Albumin-binding MR blood pool contrast agent improves diagnostic performance in human brain tumour: comparison of two contrast agents for glioblastoma

Deciphering albumin-directed drug delivery by imaging

Albumin is the most abundant plasma protein, exhibits extended circulating half-life, and its properties have long been exploited for diagnostics and therapies. Many drugs intrinsically bind albumin or have been designed to do so, yet questions remain about true rate limiting factors that govern albumin-based transport and their pharmacological impacts, particularly in advanced solid cancers. Imaging techniques have been central to quantifying - at a molecular and single-cell level - the impact of mechanisms such as phagocytic immune cell signaling, FcRn-mediated recycling, oncogene-driven macropinocytosis, and albumin-drug interactions on spatial albumin deposition and related pharmacology. Macroscopic imaging of albumin-binding probes quantifies vessel structure, permeability, and supports efficiently targeted molecular imaging. Albumin-based imaging in patients and animal disease models thus offers a strategy to understand mechanisms, guide drug development and personalize treatments.

Macrovascular Networks on Contrast-Enhanced Magnetic Resonance Imaging Improves Survival Prediction in Newly Diagnosed Glioblastoma

A higher degree of angiogenesis is associated with shortened survival in glioblastoma. Feasible morphometric parameters for analyzing vascular networks in brain tumors in clinical practice are lacking. We investigated whether the macrovascular network classified by the number of vessel-like structures (nVS) visible on three-dimensional T1-weighted contrast–enhanced (3D-T1CE) magnetic resonance imaging (MRI) could improve survival prediction models for newly diagnosed glioblastoma based on clinical and other imaging features. Ninety-seven consecutive patients (62 men; mean age, 58 ± 15 years) with histologically proven glioblastoma underwent 1.5T-MRI, including anatomical, diffusion-weighted, dynamic susceptibility contrast perfusion, and 3D-T1CE sequences after 0.1 mmol/kg gadobutrol. We assessed nVS related to the tumor on 1-mm isovoxel 3D-T1CE images, and relative cerebral blood volume, relative cerebral flow volume (rCBF), delay mean time, and apparent diffusion coefficient in volumes of interest for contrast-enhancing lesion (CEL), non-CEL, and contralateral normal-appearing white matter. We also assessed Visually Accessible Rembrandt Images scoring system features. We used ROC curves to determine the cutoff for nVS and univariate and multivariate cox proportional hazards regression for overall survival. Prognostic factors were evaluated by Kaplan-Meier survival and ROC analyses. Lesions with nVS > 5 were classified as having highly developed macrovascular network; 58 (60.4%) tumors had highly developed macrovascular network. Patients with highly developed macrovascular network were older, had higher volume_CEL, increased rCBF_CEL, and poor survival; nVS correlated negatively with survival (r = −0.286; p = 0.008). On multivariate analysis, standard treatment, age at diagnosis, and macrovascular network best predicted survival at 1 year (AUC 0.901, 83.3% sensitivity, 93.3% specificity, 96.2% PPV, 73.7% NPV). Contrast-enhanced MRI macrovascular network improves survival prediction in newly diagnosed glioblastoma.

Perfusion MRI in treatment evaluation of glioblastomas: Clinical relevance of current and future techniques

Treatment evaluation of patients with glioblastomas is important to aid in clinical decisions. Conventional MRI with contrast is currently the standard method, but unable to differentiate tumor progression from treatment-related effects. Pseudoprogression appears as new enhancement, and thus mimics tumor progression on conventional MRI. Contrarily, a decrease in enhancement or edema on conventional MRI during antiangiogenic treatment can be due to pseudoresponse and is not necessarily reflective of a favorable outcome. Neovascularization is a hallmark of tumor progression but not for posttherapeutic effects. Perfusion-weighted MRI provides a plethora of additional parameters that can help to identify this neovascularization. This review shows that perfusion MRI aids to identify tumor progression, pseudoprogression, and pseudoresponse. The review provides an overview of the most applicable perfusion MRI methods and their limitations. Finally, future developments and remaining challenges of perfusion MRI in treatment evaluation in neuro-oncology are discussed. Level of Evidence: 3 Technical Efficacy: Stage 4 J. Magn. Reson. Imaging 2019;49:11-22.

Early Blood-Brain Barrier Disruption in Ischemic Stroke Initiates Multifocally Around Capillaries/Venules

BACKGROUND AND PURPOSE

Detection and localization of the early phase of blood-brain barrier disruption (BBBD) in vivo during cerebral ischemia/reperfusion injury remain a major challenge but may be a relevant outcome parameter in stroke.

METHODS

We studied early BBBD in mice after transient middle cerebral artery occlusion by multimodal, high-field (9.4T) in vivo magnetic resonance imaging, including the contrast agent gadofluorineM as an albumin-binding tracer. GadofluorineM contrast-enhanced magnetic resonance imaging was performed to determine BBBD at 2, 6, and 24 hours after reperfusion. BBBD was confirmed and localized along the microvascular tree by using fluorescent gadofluorineM and immunofluorescence stainings (cluster of differentiation 31, ephrin type-B receptor 4, alpha smooth muscle actin, ionized calcium binding adaptor molecule 1).

RESULTS

GadofluorineM contrast-enhanced magnetic resonance imaging revealed a multifocal spatial distribution of early BBBD and its close association with the microvasculature at a resolution of 40 μm. GadofluorineM leakage was closely associated with ephrin type-B receptor 4-positive but not alpha smooth muscle actin-positive vessels. The multifocal pattern of early BBBD (already at 2 hours after reperfusion) thus occurred in the distal capillary and venular microvascular bed. These multifocal zones showed distinct imaging signs indicative of early vasogenic edema. The total volume of multifocal early BBBD accurately predicted infarct size at 24 hours after reperfusion.

CONCLUSIONS

Early BBBD in focal cerebral ischemia initiates multifocally in the distal capillary and venular bed of the cerebral microvasculature. It is closely associated with perimicrovascular vasogenic edema and microglial activation and predicts the extent of final infarction.

High-resolution blood-pool-contrast-enhanced MR angiography in glioblastoma: tumor-associated neovascularization as a biomarker for patient survival. A preliminary study

INTRODUCTION

The objective of the study was to determine whether tumor-associated neovascularization on high-resolution gadofosveset-enhanced magnetic resonance angiography (MRA) is a useful biomarker for predicting survival in patients with newly diagnosed glioblastomas.

METHODS

Before treatment, 35 patients (25 men; mean age, 64 ± 14 years) with glioblastoma underwent MRI including first-pass dynamic susceptibility contrast (DSC) perfusion and post-contrast T1WI sequences with gadobutrol (0.1 mmol/kg) and, 48 h later, high-resolution MRA with gadofosveset (0.03 mmol/kg). Volumes of interest for contrast-enhancing lesion (CEL), non-CEL, and contralateral normal-appearing white matter were obtained, and DSC perfusion and DWI parameters were evaluated. Prognostic factors were assessed by Kaplan-Meier survival and Cox proportional hazards model.

RESULTS

Eighteen (51.42 %) glioblastomas were hypervascular on high-resolution MRA. Hypervascular glioblastomas were associated with higher CEL volume and lower Karnofsky score. Median survival rates for patients with hypovascular and hypervascular glioblastomas treated with surgery, radiotherapy, and chemotherapy were 15 and 9.75 months, respectively (P < 0.001). Tumor-associated neovascularization was the best predictor of survival at 5.25 months (AUC = 0.794, 81.2 % sensitivity, 77.8 % specificity, 76.5 % positive predictive value, 82.4 % negative predictive value) and yielded the highest hazard ratio (P < 0.001).

CONCLUSIONS

Tumor-associated neovascularization detected on high-resolution blood-pool-contrast-enhanced MRA of newly diagnosed glioblastoma seems to be a useful biomarker that correlates with worse survival.

Gadofosveset-based biomarker of tissue albumin concentration: Technical validation in vitro and feasibility in vivo

PURPOSE

There is currently no adequate method of mapping physiologic and pathophysiologic tissue albumin concentrations in human subjects. The objective of this study was to devise and evaluate a biomarker of regional albumin concentration using gadofosveset-enhanced MRI.

THEORY AND METHODS

A binding and relaxation model was devised and evaluated in vitro in solutions of albumin at 3.0 Tesla (T) and 4.7T. The method was evaluated in the heart in seven volunteers at 3.0T.

RESULTS

MRI-derived estimates of albumin concentration were in good agreement with true values over the range 0.1-1.0 mM (Pearson correlation coefficients of 0.85 and 0.88 for 3.0T and 4.7T, respectively). The mean calculated albumin concentration in the myocardium for the volunteers was 0.02 mM (range, 0.01-0.03 mM).

CONCLUSION

Accurate estimates of albumin concentration in vitro suggest this may be a viable noninvasive alternative to existing techniques. In the myocardium the MRI-derived estimates of albumin concentration indicate the practical feasibility of the technique but were below expected values. Gadofosveset-enhanced MR relaxometry has potential in providing biomarkers of regional albumin concentration; further evaluation is required before it can be used reliably in vivo.

In silico evaluation of gadofosveset pharmacokinetics in different population groups using the Simcyp® simulator platform

Purpose

Gadofosveset is a Gd-based contrast agent used for magnetic resonance imaging (MRI). Gadolinium kinetic distribution models are implemented in T1-weighted dynamic contrast-enhanced perfusion MRI for characterization of lesion sites in the body. Physiology changes in a disease state potentially can influence the pharmacokinetics of drugs and to this respect modify the distribution properties of contrast agents. This work focuses on the in silico modelling of pharmacokinetic properties of gadofosveset in different population groups through the application of physiologically-based pharmacokinetic models (PBPK) embedded in Simcyp® population pharmacokinetics platform.

Methods

Physicochemical and pharmacokinetic properties of gadofosveset were introduced into Simcyp® simulator platform and a min-PBPK model was applied. In silico clinical trials were generated simulating the administration of the recommended dose for the contrast agent (i.v., 30 mg/kg) in population cohorts of healthy volunteers, obese, renal and liver impairment, and in a generated virtual oncology population. Results were evaluated regarding basic pharmacokinetic parameters of Cmax, AUC and systemic CL and differences were assessed through ANOVA and estimation of ratio of geometric mean between healthy volunteers and the other population groups.

Results

Simcyp® predicted a mean Cmax = 551.60 mg/l, a mean AUC = 4079.12 mg/L*h and a mean systemic CL = 0.56 L/h for the virtual population of healthy volunteers. Obese population showed a modulation in Cmax and CL, attributed to increased administered dose. In renal and liver impairment cohorts a significant modulation in Cmax, AUC and CL of gadofosveset is predicted. Oncology population exhibited statistical significant differences regarding AUC when compared with healthy volunteers.

Conclusions

This work employed Simcyp® population pharmacokinetics platform in order to compute gadofosveset’s pharmacokinetic profiles through PBPK models and in silico clinical trials and evaluate possible differences between population groups. The approach showed promising results that could provide new insights regarding administration of contrast agents in special population cohorts. In silico pharmacokinetics could further be used for evaluating of possible toxicity, interpretation of MRI PK image maps and development of novel contrast agents.