Abstract 4063: Image-guided fluorescent endomicroscopy of glioblastoma with SVV-GFP viral labeling

Abstract

Abstract We propose a novel method to improve detection of infiltrative microscopic GBM tumors during surgery, by labeling the infiltrative tumor cells in vivo by a single intravenous injection of a highly specific tumor seeking fluorescence virus, Seneca Valley Virus (SVV-GFP). The feasibility of this approach was demonstrated in a permissive pediatric GBM (IC-2305GBM) and an adult GBM (IC-A46GBM) orthotopic xenograft mouse model. Both models were derived from primary tissue of GBM from patients to preservethe histopathological and immunophenotypical characteristics of the original tumors. After establishing the xenograft tumors, SVV-GFP was injected intravenously at a dose of 5x1014 viral particles/kg. The animals were imaged at day 3 after SVV-GFP virus injection. During the imaging procedure, the animals were euthanized through anesthesia overdose and a small window was immediately drilled in the skull to introduce a 1mm outer diameter fiberoptic fluorescence probe through the tumor. Fluorescent labeled cells were recorded as a real-time video sequence along the track of the probe. Image quantification starts with low frequency temporal drift correction using Fast Fourier Transform based lowpass filtering. Air image frames (before probe insertion) were used as a zero reference and the intensity range of the video is shifted accordingly. A normal tissue fluorescence image was then estimated using a median statistics of all image frames acquired in normal brain tissue. This image was used to correct for lower detection sensitivity near the probe edge or any field inhomogeneity. The video sequence was then normalized to the normal tissue image to create a TBR map. By definition, air is used as reference with TBR=0 and normal tissue is at TBR=1. A cutoff of TBR>1.1 is used and tumor cells exceeding that threshold were classified as GFP-positive tumor cells. Fractional area occupied by the virus-labeled microscopic tumors were computed with the TBR exceeding 1.1 within the field of view. A low fractional area (<0.01%) was found in normal brain tissue using this method, demonstrating that our method is robust. To summarize, we demonstrated an innovative approach for microscopic tumor detection in glioblastoma that is two to three orders of magnitude smaller than those currently detected with in vivo imaging modalities.This method can potentially be applied to detect microscopic tumors in metastatic retinoblastoma, medulloblastoma, endocrine tumors and small cell lung cancer which are shown to be permissive to infection of this virus. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4063. doi:1538-7445.AM2012-4063