Improving the Synthesis of48V labeled [VO(acac)2] andIn Vitro andIn VivoValidation

1060 Objectives: Previous studies utilizing 48V labeled vanadyl (VO2+) chelate bis(acetylacetonato) oxovanadium(IV) [VO(acac)2] in PET and MR [1,2] study of xenograft Caco-2, HCT-116, and HCA-7 colorectal cancer cell line tumors in mice showed relatively low uptakes, despite research showing that VO(acac)2 is an effective contrast agent in MRI for early detection and staging of cancer [3]. To improve compound purity and enhance tumor uptake, the synthesis procedure was revisited following analysis of the cold synthesis [2] and an additional filtration step incorporated [4]. The improved compound was used for cell studies to assess the viability of the HCA-7 cell line as a xenograft model and in-vivo animal studies. We report on the improved synthesis procedure and resulting yields and demonstrate elevated tracer uptake in HCA-7 cells and animal models. Methods: Two thin natural titanium foils were irradiated via the 48Ti(p,n)48V reaction at 40 µA in an 18 MeV IBA cyclotron and left to decay to mitigate short-lived isotopes. The target was dissolved and 48V was isolated via a series of radiochemical steps [5] before being complexed with acetyl acetone under reflux to form 48V-VO(acac)2.While still hot, the solution was passed through a heated fritted glass filter. The filtrate was left to dry to allow VO(acac)2 to crystalize [4]. The VO(acac)2 was then reconstituted in DMSO to prepare for cell and animal studies. To evaluate the compound, half-life analysis and energy spectrum analysis were conducted. HCA-7 cells were grown in McCoy’s 54 medium with 10% FBS (fetal bovine serum). For cell studies, 28 dishes were plated with 5x105 cells each and incubated in 0 to 8 μCi of 48V-VO(acac)2solution at 37°C for 2 hours, washed, and assayed via gamma-ray spectrometry or Molecubes PET. Athymic nude mice were inoculated with 1 - 5 x106 HCA-7 cells and tumors allowed to grow to the appropriate size. Mice were injected with 50-85 µCi of tracer and imaged for four hours via Molecubes PET. After imaging, animals were sacrificed and tumor, muscle, and brain excised for biodistribution studies. Results: Foil irradiation for 87 hours yielded 31.6 mCi. Foils were dissolved in 30 µL HF and 400 µL H2SO4. The 25.2 mCi mixture was transferred to a platinum crucible, neutralized and oxidized at 790°C with a mixture of Na2CO3 and NaNO3 (43:1) for four hours. Several days later to ease radiation shielding, 10.5 mCi was reconstituted with water and centrifuged for 10 minutes at 5000 rpm. The 9.5 mCi supernatant was pipetted off and pH adjusted to 3-4 with HCl, then passed through a Chelex-100 column and eluted with NH3, yielding 5.6 mCi as NH4VO3. The solvent was dried at 300°C before 4.85 mCi was combined with acetyl acetonate and heated under reflux. The solution was passed through a heated, fritted glass filter, yielding 1.49 mCi, a 17% yield with decay corrections. The cell study showed that uptake is linear from 0 - 4 µCi, but plateaus between 4 and 8 µCi. After imaging, cells incubated in up to 4 µCi were still attached to the cell plate, while the cells that had incubated in 8 µCi for this time had died. Animal studies showed 1-2 %ID/mL uptake in tumor, typically higher than the 0.5-1.5 %ID/mL uptake in muscle and the 0.5-1% uptake shown in the brain, but lower than the 3-7% uptake shown in liver and 2-4.5% uptake shown in the kidneys. Conclusions: The yield of this synthesis (17%) was comparable to other runs [1,2] despite an additional filtration, indicating the compound has higher purity with similar yields. Further steps may be implemented in the future to allow the VO(acac)2 to better crystalize and separate, leading to a higher compound purity. The cell uptake curve plateaus after 4 µCi, indicating the maximum activity that can enter the cell is below 4 µCi. Finer sampling between 2 and 4 µCi is needed to determine the threshold. Animal studies demonstrated elevated uptake in tumor compared to other tissues, but high uptake in liver and kidney demonstrate that compound purity could still be improved.