ABS 056: Metabolic Profiling of PDAC Cell Lines Through Dual-Tracer PET-CT Imaging

Richard Laube ¹ , Meet Patel ¹ , Jace Baines ¹ , Christina Larson ¹ , Julienne L. Carstens ¹

¹ Department of Medicine, Division of Hematology & Oncology UAB and O’Neal Comprehensive Cancer Center

Van Wickle (2025) Volume 1, ABS 056

Introduction: Positron emission tomography-computed tomography (PET-CT) is a clinical technique serving various medicinal functions, including cancer detection and prognosis predictions. It relies on the uptake of radioisotope-labeled tracers, most commonly metabolites due to the elevated metabolic requirements of cancer. A novel use of PET-CT uses dual tracer systems in which two tracers are applied sequentially. Studies have examined the feasibility of dual tracer systems in patients by corresponding preferential tracer uptake with cancer progression, however few have examined how sub-tumor regions of preferential retention correlate with metabolic properties across phenotypically heterogenous cancers. Our experiment metabolically profiled two cell lines along the epithelial, intermediate (rosette), and squamous histological spectrum based on the spatial retention of the dual tracer 18F-fluorodeoxyglucose (FDG)/11C-acetate in transplanted subcutaneous murine tumors. Previous analyses have shown epithelial phenotypes to prefer lipid-based catabolism, therefore we hypothesized that 978U, a heterogenous, primarily epithelial cell line, would correlate with a heterogenous uptake of 11C-acetate and FDG, with epithelial areas preferentially retaining 11C-acetate. Contrarily, 28B, a homogenous, squamous cell line, would yield a homogenous retention of FDG based on the glycolytic nature of squamous cancers. Through image analysis via Visiopharm software, we developed an AI-based app to detect the spatial distribution of the three histological phenotypes for correlation with the distribution of retention for the two tracers. PET-CT uptake analysis is still being performed; however, pilot data as a proof of concept on a 28B mouse revealed a homogenous uptake of 11C-acetate and FDG across viable tissue, matching the hypothesis of homogenous retention, but not exhibiting preferential FDG uptake. By metabolically profiling histologically distinct sub-tumor regions through tracer uptake ratios, we hope to mechanistically define these differences and how it correlates to patient progression and drug response.

Methods: Nine mice underwent dual flank subcutaneous injections using two phenotypically distinct PDAC cell lines. Five mice were injected with a spontaneously generated murine KPC cell line, 978U, and four mice were injected with a murine PDAC cell line with an E. cadherin knockout, 28B. The tumors were allowed to grow until endpoint, at which point two mice from each cell line were selected for dual tracer PET-CT imaging. Imaging criteria was premised on tumor size and predicted necrosis. In imaging, 11C-acetate was injected first due to it having a short half-life of 20 minutes. This was followed by a saline flush and injection of 18F-Fluorodeoxyglucose (half-life of 110 minutes). A final saline flush was given and the mice were allowed an hour of image acquisition. Histological image analysis was done through Visiopharm software for AI-based spatial quantifications of the EMT spectrum across viable tissue through a U-Net deep learning module.

Results: We have shown that AI-based analysis provides comparable histological phenotyping capabilities to semi-quantifiable scoring methods. AI-based quantifications demonstrated the homogenously squamous nature of 28B and the heterogenous, primarily glandular/rosette phenotype of 978U. Within this, AI holds the capability for broad scale spatial quantification and high-fidelity phenotyping that is difficult to achieve in standard scoring procedures, demonstrated by the detection of small rosette regions in 28B tumors previously scores as 100% squamous. Both 978U and 28B exhibit similar levels of necrosis with significantly different EMT spectrum distributions, supporting their role in testing the efficacy of dual tracer PET-CT in sub-tumoral phenotyping.

Discussion: Spatial analysis of 978U and 28B sets the stage for alignment of dual tracer PET-CT results that are currently being developed. We have also generated MTS and CD31 IHC whole-tumor scans are that are being analyzed for the spatial distribution of collagen and micro-vessels respectively. These, combined with the spatial EMT analysis presented, will all be correlated to the relative retention of 11C-acetate and FDG. We hope to illustrate how relative rates of tracer retention correlate to the differing phenotypes of 978U and 28B. These may serve as biomarkers that are clinically applicable for less invasive measures of tumor phenotyping.