Tc-99m Radiolabeling of Phenolic Compounds and Preliminary Biological Distribution Study in Normal Rats

Phenolic compounds are the most common secondary metabolites found in plants and microorganisms such as fungi. These compounds possess widespread pharmacological properties such as anti-cancer, anti-diabetic, anti-inflammatory, anti-oxidants, anti-bacterial and etc. Potential role of some phenolic compounds as new radio-diagnostic agent has been scientifically proven. Thus, there is possibility that other phenolic compounds would possess similar property. This study was done to determine Tc^99m radiolabeling activity of selected phenolic compounds, as initial steps towards development of new natural-based radiopharmaceutical agents. Radiolabeling of phenolic compounds with Tc^99m was done at fixed concentration of compounds (100 μg) and SnCl₂ (150 μg), fixed reaction temperature (RT) and time (10-minutes) as well as at fixed pH value (4). Activity of Tc^99m added into each reaction was set at 10 mCi. Percentage of radiolabeled phenolics were determined using instant thin layer chromatography (ITLC) method. The results showed that phenolic compounds have the potential to be radiolabeled with Tc^99m. From 19 phenolic compounds evaluated, 9 compounds exhibited Tc^99m labeling activity. Punicalagin showed the highest labeling yield (98.03%), followed by kojic acid (16.93%), epigallocatechin gallate (14.31%), theaflavin (10.81%), vitexin (7.96%), Proanthocyanidin (5.00%), curcumin (4.78%), salicylic acid (1.33%) and quercetin (0.64%). Punicalagin which showed highest labelling yield was further evaluated for its preliminary biological distribution analysis in normal rats. Gamma camera images showed that the Tc99m-punicalagin complex was initially present in stomach, kidneys and bladder, which were known as the location of free pertechnetate uptake. This could be due to the dissociation of Tc^99m -punicalagin complex occurs in the rat's body. Further studies need to be done to overcome this matter. This study has demonstrated that phenolic compounds can be promising candidates for development of new radiopharmaceutical agents, as well as therapeutic radiopharmaceutical agents based on its known pharmacological activities. However, more optimization needs to be carried to obtain acceptable radiolabelling yield and stable Tc^99m -phenolics complexes for future human use. (author)