We present a novel solid-phase based 45 Ti radiolabeling methodology and the implementation of 45 Ti-PET in titanium-based antineoplastics using the showcase compound [ 45 Ti](salan)Ti(dipic). This development is intended to allow elucidation of the biodistribution and pharmacokinetics of promising new Ti-based therapeutics.

Pressed chromium-powder cyclotron targets were irradiated with 16MeV protons, producing Mn with average yields of 6.2±0.8MBq/µAh. Separation by solid-phase anion exchange from ethanol-HCl mixtures recovered 94.3±1.7% ofMn and reduced the chromium content by a factor of 2.2±0.4×10. An additional AG 1-X8 column was used to remove copper, iron, cobalt and zinc impurities from the prepared Mn in 8M HCl. The macrocyclic chelator DOTA was rapidly radiolabeled withMn in aq. ammonium acetate (pH 7.5R.T.) with a radiochemical yield >99% within 1min and was stable for >2 days in bovine serum. The improved separation and purification methodology facilitates the use of Mn in basic science and preclinical investigations.

Copolymers of ABC-type (PEG-PHEMA-PCMA) architecture were prepared by atom transfer radical polymerization and formulated as micelles with functionalizable primary alcohols in the shell-region (PHEMA-block) to which the metal-ion chelators DOTA or CB-TE2A were conjugated. Using this micelle system we compared the in vivo stabilities of DOTA and CB-TE2A as chelators of (64)Cu in micelle nanoparticles. The coumarin polymer (PCMA-block) micelle core was cross-linked by UV irradiation at 2 W/cm(2) for 30 min. The cross-linked micelles were labeled with (64)Cu at room temperature for 2 h (DOTA) or 80 °C for 3 h (CB-TE2A), giving labeling efficiencies of 60-76% (DOTA) and 40-47% (CB-TE2A). (64)Cu-micelles were injected into tumor-bearing mice (8 mg/kg) and PET/CT scans were carried out at 1, 22, and 46 h postinjection. The micelles showed good blood stability (T1/2: 20-26 h) and tumor uptake that was comparable with other nanoparticle systems. The DOTA micelles showed a biodistribution similar to the CB-TE2A micelles and the tumor uptake was comparable for both micelle types at 1 h (1.9% ID/g) and 22 h (3.9% ID/g) but diverged at 46 h with 3.6% ID/g (DOTA) and 4.9% ID/g (CB-TE2A). On the basis of our data, we conclude that cross-linked PEG-PHEMA-PCMA micelles have long circulating properties resulting in tumor accumulation and that DOTA and CB-TE2A (64)Cu-chelates show similar in vivo stability for the studied micelle system.

By taking advantage of the ability of Cu to bind nonspecifically to gold surfaces, we have developed a methodology to embed this radionuclide inside gold nanoparticles (AuNPs).Cu enables the in vivo imaging of AuNPs by positron emission tomography (PET). AuNPs have a multitude of uses within health technology and are useful tools for general nanoparticle research. Cu-AuNPs were prepared by incubating AuNP seeds withCu, followed by the entrapment of the radionuclide by grafting on a second layer of gold. This resulted in radiolabeling efficiencies of 53 ± 6%. The radiolabel showed excellent stability when incubated with EDTA for 2 days (95% radioactivity retention) and showed no loss of Cu when incubated with 50% mouse serum for 2 days. The methodology was chelator-free, removing traditional concerns over chelator instability and altered AuNP properties due to surface modification. RadiolabeledCu-AuNP cores were prepared in biomedically relevant sizes of 20-30 nm and used to investigate the in vivo stability of three different AuNP coatings by PET imaging in a murine xenograft tumor model. We found the longest plasma half-life (T about 9 h) and tumor accumulation (3.9%ID/g) to result from a polyethylene glycol coating, while faster elimination from the bloodstream was observed with both a Tween 20-stabilized coating and a zwitterionic coating based on a mixture of sulfonic acids and quaternary amines. In the in vivo model, the Cu was observed to closely follow the AuNPs for each coating, again attributed to the excellent stability of the radiolabel.

Liposomes are nanoparticles used in drug delivery that distribute over several days in humans and larger animals. Radiolabeling with long-lived positron emission tomography (PET) radionuclides, such as manganese-52 (Mn, T½=5.6days), allow the imaging of this biodistribution. We report optimized protocols for radiolabeling liposomes with Mn, through both remote-loading and surface labeling. For comparison, liposomes were also remote-loaded and surface labeled with copper-64 (Cu, T½=12.7h) through conventional means. The chelator DOTA was used in all cases. The in vivo stability of radiometal chelates is widely debated but studies that mimic a realistic in vivo setting are lacking. Therefore, we employed these four radiolabeled liposome types as platforms to demonstrate a new concept for such in vivo evaluation, here of the chelates Mn-DOTA andCu-DOTA. This was done by comparing "shielded" remote-loaded with "exposed" surface labeled variants in a CT26 tumor-bearing mouse model. Remote loading (90min at 55°C) and surface labeling (55°C for 2h) of Mn gave excellent radiolabeling efficiencies of 97-100% and 98-100% respectively, and the liposome biodistribution was imaged by PET for up to 8days. Liposomes with surface-conjugatedMn-DOTA exhibited a significantly shorter plasma half-life (T=14.4h) when compared to the remote-loaded counterpart (T=21.3h), whereas surface-conjugated Cu-DOTA cleared only slightly faster and non-significantly, when compared to remote-loaded (17.2±2.9h versus 20.3±1.2h). From our data, we conclude the successful remote-loading of liposomes withMn, and furthermore that Mn-DOTA may be unstable in vivo whereasCu-DOTA appears suitable for quantitative imaging.