Abstract 2873: Imaging tumor heterogeneity after multikinase inhibitor therapy in rat hepatocellular carcinoma
Authors: Muñoz Nina M. , Minhaj Adeeb A. , Maldonado Kiersten L. , Kingsley Charles , Nishiofuku Hideyuki , Michel Keith A. , Cortes Andrea C. , Bankson James A. , Rashid Asif , Avritscher Rony 
Published: July 2017

Abstract
Purpose To assess tumor tissue perfusion and vascular permeability through multiparametric functional imaging, and to evaluate their correspondence with histopathologic parameters of necrosis and hypoxia in a rat model of hepatocellular carcinoma treated with a multikinase inhibitor.
Materials and Methods Rat hepatoma McA-RH7777 cells were implanted in the left liver lobe of nineteen male Buffalo rats. Exactly 2 weeks after tumor inoculation, the animals were randomly assigned to remain untreated (n=10) or to receive a daily dose of 7.5 mg/kg sorafenib by oral gavage (n=9) for 2 additional weeks. T2-weighted spin-echo magnetic resonance imaging (MRI), dynamic contrast-enhanced (DCE) and contrast-enhanced ultrasound (CEUS) were performed weekly. All tumors were harvested 4 weeks post-implantation &gt;90 minutes after injecting 60mg/kg pimonidazole. Tissue sections were stained for hematoxylin-eosin and pimonidazole for quantitative assessment of necrosis and hypoxia, respectively. Differences between treatment groups were assessed using the Mann-Whitney test, and the correlation of imaging and histopathology parameters was determined by Spearman correlation analysis.
Results In spite of the relatively low dose and short treatment duration, the response to sorafenib therapy was characterized by a significantly higher median tumor necrosis (60 vs 15%, P &lt; 0.0001) and increased tumor tissue hypoxia (35 vs 18.5% pimonidazole binding, P &lt; 0.0001). Similarly, the sorafenib regimen caused a substantial decrease in vascular permeability, measured by DCE-MRI Ktrans (P = 0.002) as well as reduction in tumor perfusion evaluated by CEUS peak enhancement (PE) (P =0.043). Our findings show a strong correlation between the two histopathologic parameters we assessed, tumor tissue necrosis and hypoxia (r = 0.645, P=0.002). Furthermore, our results demonstrate significant correlation of functional imaging parameters of vascular permeability, namely DCE-MRI Ktrans and DCE-MRI normalized initial area under the curve (NIAUC), with histopathologic tissue hypoxia (r=-0.663, P= 0.002, and r= -0.512, P=0.029, respectively). In contrast, histopathologic tumor necrosis appears more strongly correlated with a functional imaging parameter of tumor perfusion, specifically, CEUS PE (r = -0.547, P = 0.028).
Conclusion Tumors exhibited wide heterogeneity in vascular perfusion and hypoxia after treatment. Interestingly, functional MRI parameters appear to correlate more strongly with tissue oxygenation, whereas functional CEUS parameters correlate with tumor viability. Novel predictive imaging biomarkers of treatment response may be developed through further analyses of spatial tumor heterogeneity in our animal model.
Citation Format: Nina M. Muñoz, Adeeb A. Minhaj, Kiersten L. Maldonado, Charles Kingsley, Hideyuki Nishiofuku, Keith A. Michel, Andrea C. Cortes, James A. Bankson, Asif Rashid, Rony Avritscher. Imaging tumor heterogeneity after multikinase inhibitor therapy in rat hepatocellular carcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2873. doi:10.1158/1538-7445.AM2017-2873