Investigation of radiopharmaceutical potential of bleomycin and bleomycin-glucuronide labeled with 99mTc

Bleomycin (BLM) is a series of glycopeptide in antibiotics isolated from the culture media of Streptomyces verticullus by Dr. Hamao UMEZAWA who was a japan scientist in 1962. Due to the cytotoxic and anti-carcinogen properties, BLM causes single- or double-strand breaks in DNA. The BLM used clinically has three distinct isomers A2 (~60%), B2 (~30%) and DM (~5%). BLM is known to form complexes with a range of metal as 131I, 67Ga,111In and 99mTc. Some of which have been showed to exhibit tumor-localizing properties as demonstrated by radiotracer experiments and subsequently by clinical imaging studies. Furthermore, it has been proposed that may be useful for targeted therapy using isotopes. BLM is used as an anti-tumor agent in the treatment of lung cancer, lymphoma, carcinoma, testicle, head, neck and other tumors.Due to the emission of optimal energy of gamma ray (140 keV), a suitable half-life (6h) and availability from 99Mo/ 99mTc generator systems, 99mTc is the most desirable radionuclide for external imaging in diagnostic nuclear medicine. Besides, it is used in combination with appropriate drugs. Due to appropriate imaging properties of 99mTc, if cytotoxic drugs as BLM combines with 99mTc, a good cancer imaging radiopharmaceutical is obtained.The aim of the current study is to label BLM and Bleomycin-glukuronid (BLMG) that is a glucuronide derivate of BLM with 99mTc and to investigate the radiopharmaceutical potential of these radiolabeled compounds using radiochemical methods like high performance liquid chromatography (HPLC), thin layer radiochromatography (TLRC); via biodistribution studies and imaging.First of all, BLMG was enzymatically synthesized using microsomal preparations, UDP-glucuronic acid and UDP-glucuronyltransferase enzyme isolated from rat liver. BLMG was purified using HPLC method. Then, both BLM and BLMG were labeled with 99mTc. The quality control studies were carried out using TLRC technique. The most appropriate solution or solution systems were determined for radiolabeled compounds. The appropriate solution for BLM was acid-citrate-dextrose (ACD) whereas the other solution for BLMG was solution with detergent. At the end of this, 99mTc-BLM and 99mTc-BLMG were prepared and their radiolabeling yield was found higher than >99%.Secondly, the stability was carried out. The stability of the complexes was investigated in the presence of human serum. At the end of the stability studies, the radiolabeled compounds were maintained stable at 37oC up to 3h of incubation.Thirdly, the n-octanol/water partition coefficient, LogP, which is used as hydrophobic parameter was measured at the room temperature. Physicochemically meaningful correlations were determined between found values and predicted values of BLM and BLMG.Finally, the imaging and biodistribution studies were performed on laboratory animals as male Albino Wistar rats and rabbits, respectively. The radioactivities of each target organs were calculated as an activity per gram tissue (% ID/g) using a Cd(Te) counter. The highest accumulation in coordination with BLM was observed in the liver, the bladder and the spinal cord. On the other hand, the highest accumulation in coordination with BLMG was observed in the lung, the liver, the kidney, the large intestine and spinal cord. Besides, the whole experimental data of biodistribution studies were evaluated SPSS 13 statistical software program.