Single Chelator-Minibody Theranostic Agents for 89Zr PET Imaging and 177Lu Radiopharmaceutical Therapy of PSMA-Expressing Prostate Cancer.

Here we describe an anti-prostate-specific membrane antigen (PSMA) minibody (IAB2MA) conjugated to an octadentate, macrocyclic chelator based on four 1-hydroxypyridin-2-one coordinating units (Lumi804 [L804]) labeled with 89Zr (PET imaging) and 177Lu (radiopharmaceutical therapy), with the goal of developing safer and more efficacious treatment options for prostate cancer. Methods: L804 was compared with the current gold standard chelators, DOTA and deferoxamine (DFO), conjugated to IAB2MA for radiolabeling with 177Lu and 89Zr in cell binding, preclinical biodistribution, imaging, dosimetry, and efficacy studies in the PSMA-positive PC3-PIP tumor-bearing mouse model of prostate cancer. Results: Quantitative radiolabeling (>99% radiochemical yield) of L804-IAB2MA with 177Lu or 89Zr was achieved at ambient temperature in under 30 min, comparable to 89Zr labeling of DFO-IAB2MA. In contrast, DOTA-IAB2MA was radiolabeled with 177Lu for 30 min at 37°C in approximately 90% radiochemical yield, requiring further purification. Using europium(III) as a luminescent surrogate, high binding affinity of Eu-L804-IAB2MA to PSMA was demonstrated in PC3-PIP cells (dissociation constant, 4.6 ± 0.6 nM). All 4 radiolabeled constructs showed significantly higher levels of internalization after 30 min in the PC3-PIP cells than in PSMA-negative PC3-FLU cells. The accumulation of 177Lu- and 89Zr-L804-IAB2MA in PC3-PIP tumors and all organs examined (i.e., heart, liver, spleen, kidney, muscle, salivary glands, lacrimal glands, carcass, and bone) was significantly lower than that of 177Lu-DOTA-IAB2MA and 89Zr-DFO-IAB2MA at 96 and 72 h after injection, respectively. Generally, SPECT/CT and PET/CT imaging data showed no significant difference in the SUVmean of the tumors or muscle between the radiotracers. Dosimetry analysis via both organ-level and voxel-level dose calculation methods indicated significantly higher absorbed doses of 177Lu-DOTA-IAB2MA in tumors, kidney, liver, muscle, and spleen than of 177Lu-L804-IAB2MA. PC3-PIP tumor-bearing mice treated with single doses of 177Lu-L804-IAB2MA (18.4 or 22.2 MBq) exhibited significantly prolonged survival and reduced tumor volume compared with unlabeled minibody control. No significant difference in survival was observed between groups of mice treated with 177Lu-L804-IAB2MA or 177Lu-DOTA-IAB2MA (18.4 or 22.2 MBq). Treatment with 177Lu-L804-IAB2MA resulted in lower absorbed doses in tumors and less toxicity than that of 177Lu-DOTA-IAB2MA. Conclusion: 89Zr- and 177Lu-L804-IAB2MA may be a promising theranostic pair for imaging and therapy of prostate cancer.

Evaluation of a bimodal, matched pair theranostic agent targeting prostate-specific membrane antigen.

BACKGROUND: Prostate cancer affects 1 in 6 men, and it is the second­leading cause of cancer-related death in American men. Surgery is one of the main treatment modalities for prostate cancer, but it often results in incomplete resection margins or complete resection that leads to nerve damage and undesirable side effects. In the present work, we have developed a new bimodal tracer, NODAGA-sCy7.5 PSMAi (prostate-specific membrane antigen inhibitor), labeled with the true matched theranostic pair 64Cu/67Cu and a near-infrared fluorescent dye. This agent could potentially be used for concomitant PET imaging, optical surgical navigation, and targeted radiopharmaceutical therapy. METHODS: A prostate-specific membrane antigen (PSMA)-targeting urea derivative was conjugated to NODAGA for copper radiolabeling and to the near-infrared fluorophore sulfo-Cy7.5 (sCy7.5). Binding studies were performed in PSMA-positive PC-3 PIP cells, as well as uptake and internalization assays in PC-3 PIP cells and PSMA-negative PC-3 wild type cells. Biodistribution studies of the 64Cu-labeled compound were performed in PC-3 PIP- and PC-3 tumor-bearing mice, and 67Cu biodistributions of the agent were obtained in PC-3 PIP tumor-carrying mice. PET imaging and fluorescence imaging were also performed, using the same molar doses, in the two mouse models. RESULTS: The PSMA conjugate bound with high affinity to PSMA-positive prostate cancer cells, as opposed to cells that were PSMA-negative. Uptake and internalization were rapid and PSMA-mediated in PC-3 PIP cells, while only minimal non-specific uptake was observed in PC-3 cells. Biodistribution studies showed specific uptake in PC-3 PIP tumors, while accumulation in PC-3 tumor-bearing mice was low. Furthermore, tumor uptake of the 67Cu-labeled agent in the PC-3 PIP model was statistically equivalent to that of 64Cu. PET and fluorescence imaging at 0.5 nmol per mouse also demonstrated that PC-3 PIP tumors could be clearly detected, while PC-3 tumors showed no tumor accumulation. CONCLUSIONS: NODAGA-sCy7.5-PSMAi was specific and selective in detecting PSMA-positive, as opposed to PSMA-negative, tumors in mouse models of prostate cancer. This bioconjugate could potentially be used for PET staging with 64Cu, targeted radiopharmaceutical therapy with 67Cu, and/or image-guided surgery with sCy7.5.

Dietary intake and glutamine-serine metabolism control pathologic vascular stiffness.

Perivascular collagen deposition by activated fibroblasts promotes vascular stiffening and drives cardiovascular diseases such as pulmonary hypertension (PH). Whether and how vascular fibroblasts rewire their metabolism to sustain collagen biosynthesis remains unknown. Here, we found that inflammation, hypoxia, and mechanical stress converge on activating the transcriptional coactivators YAP and TAZ (WWTR1) in pulmonary arterial adventitial fibroblasts (PAAFs). Consequently, YAP and TAZ drive glutamine and serine catabolism to sustain proline and glycine anabolism and promote collagen biosynthesis. Pharmacologic or dietary intervention on proline and glycine anabolic demand decreases vascular stiffening and improves cardiovascular function in PH rodent models. By identifying the limiting metabolic pathways for vascular collagen biosynthesis, our findings provide guidance for incorporating metabolic and dietary interventions for treating cardiopulmonary vascular disease.

Albumin-Binding Lutetium-177-Labeled LLP2A Derivatives as Theranostics for Melanoma.

Very late antigen-4 (VLA-4) is a transmembrane integrin protein that is highly expressed in aggressive forms of metastatic melanoma. A small-molecule peptidomimetic, LLP2A, was found to have a low pM affinity binding to VLA-4. Because LLP2A itself does not inhibit cancer cell proliferation and survival, it is an ideal candidate for the imaging and delivery of therapeutic payloads. An analog of [177Lu]Lu-labeled-LLP2A was previously investigated as a therapeutic agent in melanoma tumor-bearing mice, resulting in only a modest improvement in tumor growth inhibition, likely due to rapid clearance of the agent from the tumor. To improve the pharmacokinetic profile, DOTAGA-PEG4-LLP2A with a 4-(p-iodophenyl)butyric acid (pIBA) albumin binding moiety was synthesized. We demonstrate the feasibility of this albumin binding strategy by comparing in vitro cell binding assays and in vivo biodistribution performance of [177Lu]Lu-DOTAGA-PEG4-LLP2A ([177Lu]Lu-1) to the albumin binding [177Lu]Lu-DOTAGA-pIBA-PEG4-LLP2A ([177Lu]Lu-2). In vitro cell binding assay results for [177Lu]Lu-1 and [177Lu]Lu-2 showed Kd values of 0.40 ± 0.07 and 1.75 ± 0.40 nM, with similar Bmax values of 200 ± 6 and 315 ± 15 fmol/mg, respectively. In vivo biodistribution data for both tracers exhibited specific uptake in the tumor, spleen, thymus, and bone due to endogenous expression of VLA-4. Compound [177Lu]Lu-2 exhibited a much longer blood circulation time compared to [177Lu]Lu-1. The tumor uptake for [177Lu]Lu-1 was highest at 1 h (∼15%ID/g) and that for [177Lu]Lu-2 was highest at 4 h (∼23%ID/g). Significant clearance of [177Lu]Lu-1 from the tumor occurs at 24 h (<5%ID/g) while[177Lu]Lu-2 is retained for greater than 96 h (∼10%ID/g). An efficacy study showed that melanoma tumor-bearing mice receiving compound [177Lu]Lu-2 given in two fractions (2 × 14.8 MBq, 14 days apart) had a greater median survival time than mice administered a single 29.6 MBq dose of compound [177Lu]Lu-1, while a single 29.6 MBq dose of [177Lu]Lu-2 imparted hematopoietic toxicity. The in vitro and in vivo data show addition of pIBA to [177Lu]Lu-DOTAGA-PEG4-LLP2A slows blood clearance for a higher tumor uptake, and there is potential of [177Lu]Lu-2 as a theranostic in fractionated administered doses.

Opting In and Out: A Qualitative Study Exploring Career Break Experiences of Registered Dietitian Nutritionists.

BACKGROUND: Since 2002, an average of 17.5% of registered dietitian nutritionists (RDNs) have reported being out of the paid dietetics workforce, and approximately half of those report intention to return. With the Academy of Nutrition and Dietetics' focus on expanding workforce demand and capacity, understanding why and how dietitians opt in and out of the dietetics workforce may provide insights into how to potentially reduce the number of career breaks or expedite and enhance the reentry process. OBJECTIVE: To explore the lived experiences and perspectives of dietitians who were taking (with intention to return) or had taken a career break and returned to the paid dietetics' workforce. DESIGN: A qualitative study with semistructured interviews was conducted. PARTICIPANTS/SETTING: Participants (n = 22) were recruited through purposive sampling over social media. They were required to be credentialed as RDNs, reside in the United States, and have either previously or currently (with intent to return) taken a break from the dietetics workforce. Interviews were conducted using Zoom videoconferencing technology during September 2021. DATA ANALYSIS: Data were analyzed using a Coding Reliability Thematic Analysis approach. RESULTS: The data are summarized in four themes: (1) motivations to leave and return, (2) staying connected with dietetics, (3) preparing to return and returning to the dietetics workforce, and (4) desired resources for career breaks and reentry. CONCLUSIONS: Understanding the experiences of dietitians who take career breaks may help inform career reentry and help the profession meet the current and future workforce demand.

Tumor lipid metabolism: a mechanistic link between diet and cancer progression.

The potential for 'anti-cancer' diets to markedly alter cancer risk and prognosis has captured the imagination of patients, physicians, and researchers alike, but many of these dietary recommendations come from correlative studies that attribute certain diets to altered cancer risk. While provocative, little is known about the molecular mechanisms behind how these dietary interventions impact cancer progression. Within this context, however, changes in tumor lipid metabolism are emerging as a key contributor. In this review, we examine the current understanding of lipid metabolism in the tumor microenvironment (TME), suggesting how diet-induced changes in lipid composition may regulate tumor progression and therapeutic efficacy. By dissecting various cellular pathways involved in lipid metabolism, we highlight how diet modulates the balance between saturated and unsaturated fatty acid (FA) species in tumors to impact cancer cell and stromal cell function. Finally, we describe how current cancer therapies may synergize with diet to improve therapeutic efficacy.

Immuno-PET Imaging of CD69 Visualizes T-Cell Activation and Predicts Survival Following Immunotherapy in Murine Glioblastoma.

Glioblastoma (GBM) is the most common and malignant primary brain tumor in adults. Immunotherapy may be promising for the treatment of some patients with GBM; however, there is a need for noninvasive neuroimaging techniques to predict immunotherapeutic responses. The effectiveness of most immunotherapeutic strategies requires T-cell activation. Therefore, we aimed to evaluate an early marker of T-cell activation, CD69, for its use as an imaging biomarker of response to immunotherapy for GBM. Herein, we performed CD69 immunostaining on human and mouse T cells following in vitro activation and post immune checkpoint inhibitors (ICI) in an orthotopic syngeneic mouse glioma model. CD69 expression on tumor-infiltrating leukocytes was assessed using single-cell RNA sequencing (scRNA-seq) data from patients with recurrent GBM receiving ICI. Radiolabeled CD69 Ab PET/CT imaging (CD69 immuno-PET) was performed on GBM-bearing mice longitudinally to quantify CD69 and its association with survival following immunotherapy. We show CD69 expression is upregulated upon T-cell activation and on tumor-infiltrating lymphocytes (TIL) in response to immunotherapy. Similarly, scRNA-seq data demonstrated elevated CD69 on TILs from patients with ICI-treated recurrent GBM as compared with TILs from control cohorts. CD69 immuno-PET studies showed a significantly higher tracer uptake in the tumors of ICI-treated mice compared with controls. Importantly, we observed a positive correlation between survival and CD69 immuno-PET signals in immunotherapy-treated animals and established a trajectory of T-cell activation by virtue of CD69-immuno-PET measurements. Our study supports the potential use of CD69 immuno-PET as an immunotherapy response assessment imaging tool for patients with GBM. Significance: Immunotherapy may hold promise for the treatment of some patients with GBM. There is a need to assess therapy responsiveness to allow the continuation of effective treatment in responders and to avoid ineffective treatment with potential adverse effects in the nonresponders. We demonstrate that noninvasive PET/CT imaging of CD69 may allow early detection of immunotherapy responsiveness in patients with GBM.

Targeted imaging of very late antigen-4 for noninvasive assessment of lung inflammation-fibrosis axis.

BACKGROUND: The lack of noninvasive methods for assessment of dysregulated inflammation as a major driver of fibrosis (i.e., inflammation-fibrosis axis) has been a major challenge to precision management of fibrotic lung diseases. Here, we determined the potential of very late antigen-4 (VLA-4)-targeted positron emission tomography (PET) to detect inflammation in a mouse model of bleomycin-induced fibrotic lung injury. METHOD: Single time-point and longitudinal VLA-4-targeted PET was performed using a high-affinity peptidomimetic radiotracer, 64Cu-LLP2A, at weeks 1, 2, and 4 after bleomycin-induced (2.5 units/kg) lung injury in C57BL/6J mice. The severity of fibrosis was determined by measuring the hydroxyproline content of the lungs and expression of markers of extracellular matrix remodeling. Flow cytometry and histology was performed to determine VLA-4 expression across different leukocyte subsets and their spatial distribution. RESULTS: Lung uptake of 64Cu-LLP2A was significantly elevated throughout different stages of the progression of bleomycin-induced injury. High lung uptake of 64Cu-LLP2A at week-1 post-bleomycin was a predictor of poor survival over the 4-week follow up, supporting the prognostic potential of 64Cu-LLP2A PET during the early stage of the disease. Additionally, the progressive increase in 64Cu-LLP2A uptake from week-1 to week-4 post-bleomycin correlated with the ultimate extent of lung fibrosis and ECM remodeling. Flow cytometry revealed that LLP2A binding was restricted to leukocytes. A combination of increased expression of VLA-4 by alveolar macrophages and accumulation of VLA-4-expressing interstitial and monocyte-derived macrophages as well as dendritic cells was noted in bleomycin-injured, compared to control, lungs. Histology confirmed the increased expression of VLA-4 in bleomycin-injured lungs, particularly in inflamed and fibrotic regions. CONCLUSIONS: VLA-4-targeted PET allows for assessment of the inflammation-fibrosis axis and prediction of disease progression in a murine model. The potential of 64Cu-LLP2A PET for assessment of the inflammation-fibrosis axis in human fibrotic lung diseases needs to be further investigated.

Grammatical Perspective-Taking in Comprehension and Production.

Language use in conversation requires conversation partners to consider each other's points-of-view, or perspectives. A large body of work has explored how conversation partners take into account differences in knowledge states when choosing referring expressions. This paper explores how well findings from perspective-taking in reference generalize to a relatively understudied domain of perspective: the processing of grammatical perspectival expressions like the motion verbs come and go in English. We re-visit findings from perspective-taking in reference that conversation participants are subject to egocentric biases: they are biased towards their own perspectives. Drawing on theoretical proposals for grammatical perspective-taking and prior experimental studies of perspective-taking in reference, we compare two models of grammatical perspective-taking: a serial anchoring-and-adjustment model, and a simultaneous integration model. We test their differing predictions in a series of comprehension and production experiments using the perspectival motion verbs come and go as a case study. While our comprehension studies suggest that listeners reason simultaneously over multiple perspectives, as in the simultaneous integration model, our production findings are more mixed: we find support for only one of the simultaneous integration model's two key predictions. More generally, our findings suggest a role for egocentric bias in production for grammatical perspective-taking as well as when choosing referring expressions.

Molecular imaging of chemokine-like receptor 1 (CMKLR1) in experimental acute lung injury.

The lack of techniques for noninvasive imaging of inflammation has challenged precision medicine management of acute respiratory distress syndrome (ARDS). Here, we determined the potential of positron emission tomography (PET) of chemokine-like receptor-1 (CMKLR1) to monitor lung inflammation in a murine model of lipopolysaccharide-induced injury. Lung uptake of a CMKLR1-targeting radiotracer, [64Cu]NODAGA-CG34, was significantly increased in lipopolysaccharide-induced injury, correlated with the expression of multiple inflammatory markers, and reduced by dexamethasone treatment. Monocyte-derived macrophages, followed by interstitial macrophages and monocytes were the major CMKLR1-expressing leukocytes contributing to the increased tracer uptake throughout the first week of lipopolysaccharide-induced injury. The clinical relevance of CMKLR1 as a biomarker of lung inflammation in ARDS was confirmed using single-nuclei RNA-sequencing datasets which showed significant increases in CMKLR1 expression among transcriptionally distinct subsets of lung monocytes and macrophages in COVID-19 patients vs. controls. CMKLR1-targeted PET is a promising strategy to monitor the dynamics of lung inflammation and response to anti-inflammatory treatment in ARDS.

Transitioning From High-dose Methadone to Buprenorphine Using a Microdosing Approach: Unique Considerations at ASAM Level 3 Facilities.

Transitions from high-dose methadone to buprenorphine for treatment of opioid use disorder (OUD) present risk of precipitated withdrawal related to the introduction of a high-affinity partial agonist at the mu-opioid receptor after occupancy by a lower-affinity full agonist. Various strategies have been explored to maintain patient stability during this process, including microdosing buprenorphine. Current literature lacks consensus on an optimal setting and strategy for initiating a buprenorphine microdosing protocol and gives little detail on patients' conditions after the acute transition period. We report a 6-day microdosing transition from methadone 100 mg directly to sublingual buprenorphine, followed by a 20-day period of monitoring and additional treatment. This patient tolerated a sublingual buprenorphine microdosing protocol while using supportive medications with a peak Clinical Opiate Withdrawal Scale score of 6. The patient's most significant withdrawal symptoms occurred several days after completion of the microdosing process. This case demonstrates the feasibility of using a transmucosal buprenorphine formulation in microdosing transitions from high-dose methadone directly to buprenorphine, and highlights the utility of a medically monitored intensive inpatient setting (American Society of Addiction Medicine level 3.7) in providing appropriate monitoring and treatment during and after a microdosing transition.

Fellow and training director perspectives on personal leaves during fellowship training in neuropsychology and considerations for best practice.

Objective: Management of personal leaves represents an important component of diversity, equity, and inclusion (DEI) initiatives. This study aims to understand the ways in which both training directors and fellows in neuropsychology training programs understand, perceive, communicate about, and plan for personal leaves during fellowship training. We also aim to provide empirically based recommendations for training directors communicating with fellows about personal leaves. Method: Training directors (N = 40) and postdoctoral fellows (N = 51) were recruited to complete surveys examining their knowledge and perspectives on personal leaves through a professional listserv. Results: While most training directors reported that their programs offer paid personal leave options, a substantial minority did not. There were discrepancies between training directors' and fellows' knowledge about leave policies and perceptions of the professional implications of taking a personal leave, such that fellows reported less knowledge and a greater perception that taking a leave during training may have a negative professional impact. Conclusions: Findings suggest that training directors in neuropsychology should clearly communicate institutional leave policies early in, or even before the start of, the fellowship period and work to cultivate a culture of openness around both broad issues of work-life balance and specific issues related to personal leaves with trainees.

Combined Targeted Radiopharmaceutical Therapy and Immune Checkpoint Blockade: From Preclinical Advances to the Clinic.

Immune checkpoint inhibitors (ICIs) have revolutionized cancer care, but many patients with poorly immunogenic tumors fail to benefit. Preclinical studies have shown that external beam radiotherapy (EBRT) can synergize with ICI to prompt remarkable tumor regression and even eradication. However, EBRT is poorly suited to widely disseminated disease. Targeted radiopharmaceutical therapy (TRT) selectively delivers radiation to both the primary tumor and the metastatic sites, and promising results achieved with this approach have led to regulatory approval of certain agents (e.g., 177Lu-PSMA-617/Pluvicto for metastatic prostate cancer). To further improve therapeutic outcomes, combining TRT and ICI is a burgeoning research area, both preclinically and in clinical trials. Here we introduce basic TRT radiobiology and survey emerging and clinically translated TRT agents that have been combined with ICI.

Modular Smart Molecules for PSMA-Targeted Chemotherapy.

New targeted chemotherapeutics are urgently needed to minimize off-target toxicity and reduce the high-mortality rate associated with metastatic prostate cancer. Herein, we report on the modular synthesis, pharmacokinetics, and efficacy of two small-molecule-drug conjugates (SMDC) targeted to prostate-specific membrane antigen (PSMA) incorporating either: (i) a cathepsin-B-cleavable valine-citrulline (Val-Cit), or (ii) an acid-cleavable phosphoramidate linker. Crucial components used in the design of the conjugates include: (i) CTT1298, a nanomolar affinity ligand that binds irreversibly to PSMA and has proven in past studies to rapidly internalize and shuttle payloads into PSMA-expressing prostate cancer cells, (ii) MMAE, a known potent cytotoxic payload, and (iii) an albumin-binder, proven to improve residence time of drug conjugates. At dose of 0.8 mg/kg (∼250 nmol/kg), the two SMDCs showed significant efficacy in a PSMA(+) PC3-PIP mouse model of human prostate cancer compared with controls, without inducing systemic toxicity. Though localization of the SMDCs was observed in tissues apart from the tumor, release of MMAE was observed predominantly in tumor tissue, at levels that were 2-3 orders of magnitude higher than non-target tissues. Furthermore, SMDC2, which incorporated a novel pH-responsive phosporamidate linker, demonstrated significantly improved efficacy over SMDC1 that has a Val-Cit linker, with a 100% survival over 90 days and 4 out of 8 mice showing complete tumor growth inhibition after 6 weekly doses of 0.8 mg/kg (244 nmol/kg). Our findings demonstrate the potential of irreversible PSMA inhibitors combined with pH-responsive linkers as a way to specifically deliver chemotherapeutic drugs to prostate cancer tumors with minimal toxicity.

Synthesis of Ester-Substituted Indolizines from 2-Propargyloxypyridines and 1,3-Dicarbonyls.

Two new complementary Au(I)-catalyzed methods for the preparation of ester-substituted indolizines from easily accessible 2-propargyloxypyridines and either acetoacetates or dimethyl malonate are reported. These reactions tolerate a wide range of functionality, allowing for diversification at three distinct positions of the product (R, R1, R2). For electron-poor substrates, the highest yields are observed upon reaction with acetoacetates, while neutral and electron-rich substrates give higher yields upon treatment with dimethyl malonate.

p-NCS-Bn-NODAGA as a bifunctional chelator for radiolabeling with the 186Re/99mTc-tricarbonyl core: Radiochemistry with model complexes and a GRPR-targeting peptide.

INTRODUCTION: With the goal of developing theranostic agents for application in radiopharmaceutical chemistry, in this work, we studied p-NCS-Bn-NODAGA (1) as a bifunctional chelator for the fac-[M(CO)3]+ core (M = natRe, 186Re, 99mTc). Specifically, we studied complexes of the formula [M(CO)3(L)]+, where L denotes either Bn-NODAGA-Pyr (2) or Bn-NODAGA-Ser-Ser-RM2 (3). METHODS: The model bioconjugate molecule 2 was synthesized by conjugating pyrrolidine with 1, while 3 was derived from the conjugation of the gastrin-releasing peptide receptor (GRPR)-targeting peptide Ser-Ser-RM2 with 1. Labeling of 2 and 3 was performed with [M(CO)3(OH2)3]+ (where M = natRe, 186Re, or 99mTc). The stability of the radioactive complexes was studied against l-histidine and l-cysteine (1 mM in PBS; pH 7.4, 37 °C). GRPR affinity of both peptide 3 and its metallated counterpart, Re-3, were determined with in vitro competitive binding assays in GRPR-expressing PC-3 cells using [125I]I-Tyr4-BBN as the competitor. RESULTS: After a thorough radiolabeling optimization process, the [M(CO)3(2)]+ model complexes (M = 186Re and 99mTc) were synthesized with 94 ± 2% radiochemical yield (RCY; estimated by radio-HPLC). In stability studies, [186Re]Re-2 remained intact through 7 d in l-cysteine and l-histidine. Similarly, stability studies in rat serum at 37 °C showed 99 ± 1% intact [186Re]Re-2 through 4 h. Non-specific rat serum protein binding of [186Re]Re-2 was found to be 33 ± 4% at 4 h. The [99mTc]Tc-2 complex was found to be stable in l-histidine and l-cysteine at 37 °C through 24 h. [99mTc]Tc-2 was also stable in rat serum, with 38 ± 3% non-specific protein binding, at 4 h. The [M(CO)3(3)]+ peptide radiometal complex (M = 186Re and 99mTc) syntheses were also optimized, resulting in RCYs of 35% for [186Re]Re-3 and 47% for [99mTc]Tc-3 (estimated by radio-HPLC). [186Re]Re-3 showed 98 ± 2% and 84 ± 5% stability in l-histidine and l-cysteine, respectively, through 48 h. Similarly, stability studies in rat serum at 37 °C showed 85 ± 3% intact [186Re]Re-3 through 4 h, with 29 ± 7% non-specific protein binding in rat serum. [99mTc]Tc-3 was found to be 84 ± 3% and 82 ± 4% stable in l-histidine and l-cysteine at 24 h, respectively. [99mTc]Tc-3 in rat serum at 37 °C showed 88 ± 2% stability through 4 h, with 25 ± 2% non-specific protein binding. Both 3 and Re-3 demonstrated high GRPR affinity, with IC50 values of 3.1 nM and 3.9 nM, respectively. CONCLUSIONS: The low nanomolar IC50 values obtained for 3 and Re-3 demonstrate high affinity of this novel [M(CO)3]-labeled bioconjugate for GRPR. The encouraging stability studies and receptor affinity results demonstrate promise for further development of these metal complexes as a theranostic matched pair for targeting GRPR.

ALDH1A1 Gene Expression and Cellular Copper Levels between Low and Highly Metastatic Osteosarcoma Provide a Case for Novel Repurposing with Disulfiram and Copper.

Aldehyde dehydrogenase 1A1 (ALDH) is a cancer stem cell marker highly expressed in metastatic cells. Disulfiram (Dis) is an FDA-approved antialcoholism drug that inhibits ALDH and has been studied as a candidate for drug repurposing in multiple neoplasia. Dis cytotoxicity in cancer cells has been shown to be copper-dependent, in part due to Dis's ability to function as a bivalent metal ion chelator of copper (Cu). The objectives of this research were to test ALDH expression levels and Cu concentrations in sarcoma patient tumors and human osteosarcoma (OS) cell lines with differing metastatic phenotypes. We also sought to evaluate Dis + Cu combination therapy in human OS cells. Intracellular Cu was inversely proportional to the metastatic phenotype in human OS cell lines (SaOS2 > LM2 > LM7). Nonmetastatic human sarcoma tumors demonstrated increased Cu concentrations compared with metastatic tumors. qPCR demonstrated that ALDH expression was significantly increased in highly metastatic LM2 and LM7 human OS cell lines compared with low metastatic SaOS2. Tumor cells from sarcoma patients with metastatic disease displayed significantly increased ALDH expression compared with tumor cells from patients without metastatic disease. Serum Cu concentration in canine OS versus normal canine patients demonstrated similar trends. Dis demonstrated selective cytotoxicity compared with human multipotential stromal cells (MSCs): Dis-treated OS cells demonstrated increased apoptosis, whereas MSCs did not. CuCl2 combined with Dis and low-dose doxorubicin resulted in a superior cytotoxic effect in both SaOS2 and LM7 cell lines. In summary, ALDH gene expression and Cu levels are altered between low and highly metastatic human OS cells, canine samples, and patient tumors. Our findings support the feasibility of a repurposed drug strategy for Dis and Cu in combination with low-dose anthracycline to specifically target metastatic OS cells.

PET Imaging of VLA-4 in a New BRAFV600E Mouse Model of Melanoma.

PURPOSE: Despite unprecedented responses to immune checkpoint inhibitors and targeted therapy in melanoma, a major subset of patients progresses and have few effective salvage options. We have previously demonstrated robust, selective uptake of the peptidomimetic LLP2A labeled with Cu-64 ([64Cu]-LLP2A) for positron emission tomography (PET) imaging in subcutaneous and metastatic models of B16F10 murine melanoma. LLP2A binds with high affinity to very late antigen-4 (VLA-4, integrin α4ß1), a transmembrane protein overexpressed in melanoma and other cancers that facilitates tumor growth and metastasis. Yet B16F10 fails to faithfully reflect human melanoma biology, as it lacks certain oncogenic driver mutations, including BRAF mutations found in ≥ 50 % of clinical specimens. Here, we evaluated the PET tracer [64Cu]-CB-TE1A1P-PEG4-LLP2A ([64Cu]-LLP2A) in novel, translational BRAFV600E mutant melanoma models differing in VLA-4 expression-BPR (VLA-4-) and BPRα (VLA-4+). PROCEDURES: BPR cells were transduced with α4 (CD49d) to overexpress intact cell surface VLA-4 (BPRα). The binding affinity of [64Cu]-LLP2A to BPR and BPRα cells was determined by saturation binding assays. [64Cu]-LLP2A internalization into B16F10, BPR, and BPRα cells was quantified via a plate-based assay. Tracer biodistribution and PET/CT imaging were evaluated in mice bearing subcutaneous BPR and BPRα tumors. RESULTS: [64Cu]-LLP2A demonstrated high binding affinity to BPRα (Kd = 1.4 nM) but indeterminate binding to BPR cells. VLA-4+ BPRα and B16F10 displayed comparable time-dependent [64Cu]-LLP2A internalization, whereas BPR internalization was undetectable. PET/CT showed increased tracer uptake in BPRα tumors vs. BPR tumors in vivo, which was validated by significantly greater (p < 0.0001) BPRα tumor uptake in biodistribution analyses. CONCLUSIONS: [64Cu]-LLP2A discriminates BPRα (VLA-4+) vs. BPR (VLA-4-) melanomas in vivo, supporting translation of these BRAF-mutated melanoma models via prospective imaging and theranostic studies. These results extend the utility of LLP2A to selectively target clinically relevant and therapy-resistant tumor variants toward its use for therapeutic patient care.

Novel theranostic agent for PET imaging and targeted radiopharmaceutical therapy of tumour-infiltrating immune cells in glioma.

BACKGROUND: Malignant gliomas are deadly tumours with few therapeutic options. Although immunotherapy may be a promising therapeutic strategy for treating gliomas, a significant barrier is the CD11b+ tumour-associated myeloid cells (TAMCs), a heterogeneous glioma infiltrate comprising up to 40% of a glioma's cellular mass that inhibits anti-tumour T-cell function and promotes tumour progression. A theranostic approach uses a single molecule for targeted radiopharmaceutical therapy (TRT) and diagnostic imaging; however, there are few reports of theranostics targeting the tumour microenvironment. METHODS: Utilizing a newly developed bifunctional chelator, Lumi804, an anti-CD11b antibody (αCD11b) was readily labelled with either Zr-89 or Lu-177, yielding functional radiolabelled conjugates for PET, SPECT, and TRT. FINDINGS: 89Zr/177Lu-labeled Lumi804-αCD11b enabled non-invasive imaging of TAMCs in murine gliomas. Additionally, 177Lu-Lumi804-αCD11b treatment reduced TAMC populations in the spleen and tumour and improved the efficacy of checkpoint immunotherapy. INTERPRETATION: 89Zr- and 177Lu-labeled Lumi804-αCD11b may be a promising theranostic pair for monitoring and reducing TAMCs in gliomas to improve immunotherapy responses. FUNDING: A full list of funding bodies that contributed to this study can be found in the Acknowledgements section.

Retention of 64Cu-FLFLF, a Formyl Peptide Receptor 1-Specific PET Probe, Correlates with Macrophage and Neutrophil Abundance in Lung Granulomas from Cynomolgus Macaques.

Neutrophilic inflammation correlates with severe tuberculosis (TB), a disease caused by Mycobacterium tuberculosis (Mtb). Granulomas are lesions that form in TB, and a PET probe for following neutrophil recruitment to granulomas could predict disease progression. We tested the formyl peptide receptor 1 (FPR1)-targeting peptide FLFLF in Mtb-infected macaques. Preliminary studies in mice demonstrated specificity for neutrophils. In macaques, 64Cu-FLFLF was retained in lung granulomas and analysis of lung granulomas identified positive correlations between 64Cu-FLFLF and neutrophil and macrophage numbers (R2 = 0.8681 and 0.7643, respectively), and weaker correlations for T cells and B cells (R2 = 0.5744 and 0.5908, respectively), suggesting that multiple cell types drive 64Cu-FLFLF avidity. By PET/CT imaging, we found that granulomas retained 64Cu-FLFLF but with less avidity than the glucose analog 18F-FDG. These studies suggest that neutrophil-specific probes have potential PET/CT applications in TB, but important issues need to be addressed before they can be used in nonhuman primates and humans.