Search

The overexpression of one or more somatostatin receptors (SST1–5R) in human tumors has provided an opportunity for diagnosis and therapy with somatostatin-like radionuclide carriers. The application of “pansomatostatin” analogs is expected to broaden the clinical indications and upgrade the diagnostic/therapeutic efficacy of currently applied SST2R-prefering radioligands. In pursuit of this goal, we now introduce two bicyclic somatostatin-14 (SS14) analogs, AT5S (DOTA-Ala1-Gly2-c[Cys3-Lys4-Asn5-c[Cys6-Phe7-DTrp8-Lys9-Thr10-Cys11]-Thr12-Ser13-Cys14]) and AT6S (DOTA-Ala1-Gly2-c[Cys3-Lys4-c[Cys5-Phe6-Phe7-DTrp8-Lys9-Thr10-Phe11-Cys12]-Ser13-Cys14]), suitable for labeling with trivalent radiometals and designed to sustain in vivo degradation. Both AT5S and AT6S and the respective [111In]In-AT5S and [111In]In-AT6S were evaluated in a series of in vitro assays, while radioligand stability and biodistribution were studied in mice. The 8/12-mer bicyclic AT6S showed expanded affinity for all SST1–5R and agonistic properties at the SST2R, whereas AT5S lost all affinity to SST1–5R. Both [111In]In-AT5S and [111In]In-AT6S remained stable in the peripheral blood of mice, while [111In]In-AT6S displayed low, but specific uptake in AR4-2J tumors and higher uptake in HEK293-SST3R tumors in mice. In summary, high radioligand stability was acquired by the two disulfide bridges introduced into the SS14 motif, but only the 8/12-mer ring AT6S retained a pansomatostatin profile. In consequence, [111In]In-AT6S targeted SST2R-/SST3R-po

Peptide receptor radionuclide therapy (PRRT) has been applied to the treatment of neuroendocrine tumors (NETs) for over two decades. However, improvement is still needed, and targeted alpha therapy (TAT) with alpha emitters such as lead-212 (212Pb) represents a promising avenue. A series of ligands based on octreotate was developed. Lead-203 was used as an imaging surrogate for the selection of the best candidate for the studies with lead-212. 203/212Pb radiolabeling and in vitro assays were carried out, followed by SPECT/CT imaging and ex vivo biodistribution in NCI-H69 tumor-bearing mice. High radiochemical yields (≥99%) and purity (≥96%) were obtained for all ligands. [203Pb]Pb-eSOMA-01 and [203Pb]Pb-eSOMA-02 showed high stability in PBS and mouse serum up to 24 h, whereas [203Pb]Pb-eSOMA-03 was unstable in those conditions. All compounds exhibited a nanomolar affinity (2.5–3.1 nM) for SSTR2. SPECT/CT images revealed high tumor uptake at 1, 4, and 24 h post-injection of [203Pb]Pb-eSOMA-01/02. Ex vivo biodistribution studies confirmed that the highest uptake in tumors was observed with [212Pb]Pb-eSOMA-01. [212Pb]Pb-eESOMA-01 displayed the highest absorbed dose in the tumor (35.49 Gy/MBq) and the lowest absorbed dose in the kidneys (121.73 Gy/MBq) among the three tested radioligands. [212Pb]Pb-eSOMA-01 is a promising candidate for targeted alpha therapy of NETs. Further investigations are required to confirm its potential.

Targeted radionuclide therapy (TRT) is a promising strategy to treat different types of cancer. TRT relies on a targeting vector used to deliver a therapeutic radionuclide specifically to the tumour site. Several low molecular weight ligands targeting the prostate-specific membrane antigen (PSMA) have been synthesized, but their pharmacokinetic properties still need to be optimized. Hereby, we describe the synthesis of new conjugates, featuring the cleavable linkers Gly-Tyr-Lys (GYK) and Met-Val-Lys (MVK), to reduce the dose delivered to the kidneys. Compounds were synthesized by solid-phase peptide synthesis (SPPS) and obtained in greater than 95% chemical purity. Radiolabelling was performed with both In-111 and Lu-177 to validate potential use of the compounds as both imaging and therapeutic agents. Radiochemical purity greater than 80% was obtained for both nuclides, but significant radiolysis was observed for the methionine-containing analogue. The results obtained thus far with the GYK-PSMA conjugate could warrant further biological investigations.

Peptide receptor radionuclide therapy (PRRT), a form of internal targeted radiation treatment using [177Lu]Lu [DOTA0-Tyr3]octreotate, is used to treat patients with metastasized neuroendocrine tumors (NETs). Even though PRRT is now the second line of treatment for patients with metastasized NETs, the majority of patients will not be cured by the treatment. PRRT functions by inducing DNA damage upon radioactive decay and inhibition of DNA damage repair proteins could therefore be used as a strategy to potentiate PRRT. Previous work has shown promising results on the combination of PRRT with the PARP inhibitor olaparib in cell lines and mice and we have been taken the next step for further in vivo validation using two different xenografted mouse models. We observed that this combination therapy resulted in increased therapeutic efficacy only in one model and not the other. Overall, our findings indicate a tumor-type dependent anti-tumor response to the combination of PRRT and olaparib. These data emphasize the unmet need for the molecular stratification of tumors to predetermine the potential clinical value of combining PARP inhibition with PRRT.

Prostate specific membrane antigen targeted radionuclide therapy (PSMA-TRT) is a promising novel treatment for prostate cancer (PCa) patients. However, PSMA-TRT cannot be used for curative intent yet, thus additional research on how to improve the therapeutic efficacy is warranted. A potential way of achieving this, is combining TRT with poly ADP-ribosylation inhibitors (PARPi), which has shown promising results for TRT of neuroendocrine tumor cells. Currently, several clinical trials have been initiated for this combination for PCa, however so far, no evidence of synergism is available for PCa. Therefore, we evaluated the combination of PSMA-TRT with three classes of PARPi in preclinical PCa models. In vitro viability and survival assays were performed using PSMA-expressing PCa cell lines PC3-PIP and LNCaP to assess the effect of increasing concentrations of PARPi veliparib, olaparib or talazoparib in combination with PSMA-TRT compared to single PARPi treatment. Next, DNA damage analyses were performed by quantifying the number of DNA breaks by immunofluorescent stainings. Lastly, the potential of the combination treatments was studied in vivo in mice bearing PC3-PIP xenografts. Our results show that combining PSMA-TRT with PARPi did not synergistically affect the in vitro clonogenic survival or cell viability. DNA-damage analysis revealed only a significant increase in DNA breaks when combining PSMA-TRT with veliparib and not in the other combination treatments. Moreover, PSMA-TRT with PARPi treatment did not improve tumor control compared to PSMA-TRT monotherapy. Overall, the data presented do not support the assumption that combining PSMA-TRT with PARPi leads to a synergistic antitumor effect in PCa. These results underline that extensive preclinical research using various PCa models is imperative to validate the applicability of the combination strategy for PCa, as it is for other cancer types.

Somatostatin receptor subtype 2 (SSTR2) has become an essential target for radionuclide therapy of neuroendocrine tumors (NETs). JR11 was introduced as a promising antagonist peptide to target SSTR2. However, due to its rapid blood clearance, a better pharmacokinetic profile is necessary for more effective treatment. Therefore, two JR11 analogs (8a and 8b), each carrying an albumin binding domain, were designed to prolong the blood residence time of JR11. Both compounds were labeled with lutetium-177 and evaluated via in vitro assays, followed by in vivo SPECT/CT imaging and ex vivo biodistribution studies. [Lu-177]Lu-8a and [Lu-177]Lu-8b were obtained with high radiochemical purity (>97%) and demonstrated excellent stability in PBS and mouse serum (>95%). [Lu-177]Lu-8a showed better affinity towards human albumin compared to [Lu-177]Lu-8b. Further, 8a and 8b exhibited binding affinities 30- and 48-fold lower, respectively, than that of the parent peptide JR11, along with high cell uptake and low internalization rate. SPECT/CT imaging verified high tumor accumulation for [Lu-177]Lu-8a and [Lu-177]Lu-JR11 at 4, 24, 48, and 72 h post-injection, but no tumor uptake was observed for [Lu-177]Lu-8b. Ex vivo biodistribution studies revealed high and increasing tumor uptake for [Lu-177]Lu-8a. However, its extended blood circulation led to an unfavorable biodistribution profile for radionuclide therapy.

Purpose: The radiolabeled gastrin-releasing peptide receptor (GRPR)-targeting antagonist NeoB is a promising radioligand for imaging and therapy of GRPR-expressing malignancies. In the current study, we aimed to discover the target organs of toxicity and the radiotoxic effects to these organs, when repeated dosages of [ 177Lu]Lu-NeoB are administered to healthy female and male mice. Methods: Animals received either 3 injections, with a 7-day interval, of vehicle (control group 1), 1200 pmol [ 175Lu]Lu-NeoB (control group 2) or 40 MBq/400 pmol, 80 MBq/800 pmol, and 120 MBq/1200 pmol [ 177Lu]Lu-NeoB (treatment groups 1, 2, and 3, respectively). At week 5, 19, and 43 after the first injection acute, early, and late organ toxicity, respectively, was determined. For this, histopathological and blood analyses were performed. To correlate the observed toxicity to absorbed dose, we also performed extensive biodistribution and dosimetry studies. Results: The biodistribution study showed the highest absorbed doses in GRPR-expressing pancreas, the liver, and the kidneys (the main organs of excretion). Both control groups and almost all animals of treatment group 1 did not show any treatment-related toxicological effects. Despite the high absorbed doses, no clear microscopic signs of toxicity were found in the pancreas and the liver. Histological analysis indicated kidney damage in the form of hydronephrosis and nephropathy in treatment groups 2 and 3 that were sacrificed at the early and late time point. In the same groups, increased blood urea nitrogen levels were found. Conclusion: In general, repeated administration of [ 177Lu]Lu-NeoB was tolerated. The most significant radiotoxic effects were found in the kidneys, similar to other clinically applied radioligands. The results of this study underline the potential of [ 177Lu]Lu-NeoB as a promising option for clinical therapy.

The aim of this study was to build a simulation framework to evaluate the number of DNA double-strand breaks (DSBs) induced by in vitro targeted radionuclide therapy (TRT). This work represents the first step toward exploring underlying biologic mechanisms and the influence of physical and chemical parameters to enable a better response prediction in patients. We used this tool to characterize early DSB induction by 177Lu-DOTATATE, a commonly used TRT for neuroendocrine tumors. Methods: A multiscale approach was implemented to simulate the number of DSBs produced over 4 h by the cumulated decays of 177Lu distributed according to the somatostatin receptor binding. The approach involves 2 sequential simulations performed with Geant4/Geant4-DNA. The radioactive source is sampled according to uptake experiments on the distribution of activities within the medium and the planar cellular cluster, assuming instant and permanent internalization. A phase space is scored around the nucleus of the central cell. Then, the phase space is used to generate particles entering the nucleus containing a multiscale description of the DNA in order to score the number of DSBs per particle source. The final DSB computations are compared with experimental data, measured by immunofluorescent detection of p53-binding protein 1 foci. Results: The probability of electrons reaching the nucleus was significantly influenced by the shape of the cell compartment, causing a large variance in the induction pattern of DSBs. A significant difference was found in the DSBs induced by activity distributions in cell and medium, as is explained by the specific energy (z) distributions. The average number of simulated DSBs was 14 DSBs per cell (range, 7-24 DSBs per cell), compared with 13 DSBs per cell (range, 2-30 DSBs per cell) experimentally determined. We found a linear correlation between the mean absorbed dose to the nucleus and the number of DSBs per cell: 0.014 DSBs per cell mGy-1 for internalizat

Nuclear and optical dual-modality probes can be of great assistance in prostate cancer localization, providing the means for both preoperative nuclear imaging and intraoperative surgical guidance. We developed a series of probes based on the backbone of the established GRPR-targeting radiotracer NeoB. The inverse electron demand of the Diels–Alder reaction was used to integrate the sulfo-cyanine 5 dye. Indium-111 radiolabeling, stability studies and a competition binding assay were carried out. Pilot biodistribution and imaging studies were performed in PC-3 tumor-bearing mice, using the best two dual-labeled probes. The dual-modality probes were radiolabeled with a high yield (>92%), were proven to be hydrophilic and demonstrated high stability in mouse serum (>94% intact labeled ligand at 4 h). The binding affinity for the GRPR was in the nanomolar range (21.9–118.7 nM). SPECT/CT images at 2 h p.i. clearly visualized the tumor xenograft and biodistribution studies, after scanning confirmed the high tumor uptake (8.47 ± 0.46%ID/g and 6.90 ± 0.81%ID/g for probe [111 In]In-12 and [111 In]In-15, respectively). Receptor specificity was illustrated with blocking studies, and co-localization of the radioactive and fluorescent signal was verified by ex vivo fluorescent imaging. Although optimal tumor-to-blood and tumor-to-kidney ratios might not yet have been reached due to the prolonged blood circulation, our probes are promising candidates for the preoperative and intraoperative visualization of GRPR-positive prostate cancer.

Background: To improve peptide receptor radionuclide therapy (PRRT), we aimed to enhance the expression of somatostatin type-2 receptors (SSTR2) in vitro and in vivo, using valproic acid (VPA). Methods: Human NCI-H69 small-cell lung carcinoma cells were treated with VPA, followed by [111 In]In-DOTATATE uptake studies, RT-qPCR and immunohistochemistry analysis. Furthermore, NCI-H69 xenografted mice were treated with VPA or vehicle, followed by [177Lu]Lu-DOTATATE injection. Biodistribution studies were performed, and tissues were collected for further analysis. Results: VPA significantly increased SSTR2 expression in vitro. In animals, a statistically significant increased [177Lu]Lu-DOTATATE tumoral uptake was observed when VPA was administered eight hours before [177Lu]Lu-DOTATATE administration, but increased tumor SSTR2 expression levels were lacking. The animals also presented significantly higher [177Lu]Lu-DOTATATE blood levels, as well as an elevated renal tubular damage score. This suggests that the enhanced tumor uptake was presumably a consequence of the increased radiotracer circulation and the induced kidney damage. Conclusions: VPA increases SSTR2 expression in vitro. In vivo, the observed increase in tumoral [177Lu]Lu-DOTATATE uptake is not caused by SSTR2 upregulation, but rather by other mechanisms, e.g., an increased [177Lu]Lu-DOTATATE circulation time and renal toxicity. However, since both drugs are safely used in humans, the potential of VPA to improve PRRT remains open for investigation.

Purpose: To assess our improved NACA for the detection of tumor necrosis. Methods: We increased the blood circulation time of our NACA by adding an albumin-binding domain to the molecular structure. We tested the necrosis avidity on dead or alive cultured cells and performed SPECT and fluorescence imaging of both spontaneous and treatment-induced necrosis in murine breast cancer models. We simultaneously recorded [18F]FDG-PET and bioluminescence images for complementary detection of tumor viability. Results: We generated two albumin-binding IRDye800CW derivatives which were labeled with indium-111 with high radiochemical purity. Surprisingly, both albumin-binding NACAs had >10x higher in vitro binding towards dead cells. We selected [111In]3 for in vivo experiments which showed higher dead cell binding in vitro and in vivo stability. The doxorubicin-treated tumors showed increased [111In]3-uptake (1.74 ± 0.08%ID/g after saline treatment, 2.25 ± 0.16%ID/g after doxorubicin treatment, p = 0.044) and decreased [18F]FDGuptake (3.02 ± 0.51%ID/g after saline treatment, 1.79 ± 0.11%ID/g after doxorubicin treatment, p = 0.040), indicating therapy efficacy. Moreover, we detected increased [111In]3-uptake and tumor necrosis in more rapidly growing EMT6 tumors. Conclusions: Our albumin-binding NACA based on IRDye800CW facilitates tumor-necrosis imaging for assessment of therapy efficacy and aggressiveness in solid tumors using both fluorescence and SPECT imaging.

Background: There is a growing body of nuclear contrast agents that are repurposed for fluorescence-guided surgery. New contrast agents are obtained by substituting the radioactive tag with, or adding a fluorescent cyanine to the molecular structure of antibodies or peptides. This enables intra-operative fluorescent detection of cancerous tissue, leading to more complete tumor resection. However, these fluorescent cyanines can have a remarkable influence on pharmacokinetics and tumor uptake, especially when labeled to smaller targeting vectors such as peptides. Here we demonstrate the effect of cyanine-mediated dead cell-binding of Ac-Lys0(IRDye800CW)-Tyr3-octreotate (800CW-TATE) and how this can be used as an advantage for fluorescence-guided surgery. Results: Binding of 800CW-TATE could be blocked with DOTA0-Tyr3-octreotate (DOTA-TATE) on cultured SSTR2-positive U2OS cells and was absent in SSTR2 negative U2OS cells. However, strong binding was observed to dead cells, which could not be blocked with DOTA-TATE and was also present in dead SSTR2 negative cells. No SSTR2-mediated binding was observed in frozen tumor sections, possibly due to disruption of the cells in the process of sectioning the tissue before exposure to the contrast agent. DOTA-TATE blocking resulted in an incomplete reduction of 61.5 ± 5.8% fluorescence uptake by NCI-H69-tumors in mice. Near-infrared imaging and dead cell staining on paraffin sections from resected tumors revealed that fluorescence uptake persisted in necrotic regions upon blocking with DOTA-TATE. Conclusion: This study shows that labeling peptides with cyanines can result in dead cell binding. This does not hamper the ultimate purpose of fluorescence-guided surgery, as necrotic tissue appears in most solid tumors. Hence, the necrosis binding can increase the overall tumor uptake. Moreover, necro

Purpose: Many radioligands have been developed for the visualization of atherosclerosis by targeting inflammation. However, interpretation of in vivo signals is often limited to plaque identification. We evaluated binding of some promising radioligands in an in vitro approach in atherosclerotic plaques with different phenotypes. Methods: Tissue sections of carotid endarterectomy tissue were characterized as early plaque, fibro-calcific plaque, or phenotypically vulnerable plaque. In vitro binding assays for the radioligands [111In]In-DOTATATE; [111In]In-DOTA-JR11; [67Ga]Ga-Pentixafor; [111In]In-DANBIRT; and [111In]In-EC0800 were conducted, the expression of the radioligand targets was assessed via immunohistochemistry. Radioligand binding and expression of radioligand targets was investigated and compared. Results: In sections characterized as vulnerable plaque, binding was highest for [111In]In-EC0800; followed by [111In]In-DANBIRT; [67Ga]Ga-Pentixafor; [111In]In-DOTA-JR11; and [111In]In-DOTATATE (0.064 ± 0.036; 0.052 ± 0.029; 0.011 ± 0.003; 0.0066 ± 0.0021; 0.00064 ± 0.00014 %Added activity/mm2, respectively). Binding of [111In]In-DANBIRT and [111In]In-EC0800 was highest across plaque phenotypes, binding of [111In]In-DOTA-JR11 and [67Ga]Ga-Pentixafor differed most between plaque phenotypes. Binding of [111In]In-DOTATATE was the lowest across plaque phenotypes. The areas positive for cells expressing the radioligand’s target differed between plaque phenotypes for all targets, with lowest percentage area of expression in early plaque sections and highest in phenotypically vulnerable plaque sections. Conclusions: Radioligands targeting inflammatory cell markers showed different levels of binding in atherosclerotic plaques and among plaque phenotypes. Different radioligands might be used for

Necrosis only occurs in pathological situations and is directly related to disease severity and, therefore, is an important biomarker. Tumor necrosis occurs in most solid tumors due to improperly functioning blood vessels that cannot keep up with the rapid growth, especially in aggressively growing tumors. The amount of necrosis per tumor volume is often correlated to rapid tumor proliferation and can be used as a diagnostic tool. Furthermore, efficient therapy against solid tumors will directly or indirectly lead to necrotic tumor cells, and detection of increased tumor necrosis can be an early marker for therapy efficacy. We propose the application of necrosis avid contrast agents to detect therapy-induced tumor necrosis. Herein, we advance gallium-68-labeled IRDye800CW, a near-infrared fluorescent dye that exhibits excellent necrosis avidity, as a potential PET tracer for in vivo imaging of tumor necrosis. We developed a reliable labeling procedure to prepare [68Ga]Ga-DOTA-PEG4-IRDye800CW ([68Ga]Ga-1) with a radiochemical purity of >96% (radio-HPLC). The prominent dead cell binding of fluorescence and radioactivity from [68Ga]Ga-1 was confirmed with dead and alive cultured 4T1-Luc2 cells. [68Ga]Ga-1 was injected in 4T1-Luc2 tumor-bearing mice, and specific fluorescence and PET signal were observed in the spontaneously developing tumor necrosis. The ip injection of D-luciferin enabled simultaneous bioluminescence imaging of the viable tumor regions. Tumor necrosis binding was confirmed ex vivo by colocalization of fluorescence uptake with TUNEL dead cell staining and radioactivity uptake in dichotomized tumors and frozen tumor sections. Our presented study shows that [68Ga]Ga-1 is a promising PET tracer for the detection of tumor necrosis.

Currently, radiolabeled DOTA-[Tyr3]-octreotate (DOTA-TATE) is most commonly used in the clinic to image and treat neuroendocrine tumors. To further improve tumor uptake, and thus treatment, the amount of radiotracer that can accumulate in the tumor might be increased by prolonging the blood circulation time of the radiotracer. To achieve this, we designed Albutate-1, with both DOTA and an albumin-binding domain coupled to TATE via a suitable linker. The aim of this study was to determine the characteristics of the novel radiotracer Albutate-1. A competition binding assay was performed using [111In]In-DOTA-TATE on fresh-frozen SSTR2+ tumor sections. In vitro cell-uptake and internalization of [111In]In-Albutate-1 and [111In]In-DOTA-TATE were determined. The stability of [177Lu]Lu-Albutate-1 was tested. A biodistribution study was performed to provide tumor and organ uptake of [177Lu]Lu-Albutate-1. The biodistribution data was used to determine time-activity curves and the radiation dose for each organ and the tumor. The in vitro IC50 value of Albutate-1 was 1.2 nM. A higher amount of the tracer was found in the intracellular fraction than in the membrane fraction ([111In]In-Albutate-1 14.0 vs 1.9% of the added amount; [111In]In-DOTA-TATE 11.0 vs 1.5% of the added amount). After radiolabeling [111In] In-Albutate-1 was stable up to 3 days (93.1-88.9%) in labeling solution and very stable in mouse serum (90-94%) for at least 24 h. In vivo, [177Lu]Lu-Albutate-1 was cleared slowly from the circulation (1 h p.i. 58%ID/g, 168h p.i. 2%ID/g). The addition of an albumin-binding domain to DOTA-TATE extended the blood circulation to T1/2= 27.5h. The tumor absorbed dose was raised to 1455 mGy/MBq. Bone marrow, the dose-limiting organ in the mouse spine, unfortunately, received 765 mGy/MBq. All other organs also received a high radiation dose, reducing the therapeutic index.

Purpose: Various radiolabeled prostate-specific membrane antigen (PSMA)–targeting tracers are clinically applied for prostate cancer (PCa) imaging and targeted radionuclide therapy. The PSMA binding affinities, biodistribution, and DNA-damaging capacities of these radiotracers have not yet been compared in detail. A major concern of PSMA-targeting radiotracers is the toxicity in other PSMA-expressing organs, such as the salivary glands, thus demanding careful evaluation of the most optimal and safest radiotracer. In this extensive preclinical study, we evaluated the clinically applied PSMA-targeting small molecule inhibitors DOTA-PSMA-617 (PSMA-617) and DOTAGA-PSMA-I&T (PSMA-I&T) and the PSMA nanobody DOTA-JVZ-007 (JVZ-007) using PSMA-expressing cell lines, a unique set of PCa patient-derived xenografts (PDX) and healthy human tissues. Methods and results: In vitro displacement studies on PSMA-expressing cells and cryosections of a PSMA-positive PDX revealed high and specific binding affinity for all three tracers labeled with lutetium-177 with IC50 values in the nanomolar range. Interestingly, [177Lu]Lu-JVZ-007 could not be displaced by PSMA-617 or PSMA-I&T, suggesting that this tracer targets an alternative binding site. Autoradiography assays on cryosections of human salivary and renal tissues revealed [177Lu]Lu-PSMA-617 to have the lowest binding to these healthy organs compared with [177Lu]Lu-PSMA-I&T. In vivo biodistribution assays confirmed the in vitro results with comparable tumor uptake of [177Lu]Lu-PSMA-617 and [177Lu]Lu-PSMA-I&T at all timepoints, resulting in induction of similar levels of DNA double-strand breaks in the tumors. However, [177Lu]Lu-PSMA-I&T demonstrated approximately 40× higher renal uptake at 4 and 8 h post injection resulting in an unfavorable tumor-to-kidney ratio. Conclusion: [177Lu]Lu-PSMA-617 has the most favorable bio

Purpose: Meningioma recurrence rates can be reduced by optimizing surgical resection with the use of intraoperative molecular fluorescence guided surgery (MFGS). We evaluated the potential of the fluorescent tracer 800CW-TATE for MFGS using in vitro and in vivo models. It targets somatostatin receptor subtype 2 (SSTR2), which is overexpressed in all meningiomas. Methods: Binding affinity of 800CW-TATE was evaluated using [177Lu] Lu-DOTA-Tyr3-octreotate displacement assays. Tumor uptake was determined by injecting 800CW-TATE in (SSTR2-positive) NCI-H69 or (SSTR2-negative) CH-157MN xenograft bearing mice and FMT2500 imaging. SSTR2-specific binding was measured by comparing tumor uptake in NCI-H69 and CH-157MN xenografts, blocking experiments and non-targeted IRDye800CW-carboxylate binding. Tracer distribution was analyzed ex vivo, and the tumor-to-background ratio (TBR) was calculated. SSTR2 expression was determined by immunohistochemistry (IHC). Lastly, 800CW-TATE was incubated on frozen and fresh meningioma specimens and analyzed by microscopy. Results: 800CW-TATE binding affinity assays showed an IC50 value of 72 nM. NCI-H69 xenografted mice showed a TBR of 21.1. 800CW-TATE detection was reduced after co-administration of non-fluorescent DOTA-Tyr3-octreotate or administration of IRDye800CW. CH-157MN had no tumor specific tracer staining due to absence of SSTR2 expression, thereby serving as a negative control. The tracer bound specifically to SSTR2-positive meningioma tissues representing all WHO grades. Conclusion: 800CW-TATE demonstrated sufficient binding affinity, specific SSTR2-mediated tumor uptake, a favorable biodistribution, and high TBR. These features make this tracer very promising for use in MFGS and could potentially aid in safer and a more complete meningioma resection, especially in high-grade meningiomas or those a

Background: Imaging Somatostatin Subtype Receptor 2 (SST2) expressing macrophages by [DOTA,Tyr3]-octreotate (DOTATATE) has proven successful for plaque detection. DOTA-JR11 is a SST2 targeting ligand with a five times higher tumor uptake than DOTATATE, and holds promise to improve plaque imaging. The aim of this study was to evaluate the potential of DOTA-JR11 for plaque detection. Methods and Results: Atherosclerotic ApoE−/− mice (n = 22) fed an atherogenic diet were imaged by SPECT/CT two hours post injection of [111In]In-DOTA-JR11 (~ 200 pmol, ~ 50 MBq). In vivo plaque uptake of [111In]In-DOTA-JR11 was visible in all mice, with a target-to-background-ratio (TBR) of 2.23 ± 0.35. Post-mortem scans after thymectomy and ex vivo scans of the arteries after excision of the arteries confirmed plaque uptake of the radioligand with TBRs of 2.46 ± 0.52 and 3.43 ± 1.45 respectively. Oil red O lipid-staining and ex vivo autoradiography of excised arteries showed [111In]In-DOTA-JR11 uptake at plaque locations. Histological processing showed CD68 (macrophages) and SST2 expressing cells in plaques. SPECT/CT, in vitro autoradiography and immunohistochemistry performed on slices of a human carotid endarterectomy sample showed [111In]In-DOTA-JR11 uptake at plaque locations containing CD68 and SST2 expressing cells. Conclusions: The results of this study indicate DOTA-JR11 as a promising ligand for visualization of atherosclerotic plaque inflammation.

The Funding section in the initial online article was incomplete. The original article has been corrected.

The aim of this study was to increase somatostatin type‐2 receptor (SSTR2) expression on neuroendocrine tumor (NET) cells using histone deacetylase inhibitors (HDACis), potentially increasing the uptake of SSTR2‐targeted radiopharmaceuticals and subsequently improving treatment efficacy of peptide receptor radionuclide therapy (PRRT). Human NET cell lines BON‐1, NCI‐ H727, and GOT1 were treated with HDACis (i.e., CI‐994, entinostat, LMK‐235, mocetinostat, panobinostat, or valproic acid (VPA); entinostat and VPA were the HDACis tested in GOT1 cells) to examine SSTR2 mRNA expression levels and uptake of SSTR2‐targeting radiotracer [111In]In‐DO‐ TATATE. Reversibility of the induced effects was examined after drug‐withdrawal. Finally, the effect of VPA on radiosensitivity was investigated. A strong stimulatory effect in BON‐1, NCI‐H727, and GOT1 cells was observed after HDACi treatment, both on SSTR2 mRNA expression levels and [111In]In‐DOTATATE uptake. The effects of the HDACis were largely reversible over a period of seven days, demonstrating largest reductions within the first day. The reversibility profile of the induced effects suggests that proper timing of HDACi treatment is most likely essential for a beneficial outcome. In addition to increasing SSTR2 expression levels, VPA enhanced the radiosensitivity of all cell lines. In conclusion, HDACi treatment increased SSTR2 expression, and radiosensitivity was also enhanced upon VPA treatment.

Purpose: Atherosclerotic plaque development and progression signifies a complex inflammatory disease mediated by a multitude of proinflammatory leukocyte subsets. Using single photon emission computed tomography (SPECT) coupled with computed tomography (CT), this study tested a new dual-isotope acquisition protocol to assess each radiotracer’s capability to identify plaque phenotype and inflammation levels pertaining to leukocytes expressing leukocyte function-associated antigen-1 (LFA-1) and the leukocyte subset of proinflammatory macrophages expressing somatostatin receptor subtype-2 (SST2). Individual radiotracer uptake was quantified and the presence of corresponding immunohistological cell markers was assessed. Methods: Human symptomatic carotid plaque segments were obtained from endarterectomy. Segments were incubated in dual-isotope radiotracers [111In]In-DOTA-butylamino-NorBIRT ([111In]In-Danbirt) and [99mTc]Tc-[N0–14,Asp0,Tyr3]-octreotate ([99mTc]Tc-Demotate 2) before scanning with SPECT/CT. Plaque phenotype was classified as pathological intimal thickening, fibrous cap atheroma or fibrocalcific using histology sections based on distinct morphological characteristics. Plaque segments were subsequently immuno-stained with LFA-1 and SST2 and quantified in terms of positive area fraction and compared against the corresponding SPECT images. Results: Focal uptake of co-localising dual-radiotracers identified the heterogeneous distribution of inflamed regions in the plaques which co-localised with positive immuno-stained regions of LFA-1 and SST2. [111In]In-Danbirt and [99mTc]Tc-Demotate 2 uptake demonstrated a significant positive correlation (r = 0.651; p = 0.001). Fibrous cap atheroma plaque phenotype correlated with the highest [111In]In-Danbirt and [99mTc]Tc-Demotate 2 uptake compared with fib

Gastrin-releasing peptide receptors (GRPRs) are overexpressed in prostate cancer and are suitable for targeted radionuclidetherapy (TRT). We optimized the bombesin-derived GRPR-antagonist PEG2-RM26 for labeling with 177Lu and further determinedthe effect of treatment with 177Lu-labeled peptide alone or in combination with the anti-HER2 antibody trastuzumab in amurine model. The PEG2-RM26 analog was coupled to NOTA, NODAGA, DOTA and DOTAGA chelators. The peptide-chelatorconjugates were labeled with 177Lu and characterized in vitro and in vivo. A preclinical therapeutic study was performed in PC-3xenografted mice. Mice were treated with intravenous injections (6 cycles) of (A) PBS, (B) DOTAGA-PEG2-RM26, (C) 177LuDOTAGA-PEG2-RM26, (D) trastuzumab or (E) 177Lu-DOTAGA-PEG2-RM26 in combination with trastuzumab. 177Lu-DOTAGA-PEG2-RM26 demonstrated quantitative labeling yield at high molar activity (450 GBq/μmol), high in vivo stability (5 min pi >98% ofradioligand remained when coinjected with phosphoramidon), high affinity to GRPR (KD = 0.4 0.2 nM), and favorablebiodistribution (1 hr pi tumor uptake was higher than in healthy tissues, including the kidneys). Therapy with 177Lu-DOTAGAPEG2-RM26 induced a significant inhibition of tumor growth. The median survival for control groups was significantly shorterthan for treated groups (Group C 66 days, Group E 74 days). Trastuzumab together with radionuclide therapy significantlyimproved survival. No treatment-related toxicity was observed. In conclusion, based on in vitro and in vivo characterization ofthe four 177Lu-labeled PEG2-RM26 analogs, we concluded that 177Lu-DOTAGA-PEG2-RM26 was the most promising analog forTRT. Radiotherapy using 177Lu-DOTAGA-PEG2-RM26 effectively inhibited tumor growth in vivo in a murine prostate cancermodel. Anti-HER2 therapy additionally improved survival.

Gastrin-releasing peptide receptors (GRPRs) are overexpressed in prostate cancer and are suitable for targeted radionuclidetherapy (TRT). We optimized the bombesin-derived GRPR-antagonist PEG2-RM26 for labeling with 177Lu and further determinedthe effect of treatment with 177Lu-labeled peptide alone or in combination with the anti-HER2 antibody trastuzumab in amurine model. The PEG2-RM26 analog was coupled to NOTA, NODAGA, DOTA and DOTAGA chelators. The peptide-chelatorconjugates were labeled with 177Lu and characterized in vitro and in vivo. A preclinical therapeutic study was performed in PC-3xenografted mice. Mice were treated with intravenous injections (6 cycles) of (A) PBS, (B) DOTAGA-PEG2-RM26, (C) 177LuDOTAGA-PEG2-RM26, (D) trastuzumab or (E) 177Lu-DOTAGA-PEG2-RM26 in combination with trastuzumab. 177Lu-DOTAGA-PEG2-RM26 demonstrated quantitative labeling yield at high molar activity (450 GBq/μmol), high in vivo stability (5 min pi >98% ofradioligand remained when coinjected with phosphoramidon), high affinity to GRPR (KD = 0.4 0.2 nM), and favorablebiodistribution (1 hr pi tumor uptake was higher than in healthy tissues, including the kidneys). Therapy with 177Lu-DOTAGAPEG2-RM26 induced a significant inhibition of tumor growth. The median survival for control groups was significantly shorterthan for treated groups (Group C 66 days, Group E 74 days). Trastuzumab together with radionuclide therapy significantlyimproved survival. No treatment-related toxicity was observed. In conclusion, based on in vitro and in vivo characterization ofthe four 177Lu-labeled PEG2-RM26 analogs, we concluded that 177Lu-DOTAGA-PEG2-RM26 was the most promising analog forTRT. Radiotherapy using 177Lu-DOTAGA-PEG2-RM26 effectively inhibited tumor growth in vivo in a murine prostate cancermodel. Anti-HER2 therapy additionally improved survival.

Gastrin-releasing peptide receptors (GRPRs) are overexpressed in prostate cancer and are suitable for targeted radionuclidetherapy (TRT). We optimized the bombesin-derived GRPR-antagonist PEG2-RM26 for labeling with 177Lu and further determinedthe effect of treatment with 177Lu-labeled peptide alone or in combination with the anti-HER2 antibody trastuzumab in amurine model. The PEG2-RM26 analog was coupled to NOTA, NODAGA, DOTA and DOTAGA chelators. The peptide-chelatorconjugates were labeled with 177Lu and characterized in vitro and in vivo. A preclinical therapeutic study was performed in PC-3xenografted mice. Mice were treated with intravenous injections (6 cycles) of (A) PBS, (B) DOTAGA-PEG2-RM26, (C) 177LuDOTAGA-PEG2-RM26, (D) trastuzumab or (E) 177Lu-DOTAGA-PEG2-RM26 in combination with trastuzumab. 177Lu-DOTAGA-PEG2-RM26 demonstrated quantitative labeling yield at high molar activity (450 GBq/μmol), high in vivo stability (5 min pi >98% ofradioligand remained when coinjected with phosphoramidon), high affinity to GRPR (KD = 0.4 0.2 nM), and favorablebiodistribution (1 hr pi tumor uptake was higher than in healthy tissues, including the kidneys). Therapy with 177Lu-DOTAGAPEG2-RM26 induced a significant inhibition of tumor growth. The median survival for control groups was significantly shorterthan for treated groups (Group C 66 days, Group E 74 days). Trastuzumab together with radionuclide therapy significantlyimproved survival. No treatment-related toxicity was observed. In conclusion, based on in vitro and in vivo characterization ofthe four 177Lu-labeled PEG2-RM26 analogs, we concluded that 177Lu-DOTAGA-PEG2-RM26 was the most promising analog forTRT. Radiotherapy using 177Lu-DOTAGA-PEG2-RM26 effectively inhibited tumor growth in vivo in a murine prostate cancermodel. Anti-HER2 therapy additionally improved survival.

Affibody molecules are small proteins engineered using a nonanti-body scaffold. Radiolabeled Affibody molecules are excellent imaging probes, but their application to radionuclide therapy has been prevented by high renal reabsorption. The aim of this study was to test the hypothesis that Affibody-based peptide nucleic acid (PNA)-mediated pretargeted therapy of human epidermal growth factor receptor 2 (HER2)-expressing cancer extends survival without accompanying renal toxicity. Methods: A HER2-targeting Affibody molecule ligated with an AGTCGTGATGTAGTC PNA hybridization probe (Z(HER2:342)-SR-HP1) was used as the primary pretargeting agent. A complementary AGTCGTGATGTAGTC PNA conjugated to the chelator DOTA and labeled with the radionuclide Lu-177 (Lu-177-HP2) was used as the secondary agent. The influence of different factors on pretargeting was investigated. Experimental radionuclide therapy in mice bearing SKOV-3 xenografts was performed in 6 cycles separated by 7 d. Results: Optimal tumor targeting was achieved when 16 MBq/3.5 mu g (0.65 nmol) of Lu-177-HP2 was injected 16 h after injection of 100 mu g (7.7 nmol) of Z(HER2:342)-SR-HP1. The calculated absorbed dose to tumors was 1,075 mGy/MBq, whereas the absorbed dose to kidneys was 206 mGy/MBq and the absorbed dose to blood (surrogate of bone marrow) was 4 mGy/MBq. Survival of mice was significantly longer (P < 0.05) in the treatment group (66 d) than in the control groups treated with the same amount of Z(HER2:342)-SR-HP1 only (37 d), the same amount and activity of Lu-177-HP2 only (32 d), or phosphate-buffered saline (37 d). Conclusion: The studied pretargeting system can deliver an absorbed dose to tumors appreciably exceeding absorbed doses to critical organs, making Affibody-based PNA-mediated pretargeted radionuclide therapy highly attractive., Kristina Westerlund and Mohamed Altai contributed equally. Amelie Eriksson Karlström and Vladimir Tolmachev contributed equally.

Affibody molecules are small proteins engineered using a nonanti-body scaffold. Radiolabeled Affibody molecules are excellent imaging probes, but their application to radionuclide therapy has been prevented by high renal reabsorption. The aim of this study was to test the hypothesis that Affibody-based peptide nucleic acid (PNA)-mediated pretargeted therapy of human epidermal growth factor receptor 2 (HER2)-expressing cancer extends survival without accompanying renal toxicity. Methods: A HER2-targeting Affibody molecule ligated with an AGTCGTGATGTAGTC PNA hybridization probe (Z(HER2:342)-SR-HP1) was used as the primary pretargeting agent. A complementary AGTCGTGATGTAGTC PNA conjugated to the chelator DOTA and labeled with the radionuclide Lu-177 (Lu-177-HP2) was used as the secondary agent. The influence of different factors on pretargeting was investigated. Experimental radionuclide therapy in mice bearing SKOV-3 xenografts was performed in 6 cycles separated by 7 d. Results: Optimal tumor targeting was achieved when 16 MBq/3.5 mu g (0.65 nmol) of Lu-177-HP2 was injected 16 h after injection of 100 mu g (7.7 nmol) of Z(HER2:342)-SR-HP1. The calculated absorbed dose to tumors was 1,075 mGy/MBq, whereas the absorbed dose to kidneys was 206 mGy/MBq and the absorbed dose to blood (surrogate of bone marrow) was 4 mGy/MBq. Survival of mice was significantly longer (P < 0.05) in the treatment group (66 d) than in the control groups treated with the same amount of Z(HER2:342)-SR-HP1 only (37 d), the same amount and activity of Lu-177-HP2 only (32 d), or phosphate-buffered saline (37 d). Conclusion: The studied pretargeting system can deliver an absorbed dose to tumors appreciably exceeding absorbed doses to critical organs, making Affibody-based PNA-mediated pretargeted radionuclide therapy highly attractive., QC 20180726

Earlier studies have shown that modification of the octapeptide octreotide in positions 3 and 8 may result in compounds with increased somatostatin receptor affinity that, if radiolabelled, display improved uptake in somatostatin receptor-positive tumours. The aim of a recent research study in our laboratory was to employ the parallel peptide synthesis approach by further exchanging the amino acid in position 3 of octreotide and coupling the macrocyclic chelator DOTA(1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid) to these peptides for labelling with radiometals like gallium-67 or -68, indium-111, yttrium-90 and lutetium-177. The purpose was to find radiopeptides with an improved somatostatin receptor binding profile in order to extend the spectrum of targeted tumours. A first peptide, [111In,90Y-DOTA]-1-Nal3-octreotide (111In,90Y-DOTA-NOC), was isolated which showed an improved profile. InIII-DOTA-NOC exhibited the following IC50 values (nM) when studied in competition with [125I][Leu8, d-Trp22, Tyr25]somatostatin-28 (values for YIII-DOTA-NOC are shown in parentheses): sstr2, 2.9±0.1 (3.3±0.2); sstr3, 8±2 (26±1.9); sstr5, 11.2±3.5 (10.4±1.6). Affinity towards sstr1 and 4 was very low or absent. InIII-DOTA-NOC is superior to all somatostatin-based radiopeptides having this particular type of binding profile, including DOTA-lanreotide, and has three to four times higher binding affinity to sstr2 than InIII,YIII-DOTA-Tyr3-octreotide (InIII,YIII-DOTA-TOC). In addition, [111In]DOTA-NOC showed a specific and high rate of internalization into AR4-2J rat pancreatic tumour cells which, after 4h, was about two times higher than that of [111In]DOTA-TOC and three times higher than that of [111In]DOTA-octreotide ([111In]DOTA-OC). The internalized radiopeptides were externalized intact upon 2h of internalization followed by an acid wash. After 2-3h of externalization a plateau is reached, indicating a steady-state situation explained by reactivation of the receptors fo

Local drug delivery of Doxorubicin (Dox) with thermosensitive liposomes (TSL) and hyperthermia (HT) has shown preclinically to achieve high local drug concentrations with good therapeutic efficacy. Currently, this is clinically studied for treatment of chest wall recurrence of breast cancer, however with various outcomes. This study examines the potency of neoadjuvant TSL HT combination therapy in two orthotopic mouse models of human breast cancer, MDA-MB-231 and T-47D, which morphologically correlate to mesenchymal and epithelial phenotypes, respectively. Both cell lines showed improved in vitro chemosensitivity and Dox uptake at HT. Doxloaded TSL (TSLDox) was stable in vitro in FBS, BALB/c-nu plasma and human plasma, although release of the drug at HT was incomplete for the latter two. Combination treatment with TSLDox and HT in vivo was significantly more effective against MDA-MB-231 tumors, whereas T-47D tumors showed no significant therapeutic response. Ex vivo investigation revealed a higher mean vessel density and poorly differentiated extracellular matrix (ECM) in MDA-MB-231 tumors relative to T-47D tumors. Although in vitro results of the TSLDox and HT treatment were favorable for both cell types, the therapeutic efficacy in vivo was remarkably different. The well-differentiated and slowly-growing T-47D tumors may provide a microenvironment that limits drug delivery to the target cell and therefore renders the therapy ineffective. Mesenchymal and invasive MDAMB- 231 tumors display higher vascularization and less mature ECM, significantly enhancing tumor response to TSLDox and HT treatment. These results yield insight into the efficacy of TSL treatment within different tumor microenvironments, and further advance our understanding of factors that contribute to heterogeneous therapeutic outcomes in clinical trials.

Local drug delivery of Doxorubicin (Dox) with thermosensitive liposomes (TSL) and hyperthermia (HT) has shown preclinically to achieve high local drug concentrations with good therapeutic efficacy. Currently, this is clinically studied for treatment of chest wall recurrence of breast cancer, however with various outcomes. This study examines the potency of neoadjuvant TSL HT combination therapy in two orthotopic mouse models of human breast cancer, MDA-MB-231 and T-47D, which morphologically correlate to mesenchymal and epithelial phenotypes, respectively. Both cell lines showed improved in vitro chemosensitivity and Dox uptake at HT. Doxloaded TSL (TSLDox) was stable in vitro in FBS, BALB/c-nu plasma and human plasma, although release of the drug at HT was incomplete for the latter two. Combination treatment with TSLDox and HT in vivo was significantly more effective against MDA-MB-231 tumors, whereas T-47D tumors showed no significant therapeutic response. Ex vivo investigation revealed a higher mean vessel density and poorly differentiated extracellular matrix (ECM) in MDA-MB-231 tumors relative to T-47D tumors. Although in vitro results of the TSLDox and HT treatment were favorable for both cell types, the therapeutic efficacy in vivo was remarkably different. The well-differentiated and slowly-growing T-47D tumors may provide a microenvironment that limits drug delivery to the target cell and therefore renders the therapy ineffective. Mesenchymal and invasive MDAMB- 231 tumors display higher vascularization and less mature ECM, significantly enhancing tumor response to TSLDox and HT treatment. These results yield insight into the efficacy of TSL treatment within different tumor microenvironments, and further advance our understanding of factors that contribute to heterogeneous therapeutic outcomes in clinical trials.

Background: Single photon emission computed tomography (SPECT) is an indispensable tool in the determination of the in vivo fate of polymeric micelles. However, for this purpose, the micelles need to be radiolabeled, and almost all radiolabeling procedures published to date involve the conjugation of a chelating agent to the constituting polymer, which could actually affect their biodistribution. In this paper, we report a new facile method for radiolabeling polystyrene-b-poly(ethylene oxide) diblock copolymer micelles without the necessity of any chemical modification. Instead, we entrap the radiolabel (i.e., 111In) in the micellar core during the formation of the micelles by using tropolone as lipophilic ligand. Methods: Micelles were prepared by emulsifying a polymer solution in chloroform with a buffer containing 111In and lipophilic ligand tropolone, by stirring for about 2 h. The produced micelles were physically characterized by means of dynamic light scattering and transmission electron microscopy. The biological properties of the radiolabeled micelles were determined by means of in vivo and ex vivo evaluation. SPECT analysis was done on Balb/c-nu mice, after administration of 1 mg micelles containing 22 MBq of 111In. SPECT images were obtained over 24 h. Biodistribution of the micelles was assessed also ex vivo. Results: The radiolabeling method is robust and reproducible with constant radiolabeling efficiency (~30 %) even at indium concentrations that are much higher than the necessary for in vivo studies, and the radiolabel retention is more than 80 % in mouse serum at 48 h. Radiolabeled micelles having hydrodynamic radius of 97 ± 13 nm have been successfully evaluated in vivo and ex vivo in non-tumor-bearing mice, revealing significant blood circulation up to at least 24 h post injection, with low accumulation in most organs except for the liver and spleen, which are the natural organs for clearance of nanoparticles. C, RST/Applied Radiation & Isotopes

Background: Single photon emission computed tomography (SPECT) is an indispensable tool in the determination of the in vivo fate of polymeric micelles. However, for this purpose, the micelles need to be radiolabeled, and almost all radiolabeling procedures published to date involve the conjugation of a chelating agent to the constituting polymer, which could actually affect their biodistribution. In this paper, we report a new facile method for radiolabeling polystyrene-b-poly(ethylene oxide) diblock copolymer micelles without the necessity of any chemical modification. Instead, we entrap the radiolabel (i.e., 111In) in the micellar core during the formation of the micelles by using tropolone as lipophilic ligand. Methods: Micelles were prepared by emulsifying a polymer solution in chloroform with a buffer containing 111In and lipophilic ligand tropolone, by stirring for about 2 h. The produced micelles were physically characterized by means of dynamic light scattering and transmission electron microscopy. The biological properties of the radiolabeled micelles were determined by means of in vivo and ex vivo evaluation. SPECT analysis was done on Balb/c-nu mice, after administration of 1 mg micelles containing 22 MBq of 111In. SPECT images were obtained over 24 h. Biodistribution of the micelles was assessed also ex vivo. Results: The radiolabeling method is robust and reproducible with constant radiolabeling efficiency (~30 %) even at indium concentrations that are much higher than the necessary for in vivo studies, and the radiolabel retention is more than 80 % in mouse serum at 48 h. Radiolabeled micelles having hydrodynamic radius of 97 ± 13 nm have been successfully evaluated in vivo and ex vivo in non-tumor-bearing mice, revealing significant blood circulation up to at least 24 h post injection, with low accumulation in most organs except for the liver and spleen, which are the natural organs for clearance of nanoparticles. C, RST/Applied Radiation & Isotopes

Introduction: Personalized dosimetry based on quantitative images of radiopharmaceutical distribution in the body can substantially improve the effectiveness of radionuclide thera- py. Current nuclear medicine imaging systems are optimized for diagnostic radionuclides and suboptimal for bremsstrah- lung X- rays emitted by therapeutic radionuclides.Materials and methods: We present a novel molecular imaging modality, called CET (based on elements from CT, SPECT and PET) and specifically designed for collimating and detecting the high-energy secondary body generated bremsstrahlung X-ray photons. To efficiently detect incoming high-energy X-ray photons, conventional NaI SPECT detectors are replaced with high-density scintillators from PET. A first step in the design of the complete system is the evaluation of monolithic high- resolution detectors for this modality. LYSO, the most com- monly used PET scintillator, is intrinsically radioactive due to the presence of Lu-176. This leads to a continuous background in the energy spectrum, making this scintillator not suitable for CET. Therefore simulations (using the input of the continuous Spectrum of Y-90) and measurements of high-density thick PET BGO crystals are compared to the results of conventional NaI detectors. CET also combines these detectors with pinhole collimators (from small animal SPECT), with small accep- tance angles and minimal penetration.These are specifically designed for a wide energy spectrum and with the primary aim to reduce scatter and collimator penetration. To efficiently construct these complex collimators with high stopping power, additive manufacturing (3D printing) of tungsten powder will be used. Since no scatter windows can be used for X-rays, quantitative reconstructions will be obtained by modeling the remaining contamination in Monte Carlo-based image recon- struction. Finally Monte Carlo or other approaches will pro- vide the information on the absorbed radiation dose.Results. A BGO de

Medullary thyroid cancer (MTC) is a neuroendocrine tumor originating from the calcitonin‐secreting C cells. Surgery, consisting of a total thyroidectomy and an extensive lymph node dissection, is the only effective treatment in MTC; however, metastases are frequently found in the regional cervical lymph. The biochemical marker for MTC is calcitonin, and this is frequently used for the detection of persistent/residual/metastatic tumor. The value of 111In‐labeled somatostatin receptor scintigraphy (SRS) in patients with MTC is limited, with sensitivity ranging between 0 and 75%. Other scintigraphic imaging techniques such as 18F‐FDG PET, 18F‐DOPA PET, and PET imaging with 68Ga‐labeled DOTA peptides combined with CT imaging are upcoming. Treatment of patients with metastatic disease with the current available somatostatin analogues, octreotide and lanreotide, does not seem to have an effect on survival but may be considered to control flushing and diarrhea in some patients. Experience with peptide receptor radionuclide therapy is limited in this patient group and disappointing. New therapies in the treatment of metastatic MTC use target tyrosine kinase receptors inhibitors belonging to the same family group of proteins as RET.

In GEP‐NETs, especially the catecholamine and serotonin biosynthetic pathways are upregulated. Therefore, increased biosynthesis of these specific amines in GEP‐NETs enables imaging with specific amine precursors. For the catecholamine pathway, 6‐18F ‐l‐3,4‐dihydroxyphenylalanine (18F‐DOPA) is available, while for the serotonin pathway, carbon‐11‐labeled 5‐hydroxy‐l‐tryptophan ([11C]‐5‐HTP) is available as tracer. 11C‐5‐HTP PET and 18F‐DOPA PET are excellent functional imaging techniques for evaluating patients with proven pancreatic islet cell tumors and carcinoids. For both tracers, the combination with CT further improves the detection rate of NET, which shows that performing PET scans with these tracers in PET/CT scanners is beneficial for patients. Since well‐differentiated GEP‐NETs generally have a low glucose metabolism, 18F‐fluorodexyglucose (18F‐FDG) PET scanning has limited value for the primary staging of patients with well‐differentiated GEP‐NETs. However, in patients with rapidly progressive disease, dedifferentiation of GEP‐NET tumors can lead to a higher glucose metabolism in tumor cells. In these patients, 18F‐FDG PET can be of benefit for tumor staging. Also, 18F‐FDG PET can be of value when other malignancies are suspected in patients with GEP‐NETs, since these patients experience a higher incidence of these malignancies compared to the general population. Nowadays, (GEP)‐NETs can also be imaged with 68Ga‐labeled analogues of somatostatin, which are also PET tracers. Advantages of 68Ga‐labeled somatostatin analogues are the relatively easy generator‐based synthesis and the possibility to evaluate whether peptide (somatostatin) receptor radionuclide therapy (PRRT) for NETs can be considered.