Effects of 5,6-dimethylxanthenone-4-acetic acid on human tumor microcirculation assessed by dynamic contrast-enhanced magnetic resonance imaging

Tumor vascular disrupting agent 5,6-dimethylxanthenone-4-acetic acid (DMXAA): Suppresses macrophage capping protein beyond STING activation

The vascular disrupting agent (VDA) 5,6-dimethylxanthenone-4-acetic acid (DMXAA) induces apoptosis in vascular endothelial cells and leads to tumor hemorrhagic necrosis. While DMXAA has been proven to be a potent agonist of murine stimulator of interferon genes (mSTING), it has little effect on human-STING (hSTING). This species selectivity of DMXAA may explain its effectiveness against solid tumors in mice and its failure in clinical trials. However, DMXAA did reduce tumor volume in some patients during clinical trials. These paradoxical results have prompted us to investigate the anti-tumor mechanism of DMXAA beyond STING in the destruction of tumor vasculature in humans. In this study, we demonstrated that DMXAA binds to both human and mouse macrophage capping protein (CapG), with a KD of 5.839 μM for hCapG and a KD of 2.867 μM for mCapG, as determined by surface plasmon resonance (SPR) analysis. Homology modeling and molecular docking analysis of hCapG indicated that the critical residues involved in the hydrogen bond interaction of DMXAA with hCapG were Arg153, Thr151, and GLN141, Asn234. In addition, electrostatic pi-cation interaction occurred between DMXAA and hCapG. Further functional studies revealed that CapG protein plays a crucial role in the effects of DMXAA on human umbilical endothelial vein cell (HUEVC) angiogenesis and migration, as well as the expression of cytoskeletal proteins actin and tubulin, and the invasion of A549 lung adenocarcinoma cells. Our study has originally uncovered a novel cross-species pathway underlying the antitumor vascular disruption of DMXAA extends beyond STING activation. This finding deepens our understanding of the multifaceted actions of flavonoid VDAs in animal models and in clinical settings, and may provide insights for the precise therapy of DMXAA based on the biomarker CapG protein.

Multiparametric Quantitative Imaging Biomarker as a Multivariate Descriptor of Health: A Roadmap

Multiparametric quantitative imaging biomarkers (QIBs) offer distinct advantages over single, univariate descriptors because they provide a more complete measure of complex, multidimensional biological systems. In disease, where structural and functional disturbances occur across a multitude of subsystems, multivariate QIBs are needed to measure the extent of system malfunction. This paper, the first Use Case in a series of articles on multiparameter imaging biomarkers, considers multiple QIBs as a multidimensional vector to represent all relevant disease constructs more completely. The approach proposed offers several advantages over QIBs as multiple endpoints and avoids combining them into a single composite that obscures the medical meaning of the individual measurements. We focus on establishing statistically rigorous methods to create a single, simultaneous measure from multiple QIBs that preserves the sensitivity of each univariate QIB while incorporating the correlation among QIBs. Details are provided for metrological methods to quantify the technical performance. Methods to reduce the set of QIBs, test the superiority of the mp-QIB model to any univariate QIB model, and design study strategies for generating precision and validity claims are also provided. QIBs of Alzheimer's Disease from the ADNI merge data set are used as a case study to illustrate the methods described.

Dose-response assessment by quantitative MRI in a phase 1 clinical study of the anti-cancer vascular disrupting agent crolibulin

The vascular disrupting agent crolibulin binds to the colchicine binding site and produces anti-vascular and apoptotic effects. In a multisite phase 1 clinical study of crolibulin (NCT00423410), we measured treatment-induced changes in tumor perfusion and water diffusivity (ADC) using dynamic contrast-enhanced MRI (DCE-MRI) and diffusion-weighted MRI (DW-MRI), and computed correlates of crolibulin pharmacokinetics. 11 subjects with advanced solid tumors were imaged by MRI at baseline and 2–3 days post-crolibulin (13–24 mg/m²). ADC maps were computed from DW-MRI. Pre-contrast T₁ maps were computed, co-registered with the DCE-MRI series, and maps of area-under-the-gadolinium-concentration-curve-at-90 s (AUC_90s) and the Extended Tofts Model parameters k^trans, v_e, and v_p were calculated. There was a strong correlation between higher plasma drug \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${C}^{max}$$\end{document}Cmax and a linear combination of (1) reduction in tumor fraction with \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${AUC}_{90s}>15.8$$\end{document}AUC90s>15.8 mM s, and, (2) increase in tumor fraction with \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${v}_{e}<0.3$$\end{document}ve<0.3. A higher plasma drug AUC was correlated with a linear combination of (1) increase in tumor fraction with \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\text{ADC}} < 1.1 \times 10^{ - 3} \;{\text{mm}}^{2} /{\text{s}}$$\end{document}ADC<1.1×10-3mm2/s, and, (2) increase in tumor fraction with \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$v_{e}<0.3$$\end{document}ve<0.3. These findings are suggestive of cell swelling and decreased tumor perfusion 2–3 days post-treatment with crolibulin. The multivariable linear regression models reported here can inform crolibulin dosing in future clinical studies of crolibulin combined with cytotoxic or immune-oncology agents.

Repeatability of dynamic contrast enhanced vp parameter in healthy subjects and patients with brain tumors

PURPOSE

To study the repeatability of plasma volume (v_p) extracted from dynamic-contrast-enhanced (DCE) MRI in order to define threshold values for significant longitudinal changes, and to assess changes in patients with high-grade-glioma (HGG).

METHODS

Twenty eight healthy subjects, of which eleven scanned twice, were used to assess the repeatability of v_p within the normal-appearing brain tissue and to define threshold values for significant changes based on least-detected-differences (LDD) of mean v_p values and histogram comparisons using earth-mover's-distance (EMD). Sixteen patients with HGG were scanned longitudinally with eight patients scanned before and following bevacizumab therapy. Longitudinal changes were assessed based on defined threshold values in comparison to RANO criteria.

RESULTS

The threshold values for significant changes were: LDD = 0.0024 (ml/100 ml, 21%) for mean v_p and EMD = 4.14. In patients, in 20/24 comparisons, no significant longitudinal changes were detected for v_p within the normal-appearing brain tissue. Concurring results were obtained between changes in lesion volume (RANO criteria) and LDD or EMD values in cases diagnosed with progressive-disease, yet in about 50% of cases diagnosed with partial-response preliminary results demonstrated significant increase in v_p despite significant reductions in lesion volume. In two patients, these changes preceded progression detected at follow-up scans. In general, a good concordance was obtained between LDD and EMD.

CONCLUSION

This study shows high repeatability of v_p and provides threshold values for significant changes in longitudinal assessment of patients with brain tumors. Preliminary results suggest the use of v_p-DCE parameter to improve assessment of therapy response in patients with high-grade-glioma.

MR Imaging Biomarkers in Oncology Clinical Trials

The authors discuss eight areas of quantitative MR imaging that are currently used (RECIST, DCE-MR imaging, DSC-MR imaging, diffusion MR imaging) in clinical trials or emerging (CEST, elastography, hyperpolarized MR imaging, multiparameter MR imaging) as promising techniques in diagnosing cancer and assessing or predicting response of cancer to therapy. Illustrative applications of the techniques in the clinical setting are summarized before describing the current limitations of the methods.

Preliminary Evidence That High-Dose Vitamin C has a Vascular Disrupting Action in Mice

High intravenous doses of vitamin C (ascorbic acid) have been reported to benefit cancer patients, but the data are controversial and there is incomplete knowledge of what physiological mechanisms might be involved in any response. Vitamin C is taken up efficiently by cells expressing SVCT2 transporters and since vascular endothelial cells express SVCT2, we explored the hypothesis that administration of high-dose vitamin C (up to 5 g/kg) to mice might affect vascular endothelial function. A single administration of vitamin C to mice induced time- and dose-dependent increases in plasma concentrations of the serotonin metabolite 5-hydroxyindole acetic acid (5-HIAA), a marker for vascular disrupting effects. Responses were comparable to those for the tumor vascular disrupting agents, vadimezan and fosbretabulin. High-dose vitamin C administration decreased tumor serotonin concentrations, consistent with the release of serotonin from platelets and its metabolism to 5-HIAA. High-dose vitamin C also significantly increased the degree of hemorrhagic necrosis in tumors removed after 24 h, and significantly decreased tumor volume after 2 days. However, the effect on tumor growth was temporary. The results support the concept that vitamin C at high dose increases endothelial permeability, allowing platelets to escape and release serotonin. Plasma 5-HIAA concentrations could provide a pharmacodynamic biomarker for vitamin C effects in clinical studies.

Assessing reproducibility of diffusion-weighted magnetic resonance imaging studies in a murine model of HER2+ breast cancer

BACKGROUND AND PURPOSE

The use of diffusion-weighted magnetic resonance imaging (DW-MRI) as a surrogate biomarker of response in preclinical studies is increasing. However, before a biomarker can be reliably employed to assess treatment response, the reproducibility of the technique must be established. There is a paucity of literature that quantifies the reproducibility of DW-MRI in preclinical studies; thus, the purpose of this study was to investigate DW-MRI reproducibility in a murine model of HER2+ breast cancer.

MATERIALS AND METHODS

Test-Retest DW-MRI scans separated by approximately six hours were acquired from eleven athymic female mice with HER2+ xenografts using a pulsed gradient spin echo diffusion-weighted sequence with three b values [150, 500, and 800s/mm(2)]. Reproducibility was assessed for the mean apparent diffusion coefficient (ADC) from tumor and muscle tissue regions.

RESULTS

The threshold to reflect a change in tumor physiology in a cohort of mice is defined by the 95% confidence interval (CI), which was±0.0972×10(-3)mm(2)/s (±11.8%) for mean tumor ADC. The repeatability coefficient defines this threshold for an individual mouse, which was±0.273×10(-3)mm(2)/s. The 95% CI and repeatability coefficient for mean ADC of muscle tissue were±0.0949×10(-3)mm(2)/s (±8.30%) and±0.266×10(-3)mm(2)/s, respectively.

CONCLUSIONS

Mean ADC of tumors is reproducible and appropriate for detecting treatment-induced changes on both an individual and mouse cohort basis.

Dynamic contrast-enhanced magnetic resonance imaging in prostate cancer clinical trials: potential roles and possible pitfalls

Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) evaluates the tissue microvasculature and may have a role in assessing and predicting therapeutic response in prostate cancer (PCa). In this review, we review principles of DCE-MRI and present the potential quantitative information that can be obtained. We discuss how it may be used as a biomarker for treatment with antiangiogenic and antivascular agents and potentially identify patients with PCa who may benefit from this form of therapy. Likewise, DCE-MRI may play a role in assessing response to combined androgen deprivation therapy and radiation therapy and theoretically could be a prognostic biomarker in evaluating second-generation hormone therapies. We also address the challenges of using DCE-MRI in PCa clinical trials and discuss the difficulties with standardization of this methodology to allow for biomarker validation, with particular reference to PCa.

An update on the clinical development of drugs to disable tumor vasculature

Traditional methods of improving cancer therapy have focused primarily on achieving increased tumor cell kill. However, more recent strategies involve impairing the nutritional support system of the tumor by targeting the tumor vasculature. Rapid developments in this field in recent years have resulted in the identification of a variety of potential targets and a large number of investigational drugs, many of which are now in clinical development. In the following paper the authors review vascular disrupting therapies.

Use of pharmacokinetic/pharmacodynamic biomarkers to support rational cancer drug development

The process of drug development in oncology has struggled to alter at a pace in keeping with the rapid discovery and testing of agents that act on a wide variety of molecular targets. The rational development of such agents requires an understanding of drug effect(s) on their purported target. It is likely that testing these drugs in a framework designed to examine cytotoxic agents will fail to establish their full potential. We discuss how data gained from biomarker investigation might impact on drug development and provide examples that highlight the development, validation and use of pharmacokinetic, and especially pharmacodynamic biomarkers as drug development moves from the laboratory into clinical testing. The challenges of performing assays to satisfy regulatory requirements have been the subject of much debate. We recommend the implementation of appropriate, fit-for-purpose biomarkers in clinical trials of all new cancer drugs.

DMXAA (Vadimezan, ASA404) is a multi-kinase inhibitor targeting VEGFR2 in particular

The flavone acetic acid derivative DMXAA [5,6-dimethylXAA (xanthenone-4-acetic acid), Vadimezan, ASA404] is a drug that displayed vascular-disrupting activity and induced haemorrhagic necrosis and tumour regression in pre-clinical animal models. Both immune-mediated and non-immune-mediated effects contributed to the tumour regression. The vascular disruption was less in human tumours, with immune-mediated effects being less prominent, but nonetheless DMXAA showed promising effects in Phase II clinical trials in non-small-cell lung cancer. However, these effects were not replicated in Phase III clinical trials. It has been difficult to understand the differences between the pre-clinical findings and the later clinical trials as the molecular targets for the agent have never been clearly established. To investigate the mechanism of action, we sought to determine whether DMXAA might target protein kinases. We found that, at concentrations achieved in blood during clinical trials, DMXAA has inhibitory effects against several kinases, with most potent effects being on members of the VEGFR (vascular endothelial growth factor receptor) tyrosine kinase family. Some analogues of DMXAA were even more effective inhibitors of these kinases, in particular 2-MeXAA (2-methylXAA) and 6-MeXAA (6-methylXAA). The inhibitory effects were greatest against VEGFR2 and, consistent with this, we found that DMXAA, 2-MeXAA and 6-MeXAA were able to block angiogenesis in zebrafish embryos and also inhibit VEGFR2 signalling in HUVECs (human umbilical vein endothelial cells). Taken together, these results indicate that at least part of the effects of DMXAA are due to it acting as a multi-kinase inhibitor and that the anti-VEGFR activity in particular may contribute to the non-immune-mediated effects of DMXAA on the vasculature.

Functional imaging: what evidence is there for its utility in clinical trials of targeted therapies?

Key issues in early clinical trials of targeted agents include the determination of target inhibition, rational patient selection based on pre-treatment tumour characteristics, and assessment of tumour response in the absence of actual shrinkage. There is accumulating evidence that functional imaging using advanced techniques such as dynamic contrast enhanced (DCE)-magnetic resonance imaging (MRI), DCE-computerised tomography (CT) and DCE-ultrasound, diffusion weighted-MRI, magnetic resonance spectroscopy and positron emission tomography-CT using various labelled radioactive tracers has the potential to address all three. This article reviews this evidence with examples from trials using targeted agents with established clinical efficacy and summarises the clinical utility of the various techniques. We therefore recommend that input from specialist radiologists is sought at the early stages of trial design, in order to ensure that functional imaging is incorporated appropriately for the agent under study. There is an urgent need to strengthen the evidence base for these techniques as they evolve, and to ensure standardisation of the methodology.

Phase I/II and pharmacodynamic study of dovitinib (TKI258), an inhibitor of fibroblast growth factor receptors and VEGF receptors, in patients with advanced melanoma

PURPOSE

Dovitinib (TKI258) is an orally available inhibitor of fibroblast growth factor (FGF), VEGF, and platelet-derived growth factor receptors. This phase I/II dose-escalation study was conducted to evaluate the safety, pharmacodynamics, and preliminary efficacy of dovitinib in the treatment of advanced melanoma.

EXPERIMENTAL DESIGN

Patients with advanced melanoma resistant or refractory to standard therapies or for whom no standard therapy was available were enrolled. Dovitinib was administered at doses ranging from 200 to 500 mg/d.

RESULTS

Forty-seven patients were enrolled. The most frequently reported adverse events were fatigue (77%; grade ≥3, 28%), diarrhea (77%; grade ≥3, 11%), and nausea (77%; grade ≥3, 9%). Six dose-limiting toxicities were observed in the 400-mg and 500-mg dose cohorts, which consisted of grade 3 nausea, fatigue, and diarrhea and grade 4 fatigue events. The maximum tolerated dose was 400 mg/d. The best tumor response was stable disease, which was observed in 12 patients. Increases in plasma FGF23, VEGF, and placental growth factor and decreases in soluble VEGF receptor 2 were noted during the first cycle of treatment, consistent with FGF receptor (FGFR) and VEGF receptor (VEGFR) inhibition. Dynamic contrast-enhanced MRI analysis showed a dose-dependent decrease in tumor blood flow and vascular permeability with dovitinib therapy. A decrease in FGFR phosphorylation was observed in paired tumor biopsy samples from a patient treated with dovitinib at a dose of 400 mg/d.

CONCLUSIONS

At a dose of 400 mg/d, dovitinib showed an acceptable safety profile and limited clinical benefit and inhibited FGFR and VEGFR.

Monitoring antivascular therapy in head and neck cancer xenografts using contrast-enhanced MR and US imaging

BACKGROUND

The overall goal of this study was to non-invasively monitor changes in blood flow of squamous cell carcinoma of the head and neck (SCCHN) xenografts using contrast-enhanced magnetic resonance (MR) and ultrasound (US) imaging.

METHODS

Experimental studies were performed on mice bearing FaDu tumors and SCCHN xenografts derived from human surgical tissue. MR examinations were performed using gadofosveset trisodium at 4.7T. Change in T1-relaxation rate of tumors (ΔR1) and tumor enhancement parameters (amplitude, area under the curve-AUC) were measured at baseline and 24 h after treatment with a tumor-vascular disrupting agent (tumor-VDA), 5,6-dimethylxanthenone-4-acetic acid (DMXAA; ASA404) and correlated with tumor necrosis and treatment outcome. CE-US was performed using microbubbles (Vevo MicroMarker®) to assess the change in relative tumor blood volume following VDA treatment.

RESULTS

A marked decrease (up to 68% of baseline) in T1-enhancement of FaDu tumors was observed 1 day after VDA therapy indicative of a reduction in blood flow. Early (24 h) vascular response of individual tumors to VDA therapy detected by MRI correlated with tumor necrosis and volume estimates at 10 days post treatment. VDA treatment also resulted in a significant reduction in AUC and amplitude of patient tumor-derived SCCHN xenografts. Consistent with MRI observations, CE-US revealed a significant reduction in tumor blood volume of patient tumor-derived SCCHN xenografts after VDA therapy. Treatment with VDA resulted in a significant tumor growth inhibition of patient tumor derived SCCHN xenografts.

CONCLUSIONS

These findings demonstrate that both CE-MRI and CE-US allow monitoring of early changes in vascular function following VDA therapy. The results also demonstrate, for the first time, potent vascular disruptive and antitumor activity of DMXAA against patient tumor-derived head and neck carcinoma xenografts.

Classification and toxicities of vascular disrupting agents

Vascular disrupting agents (VDAs) are an exciting new group of targeted therapies under active clinical research in many solid tumors, in particular, lung cancer. Small-molecule VDAs are the focus of current clinical research, and consist of the flavonoids and the tubulin-binding agents. Toxicities of single-agent VDAs are characterized by acute, transient, and generally noncumulative side effects including headaches, nausea and vomiting, tumor pain, hypertension, and tachycardia. Flavonoid agents can also cause infusion site pain, visual disturbances, electrocardiac abnormalities, and symptoms consistent with an acute release of serotonin. Tubulin-binding agents can result in cardiac ischemia, abdominal pain, neuromotor abnormalities and cerebellar ataxia, and acute hemodynamic changes. Clinical trials investigating VDAs in combination with traditional chemotherapy have also shown the potential for significant pharmacologic and adverse toxicity interactions. Further research will need to focus on pharmacokinetic and pharmacodynamic parameters to optimize dosing schedules, determine effective combinations with chemotherapy, and minimize toxicities associated with VDAs.

Opportunities and pitfalls of cancer imaging in clinical trials

Cancer treatment strategies have changed considerably over the past two decades, with increasing emphasis on cancer-specific biological therapies. This situation has led to the incorporation of biomarkers, including those obtained by medical imaging, into trial designs to better understand mechanisms of action and, hopefully, to provide early evidence of treatment efficacy at a molecular or physiological level. Unlike blood tests and tissue samples, an imaging biomarker allows assessment of treatment in the whole tumor, in all tumors in the body, and at multiple time points. This situation has increased the complexity of clinical trials, as each imaging modality has issues related to cost, ease of use, patient compatibility, data analysis, and interpretation. This article reviews strengths and limitations of the current imaging methods available in clinical cancer trials, including MRI, CT, PET, and ultrasonography. The information gained by each test, and the difficulties in acquiring the data and interpreting it are also discussed in order to help researchers plan imaging in clinical trials and interpret data from such studies.

Clinical trials of vascular disrupting agents in advanced non--small-cell lung cancer

Tumor vascular disrupting agents (VDAs), such as the flavonoid compound ASA404 and the tubulin-binding compound combretastatin, selectively disrupt established tumor blood vessels, inhibit tumor blood flow, and induce extensive necrosis at the core of solid tumors. A rationale for combining tumor VDAs with standard chemotherapy for treating advanced non-small-cell lung cancer (NSCLC) includes their complementary actions on different spatial regions of solid tumors and their additive or synergistic preclinical activity in animal models of lung cancer. A randomized, phase II, multicenter, open-label trial with a single-arm extension phase evaluated outcomes in a total of 104 patients (> 18 years of age) with histologically confirmed stage IIIb or stage IV, previously untreated NSCLC that in this trial was treated with ASA404 plus standard chemotherapy vs. standard chemotherapy alone. Adding ASA404 to standard chemotherapy numerically improved tumor response, time to disease progression, and overall survival in this phase II trial, without significantly increasing the incidence or severity of side effects. Other randomized phase II and phase III clinical trials of ASA404 and combretastatin combined with standard chemotherapy in advanced NSCLC are currently ongoing or will be reported shortly.

Temporal aspects of the action of ASA404 (vadimezan; DMXAA)

IMPORTANCE OF THE FIELD

Tumor vascular disrupting agents (tumor VDAs) act by selective induction of tumor vascular failure. While their action is distinct from that of antiangiogenic agents, their clinical potential is likely to reside in improving the efficacy of combination therapy.

AREAS COVERED IN THIS REVIEW

This review describes the preclinical development, clinical trial and mode of action of ASA404, a flavonoid class tumor VDA. This class has a unique dual action, simultaneously disrupting vascular endothelial function and stimulating innate tumor immunity. This review covers the early development of ASA404, through to Phase III trial.

WHAT THE READER WILL GAIN

The reader will gain insight into the sequence of ASA404-induced changes in tumor tissue. Early events include increased vascular permeability, increased endothelial apoptosis and decreased blood flow, while later effects include the induction of serotonin, tumor necrosis factor, other cytokines and chemokines, and nitric oxide. This cascade of events induces sustained reduction of tumor blood flow, induction of tumor hypoxia and increased inflammatory responses. The reader will also gain an appreciation of how the potentiation of radiation and chemotherapeutic effects by ASA404 in murine tumors shaped the development of combination clinical trials.

TAKE HOME MESSAGE

Although there are species differences in ASA404 activity, many features of its action in mice translate to human studies. The future of ASA404 as an effective clinical agent will rely on the development of an appreciation of its ability to optimize the complex interaction between tumor vasculature and tumor immunity during therapy.

ASA404: a tumor vascular-disrupting agent with broad potential for cancer therapy

ASA404 (5,6-dimethylxanthenone-4-acetic acid) was developed as an analogue of flavone acetic acid and found to induce hemorrhagic necrosis of experimental tumors. ASA404 simultaneously targets at least two cell types - vascular endothelial cells and macrophages - within the tumor microenvironment. In murine tumors, ASA404 induces coordinated decreases in tumor blood flow, increases in vascular permeability and increases in vascular endothelial apoptosis, all occurring within 1 h of administration. Over a slightly longer time scale, ASA404 induces an increase in tumor concentrations of TNF and a number of other cytokines. Phase I clinical trials confirmed its vascular effects in humans and Phase II trials demonstrated its activity in combination with the cytotoxic agents carboplatin and paclitaxel. While the molecular target of its action is not yet identified, current results suggest that ASA404 has the potential to augment the antitumor effects of other agents in cancer treatment. Studies of changes in tumor tissue following treatment with ASA404 either alone or combined and other agents will provide new insights into the dynamics of the tumor microenvironment.

18F-fluromisonidazole PET imaging as a biomarker for the response to 5,6-dimethylxanthenone-4-acetic acid in colorectal xenograft tumors

The aim of this study was to evaluate (18)F-fluromisonidazole ((18)F-FMISO) PET for monitoring the tumor response to the antivascular compound 5,6-dimethylxanthenone-4-acetic acid (DMXAA; vadimezan).

METHODS

(18)F-FMISO PET was performed 3 h before and 24 h after treatment with DMXAA (20 mg/kg) in mice bearing HT29 xenograft tumors. Pimonidazole was coadministered with the first (18)F-FMISO injection, and 2-(2-nitro-1H-imidazol-1-yl)-N-(2,2,3,3,3-pentafluoropropyl)acetamide (EF5) was coadministered with the second one. Hoechst 33342 was administered 5 min before sacrifice. Digital autoradiograms of tumor sections were acquired; this acquisition was followed by immunofluorescence microscopic visualization of pimonidazole, EF5, the Hoechst 33342, CD31, and α-smooth muscle actin.

RESULTS

DMXAA treatment resulted in a marked reduction in the (18)F-FMISO mean standardized uptake value (SUV(mean)) in approximately half of the treated tumors. The reduction in SUV(mean) correlated with a decrease in the fraction of tumor area staining positive for both EF5 and pimonidazole. Compared with untreated controls, tumors with decreasing SUV(mean) had significantly fewer perfused microvessels.

CONCLUSION

(18)F-FMISO PET could distinguish between different tumor responses to DMXAA treatment. However, a reduction in (18)F-FMISO SUV(mean) after DMXAA treatment was indicative of reduced perfusion and therefore delivery of (18)F-FMISO, rather than a reduction in tumor hypoxia.

A Bayesian hierarchical model for DCE-MRI to evaluate treatment response in a phase II study in advanced squamous cell carcinoma of the head and neck

OBJECT

Pharmacokinetic parameters from dynamic contrast-enhanced MRI (DCE-MRI) were used to assess the perfusion effects due to treatment response using a tyrosine kinase inhibitor. A Bayesian hierarchical model (BHM) is proposed, as an alternative to voxel-wise estimation procedures, to test for a treatment effect while explicitly modeling known sources of variability.

MATERIALS AND METHODS

Nine subjects from a randomized, blinded, placebo-controlled, multicenter, phase II study of lapatinib were examined before and after treatment. Kinetic parameters were estimated, with an extended compartmental model and subject-specific arterial input function, on a voxel-by-voxel basis.

RESULTS

The group treated with lapatinib had a decrease in median K(trans) of 0.17 min⁻¹, when averaged across all voxels in the tumor ROIs, compared with no change in the placebo group based on nonlinear regression. A hypothesis test of equality between pre- and posttreatment K (trans) could not be rejected against a one-sided alternative (P = 0.09). Equality between median K(trans) in placebo and lapatinib groups posttreatment could also not be rejected using the BHM (P = 0.32). Across all scans acquired in the study, estimates of K(trans) at one site were greater on average than those at the other site by including a site effect in the BHM. The inter-voxel variability is of similar order (within 15%) when compared to the inter-patient variability.

CONCLUSION

Though the study contained a small number of subjects and no significant difference was found, the Bayesian hierarchical model provided estimates of variability from known sources in the study and confidence intervals for all estimated parameters. We believe the BHM provides a straightforward and thorough interrogation of the imaging data at the level of voxels, patients or sites in this multicenter clinical study.

Perfusion MRI in the early clinical development of antivascular drugs: decorations or decision making tools?

INTRODUCTION

Classically, the first step in the clinical development of drugs in oncology involves assessments of dose limiting toxicity (DLT) and maximum tolerated dose (MTD). New paradigms are needed for antiangiogenic drugs and vascular disrupting agents (VDAs) as they are active at doses well below the MTD and as single agents their use might not translate into anti-tumour efficacy. MRI is able to assess the antivascular effects of antivascular drugs via changes in functional kinetic parameters; however, the usefulness of MRI in decision making has been questioned by many.

OBJECTIVES

Our aim is to review the experience of using dynamic contrast-enhanced MRI (DCE-MRI) in early clinical development of vascular directed anticancer therapies over the last decade. Thirty-nine phase I and II studies including data on more than 700 patients have been published as abstracts and/or papers, documenting DCE-MRI changes after the administration of antiangiogenic drugs and VDAs.

DISCUSSION

Perfusion MRI is helpful in assessing whether mechanistic goals are achieved, in assisting dose selection for phase II studies, in selecting subpopulations enriched for response and in predicting patient benefit. Imaging tools are increasingly available. Future challenges for imaging include correlation with clinical measures of efficacy and determining relationships with blood and serum biomarkers.

The unique characteristics of tumor vasculature and preclinical evidence for its selective disruption by Tumor-Vascular Disrupting Agents

The vasculature of solid tumors is fundamentally different from that of normal vasculature and offers a unique target for anti-cancer therapy. Direct vascular-targeting with Tumor-Vascular Disrupting Agents (Tumor-VDAs) is distinctly different from anti-angiogenic strategies, and offers a complementary approach to standard therapies. Tumor-VDAs therefore have significant potential when combined with chemotherapy, radiotherapy, and angiogenesis-inhibiting agents. Preclinical studies with the different Tumor-VDA classes have demonstrated key tumor-selective anti-vascular and anti-tumor effects.

Sensitivity of quantitative metrics derived from DCE MRI and a pharmacokinetic model to image quality and acquisition parameters

RATIONALE AND OBJECTIVES

This study aims to investigate the sensitivity of quantitative metrics derived from dynamic contrast-enhanced (DCE) magnetic resonance imaging and a pharmacokinetic (PK) model to image quality and acquisition parameters.

MATERIALS AND METHODS

A computer-synthesized DCE model that consisted of a large range of values of K(trans) (transfer constant of a paramagnetic contrast agent from blood to tissue), v(p) (fractional plasma volume), and k(ep) (back flux rate) was created to test the reliability of quantitative metrics derived from a standard PK model. Effects of the contrast-to-noise ratio (CNR), total acquisition time, and sampling interval on the stability and bias of the derived metrics were investigated.

RESULTS

The instability and bias of the estimated K(trans), v(p), and k(ep) values increased with sampling interval and decreased with increasing CNR. Total acquisition times had limited influence on the estimations of K(trans) and v(p) values, but increasing the total acquisition time improved the stability of the estimation of k(ep) values. However, for small k(ep) values, the stability was still poor even with a total acquisition time of 8 minutes. Also, the stability and bias of the estimated values of K(trans), v(p), and k(ep) are interrelated.

CONCLUSIONS

Our synthesized DCE model represents perfectly reproduced data except for the presence of Gaussian-distributed random noise. Our analysis suggests minimum changes that may be considered potentially significant in longitudinal therapy assessment studies. Our data are complementary to experimental data from human subjects and phantoms, and provide guidance for the design of image acquisition strategies.

The development of the tumor vascular-disrupting agent ASA404 (vadimezan, DMXAA): current status and future opportunities

IMPORTANCE OF THE FIELD

Targeting tumor vasculature with antiangiogenic agents improves outcomes achieved with chemotherapy in some cancers, but toxicity limits their applicability. Tumor vascular-disrupting agents (tumor-VDAs) induce an acute collapse in tumor vascular supply; ASA404 (vadimezan, 5,6-dimethylxanthenone-4-acetic acid [DMXAA]) is the tumor-VDA most advanced in clinical development. Recent randomized trials of ASA404 in combination with chemotherapy suggested a survival advantage in NSCLC comparable to that achieved with bevacizumab, but with little additional toxicity. Phase III trials in advanced NSCLC have completed accrual, and a review of this exciting agent is timely.

AREAS COVERED IN THIS REVIEW

This review focuses on the development of ASA404 to date, its mechanisms of action, the current body of clinical research and potential avenues for therapeutic use. It includes all completed clinical trials since it entered clinical testing in 1995 through to 2009.

WHAT THE READER WILL GAIN

This review will help the reader to understand why ASA404 is unique among tumor-VDAs; the clinical trial methodology required to evaluate such agents; and its remarkable potential clinical utility.

TAKE HOME MESSAGE

ASA404 is a tumor-VDA that offers considerable potential to improve outcomes in cancer patients in combination with existing treatments.

Phase I clinical and magnetic resonance imaging study of the vascular agent NGR-hTNF in patients with advanced cancers (European Organization for Research and Treatment of Cancer Study 16041)

PURPOSE

This phase I trial investigating the vascular targeting agent NGR-hTNF aimed to determine the (a) dose-limiting toxicities, (b) maximum tolerated dose (MTD), (c) pharmacokinetics and pharmacodynamics, (d) vascular response by dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI), and (e) preliminary clinical activity in solid tumors.

EXPERIMENTAL DESIGN

NGR-hTNF was administered once every 3 weeks by a 20- to 60-minute i.v. infusion to cohorts of three to six patients with solid tumors in escalating doses. Pharmacokinetic and pharmacodynamic analyses in blood were done during the first four cycles. DCE-MRI was done in cycle 1 at baseline and 2 hours after the start of the infusion.

RESULTS

Sixty-nine patients received a total of 201 cycles of NGR-hTNF (0.2-60 microg/m(2)). Rigors and fever were the most frequently observed toxicities. Four dose-limiting toxicities were observed (at doses of 1.3, 8.1, and 60 microg/m(2)), of which three were infusion related. The MTD was 45 microg/m(2). The mean apparent terminal half-life ranged from 0.963 to 2.08 hours. DCE-MRI results of tumors showed a vascular response to NGR-hTNF. No objective responses were observed, but 27 patients showed stable disease with a median duration of 12 weeks.

CONCLUSIONS

NGR-hTNF was well tolerated. The MTD was 45 microg/m(2) administered in 1 hour once every 3 weeks. DCE-MRI results showed the antivascular effect of NGR-hTNF. These findings call for further research for defining the optimal biological dose and clinical activity of NGR-hTNF as a single agent or in combination with cytotoxic drugs.

RECIST revised: implications for the radiologist. A review article on the modified RECIST guideline

The purpose of this review article is to familiarize radiologists with the recently revised Response Evaluation Criteria in Solid Tumours (RECIST), used in many anticancer drug trials to assess response and progression rate. The most important modifications are: a reduction in the maximum number of target lesions from ten to five, with a maximum of two per organ, with a longest diameter of at least 10 mm; in lymph nodes (LNs) the short axis rather than the long axis should be measured, with normal LN measuring <10 mm, non-target LN ≥10 mm but <15 mm and target LN ≥15 mm; osteolytic lesions with a soft tissue component and cystic tumours may serve as target lesions; an additional requirement for progressive disease (PD) of target lesions is not only a ≥20% increase in the sum of the longest diameter (SLD) from the nadir but also a ≥5 mm absolute increase in the SLD (the other response categories of target lesion are unchanged); PD of non-target lesions can only be applied if the increase in non-target lesions is representative of change in overall tumour burden; detailed imaging guidelines. Alternative response criteria in patients with hepatocellular carcinoma and gastrointestinal stromal tumours are discussed.

Contemporary imaging in sarcoma

Sarcomas are a heterogeneous group of >50 subtypes of neoplasm. It is imperative to obtain appropriate imaging of these tumors in order to adequately assess, characterize, and stage bone and soft tissue sarcomas. Anatomic imaging such as radiographs, computed tomography, and magnetic resonance imaging (MRI) remain the foundation for both biopsy planning and postoperative evaluation of these neoplasms. However, anatomic imaging may not be entirely accurate in the evaluation of treatment response. Newer techniques, such (18)F-fluorodeoxyglucose positron emission tomography, are being used to evaluate distant metastases. Newer radiopharmaceuticals, such as (18)F-fluorodeoxythymidine, are being developed to assist in the differentiation between benign and low-grade malignant neoplasms. Newer functional imaging techniques, such as dynamic contrast-enhanced MRI and diffusion-weighted imaging, among others, are being developed to evaluate treatment response.

Feasibility of using limited-population-based average R10 for pharmacokinetic modeling of osteosarcoma dynamic contrast-enhanced magnetic resonance imaging data

Retrospective analyses of clinical dynamic contrast-enhanced (DCE) MRI studies may be limited by failure to measure the longitudinal relaxation rate constant (R(1)) initially, which is necessary for quantitative analysis. In addition, errors in R(1) estimation in each individual experiment can cause inconsistent results in derivations of pharmacokinetic parameters, K(trans) and v(e), by kinetic modeling of the DCE-MRI time course data. A total of 18 patients with lower extremity osteosarcomas underwent multislice DCE-MRI prior to surgery. For the individual R(1) measurement approach, the R(1) time course was obtained using the two-point R(1) determination method. For the average R(10) (precontrast R(1)) approach, the R(1) time course was derived using the DCE-MRI pulse sequence signal intensity equation and the average R(10) value of this population. The whole tumor and histogram median K(trans) (0.57+/-0.37 and 0.45+/-0.32 min(-1)) and v(e) (0.59+/-0.20 and 0.56+/-0.17) obtained with the individual R(1) measurement approach are not significantly different (paired t test) from those (K(trans): 0.61+/-0.46 and 0.44+/-0.33 min(-1); v(e): 0.61+/-0.19 and 0.55+/-0.14) obtained with the average R(10) approach. The results suggest that it is feasible, as well as practical, to use a limited-population-based average R(10) for pharmacokinetic modeling of osteosarcoma DCE-MRI data.

Beyond RECIST: molecular and functional imaging techniques for evaluation of response to targeted therapy

The development of targeted therapies is a major breakthrough in the treatment of cancer. By evoking necrosis and cavitation, evaluation based on tumour size alone, as is done in the RECIST criteria, is no longer an adequate method. New molecular and functional imaging techniques are developed. This review focuses on the use of new imaging modalities for the evaluation of treatment response of pathway based targeted therapies. First, the basic principles of functional and molecular imaging modalities are briefly discussed. Thereafter, their clinical application in targeted therapies is correlated to the underlying biological mechanism. In this way, the best method for response evaluation for a new agent can be identified.

Randomised phase II study of ASA404 combined with carboplatin and paclitaxel in previously untreated advanced non-small cell lung cancer

ASA404 (5,6-dimethylxanthenone-4-acetic acid or DMXAA) is a small-molecule tumour-vascular disrupting agent (Tumour-VDA). This randomised phase II study evaluated ASA404 plus standard therapy of carboplatin and paclitaxel in patients with histologically confirmed stage IIIb or IV non-small cell lung cancer (NSCLC) not previously treated with chemotherapy. Patients were randomised to receive </=6 cycles of carboplatin area under the plasma concentration-time curve 6 mg ml(-1) min and paclitaxel 175 mg m(-2) (CP, n=36) or standard therapy plus ASA404 1200 mg m(-2) (ASA404-CP, n=37). There was little change in the systemic exposure of either total or free carboplatin or paclitaxel on addition of ASA404. Safety profiles were similar and manageable in both groups, with most adverse effects attributed to standard therapy. Tumour response rate (31 vs 22%), median time to tumour progression (5.4 vs 4.4 months) and median survival (14.0 vs 8.8 months, hazard ratio 0.73, 95% CI 0.39, 1.38) were improved in the ASA404 combination group compared with the standard therapy group. In conclusion, this study establishes the feasibility of combining ASA404 with carboplatin and paclitaxel in patients with previously untreated, advanced NSCLC, demonstrating a manageable safety profile and lack of adverse pharmacokinetic interactions. The results indicate that there may be a benefit associated with ASA404, but this needs to be evaluated in a larger trial.

Imaging angiogenesis

There is a need for direct imaging of effects on tumor vasculature in assessment of response to antiangiogenic drugs and vascular disrupting agents. Imaging tumor vasculature depends on differences in permeability of vasculature of tumor and normal tissue, which cause changes in penetration of contrast agents. Angiogenesis imaging may be defined in terms of measurement of tumor perfusion and direct imaging of the molecules involved in angiogenesis. In addition, assessment of tumor hypoxia will give an indication of tumor vasculature. The range of imaging techniques available for these processes includes positron emission tomography (PET), dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI), perfusion computed tomography (CT), and ultrasound (US).

Tumour vascular disrupting agents: combating treatment resistance

A large group of tubulin-binding microtubule-depolymerizing agents act as tumour vascular disrupting agents (VDAs). Several members of this group are now in clinical trials in combination with conventional anticancer drugs and radiotherapy. Here we briefly update on the development of tubulin-binding combretastatins as VDAs, summarize what is known of their mechanisms of action and address issues relating to treatment resistance, using disodium combretastatin A-4 3-O-phosphate (CA-4-P) as an example. Characteristically, VDAs cause a rapid shutdown of blood flow to tumour tissue with much less effect in normal tissues. However, the tumour rim is relatively resistant to treatment. Hypoxia (or hypoxia reoxygenation) induces upregulation of genes associated with angiogenesis and drug resistance. It may be possible to take advantage of treatment-induced hypoxia by combining with drugs that are activated under hypoxic conditions. In summary, VDAs provide a novel approach to cancer treatment, which should effectively complement standard treatments, if treatment resistance is addressed by judicious combination treatment strategies.

Assessment of the early effects of 5,6-dimethylxanthenone-4-acetic acid using macromolecular contrast media-enhanced magnetic resonance imaging: ectopic versus orthotopic tumors

PURPOSE

To investigate the early effects of a vascular disrupting agent (VDA) in ectopic and orthotopic tumors by using macromolecular contrast media (MMCM)-enhanced magnetic resonance imaging (MMCM-MRI).

METHODS AND MATERIALS

The MMCM-MRI of ectopic and orthotopic MCA205 murine fibrosarcomas was performed using the intravascular contrast agent albumin-(gadopentetate dimeglumine)(35). Change in longitudinal relaxation rate (DeltaR1) was measured 24 hours after treatment with 5,6-dimethylxanthenone-4-acetic acid (DMXAA; 30 mg/kg) and used to compute tumor vascular volume and permeability. Correlative histologic and immunohistochemical evaluation was carried out, along with measurement of tumor necrosis factor alpha and vascular endothelial growth factor levels in whole tumor extracts using the enzyme-linked immunosorbent assay.

RESULTS

Orthotopic tumors showed higher vascular volume (p < 0.05) than ectopic tumors before treatment. Twenty-four hours after DMXAA treatment, a significant (p < 0.0001), but differential, decrease in DeltaR1 (70% in ectopic and 50% in orthotopic tumors) was observed compared with baseline estimates. Consistent with this observation, greater levels of tumor necrosis factor alpha, an important mediator of the antivascular activity of DMXAA, were measured in ectopic tumors 3 hours posttreatment compared with orthotopic tumors (p < 0.05). Immunohistochemical (CD31) and histologic (hematoxylin and eosin) sections of ectopic and orthotopic tumors showed highly tumor-selective vascular damage after treatment with the presence of viable surrounding normal tissue.

CONCLUSIONS

The MMCM-MRI provided early quantitative estimates of change in tumor perfusion after VDA treatment that showed good correlation with cytokine induction. Differences in the response of ectopic and orthotopic tumors highlight the influence of the host microenvironment in modulating the activity of VDAs.

The effect of combretastatin A4 disodium phosphate and 5,6-dimethylxanthenone-4-acetic acid on water diffusion and blood perfusion in tumours

PURPOSE

To evaluate the effect of the vascular disrupting drugs combretastatin A-4 disodium phosphate (CA4DP) and 5,6-dimethylxanthenone-4-acetic acid (DMXAA) on the intra/extracellular volume fraction of water and blood perfusion in tumours using MRI.

METHODS AND MATERIALS

Mice with C3H mammary carcinomas underwent repeated MRI T2-weighted imaging, water-diffusion and perfusion measurements before and up to 6-hours following CA4DP and DMXAA treatment.

RESULTS

CA4DP treatment caused an increase in water diffusion in those tumour areas that presented the lowest blood perfusion, however this appeared only after five hours. The blood perfusion in highly perfused tumour regions decreased immediately after administration of CA4DP. DMXAA treatment caused an early decrease in water diffusion in the low-perfused tumour segments and followed by a subsequent decrease in the remaining part of the tumour. The blood perfusion decreased early in all parts of the tumour.

CONCLUSION

The effect of CA4DP and DMXAA on tumour blood flow was comparable. The reduction in regional blood flow caused by CA4DP in the whole tumour segment occurred early, however, changes in ADC after DMXAA appeared more extended and earlier than after CA4DP treatment, especially in tumour areas already suffering from a low blood perfusion.