Dynamic contrast-enhanced magnetic resonance imaging as a surrogate marker of tumor response to anti-angiogenic therapy in a xenograft model of glioblastoma multiforme

Image-based predictive modelling frameworks for personalised drug delivery in cancer therapy

Personalised drug delivery enables a tailored treatment plan for each patient compared to conventional drug delivery, where a generic strategy is commonly employed. It can not only achieve precise treatment to improve effectiveness but also reduce the risk of adverse effects to improve patients' quality of life. Drug delivery involves multiple interconnected physiological and physicochemical processes, which span a wide range of time and length scales. How to consider the impact of individual differences on these processes becomes critical. Multiphysics models are an open system that allows well-controlled studies on the individual and combined effects of influencing factors on drug delivery outcomes while accommodating the patient-specific in vivo environment, which is not economically feasible through experimental means. Extensive modelling frameworks have been developed to reveal the underlying mechanisms of drug delivery and optimise effective delivery plans. This review provides an overview of currently available models, their integration with advanced medical imaging modalities, and code packages for personalised drug delivery. The potential to incorporate new technologies (i.e., machine learning) in this field is also addressed for development.

Longitudinal Evaluation of DCE-MRI as an Early Indicator of Progression after Standard Therapy in Glioblastoma

Background and Purpose: Distinguishing treatment-induced imaging changes from progressive disease has important implications for avoiding inappropriate discontinuation of a treatment. Our goal in this study is to evaluate the utility of dynamic contrast-enhanced (DCE) perfusion MRI as a biomarker for the early detection of progression. We hypothesize that DCE-MRI may have the potential as an early predictor for the progression of disease in GBM patients when compared to the current standard of conventional MRI. Methods: We identified 26 patients from 2011 to 2023 with newly diagnosed primary glioblastoma by histopathology and gross or subtotal resection of the tumor. Then, we classified them into two groups: patients with progression of disease (POD) confirmed by pathology or change in chemotherapy and patients with stable disease without evidence of progression or need for therapy change. Finally, at least three DCE-MRI scans were performed prior to POD for the progression cohort, and three consecutive DCE-MRI scans were performed for those with stable disease. The volume of interest (VOI) was delineated by a neuroradiologist to measure the maximum values for Ktrans and plasma volume (Vp). A Friedman test was conducted to evaluate the statistical significance of the parameter changes between scans. Results: The mean interval between subsequent scans was 57.94 days, with POD-1 representing the first scan prior to POD and POD-3 representing the third scan. The normalized maximum Vp values for POD-3, POD-2, and POD-1 are 1.40, 1.86, and 3.24, respectively (FS = 18.00, p = 0.0001). It demonstrates that Vp max values are progressively increasing in the three scans prior to POD when measured by routine MRI scans. The normalized maximum Ktrans values for POD-1, POD-2, and POD-3 are 0.51, 0.09, and 0.51, respectively (FS = 1.13, p < 0.57). Conclusions: Our analysis of the longitudinal scans leading up to POD significantly correlated with increasing plasma volume (Vp). A longitudinal study for tumor perfusion change demonstrated that DCE perfusion could be utilized as an early predictor of tumor progression.

Therapeutic targeting of angiopoietins in tumor angiogenesis and cancer development

The formation and progression of tumors in humans are linked to the abnormal development of new blood vessels known as neo-angiogenesis. Angiogenesis is a broad word that encompasses endothelial cell migration, proliferation, tube formation, and intussusception, as well as peri-EC recruitment and extracellular matrix formation. Tumor angiogenesis is regulated by angiogenic factors, out of which some of the most potent angiogenic factors such as vascular endothelial growth factor and Angiopoietins (ANGs) in the body are produced by macrophages and other immune cells within the tumor microenvironment. ANGs have a distinct function in tumor angiogenesis and behavior. ANG1, ANG 2, ANG 3, and ANG 4 are the family members of ANG out of which ANG2 has been extensively investigated owing to its unique role in modifying angiogenesis and its tight association with tumor progression, growth, and invasion/metastasis, which makes it an excellent candidate for therapeutic intervention in human malignancies. ANG modulators have demonstrated encouraging outcomes in the treatment of tumor development, either alone or in conjunction with VEGF inhibitors. Future development of more ANG modulators targeting other ANGs is needed. The implication of ANG1, ANG3, and ANG4 as probable therapeutic targets for anti-angiogenesis treatment in tumor development should be also evaluated. The article has described the role of ANG in tumor angiogenesis as well as tumor growth and the treatment strategies modulating ANGs in tumor angiogenesis as demonstrated in clinical studies. The pharmacological modulation of ANGs and ANG-regulated pathways that are responsible for tumor angiogenesis and cancer development should be evaluated for the development of future molecular therapies.

Glioblastoma Multiforme: An Overview of Emerging Therapeutic Targets

Glioblastoma multiforme (GBM) is the most common and aggressive malignant primary brain tumour in humans and has a very poor prognosis. The existing treatments have had limited success in increasing overall survival. Thus, identifying and understanding the key molecule(s) responsible for the malignant phenotype of GBM will yield new potential therapeutic targets. The treatment of brain tumours faces unique challenges, including the presence of the blood brain barrier (BBB), which limits the concentration of drugs that can reach the site of the tumour. Nevertheless, several promising treatments have been shown to cross the BBB and have shown promising pre-clinical results. This review will outline the status of several of these promising targeted therapies.

From Biology to Therapy: Improvements of Therapeutic Options in Lung Cancer

Lung cancer is the leading cause of cancer-related mortality around the world, despite effective chemotherapeutic agents, the prognosis has remained poor for a long time. The discovery of molecular changes that drive lung cancer has led to a dramatic shift in the therapeutic landscape of this disease. In "in vitro" and "in vivo" models of NSCLC (Non-Small Cell Lung Cancer), angiogenesis blockade has demonstrated an excellent anti-tumor activity, thus, a number of anti-angiogenic drugs have been approved by regulatory authorities for use in clinical practice. Much more interesting is the discovery of EGFR (Epithelial Growth Factor Receptor) mutations that predict sensitivity to the anti-EGFR Tyrosine Kinase Inhibitors (TKIs), a class of drugs that has shown to significantly improve survival when compared with standard chemotherapy in the first-line treatment of metastatic NSCLC. Nevertheless, after an initial response, resistance often occurs and prognosis becomes dismal. Biomolecular studies on cell line models have led to the discovery of mutations (e.g., T790M) that confer resistance to anti-EGFR inhibitors. Fortunately, drugs that are able to circumvent this mechanism of resistance have been developed and have been recently approved for clinical use. The discovery of robust intratumor lymphocyte infiltration in NSCLC has paved the way to several strategies able to restore the immune response. Thus, agents interfering with PD-1/PD-L1 (Programmed Death) pathways make up a significant portion of the armamentarium of cancer therapies for NSCLC. In all the above-mentioned situations, the basis of the success in treating NSCLC has started from understanding of the mutational landscape of the tumor.

Imaging biomarkers from multiparametric magnetic resonance imaging are associated with survival outcomes in patients with brain metastases from breast cancer

OBJECTIVES

The aim of this study is to investigate the correlation of survival outcomes with imaging biomarkers from multiparametric magnetic resonance imaging (MRI) in patients with brain metastases from breast cancer (BMBC).

METHODS

This study was approved by the institutional review board. Twenty-two patients with BMBC who underwent treatment involving bevacizumab on day 1, etoposide on days 2-4, and cisplatin on day 2 in 21-day cycles were prospectively enrolled for a phase II study. Three brain MRIs were performed: before the treatment, on day 1, and on day 21. Eight imaging biomarkers were derived from dynamic contrast-enhanced MRI (Peak, IAUC₆₀, K^trans, k_ep, v_e), diffusion-weighted imaging [apparent diffusion coefficient (ADC)], and MR spectroscopy (choline/N-acetylaspartate and choline/creatine ratios). The relative changes (Δ) in these biomarkers were correlated with the central nervous system (CNS)-specific progression-free survival (PFS) and overall survival (OS) using the Kaplan-Meier and Cox proportional hazard models.

RESULTS

There were no significant differences in the survival outcomes as per the changes in the biomarkers on day 1. On day 21, those with a low ΔK^trans (p = 0.024) or ΔADC (p = 0.053) reduction had shorter CNS-specific PFS; further, those with a low ΔPeak (p = 0.012) or ΔIAUC₆₀ (p = 0.04) reduction had shorter OS compared with those with high reductions. In multivariate analyses, ΔK^trans and ΔPeak were independent prognostic factors for CNS-specific PFS and OS, respectively, after controlling for age, size, hormone receptors, and performance status.

CONCLUSIONS

Multiparametric MRI may help predict the survival outcomes in patients with BMBC.

KEY POINTS

• Decreased angiogenesis after chemotherapy on day 21 indicated good survival outcome. • ΔK ^trans was an independent prognostic factors for CNS-specific PFS. • ΔPeak was an independent prognostic factors for OS. • Multiparametric MRI helps clinicians to assess patients with BMBC. • High-risk patients may benefit from more intensive follow-up or treatment strategies.

Quantitative Gd-DOTA uptake from cerebrospinal fluid into rat brain using 3D VFA-SPGR at 9.4T

PURPOSE

We propose a quantitative technique to assess solute uptake into the brain parenchyma based on dynamic contrast-enhanced MRI (DCE-MRI). With this approach, a small molecular weight paramagnetic contrast agent (Gd-DOTA) is infused in the cerebral spinal fluid (CSF) and whole brain gadolinium concentration maps are derived.

METHODS

We implemented a 3D variable flip angle spoiled gradient echo (VFA-SPGR) longitudinal relaxation time (T1) technique, the accuracy of which was cross-validated by way of inversion recovery rapid acquisition with relaxation enhancement (IR-RARE) using phantoms. Normal Wistar rats underwent Gd-DOTA infusion into CSF via the cisterna magna and continuous MRI for approximately 130 min using T1-weighted imaging. Dynamic Gd-DOTA concentration maps were calculated and parenchymal uptake was estimated.

RESULTS

In the phantom study, T1 discrepancies between the VFA-SPGR and IR-RARE sequences were approximately 6% with a transmit coil inhomogeneity correction. In the in vivo study, contrast transport profiles indicated maximal parenchymal retention of approximately 19% relative to the total amount delivered into the cisterna magna.

CONCLUSION

Imaging strategies for accurate 3D contrast concentration mapping at 9.4T were developed and whole brain dynamic concentration maps were derived to study solute transport via the glymphatic system. The newly developed approach will enable future quantitative studies of the glymphatic system in health and disease states. Magn Reson Med 79:1568-1578, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Dynamic Susceptibility Contrast Magnetic Resonance Imaging Protocol of the Normal Canine Brain

Perfusion magnetic resonance imaging (MRI), specifically dynamic susceptibility MRI (DSC-MRI) is routinely performed as a supplement to conventional MRI in human medicine for patients with intracranial neoplasia and cerebrovascular events. There is minimal data on the use of DSC-MRI in veterinary patients and a DSC-MRI protocol in the veterinary patient has not been described. Sixteen normal dogs, 6 years or older were recruited for this study. The sample population included 11 large dogs (>11 kg) and 5 small dogs (<11 kg). DSC-MRI was performed on a 1.5-T MRI using an adjusted protocol inherent to the MRI. Contrast media was injected using an automatic power injector. Injections were made after five MR measurements were obtained. Following image acquisition, an arterial input function (AIF) graph mapping the transit time of contrast within the cerebral arteries was generated. The manually selected time points along this graph were used to compute perfusion maps. A dose and rate of 0.1 mmol/kg gadolinium-based contrast media at 3 ml/s followed by 10 ml saline flush at 3 ml/s was used in all dogs greater than 11 kg. In all dogs >11 kg, a useable AIF and perfusion map was generated. One dog less than 11 kg received the same contrast dose and rate. In this patient, the protocol did not generate a useable AIF. The remainder of the dogs less than 11 kg followed a protocol of 0.2 mmol/kg gadolinium-based contrast media at 1.5 ml/s with a 10 ml saline flush at 1.5 ml/s. A useable AIF and perfusion map was generated in the remaining dogs <11 kg using the higher contrast dose and slower rate protocol. This study establishes a contrast dose and administration rate for canine DSC-MRI imaging that is different in dogs greater than 11 kg compared to dogs less than 11 kg. These protocols may be used for future applications to evaluate hemodynamic disturbances in canine intracranial pathology.

Comparison of Glioblastomas and Brain Metastases using Dynamic Contrast-Enhanced Perfusion MRI

PURPOSE

To compare glioblastoma and brain metastases using T1-weighted dynamic contrast-enhanced (DCE)-MRI perfusion technique.

METHODS

26 patients with glioblastoma and 32 patients with metastatic brain lesions with no treatment who underwent DCE-MRI were, retrospectively, analyzed. DCE perfusion parameters K(trans) and Vp were calculated for the whole tumor. Signal intensity time curves were quantified by calculating the area under the curve (AUC) and the logarithmic slope of the washout phase to explore the heterogeneous tumor characteristics.

RESULTS

Glioblastoma did not differ from all brain metastases in K(trans) (P = .34) or Vp (P = .47). Glioblastoma and melanoma metastases differed from hypovascular metastases in AUC and log slope of the washout phase of the signal intensity time curve (P < .05); however, glioblastoma and melanoma metastases did not differ from each other (AUC: P = .78, Log slope: P = .77). Glioblastoma and melanoma metastases differed from hypovascular metastases in the ratio of Voxelneg /Voxelpos (P< .03); however, they did not differ from each other. Glioblastoma and melanoma metastases differed from each other in Voxelneg_threshold at higher negative log slope threshold.

CONCLUSION

DCE-MRI showed that it has a potential to differentiate glioblastomas, melanoma metastases and hypovascular brain tumors. Logarithmic slope of the washout phase and AUC of the signal intensity time curve were shown to be the best discriminator between hypervascular and hypovascular neoplasms.

Patient characteristics influencing the variability of distributed parameter-based models in DCE-CT kinetic analysis

Kinetic parameter variability may be sensitive to kinetic model choice, kinetic model implementation or patient-specific effects. The purpose of this study was to assess their impact on the variability of dynamic contrast-enhanced computed tomography (DCE-CT) kinetic parameters. A total of 11 canine patients with sinonasal tumours received high signal-to-noise ratio, test-double retest DCE-CT scans. The variability for three distributed parameter (DP)-based models was assessed by analysis of variance. Mixed-effects modelling evaluated patient-specific effects. Inter-model variability (CV_inter ) was comparable to or lower than intra-model variability (CV_intra ) for blood flow (CV_inter :[4-28%], CV_intra :[28-31%]), fractional vascular volume (CV_inter :[3-17%], CV_intra :[16-19%]) and permeability-surface area product (CV_inter :[5-12%], CV_intra :[14-15%]). The kinetic models were significantly (P<0.05) impacted by patient characteristics for patient size, area underneath the curve of the artery and of the tumour. In conclusion, DP-based models demonstrated good agreement with similar differences between models and scans. However, high variability in the kinetic parameters and their sensitivity to patient size may limit certain quantitative applications.

PET, MRI, and simultaneous PET/MRI in the development of diagnostic and therapeutic strategies for glioma

Glioma is the most aggressive brain tumour, resulting in death often within 1-2 years. Current treatment strategies involve surgical resection followed by chemoradiation therapy. Despite continuing improvements in the delivery of adjuvant therapies, there has not been a dramatic increase in survival for glioma. Molecular imaging techniques have become central in the development of new therapeutic strategies in recent years. The multimodal imaging technology of positron emission tomography/magnetic resonance imaging (PET/MRI) has recently been realised on a preclinical scale and the effect of this technology is starting to be observed in preclinical drug development for glioma. Here, we propose that PET/MRI will play an integral part in the development of new diagnostic and therapeutic strategies for glioma.

[Oncological imaging for therapy response assessment]

This review illustrates different radiological methods for therapy response assessment in the field of oncological imaging. Unidimensional measurement of tumor size according to the response evaluation criteria in solid tumors (RECIST) is of utmost importance. The established RECIST definitions of changes in size are decisive for subdivision into the categories complete response (CR), partial response (PR), stable disease (SD) and progressive disease (PD), which are generally accepted as the concise characterization for therapy response. Problems with size-dependent response assessment occur particularly in targeted therapy and by phenomena, such as pseudoprogression. Several variants of functional imaging and their role in cancer imaging regarding practical requests are introduced.

Permeability imaging in pediatric brain tumors

While traditional computed tomography (CT) and magnetic resonance (MR) imaging illustrate the structural morphology of brain pathology, newer, dynamic imaging techniques are able to show the movement of contrast throughout the brain parenchyma and across the blood-brain barrier (BBB). These data, in combination with pharmacokinetic models, can be used to investigate BBB permeability, which has wide-ranging applications in the diagnosis and management of central nervous system (CNS) tumors in children. In the first part of this paper, we review the technical principles underlying four imaging modalities used to evaluate BBB permeability: PET, dynamic CT, dynamic T1-weighted contrast-enhanced MR imaging, and dynamic T2-weighted susceptibility contrast MR. We describe the data that can be derived from each method, provide some caveats to data interpretation, and compare the advantages and disadvantages of the different techniques. In the second part of this paper, we review the clinical applications that have been reported with permeability imaging data, including diagnosing the nature of a lesion found on imaging (neoplastic versus non-neoplastic, tumor type, tumor grade, recurrence versus pseudoprogression), predicting the natural history of a tumor, monitoring angiogenesis and tracking response to anti-angiogenic agents, optimizing chemotherapy agent selection, and aiding in the development of new antineoplastic drugs and methods to increase local delivery of chemotherapeutics.

Which combination of MR imaging modalities is best for predicting recurrent glioblastoma? Study of diagnostic accuracy and reproducibility

PURPOSE

To compare the added value of dynamic contrast material-enhanced ( CE contrast enhanced ) ( DCE dynamic CE ) magnetic resonance (MR) imaging with that of dynamic susceptibility CE contrast enhanced ( DSC dynamic susceptibility CE ) MR imaging with the combination of CE contrast enhanced T1-weighted imaging and diffusion-weighted ( DW diffusion weighted ) imaging for predicting recurrent glioblastoma.

MATERIALS AND METHODS

This retrospective study was approved by the institutional review board, with the requirement for informed patient consent waived. CE contrast enhanced T1-weighted images, DW diffusion weighted images, DSC dynamic susceptibility CE MR images, and DCE dynamic CE MR images in 169 patients with pathologically or clinicoradiologically diagnosed recurrent glioblastoma (n = 87) or radiation necrosis (n = 82) were retrospectively reviewed. Histogram cutoffs of quantitative parametric values were calculated from DW diffusion weighted images, DSC dynamic susceptibility CE MR images, and DCE dynamic CE MR images. Area under the receiver operating characteristic curve ( Az area under the ROC curve ) and interreader agreement were assessed.

RESULTS

For predicting recurrent glioblastoma, adding DCE dynamic CE MR imaging to the combination of CE contrast enhanced T1-weighted imaging and DW diffusion weighted imaging significantly improved Az area under the ROC curve from 0.84 to 0.96 for reader 1 and from 0.81 to 0.97 for reader 2, respectively. Adding DSC dynamic susceptibility CE MR imaging also significantly improved Az area under the ROC curve (0.95 for reader 1 and 0.93 for reader 2). However, there was no significant difference in Az between the combination of CE contrast enhanced T1-weighted imaging, DW diffusion weighted imaging, and DSC dynamic susceptibility CE MR imaging and the combination of CE contrast enhanced T1-weighted imaging, DW diffusion weighted imaging, and DCE dynamic CE MR imaging for both readers. The interreader agreement was highest for the combination of CE contrast enhanced T1-weighted imaging, DW diffusion weighted imaging, and DCE dynamic CE MR imaging (κ = 0.78) and lowest for CE contrast enhanced T1-weighted imaging and DW diffusion weighted imaging (κ = 0.65).

CONCLUSION

Adding perfusion MR imaging to the combination of CE contrast enhanced T1-weighted imaging and DW diffusion weighted imaging significantly improves the prediction of recurrent glioblastoma; however, selection of perfusion MR method does not affect the diagnostic performance.

Feasibility study of CT perfusion imaging for prostate carcinoma

OBJECTIVE

The aim of this feasibility study was to obtain initial data with which to assess the efficiency of perfusion CT imaging (CTpI) and to compare this with magnetic resonance imaging (MRI) in the diagnosis of prostate carcinoma.

MATERIALS AND METHODS

This prospective study involved 25 patients with prostate carcinoma undergoing MRI and CTpI. All analyses were performed on T2-weighted images (T2WI), apparent diffusion coefficient (ADC) maps, diffusion-weighted images (DWI) and CTp images. We compared the performance of T2WI combined with DWI and CTp alone. The study was approved by the local ethics committee, and written informed consent was obtained from all patients.

RESULTS

Tumours were present in 87 areas according to the histopathological results. The diagnostic performance of the T2WI+DWI+CTpI combination was significantly better than that of T2WI alone for prostate carcinoma (P < 0.001). The diagnostic value of CTpI was similar to that of T2WI+DWI in combination. There were statistically significant differences in the blood flow and permeability surface values between prostate carcinoma and background prostate on CTp images.

CONCLUSION

CTp may be a valuable tool for detecting prostate carcinoma and may be preferred in cases where MRI is contraindicated. If this technique is combined with T2WI and DWI, its diagnostic value is enhanced.

KEY POINTS

Perfusion CT is a helpful technique for prostate carcinoma diagnosis. •Colour maps allow easy and rapid visual assessment of the functional changes. Colour maps of prostate carcinoma provide information about in vivo tumoral vascularity. CTp images may be added into routine radiological examinations. CTp provides guidance for histopathological correlation if biopsy is scheduled.

Monitoring the effects of anti-angiogenesis on the radiation sensitivity of pancreatic cancer xenografts using dynamic contrast-enhanced computed tomography

PURPOSE

To image the intratumor vascular physiological status of pancreatic tumors xenografts and their response to anti-angiogenic therapy using dynamic contrast-enhanced computed tomography (DCE-CT), and to identify parameters of vascular physiology associated with tumor x-ray sensitivity after anti-angiogenic therapy.

METHODS AND MATERIALS

Nude mice bearing human BxPC-3 pancreatic tumor xenografts were treated with 5 Gy of radiation therapy (RT), either a low dose (40 mg/kg) or a high dose (150 mg/kg) of DC101, the anti-VEGF receptor-2 anti-angiogenesis antibody, or with combination of low or high dose DC101 and 5 Gy RT (DC101-plus-RT). DCE-CT scans were longitudinally acquired over a 3-week period post-DC101 treatment. Parametric maps of tumor perfusion and fractional plasma volume (Fp) were calculated and their averaged values and histogram distributions evaluated and compared to controls, from which a more homogeneous physiological window was observed 1-week post-DC101. Mice receiving a combination of DC101-plus-RT(5 Gy) were imaged baseline before receiving DC101 and 1 week after DC101 (before RT). Changes in perfusion and Fp were compared with alternation in tumor growth delay for RT and DC101-plus-RT (5 Gy)-treated tumors.

RESULTS

Pretreatment with low or high doses of DC101 before RT significantly delayed tumor growth by an average 7.9 days compared to RT alone (P ≤ .01). The increase in tumor growth delay for the DC101-plus-RT-treated tumors was strongly associated with changes in tumor perfusion (ΔP>-15%) compared to RT treated tumors alone (P=.01). In addition, further analysis revealed a trend linking the tumor's increased growth delay to its tumor volume-to-DC101 dose ratio.

CONCLUSIONS

DCE-CT is capable of monitoring changes in intratumor physiological parameter of tumor perfusion in response to anti-angiogenic therapy of a pancreatic human tumor xenograft that was associated with enhanced radiation response.

Preclinical efficacy of the anti-hepatocyte growth factor antibody ficlatuzumab in a mouse brain orthotopic glioma model evaluated by bioluminescence, PET, and MRI

PURPOSE

Ficlatuzumab is a novel therapeutic agent targeting the hepatocyte growth factor (HGF)/c-MET pathway. We summarize extensive preclinical work using this agent in a mouse brain orthotopic model of glioblastoma.

EXPERIMENTAL DESIGN

Sequential experiments were done using eight- to nine-week-old nude mice injected with 3 × 10(5) U87 MG (glioblastoma) cells into the brain. Evaluation of ficlatuzumab dose response for this brain tumor model and comparison of its response to ficlatuzumab and to temozolamide were conducted first. Subsequently, various small-animal imaging modalities, including bioluminescence imaging (BLI), positron emission tomography (PET), and MRI, were used with a U87 MG-Luc 2 stable cell line, with and without the use of ficlatuzumab, to evaluate the ability to noninvasively assess tumor growth and response to therapy. ANOVA was conducted to evaluate for significant differences in the response.

RESULTS

There was a survival benefit with ficlatuzumab alone or in combination with temozolamide. BLI was more sensitive than PET in detecting tumor cells. Fluoro-D-thymidine (FLT) PET provided a better signal-to-background ratio than 2[(18)F]fluoro-2-deoxy-d-glucose (FDG) PET. In addition, both BLI and FLT PET showed significant changes over time in the control group as well as with response to therapy. MRI does not disclose any time-dependent change. Also, the MRI results showed a temporal delay in comparison to the BLI and FLT PET findings, showing similar results one drug cycle later.

CONCLUSIONS

Targeting the HGF/c-MET pathway with the novel agent ficlatuzumab appears promising for the treatment of glioblastoma. Various clinically applicable imaging modalities including FLT, PET, and MRI provide reliable ways of assessing tumor growth and response to therapy. Given the clinical applicability of these findings, future studies on patients with glioblastoma may be appropriate.

Dynamic contrast-enhanced MRI for monitoring antiangiogenic treatment: determination of accurate and reliable perfusion parameters in a longitudinal study of a mouse xenograft model

Objective

To determine the reliable perfusion parameters in dynamic contrast-enhanced MRI (DCE-MRI) for the monitoring antiangiogenic treatment in mice.

Materials and Methods

Mice, with U-118 MG tumor, were treated with either saline (n = 3) or antiangiogenic agent (sunitinib, n = 8). Before (day 0) and after (days 2, 8, 15, 25) treatment, DCE examinations using correlations of perfusion parameters (K_ep, K_el, and A^H from two compartment model; time to peak, initial slope and % enhancement from time-intensity curve analysis) were evaluated.

Results

Tumor growth rate was found to be 129% ± 28 in control group, -33% ± 11 in four mice with sunitinib-treatment (tumor regression) and 47% ± 15 in four with sunitinib-treatment (growth retardation). K_ep (r = 0.80) and initial slope (r = 0.84) showed strong positive correlation to the initial tumor volume (p < 0.05). In control mice, tumor regression group and growth retardation group animals, K_ep (r : 0.75, 0.78, 0.81, 0.69) and initial slope (r : 0.79, 0.65, 0.67, 0.84) showed significant correlation with tumor volume (p < 0.01). In four mice with tumor re-growth, K_ep and initial slope increased 20% or greater at earlier (n = 2) than or same periods (n = 2) to when the tumor started to re-grow with 20% or greater growth rate.

Conclusion

K_ep and initial slope may a reliable parameters for monitoring the response of antiangiogenic treatment.

Magnetic resonance imaging profile of blood-brain barrier injury in patients with acute intracerebral hemorrhage

Background

Spontaneous intracerebral hemorrhage (ICH) is associated with blood–brain barrier (BBB) injury, which is a poorly understood factor in ICH pathogenesis, potentially contributing to edema formation and perihematomal tissue injury. We aimed to assess and quantify BBB permeability following human spontaneous ICH using dynamic contrast‐enhanced magnetic resonance imaging (DCE MRI). We also investigated whether hematoma size or location affected the amount of BBB leakage.

Methods and Results

Twenty‐five prospectively enrolled patients from the Diagnostic Accuracy of MRI in Spontaneous intracerebral Hemorrhage (DASH) study were examined using DCE MRI at 1 week after symptom onset. Contrast agent dynamics in the brain tissue and general tracer kinetic modeling were used to estimate the forward leakage rate (K^trans) in regions of interest (ROI) in and surrounding the hematoma and in contralateral mirror–image locations (control ROI). In all patients BBB permeability was significantly increased in the brain tissue immediately adjacent to the hematoma, that is, the hematoma rim, compared to the contralateral mirror ROI (P<0.0001). Large hematomas (>30 mL) had higher K^trans values than small hematomas (P<0.005). K^trans values of lobar hemorrhages were significantly higher than the K^trans values of deep hemorrhages (P<0.005), independent of hematoma volume. Higher K^trans values were associated with larger edema volumes.

Conclusions

BBB leakage in the brain tissue immediately bordering the hematoma can be measured and quantified by DCE MRI in human ICH. BBB leakage at 1 week is greater in larger hematomas as well as in hematomas in lobar locations and is associated with larger edema volumes.

Targeted biodegradable dendritic MRI contrast agent for enhanced tumor imaging

Highly sensitive and safe contrast agents (CAs) are essential for magnetic resonance imaging (MRI) to achieve accurate tumor detection and imaging. Dendrimer-based macromolecular MRI contrast agents are advantageous owing to their tumor-targeting ability, enhanced imaging contrast and enlarged imaging window. However, most of them have drawbacks of non-degradability and thereby long-term retention in body and toxicity. Herein, a tumor-targeting biodegradable dendritic CA (DCA) (FA-PEG-G2-DTPA-Gd) was prepared from a polyester dendrimer conjugated with gadolinium (Gd) chelates and PEG chains with distal folic acid. The DCA had a high longitudinal relaxivity up to 17.1mM(-1)s(-1), 4 times higher than the clinically used CA Magnevist. The MRI contrasted by FA-PEG-G2-DTPA-Gd outlined the inoculated tumor more clearly, and had much higher contrast enhancement for a much longer time than Magnevist. More importantly, the biodegradable FA-PEG-G2-DTPA-Gd gave much less Gd retentions in all the organs or tissues than non-degradable DCAs. Thus, the high efficiency in MRI contrast enhancement and low Gd retention merit it a promising CA for contrast enhanced tumor MRI.

Role of perfusion CT in differentiating between various cerebral masses using normalized permeability surface area product and cerebral blood volume

OBJECTIVE

The objective was to assess usefulness of a combined analysis using the perfusion computed tomography parameters permeability surface area product (PS) and cerebral blood volume (CBV) in the differential grouping of various cerebral masses.

METHODS

Thirty patients who had a cerebral mass, confirmed by pathologic verification, were included. We classified PS and CBV results for various cerebral masses by visual as well as semiquantitative assessment. To verify statistically significant differences between the groups, one-way analysis of variance was performed.

RESULTS

Patients were categorized into five groups with statistically significant differences (P<.01).

CONCLUSIONS

PS and CBV were useful in the differential diagnosis of cerebral masses.

Dynamic Contrast-Enhanced Magnetic Resonance Imaging (DCE-MRI) in Preclinical Studies of Antivascular Treatments

Antivascular treatments can either be antiangiogenic or targeting established tumour vasculature. These treatments affect the tumour microvasculature and microenvironment but may not change clinical measures like tumour volume and growth. In research on antivascular treatments, information on the tumour vasculature is therefore essential. Preclinical research is often used for optimization of antivascular drugs alone or in combined treatments. Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) is an in vivo imaging method providing vascular information, which has become an important tool in both preclinical and clinical research. This review discusses common DCE-MRI imaging protocols and analysis methods and provides an overview of preclinical research on antivascular treatments utilizing DCE-MRI.

Imaging biomarkers of angiogenesis and the microvascular environment in cerebral tumours

Conventional contrast-enhanced CT and MRI are now in routine clinical use for the diagnosis, treatment and monitoring of diseases in the brain. The presence of contrast enhancement is a proxy for the pathological changes that occur in the normally highly regulated brain vasculature and blood-brain barrier. With recognition of the limitations of these techniques, and a greater appreciation for the nuanced mechanisms of microvascular change in a variety of pathological processes, novel techniques are under investigation for their utility in further interrogating the microvasculature of the brain. This is particularly important in tumours, where the reliance on angiogenesis (new vessel formation) is crucial for tumour growth, and the resulting microvascular configuration and derangement has profound implications for diagnosis, treatment and monitoring. In addition, novel therapeutic approaches that seek to directly modify the microvasculature require more sensitive and specific biological markers of baseline tumour behaviour and response. The currently used imaging biomarkers of angiogenesis and brain tumour microvascular environment are reviewed.

A dedicated automated injection system for dynamic contrast-enhanced MRI experiments in mice

PURPOSE

To develop a reproducible small-animal dynamic contrast-enhanced (DCE) MRI set-up for mice through which volumes <100 μL can be accurately and safely injected and to test this set-up by means of DCE measurements in resting muscle and tumor tissue.

MATERIALS AND METHODS

The contrast agent (CA) injection system comprised 2 MR-compatible syringe pumps placed 50 cm from the 7T magnet bore where the fringe field is approximately 40 mT. Microbore tubing and T-connector, close to the injection site, minimized dead volume (<10 μL). For DCE-MRI measurements in 8 CB-17 SCID mice with 1500-2500 mm(3) large orthotopic neuroblastoma, a bolus of 10-fold-diluted Gd-DTPA CA solution (0.1 mmol/kg) was delivered (5 μL/s), followed by a 50-μL saline flush. Retro-orbital injections were given instead of tail vein injections, because the peripheral vasculature was reduced because of large tumor burden.

RESULTS

The CA injection was successful in 19 of 24 experiments. Optical assessment showed minimal dispersion of ink-colored CA bolus. Mean (± SD) pharmacokinetic parameters retrieved from DCE-MRI examinations in resting muscle (K(trans) = 0.038 ± 0.025 min(-1), k(ep) = 0.66 ± 0.48 min(-1), v(e) = 0.060 ± 0.014, v(p) = 0.033 ± 0.021) and tumor (K(trans) = 0.082 ± 0.071 min(-1), k(ep) = 0.82 ± 0.80 min(-1), v(e) = 0.121 ± 0.075, v(p) = 0.093 ± 0.051) agreed with those reported previously.

CONCLUSION

We successfully designed and implemented a DCE-MRI set-up system with short injection lines and low dead volume. The system can be used at any field strength with the syringe pumps placed at a sufficiently low fringe field (<40 mT).

Diagnostic performance of whole brain volume perfusion CT in intra-axial brain tumors: preoperative classification accuracy and histopathologic correlation

BACKGROUND

To evaluate the preoperative diagnostic power and classification accuracy of perfusion parameters derived from whole brain volume perfusion CT (VPCT) in patients with cerebral tumors.

METHODS

Sixty-three patients (31 male, 32 female; mean age 55.6 ± 13.9 years), with MRI findings suspected of cerebral lesions, underwent VPCT. Two readers independently evaluated VPCT data. Volumes of interest (VOIs) were marked circumscript around the tumor according to maximum intensity projection volumes, and then mapped automatically onto the cerebral blood volume (CBV), flow (CBF) and permeability Ktrans perfusion datasets. A second VOI was placed in the contra lateral cortex, as control. Correlations among perfusion values, tumor grade, cerebral hemisphere and VOIs were evaluated. Moreover, the diagnostic power of VPCT parameters, by means of positive and negative predictive value, was analyzed.

RESULTS

Our cohort included 32 high-grade gliomas WHO III/IV, 18 low-grade I/II, 6 primary cerebral lymphomas, 4 metastases and 3 tumor-like lesions. Ktrans demonstrated the highest sensitivity, specificity and positive predictive value, with a cut-off point of 2.21 mL/100mL/min, for both the comparisons between high-grade versus low-grade and low-grade versus primary cerebral lymphomas. However, for the differentiation between high-grade and primary cerebral lymphomas, CBF and CBV proved to have 100% specificity and 100% positive predictive value, identifying preoperatively all the histopathologically proven high-grade gliomas.

CONCLUSION

Volumetric perfusion data enable the hemodynamic assessment of the entire tumor extent and provide a method of preoperative differentiation among intra-axial cerebral tumors with promising diagnostic accuracy.

Comparison of dual-echo DSC-MRI- and DCE-MRI-derived contrast agent kinetic parameters

The application of dynamic susceptibility contrast (DSC) MRI methods to assess brain tumors is often confounded by the extravasation of contrast agent (CA). Disruption of the blood-brain barrier allows CA to leak out of the vasculature leading to additional T(1), T(2) and T(2) relaxation effects in the extravascular space, thereby affecting the signal intensity time course in a complex manner. The goal of this study was to validate a dual-echo DSC-MRI approach that separates and quantifies the T(1) and T(2) contributions to the acquired signal and enables the estimation of the volume transfer constant, K(trans), and the volume fraction of the extravascular extracellular space, v(e). To test the validity of this approach, DSC-MRI- and dynamic contrast enhanced (DCE) MRI-derived K(trans) and v(e) estimates were spatially compared in both 9L and C6 rat brain tumor models. A high degree of correlation (concordance correlation coefficients >0.83, Pearson's r>0.84) and agreement was found between the DSC-MRI- and DCE-MRI-derived measurements. These results indicate that dual-echo DSC-MRI can be used to simultaneously extract reliable DCE-MRI kinetic parameters in brain tumors in addition to conventional blood volume and blood flow metrics.

Monitoring the longitudinal intra-tumor physiological impulse response to VEGFR2 blockade in breast tumors using DCE-CT

PURPOSE

The purpose of this study was to quantify and model the longitudinal intra-tumor physiological response to a single dose of a monoclonal antibody specific to the VEGFR2 using dynamic contrast-enhanced CT.

MATERIAL AND METHODS

Dynamic contrast-enhanced CT imaging was performed on athymic nude mice bearing xenograft VEGF-transfected MCF-7 tumors (MCF7(VEGF)) to quantify intra-tumor physiology pre- and post-injection (days 2, 7, and 14) of a nonspecific (IgG1, controls) and specific (DC101, treated) monoclonal antibody targeting VEGFR2. Parametrical maps of tumor physiology-perfusion (F), permeability surface area (PS), fractional plasma (f(p)), and interstitial space (f (is))-were obtained at four time points over a 2-week period.

RESULTS

A temporal multistage recovery process whereby a decoupling of the fractional change in physiological parameters (f (p), F) was observed when comparing treated to control tumors: f (p) and perfusion decreased by a combined 27% (P < 0.01) and 65% (P < 0.01) on day 2, while only perfusion remained reduced by 46% (P < 0.01) on day 7. Intra-tumor heterogeneity defined by the change in variance of perfusion decreased on days 2 and 7; no change in the variance of f(p) was observed. Analysis based on a mathematical model linking perfusion and vascular morphology indicates that a decrease in f(p) and perfusion was consistent with a reduction in blood vessel radius, followed by an increase in the vascular radius and tortuosity resulting in the decoupling of f(p) and perfusion before returning to control levels.

CONCLUSION

Inhibiting VEGFR2 activity results in a temporal decoupling of physiological parameters, which can be explained by a combination of morphological changes influencing perfusion. Such a decoupling has the potential to significantly impact the delivery of pharmaceuticals and oxygen within solid tumors, critical factors in combined anti-angiogenic and radio- and chemotherapies.

MR imaging features of high-grade gliomas in murine models: how they compare with human disease, reflect tumor biology, and play a role in preclinical trials

Murine models are the most commonly used and best investigated among the animal models of HGG. They constitute an important weapon in the development and testing of new anticancer drugs and have long been used in preclinical trials. Neuroimaging methods, particularly MR imaging, offer important advantages for the evaluation of treatment response: shorter and more reliable treatment end points and insight on tumor biology and physiology through the use of functional imaging DWI, PWI, BOLD, and MR spectroscopy. This functional information has been progressively consolidated as a surrogate marker of tumor biology and genetics and may play a pivotal role in the assessment of specifically targeted drugs, both in clinical and preclinical trials. The purpose of this Research Perspectives was to compile, summarize, and critically assess the available information on the neuroimaging features of different murine models of HGGs, and explain how these correlate with human disease and reflect tumor biology.

Accurate state estimation from uncertain data and models: an application of data assimilation to mathematical models of human brain tumors

Background

Data assimilation refers to methods for updating the state vector (initial condition) of a complex spatiotemporal model (such as a numerical weather model) by combining new observations with one or more prior forecasts. We consider the potential feasibility of this approach for making short-term (60-day) forecasts of the growth and spread of a malignant brain cancer (glioblastoma multiforme) in individual patient cases, where the observations are synthetic magnetic resonance images of a hypothetical tumor.

Results

We apply a modern state estimation algorithm (the Local Ensemble Transform Kalman Filter), previously developed for numerical weather prediction, to two different mathematical models of glioblastoma, taking into account likely errors in model parameters and measurement uncertainties in magnetic resonance imaging. The filter can accurately shadow the growth of a representative synthetic tumor for 360 days (six 60-day forecast/update cycles) in the presence of a moderate degree of systematic model error and measurement noise.

Conclusions

The mathematical methodology described here may prove useful for other modeling efforts in biology and oncology. An accurate forecast system for glioblastoma may prove useful in clinical settings for treatment planning and patient counseling.

Reviewers

This article was reviewed by Anthony Almudevar, Tomas Radivoyevitch, and Kristin Swanson (nominated by Georg Luebeck).

Assessment of peripheral tissue perfusion disorder in streptozotocin-induced diabetic rats using dynamic contrast-enhanced MRI

PURPOSE

To assess peripheral tissue perfusion disorder in streptozotocin (STZ)-induced diabetic rats by using dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI).

MATERIALS AND METHODS

A rat diabetes model was produced by intravenous injection of STZ. Diabetic rats were sustainably treated with either saline or insulin using an Alzet osmotic pump. Hind paw tissue perfusion was measured by signal intensity (SI) enhancement after gadolinium diethylenetriaminepentaacetic acid injection in DCE-MRI study and quantified using the initial area under the SI-time curve (IAUC). Peripheral tissue uptake of [(14)C]iodoantipyrine (IAP) was also determined as a marker of tissue blood flow for comparison with the IAUC value indicating tissue perfusion.

RESULTS

STZ caused hyperglycemia at 1 and 2 weeks after injection. Treatment with insulin significantly alleviated hyperglycemia. At 2 weeks after STZ injection, peripheral tissue perfusion was clearly reduced in the diabetic rats and its reduction was significantly improved in the insulin-treated diabetic rats. Tissue perfusion evaluated by DCE-MRI was similar to the tissue blood flow measured by [(14)C]IAP uptake.

CONCLUSION

Our findings demonstrated that DCE-MRI can assess peripheral tissue perfusion disorder in diabetes. DCE-MRI could be suitable for noninvasive evaluation of peripheral tissue perfusion in both preclinical and clinical studies. It may also be useful for developing novel drugs to protect against diabetic vascular complications.

Treatment monitoring in gliomas: comparison of dynamic susceptibility-weighted contrast-enhanced and spectroscopic MRI techniques for identifying treatment failure

OBJECTIVE

To evaluate whether dynamic susceptibility-weighted contrast-enhanced (DSC), dynamic contrast-enhanced (DCE), and proton spectroscopic imaging ((1)H-MRSI) can identify progression and predict treatment failure during follow-up before tumor size changes, contrast agent uptake, or when new lesions become obvious. The aim was also to find out which of the aforementioned techniques had the best diagnostic performance compared with each other and standard magnetic resonance imaging (MRI).

MATERIALS AND METHODS

Thirty-seven patients with gliomas (21 women, 16 men; mean age at inclusion, 48 ± 14 years [standard deviation]) were assessed prospectively by (1)H-MRSI (point-resolved spectroscopy), DCE, and DSC perfusion MRI, each after a single dose of gadobenate dimeglumine during follow-up. Histology was available in all cases (resection, N = 18; biopsy, N = 19). All patients with low-grade gliomas (n = 20) did not receive any radio- or chemotherapy after partial resection (n = 7) or biopsy (n = 13), whereas 17 patients with high-grade gliomas had received adjuvant radiotherapy immediately after surgery. Tumor progression (progressive disease, PD) was defined as increase in longest glioma diameter by at least 20% (Response Evaluation Criteria in Solid Tumors), appearance of new lesions, or new contrast-enhancement. DSC, DCE, and MRSI image analyses comprised a detailed semiquantitative region of interest (ROI) analysis of the different parameters. Wilcoxon signed-rank test, Wilcoxon rank sum test, and Cox regression were used for statistical analysis.

RESULTS

The median follow-up time was 607 days. Twenty patients showed PD (54%), 8 of 20 with low-grade (40%) and 12 of 17 with high-grade gliomas (71%). In PD, significant positive differences between log2-transformed ROI ratios at the last measurement in comparison to the first measurement (baseline) could be detected for tumor blood flow (P < 0.006) and volume (P < 0.001) derived from DSC and for maximum choline within tumor tissue (P = 0.0029) and Cho/Cr (P = 0.032) but not choline/N-acetyl-aspartate (P = 0.37) derived from MRSI. In contrast, these parameters were not significantly higher at last measurement in stable disease. Also, the differences between last value and baseline were significantly different between PD and stable disease for tumor blood flow (P < 0.004) and volume (P < 0.002) as well as for maximum choline within tumor tissue (P = 0.0011). The best prognostic parameter for PD at Cox analysis was time-dependent difference to baseline of log2 of relative regional cerebral blood flow normalized on gray matter (hazard ratio, 2.67; 95% confidence interval, 1.25-6.08; P = 0.01), while a prognostic value of MRS parameters could not be demonstrated.

CONCLUSION

DSC perfusion imaging can identify progression and can predict treatment failure during follow-up of gliomas with the best diagnostic performance.

Brain volume perfusion CT performed with 128-detector row CT system in patients with cerebral gliomas: a feasibility study

OBJECTIVES

Validation of the feasibility and efficacy of volume perfusion computed tomography (VPCT) in the preoperative assessment of cerebral gliomas by applying a 128-slice CT covering the entire tumour.

METHODS

Forty-six patients (25 men, 21 women; mean age 52.8 years) with cerebral gliomas were evaluated with VPCT. Two readers independently evaluated VPCT data, drawing volumes of interest (VOIs) around the tumour according to maximum intensity projection volumes, which were mapped automatically onto the cerebral blood volume (CBV), flow (CBF) and permeability (Ktrans) perfusion datasets. As control, a second VOI was placed in the contralateral healthy cortex. Correlation among perfusion parameters, tumour grade, hemisphere and VOIs was assessed. The diagnostic power of perfusion parameters was analysed by receiver operating characteristics curve analyses.

RESULTS

VPCT was feasible in the assessment of the entire tumour extent. Mean values of Ktrans, CBV, CBF in high-grade gliomas were significantly higher compared with low-grade (p < 0.01). Ktrans demonstrated the highest diagnostic (97% sensitivity), positive (100%) and negative (94%) prognostic values.

CONCLUSIONS

VPCT was feasible in all subjects. All areas of different perfusion characteristics are depicted and quantified in colour-coded 3D maps. The derived parameters correlate well with tumour histopathology, differentiating low- from high-grade gliomas.

Characterization of a human tumorsphere glioma orthotopic model using magnetic resonance imaging

Magnetic resonance imaging (MRI) is the imaging modality of choice by which to monitor patient gliomas and treatment effects, and has been applied to murine models of glioma. However, a major obstacle to the development of effective glioma therapeutics has been that widely used animal models of glioma have not accurately recapitulated the morphological heterogeneity and invasive nature of this very lethal human cancer. This deficiency is being alleviated somewhat as more representative models are being developed, but there is still a clear need for relevant yet practical models that are well-characterized in terms of their MRI features. Hence we sought to chronicle the MRI profile of a recently developed, comparatively straightforward human tumor stem cell (hTSC) derived glioma model in mice using conventional MRI methods. This model reproduces the salient features of gliomas in humans, including florid neoangiogenesis and aggressive invasion of normal brain. Accordingly, the variable, invasive morphology of hTSC gliomas visualized on MRI duplicated that seen in patients, and it differed considerably from the widely used U87 glioma model that does not invade normal brain. After several weeks of tumor growth the hTSC model exhibited an MRI contrast enhancing phenotype having variable intensity and an irregular shape, which mimicked the heterogeneous appearance observed with human glioma patients. The MRI findings reported here support the use of the hTSC glioma xenograft model combined with MRI, as a test platform for assessing candidate therapeutics for glioma, and for developing novel MR methods.

Magnetic Resonance Imaging Estimation of Longitudinal Relaxation Rate Change (ΔR1) in Dual Gradient Echo Sequences Using an Adaptive Model

Magnetic Resonance Imaging (MRI) estimation of contrast agent concentration in fast pulse sequences such as Dual Gradient Echo (DGE) imaging is challenging. An Adaptive Neural Network (ANN) was trained with a map of contrast agent concentration estimated by Look-Locker (LL) technique (modified version of inversion recovery imaging) as a gold standard. Using a set of features extracted from DGE MRI data, an ANN was trained to create a voxel based estimator of the time trace of CA concentration. The ANN was trained and tested with the DGE and LL information of six Fisher rats using a K-Fold Cross-Validation (KFCV) method with 60 folds and 10500 samples. The Area Under the Receiver Operator Characteristic Curve (AUROC) for 60 folds was used for training, testing and optimization of the ANN. After training and optimization, the optimal ANN (4:7:5:1) produced maps of CA concentration which were highly correlated (r =0.89, P < 0.0001) with the CA concentration estimated by the LL technique. The estimation made by the ANN had an excellent overall performance (AUROC = 0.870).

Noninvasive monitoring of therapy-induced microvascular changes in a pancreatic cancer model using dynamic contrast-enhanced magnetic resonance imaging with P846, a new low-diffusible gadolinium-based contrast agent

A predictive technique in the management of patients with cancer could improve the therapeutic index by allowing better individualization of treatment. Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) is a noninvasive technique that can provide anatomical and physiological information on the tumor and its microenvironment. We studied the effect of chemotherapy (gemcitabine), anti-angiogenesis therapy (sunitinib) and radiotherapy on the kinetics of DCE-MRI parameters in a preclinical model of pancreatic cancer using P846, a new low-diffusible contrast agent. Mice underwent DCE-MRI before treatment (MRI1), after 1 week of treatment (MRI2), and after 1 additional week (MRI3). Combined treatment with radiotherapy and sunitinib had a synergistic effect on tumor growth. In radiotherapy/sunitinib-treated mice, a decrease in K(trans) at MRI2 predicted its superior antivascular and antitumor effect at an early time. An increased K(trans) at MRI2, as seen in gemcitabine- and gemcitabine/sunitinib-treated mice, reflects increased permeability for P846 and might predict a smaller therapeutic effect at this early time. This study shows that the kinetics of DCE-MRI parameters depends on the contrast agent used. P846 appears to be a promising low-diffusible agent to monitor therapeutic effects in this preclinical cancer model, but further studies are needed to compare its behavior with Gd-DTPA and macromolecular-weight contrast agents. Sunitinib as a radiosensitizer is promising for future clinical trials in human pancreatic cancer.

Monitoring blood-brain barrier status in a rat model of glioma receiving therapy: dual injection of low-molecular-weight and macromolecular MR contrast media

PURPOSE

To evaluate the sequential injection of a low-molecular-weight (gadoterate meglumine [Gd-DOTA], 0.5 kDa) and a macromolecular (P846, 3.5 kDa) contrast media in monitoring the effect of antitumor therapies (antiangiogenic therapy and/or microbeam radiation therapy [MRT]) on healthy brain tissue and implanted tumors.

MATERIALS AND METHODS

Animal use was compliant with official French guidelines and was assessed by the local Internal Evaluation Committee for Animal Welfare and Rights. Eighty male rats bearing 9L gliosarcoma were randomized into four groups: untreated, antiangiogenic (sorafenib) therapy, MRT, and both treatments. Magnetic resonance (MR) imaging was performed 1 day before and 1, 5, and 8 days after the start of the treatment. At all time points, vascular integrity to a macromolecular contrast medium (P846) and, 11 minutes 30 seconds later, to low-molecular-weight contrast medium (Gd-DOTA) was evaluated by using a dynamic contrast material-enhanced MR imaging approach. To quantify vessel wall integrity, areas under the signal intensity curves were computed for each contrast medium. Unpaired t tests and one-way analysis of variance were used for statistical analyses.

RESULTS

Tumor vessels receiving antiangiogenic therapy became less permeable to the macromolecular contrast medium, but their permeability to the low-molecular-weight contrast medium remained unchanged. Healthy double-irradiated vessels became permeable to the low-molecular-weight contrast medium but not to the macromolecular contrast medium.

CONCLUSION

Antiangiogenic therapy and MRT generate different effects on the extravasation of contrast medium in tumoral and healthy tissues. This study indicates that the use of a low-molecular-weight contrast medium and a macromolecular contrast medium provides complementary information and suggests that the use of two contrast media within the same MR imaging session is feasible.

A model-constrained Monte Carlo method for blind arterial input function estimation in dynamic contrast-enhanced MRI: I. Simulations

Widespread adoption of quantitative pharmacokinetic modeling methods in conjunction with dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) has led to increased recognition of the importance of obtaining accurate patient-specific arterial input function (AIF) measurements. Ideally, DCE-MRI studies use an AIF directly measured in an artery local to the tissue of interest, along with measured tissue concentration curves, to quantitatively determine pharmacokinetic parameters. However, the numerous technical and practical difficulties associated with AIF measurement have made the use of population-averaged AIF data a popular, if sub-optimal, alternative to AIF measurement. In this work, we present and characterize a new algorithm for determining the AIF solely from the measured tissue concentration curves. This Monte Carlo blind estimation (MCBE) algorithm estimates the AIF from the subsets of D concentration-time curves drawn from a larger pool of M candidate curves via nonlinear optimization, doing so for multiple (Q) subsets and statistically averaging these repeated estimates. The MCBE algorithm can be viewed as a generalization of previously published methods that employ clustering of concentration-time curves and only estimate the AIF once. Extensive computer simulations were performed over physiologically and experimentally realistic ranges of imaging and tissue parameters, and the impact of choosing different values of D and Q was investigated. We found the algorithm to be robust, computationally efficient and capable of accurately estimating the AIF even for relatively high noise levels, long sampling intervals and low diversity of tissue curves. With the incorporation of bootstrapping initialization, we further demonstrated the ability to blindly estimate AIFs that deviate substantially in shape from the population-averaged initial guess. Pharmacokinetic parameter estimates for K(trans), k(ep), v(p) and v(e) all showed relative biases and uncertainties of less than 10% for measurements having a temporal sampling rate of 4 s and a concentration measurement noise level of sigma = 0.04 mM. A companion paper discusses the application of the MCBE algorithm to DCE-MRI data acquired in eight patients with malignant brain tumors.

Molecular and clinical aspects of targeting the VEGF pathway in tumors

Tumor angiogenesis is a complex process resulting from many signals from the tumor microenvironment. From preclinical animal models to clinical trials and practice, targeting tumors with antiangiogenic therapy remains an exciting area of study. Although many scientific advances have been achieved, leading to the development and clinical use of antiangiogenic drugs such as bevacizumab, sorafenib, and sunitinib, these therapies fall short of their anticipated benefits and leave many questions unanswered. Continued research into the complex signaling cascades that promote tumor angiogenesis may yield new targets or improve upon current therapies. In addition, the development of reliable tools to track tumor responses to antiangiogenic therapy will enable a better understanding of current therapeutic efficacy and may elucidate mechanisms to predict patient response to therapy.

Dynamic CT perfusion imaging of intra-axial brain tumours: differentiation of high-grade gliomas from primary CNS lymphomas

INTRODUCTION

Perfusion computed tomography (PCT) allows to quantitatively assess haemodynamic characteristics of brain tissue. We investigated if different brain tumor types can be distinguished from each other using Patlak analysis of PCT data.

METHODS

PCT data from 43 patients with brain tumours were analysed with a commercial implementation of the Patlak method. Four patients had low-grade glioma (WHO II), 31 patients had glioblastoma (WHO IV) and eight patients had intracerebral lymphoma. Tumour regions of interest (ROIs) were drawn in a morphological image and automatically transferred to maps of cerebral blood flow (CBF), cerebral blood volume (CBV) and permeability (K (Trans)). Mean values were calculated, group differences were tested using Wilcoxon and Mann Whitney U-tests.

RESULTS

In comparison with normal parenchyma, low-grade gliomas showed no significant difference of perfusion parameters (p > 0.05) , whereas high-grade gliomas demonstrated significantly higher values (p < 0.0001 for K (Trans), p < 0.0001 for CBV and p = 0.0002 for CBF). Lymphomas displayed significantly increased mean K(Trans) values compared with unaffected cerebral parenchyma (p = 0.0078) but no elevation of CBV. High-grade gliomas show significant higher CBV values than lymphomas (p = 0.0078).

DISCUSSION

PCT allows to reliably classify gliomas and lymphomas based on quantitative measurements of CBV and K (Trans).

A theoretical framework to model DSC-MRI data acquired in the presence of contrast agent extravasation

Dynamic susceptibility contrast (DSC) MRI methods rely on compartmentalization of the contrast agent such that a susceptibility gradient can be induced between the contrast-containing compartment and adjacent spaces, such as between intravascular and extravascular spaces. When there is a disruption of the blood-brain barrier, as is frequently the case with brain tumors, a contrast agent leaks out of the vasculature, resulting in additional T(1), T(2) and T*(2) relaxation effects in the extravascular space, thereby affecting the signal intensity time course and reducing the reliability of the computed hemodynamic parameters. In this study, a theoretical model describing these dynamic intra- and extravascular T(1), T(2) and T*(2) relaxation interactions is proposed. The applicability of using the proposed model to investigate the influence of relevant MRI pulse sequences (e.g. echo time, flip angle), and physical (e.g. susceptibility calibration factors, pre-contrast relaxation rates) and physiological parameters (e.g. permeability, blood flow, compartmental volume fractions) on DSC-MRI signal time curves is demonstrated. Such a model could yield important insights into the biophysical basis of contrast-agent-extravasation-induced effects on measured DSC-MRI signals and provide a means to investigate pulse sequence optimization and appropriate data analysis methods for the extraction of physiologically relevant imaging metrics.

Characterization of tumor angiogenesis in rat brain using iron-based vessel size index MRI in combination with gadolinium-based dynamic contrast-enhanced MRI

This study aimed at combining an iron-based, steady-state, vessel size index magnetic resonance imaging (VSI MRI) approach, and a gadolinium (Gd)-based, dynamic contrast-enhanced MRI approach (DCE MRI) to characterize tumoral microvasculature. Rats bearing an orthotopic glioma (C6, n=14 and RG2, n=6) underwent DCE MRI and combined VSI and DCE MRI 4 h later, at 2.35 T. Gd-DOTA (200 mumol of Gd per kg) and ultrasmall superparamagnetic iron oxide (USPIO) (200 micromol of iron per kg) were used for DCE and VSI MRI, respectively. C6 and RG2 gliomas were equally permeable to Gd-DOTA but presented different blood volume fractions and VSI, in good agreement with histologic data. The presence of USPIO yielded reduced K(trans) values. The K(trans) values obtained with Gd-DOTA in the absence and in the presence of USPIO were well correlated for the C6 glioma but not for the RG2 glioma. It was also observed that, within the time frame of DCE MRI, USPIO remained intravascular in the C6 glioma whereas it extravasated in the RG2 glioma. In conclusion, VSI and DCE MRI can be combined provided that USPIO does not extravasate with the time frame of the DCE MRI experiment. The mechanisms at the origin of USPIO extravasation remain to be elucidated.

In vivo monitoring of angiogenesis inhibitory treatment effects by dynamic contrast-enhanced computed tomography in a xenograft tumor model

RATIONALE AND OBJECTIVES

To evaluate the potential of dynamic CT enhanced by iohexol or a novel macromolecular contrast agent, PEG12000-Gen4-triiodo, to monitor microvascular changes in tumors treated with the angiogenesis inhibitor bevacizumab.

MATERIALS AND METHODS

Ten female nude rats with MDA-MB 435 xenograft tumors were treated with 1 mg intraperitoneal bevacizumab when tumors reached 1 cm diameter and, for 4 rats, treated again 7 days later. Just before and 24 hours after the first injection of anti-VEGF antibody, the tumors were imaged by dynamic CT scans enhanced with PEG12000-Gen4-triiodo (n = 3 rats) or iohexol (n = 3 rats). The other 4 rats underwent dynamic CT scans enhanced with PEG12000-Gen4-triiodo just before and 24 hours after the second injection of anti-VEGF antibody. Microvascular leakiness (K(PS)) was calculated for the tumors using a 2-compartment tissue model.

RESULTS

PEG12000-Gen4-triiodo-enhanced CT scans showed progressive reductions in K(PS) from day 1 to 2 to 9 (from 2.55 to 1.27 to 0.69 microL min(-1) cm(-3), respectively, P < 0.005 for each comparison of day 1-2 and day 2-9). No significant difference was seen in the K(PS) estimates derived from iohexol-enhanced CT scans obtained before or after treatment (276 vs. 223.8 microL min(-1) cm(-3), respectively, P = 0.54). The microvascular leak (K(PS)) was significantly larger for iohexol than for PEG12000-Gen4-triiodo-enhanced CT, P < 0.05.

CONCLUSION

Dynamic macromolecular contrast-enhanced CT can be used to monitor serial decreases in tumor microvessel leakiness induced by repeated doses of an angiogenesis inhibitor drug.

Safety and efficacy of bevacizumab with hypofractionated stereotactic irradiation for recurrent malignant gliomas

PURPOSE

Preclinical studies suggest that inhibition of vascular endothelial growth factor (VEGF) improves glioma response to radiotherapy. Bevacizumab, a monoclonal antibody against VEGF, has shown promise in recurrent gliomas, but the safety and efficacy of concurrent bevacizumab with brain irradiation has not been extensively studied. The objectives of this study were to determine the safety and activity of this combination in malignant gliomas.

METHODS AND MATERIALS

After prior treatment with standard radiation therapy patients with recurrent glioblastoma (GBM) and anaplastic gliomas (AG) received bevacizumab (10 mg/kg intravenous) every 2 weeks of 28-day cycles until tumor progression. Patients also received 30 Gy of hypofractionated stereotactic radiotherapy (HFSRT) in five fractions after the first cycle of bevacizumab.

RESULTS

Twenty-five patients (20 GBM, 5 AG; median age 56 years; median Karnofsky Performance Status 90) received a median of seven cycles of bevacizumab. One patient did not undergo HFSRT because overlap with prior radiotherapy would exceed the safe dose allowed to the optic chiasm. Three patients discontinued treatment because of Grade 3 central nervous system intratumoral hemorrhage, wound dehiscence, and bowel perforation. Other nonhematologic and hematologic toxicities were transient. No radiation necrosis was seen in these previously irradiated patients. For the GBM cohort, overall response rate was 50%, 6-month progression-free survival was 65%; median overall survival was 12.5 months, and 1-year survival was 54%.

DISCUSSION

Bevacizumab with HFSRT is safe and well tolerated. Radiographic responses, duration of disease control, and survival suggest that this regimen is active in recurrent malignant glioma.