Quantitative Imaging of Pharmacodynamics in a Phase 1 Clinical Study of the Vascular Disrupting Agent Crolibulin (EPC2407)
Andres M. Arias Lorza1, William L. Read2, Raoul Tibes3, Ronald L. Korn4, and Natarajan Raghunand1,5

1Department of Cancer Physiology, Moffitt Cancer Center, TAMPA, FL, United States, 2Winship Cancer Institute, Emory University School of Medicine, Atlanta, GA, United States, 3Perlmutter Cancer Center, NYU Langone Health, New York, NY, United States, 4Imaging Endpoints, LLC, Scottsdale, AZ, United States, 5Department of Oncologic Sciences, University of South Florida, Tampa, FL, United States


Diffusion and DCE-MRI were performed at baseline and 2-3 days following Crolibulin (EPC2407) treatment in a phase 1 clinical study of this vascular disrupting agent. ADCw, Ktrans, Ve, and Vp parameter maps were computed and co-registered across scan dates. Over 10 subjects there was an average of 44% decrease in mean tumor Ktrans 2-3 days after initiation of therapy relative to baseline Ktrans values. The decrease in whole-tumor Ktrans was significantly greater in subjects who received 24 mg/m2 drug relative to those who received 13 mg/m2 Crolibulin. Voxel-wise analysis of changes in ADCw, Ktrans, Ve, and Vp will be presented.


Anti-cancer therapies targeting tumor vasculature fall into two main categories, antiangiogenic agents designed to prevent the formation of new blood vessels (neovascularization), and Vascular Disrupting Agents (VDAs) that target endothelial cells and pericytes of established tumor vasculature. Clinical development of VDAs has been hampered by non-availability of biomarkers to select likely responders and for identification of an Optimal Biological Dose (OBD) rather than the Maximum Tolerated Dose (MTD) (1, 2). Dynamic Contrast-Enhanced MRI (DCE-MRI) (3), Diffusion MRI (DW-MRI) (4, 5), and MR elastography (6) have shown promise in clinical and pre-clinical biomarker studies of VDAs. Crolibulin (EPC2407) is a 4-aryl-chromene single isomer microtubulin inhibitor with vascular disrupting and apoptotic activity (7, 8). DCE-MRI, carbogen-enhanced BOLD MRI, and photoacoustic imaging have been investigated in pre-clinical tumor models as biomarkers of Crolibulin action (9-11). Here we report results from a phase 1 clinical study of Crolibulin in which DW-MRI and DCE-MRI images were acquired at baseline and 2-3 days post-drug. Our objective is to combine information from DW-MRI and DCE-MRI quantitative parameter maps into a biomarker of Crolibulin pharmacodynamics and tumor response.


Crolibulin was infused over 4 h on a daily x 3, 21 day cycle schedule to extend exposure of tumor vasculature to the drug in an IRB-approved multi-site clinical study. This dosing regimen was studied in 11 subjects with advanced solid tumors: leiomyosarcoma, colorectal, ovary, hepatocellular (2), NSCLC, pancreas, carcinoid, hemangiopericytoma, larynx, and small bowel. Imaging was performed on either 1.5 T or 3 T MRI scanners, and analyzable MRIs were available from 10 subjects who received Crolibulin doses between 13-24 mg/m2. DW-MRI single-shot EPI images were acquired during a held-inhalation breathhold in 6 mm slices with isotropic diffusion weighting and b = 0, 150, 300, 450 s/mm2, and repeated with diffusion weighting applied in the superior/inferior direction. DCE-MRI data were collected on subjects repeating a “breathe-in, breathe-out, hold” pattern, with the imaging occurring during each held-expiration period. Prior to the dynamic portion of the scanning 4 pre-contrast 3D-GRE images were obtained at flip angles of 15°, 23°, 30° and 60° for computing pre-contrast T1 maps. The dynamic series portion of the imaging comprised of 24-30 3D-GRE images collected during repeated “held exhalation” breath-holds with a temporal resolution of 16-18 seconds. Typical parameters for the 3D-GRE imaging were, 12 slices reconstructed to a matrix size of 256 x 256, slice thickness = 5 mm, TR = 5.0 ms, TE = 2.1 ms, and α=30°. After 1-2 pre-contrast images had been acquired, gadolinium contrast was injected at a dose of 0.1 mmole/kg at a rate of 4 mL/s using a power-injector, and chased with a 20 mL saline flush also injected at 4 mL/s.


Per visit and between visits, all images were registered using either rigid or non-rigid registration. Pre-contrast T1 maps and proton density maps (Mo) were obtained by fitting pre-contrast T1-weighted images acquired with varying flip angles to a linearized gradient-echo signal equation (12). These maps, together with the DCE-MRI images, were used to calculate voxelwise gadolinium concentrations that were fitted to an Extended Tofts Model (13) to extract model parameters Ktrans (reflective of perfusion or microvascular permeability), Ve (extracellular extravascular volume fraction), and Vp (plasma volume fraction) using the methods presented by Mouridsen et al. (14) and Murase (15). Apparent Diffusion Coefficient of water (ADC) maps were obtained by fitting the diffusion-weighted images to the signal equation (S=So e-b ADC). An example of the quantitative parameters maps before and post-treatment of a patient with a malignant mass in the uterus is shown in Figure 1. On a whole-tumor basis the index lesions had a 44% overall reduction in Ktrans post-treatment relative to pre-treatment (Figure 2). In addition, index lesions in the 24 mg/m2 cohort had significant decline in Ktrans compared to 13 mg/m2 cohort (Figure 3, p=.03). Significant changes were observed in ADCw, Ktrans, Ve, and Vp parameter values between baseline and follow-up images on a voxelwise basis.


Whole-tumor analysis of DCE-MRI demonstrates a correlation between change in Ktrans with drug dose, providing a translatable biomarker of drug pharmacodynamics. Additionally, spatial heterogeneity of changes in the tumors were visible on all quantitative parameter maps. Our ongoing efforts are directed at identification of threshold values at baseline on mutually registered DW-MRI and DCE-MRI parameter maps that are jointly predictive of response to Crolibulin at follow-up. Our overall objective is to develop a biomarker to guide stratification of patients at baseline by likelihood of response to Crolibulin treatment.


No acknowledgement found.


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Before and post-treatment quantitative maps of a patient with a lesion in the uterus depicted in the images by an arrow. Additionally, one DCE-MRI time point with high contrast concentration is also shown. The quantitative parameter maps shown are: relaxation times (T1), maximum relaxed T1W signal (Mo), apparent diffusion coefficient (ADC), Ktrans, Ve, and Vp.

Individual lesions by subject.

Post-treatment vs. Pre-treatment Ktrans ratio for each Crolibulin doses.

Proc. Intl. Soc. Mag. Reson. Med. 27 (2019)