Improved protocol for the radiosynthesis of [18 F]FTC-146: A potent and selective sigma-1 receptor radioligand.

[18 F]FTC-146 was introduced as a very potent and selective sigma-1 receptor radioligand, which has shown promising application as an imaging agent for neuropathic pain with positron emission tomography. In line with a multi-laboratory project on animal welfare, we chose this radioligand to investigate its potential for detecting neuropathic pain and tissue damage in tumor-bearing animals. However, the radiochemical yield (RCY) of around 4-7% was not satisfactory to us, and efforts were made to improve it. Herein, we describe an improved approach for the radiosynthesis of [18 F]FTC-146 resulting in a RCY, which is sevenfold higher than that previously reported. A tosylate precursor was synthesized and radio-fluorination experiments were performed via aliphatic nucleophilic substitution reactions using either K[18 F]F-Kryptofix®222 (K2.2.2 )-carbonate system or tetra-n-butylammonium [18 F]fluoride ([18 F]TBAF). Several parameters affecting the radiolabeling reaction such as solvent, 18 F-fluorination agent with the corresponding amount of base, labeling time, and temperature were investigated. Best labeling reaction conditions were found to be [18 F]TBAF and acetonitrile as solvent at 100°C. The new protocol was then translated to an automated procedure using a FX2 N synthesis module. Finally, the radiotracer reproducibly obtained with RCYs of 41.7 ± 4.4% in high radiochemical purity (>98%) and molar activities up to 171 GBq/µmol.

Targeting of prostate-specific membrane antigen for radio-ligand therapy of triple-negative breast cancer.

BACKGROUND: Triple-negative breast cancer has extremely high risk of relapse due to the lack of targeted therapies, intra- and inter-tumoral heterogeneity, and the inherent and acquired resistance to therapies. In this study, we evaluate the potential of prostate-specific membrane antigen (PSMA) as target for radio-ligand therapy (RLT). METHODS: Tube formation was investigated after incubation of endothelial HUVEC cells in tumor-conditioned media and monitored after staining using microscopy. A binding study with 68Ga-labeled PSMA-addressing ligand was used to indicate targeting potential of PSMA on tumor-conditioned HUVEC cells. For mimicking of the therapeutic application, tube formation potential and vitality of tumor-conditioned HUVEC cells were assessed following an incubation with radiolabeled PSMA-addressing ligand [177Lu]-PSMA-617. For in vivo experiments, NUDE mice were xenografted with triple-negative breast cancer cells MDA-MB231 or estrogen receptor expressing breast cancer cells MCF-7. Biodistribution and binding behavior of [68Ga]-PSMA-11 was investigated in both tumor models at 30 min post injection using µPET. PSMA- and CD31-specific staining was conducted to visualize PSMA expression and neovascularization in tumor tissue ex vivo. RESULTS: The triple-negative breast cancer cells MDA-MB231 showed a high pro-angiogenetic potential on tube formation of endothelial HUVEC cells. The induced endothelial expression of PSMA was efficiently addressed by radiolabeled PSMA-specific ligands. 177Lu-labeled PSMA-617 strongly impaired the vitality and angiogenic potential of HUVEC cells. In vivo, as visualized by µPET, radiolabeled PSMA-ligand accumulated specifically in the triple-negative breast cancer xenograft MDA-MB231 (T/B ratio of 43.3 ± 0.9), while no [68Ga]-PSMA-11 was detected in the estrogen-sensitive MCF-7 xenograft (T/B ratio of 1.1 ± 0.1). An ex vivo immunofluorescence analysis confirmed the localization of PSMA on MDA-MB231 xenograft-associated endothelial cells and also on TNBC cells. CONCLUSIONS: Here we demonstrate PSMA as promising target for two-compartment endogenous radio-ligand therapy of triple-negative breast cancer.

Modulation of glutathione promotes apoptosis in triple-negative breast cancer cells.

Triple-negative breast cancer has an extremely high rate of relapse. This is particularly due to the existence and survival of cancer stem cells (CSCs) characterized by increased amounts of glutathione (GSH). In this study, we evaluated the potential of pharmacological GSH depletion to sensitize CSCs to ionizing radiotherapy with an I-125-labeled nucleoside analog, 5-iodo-4'-thio-2'-deoxyuridine (ITdU). CSCs were isolated using CD24-- and CD44+-specific microbeads. GSH and reactive oxygen species (ROS) were evaluated by fluorescence-activated cell sorting. GSH synthesis was inhibited with buthionine sulfoximine (BSO). Apoptotic cells were identified with propidium iodide and double-strand DNA breaks were detected by γ-H2AX staining. For therapy study, BSO treated and untreated mice xenografted with breast CSCs received weekly I-125-ITdU. Therapy efficiency was monitored by fluorodeoxyglucose-18-µ-positron emission tomography. We showed that GSH modulation sensitizes CD24- and CD44+ breast cancer cells to endogenous nanoradiotherapy. BSO synergistically affects ROS generation induced by I-125-ITdU. In an in vivo study, we demonstrated a complete tumor regression as a consequence of preconditioning with a GSH-synthesis inhibitor prior to treatment with I-125-ITdU. GSH modulation in combination with an oxidative stress-generating treatment such as endogenous radiotherapy using an Auger emitter offers an extraordinary opportunity for selective and efficient eradication of drug-resistant CSCs.-Miran, T., Vogg, A. T. J., Drude, N., Mottaghy, F. M., Morgenroth, A. Modulation of glutathione promotes apoptosis in triple-negative breast cancer cells.

Protein kinase-D1 overexpression prevents lipid-induced cardiac insulin resistance.

In the insulin resistant heart, energy fuel selection shifts away from glucose utilization towards almost complete dependence on long-chain fatty acids (LCFA). This shift results in excessive cardiac lipid accumulation and eventually heart failure. Lipid-induced cardiomyopathy may be averted by strategies that increase glucose uptake without elevating LCFA uptake. Protein kinase-D1 (PKD1) is involved in contraction-induced glucose, but not LCFA, uptake allowing to hypothesize that this kinase is an attractive target to treat lipid-induced cardiomyopathy. For this, cardiospecific constitutively active PKD1 overexpression (caPKD1)-mice were subjected to an insulin resistance-inducing high fat-diet for 20-weeks. Substrate utilization was assessed by microPET and cardiac function by echocardiography. Cardiomyocytes were isolated for measurement of substrate uptake, lipid accumulation and insulin sensitivity. Wild-type mice on a high fat-diet displayed increased basal myocellular LCFA uptake, increased lipid deposition, greatly impaired insulin signaling, and loss of insulin-stimulated glucose and LCFA uptake, which was associated with concentric hypertrophic remodeling. The caPKD1 mice on high-fat diet showed none of these characteristics, whereas on low-fat diet a shift towards cardiac glucose utilization in combination with hypertrophy and ventricular dilation was observed. In conclusion, these data suggest that PKD pathway activation may be an attractive therapeutic strategy to mitigate lipid accumulation, insulin resistance and maladaptive remodeling in the lipid-overloaded heart, but this requires further investigation.

Correction: Sankaranarayanan et al. Auger Emitter Conjugated PARP Inhibitor for Therapy in Triple Negative Breast Cancers: A Comparative In-Vitro Study. Cancers 2022, 14, 230.

The authors wish to replace the 'Author Contributions' statement and the affiliation for Jochen Maurer of this article [...].

Targeted endoradiotherapy using nucleotides.

Increased cellular proliferation is an integral part of the cancer phenotype. Hence, the sustained and continued demand on supply of DNA building blocks during the DNA replication presents a potential target for therapeutic intervention. For this propose, the α and Auger electron emitting nucleotides analogs are attractive for targeted endoradiotherapy, given that DNA of malignant cells is selectively addressed. This review summarizes development and preclinical and clinical studies of endoradiotherapeutic acting nucleoside analogs with a special focus on thymidine analogs.

Auger Emitter Conjugated PARP Inhibitor for Therapy in Triple Negative Breast Cancers: A Comparative In-Vitro Study.

PARP1 inhibitors (PARPi) are currently approved for BRCAmut metastatic breast cancer, but they have shown limited response in triple negative breast cancer (TNBC) patients. Combination of an Auger emitter with PARPis enables PARP inhibition and DNA strand break induction simultaneously. This will enhance cytotoxicity and additionally allow a theranostic approach. This study presents the radiosynthesis of the Auger emitter [125I] coupled olaparib derivative: [125I]-PARPi-01, and its therapeutic evaluation in a panel of TNBC cell lines. Specificity was tested by a blocking assay. DNA strand break induction was analysed by γH2AX immunofluorescence staining. Cell cycle analysis and apoptosis assays were studied using flow cytometry in TNBC cell lines (BRCAwt/mut). Anchorage independent growth potential was evaluated using soft agar assay. [125I]-PARPi-01 showed PARP1-specificity and higher cytotoxicity than olaparib in TNBC cell lines irrespective of BRCA their status. Cell lines harbouring DNA repair deficiency showed response to [125I]-PARPi-01 monotherapy. Combined treatment with Dox-NP further enhanced therapeutic efficiency in metastatic resistant BRCAwt cell lines. The clonogenic survival was significantly reduced after treatment with [125I]-PARPi-01 in all TNBC lines investigated. Therapeutic efficacy was further enhanced after combined treatment with chemotherapeutics. [125I]-PARPi-01 is a promising radiotherapeutic agent for low radiation dosages, and mono/combined therapies of TNBC.

PARP targeted Auger emitter therapy with [125I]PARPi-01 for triple-negative breast cancer.

BACKGROUND: Triple-negative breast cancer (TNBC) lacks biomarkers for targeted therapy. Auger emitters display the best therapeutic effect, if delivered directly into the nucleus proximal to DNA. The nuclear protein Poly (ADP-ribose)-Polymerase 1 (PARP1) is a suitable target against which few inhibitors (PARPi) are clinically approved for treatment of breast cancer with germline BRCA mutation (BRCAmut). In this study, a theranostic approach was investigated in a TNBC xenografted mouse model by radiolabelling a close derivative of a PARPi Olaparib (termed PARPi-01) with the Auger emitters 123/125I. METHODS: TNBC cell line MDA-MB-231 was subcutaneously implanted in female NOD/SCID mice. At a tumour size of ~ 500mm3, [123I]PARPi-01 was administered intravenously, and SPECT/CT images were obtained at 4 h or 24 h post injection (p.i). A therapy study was performed with [125I]PARPi-01 in 4 doses (10 MBq/dose, 10 days apart). Tumour growth was monitored by CT scans longitudinally once per week. Upon reaching study endpoint, tissues were harvested and stained with TUNEL assay for detection of apoptosis induction. RESULTS: SPECT/CT images showed rapid hepatobiliary tracer clearance at 4 h post injection (p.i.). Retention in thyroid at 24 h p.i. suggested tracer deiodination in vivo. The tumour and liver uptake were 0.2%ID/g and 2.5%ID/g, respectively. The tumour: blood ratio was 1.3. Endogenous therapy induced a significant delay in tumour growth (doubling time increased from 8.3 to 14.2 days), but no significant survival advantage. Significantly higher apoptosis ratio was observed in [125I]PARPi-01 treated tumour tissues. No radiotoxicity was detected in the liver and thyroid. CONCLUSION: Considering the radio-cytotoxic effect in the tumour tissue and a delay on tumour doubling time, [125I]PARPi-01 presents a potential radiotherapeutics for treatment of TNBC. Improvements to overcome the suboptimal pharmacokinetics are necessary for its potential clinical application.

Labelling via [Al18F]2+ Using Precomplexed Al-NODA Moieties.

Over the past 20 years, 68Ga-labelled radiopharmaceuticals have become an important part in clinical routine. However, the worldwide supply with 68Ge/68Ga generators is limited as well as the number of patient doses per batch of 68Ga radiopharmaceutical. In the recent years, a new technique appeared, making use of the ease of aqueous labelling via chelators as with 68Ga but using 18F instead. This technique takes advantage of the strong coordinative bond between aluminium and fluoride, realized in the aqueous cation [Al18F]2+. Most applications to date make use of one-pot syntheses with free Al(III) ions in the system. In contrast, we investigated the labelling approach split into two steps: generating the Al-bearing precursor in pure form and using this Al compound as a precursor in the labelling step with aqueous [18F]fluoride. Hence, no free Al3+ ions are present in the labelling step. We investigated the impact of parameters: temperature, pH, addition of organic solvent, and reaction time using the model chelator NH2-MPAA-NODA. With optimized parameters we could stably achieve a 80% radiochemical yield exerting a 30-min reaction time at 100 °C. This technique has the potential to become an important approach in radiopharmaceutical syntheses.

Preferential tumor targeting and selective tumor cell cytotoxicity of 5-[131/125I]iodo-4'-thio-2'-deoxyuridine.

PURPOSE: Auger electron emitting radiopharmaceuticals are attractive for targeted nanoirradiation therapy, provided that DNA of malignant cells is selectively addressed. Here, we examine 5-[123/125/131I]iodo-4'-thio-2'-deoxyuridine (ITdU) for targeting DNA in tumor cells in a HL60 xenograft severe combined immunodeficient mouse model. EXPERIMENTAL DESIGN: Thymidine kinase and phosphorylase assays were done to determine phosphorylation and glycosidic bond cleavage of ITdU, respectively. The biodistribution and DNA incorporation of ITdU were determined in severe combined immunodeficient mice bearing HL60 xenografts receiving pretreatment with 5-fluoro-2'-deoxyuridine (FdUrd). Organ tissues were dissected 0.5, 4, and 24 h after radioinjection and uptake of [131I]ITdU (%ID/g tissue) was determined. Cellular distribution of [125I]ITdU was imaged by microautoradiography. Apoptosis and expression of the proliferation marker Ki-67 were determined by immunohistologic staining using corresponding paraffin tissue sections. RESULTS: ITdU is phosphorylated by thymidine kinase 1 and stable toward thymidylate phosphatase-mediated glycosidic bond cleavage. Thymidylate synthase-mediated deiodination of [123/125/131I]ITdU was inhibited with FdUrd. Pretreatment with FdUrd increased preferentially tumor uptake of ITdU resulting in favorable tumor-to-normal tissue ratios and tumor selectivity. ITdU was exclusively localized within the nucleus and incorporated into DNA. In FdUrd-pretreated animals, we found in more than 90% of tumor cells apoptosis induction 24 h postinjection of ITdU, indicating a highly radiotoxic effect in tumor cells but not in cells of major proliferating tissues. CONCLUSION: ITdU preferentially targets DNA in proliferating tumor cells and leads to apoptosis provided that the thymidylate synthase is inhibited.

Optimization of the reduction of 74As(V) to 74As(III) and of the labelling of dithiol dihydrolipoic acid.

The radiochemical separation of n.c.a. arsenic on its own or for radio-labelling purposes usually involves the issue of reducing arsenic(V). Numerous approaches for reducing pentavalent arsenic have been examined. A novel HPLC method has also been presented for accessing the efficiency of the reduction in terms of *As(III)/*As(V). Labelling with trivalent radioarsenic seems to be a promising research field to access new radiopharmaceuticals, for example, using arsenic as a surrogate for phosphorus. Moreover, as a model system, the labelling reaction of *As(III) with dihydrolipoic acid has been systematically optimized.

Relevant tumor sink effect in prostate cancer patients receiving 177Lu-PSMA-617 radioligand therapy.

AIM: In metastatic prostate cancer patients PSMA targeting radioligands have gained significant impact as theranostic probes. In this study a correlation between total tumor volume (TTV) and measured kidney dose as well as salivary glands (SG) uptake in 177Lu-PSMA-617 therapy was evaluated. METHODS: Eleven consecutive prostate cancer patients receiving a first cylcle of 177Lu-PSMA-617 (administered activity of approximately 6GBq) were included. The 68Ga-PSMA-11 PET/CT scan previous to therapy was used to determine TTV and SG uptake (glandulae submandibularis) employing PMOD version 3.403 with different 68Ga-PSMA-11 thresholds based on the standardized uptake value (SUV).The kidney dose was estimated with the software ULMDOS using planar whole-body scintigrams. RESULTS: Kidney dose and SG uptake was inversely correlated to TTV, indicating high kidney dose and high SG uptake in case of low tumor load and low kidney dose and low SG uptake in case of high tumor load. CONCLUSION: Our data support the hypothesis that in 177Lu-PSMA-617 therapy an individualized treatment activity based on total tumor volume could be beneficiary.

123I-ITdU-mediated nanoirradiation of DNA efficiently induces cell kill in HL60 leukemia cells and in doxorubicin-, beta-, or gamma-radiation-resistant cell lines.

UNLABELLED: Resistance to radiotherapy or chemotherapy is a common cause of treatment failure in high-risk leukemias. We evaluated whether selective nanoirradiation of DNA with Auger electrons emitted by 5-(123)I-iodo-4'-thio-2'-deoxyuridine ((123)I-ITdU) can induce cell kill and break resistance to doxorubicin, beta-, and gamma-irradiation in leukemia cells. METHODS: 4'-thio-2'-deoxyuridine was radiolabeled with (123/131)I and purified by high-performance liquid chromatography. Cellular uptake, metabolic stability, DNA incorporation of (123)I-ITdU, and the effect of the thymidylate synthase (TS) inhibitor 5-fluoro-2'-deoxyuridine (FdUrd) were determined in HL60 leukemia cells. DNA damage was assessed with the comet assay and quantified by the olive tail moment. Apoptosis induction and irradiation-induced apoptosis inhibition by benzoylcarbonyl-Val-Ala-Asp-fluoromethyl ketone (z-VAD.fmk) were analyzed in leukemia cells using flow cytometry analysis. RESULTS: The radiochemical purity of ITdU was 95%. Specific activities were 900 GBq/micromol for (123)I-ITdU and 200 GBq/micromol for (131)I-ITdU. An in vitro cell metabolism study of (123)I-ITdU with wild-type HL60 cells demonstrated an uptake of 1.5% of the initial activity/10(6) cells of (123)I-ITdU. Ninety percent of absorbed activity from (123)I-ITdU in HL60 cells was specifically incorporated into DNA. (123)I-ITdU caused extensive DNA damage (olive tail moment > 12) and induced more than 90% apoptosis in wild-type HL60 cells. The broad-spectrum inhibitor of caspases zVAD-fmk reduced (123)I-ITdU-induced apoptosis from more than 90% to less than 10%, demonstrating that caspases were central for (123)I-ITdU-induced cell death. Inhibition of TS with FdUrd increased DNA uptake of (123)I-ITdU 18-fold and the efficiency of cell kill about 20-fold. In addition, (123)I-ITdU induced comparable apoptotic cell death (>90%) in sensitive parental leukemia cells and in leukemia cells resistant to beta-irradiation, gamma-irradiation, or doxorubicin at activities of 1.2, 4.1, 12.4, and 41.3 MBq/mL after 72 h. This finding indicates that (123)I-ITdU breaks resistance to beta-irradiation, gamma-irradiation, and doxorubicin in leukemia cells. CONCLUSION: (123)I-ITdU-mediated nanoirradiation of DNA efficiently induced apoptosis in sensitive and resistant leukemia cells against doxorubicin, beta-irradiation, and gamma-irradiation and may provide a novel treatment strategy for overcoming resistance to conventional radiotherapy or chemotherapy in leukemia. Cellular uptake and cell kill are highly amplified by inhibiting TS with FdUrd.

Synthesis and biodistribution of 3'-fluoro-5-[(131)I]iodo-2'-deoxyuridine: a comparative study of [(131)I]FLIdU and [(18)F]FLT.

The radioiodinated 3'-fluorothymidine (FLT) analogue 3'-fluoro-5-[(131)I]iodo-2'-deoxyuridine ([(131)I]FLIdU) was synthesized, with iodine mimicking the methyl group of pyrimidine. [(131)I]FLIdU was accessible by direct electrophilic iodination using Iodogen as oxidant. Optimized amounts of the oxidant allowed radiochemical yields of about 70% after a reaction time of 10 min in an aqueous buffer medium at 90 degrees C. The uptake of [(131)I]FLIdU in a DoHH2 leukemia xenograft mouse model and in healthy mice revealed moderate FLIdU accumulation, followed by a significant washout of activity in proliferating tissues such as splenic and tumor tissues. In contrast, intraperitoneal coinjection with [(18)F]FLT showed high uptake and high activity retention up to 2 h, in both splenic and tumor tissues. Uptake in stomach tissues and increasing fractions of [(131)I]iodide in urine indicated metabolic instability of [(131)I]FLIdU due to rapid deiodination. Therefore, [(131)I]FLIdU alone does not seem to be a promising compound, neither for diagnostic imaging nor for potential therapeutic applications.

Radioiodinated indomethacin amide for molecular imaging of cyclooxygenase-2 expressing tumors.

Cyclooxygenase-2 (COX-2) is an important biomarker in several tumors. Available imaging probes display relatively low tumor to background ratios (smaller than 2:1). We evaluated newly developed indomethacin (Ind) derivatives for in vivo molecular imaging of COX-2 expressing carcinoma. Radioiodinated Ind derivatives Ind-NH-(CH2)4-NH-3-[I-125]I-Bz ([I-125]5), Ind-NH-(CH2)4-NH-5-[I-124/125]I-Nic ([I-124/125]6) and Ind-NH-(CH2)4-NH-5-[I-125]I-Iphth ([I-125]7) were prepared from the respective SnBu3-precursors (45-80% radiochemical yield; > 95% radiochemical purity). The cellular uptake of [I-125]5 and [I-125]6 correlated with COX-2 expression determined by SDS page/Western blot analysis. [I-125]5 was predominantly localized in the cell membrane while [I-125]6 was internalized and displayed a diffuse and favorable cytoplasmic distribution. In contrast, [I-125]7 showed only low uptake in COX-2 positive cells. Co-incubation with the COX-2 inhibitor Celecoxib led to an almost complete suppression of cellular uptake of [I-125]5 and [I-125]6. In vivo molecular imaging using positron emission tomography (PET) in SCID mice xenografted with COX-2+ (HT29) and COX-2- (HCT116) human colorectal carcinoma cells was performed for [I-124]6. HT29 xenografts displayed a significantly higher uptake than HCT-116 xenografts (5.6 ± 1.5 vs. 0.5 ± 0.1 kBq/g, P < 0.05) with an extraordinary high tumor to muscle ratio (50.3 ± 1.5). Immunohistological staining correlated with the imaging data. In conclusion, the novel radioiodinated indomethacin derivative ([I-124/125]6) could become a valuable tool for development of molecular imaging probes for visualization of COX-2 expressing tumors.

Dual addressing of thymidine synthesis pathways for effective targeting of proliferating melanoma.

Here, we examined the potential of blocking the thymidine de novo synthesis pathways for sensitizing melanoma cells to the nucleoside salvage pathway targeting endogenous DNA irradiation. Expression of key nucleotide synthesis and proliferation enzymes thymidylate synthase (TS) and thymidine kinase 1 (TK1) was evaluated in differentiated (MITFhigh [microphthalmia-associated transcription factor] IGR1) and invasive (MITFmedium IGR37) melanoma cells. For inhibition of de novo pathways cells were incubated either with an irreversible TS inhibitor 5-fluoro-2'-deoxyuridine (FdUrd) or with a competitive dihydrofolate-reductase (DHFR) inhibitor methotrexate (MTX). Salvage pathway was addressed by irradiation-emitting thymidine analog [123/125 I]-5-iodo-4'-thio-2'-deoxyuridine (123/125 I-ITdU). The in vivo targeting efficiency was visualized by single-photon emission computed tomography. Pretreatment with FdUrd strongly increased the cellular uptake and the DNA incorporation of 125 I-ITdU into the mitotically active IGR37 cells. This effect was less pronounced in the differentiated IGR1 cells. In vivo, inhibition of TS led to a high and preferential accumulation of 123 I-ITdU in tumor tissue. This preclinical study presents profound rationale for development of therapeutic approach by highly efficient and selective radioactive targeting one of the crucial salvage pathways in melanomas.

Synthesis and evaluation of a radiometal-labeled macrocyclic chelator-derivatised thymidine analog.

Several radiolabeled thymidine analogs as metabolic probes of cell proliferation were developed specifically addressing DNA synthesis. Thymidine analogs containing carboranylalkyl groups for neutron capture therapy at the N-3 position were found to be good substrates for cytosolic thymidine kinase 1 (TK1). According to this approach, a DO3A macrocycle in N-3 position was attached to thymidine. The 3-DO3A thymidine analog was labeled with 68Ga and 111In. Different lipophilicities of the corresponding radiometal-thymidines were detected via RP-HPLC. [111In]DO3A-thymidine ([111In]D3T) was evaluated for cellular uptake in different cell lines (HL60 and DoHH2). Cellular uptake was low in both cell lines. Phosphorylation of the radioconjugates by TK1 was negligible. Although stable complexation of radiometals to thymidine was obtained, introduction of the macrocycle DO3A reduced the affinity to cytosolic TK1 drastically. Low cellular uptake can be ascribed to missing substrate specificity of [111In]DO3A-thymidine for TK1. The absence of substrate specificity may be due to the bulky macrocyclic chelator and partial charges remaining on the coordination sphere due to a more complex solution structure.

Assessing the Intracellular Integrity of Phosphine-Stabilized Ultrasmall Cytotoxic Gold Nanoparticles Enabled by Fluorescence Labeling.

As the size of nanoparticles (NPs) is in the range of biological molecules and subcellular structures, they provide new perspectives in biomedicine. This work presents studies concerning the cellular uptake and distribution of phosphine-stabilized cytotoxic 1.4 nm sized AuNPs and their probable degradation during this process. Therefore, ultrasmall phosphine-stabilized AuNPs are modified by linking a fluorophore covalently to the ligand shell. Monitoring the fluorescence on a cellular level by means of flow cytometry and confocal laser scanning microscopy allows determining the fate of the ligand shell during AuNP cell internalization, due to the fact that the fluorescence of a fluorophore bound near to the AuNP surface is quenched. Cell fractionation is conducted in order to quantify the AuNP content at the cell membrane, in the cytoplasm, and the cell nucleus. The incubation of cells with the fluorophore-modified AuNPs reveals a partial loss of the ligand shell upon AuNP cell interaction, evident by the emerging fluorescence signal. This loss is the precondition to unfold high AuNP cytotoxicity. Together with their significantly different biodistribution and enhanced circulation times compared to larger AuNPs, the findings demonstrate the high potential of ultrasmall AuNPs for drug development or therapy.

[18F]5-fluoro-2-deoxyuridine-PET for imaging of malignant tumors and for measuring tissue proliferation.

The nucleoside 5-fluoro-2-deoxyuridine is a pyrimidine analogue accumulating in proliferative cells. We prospectively evaluated biodistribution of the PET tracer [(18)F]5-fluoro-2-deoxyuridine (FdUrd), its value for imaging malignant tumors, and its correlation to both [(18)F]2-fluoro-2-deoxyglucose (FDG)-PET findings and histological proliferation indices. In 11 previously untreated patients (5 lung carcinoma; 3 soft tissue sarcoma; 2 gastrointestinal carcinoma; 1 non-Hodgkin lymphoma [NHL]), mean doses of 290 MBq FdUrd and 390 MBq FDG were administered intravenously on subsequent days. Static PET scans were initiated 50-70 min after administration and the mean standardized uptake values (SUV) were calculated. Dynamic emission FdUrd scans were performed in 8/11 patients. Time-activity curves of blood and tumors as well as SUV of tumor lesions and organs were calculated. Proliferative activity was evaluated by Ki-67 immunohistostaining of biopsies. Tracer accumulated physiologically in liver, kidney, and bladder. SUVs were: kidney, 4.8 +/- 0.66; liver, 4.1 +/- 0.36; vertebrae, 0.70 +/- 0.17; spleen, 0.37 +/- 0.06; lungs, 0.19 +/- 0.05; femora/humeri, 0.14 +/- 0.03. Five patients exhibited significant intratumoral FdUrd-uptake (2 sarcomas; 1 NHL; 2 lung carcinomas) with mean SUVs ranging from 0.7 to 10.5. Metastases were not detected. Time-activity curves showed a rapid initial increase of intratumoral activity followed by activity retention. FDG-PET was positive in 10/11 patients. Correlation between the SUV of FdUrd-PET and FDG-PET or the tissue proliferation index, respectively, was not significant. FdUrd was a suitable tracer for imaging malignant tumors only in exceptional cases: Sarcoma, NHL, and some lung carcinomas were detected. FdUrd-PET was less effective than FDG-PET. In this group of patients, it was not useful in measuring tissue proliferation.