Synthesis and evaluation of new mixed "2 + 1" Re, 99mTc and 186Re tricarbonyl dithiocarbamate complexes with different monodentate ligands.

A series of "2 + 1" mixed ligand tricarbonyl complexes of the general formula fac-[Re/99mTc/186Re(CO)3(DDTC)(L)] containing diethyldithiocarbamate (DDTC) as a monoanionic bidentate ligand and a series of monodentate ligands L was synthesized, characterized and evaluated. The impact of ligand L on the radiochemical yield (RCY) and biodistribution of the final compounds was also investigated. DDTC and the appropriate L ligand [cyclohexyl isocyanide (cisc), tert-butyl isocyanide (tbi), triphenylphosphine (PPh3), methyldiphenylphosphine (PPh2Me), triphenylarsine (AsPh3), imidazole (im), and 4-aminopyridine (4AP)] readily reacted in equimolar amounts with the [Et4N]2[Re(CO)3Br3] precursor to afford fac-[Re(CO)3(DDTC)(cisc)], Re1, fac-[Re(CO)3(DDTC)(tbi)], Re2, fac-[Re(CO)3(DDTC)(PPh3)], Re3, fac-[Re(CO)3(DDTC)(PPh2Me)], Re4, fac-[Re(CO)3(DDTC)(AsPh3)], Re5, fac-[Re(CO)3(DDTC)(im)], Re6 and fac-[Re(CO)3(DDTC)(4AP)], Re7, complexes in high yields (>80%). All Re complexes were fully characterized by IR, NMR, and in addition Re4, Re5, and Re7 with X-ray crystallography. Analogous reactions as performed with Re were subsequently explored on the 99mTc and 186Re-tracer levels using the corresponding fac-[99mTc/186Re(CO)3(H2O)3]+ precursor. Complexes 99mTc1 - 99mTc5, 186Re1 and 186Re3 were obtained in high radiochemical yield (>91%), while the complexes 99mTc6, 99mTc7 and 186Re7 formed with radiochemical yields of 55%, 28%, and 75%, respectively. The 99mTc and 186Re-complexes were characterized by comparative HPLC analysis using the analogous Re complexes. During histidine and cysteine challenge experiments at 37 °C through 6 h, complexes 99mTc1 - 99mTc5 remained > 92% stable, while complexes 99mTc6 and 99mTc7 remained only 8% stable through 3 h. Similar studies for 186Re-complexes showed that 186Re1 and 186Re3 remained > 95% stable for up to 48 h, while 186Re7 had decreased to 7% after 3 h. LogD7.4 data of 99mTc1 - 99mTc5, 186Re1, and 186Re3 complexes, which ranged from 2.59 to 3.39, suggested high lipophilicity. Biodistribution studies in healthy Swiss albino mice showed hepatobiliary excretion for 99mTc1, 99mTc2, and 99mTc4, fast blood clearance for 99mTc4, while high liver uptake and retention for 99mTc3 and 99mTc5 were measured. Moreover, 99mTc2 showed high accumulation in the lungs with sustained retention (52.80% ID/g at 4 h p.i.) and significant brain uptake at 2 min p.i. (1.89% ID/g). The study showed the great influence of monodentate ligand in the synthesis and biodistribution of the mixed ligand complexes.

Rhenium Sulfide Nanoparticles as a Biosafe Spectral CT Contrast Agent for Gastrointestinal Tract Imaging and Tumor Theranostics in Vivo.

Spectral computed tomography (CT) imaging as a novel imaging technique shows promising prospects in the accurate diagnosis of various diseases. However, clinically iodinated contrast agents suffer from poor signal-to-noise ratio, and emerging heavy-metal-based CT contrast agents arouse great biosafety concern. Herein, we show the fabrication of rhenium sulfide (ReS2) nanoparticles, a clinic radiotherapy sensitizer, as a biosafe spectral CT contrast agent for the gastrointestinal tract imaging and tumor theranostics in vivo by teaching old drugs new tricks. The ReS2 nanoparticles were fabricated in a one-pot facile method at room temperature, and exhibited sub-10 nm size, favorable monodispersity, admirable aqueous solubility, and strong X-ray attenuation capability. More importantly, the proposed nanoparticles possess an outstanding spectral CT imaging ability and undoubted biosafety as a clinic therapeutic agent. Besides, the ReS2 nanoparticles possess appealing photothermal performance due to their intense near-infrared absorption. The proposed nano-agent not only guarantees obvious contrast enhancement in gastrointestinal tract spectral CT imaging in vivo, but also allows effective CT imaging-guided tumor photothermal therapy. The proposed "teaching old drugs new tricks" strategy shortens the time and cuts the cost required for clinical application of nano-agents based on existing clinical toxicology testing and trial results, and lays down a low-cost, time-saving, and energy-saving method for the development of multifunctional nano-agents toward clinical applications.

Nuclear nanomedicine using Si nanoparticles as safe and effective carriers of 188Re radionuclide for cancer therapy.

Nuclear nanomedicine, with its targeting ability and heavily loading capacity, along with its enhanced retention to avoid rapid clearance as faced with molecular radiopharmaceuticals, provides unique opportunities to treat tumors and metastasis. Despite these promises, this field has seen limited activities, primarily because of a lack of suitable nanocarriers, which are safe, excretable and have favorable pharmacokinetics to efficiently deliver and retain radionuclides in a tumor. Here, we introduce biodegradable laser-synthesized Si nanoparticles having round shape, controllable low-dispersion size, and being free of any toxic impurities, as highly suitable carriers of therapeutic 188Re radionuclide. The conjugation of the polyethylene glycol-coated Si nanoparticles with radioactive 188Re takes merely 1 hour, compared to its half-life of 17 hours. When intravenously administered in a Wistar rat model, the conjugates demonstrate free circulation in the blood stream to reach all organs and target tumors, which is radically in contrast with that of the 188Re salt that mostly accumulates in the thyroid gland. We also show that the nanoparticles ensure excellent retention of 188Re in tumor, not possible with the salt, which enables one to maximize the therapeutic effect, as well as exhibit a complete time-delayed conjugate bioelimination. Finally, our tests on rat survival demonstrate excellent therapeutic effect (72% survival compared to 0% of the control group). Combined with a series of imaging and therapeutic functionalities based on unique intrinsic properties of Si nanoparticles, the proposed biodegradable complex promises a major advancement in nuclear nanomedicine.

Combinatorial Synthesis to Identify a Potent, Necrosis-Inducing Rhenium Anticancer Agent.

Combinatorial synthesis can be applied for developing a library of compounds that can be rapidly screened for biological activity. Here, we report the application of microwave-assisted combinatorial chemistry for the synthesis of 80 rhenium(I) tricarbonyl complexes bearing diimine ligands. This library was evaluated for anticancer activity in three different cancer cell lines, enabling the identification of three lead compounds with cancer cell growth-inhibitory activities of less than 10 µM. These three lead structures, Re-9B, Re-9C, and Re-9D, were synthesized independently and fully characterized by NMR spectroscopy, mass spectrometry, elemental analysis, and X-ray crystallography. The most potent of these three complexes, Re-9D, was further explored to understand its mechanism of action. Complex Re-9D is equally effective in both wild-type and cisplatin-resistant A2780 ovarian cancer cells, indicating that it circumvents cisplatin resistance. This compound was also shown to possess promising activity against ovarian cancer tumor spheroids. Additionally, flow cytometry showed that Re-9D does not induce cell cycle arrest or flipping of phosphatidylserine to the outer cell membrane. Analysis of the morphological changes of cancer cells treated with Re-9D revealed that this compound gives rise to rapid plasma membrane rupture. Collectively, these data suggest that Re-9D induces necrosis in cancer cells. To assess the in vivo biodistribution and stability of this compound, a radioactive 99mTc analogue of Re-9D, 99mTc-9D(H2O), was synthesized and administered to naïve BALB/c mice. Results of these studies indicate that 99mTc-9D(H2O) exhibits high metabolic stability and a distinct biodistribution profile. This research demonstrates that combinatorial synthesis is an effective approach for the development of new rhenium anticancer agents with advantageous biological properties.

Biodistribution, pharmacokinetics and radioimmunotherapy of 188Re-cetuximab in NCI-H292 human lung tumor-bearing nude mice.

Background Cetuximab is a fully humanized IgG1 subclass monoclonal that binds specifically to the human epidermal growth factor receptor (EGFR). Although EGFR is expressed in normal cells, the overexpression of EGFR is detected in many human cancers, such as colon, rectum and lung tumors. In this study, cetuximab with a combination of radiotherapy nuclear 188Re achieved better therapeutic effect on lung cancer. Methods188Re-cetuximab administered by the i.v. route in human NCI-H292 lung tumor-bearing mice was investigated. NanoSPECT/CT images were taken to evaluate the distribution and tumor targeting of 188Re-cetuximab in mice. The anti-tumor effect of 188Re-cetuximab was assessed by the tumor growth inhibition, survival ratio. Results For nanoSPECT/CT imaging, a significant uptake in tumor was observed at 24 and 48 h following the injection of 188Re-cetuximab. The anti-tumor effect of 188Re-cetuximab was assessed by tumor growth inhibition and the survival ratio. The tumor-bearing mice treated with 188Re-cetuximab showed a better mean tumor growth inhibition rate (MGI = 0.049) and longer median survival time and lifespan (62.50 d; 70.07%) than those treated with 188Re-perrhenate and cetuximab only by single injection. A synergistic effect of tumor growth inhibition was observed with the combination index exceeding one for 188Re-cetuximab (CI = 6.135 and 9.276). Conclusion The tumor targeting and localization of 188Re-cetuximab were confirmed in this study. Synergistic therapeutic efficacy was demonstrated for the radioimmunotherapy of 188Re-cetuximab. The results of this study reveal the potential advantage and benefit obtained from 188Re-cetuximab for diagnosis and therapy of oncology applications in the future.

Evaluation of chromosomal aberrations induced by 188Re-dendrimer nanosystem on B16f1 melanoma cells.

PURPOSE: To study the rhenium-188 labeling of polyamidoamine (PAMAM) generation 4 (G4) dendrimer and its evaluation on biodistribution and chromosomal aberrations in melanoma cells induced by ionizing radiation as potential treatment agent. MATERIALS AND METHODS: Dendrimers were first conjugated with Suc-HYNIC (succinimidyl 6-hydrazinopyridine-3-carboxylic acid hydrochloride). Dendrimer-HYNIC was then incubated with 188ReO4-. Biodistribution was performed administrating 188Re-dendrimer to normal (NM) or melanoma-bearing mice (MBM). Chromosome aberration test was conducted in order to measure treatment capacity of 188Re-dendrimer in melanoma cells. RESULTS: Radiolabeling yield of dendrimer was approx. 70%. Biodistribution studies in NM showed blood clearance with hepatic and renal depuration. MBM showed a similar pattern of biodistribution with tumor uptake of 6% of injected dose. Aberrant metaphases quantified in control cells were 7%, increasing to 29.5% in cells treated with 15µCi (0.555 MBq) of 188Re-dendrimer for 24 h. CONCLUSIONS: 188Re-dendrimer can produce double-stranded breaks in DNA induced by ionizing radiation in melanoma cells in vitro.

Radiotoxicity of alpha particles versus high and low energy electrons in hypoxic cancer cells.

PURPOSE: Hypoxic regions of tumors are less sensitive to radio- and chemotherapy, leading to poor prognosis of patients. One option to overcome the radioresistance is the irradiation of hypoxic tumors with high linear energy transfer (LET) α- or Auger electronemitters assuming their radiotoxicity would be less dependent on the cellular oxygenation status. Therefore, the aim of the present study was to determine whether irradiation with the intracellularly distributed Auger electron/γ-emitter 99mTc using the tracer [99mTc]TcHMPAO is a promising therapeutic option for the treatment of hypoxic tumor cells. Thus, the high LET α-particleemitter 223Ra ([223Ra]RaCl2) and the low LET ß-emitter 188Re ([188Re]NaReO4) were studied in comparison to [99mTc]Tc-HMPAO. MATERIALS AND METHODS: A431 tumor cells were incubated with [99mTc]Tc-HMPAO (1-20 MBq/2 mL), [223Ra]RaCl2 (1.4-16.3 kBq/2 mL) or [188Re]NaReO4 (0.3-13.7 MBq/2 mL) under normoxic or hypoxic conditions. The degree of radiotoxicity was analyzed using the colony forming assay (CFA), and the intracellular radionuclide uptake of the radiotracers was quantified. RESULTS: Hypoxic A431 cells are less radiosensitive to irradiation with [99mTc]Tc-HMPAO or [188Re]NaReO4 than normoxic ones. In contrast, the radiosensitivity of A431 cells is almost independent of the oxygen status when treated with the [223Ra]RaCl2. CONCLUSIONS: We demonstrate that the Auger electron/γ-emitter 99mTc ([99mTc]Tc-HMPAO), which does not bound directly to the DNA, is not a promising therapeutic option for hypoxic tumor cells. But the high LET α-particle-emitter 223Ra is more suitable for the treatment of hypoxic tumor cells than irradiation with [99mTc]Tc-HMPAO or the low LET bemitter 188Re. ZIELSETZUNG: Hypoxische Tumorregionen sind bei Radio- und Chemotherapie weniger sensitiv als Tumorregionen mit ausreichender Sauerstoffversorgung. Dies verursacht eine schlechte Prognose für Tumorpatienten. Eine Option die Radioresistenz zu überwinden, stellt die Bestrahlung mit α-Partikel-Emittern oder Auger-Elektronen-Emittern mit einem hohen linearen Energietransfer (LET) dar. In dieser Studie soll untersucht werden, ob die Bestrahlung von hypoxischen Tumorzellen mit dem intrazellulär aufgenommenen γ- sowie Auger-Elektronen-Emitter 99mTc unter Verwendung des Radiotracers [99mTc]Tc-HMPAO eine vielversprechende Therapieoption darstellen könnte. Vergleichend wurde der Hoch-LET α-Partikel-Emitter 223Ra ([223Ra]RaCl2) und der Niedrig-LET ß-Emitter 188Re ([188Re]NaReO4) eingesetzt. METHODEN: A431 Tumorzellen wurden unter normoxischen oder hypoxischen Kulturbedingungen mit [99mTc]Tc-HMPAO (1-20 MBq/2 ml), [223Ra]RaCl2 (1,4-16,3 kBq/2 ml) und [188Re]NaReO4 (0,3-13,7 MBq/2 ml) inkubiert. Zur Detektion der resultierenden strahlenbiologischen Wirkung wurde der Koloniebildungsassay angewendet. Zusätzlich wurde die intrazelluläre Aufnahme der Radiotracer quantifiziert. ERGEBNISSE: Nach Inkubation von [99mTc]Tc-HMPAO sind hypoxische A431-Zellen weniger strahlensensitiv als normoxische Zellen. Im Gegensatz zur Behandlung mit [99mTc]Tc-HMPAO oder [188Re]NaReO4 wurde bei Behandlung mit [223Ra]RaCl2 ein geringerer Einfluss des Sauerstoffstatus auf die Radiosensitivität von A431-Zellen gefunden. SCHLUSSFOLGERUNG: Damit konnte gezeigt werden, dass der nicht direkt an die DNA gebundene Auger-Elektronen-/ γ-Emitter 99mTc ([99mTc]Tc-HMPAO) die Radioresistenz von hypoxischen Tumorzellen nicht überwinden kann. Jedoch stellt der Hoch-LET α-Partikel-Emitter 223Ra ([223Ra]RaCl2) eine bessere Behandlungsoption dar.

Absorbed doses in humans from 188Re-Rituximab in the free form and bound to superparamagnetic iron oxide nanoparticles: Biodistribution study in mice.

Absorbed doses to human organs from 188Re-Rituximab in the free form and bound to superparamagnetic iron oxide nanoparticles were predicted from results of the radiopharmaceutical biodistribution studies in mice by the RADAR method. Overall, equivalent and effective doses to human organs from the radiopharmaceutical on the nanoparticles were higher because of the enhanced permeability and retention effect. Liver, spleen and kidneys received higher equivalent doses than other organs (5.29, 3.70 and 3.06mSv/MBq, respectively, for the free radiopharmaceutical and 6.12, 3.96 and 3.93mSv/MBq for the drug on the nanoparticles).

Trackable Metallodrugs Combining Luminescent Re(I) and Bioactive Au(I) Fragments.

Hetero-bimetallic and -trimetallic complexes were synthesized by the combination of different metallic fragments, a luminescent Re(I) species, and a bioactive Au(I) derivative. A ditopic P,N-donor ligand (L) was used as linker between both metals, affording six new bipyridine (bipy) Re(I)/Au(I) hetero-metallic complexes of the type fac-[Re(bipy)(CO)3(LAuCl)]+ (4-6) and [(fac-[Re(bipy)(CO)3(L)])2Au]3+ (7-9) after a thorough synthetic procedure. Their emission is associated with a triplet metal-to-ligand charge transfer (Re(dπ) → bipy(π*)) transition and red-shifted in polar solvents with lifetimes in the range of nanoseconds and quantum yield values up to 12.5%. Cytotoxicity values in A549 cells of hetero-trimetallic species are almost twice that for the hetero-bimetallic (ca. 37 vs 69 µM, respectively), being the L-Au fragment the source of the antiproliferative activity. Species 7 and 8 showed similar behavior by fluorescence microscopy, with a nonuniform cytoplasmatic distribution, a clear accumulation in single spots at the edge of the inner cell membrane as well as in areas within the nucleus. Preliminary studies suggest the DNA as one of the targets and passive diffusion as the entrance pathway.

In Vitro Anticancer Activity and in Vivo Biodistribution of Rhenium(I) Tricarbonyl Aqua Complexes.

Seven rhenium(I) complexes of the general formula fac-[Re(CO)3(NN)(OH2)]+ where NN = 2,2'-bipyridine (8), 4,4'-dimethyl-2,2'-bipyridine (9), 4,4'-dimethoxy-2,2'-bipyridine (10), dimethyl 2,2'-bipyridine-4,4'-dicarboxylate (11), 1,10-phenanthroline (12), 2,9-dimethyl-1,10-phenanthroline (13), or 4,7-diphenyl-1,10-phenanthroline (14), were synthesized and characterized by 1H NMR spectroscopy, IR spectroscopy, mass spectrometry, and X-ray crystallography. With the exception of 11, all complexes exhibited 50% growth inhibitory concentration (IC50) values that were less than 20 µM in HeLa cells, indicating that these compounds represent a new potential class of anticancer agents. Complexes 9, 10, and 13 were as effective in cisplatin-resistant cells as wild-type cells, signifying that they circumvent cisplatin resistance. The mechanism of action of the most potent complex, 13, was explored further by leveraging its intrinsic luminescence properties to determine its intracellular localization. These studies indicated that 13 induces cytoplasmic vacuolization that is lysosomal in nature. Additional in vitro assays indicated that 13 induces cell death without causing an increase in intracellular reactive oxygen species or depolarization of the mitochondrial membrane potential. Further studies revealed that the mode of cell death does not fall into one of the canonical categories such as apoptosis, necrosis, paraptosis, and autophagy, suggesting that a novel mode of action may be operative for this class of rhenium compounds. The in vivo biodistribution and metabolism of complex 13 and its 99mTc analogue 13* were also evaluated in naïve mice. Complexes 13 and 13* exhibited comparable biodistribution profiles with both hepatic and renal excretion. High-performance liquid chromatography inductively coupled plasma mass-spectrometry (HPLC-ICP-MS) analysis of mouse blood plasma and urine postadministration showed considerable metabolic stability of 13, rendering this potent complex suitable for in vivo applications. These studies have shown the biological properties of this class of compounds and demonstrated their potential as promising theranostic anticancer agents that can circumvent cisplatin resistance.

Imaging, biodistribution and efficacy evaluation of 188Re-human serum albumin microspheres via intraarterial route in an orthotopic hepatoma model.

PURPOSE: Liver cancer is the second most common cause of death worldwide. This study was to investigate the SPECT/CT, ultrasound, biodistribution and therapeutic evaluation of 188Re-human serum albumin microspheres (188Re-HSAM) in the GP7TB orthotopic hepatoma rat model. MATERIALS AND METHODS: HSAM was labeled with 188Re by using a home-made kit and microwave system. The 188Re-HSAM was administered via intraarterial route. The in vivo distribution of 188Re-HSAM was determined by biodistribution analysis and nanoSPECT/CT system. In efficacy, tumor volumes were tracked longitudinally by three-dimensional ultrasound. RESULTS: The biodistribution and nanoSPECT/CT imaging showed that 188Re-HSAM could accumulate in liver and tumor. The correlation coefficient of tumor volumes done by three-dimensional ultrasound and at autopsy was 0.997. In efficacy, tumor volume in the normal saline-treated group was 1803.2 mm3 at 54 days after tumor inoculation. Tumor volumes in the 103.6 MBq and 240.5 MBq of 188Re-HSAM treated groups were 381 and 267.4 mm3 (p = 0.001 and 0.004), respectively. CONCLUSIONS: These results show that three-dimensional ultrasound with a high spatial resolution and contrast in soft tissue can become imaging modality in assessing tumor burden and tumor progression in an orthotopic rat model. The longitudinally therapeutic evaluation of 188Re-HSAM demonstrated dose-dependent tumor growth inhibition with increased dose in the GP7TB orthotopic hepatoma rat model.

Characterization of the distribution, retention, and efficacy of internal radiation of 188Re-lipid nanocapsules in an immunocompromised human glioblastoma model.

Internal radiation strategies hold great promise for glioblastoma (GB) therapy. We previously developed a nanovectorized radiotherapy that consists of lipid nanocapsules loaded with a lipophilic complex of Rhenium-188 (LNC188Re-SSS). This approach resulted in an 83 % cure rate in the 9L rat glioma model, showing great promise. The efficacy of LNC188Re-SSS treatment was optimized through the induction of a T-cell immune response in this model, as it is highly immunogenic. However, this is not representative of the human situation where T-cell suppression is usually encountered in GB patients. Thus, in this study, we investigated the efficacy of LNC188Re-SSS in a human GB model implanted in T-cell deficient nude mice. We also analyzed the distribution and tissue retention of LNC188Re-SSS. We observed that intratumoral infusion of LNCs by CED led to their complete distribution throughout the tumor and peritumoral space without leakage into the contralateral hemisphere except when large volumes were used. Seventy percent of the 188Re-SSS activity was present in the tumor region 24 h after LNC188Re-SSS injection and no toxicity was observed in the healthy brain. Double fractionated internal radiotherapy with LNC188Re-SSS triggered survival responses in the immunocompromised human GB model with a cure rate of 50 %, which was not observed with external radiotherapy. In conclusion, LNC188Re-SSS can induce long-term survival in an immunosuppressive environment, highlighting its potential for GB therapy.

Involvement of let-7 microRNA for the therapeutic effects of Rhenium-188-embedded liposomal nanoparticles on orthotopic human head and neck cancer model.

Human head and neck squamous cell carcinoma (HNSCC) is usually treated by surgical resection with adjuvant radio-chemotherapy. In this study, we examined whether the radiopharmaceutical 188Re-liposome could suppress the growth of HNSCC followed by an investigation of molecular mechanisms. The orthotopic HNSCC tumor model was established by human hypopharyngeal FaDu carcinoma cells harboring multiple reporter genes. The drug targeting and therapeutic efficacy of 188Re-liposome were examined using in vivo imaging, bio-distribution, pharmacokinetics, and dosimetry. The results showed that 188Re-liposome significantly accumulated in the tumor lesion compared to free 188Re. The circulation time and tumor targeting of 188Re-liposome were also longer than that of free 188Re in tumor-bearing mice. The tumor growth was suppressed by 188Re-liposome up to three weeks using a single dose treatment. Subsequently, microarray analysis followed by Ingenuity Pathway Analysis (IPA) showed that tumor suppressor let-7 microRNA could be an upstream regulator induced by 188Re-liposome to regulate downstream genes. Additionally, inhibition of let-7i could reduce the effects of 188Re-liposome on suppression of tumor growth, suggesting that let-7 family was involved in 188Re-liposome mediated suppression of tumor growth in vivo. Our data suggest that 188Re-liposome could be a novel strategy for targeting HNSCC partially via induction of let-7 microRNA.

Mono- and Dinuclear Phosphorescent Rhenium(I) Complexes: Impact of Subcellular Localization on Anticancer Mechanisms.

Elucidation of relationship among chemical structure, cellular uptake, localization, and biological activity of anticancer metal complexes is important for the understanding of their mechanisms of action. Organometallic rhenium(I) tricarbonyl compounds have emerged as potential multifunctional anticancer drug candidates that can integrate therapeutic and imaging capabilities in a single molecule. Herein, two mononuclear phosphorescent rhenium(I) complexes (Re1 and Re2), along with their corresponding dinuclear complexes (Re3 and Re4), were designed and synthesized as potent anticancer agents. The subcellular accumulation of Re1-Re4 was conveniently analyzed by confocal microscopy in situ in live cells by utilizing their intrinsic phosphorescence. We found that increased lipophilicity of the bidentate ligands could enhance their cellular uptake, leading to improved anticancer efficacy. The dinuclear complexes were more potent than the mononuclear counterparts. The molecular anticancer mechanisms of action evoked by Re3 and Re4 were explored in detail. Re3 with a lower lipophilicity localizes to lysosomes and induces caspase-independent apoptosis, whereas Re4 with higher lipophilicity specially accumulates in mitochondria and induces caspase-independent paraptosis in cancer cells. Our study demonstrates that subcellular localization is crucial for the anticancer mechanisms of these phosphorescent rhenium(I) complexes.

(99m)Tc-Cyclopentadienyl Tricarbonyl Chelate-Labeled Compounds as Selective Sigma-2 Receptor Ligands for Tumor Imaging.

We have designed and synthesized a series of cyclopentadienyl tricarbonyl rhenium complexes containing a 5,6-dimethoxyisoindoline or a 6,7-dimethoxy-1,2,3,4-tetrahydroisoquinoline pharmacophore as σ2 receptor ligands. Rhenium compound 20a possessed low nanomolar σ2 receptor affinity (K(i) = 2.97 nM) and moderate subtype selectivity (10-fold). Moreover, it showed high selectivity toward vesicular acetylcholine transporter (2374-fold), dopamine D2L receptor, NMDA receptor, opiate receptor, dopamine transporter, norepinephrine transporter, and serotonin transporter. Its corresponding radiotracer [(99m)Tc]20b showed high uptake in a time- and dose-dependent manner in DU145 prostate cells and C6 glioma cells. In addition, this tracer exhibited high tumor uptake (5.92% ID/g at 240 min) and high tumor/blood and tumor/muscle ratios (21 and 16 at 240 min, respectively) as well as specific binding to σ receptors in nude mice bearing C6 glioma xenografts. Small animal SPECT/CT imaging of [(99m)Tc]20b in the C6 glioma xenograft model demonstrated a clear visualization of the tumor at 180 min after injection.

Toward hypoxia-selective rhenium and technetium tricarbonyl complexes.

With the aim of preparing hypoxia-selective imaging and therapeutic agents, technetium(I) and rhenium(I) tricarbonyl complexes with pyridylhydrazone, dipyridylamine, and pyridylaminocarboxylate ligands containing nitrobenzyl or nitroimidazole functional groups have been prepared. The rhenium tricarbonyl complexes were synthesized with short reaction times using microwave irradiation. Rhenium tricarbonyl complexes with deprotonated p-nitrophenyl pyridylhydrazone ligands are luminescent, and this has been used to track their uptake in HeLa cells using confocal fluorescent microscopy. Selected rhenium tricarbonyl complexes displayed higher uptake in hypoxic cells when compared to normoxic cells. A (99m)Tc tricarbonyl complex with a dipyridylamine ligand bearing a nitroimidazole functional group is stable in human serum and was shown to localize in a human renal cell carcinoma (RCC; SK-RC-52) tumor in a mouse.

External beam radiotherapy synergizes ¹88Re-liposome against human esophageal cancer xenograft and modulates ¹88Re-liposome pharmacokinetics.

External beam radiotherapy (EBRT) treats gross tumors and local microscopic diseases. Radionuclide therapy by radioisotopes can eradicate tumors systemically. Rhenium 188 ((188)Re)-liposome, a nanoparticle undergoing clinical trials, emits gamma rays for imaging validation and beta rays for therapy, with biodistribution profiles preferential to tumors. We designed a combinatory treatment and examined its effects on human esophageal cancer xenografts, a malignancy with potential treatment resistance and poor prognosis. Human esophageal cancer cell lines BE-3 (adenocarcinoma) and CE81T/VGH (squamous cell carcinoma) were implanted and compared. The radiochemical purity of (188)Re-liposome exceeded 95%. Molecular imaging by NanoSPECT/CT showed that BE-3, but not CE81T/VGH, xenografts could uptake the (188)Re-liposome. The combination of EBRT and (188)Re-liposome inhibited tumor regrowth greater than each treatment alone, as the tumor growth inhibition rate was 30% with EBRT, 25% with (188)Re-liposome, and 53% with the combination treatment at 21 days postinjection. Combinatory treatment had no additive adverse effects and significant biological toxicities on white blood cell counts, body weight, or liver and renal functions. EBRT significantly enhanced the excretion of (188)Re-liposome into feces and urine. In conclusion, the combination of EBRT with (188)Re-liposome might be a potential treatment modality for esophageal cancer.

Evaluation of 188Re-labeled PEGylated nanoliposome as a radionuclide therapeutic agent in an orthotopic glioma-bearing rat model.

PURPOSE: In this study, the (188)Re-labeled PEGylated nanoliposome ((188)Re-liposome) was prepared and evaluated as a therapeutic agent for glioma. MATERIALS AND METHODS: The reporter cell line, F98(luc) was prepared via Lentivector expression kit system and used to set up the orthotopic glioma-bearing rat model for non-invasive bioluminescent imaging. The maximum tolerated dose applicable in Fischer344 rats was explored via body weight monitoring of the rats after single intravenous injection of (188)Re-liposome with varying dosages before the treatment study. The OLINDA/EXM 1.1 software was utilized for estimating the radiation dosimetry. To assess the therapeutic efficacy, tumor-bearing rats were intravenously administered (188)Re-liposome or normal saline followed by monitoring of the tumor growth and animal survival time. In addition, the histopathological examinations of tumors were conducted on the (188)Re-liposome-treated rats. RESULTS: By using bioluminescent imaging, the well-established reporter cell line (F98(luc)) showed a high relationship between cell number and its bioluminescent intensity (R(2)=0.99) in vitro; furthermore, it could also provide clear tumor imaging for monitoring tumor growth in vivo. The maximum tolerated dose of (188)Re-liposome in Fischer344 rats was estimated to be 333 MBq. According to the dosimetry results, higher equivalent doses were observed in spleen and kidneys while very less were in normal brain, red marrow, and thyroid. For therapeutic efficacy study, the progression of tumor growth in terms of tumor volume and/or tumor weight was significantly slower for the (188)Re-liposome-treated group than the control group (P<0.05). As a result, the lifespan of glioma-bearing rats treated with (188)Re-liposome was prolonged 10.67% compared to the control group. CONCLUSION: The radiotherapeutic evaluation by dosimetry and survival studies have demonstrated that passive targeting (188)Re-liposome via systemic administration can significantly prolong the lifespan of orthotopic glioma-bearing rats while maintaining reasonable systemic radiation safety. Therefore, (188)Re-liposome could be a potential therapeutic agent for glioblastoma multiforme treatment.

Therapeutic and scintigraphic applications of polymeric micelles: combination of chemotherapy and radiotherapy in hepatocellular carcinoma.

This study evaluated a multifunctional micelle simultaneously loaded with doxorubicin (Dox) and labeled with radionuclide rhenium-188 ((188)Re) as a combined radiotherapy and chemotherapy treatment for hepatocellular carcinoma. We investigated the single photon emission computed tomography, biodistribution, antitumor efficacy, and pathology of (188)Re-Dox micelles in a murine orthotopic luciferase-transfected BNL tumor cells hepatocellular carcinoma model. The single photon emission computed tomography and computed tomography images showed high radioactivity in the liver and tumor, which was in agreement with the biodistribution measured by γ-counting. In vivo bioluminescence images showed the smallest size tumor (P<0.05) in mice treated with the combined micelles throughout the experimental period. In addition, the combined (188)Re-Dox micelles group had significantly longer survival compared with the control, (188)ReO4 alone (P<0.005), and Dox micelles alone (P<0.01) groups. Pathohistological analysis revealed that tumors treated with (188)Re-Dox micelles had more necrotic features and decreased cell proliferation. Therefore, (188)Re-Dox micelles may enable combined radiotherapy and chemotherapy to maximize the effectiveness of treatment for hepatocellular carcinoma.

The PEGylated liposomal doxorubicin improves the delivery and therapeutic efficiency of 188Re-Liposome by modulating phagocytosis in C26 murine colon carcinoma tumor model.

Liposome in delivering radionuclide for cancer therapy has been expansively studied; however, liposome itself can be deliberately entrapped and destroyed by the reticuloendothelial system, causing an insufficiency of the drug delivery, which in turn would restrict the effectiveness of the drug. In this study, mice with subcutaneous implantation of C26 murine colon cancer received an experimental treatment regimen in which mice took delivery of PEGylated liposomal doxorubicin (LipoDox) first, after a three-day interval, of Rhenium-188 encapsulated into PEGylated liposome ((188)Re-Liposome) subsequently and by which suppressed the functioning of reticuloendothelial system for the short term. The data showed that based upon the biodistribution assay and the evaluation of the therapeutic efficacy, (188)Re-Liposome was more sufficiently delivered to tumor sites in mice with this treatment regimen than mice without the regimen, and that cancer mortalities in mice with the treatment regimen were much lower than the mortalities in mice without the regimen. Taken together, a new strategy proposed in this study significantly improved both the (188)Re-Liposome delivery and the effectiveness of (188)Re-Liposome, suggesting that the strategy can be an ideal treatment for cancer.