PET Imaging Using 89Zr Labeled StarPEG Nanocarriers Reveals Heterogeneous Enhanced Permeability and Retention (EPR) in Prostate Cancer.

The enhanced permeability and retention (EPR) effect controls passive nanodrug uptake in tumors, and may provide a high tumor payload with prolonged retention for cancer treatment. However, EPR-mediated tumor uptake and distribution vary by cancer phenotype. Thus, we hypothesized that a companion PET-imaging surrogate may benefit EPR-mediated therapeutic drug delivery. We developed two 89Zr-radiolabeled nanocarriers based on 4-armed-starPEG40kDa with or without talazoparib (TLZ), a potent PARPi, as surrogates for the PEG-TLZ4 therapeutic scaffold. For PET imaging, PEG-DFB4 and PEG-DFB1-TLZ3 were radiolabeled with 89Zr by replacing one or all four TLZ on PEG-TLZ4 with deferoxamine B (DFB). The radiolabeled nanodrugs [89Zr]PEG-DFB4 and [89Zr]PEG-DFB1-TLZ3 were tested in vivo in prostate cancer subcutaneous xenografts (22Rv1, LTL-545, and LTL-610) and 22Rv1 metastatic models. Their EPR-mediated tumoral uptake and penetration was compared to CT26, a known EPR-high MicroPET/CT images, organ biodistribution, and calculated kinetic parameters showed high uptake in CT26 and LTL-545, moderate to low uptake in LTL-610 and 22Rv1. MicroPET/CT and high-resolution autoradiographic images showed nanocarrier penetration into highly permeable CT26, but heterogeneous peripheral accumulation was observed in LTL-545, LTL-610, and 22Rv1 subcutaneous xenografts and metastatic tumors. CD31 staining of tumor sections showed homogenous vascular development in CT26 tumors and heterogeneity in other xenografts. Both [89Zr]PEG-DFB4 and [89Zr]PEG-DFB1-TLZ3 showed similar accumulation and distribution in subcutaneous and metastatic tumor models. Both nanocarriers can measure tumor model passive uptake heterogeneity. Although heterogeneous, prostate cancer xenografts had low EPR. These starPEG nanocarriers could be used as PET imaging surrogates to predict drug delivery and efficacy.

3D small-scale dosimetry and tumor control of 225Ac radiopharmaceuticals for prostate cancer.

Radiopharmaceutical therapy using α -emitting 225 Ac is an emerging treatment for patients with advanced metastatic cancers. Measurement of the spatial dose distribution in organs and tumors is needed to inform treatment dose prescription and reduce off-target toxicity, at not only organ but also sub-organ scales. Digital autoradiography with α -sensitive detection devices can measure radioactivity distributions at 20-40 µ m resolution, but anatomical characterization is typically limited to 2D. We collected digital autoradiographs across whole tissues to generate 3D dose volumes and used them to evaluate the simultaneous tumor control and regional kidney dosimetry of a novel therapeutic radiopharmaceutical for prostate cancer, [225Ac]Ac-Macropa-PEG4-YS5, in mice. 22Rv1 xenograft-bearing mice treated with 18.5 kBq of [225Ac]Ac-Macropa-PEG4-YS5 were sacrificed at 24 h and 168 h post-injection for quantitative α -particle digital autoradiography and hematoxylin and eosin staining. Gamma-ray spectroscopy of biodistribution data was used to determine temporal dynamics and 213 Bi redistribution. Tumor control probability and sub-kidney dosimetry were assessed. Heterogeneous 225 Ac spatial distribution was observed in both tumors and kidneys. Tumor control was maintained despite heterogeneity if cold spots coincided with necrotic regions. 225 Ac dose-rate was highest in the cortex and renal vasculature. Extrapolation of tumor control suggested that kidney absorbed dose could be reduced by 41% while maintaining 90% TCP. The 3D dosimetry methods described allow for whole tumor and organ dose measurements following 225 Ac radiopharmaceutical therapy, which correlate to tumor control and toxicity outcomes.

A Feasibility Study of [18F]F-AraG Positron Emission Tomography (PET) for Cardiac Imaging-Myocardial Viability in Ischemia-Reperfusion Injury Model.

PURPOSE: Myocardial infarction (MI) with subsequent inflammation is one of the most common heart conditions leading to progressive tissue damage. A reliable imaging marker to assess tissue viability after MI would help determine the risks and benefits of any intervention. In this study, we investigate whether a new mitochondria-targeted imaging agent, 18F-labeled 2'-deoxy-2'-18F-fluoro-9-ß-d-arabinofuranosylguanine ([18F]F-AraG), a positron emission tomography (PET) agent developed for imaging activated T cells, is suitable for cardiac imaging and to test the myocardial viability after MI. PROCEDURE: To test whether the myocardial [18F]-F-AraG signal is coming from cardiomyocytes or immune infiltrates, we compared cardiac signal in wild-type (WT) mice with that of T cell deficient Rag1 knockout (Rag1 KO) mice. We assessed the effect of dietary nucleotides on myocardial [18F]F-AraG uptake in normal heart by comparing [18F]F-AraG signals between mice fed with purified diet and those fed with purified diet supplemented with nucleotides. The myocardial viability was investigated in rodent model by imaging rat with [18F]F-AraG and 2-deoxy-2[18F]fluoro-D-glucose ([18F]FDG) before and after MI. All PET signals were quantified in terms of the percent injected dose per cc (%ID/cc). We also explored [18F]FDG signal variability and potential T cell infiltration into fibrotic area in the affected myocardium with H&E analysis. RESULTS: The difference in %ID/cc for Rag1 KO and WT mice was not significant (p = ns) indicating that the [18F]F-AraG signal in the myocardium was primarily coming from cardiomyocytes. No difference in myocardial uptake was observed between [18F]F-AraG signals in mice fed with purified diet and with purified diet supplemented with nucleotides (p = ns). The [18F]FDG signals showed wider variability at different time points. Noticeable [18F]F-AraG signals were observed in the affected MI regions. There were T cells in the fibrotic area in the H&E analysis, but they did not constitute the predominant infiltrates. CONCLUSIONS: Our preliminary preclinical data show that [18F]F-AraG accumulates in cardiomyocytes indicating that it may be suitable for cardiac imaging and to evaluate the myocardial viability after MI.

Tissue-based T cell activation and viral RNA persist for up to 2 years after SARS-CoV-2 infection.

The mechanisms of postacute medical conditions and unexplained symptoms after SARS-CoV-2 infection [Long Covid (LC)] are incompletely understood. There is growing evidence that viral persistence, immune dysregulation, and T cell dysfunction may play major roles. We performed whole-body positron emission tomography imaging in a well-characterized cohort of 24 participants at time points ranging from 27 to 910 days after acute SARS-CoV-2 infection using the radiopharmaceutical agent [18F]F-AraG, a selective tracer that allows for anatomical quantitation of activated T lymphocytes. Tracer uptake in the postacute COVID-19 group, which included those with and without continuing symptoms, was higher compared with prepandemic controls in many regions, including the brain stem, spinal cord, bone marrow, nasopharyngeal and hilar lymphoid tissue, cardiopulmonary tissues, and gut wall. T cell activation in the spinal cord and gut wall was associated with the presence of LC symptoms. In addition, tracer uptake in lung tissue was higher in those with persistent pulmonary symptoms specifically. Increased T cell activation in these tissues was also observed in many individuals without LC. Given the high [18F]F-AraG uptake detected in the gut, we obtained colorectal tissue for in situ hybridization of SARS-CoV-2 RNA and immunohistochemical studies in a subset of five participants with LC symptoms. We identified intracellular SARS-CoV-2 single-stranded spike protein-encoding RNA in rectosigmoid lamina propria tissue in all five participants and double-stranded spike protein-encoding RNA in three participants up to 676 days after initial COVID-19, suggesting that tissue viral persistence could be associated with long-term immunologic perturbations.

[18F]F-AraG imaging reveals association between neuroinflammation and brown- and bone marrow adipose tissue.

Brown and brown-like adipose tissues have attracted significant attention for their role in metabolism and therapeutic potential in diabetes and obesity. Despite compelling evidence of an interplay between adipocytes and lymphocytes, the involvement of these tissues in immune responses remains largely unexplored. This study explicates a newfound connection between neuroinflammation and brown- and bone marrow adipose tissue. Leveraging the use of [18F]F-AraG, a mitochondrial metabolic tracer capable of tracking activated lymphocytes and adipocytes simultaneously, we demonstrate, in models of glioblastoma and multiple sclerosis, the correlation between intracerebral immune infiltration and changes in brown- and bone marrow adipose tissue. Significantly, we show initial evidence that a neuroinflammation-adipose tissue link may also exist in humans. This study proposes the concept of an intricate immuno-neuro-adipose circuit, and highlights brown- and bone marrow adipose tissue as an intermediary in the communication between the immune and nervous systems. Understanding the interconnectedness within this circuitry may lead to advancements in the treatment and management of various conditions, including cancer, neurodegenerative diseases and metabolic disorders.

Comparative Uptake Patterns of Radioactive Iodine and [18F]-Fluorodeoxyglucose (FDG) in Metastatic Differentiated Thyroid Cancers.

Background: Metastatic differentiated thyroid cancer (DTC) represents a molecularly heterogeneous group of cancers with varying radioactive iodine (RAI) and [18F]-fluorodeoxyglucose (FDG) uptake patterns potentially correlated with the degree of de-differentiation through the so-called "flip-flop" phenomenon. However, it is unknown if RAI and FDG uptake patterns correlate with molecular status or metastatic site. Materials and Methods: A retrospective analysis of metastatic DTC patients (n = 46) with radioactive 131-iodine whole body scan (WBS) and FDG-PET imaging between 2008 and 2022 was performed. The inclusion criteria included accessible FDG-PET and WBS studies within 1 year of each other. Studies were interpreted by two blinded radiologists for iodine or FDG uptake in extrathyroidal sites including lungs, lymph nodes, and bone. Cases were stratified by BRAF V600E mutation status, histology, and a combination of tumor genotype and histology. The data were analyzed by McNemar's Chi-square test. Results: Lung metastasis FDG uptake was significantly more common than iodine uptake (WBS: 52%, FDG: 84%, p = 0.04), but no significant differences were found for lymph or bone metastases. Lung metastasis FDG uptake was significantly more prevalent in the papillary pattern sub-cohort (WBS: 37%, FDG: 89%, p = 0.02) than the follicular pattern sub-cohort (WBS: 75%, FDG: 75%, p = 1.00). Similarly, BRAF V600E+ tumors with lung metastases also demonstrated a preponderance of FDG uptake (WBS: 29%, FDG: 93%, p = 0.02) than BRAF V600E- tumors (WBS: 83%, FDG: 83%, p = 1.00) with lung metastases. Papillary histology featured higher FDG uptake in lung metastasis (WBS: 39%, FDG: 89%, p = 0.03) compared with follicular histology (WBS: 69%, FDG: 77%, p = 1.00). Patients with papillary pattern disease, BRAF V600E+ mutation, or papillary histology had reduced agreement between both modalities in uptake at all metastatic sites compared with those with follicular pattern disease, BRAF V600E- mutation, or follicular histology. Low agreement in lymph node uptake was observed in all patients irrespective of molecular status or histology. Conclusions: The pattern of FDG-PET and radioiodine uptake is dependent on molecular status and metastatic site, with those with papillary histology or BRAF V600E+ mutation featuring increased FDG uptake in distant metastasis. Further study with an expanded cohort may identify which patients may benefit from specific imaging modalities to recognize and surveil metastases.

Aurora Kinase A inhibition enhances DNA damage and tumor cell death with 131I-MIBG therapy in high-risk neuroblastoma.

BACKGROUND: Neuroblastoma is the most common extra-cranial pediatric solid tumor. 131I-metaiodobenzylguanidine (MIBG) is a targeted radiopharmaceutical highly specific for neuroblastoma tumors, providing potent radiotherapy to widely metastatic disease. Aurora kinase A (AURKA) plays a role in mitosis and stabilization of the MYCN protein in neuroblastoma. We aimed to study the impact of AURKA inhibitors on DNA damage and tumor cell death in combination with 131I-MIBG therapy in a pre-clinical model of high-risk neuroblastoma. RESULTS: Using an in vivo model of high-risk neuroblastoma, we demonstrated a marked combinatorial effect of 131I-MIBG and alisertib on tumor growth. In MYCN amplified cell lines, the combination of radiation and an AURKA A inhibitor increased DNA damage and apoptosis and decreased MYCN protein levels. CONCLUSION: The combination of AURKA inhibition with 131I-MIBG treatment is active in resistant neuroblastoma models.

PVA Hydrogels Supplemented with PLA Mesh for Tissue Regeneration Scaffold.

This study examined the tensile strength and biocompatibility properties of polyvinyl alcohol (PVA) hydrogel tissue regeneration scaffolds with polylactic acid (PLA) mesh fabric added as reinforcement, with a focus on the impact of heat treatment temperature and the number of layers of the PLA mesh fabric. The hydrogel scaffolds were prepared using a freeze-thaw method to create PVA hydrogel, with the PLA mesh fabric placed inside the hydrogel. The swelling ratio of the PVA/PLA hydrogel scaffolds decreased with increasing layer number and heat treatment temperature of the PLA mesh. The gel strength was highest when five layers of PLA mesh fabric were added, heat-treated at 120 °C, and confirmed to be properly placed inside the hydrogel by SEM images. The MTT assay and DAPI staining using HaCaT cells demonstrated that the cell proliferation was uninterrupted throughout the experimental period, confirming the biocompatibility of the scaffold. Therefore, we confirmed the possibility of using PLA mesh fabric as a reinforcement for PVA hydrogel to improve the strength of scaffolds for tissue regeneration, and we confirmed the potential of PLA mesh fabric as a reinforcement for various biomaterials.

A feasibility study of [18F]F-AraG positron emission tomography (PET) for cardiac imaging - myocardial viability in ischemia-reperfusion injury model.

Purpose: Myocardial infarction (MI) with subsequent inflammation is one of the most common heart conditions leading to progressive tissue damage. A reliable imaging marker to assess tissue viability after MI would help determine the risks and benefits of any intervention. In this study, we investigate whether a new mitochondria-targeted imaging agent, 18F-labeled 2'-deoxy-2'-18F-fluoro-9-ß-d-arabinofuranosylguanine ([18F]F-AraG), a positron emission tomography (PET) agent developed for imaging activated T cells, is suitable for cardiac imaging and to test the myocardial viability after MI. Procedure: To test whether the myocardial [18F]-F-AraG signal is coming from cardiomyocytes or immune infiltrates, we compared cardiac signal in wild-type (WT) mice with that of T cell deficient Rag1 knockout (Rag1 KO) mice. We assessed the effect of dietary nucleotides on myocardial [18F]F-AraG uptake in normal heart by comparing [18F]F-AraG signals between mice fed with purified diet and those fed with purified diet supplemented with nucleotides. The myocardial viability was investigated in rodent model by imaging rat with [18F]F-AraG and 2-deoxy-2[18F]fluoro-D-glucose ([18F]FDG) before and after MI. All PET signals were quantified in terms of the percent injected dose per cc (%ID/cc). We also explored [18F]FDG signal variability and potential T cell infiltration into fibrotic area in the affected myocardium with H&E analysis. Results: The difference in %ID/cc for Rag1 KO and WT mice was not significant (p = ns) indicating that the [18F]F-AraG signal in the myocardium was primarily coming from cardiomyocytes. No difference in myocardial uptake was observed between [18F]F-AraG signals in mice fed with purified diet and with purified diet supplemented with nucleotides (p = ns). The [18F]FDG signals showed wider variability at different time points. Noticeable [18F]F-AraG signals were observed in the affected MI regions. There were T cells in the fibrotic area in the H&E analysis, but they did not constitute the predominant infiltrates. Conclusions: Our preliminary preclinical data show that [18F]F-AraG accumulates in cardiomyocytes indicating that it may be suitable for cardiac imaging and to evaluate the myocardial viability after MI.

Prostate-Specific Membrane Antigen Targeted StarPEG Nanocarrier for Imaging and Therapy of Prostate Cancer.

The tumor uptake of large non-targeted nanocarriers primarily occurs through passive extravasation, known as the enhanced permeability and retention (EPR) effect. Prior studies demonstrated improved tumor uptake and retention of 4-arm 40 kDa star polyethylene glycol (StarPEG) polymers for cancer imaging by adding prostate-specific membrane antigen (PSMA) targeting small molecule ligands. To test PSMA-targeted delivery and therapeutic efficacy, StarPEG nanodrugs with/without three copies of PSMA-targeting ligands, ACUPA, are designed and synthesized. For single-photon emission computed tomography (SPECT) imaging and therapy, each nanocarrier is labeled with 177Lu using DOTA radiometal chelator. The radiolabeled nanodrugs, [177Lu]PEG-(DOTA)1 and [177Lu]PEG-(DOTA)1(ACUPA)3, are evaluated in vitro and in vivo using PSMA+ PC3-Pip and/or PSMA- PC3-Flu cell lines, subcutaneous xenografts and disseminated metastatic models. The nanocarriers are efficiently radiolabeled with 177Lu with molar activities 10.8-15.8 MBq/nmol. Besides excellent in vitro PSMA binding affinity (kD = 51.7 nM), the targeted nanocarrier, [177Lu]PEG-(DOTA)1(ACUPA)3, demonstrated excellent in vivo SPECT imaging contrast with 21.3% ID/g PC3-Pip tumors uptake at 192 h. Single doses of 18.5 MBq [177Lu]PEG-(DOTA)1(ACUPA)3 showed complete resolution of the PC3-Pip xenografts observed up to 138 days. Along with PSMA-targeted excellent imaging contrast, these results demonstrated high treatment efficacy of [177Lu]PEG-(DOTA)1(ACUPA)3 for prostate cancer, with potential for clinical translation.

68Ga-FAP-2286 PET of Solid Tumors: Biodistribution, Dosimetry, and Comparison with 18F-FDG.

Fibroblast activation protein (FAP), expressed in the tumor microenvironment of a variety of cancers, has become a target of novel PET tracers. The purpose of this report is to evaluate the imaging characteristics of 68Ga-FAP-2286, present the first-to our knowledge-dosimetry analysis to date, and compare the agent with 18F-FDG and FAPI compounds. Methods: Patients were administered 219 ± 43 MBq of 68Ga-FAP-2286 and scanned after 60 min. Uptake was measured in up to 5 lesions per patient and within the kidneys, spleen, liver, and mediastinum (blood pool). Absorbed doses were evaluated using MIM Encore and OLINDA/EXM version 1.1 using the International Commission on Radiological Protection publication 103 tissue weighting factor. Results: Forty-six patients were imaged with 68Ga-FAP-2286 PET. The highest average uptake was seen in sarcoma, cholangiocarcinoma, and colon cancer. The lowest uptake was found in lung cancer and testicular cancer. The average SUVmax was significantly higher on 68Ga-FAP-2286 PET than on 18F-FDG PET in cholangiocarcinoma (18.2 ± 6.4 vs. 9.1 ± 5.0, P = 0.007), breast cancer (11.1 ± 6.8 vs. 4.1 ± 2.2, P < 0.001), colon cancer (13.8 ± 2.2 vs. 7.6 ± 1.7, P = 0.001), hepatocellular carcinoma (9.3 ± 3.5 vs. 4.7 ± 1.3, P = 0.01), head and neck cancer (11.3 ± 3.5 vs. 7.6 ± 5.5, P = 0.04), and pancreatic adenocarcinoma (7.4 ± 1.8 vs. 3.7 ± 1.0, P = 0.01). The total-body effective dose was estimated at 1.16E-02 mSv/MBq, with the greatest absorbed organ dose in the urinary bladder wall (9.98E-02 mGy/MBq). Conclusion: 68Ga-FAP-2286 biodistribution, dosimetry, and tumor uptake were similar to those of previously reported FAPI compounds. Additionally,68Ga-FAP-2286 PET had consistently higher uptake than 18F-FDG PET. These results are especially promising in the setting of small-volume disease and differentiating tumor from inflammatory uptake.

18F-FDG Dedicated Breast PET Complementary to Breast MRI for Evaluating Early Response to Neoadjuvant Chemotherapy.

Purpose To compare quantitative measures of tumor metabolism and perfusion using fluorine 18 (18F) fluorodeoxyglucose (FDG) dedicated breast PET (dbPET) and breast dynamic contrast-enhanced (DCE) MRI during early treatment with neoadjuvant chemotherapy (NAC). Materials and Methods Prospectively collected DCE MRI and 18F-FDG dbPET examinations were analyzed at baseline (T0) and after 3 weeks (T1) of NAC in 20 participants with 22 invasive breast cancers. FDG dbPET-derived standardized uptake value (SUV), metabolic tumor volume, and total lesion glycolysis (TLG) and MRI-derived percent enhancement (PE), signal enhancement ratio (SER), and functional tumor volume (FTV) were calculated at both time points. Differences between FDG dbPET and MRI parameters were evaluated after stratifying by receptor status, Ki-67 index, and residual cancer burden. Parameters were compared using Wilcoxon signed rank and Mann-Whitney U tests. Results High Ki-67 tumors had higher baseline SUVmean (difference, 5.1; P = .01) and SUVpeak (difference, 5.5; P = .04). At T1, decreases were observed in FDG dbPET measures (pseudo-median difference T0 minus T1 value [95% CI]) of SUVmax (-6.2 [-10.2, -2.6]; P < .001), SUVmean (-2.6 [-4.9, -1.3]; P < .001), SUVpeak (-4.2 [-6.9, -2.3]; P < .001), and TLG (-29.1 mL3 [-71.4, -6.8]; P = .005) and MRI measures of SERpeak (-1.0 [-1.3, -0.2]; P = .02) and FTV (-11.6 mL3 [-22.2, -1.7]; P = .009). Relative to nonresponsive tumors, responsive tumors showed a difference (95% CI) in percent change in SUVmax of -34.3% (-55.9%, 1.5%; P = .06) and in PEpeak of -42.4% (95% CI: -110.5%, 8.5%; P = .08). Conclusion 18F-FDG dbPET was sensitive to early changes during NAC and provided complementary information to DCE MRI that may be useful for treatment response evaluation. Keywords: Breast, PET, Dynamic Contrast-enhanced MRI Clinical trial registration no. NCT01042379 Supplemental material is available for this article. © RSNA, 2024.

A Technique to Quantify Very Low Activities in Regions of Interest With a Collimatorless Detector.

We present a new method to measure sub-microcurie activities of photon-emitting radionuclides in organs and lesions of small animals in vivo. Our technique, named the collimator-less likelihood fit, combines a very high sensitivity collimatorless detector with a Monte Carlo-based likelihood fit in order to estimate the activities in previously segmented regions of interest along with their uncertainties. This is done directly from the photon projections in our collimatorless detector and from the region of interest segmentation provided by an x-ray computed tomography scan. We have extensively validated our approach with 225Ac experimentally in spherical phantoms and mouse phantoms, and also numerically with simulations of a realistic mouse anatomy. Our method yields statistically unbiased results with uncertainties smaller than 20% for activities as low as ~111Bq (3nCi) and for exposures under 30 minutes. We demonstrate that our method yields more robust recovery coefficients when compared to SPECT imaging with a commercial pre-clinical scanner, specially at very low activities. Thus, our technique is complementary to traditional SPECT/CT imaging since it provides a more accurate and precise organ and tumor dosimetry, with a more limited spatial information. Finally, our technique is specially significant in extremely low-activity scenarios when SPECT/CT imaging is simply not viable.

Development of CD46 targeted alpha theranostics in prostate cancer using 134Ce/225Ac-Macropa-PEG4-YS5.

Rationale: 225Ac, a long-lived α-emitter with a half-life of 9.92 days, has garnered significant attention as a therapeutic radionuclide when coupled with monoclonal antibodies and other targeting vectors. Nevertheless, its clinical utility has been hampered by potential off-target toxicity, a lack of optimized chelators for 225Ac, and limitations in radiolabeling methods. In a prior study evaluating the effectiveness of CD46-targeted radioimmunotherapy, we found great therapeutic efficacy but also significant toxicity at higher doses. To address these challenges, we have developed a radioimmunoconjugate called 225Ac-Macropa-PEG4-YS5, incorporating a stable PEGylated linker to maximize tumoral uptake and increase tumor-to-background ratios. Our research demonstrates that this conjugate exhibits greater anti-tumor efficacy while minimizing toxicity in prostate cancer 22Rv1 tumors. Methods: We synthesized Macropa.NCS and Macropa-PEG4/8-TFP esters and prepared Macropa-PEG0/4/8-YS5 (with nearly ~1:1 ratio of macropa chelator to antibody YS5) as well as DOTA-YS5 conjugates. These conjugates were then radiolabeled with 225Ac in a 2 M NH4OAc solution at 30 °C, followed by purification using YM30K centrifugal purification. Subsequently, we conducted biodistribution studies and evaluated antitumor activity in nude mice (nu/nu) bearing prostate 22Rv1 xenografts in both single-dose and fractionated dosing studies. Micro-PET imaging studies were performed with 134Ce-Macropa-PEG0/4/8-YS5 in 22Rv1 xenografts for 7 days. Toxicity studies were also performed in healthy athymic nude mice. Results: As expected, we achieved a >95% radiochemical yield when labeling Macropa-PEG0/4/8-YS5 with 225Ac, regardless of the chelator ratios (ranging from 1 to 7.76 per YS5 antibody). The isolated yield exceeded 60% after purification. Such high conversions were not observed with the DOTA-YS5 conjugate, even at a higher ratio of 8.5 chelators per antibody (RCY of 83%, an isolated yield of 40%). Biodistribution analysis at 7 days post-injection revealed higher tumor uptake for the 225Ac-Macropa-PEG4-YS5 (82.82 ± 38.27 %ID/g) compared to other conjugates, namely 225Ac-Macropa-PEG0/8-YS5 (38.2 ± 14.4/36.39 ± 12.4 %ID/g) and 225Ac-DOTA-YS5 (29.35 ± 7.76 %ID/g). The PET Imaging of 134Ce-Macropa-PEG0/4/8-YS5 conjugates resulted in a high tumor uptake, and tumor to background ratios. In terms of antitumor activity, 225Ac-Macropa-PEG4-YS5 exhibited a substantial response, leading to prolonged survival compared to 225Ac-DOTA-YS5, particularly when administered at 4.625 kBq doses, in single or fractionated dose regimens. Chronic toxicity studies observed mild to moderate renal toxicity at 4.625 and 9.25 kBq doses. Conclusions: Our study highlights the promise of 225Ac-Macropa-PEG4-YS5 for targeted alpha particle therapy. The 225Ac-Macropa-PEG4-YS5 conjugate demonstrates improved biodistribution, reduced off-target binding, and enhanced therapeutic efficacy, particularly at lower doses, compared to 225Ac-DOTA-YS5. Incorporating theranostic 134Ce PET imaging further enhances the versatility of macropa-PEG conjugates, offering a more effective and safer approach to cancer treatment. Overall, this methodology has a high potential for broader clinical applications.

Hypoxia-informed RBE-weighted beam orientation optimization for intensity modulated proton therapy.

BACKGROUND: Variable relative biological effectiveness (RBE) models in treatment planning have been proposed to optimize the therapeutic ratio of proton therapy. It has been reported that proton RBE decreases with increasing tumor oxygen level, offering an opportunity to address hypoxia-related radioresistance with RBE-weighted optimization. PURPOSE: Here, we obtain a voxel-level estimation of partial oxygen pressure to weigh RBE values in a single biologically informed beam orientation optimization (BOO) algorithm. METHODS: Three glioblastoma patients with [18 F]-fluoromisonidazole (FMISO)-PET/CT images were selected from the institutional database. Oxygen values were derived from tracer uptake using a nonlinear least squares curve fitting. McNamara RBE, calculated from proton dose, was then weighed using oxygen enhancement ratios (OER) for each voxel and incorporated into the dose fidelity term of the BOO algorithm. The nonlinear optimization problem was solved using a split-Bregman approach, with FISTA as the solver. The proposed hypoxia informed RBE-weighted method (HypRBE) was compared to dose fidelity terms using the constant RBE of 1.1 (cRBE) and the normoxic McNamara RBE model (RegRBE). Tumor homogeneity index (HI), maximum biological dose (Dmax), and D95%, as well as OAR therapeutic index (TI = gEUDCTV /gEUDOAR ) were evaluated along with worst-case statistics after normalization to normal tissue isotoxicity. RESULTS: Compared to [cRBE, RegRBE], HypRBE increased tumor HI, Dmax, and D95% across all plans by on average [31.3%, 31.8%], [48.6%, 27.1%], and [50.4%, 23.8%], respectively. In the worst-case scenario, the parameters increase on average by [12.5%, 14.7%], [7.3%,-8.9%], and [22.3%, 2.1%]. Despite increased OAR Dmean and Dmax by [8.0%, 3.0%] and [13.1%, -0.1%], HypRBE increased average TI by [22.0%, 21.1%]. Worst-case OAR Dmean, Dmax, and TI worsened by [17.9%, 4.3%], [24.5%, -1.2%], and [9.6%, 10.5%], but in the best cases, HypRBE escalates tumor coverage significantly without compromising OAR dose, increasing the therapeutic ratio. CONCLUSIONS: We have developed an optimization algorithm whose dose fidelity term accounts for hypoxia-informed RBE values. We have shown that HypRBE selects bE:\Alok\aaeams better suited to deliver high physical dose to low RBE, hypoxic tumor regions while sparing the radiosensitive normal tissue.

Aurora Kinase A inhibition enhances DNA damage and tumor cell death with 131I-MIBG therapy in high-risk neuroblastoma.

Background: Neuroblastoma is the most common extra-cranial pediatric solid tumor. 131I-metaiodobenzylguanidine (MIBG) is a targeted radiopharmaceutical highly specific for neuroblastoma tumors, providing potent radiotherapy to widely metastatic disease. Aurora kinase A (AURKA) plays a role in mitosis and stabilization of the MYCN protein in neuroblastoma. Here we explore whether AURKA inhibition potentiates a response to MIBG therapy. Results: Using an in vivo model of high-risk neuroblastoma, we demonstrated a marked combinatorial effect of 131I-MIBG and alisertib on tumor growth. In MYCN amplified cell lines, the combination of radiation and an AURKA A inhibitor increased DNA damage and apoptosis and decreased MYCN protein levels. Conclusion: The combination of AURKA inhibition with 131I-MIBG treatment is active in resistant neuroblastoma models and is a promising clinical approach in high-risk neuroblastoma.

CD46-Targeted Theranostics for PET and 225Ac-Radiopharmaceutical Therapy of Multiple Myeloma.

PURPOSE: Multiple myeloma is a plasma cell malignancy with an unmet clinical need for improved imaging methods and therapeutics. Recently, we identified CD46 as an overexpressed therapeutic target in multiple myeloma and developed the antibody YS5, which targets a cancer-specific epitope on this protein. We further developed the CD46-targeting PET probe [89Zr]Zr-DFO-YS5 for imaging and [225Ac]Ac-DOTA-YS5 for radiopharmaceutical therapy of prostate cancer. These prior studies suggested the feasibility of the CD46 antigen as a theranostic target in multiple myeloma. Herein, we validate [89Zr]Zr-DFO-YS5 for immunoPET imaging and [225Ac]Ac-DOTA-YS5 for radiopharmaceutical therapy of multiple myeloma in murine models. EXPERIMENTAL DESIGN: In vitro saturation binding was performed using the CD46 expressing MM.1S multiple myeloma cell line. ImmunoPET imaging using [89Zr]Zr-DFO-YS5 was performed in immunodeficient (NSG) mice bearing subcutaneous and systemic multiple myeloma xenografts. For radioligand therapy, [225Ac]Ac-DOTA-YS5 was prepared, and both dose escalation and fractionated dose treatment studies were performed in mice bearing MM1.S-Luc systemic xenografts. Tumor burden was analyzed using BLI, and body weight and overall survival were recorded to assess antitumor effect and toxicity. RESULTS: [89Zr]Zr-DFO-YS5 demonstrated high affinity for CD46 expressing MM.1S multiple myeloma cells (Kd = 16.3 nmol/L). In vitro assays in multiple myeloma cell lines demonstrated high binding, and bioinformatics analysis of human multiple myeloma samples revealed high CD46 expression. [89Zr]Zr-DFO-YS5 PET/CT specifically detected multiple myeloma lesions in a variety of models, with low uptake in controls, including CD46 knockout (KO) mice or multiple myeloma mice using a nontargeted antibody. In the MM.1S systemic model, localization of uptake on PET imaging correlated well with the luciferase expression from tumor cells. A treatment study using [225Ac]Ac-DOTA-YS5 in the MM.1S systemic model demonstrated a clear tumor volume and survival benefit in the treated groups. CONCLUSIONS: Our study showed that the CD46-targeted probe [89Zr]Zr-DFO-YS5 can successfully image CD46-expressing multiple myeloma xenografts in murine models, and [225Ac]Ac-DOTA-YS5 can effectively inhibit the growth of multiple myeloma. These results demonstrate that CD46 is a promising theranostic target for multiple myeloma, with the potential for clinical translation.

SENTRI: Single-Particle Energy Transducer for Radionuclide Injections for Personalized Targeted Radionuclide Cancer Therapy.

PURPOSE: Targeted radionuclide therapy (TRT), whereby a tumor-targeted molecule is linked to a therapeutic beta- or alpha-emitting radioactive nuclide, is a promising treatment modality for patients with metastatic cancer, delivering radiation systemically. However, patients still progress due to suboptimal dosing, driven by the large patient-to-patient variability. Therefore, the ability to continuously monitor the real-time dose deposition in tumors and organs at risk provides an additional dimension of information during clinical trials that can enable insights into better strategies to personalize TRT. METHODS AND MATERIALS: Here, we present a single beta-particle sensitive dosimeter consisting of a 0.27-mm3 monolithic silicon chiplet directly implanted into the tumor. To maximize the sensitivity and have enough detection area, minimum-size diodes (1 µm2) are arrayed in 64 × 64. Signal amplifiers, buffers, and on-chip memories are all integrated in the chip. For verification, PC3-PIP (prostate-specific membrane antigen [PSMA]+) and PC3-flu (PSMA-) cell lines are injected into the left and right flanks of the mice, respectively. The devices are inserted into each tumor and measure activities at 5 different time points (0-2 hours, 7-9 hours, 12-14 hours, 24-26 hours, and 48-50 hours) after 177Lu-PSMA-617 injections. Single-photon emission computed tomography/computed tomography scans are used to verify measured data. RESULTS: With a wide detection range from 0.013 to 8.95 MBq/mL, the system is capable of detecting high tumor uptake as well as low doses delivered to organs at risk in real time. The measurement data are highly proportional (R2 > 0.99) to the 177Lu-PSMA-617 activity. The in vivo measurement data agree well with the single-photon emission computed tomography/computed tomography results within acceptable errors (±1.5%ID/mL). CONCLUSIONS: Given the recent advances in clinical use of TRT in prostate cancer, the proposed system is verified in a prostate cancer mouse model using 177Lu-PSMA-617.

Low cost, high temporal resolution optical fiber-based γ-photon sensor for real-time pre-clinical evaluation of cancer-targeting radiopharmaceuticals.

Cancer radiopharmaceutical therapies (RPTs) have demonstrated great promise in the treatment of neuroendocrine and prostate cancer, giving hope to late-stage metastatic cancer patients with currently very few treatment options. These therapies have sparked a large amount of interest in pre-clinical research due to their ability to target metastatic disease, with many research efforts focused towards developing and evaluating targeted RPTs for different cancer types in in vivo models. Here we describe a method for monitoring real-time in vivo binding kinetics for the pre-clinical evaluation of cancer RPTs. Recognizing the significant heterogeneity in biodistribution of RPTs among even genetically identical animal models, this approach offers long-term monitoring of the same in vivo organism without euthanasia in contrast to ex vivo tissue dosimetry, while providing high temporal resolution with a low-cost, easily assembled platform, that is not present in small-animal SPECT/CTs. The method utilizes the developed optical fiber-based γ-photon biosensor, characterized to have a wide linear dynamic range with Lutetium-177 (177Lu) activity (0.5-500 µCi/mL), a common radioisotope used in cancer RPT. The probe's ability to track in vivo uptake relative to SPECT/CT and ex vivo dosimetry techniques was verified by administering 177Lu-PSMA-617 to mouse models bearing human prostate cancer tumors (PC3-PIP, PC3-flu). With this method for monitoring RPT uptake, it is possible to evaluate changes in tissue uptake at temporal resolutions <1 min to determine RPT biodistribution in pre-clinical models and better understand dose relationships with tumor ablation, toxicity, and recurrence when attempting to move therapies towards clinical trial validation.

Imaging the Bacterial Cell Wall Using N-Acetyl Muramic Acid-Derived Positron Emission Tomography Radiotracers.

Imaging infections in patients is challenging using conventional methods, motivating the development of positron emission tomography (PET) radiotracers targeting bacteria-specific metabolic pathways. Numerous techniques have focused on the bacterial cell wall, although peptidoglycan-targeted PET tracers have been generally limited to the short-lived carbon-11 radioisotope (t1/2 = 20.4 min). In this article, we developed and tested new tools for infection imaging using an amino sugar component of peptidoglycan, namely, derivatives of N-acetyl muramic acid (NAM) labeled with the longer-lived fluorine-18 (t1/2 = 109.6 min) radioisotope. Muramic acid was reacted directly with 4-nitrophenyl 2-[18F]fluoropropionate ([18F]NFP) to afford the enantiomeric NAM derivatives (S)-[18F]FMA and (R)-[18F]FMA. Both diastereomers were easily isolated and showed robust accumulation by human pathogens in vitro and in vivo, including Staphylococcus aureus. These results form the basis for future clinical studies using fluorine-18-labeled NAM-derived PET radiotracers.