Oncogenes and tumor angiogenesis

Targeted modulation of gut and intra-tumor microbiota to improve the quality of immune checkpoint inhibitor responses

Immune checkpoint inhibitor (ICI) therapies, such as those blocking the interaction of PD-1 with its ligands, can restore the immune-killing function of T cells. However, ICI therapy is clinically beneficial in only a small number of patients, and it is difficult to predict post-treatment outcomes, thereby limiting its widespread clinical use. Research suggests that gut microbiota can regulate the host immune system and affect cancer progression and treatment. Moreover, the effectiveness of immunotherapy is related to the composition of the patient's gut microbiota; different gut microbial strains can either activate or inhibit the immune response. However, the importance of the microbial composition within the tumor has not been explored until recently. This study describes recent advances in the crosstalk between microbes in tumors and gut microbiota, which can modulate the tumor microbiome by directly translocating into the tumor and altering the tumor microenvironment. This study focused on the potential manipulation of the tumor and gut microbiota using fecal microbiota transplantation (FMT), probiotics, antimicrobials, prebiotics, and postbiotics to enrich immune-boosting bacteria while decreasing unfavorable bacteria to proactively improve the efficacy of ICI treatments. In addition, the use of genetic technologies and nanomaterials to modify microorganisms can largely optimize tumor immunotherapy and advance personalized and precise cancer treatment.

Ultrasound-Induced Tumor Perfusion Changes and Doxorubicin Delivery: A Study on Pulse Length and Pulse Repetition Frequency

OBJECTIVES

To investigate the appropriate combination of pulse length (PL) and pulse repetition frequency (PRF) when performing ultrasound stimulated microbubble (USMB) to enhance doxorubicin (DOX) delivery to tumors.

METHODS

A total of 48 tumor-bearing mice were divided into four groups, namely groups A-D. The mice in groups B-D were treated with chemotherapy and USMB treatment with different combinations of PL and PRF, and group A was control. Contrast-enhanced ultrasound imaging was conducted to analyze tumor blood perfusion. Fluorescence microscopy and high-performance liquid chromatography were used to qualitatively and quantitatively analyse DOX release. The structural changes of tumors were observed under light microscope and transmission electron microscope. Furthermore, another 24 tumor-bearing mice were treated with sonochemotherapy and some related inflammatory factors were measured to explore the underlying mechanism.

RESULTS

With PL of three cycles and PRF of 2 kHz, the tumor perfusion area ratio increased by 26.67%, and the DOX concentration was 4.69 times higher than the control (P < .001). With PL of 34.5 cycles and PRF of 200 Hz, the tumor perfusion area ratio decreased by 12.7% and DOX did not exhibit increased extravasation compared with the control. Microvascular rupture and hemorrhage were observed after long PL and low PRF treatment. While vasodilation and higher levels of some vasodilator inflammatory factors were found after treatment with short PL and high PRF.

CONCLUSIONS

USMB treatment using short PL and high PRF could enhance tumor blood perfusion and increase DOX delivery, whereas long PL and low PRF could not serve the same purpose.

The application and research progress of anti-angiogenesis therapy in tumor immunotherapy

Tumor immunotherapy, as the focus of scientific research and clinical tumor treatment in recent years, has received extensive attention. Due to its remarkable curative effect and fewer side effects than traditional treatments, it has significant clinical benefits for the treatment of various advanced cancers and can improve cancer patient survival in the long term. Currently, most patients cannot benefit from immunotherapy, and some patients may experience tumor recurrence and drug resistance even if they achieve remission overcome. Numerous studies have shown that the abnormal angiogenesis state of tumors can lead to immunosuppressive tumor microenvironment, which affects the efficacy of immunotherapy. Actually, to improve the efficacy of immunotherapy, the application of anti-angiogenesis drugs to normalize abnormal tumor vessel has been widely confirmed in basic and clinical research. This review not only discusses the risk factors, mechanisms, and effects of abnormal and normalized tumor angiogenesis state on the immune environment, but summarizes the latest progress of immunotherapy combined with anti-angiogenic therapy. We hope this review provides an applied reference for anti-angiogenesis drugs and synergistic immunotherapy therapy.

The Tissue Factor Pathway in Cancer: Overview and Role of Heparan Sulfate Proteoglycans

Historically, the only focus on tissue factor (TF) in clinical pathophysiology has been on its function as the initiation of the extrinsic coagulation cascade. This obsolete vessel-wall TF dogma is now being challenged by the findings that TF circulates throughout the body as a soluble form, a cell-associated protein, and a binding microparticle. Furthermore, it has been observed that TF is expressed by various cell types, including T-lymphocytes and platelets, and that certain pathological situations, such as chronic and acute inflammatory states, and cancer, may increase its expression and activity. Transmembrane G protein-coupled protease-activated receptors can be proteolytically cleaved by the TF:FVIIa complex that develops when TF binds to Factor VII (PARs). The TF:FVIIa complex can activate integrins, receptor tyrosine kinases (RTKs), and PARs in addition to PARs. Cancer cells use these signaling pathways to promote cell division, angiogenesis, metastasis, and the maintenance of cancer stem-like cells. Proteoglycans play a crucial role in the biochemical and mechanical properties of the cellular extracellular matrix, where they control cellular behavior via interacting with transmembrane receptors. For TFPI.fXa complexes, heparan sulfate proteoglycans (HSPGs) may serve as the primary receptor for uptake and degradation. The regulation of TF expression, TF signaling mechanisms, their pathogenic effects, and their therapeutic targeting in cancer are all covered in detail here.

Erythrocyte Membrane-Coated Invisible Acoustic-Sensitive Nanoparticle for Inducing Tumor Thrombotic Infarction by Precisely Damaging Tumor Vascular Endothelium

Selective induction of tumor thrombus infarction is a promising antitumor strategy. Non-persistent embolism due to non-compacted thrombus and activated fibrinolytic system within the tumor large blood vessels and tumor margin recurrence are the main therapeutic bottlenecks. Herein, an erythrocyte membrane-coated invisible acoustic-sensitive nanoparticle (TXA+DOX/PFH/RBCM@cRGD) is described, which can induce tumor thrombus infarction by precisely damaging tumor vascular endothelium. It is revealed that TXA+DOX/PFH/RBCM@cRGD can effectively accumulate on the endothelial surface of tumor vessels with the help of the red blood cell membrane (RBCM) stealth coating and RGD cyclic peptide (cRGD), which can be delivered in a targeted manner as nanoparticle missiles. As a kind of phase-change material, perfluorohexane (PFH) nanodroplets possess excellent acoustic responsiveness. Acoustic-sensitive missiles can undergo an acoustic phase transition and intense cavitation with response to low-intensity focused ultrasound (LIFU), damaging the tumor vascular endothelium, rapidly initiating the coagulation cascade, and forming thromboembolism in the tumor vessels. The drugs loaded in the inner water phase are released explosively. Tranexamic acid (TXA) inhibits the fibrinolytic system, and doxorubicin (DOX) eliminates the margin survival. In summary, a stealthy and acoustically responsive multifunctional nanoparticle delivery platform is successfully developed for inducing thrombus infarction by precisely damaging tumor vascular endothelium.

Inhibition of PFKFB3 in HER2-positive gastric cancer improves sensitivity to trastuzumab by inducing tumour vessel normalisation

BACKGROUND

Multiple mechanisms have been proposed that lead to reduced effectiveness of trastuzumab in HER2-positive gastric cancer (GC), yet resistance to trastuzumab remains a challenge in clinics.

METHODS

We established trastuzumab-resistant cells and patient-derived xenografts models to measure metabolic levels and vascular density and shape. The HER2-positive GC patient samples were used to determine clinical significance. We also measured protein expression and phosphorylation modifications to determine those alterations related to resistance. In vivo studies combining inhibitor of PFKFB3 with trastuzumab corroborated the in vitro findings.

RESULTS

The 6-phosphofructo-2-kinase (PFKFB3)-mediated trastuzumab resistance pathways in HER2-positive GC by activating the glycolytic pathway. We also found vessels are chaotic and destabilised in the tumour during the trastuzumab resistance process. Inhibition of PFKFB3 significantly diminished tumour proliferation and promoted vessel normalisation in the patient-derived xenograft model. Mechanistically, PFKFB3 promoted the secretion of CXCL8 into the tumour microenvironment, and phosphorylated Ser1151 of ERBB2, enhancing the transcription of CXCL8 by activating the PI3K/AKT/NFκB p65 pathway.

CONCLUSIONS

Our current findings discover that PFKFB3 inhibitors might be effective tools to overcome adjuvant therapy resistance in HER2-positive GC and reshaping the microenvironment by normalising tumour vessels is a novel strategy to overcome trastuzumab resistance.

Apoplastic Production of Recombinant AntiVEGF Protein Using Plant-Virus Transient Expression Vector

Targeting of vascular endothelial growth factor (VEGF) using AntiVEGF can be a promising approach for angiogenesis inhibition and cancer therapy. In this study, we direct AntiVEGF recombinant protein accumulation to cucurbit plant apoplast using a suitable signal (Pr1b) sequence. After assembling the target gene construct and cloning into the expression vector, we infected the plants with the resulting pZYMV-AntiVEGF viral vector. Transcription of the target gene was confirmed with RT-PCR assays. The apoplast-targeted AntiVEGF recombinant protein was detected in infected plants by Dot-blot, western blot, and ELISA analysis. AntiVEGF protein accumulation in the apoplast resulted in levels of 1.2% of TSP (Total Soluble Protein) that demonstrated a two-order increase compared to the cytoplasm-targeted protein. After purification of AntiVEGF protein using aqueous two-phase system (ATPS), purified protein was analyzed with MTT assay. Our results reveal that production of biologically active and correctly processed apoplast-targeted AntiVEGF recombinant protein is possible in plant apoplast. The low level of cytoplasm-targeted AntiVEGF recombinant protein might result from the degradation of improperly folded protein.

2-Methoxy-1,4-naphthoquinone (MNQ) regulates cancer key genes of MAPK, PI3K, and NF-κB pathways in Raji cells

2-Methoxy-1,4-naphthoquinone (MNQ) has been shown to cause cytotoxic towards various cancer cell lines. This study is designed to investigate the regulatory effect of MNQ on the key cancer genes in mitogen-activated protein kinase, phosphoinositide 3-kinase, and nuclear factor кB signaling pathways. The expression levels of the genes were compared at different time point using polymerase chain reaction arrays and Ingenuity Pathway Analysis was performed to identify gene networks that are most significant to key cancer genes. A total of 43 differentially expressed genes were identified with 21 up-regulated and 22 down-regulated genes. Up-regulated genes were involved in apoptosis, cell cycle and act as tumor suppressor while down-regulated genes were involved in anti-apoptosis, angiogenesis, cell cycle and act as transcription factor as well as proto-oncogenes. MNQ exhibited multiple regulatory effects on the cancer key genes that targeting at cell proliferation, cell differentiation, cell transformation, apoptosis, reduce inflammatory responses, inhibits angiogenesis and metastasis.

PO2-based biodosimetry evaluation using an EPR technique acts as a sensitive index for chemotherapy

The partial pressure of oxygen (PO₂) in the tumor microenvironment directly affects tumor sensitivity to chemotherapy. In the present study, a lithium phthalocyanine probe was implanted into MCF-7 human breast cancer cells, followed by transplant of the cells into nude mice. The present study used an electron paramagnetic resonance (EPR) oximetry measuring technique to dynamically monitor PO₂ in the tumor microenvironment prior to and following chemotherapy, and aimed to determine the precise time window in which the microenvironmental PO₂ peaked following chemotherapy. The results indicated that PO₂ was significantly higher in breast cancer compared with control (P<0.05). Following four cycles of chemotherapy, the activity of NADH dehydrogenase, succinate-cytochrome c reductase and cytochrome c oxidase in the mitochondria of cells was significantly reduced when compared with their activity prior to chemotherapy (P<0.05). Regional blood flow in tumor tissues undergoing chemotherapy was significantly lower than that prior to chemotherapy (P<0.05). The rate of cellular apoptosis in the PO₂ peak-based chemotherapy group was significantly greater than that in the conventional chemotherapy group after two and four cycles of chemotherapy (P<0.05). Tumor volume in the PO₂ peak-based chemotherapy group was significantly reduced compared with that in the 0.9% NaCl solution control and the conventional chemotherapy groups after four cycles of chemotherapy (P<0.05). The tumor inhibitory rate of the experimental group was significantly higher than that of the conventional chemotherapy group (P<0.01). In conclusion, the present study may provide guidance for the development of effective strategies depending on tumor-maximal response to chemotherapy in an oxygen-rich environment. Additionally, the present study aimed to establish a foundation for a clinical noninvasive assessment intended to guide treatment and formulate individual regimens, in order to improve cancer therapeutics, sensitivity monitoring and curative effect estimation.

RAS-mediated oncogenic signaling pathways in human malignancies

Abnormally activated RAS proteins are the main oncogenic driver that governs the functioning of major signaling pathways involved in the initiation and development of human malignancies. Mutations in RAS genes and or its regulators, most frequent in human cancers, are the main force for incessant RAS activation and associated pathological conditions including cancer. In general, RAS is the main upstream regulator of the highly conserved signaling mechanisms associated with a plethora of important cellular activities vital for normal homeostasis. Mutated or the oncogenic RAS aberrantly activates a web of interconnected signaling pathways including RAF-MEK (mitogen-activated protein kinase kinase)-ERK (extracellular signal-regulated kinase), phosphoinositide-3 kinase (PI3K)/AKT (protein kinase B), protein kinase C (PKC) and ral guanine nucleotide dissociation stimulator (RALGDS), etc., leading to uncontrolled transcriptional expression and reprogramming in the functioning of a range of nuclear and cytosolic effectors critically associated with the hallmarks of carcinogenesis. This review highlights the recent literature on how oncogenic RAS negatively use its signaling web in deregulating the expression and functioning of various effector molecules in the pathogenesis of human malignancies.

Tumor angiogenesis and vascular normalization: alternative therapeutic targets

Tumor blood vessels are a key target for cancer therapeutic management. Tumor cells secrete high levels of pro-angiogenic factors which contribute to the creation of an abnormal vascular network characterized by disorganized, immature and permeable blood vessels, resulting in poorly perfused tumors. The hypoxic microenvironment created by impaired tumor perfusion can promote the selection of more invasive and aggressive tumor cells and can also impede the tumor-killing action of immune cells. Furthermore, abnormal tumor perfusion also reduces the diffusion of chemotherapeutic drugs and radiotherapy efficiency. To fight against this defective phenotype, the normalization of the tumor vasculature has emerged as a new therapeutic strategy. Vascular normalization, by restoring proper tumor perfusion and oxygenation, could limit tumor cell invasiveness and improve the effectiveness of anticancer treatments. In this review, we investigate the mechanisms involved in tumor angiogenesis and describe strategies used to achieve vascular normalization.

MEK inhibitor can reverse the resistance to bevacizumab in A549 cells harboring Kirsten rat sarcoma oncogene homolog mutation

Background

Bevacizumab (BV) is broadly used to treat a number of cancers; however, BV resistance mechanisms and strategies to overcome this resistance are yet to be determined.

Methods

We established xenograft mice models harboring Kirsten rat sarcoma oncogene homolog (KRAS) mutations based on the A549 cell line, and tested the responses of xenograft tumors to a series of drugs in ex vivo and in vivo experiments. Changes in transcriptive level were analyzed by ribonucleic acid (RNA) sequencing and the expressions of connexins were determined by immunohistochemistry staining.

Results

A549 cell mutation type (KRAS G12S) was confirmed by sequencing. After treating the xenograft tumors with BV, the median interval time from BV administration to tumor volume more than 2.5‐fold of the original was 37 days, compared with 21 days in the control (P = 0.025). A549 cells showed resistantance to selumitinib (MEK inhibitor) but were sensitive to selumitinib plus BEZ235 (phosphoinositide 3‐kinase/mammalian target of rapamycin dual inhibitor). However, selumitinib could effectively reverse the resistance to BV in in vivo experiments. RNA sequencing showed that mouse genes, but not human genes, activated the mitogen‐activated protein kinase signaling pathway, accompanied by activation of the Wnt and Hedgehog pathways. Connexin43 (S261) was phosphorylated before and during BV treatment, and subsequently transitioned to negative phosphorylated‐connexin 43‐S261 after resistance to BV.

Conclusion

Combining an MEK inhibitor with BV was a potential strategy to reverse initial BV resistance. Phosphorylated‐connexin 43 might be associated with the response to BV.

Upregulation of ATG3 contributes to autophagy induced by the detachment of intestinal epithelial cells from the extracellular matrix, but promotes autophagy-independent apoptosis of the attached cells

Detachment of nonmalignant intestinal epithelial cells from the extracellular matrix (ECM) triggers their growth arrest and, ultimately, apoptosis. In contrast, colorectal cancer cells can grow without attachment to the ECM. This ability is critical for their malignant potential. We found previously that detachment-induced growth arrest of nonmalignant intestinal epithelial cells is driven by their detachment-triggered autophagy, and that RAS, a major oncogene, promotes growth of detached cells by blocking such autophagy. In an effort to identify the mechanisms of detachment-induced autophagy and growth arrest of nonmalignant cells we found here that detachment of these cells causes upregulation of ATG3 and that ATG3 upregulation contributes to autophagy and growth arrest of detached cells. We also observed that when ATG3 expression is artificially increased in the attached cells, ATG3 promotes neither autophagy nor growth arrest but triggers their apoptosis. ATG3 upregulation likely promotes autophagy of the detached but not that of the attached cells because detachment-dependent autophagy requires other detachment-induced events, such as the upregulation of ATG7. We further observed that those few adherent cells that do not die by apoptosis induced by ATG3 become resistant to apoptosis caused by cell detachment, a property that is critical for the ability of normal epithelial cells to become malignant. We conclude that cell-ECM adhesion can switch ATG3 functions: when upregulated in detached cells in the context of other autophagy-promoting events, ATG3 contributes to autophagy. However, when overexpressed in the adherent cells, in the circumstances not favoring autophagy, ATG3 triggers apoptosis.

Synergistic effects of curcumin and bevacizumab on cell signaling pathways in hepatocellular carcinoma

The aim of the present study was to explore the effects of curcumin in combination with bevacizumab on the vascular endothelial growth factor (VEGF)/VEGF receptor (VEGFR)/K-ras pathway in hepatocellular carcinoma. A total of 30 Sprague Dawley (SD) rats were randomly divided into five groups: Control, model, curcumin, VEGF blocker, and curcumin + VEGF blocker groups. The mRNA levels of VEGF and VEGFR in all groups were subsequently measured by quantitative reverse transcriptase-polymerase chain reaction and the protein expression of K-ras was detected by western blot analysis. Compared with the control group, the mRNA levels of VEGF and VEGFR were revealed to be significantly increased in the model, curcumin and VEGF blocker groups. The VEGF mRNA levels in the curcumin, VEGF blocker and curcumin + VEGF blocker groups were all decreased when compared with the model group. In addition, the VEGF mRNA levels in the curcumin + VEGF blocker group were significantly lower compared with the curcumin group (P<0.05). The VEGF mRNA levels in the curcumin, VEGF blocker and curcumin + VEGF blocker groups were decreased when compared with the model group (P=0.0001). No significant differences in VEGF mRNA levels were identified between the VEGF blocker and curcumin groups (P=0.863), whereas the VEGF mRNA levels in the curcumin + VEGF blocker group were significantly lower than that of the curcumin group (P=0.025). Curcumin and the VEGF blocker are each capable of inhibiting hepatocellular carcinoma progression by regulating the VEGF/VEGFR/K-ras pathway. The combination of the two compounds has a synergistic effect on the inhibition of the effects of the VEGF signaling pathways in hepatocellular carcinoma progression.

Expression and purification of functional human vascular endothelial growth factor-a121; the most important angiogenesis factor

PURPOSE

Angiogenesis or formation of new blood vessels is an essential process for tumor growth, invasion and metastasis. Vascular Endothelial Growth Factor (VEGF) and its receptors play an important role in angiogenesis-dependent tumors. VEGF-A is the most important factor in angiogenesis process. Human VEGF-A gene consists of eight exons that undergoes alternative exon splicing and produce five different proteins consisting of 121, 145, 165, 189 and 206 amino acids (named VEGF121, VEGF145, VEGF165, VEGF189, and VEGF206).

METHODS

In this study, VEGF121 gene synthesized and cloned into the pET-26b plasmid. The recombinant plasmid was transferred into appropriate expression strain of BL-21. Expression of VEGF121 induced by IPTG (Isopropyl β-D-1-thiogalactopyranoside) and confirmed by SDS-PAGE and Western-Blotting. Recombinant VEGF121 was purified by nickel affinity chromatography. HUVECs (Human Umbilical Vein Endothelia Cells) cells were isolated from umbilical vein and the effect of VEGF121 on tube formation of endothelial cells was investigated.

RESULTS

SDS-PAGE and Western-Blotting results verified the purification of VEGF121. The final yield of recombinant protein was about 5mg per liter. Endothelial cell tube formation assay results showed that VEGF121 leads to tube formation of endothelial cell on matrix and induces angiogenesis in vitro.

CONCLUSION

Recombinant VEGF121 is important factor in tube formation of endothelial cell, so it could be used in different cancer researches and angiogenesis assay.

Stabilization of VEGF G-quadruplex and inhibition of angiogenesis by quindoline derivatives

BACKGROUND

Angiogenesis is thought to be important in tumorigenesis and tumor progress. Vascular endothelial growth factor (VEGF) is a pluripotent cytokine and angiogenic growth factor that plays crucial roles in embryonic development and tumor progression. In many types of cancer, VEGF is overexpressed and is generally associated with tumor progression and survival rate. The polypurine/polypyrimidine sequence located upstream of the promoter region in the human VEGF gene can form specific parallel G-quadruplex structures, raising the possibility for transcriptional control of VEGF through G-quadruplex ligands.

METHODS

PCR stop assay, circular dichroism (CD) spectra, RNA extraction and RT-PCR, enzyme-linked immunosorbent assay (ELISA), luciferase Assays, cell scrape test, xCELLigence real-time cell analysis (RTCA), and chick embryo chorioallantoic membrane (CAM) assay.

RESULTS AND CONCLUSIONS

We found that quindoline derivatives can interact with the G-rich DNA sequences of the VEGF promoter to stabilize this G-quadruplex and suppress the transcription and expression of the VEGF protein. We also demonstrated that these derivatives exhibit potential anti-angiogenic activity in chick embryos and antitumor activity, including the inhibition of cell proliferation and migration.

GENERAL SIGNIFICANCE

Our new findings have significances not only for understanding the mechanism of the G-quadruplex ligands mediating the VEGF transcription inhibition, but also for exploring a new anti-tumor strategy to blocking the transcription of VEGF to inhibit the angiogenesis in cancer cells.

Resistance to antiangiogenic therapies

ABSTRACT: 

Angiogenesis is a key process for tumoral growth, which has become a main target for anticancer treatments. A wide number of agents targeting both VEGF and its receptor have recently become standard treatments for different tumor types. Unfortunately, most of the tumors become resistant to these agents after few months of treatment. Different mechanisms of resistance to antiangiogenic drugs have been proposed and investigated; some agents demonstrated to be able to restore sensitivity to antiangiogenic drugs by blocking pathways or molecules involved in the resistance in preclinical models. Biomarkers for the prediction of response or resistance to antiangiogenic agents are under evaluation.

MYC and the art of microRNA maintenance

MYC is a noncanonical transcription factor that binds to thousands of genomic loci and affects >15% of the human transcriptome, with surprisingly little overlap between MYC-bound and -regulated genes. This discordance raises the question whether MYC chooses its targets based on their individual biological effects ("a la carte") or by virtue of belonging to a certain group of genes (on a "prix fixe" basis). This review presents evidence for a prix fixe, posttranscriptional model whereby MYC initially deregulates a select number of microRNAs. These microRNAs then target a broad spectrum of genes based solely on the presence in their 3' UTRs (untranslated regions) of distinct "seed" sequences. Existing evidence suggests that there are significant microRNA components to all key MYC-driven phenotypes, including cell-cycle progression, apoptosis, metabolism, angiogenesis, metastasis, stemness, and hematopoiesis. Furthermore, each of these cell-intrinsic and -extrinsic phenotypes is likely attributable to deregulation of multiple microRNA targets acting in different, yet frequently overlapping, pathways. The habitual targeting of multiple genes within the same pathway might account for the robustness and persistence of MYC-induced phenotypes.

Oncogenes and angiogenesis: a way to personalize anti-angiogenic therapy?

The acquisition of oncogenic mutations and promotion of angiogenesis are key hallmarks of cancer. These features are often thought of as separate events in tumor progression and the two fields of research have frequently been considered as independent. However, as we highlight in this review, activated oncogenes and deregulated angiogenesis are tightly associated, as mutations in cancer cells can lead to perturbation of the pro- and anti-angiogenic balance thereby causing aberrant angiogenesis. We propose that normalization of the vascular network by targeting oncogenes in the tumor cells might lead to more efficient and sustained therapeutic effects compared to therapies targeting tumor vessels. We discuss how pharmacological inhibition of oncogenes in tumor cells restores a functional vasculature by bystander anti-angiogenic effect. As genetic alterations are tumor-specific, targeted therapy, which potentially blocks the angiogenic program activated by individual oncogenes may lead to personalized anti-angiogenic therapy.

H-ras oncogene expression and angiogenesis in experimental liver cirrhosis

Background. Proto-oncogenes, particularly ras, may not only affect cell proliferation but also contribute to angiogenesis by influencing both proangiogenic and antiangiogenic mediators. The aim of this study was to investigate whether any relationship exists between ras expression and angiogenesis during diethylnitrosamine- (DEN-) induced experimental liver fibrosis. Materials and Methods. Liver cirrhosis was induced in rats by intraperitoneal injections of DEN. The animals were sacrificed 2 weeks after the last administrations and a hepatectomy was performed. Masson's trichrome staining was used in the evaluation of the extent of liver fibrosis. The vascular density in portal and periportal areas was assessed by determining the count of CD34 labeled vessel sections. For quantitative evaluation of H-ras expression, in each section positive and negative cells were counted. Results. In fibrotic group H-ras expression was higher than that in nonfibrotic group and was more widespread in cirrhotic livers. Friedman's test showed that there was a significant correlation between H-ras expression and VD (P < 0.01). Conclusion. The results of this descriptive study reveal that H-ras expression gradually increases according to the severity of fibrosis and strongly correlates with angiogenesis.

Microvessel density and p53 mutations in advanced-stage epithelial ovarian cancer

We planned to determine the relationship between angiogenesis and p53 mutational status in advanced-stage epithelial ovarian cancer. Using 190 tumor samples from patients with stage III and IV ovarian cancer we performed p53 sequencing, immunohistochemistry, and CD31 microvessel density (MVD) determination. MVD was elevated in tumors with p53 null mutations compared to p53 missense mutation or no mutation. Disease recurrence was increased with higher MVD in both unadjusted and adjusted analyses. In adjusted analysis, p53 null mutation was associated with increased recurrence and worse overall survival. Worse overall survival and increased recurrence risk were also associated with the combination of CD31 MVD values >25 vessels/HPF and any p53 mutation. P53 mutation status and MVD may have prognostic significance in patients with advanced-stage ovarian cancer. Tumors with p53 null mutations are likely to be more vascular, contributing to decreased survival and increased recurrence probability.

Recent advances in stealth coating of nanoparticle drug delivery systems

Modifying surfaces of nanoparticles (NPs) with polyethylene glycol (PEG), the so-called PEGylation, is the most commonly used method for reducing premature clearance of NPs from the circulation. However, several reports point out that PEGylation may negatively influence the performance of NPs as a drug carrier. Alternative surface modification strategies, including substitute polymers, conditional removal of PEG, and biomimetic surface modification, may provide solutions for the limitations of PEG.

RAS oncogenes: weaving a tumorigenic web

RAS proteins are essential components of signalling pathways that emanate from cell surface receptors. Oncogenic activation of these proteins owing to missense mutations is frequently detected in several types of cancer. A wealth of biochemical and genetic studies indicates that RAS proteins control a complex molecular circuitry that consists of a wide array of interconnecting pathways. In this Review, we describe how RAS oncogenes exploit their extensive signalling reach to affect multiple cellular processes that drive tumorigenesis.

Phosphatidylinositol 3′-kinase signaling pathway is essential for Rac1-induced hypoxia-inducible factor-1α and vascular endothelial growth factor expression

We have previously demonstrated the roles of RhoA, Rac1, and Cdc42 in hypoxia-driven angiogenesis. However, the role of oncogenes in hypoxia signaling is poorly understood. Given the importance of Rho proteins in the hypoxic response, we hypothesized that Rho family members could act as mediators of hypoxic signal transduction. We investigated the cross-talk between hypoxia and oncogene-driven signal transduction pathways and explored the role of Rac1 on hypoxia-induced hypoxia-inducible factor (HIF)-1α and VEGF expression. Since the phosphatidylinositol 3′-kinase (PI3K) pathway is involved in signal transduction of many oncogenes, we explored the role of PI3K on Rac1-mediated expression of HIF-1α and VEGF in hypoxia. We showed that LY-294002, a PI3K inhibitor, suppressed HIF-1α and VEGF induction under hypoxic conditions by up to 50%. Activation of Rac1 resulted in an upregulation of hypoxia-induced HIF-1α expression, which was blocked by LY-294002. These data suggested that Rac1 is an intermediate in the PI3K-mediated induction of HIF-1α. Interestingly, there was a significant downregulation of the tumor suppressor genes p53 and von Hippel-Lindau tumor suppressor (VHL) in cells expressing a constitutively active form of Rac1. Rac1-mediated inhibition of p53 and VHL could therefore be implicated in the upregulation of HIF-1α expression.

Immunohistochemical evaluation for P53 and VEGF (Vascular Endothelial Growth Factor) is not prognostic for long term survival in end stage esophageal adenocarcinoma

OBJECTIVES

To correlate the expression of p53 protein and VEGF with the prognosis of patients submitted to curative resection to treat esophageal adenocarcinoma.

METHODS

Forty-six patients with esophageal adenocarcinoma, submitted to curative resection, were studied. The expressions of p53 protein and VEGF were assessed by immunohistochemistry in 52.2% and 47.8% of tumors, respectively.

RESULTS

P53 protein and VEGF expressions coincided in 26% of the cases, and no correlation between these expressions was observed. None of the clinicopathological factors showed a significant correlation with p53 protein or VEGF expressions. There was no significant association between p53 protein and VEGF expressions and long-term survival.

CONCLUSION

The expression of p53 protein and VEGF did not correlate with prognosis in esophageal adenocarcinoma patients submitted to curative resection.

In vivo chemoresistance of prostate cancer in metronomic cyclophosphamide therapy

A human prostate cancer (PC3) xenograft model was established which reflects acquired in vivo resistance towards metronomic cyclophosphamide (CPA) treatment. Cell cultures of two in vivo resistant PC3 tumors were established which maintain chemoresistant phenotypes upon xenografting into mice. A comparative proteome analysis of the two resistant cell lines PC3-D3 and -D4 versus the non-resistant parental PC3 cell line by 2D-DIGE approach followed by MALDI-TOF-TOF analysis revealed a total of 25 differently expressed proteins. Validation of protein candidates by Western blot analysis of the corresponding in vivo tumor xenografts identified three differentially expressed proteins (thioredoxin containing protein 5, cathepsin B, and annexin A3). Thioredoxin containing protein 5 was up-regulated in resistant xenografts only upon in vivo CPA therapy. A truncated version of cathepsin B translocated into mitochondria in the resistant clones whereas it stays cytoplasmic in corresponding parental PC3 cells. Annexin A3 (ANXA3) presents a very interesting candidate which was found to be up-regulated both in vitro and in xenografts, with protein levels further increased by metronomic CPA treatment in vivo. It is noteworthy that independent studies in other epithelial cancers recently identified ANXA3 as cancer progression and resistance marker.

Evading tumor evasion: current concepts and perspectives of anti-angiogenic cancer therapy

Within three decades, anti-angiogenic therapy has rapidly evolved into an integral component of current standard anti-cancer treatment. Anti-angiogenic therapy has fulfilled a number of its earlier proposed promises. The universality of this approach is demonstrated by the broad spectrum of malignant and benign tumor entities, as well as non-neoplastic diseases, that are currently treated with anti-angiogenic agents. In contrast to tumor cell targeting therapies, the development of acquired drug resistance (e.g., via mutations in growth factor receptor signaling genes) has not been described yet for the principal target of anti-angiogenic therapy--the tumor endothelium. Moreover, the tumor endothelium has emerged as a critical target of conventional cancer therapies, such as chemotherapy and radiotherapy. The presumption that tumor growth and metastasis are angiogenesis-dependent implies that the number of potential targets of an anti-cancer therapy could be reduced to those that stimulate the angiogenesis process. Therefore, the set of endogenous angiogenesis stimulants might constitute an "Achilles heel" of cancer. Direct targeting of tumor endothelium via, e.g., endogenous angiogenesis inhibitors poses another promising but clinically less explored therapeutic strategy. Indeed, the majority of current anti-angiogenic approaches block the activity of a single or at most a few pro-angiogenic proteins secreted by tumor cells or the tumor stroma. Based on our systems biology work on the angiogenic switch, we predicted that the redundancy of angiogenic signals might limit the efficacy of anti-angiogenic monotherapies. In support of this hypothesis, emerging experimental evidence suggests that tumors may become refractory or even evade the inhibition of a single pro-angiogenic pathway via compensatory upregulation of alternative angiogenic factors. Here, we discuss current concepts and propose novel strategies to overcome tumor evasion of anti-angiogenic therapy. We believe that early detection of tumors, prediction of tumor evasive mechanisms and rational design of anti-angiogenic combinations will direct anti-angiogenic therapy towards its ultimate goal--the conversion of cancer to a dormant, chronic, manageable disease.

Vascular determinants of cancer stem cell dormancy--do age and coagulation system play a role?

The inability of tumour-initiating cancer stem cells (CSCs) to bring about a net increase in tumour mass could be described as a source of tumour dormancy. While CSCs may be intrinsically capable of driving malignant growth, to do so they require compatible surroundings of supportive cells, growth factors, adhesion molecules and energy sources (e.g. glucose and oxygen), all of which constitute what may be referred to as a 'permissive' CSC niche. However, in some circumstances, the configuration of these factors could be incompatible with CSC growth (a 'non-permissive' niche) and lead to their death or dormancy. CSCs and their niches may also differ between adult and paediatric cancers. In this regard the various facets of the tumour-vascular interface could serve as elements of the CSC niche. Indeed, transformed cells with an increased tumour-initiating capability may preferentially reside in specific zones adjacent to tumour blood vessels, or alternatively originate from poorly perfused and hypoxic areas, to which they have adapted. CSCs themselves may produce increased amounts of angiogenic factors, or rely for this on their progeny or activated host stromal cells. It is likely that 'vascular' properties of tumour-initiating cells and those of their niches may diversify and evolve with tumour progression. The emerging themes in this area include the role of vascular (and bone marrow) aging, vascular and metabolic comorbidities (e.g. atherosclerosis) and the effects of the coagulation system (both at the local and systemic levels), all of which could impact the functionality of CSCs and their niches and affect tumour growth, dormancy and formation of occult as well as overt metastases. In this article we will discuss some of the vascular properties of CSCs relevant to tumour dormancy and progression, including: (i) the role of CSCs in regulating tumour vascular supply, i.e the onset and maintenance of tumour angiogenesis; (ii) the consequences of changing vascular demand (vascular dependence) of CSC and their progeny; (iii) the interplay between CSCs and the vascular system during the process of metastasis, and especially (iv) the impact of the coagulation system on the properties of CSC and their niches. We will use the oncogene-driven expression of tissue factor (TF) in cancer cells as a paradigm in this regard, as TF represents a common denominator of several vascular processes that commonly occur in cancer, most notably coagulation and angiogenesis. In so doing we will explore the therapeutic implications of targeting TF and the coagulation system to modulate the dynamics of tumour growth and tumour dormancy.

VEGF-A and the induction of pathological angiogenesis

Tumors, wounds, and chronic inflammatory disorders generate a new vascular supply by a process known as pathological angiogenesis. Whereas formation of the normal blood vasculature requires the interaction of many different agonists and inhibitors, including vascular endothelial growth factor-A (VEGF-A) and other members of the vascular permeability factor/VEGF family, pathological angiogenesis is a cruder, simpler process that can be replicated by a single VEGF-A isoform, VEGF-A(164/5). VEGF-A(164/5) induces the formation of several distinctly different types of new blood vessels that differ from normal blood vessels with respect to organization, structure, and function. Elucidating the properties of these new vessels has led to a better understanding of angiogenesis and will hopefully lead to new approaches to antiangiogenic therapy.

G-quadruplexes: targets in anticancer drug design

G-quadruplexes are special secondary structures adopted in some guanine-rich DNA sequences. As guanine-rich sequences are present in important regions of the eukaryotic genome, such as telomeres and the regulatory regions of many genes, such structures may play important roles in the regulation of biological events in the body. G-quadruplexes have become valid targets for new anticancer drugs in the past few decades. Many leading compounds that target these structures have been reported, and a few of them have entered preclinical or clinical trials. Nonetheless, the selectivity of this kind of antitumor compound has yet to be improved in order to suppress the side effects caused by nonselective binding. As drug design targets, the topology and structural characteristics of quadruplexes, their possible biological roles, and the modes and sites of small-ligand binding to these structures should be understood clearly. Herein we provide a summary of published research that has set out to address the above problem to provide useful information on the design of small ligands that target G-quadruplexes. This review also covers research methodologies that have been developed to study the binding of ligands to G-quadruplexes.

The role of angiopoietin-like proteins in angiogenesis and metabolism

Recently, a family of proteins structurally similar to the angiogenic regulating factors angiopoietins was identified and designated "angiopoietin-like proteins" (Angptls). Encoded by seven genes, Angptls 1 to 7 all possess an N-terminal coiled-coil domain and a C-terminal fibrinogen-like domain, both characteristic of angiopoietins. However, Angptls do not bind to either the angiopoietin receptor Tie2 or the related protein Tie1 and remain orphan ligands. Nonetheless, Angptls 1, 2, 3, 4, and Angptl6/angiopoietin-related growth factor function to regulate angiogenesis. Angptls 3, 4, and Angptl6/angiopoietin-related growth factor also appear to directly regulate lipid, glucose, and energy metabolism independently of angiogenic effects. Recently, several lines of evidence reveal differential roles of Angptl structural domains in both angiogenesis and metabolism. Here, we briefly review what is currently known about Angptls function.

Ionizing radiation antagonizes tumor hypoxia induced by antiangiogenic treatment

PURPOSE

The combined treatment modality of ionizing radiation with inhibitors of angiogenesis is effective despite the supposition that inhibition of angiogenesis might increase tumor hypoxia and thereby negatively affect radiation sensitivity. To directly assess this still controversial issue, we analyzed treatment-dependent alterations of tumor oxygenation in response to inhibition of angiogenesis alone, ionizing radiation, and combined treatment.

EXPERIMENTAL DESIGN

Serial measurements with high-resolution [18F]fluoromisonidazole positron emission tomography and immunohistochemical detection of the endogenous hypoxia marker glucose transporter-1 were done to determine tumor hypoxia in a murine mammary carcinoma allograft model.

RESULTS

Inhibition of angiogenesis with the clinically relevant vascular endothelial growth factor receptor tyrosine kinase inhibitor PTK787/ZK222584 reduced microvessel density but had only minimal effects on tumor growth, tumor cell apoptosis, and proliferation. However, PTK787/ZK222584 treatment increased overall and local tumor hypoxia as revealed by extended expression of the hypoxia marker glucose transporter-1 and increased uptake of [18F]fluoromisonidazole. Fractionated irradiation induced a strong growth delay, which was associated with enhanced apoptosis and reduced proliferation of tumor cells but only minor effects on microvessel density and allograft oxygenation. Combined treatment with fractionated irradiation resulted in extended tumor growth delay and tumor cell apoptosis but no increase in tumor hypoxia.

CONCLUSIONS

These results show that irradiation antagonizes the increase of hypoxia by vascular endothelial growth factor receptor tyrosine kinase inhibition and abrogates the potential negative effect on tumor hypoxia. Thus, the risk of treatment-induced hypoxia by inhibitors of angiogenesis exists but is kept minimal when combined with a cytotoxic treatment modality.

Acute L-glutamine deprivation compromises VEGF-a upregulation in A549/8 human carcinoma cells

Tumor ischemia participates in angiogenesis and cancer progression through cellular responses to hypoxia and nutrient deprivation. However, the contribution of amino acids limitation to this process remains poorly understood. Using serum-free cell culture conditions, we tested the impact of L-glutamine deprivation on metabolic and angiogenic responses in A549/8 carcinoma cells. In these cells, lowering glutamine concentration modified the cell cycle distribution and significantly induced apoptosis/necrosis. Although glutamine deprivation led to a HIF-independent increase in VEGF-A mRNA, the corresponding protein level remained low and correlated with the inhibition of protein synthesis and activation of the GCN2/eIF2alpha pathway. Limitation of glutamine availability also hampers hypoxia- and hypoglycemia-induced VEGF-A protein upregulation. Thus, glutamine deprivation may have no direct effect on VEGF-dependent angiogenesis, compared to hypoxia or to glucose deprivation, and may instead be detrimental to cancer progression by antagonizing ischemia-induced stresses.

Physiological stress induces the metastasis marker AGR2 in breast cancer cells

As an approach to understanding the factors that activate expression of tumor progression genes, the role of physiological stress in the activation of a panel of tumor cell markers was investigated. These studies identify the developmental gene product, anterior gradient 2 (AGR2) as a cancer cell marker specifically up-regulated in response to depletion of serum and oxygen. AGR2 has been identified as a tumor marker in primary and secondary cancer lesions, and as a marker for detection of circulating tumor cells (CTCs). Elevated levels of AGR2 are known to increase the metastatic potential of cancer cells, but conditions leading to increased expression of AGR2 are not well understood. The present results identify novel physiological parameters likely to contribute to AGR2 induction in situ.

Inhibition of phosphatidylinositol-3-kinase and mitogen-activated protein kinase kinase 1/2 prevents melanoma development and promotes melanoma regression in the transgenic TPRas mouse model

A number of human melanomas show hyperactivation of the Ras pathway due to mutations of the molecule or alteration of upstream or downstream effectors. In this study, we evaluated the effect of blocking the two Ras downstream pathways phosphatidylinositol-3-kinase/Akt and Raf/mitogen-activated protein kinase kinase/extracellular signal-regulated kinase on melanoma development and regression in the TPRas mouse model. The inhibition of these two signaling cascades by topically applied Ly294002 and U0126 significantly delayed melanoma development and significantly decreased the tumor incidence, particularly when the drugs were applied in combination. Treatment with the inhibitors of established melanomas resulted in complete remission in 33% of mice and partial regression in 46% of mice when drugs were delivered in combination. These responses correlated with increased apoptosis and decreased proliferation both in vitro and in vivo and reduced tumor angiogenesis. In conclusion, this study strongly supports the role of the phosphatidylinositol-3-kinase/Akt and Raf/mitogen-activated protein kinase kinase/extracellular signal-regulated kinase pathways in the development and maintenance of Ras-dependent melanomas and supports the notion that specific inhibition of these effectors may represent a very promising avenue for the treatment and prevention of the disease.

Evaluation of CD31 (PECAM-1) expression using tissue microarray in patients with renal cell carcinoma

Intratumoural microvessel density (MVD) has prognostic significance in selected neoplasms. To evaluate the prognostic information of MVD in renal cell carcinoma (RCC) we assessed the immunohistochemical expression of CD31 in 208 tumours using the tissue microarray technique. The expression was related to tumour cell type, TNM stage, nuclear grade and survival. CD31 expression was significantly (p < 0.001) higher in 167 conventional RCCs (clear cell) compared to 28 papillary RCCs. In conventional RCC, CD31 expression was inversely correlated to TNM stage (p = 0.024) and nuclear grade (p = 0.010). To evaluate the impact of CD31 expression on tumour-specific survival, the conventional RCC tumours were subdivided into quartiles according to the CD31 expression. In univariate analysis, patients with tumours in the quartile with the highest expression had a more favourable prognosis (p = 0.01) compared to those with lower CD31 expression. A multivariate analysis of prognostic factors in conventional RCC showed that TNM stage and nuclear grade were independent predictors of prognosis, but CD31 expression did not add further prognostic information.

Preclinical Evaluation of Antiangiogenic Thrombospondin-1 Peptide Mimetics, ABT-526 and ABT-510, in Companion Dogs with Naturally Occurring Cancers

PURPOSE

The angiogenic phenotype of malignant cancers has been established as a target for cancer therapy. ABT-526 and ABT-510, two peptide mimetics of thrombospondin-1 (TSP-1), block angiogenesis in vitro and in vivo and slow tumor growth in mice. To guide the clinical development of these drugs, translational studies in dogs with naturally occurring cancers were initiated.

EXPERIMENTAL DESIGN

A prospective open-label trial using ABT-510 or ABT-526 in pet dogs with measurable malignant spontaneously arising tumors. Endpoints included safety, pharmacokinetics, antitumor activity, and preliminary assessment of changes in circulating endothelial cell populations.

RESULTS

Two-hundred and forty-two dogs were sequentially entered to this open-label trial. The elimination half-life for ABT-510 and ABT-526 was 0.7 and 0.8 h, respectively (range, 0.5-1 h). No dose-limiting toxicities were seen in any dogs (N = 242). Forty-two dogs receiving peptide had objective responses (>50% reduction in tumor size; n = 6) or significant disease stabilization. Most objective responses were seen after 60 days of exposure to the TSP-1 peptide. Antitumor activity was similar for both peptides and was seen in several histologies, including mammary carcinoma, head and neck carcinoma, soft tissue sarcoma, cutaneous T-cell lymphoma, and non-Hodgkin's lymphoma. Assessment of circulating endothelial cell populations in a small subset of dogs suggested that effective exposure to TSP-1 peptides may be associated with reductions in circulating endothelial cells.

CONCLUSIONS

These results support the safety and activity of ABT-526 and ABT-510 in dogs with naturally occurring malignant cancers. Data from this preclinical trial support the development of TSP-1 mimetic peptides as anticancer agents.

Regulation of angiogenesis and invasion by human Pituitary tumor transforming gene (PTTG) through increased expression and secretion of matrix metalloproteinase-2 (MMP-2)

Background

Pituitary tumor transforming gene (PTTG) is a novel oncogene that is expressed at higher level in most of the tumors analyzed to date compared to normal tissues. Existence of a relationship between PTTG levels and tumor angiogenesis and metastasis has been reported. However, the mechanisms by which PTTG achieve these functions remain unknown. In the present study, we investigated the effect of overexpression of PTTG on secretion and expression of metastasis-related metalloproteinase-2 (MMP-2) in HEK293 cells, cell migration, invasion and tubule formation.

Results

Transient or stable transfection of HEK293 cells with PTTG cDNA showed a significant increase in secretion and expression of MMP-2 measured by zymography, reverse transcriptase (RT/PCR), ELISA, and MMP-2 gene promoter activity. Furthermore, in our studies, we showed that tumor developed in nude mice on injection of HEK293 cells that constitutively express PTTG expressed high levels of both MMP-2 mRNA and protein, and MMP-2 activity. Conditioned medium collected from the HEK293 cells overexpressing PTTG showed a significant increase in cell migration, invasion and tubule formation of human umbilical vein endothelial cells (HUVEC). Pretreatment of conditioned medium with MMP-2-specific antibody significantly decreased these effects, suggesting that PTTG may contribute to tumor angiogenesis and metastasis via activation of proteolysis and increase in invasion through modulation of MMP-2 activity and expression.

Conclusion

Our results provide novel information that PTTG contributes to cell migration, invasion and angiogenesis by induction of MMP-2 secretion and expression. Furthermore, we showed that tumors developed in nude mice on injection of HEK293 cells that constitutively express PTTG induce expression of MMP-2 and significantly increase its functional activity, suggesting a relationship between PTTG levels and MMP-2 which may play a critical role in regulation of tumor growth, angiogenesis and metastasis. Blocking of function of PTTG or down regulation of its expression in tumors may result in suppression of tumor growth and metastasis, through the down regulation of MMP-2 expression and activity. To our knowledge, this study is the first study demonstrating the modulation of MMP-2 expression and biological activity by PTTG.

Angiogenic and antiangiogenic gene therapy

Gene therapy is thought to be a promising method for the treatment of various diseases. One gene therapy strategy involves the manipulations on a process of formation of new vessels, commonly defined as angiogenesis. Angiogenic and antiangiogenic gene therapy is a new therapeutic approach to the treatment of cardiovascular and cancer patients, respectively. So far, preclinical and clinical studies are successfully focused mainly on the treatment of coronary artery and peripheral artery diseases. Plasmid vectors are often used in preparations in angiogenic gene therapy trials. The naked plasmid DNA effectively transfects the skeletal muscles or heart and successfully expresses angiogenic genes that are the result of new vessel formation and the improvement of the clinical state of patients. The clinical preliminary data, although very encouraging, need to be well discussed and further study surely continued. It is really possible that further development of molecular biology methods and advances in gene delivery systems will cause therapeutic angiogenesis as well as antiangiogenic methods to become a supplemental or alternative option to the conventional methods of treatment of angiogenic diseases.

Mutually exclusive NRASQ61R and BRAFV600E mutations at the single-cell level in the same human melanoma

Activating BRAF or NRAS mutations have been found in 80% of human sporadic melanomas, but only one of these genetic alterations could be detected in each tumour. This suggests that BRAF and NRAS 'double mutants' may not provide advantage for tumour growth, or may even be selected against during tumorigenesis. However, by applying mutant-allele-specific-amplification-PCR method to short-term melanoma lines, one out of 14 tumours was found to harbour both BRAFV600E and the activating NRASQ61R mutations. On the other hand, analysis of 21 melanoma clones isolated by growth in soft agar from this tumour indicated that 16/21 clones harboured a BRAFV600E, but were wild-type for NRAS, whereas the remaining had the opposite genotype (NRASQ61R/wild-type BRAF). When compared to BRAFV600E clones, NRASQ61R clones displayed reduced growth in soft agar, but higher proliferative ability in vitro in liquid medium and even in vivo after grafting into SCID/SCID mice. These data suggest that NRAS and BRAF activating mutations can coexist in the same melanoma, but are mutually exclusive at the single-cell level. Moreover, the presence of NRASQ61R or BRAFV600E is associated with distinct in vitro and in vivo growth properties of neoplastic cells.

Molecular regulation of tumor angiogenesis: mechanisms and therapeutic implications

Angiogenesis, the process of new capillary formation from a pre-existing vessel plays an essential role in both embryonic and postnatal development, in the remodeling of various organ systems, and in several pathologies, particularly cancer. In the last 20 years of angiogenesis research, a variety of angiogenic regulators, both positive and negative, have been identified. The discovery of several anti-angiogenic factors has led to the development of novel cancer therapies based on targeting a tumor's vascular supply. A number of these new therapies are currently being tested in clinical trials in the U.S.A. and elsewhere. A major advance in the field of anti-angiogenic therapy occurred recently when the FDA approved Avastin (bevacizumab), the first solely anti-angiogenesis therapy approved for treatment of human cancer. While it has long been appreciated that tumor growth and progression are dependent on angiogenesis, it is only recently that progress has been made in elucidating the molecular mechanisms that regulate the earliest stage in the angiogenic program, the angiogenic switch. This checkpoint is characterized by the transition of a dormant, avascular tumor into an active, vascular one. Anti-angiogenic therapies to date have essentially been designed to suppress the neovasculature in established tumors. However, identifying the mechanisms that cause a tumor to acquire an angiogenic phenotype may lead to the discovery of new therapeutic modalities and complementary diagnostics that could be used to block the angiogenic switch, thereby preventing subsequent tumor progression. In this chapter on the role of angiogenesis in cancer, we (1) provide an overview of the process of angiogenesis with special regard to the molecules and physiological conditions that regulate this process, (2) review recent studies describing the use of anti-angiogenic approaches in the treatment of a variety of human cancers, and (3) discuss the recent literature focused on the study of the molecules and molecular mechanisms that may be regulating the initiation of the angiogenic phenotype in tumors, and the clinical impact that this knowledge may have in the future.

Oncogenes as novel targets for cancer therapy (part II): Intermediate signaling molecules

This is the second part of a four-part review on potential therapeutic targeting of oncogenes. The previous part introduced the new technologies responsible for the advancement of oncogene identification, target validation, and drug design. Because of such advances, new specific and more efficient therapeutic agents can be developed for cancer. This part of the review continues the exploration of various oncogenes, which we have grouped within seven categories: growth factors, tyrosine kinases, intermediate signaling molecules, transcription factors, cell cycle regulators, DNA damage repair genes, and genes involved in apoptosis. Part I included a discussion of growth factors and tyrosine kinases. This portion of the review covers intermediate signaling molecules and the various strategies used to inhibit their expression or decrease their activities.

Molecular consequences of silencing mutant K-ras in pancreatic cancer cells: justification for K-ras-directed therapy

Mutation of the K-ras gene is an early event in the development of pancreatic adenocarcinoma and, therefore, RNA interference (RNAi) directed toward mutant K-ras could represent a novel therapy. In this study, we examine the phenotypic and molecular consequences of exposure of pancreatic tumor cells to mutant-specific K-ras small interfering RNA. Specific reduction of activated K-ras via RNAi in Panc-1 and MiaPaca-2 cells resulted in cellular changes consistent with a reduced capacity to form malignant tumors. These changes occur through distinct mechanisms but likely reflect an addiction of each cell line to oncogene stimulation. Both cell lines show reduced proliferation after K-ras RNAi, but only MiaPaca-2 cells showed increased apoptosis. Both cell lines showed reduced migration after K-ras knockdown, but changes in integrin levels were not consistent between the cell lines. Both cell lines showed alteration of the level of GLUT-1, a metabolism-associated gene that is downstream of c-myc, with Panc-1 cells demonstrating decreased GLUT-1 levels, whereas MiaPaca-2 cells showed increased levels of expression after K-ras knockdown. Furthermore, after K-ras RNAi, there was a reduction in angiogenic potential of both Panc-1 and MiaPaca-2 cells. Panc-1 cells increased the level of expression of thrombospondin-1, an endogenous inhibitor of angiogenesis, whereas MiaPaca-2 cells decreased the production of vascular endothelial growth factor, a primary stimulant of angiogenesis in pancreatic tumors. We have found that silencing mutant K-ras through RNAi results in alteration of tumor cell behavior in vitro and suggests that targeting mutant K-ras specifically might be effective against pancreatic cancer in vivo.

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

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

Microenvironmental adaptation of experimental tumours to chronic vs acute hypoxia

This study investigated long-term microenvironmental responses (oxygenation, perfusion, metabolic status, proliferation, vascular endothelial growth factor (VEGF) expression and vascularisation) to chronic hypoxia in experimental tumours. Experiments were performed using s.c.-implanted DS-sarcomas in rats. In order to induce more pronounced tumour hypoxia, one group of animals was housed in a hypoxic atmosphere (8% O₂) for the whole period of tumour growth (chronic hypoxia). A second group was acutely exposed to inspiratory hypoxia for only 20 min prior to the measurements (acute hypoxia), whereas animals housed under normal atmospheric conditions served as controls. Acute hypoxia reduced the median oxygen partial pressure (pO₂) dramatically (1 vs 10 mmHg in controls), whereas in chronically hypoxic tumours the pO₂ was significantly improved (median pO₂=4 mmHg), however not reaching the control level. These findings reflect the changes in tumour perfusion where acutely hypoxic tumours show a dramatic reduction of perfused tumour vessels (maybe the result of a simultaneous reduction in arterial blood pressure). In animals under chronic inspiratory hypoxia, the number of perfused vessels increased (compared to acute hypoxia), although the perfusion pattern found in control tumours was not reached. In the chronically hypoxic animals, tumour cell proliferation and tumour growth were significantly reduced, whereas no differences in VEGF expression and vascular density between these groups were observed. These results suggest that long-term adaptation of tumours to chronic hypoxia in vivo, while not affecting vascularity, does influence the functional status of the microvessels in favour of a more homogeneous perfusion.

Ras-induced interleukin-8 expression plays a critical role in tumor growth and angiogenesis

The role of Ras oncogenes in promoting cellular transformation is well established. However, the contribution of Ras signaling to interactions between tumor cells and their host environment remains poorly characterized. Here, we demonstrate that the inflammatory mediator interleukin-8 (CXCL-8/IL-8) is a transcriptional target of Ras signaling. Using a tumor xenograft model, we show that Ras-dependent CXCL-8 secretion is required for the initiation of tumor-associated inflammation and neovascularization. Collectively, our data identify a novel mechanism by which the Ras oncogene can elicit a stromal response that fosters cancer progression.