Functional evaluation of therapeutic response for a mouse model of medulloblastoma.

Medulloblastoma is an aggressive childhood cerebellar tumor. We recently reported a mouse model with conditional deletion of Patched1 gene that recapitulates many characteristics of the human medulloblastoma. Qualitative symptoms observed in the mouse model include irregular stride length, impaired cranial nerve function and decreased motor coordination and performance. In our current study, several quantitative behavioral assays including a mouse rotarod, a forced air challenge, a screen inversion test, a horizontal wire test, and stride length analysis were evaluated to determine the most sensitive and cost-effective functional assay for impaired neuromotor behavior associated with disease progression. Magnetic resonance imaging (MRI) was used to confirm and monitor tumor growth and as an anatomical biomarker for therapeutic response. Wild type mice or medulloblastoma-prone, conditional Patched1 knockout mice were observed by behavioral assays and MRI from postnatal weeks 3-6. Bortezomib treatment was administered during this period and therapeutic response was assessed using cerebellar volumes at the end of treatment. Of the behavioral tests assessed in this study, stride length analysis was best able to detect differences between tumor-prone mice and wild type mice as early as postnatal day 37 (P=0.003). Significant differences between stride lengths of bortezomib treated and control tumor-bearing mice could be detected as early as postnatal day 42 (P=0.020). Cerebellar volumes measured by MRI at the end of treatment validated the therapeutic effects seen by behavioral tests (P=0.03). These findings suggest that stride length analysis may serve as one of the more sensitive and cost-effective method for assessing new therapeutic compounds in this and other preclinical model of brain tumors.

MicroCT-based virtual histology evaluation of preclinical medulloblastoma.

PURPOSE: The purpose of this paper is to validate a rapid and cost-effective ex vivo technique, microCT-based virtual histology, as an alternative to MRI imaging for assessing the therapeutic response in genetically engineered mouse models of cancer. PROCEDURES: All animal procedures were conducted in accordance with the Guidelines for the Care and Use of Laboratory Animals and were approved by the Institutional Animal Care and Use Committee (IACUC) at the University of Texas Health Science Center at San Antonio. MRI imaging was performed on 6-week-old, bortezomib-treated genetically engineered Patched1, p53 mice that recapitulate the characteristics of human medulloblastoma. After MRI scans, the same mice were euthanized to collect brain or spine samples for virtual histology staining followed by microCT scanning. RESULTS: Nine-micrometer resolution ex vivo micro X-ray computed tomography (microCT)-based virtual histology images were qualitatively reflective of high-field live animal images obtained with magnetic resonance imaging (MRI) and histopathology. Cerebellar volumes on microCT-based virtual histology correlated closely with MRI cerebellar volumes (R = 0.998). MRI and microCT-based virtual histology both indicated a significant difference between cerebellar volumes of untreated and treated mice (p = 0.02 and p = 0.04, respectively). The ex vivo microCT method also allowed a 7,430-fold improvement in voxel resolution (voxel volume of 729 µm³ for 9-µm isometric resolution microCT vs. 5,416,800 µm³ for 400 × 111 × 122 µm resolution MRI) at a 28% cost savings ($400 vs. $555 per animal). CONCLUSION: The ex vivo, en bloc technique of microCT-based virtual histology matched MRI in reflecting histopathology. MicroCT-based virtual histology proved to be a more cost-effective technique and less labor-intensive. On the other hand, MRI provides ability to perform in vivo imaging, faster scanning and lower radiation dose by sacrificing the spatial resolution. Thus, both in vivo MRI and ex vivo microCT-based virtual histology are effective means of quantitatively evaluating therapeutic response in preclinical models of cerebellar tumors including the childhood cancer, medulloblastoma.