival across all cultured cancer cell lines evaluated. More troubling, however, were data showing that all of the cell lines, grown either in vitro or in vivo, bear more resemblance to each other, regardless of the tissue of origin, than to the clinical samples they are supposed to model. Although cultured cells can be used to study many aspects of cancer biology and response of cells to drugs, this study emphasizes the necessity for new in vitro cancer models and the use of primary tumor models in which gene expression can be manipulated and small molecules tested in a setting that more closely mimics the in vivo cancer microenvironment so as to avoid radical changes in gene expression profiles brought on by extended periods of cell culture.

Leptin Signaling Promotes the Growth of Mammary Tumors and Increases the Expression of Vascular Endothelial Growth Factor (VEGF) and Its Receptor Type Two (VEGF-R2)

To gain insight into the mechanism(s) by which leptin contributes to mammary tumor (MT) development we investigated the effects of leptin, kinase inhibitors, and/or leptin receptor antagonists (LPrA2) on 4T1 mouse mammary cancer cells in vitro and LPrA2 on 4T1-MT development in vivo. Leptin increases the expression of vascular endothelial growth factor (VEGF), its receptor (VEGF-R2), and cyclin D1 through phosphoinositide 3-kinase, Janus kinase 2/signal transducer and activator of transcription 3, and/or extracellular signal-activated kinase 1/2 signaling pathways. In contrast to leptin-induced levels of cyclin D1 the changes in VEGF or VEGF-R2 were more dependent on specific signaling pathways. Incubation of 4T1 cells with anti-VEGF-R2 antibody increased leptin-mediated VEGF expression suggesting an autocrine/paracrine loop. Pretreatment of syngeneic mice with LPrA2 prior to inoculation with 4T1 cells delayed the development and slowed the growth of MT (up to 90%) compared with controls. Serum VEGF levels and VEGF/VEGF-R2 expression in MT were significantly lower in mice treated with LPrA2. Interestingly, LPrA2-induced effects were more pronounced in vivo than in vitro suggesting paracrine actions in stromal, endothelial, and/or inflammatory cells that may impact the growth of MT. Although all the mechanism(s) by which leptin contributes to tumor development are unknown, it appears leptin stimulates an increase in cell numbers, and the expression of VEGF/VEGF-R2. Together, these results provide further evidence suggesting leptin is a MT growth-promoting factor. The inhibition of leptin signaling could serve as a potential adjuvant therapy for treatment of breast cancer and/or provide a new target for the designing strategies to prevent MT development.

Decreased Progesterone Levels and Progesterone Receptor Antagonists Promote Apoptotic Cell Death in Bovine Luteal Cells

Abstract We tested the hypothesis that progesterone (P4) acts at a local level to inhibit luteal apoptosis. Initial experiments employed aminoglutethimide, a P450 cholesterol side-chain cleavage inhibitor, to inhibit steroid synthesis. Cultured bovine luteal cells were treated with aminoglutethimide (0.15 mM) ± P4 (500 ng/ml) for 48 h. Luteal cells were recovered and snap frozen for isolation and analysis of oligonucleosomal DNA fragmentation or fixed for morphological analysis. Medium was collected for analysis of P4 levels by RIA. Aminoglutethimide inhibited P4 synthesis by > 95% and increased the level of apoptosis as evidenced by 32P-labeled oligonucleosomal DNA fragmentation (> 40%). P4 supplementation inhibited the onset of apoptosis that was induced by aminoglutethimide. These data were further supported by morphological assessment of apoptotic cells utilizing a Hoechst staining technique and together strongly suggest that P4 has anti-apoptotic capacity. Using reverse transcription-polymerase chain reaction, we were able to isolate a 380-base pair cDNA from the bovine corpus luteum (CL) that was 100% homologous to the progesterone receptor (PR) previously found in bovine oviductal tissue. Furthermore, PR transcripts were present in large and small luteal cells. Immunohistochemistry also revealed that PR protein was present in both large and small luteal cells. To determine whether the anti-apoptotic effect of P4 was regulated at the receptor level, luteal cells were cultured in the presence of PR antagonists, RU-486 and onapristone, for 48 h. Both antagonists caused approximately a 40% increase in 32P-labeled oligonucleosomal DNA fragmentation. Interestingly, there was no difference (P ≥ 0.05) in P4 levels after treatment with PR antagonists. These observations support the concept that P4 represses the onset of apoptosis in the CL by a PR-dependent mechanism.

Leptin-Signaling Inhibition Results in Efficient Anti-Tumor Activity in Estrogen Receptor Positive or Negative Breast Cancer

IntroductionWe have shown previously that treatment with pegylated leptin peptide receptor antagonist 2 (PEG-LPrA2) reduced the expression of vascular endothelial growth factor (VEGF), vascular endothelial growth factor receptor type 2 (VEGFR2) and growth of 4T1-breast cancer (BC) in syngeneic mice. In this investigation, PEG-LPrA2 was used to evaluate whether the inhibition of leptin signaling has differential impact on the expression of pro-angiogenic and pro-proliferative molecules and growth of human estrogen receptor-positive (ER+) and estrogen receptor-negative (ER-) BC xenografts hosted by immunodeficient mice.MethodsTo test the contribution of leptin signaling to BC growth and expression of leptin-targeted molecules, PEG-LPrA2 treatment was applied to severe immunodeficient mice hosting established ER+ (MCF-7 cells; ovariectomized/supplemented with estradiol) and ER- (MDA-MB231 cells) BC xenografts. To further assess leptin and PEG-LPrA2 effects on ER+ and ER- BC, the expression of VEGF and VEGFR2 (protein and mRNA) was investigated in cell cultures.ResultsPEG-LPrA2 more effectively reduced the growth of ER+ (>40-fold) than ER- BC (twofold) and expression of pro-angiogenic (VEGF/VEGFR2, leptin/leptin receptor OB-R, and IL-1 receptor type I) and pro-proliferative molecules (proliferating cell nuclear antigen and cyclin D1) in ER+ than in ER- BC. Mouse tumor stroma in ER+ BC expressed high levels of VEGF and leptin that was induced by leptin signaling. Leptin upregulated the transcriptional expression of VEGF/VEGFR2 in MCF-7 and MDA-MB231 cells.ConclusionsThese results suggest that leptin signaling plays an important role in the growth of both ER+ and ER- BC that is associated with the leptin regulation of pro-angiogenic and pro-proliferative molecules. These data provide support for the potential use of leptin-signaling inhibition as a novel treatment for ER+ and ER- BC.

HIF-1α and HIF-2α have divergent roles in colon cancer

Hypoxia‐inducible factor (HIF)‐1 and HIF‐2 are heterodimeric transcription factors that mediate the cellular response to hypoxia. Their key regulatory subunits, HIF‐1α and HIF‐2α, are induced similarly by hypoxia, but their functional roles in cancer may be distinct and isoform‐specific. SW480 colon cancer cells with stable expression of siRNA to HIF‐1α or HIF‐2α or both were established. HIF‐1α‐deficient cells displayed lower rates of proliferation and migration, but HIF‐2α‐deficient cells exhibited enhanced anchorage independent growth in a soft agar assay. Xenograft studies revealed that HIF‐1α deficiency inhibited overall tumor growth, whereas deficiency of HIF‐2α stimulated tumor growth. In human colon cancer tissues, expression of HIF‐1α and to a lesser extent, HIF‐2α, was linked to upregulation of VEGF and tumor angiogenesis. However, loss of expression of HIF‐2α but not HIF‐1α was strongly correlated with advanced tumor stage. DNA microarray analysis identified distinct sets of HIF‐1α and HIF‐2α target genes that may explain these phenotypic differences. Collectively, these findings suggest that HIF isoforms may have differing cellular functions in colon cancer. In particular, HIF‐1α promoted the growth of SW480 colon cancer cells but HIF‐2α appeared to restrain growth. Consequently, therapeutic approaches that target HIF may need to consider these isoform‐specific properties.

Caspase-3 is a pivotal mediator of apoptosis during regression of the ovarian corpus luteum

Because caspase-3 is considered a primary executioner of apoptosis and has been implicated as a mediator of luteal regression, we hypothesized that corpora lutea (CL) derived from caspase-3 null mice would exhibit a delayed onset of apoptosis during luteal regression, when compared with CL derived from wild-type (WT) mice. To test this hypothesis, ovulation was synchronized in immature (postpartum d 24 –27) WT and caspase-3-deficient female littermates by exogenous gonadotropins. Individual CL were isolated by manual dissection, 30 h after ovulation, and placed in organ culture dishes in the absence of serum and growth factors. At the time of isolation (0 h) and after 24, 48, and 72 h in culture, the CL were removed and assessed for the presence of processed (active) caspase-3 enzyme and for apoptosis by multiple criteria. There was no evidence of active caspase-3 enzyme or apoptosis in either WT or caspase-3-deficient CL before culture. However, CL derived from the WT mice exhibited a time-dependent increase in the level of active caspase-3 and apoptosis during culture. By comparison, CL derived from caspase-3-deficient mice, cultured in parallel, failed to exhibit any detectable active caspase-3 and showed attenuated rates of apoptosis. To extend these findings derived from ex vivo culture experiments, ovaries were collected from WT and caspase-3 null female littermates at 2, 4, or 6 d post ovulation, and the occurrence of apoptosis within the CL was analyzed. Whereas ovaries of WT mice had only residual luteal tissue at d 6 post ovulation, ovaries collected from caspase-3-deficient mice retained many CL, at d 6 post ovulation, that were similar in size to those observed in the early luteal phase of WT mice. Importantly, there was no dramatic increase in apoptosis in CL of caspase-3-deficient mice at any time point examined post ovulation, indicating that the involution process had indeed been delayed. In contrast, the levels of progesterone declined regardless of genotype. These data provide the first direct evidence that caspase-3 is functionally required for apoptosis to proceed normally during luteal regression. However, caspase-3 is not a direct mediator of the decrease in steroidogenesis associated with luteolysis. (Endocrinology 143: 1495–1501, 2002)

Microvascular endothelial cells of the corpus luteum

The cyclic nature of the capillary bed in the corpus luteum offers a unique experimental model to examine the life cycle of endothelial cells, involving discrete physiologically regulated steps of angiogenesis, blood vessel maturation and blood vessel regression. The granulosa cells and theca cells of the developing antral follicle and the steroidogenic cells of the corpus luteum produce and respond to angiogenic factors and vasoactive peptides. Following ovulation the neovascularization during the early stages of corpus luteum development has been compared to the rapid angiogenesis observed during tumor formation. On the other end of the spectrum, the microvascular endothelial cells are the first cells to undergo apoptosis at the onset of corpus luteum regression. Important insights on the morphology and function of luteal endothelial cells have been gained from a combination of in vitro and in vivo studies on endothelial cells. Endothelial cells communicate with cells comprising the functional unit of the corpus luteum, i.e., other vascular cells, steroidogenic cells, and immune cells. This review is designed to provide an overview of the types of endothelial cells present in the corpus luteum and their involvement in corpus luteum development and regression. Available evidence indicates that microvascular endothelial cells of the corpus luteum are not alike, and may differ during the process of angiogenesis and angioregression. The contributions of vasoactive peptides generated by the luteal endothelin-1 and the renin-angiotensin systems are discussed in context with the function of endothelial cells during corpus luteum formation and regression. The ability of two cytokines, tumor necrosis factor alpha and interferon gamma, are evaluated as paracrine mediators of endothelial cell function during angioregression. Finally, chemokines are discussed as a vital endothelial cell secretory products that contribute to the recruitment of eosinophils and macrophages. The review highlights areas for future investigation of ovarian microvascular endothelial cells. The potential clinical applications of research directed on corpus luteum endothelial cells are intriguing considering reproductive processes in which vascular dysfunctions may play a role such as ovarian failure, polycystic ovary syndrome (PCOS), and ovarian hyperstimulation syndrome (OHSS).

Constitutive Activation of Beta-Catenin in Uterine Stroma and Smooth Muscle Leads to the Development of Mesenchymal Tumors in Mice

Leiomyomas and other mesenchymally derived tumors are the most common neoplasms of the female reproductive tract. Presently, very little is known about the etiology and progression of these tumors, which are the primary indication for hysterectomies. Dysregulated WNT signaling through beta-catenin is a well-established mechanism for tumorigenesis. We have developed a mouse model that expresses constitutively activated beta-catenin in uterine mesenchyme driven by the expression of Cre recombinase knocked into the Müllerian-inhibiting substance type II receptor promoter locus to investigate its effects on uterine endometrial stroma and myometrium. These mice show myometrial hyperplasia and develop mesenchymal tumors with 100% penetrance that exhibit histological and molecular characteristics of human leiomyomas and endometrial stromal sarcomas. By immunohistochemistry, we also show that both transforming growth factor beta and the mammalian target of rapamycin are induced by constitutive activation of beta-catenin. The prevalence of the tumors was greater in multiparous mice, suggesting that their development may be a hormonally driven process or that changes in uterine morphology during pregnancy and after parturition induce injury and repair mechanisms that stimulate tumorigenesis from stem/progenitor cells, which normally do not express constitutively activated beta-catenin. Additionally, adenomyosis and endometrial gland hyperplasia were occasionally observed in some mice. These results show evidence suggesting that dysregulated, stromal, and myometrial WNT/beta-catenin signaling has pleiotropic effects on uterine function and tumorigenesis.