Persistence of microscopic human cancers in mice: alterations in the angiogenic balance accompanies loss of tumor dormancy

Unveiling cancer dormancy: Intrinsic mechanisms and extrinsic forces

Tumor cells disseminate in various distant organs at early stages of cancer progression. These disseminated tumor cells (DTCs) can stay dormant/quiescent without causing patient symptoms for years or decades. These dormant tumor cells survive despite curative treatments by entering growth arrest, escaping immune surveillance, and/or developing drug resistance. However, these dormant cells can reactivate to proliferate, causing metastatic progression and/or relapse, posing a threat to patients' survival. It's unclear how cancer cells maintain dormancy and what triggers their reactivation. What are better approaches to prevent metastatic progression and relapse through harnessing cancer dormancy? To answer these remaining questions, we reviewed the studies of tumor dormancy and reactivation in various types of cancer using different model systems, including the brief history of dormancy studies, the intrinsic characteristics of dormant cells, and the external cues at the cellular and molecular levels. Furthermore, we discussed future directions in the field and the strategies for manipulating dormancy to prevent metastatic progression and recurrence.

Visualization of hypoxia in cancer cells from effusions in animals and cancer patients

Objective

Tumor hypoxia is frequently observed in primary solid malignancies, but the hypoxic status of tumor cells floating in body cavity effusions is largely unknown, especially in patients. This study was to observe the hypoxia and proliferation status of cancer cells floating in effusions in mice and patients.

Methods

The distribution of hypoxia in cancer cells floating in ascites was first studied in nude mice. Hypoxia was detected by immunofluorescent visualization of pimonidazole and GLUT-1. For cancer patients, we retrospectively collected 21 ascites and 7 pleural effusion sample blocks of cancer patients, which were confirmed to contain tumor cells. Immunohistochemistry was performed to detect the expression of endogenous hypoxic markers HIF-1α and GLUT-1, proliferation index Ki-67. ¹⁸F-FDG PET/CT was performed to detect the glucose metabolism status of tumor cells in effusions.

Results

The tumor cells collected from ascites were positive for pimonidazole and GLUT-1, which suggesting that the cancer cells floating in ascites were hypoxic. Patterns of tumor hypoxia in human patients are similar to those observed in animal. HIF-1α and GLUT-1 were expressed by tumor cells in nearly all 28 cytological cases. For Ki-67 index, ascites tumor cells had a relatively low expression level compared with their corresponding primary or its metastatic lesions. Tumor cells in effusions showed high ¹⁸F-FDG uptake indicated the enhanced activity of glucose metabolism.

Conclusion

Tumor cells in body cavity effusions, as a unique subgroup of tumor, are in a state of hypoxia and low proliferation, which would be one of the driven causes of chemo-radiotherapy resistance. Novel therapeutic interventions are urgently needed to overcome tumor hypoxia.

Enhancer RNA SLIT2 Inhibits Bone Metastasis of Breast Cancer Through Regulating P38 MAPK/c-Fos Signaling Pathway

BACKGROUND

Breast cancer (BRCA) is the most common cancer in women, while the bones are one of the most common sites of metastasis. Although new diagnostic methods or radiation or chemotherapies and targeted therapies have made huge advances, the occurrence of bone metastasis is also linked with poorer survival. Enhancer RNAs (eRNAs) have been demonstrated to participate in the progression of tumorigenesis and metastasis. However, the role of eRNAs in BRCA bone metastasis remains largely unclear.

METHOD

Gene expression profiling of 1,211 primary BRCA and 17 bone metastases samples were retrieved from The Cancer Genome Atlas (TCGA) database, and the significant prognostic eRNAs were identified by Cox regression and least absolute shrinkage and selection operator (LASSO) regression. The acceptable accuracy and discrimination of the nomogram were indicated by the receiver operating characteristic (ROC) and the calibration curves. Then target genes of eRNA, immune cell percentage by CIBERSORT analysis, immune genes by single-sample gene set enrichment analysis (ssGSEA), hallmark of cancer signaling pathway by gene set variation analysis (GSVA), and reverse phase protein array (RPPA) protein chip were used to build a co-expression regulation network and identified the key eRNAs in bone metastasis of BRCA. Finally, Cell Counting Kit-8 (CCK8) assay, cell cycle assay, and transwell assay were used to study changes in cell proliferation, migration, and invasiveness. Immunoprecipitation assay and Western blotting were used to test the interaction and the regulation signaling pathways.

RESULTS

The 27 hub eRNAs were selected, and a survival-related linear risk assessment model with a relatively high accuracy (area under curve (AUC): 0.726) was constructed. In addition, seven immune-related eRNAs (SLIT2, CLEC3B, LBPL1, FRY, RASGEF1B, DST, and ITIH5) as prognostic signatures for bone metastasis of BRCA were further confirmed by LASSO and multivariate Cox regression and CIBERSORT analysis. Finally, in vitro assay demonstrated that overexpression of SLIT2 reduced proliferation and metastasis in BRCA cells. Using high-throughput co-expression regulation network, we identified that SLIT2 may regulating P38 MAPK/c-Fos signaling pathway to promote the effects of metastasis.

CONCLUSION

Based on the co-expression network for bone metastasis of BRCA, we screened key eRNAs to explore a prognostic model in predicting the bone metastasis by bioinformatics analysis. Besides, we identified the potential regulatory signaling pathway of SLIT2 in BRCA bone metastasis, which provides a promising therapeutic strategy for metastasis of BRCA.

Hypoxia and the Tumor Microenvironment

Hypoxia is an important feature of the tumor microenvironment, and is closely associated with cell proliferation, angiogenesis, metabolism and the tumor immune response. All these factors can further promote tumor progression, increase tumor aggressiveness, enhance tumor metastatic potential and lead to poor prognosis. In this review, these effects of hypoxia on tumor biology will be discussed, along with their significance for tumor detection and treatment.

Reexamining the role of tissue inflammation in radiation carcinogenesis: a hypothesis to explain an earlier onset of cancer

PURPOSE

Ionizing radiation is a well-known carcinogen, and epidemiologic efforts have been made to evaluate cancer risks following a radiation exposure. The basic approach has been to estimate increased levels of cancer mortality resulting from exposures to radiation, which is consistent with the somatic mutation theory of cancer. However, the possibility that an irradiation might cause an earlier onset of cancer has also been raised since the earliest days of animal studies. Recently, the mutation induction model has been challenged because it is unable to explain the observed dose-related parallel shift of entire mouse survival curves toward younger ages following an irradiation. This is because if it is assumed that only a fraction of the irradiated individuals are affected, the irradiated population would consist of two subpopulations with different mean lifespans, which makes the overall distribution of individual lifespans broader, and hence the slope of the survival curves shallower. To explain this parallel shift, it is necessary to assume that all individuals of a population are affected. As a result of these observations, possible mechanisms which could account for the parallel shift of mouse survival curves were sought by examining the radiation induction of various types of tissue damage which could facilitate an earlier onset of spontaneously arising cancers.

CONCLUSION

A proposed mechanism postulates that a radiation exposure leads to tissue inflammation which subsequently stimulates spontaneously arising cancers and allows them to appear earlier than usual. This notion is not unprecedented, and because the background incidence of cancer increases exponentially with an increase in age, a slight shift of the onset age toward younger ages may make it appear as if the risk is increased. In this scenario, a radiation exposure induces DNA damage, cell death, chromosome aberrations etc., which leads to the multi-pathway responses including activation of stromal fibroblasts, macrophages and various inflammatory factors. Such an inflamed microenvironment favors the growth of spontaneously arising tumor cells although currently, the sequential order or relative importance of the individual factors remains to be known.

Dormancy and NKG2D system in brain metastases: Analysis of immunogenicity

Patients with breast cancer (BC) and lung cancer (LC) are prone to developing brain metastases, which are associated with devastating prognoses. Dormant tumor cells, a population of non-apoptotic quiescent cells and immunological escape mechanisms, including the Natural Killer Group 2 member D (NKG2D) receptor-ligand system, represent potential mechanisms of tumor recurrence. To date, the immunological characteristics of dormant tumor cells concerning the NKG2D system in cerebral malignancies are mostly unknown. In the present study, an extensive characterization of dormant and NKG2D ligand (NKG2DL)⁺ cells in cerebral metastases was performed. The expression profiles and localization patterns of various NKG2DL and several dormancy markers were analyzed in solid human brain metastases from patients with BC and LC using immunostaining and reverse transcription-quantitative polymerase chain reaction analyses. Statistical analysis was performed using Student's t-test and Bravais-Pearson correlation analysis. Not only 'peripheral', but also 'central' dormancy markers, which had been previously described in primary brain tumors, were identified in all cerebral metastases at detectable levels at protein and mRNA levels. Notably, the majority of NKG2DL⁺ cells were also positive for 'central' dormancy markers, but not 'peripheral' dormancy markers in both patient groups. This cell population may represent a promising future therapeutic target.

CXCR2: A Novel Mediator of Mammary Tumor Bone Metastasis

Most breast cancer patients die due to bone metastasis. Although metastasis accounts for 5% of the breast cancer cases, it is responsible for most of the deaths. Sometimes even before the detection of a primary tumor, most of the patients have bone and lymph node metastasis. Moreover, at the time of death, breast cancer patients have the bulk of the tumor burden in their bones. Therapy options are available for the treatment of primary tumors, but there are minimal options for treating breast cancer patients who have bone metastasis. C-X-C motif chemokine receptor type 2 (CXCR2) receptor-mediated signaling has been shown to play a critical role during bone-related inflammations and its ligands C-X-C motif chemokine ligand 6 (CXCL6) and 8 (CXCL8) aid in the resorption of bone during bone metastasis. In this study, we tested the hypothesis that CXCR2 contributes to mammary tumor-induced osteolysis and bone metastasis. In the present study, we examined the role of both tumor cell-derived and host-derived CXCR2 in influencing mammary tumor cell bone metastasis. For understanding the role of tumor cell-derived CXCR2, we utilized Cl66 CXCR2 knockdown (Cl66-shCXCR2) and Cl66-Control cells (Cl66-Control) and observed a significant decrease in tumor growth and tumor-induced osteolysis in Cl66-shCXCR2 cells in comparison with the Cl66-Control cells. Next, for understanding the role of host-derived CXCR2, we utilized mice with genomic knockdown of CXCR2 (Cxcr2^-/-) and injected Cl66-Luciferase (Cl66-Luc) or 4T1-Luciferase (4T1-Luc) cells. We observed decreased bone destruction and metastasis in the bone of Cxcr2^-/- mice. Our data suggest the importance of both tumor cell- and host-derived CXCR2 signaling in the bone metastasis of breast cancer cells.

Identification of Dormancy-Associated MicroRNAs for the Design of Osteosarcoma-Targeted Dendritic Polyglycerol Nanopolyplexes

The presence of dormant, microscopic cancerous lesions poses a major obstacle for the treatment of metastatic and recurrent cancers. While it is well-established that microRNAs play a major role in tumorigenesis, their involvement in tumor dormancy has yet to be fully elucidated. We established and comprehensively characterized pairs of dormant and fast-growing human osteosarcoma models. Using these pairs of mouse tumor models, we identified three novel regulators of osteosarcoma dormancy: miR-34a, miR-93, and miR-200c. This report shows that loss of these microRNAs occurs during the switch from dormant avascular into fast-growing angiogenic phenotype. We validated their downregulation in patients' tumor samples compared to normal bone, making them attractive candidates for osteosarcoma therapy. Successful delivery of miRNAs is a challenge; hence, we synthesized an aminated polyglycerol dendritic nanocarrier, dPG-NH2, and designed dPG-NH2-microRNA polyplexes to target cancer. Reconstitution of these microRNAs using dPG-NH2 polyplexes into Saos-2 and MG-63 cells, which generate fast-growing osteosarcomas, reduced the levels of their target genes, MET proto-oncogene, hypoxia-inducible factor 1α, and moesin, critical to cancer angiogenesis and cancer cells' migration. We further demonstrate that these microRNAs attenuate the angiogenic capabilities of fast-growing osteosarcomas in vitro and in vivo. Treatment with each of these microRNAs using dPG-NH2 significantly prolonged the dormancy period of fast-growing osteosarcomas in vivo. Taken together, these findings suggest that nanocarrier-mediated delivery of microRNAs involved in osteosarcoma tumor-host interactions can induce a dormant-like state.

Escape from tumor dormancy and time to angiogenic switch as mitigated by tumor-induced stimulation of stroma

A variety of mechanisms have been proposed to explain "cancer without disease", the state of tumor dormancy, characterized by balance in cell proliferation and cell death within a tumor. Here we have investigated a theoretical construct, whereby one of such mechanisms, the time to induction of angiogenesis, or "angiogenic switch", is mitigated by the degree of stromal stimulation by the tumor. We tested this hypothesis and its implications by introducing a mathematical model that captures how angiogenesis regulators, released from the platelet clot, contribute to formation of normal vasculature. We then modified the model to introduce tumor-induced increase in production of angiogenesis regulators and were able to simulate pathological angiogenesis. Through varying parameters governing the degree of tumor-induced stromal stimulation, we were able to qualitatively replicate experimentally observed growth curves for both dormant and actively growing tumors of breast cancer and liposarcoma. In fact, variation of very few parameters was sufficient to replicate any experimentally observed time to angiogenic switch in the available data. Finally, we investigated the effects of tighter binding isoforms of angiogenesis stimulators on neovasculature formation and tumor growth, which may provide an explanation for variations in angiogenesis -dependence in tumors of different tissue origin.

The effect of chemotherapeutic agents on tumor vasculature in subcutaneous and orthotopic human tumor xenografts

Background

The growth of solid tumors and their regrowth after treatment is dependent upon functional tumor vasculature. Some chemotherapeutic agents have shown anti-angiogenic properties but there are limited studies of the effect of chemotherapy on tumor vasculature. Here we investigate the effect of paclitaxel, 5-fluorouracil (5-FU) and doxorubicin on tumor vasculature in subcutaneous and orthotopic xenografts in mice.

Methods

The vascular density and percentage of functional blood vessels were evaluated in subcutaneous A431 human vulvar cancer xenografts, and in subcutaneous and orthotopic MCF-7 human breast cancer xenografts, following single doses of paclitaxel, 5-FU or doxorubicin.

Results

There was no significant difference in total (CD31+) blood vessels between untreated ectopic and orthotopic MCF-7 tumors, but there was a significantly lower proportion of functional blood vessels in orthotopic tumors. After paclitaxel treatment, there was a decrease in functional tumor vasculature in A431 subcutaneous xenografts, followed by a subsequent rebound. There was a significant decrease in total vascular density on day 12 in A431 tumors following 5-FU or doxorubicin treatment, but no change in the percentage of functional vessels. An increase in functional blood vessels or percentage of functional vasculature was noted in MCF-7 subcutaneous and orthotopic xenografts following chemotherapy treatment.

Conclusions

There are differences in the vasculature and microenvironment of ectopic and orthotopic xenografts in mice. Anti-tumor effects of chemotherapy may be due, in part, to effects on tumor vasculature and may vary in different tumor models.

Metastases in immune-mediated dormancy: a new opportunity for targeting cancer

The aim of any anticancer treatment is to avoid, control, or eliminate disseminated tumor cells. Clinical and experimental evidence has revealed that metastases can remain in a latency state, that is, metastasis dormancy. Three mechanisms are thought to be involved in cancer dormancy: cellular dormancy, angiogenic dormancy, and immune-mediated dormancy. Here, we review the mechanisms and cells involved in immune-mediated cancer dormancy and discuss current and future immunotherapeutic strategies. Recent results indicate that the immune system can restrain disseminated cancer cells, promoting their permanent dormancy. CD8(+) T lymphocytes play a relevant role in maintaining immune equilibrium with metastatic dormant cells, and MHC class I surface expression on tumor cells may also be involved. Natural killer (NK) cells have an activator function that triggers a cytotoxic T lymphocyte (CTL) response. Furthermore, immune dormancy promotes cancer cell growth arrest and angiogenic control. Immunotherapeutic interventions in metastatic dormancy may help to control or eradicate cancer disease. Treatments that activate or increase the CTL immune response or reverse cancer cell-induced CTL immunosuppression might be useful to restrain or destroy metastatic cells. These objectives may be achieved by recovering or increasing MHC class I surface expression on cancer cells or even by activating NK cells. Immune-mediated metastasis dormancy provides an opportunity for targeting cancer in novel immune treatments.

Thrombospondin-1 repression is mediated via distinct mechanisms in fibroblasts and epithelial cells

Tumor-associated angiogenesis is postulated to be regulated by the balance between pro- and anti-angiogenic factors. We demonstrate here that the critical step in establishing the angiogenic capability of human tumor cells is the repression of a key secreted anti-angiogenic factor, thrombospondin-1 (Tsp-1). This repression is essential for tumor formation by mammary epithelial cells and kidney cells engineered to express SV40 early region proteins, hTERT, and H-RasV12. In transformed epithelial cells, a signaling pathway leading from Ras to Tsp-1 repression induces the sequential activation of PI3 kinase, Rho and ROCK, leading to activation of Myc through phosphorylation, thereby enabling Myc to repress Tsp-1 transcription. In transformed fibroblasts, however, the repression of Tsp-1 can be achieved by an alternative mechanism involving inactivation of both p53 and pRb. We thus describe novel mechanisms by which the activation of oncogenes in epithelial cells and the inactivation of tumor suppressors in fibroblasts permits angiogenesis and, in turn, tumor formation.

Spontaneous reversion of the angiogenic phenotype to a nonangiogenic and dormant state in human tumors

The angiogenic switch, a rate-limiting step in tumor progression, has already occurred by the time most human tumors are detectable. However, despite significant study of the mechanisms controlling this switch, the kinetics and reversibility of the process have not been explored. The stability of the angiogenic phenotype was examined using an established human liposarcoma xenograft model. Nonangiogenic cells inoculated into immunocompromised mice formed microscopic tumors that remained dormant for approximately 125 days (vs. <40 days for angiogenic cells) whereupon the vast majority (>95%) initiated angiogenic growth with second-order kinetics. These original, clonally derived angiogenic tumor cells were passaged through four in vivo cycles. At each cycle, a new set of single-cell clones was established from the most angiogenic clone and characterized for in vivo for tumorigenic activity. A total of 132 single-cell clones were tested in the second, third, and fourth in vivo passage. Strikingly, at each passage, a portion of the single-cell clones formed microscopic, dormant tumors. Following dormancy, like the original cell line, these revertant tumors spontaneously switched to the angiogenic phenotype. Finally, revertant clones were transcriptionally profiled and their angiogenic output determined. Collectively, these data demonstrate that the angiogenic phenotype in tumors is malleable and can spontaneously revert to the nonangiogenic phenotype in a population of human tumor cells.

IMPLICATIONS

Leveraging the rate of reversion to the nonangiogenic phenotype and tumor dormancy may be a novel anticancer strategy.

Tumor dormancy and the neuroendocrine system: an undisclosed connection?

Tumor dormancy is a poorly understood phenomenon conceptualized as a protracted quiescent state during which cancer cells are present but clinical disease is not apparent, a condition referred to as "cancer without disease" by Folkman. Examples include the incidental detection of occult in situ tumors in post-mortem organ analysis and cancer recurrence after long disease-free periods. Lack of angiogenic competency has been proposed as a major determinant of the fate of dormant tumors. Other proposed processes include establishment of homeostatic equilibrium between tumor cells and the host's immune system response and a non-permissive microenvironment for tumor growth. Recent cellular and molecular studies suggest that neuroendocrine mediators regulate the biology of tumor progression and act as endogenous modulators of angiogenesis, inflammation, and other molecular processes involved in tumor reactivation from dormancy. We review experimental and clinical evidence and propose that neuroendocrine dynamics of the sympathetic nervous system and the hypothalamic-pituitary-adrenal axis might contribute to the loss of tumor dormancy.

Transcriptional changes induced by the tumor dormancy-associated microRNA-190

Tumor dormancy is a highly prevalent stage in cancer progression. We have previously generated and characterized in vivo experimental models of human tumor dormancy in which micro-tumors remain occult until they spontaneously shift into rapid tumor growth. We showed that the dormant micro-tumors undergo a stable microRNA (miRNA) switch during their transition from dormancy to a fast-growing phenotype and reported the identification of a consensus signature of human tumor dormancy-associated miRNAs (DmiRs). miRNA-190 (miR-190) is among the most upregulated DmiRs in all dormant tumors analyzed. Upregulation of miR-190 led to prolonged tumor dormancy in otherwise fast-growing glioblastomas and osteosarcomas. Here we investigate the transcriptional changes induced by miR-190 expression in cancer cells and show similar patterns of miR-190 mediated transcriptional reprogramming in both glioblastoma and osteosarcoma cells. The data suggests that miR-190 mediated effects rely on an extensive network of molecular changes in tumor cells and that miR-190 affects several transcriptional factors, tumor suppressor genes and interferon response pathways. The molecular mechanisms governing tumor dormancy described in this work may provide promising targets for early prevention of cancer and may lead to novel treatments to convert the malignant tumor phenotype into an asymptomatic dormant state.

Progression of ocular melanoma metastasis to the liver: the 2012 Zimmerman lecture

IMPORTANCE

To the best of my knowledge, this study demonstrates for the first time small, apparently dormant micrometastasis in the liver of patients with uveal melanoma.

OBJECTIVE

To evaluate the histological and immunohistochemical findings in metastatic uveal melanoma to the liver.

DESIGN

Samples of liver were obtained at autopsy from patients who died of metastatic uveal melanoma to the liver.

SETTING

L. F. Montgomery Laboratory, Emory Eye Center, Atlanta, Georgia.

PARTICIPANTS

A total of 10 patients who died of metastatic uveal melanoma to the liver.

INTERVENTION

Sections of the liver were examined with hematoxylin-eosin, periodic acid-Schiff, Masson trichrome, or reticulin stains.

MAIN OUTCOME MEASURES

The tumors' morphology, growth pattern, mean vascular density, and mitotic index were determined with the aid of immunohistochemical stains for S100, HMB45, CD31, and Ki67.

RESULTS

Stage 1 metastases (defined as tumor clusters ≤50 μm in diameter) were identified in the sinusoidal spaces of 9 of 10 patients (90%). Stage 1 metastases were avascular and lacked mitotic activity. Stage 2 metastases (defined as tumors measuring 51-500 μm in diameter) and stage 3 metastases (defined as tumors measuring >500 μm in diameter) were found in all patients. Immunohistochemical stains were positive for S100 or HMB45 in all tumors. Overall, stage 1 metastases outnumbered stage 2 metastases (which outnumbered stage 3 metastases). The mean vascular density and mitotic index increased from stage 2 to stage 3 metastases (P < .05). The architecture of stage 2 metastases mimicked the surrounding hepatic parenchyma, whereas stage 3 metastases exhibited either lobular or portal growth patterns.

CONCLUSIONS

Uveal melanoma that spreads to the liver can be categorized as stage 1 (≤50 μm in diameter), stage 2 (51-500 μm in diameter), or stage 3 (>500 μm in diameter) metastases. The later stage exhibits a lobular or portal pattern of growth. During this progression, tumors become vascularized and mitotically active.

Genes and regulatory pathways involved in persistence of dormant micro-tumors

Micro-tumors can remain dormant for prolonged periods of time before they switch and enter the rapid growth phase. This initial stage in tumor progression is clearly understudied. In spite of high prevalence, significant clinical implications and increased interest by the research community, tumor dormancy is still poorly understood. The topic of tumor dormancy also suffers from a lack of definition and an agreed upon terminology to describe it. Additionally, the number of reproducible experimental models available for studying indolence of human micro-tumors is quite limited. Here, we describe the development of a general class of in vivo models of indolent human tumors and how these models can be used to elucidate molecular and cellular mechanisms involved in the regulation of dormancy. The models consist of human tumor cell lines that form microscopic cancerous lesions in mice. Although these lesions contain viable and fully malignant cancer cells, the tumors do not expand in size but remain occult for prolonged periods until they eventually spontaneously switch and become fast-growing tumors. Consistent with Judah Folkman's vision that tumors will remain occult and microscopic until they acquire the ability to recruit new and functional blood vessels, the dormancy period of the micro-tumors is associated with impaired angiogenic capacity. Such models can be used for dissecting the host and the tumor-derived regulatory mechanisms of tumor dormancy. Understanding the process by which dormant tumors can overcome growth constraints and emerge from dormancy, resuming size expansion, may provide insights into novel strategies to prolong the dormancy state or to block tumor formation in the early stages, before they are physically detected or become symptomatic.

Insights into the regulation of tumor dormancy by angiogenesis in experimental tumors

While it is well established that an angiogenic switch marks escape from tumor dormancy in xenograft models, the molecular pathways involved in the control of tumor cell proliferation or survival by angiogenesis remain substantially uncharted. We recently demonstrated that signals stemming from angiogenic endothelial cells (EC) regulate the behavior of dormant cancer cells. Specifically, we observed that the Notch ligand Dll4, induced by angiogenic factors in EC, triggers Notch3 activation in neighboring tumor cells and promotes a tumorigenic phenotype. Evidence that Notch signaling is involved in tumor dormancy was further strengthened by the observation that MKP-1 levels-a broadly expressed phosphatase-are controlled by Notch3 by regulation of protein ubiquitination and stability. Notch3 and MKP-1 levels are consistently low in dormant tumors, and this is accompanied by relatively high levels of phosphorylated p38, a canonical MKP-1 target previously associated with maintenance of tumor dormancy. These results elucidate a novel angiogenesis-driven mechanism involving the Notch and MAPK pathways that controls tumor dormancy. More in general, angiogenic EC could form part of the vascular niche, a specialized microenvironment which appears to regulate metastatic outgrowth and future studies are needed to clarify the contribution of EC in the regulation of cancer stem cell behavior in the niche.The notion that EC could communicate signals to tumor cells raises questions about the possibility of achieving tumor dormancy by counteracting angiogenesis. In experimental tumors, anti-VEGF drugs typically prune the newly formed vasculature, thus reducing microvessel density, blood flow, and perfusion. These drugs eventually increase hypoxia and cause tumor necrosis but dormancy is rarely observed. Our group recently reported that anti-VEGF therapy causes a dramatic depletion of glucose and an exhaustion of ATP levels in tumors. Moreover, we found that the central metabolic checkpoint LKB1/AMPK-a cellular sensor of ATP levels that supports cell viability in response to energy stress-is activated by anti-VEGF therapy in experimental tumors and it has a key role in induction of sustained tumor regression. These functional links between activation of the LKB1/AMPK by anti-angiogenic therapy and tumor dormancy suggest a role for metabolism in the regulation of this phenomenon.

The host support niche as a control point for tumor dormancy: implications for tumor development and beyond

An increasingly appreciated focus of carcinogenesis research is on mechanisms governing tumor growth after the fact of cancer cell creation. Of particular interest are dynamical interactions between tumor and host cell populations that can themselves strongly impact the fate of established cancer lesions. Regardless of tumor type, all cancers face the common problem of having to breach the barrier of angiogenic competency in order to advance from a microscopic lesion to symptomatic disease. If pre-angiogenic tumor cells are held in dormancy due to cell cycle arrest, this will postpone the need to traverse this higher-level barrier. On the other hand, the barrier itself may prove limiting to a tumor at its diffusion-limited size, creating a population-level dormancy characterized by balanced proliferation and cell death. In both cases of dormancy, the "angiogenic switch" has not yet occurred. We here describe and mathematically quantify an underappreciated third dormancy state defined by an angiogenic balance following the angiogenic switch. In this state we term "post-vascular dormancy," a tumor has attained angiogenic competency, but again demonstrates balanced proliferation and cell death because ambient pro- and anti-angiogenic influences are offsetting. Interestingly, autopsies have shown virtually all of us carry latent tumors in pre- or post-vascular states, many of which lie under the threshold of routine clinical detection. We show how, in the post-vascular case, tumor latency can arise from an elaborate mechanism of self-controlled growth, mediated through the tumor-vascular interaction. Underlying this observation is the finding that a tumor produces both angiogenesis stimulators and inhibitors, with the latter having greater influence, both locally and systemically, as the tumor grows-a mechanism we hypothesize is an aberrant co-option of normal organogenic regulation. That a tumor can limit its own growth raises the prospect that chronic therapies aimed at suppressing this tumor-host dynamic may compare favorably to current strategies which often yield favorable short-term responses but fail to deliver long-term tumor suppression.

Tumor dormancy and cancer stem cells: two sides of the same coin?

Increasing evidence suggests that tumor dormancy represents an important mechanism underlying the observed failure of existing therapeutic modalities to fully eradicate cancers. In addition to its more established role in maintaining minimal residual disease after treatment, dormancy might also critically contribute to early stages of tumor development and the formation of clinically undetectable micrometastatic foci. There are striking parallels between the concept of tumor dormancy and the cancer stem cell (CSC) theory of tumor propagation. For instance, the CSC hypothesis similarly predicts that a subset of self-renewing cancer cells-that is CSCs-is responsible for tumor initiation, bears the preferential ability to survive tumor therapy, and persists long term to ultimately cause delayed cancer recurrence and metastatic progression. Additionally, many of the biological mechanisms involved in controlling the dormant state of a tumor can also govern CSC behavior, including cell cycle modifications, alteration of angiogenic processes, and modulation of antitumor immune responses. In fact, quiescence and immune escape are emerging hallmark features of at least some CSCs, indicating significant overlap between dormant cancer populations and CSCs. Herein, we crucially dissect whether CSCs occupy specific roles in orchestrating the switch between dormancy and exuberant tumor growth. We elucidate how recently uncovered CSC biological features could enable these cells to evade immunologic clearance and regulate cancer expansion, relapse, and progression. We propose that the study of CSC immunobiological pathways holds the promise to critically advance our understanding of the processes mediating tumor dormancy. Ultimately, such research endeavors could unravel novel therapeutic avenues that efficiently target both proliferating and dormant CSCs to minimize the risk of tumor recurrence in cancer patients.

Common polymorphisms in angiogenesis

A wide variety of diseases have a significant genetic component, including major causes of morbidity and mortality in the western world. Many of these diseases are also angiogenesis dependent. In humans, common polymorphisms, although more subtle in effect than rare mutations that cause Mendelian disease, are expected to have greater overall effects on human disease. Thus, common polymorphisms in angiogenesis-regulating genes may affect the response to an angiogenic stimulus and thereby affect susceptibility to or progression of such diseases. Candidate gene studies have identified several associations between angiogenesis gene polymorphisms and disease. Similarly, emerging pharmacogenomic evidence indicates that several angiogenesis-regulating polymorphisms may predict response to therapy. In contrast, genome-wide association studies have identified only a few risk alleles in obvious angiogenesis genes. As in other traits, regulatory polymorphisms appear to dominate the landscape of angiogenic responsiveness. Rodent assays, including the mouse corneal micropocket assay, tumor models, and a macular degeneration model have allowed the identification and comparison of loci that directly affect the trait. Complementarity between human and animal approaches will allow increased understanding of the genetic basis for angiogenesis-dependent disease.

Prospective identification of glioblastoma cells generating dormant tumors

Although dormant tumors are highly prevalent within the human population, the underlying mechanisms are still mostly unknown. We have previously identified the consensus gene expression pattern of dormant tumors. Here, we show that this gene expression signature could be used for the isolation and identification of clones which generate dormant tumors. We established single cell-derived clones from the aggressive tumor-generating U-87 MG human glioblastoma cell line. Based only on the expression pattern of genes which were previously shown to be associated with tumor dormancy, we identified clones which generate dormant tumors. We show that very high expression levels of thrombospondin and high expression levels of angiomotin and insulin-like growth factor binding protein 5 (IGFBP5), together with low levels of endothelial specific marker (ESM) 1 and epithelial growth factor receptor (EGFR) characterize the clone which generates dormant U-87 MG derived glioblastomas. These tumors remained indolent both in subcutaneous and orthotopic intracranial sites, in spite of a high prevalence of proliferating cells. We further show that tumor cells which form U-87 MG derived dormant tumors have an impaired angiogenesis potential both in vitro and in vivo and have a slower invasion capacity. This work demonstrates that fast-growing tumors contain tumor cells that when isolated will form dormant tumors and serves as a proof-of-concept for the use of transcriptome profiles in the identification of such cells. Isolating the tumor cells that form dormant tumors will facilitate understanding of the underlying mechanisms of dormant micro-metastases, late recurrence, and changes in rate of tumor progression.

Consice review: Contribution of cancer stem cells to neovascularization

Cancer stem cells (CSCs), a special subpopulation of tumor cells, are considered as tumor initiating cells. More recently, these cells have also been identified as initiators of tumor neovascularization. A better understanding of the contribution of CSCs to neovascularization should elucidate the mechanisms of cancer initiation and progression as well as establish new concepts for cancer diagnosis and treatment. In this review, we discuss the evidence for the roles of CSCs in tumor vascularization, including production of proangiogenic factors, transdifferentiation into vascular mural cells such as endothelial and smooth muscle-like cells, and formation of nonendothelium-lined vasculogenic mimicry. In addition, the potential therapeutic significance of targeting CSCs is envisaged.

Oncologic Angiogenesis Imaging in the clinic---how and why

The ability to control the growth of new blood vessels would be an extraordinary therapeutic tool for many disease processes. Too often, the promises of discoveries in the basic science arena fail to translate to clinical success. While several anti angiogenic therapeutics are now FDA approved, the envisioned clinical benefits have yet to be seen. The ability to clinically non-invasively image angiogenesis would potentially be used to identify patients who may benefit from anti-angiogenic treatments, prognostication/risk stratification and therapy monitoring. This article reviews the current and future prospects of implementing angiogenesis imaging in the clinic.

Some implications of Scale Relativity theory in avascular stages of growth of solid tumors in the presence of an immune system response

We present a traveling-wave analysis of a reduced mathematical model describing the growth of a solid tumor in the presence of an immune system response in the framework of Scale Relativity theory. Attention is focused upon the attack of tumor cells by tumor-infiltrating cytotoxic lymphocytes (TICLs), in a small multicellular tumor, without necrosis and at some stage prior to (tumor-induced) angiogenesis. For a particular choice of parameters, the underlying system of partial differential equations is able to simulate the well-documented phenomenon of cancer dormancy and propagation of a perturbation in the tumor cell concentration by cnoidal modes, by depicting spatially heterogeneous tumor cell distributions that are characterized by a relatively small total number of tumor cells. This behavior is consistent with several immunomorphological investigations. Moreover, the alteration of certain parameters of the model is enough to induce soliton like modes and soliton packets into the system, which in turn result in tumor invasion in the form of a standard traveling wave. In the same framework of Scale Relativity theory, a very important feature of malignant tumors also results, that even in avascular stages they might propagate and invade healthy tissues, by means of a diffusion on a Newtonian fluid.

Tumor-initiating cells and tumor vascularization

Tumor-initiating cells (TICs) with stem-like cell properties initiate and sustain progressive growth, resulting in a heterogeneous tumor mass. The survival and growth of tumors rely on the development of a vasculature to provide nutrients and oxygen. Crosstalk between TICs and vascularization may be one of the central players in the initiation, long-term maintenance, and progression of tumors. This review surveys current evidence concerning the crosstalk that occurs in tumor/stromal interactions, including genetic change, vascular niche, hypoxia, and dormancy of tumors. A better understanding of this crosstalk might help provide the basis for developing more effective therapeutic drug targets.

Platelet proteome and tumor dormancy: can platelets content serve as predictive biomarkers for exit of tumors from dormancy?

Although tumor dormancy is highly prevalent, the underling mechanisms are still mostly unknown. It is unclear which lesions will progress and become a disseminated cancer, and which will remain dormant and asymptomatic. Yet, an improved ability to predict progression would open the possibility of timely treatment and improvement in outcomes. We have recently described the ability of platelets to selectively uptake angiogenesis regulators very early in tumor growth, and proposed their use as an early marker of malignancy. In this review we will summarize current knowledge about these processes and will discuss the possibility of using platelet content to predict presence of occult tumors.

Phenotype and genotype of pancreatic cancer cell lines

The dismal prognosis of pancreatic adenocarcinoma is due in part to a lack of molecular information regarding disease development. Established cell lines remain a useful tool for investigating these molecular events. Here we present a review of available information on commonly used pancreatic adenocarcinoma cell lines as a resource to help investigators select the cell lines most appropriate for their particular research needs. Information on clinical history; in vitro and in vivo growth characteristics; phenotypic characteristics, such as adhesion, invasion, migration, and tumorigenesis; and genotypic status of commonly altered genes (KRAS, p53, p16, and SMAD4) was evaluated. Identification of both consensus and discrepant information in the literature suggests careful evaluation before selection of cell lines and attention be given to cell line authentication.

Purinergic mechanisms in breast cancer support intravasation, extravasation and angiogenesis

Several advances have recently expanded models of tumor growth and promoted the concept of tumor homeostasis, the hypothesis that primary tumors exert an anti-proliferative effect on both themselves and subclinical secondary metastases. Recent trials indicate that the characterization of tumor growth as uncontrolled is inconsistent with animal models, clinical models, and epidemiological models. There is a growing body of evidence which lends support to an updated concept of tumor growth: tumor homeostasis. In the case of breast cancer, if not all metastasizing tumors, these advances suggest an inconvenient truth. That is, if breast tumor cells metastasize to distant sites early in the tumorigenesis process, then removal of a breast tumor may hasten the development of its metastases. We explore the heretofore unappreciated notion that nucleotides generated by tumor cells following the secretion of an ADP-kinase can promote metastasis and support angiogenesis. Evidence is presented that blockade of the actions of nucleotides in the setting of newly diagnosed breast cancer may provide a useful adjunct to current anti-angiogenesis treatment.

Molecular mechanisms underlying tumor dormancy

Evidence suggests that dormant, microscopic tumors are not only common, but are highly prevalent in otherwise healthy individuals. Due to their small size and non-invasive nature, these dormant tumors remain asymptomatic and, in most cases, undetected. With advances in diagnostic imaging and molecular biology, it is now becoming clear that such neoplasms can remain in an asymptomatic, dormant stage for considerable periods of time without expanding in size. Although a number of processes may play a role in thwarting the expansion of microscopic tumors, one critical mechanism behind tumor dormancy is the ability of the tumor population to induce angiogenesis. Although cancer can arise through multiple pathways, it is assumed that essentially most tumors begin as microscopic, non-angiogenic neoplasms which cannot expand in size until vasculature is established. It is now becoming clear that cancer does not progress through a continuous exponential growth and mass expansion. Clinical cancer is usually manifested only in late, unavoidably symptomatic stages of the disease when tumors are sufficiently large to be readily detected. While dormancy in primary tumors is best defined as the time between the carcinogenic transformation event and the onset of inexorable progressive growth, it can also occur as minimal residual or occult disease from treated tumors or as micro-metastases. The existence of dormant tumors has important implications for the early detection and treatment of cancer. Elucidating the regulatory machinery of these processes will be instrumental in identifying novel early cancer biomarkers and could provide a rationale for the development of dormancy-promoting tumor therapies. Despite the high prevalence of microscopic, dormant tumors in humans and the significant clinical implications of their early detection, this area in cancer research has, to date, been under-investigated. In this mini review observations, models and experimental approaches to study tumor dormancy are summarized. Additionally, analogies and distinctions between the concepts of "tumor dormancy" and that of the "cellular dormancy" of tumor cells, as well as between the "exit from tumor dormancy" and the "onset of the angiogenic switch" are discussed.

Regulation of vascularization by hypoxia-inducible factor 1

Vascularization and vascular remodeling represent critical adaptive responses to tissue hypoxia that are mediated by hypoxia-inducible factor 1 (HIF-1). In patients with peripheral arterial disease, these responses are impaired by aging and diabetes, leading to critical limb ischemia and amputation. Intramuscular injection of an adenovirus encoding a constitutively active form of the HIF-1alpha subunit (CA5) increases the recovery of blood flow following femoral artery ligation in a mouse model of age-dependent critical limb ischemia. Intradermal injection of a plasmid encoding CA5 promotes healing of cutaneous wounds in a mouse model of diabetes. In cancer, vascularization is required for tumors to grow beyond microscopic size, a process that involves HIF-1-dependent production of angiogenic growth factors. Daily treatment of prostate cancer xenograft-bearing mice with low-dose anthracycline (doxorubicin or daunorubicin) chemotherapy inhibits HIF-1 DNA-binding activity, HIF-1-dependent expression of angiogenic growth factors, mobilization of circulating angiogenic cells, and tumor vascularization, thereby arresting tumor growth.

Design and modification of EGF4KDEL 7Mut, a novel bispecific ligand-directed toxin, with decreased immunogenicity and potent anti-mesothelioma activity

BACKGROUND

Potency, immunogenicity, and toxicity are three problems that limit the use of targeted toxins in solid tumour therapy.

METHODS

To address potency, we used genetic engineering to develop a novel bispecific ligand-directed toxin (BLT) called EGF4KDEL, a novel recombinant anti-mesothelioma agent created by linking human epidermal growth factor (EGF) and interleukin-4 (IL-4) to truncated pseudomonas exotoxin (PE38) on the same single-chain molecule. Immunogenicity was reduced by mutating seven immunodominant B-cell epitopes on the PE38 molecule to create a new agent, EGF4KDEL 7Mut.

RESULTS

In vitro, bispecific EGF4KDEL showed superior anti-mesothelioma activity compared with its monospecific counterparts. Toxicity in mice was diminished by having both ligands on the same molecule, allowing administration of a 10-fold greater dose of BLT than a mixture of monomeric IL4KDEL and EGFKDEL. EGF4KDEL 7Mut, retained all of its functional activity and induced about 87% fewer anti-toxin antibodies than mice given the parental, non-mutated form. In vivo, intraperitoneal (IP) injection of the BLT showed significant (P<0.01) and impressive effects against two aggressive, malignant IP mesothelioma models when treatment was begun 14-16 days post tumour innoculation.

CONCLUSION

These data show that EGF4KDEL 7Mut is a promising new anti-mesothelioma agent that was developed to specifically address the obstacles facing clinical utility of targeted toxins.

Tumor dormancy and metastasis

Metastasis--the spread of cancer to distant organs--is responsible for most cancer deaths. Current adjuvant therapy is based on prognostic indicators that stratify patients into defined risk groups. However, some patients believed to have a good prognosis nonetheless develop metastases, in some cases many years after apparently successful treatment of their primary cancer. This period of clinical dormancy leads to many questions about how best to manage patients, including how to better assign risk of late recurrence, how long to monitor patients, and whether some patients will benefit from extended therapy to prevent late recurrences. The development of targeted therapies with fewer side effects is leading to clinical trials aimed at determining the effectiveness of such long-term therapy. However, much remains to be learned about tumor dormancy. Experimental studies are shedding light on biological and molecular mechanisms potentially responsible for tumor dormancy. Emerging research into tumor initiating cells, immunotherapy, and metastasis suppressor genes, may lead to new approaches for targeted antimetastatic therapy to prolong tumor dormancy. An improved understanding of tumor dormancy is needed for better management of patients at risk for late-developing metastases.

New concepts in breast cancer emerge from analyzing clinical data using numerical algorithms

A small international group has recently challenged fundamental concepts in breast cancer. As a guiding principle in therapy, it has long been assumed that breast cancer growth is continuous. However, this group suggests tumor growth commonly includes extended periods of quasi-stable dormancy. Furthermore, surgery to remove the primary tumor often awakens distant dormant micrometastases. Accordingly, over half of all relapses in breast cancer are accelerated in this manner. This paper describes how a numerical algorithm was used to come to these conclusions. Based on these findings, a dormancy preservation therapy is proposed.

Regulation of tumor dormancy as a function of tumor-mediated paracrine regulation of stromal Tsp-1 and VEGF expression

Tumor dormancy is a critical yet poorly understood phenomenon affecting both the diagnosis and treatment of human cancers. This is due in large part to the lack of model systems available to study dormant tumor cells and the length of time needed to adequately examine the models that do exist. It has been demonstrated in several types of human cancer that tumor dormancy is a function of an impairment in angiogenesis. The intracellular signaling pathways regulating the expression of several pro- and anti-angiogenic proteins have been well characterized in human cancer cells. The intercellular signaling that takes place between tumor cells and the surrounding tumor-associated stroma has not been as extensively studied with regard to the regulation of angiogenesis, and as a result dormancy. In this review we define the key players in the regulation of angiogenesis and examine how their expression is regulated in the tumor-associated stroma. The resulting analysis is often seemingly paradoxical, underscoring the complexity of intercellular signaling within tumors and the need to better understand the environmental context underlying these signaling mechanisms.

Tumor dormancy of primary and secondary cancers

Tumor dormancy is a phenomenon whereby cancer cells persist below the threshold of diagnostic detection for months to decades. This condition may arise due to either cell cycle arrest or a dynamic equilibrium state in which cell proliferation is in balance with cells undergoing apoptosis. Tumor dormancy is usually a reference to occult cancer cells that persist for an extended period of time after treatment, but primary cancers can also exhibit extended growth plateaus below the limits of detection. For example, autopsies of individuals who died of trauma reveal that most individuals harbor microscopic primary cancers. Mechanisms that operate independently or successively may restrict tumor expansion throughout tumor progression from incipiency to late-stage cancer. Proposed mechanisms include cell cycle withdrawal, immune surveillance, and blocked angiogenesis. The precise mechanisms underlying dormancy remain to be established, and relevant models will have an important impact on diagnostic and therapeutic strategies for treating cancer. This review summarizes the phenomenon of tumor dormancy, experimental models, and potential mechanisms.

Cellular interactions in the vascular niche: implications in the regulation of tumor dormancy

Angiogenesis plays an established role in the promotion of growth of dormant micrometastasis, because blood vessels deliver oxygen and nutrients to the tumor microenvironment. In addition to this feeding function, however, there is accumulating evidence suggesting that endothelial cells-and perhaps other cellular components of the microenvironment--could communicate both positive and negative signals to tumor cells. This cross-talk between heterogeneous cell types could turn out to be important in the regulation of cancer cell behavior. Normal cells recruited during the angiogenic process, or attracted to future sites of metastasis by soluble products released by cancer cells, have been shown to create a niche favorable to tumor cell proliferation and survival. In addition, following an exogenous angiogenic spike, as may occur during inflammation, the same mechanisms could lead to re-activation of poorly angiogenic tumor cells seeded into tissues. In this review, we discuss the possible implications of this hypothesis for our understanding of the phenomenon of tumor dormancy.

The role of metastasis suppressor genes in metastatic dormancy

Metastasis suppressor genes (MSGs) are defined by their ability to inhibit overt metastasis in a secondary organ without affecting tumor growth at the primary site. Over 20 MSGs have been confirmed in vivo. This class of genes is only unified by their capacity to suppress metastasis, as they encode for proteins with a wide range of biochemical activities that are components of a variety of signaling pathways. In addition, metastasis suppressors impinge upon different stages of the metastatic cascade to manifest their suppressive effects. The MSGs KISS1, KAI1, MKK4/7 and Nm23-H1 promote tumor dormancy at the metastatic site, since tumor cells with induced expression of these MSGs disseminate, but do not form overt metastases in the secondary organ throughout the duration of a metastasis assay. Evidence suggests that KISS1 triggers dormancy in solitary, metastatic tumor cells by causing growth arrest of solitary cells at the secondary site. KAI1 induces growth arrest prior to extravasation by binding a vascular endothelial cell surface marker. MKK4, MKK7 and Nm23-H1 appear to promote dormancy of micrometastatic colonies, after disseminated tumor cells have undergone several rounds of proliferation. Other MSGs may also function in tumor dormancy, but so far their role has not been fully elucidated. Therapeutic approaches that either mimic the effects of MSGs or re-establish MSG expression in metastatic lesions may hold promise for the establishment or maintenance of dormancy.

Hypoxia in microscopic tumors

Tumor hypoxia has been commonly observed in a broad spectrum of primary solid malignancies. Hypoxia is associated with tumor progression, increased aggressiveness, enhanced metastatic potential and poor prognosis. Hypoxic tumor cells are resistant to radiotherapy and some forms of chemotherapy. Using an animal model, we recently showed that microscopic tumors less than 1mm diameter were severely hypoxic. In this review, models and techniques for the study of hypoxia in microscopic tumors are discussed.

COL18A1 is highly expressed during human adipocyte differentiation and the SNP c.1136C > T in its "frizzled" motif is associated with obesity in diabetes type 2 patients

Collagen XVIII can generate two fragments, NC11-728 containing a frizzled motif which possibly acts in Wnt signaling and Endostatin, which is cleaved from the NC1 and is a potent inhibitor of angiogenesis. Collagen XVIII and Wnt signaling have recently been associated with adipogenic differentiation and obesity in some animal models, but not in humans. In the present report, we have shown that COL18A1 expression increases during human adipogenic differentiation. We also tested if polymorphisms in the Frizzled (c.1136C>T; Thr379Met) and Endostatin (c.4349G>A; Asp1437Asn) regions contribute towards susceptibility to obesity in patients with type 2 diabetes (113 obese, BMI =30; 232 non-obese, BMI < 30) of European ancestry. No evidence of association was observed between the allele c.4349G>A and obesity, but we observed a significantly higher frequency of homozygotes c.1136TT in obese (19.5%) than in non-obese individuals (10.9%) [P = 0.02; OR = 2.0 (95%CI: 1.07-3.73)], suggesting that the allele c.1136T is associated to obesity in a recessive model. This genotype, after controlling for cholesterol, LDL cholesterol, and triglycerides, was independently associated with obesity (P = 0.048), and increases the chance of obesity in 2.8 times. Therefore, our data suggest the involvement of collagen XVIII in human adipogenesis and susceptibility to obesity.

Possible prognostic role of IL-17R in osteosarcoma

PURPOSE

An intense vascularization of primary tumor mass is associated with a fatal outcome in various types of invasive solid tumors. Interleukin 17 (IL-17), a CD4+ T-cell-derived cytokine, stimulates some tumor cells to secrete angiogenic factors, among which venous endothelial growth factor (VEGF). We assessed whether the expression of IL-17 receptor (IL-17R) represents a marker for the metastasizing ability of osteosarcoma (OS), a very malignant bone tumor.

METHODS

We immunoassayed the amount of VEGF secreted by three OS cell lines expressing IL-17R in differing amounts: HOS, MG63 and U-2 OS, and their sensitivity to IL-17 stimulation to secrete VEGF.

RESULTS

U-2 OS, which best expresses IL-17R, secreted the highest amounts of VEGF and was the most sensitive to IL-17, whereas MG63 expressed the lowest level of IL-17R, secreted the lowest amount of VEGF and was not sensitive to IL-17. IL-17R expression correlated with VEGF secretion and IL-17 sensitivity. U-2 OS expressed the most dedifferentiated phenotype, which is associated with tumor malignancy.

CONCLUSIONS

These results suggest that IL-17R in OS might represent a marker of tumor metastasis potential.

A controversial tumor marker: is SM22 a proper biomarker for gastric cancer cells?

SM22, a dominant protein in smooth muscle cells (SMCs), has been widely reported to be abnormally expressed in many solid tumors. However, the expression patterns of SM22 are not consistent in all tumors, not even in the same ones. Whether SM22 should be considered a tumor biomarker is still debated in different laboratories. Herein, we have carried out a systematical investigation to validate SM22 expression in the primary tissues of gastric cancer (GC). Of eight cases, seven samples were found in the elevated expression of SM22 proteins through proteomic analysis. The observation was further verified by the approaches of Western blotting and quantitative RT-PCR. Surprisingly, the results achieved from tissue microarray in 126 GC cases appeared contrary to the proteomic conclusion, in which the highly expressed SM22 was mainly found in smooth muscle layers, blood vessels, and myofibroblasts. This suggested that the increased abundance of SM22 in the cancerous regions was not caused by the presence of the GC cells. Furthermore, the expression of SM22 was measured in different GC cell lines and SMCs with Western blotting and quantitative RT-PCR. The results revealed that SM22 expression in SMCs was dramatically higher than that of the GC cells, which indicates that SM22 is unlikely to be a proper biomarker for GC. Instead, it can be considered a potential indicator for the abnormal developments of smooth muscles, blood vessels, or myofibroblasts triggered by tumorigenesis.