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.

Bone invasion-targeted chemotherapy with a novel anionic platinum complex (3Pt) for oral squamous cell carcinoma.

Cisplatin (CDDP) is an important drug for chemotherapy in patients with head and neck squamous cell carcinoma. Nephrotoxicity and lack of an effect on bone invasion are limitations of CDDP. To increase its antitumor effect on bone invasion and reduce toxicity problems, anionic Pt complex (3Pt) has been developed. The present study aimed to characterize the basis of the cytotoxicity of the novel platinum complex 3Pt in comparison with that of CDDP for oral squamous cell carcinoma. The ionic platinum complex was prepared to increase solubility and avoid platinum nephrotoxicity. Furthermore, 3Pt was designed to target bone hydroxyapatite and has germinal bisphosphonate moieties for drug delivery. In vitro antitumor activity was assayed in two oral squamous cell carcinoma cell lines. To investigate the antitumor and nephrotoxic effects of 3Pt, nude mice with OSC-19 were given 3Pt and CDDP. The in vitro growth-inhibitory effect of 3Pt was significantly less than that of CDDP. However, both 3Pt and CDDP showed equivalent antitumor effects in vivo. Mice injected with CDDP developed renal cell apoptosis; however, those injected with 3Pt were almost free of renal cell injury. In addition to similar in vivo antitumor effects, 3Pt decreased the volume of bone resorption compared to that with CDDP in a bone invasion model using OSC-19. In conclusion, considering the potential advantages in terms of noticeable antitumor activity on bone invasion and reduced nephrotoxicity, 3Pt represents a significant improvement in the development of bone-targeting platinum drugs.

Syntheses and evaluation of a homologous series of aza-vesamicol as improved radioiodine-labeled probes for sigma-1 receptor imaging.

Sigma-1 receptor imaging probes for determining the expression levels are desirable for diagnoses of various diseases and companion diagnoses of therapeutic agents targeting the sigma-1 receptor. In this study, we aimed to develop probes with higher affinity for the sigma-1 receptor. For this purpose, we synthesized and evaluated compounds, namely, vesamicol derivatives, in which alkyl chains of varying chain length were introduced between a piperazine ring and a benzene ring. The binding affinity of the vesamicol derivatives for the sigma-1 receptor tended to increase depending on the length of the alkyl chain between the benzene ring and the piperazine ring. The sigma-1 receptor of 2-(4-(3-phenylpropyl)piperazin-1-yl)cyclohexan-1-ol (5) (Ki = 5.8 nM) exhibited the highest binding affinity; therefore, we introduced radioiodine into the benzene ring in 5. The radioiodine labeled probe [125I]2-(4-(3-(4-iodophenyl)propyl)piperazin-1-yl)cyclohexan-1-ol ([125I]10) showed high accumulation in the sigma-1 receptor expressing DU-145 cells both in vitro and in vivo. Co-injection of [125I]10 with an excess level of a sigma receptor ligand, haloperidol, resulted in a significant decrease in the tumor accumulation in vitro and in vivo, indicating sigma receptor-mediated tumor uptake. These results provide useful information for developing sigma-1 receptor imaging probes.

Design, synthesis, and biological evaluation of radioiodinated benzo[d]imidazole-quinoline derivatives for platelet-derived growth factor receptor ß (PDGFRß) imaging.

Several malignant tumors and fibrotic diseases are associated with PDGFRß overexpression and excessive signaling, making this receptor attractive for molecular targeting and imaging approaches. A series of benzo[d]imidazole-quinoline derivatives were designed and synthesized to develop radioiodinated compounds as PDGFRß-specific imaging probes. The structure activity relationship (SAR) evaluation of the designed compounds was performed. Among them, 2-[5-(2-methoxyethoxy)-1H-benzo[d]imidazol-1-yl]-8-(piperazin-1-yl)quinoline (5a) and 4-{2-[5-(2-methoxyethoxy)-1H-benzo[d]imidazol-1-yl]quinolin-8-yl}morpholine (5d) exhibited a relatively high PDGFRß-TK inhibitory potency, whereas iodinated 5a derivative 5-iodo-2-[5-(2-methoxyethoxy)-1H-benzo[d]imidazol-1-yl]-8-(piperazin-1-yl)quinoline (8) exhibited a superior inhibitory potency as PDGFRß inhibitor than iodinated 5d derivative 4-{5-iodo-2-[5-(2-methoxyethoxy)-1H-benzo[d]imidazol-1-yl]quinolin-8-yl}morpholine (11). Furthermore, [125I]8 and [125I]11 were synthesized and evaluated for PDGFRß radioligand ability, both in vitro and in vivo. Cellular uptake experiments showed that [125I]8 had a higher uptake in BxPC3-luc cells as PDGFRß-positive cells than [125I]11. Incubation of [125I]8 after pretreatment of PDGFRß ligands significantly reduced the uptake of [125I]8. In biodistribution experiments using tumor-bearing mice, [125I]8 accumulation in the tumor 1 h postinjection was higher than that of the benzo[d]imidazol-quinoline derivative [125I]IIQP, used in our previous research. These results indicate that [125I]8 could be a promising PDGFRß imaging agent. Although its clinical application requires further structural modifications, the results obtained in this research may be useful for the development of PDGFRß-specific radioligands.

Comparison of Radioiodine- or Radiobromine-Labeled RGD Peptides between Direct and Indirect Labeling Methods.

Radiolabeled cyclic peptides containing the (Arg-Gly-Asp) RGD sequence for use in positron emission tomography (PET) imaging, single-photon emission computed tomography (SPECT) imaging, and targeted radionuclide therapy of cancer have been reported. In this study, RGD was used as a model carrier peptide for diagnosis and therapy of cancer. To evaluate the characteristics of radiohalogen-labeled peptides, several kinds of labeled RGD peptides [125I-c(RGDyK), 77Br-c(RGDyK), [125I]SIB-c(RGDfK), [77Br]SBrB-c(RGDfK), [125I]SIB-EG2-c(RGDfK), and [77Br]SBrB-EG2-c(RGDfK)] were designed, prepared, and evaluated. In these initial studies, 77Br (t1/2=57.0 h) and 125I (t1/2=59.4 d) were used because of their longer half-lives. Precursor peptides were synthesized using a standard 9-fluorenylmethyloxycarbonyl (Fmoc)-based solid-phase methodology. Radiolabeled peptides were prepared by chloramine-T method or conjugation of RGD peptides with [125I]N-succinimidyl 3-iodobenzoate ([125I]SIB) or [77Br]N-succinimidyl 3-bromobenzoate ([77Br]SBrB). Measurement of the partition coefficients, integrin binding assay, and biodistribution experiments in tumor-bearing mice were performed. 125I and 77Br labeling were successfully performed using similar methods, and in vitro characteristics and biodistributions were similar between the 125I-labeled and corresponding 77Br-labeled peptides. [125I]SIB- and [77Br]SBrB-conjugated RGD peptides showed higher partition coefficients, lower tumor uptakes, and higher intestinal uptake than 125I-c(RGDyK) and 77Br-c(RGDyK). [125I]SIB-EG2-c(RGDfK) and [77Br]SBrB-EG2-c(RGDfK), which possess an ethylene glycol linker, decreased lipophilicity and uptake in intestine compared with [125I]SIB-c(RGDfK) and [77Br]SBrB-c(RGDfK), which possess no linker. However, the improvement in biodistribution of [125I]SIB-EG2-c(RGDfK) and [77Br]SBrB-EG2-c(RGDfK)] was insufficient. In conclusion, directly radiohalogenated c(RGDyK) peptides are potentially more useful for tumor imaging and therapy than indirectly radiohalogenated ones.

Synthesis and evaluation of radioiodinated 1-{2-[5-(2-methoxyethoxy)-1H-benzo[d]imidazol-1-yl]quinolin-8-yl}piperidin-4-amine derivatives for platelet-derived growth factor receptor ß (PDGFRß) imaging.

Platelet-derived growth factor receptor ß (PDGFRß) is a transmembrane tyrosine kinase receptor and it is upregulated in various malignant tumors. Radiolabeled PDGFRß inhibitors can be a convenient tool for the imaging of tumors overexpressing PDGFRß. In this study, [125I]-1-{5-iodo-2-[5-(2-methoxyethoxy)-1H-benzo[d]imidazol-1-yl]quinoline-8-yl}piperidin-4-amine ([125I]IIQP) and [125I]-N-3-iodobenzoyl-1-{2-[5-(2-methoxyethoxy)-1H-benzo[d]imidazol-1-yl]quinolin-8-yl}-piperidin-4-amine ([125I]IB-IQP) were designed and synthesized, and their potential as PDGFRß imaging agents was evaluated. In cellular uptake experiments, [125I]IIQP and [125I]IB-IQP showed higher uptake by PDGFRß-positive cells than by PDGFRß-negative cells, and the uptake in PDGFRß-positive cells was inhibited by co-culture with PDGFRß ligands. The biodistribution of both radiotracers in normal mice exhibited hepatobiliary excretion as the main route. In mice inoculated with BxPC3-luc (PDGFRß-positive), the tumor uptake of radioactivity at 1h after the injection of [125I]IIQP was significantly higher than that after the injection of [125I]IB-IQP. These results indicated that [125I]IIQP can be a suitable PDGFRß imaging agent. However, further modification of its structure will be required to obtain a more appropriate PDGFRß-targeted imaging agent with a higher signal/noise ratio.

Complexes of myo-Inositol-Hexakisphosphate (IP6) with Zinc or Lanthanum for the Decorporation of Radiocesium.

Radioactive nuclides leak into the surrounding environment after nuclear power plant disasters, such as the Chernobyl accident and the Fukushima Daiichi Nuclear Power Plant disaster. Cesium-137 (137Cs) (t1/2=30.1 year), a water-soluble radionuclide with a long physical half-life, contaminates aquatic ecosystems and food products. In humans, 137Cs concentrates in muscle tissue and has a long biological half-life, indicating it may be harmful. myo-Inositol-hexakisphosphate (IP6) is a compound found in grain, beans, and oil seeds. IP6 has the ability to form insoluble complexes with metals, including lanthanum (La) and zinc (Zn). We hypothesized that La-IP6 and Zn-IP6 may promote the elimination of 137Cs from the body through the adsorption of La-IP6 and Zn-IP6 to 137Cs in the gastrointestinal tract. Therefore, in this study, we evaluated the adsorptive capacity of La-IP6 and Zn-IP6 complexes with 137Cs in vitro and in vivo. La-IP6 and Zn-IP6 complexes were stable in acidic solution (pH 1.2) at 37°C. In vitro binding assays indicated that La-IP6 and Zn-IP6 complexes adsorbed 137Cs, with the adsorption capacity of Zn-IP6 to 137Cs greater than that of La-IP6. To evaluate the usefulness of La-IP6 and Zn-IP6 in vivo, La-IP6 or Zn-IP6 was administrated to mice after intravenous injection of 137Cs. However, the biodistribution of 137Cs in the La-IP6 treated group and the Zn-IP6 treated group was nearly identical to the non-treated control group, indicating that La-IP6 and Zn-IP6 were not effective at promoting the elimination of 137Cs in vivo.

Radiogallium Complex-Conjugated Bifunctional Peptides for Detecting Primary Cancer and Bone Metastases Simultaneously.

(68)Ga (T(1/2) = 68 min, a generator-produced nuclide) is an interesting radionuclide for clinical positron emission tomography (PET). Recently, it was reported that radiogallium-labeled 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA)-conjugated (Asp)n peptide [Ga-DOTA-(Asp)n] has great potential for bone metastases imaging. In the current study, a compound containing an aspartic acid peptide linker (D11) as a carrier to bone metastases, an RGD peptide [c(RGDfK) peptide] as a carrier to the primary cancer, and Ga-DOTA as a stable radiometal complex for imaging in one molecule, Ga-DOTA-D11-c(RGDfK), was designed, prepared, and evaluated to detect both the primary cancer and bone metastases simultaneously using (67)Ga, which is easy to handle. After DOTA-D11-c(RGDfK) was synthesized using Fmoc-based solid-phase methodology, (67)Ga-DOTA-D11-c(RGDfK) was prepared by complexing DOTA-D11-c(RGDfK) with (67)Ga. Hydroxyapatite binding assays, integrin binding assays, biodistribution experiments, and single photon emission tomography (SPECT) imaging using tumor-bearing mice were performed using (67)Ga-DOTA-D11-c(RGDfK). (67)Ga-DOTA-D11-c(RGDfK) was prepared with a radiochemical purity of >97%. In vitro, (67)Ga-DOTA-D11-c(RGDfK) had a high affinity for hydroxyapatite and αvß3 integrin. In vivo, (67)Ga-DOTA-D11-c(RGDfK) exhibited high uptake in bone and tumor. The accumulation of (67)Ga-DOTA-D11-c(RGDfK) in tumor decreased when it was co-injected with c(RGDfK) peptide. (68)Ga-DOTA-D11-c(RGDfK) has great potential as a PET tracer for the diagnosis of both the primary cancer and bone metastases simultaneously.

Universal reaction mechanism of boronic acids with diols in aqueous solution: kinetics and the basic concept of a conditional formation constant.

To establish a detailed reaction mechanism for the condensation between a boronic acid, RB(OH)2, and a diol, H2L, in aqueous solution, the acid dissociation constants (Ka(BL)) of boronic acid diol esters (HBLs) were determined based on the well-established concept of conditional formation constants of metal complexes. The pKa values of HBLs were 2.30, 2.77, and 2.00 for the reaction systems, 2,4-difluorophenylboronic acid and chromotropic acid, 3-nitrophenylboronic acid and alizarin red S, and phenylboronic acid and alizarin red S, respectively. A general and precise reaction mechanism of RB(OH)2 with H2L in aqueous solution, which can serve as a universal reaction mechanism for RB(OH)2 and H2L, was proposed on the basis of (a) the relative kinetic reactivities of the RB(OH)2 and its conjugate base, that is, the boronate ion, toward H2L, and (b) the determined pKa values of HBLs. The use of the conditional formation constant, K', based on the main reaction: RB(OH)2 + H2L (K1)⇌ RB(L)(OH)(-) + H3O(+) instead of the binding constant has been proposed for the general reaction of uncomplexed boronic acid species (B') with uncomplexed diol species (L') to form boronic acid diol complex species (esters, BL') in aqueous solution at pH 5-11: B' + L' (K')⇌ BL'. The proposed reaction mechanism explains perfectly the formation of boronic acid diol ester in aqueous solution.

The phosphate clamp: a small and independent motif for nucleic acid backbone recognition.

The 1.7 Å X-ray crystal structure of the B-DNA dodecamer, [d(CGCGAATTCGCG)]2 (DDD)-bound non-covalently to a platinum(II) complex, [{Pt(NH3)3}2-µ-{trans-Pt(NH3)2(NH2(CH2)6NH2)2}](NO3)6 (1, TriplatinNC-A,) shows the trinuclear cation extended along the phosphate backbone and bridging the minor groove. The square planar tetra-am(m)ine Pt(II) units form bidentate N-O-N complexes with OP atoms, in a Phosphate Clamp motif. The geometry is conserved and the interaction prefers O2P over O1P atoms (frequency of interaction is O2P > O1P, base and sugar oxygens > N). The binding mode is very similar to that reported for the DDD and [{trans-Pt(NH3)2(NH2(CH2)6(NH3(+))}2-µ-{trans-Pt(NH3)2(NH2(CH2)6NH2)2}](NO3)8 (3, TriplatinNC), which exhibits in vivo anti-tumour activity. In the present case, only three sets of Phosphate Clamps were found because one of the three Pt(II) coordination spheres was not clearly observed and was characterized as a bare Pt²(+) ion. Based on the electron density, the relative occupancy of DDD and the sum of three Pt(II) atoms in the DDD-1 complex was 1:1.69, whereas the ratio for DDD-2 was 1:2.85, almost the mixing ratio in the crystallization drop. The high repetition and geometric regularity of the motif suggests that it can be developed as a modular nucleic acid binding device with general utility.

Superoxide scavenging and xanthine oxidase inhibiting activities of copper-ß-citryl-L-glutamate complex.

ß-Citryl-L-glutamate (ß-CG) is a unique compound initially isolated from developing brains, which also appears in high concentrations during the period characterized by growth and differentiation of neurons in developing animals, and then decreases with maturation. However, its functional roles remain unclear. The stability constant obtained in our previous pH titration studies showed that ß-CG forms relatively strong complexes with copper. Reactive oxygen species (ROS) and nitric oxide (NO) have been suggested to act as mediators of the cell death that occurs in neurons during development of the nervous system. However, regulation of ROS and NO formation by Cu in the developing brain remains poorly understood. The activity of superoxide dismutase (SOD), a key superoxide scavenging enzyme, is low in the developing brain. Furthermore, xanthine oxidase (XO) has been implicated in diverse pathological situations due to its capability of generating both ROS and NO. Therefore, we examined the effects of ß-CG and its Cu-complex on SOD and XO activities. We found that the [Cu(II)(ß-CG)] complex had SOD activity and a strong competitive inhibition of XO, while reduced glutathione caused concentration-dependent decreases of the XO inhibitory activities in the [Cu(II)(ß-CG)] complex.

beta-Citryl-L-glutamate is an endogenous iron chelator that occurs naturally in the developing brain.

The compound beta-citryl-L-glutamate (beta-CG) was initially isolated from developing brains, while it has also been found in high concentrations in testes and eyes. However, its functional roles are unclear. To evaluate its coordination with metal ions, we performed pH titration experiments. The stability constant, logbeta(pqr) for M(p)(beta-CG)(q)H(r) was calculated from pH titration data, which showed that beta-CG forms relatively strong complexes with Fe(III), Cu(II), Fe(II) and Zn(II). beta-CG was also found able to solubilize Fe more effectively from Fe(OH)(2) than from Fe(OH)(3). Therefore, we examined the effects of beta-CG on Fe-dependent reactive oxygen species (ROS)-generating systems, as well as the potential ROS-scavenging activities of beta-CG and metal ion-(beta-CG) complexes. beta-CG inhibited the Fe-dependent degradation of deoxyribose and Fe-dependent damage to DNA or plasmid DNA in a dose-dependent manner, whereas it had no effect on Cu-mediated DNA damage. In addition, thermodynamic data showed that beta-CG in a physiological pH solution is an Fe(II) chelator rather than an Fe(III) chelator. Taken together, these findings suggest that beta-CG is an endogenous low molecular weight Fe chelator.

Characterization of platinum(II) complexes exhibiting inhibitory activity against the 20S proteasome.

Proteasome inhibitors are useful for biochemical research and clinical treatment. In our previous study, we reported that the 4N-coordinated platinum complexes with anthracenyl ring and heterocycle exhibited proteasome-inhibitory activity. In the present study, the structure-activity relationships and characterization of these complexes were determined for the elucidation of the role of aromatic ligands. Lineweaver-Burk analysis revealed that the chemical structure of heterocycles affects the binding mode of platinum complexes. Platinum complexes with anthracenyl ring and pyridine showed competitive inhibition, although platinum complexes with anthracenyl ring and phenanthroline showed non-competitive inhibition. The structure-activity relationships demonstrated that anthracenyl moiety plays a crucial role in proteasome-inhibitory activity. The platinum complexes with naphthyl or phenyl rings exhibited lower inhibitory activities than the platinum complex with anthracenyl ring. The reactivity with N-acetylcysteine varied according to the chemical structure of complexes.

Decreasing undesirable absorbed radiation to the intestine after administration of radium-223 dichloride for treatment of bone metastases.

[223Ra]RaCl2 is the first alpha-particle emitting radiopharmaceutical to be used for castration-resistant prostate cancer patients with bone metastases because of its excellent therapeutic effects. [223Ra]RaCl2 is excreted via the intestine into feces, and some is absorbed from the intestine into the blood, which may be undesirable in terms of the exposure to radiation. Recently, we showed that a complex of myo-inositol-hexakisphosphate (InsP6) with zinc is a useful decorporation agent against radiostrontium. In this study, we hypothesized that Zn-InsP6 could bind to not only strontium but also to radium, and could inhibit the absorption of radium from the intestine. In in vitro binding experiments, Zn-InsP6 showed a high binding affinity for radium. In in vivo biodistribution experiments by intravenous injection of [223Ra]RaCl2 after treatment of Zn-InsP6, mice treated with Zn-InsP6 showed significantly lower bone accumulation of radioactivity (34.82 ± 1.83%Dose/g) than the mice in the non-treatment control group (40.30 ± 2.78%Dose/g) at 48 h postinjection. These results indicate that Zn-InsP6 bound radium in the intestine and inhibited the absorption of radium into the blood. Therefore, the insoluble Zn-InsP6 complex has high potential to decrease the side effects of [223Ra]RaCl2.

A Novel Anionic-phosphate-platinum Complex Effectively Targets a Cisplatinum-resistant Osteosarcoma in a Patient-derived Orthotopic Xenograft Mouse Model.

BACKGROUND/AIM: We have previously developed a novel bone-targeting platinum compound, 3Pt, and showed that it has strong inhibitory activity against osteosarcoma cells and orthotopic cell-line xenograft mouse models. In the present report, we compared the efficacy of 3Pt to cisplatinum (CDDP) in a CDDP-resistant relapsed osteosarcoma patient-derived orthotopic xenograft (PDOX) mouse model. PATIENTS AND METHODS: The tumor of a patient with osteosarcoma of the distal femur was treated with CDDP-based chemotherapy followed by surgery. The surgical specimen was used to establish a PDOX model. An osteosarcoma cell line was also established from the original patient tumor. Osteosarcoma cell viability was assessed with the WST-8 assay and the IC50 values were calculated. The PDOX models were randomized into three groups: untreated control, CDDP-treated group, and 3Pt-treated group. Tumor size and body weight were measured twice a week. RESULTS: 3Pt had a strong concentration-dependent cytocidal effect in vitro. The IC50 value of 3Pt was significantly lower than that of CDDP. On day 14 of the treatment, 3Pt caused a significantly greater tumor growth inhibition compared to the untreated control and CDDP-treated mice. CONCLUSION: 3Pt is a promising clinical candidate for the treatment of recalcitrant osteosarcoma.

Development of radiolabeled bis(zinc(II)-dipicolylamine) complexes for cell death imaging.

PURPOSE: Although it has been traditionally surmised that phosphatidylserine (PS) externalization is a hallmark of apoptosis, most other non-apoptotic modes of cell death, such as necrosis, are also associated with PS externalization. Bis(zinc-dipicolylamine) (ZnDPA) complexes have been reported to exhibit affinity for PS. The present study aimed to develop novel radiolabeled ZnDPA derivatives for cell death imaging in tumor after treatment with anticancer drugs. METHODS: [125I]IB-EG2-ZnDPA and [99mTc]Tc-MAG3-EG2-ZnDPA were designed and prepared. The stabilities of these radiotracers were determined in 0.1 M phosphate buffer (pH 7.4) or murine plasma at 37 °C, and their 1-octanol/water partition coefficients (logP) were measured. The uptake of radioactivity in cancer cells, which were preincubated in a normal medium or in a medium containing 5-FU, was measured after incubation with radiotracers. Accumulation of [99mTc]Tc-MAG3-EG2-ZnDPA in the tumor was evaluated in tumor-bearing mice treated with or without 5-FU, and then TUNEL staining was performed to detect dead cells in the tumor tissue sections. RESULTS: The radiochemical purities of [125I]IB-EG2-ZnDPA and [99mTc]Tc-MAG3-EG2-ZnDPA exceeded 95%. Although [125I]IB-EG2-ZnDPA gradually decomposing with time, more than 90% of [99mTc]Tc-MAG3-EG2-ZnDPA remained in its intact form in phosphate buffer through 6 h of incubation. Neither [125I]IB-EG2-ZnDPA nor [99mTc]Tc-MAG3-EG2-ZnDPA decomposed so much after 6-h incubation in murine plasma. [125I]IB-EG2-ZnDPA could not specifically recognize PS on the cell surface because of its high lipophilicity. Conversely, [99mTc]Tc-MAG3-EG2-ZnDPA accumulated in cancer cells after treatment with an anticancer drug both in vitro and in vivo, and its accumulation was correlated with the number of TUNEL-positive cells. However, the biodistribution of [99mTc]Tc-MAG3-EG2-ZnDPA was not suitable for imaging because of its low accumulation in tumor and high uptake in abdomen organs. CONCLUSION: [99mTc]Tc-MAG3-EG2-ZnDPA could be useful for the early detection of treatment effects after chemotherapy. Since the signal-to-noise ratio is not enough for single photon emission computed tomography imaging, further modification is needed to improve its biodistribution and affinity for PS.

Fundamental study of radiogallium-labeled aspartic acid peptides introducing octreotate derivatives.

OBJECTIVE: Somatostatin receptors are highly expressed in neuroendocrine tumors, and many radiolabeled somatostatin analogs for diagnosis and treatment have been developed. To simultaneously detect not only primary cancer but also bone metastases, this study aimed to develop a positron emission tomography probe using generator-produced nuclide Gallium-68 (T1/2 = 68 min), in which a carrier for primary cancer, a carrier for bone metastases lesions, and a stable gallium complex are introduced into the one molecule. Based on this strategy, the somatostatin receptor-targeted peptide, [Tyr3]-octreotate (TATE), aspartic acid peptide (Dn) with high binding affinity for hydroxyapatite, and Ga-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) as a stable gallium complex were selected. The novel complexes, Ga-DOTA-Dn-TATE (n = 0, 2, 5, 8, or 11), were designed, synthesized, and evaluated. The radiogallium complexes were prepared using the easy-to-handle radioisotope 67Ga due to relatively long half-life. METHODS: The radiogallium complex precursor DOTA-Dn-TATE was synthesized by the Fmoc-based solid-phase method and by the air oxidation method to form the disulfide bond. [67Ga]Ga-DOTA-Dn-TATE was synthesized by reacting DOTA-Dn-TATE and 67Ga. Hydroxyapatite binding assays, in vitro cellular uptake experiments in AR42J tumor cells, in biodistribution experiments in AR42J tumor-bearing mice, were performed using [67Ga]Ga-DOTA-Dn-TATE. RESULTS: The radiochemical purities of [67Ga]Ga-DOTA-Dn-TATE were > 96.0%. In in vitro and in vivo experiments, [67Ga]Ga-DOTA-D11-TATE had a high affinity for hydroxyapatite and highly accumulated in bone. However, the uptake of [67Ga]Ga-DOTA-D11-TATE into somatostatin receptor-positive AR42J cells was lower than that of [67Ga]Ga-DOTA-TATE, and the accumulation of [67Ga]Ga-DOTA-D11-TATE in tumor was significantly low. CONCLUSION: Ga-DOTA-D11-TATE may not be recognized by somatostatin receptor by the introduction of D11, and the charge adjustment may be important for somatostatin receptor-positive cell uptake.

Complexes of myo-inositol-hexakisphosphate (InsP6) with zinc or lanthanum to enhance excretion of radioactive strontium from the body.

90Sr, which was released into the atmosphere and the ocean following the Chernobyl and Fukushima Daiichi nuclear power plant disasters, is an important nuclear fission element. Compounds that inhibit the absorption of 90Sr into the bloodstream and enhance its elimination can be beneficial in decreasing the absorbed radiation dose in people exposed to 90Sr. Recently, we prepared complexes of myo-inositol-hexakisphosphate (InsP6) with zinc or lanthanum as decorporation agents. These complexes, called Zn-InsP6 and La-InsP6 respectively, are insoluble in water and can potentially chelate additional metal cations. Hypothesizing that these complexes can assist the excretion of 90Sr from the body, we evaluated them using 85Sr instead of 90Sr. In in vitro binding experiments, Zn-InsP6 showed higher strontium adsorption capacity than La-InsP6. We then performed in vivo biodistribution experiments of Zn-InsP6 in mice after oral administration of 85SrCl2. Mice treated with Zn-InsP6 showed significantly lower bone accumulation of radioactivity than mice in a non-treatment control group. Zn-InsP6 adsorbed radiostrontium in the gastrointestinal tract, inhibited this ion's absorption into the bloodstream, and enhanced its excretion in the feces. Therefore, Zn-InsP6 appears to be a promising 90Sr "decorporation" agent.

Development of a novel radiobromine-labeled sigma-1 receptor imaging probe.

INTRODUCTION: Sigma-1 receptor is a target for tumor imaging. In a previous study, we synthesized a vesamicol analog, (+)-2-[4-(4-bromophenyl)piperidino]cyclohexanol [(+)-pBrV], with a high affinity for sigma-1 receptor, and synthesized radiobrominated (+)-pBrV. This radiobrominated (+)-pBrV showed high tumor uptake in tumor-bearing mice; however, radioactivity accumulation in normal tissues, such as the liver, was high. We assumed that the accumulation of (+)-pBrV in the non-target tissues was partially derived from its high lipophilicity; therefore, we synthesized and evaluated (+)-4-[1-(2-hydroxycyclohexyl)piperidine-4-yl]-2-bromophenol [(+)-BrV-OH], which is a more hydrophilic compound. Although we aimed to develop a PET tracer using 76Br, in these initial studies, we used 77Br because of its longer half-life. METHODS: (+)-[77Br]BrV-OH was synthesized using the chloramine-T method with a radiochemical purity of 95%. Lipophilicity and affinity for sigma-1 receptor of (+)-[77Br]BrV-OH were determined, and biodistribution experiments were performed. We also performed an in vivo blocking study by co-injecting excess amounts of the sigma-1 receptor ligand, SA4503, into mice. RESULTS: The lipophilicity and affinity for sigma-1 receptor of (+)-[77Br]BrV-OH were lower than those of (+)-[77Br]pBrV. (+)-[77Br]BrV-OH also showed high tumor uptake in biodistribution experiments in DU-145 tumor-bearing mice,. Although (+)-[77Br]pBrV was retained in most tissues, (+)-[77Br]BrV-OH was cleared from these tissues. In blocking studies, the co-injection of SA4503 significantly decreased the tumor uptake of (+)-[77Br]BrV-OH. CONCLUSION: These results indicate that (+)-[76Br]BrV-OH has potential as a PET probe for sigma-1 receptor imaging.

Radiobrominated benzimidazole-quinoline derivatives as Platelet-derived growth factor receptor beta (PDGFRß) imaging probes.

Platelet-derived growth factor receptor beta (PDGFRß) affects in numerous human cancers and has been recognized as a promising molecular target for cancer therapies. The overexpression of PDGFRß could be a biomarker for cancer diagnosis. Radiolabeled ligands having high affinity for the molecular target could be useful tools for the imaging of overexpressed receptors in tumors. In this study, we aimed to develop radiobrominated PDGFRß ligands and evaluate their effectiveness as PDGFRß imaging probes. The radiolabeled ligands were designed by modification of 1-{2-[5-(2-methoxyethoxy)-1H- benzo[d]imidazol-1-yl]quinolin-8-yl}piperidin-4-amine (1), which shows selective inhibition profile toward PDGFRß. The bromine atom was introduced directly into C-5 of the quinoline group of 1, or indirectly by the conjugation of 1 with the 3-bromo benzoyl group. [77Br]1-{5-Bromo-2-[5-(2-methoxyethoxy)-1H-benzo[d]imidazol-1-yl]quinoline-8-yl}piperidin-4-amine ([77Br]2) and [77Br]-N-3-bromobenzoyl-1-{2-[5-(2-methoxyethoxy)-1H-benzo[d]imidazol-1-yl]quinolin-8-yl}-piperidin-4-amine ([77Br]3) were prepared using a bromodestannylation reaction. In a cellular uptake study, [77Br]2 and [77Br]3 more highly accumulatd in BxPC3-luc cells (PDGFRß-positive) than in MCF7 cells (PDGFRß-negative), and their accumulation was significantly reduced by pretreatment with inhibitors. In biodistribution experiments, [77Br]2 accumulation was higher than [77Br]3 accumulation at 1 h postinjection. These findings suggest that [76Br]2 is more promising for positron emission tomography (PET) imaging of PDGFRß than [76Br]3.