The Impact of Monosodium Glutamate on ⁶⁸Ga-PSMA-11 Biodistribution in Men with Prostate Cancer: A Prospective Randomized, Controlled Imaging Study.

Abstract

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 ⁶⁸Ga-PSMA-11 PET imaging. <b>Methods:</b> Sixteen men with prostate cancer were randomized (1:1) into oral ingestion and oral topical application ("swishing") arms. Each subject underwent 2 ⁶⁸Ga-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_mean and SUV_max and compared parameters within each patient. <b>Results:</b> For the oral ingestion arm, salivary gland SUV_mean and SUV_max decreased on average from the control scan to the MSG scan by 45% ± 15% (<i>P</i> = 0.004) and 53% ± 11% (<i>P</i> < 0.001), respectively. Tumor lesion SUV_mean and SUV_max also decreased by 38% (interquartile range, -67% to -33%) and -52% (interquartile range, -70% to -49%), respectively (<i>P</i> = 0.018). Swishing had no significant effect on ⁶⁸Ga-PSMA-11 accumulation in normal organs or tumor lesions. <b>Conclusion:</b> Oral ingestion but not topical application of MSG reduced ⁶⁸Ga-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.