Distributable, metabolic PET reporting of tuberculosis.

Tuberculosis remains a large global disease burden for which treatment regimens are protracted and monitoring of disease activity difficult. Existing detection methods rely almost exclusively on bacterial culture from sputum which limits sampling to organisms on the pulmonary surface. Advances in monitoring tuberculous lesions have utilized the common glucoside [18F]FDG, yet lack specificity to the causative pathogen Mycobacterium tuberculosis (Mtb) and so do not directly correlate with pathogen viability. Here we show that a close mimic that is also positron-emitting of the non-mammalian Mtb disaccharide trehalose - 2-[18F]fluoro-2-deoxytrehalose ([18F]FDT) - is a mechanism-based reporter of Mycobacteria-selective enzyme activity in vivo. Use of [18F]FDT in the imaging of Mtb in diverse models of disease, including non-human primates, successfully co-opts Mtb-mediated processing of trehalose to allow the specific imaging of TB-associated lesions and to monitor the effects of treatment. A pyrogen-free, direct enzyme-catalyzed process for its radiochemical synthesis allows the ready production of [18F]FDT from the most globally-abundant organic 18F-containing molecule, [18F]FDG. The full, pre-clinical validation of both production method and [18F]FDT now creates a new, bacterium-selective candidate for clinical evaluation. We anticipate that this distributable technology to generate clinical-grade [18F]FDT directly from the widely-available clinical reagent [18F]FDG, without need for either custom-made radioisotope generation or specialist chemical methods and/or facilities, could now usher in global, democratized access to a TB-specific PET tracer.

Distributable, Metabolic PET Reporting of Tuberculosis.

Tuberculosis remains a large global disease burden for which treatment regimens are protracted and monitoring of disease activity difficult. Existing detection methods rely almost exclusively on bacterial culture from sputum which limits sampling to organisms on the pulmonary surface. Advances in monitoring tuberculous lesions have utilized the common glucoside [18F]FDG, yet lack specificity to the causative pathogen Mycobacterium tuberculosis (Mtb) and so do not directly correlate with pathogen viability. Here we show that a close mimic that is also positron-emitting of the non-mammalian Mtb disaccharide trehalose - 2-[18F]fluoro-2-deoxytrehalose ([18F]FDT) - can act as a mechanism-based enzyme reporter in vivo. Use of [18F]FDT in the imaging of Mtb in diverse models of disease, including non-human primates, successfully co-opts Mtb-specific processing of trehalose to allow the specific imaging of TB-associated lesions and to monitor the effects of treatment. A pyrogen-free, direct enzyme-catalyzed process for its radiochemical synthesis allows the ready production of [18F]FDT from the most globally-abundant organic 18F-containing molecule, [18F]FDG. The full, pre-clinical validation of both production method and [18F]FDT now creates a new, bacterium-specific, clinical diagnostic candidate. We anticipate that this distributable technology to generate clinical-grade [18F]FDT directly from the widely-available clinical reagent [18F]FDG, without need for either bespoke radioisotope generation or specialist chemical methods and/or facilities, could now usher in global, democratized access to a TB-specific PET tracer.

Albumin-chaperoned cyanine dye yields superbright NIR-II fluorophore with enhanced pharmacokinetics.

NIR-II fluorescence imaging greatly reduces scattering coefficients for nearly all tissue types at long wavelengths, benefiting deep tissue imaging. However, most of the NIR-II fluorophores suffer from low quantum yields and/or short circulation time that limit the quality of NIR-II imaging. Here, we engineered a supramolecular assembly of protein complex with lodged cyanine dyes to produce a brilliant NIR-II fluorophore, providing a NIR-II quantum yield of 21.2% with prolonged circulation time. Computational modeling revealed the mechanism for fluorescence enhancement and identified key parameters governing albumin complex for NIR-II fluorophores. Our complex afforded high-resolution microvessel imaging, with a 3-hour imaging window compared to 2 min for free dye alone. Furthermore, the complexation strategy was applied to an antibody-derived assembly, offering high-contrast tumor imaging without affecting the targeting ability of the antibody. This study provides a facile strategy for producing high-performance NIR-II fluorophores by chaperoning cyanine dyes with functional proteins.

3-18F-fluoropropane-1-thiol and 18F-PEG4-1-thiol: Versatile prosthetic groups for radiolabeling maleimide functionalized peptides.

The efficient radiosynthesis of biomolecules utilizing minute quantities of maleimide substrate is important for availability of novel peptide molecular imaging agents. We evaluated both 3-18F-fluoropropane-1-thiol and 2-(2-(2-(2-18F-fluoroethoxy)ethoxy)ethoxy)ethane-1-thiol (18F-fluoro-PEG4 thiol) as prosthetic groups for radiolabeling under physiological conditions. The precursor employed a benzoate for protection of the thiol and an arylsulfonate leaving group. The radiofluorination was fully automated on an Eckert & Ziegler synthesis system using standard Kryptofix222/K2CO3 conditions. In order to minimize the amount of biological molecule required for subsequent conjugation, the intermediates, S-(3-18F-fluoropropyl) benzothioate and 18F-fluoro-PEG4 benzothioate, were purified by HPLC. The intermediates were isolated from the HPLC in yields of 37-47% and 28-35%, respectively, and retrieved from eluate using solid phase extraction. Treatment of the benzothioates with sodium methoxide followed by acetic acid provided the free thiols. The desired maleimide substrate in acetonitrile or phosphate buffer was then added and incubated at room temperature for 15 min. The final radiolabeled bioconjugate was purified on a separate HPLC or NAP-5 column. Maleimides utilized for the coupling reaction included phenyl maleimide, an Evans Blue maleimide derivative, a dimeric RGDfK maleimide (E[c(RGDfK)]2), two aptamer maleimides, and PSMA maleimide derivative. Isolated radiochemical yields (non-decay corrected) of maleimide addition products based on starting 18F-fluoride ranged from 6 to 22% in a synthesis time of about 90 min. 18F-thiol prosthetic groups were further tested in vivo by conjugation to E[c(RGDfK)]2 maleimide in a U87MG xenograft model. PET studies demonstrated similar tumor accumulation of both prosthetic groups. 18F-fluoro-PEG4-S-E[c(RGDfK)]2 displayed a somewhat favorable pharmacokinetics compared to 18F-fluoropropyl-S-E[c(RGDfK)]2. Bone uptake was low for both indicating in vivo stability.

Organosilica-Based Hollow Mesoporous Bilirubin Nanoparticles for Antioxidation-Activated Self-Protection and Tumor-Specific Deoxygenation-Driven Synergistic Therapy.

A major concern about glucose oxidase (GOx)-mediated cancer starvation therapy is its ability to induce serious oxidative damage to normal tissues through the massive production of H2O2 byproducts in the oxygen-involved glucose decomposition reaction, which may be addressed by using a H2O2 scavenger, known as an antioxidation agent. Surprisingly, H2O2 removal accelerates the aerobic glycometabolism of tumors by activating the H2O2-dependent "redox signaling" pathway of cancer cells. Simultaneous oxygen depletion further aggravates tumor hypoxia to increase the toxicity of a bioreductive prodrug, such as tirapazamine (TPZ), thereby improving the effectiveness of cancer starvation therapy and bioreductive chemotherapy. Herein, a "nitrogen-protected silica template" method is proposed to design a nanoantioxidant called an organosilica-based hollow mesoporous bilirubin nanoparticle (HMBRN), which can act as an excellent nanocarrier to codeliver GOx and TPZ. In addition to efficient removal of H2O2 for self-protection of normal tissues via antioxidation, GOx/TPZ-coloaded HMBRN can also rapidly deplete intratumoral glucose/oxygen to promote a synergistic starvation-enhanced bioreductive chemotherapeutic effect for the substantial suppression of solid tumor growth. Distinct from the simple combination of two treatments, this study introduces antioxidation-activated self-protection nanotechnology for the significant improvement of tumor-specific deoxygenation-driven synergistic treatment efficacy without additional external energy input, thus realizing the renaissance of precise endogenous cancer therapy with negligible side effects.

In situ polymerization on nanoscale metal-organic frameworks for enhanced physiological stability and stimulus-responsive intracellular drug delivery.

Metal-organic framework (MOF) nanoparticles have shown great potential as carrier platforms in theranostic applications. However, their poor physiological stability in phosphate-based media has limited their biological applications. Here, we studied the dissociation of MOF nanoparticles under physiological conditions, both in vitro and in vivo, and developed an in situ polymerization strategy on MOF nanoparticles for enhanced stability under physiological conditions and stimulus-responsive intracellular drug release. With polymer wrapped on the surface serving as a shield, the nanoscale MOFs were protected from decomposition by phosphate ions or acid and prevented the loaded cargos from leaking. An in vivo positron emission tomography (PET) study of 64Cu-labelled porphyrinic MOF indicated prolonged circulation time of the in situ polymerized MOF nanoparticles and greater tumor accumulation than unmodified MOF nanoparticles. With enhanced stability, cargos loaded into MOF nanoparticles or prodrugs conjugated on the surface can be efficiently delivered and released upon stimulus-responsive cleavage.

Tumor Microenvironment-Activated Ultrasensitive Nanoprobes for Specific Detection of Intratumoral Glutathione by Ratiometric Photoacoustic Imaging.

Glutathione (GSH), one of the most significant reducing species in vivo, plays important roles in a variety of diseases and cellular functions. Precise quantification of GSH via advanced noninvasive photoacoustic imaging (PAI) is of vital significance for the early diagnosis and prompt treatment of GSH-related deep-seated diseases, which stresses the need for custom-design of GSH-sensitive PAI probes with changeable near-infrared spectroscopy (NIR) absorption. In this work, a novel intelligent tumor microenvironment-activated ratiometric PAI nanoprobe is first developed with the intention of specific ultrasensitive detection of intratumoral GSH by overcoming the limitations of previously reported fluorescent or PA imaging sensors. This special ratiometric PAI nanoprobe (CR-POM) is synthesized through the self-assembly of croconaine (CR) dye and molybdenum-based polyoxometalate (POM) clusters with opposite NIR absorbance change in response to GSH. The resulting amplified ratiometric absorbance (Ab866/Ab700), the relatively low limit of detection value (0.51 mM), and the unique acidity-activated self-aggregation contribute to the prolonged intratumoral retention and enhanced tumor accumulation of CR-POM for accurate quantification of intratumoral GSH (0.5-10 mM). Featuring the additional merit of 64Cu radiolabeling for whole-body positron-emission tomography imaging, the smartly designed CR-POM nanoprobe will open new horizons for real-time noninvasive monitoring of biodistribution and simultaneous accurate quantification of GSH levels, especially in tumor and other GSH-related pathophysiological processes.

Improving the Theranostic Potential of Exendin 4 by Reducing the Renal Radioactivity through Brush Border Membrane Enzyme-Mediated Degradation.

As highly expressed in insulinomas, the glucagon-like peptide-1 receptor (GLP-1R) is believed to be an attractive target for diagnosis, localization, and treatment with radiolabeled exendin 4. However, the high and persistent radioactivity accumulation of exendin 4 in the kidneys limits accurate diagnosis and safe, as well as effective, radiotherapy in insulinomas. In this study, we intend to reduce the renal accumulation of radiolabeled exendin 4 through degradation mediated by brush border membrane enzymes. A new exendin 4 ligand NOTA-MVK-Cys40-Leu14-Exendin 4 containing Met-Val-Lys (MVK) linker between the peptide and 1,4,7-triazacyclononane-1,4,7-triacetic acid (NOTA) chelator was synthesized and labeled with 68Ga. The in vitro mouse serum stability and cell binding affinity of the tracer were evaluated. Initial in vitro cleavage of the linker was determined by incubation of a model compound Boc-MVK-Dde with brush border membrane vesicles (BBMVs) with and without the inhibitor of neutral endopeptidase (NEP). Further cleavage studies were performed with the full structure of NOTA-MVK-Cys40-Leu14-Exendin 4. Kidney and urine samples were collected in the in vivo metabolism study after intravenous injection of 68Ga-NOTA-MVK-Cys40-Leu14-Exendin 4. The microPET images were acquired in INS-1 tumor model at different time points; the radioactivity uptake of 68Ga-NOTA-MVK-Cys40-Leu14-Exendin 4 in tumor and kidneys were determined and compared with the control radiotracer without MVK linker. 68Ga-NOTA-MVK-Cys40-Leu14-Exendin 4 was stable in mouse serum. The MVK modification did not affect the affinity of NOTA-MVK-Cys40-Leu14-Exendin 4 toward GLP-1R. The in vitro cleavage study and in vivo metabolism study confirmed that the MVK sequence can be recognized by BBM enzymes and cleaved at the amide bond between Met and Val, thus releasing the small fragment containing Met. MicroPET images showed that the tumor uptake of 68Ga-NOTA-MVK-Cys40-Leu14-Exendin 4 was comparable to that of the control, while the kidney uptake was significantly reduced. As a result, more favorable tumor to kidney ratios were achieved. In this study, a novel exendin 4 analogue, NOTA-MVK-Cys40-Leu14-Exendin 4, was successfully synthesized and labeled with 68Ga. With the cleavable MVK sequence, this ligand could be cleaved by the enzymes on kidneys, and releasing the fragment of 68Ga-NOTA-Met-OH, which will rapidly excrete from urine. As the high and consistent renal radioactivity accumulation could be significantly reduced, NOTA-MVK-Cys40-Leu14-Exendin 4 shows great potential in the diagnosis and radiotherapy for insulinoma.

An Albumin Sandwich Enhances in Vivo Circulation and Stability of Metabolically Labile Peptides.

The effectiveness of numerous molecular drugs is hampered by their poor pharmacokinetics. Different from previous approaches with limited effectiveness, most recently, emerging high-affinity albumin binding moieties (ABMs) for in vivo hitchhiking of endogenous albumin opens up an avenue to chaperone small molecules for long-acting therapeutics. Although several FDA-approved fatty acids have shown prolonged residence and therapeutic effect, an easily synthesized, water-soluble, and high-efficiency ABM with versatile drug loading ability is urgently needed to improve the therapeutic efficacy of short-lived constructs. We herein identified an ideal bivalent Evans blue derivative, denoted as N(tEB)2, as a smart ABM-delivery platform to chaperone short-lived molecules, through both computational modeling screening and efficient synthetic schemes. The optimal N(tEB)2 could reversibly link two molecules of albumin through its two binding heads with a preferable spacer, resulting in significantly extended circulation half-life of a preloaded cargo and water-soluble. Notably, this in situ dimerization of albumin was able to sandwich peptide therapeutics to protect them from proteolysis. As an application, we conjugated N(tEB)2 with exendin-4 for long-acting glucose control in a diabetic mouse model, and it was superior to both previously tested NtEB-exendin-4 (Abextide) and the newly FDA-approved semaglutide, which has been arguably the best commercial weekly formula so far. Hence, this novel albumin binder has excellent clinical potential for next-generation biomimetic drug delivery systems.

A Logic-Gated Modular Nanovesicle Enables Programmable Drug Release for On-Demand Chemotherapy.

It remains a major challenge to achieve precise on-demand drug release. Here, we developed a modular nanomedicine integrated with logic-gated system enabling programmable drug release for on-demand chemotherapy. Methods: We employed two different logical AND gates consisting of four interrelated moieties to construct the nanovesicles, denoted as v-A-CED2, containing oxidation-responsive nanovesicles (v), radical generators (A), and Edman linker conjugated prodrugs (CED2). The first AND logic gate is connected in parallel by mild hyperthermia ( I ) and acidic pH ( II ), which executes NIR laser triggered prodrug-to-drug transformation through Edman degradation. Meanwhile, the mild hyperthermia effect triggers alkyl radical generation ( III ) which contributes to internal oxidation and degradation of nanovesicles ( IV ). The second AND logic gate is therefore formed by the combination of I-IV to achieve programmable drug release by a single stimulus input NIR laser. The biodistribution of the nanovesicles was monitored by positron emission tomography (PET), photoacoustic, and fluorescence imaging. Results: The developed modular nanovesicles exhibited high tumor accumulation and effective anticancer effects both in vitro and in vivo. Conclusions: This study provides a novel paradigm of logic-gated programmable drug release system by a modular nanovesicle, which may shed light on innovation of anticancer agents and strategies.

In Situ Dendritic Cell Vaccine for Effective Cancer Immunotherapy.

A cancer vaccine is an important form of immunotherapy. Given their effectiveness for antigen processing and presentation, dendritic cells (DCs) have been exploited in the development of a therapeutic vaccine. Herein, a versatile polymersomal nanoformulation that enables generation of tumor-associated antigens (TAAs) and simultaneously serves as adjuvant for an in situ DC vaccine is reported. The chimeric cross-linked polymersome (CCPS) is acquired from self-assembly of a triblock copolymer, polyethylene glycol-poly(methyl methyacrylate- co-2-amino ethyl methacrylate (thiol/amine))-poly 2-(dimethylamino)ethyl methacrylate (PEG-P(MMA- co-AEMA (SH/NH2)-PDMA). CCPS can encapsulate low-dose doxorubicin hydrochloride (DOX) to induce immunogenic cell death (ICD) and 2-(1-hexyloxyethyl)-2-devinyl pyropheophorbide-a (HPPH), a photosensitizer to facilitate photodynamic therapy (PDT) for reactive oxygen species (ROS) generation. This combination is able to enhance the population of TAAs and DC recruitment, eliciting an immune response cascade. In addition, CCPS with primary and tertiary amines act as adjuvant, both of which can stimulate DCs recruited to form an in situ DC vaccine after combination with TAAs for MC38 colorectal cancer treatment. In vivo results indicate that the all-in-one polymersomal nanoformulation (CCPS/HPPH/DOX) increases mature DCs in tumor-draining lymph nodes (tdLNs) and CD8+ T cells in tumor tissues to inhibit primary and distant MC38 tumor growth following a single intravenous injection with a low dose of DOX and HPPH.

Rational design of a super-contrast NIR-II fluorophore affords high-performance NIR-II molecular imaging guided microsurgery.

In vivo molecular imaging in the "transparent" near-infrared II (NIR-II) window has demonstrated impressive benefits in reaching millimeter penetration depths with high specificity and imaging quality. Previous NIR-II molecular imaging generally relied on high hepatic uptake fluorophores with an unclear mechanism and antibody-derived conjugates, suffering from inevitable nonspecific retention in the main organs/skin with a relatively low signal-to-background ratio. It is still challenging to synthesize a NIR-II fluorophore with both high quantum yield and minimal liver-retention feature. Herein, we identified the structural design and excretion mechanism of novel NIR-II fluorophores for NIR-II molecular imaging with an extremely clean background. With the optimized renally excreted fluorophore-peptide conjugates, superior NIR-II targeting imaging was accompanied by the improved signal-to-background ratio during tumor detection with reducing off-target tissue exposure. An unprecedented NIR-II imaging-guided microsurgery was achieved using such an imaging platform, which provides us with a great preclinical example to accelerate the potential clinical translation of NIR-II imaging.

Antidiabetic Effect of Abextide, a Long-Acting Exendin-4 Analogue in Cynomolgus Monkeys.

Abextide, synthesized by conjugating an albumin-binding moiety-truncated Evans blue-to glucagon-like peptide 1 receptor (GLP-1R) agonist exendin-4, shows extended drug release and enhanced hypoglycemic effect in diabetic mice. The aim of this study is to evaluate the pharmacodynamics of Abextide in nonhuman primates. Two batches of elderly cynomolgus monkeys with naturally occurring diabetes are used for this study. During the whole experiment period, no abnormalities such as swelling at the injection site, lethargy, or hypoglycemia are observed in all animals. The monkeys in the Abextide group lose appetite after drug administration and then recover over time. In the single dose treatment, at day 1 and day 3 after treatment, decreased plasma glucose level is observed in the Abextide-treated group but not in placebo or Albiglutide-treated group. For monkeys that receive two doses of drug, the blood glucose level in all subjects in Abextide group decreases rapidly upon drug administration and return to a plateau by day 3. A similar pattern of response is seen after the second dose administration. The delayed drug release and hypoglycemic effect of Abextide make it potentially useful as an antidiabetic drug for weekly subcutaneous administration.

Single Low-Dose Injection of Evans Blue Modified PSMA-617 Radioligand Therapy Eliminates Prostate-Specific Membrane Antigen Positive Tumors.

Prostate cancer is the most frequently diagnosed malignant tumor in men worldwide. Prostate-specific membrane antigen (PSMA) is a surface molecule specifically expressed by prostate tumors that has been shown to be a valid target for internal radionuclide therapy in both preclinical and clinical settings. The most common radiotherapeutic agent is the small molecule 177Lu-PSMA-617, which is under clinical evaluation in multiple countries. Nevertheless, its efficacy in causing tumor regression is still suboptimal, even when administered in several cycles per patient, perhaps due to poor pharmacokinetics (PK), which limits uptake by the tumor cells. We postulated that the addition of the Evans blue (EB) moiety to PSMA-617 would improve the PK by extending circulation half-life, which would increase tumor uptake and improve radiotherapeutic efficacy. PSMA-617 was modified by conjugation of a 2-thiol acetate group onto the primary amine and thereafter reacted with a maleimide functional group of an EB derivative, to give EB-PSMA-617. The PK and radiotherapeutic efficacy of 90Y- or 177Lu-EB-PSMA-617 was compared to the clinically used radiopharmaceutical 90Y- or 177Lu- PSMA-617 in PC3-PIP tumor-bearing mice. EB-PSMA-617 retained binding to serum albumin as well as a high internalization rate by tumor cells. Upon injection, metal-labeled EB-PSMA-617 demonstrated an extended blood half-life compared to PSMA-617 and, thereby, prolonged the time window for binding to PSMA. The improved PK of EB-PSMA-617 resulted in significantly higher accumulation in PSMA+ tumors and highly effective radiotherapeutic efficacy. Remarkably, a single dose of 1.85 MBq of 90Y- or 177Lu-EB-PSMA-617 was sufficient to eradicate established PMSA+ tumors in mice. No significant body weight loss was observed, suggesting little to no gross toxicity. The construct described here, EB-PSMA-617, may improve the radiotherapeutic efficacy for patients with PSMA-positive tumors by reducing both the amount of activity needed for therapy as well as the frequency of administration, as compared to PSMA-617.

Automated radiosynthesis of [18F]FBEM, a sulfhydryl site specific labeling agent for peptides and proteins.

In the process of developing [18F]FBEM coupled target peptide, we have instituted a robust automated synthesis of [18F]FBEM, a sulfhydryl (-SH) site specific agent for radiolabeling of peptides and proteins. The radiosynthesis generated 1.67-3.89 GBq (45.1-105.1 mCi, 7.5-18.8% non-decay corrected yield) of [18F]FBEM from 22.2 GBq (600 mCi) of starting [18F]fluoride with molar activity of 31.8 ±â€¯5.3 GBq/µmol (0.86 ±â€¯0.14 mCi/nmol) (n = 3) at the end of synthesis. Radiochemical purity was greater than 98%, and total synthesis time was ~90 min.

Repurposing Cyanine NIR-I Dyes Accelerates Clinical Translation of Near-Infrared-II (NIR-II) Bioimaging.

The significantly reduced tissue autofluorescence and scattering in the NIR-II region (1000-1700 nm) opens many exciting avenues for detailed investigation of biological processes in vivo. However, the existing NIR-II fluorescent agents, including many molecular dyes and inorganic nanomaterials, are primarily focused on complicated synthesis routes and unknown immunogenic responses with limited potential for clinical translation. Herein, the >1000 nm tail emission of conventional biocompatible NIR cyanine dyes with emission peaks at 700-900 nm is systematically investigated, and a type of bright dye for NIR-II imaging with high potential for accelerating clinical translation is identified. The asymmetry of the π domain in the S1 state of NIR cyanine dyes is proven to result in a twisted intramolecular charge-transfer process and NIR-II emission, establishing a general rule to guide future NIR-I/II fluorophore synthesis. The screened NIR dyes are identified to possess a bright emission tail in the NIR-II region along with high quantum yield, high molar-extinction coefficient, rapid fecal excretion, and functional groups amenable for bioconjugation. As a result, NIR cyanine dyes can be used for NIR-II imaging to afford superior contrast and real-time imaging of several biological models, facilitating the translation of NIR-II bioimaging to clinical theranostic applications.

Radioligand Therapy of Prostate Cancer with a Long-Lasting Prostate-Specific Membrane Antigen Targeting Agent 90Y-DOTA-EB-MCG.

Several radioligands targeting prostate-specific membrane antigen (PSMA) have been clinically introduced as a new class of radiotheranostics for the treatment of prostate cancer. Among them, ((( R)-1-carboxy-2-mcercaptoethyl)carbamoyl)-l-glutamic acid (MCG) has been successfully labeled with radioisotopes for prostate cancer imaging. The aim of this study is to conjugate MCG with an albumin binding moiety to further improve the in vivo pharmacokinetics. MCG was conjugated with an Evans blue (EB) derivative for albumin binding and a DOTA chelator. PSMA positive (PC3-PIP) and PSMA negative (PC3) cells were used for both in vitro and in vivo studies. Longitudinal PET imaging was performed at 1, 4, 24, and 48 h post-injection to evaluate the biodistribution and tumor uptake of 86Y-DOTA-EB-MCG. DOTA-EB-MCG was also labeled with 90Y for radionuclide therapy. Besides tumor growth measurement, tumor response to escalating therapeutic doses were also evaluated by immunohistochemistry and fluorescence microscopy. Based on quantification from 86Y-DOTA-EB-MCG PET images, the tracer uptake in PC3-PIP tumors increased from 22.33 ± 2.39%ID/g at 1 h post-injection (p.i.), to the peak of 40.40 ± 4.79%ID/g at 24 h p.i. Administration of 7.4 MBq of 90Y-DOTA-EB-MCG resulted in significant regression of tumor growth in PSMA positive xenografts. No apparent toxicity or body weight loss was observed in all treated mice. Modification of MCG with an Evans blue derivative resulted in a highly efficient prostate cancer targeting agent (EB-MCG), which showed great potential in prostate cancer treatment after being labeled with therapeutic radioisotopes.

Chronic neuropathic pain reduces opioid receptor availability with associated anhedonia in rat.

The opioid system plays a critical role in both the experience and management of pain. Although acute activation of the opioid system can lead to pain relief, the effects of chronic pain on the opioid system remain opaque. Cross-sectional positron emission tomography (PET) studies show reduced availability of brain opioid receptors in patients with chronic pain but are unable to (1) determine whether these changes are due to the chronic pain itself or due to preexisting or medication-induced differences in the endogenous opioid system, and (2) identify the neurobiological substrate of reduced opioid receptor availability. We investigated these possibilities using a well-controlled longitudinal study design in rat. Using [F]-FDPN-PET in either sham rats (n = 17) or spared nerve injury rats (n = 17), we confirmed reduced opioid receptor availability in the insula, caudate-putamen, and motor cortex of nerve injured rats 3 months after surgery, indicating that painful neuropathy altered the endogenous opioid system. Immunohistochemistry showed reduced expression of the mu-opioid receptor, MOR1, in the caudate-putamen and insula. Neither the opioid peptide enkephalin nor the neuronal marker NeuN differed between groups. In nerve-injured animals, sucrose preference, a measure of anhedonia/depression-like behavior, positively correlated with PET opioid receptor availability and MOR1-immunoreactivity in the caudate-putamen. These findings provide new evidence that the altered supraspinal opioid receptor availability observed in human patients with chronic pain may be a direct result of chronic pain. Moreover, reduced opioid receptor availability seems to reflect decreased receptor expression, which may contribute to pain-induced depression.

A paclitaxel prodrug with bifunctional folate and albumin binding moieties for both passive and active targeted cancer therapy.

Folate receptor (FR) has proven to be a valuable target for chemotherapy using folic acid (FA) conjugates. However, FA-conjugated chemotherapeutics still have low therapeutic efficacy accompanied with side effects, resulting from complications such as short circulation half-life, limited tumor delivery, as well as high kidney accumulation. Herein, we present a novel FA-conjugated paclitaxel (PTX) prodrug which was additionally conjugated with an Evans blue (EB) derivative for albumin binding. The resulting bifunctional prodrug prolonged blood circulation, enhanced tumor accumulation, and consequently improved tumor therapeutic efficacy. Methods: Fmoc-Cys(Trt)-OH was coupled onto PTX at the 7'-OH position for further synthesis of ester prodrug FA-PTX-EB. The targeting ability was investigated using confocal microscopy and flow cytometry. The pharmacokinetics of this bifunctional compound was also studied. Meanwhile, cell viability was evaluated in normal cells and three cancer cell lines by MTT assay. In vivo therapeutic effect was tested on FR-α overexpressing MDA-MB-231 tumor model. Results: Compared with free PTX, the FA-PTX, PTX-EB and FA-PTX-EB prodrugs increased circulation half-life in mice from 2.19 to 3.82, 4.41, and 7.51 h, respectively. Pharmacokinetics studies showed that the FA-PTX-EB delivered more PTX to tumors than FA-PTX and free PTX. In vitro and in vivo studies demonstrated that FA-EB-conjugated PTX induced potent antitumor activity. Conclusion: FA-PTX-EB showed prolonged blood circulation, enhanced drug accumulation in tumors, higher therapeutic index, and lower side effects than either free PTX or monofunctional FA-PTX and EB-PTX. The results support the potential of using EB for the development of long-acting therapeutics.

Evans Blue Attachment Enhances Somatostatin Receptor Subtype-2 Imaging and Radiotherapy.

Purpose: Radionuclide therapy directed against tumors that express somatostatin receptors (SSTRs) has proven effective for the treatment of advanced, low- to intermediate-grade neuroendocrine tumors in the clinic. In clinical usage, somatostatin peptide-based analogs, labeled with therapeutic radionuclides, provide an overall response rate of about 30%, despite the high cumulative activity injected per patient. We set out to improve the effectiveness of somatostatin radiotherapy by preparing a chemical analog that would clear more slowly through the urinary tract and, concomitantly, have increased blood circulation half-life and higher targeted accumulation in the tumors. Experimental Design: We conjugated a common, clinically-used SST peptide derivative, DOTA-octreotate, to an Evans blue analog (EB), which reversibly binds to circulating serum albumin. The resulting molecule was used to chelate 86Y and 90Y, a diagnostic and a therapeutic radionuclide, respectively. The imaging capabilities and the radiotherapeutic efficacy of the resulting radioligand was evaluated in HCT116/SSTR2, HCT116, and AR42J cell lines that express differing levels of SST2 receptors. Results: The synthesized radiopharmaceutical retained affinity and specificity to SSTR2. The new molecule also retained the high internalization rate of DOTA-octreotate, and therefore, showed significantly higher accumulation in SSTR2-positive tumors. Labeling of our novel EB-octreotate derivative with the therapeutic, pure beta emitter, 90Y, resulted in improved tumor response and survival rates of mice bearing SSTR2 xenografts and had long term efficacy when compared to DOTA-octreotate itself. Conclusions: The coupling of a targeted peptide, a therapeutic radionuclide, and the EB­based albumin binding provides for effective treatment of SSTR2-containing tumors.