Evaluation of Radiation Dose-Response in a Breast Cancer Brain Metastasis Model

The second incidence of brain metastases is from breast cancer. Radiotherapy, a standard treatment for brain metastasis, limits cancer division by inducing DNA double-stranded breaks (DSBs). Currently, identical radiation doses are prescribed for all types of brain metastases but little is known about their histological responses. In this thesis, we initiated a radiation dose-response study in a triple-negative human breast cancer brain metastasis mouse model using a custom designed 3D-printed restrainer to assist half-brain irradiation. We quantified the amount of DSBs in tumors and mouse brain tissues using γ-H2AX marker at 30 minutes (acute) and 11 days (longitudinal) after treatment with doses of 8-24 Gy. We also evaluated tumors’ response using histology and MRI. In the longitudinal study we found significant differences in the amount of DSBs, tumor cell density, and nucleus size between irradiated surviving and non-irradiated tumors. These results gave insights to brain metastasis response after radiotherapy

Half brain irradiation in a murine model of breast cancer brain metastasis: Magnetic resonance imaging and histological assessments of dose-response

Background: Brain metastasis is becoming increasingly prevalent in breast cancer due to improved extra-cranial disease control. With emerging availability of modern image-guided radiation platforms, mouse models of brain metastases and small animal magnetic resonance imaging (MRI), we examined brain metastases\u27 responses from radiotherapy in the pre-clinical setting. In this study, we employed half brain irradiation to reduce inter-subject variability in metastases dose-response evaluations. Methods: Half brain irradiation was performed on a micro-CT/RT system in a human breast cancer (MDA-MB-231-BR) brain metastasis mouse model. Radiation induced DNA double stranded breaks in tumors and normal mouse brain tissue were quantified using γ-H2AX immunohistochemistry at 30 min (acute) and 11 days (longitudinal) after half-brain treatment for doses of 8, 16 and 24 Gy. In addition, tumor responses were assessed volumetrically with in-vivo longitudinal MRI and histologically for tumor cell density and nuclear size. Results: In the acute setting, γ-H2AX staining in tumors saturated at higher doses while normal mouse brain tissue continued to increase linearly in the phosphorylation of H2AX. While γ-H2AX fluorescence intensities returned to the background level in the brain 11 days after treatment, the residual γ-H2AX phosphorylation in the radiated tumors remained elevated compared to un-irradiated contralateral tumors. With radiation, MRI-derived relative tumor growth was significantly reduced compared to the un-irradiated side. While there was no difference in MRI tumor volume growth between 16 and 24 Gy, there was a significant reduction in tumor cell density from histology with increasing dose. In the longitudinal study, nuclear size in the residual tumor cells increased significantly as the radiation dose was increased. Conclusions: Radiation damages to the DNAs in the normal brain parenchyma are resolved over time, but remain unrepaired in the treated tumors. Furthermore, there is a radiation dose response in nuclear size of surviving tumor cells. Increase in nuclear size together with unrepaired DNA damage indicated that the surviving tumor cells post radiation had continued to progress in the cell cycle with DNA replication, but failed cytokinesis. Half brain irradiation provides efficient evaluation of dose-response for cancer cell lines, a pre-requisite to perform experiments to understand radio-resistance in brain metastases

Abstracts from the 20th International Symposium on Signal Transduction at the Blood-Brain Barriers

https://deepblue.lib.umich.edu/bitstream/2027.42/138963/1/12987_2017_Article_71.pd

Improved Detection of Molecularly Targeted Iron Oxide Particles in Small Animals with High Resolution MRI

Authors: Paul Kinchesh, Stuart Gilchrist, Niloufar Zarghami, Alexandre A Khrapitchev, Nicola R Sibson, Veerle Kersemans, Sean C Smart. High resolution multi-gradient echo (MGE) scanning is typically used for detection of molecularly targeted iron oxide particles. The images of individual echoes are often combined to generate a composite image with improved SNR from the early echoes and boosted contrast from later echoes. In 3D implementations prolonged scanning at high gradient duty cycles induces a B0 shift that predominantly affects image alignment in the slow phase encoding dimension of 3D MGE images. The effect corrupts the composite echo image and limits the image resolution that is realised. A real-time adaptive B0 stabilisation during respiration gated 3D MGE scanning reduces image misalignment and improves detection of molecularly targeted iron oxide particles in composite images of the mouse brain. Respiration gated MGE 3D scans were performed to visualise molecularly targeted MPIO in a BALB/c mouse model of acute neuroinflammation. Data were acquired with and without B0 stabilisation for comparison. The slow phase encode image dimension runs in the left-right direction of the brain. It is particularly instructive to inspect the registration of image data by selecting an axial slice and scrolling through the acquired echoes. The echoes can be summed to form a simple composite image. The data in this archive demonstrate that high resolution imaging for the detection of molecularly targeted iron oxide particles in the mouse brain requires good stabilisation of the main B0 field so that the composite image resolution reflects the prescribed image resolution. Data were acquired on a 9.4 T 160 mm horizontal bore VNMRS preclinical imaging system equipped with 100 mm bore gradient insert (Varian Inc, CA) and are available for 6 mice. The *.nii files are NIfTI-1 formatted image files, http://nifti.nimh.nih.gov/ ImageJ is a suitable viewer, http://imagej.nih.gov/ij/ M#_compensatedXXX.nii: Mouse #, B0 stabilisation of a XXX Hz frequency drift. M#_uncompensatedYYY.nii: Mouse #, a YYY Hz frequency drift without B0 compensation. # = [1,6

Half brain irradiation in a murine model of breast cancer brain metastasis: magnetic resonance imaging and histological assessments of dose-response

Abstract Background Brain metastasis is becoming increasingly prevalent in breast cancer due to improved extra-cranial disease control. With emerging availability of modern image-guided radiation platforms, mouse models of brain metastases and small animal magnetic resonance imaging (MRI), we examined brain metastases’ responses from radiotherapy in the pre-clinical setting. In this study, we employed half brain irradiation to reduce inter-subject variability in metastases dose-response evaluations. Methods Half brain irradiation was performed on a micro-CT/RT system in a human breast cancer (MDA-MB-231-BR) brain metastasis mouse model. Radiation induced DNA double stranded breaks in tumors and normal mouse brain tissue were quantified using γ-H2AX immunohistochemistry at 30 min (acute) and 11 days (longitudinal) after half-brain treatment for doses of 8, 16 and 24 Gy. In addition, tumor responses were assessed volumetrically with in-vivo longitudinal MRI and histologically for tumor cell density and nuclear size. Results In the acute setting, γ-H2AX staining in tumors saturated at higher doses while normal mouse brain tissue continued to increase linearly in the phosphorylation of H2AX. While γ-H2AX fluorescence intensities returned to the background level in the brain 11 days after treatment, the residual γ-H2AX phosphorylation in the radiated tumors remained elevated compared to un-irradiated contralateral tumors. With radiation, MRI-derived relative tumor growth was significantly reduced compared to the un-irradiated side. While there was no difference in MRI tumor volume growth between 16 and 24 Gy, there was a significant reduction in tumor cell density from histology with increasing dose. In the longitudinal study, nuclear size in the residual tumor cells increased significantly as the radiation dose was increased. Conclusions Radiation damages to the DNAs in the normal brain parenchyma are resolved over time, but remain unrepaired in the treated tumors. Furthermore, there is a radiation dose response in nuclear size of surviving tumor cells. Increase in nuclear size together with unrepaired DNA damage indicated that the surviving tumor cells post radiation had continued to progress in the cell cycle with DNA replication, but failed cytokinesis. Half brain irradiation provides efficient evaluation of dose-response for cancer cell lines, a pre-requisite to perform experiments to understand radio-resistance in brain metastases