Potentiation of cyclophosphamide chemotherapy using the anti-angiogenic drug thalidomide: importance of optimal scheduling to exploit the 'normalization' window of the tumor vasculature

Changes in perfusion and permeability in glioblastoma model induced by the anti-angiogenic agents cediranib and thalidomide

BACKGROUND AND PURPOSE

The poor delivery of drugs to infiltrating tumor cells contributes to therapeutic failure in glioblastoma. During the early phase of an anti-angiogenic treatment, a remodeling of the tumor vasculature could occur, leading to a more functional vessel network that could enhance drug delivery. However, the restructuration of blood vessels could increase the proportion of normal endothelial cells that could be a barrier for the free diffusion of drugs. The net balance, in favor or not, of a better delivery of compounds during the course of an antiangiogenic treatment remains to be established. This study explored whether cediranib and thalidomide could modulate perfusion and vessel permeability in the brain U87 tumor mouse model.

METHODS

The dynamic evolution of the diffusion of agents outside the tumor core using the fluorescent dye Evans Blue in histology and Gd-DOTA using dynamic contrast-enhanced (DCE)-MRI. CD31 labelling of endothelial cells was used to measure the vascular density.

RESULTS AND INTERPRETATION

Cediranib and thalidomide effectively reduced tumor size over time. The accessibility of Evans Blue outside the tumor core continuously decreased over time. The vascular density was significantly decreased after treatment while the proportion of normal vessels remained unchanged over time. In contrast to histological studies, DCE-MRI did not tackle any significant change in hemodynamic parameters, in the core or margins of the tumor, whatever the parameter used or the pharmacokinetic model used. While cediranib and thalidomide were effective in decreasing the tumor size, they were ineffective in transiently increasing the delivery of agents in the core and the margins of the tumor.

Vascular regional analysis unveils differential responses to anti-angiogenic therapy in pancreatic xenografts through macroscopic photoacoustic imaging

Pancreatic cancer (PC) is a highly lethal malignancy and the third leading cause of cancer deaths in the U.S. Despite major innovations in imaging technologies, there are limited surrogate radiographic indicators to aid in therapy planning and monitoring. Amongst the various imaging techniques Ultrasound-guided photoacoustic imaging (US-PAI) is a promising modality based on endogenous blood (hemoglobin) and blood oxygen saturation (StO 2 ) contrast to monitor response to anti-angiogenic therapies. Adaptation of US-PAI to the clinical realm requires macroscopic configurations for adequate depth visualization, illuminating the need for surrogate radiographic markers, including the tumoral microvessel density (MVD). In this work, subcutaneous xenografts with PC cell lines AsPC-1 and MIA-PaCa-2 were used to investigate the effects of receptor tyrosine kinase inhibitor (sunitinib) treatment on MVD and StO 2 . Through histological correlation, we have shown that regions of high and low vascular density (HVD and LVD) can be identified through frequency domain filtering of macroscopic PA images which could not be garnered from purely global analysis. We utilized vascular regional analysis (VRA) of treatment-induced StO 2 and total hemoglobin (HbT) changes. VRA as a tool to monitor treatment response allowed us to identify potential timepoints of vascular remodeling, highlighting its ability to provide insights into the TME not only for sunitinib treatment but also other anti-angiogenic therapies.

Clinical results of the EVESOR trial, a multiparameter phase I trial of everolimus and sorafenib combination in solid tumors

PURPOSE

Everolimus (EVE) and sorafenib (SOR) combination was associated with synergistic activity in preclinical models. However, previous clinical studies were hampered by cumulative toxicities when both were given continuously. The academic EVESOR trial (NCT01932177) was designed to assess alternative doses and intermittent dosing schedules of EVE and SOR combination therapy to improve the benefit-risk ratio for patients with solid tumors.

METHODS

EVESOR is a multiparameter dose-escalation phase I trial investigating different doses and dosing schedules, with the final objective of generating data for modeling and simulation. Patients were allocated into continuous (A and B) or intermittent (C and D) schedules to determine the recommended phase II dose (RP2D). The clinical outcomes are presented here.

RESULTS

Forty-three patients were included from 2013 to 2019. Most of them had gynecological (25.6%), cholangiocarcinomas (23.2%), colorectal (14.0%), and breast cancers (11.6%). Dose-escalation up to EVE 10 mg QD and SOR 400 mg BID was possible on intermittent schedules. Five dose-limiting toxicities were observed, and dose reductions were required in 39.5% patients, stabilizing at EVE 5 mg and SOR 200 mg BID for 58.1% of them. The overall response rate was 6.3%, and disease control rate was 75.0%. The median progression-free survival (PFS) was 3.6 months. The longest median PFS were observed in cholangiocarcinomas (9.9 months), and gynecological adenocarcinomas (9.2 months).

CONCLUSION

Intermittent arms were associated with improved efficacy/toxicity profiles; and EVE 5 mg QD and SOR 200 mg BID was defined a clinically feasible dose. Strong signs of efficacy were found in cholangiocarcinomas and gynecologic carcinomas.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT01932177.

The Role of Imaging Biomarkers to Guide Pharmacological Interventions Targeting Tumor Hypoxia

Hypoxia is a common feature of solid tumors that contributes to angiogenesis, invasiveness, metastasis, altered metabolism and genomic instability. As hypoxia is a major actor in tumor progression and resistance to radiotherapy, chemotherapy and immunotherapy, multiple approaches have emerged to target tumor hypoxia. It includes among others pharmacological interventions designed to alleviate tumor hypoxia at the time of radiation therapy, prodrugs that are selectively activated in hypoxic cells or inhibitors of molecular targets involved in hypoxic cell survival (i.e., hypoxia inducible factors HIFs, PI3K/AKT/mTOR pathway, unfolded protein response). While numerous strategies were successful in pre-clinical models, their translation in the clinical practice has been disappointing so far. This therapeutic failure often results from the absence of appropriate stratification of patients that could benefit from targeted interventions. Companion diagnostics may help at different levels of the research and development, and in matching a patient to a specific intervention targeting hypoxia. In this review, we discuss the relative merits of the existing hypoxia biomarkers, their current status and the challenges for their future validation as companion diagnostics adapted to the nature of the intervention.

Chemotherapy response prediction with diffuser elapser network

In solid tumors, elevated fluid pressure and inadequate blood perfusion resulting from unbalanced angiogenesis are the prominent reasons for the ineffective drug delivery inside tumors. To normalize the heterogeneous and tortuous tumor vessel structure, antiangiogenic treatment is an effective approach. Additionally, the combined therapy of antiangiogenic agents and chemotherapy drugs has shown promising effects on enhanced drug delivery. However, the need to find the appropriate scheduling and dosages of the combination therapy is one of the main problems in anticancer therapy. Our study aims to generate a realistic response to the treatment schedule, making it possible for future works to use these patient-specific responses to decide on the optimal starting time and dosages of cytotoxic drug treatment. Our dataset is based on our previous in-silico model with a framework for the tumor microenvironment, consisting of a tumor layer, vasculature network, interstitial fluid pressure, and drug diffusion maps. In this regard, the chemotherapy response prediction problem is discussed in the study, putting forth a proof of concept for deep learning models to capture the tumor growth and drug response behaviors simultaneously. The proposed model utilizes multiple convolutional neural network submodels to predict future tumor microenvironment maps considering the effects of ongoing treatment. Since the model has the task of predicting future tumor microenvironment maps, we use two image quality evaluation metrics, which are structural similarity and peak signal-to-noise ratio, to evaluate model performance. We track tumor cell density values of ground truth and predicted tumor microenvironments. The model predicts tumor microenvironment maps seven days ahead with the average structural similarity score of 0.973 and the average peak signal ratio of 35.41 in the test set. It also predicts tumor cell density at the end day of 7 with the mean absolute percentage error of [Formula: see text].

Improving cancer treatments via dynamical biophysical models

Despite significant advances in oncological research, cancer nowadays remains one of the main causes of mortality and morbidity worldwide. New treatment techniques, as a rule, have limited efficacy, target only a narrow range of oncological diseases, and have limited availability to the general public due their high cost. An important goal in oncology is thus the modification of the types of antitumor therapy and their combinations, that are already introduced into clinical practice, with the goal of increasing the overall treatment efficacy. One option to achieve this goal is optimization of the schedules of drugs administration or performing other medical actions. Several factors complicate such tasks: the adverse effects of treatments on healthy cell populations, which must be kept tolerable; the emergence of drug resistance due to the intrinsic plasticity of heterogeneous cancer cell populations; the interplay between different types of therapies administered simultaneously. Mathematical modeling, in which a tumor and its microenvironment are considered as a single complex system, can address this complexity and can indicate potentially effective protocols, that would require experimental verification. In this review, we consider classical methods, current trends and future prospects in the field of mathematical modeling of tumor growth and treatment. In particular, methods of treatment optimization are discussed with several examples of specific problems related to different types of treatment.

Tumor Hypoxia: Impact on Radiation Therapy and Molecular Pathways

Tumor hypoxia is a common feature of the microenvironment in solid tumors, primarily due to an inadequate, and heterogeneous vascular network. It is associated with resistance to radiotherapy and results in a poorer clinical outcome. The presence of hypoxia in tumors can be identified by various invasive and non-invasive techniques, and there are a number of approaches by which hypoxia can be modified to improve outcome. However, despite these factors and the ongoing extensive pre-clinical studies, the clinical focus on hypoxia is still to a large extent lacking. Hypoxia is a major cellular stress factor and affects a wide range of molecular pathways, and further understanding of the molecular processes involved may lead to greater clinical applicability of hypoxic modifiers. This review is a discussion of the characteristics of tumor hypoxia, hypoxia-related molecular pathways, and the role of hypoxia in treatment resistance. Understanding the molecular aspects of hypoxia will improve our ability to clinically monitor hypoxia and to predict and modify the therapeutic response.

TSP-1 as a novel biological marker of tumor vasculature normalization in colon carcinoma induced by Endostar

Blood vessels in tumors often exhibit abnormal morphology and function, which promotes the growth, metastasis and resistance of tumors to conventional therapies. Therefore, vascular normalization is an emerging strategy to enhance the effectiveness of radiotherapy and chemotherapy when used in combination; however, there is a lack of evidence regarding the optimal schedule for the co-administration of anti-angiogenic and chemotherapeutic drugs. Scheduling treatment is important as the period for normalization is transient, also known as the ‘time window’; however, no biomarker has been identified to detect this window. In the present study, recombinant human endostatin (rhES) was employed as an anti-angiogenic agent in xenograft tumor tissue in mice. Following rhES or control (saline) treatment, the density and integrity of tumor vessels were detected by immunofluorescence staining for cluster of differentiation 31 and α-smooth muscle actin; the level of hypoxia in tumor tissue was examined by immunohistochemistry with pimonidazole; the necrotic area was evaluated by hematoxylin and eosin staining; and the level of thrombospondin-1 (TSP-1) in plasma was tested by ELISA. The Cell Counting Kit-8 assay was also used to evaluate the effect of rhES on the proliferation of colon carcinoma SW620 cells. A ‘time window’ normalized vasculature was determined between day 4 and 6 following rhES treatment, and accompanied by a decrease in hypoxia in tumor tissue. Decreasing plasma TSP-1 levels were consistent with changes in vascular morphology and hypoxia, which exhibited features of normalization. In addition, rhES had no effect on the proliferation of SW620 cells, suggesting that the reduction in TSP-1 was associated with increased oxygen content during vascular normalization, rather than inhibited cell proliferation. In conclusion, TSP-1 may be a potential biomarker for predicting the normalization window of colon cancer vessels.

Antiangiogenic therapy: Markers of response, "normalization" and resistance

Currently in cancer treatment, one premise is to use antiangiogenic therapies in association with chemotherapy or radiotherapy to augment their efficacy by benefiting from the vascular "normalization" induced by antiangiogenic therapy. This concept defines the time during which the tumor blood vessels adopt normal-like morphology and functionality, i.e. the blood vessels become more mature, the perfusion augments and hypoxia decreases. To date, there is such a diversity of treatment protocols where the type of antiangiogenic to adopt, its dose and duration of administration are different, that knowing when and how to treat is problematic. In this review, we analyzed thoroughly preclinical and clinical studies that use antiangiogenic treatments to benefit from the "normalization" and showed that the effects depend on the type of antiangiogenic administrated (anti-VEGF, anti-VEGFR, Multi-Kinase Inhibitor) and on the duration of treatment. Finally, biomarkers of "normalization" and resistance that could be used in the clinic are presented.

Contribution of Harold M. Swartz to In Vivo EPR and EPR Dosimetry

In 2015, we are celebrating half a century of research in the application of Electron Paramagnetic Resonance (EPR) as a biodosimetry tool to evaluate the dose received by irradiated people. During the EPR Biodose 2015 meeting, a special session was organized to acknowledge the pioneering contribution of Harold M. (Hal) Swartz in the field. The article summarizes his main contribution in physiology and medicine. Four emerging themes have been pursued continuously along his career since its beginning: (1) radiation biology; (2) oxygen and oxidation; (3) measuring physiology in vivo; and (4) application of these measurements in clinical medicine. The common feature among all these different subjects has been the use of magnetic resonance techniques, especially EPR. In this article, you will find an impressionist portrait of Hal Swartz with the description of the 'making of' this pioneer, a time-line perspective on his career with the creation of three National Institutes of Health-funded EPR centers, a topic-oriented perspective on his career with a description of his major contributions to Science, his role as a mentor and his influence on his academic children, his active role as founder of scientific societies and organizer of scientific meetings, and the well-deserved international recognition received so far.

Importance of the interaction between immune cells and tumor vasculature mediated by thalidomide in cancer treatment (Review)

Over the past 60 years, thalidomide has metamorphosized from a drug prescribed to treat morning sickness in pregnant women, which was subsequently found to induce birth defects, into a highly effective therapy for treating leprosy and multiple myeloma. Several mechanisms have been proposed to explain the anticancer effects of thalidomide, including antiangiogenic and immunomodulatory activities. At present, evidence suggests that thalidomide may induce vessel maturation. Vascular normalization may be an effective strategy to enhance cancer immunotherapy. Numerous studies have shown that the tumor infiltrating immune cell subsets are important in regulating the process of tumor angiogenesis. The mechanisms associated with antiangiogenesis and the potent immunomodulatory effects of thalidomide obtained the most support. The studies of the antiangiogenic activity of thalidomide were guided in a novel direction by a hypothesis regarding the vascular normalization of tumors. Hence, thalidomide is effective in cancer treatment due to the interaction between immune cells and tumor vasculature. This mechanism provides new avenues to explore for the treatment of cancer.

The modulation of tumor vessel permeability by thalidomide and its impacts on different types of targeted drug delivery systems in a sarcoma mouse model

The transport of nanocarriers is supposed to be based on EPR effect which is affected by diverse factors, so the modulation of EPR effect seems very significant for nanocarriers including targeted drug delivery systems (TDDSs). Besides, it is extremely unclear how the EPR effect impacts the fate of different types of TDDSs. To make the most advantage of EPR effect for TDDSs, it is definitely necessary to clarify these key issues. Here, we construct and characterize various TDDSs, including sterically-stabilized liposomes (SSL), RGD functionalized SSL (RGD-SSL) and novel 7PEP functionalized SSL (7PEP-SSL), loaded with doxorubicin (DOX), DIR or DID. Here, we modulate the permeability of tumor vessels by thalidomide (THD) in a sarcoma-bearing EPR mouse model via monitoring endogenous deoxygenated hemoglobin in circulation, and then we confirm the effect of THD on tumor vessel permeability by vessel density, vessel maturity, VEGF expression and so on. Importantly, we investigate and find the impacts of EPR effect on the antitumor efficacy, in vivo distribution and intratumoral microdistribution of the three TDDSs. Interestingly, the EPR effects affect different TDDSs differently. The elevated EPR effect enhances the tumor accumulation of SSL and RGD-SSL but fails to increase their efficacy. The RGD-SSL exhibits the best efficacy with the least fluctuation, demonstrating the advantage of angiogenesis targeted systems. 7PEP-SSL seems the biggest beneficiary of EPR effect, suggesting the significance of EPR modulation for cells targeted systems. Generally, this study demonstrates the feasibility of modulating EPR effect bidirectionally by THD as well as the impacts of EPR effect on different type of testing TDDSs based on this animal model. It certainly provides novel insight into the design and potential use of TDDSs.

Hyaluronidase To Enhance Nanoparticle-Based Photodynamic Tumor Therapy

Photodynamic therapy (PDT) is considered as a safe and selective way to treat a wide range of cancers as well as nononcological disorders. However, as oxygen is required in the process of PDT, the hypoxic tumor microenvironment has largely limited the efficacy of PDT to treat tumors especially those with relatively large sizes. To this end, we uncover that hyaluronidase (HAase), which breaks down hyaluronan, a major component of extracellular matrix (ECM) in tumors, would be able to enhance the efficacy of nanoparticle-based PDT for in vivo cancer treatment. It is found that the administration of HAase would lead to the increase of tumor vessel densities and effective vascular areas, resulting in increased perfusion inside the tumor. As a result, the tumor uptake of nanomicelles covalently linked with chlorine e6 (NM-Ce6) would be increased by ∼2 folds due to the improved "enhanced permeability and retention" (EPR) effect, while the tumor oxygenation level also shows a remarkable increase, effectively relieving the hypoxia state inside the tumor. Those effects taken together offer significant benefits in greatly improving the efficacy of PDT delivered by nanoparticles. Taking advantage of the effective migration of HAase from the primary tumor to its drainage sentinel lymph nodes (SLNs), we further demonstrate that this strategy would be helpful to the treatment of metastatic lymph nodes by nanoparticle-based PDT. Lastly, both enhanced EPR effect of NM-Ce6 and relieved hypoxia state of tumor are also observed after systemic injection of modified HAase, proving its potential for clinical translation. Therefore, our work presents a new concept to improve the efficacy of nanomedicine by modulating the tumor microenvironment.

Pharmacokinetic strategies to improve drug penetration and entrapment within solid tumors

Despite the discovery of a large number of anticancer agents, cancer still remains among the leading causes of death since the middle of the twentieth century. Solid tumors possess a high degree of genetic instability and emergence of treatment resistance. Tumor resistance has emerged for almost all approved anticancer drugs and will most probably emerge for newly discovered anticancer agents as well. The use of pharmacokinetic approaches to increase anticancer drug concentrations within the solid tumor compartment and prolong its entrapment might diminish the possibility of resistance emergence at the molecular pharmacodynamic level and might even reverse tumor resistance. Several novel treatment modalities such as metronomic therapy, angiogenesis inhibitors, vascular disrupting agents and tumor priming have been introduced to improve solid tumor treatment outcomes. In the current review we will discuss the pharmacokinetic aspect of these treatment modalities in addition to other older treatment modalities, such as extracellular matrix dissolving agents, extracellular matrix synthesis inhibitors, chemoembolization and cellular efflux pump inhibition. Many of these strategies showed variable degrees of success/failure; however, reallocating these modalities based on their influence on the intratumoral pharmacokinetics might improve their understanding and treatment outcomes.

Influence of vascular normalization on interstitial flow and delivery of liposomes in tumors

Elevated interstitial fluid pressure is one of the barriers of drug delivery in solid tumors. Recent studies have shown that normalization of tumor vasculature by anti-angiogenic factors may improve the delivery of conventional cytotoxic drugs, possibly by increasing blood flow, decreasing interstitial fluid pressure, and enhancing the convective transvascular transport of drug molecules. Delivery of large therapeutic agents such as nanoparticles and liposomes might also benefit from normalization therapy since their transport depends primarily on convection. In this study, a mathematical model is presented to provide supporting evidence that normalization therapy may improve the delivery of 100 nm liposomes into solid tumors, by both increasing the total drug extravasation and providing a more homogeneous drug distribution within the tumor. However these beneficial effects largely depend on tumor size and are stronger for tumors within a certain size range. It is shown that this size effect may persist under different microenvironmental conditions and for tumors with irregular margins or heterogeneous blood supply.

Multiple drug resistance due to resistance to stem cells and stem cell treatment progress in cancer (Review)

In recent years, the cancer stem cell (CSC) theory has provided a new angle in the research of cancer, and has gradually gained significance. According to this theory, the multiple drug resistance (MDR) of cancer is most likely due to the resistance of CSCs, and a significant quantity of research has been carried out into the MDR mechanisms of CSC. Over time, some of these mechanisms have been gradually accepted, including ATP-binding cassette transporters, aldehyde dehydrogenase, the CSC microenvironment and epithelial to mesenchymal transition. In the present review, we summarize these mechanisms in detail and review possible appropriate therapy plans against CSCs based on CSC theory.

Electron paramagnetic resonance: a powerful tool to support magnetic resonance imaging research

The purpose of this paper is to describe some of the areas where electron paramagnetic resonance (EPR) has provided unique information to MRI developments. The field of application mainly encompasses the EPR characterization of MRI paramagnetic contrast agents (gadolinium and manganese chelates, nitroxides) and superparamagnetic agents (iron oxide particles). The combined use of MRI and EPR has also been used to qualify or disqualify sources of contrast in MRI. Illustrative examples are presented with attempts to qualify oxygen sensitive contrast (i.e. T1 - and T2 *-based methods), redox status or melanin content in tissues. Other areas are likely to benefit from the combined EPR/MRI approach, namely cell tracking studies. Finally, the combination of EPR and MRI studies on the same models provides invaluable data regarding tissue oxygenation, hemodynamics and energetics. Our description will be illustrative rather than exhaustive to give to the readers a flavour of 'what EPR can do for MRI'.

Significance of Fractionated Administration of Thalidomide Combined With γ-Ray Irradiation in Terms of Local Tumor Response and Lung Metastasis

Background

The aim of this study was to evaluate the significance of fractionated administration of thalidomide combined with γ-ray irradiation in terms of local tumor response and lung metastatic potential, referring to the response of intratumor quiescent (Q) cells.

Methods

B16-BL6 melanoma tumor-bearing C57BL/6 mice were continuously given 5-bromo-2’-deoxyuridine (BrdU) to label all proliferating (P) cells. The tumor-bearing mice then received γ-ray irradiation after thalidomide treatment through a single or two consecutive daily intraperitoneal administrations up to a total dose of 400 mg/kg in combination with an acute hypoxia-releasing agent (nicotinamide) or mild temperature hyperthermia (MTH). Immediately after the irradiation, cells from some tumors were isolated and incubated with a cytokinesis blocker. The responses of the Q and total (= P + Q) cell populations were assessed based on the frequency of micronuclei using immunofluorescence staining for BrdU. In other tumor-bearing mice, 17 days after irradiation, macroscopic lung metastases were enumerated.

Results

Thalidomide raised the sensitivity of the total cell population more remarkably than Q cells in both single and daily administrations. Daily administration of thalidomide elevated the sensitivity of both the total and Q cell populations, but especially the total cell population, compared with single administration. Daily administration, especially combined with MTH, decreased the number of lung metastases.

Conclusion

Daily fractionated administration of thalidomide in combination with γ-ray irradiation was thought to be more promising than single administration because of its potential to enhance local tumor response and repress lung metastatic potential.

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.

Low-molecular contrast agent dynamic contrast-enhanced (DCE)-MRI and diffusion-weighted (DW)-MRI in early assessment of bevacizumab treatment in breast cancer xenografts

PURPOSE

To investigate the effect of bevacizumab treatment on vascular architecture and function in two xenograft models with different angiogenic properties using diffusion-weighted magnetic resonance imaging (DW-MRI) and dynamic contrast-enhanced MRI (DCE-MRI).

MATERIALS AND METHODS

Mice carrying basal-like (MAS98.12) or luminal-like (MAS98.06) orthotopic breast cancer xenografts were treated with bevacizumab (5 mg/kg), doxorubicin (8 mg/kg), or both drugs in combination. DW-MRI and DCE-MRI were performed before and 3 days after treatment using a Bruker 7T preclinical scanner. Mean microvessel density (MVD) and proliferating microvessel density (pMVD) in the tumors were determined for evaluation of vascular response to bevacizumab treatment.

RESULTS

No changes in DCE-MRI or DW-MRI parameters were observed in untreated controls during the experiment period. DW-MRI showed increased apparent diffusion coefficient (ADC) values in all treatment groups in both basal-like and luminal-like xenografts. DCE-MRI showed increased contrast agent uptake, particularly in central regions of the tumors, after bevacizumab/combination treatment in both xenograft models. This was accompanied by decreased MVD and pMVD in basal-like xenografts. Doxorubicin treatment had no effect on DCE-MRI parameters in any of the xenograft models.

CONCLUSION

Both DW-MRI and DCE-MRI demonstrated an early response to bevacizumab treatment in the xenograft tumors. Increased contrast agent uptake and reduced MVD/pMVD is consistent with a normalization of vascular function.

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.

Antiangiogenic and radiation therapy: early effects on in vivo computed tomography perfusion parameters in human colon cancer xenografts in mice

OBJECTIVES

To assess early treatment effects on computed tomography (CT) perfusion parameters after antiangiogenic and radiation therapy in subcutaneously implanted, human colon cancer xenografts in mice and to correlate in vivo CT perfusion parameters with ex vivo assays of tumor vascularity and hypoxia.

MATERIALS AND METHODS

Dynamic contrast-enhanced CT (perfusion CT, 129 mAs, 80 kV, 12 slices × 2.4 mm; 150 μL iodinated contrast agent injected at a rate of 1 mL/min intravenously) was performed in 100 subcutaneous human colon cancer xenografts on baseline day 0. Mice in group 1 (n=32) received a single dose of the antiangiogenic agent bevacizumab (10 mg/kg body weight), mice in group 2 (n=32) underwent a single radiation treatment (12 Gy), and mice in group 3 (n=32) remained untreated. On days 1, 3, 5, and 7 after treatment, 8 mice from each group underwent a second CT perfusion scan, respectively, after which tumors were excised for ex vivo analysis. Four mice were killed after baseline scanning on day 0 for ex vivo analysis. Blood flow (BF), blood volume (BV), and flow extraction product were calculated using the left ventricle as an arterial input function. Correlation of in vivo CT perfusion parameters with ex vivo microvessel density and extent of tumor hypoxia were assessed by immunofluorescence. Reproducibility of CT perfusion parameter measurements was calculated in an additional 8 tumor-bearing mice scanned twice within 5 hours with the same CT perfusion imaging protocol.

RESULTS

The intraclass correlation coefficients for BF, BV, and flow extraction product from repeated CT perfusion scans were 0.93 (95% confidence interval: 0.78, 0.97), 0.88 (0.66, 0.95), and 0.88 (0.56, 0.95), respectively. Changes in perfusion parameters and tumor volumes over time were different between treatments. After bevacizumab treatment, all 3 perfusion parameters significantly decreased from day 1 (P ≤ 0.006) and remained significantly decreased until day 7 (P ≤ 0.008); tumor volume increased significantly only on day 7 (P=0.04). After radiation treatment, all 3 perfusion parameters decreased significantly on day 1 (P < 0.001); BF and flow extraction product increased again on day 3 and 5, although without reaching statistically significant difference; and tumor volumes did not change significantly at all time points (P ≥ 0.3). In the control group, all 3 perfusion parameters did not change significantly, whereas tumor volume increased significantly at all the time points, compared with baseline (P ≤ 0.04). Ex vivo immunofluorescent staining showed good correlation between all 3 perfusion parameters and microvessel density (ρ=0.71, 0.66, and 0.69 for BF, BV, and flow extraction product, respectively; P < 0.001). There was a trend toward negative correlation between extent of hypoxia and all 3 perfusion parameters (ρ=-0.53, -0.47, and -0.40 for BF, BV, and flow extraction product, respectively; P ≥ 0.05).

CONCLUSIONS

CT perfusion allows a reproducible, noninvasive assessment of tumor vascularity in human colon cancer xenografts in mice. After antiangiogenic and radiation therapy, BF, BV, and flow extraction product significantly decrease and change faster than the tumor volume.

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.

Effect of a topical vasodilator on tumor hypoxia and tumor oxygen guided radiotherapy using EPR oximetry

We sought to reduce tumor hypoxia by topical application of a vasodilator, benzyl nicotinate (BN), and investigated its effect on the growth of tumors irradiated at times when tumor pO(2) increased. EPR oximetry was used to follow the changes in the tissue pO(2) of subcutaneous radiation-induced fibrosarcoma (RIF-1) tumors during topical applications of 1.25-8% BN formulations for 5 consecutive days. The RIF-1 tumors were hypoxic with a tissue pO(2) of 4.6-7.0 mmHg. A significant increase in tumor pO(2) occurred 10-30 min after BN application. The formulation with the minimal BN concentration that produced a significant increase in tumor pO(2) was used for the radiation study. The tumors were irradiated (4 Gy x 5) at the time of the maximum increase in pO(2) observed with the 2.5% BN formulation. The tumors with an increase in pO(2) of greater than 2 mmHg from the baseline after application of BN on day 1 had a significant growth inhibition compared to the tumors with an increase in pO(2) of less than 2 mmHg. The results indicate that the irradiation of tumors at the time of an increase in pO(2) after the topical application of the 2.5% BN formulation led to a significant growth inhibition. EPR oximetry provided dynamic information on the changes in tumor pO(2), which could be used to identify responders and non-responders and schedule therapy during the experiments.

Use of Xanthinol Nicotinate as a co-treatment for radio- and chemo-therapy in experimental tumors

The tumor micro-environment plays a key role in the tumor resistance to cytotoxic treatments. It has been demonstrated that it is possible to modulate the tumor microenvironment to potentiate anti-cancer therapy. Here, we made the hypothesis that the vasoactive agent xanthinol nicotinate (XN) could be an important modulator of the tumor perfusion and oxygenation. Using functional non invasive techniques (in vivo EPR oximetry and dynamic contrast enhanced MRI), we were able to define a time window in which tumor oxygenation, flow and permeability were significantly increased in the TLT tumor model implanted in muscles of mice. As a consequence of the alleviation of tumor hypoxia, we found out that XN was able to radiosensitize the tumors when applying 10 Gy of X-Rays during the reoxygenation of the tumors (enhancement in radiation response of 1.4). Moreover, the administration of cyclosphosphamide (50 mg/kg) used as a chemotherapeutic agent was more efficient when applying the treatment after XN administration (enhancement in response to chemotherapy of 2.7). These results show the importance of the dynamic evolution of the tumor microenvironment on the response to treatments, and that XN is an efficient modulator of the tumor hemodynamics that may potentiate cytotoxic treatments.

Decrease in tumor cell oxygen consumption after treatment with vandetanib (ZACTIMA; ZD6474) and its effect on response to radiotherapy

We investigated the early effects of vandetanib (ZACTIMA; ZD6474), an inhibitor of VEGFR-dependent angiogenesis, on tumor oxygenation and on the possible consequences of combining vandetanib with radiotherapy. Tumor oxygenation, perfusion, cellular consumption of oxygen, and radiation sensitivity were studied in transplantable liver tumors after daily doses of vandetanib (25 mg kg(-1) i.p.). Measurements of oxygenation (pO(2)) and tumor cell oxygen consumption were carried out using electron paramagnetic resonance (EPR), and perfusion parameters were assessed by dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI). Regrowth delay assays were performed after treatment with vandetanib alone, radiation alone or a combination of both treatments. Vandetanib induced an early increase in tumor oxygenation that did not correlate with remodeling of the tumor vasculature or with changes in tumor perfusion. A decrease in tumor cell oxygen consumption was observed that could have been responsible for this increase in tumor oxygenation. Consistent with this increase in tumor oxygenation, we found that vandetanib potentiated the tumor response to radiotherapy. Our results confirm that treatment with an inhibitor of VEGFR signaling reduces oxygen consumption rate by tumor cells. The observation that vandetanib causes an early increase in tumor oxygenation has implications for the timing and sequencing of treatment with VEGF signaling inhibitors in combination with radiation.

Characterization of response to radiation mediated gene therapy by means of multimodality imaging

Imaging techniques are under development to facilitate early analysis of spatial patterns of tumor response to combined radiation and antivascular gene therapy. A genetically modified, replication defective adenoviral vector (Ad.EGR-TNFalpha), injected intratumorally, mediates infected cells to express tumor necrosis factor alpha (TNFalpha), which is increased after exposure to radiation. The goal of this study was to characterize an image based "signature" for response to this combined radiation and gene therapy in mice with human prostate xenografts. This study is part of an imaged guided therapy project where such a signature would be useful in guiding subsequent treatments. Changes in the tumor micro-environment were assessed using MRI registered with electron paramagnetic resonance imaging which provides images of tissue oxygenation. Dynamic contrast-enhanced MRI was used to assess tissue perfusion. When compared with null vector (control) treatment, the ratio of contrast agent (Gd-DTPA-BMA) washout rate to uptake rate was lower (P = 0.001) after treatment, suggesting a more balanced perfusion. Concomitantly, oxygenation significantly increased in the treated animals and decreased or did not change in the control animals (P < 0.025). This is the first report of minimally invasive, quantitative, absolute oxygen measurements correlated with tissue perfusion in vivo.

Dominant effect of antiangiogenesis in combination therapy involving cyclophosphamide and axitinib

PURPOSE

Antiangiogenic drug treatment inhibits tumor growth by decreasing blood supply, which can also reduce the delivery of other therapeutic agents. Presently, we investigated the effect of the vascular endothelial growth factor receptor tyrosine kinase inhibitor axitinib (AG-013736) on tumor vascular patency and chemotherapeutic drug uptake. Furthermore, the effect of axitinib on the antitumor activity of combination treatments with cyclophosphamide was examined.

EXPERIMENTAL DESIGN

Prostate cancer PC-3 xenografts were used to evaluate the effect of axitinib treatment on tumor vascular morphology, fluorescent dye perfusion, hypoxia, and uptake of 4-hydroxycyclophosphamide, the active metabolite of the chemotherapeutic prodrug cyclophosphamide. Sequential or simultaneous schedules for axitinib and cyclophosphamide administration were evaluated in both PC-3 tumors and 9L gliosarcoma xenograft models.

RESULTS

Axitinib monotherapy induced sustained growth stasis in PC-3 tumors in association with extensive apoptotic cell death. A substantial decrease in tumor vascular patency was observed, exemplified by a near complete loss of Hoechst 33342 perfusion and the absence of pimonidazole staining in the increasingly hypoxic tumors. Antitumor activity was significantly enhanced in both PC-3 and 9L tumors treated using an optimized schedule of sequential, intermittent axitinib-cyclophosphamide combination therapy despite a 40% to 70% decrease in tumor tissue uptake of 4-hydroxycyclophosphamide.

CONCLUSIONS

In axitinib-cyclophosphamide combination therapy, enhanced anticancer activity can be achieved when the reduced tumor cell exposure to the cancer chemotherapeutic agent is compensated by antiangiogenesis-induced tumor cell starvation. This intrinsic antitumor effect was particularly evident in PC-3 tumor xenografts, where tumor blood flow deprivation dominates the overall therapeutic response.

Anti-angiogenic therapy using thalidomide combined with chemotherapy in small cell lung cancer: a randomized, double-blind, placebo-controlled trial

BACKGROUND

Cancer cells rely on angiogenesis for growth and dissemination, and small cell lung cancer (SCLC) is a highly angiogenic tumor. We evaluated thalidomide, an anti-angiogenic agent, when combined with chemotherapy and as maintenance treatment.

METHODS

A total of 724 patients (51% with limited and 49% with extensive disease) were randomly assigned to receive placebo or thalidomide capsules, 100-200 mg daily for up to 2 years. All patients received etoposide and carboplatin every 3 weeks for up to six cycles. Endpoints were overall survival, progression-free survival, tumor response rate, toxicity, and quality of life (QoL). Hazard ratios (HRs) for comparing thalidomide against placebo were estimated using Cox regression modeling. Statistical tests were two-sided.

RESULTS

The median overall survival was 10.5 months (placebo) and 10.1 months (thalidomide) (HR for death = 1.09, 95% confidence interval [CI] = 0.93 to 1.27; P = .28). Among patients with limited-stage disease, there was no evidence of a survival difference (HR for death = 0.91, 95% CI = 0.73 to 1.15), but among patients with extensive disease, survival was worse in the thalidomide group (HR for death = 1.36, 95% CI = 1.10 to 1.68). Progression-free survival rates were also similar in the two groups (HR = 1.07, 95% CI = 0.92 to 1.24). Thalidomide was associated with an increased risk of having a thrombotic event, mainly pulmonary embolus and deep vein thrombosis (19% thalidomide vs 10% placebo; HR = 2.13, 95% CI = 1.41 to 3.20; P < .001). There were no statistically significant differences between treatments in hematological and nonhematological toxic effects, except more patients in the thalidomide group had rash, constipation, or neuropathy. Overall, QoL scores were similar in the two treatment groups, but thalidomide was associated with less insomnia and diarrhea and more constipation and peripheral neuropathy.

CONCLUSIONS

In this large randomized trial, thalidomide in combination with chemotherapy did not improve survival of patients with SCLC but was associated with an increased risk of thrombotic events.

Translating preclinical findings of (endothelial) progenitor cell mobilization into the clinic; from bedside to bench and back

It is generally accepted that angiogenesis plays a major role in tumor growth and numerous targeting agents directed against angiogenesis pathways have been developed and approved for clinical use. In the past years the concept of angiogenesis has developed into a multi-faceted process in which, besides local activation and division of endothelial cells, bone marrow derived progenitor cells (BMDPCs) contribute to neovascularization. A multitude of preclinical and clinical data indicates that the release of BMDPCs influences the response to certain anti-cancer modalities. In this review we provide an overview of all the preclinical and clinical studies contributing to this hypothesis and translate these findings to the clinic by pointing out the clinical implications these findings might have. The recent insight in the mechanism of a systemic host response, in response to various treatment modalities has shed new light on the mechanism of tumor regrowth, early recurrence and metastasis formation during or after treatment. This provides various new targets for therapy which can be used to improve conventional chemotherapy. Furthermore it provides a potential explanation why bevacizumab selectively enhances the effectiveness of only certain types of chemotherapy.

Combination of antiangiogenesis with chemotherapy for more effective cancer treatment

Angiogenesis is a hallmark of tumor development and metastasis and is now a validated target for cancer treatment. However, the survival benefits of antiangiogenic drugs have thus far been rather modest, stimulating interest in developing more effective ways to combine antiangiogenic drugs with established chemotherapies. This review discusses recent progress and emerging challenges in this field; interactions between antiangiogenic drugs and conventional chemotherapeutic agents are examined, and strategies for the optimization of combination therapies are discussed. Antiangiogenic drugs such as the anti-vascular endothelial growth factor antibody bevacizumab can induce a functional normalization of the tumor vasculature that is transient and can potentiate the activity of coadministered chemoradiotherapies. However, chronic angiogenesis inhibition typically reduces tumor uptake of coadministered chemotherapeutics, indicating a need to explore new approaches, including intermittent treatment schedules and provascular strategies to increase chemotherapeutic drug exposure. In cases where antiangiogenesis-induced tumor cell starvation augments the intrinsic cytotoxic effects of a conventional chemotherapeutic drug, combination therapy may increase antitumor activity despite a decrease in cytotoxic drug exposure. As new angiogenesis inhibitors enter the clinic, reliable surrogate markers are needed to monitor the progress of antiangiogenic therapies and to identify responsive patients. New targets for antiangiogenesis continue to be discovered, increasing the opportunities to interdict tumor angiogenesis and circumvent resistance mechanisms that may emerge with chronic use of these drugs.

Modulation of the antitumor activity of metronomic cyclophosphamide by the angiogenesis inhibitor axitinib

The promising but still limited efficacy of angiogenesis inhibitors as monotherapies for cancer treatment indicates a need to integrate these agents into existing therapeutic regimens. Presently, we investigate the antitumor activity of the small-molecule angiogenesis inhibitor axitinib (AG-013736) and its potential for combination with metronomic cyclophosphamide. Axitinib significantly inhibited angiogenesis in rat 9L tumors grown s.c. in scid mice but only moderately delayed tumor growth. Combination of axitinib with metronomic cyclophosphamide fully blocked 9L tumor growth on initiation of drug treatment. In contrast, metronomic cyclophosphamide alone required multiple treatment cycles to halt tumor growth. However, in contrast to the substantial tumor regression that is ultimately induced by metronomic cyclophosphamide, the axitinib/cyclophosphamide combination was tumor growth static. Axitinib did not inhibit hepatic activation of cyclophosphamide or export of its activated metabolite, 4-hydroxy-cyclophosphamide (4-OH-CPA), to extrahepatic tissues; rather, axitinib selectively decreased 9L tumor uptake of 4-OH-CPA by 30% to 40%. The reduced tumor penetration of 4-OH-CPA was associated with a decrease in cyclophosphamide-induced tumor cell apoptosis and a block in the induction of the endogenous angiogenesis inhibitor thrombospondin-1 in tumor-associated host cells, which may contribute to the absence of tumor regression with the axitinib/cyclophosphamide combination. Finally, axitinib transiently increased 9L tumor cell apoptosis, indicating that its effects are not limited to the endothelial cell population. These findings highlight the multiple effects that may characterize antiangiogenic agent/metronomic chemotherapy combinations and suggest that careful optimization of drug scheduling and dosages will be required to maximize antitumor responses.

Lessons from multidisciplinary translational trials on anti-angiogenic therapy of cancer

The importance of multidisciplinary translational clinical trials is obvious; however, making them work is complex and challenging. Here I present an argument for designing and implementing multidisciplinary mechanistic trials and present the lessons our team at the Massachusetts General Hospital Cancer Center has learned from two such trials in cancer patients with locally advanced rectal carcinomas and recurrent glioblastomas.

19F NMR in vivo spectroscopy reflects the effectiveness of perfusion-enhancing vascular modifiers for improving gemcitabine chemotherapy

Nuclear magnetic resonance spectroscopy of fluorine-19 ((19)F NMR) has proven useful for evaluating kinetics of fluorinated chemotherapy drugs in tumors in vivo. This work investigated how three perfusion-enhancing vascular modifiers (BQ123, thalidomide, and Botulinum neurotoxin type A [BoNT-A]) would affect the chemotherapeutic efficacy of gemcitabine, a fluorinated drug widely used in human cancer treatment. Murine tumor growth experiments demonstrated that only BoNT-A showed a strong trend to enhance tumor growth inhibition by gemcitabine (1.7 days growth delay, P = 0.052, Student t-test). In accord with these results, (19)F NMR experiments showed that only BoNT-A increased significantly the uptake of gemcitabine in tumors (50% increase, P = 0.0008, Student t-test). Further experiments on gemcitabine kinetics (NMR vs time) and distribution ((19)F MRI) confirmed the uptake-enhancing properties of BoNT-A. The results of this study demonstrate that (19)F NMR can monitor modulation of the pharmacokinetics of fluorinated chemotherapy drugs in tumors. The results also show that (19)F NMR data can give a strong indication of the effectiveness of perfusion-enhancing vascular modifiers for improving gemcitabine chemotherapy in murine tumors. (19)F NMR is a promising tool for preclinical evaluation of such vascular modifiers and may ultimately be used in the clinic to monitor how these modifiers affect chemotherapy.

Mechanism of reoxygenation after antiangiogenic therapy using SU5416 and its importance for guiding combined antitumor therapy

Emerging preclinical studies support the concept of a transient "normalization" of tumor vasculature during the early stage of antiangiogenic treatment, with possible beneficial effects on associated radiotherapy or chemotherapy. One key issue in this area of research is to determine whether this feature is common to all antiangiogenic drugs and whether the phenomenon occurs in all types of tumors. In the present study, we characterized the evolution of the tumor oxygenation (in transplantable liver tumor and FSAII tumor models) after administration of SU5416, an antagonist of the vascular endothelial growth factor receptor. SU5416 induced an early increase in tumor oxygenation [measured by electronic paramagnetic resonance (EPR)], which did not correlate with remodeling of the tumor vasculature (assessed by CD31 labeling using immunohistochemistry) or with tumor perfusion (measured by dynamic contrast enhanced-magnetic resonance imaging). Inhibition of mitochondrial respiration (measured by EPR) was responsible for this early reoxygenation. Consistent with these unique findings in the tumor microenvironment, we found that SU5416 potentiated tumor response to radiotherapy but not to chemotherapy. In addition to the fact that the characterization of the tumor oxygenation is essential to enable correct application of combined therapies, our results show that the long-term inhibition of oxygen consumption is a potential novel target in this class of compounds.

Drug Resistance and the Solid Tumor Microenvironment

Resistance of human tumors to anticancer drugs is most often ascribed to gene mutations, gene amplification, or epigenetic changes that influence the uptake, metabolism, or export of drugs from single cells. Another important yet little-appreciated cause of anticancer drug resistance is the limited ability of drugs to penetrate tumor tissue and to reach all of the tumor cells in a potentially lethal concentration. To reach all viable cells in the tumor, anticancer drugs must be delivered efficiently through the tumor vasculature, cross the vessel wall, and traverse the tumor tissue. In addition, heterogeneity within the tumor microenvironment leads to marked gradients in the rate of cell proliferation and to regions of hypoxia and acidity, all of which can influence the sensitivity of the tumor cells to drug treatment. In this review, we describe how the tumor microenvironment may be involved in the resistance of solid tumors to chemotherapy and discuss potential strategies to improve the effectiveness of drug treatment by modifying factors relating to the tumor microenvironment.

Bevacizumab-induced transient remodeling of the vasculature in neuroblastoma xenografts results in improved delivery and efficacy of systemically administered chemotherapy

PURPOSE

Dysfunctional tumor vessels can be a significant barrier to effective cancer therapy. However, increasing evidence suggests that vascular endothelial growth factor (VEGF) inhibition can effect transient "normalization" of the tumor vasculature, thereby improving tumor perfusion and, consequently, delivery of systemic chemotherapy. We sought to examine temporal changes in tumor vascular function in response to the anti-VEGF antibody, bevacizumab.

EXPERIMENTAL DESIGN

Established orthotopic neuroblastoma xenografts treated with bevacizumab were evaluated at serial time points for treatment-associated changes in intratumoral vascular physiology, penetration of systemically administered chemotherapy, and efficacy of combination therapy.

RESULTS

After a single bevacizumab dose, a progressive decrease in tumor microvessel density to <30% of control was observed within 7 days. Assessment of the tumor microenvironment revealed a rapid, sustained decrease in both tumor vessel permeability and tumor interstitial fluid pressure, whereas intratumoral perfusion, as assessed by contrast-enhanced ultrasonography, was improved, although this latter change abated by 1 week. Intratumoral drug delivery mirrored these changes; penetration of chemotherapy was improved by as much as 81% when given 1 to 3 days after bevacizumab, compared with when both drugs were given concomitantly, or 7 days apart. Finally, administering topotecan to tumor-bearing mice 3 days after bevacizumab resulted in greater tumor growth inhibition (36% of control size) than with monotherapy (88% bevacizumab, 54% topotecan) or concomitant administration of the two drugs (44%).

CONCLUSIONS

Bevacizumab-mediated VEGF blockade effects alterations in tumor vessel physiology that allow improved delivery and efficacy of chemotherapy, although careful consideration of drug scheduling is required to optimize antitumor activity.