Objectives: Peptide receptor radionuclide therapy (PRRT) of neuroendocrine tumors (NETs) commonly relies on somatostatin receptor subtype 2 (SSTR2) agonists such as DOTA-TOC/TATE, which may show limited efficacy due to high hepatic uptake and therapy resistance in some patients. SSTR2 antagonists have demonstrated superior tumor targeting. This study aimed to establish the production and quality control of the Actinium-225-labeled SSTR2 antagonist [225Ac]Ac-DOTA-LM3 and to report in-human clinical experience with targeted alpha therapy (TAT). Methods: [225Ac]Ac-DOTA-LM3 was produced by radiolabeling DOTA-LM3 with Actinium-225 under validated conditions. Radiochemical conversion, purity, yield, and stability were assessed using radio-TLC, fractionated radio-HPLC combined with gamma spectroscopy, and in vitro serum stability testing. Clinical feasibility and therapeutic response were evaluated in a patient with metastatic neuroendocrine pancreatic neoplasm refractory to prior 177Lu-based PRRT. Results: Radiolabeling achieved reproducibly high radiochemical purity (>97%) and decay-corrected yields exceeding 80%. The radiopharmaceutical showed high in vitro stability with minimal release of free Actinium-225 over five days. Fractionated radio-HPLC enabled indirect purity assessment. In the reported patient, [225Ac]Ac-DOTA-LM3 therapy resulted in partial remission without clinically relevant hematologic, renal, or hepatic toxicity and was associated with marked clinical improvement. Conclusions: [225Ac]Ac-DOTA-LM3 can be produced with high purity and stability using clinically applicable procedures. In-human results suggest promising efficacy and safety, supporting further clinical investigation of Actinium-225-labeled SSTR2 antagonists for advanced NETs.

Objective: To compare metastatic lesion detection on [68Ga]Ga-DOTA.SA.FAPi and [18F]FDG PET/CT in metastatic breast and lung cancers and to assess the relationship between PET-derived imaging parameters and progression-free survival (PFS). Methods: In this prospective dual-cohort study, 45 patients (23 breast cancer, 22 lung adenocarcinoma) underwent paired [68Ga]Ga-DOTA.SA.FAPi and [18F]FDG PET/CT within four weeks. Semiquantitative (SUVmax, SUVmean) and volumetric (MTV, TLG, STV, TLF) PET parameters were measured. Metastatic detection was compared, and correlations with PFS were assessed. Results: In breast cancer, [18F]FDG demonstrated higher primary tumor uptake, whereas [68Ga]Ga-DOTA.SA.FAPi showed lower background activity, resulting in higher tumor-to-background ratios for brain and bone metastases. Whole-body volumetric indices (wbTLG, wbTLF) showed strong inverse correlations with PFS. In lung adenocarcinoma, volumetric FAPi-derived parameters (wbTLF, wbSTV) demonstrated modest but significant correlations with PFS. [68Ga]Ga-DOTA.SA.FAPi PET/CT detected more brain metastases than [18F]FDG PET/CT in both cohorts (breast: 15/15 vs. 8/15; lung: 14/14 vs. 4/14). Conclusions: [68Ga]Ga-DOTA.SA.FAPi and [18F]FDG PET/CT provide complementary diagnostic and prognostic information. In metastatic breast cancer, FAPi-derived volumetric parameters strongly correlate with PFS and improve detection of brain metastases. In lung adenocarcinoma, [68Ga]Ga-DOTA.SA.FAPi PET/CT offers low background uptake and prognostically relevant stromal metrics. These findings support a potential role for integrating [68Ga]Ga-DOTA.SA.FAPi PET/CT into disease staging, prognostication, and treatment monitoring. This study did not involve prospective assignment to health-related interventions and therefore did not require clinical trial registration.

Radiolabeled somatostatin receptor (SSTR) agonists 68Ga-DOTA-TATE and 68Ga-DOTA-TOC are widely applied for imaging of patients with neuroendocrine tumors (NETs). Preclinical and preliminary clinical evidence has indicated that SSTR antagonists perform better for NET imaging. In this study, we assessed the feasibility of using a new hybrid chelator DATA5m ((6-pentanoic acid)-6-(amino)methyl-1,4-diazepinetriacetate))-conjugated kit-type SSTR antagonist 68Ga-DATA5m-LM4 for PET and evaluated the safety, biodistribution, and preliminary diagnostic efficacy of 68Ga-DATA5m-LM4 in patients with metastatic NETs. Methods: The DATA5m-conjugated form of LM4, was labeled with 68Ga. A total of 27 patients (19 men/8 women; mean age 61 years) with histopathologically confirmed well-differentiated NETs underwent 68Ga-DATA5m-LM4 PET/CT for the staging and restaging or patient selection for PRRT. All the patients underwent PET/CT scans 60 min after intravenous bolus injection of 1.85 MBq (0.05 mCi) per kilogram of body weight (151 ± 54 MBq mean ± SD) of 68Ga-DATA5m-LM4. Results: DATA5m-LM4 was successfully labeled with 68Ga, achieving high yield and purity. After decay correction, radiochemical yields (RCYs) of 80-95% and radiochemical purities (RCP) greater than 98% were obtained. 68Ga -DATA5m-LM4 was well tolerated in all patients, without clinically relevant adverse effects. A significantly lower uptake in normal liver parenchyma was observed with 68Ga-DATA5m-LM4 compared to 68Ga-DOTA-TATE PET/CT (3.90 ± 0.88 vs. 9.12 ± 3.64, P < 0.000001). Additionally, uptake in the thyroid gland, pancreas, and spleen was also lower (P < 0.05). 14 patients underwent 68Ga-DOTA-TOC PET/CT. 68Ga-DATA5m-LM4 uptakes in the liver and spleen were significantly lower than those of 68Ga-DOTA-TOC uptake (3.70 ± 0.79 vs. 5.33 ± 2.43, P = 0.0397; 11.88 ± 6.88 vs. 26.55 ± 16.07, P = 0.0022). Tumor lesions showed high uptake intensity on 68Ga-DATA5m-LM4 PET/CT, with the highest SUVmax up to 167.93 (mean ± SD, 44.47 ± 36.22). With SUVmean of healthy liver, kidneys, and blood pool as background to normalize the SUVmax of the single most intense lesion, tumor-to-background ratios were 20.32 ± 19.97 (range, 3.40 - 98.78) and 4.30 ± 3.03 (range, 0.65 - 14.70), 38.63 ± 35.97 (range, 4.1 - 173.12), respectively. Conclusion: This study demonstrated that the novel SSTR antagonist 68Ga-DATA5m-LM4 can be efficiently labeled with high radiochemical yield and purity, supported by a highly convenient production process. The tracer exhibited excellent imaging performance, with a highly favorable biodistribution characterized by high tumor contrast and minimal uptake in normal organs, particularly the liver, enabling superior lesion detection. The practical advantages of this straightforward labeling process, achieved without any apparent loss in diagnostic efficacy, offer a significant benefit over other competing antagonists. The ease of production, including the potential for a "kit-type" labeling method, makes 68Ga-DATA5m-LM4 an overall extraordinarily promising radiopharmaceutical for the staging and restaging of NET patients.

This study evaluates the potential of a 177Lu-labeled GRPR-targeting antagonist as a radiotherapeutic agent for tumors expressing the gastrin-releasing peptide receptor (GRPR). The therapeutic effect of the radioligand was investigated both as a monotherapy and in combination with the mTOR inhibitor everolimus. The GRPR antagonist, LF1 (AAZTA5-Pip-d-Phe-Gln-Trp-Ala-Val-Gly-His-Sta-Leu-NH2), was synthesized using the chelator AAZTA5 linked via a 4-amino-1-carboxymethylpiperidine (Pip) spacer and radiolabeled with lutetium-177. The preclinical evaluation included assessments of binding kinetics, blood and organ clearance, plasma protein binding, and metabolic stability. SPECT/CT imaging and biodistribution studies were performed in mice bearing PC3 xenograft tumors. To assess its therapeutic efficacy, PC-3-mice were treated with [177Lu]-Lu-LF1 either alone or following everolimus pretreatment. [177Lu]-Lu-LF1 showed high binding affinity (Kd = 0.12 ± 0.01 nM) and favorable pharmacokinetics, including rapid blood clearance and low plasma protein binding (2-3% at 5 and 15 min p.i.). Although subject to enzymatic degradation, the radioligand demonstrated high, sustained, and specific tumor uptake (42 ± 5.0% IA/g at 1 h and 3.9 ± 1.1% IA/g at 144 h p.i.). Pancreatic uptake cleared quickly, allowing for high-contrast SPECT/CT imaging. Therapeutically, tumors treated with 93 MBq of [177Lu]-Lu-LF1 grew more slowly than those treated with 41 MBq. The combination of everolimus and [177Lu]-Lu-LF1 resulted in significant tumor growth inhibition, compared to the relevant monotherapies with either [177Lu]-Lu-LF1 or everolimus. [177Lu]-Lu-LF1 shows promise as a therapeutic radioligand for GRPR-positive prostate cancer, offering high tumor uptake and rapid clearance from nontarget tissues. Mice bearing PC3 xenograft tumors were well tolerated and demonstrated enhanced therapeutic efficacy when combined with everolimus.

This study aims to assess DOTAGA.Glu.(FAPI)2 and DO3A.Glu.(FAPI)2, specifically engineered as precursors for the development of theranostic FAPI-targeted radioligands. DOTAGA.Glu.(FAPI)2 and DO3A.Glu.(FAPI)2 were radiolabeled with gallium-68 and lutetium-177, followed by in vitro (lipophilicity, protein binding, saturation, internalization and externalization) studies on FAP+ CAFs. In vivo (biodistribution, metabolic stability, blood kinetics, PET/SPECT/CT imaging) and ex vivo, (autoradiography, immunohistochemistry) conducted on PC3-mice. Murine dosimetry data were extrapolated to human estimates. All radioligands achievied > 98

PurposeThis study explores the use of fibroblast activation protein inhibitors (FAPI) targeting radiopharmaceuticals as a new approach for pan-cancer treatment, focusing on key factors affecting their effectiveness. We hypothesized that adjusting the administered radiotracer dose one could enhance the tumor-to-background ratios.MethodsIn a dose-escalation study with PC3 xenografts, all radiotracers were administered at doses between 10 and 1500 pmol, followed by biodistribution and PET/CT imaging. Their selectivity towards FAP, PREP, and DDP4, along with their stability in vivo, was assessed by biodistribution and metabolite analysis, respectively. Organ FAP expression was quantified using qPCR, and circulating FAP (sFAP) levels were measured in mouse and human blood samples via ELISA. Proof-of-principle human studies were also conducted.ResultsIncreasing the dose from 10 to 600 pmol significantly reduced blood uptake and enhanced tumor uptake, optimizing their in vivo performance. All radiotracers showed peak efficacy at 350-600 pmol, with altered pharmacokinetics beyond 600 pmol. Biodistribution studies validated the in vivo selectivity of all radiotracers towards FAP, even in the presence of PREP and DPP4 inhibitors, while they demonstrated remarkable stability in vivo. FAP expression was confirmed in various organs, with sFAP quantified in both healthy mice and humans. Human studies with [68Ga]Ga-DOTA.SA.FAPI revealed reduced off-target uptake (e.g., pancreas, salivary glands, heart), aligning with the preclinical findings.ConclusionThe study highlights the crucial need for precise FAPI-radiotracer dosing, optimizing PET imaging, reducing radiation exposure, and enhancing treatment by accounting for FAP biology and sFAP's influence on pharmacokinetics.

This study investigates the theranostic potential of a 44/47Sc-labeled antagonist targeting the gastrin-releasing peptide receptor (GRPR) in prostate and breast tumors. A statine-based GRPR antagonist (AAZTA5-Pip-D-Phe-Gln-Trp-Ala-Val-Gly-His-Sta-Leu-NH2: LF1) was radiolabeled with scandium-44/47. Detailed in vitro evaluation was carried out in PC3 and T47D cancer cells. In vivo studies, including blood and organ clearance, plasma protein binding, metabolic stability and SPECT/CT imaging, were performed in PC3- and T47D-mice. To assess its therapeutic efficacy, PC3-mice were treated with [47Sc]Sc-LF1 either alone or in combination with everolimus. [47Sc]Sc-LF1 exhibited high binding affinity, low internalization rate (< 10

Fibroblast activation protein α (FAP) is a serine protease that has emerged as an attractive, pan-cancer radiotheranostic target. The development of effective FAP-targeting radiotheranostics critically relies on the identification of FAP inhibitors that achieve prolonged tumor retention, thereby maximizing therapeutic efficacy and ensuring sustained tumor irradiation, regardless of radionuclide half-life considerations. Here, we present the design, synthesis, and biological evaluation of potent and selective FAP inhibitors bearing an electrophilic α-ketoamide warhead (ketoFAPIs). Through structure-activity relationship studies, we identified highly potent compounds with selectivity over prolyl oligopeptidase (PREP) by up to 3 orders of magnitude. Moreover, this manuscript shows for the first time that ketoFAPIs can exhibit significantly longer target residence times than first-generation FAPIs comprising an electrophilic carbonitrile warhead, which in turn translates into extended tumor retention in a mouse cancer model. This work lays the groundwork for the use of ketoFAPIs as a versatile platform for the development of FAP-targeted radiopharmaceuticals.

Fibroblast activation protein α (FAP) is a transmembrane serine protease overexpressed in cancer-associated fibroblasts and implicated in tumor progression and fibrosis. Although several FAP inhibitors (FAPIs) show excellent tumor uptake for positron emission tomography (PET) imaging, rapid target dissociation often limits tumor retention and constrains their use in theranostic radioligand therapy. Considerable effort is directed toward FAPI radioligands with prolonged tumor residence time, yet a validated, medium-throughput in vitro method to estimate FAPI-target residence time remains lacking, hindering correct prioritization of lead radioligands for preclinical evaluation. In this study, we employ a jump-dilution assay to determine the dissociation rate constant (koff) of FAPIs under tight-binding conditions, providing a direct handle on drug-target residence time (τ = 1/koff). We combine this assay with progress-curve assays to determine the association rate constant (kon) and inhibition constant (Kᵢ). By resolving binding kinetics, especially koff, this approach addresses limitations of conventional IC50-based screening, offering a finer discrimination among leads and enabling data-driven ranking based on target residence time. We demonstrate the utility of this workflow through a kinetic structure-activity relationship (SAR) analysis on FAPIs with varying structural features and warhead chemistries (carbonitrile, α-ketoamide). Molecular docking studies allowed us to correlate experimental kinetic parameters with predicted binding modes within the three-dimensional structure of FAP, focusing on critical interactions within the active site. These findings highlight the value of kinetic profiling in FAPI development and support the rational design of theranostic agents with prolonged target retention.

Aim: The study aimed to analyze the long-term outcomes of [177Lu]Lu-DOTAGA.FAPi dimer therapy in individuals diagnosed with radioiodine-resistant (RAI-R) follicular cell-derived thyroid cancer. Materials and Methods: In this retrospective study, 73 patients with RAI-R follicular thyroid carcinoma who had undergone multiple lines of previous treatments were included. Following [68Ga]Ga-DOTA.SA.FAPi positron emission tomography-computed tomography scan, among the 73 patients, 65 received [177Lu]Lu-DOTAGA.FAPi dimer monotherapy with a median activity of 5.5 GBq per cycle at 8-week intervals. The remaining eight patients underwent tandem [177Lu]Lu/[225Ac]Ac-DOTAGA.FAPi dimer therapy, consisting of a median of two cycles of [177Lu]Lu-DOTAGA.FAPi dimer followed by one cycle of [225Ac]Ac-DOTAGA.FAPi dimer, also at 8-week intervals. The primary endpoint included progression-free survival (PFS) and overall survival (OS). Secondary endpoints included PERCIST criteria response assessment and safety assessment according to Common Terminology Criteria for Adverse Events (V5.0). Results: We enrolled 37 female and 36 male patients, with a mean age of 54.3 years (range: 27 - 80 years). The patients received a median cumulative activity of 22.2 GBq (range, 4 GBq-55.5 GBq) of [177Lu]Lu-DOTAGA-FAPi dimer over one to nine cycles, with a median of three cycles. Among 73 patients, 20 died and 16 deaths were due to thyroid cancer. Nineteen patients experienced disease progression, with an estimated median PFS of 29 months [CI 14-34 months]. The estimated median OS was 32 months [CI 21-40 months]. Four patients (5.4%) encountered grade III anemia, primarily linked to bone metastasis in three cases and neck tumor mass bleed in one. Grade III thrombocytopenia occurred in three patients (4%). No grade III renal or hepatotoxicity was observed. Conclusion: In this study, [177Lu]Lu-DOTAGA.FAPi dimer therapy showed promising safety and efficacy in aggressive, radioiodine-resistant thyroid cancer, achieving a median PFS and OS of 29 and 32 months, respectively, with manageable adverse events. Confirmation of our findings is needed from prospective clinical trials comparing [177Lu]Lu-DOTAGA.FAPi dimer therapy to other treatments.

Purpose This study aimed to compare the diagnostic efficacy of [ 68 Ga]Ga-DOTA.SA.FAPi and [ 18 F]F-FDG PET/CT for detecting primary and metastatic lesions in sarcoma patients. Materials and Methods The analysis included both patient-based and lesion-based comparisons of PET/CT scans in individuals with histologically confirmed sarcoma. Results A total of 23 sarcoma patients (mean age 43.0 ± 16.5 years; range: 21–76 years) underwent both [ 18 F]F-FDG and [ 68 Ga]Ga-DOTA.SA.FAPi PET/CT scans. Histological distribution included 30% synovial sarcoma, 13% liposarcoma, and 21.7% leiomyosarcoma, with 70% of patients presenting with distant metastases. Detection rates for primary tumors were similar between [ 68 Ga]Ga-DOTA.SA.FAPi and [ 18 F]F-FDG PET/CT (85.7% vs 100%, P = 0.149). Lymph node detection rates were also comparable (80% vs 100%, P = 0.146). Lesion-based analysis revealed that [ 68 Ga]Ga-DOTA.SA.FAPi detected 220 lesions (83% efficiency) compared with 249 lesions (94% efficiency) for [ 18 F]F-FDG ( P < 0.0001). Notably, [ 68 Ga]Ga-DOTA.SA.FAPi demonstrated superior detection of liver (54 vs 38 lesions, P < 0.0001) and bone metastases (125 vs 102 lesions, P < 0.0001). Conclusion Our study shows that although [ 18 F]F-FDG PET/CT offers superior overall lesion detection efficiency, [ 68 Ga]Ga-DOTA.SA.FAPi PET/CT excels in identifying specific metastatic sites, particularly in bone and liver. These findings highlight the complementary roles of both imaging modalities in sarcoma evaluation.

Background/Objectives: Radiolabeled fibroblast activation protein inhibitors (FAPIs) are emerging as promising imaging agents assessing fibrotic diseases. This study evaluates [68Ga]Ga-DATA5m.SA.FAPi for imaging pulmonary fibrosis in two mouse models, bleomycin-induced (BLM) and a transgenic (fra-2tg) model, both displaying characteristics of human pulmonary fibrotic diseases. Methods: In the BLM model, C57BL/6 mice were treated with bleomycin or isotonic sodium chloride (controls) for 4, 5, and 6 weeks, followed by [68Ga]Ga-DATA5m.SA.FAPi PET/CT scans. Fra-2tg mice and wildtype (WT) littermates underwent at 7, 11, and 18/19 weeks of age a PET/CT scan. The selected timepoints correspond to early, middle, and late disease stages for each model. Imaging was complemented by ex vivo quantification, histological, and immunohistochemical (IHC) analyses. Results: In BLM mice, pulmonary [68Ga]Ga-DATA5m.SA.FAPi uptake showed a trend toward increase as early as 5 weeks of treatment compared with the controls, which was confirmed by ex vivo analysis (BLM: 3.31 ± 0.29%ID/g, n = 5; control: 1.61 ± 0.29%ID/g, n = 4; p = 0.0035). In fra-2tg mice, no significant differences could be detected. IHC revealed elevated pulmonary FAP expression specifically at early (BLM) and mild (fra-2tg) disease stages, whereas for BLM, tracer uptake was more pronounced at later stages. Conclusions: Our findings complement and extend observations from previous studies and support the potential of FAPI tracers as molecular imaging agents for pulmonary fibrosis.

Background/Objectives: Fibroblast activation protein (FAP) has gained tremendous traction as a target for tumor imaging and cancer treatment, while also playing a key role in fibrosis. Our study aimed to evaluate [68Ga]Ga-DATA5m.SA.FAPi for PET imaging of replacement fibrosis following myocardial infarction (MI) or interstitial fibrosis associated with hypertrophy. Methods: MI or transverse aortic constriction (TAC)-induced hypertrophy was induced in C57BL/6 mice, with sham-operated animals serving as controls. At multiple time points during disease progression (1, 2, and 6 weeks post-surgery), [68Ga]Ga-DATA5m.SA.FAPi PET/CT scans were performed, followed by ex vivo investigations. Additionally, in vitro cell uptake experiments simulating hypertrophy were conducted. Results: Cardiac uptake of [68Ga]Ga-DATA5m.SA.FAPi significantly increased two weeks after MI induction (MI: 2.1 ± 0.2%ID/g, n = 7 vs. SHAM: 1.1 ± 0.2%ID/g, n = 5; p = 0.002), confirmed by ex vivo autoradiography. No significant difference was observed at six weeks post-MI (MI: 1.1 ± 0.1%ID/g, n = 4 vs. SHAM: 0.8 ± 0.0%ID/g, n = 3), indicating infarct healing completion. In contrast, TAC mice showed increased uptake after six weeks (TAC: 1.8 ± 0.2%ID/g, n = 6; p = 0.007), related to interstitial fibrosis progression. Consistently, high-stretched cardiac fibroblasts demonstrated a higher uptake compared to low-stretched conditioned ones, suggesting the stretch mediates regulation of FAP. Conclusions: This study demonstrated the efficacy of [68Ga]Ga-DATA5m.SA.FAPi for longitudinal imaging of cardiac fibrosis in response to different cardiac injuries. In vivo FAP imaging during cardiac remodeling may serve as a valuable tool for diagnosing and predicting disease progression, ultimately aiding in the clinical management of patients.

Purpose This study aimed to assess the biodistribution and radiation dosimetry of 68Ga-DATA5m LM4 in patients with gastroenteropancreatic neuroendocrine tumors. Patients and Methods Eight patients (5 females and 3 males) with various gastroenteropancreatic neuroendocrine tumors were included in the study. Each patient underwent 3 whole-body PET scans at 10, 60, and 120 minutes after receiving an IV injection of approximately 162.5 MBq of 68Ga-DATA5m LM4. Organs considered for dosimetric analysis included the liver, heart, spleen, kidneys, adrenal glands, and lumbar vertebrae (L2 to L4). Dosimetric calculations were performed using the OLINDA/EXM 2.2 software. Results Physiological uptake of 68Ga-DATA5m LM4 was observed in the pituitary gland, spleen, liver, adrenal glands, and the urinary tract (kidneys and urinary bladder) for all patients. The kidneys received the highest absorbed doses at (4.77E-02 ± 1.49E-02 mSv/MBq). The mean effective dose was 2.61E-03 ± 5.99E-04 mSv/MBq. Conclusions 68Ga-DATA5m LM4 injection is safe and is primarily excreted through urine, delivering the highest radiation dose to the kidneys.