RadioFlow Cytometry Reveals That [18F]FDG Uptake in K-RAS Lung Cancer Is Driven by Immune Cells: An Analysis on a Single-Cell Level

Tumor metabolism is a hallmark of cancer, yet cellular heterogeneity within the tumor microenvironment presents a significant challenge, as bulk analysis masks the diverse metabolic profiles of individual cell populations. This complexity complicates our understanding of [¹⁸F]FDG uptake by distinct cell types in the tumor microenvironment. This study aims to investigate [¹⁸F]FDG uptake at the single-cell level in the lung of Kirsten rat sarcoma virus–driven cancer mouse models using the novel technique radio–flow cytometry (radioFlow). Methods: Two Kirsten rat sarcoma virus–driven lung cancer mouse models were injected with [¹⁸F]FDG for small-animal PET/CT and subsequent fluorescence-activated cell sorting of the lung. For radioFlow, the sorted cell fractions were then measured in a γ-counter and their radioactivity was normalized to the number of cells. Results: RadioFlow analysis of the lung tissue of both models showed a robust cell type–specific uptake pattern across experiments. Our key findings indicate that the [¹⁸F]FDG PET signal predominantly derives from immune cells (CD45⁺, F4/80⁻, 78.3% ± 6.6%; macrophage, 13.9% ± 4.3%), whereas tumor cells contributed only with 2.8% ± 1.0%, similar to the uptake of structural cells (CD45⁻; tumor cells, 5.0% ± 2.3%). Normalization showed that macrophages exhibited the highest glucose metabolism in both tumor models (57% ± 8%), followed by the remaining immune cells (27% ± 3%). Conclusion: These findings highlight the critical influence of immune cell metabolism on [¹⁸F]FDG imaging, emphasizing the need to account for immune contributions when interpreting [¹⁸F]FDG imaging in cancer.