A systems approach to cancer therapy. (Antioncogenics + standard cytotoxics-->mechanism(s) of interaction)

Investigation of the evolution of tumor-induced microvascular network under the inhibitory effect of anti-angiogenic factor, angiostatin: A mathematical study

Anti-angiogenesis as a treatment strategy for normalizing the microvascular network of tumors is of great interest among researchers, especially in combination with chemotherapy or radiotherapy. According to the vital role that angiogenesis plays in tumor growth and in exposing the tumor to therapeutic agents, this work develops a mathematical framework to study the influence of angiostatin, a plasminogen fragment that shows the anti-angiogenic function, in the evolutionary behavior of tumor-induced angiogenesis. Angiostatin-induced microvascular network reformation is investigated in a two-dimensional space by considering two parent vessels around a circular tumor by a modified discrete angiogenesis model in different tumor sizes. The effects of imposing modifications on the existing model, i.e., the matrix-degrading enzyme effect, proliferation and death of endothelial cells, matrix density function, and a more realistic chemotactic function, are investigated in this study. Results show a decrease in microvascular density in response to the angiostatin. A functional relationship exists between angiostatin's ability to normalize the capillary network and tumor size or progression stage, such that capillary density decreases by 55%, 41%, 24%, and 13% in tumors with a non-dimensional radius of 0.4, 0.3, 0.2, and 0.1, respectively, after angiostatin administration.

Mitochondrial oxidative stress in the tumor microenvironment and cancer immunoescape: foe or friend?

The major concept of "oxidative stress" is an excess elevated level of reactive oxygen species (ROS) which are generated from vigorous metabolism and consumption of oxygen. The precise harmonization of oxidative stresses between mitochondria and other organelles in the cell is absolutely vital to cell survival. Under oxidative stress, ROS produced from mitochondria and are the major mediator for tumorigenesis in different aspects, such as proliferation, migration/invasion, angiogenesis, inflammation, and immunoescape to allow cancer cells to adapt to the rigorous environment. Accordingly, the dynamic balance of oxidative stresses not only orchestrate complex cell signaling events in cancer cells but also affect other components in the tumor microenvironment (TME). Immune cells, such as M2 macrophages, dendritic cells, and T cells are the major components of the immunosuppressive TME from the ROS-induced inflammation. Based on this notion, numerous strategies to mitigate oxidative stresses in tumors have been tested for cancer prevention or therapies; however, these manipulations are devised from different sources and mechanisms without established effectiveness. Herein, we integrate current progress regarding the impact of mitochondrial ROS in the TME, not only in cancer cells but also in immune cells, and discuss the combination of emerging ROS-modulating strategies with immunotherapies to achieve antitumor effects.

Numerical Investigation on the Anti-Angiogenic Therapy-Induced Normalization in Solid Tumors

This study numerically analyzes the fluid flow and solute transport in a solid tumor to comprehensively examine the consequence of normalization induced by anti-angiogenic therapy on drug delivery. The current study leads to a more accurate model in comparison to previous research, as it incorporates a non-homogeneous real-human solid tumor including necrotic, semi-necrotic, and well-vascularized regions. Additionally, the model considers the effects of concurrently chemotherapeutic agents (three macromolecules of IgG, F(ab′)2, and F(ab′)) and different normalization intensities in various tumor sizes. Examining the long-term influence of normalization on the quality of drug uptake by necrotic area is another contribution of the present study. Results show that normalization decreases the interstitial fluid pressure (IFP) and spreads the pressure gradient and non-zero interstitial fluid velocity (IFV) into inner areas. Subsequently, wash-out of the drug from the tumor periphery is decreased. It is also demonstrated that normalization can improve the distribution of solute concentration in the interstitium. The efficiency of normalization is introduced as a function of the time course of perfusion, which depends on the tumor size, drug type, as well as normalization intensity, and consequently on the dominant mechanism of drug delivery. It is suggested to accompany anti-angiogenic therapy by F(ab′) in large tumor size (Req=2.79  cm) to improve reservoir behavior benefit from normalization. However, IgG is proposed as the better option in the small tumor (Req=0.46  cm), in which normalization finds the opportunity of enhancing uniformity of IgG average exposure by 22%. This study could provide a perspective for preclinical and clinical trials on how to take advantage of normalization, as an adjuvant treatment, in improving drug delivery into a non-homogeneous solid tumor.

Assessing Oximetry Response to Chimeric Antigen Receptor T-cell Therapy against Glioma with 19F MRI in a Murine Model

Purpose

To assess the cell-specific, intracellular partial pressure of oxygen (Po₂) dynamics of both tumor and chimeric antigen receptor (CAR) T cells in a murine immunotherapy model.

Materials and Methods

Human glioblastoma cells or human T cells were intracellularly labeled with perfluorocarbon nanoemulsion droplet sensors prior to in vivo injection in severe combined immunodeficient mice to measure Po₂ in the two cell types in response to treatment. Two main sets of experiments were performed: (a) mice were injected in the flank with perfluorocarbon-labeled human glioblastoma cells and were then inoculated with either CAR T cells or untransduced T cells or were untreated 5 days after tumor inoculation; and (b) mice with unlabeled glioblastoma tumors were inoculated with perfluorocarbon-labeled CAR T cells or untransduced T cells 5 days after tumor inoculation. Longitudinal fluorine 19 (¹⁹F) spin-lattice relaxation time measurements of the tumor mass were used to ascertain absolute Po₂ in vivo. Results were analyzed for significance using an analysis of variance, a linear mixed-effect model, and a Pearson correlation coefficient test, as appropriate.

Results

The intracellular tumor cell Po₂ temporal dynamics exhibited delayed, transient hyperoxia at 3 days after infusion of CAR T cells, commensurate with significant tumor cell killing and CAR T-cell infiltration, as observed by bioluminescence imaging and histologic findings. Conversely, no significant changes were detected in CAR or untransduced T-cell intracellular Po₂ over time in tumor using these same methods. Moreover, it was observed that the total ¹⁹F tumor cell signal quenches with treatment, consistent with rapid tissue clearance of probe from apoptotic tumor cells.

Conclusion

Cell-specific Po₂ measurements using perfluorocarbon probes can provide insights into effector cell function and tumor response in cellular immunotherapeutic cancer models.Keywords: Animal Studies, MR-Imaging, MR-Spectroscopy, Molecular Imaging-Cancer, Molecular Imaging-Immunotherapy Supplemental material is available for this article. © RSNA, 2021See also commentary by Bulte in this issue.

ABL001, a Bispecific Antibody Targeting VEGF and DLL4, with Chemotherapy, Synergistically Inhibits Tumor Progression in Xenograft Models

Delta-like-ligand 4 (DLL4) is a promising target to augment the effects of VEGF inhibitors. A simultaneous blockade of VEGF/VEGFR and DLL4/Notch signaling pathways leads to more potent anti-cancer effects by synergistic anti-angiogenic mechanisms in xenograft models. A bispecific antibody targeting VEGF and DLL4 (ABL001/NOV1501/TR009) demonstrates more potent in vitro and in vivo biological activity compared to VEGF or DLL4 targeting monoclonal antibodies alone and is currently being evaluated in a phase 1 clinical study of heavy chemotherapy or targeted therapy pre-treated cancer patients (ClinicalTrials.gov Identifier: NCT03292783). However, the effects of a combination of ABL001 and chemotherapy on tumor vessels and tumors are not known. Hence, the effects of ABL001, with or without paclitaxel and irinotecan were evaluated in human gastric or colon cancer xenograft models. The combination treatment synergistically inhibited tumor progression compared to each monotherapy. More tumor vessel regression and apoptotic tumor cell induction were observed in tumors treated with the combination therapy, which might be due to tumor vessel normalization. Overall, these findings suggest that the combination therapy of ABL001 with paclitaxel or irinotecan would be a better clinical strategy for the treatment of cancer patients.

The role of tumor-derived exosomes in tumor angiogenesis and tumor progression

Exosomes, belonging to the group of extracellular bodies, are released by healthy as well as cancerous cells and serve as a communication pathway. Tumor-derived exosomes (TEX) possess the capacity to reprogram the function of normal cells owing to their genetic and molecular cargo. Such exosomes target endothelial cells (among others) in the tumor microenvironment to promote angiogenesis. Blood supply is essential in solid tumor growth and metastasis. The potential of pro-angiogenic changes is enhanced by an increased amount of circulating tumor-derived exosomes in the body fluids of cancer patients. A vascular network is important, since the proliferation, as well as the metastatic spread of cancer cells depends on an adequate supply of oxygen and nutrients, and the removal of waste products. New blood vessels and lymphatic vessels are formed through processes called angiogenesis and lymphangiogenesis, respectively. Angiogenesis is regulated by both activator and inhibitor molecules. Thousands of patients have received anti-angiogenic therapy to date. Despite their theoretical efficacy, anti-angiogenic treatments have not proved beneficial in terms of long-term survival. Tumor-derived exosomes carrying pro-angiogenic factors might be a target for new anti-cancer therapy.

Apj+ Vessels Drive Tumor Growth and Represent a Tractable Therapeutic Target

Identification of cellular surface markers that distinguish tumorous from normal vasculature is important for the development of tumor vessel-targeted therapy. Here, we show that Apj, a G protein-coupled receptor, is highly enriched in tumor endothelial cells but absent from most endothelial cells of adult tissues in homeostasis. By genetic targeting using Apj-CreER and Apj-DTRGFP-Luciferase, we demonstrated that hypoxia-VEGF signaling drives expansion of Apj⁺ tumor vessels and that targeting of these vessels, genetically and pharmacologically, remarkably inhibits tumor angiogenesis and restricts tumor growth. These in vivo findings implicate Apj⁺ vessels as a key driver of pathological angiogenesis and identify Apj⁺ endothelial cells as an important therapeutic target for the anti-angiogenic treatment of tumors.

Epigallocatechin-3-gallate-induced vascular normalization in A549-cell xenograft-bearing nude mice: therapeutic efficacy in combination with chemotherapy

Purpose

Large-scale studies have revealed that appropriate antiangiogenic treatment enables the recovery of the normal structure and function of solid tumor vessels. Epigallocatechin-3-gallate (EGCG), a natural extract of green tea, has multiple effects on angiogenesis. However, normalization of blood vessels due to natural ingredients has not yet been reported. Therefore, we examined the microvasculature, microenvironment, and efficacy of EGCG combined with chemotherapy in a xenograft model.

Methods

We treated A549 cell (human lung adenocarcinoma cell line) xenograft-bearing nude mice with EGCG in vivo. CD31, αSMA, and collagen IV were labeled and detected using quantum-dot double-labeled immunofluorescence to measure microvessel density, microvessel pericyte-coverage index, and collagen IV expression. Vessel-perfusion function was determined by lectin injection, permeability by Evans blue extravasation, interstitial fluid pressure using the wick-in-needle technique, and hypoxia levels using a polarographic electrode and immunohistochemical pimonidazole labeling. Cisplatin concentration in tumor tissue was detected using graphite-furnace atomic absorption spectrophotometry. Xenograft mice were randomized into five groups: treated with saline, cisplatin, EGCG, EGCG + cisplatin on day 1, or EGCG + cisplatin during the vascular normalization window. Tumor-growth delay and tumor-suppression rate were measured to evaluate tumor growth.

Results

EGCG treatment in vivo caused temporary changes, including transient depression of microvessel density, microvessel pericyte-coverage index, and collagen IV expression, transient elevation of vessel perfusion and permeability, and decreased interstitial fluid pressure and hypoxia. During vascular normalization, pretreatment with EGCG increased cisplatin concentration in tumor tissue compared with treatment with cisplatin only. Tumor-growth delay after treatment in the five groups during the vascular normalization window was 6.3±1.51, 7.5±1.57, 8.3±1.79, 12.1±1.35, and 15.4±1.99 days, indicating synergistic EGCG–cisplatin effects, especially during the vascular normalization window (P<0.01).

Conclusion

EGCG-induced vascular normalization in human lung adenocarcinoma may be a novel modality for enhancing chemotherapy effects.

Nanoparticle-Mediated Combination Therapy: Two-in-One Approach for Cancer

Cancer represents a group of heterogeneous diseases characterized by uncontrolledgrowth and spread of abnormal cells, ultimately leading to death. Nanomedicine plays a significantrole in the development of nanodrugs, nanodevices, drug delivery systems and nanocarriers. Someof the major issues in the treatment of cancer are multidrug resistance (MDR), narrow therapeuticwindow and undesired side effects of available anticancer drugs and the limitations of anticancerdrugs. Several nanosystems being utilized for detection, diagnosis and treatment such as theranosticcarriers, liposomes, carbon nanotubes, quantum dots, polymeric micelles, dendrimers and metallicnanoparticles. However, nonbiodegradable nanoparticles causes high tissue accumulation andleads to toxicity. MDR is considered a major impediment to cancer treatment due to metastatictumors that develop resistance to chemotherapy. MDR contributes to the failure of chemotherapiesin various cancers, including breast, ovarian, lung, gastrointestinal and hematological malignancies.Moreover, the therapeutic efficiency of anticancer drugs or nanoparticles (NPs) used alone is lessthan that of the combination of NPs and anticancer drugs. Combination therapy has long beenadopted as the standard first-line treatment of several malignancies to improve the clinical outcome.Combination therapy with anticancer drugs has been shown to generally induce synergistic drugactions and deter the onset of drug resistance. Therefore, this review is designed to report andanalyze the recent progress made to address combination therapy using NPs and anticancer drugs.We first provide a comprehensive overview of the angiogenesis and of the different types of NPscurrently used in treatments of cancer; those emphasized in this review are liposomes, polymericNPs, polymeric micelles (PMs), dendrimers, carbon NPs, nanodiamond (ND), fullerenes, carbonnanotubes (CNTs), graphene oxide (GO), GO nanocomposites and metallic NPs used forcombination therapy with various anticancer agents. Nanotechnology has provided the convenienttools for combination therapy. However, for clinical translation, we need continued improvementsin the field of nanotechnology.

Thalidomide Combined with Transcatheter Arterial Chemoembolization (TACE) for Intermediate or Advanced Hepatocellular Carcinoma: A Systematic Review and GRADE Approach

Objective:According to current guidelines, there is no clear second-line treatment for advanced liver cancer. In practice, clinicians have attempted to use thalidomide(TLD) combined with transcatheter arterial chemoembolization (TACE) for treating liver cancer. This study aims to assess the clinical efficacy and safety of TLD combined with TACE in patients with intermediate or advanced hepatocellular carcinoma. Methods: Medline, Embase, the Cochrane Central Register of Controlled Trials (CENTRAL), database of ClinicalTrials.gov, CBM, CNKI, VIP and Wanfang database were searched for eligible studies. Criteria for inclusion in our meta-analysis included a study that patients diagnosed with intermediate or advanced HCC, the use of TACE plus TLD or its derivatives, and the availability of outcome data for survival. A meta-analysis was conducted to summarize the evidences of randomized controlled trials (RCTs). And finally, the GRADE approach was used to assess the quality of these evidences. Results: Twelve RCTs involving 894 Hepatocellular Carcinoma (HCC) patients were included. The meta-analysis results showed that TACE plus TLD was significantly superior than TACE alone in terms of 12-month survival rate (OR=2.55, 95% CI:1.78-3.64, P<0.01), 24-month survival rate (OR=2.95, 95% CI:1.96-4.44, P<0.01), 36-month survival rate (OR=2.95, 95% CI:1.41-6.19, P<0.004), progression-free survival (PFS) (MD=2.23, 95% CI:1.19-3.28 , P<0.001), objective response rate (OR=1.84, 95% CI:1.34-2.52, P<0.0001), and disease control rate (OR=2.68, 95% CI:1.80-3.99). Subgroup analysis demonstrated no differences across related outcomes. Sensitivity analyses showed no important differences in the estimates of effects. Quality of evidence for all outcomes was rated moderate to very low after applying GRADE approach. Conclusions: Current evidence seemed to support the suggestion that TACE plus TLD as the second line treatment for patients with intermediate or advanced HCC. However, this finding is not definitive due to the poor quality of included studies, more carefully designed and conducted RCTs are warranted to confirm above conclusions.

Multi-parameter MRI to investigate vasculature modulation and photo-thermal ablation combination therapy against cancer

Nanotransducer-mediated photothermal therapy (PTT) has emerged as an attractive therapy modality against cancer, but its efficacy is often limited by the amount of nanoparticles delivered to tumors. Previous studies showed a vasculature modulation treatment, which dilates or prunes tumor blood vessels, may enhance tumor uptake of nanoparticles. However, exploiting these approaches for improved PTT has seldom been studied. In this study, we investigated the impact of mild hyperthermia or anti-angiogenesis therapy on PTT. Briefly, we gave tumor-bearing balb/c mice low doses of sunitinib or submerged tumors in a 42 °C water bath. Next, we injected PEGylated reduced graphene oxide (RGO-PEG) and irradiated the tumors to induce PTT. We then followed up the treatment with multi-parameter MRI. Contrary to expectation, both vessel modulation strategies led to diminished PTT efficacy. Our results show that vessel modulation does not warrant improved PTT, and should be carefully gauged when used in combination with PTT.

Biopsy proportion of tumour predicts pathological tumour response and benefit from chemotherapy in resectable oesophageal carcinoma: results from the UK MRC OE02 trial

Background

Neoadjuvant chemotherapy followed by surgery is the standard of care for UK patients with locally advanced resectable oesophageal carcinoma (OeC). However, not all patients benefit from multimodal treatment and there is a clinical need for biomarkers which can identify chemotherapy responders. This study investigated whether the proportion of tumour cells per tumour area (PoT) measured in the pre-treatment biopsy predicts chemotherapy benefit for OeC patients.

Patients and methods

PoT was quantified using digitized haematoxylin/eosin stained pre-treatment biopsy slides from 281 OeC patients from the UK MRC OE02 trial (141 treated by surgery alone (S); 140 treated by 5-fluorouracil/cisplatin followed by surgery (CS)). The relationship between PoT and clinicopathological data including tumour regression grade (TRG), overall survival and treatment interaction was investigated.

Results

PoT was associated with chemotherapy benefit in a non-linear fashion (test for interaction, P=0.006). Only patients with a biopsy PoT between 40% and 70% received a significant survival benefit from neoadjuvant chemotherapy (N=129; HR (95%CI):1.94 (1.39-2.71), unlike those with lower or higher PoT (PoT<40%, N=39, HR:1.25 (0.66-2.35); PoT>70% (N=28, HR:0.65 (0.36-1.18)). High pre-treatment PoT was related to lack of primary tumour regression (TRG 4 or 5), P=0.0402.

Conclusions

This is the first study to identify in a representative subgroup of OeC patients from a large randomized phase III trial that the proportion of tumour in the pre-chemotherapy biopsy predicts benefit from chemotherapy and may be a clinically useful biomarker for patient treatment stratification.

Proportion of tumour is a novel biomarker which can be measured in the pre-treatment diagnostic biopsy and which may enable the identification of chemotherapy responders and non-responders among patients with oesophageal carcinoma. Proportion of tumour could easily become part of the routine reporting of oesophageal cancer biopsies and may aid in managing patients with borderline resectable cancer.

Therapy for Cancer: Strategy of Combining Anti-Angiogenic and Target Therapies

The concept that blood supply is required and necessary for cancer growth and spreading is intuitive and was firstly formalized by Judah Folkman in 1971, when he demonstrated that cancer cells release molecules able to promote the proliferation of endothelial cells and the formation of new vessels. This seminal result has initiated one of the most fascinating story of the medicine, which is offering a window of opportunity for cancer treatment based on the use of molecules inhibiting tumor angiogenesis and in particular vascular-endothelial growth factor (VEGF), which is the master gene in vasculature formation and is the commonest target of anti-angiogenic regimens. However, the clinical results are far from the remarkable successes obtained in pre-clinical models. The reasons of this discrepancy have been partially understood and well addressed in many reviews (Bergers and Hanahan, 2008; Bottsford-Miller et al., 2012; El-Kenawi and El-Remessy, 2013; Wang et al., 2015; Jayson et al., 2016). At present anti-angiogenic regimens are not used as single treatments but associated with standard chemotherapies. Based on emerging knowledge of the biology of VEGF, here we sustain the hypothesis of the efficacy of a dual approach based on targeting pro-angiogenic pathways and other druggable targets such as mutated oncogenes or the immune system.

Endostatin and irradiation modifies the activity of ADAM10 and neprilysin in breast cancer cells

Angiogenesis, the formation of new blood vessels, is regarded as a key cancer cell property. Endostatin (ES) is a potential antiangiogenic agent and it may be useful when implemented in combination with other cancer therapeutic strategies. The present study investigated the in vitro effects of ES, radiotherapy (RT) or combination therapy (ES + RT) on two important proteases, a disintegrin and metalloproteinase domain‑containing protein 10 (ADAM10) and neprilysin (NEP) in 4T1 mouse breast cancer cells and the more metastatic phenotype of 4THMpc breast cancer cells. 4T1 and 4THMpc cells were treated with recombinant murine ES (4 µg/ml) alone, RT (45 Gy) alone or with ES + RT. ADAM10 enzyme activity was determined using a tumor necrosis factor‑α converting enzyme (α‑secretase) activity assay kit, and NEP enzyme activity was measured with a fluorometric assay based on the generation of free dansyl‑D‑Ala‑Gly from N-dansyl-Ala-Gly-D-nitro-Phe-Gly, the substrate of NEP. Western blotting analysis was performed to determine whether the altered enzyme activity levels of the two cell lines occurred due to changes in expression level. These data indicate that ES independently potentiates the activity of ADAM10 and NEP enzymes in 4T1 and 4THMpc breast cancer cells.

Radiation-enhanced Endostatin Gene Expression and Effects of Combination Treatment

Targeting cells that support tumor growth by administering potent angiogenesis inhibitors is currently an area of intense interest. In the present study, a unique plasmid vector for the mouse endostatin gene, pXLG-mEndo, was constructed and evaluated with and without radiation using the Lewis lung carcinoma (LLC) cell line. The physical properties of the expressed endostatin protein were validated by PCR, gel electrophoresis, and Western blot. Enzyme-linked immunosorbent and immunocytochemical analyses for the therapeutic gene demonstrated that transfected LLC cells secreted the protein into the medium. Exposure of the cells to 2 gray (Gy) γ-rays reduced the time to reach the maximum expression level of the endostatin gene and also increased the amount of secreted endostatin protein (P<0.001). Biological activity of the endostatin was demonstrated by the inhibition of tube formation by human umbilical vein endothelial cells (HUVEC). Based on 3 H-thymidine incorporation, endostatin expression significantly depressed DNA synthesis in HUVEC and LLC cells compared to controls transfected with parental vector or no vector (P>0.005). In addition, radiation increased the efficiency of endostatin-mediated inhibition of both cell types over a 3-day period post-exposure (P<0.05 or less). Intratumoral injection of 100 μg pXLG-mEndo combined with 10 Gy radiation significantly delayed LLC tumor growth, especially when each modality was delivered twice (P<0.05 or less compared to all other groups). No toxicity was observed. These findings are very promising and suggest that endostatin therapy with a plasmid vector, such as pXLG-mEndo, may enhance the efficacy of radiotherapy for lung cancer.

Avastin® in combination with gemcitabine and cisplatin significantly inhibits tumor angiogenesis and increases the survival rate of human A549 tumor-bearing mice

The aim of this study was to investigate the effect of Avastin® in combination with gemcitabine and cisplatin (GP) on the tumor growth of A549 tumor-bearing mice and the potential anti-tumor mechanism. A total of 30 human A549 tumor-bearing nude mice were randomly divided into the Avastin, chemotherapy and combined treatment groups for treatment with an intraperitoneal injection of Avastin (5 mg/kg) (Avastin group); an intraperitoneal injection of gemcitabine (4 mg/kg) and cisplatin (4 mg/kg) (chemotherapy group); or intraperitoneal injections of Avastin and GP (combined treatment group). The mice were observed for 30 days and the tumor growth, survival and body weight of the mice in the three groups were analyzed. The protein level of vascular endothelial growth factor (VEGF) in the tumor tissues was analyzed by ELISA. The vascular density and structural changes of the tumor were analyzed using immunohistochemistry. Compared with the Avastin and chemotherapy groups, the tumor growth of mice in the combined treatment group was significantly inhibited, and the survival rate of the mice was increased significantly. No difference in body weight was observed among the three groups of mice (P>0.05). The levels of VEGF in the combined treatment group tumor tissues were significantly reduced compared with those in the chemotherapy group tumor tissues (P<0.05). Furthermore, the vessel density of the tumor tissue in the combined treatment group was significantly reduced compared with that in the chemotherapy group (P<0.05), and the number of normal vessels in the combined treatment group tumors was significantly higher than that in the chemotherapy group tumors after 7 days of treatment (P<0.05). In conclusion, Avastin can significantly decrease the level of VEGF in tumor tissue, inhibit tumor angiogenesis and promote the normalization of tumor vascular structure, which may explain the enhanced efficacy of Avastin in combination with chemotherapy.

Antiangiogenic effects of marine sponge derived compounds on cancer

The term "angiogenic switch" refers to a time-restricted event during tumor progression where the balance between pro- and anti-angiogenic factors, resulting in the transition from dormant avascularized hyperplasia to outgrowing vascularized tumor and eventually to malignant tumor progression. Targeting angiogenesis and its mechanistic pathways are critical target for cancer therapy. Recently, marine derived compounds, plays major role in cancer research. Several sponge derived compounds such as alkaloids, terpenes, macrocylic lactone and polyketide are leading drugs in the treatment of different types of diseases including cancer. Those marine sponge compounds inhibit cancer cell proliferation and tumor angiogenesis. Hence, this review sheds light on angiogenic regulators and marine sponge derived antiangiogenic compounds for cancer.

Angiogenesis inhibitors in cancer therapy: mechanistic perspective on classification and treatment rationales

Angiogenesis, a process of new blood vessel formation, is a prerequisite for tumour growth to supply the proliferating tumour with oxygen and nutrients. The angiogenic process may contribute to tumour progression, invasion and metastasis, and is generally accepted as an indicator of tumour prognosis. Therefore, targeting tumour angiogenesis has become of high clinical relevance. The current review aimed to highlight mechanistic details of anti-angiogenic therapies and how they relate to classification and treatment rationales. Angiogenesis inhibitors are classified into either direct inhibitors that target endothelial cells in the growing vasculature or indirect inhibitors that prevent the expression or block the activity of angiogenesis inducers. The latter class extends to include targeted therapy against oncogenes, conventional chemotherapeutic agents and drugs targeting other cells of the tumour micro-environment. Angiogenesis inhibitors may be used as either monotherapy or in combination with other anticancer drugs. In this context, many preclinical and clinical studies revealed higher therapeutic effectiveness of the combined treatments compared with individual treatments. The proper understanding of synergistic treatment modalities of angiogenesis inhibitors as well as their wide range of cellular targets could provide effective tools for future therapies of many types of cancer.

Tumor delivery of chemotherapy combined with inhibitors of angiogenesis and vascular targeting agents

Numerous angiogenesis-vascular targeting agents have been admitted to the ranks of cancer therapeutics; most are used in polytherapy regimens. This review looks at recent progress and our own preclinical experience in combining angiogenesis inhibitors, mainly acting on VEGF/VEGFR pathways, and vascular targeting agents with conventional chemotherapy, discussing the factors that determine the outcome of these treatments. Molecular and morphological modifications of the tumor microenvironment associated with drug distribution and activity are reviewed. Modalities to improve drug delivery and strategies for optimizing combination therapy are examined.

Vascular normalization as a therapeutic strategy for malignant and nonmalignant disease

Pathological angiogenesis-driven by an imbalance of pro- and antiangiogenic signaling-is a hallmark of many diseases, both malignant and benign. Unlike in the healthy adult in which angiogenesis is tightly regulated, such diseases are characterized by uncontrolled new vessel formation, resulting in a microvascular network characterized by vessel immaturity, with profound structural and functional abnormalities. The consequence of these abnormalities is further modification of the microenvironment, often serving to fuel disease progression and attenuate response to conventional therapies. In this article, we present the "vascular normalization" hypothesis, which states that antiangiogenic therapy, by restoring the balance between pro- and antiangiogenic signaling, can induce a more structurally and functionally normal vasculature in a variety of diseases. We present the preclinical and clinical evidence supporting this concept and discuss how it has contributed to successful treatment of both solid tumors and several benign conditions.

MicroRNAs and tumor vasculature normalization: impact on anti-tumor immune response

Inefficient immune response is a major glitch during tumor growth and progression. Chaotic and leaky blood vessels created in the process of angiogenesis allow tumor cells to escape and extricate anti-cancer immunity. Proangiogenic characteristics of hypoxic tumor microenvironment maintained by low oxygen tension attract endothelial progenitor cells, drive expansion of cancer stem cells, and deviantly differentiate monocyte descendants. Such cellular milieu further boosts immune tolerance and eventually appoint immunity for cancer advantage. Blood vessel normalization strategies that equilibrate oxygen levels within tumor and fix abnormal vasculature bring exciting promises to future anticancer therapies especially when combined with conventional chemotherapy. Recently, a new group of microRNAs (miRs) engaged in angiogenesis, called angiomiRs and hypoxamiRs, emerged as new therapeutic targets in cancer. Some of those miRs were found to efficiently regulate cancer immunity and their dysregulation efficiently programs aberrant angiogenesis and cancer metastasis. The present review highlights new findings in the field of miRs proficiency to normalize aberrant angiogenesis and to restore anti-tumor immune responses.

Class 3 semaphorins: physiological vascular normalizing agents for anti-cancer therapy

Findings from preclinical and clinical studies show that vascular normalization represents a novel strategy to enhance the efficacy of and overcome the acquired resistance to anti-angiogenic therapies in cancer. Several mechanisms of tumour vessel normalization have been revealed. Amongst them, secreted class 3 semaphorins (Sema3), which regulate axon guidance and angiogenesis, have been recently identified as novel vascular normalizing agents that inhibit metastatic dissemination by restoring vascular function. Here, we discuss the different biological functions and mechanisms of action of Sema3 in the context of tumour vascular normalization, and their impact on the different cellular components of the tumour microenvironment.

The tyrosine kinase inhibitor E-3810 combined with paclitaxel inhibits the growth of advanced-stage triple-negative breast cancer xenografts

E-3810 is a novel small molecule that inhibits VEGF receptor-1, -2, and -3 and fibroblast growth factor receptor-1 tyrosine kinases at nmol/L concentrations currently in phase clinical II. In preclinical studies, it had a broad spectrum of antitumor activity when used as monotherapy in a variety of human xenografts. We here investigated the activity of E-3810 combined with different cytotoxic agents in a MDA-MB-231 triple-negative breast cancer xenograft model. The molecule could be safely administered with 5-fluorouracil, cisplatin, and paclitaxel. The E-3810-paclitaxel combination showed a striking activity with complete, lasting tumor regressions; the antitumor activity of the combination was also confirmed in another triple-negative breast xenograft, MX-1. The activity was superior to that of the combinations paclitaxel+brivanib and paclitaxel+sunitinib. Pharmacokinetics studies suggest that the extra antitumor activity of the combination is not due to higher paclitaxel tumor levels, which in fact were lower in mice pretreated with all three kinase inhibitors, and the paclitaxel plasma levels excluded reduced drug availability. Pharmacodynamic studies showed that E-3810, brivanib, and sunitinib given as single agents or in combination with paclitaxel reduced the number of vessels, but did not modify vessel maturation. Reduced tumor collagen IV and increased plasma collagen IV, associated with increased matrix metalloproteinases (MMP), particularly host MMP-9, indicate a proteolytic remodeling of the extracellular matrix caused by E-3810 that in conjunction with the cytotoxic effect of paclitaxel on the tumor cells (caspase-3/7 activity) may contribute to the striking activity of their combination. These data support the therapeutic potential of combining E-3810 with conventional chemotherapy.

Anti-angiogenic drug discovery: lessons from the past and thoughts for the future

INTRODUCTION

Since the pioneering work of Judah Folkman, the discovery of bevacizumab has introduced the use of anti-angiogenic agents as a new modality for the treatment of cancer. Currently, hundreds of clinical trials involving anti-angiogenic agents, targeting different elements of the tumour angiogenesis pathway, are underway. However, thus far, the benefits of anti-angiogenic therapy in unselected patient populations are often marginal with harmful side effects.

AREAS COVERED

This article presents a detailed discussion of the lessons learnt from the use of bevacizumab and other VEGF pathway inhibitors in the clinical setting. Specifically, this article provides a review of the literature on anti-VEGF agents and other angiogenesis inhibitors used in pre-clinical and clinical trials for cancer treatment.

EXPERT OPINION

Future anti-angiogenic drug design centres on multiple protein targets and combinations including: growth factors, hypoxia-inducible factor and tumour endothelial cell markers unique to the tumour vasculature. Furthermore, treatment dosing, scheduling and combination with radiation and chemotherapy require further investigation, as does the potential of treating early disease, and the development of biomarkers which accurately predict response to therapy. These are essential for the future development of these drugs with individualised therapy likely to be the ultimate goal.

Bevacizumab-induced alterations in vascular permeability and drug delivery: a novel approach to augment regional chemotherapy for in-transit melanoma

PURPOSE

To investigate whether the systemically administered anti-VEGF monoclonal antibody bevacizumab could improve regional chemotherapy treatment of advanced extremity melanoma by enhancing delivery and tumor uptake of regionally infused melphalan (LPAM).

EXPERIMENTAL DESIGN

After treatment with systemic bevacizumab or saline, changes in vascular permeability were determined by spectrophotometric analysis of tumors infused with Evan's blue dye. Changes in vascular structure and tumor hemoglobin-oxygen saturation HbO(2) were determined by intravital microscopy and diffuse reflectance spectroscopy, respectively. Rats bearing the low-VEGF secreting DM738 and the high-VEGF secreting DM443 melanoma xenografts underwent isolated limb infusion (ILI) with melphalan (LPAM) or saline via the femoral vessels. The effect of bevacizumab on terminal drug delivery was determined by immunohistochemical analysis of LPAM-DNA adducts in tumor tissues.

RESULTS

Single-dose bevacizumab given three days before ILI with LPAM significantly decreased vascular permeability (50.3% in DM443, P < 0.01 and 35% in DM738, P < 0.01) and interstitial fluid pressure (57% in DM443, P < 0.01 and 50% in DM738, P = 0.01). HbO(2) decreased from baseline in mice following treatment with bevacizumab. Systemic bevacizumab significantly enhanced tumor response to ILI with LPAM in two melanoma xenografts, DM443 and DM738, increasing quadrupling time 37% and 113%, respectively (P = 0.03). Immunohistochemical analyses of tumor specimens showed that pretreatment with systemic bevacizumab markedly increased LPAM-DNA adduct formation.

CONCLUSIONS

Systemic treatment with bevacizumab before regional chemotherapy increases delivery of LPAM to tumor cells and represents a novel way to augment response to regional therapy for advanced extremity melanoma.

Clinical implications of genetic variations in the VEGF system in relation to colorectal cancer

Colorectal cancer (CRC) constitutes one of the most common malignancies in the world and, despite advances in diagnostics and treatments, patients still face a poor prognosis and a more individualized treatment approach appears necessary. The VEGF system and angiogenesis are involved in many aspects of tumor biology and the efficacy of chemotherapy, and some targeted therapeutics appear to be related to the function of these processes. There are many reasons why genetic variations are optimal biomarkers and in relation to the VEGF system may prove to be of clinical relevance. This review evaluates the literature on SNPs in relation to the risk of CRC and the possible prognostic and predictive value and argues for the role of these biomarkers in the future treatment of patients with CRC.

Continuous local delivery of interferon-β stabilizes tumor vasculature in an orthotopic glioblastoma xenograft resection model

BACKGROUND

High-grade glioblastomas have immature, leaky tumor blood vessels that impede the efficacy of adjuvant therapy. We assessed the ability of human interferon (hIFN)-β delivered locally via gene transfer to effect vascular stabilization in an orthotopic model of glioblastoma xenograft resection.

METHODS

Xenografts were established by injecting 3 grade IV glioblastoma cell lines (GBM6-luc, MT330-luc, and SJG2-luc) into the cerebral cortex of nude rats. Tumors underwent subtotal resection, and then had gel foam containing an adeno-associated virus vector encoding either hIFN-β or green fluorescence protein (control) placed in the resection cavity. The primary endpoint was stabilization of tumor vasculature, as evidenced by CD34, α-SMA, and CA IX staining. Overall survival was a secondary endpoint.

RESULTS

hIFN-β treatment altered the tumor vasculature of GBM6-luc and SJG2-luc xenografts, decreasing the density of endothelial cells, stabilizing vessels with pericytes, and decreasing tumor hypoxia. The mean survival for rats with these neoplasms was not improved, however. In rats with MT330-luc xenografts, hIFN-β resulted in tumor regression with a 6-month survival of 55% (INF-β group) and 9% (control group).

CONCLUSION

The use of AAV hIFN-β in our orthotopic model of glioblastoma resection stabilized tumor vasculature and improved survival in rats with MT330 xenografts.

Pharmacodynamic study using FLT PET/CT in patients with renal cell cancer and other solid malignancies treated with sunitinib malate

PURPOSE

To characterize proliferative changes in tumors during the sunitinib malate exposure/withdrawal using 3'-deoxy-3'-[(18)F]fluorothymidine (FLT) positron emission tomography (PET)/computed tomography (CT) imaging.

PATIENTS AND METHODS

Patients with advanced solid malignancies and no prior anti-VEGF exposure were enrolled. All patients had metastatic lesions amenable to FLT PET/CT imaging. Sunitinib was initiated at the standard dose of 50 mg p.o. daily either on a 4/2 or 2/1 schedule. FLT PET/CT scans were obtained at baseline, during sunitinib exposure, and after sunitinib withdrawal within cycle #1 of therapy. VEGF levels and sunitinib pharmacokinetic (PK) data were assessed at the same time points.

RESULTS

Sixteen patients (8 patients on 4/2 schedule and 8 patients on 2/1 schedule) completed all three planned FLT PET/CT scans and were evaluable for pharmacodynamic imaging evaluation. During sunitinib withdrawal (change from scans 2 to 3), median FLT PET standardized uptake value (SUV(mean)) increased +15% (range: -14% to 277%; P = 0.047) for the 4/2 schedule and +19% (range: -5.3% to 200%; P = 0.047) for the 2/1 schedule. Sunitinib PK and VEGF ligand levels increased during sunitinib exposure and returned toward baseline during the treatment withdrawal.

CONCLUSIONS

The increase of cellular proliferation during sunitinib withdrawal in patients with renal cell carcinoma and other solid malignancies is consistent with a VEGF receptor (VEGFR) tyrosine kinase inhibitor (TKI) withdrawal flare. Univariate and multivariate analysis suggest that plasma VEGF is associated with this flare, with an exploratory analysis implying that patients who experience less clinical benefit have a larger withdrawal flare. This might suggest that patients with a robust compensatory response to VEGFR TKI therapy experience early "angiogenic escape."

Tumor endothelial marker 7 (TEM-7): a novel target for antiangiogenic therapy

Antiangiogenesis has been validated as a therapeutic strategy to treat cancer, however, a need remains to identify new targets and therapies for specific diseases and to improve clinical benefit from antiangiogenic agents. Tumor endothelial marker 7 (TEM-7) was investigated as a possible target for therapeutic antiangiogenic intervention in cancer. TEM-7 expression was assessed by in situ hybridization or by immunohistochemistry (IHC) in 130 formalin-fixed paraffin-embedded (FFPE) and 410 frozen human clinical specimens of cancer plus 301 normal tissue samples. In vitro TEM-7 expression was evaluated in 4 human endothelial cell models and in 32 human cancer cell lines by RT-PCR and flow cytometry. An anti-TEM-7 antibody was tested in vitro on human SKOV3 ovarian and MDA-MB-231 breast carcinoma cells that expressed TEM-7 in antibody-dependent cellular cytotoxicity (ADCC) and phagocytosis assays. In frozen tumor tissues, TEM-7 mRNA and protein was detected in all but one of the cancer types tested and was infrequently expressed in normal frozen tissues. In FFPE tumor tissues, TEM-7 protein was detected by IHC in colon, breast, lung, bladder, ovarian and endometrial cancers and in sarcomas. TEM-7 protein was not detected in head and neck, prostate or liver cancers. TEM-7 expression was restricted to the vasculature and was absent from tumor cells. In vitro, TEM-7 was not detected in human microvascular endothelial cells (HMVEC) or human umbilical vein endothelial cells (HUVEC) but was induced in endothelial precursor/progenitor cells (EPC) in the presence of the mitogen phorbol ester PMA. An anti-TEM-7 antibody mediated ADCC and phagocytosis in SKOV3 and MDA-MB-231 cell lines infected with an adenovirus expressing TEM-7. These data demonstrate that TEM-7 is a vascular protein associated with angiogenic states. TEM-7 is a novel and attractive target for antiangiogenic therapy.

Normalization of the vasculature for treatment of cancer and other diseases

New vessel formation (angiogenesis) is an essential physiological process for embryologic development, normal growth, and tissue repair. Angiogenesis is tightly regulated at the molecular level. Dysregulation of angiogenesis occurs in various pathologies and is one of the hallmarks of cancer. The imbalance of pro- and anti-angiogenic signaling within tumors creates an abnormal vascular network that is characterized by dilated, tortuous, and hyperpermeable vessels. The physiological consequences of these vascular abnormalities include temporal and spatial heterogeneity in tumor blood flow and oxygenation and increased tumor interstitial fluid pressure. These abnormalities and the resultant microenvironment fuel tumor progression, and also lead to a reduction in the efficacy of chemotherapy, radiotherapy, and immunotherapy. With the discovery of vascular endothelial growth factor (VEGF) as a major driver of tumor angiogenesis, efforts have focused on novel therapeutics aimed at inhibiting VEGF activity, with the goal of regressing tumors by starvation. Unfortunately, clinical trials of anti-VEGF monotherapy in patients with solid tumors have been largely negative. Intriguingly, the combination of anti-VEGF therapy with conventional chemotherapy has improved survival in cancer patients compared with chemotherapy alone. These seemingly paradoxical results could be explained by a "normalization" of the tumor vasculature by anti-VEGF therapy. Preclinical studies have shown that anti-VEGF therapy changes tumor vasculature towards a more "mature" or "normal" phenotype. This "vascular normalization" is characterized by attenuation of hyperpermeability, increased vascular pericyte coverage, a more normal basement membrane, and a resultant reduction in tumor hypoxia and interstitial fluid pressure. These in turn can lead to an improvement in the metabolic profile of the tumor microenvironment, the delivery and efficacy of exogenously administered therapeutics, the efficacy of radiotherapy and of effector immune cells, and a reduction in number of metastatic cells shed by tumors into circulation in mice. These findings are consistent with data from clinical trials of anti-VEGF agents in patients with various solid tumors. More recently, genetic and pharmacological approaches have begun to unravel some other key regulators of vascular normalization such as proteins that regulate tissue oxygen sensing (PHD2) and vessel maturation (PDGFRβ, RGS5, Ang1/2, TGF-β). Here, we review the pathophysiology of tumor angiogenesis, the molecular underpinnings and functional consequences of vascular normalization, and the implications for treatment of cancer and nonmalignant diseases.

Time-course imaging of therapeutic functional tumor vascular normalization by antiangiogenic agents

We describe here new technology that enables noninvasive imaging of therapeutic functional normalization of tumor blood vessels by antiangiogenic agents. Noninvasive variable-magnification in vivo-fluorescence imaging as well as fluorescence tomography was used to visualize functional vessel normalization. Changes in the same vessel before and after drug treatment were imaged with high resolution in real time. Differences in vascular responses to the mTOR inhibitor rapamycin and to an anti-VEGF antibody were functionally imaged. Tumor vessel normalization was shown by significantly reduced leakiness and subsequent improved tumor delivery of Paclitaxel-BODPY as well as by normalized morphology. The tumor vascular pool agent, AngioSense(750), was retained only in tumors after either anti-VEGF antibody or rapamycin treatment, as visualized by noninvasive fluorescence tomography. The antiangiogenic therapy normalized vessels, which significantly enhanced the antitumor efficacy of paclitaxel because of increased drug penetration throughout the tumor. The optical imaging technology described here is thus a powerful, noninvasive, time-course imaging tool of functional tumor vessel normalization and its therapeutic consequences.

Characteristics of human Ewing/PNET sarcoma models

Ewing/PNET (peripheral neuroepithelioma) tumors are rare aggressive bone sarcomas occurring in young people. Rare-disease clinical trials can require global collaborations and many years. In vivo models that as accurately as possible reflect the clinical disease are helpful in selecting therapeutics with the most promise of positive clinical impact. Human Ewing/PNET sarcoma cell lines developed over the past 45 years are described. Several of these have undergone genetic analysis and have been confirmed to be those of Ewing/PNET sarcoma. The A673 Ewing sarcoma line has proven to be particularly useful in understanding the biology of this disease in the mouse. The chromosomal translocation producing the EWS/FLI1 fusion transcript characterizes clinical Ewing sarcoma. Cell lines that express this genetic profile are confirmed to be those of Ewing sarcoma. The A673 Ewing sarcoma line grows in culture and as a xenograft in immunodeficient mice. The A673 model has been used to study Ewing sarcoma angiogenesis and response to antiangiogenic agents. Many Ewing sarcoma clinical specimens express the cell surface protein endosialin. Several Ewing sarcoma cell lines, including the A673 line, also express cell surface endosialin when grown as subcutaneous tumor nodules and as disseminated disease; thus the A673 is a useful model for the study of endosialin biology and endosialin-directed therapies. With the advent of tools that allow characterization of clinical disease to facilitate optimal treatment, it becomes imperative, especially for rare tumors, to develop preclinical models reflecting disease subsets. Ewing PNET sarcomas are a rare disease where models are available.

Extracellular matrix proteins and tumor angiogenesis

Tumor development is a complex process that relies on interaction and communication between a number of cellular compartments. Much of the mass of a solid tumor is comprised of the stroma which is richly invested with extracellular matrix. Within this matrix are a host of matricellular proteins that regulate the expression and function of a myriad of proteins that regulate tumorigenic processes. One of the processes that is vital to tumor growth and progression is angiogenesis, or the formation of new blood vessels from preexisting vasculature. Within the extracellular matrix are structural proteins, a host of proteases, and resident pro- and antiangiogenic factors that control tumor angiogenesis in a tightly regulated fashion. This paper discusses the role that the extracellular matrix and ECM proteins play in the regulation of tumor angiogenesis.

[Targeted therapies in hepatocellular carcinoma]

Hepatocellular carcinoma (HCC) stands as a major health problem worldwide. The management of advanced HCC, limited for a longtime by the disappointing results of conventional cytotoxic chemotherapies, has recently changed with the publication of the results of the Sorafenib Hepatocellular Carcinoma Assessment Randomized Protocol (SHARP) trial, which demonstrated an overall survival benefit over placebo in patients with advanced HCC. This study was further confirmed by the Asian-Pacific trial using sorafenib in Eastern patients. Those trials demonstrated that therapeutic benefits may derive from improving our knowledge of deregulated signaling pathways involved in HCC carcinogenesis. This review summarizes the results of clinical trials in which targeted therapies are currently evaluated aiming to enlarge the therapeutic armamentarium for HCC in a near future.

Use of anti-VEGF adjuvant therapy in cancer: challenges and rationale

Several ongoing clinical studies are designed to test the efficacy of antiangiogenic therapies in the adjuvant setting, where the goal is to increase the cure rate in patients who have just undergone surgical resection of all visible disease. Tumors depend on angiogenesis to support their growth and progression and blockade of this process has proven to be a valid strategy for treating multiple types of advanced metastatic cancer. However, results from the first of these clinical adjuvant studies were disappointing, stimulating extensive debate as to the potential of this approach. It will require additional clinical studies before we realize whether the effects of angiogenic blockade are durable, and if they are able to cure a subset of patients with early stage cancer.

The effects of vandetanib on paclitaxel tumor distribution and antitumor activity in a xenograft model of human ovarian carcinoma

This study was designed to determine the effects of vandetanib, a small-molecule receptor tyrosine kinase inhibitor of vascular endothelial growth factor and epidermal growth factor receptor, on paclitaxel (PTX) tumor distribution and antitumor activity in xenograft models of human ovarian carcinoma. Nude mice bearing A2780-1A9 xenografts received daily (5, 10, or 15 days) doses of vandetanib (50 mg/kg per os), combined with PTX (20 mg/kg intravenously). Morphologic and functional modifications associated with the tumor vasculature (CD31 and alpha-smooth muscle actin staining and Hoechst 33342 perfusion) and PTX concentrations in plasma and tumor tissues were analyzed. Activity was evaluated as inhibition of tumor growth subcutaneously and spreading into the peritoneal cavity. Vandetanib treatment produced no significant change in tumor vessel density, although a reduced number of large vessels, an increased percentage of mature vessels, and diminished tumor perfusion were evident. Pretreatment with vandetanib led to decreased tumor PTX levels within 1 hour of PTX injection, although 24 hours later, tumor PTX levels were comparable with controls. In efficacy studies, the combination of vandetanib plus PTX improved antitumor activity compared with vandetanib or PTX alone, with greater effects being obtained when PTX was administered before vandetanib. The combination of PTX plus vandetanib reduced tumor burden in the peritoneal cavity of mice and significantly increased their survival. Analysis of vascular changes and PTX tumor uptake in vandetanib-treated tumors may help to guide the scheduling of vandetanib plus PTX combinations and may have implications for the design of clinical trials with these drugs.

Targeting the Vascular Endothelial Growth Factor Pathway in the Treatment of Human Malignancy

Over 30 years ago, it was proposed that blocking new blood vessel formation would significantly inhibit solid tumor growth and hence, limit cancer progression. Efforts guided by this philosophy have resulted in a better understanding of the molecular basis of tumor angiogenesis. The first successful therapeutic to emerge from this work, an antibody (bevacizumab) targeting the vascular endothelial growth factor (VEGF), was recently approved for the treatment of colorectal cancer. Additional positive clinical data with bevacizumab in the treatment of breast and lung carcinoma have also been reported. These clinical achievements have validated the approach of anti-angiogenesis therapy for cancer and provided further confirmation for antibodies as a therapeutic class in this disease. Nevertheless, important unanswered questions with regard to preclinical and clinical results of VEGF pathway inhibitors remain. For example, preclinical models with a number of VEGF pathway inhibitors suggest that these agents would have significant clinical activity on their own; yet, clinical activity in patients with bevacizumab or other VEGF pathway inhibitors as monotherapy have been disappointing. Moreover, while bevacizumab is approved for the treatment of colorectal cancer in combination with cytotoxics, the mechanism for the benefits of this combination are still poorly understood, with a number of viable mechanisms under active experimental evaluation. The 3-8-month survival benefit in colorectal cancer patients treated with bevacizumab is a positive step forward. However, improving our understanding of the mechanism for these effects, as well as the mechanism underlying the inability as yet to achieve greater effects, is needed in order to follow up on the positive clinical results with improved strategies. This review discusses the experimental results surrounding the current status of our understanding of the mechanism of action of VEGF signaling inhibitors, and the potential for utilizing these agents in the future so that clinical benefits will be measured in years rather than months.

Integrins: Signaling, disease, and therapy

BACKGROUND

Integrins are a family of transmembrane receptors that mediate cell-cell and cell-matrix adhesion. They are involved in stable cell adhesion and migration of cells. In addition, integrin-mediated interactions modulate the response to most, if not all growth factors, cytokines, and other soluble factors.

PURPOSE

In this review, we briefly explain how integrins can affect the multitude of signal transduction cascades in control of survival, proliferation, and differentiation. Subsequently, we primarily focus on targeting integrins alpha5beta1 and alphanubeta3 in disease and we discuss how antagonists of these integrins, including disintegrins, RGD peptides, small molecules, and function blocking antibodies, may be of therapeutical value either alone or, especially in the treatment of cancer, in combination with existing therapeutical strategies.

Structural adaptation and heterogeneity of normal and tumor microvascular networks

Relative to normal tissues, tumor microcirculation exhibits high structural and functional heterogeneity leading to hypoxic regions and impairing treatment efficacy. Here, computational simulations of blood vessel structural adaptation are used to explore the hypothesis that abnormal adaptive responses to local hemodynamic and metabolic stimuli contribute to aberrant morphological and hemodynamic characteristics of tumor microcirculation. Topology, vascular diameter, length, and red blood cell velocity of normal mesenteric and tumor vascular networks were recorded by intravital microscopy. Computational models were used to estimate hemodynamics and oxygen distribution and to simulate vascular diameter adaptation in response to hemodynamic, metabolic and conducted stimuli. The assumed sensitivity to hemodynamic and conducted signals, the vascular growth tendency, and the random variability of vascular responses were altered to simulate ‘normal’ and ‘tumor’ adaptation modes. The heterogeneous properties of vascular networks were characterized by diameter mismatch at vascular branch points (d³_var) and deficit of oxygen delivery relative to demand (O_2def). In the tumor, d³_var and O_2def were higher (0.404 and 0.182) than in normal networks (0.278 and 0.099). Simulated remodeling of the tumor network with ‘normal’ parameters gave low values (0.288 and 0.099). Conversely, normal networks attained tumor-like characteristics (0.41 and 0.179) upon adaptation with ‘tumor’ parameters, including low conducted sensitivity, increased growth tendency, and elevated random biological variability. It is concluded that the deviant properties of tumor microcirculation may result largely from defective structural adaptation, including strongly reduced responses to conducted stimuli.

Blood vessels of tumors have abnormal structures, being irregular and tortuous. Oxygen supply to tumors is heterogeneous, with regions of low oxygen that resist radiation treatment and some types of chemotherapy. Blood vessels undergo continual structural change (adaptation) in response to blood flow and metabolite levels. Our hypothesis is that abnormal adaptation of tumor microvessels causes their heterogeneous structure and impaired function. We used computational models to estimate blood flow and oxygen delivery and to simulate diameter adaptation in networks of microvessels, using network structures derived from microscopic observations of living normal and tumor tissues. The simulation of adaptation depends on several parameters that describe vessel sensitivity to fluid shear stress, to blood pressure, to oxygen levels, and to signals propagated along vessel walls (conducted response). We found that structural adaptation of a tumor network using parameters derived from normal tissues could ‘normalize’ the network, giving it properties similar to a normal tissue. Conversely, adaptation of normal networks using parameters derived from the tumor network, including reduced conducted response, gave tumor-like properties. We conclude that the deviant properties of tumor microcirculation may result largely from defective structural adaptation, including reduced conducted responses.

Angiogenesis and vascular remodelling in normal and cancerous tissues

Vascular development and homeostasis are underpinned by two fundamental features: the generation of new vessels to meet the metabolic demands of under-perfused regions and the elimination of vessels that do not sustain flow. In this paper we develop the first multiscale model of vascular tissue growth that combines blood flow, angiogenesis, vascular remodelling and the subcellular and tissue scale dynamics of multiple cell populations. Simulations show that vessel pruning, due to low wall shear stress, is highly sensitive to the pressure drop across a vascular network, the degree of pruning increasing as the pressure drop increases. In the model, low tissue oxygen levels alter the internal dynamics of normal cells, causing them to release vascular endothelial growth factor (VEGF), which stimulates angiogenic sprouting. Consequently, the level of blood oxygenation regulates the extent of angiogenesis, with higher oxygenation leading to fewer vessels. Simulations show that network remodelling (and de novo network formation) is best achieved via an appropriate balance between pruning and angiogenesis. An important factor is the strength of endothelial tip cell chemotaxis in response to VEGF. When a cluster of tumour cells is introduced into normal tissue, as the tumour grows hypoxic regions form, producing high levels of VEGF that stimulate angiogenesis and cause the vascular density to exceed that for normal tissue. If the original vessel network is sufficiently sparse then the tumour may remain localised near its parent vessel until new vessels bridge the gap to an adjacent vessel. This can lead to metastable periods, during which the tumour burden is approximately constant, followed by periods of rapid growth.

Antiangiogenic effects of noscapine enhance radioresponse for GL261 tumors

PURPOSE

To assess the effects of noscapine, a tubulin-binding drug, in combination with radiation in a murine glioma model.

METHODS AND MATERIALS

The human T98G and murine GL261 glioma cell lines treated with noscapine, radiation, or both were assayed for clonogenic survival. Mice with established GL261 hind limb tumors were treated with noscapine, radiation, or both to evaluate the effect of noscapine on radioresponse. In a separate experiment with the same treatment groups, 7 days after radiation, tumors were resected and immunostained to measure proliferation rate, apoptosis, and angiogenic activity.

RESULTS

Noscapine reduced clonogenic survival without enhancement of radiosensitivity in vitro. Noscapine combined with radiation significantly increased tumor growth delay: 5, 8, 13, and 18 days for control, noscapine alone, radiation alone, and the combination treatment, respectively (p < 0.001). To assess the effect of the combination of noscapine plus radiation on the tumor vasculature, tubule formation by the murine endothelial 2H11 cells was tested. Noscapine with radiation significantly inhibited tubule formation compared with radiation alone. By immunohistochemistry, tumors treated with the combination of noscapine plus radiation showed a decrease in BrdU incorporation, an increase in apoptosis by terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end labeling, and a decrease in tumor vessel density compared with tumors treated with radiation alone.

CONCLUSION

Noscapine enhanced the sensitivity of GL261 glioma tumors to radiation, resulting in a significant tumor growth delay. An antiangiogenic mechanism contributed to the effect. These findings are clinically relevant, particularly in view of the mild toxicity profile of this drug.

Transforming growth factor-beta and the immune response to malignant disease

Transforming growth factor-beta (TGF-beta) is a key player in malignant disease through its actions on host tissues and cells. Malignant cells often secrete large amounts of TGF-beta that act on nontransformed cells present in the tumor mass as well as distal cells in the host to suppress antitumor immune responses creating an environment of immune tolerance, augmenting angiogenesis, invasion and metastasis, and increasing tumor extracellular matrix deposition. Cells of the innate immune system contribute to the high concentrations of TGF-beta found in tumor masses. In addition, dendritic cell subpopulations secreting TGF-beta contribute to the generation of regulatory T cells that actively inhibit the activity of other T cells. Elevated levels of plasma TGF-beta are associated with advanced stage disease and may separate patients into prognostically high-risk populations. Anti-TGF-beta therapy could reverse the immunosuppressive effects of this cytokine on the host as well as decrease extracellular matrix formation, decrease angiogenesis, decrease osteolytic activity, and increase the sensitivity of the malignant cells to cytotoxic therapies and immunotherapies. Phase I clinical trials of an inhibitor of TGF-beta receptor type I kinase activity and a TGF-beta neutralizing antibody are under way.