In vivo molecular malacological screening of specific uptake of commonly used radiopharmaceuticals in the leopard slug (Limax maximus) PET/SPECT imaging to determine effectiveness and human homology

<title>Abstract</title> <p> Terrestrial gastropods such as the leopard slug ( <italic>Limax maximus</italic> ) may represent an ethically favorable alternative to vertebrate models due to their simplified husbandry and breeding. This study evaluated the in vivo biodistribution of eight commonly used radiopharmaceuticals in slugs using PET/SPECT imaging and compared the observed patterns with established vertebrate data. Organ activity was normalized to activity in the foot, which served as the reference tissue. Distinct patterns were observed for each tracer. [ ^99m Tc]Tc-sestamibi showed increased uptake in the ganglia, heart, stomach, and digestive gland, whereas [ ¹²³ I]I-mIBGaccumulated predominantly in the heart/kidney complex. [ ^99m Tc]Tc-HDP localized mainly to the internal shell. [ ⁶⁸ Ga]Ga-PSMA demonstrated uptake in the digestive gland and a structure resembling the intestine/stomach. [ ⁶⁸ Ga]Ga-edotreotide and [ ¹⁸ F]FDG showed activity in the heart/kidney region, with [ ¹⁸ F]FDG also identifying potential heart chambers. [ ¹²³ I]I-ioflupane highlighted the stomach and digestive gland, with minor uptake in the heart/kidney complex and pneumostome. [ ¹⁸ F] NaF accumulated in the heart/kidney region but not in the internal shell. Across tracers, the digestive gland, stomach, and heart/kidney complex showed the most consistent uptake. The leopard slug shows promise as a novel alternative model for molecular imaging research. Further studies are needed to better understand gastropod physiology and assess the translational relevance of these findings to mammals and humans. </p>