Interspecies Variability in Biodistribution and PET Imaging Performance of [18F]Di-PyL: A Dimeric, PSMA-Targeted PET Agent for Prostate Cancer

Prostate cancer (PCa) is a leading cause of cancer deaths, making effective early detection, precise staging, and monitoring of biochemical recurrence crucial. Next-generation prostate-specific membrane antigen (PSMA) PET tracers could detect small or early metastatic lesion, especially in patients with low prostate-specific antigen. However, species differences in PSMA expression affect tracer biodistribution and imaging performance, highlighting the need for cross-species studies to optimize design and ensure clinical accuracy. Methods: We developed [¹⁸F]Di-PyL, a dimeric, PSMA-targeted radiotracer based on the structure of [¹⁸F]DCFPyL, and systematically evaluated the biodistribution of [¹⁸F]Di-PyL in mice, pigs, dogs, and cynomolgus monkeys before conducting a preliminary imaging study in humans. The aim of these comparative analyses was to provide critical insights into the interspecies biodistribution and imaging performance of this dimeric agent, while highlighting its potential to improve the detection of PCa, particularly in patients with low prostate-specific antigen levels and biochemical recurrence. Results: [¹⁸F]Di-PyL showed a 23-fold higher PSMA-binding affinity than did [¹⁸F]DCFPyL. In vitro assays showed increased cellular uptake of [¹⁸F]Di-PyL in PSMA-positive cells. Biodistribution studies revealed significant interspecies differences, with the kidneys showing the highest uptake across all species. Distinct uptake patterns were observed in the lungs and hearts of beagles and pigs, whereas cynomolgus monkeys exhibited high uptake in salivary glands and vertebrae. In humans, significant uptake was noted in the liver and spleen. PET/CT imaging in patients with PCa revealed strong tumor localization and excellent contrast in bone metastases. Conclusion: [¹⁸F]Di-PyL is a promising PSMA PET tracer with enhanced binding affinity and excellent performance in vitro and in vivo. [¹⁸F]Di-PyL PET studies across species revealed significant biodistribution variability but consistently highlighted the tracer's superior PSMA-targeting capability. These findings provide critical data to support further preclinical animal studies and lay a solid foundation for subsequent clinical trials.