Imaging, histological, and molecular characterization of a preclinical, orthotopic model of recurrent glioblastoma following image-guided laser ablation of the primary tumor.

Abstract

Image-guided laser interstitial thermal therapy (LITT) is a minimally invasive cytoreductive treatment for recurrent gliomas and tumors in eloquent regions. This technique was adapted to develop an image-guided glioblastoma (GBM) ablation model of recurrence. The efficacy of imaging biomarkers for evaluating tumor ablation and recurrence was evaluated by comparing the cytopathology and molecular signatures of primary and recurrent tumors. Immune-compromised female rats were implanted with U251N tumor cells in 1 brain hemisphere (n = 20). Tumor growth was monitored using MRI and dynamic contrast-enhanced (DCE)-MRI. When tumors reached about 3.5-4.5 mm in diameter at their largest extent, they were ablated using a clinical LITT system (Visualase), guided by diffusion-weighted MRI. Five rats implanted with U251N tumors were used as unablated controls. Postablation DCE-MRI data were acquired at 24 hours and 2 and 4 weeks. Rats were euthanized at 2 and 4 weeks, and brain sections were stained for hematoxylin and eosin (H&E), human major histocompatibility complex (MHC), Ki-67, SOX2, OLIG2, and mesenchymal marker CD44. Additional rats with primary (n = 4) and postablation recurrent (n = 4) U251N tumors were used to compare molecular compositions using RNA sequencing (RNA-Seq). All rats survived the LITT procedure. Sham controls showed increased tumor burden by 2 weeks and were euthanized. In the ablated groups, MRI revealed little tumor tissue at 24 hours after ablation, signs of recurrence at 2 weeks, and significant tumor tissue at 4 weeks. Tumor DCE-MRI parameters showed elevated intratumoral vascular permeability values (i.e., blood-to-tissue forward volumetric transfer constant [Ktrans]) at pre-LITT imaging that shifted to the ablation site periphery at 24 hours after ablation. A progressive decrease in Ktrans was seen until 1 week after LITT. Increasing Ktrans values at 2 weeks and after 4 weeks coincided with histological evidence of tumor recurrence. RNA-Seq showed that cell cycle, cellular movement, and inflammatory disease genes were the most differentially expressed genes (DEGs) in recurrent tumors compared to primary tumors. These results suggest that DCE-MRI can serve as an efficient imaging biomarker for evaluating glioma cytoablation and for tracking post-LITT recurrence. Functions that influence cell cycle, cell motility, and inflammatory processes were upregulated in the recurrent tumor. This represents a new preclinical, image-guided tumor ablation model of recurrent GBM that can be used to test potential therapies.