Glycyrrhizic acid alters [99mTc]Tc-PSMA biodistribution and tumour progression in a DMBA-induced breast cancer model.

Breast cancer remains a major global health challenge, and understanding interactions between pharmacological agents and radiopharmaceuticals is important for interpreting molecular imaging findings. Glycyrrhizic acid (GA), a bioactive triterpenoid derived from Glycyrrhiza glabra, has reported anti-inflammatory and anticancer activities; however, its effects on PSMA-targeted radiotracer biodistribution remain poorly investigated. This study evaluated GA effects on tumour-related biological responses and [99mTc]Tc-PSMA biodistribution in vitro and in vivo. Cytotoxicity, migration, and invasion were assessed in MDA-MB-231 breast cancer cells. Cell-free PSMA enzyme kinetics and a separate cellular [99mTc]Tc-PSMA uptake assay were performed to distinguish effects on PSMA enzymatic activity from cell-associated radiotracer uptake. In vivo studies used a DMBA-induced mammary tumour model in female Sprague-Dawley rats, followed by SPECT/CT imaging and tissue biodistribution analysis. GA reduced cell viability concentration-dependently (IC₅₀ = 20 µM at 48 h) and suppressed migration and invasion. Cell-free kinetic analysis showed an apparent non-competitive PSMA inhibition pattern (Ki = 12.4 ± 1.5 µM), although this does not establish the molecular binding site. In vivo, GA reduced tumour uptake of [99mTc]Tc-PSMA by 57% (P < 0.005) and altered non-target tissue distribution. Despite reduced absolute tumour uptake, the tumour-to-background ratio increased because background activity decreased proportionally more. GA was also associated with reduced tumour growth and metastatic burden and altered inflammatory, angiogenic, and apoptotic markers. Overall, GA alters tumour biology and [99mTc]Tc-PSMA biodistribution, while the mechanism underlying radiotracer changes remains unresolved.