First-in-human imaging using [11C]MDTC: a radiotracer targeting the cannabinoid receptor type 2.

PURPOSE: We report findings from the first-in-human study of [11C]MDTC, a radiotracer developed to image the cannabinoid receptor type 2 (CB2R) with positron emission tomography (PET). METHODS: Ten healthy adults were imaged according to a 90-min dynamic PET protocol after bolus intravenous injection of [11C]MDTC. Five participants also completed a second [11C]MDTC PET scan to assess test-retest reproducibility of receptor-binding outcomes. The kinetic behavior of [11C]MDTC in human brain was evaluated using tissue compartmental modeling. Four additional healthy adults completed whole-body [11C]MDTC PET/CT to calculate organ doses and the whole-body effective dose. RESULTS: [11C]MDTC brain PET and [11C]MDTC whole-body PET/CT was well-tolerated. A murine study found evidence of brain-penetrant radiometabolites. The model of choice for fitting the time activity curves (TACs) across brain regions of interest was a three-tissue compartment model that includes a separate input function and compartment for the brain-penetrant metabolites. Regional distribution volume (VT) values were low, indicating low CB2R expression in the brain. Test-retest reliability of VT demonstrated a mean absolute variability of 9.91%. The measured effective dose of [11C]MDTC was 5.29 µSv/MBq. CONCLUSION: These data demonstrate the safety and pharmacokinetic behavior of [11C]MDTC with PET in healthy human brain. Future studies identifying radiometabolites of [11C]MDTC are recommended before applying [11C]MDTC PET to assess the high expression of the CB2R by activated microglia in human brain.

[18F]FNDP PET neuroimaging test-retest repeatability and whole-body dosimetry in humans.

PURPOSE: Soluble epoxide hydrolase (sEH) is an enzyme that shapes immune signaling through its role in maintaining the homeostasis of polyunsaturated fatty acids and their related byproducts. [18F]FNDP is a radiotracer developed for use with positron emission tomography (PET) to image sEH, which has been applied to imaging sEH in the brains of healthy individuals. Here, we report the test-retest repeatability of [18F]FNDP brain PET binding and [18F]FNDP whole-body dosimetry in healthy individuals. METHODS: Seven healthy adults (4 men, 3 women, ages 40.1 ± 4.6 years) completed [18F]FNDP brain PET on two occasions within a period of 14 days in a test-retest study design. [18F]FNDP regional total distribution volume (VT) values were derived from modeling time-activity data with a metabolite-corrected arterial input function. Test-retest variability, mean absolute deviation, and intraclass correlation coefficient (ICC) were investigated. Six other healthy adults (3 men, 3 women, ages 46.0 ± 7.0 years) underwent [18F]FNDP PET/CT for whole-body dosimetry, which was acquired over 4.5 h, starting immediately after radiotracer administration. Organ-absorbed doses and the effective dose were then estimated. RESULTS: The mean test-retest difference in regional VT (ΔVT) was 0.82 ± 5.17%. The mean absolute difference in regional VT was 4.01 ± 3.33%. The ICC across different brain regions ranged from 0.92 to 0.99. The organs with the greatest radiation-absorbed doses included the gallbladder (0.081 ± 0.024 mSv/MBq), followed by liver (0.077 ± 0.018 mSv/MBq) and kidneys (0.063 ± 0.006 mSv/MBq). The effective dose was 0.020 ± 0.003 mSv/MBq. CONCLUSION: These data support a favorable test-retest repeatability of [18F]FNDP brain PET regional VT. The radiation dose to humans from each [18F]FNDP PET scan is similar to that of other 18F-based PET radiotracers.

PET imaging of microglia by targeting macrophage colony-stimulating factor 1 receptor (CSF1R).

While neuroinflammation is an evolving concept and the cells involved and their functions are being defined, microglia are understood to be a key cellular mediator of brain injury and repair. The ability to measure microglial activity specifically and noninvasively would be a boon to the study of neuroinflammation, which is involved in a wide variety of neuropsychiatric disorders including traumatic brain injury, demyelinating disease, Alzheimer's disease (AD), and Parkinson's disease, among others. We have developed [11C]CPPC [5-cyano-N-(4-(4-[11C]methylpiperazin-1-yl)-2-(piperidin-1-yl)phenyl)furan-2-carboxamide], a positron-emitting, high-affinity ligand that is specific for the macrophage colony-stimulating factor 1 receptor (CSF1R), the expression of which is essentially restricted to microglia within brain. [11C]CPPC demonstrates high and specific brain uptake in a murine and nonhuman primate lipopolysaccharide model of neuroinflammation. It also shows specific and elevated uptake in a murine model of AD, experimental allergic encephalomyelitis murine model of demyelination and in postmortem brain tissue of patients with AD. Radiation dosimetry in mice indicated [11C]CPPC to be safe for future human studies. [11C]CPPC can be synthesized in sufficient radiochemical yield, purity, and specific radioactivity and possesses binding specificity in relevant models that indicate potential for human PET imaging of CSF1R and the microglial component of neuroinflammation.

First-in-human neuroimaging of soluble epoxide hydrolase using [18F]FNDP PET.

PURPOSE: Soluble epoxide hydrolase (sEH) is an enzyme with putative effect on neuroinflammation through its influence on the homeostasis of polyunsaturated fatty acids and related byproducts. sEH is an enzyme that metabolizes anti-inflammatory epoxy fatty acids to the corresponding, relatively inert 1,2-diols. A high availability or activity of sEH promotes vasoconstriction and inflammation in local tissues that may be linked to neuropsychiatric diseases. We developed [18F]FNDP to study sEH in vivo with positron emission tomography (PET). METHODS: Brain PET using bolus injection of [18F]FNDP followed by emission imaging lasting 90 or 180 min was completed in healthy adults (5 males, 2 females, ages 40-53 years). The kinetic behavior of [18F]FNDP was evaluated using a radiometabolite-corrected arterial plasma input function with compartmental or graphical modeling approaches. RESULTS: [18F]FNDP PET was without adverse effects. Akaike information criterion favored the two-tissue compartment model (2TCM) in all ten regions of interest. Regional total distribution volume (VT) values from each compartmental model and Logan analysis were generally well identified except for corpus callosum VT using the 2TCM. Logan analysis was assessed as the choice model due to stability of regional VT values from 90-min data and due to high correlation of Logan-derived regional VT values with those from the 2TCM. [18F]FNDP binding was higher in human cerebellar cortex and thalamus relative to supratentorial cortical regions, which aligns with reported expression patterns of the epoxide hydrolase 2 gene in human brain. CONCLUSION: These data support further use of [18F]FNDP PET to study sEH in human brain.

Dual-Modality PET-SPECT Image-Guided Pretargeting Delivery in HER2(+) Breast Cancer Models.

Pretargeted drug delivery has been explored for decades as a promising approach in cancer therapy. An image-guided pretargeting strategy significantly enhances the intrinsic advantages of this approach since imaging the pretargeting step can be used for diagnostic purposes, while imaging of the drug delivery step can be utilized to evaluate drug distribution and assess therapeutic response. A trastuzumab (Tz)-based HER2 pretargeting component (Tz-TCO-[89Zr-DFO]) was developed by conjugating with trans-cyclooctene (TCO) bioorthogonal click chemistry functional groups and deferoxamine (DFO) to enable radiolabeling with a 89Zr PET tracer. The drug delivery component (HSA-DM1-Tt-[99mTc-HyNic]) was developed by conjugating human serum albumin (HSA) with mertansine (DM1), tetrazine (Tt) functional groups, and a HyNic chelator and radiolabeling with 99mTc. For ex vivo biodistribution studies, pretargeting and delivery components (without drug) were administered subsequently to mice bearing human HER2(+) breast cancer xenografts, and a high tumor uptake of Tz-TCO-[89Zr-DFO] (26.4% ID/g) and HSA-Tt-[99mTc-HyNic] (4.6% ID/g) was detected at 24 h postinjection. In vivo treatment studies were performed in the same HER2(+) breast cancer model using PET-SPECT image guidance. The increased tumor uptake of the pretargeting and drug delivery components was detected by PET-CT and SPECT-CT, respectively. The study showed a significant 92% reduction of the relative tumor volume in treated mice (RTV = 0.08 in 26 days), compared to the untreated control mice (RTV = 1.78 in 11 days) and to mice treated with only HSA-DM1-Tt-[99mTc-HyNic] (RTV = 1.88 in 16 days). Multimodality PET-SPECT image-guided and pretargeted drug delivery can be utilized to maximize efficacy, predict therapeutic response, and minimize systemic toxicity.

Development of [18F]FPy-WL12 as a PD-L1 Specific PET Imaging Peptide.

Expression of programmed cell death ligand 1 (PD-L1) within tumors is an important biomarker for guiding immune checkpoint therapies; however, immunohistochemistry-based methods of detection fail to provide a comprehensive picture of PD-L1 levels in an entire patient. To facilitate quantification of PD-L1 in the whole body, we developed a peptide-based, high-affinity PD-L1 imaging agent labeled with [18F]fluoride for positron emission tomography (PET) imaging. The parent peptide, WL12, and the nonradioactive analog of the radiotracer, 19FPy-WL12, inhibit PD-1/PD-L1 interaction at low nanomolar concentrations (half maximal inhibitory concentration [IC50], 26-32 nM). The radiotracer, [18F]FPy-WL12, was prepared by conjugating 2,3,5,6-tetrafluorophenyl 6-[18F]fluoronicotinate ([18F]FPy-TFP) to WL12 and assessed for specificity in vitro in 6 cancer cell lines with varying PD-L1 expression. The uptake of the radiotracer reflected the PD-L1 expression assessed by flow cytometry. Next, we performed the in vivo evaluation of [18F]FPy-WL12 in mice bearing cancer xenografts by PET imaging, ex vivo biodistribution, and blocking studies. In vivo data demonstrated a PD-L1-specific uptake of [18F]FPy-WL12 in tumors that is reduced in mice receiving a blocking dose. The majority of [18F]FPy-WL12 radioactivity was localized in the tumors, liver, and kidneys indicating the need for optimization of the labeling strategy to improve the in vivo pharmacokinetics of the radiotracer.

PET imaging of distinct brain uptake of a nanobody and similarly-sized PAMAM dendrimers after intra-arterial administration.

INTRODUCTION: We have recently shown that intracerebral delivery of an anti-VEGF monoclonal antibody bevacizumab using an intra-arterial (IA) infusion is more effective than intravenous administration. While antibodies are quickly emerging as therapeutics, their disadvantages such as large size, production logistics and immunogenicity motivate search for alternatives. Thus we have studied brain uptake of nanobodies and polyamidoamine (PAMAM) dendrimers. METHODS: Nanobodies were conjugated with deferoxamine (DFO) to generate NB(DFO)2. Generation-4 PAMAM dendrimers were conjugated with DFO, and subsequently primary amines were capped with butane-1,2-diol functionalities to generate G4(DFO)3(Bdiol)110. Resulting conjugates were radiolabeled with zirconium-89. Brain uptake of 89ZrNB(DFO)2 and 89ZrG4(DFO)3(Bdiol)110 upon carotid artery vs tail vein infusions with intact BBB or osmotic blood-brain barrier opening (OBBBO) with mannitol in mice was monitored by dynamic positron emission tomography (PET) over 30 min to assess brain uptake and clearance, followed by whole-body PET-CT (computed tomography) imaging at 1 h and 24 h post-infusion (pi). Imaging results were subsequently validated by ex-vivo biodistribution. RESULTS: Intravenous administration of 89ZrNB(DFO)2 and 89ZrG4(DFO)3(Bdiol)110 resulted in their negligible brain accumulation regardless of BBB status and timing of OBBBO. Intra-arterial (IA) administration of 89ZrNB(DFO)2 dramatically increased its brain uptake, which was further potentiated with prior OBBBO. Half of the initial brain uptake was retained after 24 h. In contrast, IA infusion of 89ZrG4(DFO)3(Bdiol)110 resulted in poor initial accumulation in the brain, with complete clearance within 1 h of administration. Ex-vivo biodistribution results reflected those on PET-CT. CONCLUSIONS: IA delivery of nanobodies might be an attractive therapeutic platform for CNS disorders where prolonged intracranial retention is necessary.

Evaluation of PSMA-Targeted PAMAM Dendrimer Nanoparticles in a Murine Model of Prostate Cancer.

The prostate-specific membrane antigen (PSMA) is a validated target for detection and management of prostate cancer (PC). It has also been utilized for targeted drug delivery through antibody-drug conjugates and polymeric micelles. Polyamidoamine (PAMAM) dendrimers are emerging as a versatile platform in a number of biomedical applications due to their unique physicochemical properties, including small size, large number of reactive terminal groups, bulky interior void volume, and biocompatibility. Here, we report the synthesis of generation 4 PSMA-targeted PAMAM dendrimers [G4(MP-KEU)] and evaluation of their targeting properties in vitro and in vivo using an experimental model of PC. A facile, one-pot synthesis gave nearly neutral nanoparticles with a narrow size distribution of 5 nm in diameter and a molecular weight of 27.3 kDa. They exhibited in vitro target specificity with a dissociation constant ( Kd) of 0.32 ± 0.23 µm and preferential accumulation in PSMA+ PC3 PIP tumors versus isogenic PSMA- PC3 flu tumors. Positron emission tomography-computed tomography imaging and ex vivo biodistribution studies of dendrimers radiolabeled with 64Cu, [64Cu]G4(MP-KEU), demonstrated high accumulation in PSMA+ PC3 PIP tumors at 24 h post-injection (45.83 ± 20.09% injected dose per gram of tissue, %ID/g), demonstrating a PSMA+ PC3 PIP/PSMA- PC3 flu ratio of 7.65 ± 3.35. Specific accumulation of G4(MP-KEU) and [64Cu]G4(MP-KEU) in PSMA+ PC3 PIP tumors was inhibited by the known small-molecule PSMA inhibitor, ZJ-43. On the contrary, G4(Ctrl), control dendrimers without PSMA-targeting moieties, showed comparable low accumulation of ∼1%ID/g in tumors irrespective of PSMA expression, further confirming PSMA+ tumor-specific uptake of G4(MP-KEU). These results suggest that G4(MP-KEU) may represent a suitable scaffold by which to target PSMA-expressing tissues with imaging and therapeutic agents.

The distribution of the alpha7 nicotinic acetylcholine receptor in healthy aging: An in vivo positron emission tomography study with [18F]ASEM.

Altered function of the alpha7 nicotinic acetylcholine receptor (α7-nAChR) is implicated in several neuropsychiatric diseases. Nevertheless, studies of the human cerebral α7-nAChR even in healthy aging are limited in number and to postmortem tissue. METHODS: The distribution of the cerebral α7-nAChR was estimated in nine brain regions in 25 healthy volunteers (ages 21-86 years; median 57 years, interquartile range 52 years) using [18F]ASEM with positron emission tomography (PET) imaging. Regional total distribution volume (VT) measurements were calculated using the Logan method from each subject's 90 min dynamic PET data and their metabolite-corrected plasma input function. Spearman's rank or Pearson's correlation analysis was used depending on the normality of the data. Correlation between age and regional 1) volume relative to intracranial volume (volume ratio) and 2) [18F]ASEM VT was tested. Correlation between regional volume ratio and [18F]ASEM VT was also evaluated. Finally, the relationship between [18F]ASEM VT and neuropsychological measures was investigated in a subpopulation of 15 elderly healthy participants (those 50 years of age and older). Bonferroni correction for multiple comparisons was applied to statistical analyses. RESULTS: A negative correlation between tissue volume ratio and age was observed in six of the nine brain regions including striatum and five cortical (temporal, occipital, cingulate, frontal, or parietal) regions. A positive correlation between [18F]ASEM VT and age was observed in all nine brain regions of interest (ROIs). There was no correlation between [18F]ASEM VT and volume ratio in any ROI after controlling for age. Regional [18F]ASEM VT and neuropsychological performance on each of eight representative subtests were not correlated among the well-performing subpopulation of elderly healthy participants. CONCLUSIONS: Our results suggest an increase in cerebral α7-nAChR distribution over the course of healthy aging that should be tested in future longitudinal studies. The preservation of the α7-nAChR in the aging human brain supports the development of therapeutic agents that target this receptor for use in the elderly. Further study of the relationship between α7-nAChR availability and cognitive impairment over aging is needed.

Imaging glial activation in patients with post-treatment Lyme disease symptoms: a pilot study using [11C]DPA-713 PET.

The pathophysiology of post-treatment Lyme disease syndrome (PTLDS) may be linked to overactive immunity including aberrant activity of the brain's resident immune cells, microglia. Here we used [11C]DPA-713 and positron emission tomography to quantify the 18 kDa translocator protein, a marker of activated microglia or reactive astrocytes, in the brains of patients with post-treatment Lyme disease symptoms of any duration compared to healthy controls. Genotyping for the TSPO rs6971 polymorphism was completed, and individuals with the rare, low affinity binding genotype were excluded. Data from eight brain regions demonstrated higher [11C]DPA-713 binding in 12 patients relative to 19 controls. [11C]DPA-713 PET is a promising tool to study cerebral glial activation in PTLDS and its link to cognitive symptoms.

Noninvasive Imaging of Immune Checkpoint Ligand PD-L1 in Tumors and Metastases for Guiding Immunotherapy.

Immunotherapy holds great promise in cancer treatment. The challenges in advancing immunotherapies lie in patient stratification and monitoring therapy. Noninvasive detection of immune checkpoint ligand PD-L1 can serve as an important biomarker for guidance and monitoring of immunotherapy. Here in, we provide an overview of our efforts to develop clinically translatable PD-L1-specific imaging agents for quantitative and real-time assessment of PD-L1 expression in tumor microenvironment.

Rapid PD-L1 detection in tumors with PET using a highly specific peptide.

Molecular imaging can report on the status of the tumor immune microenvironment and guide immunotherapeutic strategies to enhance the efficacy of immune modulation therapies. Imaging agents that can rapidly report on targets of immunomodulatory therapies are few. The programmed death ligand 1 (PD-L1) is an immune checkpoint protein over-expressed in several cancers and contributes to tumor immune suppression. Tumor PD-L1 expression is indicative of tumor response to PD-1 and PD-L1 targeted therapies. Herein, we report a highly specific peptide-based positron emission tomography (PET) imaging agent for PD-L1. We assessed the binding modes of the peptide WL12 to PD-L1 by docking studies, developed a copper-64 labeled WL12 ([64Cu]WL12), and performed its evaluation in vitro, and in vivo by PET imaging, biodistribution and blocking studies. Our results show that [64Cu]WL12 can be used to detect tumor PD-L1 expression specifically and soon after injection of the radiotracer, to fit within the standard clinical workflow of imaging within 60 min of administration.

Maternal Inflammation Results in Altered Tryptophan Metabolism in Rabbit Placenta and Fetal Brain.

Maternal inflammation has been linked to neurodevelopmental and neuropsychiatric disorders such as cerebral palsy, schizophrenia, and autism. We had previously shown that intrauterine inflammation resulted in a decrease in serotonin, one of the tryptophan metabolites, and a decrease in serotonin fibers in the sensory cortex of newborns in a rabbit model of cerebral palsy. In this study, we hypothesized that maternal inflammation results in alterations in tryptophan pathway enzymes and metabolites in the placenta and fetal brain. We found that intrauterine endotoxin administration at gestational day 28 (G28) resulted in a significant upregulation of indoleamine 2,3-dioxygenase (IDO) in both the placenta and fetal brain at G29 (24 h after treatment). This endotoxin-mediated IDO induction was also associated with intense microglial activation, an increase in interferon gamma expression, and increases in kynurenine and the kynurenine pathway metabolites kynurenine acid and quinolinic acid, as well as a significant decrease in 5-hydroxyindole acetic acid (a precursor of serotonin) levels in the periventricular region of the fetal brain. These results indicate that maternal inflammation shunts tryptophan metabolism away from the serotonin to the kynurenine pathway, which may lead to excitotoxic injury along with impaired development of serotonin-mediated thalamocortical fibers in the newborn brain. These findings provide new targets for prevention and treatment of maternal inflammation-induced fetal and neonatal brain injury leading to neurodevelopmental disorders such as cerebral palsy and autism.

In vivo Evaluation of an Engineered Cyclotide as Specific CXCR4 Imaging Reagent.

The CXCR4 chemokine receptor plays a key regulatory role in many biological functions, including embryonic development and controlling leukocyte functions during inflammation and immunity. CXCR4 has been also associated with multiple types of cancers where its overexpression/activation promotes metastasis, angiogenesis, and tumor growth and/or survival. Furthermore, CXCR4 is involved in HIV replication, as it is a co-receptor for viral entry into host cells. Altogether, these features make CXCR4 a very attractive target for the development of imaging and therapeutic agents. Here, the in vivo evaluation of the MCoTI-based cyclotide, MCo-CVX-5c, for the development of imaging agents that target CXCR4 is reported. Cyclotide MCo-CVX-5c is a potent CXCR4 antagonist with a remarkable in vivo resistance to biological degradation in serum. A [64 Cu]-DOTA-labeled version of this cyclotide demonstrated high and significant uptake in U87-stb-CXCR4 tumors compared to the control U87 tumors. Furthermore, protracted imaging studies demonstrated radiotracer retention in the U87-stb-CXCR4 tumor at 24 h post injection. Uptake in U87-stb-CXCR4 tumors could be blocked by unlabeled MCo-CVX-5c, showing high in vivo specificity. These results demonstrate the in vivo specificity and retention of a bioactive molecularly targeted cyclotide and highlight the potential of bioactive cyclotides for the development of new imaging agents that target CXCR4.

Salicylic Acid Conjugated Dendrimers Are a Tunable, High Performance CEST MRI NanoPlatform.

Chemical exchange saturation transfer (CEST) is a novel MRI contrast mechanism that is well suited for imaging, however, existing small molecule CEST agents suffer from low sensitivity. We have developed salicylic acid conjugated dendrimers as a versatile, high performance nanoplatform. In particular, we have prepared nanocarriers based on generation 5-poly(amidoamine) (PAMAM) dendrimers with salicylic acid covalently attached to their surface. The resulting conjugates produce strong CEST contrast 9.4 ppm from water with the proton exchange tunable from ∼1000 s(-1) to ∼4500 s(-1) making these dendrimers well suited for sensitive detection. Furthermore, we demonstrate that these conjugates can be used for monitoring convection enhanced delivery into U87 glioblastoma bearing mice, with the contrast produced by these nanoparticles persisting for over 1.5 h and distributed over ∼50% of the tumors. Our results demonstrate that SA modified dendrimers present a promising new nanoplatform for medical applications.

PD-L1 Detection in Tumors Using [(64)Cu]Atezolizumab with PET.

The programmed death protein 1 (PD-1) and programmed death-ligand 1 (PD-L1) pair is a major immune checkpoint pathway exploited by cancer cells to develop and maintain immune tolerance. With recent approvals of anti-PD-1 and anti-PD-L1 therapeutic antibodies, there is an urgent need for noninvasive detection methods to quantify dynamic PD-L1 expression in tumors and to evaluate the tumor response to immune modulation therapies. To address this need, we assessed [(64)Cu]atezolizumab for the detection of PD-L1 expression in tumors. Atezolizumab (MPDL3208A) is a humanized, human and mouse cross-reactive, therapeutic PD-L1 antibody that is being investigated in several cancers. Atezolizumab was conjugated with DOTAGA and radiolabeled with copper-64. The resulting [(64)Cu]atezolizumab was assessed for in vitro and in vivo specificity in multiple cell lines and tumors of variable PD-L1 expression. We performed PET-CT imaging, biodistribution, and blocking studies in NSG mice bearing tumors with constitutive PD-L1 expression (CHO-hPD-L1) and in controls (CHO). Specificity of [(64)Cu]atezolizumab was further confirmed in orthotopic tumor models of human breast cancer (MDAMB231 and SUM149) and in a syngeneic mouse mammary carcinoma model (4T1). We observed specific binding of [(64)Cu]atezolizumab to tumor cells in vitro, correlating with PD-L1 expression levels. Specific accumulation of [(64)Cu]atezolizumab was also observed in tumors with high PD-L1 expression (CHO-hPD-L1 and MDAMB231) compared to tumors with low PD-L1 expression (CHO, SUM149). Collectively, these studies demonstrate the feasibility of using [(64)Cu]atezolizumab for the detection of PD-L1 expression in different tumor types.

Structural characterization and in vivo evaluation of ß-Hairpin peptidomimetics as specific CXCR4 imaging agents.

The CXCR4 chemokine receptor is integral to several biological functions and plays a pivotal role in the pathophysiology of many diseases. As such, CXCR4 is an enticing target for the development of imaging and therapeutic agents. Here we report the evaluation of the POL3026 peptidomimetic template for the development of imaging agents that target CXCR4. Structural and conformational analyses of POL3026 and two of its conjugates, DOTA (POL-D) and PEG12-DOTA (POL-PD), by circular dichroism, two-dimensional NMR spectroscopy and molecular dynamics calculations are reported. In silico observations were experimentally verified with in vitro affinity assays and rationalized using crystal structure-based molecular modeling studies. [(111)In]-labeled DOTA conjugates were assessed in vivo for target specificity in CXCR4 expressing subcutaneous U87 tumors (U87-stb-CXCR4) through single photon emission computed tomography (SPECT/CT) imaging and biodistribution studies. In silico and in vitro studies show that POL3026 and its conjugates demonstrate similar interactions with different micelles that mimic cellular membrane and that the ε-NH2 of lysine(7) is critical to maintain high affinity to CXCR4. Modification of this group with DOTA or PEG12-DOTA led to the decrease of IC50 value from 0.087 nM for POL3026 to 0.47 nM and 1.42 nM for POL-D and POL-PD, respectively. In spite of the decreased affinity toward CXCR4, [(111)In]POL-D and [(111)In]POL-PD demonstrated high and significant uptake in U87-stb-CXCR4 tumors compared to the control U87 tumors at 90 min and 24 h post injection. Uptake in U87-stb-CXCR4 tumors could be blocked by unlabeled POL3026, indicating specificity of the agents in vivo. These results suggest POL3026 as a promising template to develop new imaging agents that target CXCR4.

Fetal uptake of intra-amniotically delivered dendrimers in a mouse model of intrauterine inflammation and preterm birth.

Intrauterine inflammation is associated with preterm birth and can lead to fetal neuroinflammation and neurobehavioral disorders in newborns. Dendrimers can intrinsically target and deliver drugs for the treatment of neuroinflammation. We explore whether hydroxyl polyamidoamine (PAMAM) dendrimer (G4-OH)-based nanomedicines can be delivered to the fetus by intra-amniotic administration, in a mouse model of intrauterine inflammation. The time-dependent accumulation of G4-OH-fluorophore conjugate was quantified by fluorescence. These studies suggest that, after intra-amniotic administration, there is significant accumulation of dendrimer in the fetus gut and brain. In addition, there is some fetal-maternal transport of the dendrimer. Confocal microscopy confirmed the presence of G4-OH in the fetal brain, with a large accumulation in the brain blood vessels and the brain parenchyma, and some microglial uptake. We believe that intra-amniotic administration of G4-OH-drug nanomedicines may enable the treatment of diseases related to intrauterine inflammation and fetal neuroinflammation. FROM THE CLINICAL EDITOR: Using a mouse model of intrauterin inflammation leading to neuroinflammation in the fetus, these investigators demonstrate that intra-amniotic delivery of hydroxyl polyamidoamine (PAMAM) dendrimer (G4-OH)-based nanomedicines may provide an effective method in preventing this complication.

PET-MR Guided, Pre-targeted delivery to HER2(+) Breast Cancer Model.

Purpose: HER2(+) metastatic breast cancer (mBC) is one of the most aggressive and lethal cancer types among females. While initially effective, targeted therapeutic approaches with trastuzumab and pertuzumab antibodies and antibody-drug conjugates (ADC) lack long-term efficacy against HER2(+) mBC and can cause severe systemic toxicity due to off-target effects. Therefore, the development of novel targeted delivery platforms that minimize toxicity and increase therapeutic efficacy is critical to the treatment of HER2(+) breast cancer (BC). A pretargeting delivery platform can minimize the non-specific accumulation and off-target toxicity caused by traditional one-step delivery method by separating the single delivery step into a pre-targeting step with high-affinity biomarker binding ligand followed by the subsequent delivery step of therapeutic component with fast clearance. Each delivery component is functionalized with bioorthogonal reactive groups that quickly react in situ, forming cross-linked clusters on the cell surface, which facilitates rapid internalization and intracellular delivery of therapeutics. Procedures: We have successfully developed a click chemistry-based pretargeting platform for HER2(+) BC enabling PET-MR image guidance for reduced radiation dose, high sensitivity, and good soft tissue contrast. Radiolabeled trastuzumab and superparamagnetic iron-oxide carriers (uSPIO) were selected as pretargeting and delivery components, respectively. HER2(+) BT-474 cell line and corresponding xenografts were used for in vitro and in vivo studies. Results: An enhanced tumor accumulation as well as tumor-to-organ accumulation ratio was observed in pretargeted mice up to 24 h post uSPIO injection. A 40% local T1 decrease in the pretargeted mice tumor was observed within 4 h, and an overall 15% T1 drop was retained for 24 h post uSPIO injection. Conclusions: Prolonged tumor retention and increased tumor-to-organ accumulation ratio provided a solid foundation for pretargeted image-guided delivery approach for in vivo applications.

Beyond synthetic aperture focusing: deconvolution-based elevation resolution enhancement using simulated point spread function for linear array-based three-dimensional photoacoustic imaging.

This paper introduces a deconvolution-based method to enhance the elevation resolution of a linear array-based three-dimensional (3D) photoacoustic (PA) imaging system. PA imaging combines the high contrast of optical imaging with the deep, multi-centimeter spatial resolution of ultrasound (US) imaging, providing structural and functional information about biological tissues. Linear array-based 3D PA imaging is easily accessible and applicable for ex vivo studies, small animal research, and clinical applications in humans. However, its elevation resolution is limited by the acoustic lens geometry, which establishes a single elevation focus. Previous work used synthetic aperture focusing (SAF) to enhance elevation resolution, but the resolution achievable by SAF is constrained by the size of the elevation focus. Here, we introduce the application of Richardson-Lucy deconvolution, grounded in simulated point-spread-functions, to surpass the elevation resolution attainable with SAF alone. We validated this approach using both simulation and experimental data, demonstrating that the full-width-at-half-maximum of point targets on the elevation plane was reduced compared to using SAF only, suggesting resolution improvement. This method shows promise for improving 3D image quality of existing linear array-based PA imaging systems, offering potential benefits for disease diagnosis and monitoring.