| Abstract: |
Rvadiotherapeutic Agents-Some Iodine 125radiotherapeutic agent in the treatment of differen t typesof cancers.Cytarabine was labelled with iodine-125 using iodogen as oxidizing agent. This process was done via electrophilic substitution of iodonium ion [I+] for hydrogen atom of the heterocyclic ring of cytarabine. The iodogen quantity which was found to be sufficient to proceed the reaction was 200 μg in the form of thin film on the walls of the reaction tube. The yield of the labelled compound was maximum when the concentration of cytarabine was 50 μg and this was found to be related to the required activity. Theoretically each molecule of cytarabine requires one iodine atom and this factor depends largely on the specific activity of iodine-125. A nother important factors which control the percentage of the yield is the reaction temperature. The optimum temperature required to give high radiochemical yield (99.2 %) was 65 oC, below or above this temperature, the yield was decreased and the reaction was slow.Cytarabine was efficiently labelled when the reaction was carried out at pH 7. The reaction between iodine-125 and cytarabine in the presence of iodogen proceeds quickly as the reaction time was increased and reached maximum when the reaction mixture was heated for 30 min at 65 oC.The radiochemical purity of 125I-cytarabine was determined using paper electrophoresis in addition to the reversed phase high performance liquid chromatography (HPLC/RP-18). Due to the resolution ability of the HPLC/RP-18 and paper electrophoresis, they demonstrated the presence of 2 peaks, corresponding to iodide and iodocytarabine.The labelled cytarabine was injected in both normal and tumour bearing mice via intravenous route. The uptake in ascitic fluid was very high (38 %) especially at 24 h.p.i. while the activity was rapidly cleared from other non-target tissues.CHAPTER II“LABELLING, RADIOCHEMICAL AND BIOLOGICAL EVALUATION OF 6-MERCAPTOPURINE”6-Mercaptopurine is an antimetabolite drug, which is 6-thiol analogue of the endogenous 6-OH purine bases so it prevents the naturally occurring nucleic acids.Labelling was carried out by direct iodination of 6-mercaptopurine (50 μg) with radioiodine in a fast, single step at 80 oC, to produce iodo-6-mercaptopurine. Iodogen was used as an oxidizing agent to oxidize the iodide ion [I-] to the iodonium ion [I+] in a concentration of 300 μg, at pH 7 and the reaction time was 30 min. This method afforded a pure radiochemical yield of 90.3 %, which facilitate its clinical use for human application.The radiochemical purity of 125I-6-mercaptopurine obtained after HPLC separation on RP-18 column at the optimum conditions, resulted in three peaks, one peak was obtained after 6 min while the second after 9 min and the third after 12 min elution time. The first corresponding to free iodide and the oxidized species while the second corresponding to the mono-iodo-compound and the third corresponding to the di-iodo-6-mercaptopurine.Biodistribution of 125I-6-MP was studied by injecting the tracer in both normal and tumor bearing mice. The uptake in ascites was 45.4 and 30.8 % after 1 and 24 h.p.i. respectively. Also, the uptake in solid tumour was 10.2 % and 8.8 % after 1 and 24 h.p.i. respectively. The clearance of the tracer from the blood was high and the accumulation of the activity in urine was 39 % after 24 h.p.i. In-vivo deiodination of the tracer was very low, as the thyroid uptake not exceed 4.1 % after 24 h.p.i.PART TWO“PHARMACEUTICAL FORMULATION OF FREEZE-DRIED CYTARABINE AND 6- MERCAPTOPURINE KITSLABELLED WITH IODINE-125”It is very important in the field of radiopharmacy, that the product must be ease and safe during transportation. Also, the labelled compound must be prepared quickly and safely in the nuclear medicine centers. To satisfy these requirements, the formula must be freeze-dried. The freeze-dried vials of both cytarabine and 6-mercaptopurine were formulated.Solutions of both cytarabine and 6-mercaptopurine in 0.5 M phosphate buffer pH 7 were sterilized by passing through 0.22 μm millipore filter and dispensed in sterile iodogen coated vials under aseptic conditions. The vials were plugged with forked rubber closures and then subjected to freeze-drying. The freeze-dried cycle start by freezing the sample to -40 oC, then the condensed temperature was set at -60 oC, and the vacuum was fixed at 28 millitorr. After 4 hours, the shelf temperature was set at +13 oC, to supply latent heat to the frozen samples to help in sublimation of ice. The process of lyophilization was continued for 24 hours. At the end of the cycle, the vials were closed under positive nitrogen gas, capped with aluminum caps and stored at 2-8 oC.The freeze-dried formula of cytarabine or 6-mercaptopurine is:250 μg substrate200 μg iodogen750 μl 0.5 M phosphate buffer pH 7The in-house prepared freeze-dried vials of both cytarabine and 6-mercaptopurine were sterile, pyrogen free and have no toxicity. The percent moisture content of the freeze-dried vials was equal to 0.1 % and this is in a good agreement with the limits of the Egyptian Pharmacopoeia.The radiochemical purity and high stability of the labelled freeze-dried vials of both cytarabine and 6-mercaptopurine was determined using HPLC/RP-18 reverse phase system. Methanol/water system with different percentages in gradient elution pattern at a flow rate of 1 ml/min and acetonitrile: acetic acid: water system (3.4: 0.2: 96.4) at a flow rate of 1 ml/min as mobile solvents were used. Purity was found to be 99.2 % and 90.3 % respectively.The biodistribution of both 125I-cytarabine and 125I-6-MP resulted from the labelling of the freeze-dried vials was studied by injecting the tracer in tumour bearing mice. The uptake in ascities was ~ 6.9 % and 8.5% per gram after 1 h.p.i. for both 125I-cytarabine and 125I-6-MP respectively. The activity remained associated with the ascitic fluid at 24 h.p.i. was ~ 38 and 30 % for both 125I-cytarabine and 125I-6-MP respectively. Also the clearance of the tracer from the blood was low and the excreted activity was accumulated in urine in the range of 23-28 % after 24 h.p.i. These data demonstrate that a new radiopharmaceutical agent which may be useful for treatment of different types of malignancies was obtained.
|
|
|