Simultaneous <i>In Vivo</i> Fluorescent Markers for Perfusion, Protoporphyrin Metabolism, and EGFR Expression for Optically Guided Identification of Orthotopic Glioma

Abstract

<b>Purpose:</b> While extent of tumor resection is an important predictor of outcome in glioma, margin delineation remains challenging due to lack of inherent contrast between tumor and normal parenchyma. Fluorescence-guided surgery is promising for its ability to enhance contrast through exogenous fluorophores; however, the specificity and sensitivity of the underlying contrast mechanism and tumor delivery and uptake vary widely across approved and emerging agents.<b>Experimental Design:</b> Rats with orthotopic F98 wild-type and F98 EGFR-positive (EGFR⁺) gliomas received <i>in vivo</i> administration of IRDye680RD, 5-aminioleuvulinic acid, and ABY-029-markers of perfusion, protoporphyrin metabolism, and EGFR expression, respectively. <i>Ex vivo</i> imaging demonstrates the contrast mechanism-dependent spatial heterogeneity and enables within-animal comparisons of tumor-to-background ratio (TBR).<b>Results:</b> Generally, ABY-029 outperformed PpIX in F98_EGFR orthotopic tumor margins and core (50% and 60% higher TBR, respectively). PpIX outperformed ABY-029 in F98_wt margins by 60% but provided equivalent contrast in the bulk tumor. IRDye680RD provided little contrast, having an average TBR of 1.7 ± 0.2. The unique spatial patterns of each agent were combined into a single metric, the multimechanistic fluorescence-contrast index (MFCI). ABY-029 performed best in EGFR⁺ tumors (91% accuracy), while PpIX performed best in wild-type tumors (87% accuracy). Across all groups, ABY-029 and PpIX performed similarly (80% and 84%, respectively) but MFCI was 91% accurate, supporting multiagent imaging when tumor genotype was unknown.<b>Conclusions:</b> Human use of ABY-029 for glioma resection should enhance excision of EGFR⁺ tumors and could be incorporated into current PpIX strategies to further enhance treatment in the general glioma case. <i>Clin Cancer Res; 23(9); 2203-12. ©2016 AACR</i>.