Suitability of [18F]Altanserin and PET to Determine 5-HT2A Receptor Availability in the Rat Brain: In Vivo and In Vitro Validation of Invasive and Non-Invasive Kinetic Models

Purpose

While the selective 5-hydroxytryptamine type 2a receptor (5-HT_2AR) radiotracer [¹⁸F]altanserin is well established in humans, the present study evaluated its suitability for quantifying cerebral 5-HT_2ARs with positron emission tomography (PET) in albino rats.

Procedures

Ten Sprague Dawley rats underwent 180 min PET scans with arterial blood sampling. Reference tissue methods were evaluated on the basis of invasive kinetic models with metabolite-corrected arterial input functions. In vivo 5-HT_2AR quantification with PET was validated by in vitro autoradiographic saturation experiments in the same animals.

Result

Overall brain uptake of [¹⁸F]altanserin was reliably quantified by invasive and non-invasive models with the cerebellum as reference region shown by linear correlation of outcome parameters. Unlike in humans, no lipophilic metabolites occurred so that brain activity derived solely from parent compound. PET data correlated very well with in vitro autoradiographic data of the same animals.

Conclusion

[¹⁸F]Altanserin PET is a reliable tool for in vivo quantification of 5-HT_2AR availability in albino rats. Models based on both blood input and reference tissue describe radiotracer kinetics adequately. Low cerebral tracer uptake might, however, cause restrictions in experimental usage.     

Magnetomotive Optical Coherence Tomography for the Assessment of Atherosclerotic Lesions Using αvβ3 Integrin-Targeted Microspheres

Purpose

We investigated the early-stage fatty streaks/plaques detection using magnetomotive optical coherence tomography (MM-OCT) in conjunction with α_vβ₃ integrin-targeted magnetic microspheres (MSs). The targeting of functionalized MSs was investigated by perfusing ex vivo aortas from an atherosclerotic rabbit model in a custom-designed flow chamber at physiologically relevant pulsatile flow rates and pressures.

Procedures

Aortas were extracted and placed in a flow chamber. Magnetic MS contrast agents were perfused through the aortas and MM-OCT, fluorescence confocal, and bright field microscopy were performed on the ex vivo aorta specimens for localizing the MSs.

Results

The results showed a statistically significant and stronger MM-OCT signal (3.30?±?1.73 dB) from the aorta segment perfused with targeted MSs, compared with the nontargeted MSs (1.18?±?0.94 dB) and control (0.78?±?0.41 dB) aortas. In addition, there was a good co-registration of MM-OCT signals with confocal microscopy.

Conclusions

Early-stage fatty streaks/plaques have been successfully detected using MM-OCT in conjunction with α_vβ₃ integrin-targeted magnetic MSs.     

Effects of Chelator Modifications on 68Ga-Labeled [Tyr3]Octreotide Conjugates

Purpose

Somatostatin receptors (SSTR) have been reported as promising targets for imaging agents for cancer. Recently, ⁶⁸Ga-DOTATOC-based PET imaging has been used successfully for diagnosis and management of SSTR-expressing tumors. The purpose of this study was to evaluate the influence of chelator modifications and charge on ⁶⁸Ga-labeled peptide conjugates.

Procedures

We have synthesized a series of [Tyr³]octreotide conjugates that consisted of different NOTA-based chelators with two to five carboxylate moieties, and compared our results with ⁶⁸Ga-DOTATOC in both in vitro and in vivo studies.

Results

With the exception of ⁶⁸Ga-1 (three carboxylates), the increased number of carboxylates on the NOTA-based chelators resulted in a reduced binding affinity and internalization. Additionally, the tumor uptake for ⁶⁸Ga-2 (four carboxylates) and ⁶⁸Ga-3 (five carboxylates) was reduced compared to that of ⁶⁸Ga-DOTATOC (three carboxylates) and ⁶⁸Ga-NO2ATOC (two carboxylates) and ⁶⁸Ga-1 (three carboxylates) at 2 h p.i. suggesting the presence of an optimal charge for this compound.

Conclusions

Chelator modifications can lead to the altered pharmacokinetics. These results may impact further design considerations for peptide-based imaging agents.     

Sunitinib–CLIO Conjugate: A VEGFR/PDGFR-Targeting Active MR Probe

Purpose

This study was conducted to evaluate feasibility of sunitinib–CLIO conjugate as a vascular endothelial growth factor receptor/platelet-derived growth factor receptor (VEGFR/PDGFR)-specific magnetic resonance (MR) probe.

Procedure

VEGFR/PDGFR-targeting MR probe was synthesized by conjugating cross-linked iron-oxide (CLIO) with tyrosine-kinase inhibitor (sunitinib). In VEGFR/PDGFR-positive (U118MG) and VEGFR/PDGFR-negative (HT29) cells and tumor models, conjugate-driven ΔR ₂ was estimated, while CLIO was used as control. Prussian-blue staining was performed for quantifying the amount of tumor-binding conjugates.

Results

ΔR ₂ between sunitinib–CLIO-treated and non-treated cells was greater in U118MG (mean, 2.1/s) than in HT29 cells (1.0/s). In in vivo study, conjugate induced a greater ΔR ₂ in U118MG (11.2/s) than HT29 tumors (5.9/s). Conjugate-induced R ₂ changes were not correlated with degree of Gd-DTPA enhancement, demonstrating that tumor binding of sunitinib–CLIO was independent of enhanced permeability and retention effect. % area of Prussian-blue staining was greater in U118MG (8.5 %) than in HT29 (1.4 %).

Conclusions

Sunitinib–CLIO conjugate can be used as an active MR probe for quantifying VEGFR/PDGFR.     

MRI of ICAM-1 Upregulation After Stroke: the Importance of Choosing the Appropriate Target-Specific Particulate Contrast Agent

Purpose

Magnetic resonance imaging (MRI) with targeted contrast agents provides a promising means for diagnosis and treatment monitoring after cerebrovascular injury. Our goal was to demonstrate the feasibility of this approach to detect the neuroinflammatory biomarker intercellular adhesion molecule-1 (ICAM-1) after stroke and to establish a most efficient imaging procedure.

Procedures

We compared two types of ICAM-1-functionalized contrast agent: T ₁-shortening gadolinium chelate-containing liposomes and T ₂ ⁽*⁾-shortening micron-sized iron oxide particles (MPIO). Binding efficacy and MRI contrast effects were tested in cell cultures and a mouse stroke model.

Results

Both ICAM-1-targeted agents bound effectively to activated cerebrovascular cells in vitro, generating significant MRI contrast-enhancing effects. Direct in vivo MRI-based detection after stroke was only achieved with ICAM-1-targeted MPIO, although both contrast agents showed similar target-specific vascular accumulation.

Conclusions

Our study demonstrates the potential of in vivo MRI of post-stroke ICAM-1 upregulation and signifies target-specific MPIO as most suitable contrast agent for molecular MRI of cerebrovascular inflammation.     

Effects of exercise training on exercise capacity in patients with non-small cell lung cancer receiving targeted therapy

Purpose

Peak oxygen consumption (VO_2peak) is an important predictive factor for long-term prognosis in patients with non-small cell lung cancer (NSCLC). The purpose of this study was to investigate whether 8 weeks of exercise training improves exercise capacity, as assessed by VO_2peak, and other related factors in patients with NSCLC receiving targeted therapy.

Methods

A total of 24 participants with adenocarcinoma were randomly assigned to either the control group (n?=?11) or the exercise group (n?=?13). Subjects in the exercise group participated in individualized, high-intensity aerobic interval training of exercise. The outcome measures assessed at baseline and after 8?weeks were as follows: VO_2peak and the percentage of predicted VO_2peak (%predVO_2peak), muscle strength and endurance of the right quadriceps, muscle oxygenation during exercise, insulin resistance as calculated by the homeostasis model, high-sensitivity C-reactive protein, and quality of life (QoL) questionnaire inventory.

Results

No exercise-related adverse events were reported. After exercise training, VO_2peak and %predVO_2peak increased by 1.6?mL?kg^?1?min^?1 and 5.3% (p?<?0.005), respectively; these changes were associated with improvements in circulatory, respiratory, and muscular functions at peak exercise (all p?=?0.001). The exercise group also had less dyspnea (p?=?0.01) and favorably lower fatigue (p?=?0.05) than baseline.

Conclusions

Patients with NSCLC receiving targeted therapy have quite a low exercise capacity, even with a relatively high QoL. Exercise training appears to improve exercise capacity and alleviate some cancer-related symptoms.     

Electrophilic Addition of Chlorine Monofluoride for PET tracers

Purpose

We have studied the utility of [¹⁸F]ClF electrophilic addition to the carbon–carbon double bond of analogues of a model positron emission tomography (PET) tracer, [¹⁸F]EF5. The consequence of simultaneous chlorine/fluorine addition on lipophilicity and biological activity of the molecule is evaluated.

Procedures

Post-target produced [¹⁸F]F₂ was reacted with Cl₂ to produce [¹⁸F]ClF, which was used in electrophilic addition.

Results

[¹⁸F]ClF was produced and used to label chlorinated analogues of [¹⁸F]EF5. The chlorinated analogues, [¹⁸F]EF4Cl_a and [¹⁸F]EF4Cl_b, were synthesized simultaneously. The in vivo uptake of the analogues compared well with [¹⁸F]EF5 uptake in tumor-bearing mice.

Conclusion

[¹⁸F]ClF is a suitable labeling reagent for electrophilic addition to double bonds of PET tracers. The results show that the modification of the pentafluoro group of [¹⁸F]EF5 by monofluorine-for-chlorine exchange affected the lipophilicity, but the hypoxia avidity of these molecules was not apparently altered.     

Fully Automated Radiosynthesis of 2-[18F]Fludarabine for PET Imaging of Low-Grade Lymphoma

Purpose

An efficient and fully automated radiosynthesis of 2-[¹⁸F]fluoro-9-β-d-arabinofuranosyl-adenine (2-[¹⁸F]fludarabine, [¹⁸F]-5) based on a GE TRACERlab? FX-FN module has been developed.

Procedures

A 2-nitro purine derivative 3 was developed as precursor for labeling with fluorine-18. The radiosynthesis of [¹⁸F]-5 was performed in two steps in a single reactor with an intermediary purification on Sep-Pak® silica which involved the addition of a three-way valve on the original module. After hydrolysis, [¹⁸F]-5 was purified by semi-preparative high-pressure liquid chromatography (HPLC) and a quality control was established.

Results

The labeling precursor 3 was obtained in 45 % overall yield. Nucleophilic substitution with K¹⁸F/K_2.2.2 afforded protected 2-[¹⁸F]fludarabine ([¹⁸F]-4) in 73?±?4 % , radiochemical yield (decay corrected to the end of bombardment (EOB)) and based on the initial [¹⁸F]F^? activity. An aqueous ammonia/methanol solution was used for the deprotection reaction and gave the desired [¹⁸F]-5 in 67?±?3 % yield after 20 min at 70 °C based on HPLC profile.

Conclusions

The process afforded pure 2-[¹⁸F]fludarabine in 48?±?3 % yield (decay corrected to the EOB) in 85 min, with a specific activity of 310?±?72 GBq/μmol at the end of synthesis (EOS) and a radiochemical purity up to 99 %.     

Positron Emission Tomography with [18F]-3′-Deoxy-3′fluorothymidine (FLT) as a Predictor of Outcome in Patients with Locally Advanced Resectable Rectal Cancer: a Pilot Study

Purpose

This pilot study was performed to evaluate whether tumor uptake of ¹⁸F-labeled 3′-deoxy-3′fluorothymidine (FLT), a proliferative radiotracer, at baseline and early during therapy, is predictive of outcome in locally advanced rectal cancer.

Procedures

Fourteen patients underwent positron emission tomography (PET) with 2-deoxy-2-[¹⁸F]fluoro-d-glucose (FDG) and FLT before therapy and PET with FLT approximately 2 weeks after initiating neoadjuvant chemoradiotherapy. FLT and FDG uptake were evaluated qualitatively and by maximum standardized uptake value (SUV_max). Tumor FLT and FDG uptake were correlated with disease-free survival (DFS).

Results

Thirteen patients underwent surgery after therapy, one died before surgery with progressive disease. FDG-PET/computed tomography detected regional lymph node metastases in five and FLT-PET was positive in one. High pretherapy FDG uptake (SUV_max?≥?14.3), low during-therapy FLT uptake (SUV_max?<?2.2), and high percentage change in FLT uptake (≥60 %) were predictive of improved DFS (p?<?0.05 for all three values).

Conclusion

Pretherapy FDG uptake, during-therapy FLT uptake, and percentage change in FLT uptake were equally predictive of DFS.     

Reproducibility of Non-Invasive A1 Adenosine Receptor Quantification in the Rat Brain Using [18F]CPFPX and Positron Emission Tomography

Purpose

The A₁AR antagonist 8-cyclopentyl-3-(3-fluoropropyl)-1-propylxanthine ([¹⁸F]CPFPX) has recently been shown to be a suitable radiotracer for quantitative in vivo imaging of the A₁ adenosine receptor (A₁AR) in rats. The present study evaluates the reproducibility of non-invasive longitudinal A₁AR studies with [¹⁸F]CPFPX and a dedicated small animal positron emission tomography (PET) scanner.

Procedures

Twelve male Sprague Dawley rats underwent four repeated dynamic PET scans with a bolus injection of [¹⁸F]CPFPX. A₁AR availability was determined by different non-invasive approaches including simplified and multilinear reference tissue (olfactory bulb)-based models and graphical methods. The outcome parameter binding potential (BP) was evaluated in terms of variability and reproducibility.

Results

Repeated estimations of [¹⁸F]CPFPX BP _ND gave reliable results with acceptable variability (mean 12 %) and reproducibility (intraclass correlation coefficients raging from 0.57 to 0.68) in cortical and subcortical regions of the rat brain. With regard to kinetic models, test-retest stability of the simplified reference-tissue model (SRTM) was superior to multilinear and graphical approaches.

Conclusions

Non-invasive quantification of A₁AR density in the rat brain is reproducible and reliable with [¹⁸F]CPFPX PET and allows longitudinal designs of in vivo imaging studies in rodents.     

Intramucosal–arterial PCO 2 gap fails to reflect intestinal dysoxia in hypoxic hypoxia

Introduction

An elevation in intramucosal–arterial PCO ₂ gradient (ΔPCO ₂) could be determined either by tissue hypoxia or by reduced blood flow. Our hypothesis was that in hypoxic hypoxia with preserved blood flow, ΔPCO ₂ should not be altered.

Methods

In 17 anesthetized and mechanically ventilated sheep, oxygen delivery was reduced by decreasing flow (ischemic hypoxia, IH) or arterial oxygen saturation (hypoxic hypoxia, HH), or no intervention was made (sham). In the IH group (n = 6), blood flow was lowered by stepwise hemorrhage; in the HH group (n = 6), hydrochloric acid was instilled intratracheally. We measured cardiac output, superior mesenteric blood flow, gases, hemoglobin, and oxygen saturations in arterial blood, mixed venous blood, and mesenteric venous blood, and ileal intramucosal PCO ₂ by tonometry. Systemic and intestinal oxygen transport and consumption were calculated, as was ΔPCO ₂. After basal measurements, measurements were repeated at 30, 60, and 90 minutes.

Results

Both progressive bleeding and hydrochloric acid aspiration provoked critical reductions in systemic and intestinal oxygen delivery and consumption. No changes occurred in the sham group. ΔPCO ₂ increased in the IH group (12 ± 10 [mean ± SD] versus 40 ± 13 mmHg; P < 0.001), but remained unchanged in HH and in the sham group (13 ± 6 versus 10 ± 13 mmHg and 8 ± 5 versus 9 ± 6 mmHg; not significant).

Discussion

In this experimental model of hypoxic hypoxia with preserved blood flow, ΔPCO ₂ was not modified during dependence of oxygen uptake on oxygen transport. These results suggest that ΔPCO ₂ might be determined primarily by blood flow.     

Breast Cancer Cells Imaging By Targeting Methionine Transporters with Gadolinium-Based Nanoprobe

Purpose

Early cancer diagnosis using MRI imaging is of high global interest as a non-invasive and powerful modality. In this study, methionine was conjugated on gadolinium-based mesoporous silica nanospheres to evaluate intra-cellular uptake and its accumulation in human breast cancer cells.

Procedures

The contrast agent was synthesized and characterized using different techniques including N₂ physisorption, thermal gravimetric analysis, dynamic light scattering, and inductively coupled plasma atomic emission spectroscopy (ICP-AES). The intra-cellular uptake of Gd³⁺ was measured by ICP-AES, fluorescent microscopy, and flow cytometry. Finally, cellular and tumor MR imaging were performed to determine in vitro and in vivo relaxometry.

Results

According to the results, the contrast agents accumulated in tumor cells both in vitro and in vivo. There was no significant cellular toxicity on either normal or cancer cells along with strong intense signal on T ₁ compared to the unlabeled cells.

Conclusions

The results showed that the novel contrast agent could become a useful tool in early detection of cancer.     

Facile Synthesis of Folic Acid-Modified Iron Oxide Nanoparticles for Targeted MR Imaging in Pulmonary Tumor Xenografts

Purpose

The purpose of this study was to develop folic acid (FA)-modified iron oxide (Fe₃O₄) nanoparticles (NPs) for targeted magnetic resonance imaging (MRI) of H460 lung carcinoma cells.

Procedures

Water-dispersible Fe₃O₄ NPs synthesized via a mild reduction method were conjugated with FA to generate FA-targeted Fe₃O₄ NPs. The specificity of FA-targeted Fe₃O₄ NPs to bind FA receptor was investigated in vitro by cellular uptake and cell MRI and in vivo by MRI of H460 tumors.

Results

The formed NPs displayed good biocompatibility and ultrahigh r ₂ relaxivity (440.01/mM/s). The targeting effect of the NPs to H460 cells was confirmed by in vitro cellular uptake and cell MRI. H460 tumors showed a significant reduction in T₂ signal intensity at 0.85 h, which then recovered and returned to control at 2.35 h.

Conclusions

The results indicate that the prepared FA-targeted Fe₃O₄ NPs have potential to be used as T₂ negative contrast agents in targeted MRI.

     

Imaging Integrin αvβ3 and NRP-1 Positive Gliomas with a Novel Fluorine-18 Labeled RGD-ATWLPPR Heterodimeric Peptide Probe

Purpose

Radiolabeled Arg-Gly-Asp (RGD) and Ala-Thr-Trp-Leu-Pro-Pro-Arg (ATWLPPR) peptide analogs have received interests for their capability to serve as radiopharmaceuticals for imaging integrin α_vβ₃ and Neuropilin-1 (NRP-1) positive tumors, respectively. In this study, we developed a RGD-ATWLPPR heterodimeric peptide which contained both RGD and ATWLPPR motifs in one molecular probe. The aim of this study was to investigate the dual receptor-targeting property and tumor diagnostic value of RGD-ATWLPPR heterodimeric peptide labeled with fluorine-18 (F-18).

Procedures

A RGD-ATWLPPR heterodimer was synthesized from c(RGDyK) and ATWLPPR through a glutamate linker. The peptide was radiolabeled by reacting the [¹⁸F]fluoride–aluminum complex with the cyclic chelator, 1,4,7-triazacyclononane-1,4,7-triacetic acid (NOTA). The receptor-binding characteristics and tumor-targeting efficacy of [¹⁸F]FAl-NOTA-RGD-ATWLPPR were tested in vitro and in vivo.

Results

RGD-ATWLPPR had affinity for both integrin α_vβ₃ and NRP-1 in vitro. [¹⁸F]FAl-NOTA-RGD-ATWLPPR displayed significantly higher tumor uptake than [¹⁸F]FAl-NOTA-RGD and [¹⁸F]FAl-NOTA-ATWLPPR, both in vitro and in vivo. The uptake of the F-18 labeled heterodimer by an U87MG tumor was inhibited only partially in the presence of an excess amount of unlabeled RGD or ATWLPPR but was blocked completely in the presence of both RGD and ATWLPPR. Compared with the monomeric RGD and ATWLPPR peptides, [¹⁸F]FAl-NOTA-RGD-ATWLPPR showed improved in vivo pharmacokinetics, resulting in a more preferable imaging quality.

Conclusions

[¹⁸F]FAl-NOTA-RGD-ATWLPPR exhibited significantly improved receptor-targeting properties both in vitro and in vivo compared with the F-18 labeled RGD or ATWLPPR monomers. The improved targeting and localization exhibited by the RGD-ATWLPPR heterodimer provide a foundation for further investigations of its applicability in clinical tumor imaging.     

In Vitro and In Vivo Evaluation of the Caspase-3 Substrate-Based Radiotracer [18F]-CP18 for PET Imaging of Apoptosis in Tumors

Purpose

A novel caspase-3 substrate-based probe [¹⁸F]-CP18 was evaluated as an in vivo positron emission tomography (PET) imaging agent for monitoring apoptosis in tumors.

Methods

Uptake of [¹⁸F]-CP18 in cell assays and tumors was measured. Caspase-3/7 activities in cell lysates and tumor homogenates were determined. Autoradiography,Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL), and cleaved caspase-3 immunostaining were performed on adjacent tumor sections to identify areas of apoptosis.

Results

The in vitro cell assays showed caspase-3-dependent uptake of [¹⁸F]-CP18 in tumor cells when treated with an apoptosis inducer. The in vivo microPET imaging signal of [¹⁸F]-CP18 in xenograft tumors correlated with the ex vivo caspase-3/7 activities in these tumors. Furthermore, tumor autoradiographies of [¹⁸F]-CP18 in tumor sections matched adjacent sections stained by TUNEL and caspase-3 immunohistochemistry (IHC).

Conclusions

[¹⁸F]-CP18 demonstrated high affinity and selectivity for activated caspase-3 both in vitro and in vivo, and the results support [¹⁸F]-CP18 as a promising new PET imaging agent for apoptosis.     

Comparison of volumetric capnography and mixed expired gas methods to calculate physiological dead space in mechanically ventilated ICU patients

Introduction

Physiological dead space should be a routine measurement in ventilated patients but measuring dead space using the Douglas bag (DB) method is cumbersome and requires corrections for compressed ventilator gas. These factors make this method impractical in the critical care setting. Volumetric capnography (VCAP) offers a relatively simple solution to calculating dead space. Few studies have been conducted to directly compare dead space measured by VCAP and the DB method in critically unwell adults.

Method

Prospective observational study of 48 mechanically ventilated adults ICU patients. Dead space was calculated simultaneously using VCAP (CO₂SMO) and the Bohr–Enghoff equation. In total, 168 paired readings were taken. Single-breath CO₂ waveform areas under the curve were computed automatically by software to calculate physiological dead space. The calculated value of $ P_{{\bar{E}_{{{\text{CO}}_{2} }} }} $ was also recorded from the CO₂SMO device. Exhaust ventilator gas was collected in a 10-l mixing chamber. $ P_{{\bar{E}_{{{\text{CO}}_{2} }} }} $ was measured in the chamber following correction for compressed gas.

Results

The study demonstrated good agreement between physiological V _D/V _T calculated by VCAP and corrected (mean bias 0.03), and uncorrected (mean bias 0.02) Bohr–Enghoff method. There was good correlation between the two methods of measurement (VCAP vs corrected r ²?=?0.90 P?<?0.001, VCAP vs uncorrected r ²?=?0.90, P?<?0.001). There was good correlation between $ P_{{\bar{E}_{{{\text{CO}}_{2} }} }} $ calculated by the CO₂SMO and in the exhaust collected gas (mean bias 0.08).

Conclusions

VCAP shows good agreement with Douglas Bag method in measuring physiological V _D/V _T over a wide range of dead space fractions.     

Synthesis and Ex Vivo Autoradiographic Evaluation of Ethyl-��-d-galactopyranosyl-(1,4��)-2��-deoxy-2��-[18F]fluoro-��-d-glucopyranoside��A Novel Radioligand for Lactose-Binding Protein: Implications for Early Detection of Pancreatic Carcinomas with PET

Introduction

Previous studies demonstrated that the lactose-binding protein (hepatocellular carcinoma?Cintestine?Cpancreas and pancreatitis-associated proteins (HIP/PAP)) is upregulated >130 times in peritumoral pancreatic tissue as compared to normal pancreatic tissue. Therefore, we developed a new radiolabeled ligand of HIP/PAP, the ethyl-??-d-galactopyranosyl-(1,4??)-2??-deoxy-2??-[¹⁸F]fluoro-??-d-glucopyranoside (Et-[¹⁸F]FDL) for noninvasive imaging of pancreatic carcinoma using positron emission tomography and computerized tomography (PET/CT).

Methods

The novel precursor and radiolabeling methods for synthesis of Et-[¹⁸F]FDL produced no isomers; the average decay-corrected radiochemical yield was 68%, radiochemical purity >99%, and specific activity >74 GBq/µmol. The radioligand properties of Et-[¹⁸F]FDL were evaluated using an ex vivo autoradiography and immunohistochemistry in pancreatic tissue sections obtained from mice-bearing orthotopic pancreatic tumor xenografts.

Results and Discussion

Et-[¹⁸F]FDL binding to peritumoral pancreatic tissue sections strongly correlated with HIP/PAP expression (r?=?0.81) and could be completely blocked by treatment with 1 mM lactose.

Conclusion

These results suggest that Et-[¹⁸F]FDL is a promising agent which should be evaluated for detection of early pancreatic carcinomas by PET/CT imaging.     

Incongruity of Imaging Using Fluorescent 2-DG Conjugates Compared to 18F-FDG in Preclinical Cancer Models

Purpose

We compared the use of near-infrared conjugates of 2-deoxyglucose (NIR 2-DG) to 2-deoxy-2-[¹⁸F]fluoro-d-glucose (¹⁸F-FDG) for the purposes of imaging tumors, as well as response to therapy.

Procedures

Uptake of both ¹⁸F-FDG and NIR 2-DG within gastrointestinal stromal tumor xenografts were imaged before and after nilotinib treatment. Confocal microscopy was performed to determine NIR 2-DG distribution in tumors.

Results

Treatment with nilotinib resulted in a rapid reduction in ¹⁸F-FDG uptake and reduced tumor cell viability which was predictive of long-term antitumor efficacy. In contrast, optical imaging with NIR 2-DG probes was unable to differentiate control from niltonib-treated animals, and microscopic analysis revealed no change in probe distribution as a result of treatment.

Conclusions

These results suggest that conjugation of large bulky fluorophores to 2-DG disrupts the facilitated transport and retention of these probes in cells. Therefore, optical imaging of NIR 2-DG probes cannot substitute for ¹⁸F-FDG positron emission tomography imaging as a biomarker of tumor cell viability and metabolism.     

Comparison of Ga-68-Labeled Fusarinine C-Based Multivalent RGD Conjugates and [<Superscript>68</Superscript>Ga]NODAGA-RGD—<Emphasis Type="Italic">In Vivo</Emphasis> Imaging Studies in Human Xenograft Tumors

Purpose

Multimeric arginine-glycine-aspartic acid (RGD) peptides have advantages for imaging integrin α_vβ₃ expression. Here, we compared the in vitro and in vivo behavior of three different Ga-68-labeled multimeric Fusarinine C-RGD (FSC-RGD) conjugates, whereby RGD was coupled directly, via a succinic acid or PEG linker (FSC(RGDfE)₃, FSC(succ-RGD)₃, FSC(Mal-RGD)₃). The positron emission tomography/X-ray computed tomography (PET/CT) imaging properties were further compared using [⁶⁸Ga]FSC(succ-RGD)₃ with the monomeric [⁶⁸Ga]NODAGA-RGD in a murine tumor model.

Procedure

FSC-RGD conjugates were labeled with Ga-68, and stability properties were studied. For in vitro characterization, the partition coefficient, integrin α_vβ₃ binding affinity, and cell uptake were determined. To characterize the in vivo properties, biodistribution studies and microPET/CT were carried out using mice bearing either human M21/M21-L melanoma or human U87MG glioblastoma tumor xenografts.

Results

All FSC-RGD conjugates were quantitatively labeled with Ga-68 within 10 min at RT. The [⁶⁸Ga]FSC-RGD conjugates exhibited high stability and hydrophilic character, with only minor differences between the different conjugates. In vitro and in vivo studies showed enhanced integrin α_vβ₃ binding affinity, receptor-selective tumor uptake, and rapid renal excretion resulting in good imaging properties.

Conclusions

The type of linker between FSC and RGD had no pronounced effect on targeting properties of [⁶⁸Ga]FSC-RGD trimers. In particular, [⁶⁸Ga]FSC(succ-RGD)₃ exhibited improved properties compared to [⁶⁸Ga]NODAGA-RGD, making it an alternative for imaging integrin α_vβ₃ expression.