Optimizing the pharmacokinetics of an 211At-labeled RGD peptide with an albumin-binding moiety via the administration of an albumin-binding inhibitor.

PURPOSE: A probe for targeted alpha therapy (TAT) using the RGD peptide (Ga-DOTA-K([211At]APBA)-c(RGDfK) ([211At]1)) with albumin-binding moiety (ABM) was recently developed. [211At]1 highly accumulated in tumors and significantly inhibited tumor growth in U-87 MG tumor-bearing mice. However, high [211At]1 retention in blood may cause critical adverse events, such as hematotoxicity. Therefore, we attempted to accelerate the blood clearance of [211At]1 by competitively inhibiting the binding of [211At]1 to albumin to modulate the pharmacokinetics of the former. METHODS: To evaluate the effects of albumin-binding inhibitors in normal mice, sodium 4-(4-iodophenyl)butanoate at 2, 5, or 10 molar equivalents of blood albumin was administered at 1-h postinjection of [211At]1. The biodistribution of [211At]1, SPECT/CT imaging of [67Ga]Ga-DOTA-K(IPBA)-c(RGDfK) ([67Ga]2), and the therapeutic effects of [211At]1 were compared with or without IPBA administration in U-87 MG tumor-bearing mice. RESULTS: Blood radioactivity of [211At]1 was decreased in a dose-dependent manner with IPBA in normal mice. In U-87 MG tumor-bearing mice, the blood radioactivity and accumulation in nontarget tissues of [211At]1 were decreased by IPBA. Meanwhile, tumor [211At]1 accumulation was not changed at 3-h postinjection of IPBA. In SPECT/CT imaging of [67Ga]2, IPBA administration dramatically decreased radioactivity in nontarget tissues, and only tumor tissue was visualized. In therapeutic experiments, [211At]1 with IPBA injected-group significantly inhibited tumor growth compared to the control group. CONCLUSION: IPBA administration (as an albumin-binding inhibitor) could modulate the pharmacokinetics and enhance the therapeutic effects of [211At]1.

Development of probes for radiotheranostics with albumin binding moiety to increase the therapeutic effects of astatine-211 (211At).

PURPOSE: We have developed probes for multiradionuclides radiotheranostics using RGD peptide ([67Ga]Ga-DOTA-c[RGDf(4-I)K] ([67Ga]1) and Ga-DOTA-[211At]c[RGDf(4-At)K] ([211At]2)) for clinical applications. The introduction of an albumin binding moiety (ABM), such as 4-(4-iodophenyl)-butyric acid (IPBA), that has high affinity with the blood albumin and prolongs the circulation half-life can improve the pharmacokinetics of drugs. To perform more effective targeted alpha therapy (TAT), we designed and synthesized Ga-DOTA-K([211At]APBA)-c(RGDfK) ([211At]5) with 4-(4-astatophenyl)-butyric acid (APBA), which has an astato group instead of an iodo group in IPBA. We evaluated whether APBA functions as ABM and [211At]5 is effective for TAT. In addition, we prepared 67Ga-labeled RGD peptide without ABM, [67Ga]Ga-DOTA-K-c(RGDfK) ([67Ga]3), and 125I-labeled RGD peptide with ABM, Ga-DOTA-K([125I]IPBA)-c(RGDfK) ([125I]4), to compare with [211At]5. METHODS: Biodistribution experiments of [67Ga]3 without ABM, [125I]4 and [211At]5 with ABM were conducted in normal mice and U-87 MG tumor-bearing mice. In addition, two doses of [211At]5 (370 or 925 kBq) were administered to U-87 MG tumor-bearing mice to confirm the therapeutic effects. RESULTS: The blood retention of [125I]4 and [211At]5 was remarkably increased compared to [67Ga]3. Also, [125I]4 and [211At]5 showed similar biodistribution and significantly greater tumor accumulation and retention compared to [67Ga]3. In addition, [211At]5 inhibited tumor growth in a dose-dependent manner. CONCLUSION: The functionality of APBA as ABM like IPBA, and the usefulness of [211At]5 as the radionuclide therapy agent for TAT was revealed.

Synthesis and Evaluation of Radiogallium Labeled Bone-Imaging Probes Using Oligo-γ-Carboxy Glutamic Acid Peptides as Carriers to Bone.

We investigated the importance of the carboxy group density in bone affinity during the development of peptide-based bone-seeking radiopharmaceuticals and carriers. Oligo-γ-carboxy glutamic acid peptides [(Gla)n] with higher carboxy group density than oligo-glutamic acid peptides [(Glu)n] and oligo-aspartic acid peptides [(Asp)n] were chosen. Using the radiogallium chelator N,N'-bis-[2-hydroxy-5-(carboxyethyl)benzyl]ethylenediamine-N,N'-diacetic acid (HBED-CC), we synthesized [67Ga]Ga-HBED-CC-(Gla)n (n = 1, 2, 5, 8, 11, or 14) with high yields. Hydroxyapatite-binding assays, biodistribution, and SPECT imaging showed higher affinity and bone accumulation for [67Ga]Ga-HBED-CC-(Gla)n compared to [67Ga]Ga-HBED-CC-(Glu)n. Notably, [67Ga]Ga-HBED-CC-(Gla)8 and [67Ga]Ga-HBED-CC-(Gla)11 exhibited superior bone accumulation and rapid blood clearance. SPECT/CT imaging with [67Ga]Ga-HBED-CC-(Gla)8 exclusively visualized the bone tissue. These findings support the potential use of [67Ga]Ga-HBED-CC-(Gla)n as excellent bone-imaging PET probes, suggesting (Gla)n peptides are superior bone-seeking carriers.

125I-labeled 2-[4-(2-iodophenyl)piperidino]cyclopentanol (125I-OI5V) imaging visualized augmented sigma-1 receptor expression according to the severity of myocardial ischemia.

BACKGROUND: We aimed to explore how the severity of myocardial ischemia affects myocardial sigma-1 receptor (Sig-1R) expression using 125I-labeled 2-[4-(2-iodophenyl)piperidino]cyclopentanol (125I-OI5V) imaging. METHODS AND RESULTS: The left coronary artery was occluded for 30, 20, and 10 minute, to vary the severity of myocardial ischemia, followed by reperfusion. Dual-tracer autoradiography of the left ventricular short-axis slices was performed 3 and 7 days after reperfusion. 125I-OI5V was injected 30 minute before sacrifice and the area at risk (AAR) was evaluated by 99mTc-MIBI. Intense 125I-OI5V uptake was observed in the AAR and was significantly increased with increasing ischemia duration. To evaluate salvaged and nonsalvaged areas (preserved and decreased perfusion areas), triple-tracer autoradiography was performed 3 days after reperfusion. After dual-tracer autoradiography, 201Tl was injected 20 minute post 125I-OI5V injection. On triple-tracer autoradiography, the AAR/normally perfused area 125I-OI5V uptake ratio was positively correlated with the nonsalvaged area/whole left ventricular (LV) area ratio (P < .05). The AAR/normally perfused area 125I-OI5V uptake ratio was negatively correlated with the 201Tl uptake ratio of the AAR to normally perfused areas (P < .05). The comparison of the immunostaining distribution of 125I-OI5V and the macrophage marker CD68 revealed that 125I-OI5V was present mainly in, and immediately adjacent to the macrophage infiltration area. CONCLUSIONS: Significant 125I-OI5V uptake in the AAR depends on the duration of ischemia and reduced 201Tl uptake; furthermore, 125I-OI5V was found in and around the macrophage infiltrate area. These results indicate that iodine-labeled OI5V is a promising tool for visualizing Sig-1R expression according to the ischemic burden.

Synthesis and evaluation of a deltic guanidinium analogue of a cyclic RGD peptide.

A guanidine group is abundantly found in natural products and drugs. Guanidine has the highest basicity among many common functional groups in nature. Because of its high basicity, it generally exists as a protonated guanidinium and functions as a cationic hydrogen bond donor. Finding an appropriate bioisostere of guanidinium is challenging because of its high basicity and unique trigonal planar shape. In this study, we explored the possibility of "deltic guanidinium" as a bioisostere of guanidinium using a cyclic arginine-glycine-aspartic acid (RGD) peptide as a parent compound. We synthesized c(deltic RGDyK), in which a guanidinium group of an arginine residue in c(RGDyK) is replaced with deltic guanidinium. A target binding assay, biodistribution study, and metabolic stability assay were conducted with c(deltic RGDyK) and its radioiodinated variant. The deltic guanidinium analog peptides exhibited similar biological properties to the parent peptides and improved in vivo stability, indicating that deltic guanidinium could work as a unique bioisostere of guanidinium.

Preparation and Evaluation of Thermosensitive Liposomes Encapsulating I-125-Labeled Doxorubicin Derivatives for Auger Electron Therapy.

Auger electrons (AEs) are very low-energy electrons emitted by radionuclides such as I-125 (125I). This energy is deposited across a small distance (<0.5 µm), resulting in high linear energy transfer that is potent for causing lethal damage to cancer cells. Thus, AE-emitting radiotherapeutic agents have great potential for cancer treatment. In this study, thermosensitive liposomes (TSLs) encapsulating 125I-labeled doxorubicin (DOX) derivatives were developed for Auger electron therapy, targeting the DNA of cancer cells. A radioiodinated DOX derivative [125I]5 highly accumulated in the nuclei of cancer cells and showed potent cytotoxicity against Colon 26 cancer cells by AEs. Subsequently, [125I]5 was loaded into the TSLs with high encapsulation efficiency. Potent release of [125I]5 from TSLs was achieved with heating, whereas a decreased release was observed without heating. Furthermore, TSLs encapsulating [125I]5 showed a high uptake in the nuclei at 42 °C for 1 h. We supposed that [125I]5 was released by heating at 42 °C and accumulated in the nuclei in the cells. These results suggest that the combination of TSLs encapsulating [125I]5 and hyperthermia is an effective cancer therapy.

Borealin-Derived Peptides as Survivin-Targeting Cancer Imaging and Therapeutic Agents.

Survivin is overexpressed in most cancer cells but is rarely expressed in normal adult tissues. It is associated with poor prognosis and resistance to radiation therapy and chemotherapy. In this study, we designed and synthesized borealin-derived small peptides (Bor peptides) to function as survivin-targeting agents for the diagnosis and treatment of cancers. These peptides exhibited binding affinities for recombinant human survivin (Kd = 49.6-193 nM), with Bor65-75 showing the highest affinity (Kd = 49.6 nM). Fluorescence images of fluorescein isothiocyanate-labeled Bor65-75 showed its co-localization with survivin expression in the human pancreatic cancer cell line, MIA PaCa-2. In the WST-1 assay, cell penetrable nona-d-arginine-conjugated Bor65-75 (r9-Bor65-75) inhibited the growth of MIA PaCa-2 cells and MDA-MB-231 cells (89 and 88% inhibition at 10 µM, respectively), whereas it had almost no effect on the human mammary epithelial cell line, MCF-10A, that inherently does not have high survivin expression. Flow cytometry with annexin V and propidium iodide staining revealed that r9-Bor65-75 induced apoptosis in MIA PaCa-2 cells in a dose-dependent manner. An increase in cleaved poly ADP-ribose polymerase protein expression was observed in MIA PaCa-2 cells exposed to r9-Bor65-75 by western blotting, suggesting that r9-Bor65-75 inhibits cell proliferation by inducing apoptosis. In vivo, r9-Bor65-75 significantly suppressed tumor growth in MIA PaCa-2 xenograft mice, without any marked weight loss. Hence, Bor peptides are promising candidates for the development of cancer imaging and anticancer agents targeting survivin.

Development and evaluation of a theranostic probe with RGD peptide introduced platinum complex to enable tumor-specific accumulation.

Cisplatin (CDDP) has been widely used for chemotherapy. However, it has several unfavorable side effects due to its low tumor selectivity. In this study, we designed, synthesized, and evaluated Pt(IV)-[c(RGDyK)]2 (9), in which two molecules of an RGD peptide are introduced as a carrier molecule to cancer into oxoplatin, a Pt(IV) prodrug of CDDP, to enhance cancer selectivity. Furthermore, we prepared and evaluated Pt(IV)-[c(RGDyK)]{[125I]c[RGDy(3-I)K]} ([125I]10) for a preliminary step of nuclear medicine imaging and theranostics. Compound 9 inhibited cell growth in the cell viability assay and, [125I]10 was highly accumulated in tumor tissues (1 h: 3.53 ± 0.53 %ID/g) in the biodistribution study. These results indicate that implementing RGD peptides into oxoplatin enabled tumor-specific accumulation, and combining [123/124I]10 and 9 for diagnostic imaging and therapy could be useful for cancer theranostics.

Synthesis and Characterization of Hydroxyethylamino- and Pyridyl-Substituted 2-Vinyl Chromone Derivatives for Detection of Cerebral Abnormal Prion Protein Deposits.

Prion diseases are fatal neurodegenerative diseases characterized by the deposition of abnormal prion protein aggregates (PrPSc) in the brain. In this study, we developed hydroxyethylamino-substituted styrylchromone (SC) and 2-(2-(pyridin-3-yl)vinyl)-4H-chromen-4-one (VPC) derivatives for single-photon emission computed tomography (SPECT) imaging of PrPSc deposits in the brain. The binding affinity of these compounds was evaluated using recombinant mouse prion protein (rMoPrP) aggregates, which resulted in the inhibition constant (Ki) value of 61.5 and 88.0 nM for hydroxyethyl derivative, (E)-2-(4-((2-hydroxyethyl)amino)styryl)-6-iodo-4H-chromen-4-one (SC-NHEtOH) and (E)-2-(4-((2-hydroxyethyl)(methyl)amino)styryl)-6-iodo-4H-chromen-4-one (SC-NMeEtOH), respectively. However, none of the VPC derivatives showed binding affinity for the rMoPrP aggregates. Fluorescent imaging demonstrated that the accumulation pattern of SC-NHEtOH matched with the presence of PrPSc in the brain slices from mouse-adapted bovine spongiform encephalopathy-infected mice. A biodistribution study of normal mice indicated low initial brain uptake of [125I]SC-NHEtOH (0.88% injected dose/g (% ID/g) at 2 min) despite favorable washout from the brain (0.26% ID/g, at 180 min) was displayed. [125I]SC-NHEtOH exhibited binding affinities to both artificial prion aggregates as well as prion deposits in the brain. However, significant improvement in the binding affinity for PrPSc and blood-brain barrier permeability is necessary for the development of successful in vivo imaging probes for the detection of cerebral PrPSc in the brain.

In Vivo Evaluation of the Combined Anticancer Effects of Cisplatin and SAHA in Nonsmall Cell Lung Carcinoma Using [18F]FAHA and [18F]FDG PET/CT Imaging.

Combining standard drugs with low doses of histone deacetylase inhibitors (HDACIs) is a promising strategy to increase the efficacy of chemotherapy. The ability of well-tolerated doses of HDACIs that act as chemosensitizers for platinum-based chemotherapeutics has recently been proven in many types and stages of cancer in vitro and in vivo. Detection of changes in HDAC activity/expression may provide important prognostic and predictive information and influence treatment decision-making. Use of [18F] FAHA, a HDAC IIa-specific radionuclide, for molecular imaging may enable longitudinal, noninvasive assessment of HDAC activity/expression in metastatic cancer. We evaluated the synergistic anticancer effects of cisplatin and the histone deacetylase inhibitor suberoylanilide hydroxamic acid (SAHA) in xenograft models of nonsmall cell lung cancer (NSCLC) using [18F] FAHA and [18F] FDG PET/CT imaging. Cisplatin alone significantly increased [18F] FAHA accumulation and reduced [18F] FDG accumulation in H441 and PC14 xenografts; coadministration of cisplatin and SAHA resulted in the opposite effects. Immunochemical staining for acetyl-histone H3 confirmed the PET/CT imaging findings. Moreover, SAHA had a more significant effect on the acetylome in PC14 (EGFR exon 19 deletion mutation) xenografts than H441 (wild-type EGFR and KRAS codon 12 mutant) xenografts. In conclusion, [18F] FAHA enables quantitative visualization of HDAC activity/expression in vivo, thus, may represent a clinically useful, noninvasive tool for the management of patients who may benefit from synergistic anticancer therapy.

68Ga- and 211At-Labeled RGD Peptides for Radiotheranostics with Multiradionuclides.

Probes for radiotheranostics could be produced by introducing radionuclides with similar chemical characteristics into the same precursors. We recently developed an 211At-labeled RGD peptide and a corresponding radioiodine-labeled RGD peptide. Both labeled peptides accumulated in large quantities in the tumor with similar biodistribution, demonstrating their usefulness for radiotheranostics. In this study, we hypothesized that probes for radiotheranostics combined with multiradionuclides, such as 68Ga and 211At, have useful clinical applications. New radiolabeled RGD peptide probes were synthesized via a molecular design approach, with two labeling sites for metal and halogen. These probes were evaluated in biodistribution experiments using tumor-bearing mice. [67Ga]Ga-DOTA-c[RGDf(4-I)K] ([67Ga]4), Ga-DOTA-[125I]c[RGDf(4-I)K] ([125I]4), and Ga-DOTA-[211At]c[RGDf(4-At)K] ([211At]7) showed similar biodistribution, with high and equivalent accumulation in tumors. These results indicate the usefulness of these probes in radiotheranostics with multiradionuclides, such as a radiometal and a radiohalogen, and they could contribute to a personalized medicine regimen.

Visualization of Dynamic Expression of Myocardial Sigma-1 Receptor After Myocardial Ischemia and Reperfusion Using Radioiodine-Labeled 2-[4-(2-iodophenyl)piperidino]cyclopentanol (OI5V) Imaging.

BACKGROUND: This study chronologically evaluated the expression of the intensity and distribution of the sigma-1 receptor (σ1R) demonstrated by radiolabeled 2-[4-(2-iodophenyl)piperidino]cyclopentanol (OI5V) in a rat model of myocardial ischemia and reperfusion.Methods and Results:The left coronary artery was occluded for 30 min, followed by reperfusion. Dual-tracer autoradiography with 125I-OI5V and 99 mTc-MIBI was performed to assess the spatiotemporal changes in 125I-OI5V uptake (n=5-6). Significant and peaked 125I-OI5V uptake in the ischemic area was observed at 3 days after reperfusion, and the 125I-OI5V uptake ratio of ischemic area to normally perfused left ventricular area decreased gradually from 3 to 28 days (mean value±SD; 0.90±0.12 at 1 day, 1.89±0.19 at 3 days, 1.52±0.17 at 7 days, 1.34±0.13 at 14 days, and 1.16±0.14 at 28 days, respectively). Triple-tracer autoradiography with 125I-OI5V, 99 mTc-MIBI, and 201TlCl was performed to evaluate 125I-OI5V uptake in the ischemic area in relation to the residual perfusion at 7 days (n=4). The 125I-OI5V uptake ratio of the non-salvaged area was higher compared to that of the salvaged area in the ischemic area. 123I-OI5V and 99 mTc-MIBI SPECT/CT was performed 3 days after reperfusion (n=3), and the in vivo images showed clear uptake of 123I-OI5V in the perfusion defect area. CONCLUSIONS: The present study confirmed the spatiotemporal expression pattern of σ1R expression. Non-invasive σ1R imaging with 123I or 125I-OI5V was feasible to monitor the expression of σ1R after myocardial ischemia and reperfusion.

Synthesis and Evaluation of a Dimeric RGD Peptide as a Preliminary Study for Radiotheranostics with Radiohalogens.

We recently developed 125I- and 211At-labeled monomer RGD peptides using a novel radiolabeling method. Both labeled peptides showed high accumulation in the tumor and exhibited similar biodistribution, demonstrating their usefulness for radiotheranostics. This study applied the labeling method to a dimer RGD peptide with the aim of gaining higher accumulation in tumor tissues based on improved affinity with αvß3 integrin. We synthesized an iodine-introduced dimer RGD peptide, E[c(RGDfK)] (6), and an 125/131I-labeled dimer RGD peptide, E[c(RGDfK)]{[125/131I]c[RGDf(4-I)K]} ([125/131I]6), and evaluated them as a preliminary step to the synthesis of an 211At-labeled dimer RGD peptide. The affinity of 6 for αvß3 integrin was higher than that of a monomer RGD peptide. In the biodistribution experiment at 4 h postinjection, the accumulation of [125I]6 (4.12 ± 0.42% ID/g) in the tumor was significantly increased compared with that of 125I-labeled monomer RGD peptide (2.93 ± 0.08% ID/g). Moreover, the accumulation of [125I]6 in the tumor was greatly inhibited by co-injection of an excess RGD peptide. However, a single injection of [131I]6 (11.1 MBq) did not inhibit tumor growth in tumor-bearing mice. We expect that the labeling method for targeted alpha therapy with 211At using a dimer RGD peptide could prove useful in future clinical applications.

(-)-o-[11 C]methyl-trans-decalinvesamicol ((-)-[11 C]OMDV) as a PET ligand for the vesicular acetylcholine transporter.

To develop a PET imaging agent to visualize brain cholinergic neurons and synaptic changes caused by Alzheimer's disease, (-)- and (+)-o-[11 C]methyl-trans-decalinvesamicol ([11 C]OMDV) were isolated and investigated for differences in not only their binding affinity and selectivity to vesicular acetylcholine transporter (VAChT), but also their in vivo activities. [11 C]OMDV has a high binding affinity for VAChT both in vitro and in vivo. Racemic OMDV and o-trimethylstannyl-trans-decalinvesamicol (OTDV), which are precursors for synthesis of [11 C]OMDV, were separated into (-)-optical isomers ((-)-OMDV and (-)-OTDV) and (+)-optical isomers ((+)-OMDV and (+)-OTDV) by HPLC. In the in vitro binding assay, (-)-OMDV(7.2 nM) showed eight times higher binding affinity (Ki) to VAChT than that of (+)-OMDV(57.5 nM). In the biodistribution study, the blood-brain barrier permeability of both enantiomers ((-)-[11 C]OMDV and (+)-[11 C]OMDV) was similarly high (about 1.0%ID/g) at 2 min post-injection. However, (+)-[11 C]OMDV clearance from the brain was faster than (-)-[11 C]OMDV. In the in vivo blocking study, accumulation of (-)-[11 C]OMDV in the cortex was markedly decreased (approximately 30% of control) by coadministration of vesamicol, and brain uptake of (-)-[11 C]OMDV was not significantly altered by coadministration of (+)-pentazocine or (+)-3-(3-hydroxyphenyl)-N-propylpiperidine ((+)-3-PPP). PET-CT imaging revealed inhibition of the rat brain uptake of (-)-[11 C]OMDV by coadministration of vesamicol. In conclusion, (-)-[11 C]OMDV, which is an enantiomer of OMDV, selectively binds to VAChT with high affinity in the rat brain in vivo. (-)-[11 C]OMDV may be utilized as a potential PET ligand for studying presynaptic cholinergic neurons in the brain.

Inorganic and Metal-Organic Nanocomposites for Cascade-Responsive Imaging and Photochemical Synergistic Effects.

Porphyrins coordinated with platinum(II) chemotherapeutic drugs are attractive for the development of photosensitizers for photodynamic therapy (PDT) of cancer. In this paper, inorganic and metal-organic nanocomposites were synthesized with cascade-responsive imaging and photochemical synergistic effects. After endo/lysosomal escape, the outer metal-organic frameworks were degraded, leading to the release of an excellent photosensitizer (tetrapyridylporphyrin, PtTPyP). Subsequently, doxorubicin (DOX), inserted in the adenosine triphosphate (ATP) aptamer-functionalized gold nanoparticles, was released under the stimulation of endogenous ATP, synergistically enhancing cancer treatment. Fluorescence imaging allowed tracking of PtTPyP and DOX for real-time detection and on-demand therapy. This strategy endowed the nanocomposites with stability, responsiveness, effectiveness, and ease of synthesis, namely, sTREE strategy. Accordingly, our demonstration provided a promising and smart nanocarrier for imaging and drug delivery.

Preliminary Evaluation of Astatine-211-Labeled Bombesin Derivatives for Targeted Alpha Therapy.

There are various diagnostic and therapeutic agents for prostate cancer using bombesin (BBN) derivatives, but astatine-211 (211At)-labeled BBN derivatives have yet to be studied. This study presented a preliminary evaluation of 211At-labeled BBN derivative. Several nonradioactive iodine-introduced BBN derivatives (IB-BBNs) with different linkers were synthesized and their binding affinities measured. Because IB-3 exhibited a comparable affinity to native BBN, [211At]AB-3 was synthesized and the radiochemical yields of [211At]AB-3 was 28.2 ± 2.4%, with a radiochemical purity of >90%. The stability studies and cell internalization/externalization experiments were performed. [211At]AB-3 was taken up by cells and internalized; however, radioactivity effluxed from cells over time. In addition, the biodistribution of [211At]AB-3, with and without excess amounts of BBN, were evaluated in PC-3 tumor-bearing mice. Despite poor stability in murine plasma, [211At]AB-3 accumulated in tumor tissue (4.05 ± 0.73%ID/g) in PC-3 tumor-bearing mice, which was inhibited by excess native BBN (2.56 ± 0.24%ID/g). Accumulated radioactivity in various organs is probably due to free 211At. Peptide degradation in murine plasma and radioactivity efflux from cells are areas of improvement. The development of 211At-labeled BBN derivatives requires modifying the BBN sequence and preventing deastatination.

Development of Radiogallium-Labeled Peptides for Platelet-Derived Growth Factor Receptor ß (PDGFRß) Imaging: Influence of Different Linkers.

The purpose of this study is to develop peptide-based platelet-derived growth factor receptor ß (PDGFRß) imaging probes and examine the effects of several linkers, namely un-natural amino acids (D-alanine and ß-alanine) and ethylene-glycol (EG), on the properties of Ga-DOTA-(linker)-IPLPPPRRPFFK peptides. Seven radiotracers, 67Ga-DOTA-(linker)-IPLPPPRRPFFK peptides, were designed, synthesized, and evaluated. The stability and cell uptake in PDGFRß positive peptide cells were evaluated in vitro. The biodistribution of [67Ga]Ga-DOTA-EG2-IPLPPPRRPFFK ([67Ga]27) and [67Ga]Ga-DOTA-EG4-IPLPPPRRPFFK ([67Ga]28), which were selected based on in vitro stability in murine plasma and cell uptake rates, were determined in BxPC3-luc-bearing nu/nu mice. Seven 67Ga-labeled peptides were successfully synthesized with high radiochemical yields (>85%) and purities (>99%). All evaluated radiotracers were stable in PBS (pH 7.4) at 37 °C. However, only [67Ga]27 and [67Ga]28 remained more than 75% after incubation in murine plasma at 37 °C for 1 h. [67Ga]27 exhibited the highest BxPC3-luc cell uptake among the prepared radiolabeled peptides. As regards the results of the biodistribution experiments, the tumor-to-blood ratios of [67Ga]27 and [67Ga]28 at 1 h post-injection were 2.61 ± 0.75 and 2.05 ± 0.77, respectively. Co-injection of [67Ga]27 and an excess amount of IPLPPPRRPFFK peptide as a blocking agent can significantly decrease this ratio. However, tumor accumulation was not considered sufficient. Therefore, further probe modification is required to assess tumor accumulation for in vivo imaging.

Synthesis and Fundamental Evaluation of Radioiodinated Rociletinib (CO-1686) as a Probe to Lung Cancer with L858R/T790M Mutations of Epidermal Growth Factor Receptor (EGFR).

Rociletinib (CO-1686), a 2,4-diaminopyrimidine derivative, is a highly potent tyrosine kinase inhibitor (TKI) that acts on epidermal growth factor receptor (EGFR) with L858R/T790M mutations. We supposed radioiodinated CO-1686 would function as a useful tool for monitoring EGFR L858R/T790M mutations. To aid in patient selection before therapy with EGFR-TKIs, this study aimed to develop a 125I-labeled derivative of CO-1686, N-{3-[(2-{[4-(4-acetylpiperazin-1-yl)-2-methoxyphenyl]amino}-5-(trifluoromethyl)pyrimidine-4-yl] amino}-5-([125I]iodophenyl)acrylamide ([125I]ICO1686) and evaluate its selectivity toward EGFR L858R/T790M. Radiosynthesis was performed by iododestannylation of the corresponding tributylstannyl precursor with [125I]NaI and N-chlorosuccinimide. The selectivity of the tracer for detecting EGFR L858R/T790M was evaluated using three relevant non-small cell lung cancer (NSCLC) cell lines-H1975, H3255 and H441 overexpressing the dual mutation EGFR L858R/T790M, active mutant EGFR L858R and wild-type EGFR, respectively. The nonradioactive ICO1686 and the precursor compound were successfully synthesized. A novel radiolabeled probe, [125I]ICO1686, was prepared with high radiochemical yield (77%) and purity (>99%). ICO1686 exhibited high cytotoxicity toward H1975 (IC50 0.20 ± 0.05 µM) and H3255 (IC50 0.50 ± 0.21 µM), which is comparable to that of CO-1686. In contrast, the cytotoxicity of ICO1686 toward H441 was 10-fold lower than that toward H1975. In the cell uptake study, the radioactivity uptake of [125I]ICO1686 in H1975 was 101.52% dose/mg, whereas the uptakes in H3255 and H441 were 33.52 and 8.95% dose/mg, respectively. The uptake of [125I]ICO1686 in H1975 was greatly reduced to 45.61% dose/mg protein by treatment with excess CO-1686. In vivo biodistribution study of the radiotracer found that its accumulation in H1975 tumor (1.77 ± 0.43% ID/g) was comparable to that in H3255 tumor (1.63 ± 0.23% ID/g) and the accumulation in H1975 tumor was not reduced by pretreatment with an excess dose of CO-1686. Although this radiotracer exhibited highly specific in vitro uptake in target cancer cells, structural modification is required to improve in vivo biodistribution.

Thermodynamic and Spectroscopic Studies of the Complexes Formed in Tartaric Acid and Lanthanide(III) Ions Binary Systems.

Binary complexes of tartaric acid with lanthanide(III) ions were investigated. The studies have been performed in aqueous solution using the potentiometric method with computer analysis of the data for detection of the complexes set, determination of the stability constants of these compounds. The mode of the coordination of complexes found was determined using spectroscopy, which shows: Infrared, circular dichroism, ultraviolet, visible as well as luminescence spectroscopy. The overall stability constants of the complexes as well as the equilibrium constants of the reaction were determined. Analysis of the equilibrium constants of the reactions and spectroscopic data allowed the effectiveness of the carboxyl groups in the process of complex formation.

Postconditioning Accelerates Myocardial Inflammatory Resolution Demonstrated by 14C-Methionine Imaging and Attenuates Ventricular Remodeling After Ischemia and Reperfusion.

BACKGROUND: Methionine uptake after myocardial infarction has been proven to reflect myocardial inflammation. The effect of postconditioning on the post-infarction inflammatory process, however, remains to be elucidated.Methods and Results:In control (n=22) and postconditioning rats (n=23), the left coronary artery was occluded for 30 min, followed by reperfusion for 1, 3, 7, and 14 days. Postconditioning was performed immediately following the reperfusion. 14C-methinine (0.74 MBq) and 201Tl (14.8 MBq) were injected 20 and 10 min prior to sacrifice, respectively. One minute before sacrifice, 150-180 MBq of 99 mTc-MIBI was injected immediately following the re-occlusion of the left coronary artery to verify the area at risk, and left ventricular triple-tracer autoradiography was performed. To examine the ventricular remodeling, echocardiography was performed 2 months after reperfusion in both groups (n=6 each). In the control rats, the methionine uptake ratios on days 1, 3, 7, and 14 were 0.74±0.12, 1.85±0.16, 1.48±0.10, 1.25±0.04, respectively. With postconditioning, methionine uptake was similar on day 3 (1.90±0.21), but was lower on day 7 (1.23±0.22, P<0.05) and day 14 (1.08±0.09, P<0.005). Echocardiography revealed that postconditioning reduced the ventricular end-diastolic (0.97±0.16 to 0.78±0.12 cm, P<0.05) and systolic (0.85±0.21 to 0.55±0.23 cm, P<0.05) dimensions and improved ventricular percentage fractional shortening (12±6.2 to 29±12 %, P=0.01). CONCLUSIONS: 14C-methinine imaging revealed that postconditioning accelerated resolution of inflammation and attenuated ventricular remodeling.