Multimodality multiparametric imaging of early tumor response to a novel antiangiogenic therapy based on anticalins.

Anticalins are a novel class of targeted protein therapeutics. The PEGylated Anticalin Angiocal (PRS-050-PEG40) is directed against VEGF-A. The purpose of our study was to compare the performance of diffusion weighted imaging (DWI), dynamic contrast enhanced magnetic resonance imaging (DCE)-MRI and positron emission tomography with the tracer [18F]fluorodeoxyglucose (FDG-PET) for monitoring early response to antiangiogenic therapy with PRS-050-PEG40. 31 mice were implanted subcutaneously with A673 rhabdomyosarcoma xenografts and underwent DWI, DCE-MRI and FDG-PET before and 2 days after i.p. injection of PRS-050-PEG40 (n = 13), Avastin (n = 6) or PBS (n = 12). Tumor size was measured manually with a caliper. Imaging results were correlated with histopathology. In the results, the tumor size was not significantly different in the treatment groups when compared to the control group on day 2 after therapy onset (P = 0.09). In contrast the imaging modalities DWI, DCE-MRI and FDG-PET showed significant differences between the therapeutic compared to the control group as early as 2 days after therapy onset (P<0.001). There was a strong correlation of the early changes in DWI, DCE-MRI and FDG-PET at day 2 after therapy onset and the change in tumor size at the end of therapy (r = -0.58, 0.71 and 0.67 respectively). The imaging results were confirmed by histopathology, showing early necrosis and necroptosis in the tumors. Thus multimodality multiparametric imaging was able to predict therapeutic success of PRS-050-PEG40 and Avastin as early as 2 days after onset of therapy and thus promising for monitoring early response of antiangiogenic therapy

Scatter plots illustrating the degree of correlation between the percentage change of tumor size (pre vs. day 7 after onset of therapy) plotted along the horizontal axis versus DWI (hollow circle, r = −0.58, P = 0.001), DCE-MRI (grey circle, r = 0.71, P = 0.001) and FDG-PET (black circle, r = 0.67, P<0.001) (pre vs. day 2 after onset of therapy) plotted along the vertical axis.

<p>Scatter plots illustrating the degree of correlation between the percentage change of tumor size (pre vs. day 7 after onset of therapy) plotted along the horizontal axis versus DWI (hollow circle, r = −0.58, P = 0.001), DCE-MRI (grey circle, r = 0.71, P = 0.001) and FDG-PET (black circle, r = 0.67, P<0.001) (pre vs. day 2 after onset of therapy) plotted along the vertical axis.</p

Representative DWI (transverse slices; b = 20, b = 200, ADC map), T1 map (T1 values are shown in color scale (ms)) of DCE-MRI from a single time point (transverse slices; pre and post i.v. injection of Gadolinium) used for T1 quantification and FDG-PET (from left to right: transverse, coronal and sagittal reconstruction) images of the A673 rhabdomyosarcoma xenografts (arrows) subcutaneously implanted in the right lateral flank.

<p>Representative DWI (transverse slices; b = 20, b = 200, ADC map), T1 map (T1 values are shown in color scale (ms)) of DCE-MRI from a single time point (transverse slices; pre and post i.v. injection of Gadolinium) used for T1 quantification and FDG-PET (from left to right: transverse, coronal and sagittal reconstruction) images of the A673 rhabdomyosarcoma xenografts (arrows) subcutaneously implanted in the right lateral flank.</p

Semiquantitative analysis of the microvessel density (MVD) as assessed by CD31 and SMA staining.

<p>Quantification (%) of the necrotic areas in the tumor tissue before and 2 or 7 days post therapy (p.t.).</p

Representative H&E, SMA and CD31 stains of PRS-050-PEG40, Avastin or PBS treated tumors at day 2 after onset of therapy.

<p>The representative Anticalin treated tumor shows extensive necrosis (black star) and necroptosis (white star), the Avastin treated tumors shows extensive necrosis and a mitosis (block dot). In contrary the PBS treated control tumor shows no necrosis or apoptosis. The black arrows indicate vessels, black arrowheads indicate musculature and black dash indicates apoptosis.</p