SCOPE-seq Analysis of Intra-operative Labeling Specificity of 5-ALA for Glioblastoma

Glioblastoma (GBM) is the most common and aggressive malignant primary brain tumor, and surgical resection is a key part of the standard-of-care. In fluorescence-guided surgery (FGS), fluorophores are used to differentiate tumor tissue from surrounding normal brain. The heme synthesis pathway converts 5-aminolevulinic acid (5-ALA), a fluorogenic substrate, to the fluorophore protoporphyrin IX (PpIX). The resulting fluorescence is thought to be specific to transformed glioma cells, but this specificity has not been examined at single cell level. Here, we performed paired single cell imaging and RNA sequencing of individual cells (SCOPE-seq2) on human GBM surgical specimens with visible PpIX fluorescence from patients who received 5-ALA prior to surgery. SCOPE-seq2 allows us to simultaneously measure PpIX fluorescence by imaging and unambiguously identify transformed glioma cells from single-cell RNA-seq (scRNA-seq). We observed that 5-ALA treatment results in labeling that is not specific to transformed tumor cells. In cell culture experiments, we further demonstrated untransformed cells can be labeled by 5-ALA directly or by PpIX secreted from surrounding transformed cells. In acute slice cultures from mouse glioma models, we showed that 5-ALA preferably labels GBM tumor tissue over non-neoplastic brain tissue at bulk level, and that this contrast is not due to blood-brain-barrier disruption. Taken together, our findings support the use of 5-ALA as an indicator of GBM tissue, but not as a specific marker of transformed glioma cells. Overall design: Performed SCOPE-seq2 on single cells dissociated from human GBM surgical specimens with visible intra-operative 5-ALA fluorescence.