The Impact of Monosodium Glutamate on Ga-PSMA-11 Biodistribution in Men with Prostate Cancer: A Prospective Randomized, Controlled Imaging Study.

The prostate-specific membrane antigen (PSMA) has been targeted for PET imaging and radioligand therapy (RLT) in patients with prostate cancer. Xerostomia is a common side effect of RLT because of the high salivary gland uptake of PSMA radioligands. Here, we aimed to determine the impact of monosodium glutamate (MSG) administration on PSMA-radioligand biodistribution within healthy organs and tumor lesions by using Ga-PSMA-11 PET imaging. Sixteen men with prostate cancer were randomized (1:1) into oral ingestion and oral topical application ("swishing") arms. Each subject underwent 2 Ga-PSMA-11 PET/CT scans within 14 d under baseline and MSG conditions. The salivary glands and whole-body tumor lesions were segmented using qPSMA software. We quantified tracer uptake via SUV and SUV and compared parameters within each patient. For the oral ingestion arm, salivary gland SUV and SUV decreased on average from the control scan to the MSG scan by 45% ± 15% ( = 0.004) and 53% ± 11% ( < 0.001), respectively. Tumor lesion SUV and SUV also decreased by 38% (interquartile range, -67% to -33%) and -52% (interquartile range, -70% to -49%), respectively ( = 0.018). Swishing had no significant effect on Ga-PSMA-11 accumulation in normal organs or tumor lesions. Oral ingestion but not topical application of MSG reduced Ga-PSMA-11 uptake in salivary glands. Tumor uptake also declined; therefore, the clinical application of MSG is unlikely to be useful in the framework of RLT.