Abstracts of Presentations and Posters
Paloma Bragado, Ph.D.
Mount Sinai School of Medicine, New York, New York, U.S.A.
Regulation of disseminated tumor cells dormancy by p38, BHLHB3 and p53 signaling.
Metastases develop from disseminated tumor cells (DTCs) years or even decades after primary tumor treatment. This is thought to be due to the ability of residual DTCs to remain dormant, but the mechanisms controlling this state are poorly understood. We studied the mechanisms of tumor cell dormancy using the HEp3 HNSCC model. When injected in nude mice, HEp3-GFP cells form tumors with 100% efficiency and spontaneously disseminate to lungs (95% incidence) and bone marrow (BM) (30% incidence). Tracking of GFP-tagged DTCs showed that after ~2 weeks the quiescent DTCs in lungs start to grow to form overt metastasis in 95% of mice. In contrast, those in the BM remain at constant numbers suggesting a dormant phenotype. We published that prolonged in vitro culture (>40 generations) of tumorigenic HEp3 (T-HEp3) cells induced a reprogramming into a dormant phenotype (D-HEp3). This behavior is revealed upon reinoculation of D-HEp3 cells in mice or chick embryo CAMs. The loss of malignancy is in part due to the activation of p38α that antagonizes ERK activation. This high p38α/β activity can be induced by microenvironmental cues because systemic inhibition of p38α/β accelerated lung metastasis and surprisingly allowed the detection of DTCs, micro- and macro-metastasis at distant sites where they never grow (liver, spleen and spinal fluid). This suggests that dormant occult DTCs can be activated to proliferate by p38α/β. Analysis of the expression profiles regulated by p38 in dormant HEp-3 cells showed that the transcription factors p53 and BHLHB3/Dec2 (a metastasis suppressor) are transcriptionally induced by p38α/β and required for the induction of HEp3 cells quiescence in vivo. We also found that TGFβ2 was upregulated by p38 in D-HEp3 cells. Overexpression of Dec2 in T-HEp3 cells inhibits proliferation and this correlated with upregulation of p53 protein and activity. This led to induction of p21 in vivo. RNAi-mediated downregulation of Dec2 in dormant HEp3 cells reduced p53 expression and activity. TGFb2 signaling was also found to regulate p38 activation, Dec2 expression and dormancy of D-HEp3 cells. To test if the mechanisms identified in D-Hep3 cells might be recapitulated by microenvironment induced dormancy we established cell lines from GFP-T-HEp3 DTCs isolated from BM (BM-HEp3) and lungs (Lu-HEp3). Lu-HEp3 cells displayed a high ERK/p38 signaling ratio and are tumorigenic in vivo. Meanwhile in vitro expanded BM-HEp3-derived cell lines remain dormant when inoculated in vivo and are characterized by a low ERK/p38 activity ratio and by increased Dec2 and p53 expression compared to primary tumor or lung derived HEp3 cells. BM-HEp3 cell dormancy was also functionally linked to TGFb signaling. We conclude that reprogramming of DTCs into dormancy in growth restrictive microenvironments might induce a gene network activated by stress signaling mediated at least by p38α/β signaling.
Colette Calmelet, Ph.D.
California State University, Chico, California, U.S.A.
A temporal mathematical model and cancer stem cells influence in tumor dormancy.
Due to their characteristics of self-renewal and quiescence, cancer stem cells are believed to play an important role in tumor dormancy and cancer recurrence. A temporal mathematical model of eight compartments at the normal and cancer cell levels is considered. Initially, a baseline normal stem cell model is proposed featuring populations of different cell categories, their proliferation, serial differentiation or apoptosis, and exhibiting a low stem cell compartment. A feedback from differentiated cells to normal progenitor cells is assumed. Two controlled oncogenic mutation events are also introduced. As an empirical test, the tumor grading and progression, typically collected in the pathologic lab, is used to correlate the outcomes of the model with the tumor development stages. In addition, the model is able to quantitatively account for the temporal development of the population of observed cell types. Several therapeutic treatment models are investigated in a search for an optimal low dose. The model provides a number of experimentally testable predictions.
Eungchun Cho, Ph.D.
Kentucky State University, Frankfort, Kentucky, U.S.A.
Frequent sets and pattern recognition.
Given a set X and a set C of subsets of X, frequent sets are subsets of X that are covered by many sets in C. Interest in frequent sets occurs in many application settings such as pattern recognition, statistics, surveillance, sensor network, and data mining. Characterization of k-frequent sets and equivalence class decomposition of X that makes identifying frequent sets efficient are given. An algorithm of finding frequent sets and its implementation in MATLAB code is given.
Institute of Life Science, Tzu-Chi University, Hualien, Taiwan, R.O.C.
Ursolic acid and oleanolic acid inhibit angiogenesis and metastasis in HepG2 cells through the PI3K/AKT/ERK pathways.
Introduction: Hepatocellular carcinoma (HCC) is one of the most malignant tumors with high rate of recurrence and metastasis. Angiogenesis is a very important process that mediates tumor growth and metastasis and can be used as a therapeutic target among all the strategies for many cancers. Ursolic acid (UA) and its derivative oleanolic acid (OA), are two glycyrrhetinic acid related pentacyclic triterpenoids that showed different effects on anti-tumor in HepG2 cells in our previous studies. The aim of this study is to further investigate whether UA and OA have the inhibitory effect on angiogenesis and metastasis in HepG2 cells.
Methods: Inhibitory effect of UA and OA on adhesion of HepG2 cells was detected by MTT assay. The anti-angiogenic and anti-metastatic effect of UA and OA was examined through in vitro analysis including wound-healing, transwell and capillary-like tube formation assay. Chicken chorioallantoic membrane (CAM) model and mice matrigel plug model were employed to investigate the negative biological effect of UA and OA on HepG2 cells in vivo. Western blot was used to detect the expression of angiogenesis-associated proteins.
Results: Our investigations showed that UA and OA inhibited angiogenesis and metastasis in a dose-dependent manner directly through phosphatidylinositol 3-kinase (PI3K)/protein kinase B (AKT/PKB) and extracellular signal-regulated kinase (ERK)-mediated pathways that are important signal molecules among all the pathways associated with cells angiogenesis and metastasis.
Discussion: This study revealed that both UA and OA, in addition to their anti-tumor effects, can suppress tumor growth through inhibition of tumor angiogenesis in vitro and in vivo via targeting PI3K/AKT and ERK signaling pathways. Both UA and OA have the potential to be used as a therapeutic strategy for liver cancer in the future.
Sofie Claerhout, Ph.D.
The University of Texas MD Anderson Cancer Center, Houston, Texas, U.S.A.
Mechanisms underlying delayed recurrence of ER positive breast cancer: a critical step in the development of effective biomarkers and therapies.
ER positive (ER+) breast cancer has an unfortunate propensity to recur after decades of remission. The long-term outcome for these patients is remarkable worse than for patients with non-ER tumors. The late relapse is most likely due to tumor dormancy with recurrence occurring when tumor cells exit the quiescent state and re-enter the cell cycle. An understanding of the mechanisms underlying the entry, maintenance and exit from dormancy could potentially provide both biomarkers and therapeutic targets.
We specifically aim to determine the role of autophagy in dormancy and therapy resistance, and whether genomic and mutational events are selected during dormancy. Therefore, we use different model systems to induce dormancy in a set of highly characterized breast cancer cell lines. To identify molecular markers and particular genomic aberrations related to dormancy, we aim to extensively assess human tumors with delayed recurrence with their matched primary tumors.
Preliminary results with several ER+ and ER- breast cancer cell lines show that ER+ cell lines have a greater propensity to enter dormancy and survive for prolonged periods compared to the ER- cells that die shortly after induction of dormancy. Moreover, we also found that autophagy is induced in ER+ cells which may indicate this process plays a role during the dormant state. In contrast to ER- cells that could not be recovered, we could "reawaken" ER+ breast cancer cells by transferring them to proliferative conditions. Thus ER+ breast cancer cells are able to enter into and exit from dormancy.
Silvia Cortelli, Ph.D.
Polyclinic Tor Vergata University, Rome, Italy
MicroRNAs silenced by DNA methylation in prostate cancer.
Background: Epigenetics refers to heritable changes in gene expression not involving the DNA sequence. Part of the epigenome involvse the methylation of cytosine in regions concetrated with CpG dinucleotides termed "CpG islands". The ilands situate at promoter regions and their methylation silenced a gene's transcription. In cancer aberrant promoter methylation has begun to explain the deregulated expression of small, endogenous RNAs called microRNA. MicroRNAs inhibit mRNA translation to fine tune gene network. In prostate cancer, the downregulation of microRNAs may contribute to cancer initiation and development, and the cause may be promoter hypermethylation.
Here, we attempt to decipher tumor-suppressor microRNAs whose expression is diminished or silenced by CpG islands hypermethylation in prostate cancer to discover novel biomarkers and ideas for therapy.
Methods: To unmask potentially silenced microRNAs, the prostate carcinoma cell lines PC3, DU145 and LNCaP were treated with the demethylating agent 5-aza-2'-deoxycytidine. For each cell line, the expression profiles of 650 microRNAs were analyzed by rel-time quantitative PCR bifore and after tretment. With methylation specific PCR, those microRNAs upregulated by ≥ 2 fold and having CpG islands within 10Kb upstream of their 5'end will be analyzed for CpG islands methylation in cell lines.
The status of positive microRNAs will be evaluated in prostate carcinoma tissues and compared to benign prostate hyperplasia.
Results: In the prostate carcinoma cell lines (PC3, DU145, LNCaP), 15 microRNAs had incresed expression bifore and after tretment by ≥ 2 fold compared to control (PREC), as well as a CpG island. Based on precious studies in other cancers, we expect cancer-specific methylation of two to eight microRNAs in tissues. We also anticipate certain microRNAs will show methylation in both cancer and control specimens.
Future Directions: We welcome expanding the aims of this work or partecipating in follow-up projects to include, for example, advanced cell biology investigations such as transfections with silenced tumor-suppressor miRNAs.
Jayanta Debnath, M.D.
University of California, San Francisco, California, U.S.A.
Autophagy and cell survival during quiescence: Implications for tumor cell dormancy in gastrointestinal stromal tumor (GIST) and breast cancer.
Autophagy is a tightly regulated catabolic process in which a cell digests its own cytosolic contents under various forms of duress. Due to its conserved role in promoting cell survival and fitness in response to diverse stresses, interest in manipulating autophagy to treat human cancers has rapidly intensified. Remarkably, in C. elegans, autophagy is essential for survival during dauer diapause, a stress-induced, dormancy-like state that occurs when larvae are exposed to hostile environments. Nonetheless, most studies of autophagy in cancer treatment have concentrated on modulating self-eating in rapidly proliferating cancerous cells and tissues. In contrast, the precise contributions of autophagy to tumor cell dormancy remain unclear.
Recently, in a sarcoma called Gastrointestinal Stromal Tumor (GIST), we demonstrated that autophagy serves as an essential survival pathway in dormant tumor cells. Although gastrointestinal stromal tumors (GIST) harboring activating KIT mutations respond to treatment with targeted inhibitors such as imatinib mesylate (Gleevac), these agents are rarely cytotoxic. Rather, a sizeable tumor cell population survives and remains dormant for years (termed stable disease), eventually resulting in acquired resistance and treatment failure. We discovered that imatinib induces autophagy as a survival pathway in quiescent GIST cells. Inhibiting autophagy, using RNAi-mediated silencing of autophagy regulators (ATGs) or anti-malarial lysosomotrophic agents promoted the apoptosis of quiescent GISTs cells in vitro and prevented the establishment of imatinib-induced dormancy and stable disease in vivo.
Jeffrey E. Green, M.D.
Laboratory of Cancer Biology and Genetics, National Cancer Institute, Bethesda, Maryland, U.S.A.
No title or abstract available.
Institute of Medical Sciences, Tzu-Chi University, Hualien, Taiwan, R.O.C.
Enhanced anticancer effect of cisplatin combined with triptolide causes apotosis in human gastric cancer cells.
Gastric carcinoma is one of the most frequent cancer and considered as the second leading cause of cancer-related death in the world. Cisplatin (CDDP)-based chemotherapy has been long-term used for treatment of gastric cancers, although a significant toxicity and poor prognosis of patients with innate or acquired resistance to chemotherapy limit the therapeutic efficacy. To improve that, it is important to search for other possible targets by enhancing specific cell-killing mechanisms in gastric cancer cells. Triptolide is a diterpenoid triepoxide derived from the herb tripterygium wilfordii, which has been used as a traditional medicine for immuno-deficient diseases in China. Although it was considered to be effective in the treatment of inflammatory or autoimmune disorders by the inhibition of cytokine production, triptolide has also been reported to have anti-tumor effects in vitro and in vivo. However, the systemic cytotoxicity is one of the reasons that limits its development alone. In this study, we want to evaluate whether a lower dose of triptolide that with negligent damages on normal cells can enhance the sensitivity of human gastric cancer cells to chemotherapeutic drugs. We used SC-M1 cells to evaluate the cytotoxicity induced by triptolide and cisplatin. Our data indicate that triptolide used at a dose of 5 ng/mL alone does not induce obvious cytotoxicity, but synergizes the apoptosis induced by cisplatin on SC-M1 cells, thereby confirming the potential interest of such a synergy in further development of cancer therapy.
University of California, Irvine, Irvine, California, U.S.A.
Lattice gas cellular automata modeling of lineage dynamics and feedback control.
This study is important in understanding the mechanism and dynamics of some biological problems such as tumor invasion and wound healing. Firstly, we describe microscopically the model and we derive the corresponding mesoscopic approximation, via the mean field assumption. In the following, we upscale our model providing a PDE which serves as a macroscopic manifestation of the underlying cellular interactions. We focus on investigating the speed and the structure of the invasion front, using the above mentioned approximations, as functions of the underling cell phenotypes and microenvironmental factors (i.e. nutrients).
David H. Nguyen
New York University (NYU) School of Medicine, New York, New York, U.S.A.
Low dose radiation induces an inflammatory program, including infiltration by Cd11b+/Mmp9+ macrophages, in the mouse mammary gland.
Background and Objectives: Though ionizing radiation (IR) is a well studied breast carcinogen, most studies focus on DNA damage as the driver of cancer. I ncreasing evidence, however, suggests that IR can dramatically promote cancer by altering the microenvironment via non-mutagenic means. Using the radiation chimera model in which we remove endogenous mammary epithelia, irradiate the mouse, and then orthotopically transplant a syngeneic epithelial source, we can study the carcinogenic properties of IR specifically via the host. Previous work showed that host-irradiation is sufficient to promote tumorigenesis of un-irradiated mammary epithelial cells (Barcellos-Hoff and Ravani, Cancer Research, 2000). Subsequent unpublished studies transplanting Trp53 (p53) null mammary fragments recapitulated this effect. p53 null tumors of the BALB/c strain exhibit characteristics common to human breast cancer, including long latency, variable estrogen receptor-α (ER) status, and multiple tumor types. Host-irradiation (10-100 cGy) increased tumor frequency and growth rate, while decreasing latency and the frequency of ER+ tumors. Microarray analysis of differences between tumors arising in irradiated hosts and controls implicated inflammation as a potential mechanism of a non-mutagenic mode of tumor promotion by radiation (Nguyen et al. In preparation). Here we report that gene expression programs characteristic of multiple inflammatory processes are enriched by radiation in the intact mouse mammary gland. Consistent with this, we found that Cd11b+/Mmp9+ macrophages, which are associated with tumorigenesis in other models, are increased around mammary ducts three months after irradiation.
Methods: 8 week-old (wk) BALB/c mice were irradiated with 10 cGy, and inguinal mammary glands were collected between 1 and 12 weeks post-irradiation. Total RNA was extracted and underwent microarray analysis, RMA normalization, and then a pattern matching algorithm (Pavlidis Template Matching (PTM), p=0.05) to detect genes regulated at specific time points above 1.25-fold (many were induced > 1.5 fold). The ConceptGen database was used for enrichment analysis of these lists with gene profiles from known biological processes. Dual staining for Cd11b+ and Mmp9+ macrophages were quantified using immunofluorescence in paraffin-embedded sections of glands from this time course. Macrophage index was determined by counting the number of double-positive cells localized within 250 μm of ducts.
Results: PTM and ConceptGen analyses of genes induced by radiation at either 1-wk, 4-wks, or both, suggested that T-cells, B-cells, and dendritic cells, were highly activated at 1-wk but subsided by 4-wks, while macrophage programs were induced at 1- and persisted to 4-wks post-irradiation. Radiation increased Cd11b+/Mmp9+ macrophages 2.6-fold (p<0.004, Fisher Test) at 12 weeks after irradiation.
Conclusions and Impact: The observed inflammatory gene expression at 4-wks and Cd11b+/Mmp9+ macrophage infiltration at 12-wks suggest that active inflammation is persistent long after radiation exposure. Given the prior reports that Cd11b+/Mmp9+ macrophages are pro-tumorigenic, our data suggest that they may be a host derived, IR-induced mechanism of the tumor promotion, implicating them as potential therapeutic targets for breast cancer prevention after radiation exposure.
Monika Joanna Piotrowska, Ph.D.
University of Warsaw, Faculty of Mathematics, Informatics and Mechanics, Institute of Applied Mathematics, Warsaw, Poland
Estimation of irradiation induced cell cycle delays by numerical simulation.
Whilst the experimental literature hints at the mechanism by which irradiation simultaneously delays proliferation and leads to cell lysis, much of the detail is presently unobservable. However, to build effective models that contribute to clinical advances the cell phase delay mechanism must be estimated. By building on our previous quasi-2D scaled CA model of EMT6/Ro MCS tumor growth and utilising results from several key in vitro and in vivo irradiation studies, we develop, calibrate and demonstrate a model of cell damage and repair in response to irradiation. Unlike previous computational studies of irradiation, our calibrated model shows close adherence to dynamic bulk-, cell phase-, necrotic- and metabolic-, tumor characteristics. We thus provide estimates of the cell phase delay -- fractional dose response function and provide estimates of various tumor characteristics previously unreported in the literature.
University of Warsaw, Institute of Applied Mathematics, Warsaw, Poland
Optimal and suboptimal treatment protocols for anti-angiogenic therapy.
In 1971 Judah Folkman discovered that growth of any tumour is strongly dependent on the amount of blood vessels that it induces to grow. He surmised that, if a tumour could be stopped from growing its own blood supply, it would wither and die. Anti-angiogenic therapy is a novel treatment approach that aims at preventing a tumour from developing its own blood supply system. On the basis of the biologically validated model proposed by Hahnfeldt, Panigrahy, Folkman and Hlatky in 1999, with the usage of the optimal control theory, some protocols of anti-angiogenic treatment were proposed. However, in our opinion the formulation of that model is valid only for the anti-vascular treatment, that is treatment that is focused on destroying endothelial cells. Therefore, we propose a modification of the original model which is valid in the case of treatment which is focused on blocking angiogenic signaling.
We propose also a new mathematical description of the anti-angiogenic treatment goal. In current studies it is assumed that the main goal of anti-angiogenic treatment is to minimize the tumor volume at the end of treatment. On the other hand, chemotherapy is still the main kind of cancer treatment, while anti-angiogenic treatment is only a supplement. The efficient treatment with chemotherapy is possible only when the drug can be distributed evenly, that is when vessels penetrate most of the tumour regions. Therefore, we assume that the main goal of anti-angiogenic treatment, despite the minimization of the tumour volume, is to maintain high ratio of vessels volume that support the tumour to the actual tumour volume. We analyze it as an optimal control problem and a solution of the problem is given in some cases.
Roberta Sarmiento, M.D.
San Filippo Neri Hospital, Rome, Italy
Predictive value of molecular markers expression in locally advanced rectal cancer (LARC) treated with neoadjuvant bevacizumab (BEV) and capecitabine (CAPE) + standard radiotherapy (RT).
Purpose: The aim of the study was to determine the value of a panel of molecular markers as predictors of complete pathologic tumor regression (pCR) or residual tumor area (RTA) in patients treated with preoperative chemo-RT (pre-CRT) and antiangiogenic therapy for LARC.
Methods: Microvascular density (VD; CD31, CD34), CD68, M30, VEGFR2, thymidine phosphorylase, thymidine synthase and Ki67 were evaluated by immunohistochemistry. Pre- and post-treatment (pre-t; post-t) tumor samples were obtained from 27/43 patients (pts) treated with pelvic RT (50.4Gy) plus concurrent CAPE (825mg/mq bid concurrently with RT) and BEV (5mg/Kg every 2 wks for 4 courses, the first administration 2 wks before pre-CRT). Pathological assessment was performed by central review blinded of clinicopathologic data. Residual tumor was assessed based on the RTA and fibrosis. Tumor necrosis area (TNA) was evaluated as necrosis area/necrosis area + fibrosis area.
Results: A pCR was observed in 6 pts (13.9%); 12 pts (27.9%) had only focal RTA (≤10%). Pre-t level of CD34+ VD was associated to treatment response. Patients with RTA ≤15% showed higher CD34+ VD than those with larger RTA (>15%) (p=0.037), suggesting that tumors highly vascularized respond better to treatment. Also the CD31 ratio (pre/post-treatment) was significantly predictive of residual disease <15% (p=0.017). In addition, the association between post-t levels of each marker and RTA or TNA was examined. A significant correlation between post-t-Ki67 labeling index (LI) and RTA was observed (p<0.0001), suggesting that residual cancer cells may have a high proliferating phenotype. Post-t-Ki67 LI also correlated with TNA (p=0.009). Also a significant correlation between post-t levels of VEGFR2 expression in cancer cells and RTA (p=0.007) was found.
Conclusion: These results suggest that pre-t level of CD34+ VD is predictive of response of pre-CRT including BEV and that post-t VEGFR2 and Ki67 index correlate to TNA and RTA, respectively. However, further prospective correlative studies with larger series of pts are needed to confirm the predictive value of the evaluated markers.
Maria Soledad Sosa, Ph.D.
Mount Sinai School of Medicine, New York, New York, U.S.A.
The orphan nuclear receptor NR2F1/COUP-TF1 mediates growth arrest of dormant cells by inducing Sox9, Hes-1 and cell cycle inhibitors.
The mechanisms by which single disseminated tumor cells (DTCs) found in secondary organs like bone marrow undergo dormancy remain unknown. Further, whether specific target organ microenvironment signals can induce DTC dormancy is also unclear. Here we show that retinoic acid (RA) signaling together with TGF-β2 action induce a dormant phenotype in aggressive human squamous carcinoma cell line (HEp3). Expression profiling and transcription factor (TF) network analysis of in vivo dormant cells (D-HEp3) vs. proliferating parental HEp3 tumor cells or those that escape dormancy, identified the orphan nuclear receptor NR2F1 as a TF node induced in quiescent tumor cells and regulated by RA and TGFβ2. NR2F1 is epigenetically silenced in proliferating tumor cells and in agreement with a growth suppressive function, NR2F1 was downregulated in human HNSCC and breast tumor samples as well as in MMTV-Neu and -myc primary tumors from transgenic mice. NR2F1 re-expression via cDNA overexpression resulted in tumor growth arrest in vivo. On the other hand silencing of NR2F1 by siRNA techniques induced tumor growth of dormant HEp3 cells. Importantly, we found that NR2F1 expression was induced in dormant HEp3 cells derived from bone marrow DTCs, where these tumor cells persist at low numbers. In contrast, NR2F1 expression was low in proliferative tumor cells derived from lung DTCs, where metastasis always develop, or from matched primary tumors. Mechanism analysis revealed that NR2F1 induces quiescence through the modulation of Sox9, Hes-1 (notch-activated TF), p27, p16 and pRB. We also show that all-trans RA treatment can mimic dormancy induction by inducing NR2F1 and p21 expression while reducing the levels of ERK1/2 phosphorylation and overall Ki67 staining. Our data identifies microenvironmental cues and a mechanism dependent on the NR2F1 pathway that induces tumor cell dormancy. This may lead to the development of dormancy-inducing/maintaining therapies for residual disease.
Gabriel Limaverde Soares Costa Sousa, Ph.D.
Brazilian National Cancer Institute - INCA, Rio de Janeiro, Brazil
Structural analysis of the N-terminal fragment of the antiangiogenic protein endostatin: A molecular dynamics study.
Endostatin is a potent antiangiogenic protein derived from the non-collagenous domain 1 (NC1) of collagen XVIII. The mechanism by which endostatin exerts its antiangiogenic effect is still incompletely understood. It has been shown that the 27 amino acid N-terminal fragment of murine endostatin has antitumor, antimigration and antipermeability activities comparable to the full soluble protein. In order to understand how this peptide can exert such elaborate function, we performed structural analysis using molecular dynamics to evaluate the behavior of this fragment in aqueous environment. Here we show that the N-terminal peptide of murine endostatin is able to assume a well-defined structure, folding into a zinc-dependent beta-hairpin conformation. Analyzing the folding mechanism, we were able to understand why the N-terminal peptide of human endostatin with the same length failed to acquire a stable conformation. Conversely, we were able to predict the successful folding of the R4Q mutant and of a shorter form of the human peptide with 25 residues. Finally, we show that the beta-hairpin conformation assumed by the zinc-bound peptide of murine endostatin has a high structural similarity with fragments of another family of angiogenesis inhibitors: the integrin-binding portion of the NC1 domain of collagen IV.
Poonam Vohra, M.D.
Govt. of India-Postgraduate Institute of Medical Education and Research (PGIMER), Dr. Ram Manohar Lohia Hospital, New Delhi, India
MR imaging -- A vital tool in tumor angiogenesis.
Tumor progression, as such, depends on sequential events- the most one contributed to a switch to the angiogenic phenotype i.e., initial recruitment of blood vessels. Failure of a microscopic tumor to complete one or more early steps in this process may lead to delayed clinical manifestation of cancer. Microscopic human cancers can remain in an asymptomatic, nondetectable and occult state for the life of a person. Tumor dormancy is basically a phenomenon observed in patients who have been treated for primary cancer and relapsed after a long disease-free period. Clinical and experimental evidence suggest that the malignant cells, shed from the primary mass, are able to remain viable for long periods of time as microscopic lesions, to express their tumorigenic potential at a later date as a consequence of a shift in the balance between host and tumor. It is well established that tumor growth beyond the size of 1-2mms is angiogenesis-dependent and failure to induce an angiogenic response has been proposed as one of the mechanisms that may be responsible for the dormant state. There is evidence of reduced blood vessel density in dormant metastases. It is proposed that there is dynamic remodelling of the vascular bed which precedes the exit of tumor from dormancy. The hypoxic regulation of vascular endothelial growth factor (VEGF), platelet derived growth factor (PDGF), fibroblast growth factor (FGF) and various other interleukins are essential survival factors for newly formed blood vessels. Vascular maturation, manifested by physiological vasodilatory response to carbon dioxide, may be important for conferring vascular stability and exit from dormancy. Though High frequency Doppler Ultrasound, PET-CT have been widely used to study Angiogenesis in Tumors, MR Imaging is still the gold standard modality for imaging Angiogenesis. Vascular remodelling can be followed using 3T/higher instrumentation where vessel density can be determined by the intrinsic contrast provided by paramagnetic deoxyhaemoglobin in vessels which shortens T2 relaxation time and thus reduces the signal intensity. Gradient echo images, if, taken, reflect the changes in response to hypercapnia (95% air, 5% carbon dioxide) or hyperoxia (95% oxygen, 5% carbon dioxide), help in physiological assessment of vascular functionality and maturation. Several MRI techniques have been developed for imaging Angiogenesis, which are broadly divided into two categories:
1/ Those that use extrinsic contrast agents like dynamic contrast enhanced (DCE)MRI.
2/ Those that do not use contrast agents such as Arterial spin labelling (ASL).
DCE-MRI is the most common method used to evaluate angiogenesis in clinical trials. In T1-weighted DCE-MRI, a gadolinium-based contrast is administered intravenously, which enters tumor arterioles, passes through capillary beds and then drains via tumor veins. Gadolinium ions interact with nearby hydrogen nuclei to shorten T1 relaxation times in local tissue water, which causes an increase in signal intensity on T1-weighted images to a variable extent within each voxel. ASL is a noninvasive imaging technique for measuring blood flow, predominantly used in studies of cerebral physiology and disease. Protons in tissue water can be magnetically labeled using radiofrequency pulses. This enables measurement of blood flow by detecting the difference between control and ‘labeled’ images, without the need for administration of exogenous contrast media. Hence, MR Imaging has proved to play a pivotal role in evaluating Angiogenetic switch in Tumor dormancy.
Kathleen Wilkie, Ph.D.
Center of Cancer Systems Biology, Steward St. Elizabeth's Medical Center, Tufts University School of Medicine, Boston, Massachusetts, U.S.A.
Modeling immunomodulation of tumor growth.
The physical presence and activities of cancer cells elicit an immune response in the host. In turn, this immune response has been shown to be both stimulatory and inhibitory to tumor growth. This interplay therefore has complex implications for tumor development. To explore these, we have developed a system of differential equations to investigate the role of the immune response in tumor growth. The two-compartment model consists of both cancer and immune cells: the cancer cells proliferate on their own and their growth can either be inhibited or stimulated by immune cells in a manner dependent on the states of each, while the immune cells are recruited to the tumor site by either the cancer cells or by the interaction of the cancer cells with the immune cells. Cancer cells, innate immune cells (such as platelets, dendritic cells, macrophages, and natural killer cells) and adaptive immune cells (such as T and B lymphocytes) communicate with each other through cytokine and chemokine production which controls and shapes tumor growth. The cumulative result of the interactions of these diverse cells determines whether tumor-promoting inflammation or antitumor immunity occurs, and it is this wholistic response that we attempt to capture in our model. Most mathematical models of the immune response to cancer focus on single immune cells and their specific function in cancer cell killing. One of the main advantages of this model is that it combines the effects of all immune cell types and the physical process of inflammation into one quantitative model setting. Thus, it is better positioned to predict immunomodulation of tumor growth, and to assist in the design of novel treatment approaches that exploit immune response to improve tumor suppression.
Xiaoming Zheng, Ph.D.
Central Michigan University, Mount Pleasant, Michigan, U.S.A.
A mathematical model of angiogenesis: Initiation, extension, and maturation of new blood vessels modulated by VEFG, angiopoietins, PDGF-B and pericytes.
This work presents a mathematical model for three consecutive events in angiogenesis: initiation, sprout extension, and vessel maturation. We carefully examine the regulating mechanisms of vascular endothelial growth factor (VEGF) and angiopoietins (Ang1 and Ang2) on the proliferation, migration and maturation of endothelial cells through their endothelium-specific receptor tyrosine kinase VEGFR2 and Tie2, respectively. We also consider the effect of platelet-derived growth factor-B (PDGF-B) on the proliferation and migration of pericytes. This multiscale model integrates events across molecular, cellular, and tissue levels. At the molecular level, we model the binding kinetics of VEGF/VEGFR-2, Ang1/Tie2, and Ang2/Tie2. At the cellular level, we consider the variations of maturity and mass densities of ECs and pericytes. At the tissue level, we study the diffusion of all growth factors. A novel multiscale model integrating molecular reactions on blood vessels and tissue-level diffusion is presented. For the capillary extension, we develop a new continuous, visco-elastic model to couple the tip protrusion, endothelium elasticity, and stalk cell proliferation. Our model reproduces corneal angiogenesis experiments and several anti-angiogenesis therapy results, and demonstrates that (1) the competition between Ang1 and Ang2 is the angiogenic switch; (2) maturation process modulated by pericytes and angiopoietins is crucial to vessel normalization.