First-in-Human Evaluation of [18F]FDOPA Produced by Organo-Photoredox Reactions.

Photoredox is a powerful synthetic tool in organic chemistry and has been widely used in various fields, including nuclear medicine and molecular imaging. In particular, acridinium-based organophotoredox radiolabeling has significantly impacted the production and discovery of positron emission tomography (PET) agents. Despite their extensive use in preclinical research, no PET agents synthesized by acridinium photoredox labeling have been tested in humans. [18F]FDOPA is clinically used for tumor diagnosis and the evaluation of neuropsychiatric disorders, but its application is limited by complex synthesis methods, the need for expensive modules, and/or the high cost of consumable materials/cassettes. In this report, we integrated a photoredox labeling unit with an automated module and produced [18F]FDOPA for human study. This research not only represents the first human study of a PET agent generated by acridinium-based organophotoredox reactions but also demonstrates the safety of this novel labeling method, serving as a milestone/reference for the clinical translation of other PET agents generated by this technique in the future.

Radiolabeling Diaminosarcophagine with Cyclotron-Produced Cobalt-55 and [55Co]Co-NT-Sarcage as a Proof of Concept in a Murine Xenograft Model.

Cobalt-sarcophagine complexes exhibit high kinetic inertness under various stringent conditions, but there is limited literature on radiolabeling and in vivo positron emission tomography (PET) imaging using no carrier added 55Co. To fill this gap, this study first investigates the radiolabeling of DiAmSar (DSar) with 55Co, followed by stability evaluation in human serum and EDTA, pharmacokinetics in mice, and a direct comparison with [55Co]CoCl2 to assess differences in pharmacokinetics. Furthermore, the radiolabeling process was successfully used to generate the NTSR1-targeted PET agent [55Co]Co-NT-Sarcage (a DSar-functionalized SR142948 derivative) and administered to HT29 tumor xenografted mice. The [55Co]Co-DSar complex can be formed at 37 °C with purity and stability suitable for preclinical in vivo radiopharmaceutical applications, and [55Co]Co-NT-Sarcage demonstrated prominent tumor uptake with a low background signal. In a direct comparison with [64Cu]Cu-NT-Sarcage, [55Co]Co-NT-Sarcage achieved a higher tumor-to-liver ratio but with overall similar biodistribution profile. These results demonstrate that Sar would be a promising chelator for constructing Co-based radiopharmaceuticals including 55Co for PET and 58mCo for therapeutic applications.

Chelator boosted tumor-retention and pharmacokinetic properties: development of 64Cu labeled radiopharmaceuticals targeting neurotensin receptor.

PURPOSE: Accumulating evidence suggests that neurotensin (NTS) and neurotensin receptors (NTSRs) play key roles in lung cancer progression by triggering multiple oncogenic signaling pathways. This study aims to develop Cu-labeled neurotensin receptor 1 (NTSR1)-targeting agents with the potential for both imaging and therapeutic applications. METHOD: A series of neurotensin receptor antagonists (NRAs) with variable propylamine (PA) linker length and different chelators were synthesized, including [64Cu]Cu-CB-TE2A-iPA-NRA ([64Cu]Cu-4a-c, i = 1, 2, 3), [64Cu]Cu-NOTA-2PA-NRA ([64Cu]Cu-4d), [64Cu]Cu-DOTA-2PA-NRA ([64Cu]Cu-4e, also known as [64Cu]Cu-3BP-227), and [64Cu]Cu-DOTA-VS-2PA-NRA ([64Cu]Cu-4f). The series of small animal PET/CT were conducted in H1299 lung cancer model. The expression profile of NTSR1 was also confirmed by IHC using patient tissue samples. RESULTS: For most of the compounds studied, PET/CT showed prominent tumor uptake and high tumor-to-background contrast, but the tumor retention was strongly influenced by the chelators used. For previously reported 4e, [64Cu]Cu-labeled derivative showed initial high tumor uptake accompanied by rapid tumor washout at 24 h. The newly developed [64Cu]Cu-4d and [64Cu]Cu-4f demonstrated good tumor uptake and tumor-to-background contrast at early time points, but were less promising in tumor retention. In contrast, our lead compound [64Cu]Cu-4b demonstrated 9.57 ± 1.35, 9.44 ± 2.38 and 9.72 ± 4.89%ID/g tumor uptake at 4, 24, and 48 h p.i., respectively. Moderate liver uptake (11.97 ± 3.85, 9.80 ± 3.63, and 7.72 ± 4.68%ID/g at 4, 24, and 48 h p.i.) was observed with low uptake in most other organs. The PA linker was found to have a significant effect on drug distribution. Compared to [64Cu]Cu-4b, [64Cu]Cu-4a had a lower background, including a greatly reduced liver uptake, while the tumor uptake was only moderately reduced. Meanwhile, [64Cu]Cu-4c showed increased uptake in both the tumor and the liver. The clinical relevance of NTSR1 was also demonstrated by the elevated tumor expression in patient tissue samples. CONCLUSIONS: Through the side-by-side comparison, [64Cu]Cu-4b was identified as the lead agent for further evaluation based on its high and sustained tumor uptake and moderate liver uptake. It can not only be used to efficiently detect NTSR1 expression in lung cancer (for diagnosis, patient screening, and treatment monitoring), but also has the great potential to treat NTSR-positive lesions once chelating to the beta emitter 67Cu.

Expression of the Calcium-Sensing Receptor on Normal and Abnormal Parathyroid and Thyroid Tissue.

INTRODUCTION: Current imaging techniques have several limitations in detecting parathyroid glands. We have investigated the calcium-sensing receptor (CaSR) as a potential target for specifically labeling parathyroid glands for radiologic detection. For accurate imaging it is vital that a large differential expression exists between the target tissue and adjacent structures. We sought to investigate the relative abundance of the CaSR in normal and abnormal parathyroid tissue, as well as normal and abnormal thyroid. METHODS: Existing clinical specimens were selected that represented a wide variety of pathologically and clinically confirmed malignant and benign thyroid and parathyroid specimens. Sections were stained for the CaSR using immunohistochemistry and scored for intensity and abundance of expression. (H score = intensity scored from 0 to 3 multiplied by the % of cells at each intensity. Range 0-300). RESULTS: All parathyroid specimens expressed the CaSR to a high degree. Normal parathyroid had the highest H score (271, s.d. 25.4). Abnormal parathyroid specimens were slightly lower but still much higher than normal thyroid (H score 38.3, s.d. 23.3). Medullary thyroid cancer also expressed the CaSR significantly higher than normal thyroid (H score 182, s.d. 69.1, P < 0.001) but below parathyroid levels. Hürthle cell carcinoma expressed the CaSR to a lesser degree but higher than normal thyroid (H score 101, s.d. 46.4, P = 0.0037). CONCLUSIONS: The CaSR is differentially expressed on parathyroid tissue making it a feasible target for parathyroid imaging. False positives might be anticipated with medullary and Hürthle cell cancers.

Modular PET Agent Construction Strategy through Strain-Promoted Double-Click Reagent with Efficient Photoclick Step.

An efficient modular strategy for rapid assembly of positron emission tomography (PET) agents has been developed. The use of a sequential, rapid, and selective double-click reaction allows for a combinatorial approach to the cross-linking of positron emitter-bearing prosthetic groups with various ligands. The strain-promoted azide alkyne cyclization (SPAAC) coupling of 18F-labeled azide synthon with MC-DIBOD, a cyclooctadiyne with one of the triple bonds caged as a cyclopropenone moiety, produces a stable intermediate. A brief exposure of the latter to 350-420 nm light removes protection of the second triple bond allowing for the addition of an azide-tagged biomolecule. The utility of this strategy has been demonstrated by the construction of several PET agents. The value of modularity was demonstrated in the preparation of PSMA PET agents, where the hydrophilicity was easily modified to improve tumor to background contrast.

Development of 18F-Labeled Vinyl Sulfone-PSMAi Conjugates as New PET Agents for Prostate Cancer Imaging.

Radiolabeled prostate-specific membrane antigen (PSMA) ligands have been rapidly adopted as part of patient care for prostate cancer. In this study, a new series of 18F-labeled PSMA-targeting agents was developed based on the high-affinity Glu-ureido-Lys scaffold and 18F-vinyl sulfones (VSs), the tumor uptake and tumor/major organ contrast of which could be tuned by pharmacokinetic linkers within the molecules. In particular, 18F-PEG3-VS-PSMAi showed the highest tumor uptake (12.1 ± 2.2%ID/g at 0.5 h p.i.) and 18F-PEG2-VS-PSMAi showed the highest tumor-to-liver ratio (T/L = 3.7 ± 1.0, 4.8 ± 1.2, and 6.3 ± 1.1 at 0.5, 1.5, and 3 h p.i. respectively). Significantly, compared with the FDA-approved 68Ga-PSMA-11, the newly developed 18F-PEG3-VS-PSMAi has an almost double tumor uptake (P < 0.0001) when tested in the same animal model. In conclusion, 18F-VS-labeled PSMA ligands are promising PET agents with prominent tumor uptake and high contrast. The lead agents 18F-PEG2-VS-PSMAi and 18F-PEG3-VS-PSMAi warrant further evaluation in prostate cancer patients.

The Synthesis and Initial Evaluation of MerTK Targeted PET Agents.

MerTK (Mer tyrosine kinase), a receptor tyrosine kinase, is ectopically or aberrantly expressed in numerous human hematologic and solid malignancies. Although a variety of MerTK targeting therapies are being developed to enhance outcomes for patients with various cancers, the sensitivity of tumors to MerTK suppression may not be uniform due to the heterogeneity of solid tumors and different tumor stages. In this report, we develop a series of radiolabeled agents as potential MerTK PET (positron emission tomography) agents. In our initial in vivo evaluation, [18F]-MerTK-6 showed prominent uptake rate (4.79 ± 0.24%ID/g) in B16F10 tumor-bearing mice. The tumor to muscle ratio reached 1.86 and 3.09 at 0.5 and 2 h post-injection, respectively. In summary, [18F]-MerTK-6 is a promising PET agent for MerTK imaging and is worth further evaluation in future studies.

Image-guided selection of Gd@C-dots as sensitizers to improve radiotherapy of non-small cell lung cancer.

BACKGROUND: Recently, gadolinium-intercalated carbon dots (Gd@C-dots) have demonstrated potential advantages over traditional high-Z nanoparticles (HZNPs) as radiosensitizers due to their high stability, minimal metal leakage, and remarkable efficacy. RESULTS: In this work, two Gd@C-dots formulations were fabricated which bore carboxylic acid (CA-Gd@C-dots) or amino group (pPD-Gd@C-dots), respectively, on the carbon shell. While it is critical to develop innovative nanomateirals for cancer therapy, determining their tumor accumulation and retention is equally important. Therefore, in vivo positron emission tomography (PET) was performed, which found that 64Cu-labeled pPD-Gd@C-dots demonstrated significantly improved tumor retention (up to 48 h post injection) compared with CA-Gd@C-dots. Indeed, cell uptake of 64Cu-pPD-Gd@C-dots reached close to 60% of total dose compared with ~ 5% of 64Cu-CA-Gd@C-dots. pPD-Gd@C-dots was therefore further evaluated as a new radiosensitizer for non-small cell lung cancer treatment. While single dose radiation plus intratumorally injected pPD-Gd@C-dots did lead to improved tumor suppression, the inhibition effect was further improved with two doses of radiation. The persistent retention of pPD-Gd@C-dots in tumor region eliminates the need of reinjecting radiosensitizer for the second radiation. CONCLUSIONS: PET offers a simple and straightforward way to study nanoparticle retention in vivo, and the selected pPD-Gd@C-dots hold great potential as an effective radiosensitizer.

Escalating morphine dosing in HIV-1 Tat transgenic mice with sustained Tat exposure reveals an allostatic shift in neuroinflammatory regulation accompanied by increased neuroprotective non-endocannabinoid lipid signaling molecules and amino acids.

BACKGROUND: Human immunodeficiency virus type-1 (HIV-1) and opiates cause long-term inflammatory insult to the central nervous system (CNS) and worsen disease progression and HIV-1-related neuropathology. The combination of these proinflammatory factors reflects a devastating problem as opioids have high abuse liability and continue to be prescribed for certain patients experiencing HIV-1-related pain. METHODS: Here, we examined the impact of chronic (3-month) HIV-1 transactivator of transcription (Tat) exposure to short-term (8-day), escalating morphine in HIV-1 Tat transgenic mice that express the HIV-1 Tat protein in a GFAP promoter-regulated, doxycycline (DOX)-inducible manner. In addition to assessing morphine-induced tolerance in nociceptive responses organized at spinal (i.e., tail-flick) and supraspinal (i.e., hot-plate) levels, we evaluated neuroinflammation via positron emission tomography (PET) imaging using the [18F]-PBR111 ligand, immunohistochemistry, and cytokine analyses. Further, we examined endocannabinoid (eCB) levels, related non-eCB lipids, and amino acids via mass spectrometry.  RESULTS: Tat-expressing [Tat(+)] transgenic mice displayed antinociceptive tolerance in the tail withdrawal and hot-plate assays compared to control mice lacking Tat [Tat(-)]. This tolerance was accompanied by morphine-dependent increases in Iba-1 ± 3-nitrotryosine immunoreactive microglia, and alterations in pro- and anti-inflammatory cytokines, and chemokines in the spinal cord and striatum, while increases in neuroinflammation were absent by PET imaging of [18F]-PBR111 uptake. Tat and morphine exposure differentially affected eCB levels, non-eCB lipids, and specific amino acids in a region-dependent manner. In the striatum, non-eCB lipids were significantly increased by short-term, escalating morphine exposure, including peroxisome proliferator activator receptor alpha (PPAR-α) ligands N-oleoyl ethanolamide (OEA) and N-palmitoyl ethanolamide (PEA), as well as the amino acids phenylalanine and proline. In the spinal cord, Tat exposure increased amino acids leucine and valine, while morphine decreased levels of tyrosine and valine but did not affect eCBs or non-eCB lipids. CONCLUSION: Overall results demonstrate that 3 months of Tat exposure increased morphine tolerance and potentially innate immune tolerance evidenced by reductions in specific cytokines (e.g., IL-1α, IL-12p40) and microglial reactivity. In contrast, short-term, escalating morphine exposure acted as a secondary stressor revealing an allostatic shift in CNS baseline inflammatory responsiveness from sustained Tat exposure.

Tetrazine-TCO Ligation: A Potential Simple Approach to Improve Tumor Uptake through Enhanced Blood Circulation.

Targeted imaging via peptides has been extensively investigated for both diagnostic and therapeutic applications. However, peptides can be cleared out from the blood circulation quickly, leading to only moderate to low accumulation in regions of interest. Previously, 18F-sTCO-DiPhTz-RGDyK demonstrated relatively high blood retention with increased tumor uptake at the late time point (5.3 ± 0.4 and 8.9 ± 0.5%ID/g tumor uptake at 1 h p.i. and 4 h p.i., respectively). In this study, we aim to develop a novel platform based on TCO/tetrazine ligation that could be used not only to label the peptides with F-18 for PET but also to lead to increased or persistent tumor uptake potentially due to enhanced blood circulation of the labeled peptides. We first constructed systems containing different combinations of TCOs/tetrazines and found that the tetrazine moiety played a more important role to facilitate the enhanced blood circulation compared with TCO moiety. Four clinically relevant peptides including NT20.3, RGD, BBN, and exendin-4 were then evaluated, and the increased tumor uptake at a late time point was demonstrated by the combination of 18F-sTCO-DiPhTz system to NT20.3, RGD, and exendin-4. The plasma binding components of the PET agents were investigated by electrophoresis and autoradiography and indicated that transferrin and hemopexin could be the major proteins in blood plasma for binding with 18F-sTCO-DiPhTz conjugates. In summary, we have discovered a TCO/tetrazine system that could not only be used for PET probe construction but also potentially improve the tumor uptake and retention of fast-clearing peptides. Although additional binding experiments are still needed for some of the constructs, the promising preliminary result suggested that this strategy may be used to convert fast-clearing bioligands into relatively long circulating agents with enhanced tumor uptake/retention for either imaging or therapy applications.

RXH-Reactive 18F-Vinyl Sulfones as Versatile Agents for PET Probe Construction.

Efficient radiolabeling reactions are important chemical tools in biomedical research especially in probe construction. Herein, three 18F-labeled vinyl sulfones were prepared. In particular, 18F-PEG1-VS (((2-(2-(fluoro-18F)ethoxy)ethyl)sulfonyl)ethane) could not only allow chemoselective labeling of bioactive molecules containing -XH (X = S, NH) groups, but also react with red blood cells both in vitro and in living mice for potential cell tracking applications. In addition, these hydrophilic agents were found to cross the blood brain barrier (BBB) efficiently and localize at the cerebellum region. In summary, 18F-labeled vinyl sulfones provide a versatile platform for PET probe construction.

Development of Bispecific NT-PSMA Heterodimer for Prostate Cancer Imaging: A Potential Approach to Address Tumor Heterogeneity.

Prostate cancer is a heterogeneous disease with a poor survival rate at late stage. In this report, a dual targeting PET agent was developed to partially address the tumor heterogeneity issue. The heterodimer F-BCN-PSMA-NT was designed to target PSMA and neurotensin receptor1 (NTR1), both of which have demonstrated great potential in prostate cancer management. The heterodimer was synthesized through the conjugation of Glu-urea-lys(Ahx) (PSMA targeting motif) and NT20.3 (NTR1 targeting motif) to a symmetric trifunctional linker, bearing an azide group for further modification. Radio-labeling was performed using strain promoted azide-alkyne click reaction with high yield. Cell based assays suggested that F-BCN-PSMA-NT has comparable or only slightly reduced binding affinity with the corresponding monomers. Small animal PET clearly demonstrated that the heterodimer probe has prominent uptake not only in NTR1 positive/PSMA negative PC-3 tumors (1.4 ± 0.3%ID/g), but also in the PSMA positive/NTR1 negative LnCap tumors (1.3 ± 0.2%ID/g). The tracer showed comparable tumor to background ratio with each monomer. In summary, prostate cancer is a heterogeneous disease in need of improved diagnostics and treatments. The PSMA-NT heterodimer represents a new class of molecules that can be used to target two distinct antigens related to prostate cancer. In addition to the imaging applications demonstrated in this study, the agent also holds great potential on the treatment of heterogeneous prostate cancer.

Evaluation of neurotensin receptor 1 as potential biomarker for prostate cancer theranostic use.

INTRODUCTION: Despite recent developments in the diagnosis and treatment of prostate cancer, the advanced stages still have poor survival rates. This warrants further exploration of related molecular targets for patient screening, detection of metastatic disease, and treatment/treatment monitoring. Recent studies have indicated that neurotensin receptors (NTSRs) and their ligand neurotensin (NTS) critically affect the progression of prostate cancers. In this study, we evaluated the expression of neurotensin receptor1 (NTSR1) in patient tissues and performed NTSR1 PET imaging in a prostate cancer animal model. METHODS: The NTSR1 expression was evaluated in 97 cases of prostate cancer and 100 cases of benign prostatic hyperplasia (BPH) of clinical patients by immunohistochemistry staining. The expression profile of PSMA and GRPR was also performed for comparison. The mRNA expression of NTSR1 in LnCap and PC-3 cells was measured by PCR. NTSR1 PET, and biodistribution studies were performed in PC-3 xenografts using 18F-DEG-VS-NT. RESULTS: NTSR1 showed high or moderate expression in 91.8% of prostate cancer tissue, compared with PSMA (86.7%) and GRPR (65.3%). All examined PSMA-negative tissues showed positive NTSR1 expression, suggesting the potential complementary role of NTSR1 targeted imaging or therapy. Only 8% of BPH shows strong or moderate expression of NTSR1, which is significantly lower than that in prostate cancer (91.8%). PCR results indicated LNCap (an androgen-dependent prostate cancer cell) showed negative NTSR1 expression while PC-3 demonstrated positive expression (an androgen-independent prostate cancer cell), which correlated well with previously reported western blot results. In a preclinical animal model, NTSR1 targeted PET probe 18F-DEG-VS-NT demonstrated prominent tumor accumulation and low background. CONCLUSION: We have demonstrated that NTSR1 is a promising molecular marker for prostate cancer based on patient tissue staining. The NTSR targeted probe 18F-DEG-VS-NT demonstrated high tumor to background contrast in animal models, which could be valuable in selecting patients for therapies targeting NTSR1 as well as monitoring therapeutic efficacy during treatment accordingly.

Development of [18F]AlF-NOTA-NT as PET Agents of Neurotensin Receptor-1 Positive Pancreatic Cancer.

Several studies have suggested that neurotensin receptors (NTRs) and neurotensin (NT) greatly affect the growth and survival of pancreatic ductal adenocarcinoma (PDAC). Developing NTR-targeted PET probes could therefore be important for the management of a pancreatic cancer patient by providing key information on the NTR expression profile noninvasively. Despite the initial success on the synthesis of 18F-labeled NT PET probes, the labeling procedure generally requires lengthy steps including azeotropic drying of 18F. Using a straightforward chelation method, here we report the simple preparation of aluminum-18F-NOTA-NT starting from aqueous 18F. The cell binding test demonstrated that [19F]AlF-NOTA-NT maintained high receptor-binding affinity to NTR1. This probe was then further evaluated in NTR1 positive pancreatic tumor models (AsPC-1 and PANC-1). After the administration of [18F]AlF-NOTA-NT, small animal PET studies showed a high contrast between tumor and background in both models at 1 and 4 h time points. A blocking experiment was performed to demonstrate the receptor specificity: the tumor uptake in AsPC1 without and with blocking agent was 1.0 ± 0.2 and 0.1 ± 0.0%ID/g, respectively, at 4 h post injection. In summary, a NTR specific PET agent, [18F]AlF-NOTA-NT, was prepared through the simple chelation method. This NTR-targeted PET probe may not only be used to detect NTR1 positive pancreatic tumors (diagnosis), but also it may be fully integrated to NTR target therapy leading to personalized medicine (theranostic).

Protein Nanocage Mediated Fibroblast-Activation Protein Targeted Photoimmunotherapy To Enhance Cytotoxic T Cell Infiltration and Tumor Control.

Carcinoma-associated fibroblasts (CAFs) are found in many types of cancer and play an important role in tumor growth and metastasis. Fibroblast-activation protein (FAP), which is overexpressed on the surface of CAFs, has been proposed as a universal tumor targeting antigen. However, recent studies show that FAP is also expressed on multipotent bone marrow stem cells. A systematic anti-FAP therapy may lead to severe side effects and even death. Hence, there is an urgent need of a therapy that can selectively kill CAFs without causing systemic toxicity. Herein we report a nanoparticle-based photoimmunotherapy (nano-PIT) approach that addresses the need. Specifically, we exploit ferritin, a compact nanoparticle protein cage, as a photosensitizer carrier, and we conjugate to the surface of ferritin a FAP-specific single chain variable fragment (scFv). With photoirradiation, the enabled nano-PIT efficiently eliminates CAFs in tumors but causes little damage to healthy tissues due to the localized nature of the treatment. Interestingly, while not directly killing cancer cells, the nano-PIT caused efficient tumor suppression in tumor-bearing immunocompetent mice. Further investigations found that the nano-PIT led to suppressed C-X-C motif chemokine ligand 12 (CXCL12) secretion and extracellular matrix (ECM) deposition, both of which are regulated by CAFs in untreated tumors and mediate T cell exclusion that prevents physical contact between T cells and cancer cells. By selective killing of CAFs, the nano-PIT reversed the effect, leading to significantly enhanced T cell infiltration, followed by efficient tumor suppression. Our study suggests a new and safe CAF-targeted therapy and a novel strategy to modulate tumor microenvironment (TME) for enhanced immunity against cancer.

Imaging Neurotensin Receptor in Prostate Cancer With 64Cu-Labeled Neurotensin Analogs.

INTRODUCTION: Neurotensin receptor 1 (NTR-1) is expressed and activated in prostate cancer cells. In this study, we explore the NTR expression in normal mouse tissues and study the positron emission tomography (PET) imaging of NTR in prostate cancer models. MATERIALS AND METHODS: Three 64Cu chelators (1, 4, 7, 10-tetraazacyclododecane-1, 4, 7, 10-tetraacetic acid [DOTA], 1,4,7-triazacyclononane-N,N',N″-triacetic acid [NOTA], or AmBaSar) were conjugated to an NT analog. Neurotensin receptor binding affinity was evaluated using cell binding assay. The imaging profile of radiolabeled probes was compared in well-established NTR+ HT-29 tumor model. Stability of the probes was tested. The selected agents were further evaluated in human prostate cancer PC3 xenografts. RESULTS: All 3 NT conjugates retained the majority of NTR binding affinity. In HT-29 tumor, all agents demonstrated prominent tumor uptake. Although comparable stability was observed, 64Cu-NOTA-NT and 64Cu-AmBaSar-NT demonstrated improved tumor to background contrast compared with 64Cu-DOTA-NT. Positron emission tomography/computed tomography imaging of the NTR expression in PC-3 xenografts showed high tumor uptake of the probes, correlating with the in vitro Western blot results. Blocking experiments further confirmed receptor specificity. CONCLUSIONS: Our results demonstrated that 64Cu-labeled neurotensin analogs are promising imaging agents for NTR-positive tumors. These agents may help us identify NTR-positive lesions and predict which patients and individual tumors are likely to respond to novel interventions targeting NTR-1.

Evaluation of neurotensin receptor 1 as a potential imaging target in pancreatic ductal adenocarcinoma.

Pancreatic cancer is one of the deadliest human malignancies and lack of effective diagnostic and therapeutic methods. Accumulating evidence suggests that the neurotensin (NT) and neurotensin receptors (NTRs) play key roles in pancreatic adenocarcinoma growth and survival. In this study, we not only evaluate the NTR1 expression in pancreatic cancer patient samples, but also explore the PET and fluorescence imaging of NTR1 expression in pancreatic cancer animal models. The NTR1 expression was evaluated by immunohistochemistry staining in clinical patient tissue samples with pancreatic ductal adenocarcinoma, insulinoma, and pancreatitis. The results showed 79.4% positive rate of NRT1 expression in pancreatic ductal adenocarcinoma, compared with 33.3 and 22.7% in insulinoma and pancreatitis samples, respectively. High NTR1 gene expression was also found in Panc-1 cells and confirmed by cell immunofluorescence. 64Cu-AmBaSar-NT and IRDye800-NT were synthesized as imaging probes and maintained the majority of NTR1-binding affinity. In vivo imaging demonstrated that 64Cu-AmBaSar-NT has prominent tumor uptake (3.76 ± 1.45 and 2.29 ± 0.10%ID/g at 1 and 4 h post-injection). NIR fluorescent imaging with IRDye800-NT demonstrated good tumor-to-background contrast (8.09 ± 0.38 × 108 and 6.67 ± 0.43 × 108 (p/s/cm2/sr)/(µW/cm2) at 30 and 60 min post-injection). Fluorescence guided surgery was also performed as a proof of principle experiment. In summary, our results indicated that NTR1 is a promising target for pancreatic ductal adenocarcinoma imaging and therapy. The imaging probes reported here may not only be considered for improved diagnosis of pancreatic ductal adenocarcinoma, but also has the potential to be fully integrated into patient screening and treatment monitoring of future NTR1 targeted therapies.

Molecular Imaging of P-glycoprotein in Chemoresistant Tumors Using a Dual-Modality PET/Fluorescence Probe.

Overexpression of P-glycoprotein (Pgp) has been considered a primary cause for multidrug resistance in a variety of cancers for three decades. However, clinical translation of Pgp targeted therapeutics has been hindered by lack of patient preselection based on the Pgp presence in tumors. We aim to develop a molecularly targeted probe for imaging tumoral Pgp in vivo with positron emission tomography (PET) and fluorescence, and to provide a tool for preselecting the patients with tumoral Pgp expression. Thus, a Pgp monoclonal antibody 15D3 was chemically modified with IRDye800 (IR800) and DOTA chelator. The specificity of the antibody conjugates DOTA-Pab-IR800 was verified in Pgp-expressing 3T3-MDR1 and control 3T3 cells. After radiolabeling with 64Cu, the probe was applied in small animal PET imaging of Pgp in a mouse xenograft model of NCI/ADR-Res cells, which are chemoresistant through overexpression of Pgp. Quantification analysis of the PET images demonstrated that the tumor uptake of the radioactive probe was 9.9 ± 1.4, 12.1 ± 1.2, and 10.5 ± 1.0%ID/g at 4, 24, and 48 h post injection. The tumor-to-muscle ratio was 20.9 at 48 h post injection based on biodistribution studies. Fluorescence imaging was performed following PET experiments, and it demonstrated excellent tumor accumulation of this dual-modality probe in the NCI/ADR-Res tumors. Further, an image-guided surgery was successfully performed using the fluorescence modality of the probe, demonstrating potential utility of this probe in image-guided surgical removal of Pgp-positive drug resistant tumors in the patients. In conclusion, this study clearly demonstrated that the Pgp-targeted antibody probe, 64Cu-DOTA-Pab-IR800, could provide a promising diagnosis tool for detection of Pgp-expressing tumors in vivo.

Synthesis and Evaluation of [(18) F]-Ammonium BODIPY Dyes as Potential Positron Emission Tomography Agents for Myocardial Perfusion Imaging.

Recently, we demonstrated the potential of a [(18) F]-trimethylammonium BODIPY dye for cardiac imaging. This is the first example of the use of the [(18) F]-ammonium BODIPY dye for positron emission tomography (PET) myocardial perfusion imaging (MPI). In this report, we extend our study to other ammonium BODIPY dyes with different nitrogen substituents. These novel ammonium BODIPY dyes were successfully prepared and radiolabeled by the SnCl4 -assisted (18) F-(19) F isotopic exchange method. The microPET results and the biodistribution data reveal that nitrogen substituent changes have a significant effect on the in vivo and pharmacological properties of the tracers. Of the novel [(18) F]-ammonium BODIPY dyes prepared in this work, the [(18) F]-dimethylethylammonium BODIPY is superior in terms of myocardium uptake and PET imaging contrast. These results support our hypothesis that the ammonium BODIPY dyes have a great potential for use as PET/optical dual-modality MPI probes.