Overexpression of folate receptors (FRs) on different tumor types (e.g., ovarian, lung) make FRs attractive in vivo targets for directed diagnostic/therapeutic agents. Currently, no diagnostic agent suitable for positron emission tomography (PET) has been adopted for clinical FR imaging. In this work, two 55Co-labeled albumin-binding folate derivatives-[55Co]Co-cm10 and [55Co]Co-rf42-with characteristics suitable for PET imaging have been developed and evaluated. High radiochemical yields (≥95%) and in vitro stabilities (≥93%) were achieved for both compounds, and cell assays demonstrated FR-mediated uptake. Both 55Co-labeled folate conjugates demonstrated high tumor uptake of 17% injected activity per gram of tissue (IA/g) at 4 h in biodistribution studies performed in KB tumor-bearing mice. Renal uptake was similar to other albumin-binding folate derivatives, and liver uptake was lower than that of previously reported [64Cu]Cu-rf42. Small animal PET/CT images confirmed the biodistribution results and showed the clear delineation of FR-expressing tumors.

Radionuclide-functionalized drug delivery vehicles capable of being imaged via positron emission tomography (PET) are of increasing interest in the biomedical field as they can reveal the in vivo behavior of encapsulated therapeutics with high sensitivity. However, the majority of current PET-guided theranostic agents suffer from poor retention of radiometal over time, low drug loading capacities, and time-limited PET imaging capability. To overcome these challenges, we have developed hollow microcapsules with a thin (<100 nm) multilayer shell as advanced theranostic delivery systems for multiday PET tracking in vivo. The 3 μm capsules were fabricated via the aqueous multilayer assembly of a natural antioxidant, tannic acid (TA), and a poly(N-vinylpyrrolidone) (PVPON) copolymer containing monomer units functionalized with deferoxamine (DFO) to chelate the 89 Zr radionuclide, which has a half-life of 3.3 days. We have found using radiochromatography that (TA/PVPON-DFO) 6 capsules retained on average 17% more 89 Zr than their (TA/PVPON) 6 counterparts, which suggests that the covalent attachment of the DFO to PVPON provides stable 89 Zr chelation. In vivo PET imaging studies performed in mice demonstrated that excellent stability and imaging contrast were still present 7 days postinjection. Animal biodistribution analyses showed that capsules primarily accumulated in the spleen, liver, and lungs with negligible accumulation in the femur, with the latter confirming the stable binding of the radiotracer to the capsule walls. The application of therapeutic ultrasound (US) (60 s of 20 kHz US at 120 W cm −2 ) to Zr-functionalized capsules could release the hydrophilic anticancer drug doxorubicin from the capsules in the therapeutic amounts. Polymeric capsules with the capability of extended in vivo PET-based tracking and US-induced drug release provide an advanced platform for development of precisiontargeted therapeutic carriers and could aid in the development of more effective drug delivery systems.

Background In molecular imaging and nuclear medicine, theranostic agents that integrate radionuclide pairs are successfully being used for individualized care, which has led to rapidly growing interest in their continued development. These compounds, which are radiolabeled with one radionuclide for imaging and a chemically identical or similar radionuclide for therapy, may improve patient-specific treatment and outcomes by matching the properties of different radionuclides with a targeting vector for a particular tumor type. One proposed theranostic radionuclide is scandium-47 ( 47 Sc, T 1/2 = 3.35 days), which can be used for targeted radiotherapy and may be paired with the positron emitting radionuclides, 43 Sc ( T 1/2 = 3.89 h) and 44 Sc ( T 1/2 = 3.97 h) for imaging. The aim of this study was to investigate the photonuclear production of 47 Sc via the 48 Ti(γ,p) 47 Sc reaction using an electron linear accelerator (eLINAC), separation and purification of 47 Sc, the radiolabeling of somatostatin receptor-targeting peptide DOTATOC with 47 Sc, and in vitro receptor-mediated binding of [ 47 Sc]Sc-DOTATOC in AR42J somatostatin receptor subtype two (SSTR2) expressing rat pancreatic tumor cells. Results The rate of 47 Sc production in a stack of natural titanium foils ( n = 39) was 8 × 10 7 Bq/mA·h ( n = 3). Irradiated target foils were dissolved in 2.0 M H 2 SO 4 under reflux. After dissolution, trivalent 47 Sc ions were separated from natural Ti using AG MP-50 cation exchange resin. The recovered 47 Sc was then purified using CHELEX 100 ion exchange resin. The average decay-corrected two-step 47 Sc recovery ( n = 9) was (77 ± 7)%. A radiolabeling yield of > 99.9% of [ 47 Sc]Sc-DOTATOC (0.384 mg in 0.3 mL) was achieved using 1.7 MBq of 47 Sc. Blocking studies using Octreotide illustrated receptor-mediated uptake of [ 47 Sc]Sc-DOTATOC in AR42J cells. Conclusions 47 Sc can be produced via the 48 Ti(γ,p) 47 Sc reaction and separated from natural Ti targets with a yield and radiochemical purity suitable for radiolabeling of peptides for in vitro studies. The data in this work supports the potential use of eLINACs for studies of photonuclear production of medical radionuc...

A [Tc(CO)(N,S,N)] chelate was employed for radiolabeling of an SSTR-targeting antagonist peptide. Synthesis of TcL-sst-ANT was achieved in high RCY, and the resulting complex displayed high in vitro stability. Somatostatin receptor affinity was retained in both cells and in tumor-bearing mice, where the complex successfully targeted SSTR-positive tumors via a receptor-mediated process. Advances in Knowledge and Implications for Patient Care. This first Tc-tricarbonyl-labeled SSTR antagonist peptide showed promising in vivo tumor targeting in mice. Future studies may lead to translation of a similar design into the clinic.

With the long-term goal of developing theranostic agents for applications in nuclear medicine, in this work we evaluated the well-known NOTA and NODAGA chelators as bifunctional chelators (BFCs) for the [99mTc/186Re]­Tc/Re-tricarbonyl core. In particular, we report model complexes of the general formula fac-[M­(L)­(CO)3]+ (M = Re, 99mTc, 186Re) where L denotes NOTA-Pyr (1) or NODAGA-Pyr (2), which are derived from conjugation of NOTA/NODAGA with pyrrolidine (Pyr). Further, as proof-of-principle, we synthesized the peptide bioconjugate NODAGA-sst2-ANT (3) and explored its complexation with the fac-[Re­(CO)3]+ and fac-[99mTc]­[Tc­(CO)3]+ cores; sst2-ANT denotes the somatostatin receptor (SSTR) antagonist 4-NO2-Phe-c­(DCys-Tyr-DTrp-Lys-Thr-Cys)-DTyr-NH2. Rhenium complexes Re-1 through Re-3 were synthesized and characterized spectroscopically, and receptor binding affinity was demonstrated for Re-3 in SSTR-expressing cells (AR42J, IC50 = 91 nM). Radiolabeled complexes [99mTc]­Tc/[186Re]­Re-1/2 and [99mTc]­Tc-3 were prepared in high radiochemical yield (>90%, determined by radio-HPLC) by reacting [99mTc]/[186Re]­[Tc/Re­(OH2)3(CO)3]+ with 1–3 and correlated well with the respective Re-1 through Re-3 standards in comparative HPLC studies. All radiotracers remained intact through 24 h (99mTc-labeled complexes) or 48 h (186Re-labeled complexes) against 1 mM l-histidine and 1 mM l-cysteine (pH 7.4, 37 °C). Similarly, rat serum stability studies displayed no decomposition and low nonspecific binding of 9–24% through 4 h. Biodistribution of [99mTc]­Tc-3 in healthy CF-1 mice demonstrated a favorable pharmacokinetic profile. Rapid clearance was observed within 1 h post-injection, predominantly via the renal system (82% of the injected dose was excreted in urine by 1 h), with low kidney retention (% ID/g: 11 at 1 h, 5 at 4 h, and 1 at 24 h) and low nonspecific uptake in other organs/tissues. Our findings establish NOTA and NODAGA as outstanding BFCs for the fac-[M­(CO)3]+ core in the design and development of organometallic radiopharmaceuticals. Future in vivo studies of [99mTc]­Tc- and [186Re]­Re-tricarbonyl complexes of NODAGA/NOTA-biomolecule conjugates will further probe the potential of these chelates for nuclear medicine applications in diagnostic imaging and targeted radiotherapy, respectively.

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We demonstrate a scalable method for the separation of the bacterial periplasm from the cytoplasm. This method is used to purify periplasmic protein for the purpose of biophysical characterization, and measure substrate transfer between periplasmic and cytoplasmic compartments. By carefully limiting the time that the periplasm is separated from the cytoplasm, the experimenter can extract the protein of interest and assay each compartment individually for substrate without carry-over contamination between compartments. The extracted protein from fractionation can then be further analyzed for three-dimensional structure determination or substrate-binding profiles. Alternatively, this method can be performed after incubation with a radiotracer to determine total percent uptake, as well as distribution of the tracer (and hence metal transport) across different bacterial compartments. Experimentation with a radiotracer can help differentiate between a physiological substrate and artefactual substrate, such as those caused by mismetallation.X-ray fluorescence can be used to discover the presence or absence of metal incorporation in a sample, as well as measure changes that may occur in metal incorporation as a product of growth conditions, purification conditions, and/or crystallization conditions. X-ray fluorescence also provides a relative measure of abundance for each metal, which can be used to determine the best metal energy absorption peak to use for anomalous X-ray scattering data collection. Radiometal uptake can be used as a method to validate the physiological nature of a substrate detected by X-ray fluorescence, as well as support the discovery of novel substrates.