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Human periodontal ligament cells (hPDLCs) contain multipotent postnatal stem cells that can differentiate into PDL fibroblasts, osteoblasts, and cementoblasts. Interaction between the extracellular environment and stem cells is an important factor for differentiation into other progenitor cells. To identify cell surface molecules that induce PDL fibroblastic differentiation, we developed a series of monoclonal antibodies against membrane/ECM molecules. One of these antibodies, an anti-PDL25 antibody, recognizes approximately a 100 kDa protein, and this antigenic molecule accumulates in the periodontal ligament region of tooth roots. By mass spectrometric analysis, we found that the antigenic molecule recognized by the anti-PDL25 antibody is fibroblast activation protein α (FAPα). The expression level of FAPα/PDL25 increased in TGF-ß1-induced PDL fibroblasts, and this protein was localized in the cell boundaries and elongated processes of the fibroblastic cells. Ectopic expression of FAPα induced fibroblastic differentiation. In contrast, expression of representative markers for PDL differentiation was decreased by knock down and antibody blocking of FAPα/PDL25. Inhibition of dipeptidyl peptidase activity by a potent FAPα inhibitor dramatically inhibited PDL fibroblastic marker expression but did not affect in cell proliferation and migration.

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Fibroblast activation protein (FAP) is abundantly expressed in the stroma of most human solid tumors. Clinical-stage radiolabeled FAP ligands are increasingly used as tools for the detection of various cancer lesions. To unleash the full therapeutic potential of FAP-targeting agents, ligands need to remain at the tumor site for several days after administration. We recently described the discovery of OncoFAP, a high-affinity small organic ligand of FAP with a rapid accumulation in tumors and low uptake in healthy tissues in cancer patients. Trimerization of OncoFAP provided a derivative (named TriOncoFAP, or OncoFAP-23) with improved FAP affinity. In this work, we evaluated the tissue biodistribution profile and the therapeutic performance of OncoFAP-23 in tumor-bearing mice. Methods: OncoFAP-23 was radiolabeled with the theranostic radionuclide 177Lu. Preclinical experiments were conducted on mice bearing SK-RC-52.hFAP (BALB/c nude mice) or CT-26.hFAP (BALB/c mice) tumors. 177Lu-OncoFAP and 177Lu-FAP-2286 were included in the biodistribution study as controls. Toxicologic evaluation was performed on Wistar rats and CD1 mice by injecting high doses of OncoFAP-23 or its cold-labeled counterpart, respectively. Results: 177Lu-OncoFAP-23 emerged for its best-in-class biodistribution profile, high and prolonged tumor uptake (i.e., ∼16 percentage injected dose/g at 96 h), and low accumulation in healthy organs, which correlates well with its potent single-agent anticancer activity at low levels of administered radioactivity. Combination treatment with the tumor-targeted interleukin 2 (L19-IL2, a clinical-stage immunocytokine) further expands the therapeutic window of 177Lu-OncoFAP-23 by potentiating its in vivo antitumor activity. Proteomics studies revealed a potent tumor-directed immune response on treatment with the combination. OncoFAP-23 and natLu-OncoFAP-23 exhibited a favorable toxicologic profile, without showing any side effects or signs of toxicity. Conclusion: OncoFAP-23 presents enhanced tumor uptake and tumor retention and low accumulation in healthy organs, findings that correspond to a strongly improved in vivo antitumor efficacy. The data presented in this work support the clinical development of 177Lu-OncoFAP-23 for the treatment of FAP-positive solid tumors.

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Fibrous dysplasia (FD) is a mosaic skeletal disorder involving the development of benign, expansile fibro-osseous lesions during childhood that cause deformity, fractures, pain, and disability. There are no well-established treatments for FD. Fibroblast activation protein (FAPα) is a serine protease expressed in pathological fibrotic tissues that has promising clinical applications as a biomarker and local pro-drug activator in several pathological conditions. In this study, we explored the expression of FAP in FD tissue and cells through published genetic expression datasets and measured circulating FAPα in plasma samples from patients with FD and healthy donors. We found that FAP genetic expression was increased in FD tissue and cells, and present at higher concentrations in plasma from patients with FD compared to healthy donors. Moreover, FAPα levels were correlated with skeletal disease burden in patients with FD. These findings support further investigation of FAPα as a potential imaging and/or biomarker of FD, as well as a pro-drug activator specific to FD tissue.

Asunto(s)

Endopeptidasas , Displasia Fibrosa Ósea , Gelatinasas , Proteínas de la Membrana , Serina Endopeptidasas , Humanos , Serina Endopeptidasas/metabolismo , Serina Endopeptidasas/genética , Femenino , Masculino , Endopeptidasas/metabolismo , Endopeptidasas/genética , Gelatinasas/metabolismo , Gelatinasas/genética , Proteínas de la Membrana/metabolismo , Proteínas de la Membrana/genética , Displasia Fibrosa Ósea/metabolismo , Displasia Fibrosa Ósea/genética , Displasia Fibrosa Ósea/patología , Adulto , Adolescente , Niño , Biomarcadores/metabolismo , Biomarcadores/sangre , Osteoblastos/metabolismo , Osteoblastos/patología , Persona de Mediana Edad

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OBJECTIVES: Mesenchymal stromal cells in muscles participate in regeneration following muscle injury. This study explored the potential of [18F]fibroblast activation protein inhibitor (FAPI)-42 positron emission tomography (PET) targeting mesenchymal stromal cells to evaluate disease activity of idiopathic inflammatory myopathy (IIM). METHODS: Patients with IIM (n = 26) were prospectively included and underwent [18F]FAPI-42 PET/CT and whole-body MRI between January 2023 and July 2023. Patients with malignancies were retrospectively included in the control group and only underwent [18F]FAPI-42 PET/CT (n = 28). [18F]FAPI-42 PET/CT images were evaluated using for avid-FAPI uptake and the target-to-background ratio (TBR). Whole-body MRI was evaluated for oedema, fatty infiltration, and atrophy in 42 muscles in the IIM group. The global FAPI- and MRI-derived parameters were calculated for each. PATIENT: . Clinical assessment of disease activity and muscle strength were collected. RESULTS: Patients with IIM had significantly higher global FAPI-avid muscle ratios (0.68 [interquartile range (IQR): 0.45, 0.79] vs 0.06 [IQR: 0, 0.11], p< 0.001) and global muscle TBR (2.26 [IQR: 1.71, 2.75] vs 1.23 [IQR: 1.02, 1.52], p< 0.001) compared with controls. In the IIM group, the median TBR was higher in muscles with oedema than in those without (2.44 [IQR: 1.46, 3.27] vs 1.31 [IQR: 0.95, 1.99], p< 0.001). Global FAPI-avid muscle ratios significantly correlated with global oedema score (r = 0.833), muscle strength (r=-0.649), serum creatine kinase (r = 0.456), and disease activity index (r = 0.495-0.621). CONCLUSION: Increased [18F]FAPI-42 uptake was associated with muscle oedema in IIM. FAPI-derived parameters correlated with IIM disease activity. [18F]FAPI-42 is a promising PET tracer for evaluating IIM disease activity.

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PURPOSE: Targeted radionuclide therapy (TRT) is a cancer treatment with relative therapeutic efficacy across various cancer types. We studied the therapeutic potential of TRT using fibroblast activation protein-α (FAP) targeting sdAbs (4AH29) labelled with 225Ac or 131I in immunocompetent mice in a human FAP (hFAP) expressing lung cancer mouse model. We further explored the combination of TRT with programmed cell death ligand 1 (PD-L1) immune checkpoint blockade (ICB). METHODS: We studied the biodistribution and tumour uptake of [131I]I-GMIB-4AH29 and [225Ac]Ac-DOTA-4AH29 by ex vivo γ-counting. Therapeutic efficacy of [131I]I-GMIB-4AH29 and [225Ac]Ac-DOTA-4AH29 was evaluated in an immunocompetent mouse model. Flow cytometry analysis of tumours from [225Ac]Ac-DOTA-4AH29 treated mice was performed. Treatment with [225Ac]Ac-DOTA-4AH29 was repeated in combination with PD-L1 ICB. RESULTS: The biodistribution showed high tumour uptake of [131I]I-GMIB-4AH29 with 3.5 ± 0.5% IA/g 1 h post-injection (p.i.) decreasing to 0.9 ± 0.1% IA/g after 24 h. Tumour uptake of [225Ac]Ac-DOTA-4AH29 was also relevant with 2.1 ± 0.5% IA/g 1 h p.i. with a less steep decrease to 1.7 ± 0.2% IA/g after 24 h. Survival was significantly improved after treatment with low and high doses [131I]I-GMIB-4AH29 or [225Ac]Ac-DOTA-4AH29 compared to vehicle solution. Moreover, we observed significantly higher PD-L1 expression in tumours of mice treated with [225Ac]Ac-DOTA-4AH29 compared to vehicle solution. Therefore, we combined high dose [225Ac]Ac-DOTA-4AH29 with PD-L1 ICB showing therapeutic synergy. CONCLUSION: [225Ac]Ac-DOTA-4AH29 and [131I]I-GMIB-4AH29 exhibit high and persistent tumour targeting, translating into prolonged survival in mice bearing aggressive tumours. Moreover, we demonstrate that the combination of PD-L1 ICB with [225Ac]Ac-DOTA-4AH29 TRT enhances its therapeutic efficacy.

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Introduction: Fibroblast activation protein (FAP) overexpression on cancer-associated fibroblasts (CAFs) is associated with poor prognosis and worse clinical outcomes. Selective ablation of pro-tumorgenic FAP+ stromal cells with CAR-T cells may be a new therapeutic strategy. However, the clinical use of FAP-CAR T cells is suggested to proceed with caution for occasional poor efficacy and induction of on-target off-tumor toxicity (OTOT), including lethal osteotoxicity and cachexia. Hence, more investigations and preclinical trials are required to optimize the FAP-CAR T cells and to approve their safety and efficacy. Methods: In this study, we designed second-generation CAR T cells targeting FAP with 4-1BB as a co-stimulatory molecule, and tested their cytotoxicity against FAP-positive cells (hFAP-HT1080 cells and a variety of primary CAFs) in vitro and in Cell line-derived xenograft (CDX) and a patient-derived xenograft (PDX) model. Results: Results showed that our FAP-CAR T cells were powerfully potent in killing human and murine FAP-positive tumor cells and CAFs in multiple types of tumors in BALB/c and C57BL/6 mice and in patient-derived xenografts (PDX) model. And they were proved to be biologically safe and exhibit low-level OTOT. Discussion: Taken together, the human/murine cross-reactive FAP-CAR T cells were powerfully potent in killing human and murine FAP positive tumor cells and CAFs. They were biologically safe and exhibit low-level OTOT, warranting further clinical investigation into our FAP-CAR T cells.

Asunto(s)

Inmunoterapia Adoptiva , Receptores Quiméricos de Antígenos , Animales , Femenino , Humanos , Ratones , Fibroblastos Asociados al Cáncer/inmunología , Fibroblastos Asociados al Cáncer/metabolismo , Línea Celular Tumoral , Reacciones Cruzadas/inmunología , Endopeptidasas , Gelatinasas/inmunología , Gelatinasas/metabolismo , Inmunoterapia Adoptiva/métodos , Inmunoterapia Adoptiva/efectos adversos , Proteínas de la Membrana/inmunología , Proteínas de la Membrana/genética , Ratones Endogámicos BALB C , Ratones Endogámicos C57BL , Neoplasias/inmunología , Neoplasias/terapia , Receptores Quiméricos de Antígenos/inmunología , Receptores Quiméricos de Antígenos/genética , Serina Endopeptidasas/inmunología , Serina Endopeptidasas/genética , Serina Endopeptidasas/metabolismo , Linfocitos T/inmunología , Ensayos Antitumor por Modelo de Xenoinjerto

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Idiopathic pulmonary fibrosis (IPF) is a devastating condition characterized by progressive lung scarring and uncontrolled fibroblast proliferation, inevitably leading to organ dysfunction and mortality. While elevated iron levels have been observed in patients and animal models of lung fibrosis, the mechanisms linking iron dysregulation to lung fibrosis pathogenesis, particularly the role of macrophages in orchestrating this process, remain poorly elucidated. Here we evaluate iron metabolism in macrophages during pulmonary fibrosis using both in vivo and in vitro approaches. In murine bleomycin- and amiodarone-induced pulmonary fibrosis models, we observed significant iron deposition and lipid peroxidation in pulmonary macrophages. Intriguingly, the ferroptosis regulator glutathione peroxidase 4 (GPX4) was upregulated in pulmonary macrophages following bleomycin instillation, a finding corroborated by single-cell RNA sequencing analysis. Moreover, macrophages isolated from fibrotic mouse lungs exhibited increased transforming growth factor (TGF)-ß1 expression that correlated with lipid peroxidation. In vitro, iron overload in bone marrow-derived macrophages triggered lipid peroxidation and TGF-ß1 upregulation, which was effectively suppressed by ferroptosis inhibitors. When co-cultured with iron-overloaded macrophages, lung fibroblasts exhibited heightened activation, evidenced by increased α-smooth muscle actin and fibronectin expression. Importantly, this pro-fibrotic effect was attenuated by treating macrophages with a ferroptosis inhibitor or blocking TGF-ß receptor signaling in fibroblasts. Collectively, our study elucidates a novel mechanistic paradigm in which the accumulation of iron within macrophages initiates lipid peroxidation, thereby amplifying TGF-ß1 production, subsequently instigating fibroblast activation through paracrine signaling. Thus, inhibiting iron overload and lipid peroxidation warrants further exploration as a strategy to suppress fibrotic stimulation by disease-associated macrophages.

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Disulfiram (DSF), an FDA-approved drug for treating alcoholism, has been verified with Cu2+-dependent anticancer activity by forming Cu(DTC)2, the complex of one of its metabolites diethyldithiocarbamate (DTC) and Cu2+. Nevertheless, the antitumor effect is limited by insufficient Cu(DTC)2 formation in suit and off-target system toxicity. Herein, we developed a fibroblast activation protein α (FAPα) activatable nanoagent (HfD-HID-Cu) for co-delivery of DTC polymeric prodrug and exogenous Cu2+ to achieve enhanced cancer-specific therapy and activatable in situ fluorescence imaging meanwhile. HfD-HID-Cu was simply constructed through the co-assembly of the DTC polymeric prodrug (HA-fap-DTC) and the copper-loaded IR808-conjugated polymer (HA-IR-DPA-Cu), which could serve as the "OFF-to-ON" switch for chemotherapy and fluorescence. With the high expression of FAPα in tumor tissues, HA-fap-DTC could be activated specifically to release DTC, while maintaining inactive in normal tissues. The liberated DTC within tumor tissues could contend for Cu2+ from HA-IR-DPA-Cu, resulting in the formation of highly cytotoxic Cu(DTC)2in situ for chemotherapy, concomitant with the fluorescence recovery of cyanine dye for tumor imaging. This work provides an effective strategy for co-delivery of DTC prodrug and Cu2+ for tumor theranostic with improved selectivity and minimal side effects. STATEMENT OF SIGNIFICANCE: DSF-based antitumor therapy is highly dependent on Cu2+. However, the non-synchronous distribution of DSF/DTC and Cu2+ in tumor tissues attenuates the antitumor efficacy. The insufficient Cu(DTC)2 formation in suit and off-target distribution greatly limit the anti-tumor application. This study provides a nanoagent for co-delivery of DTC polymeric prodrug and Cu2+ by simple co-assembly to achieve their synchronous tumor distribution. It can be selectively activated by FAPα, forming cytotoxic Cu(DTC)2in suit for tumor-specific chemotherapy and reducing the systemic toxicity. In addition to chemotherapy, the nanoagent can emit fluorescence under the sequential triggering of FAPα and released DTC for tumor imaging. Overall, this study renders a promising strategy for improved Cu(DTC)2-based antitumor therapy and imaging.

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The aim of this study was to synthesize a quinoline-based MRI contrast agent, Gd-DOTA-FAPI04, and assess its capacity for targeting fibroblast activation protein (FAP)-positive tumors in vivo. Gd-DOTA-FAPI04 was synthesized by attaching a 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) complex of gadolinium(III) to FAP inhibitor FAPI04. The longitudinal relaxation time (T1) of the contrast agent was measured using a Siemens Prisma 3.0T MR system, and the CCK-8 assay was performed to evaluate its potential cytotoxicity. Male nude mice bearing tumors grown from FAP-expressing fibrosarcoma cells were divided into experimental (n = 4) and control (n = 4) groups, and T1-weighted image enhancement was measured at different times (0, 10, 30, 60, 90, and 120 min) postinjection of Gd-DOTA-FAPI04. The control group received an additional preinjection of excess FAPI04. FAP expression in tumor tissue was investigated by using immunohistochemistry with an anti-FAP antibody. The longitudinal relaxivities of gadodiamide and Gd-DOTA-FAPI04 were measured to be 3.734 mM-1 s-1 and 5.323 mM-1 s-1, respectively. The CCK-8 assay demonstrated that Gd-DOTA-FAPI04 has minimal toxicity to cultured human fibrosarcoma cells. In vivo MRI showed that peak accumulation of Gd-DOTA-FAPI04 in FAP-expressing tumors occurred 1 h postinjection and could be blocked by preinjection of excess FAPI04. Immunohistochemical analysis of harvested tumor tissue supported the above findings. Gd-DOTA-FAPI04 is a promising contrast agent for in vivo imaging of FAP.

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Background: Accurately and promptly predicting the response of gastrointestinal stromal tumors (GISTs) to targeted therapy is essential for optimizing treatment strategies. However, some fractions of recurrent or metastatic GISTs present as non-FDG-avid lesions, limiting the value of [18F]fluorodeoxyglucose positron emission tomography/computed tomography ([18F]FDG PET/CT) in treatment evaluation. This study evaluated the efficacy of [18F]F-fibroblast activation protein inhibitor (FAPI)-42 [18F]FAPI-42) PET/CT for assessing the treatment response in recurrent or metastatic GISTs, in comparison to [18F]FDG PET/CT and explores a model integrating PET/CT imaging and clinical parameters to optimize the clinical use of these diagnostic tools. Methods: Our retrospective analysis included 27 patients with recurrent or metastatic GISTs who underwent [18F]FAPI-42 PET/CT and [18F]FDG PET/CT at baseline before switching targeted therapy. Treatment response status was divided into a progression group (PG) and a non-progression group (NPG) based on the Response Criteria in Solid Tumors (RECIST) 1.1, according to the contrast-enhanced computed tomography (CT) scan at six months. [18F]FAPI-42 and [18F]FDG PET/CT parameters including the mean standardized uptake value (SUVmean), the standard uptake value corrected for lean body mass (SULpeak), the maximum standardized uptake value (SUVmax), tumor-to-blood pool SUV ratio (TBR), tumor-to-liver SUV ratio (TLR), metabolic tumor volume (MTV)/FAPI-positive tumor volume (GTV-FAPI), total lesion glycolysis (TLG)/FAPI-positive total lesion accumulation (TLF) were correlated with the response status to identify indicative of treatment response. The predictive performance of them was quantified by generating receiver operating characteristic curves (ROC), calibration curves, and cross-validation. Results: A total of 110 lesions were identified in 27 patients. Compared with PG, NPG was associated with lower levels of TBR and SUVmean in FDG PET/CT (TBR-FDG, SUVmean-FDG; P=0.033 and P=0.038, respectively), with higher SULpeak and TLF in FAPI PET/CT (SULpeak-FAPI, TLF-FAPI; P=0.10 and P=0.049, respectively). The predictive power of a composite-parameter model, including TBR-FDG, SULpeak-FAPI, gene mutation, and type of targeted therapy [area under the curve (AUC) =0.865], was superior to the few-parameter models incorporating TBR-FDG (AUC =0.637, P<0.001), SULpeak-FAPI (AUC =0.665, P<0.001) or both (AUC =0.721, P<0.001). Conclusions: Both [18F]FAPI-42 PET/CT and [18F]FDG PET/CT have value in predicting the treatment response of recurrent or metastatic GISTs. And [18F]FAPI-42 PET/CT offers synergistic value when used in combination with [18F]FDG PET/CT. Notably, the nomogram generated from the model incorporating [18F]FAPI-42 PET/CT, [18F]FDG PET/CT parameters, gene mutation, and type of targeted therapy could yield more precise predictions of the response of recurrent metastatic GISTs.

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Purpose: 68Ga-labeled fibroblast activation protein inhibitor (FAPI) is a novel PET tracer with great potential for staging pancreatic cancer. Data on locally advanced or recurrent disease is sparse, especially on tracer uptake before and after high dose chemoradiotherapy (CRT). The aim of this study was to evaluate [68Ga]Ga-FAPI-46 PET/CT staging in this setting. Methods: Twenty-seven patients with locally recurrent or locally advanced pancreatic adenocarcinoma (LRPAC n = 15, LAPAC n = 12) in stable disease or partial remission after chemotherapy underwent FAPI PET/CT and received consolidation CRT in stage M0 with follow-up FAPI PET/CT every three months until systemic progression. Quantitative PET parameters SUVmax, SUVmean, FAPI-derived tumor volume and total lesion FAPI-uptake were measured in baseline and follow-up PET/CT scans. Contrast-enhanced CT (ceCT) and PET/CT data were evaluated blinded and staged according to TNM classification. Results: FAPI PET/CT modified staging compared to ceCT alone in 23 of 27 patients in baseline, resulting in major treatment alterations in 52% of all patients (30%: target volume adjustment due to N downstaging, 15%: switch to palliative systemic chemotherapy only due to diffuse metastases, 7%: abortion of radiotherapy due to other reasons). Regarding follow-up scans, major treatment alterations after performing FAPI PET/CT were noted in eleven of 24 follow-up scans (46%) with switch to systemic chemotherapy or best supportive care due to M upstaging and ablative radiotherapy of distant lymph node and oligometastasis. Unexpectedly, in more than 90 % of the follow-up scans, radiotherapy did not induce local fibrosis related FAPI uptake. During the first follow-up, all quantitative PET metrics decreased, and irradiated lesions showed significantly lower FAPI uptake in locally controlled disease (SUVmax p = 0.047, SUVmean p = 0.0092) compared to local failure. Conclusion: Compared to ceCT, FAPI PET/CT led to major therapeutic alterations in patients with LRPAC and LAPAC prior to and after radiotherapy, which might help identify patients benefiting from adjustments in every treatment stage. FAPI PET/CT should be considered a useful diagnostic tool in LRPAC or LAPAC before and after CRT.

Asunto(s)

Quimioradioterapia , Radioisótopos de Galio , Recurrencia Local de Neoplasia , Estadificación de Neoplasias , Neoplasias Pancreáticas , Tomografía Computarizada por Tomografía de Emisión de Positrones , Humanos , Tomografía Computarizada por Tomografía de Emisión de Positrones/métodos , Femenino , Masculino , Persona de Mediana Edad , Anciano , Neoplasias Pancreáticas/terapia , Neoplasias Pancreáticas/diagnóstico por imagen , Neoplasias Pancreáticas/patología , Neoplasias Pancreáticas/tratamiento farmacológico , Quimioradioterapia/métodos , Adulto , Radiofármacos , Adenocarcinoma/terapia , Adenocarcinoma/diagnóstico por imagen , Adenocarcinoma/patología , Adenocarcinoma/tratamiento farmacológico , Anciano de 80 o más Años , Quinolinas

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Fibroblast Activation Protein Inhibitor (FAPI) positron emission tomography (PET) imaging has emerged as a useful method for identifying pancreatic disorders, notably pancreatitis. Unlike Fluorine-18 fluorodeoxyglucose (FDG), FAPI uptake is directly proportional to the degree of fibrosis, making it very useful in separating pancreatic tumors from inflammation. Recent investigations have shown that FAPI positron emission tomography/computer tomography (PET/CT) can identify pancreatic inflammation with great sensitivity, providing vital diagnostic information. In this case study, a 52-year-old male with a history of Ewing sarcoma presented with epigastric pain. Pancreatitis was confirmed on a computer tomography (CT) scan showing mild fat stranding in the pancreatic body and tail, in addition to a significant increase in pancreatic head mass, necessitating further evaluation with FDG PET/CT and FAPI PET/CT, as the patient was known to have metastatic sarcoma. While FDG PET/CT revealed an avid infiltrative lesion in the duodenal/pancreatic head area, FAPI PET/CT showed diffuse uptake in the pancreatic body and tail, indicating fibroblast-mediated inflammation consistent with pancreatitis. This case demonstrates the usefulness of FAPI imaging in discriminating between pancreatic metastasis and pancreatitis, with FAPI PET/CT providing crucial diagnostic information when FDG uptake is ambiguous.

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Fibroblast activation protein-α (FAP) has emerged as a promising target in the field of radiopharmaceuticals due to its selective expression in cancer-associated fibroblasts (CAFs) and other pathological conditions involving fibrosis and inflammation. Recent advancements have focused on developing FAP-specific radioligands for diagnostic imaging and targeted radionuclide therapy. This perspective summarized the latest progress in FAP radiopharmaceutical development, highlighting novel radioligands, preclinical evaluations, and potential clinical applications. Additionally, we analyzed the advantages and existing problems of targeted FAP radiopharmaceuticals, and discussed the key breakthrough directions of this target, so as to improve the development and conversion of FAP-targeted radiopharmaceuticals.

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Endopeptidasas , Gelatinasas , Proteínas de la Membrana , Radiofármacos , Serina Endopeptidasas , Humanos , Radiofármacos/química , Radiofármacos/farmacología , Endopeptidasas/metabolismo , Animales , Gelatinasas/metabolismo , Gelatinasas/antagonistas & inhibidores , Serina Endopeptidasas/metabolismo , Proteínas de la Membrana/metabolismo , Proteínas de la Membrana/antagonistas & inhibidores

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A major challenge in prevention and early treatment of organ fibrosis is the lack of valuable tools to assess the evolving profibrotic maladaptive repair after injury in vivo in a non-invasive way. Here, using acute kidney injury (AKI) as an example, we tested the utility of fibroblast activation protein (FAP) imaging for dynamic assessment of maladaptive repair after injury. The temporospatial pattern of kidney FAP expression after injury was first characterized. Single-cell RNA sequencing and immunostaining analysis of patient biopsies were combined to show that FAP was specifically upregulated in kidney fibroblasts after AKI and was associated with fibroblast activation and chronic kidney disease (CKD) progression. This was corroborated in AKI mouse models, where a sustained and exaggerated kidney FAP upregulation was coupled to persistent fibroblast activation and a fibrotic outcome, linking kidney FAP level to post-insult maladaptive repair. Furthermore, using positron emission tomography (PET)/CT scanning with FAP-inhibitor tracers ([18F]FAPI-42, [18F]FAPT) targeting FAP, we demonstrated the feasibility of non-invasively tracking of maladaptive repair evolution toward kidney fibrosis. Importantly, a sustained increase in kidney [18F]FAPT (less hepatobiliary metabolized than [18F]FAPI-42) uptake reflected persistent kidney upregulation of FAP and characterized maladaptive repair after AKI. Kidney [18F]FAPT uptake at hour 2-day 7 correlated with kidney fibrosis 14 days after AKI. Similar changes in [18F]FAPI-42 PET/CT imaging were observed in patients with AKI and CKD progression. Thus, persistent kidney FAP upregulation after AKI was associated with maladaptive repair and a fibrotic outcome. Hence, FAP-specific PET/CT imaging enables dynamic visualization of maladaptive repair after AKI and prediction of kidney fibrosis within a clinically actionable window.

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PURPOSE: The fibroblast activation protein inhibitor-04 (FAPI-04) specifically binds to the FAP of activated myocardial fibroblasts, which makes 68Ga-labelled FAPI-04 (68Ga-FAPI-04) positron emission tomography (PET)/magnetic resonance (MR) a new potential imaging technique for the evaluation of myocardial fibrosis. This study aimed to evaluate the potential value of 68Ga-FAPI-04 PET/MR in assessing and predicting changes in renal function in patients with acute ST-elevation myocardial infarction (STEMI). METHODS: Thirty-three patients with STEMI were included in this study. 68Ga-FAPI-04 PET/MR and cardiac magnetic resonance were performed before discharge in all patients. Worsening renal function(WRF) was defined as ≥20% decrease in estimated glomerular filtration rate(eGFR) from baseline to 12 months. RESULTS: The WRF group demonstrated higher 68Ga-FAPI-04 uptake volume (UV) at baseline than the non-WRF group(P = 0.009). 68Ga-FAPI-04 UV at baseline was correlated with follow-up eGFR (r = -0.493, P = 0.004). 68Ga-FAPI-04 UV at baseline was a significant predictor of WRF (OR = 1.014, P = 0.029) at 12 months after STEMI. CONCLUSIONS: As an effective tool to non-invasively quantify myocardial fibroblast activation, 68Ga-FAPI-04 PET/MR has potential value for assessing and predicting worsening renal function in patients with STEMI.

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Radioisótopos de Galio , Tomografía de Emisión de Positrones , Valor Predictivo de las Pruebas , Infarto del Miocardio con Elevación del ST , Humanos , Masculino , Femenino , Infarto del Miocardio con Elevación del ST/diagnóstico por imagen , Infarto del Miocardio con Elevación del ST/fisiopatología , Persona de Mediana Edad , Tomografía de Emisión de Positrones/métodos , Anciano , Tasa de Filtración Glomerular/fisiología , Imagen por Resonancia Cinemagnética/métodos , Estudios de Seguimiento , Radiofármacos , Quinolinas

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PURPOSE: This prospective study aims to evaluate the value of [18F]AlF-NOTA-fibroblast activation protein inhibitor (FAPI)-04 positron emission tomography-computed tomography (PET/CT) in predicting molecular subtypes of breast cancer. METHODS: The study consecutively recruited patients suspected of having breast cancer from a single center who were prospectively enrolled from July 2023 to May 2024 and underwent [18F]AlF-NOTA-FAPI-04 PET/CT. This study compared the differences in tracer uptake among breast cancers with different adverse prognostic factors and molecular subtypes. The classification performance for each molecular subtype of breast cancer was assessed using a receiver operating characteristic (ROC) curve. RESULTS: Fifty-three participants (mean age, 51 ± 11 years; 52 females) were evaluated. Breast cancer lesions with adverse prognostic factors showed higher tracer uptake. The five different molecular subtypes exhibited varying levels of uptake. The luminal A and luminal B (HER2-negative) subtypes had relatively low uptake, while the luminal B (HER2-positive), HER2-positive, and triple-negative subtypes had relatively high uptake. ROC analysis identified the max standardized uptake value (SUVmax) as a significant classifier (AUC = 0.912, P = 0.0005) for the luminal A subtype, with 100% sensitivity and 83% specificity. For predicting the luminal B (HER2-negative) subtype, SUVmax had an AUC of 0.770 (P = 0.0015). SUVmax, with an AUC of 0.781 (P = 0.003), was used to identify the triple-negative subtype tumors, resulting in a sensitivity of 100% and specificity of 51%. Lastly, the ROC curve showed the cut-off 15.40 (AUC = 0.921, P < 0.0001) could classify luminal A & luminal B (HER2-negative), and luminal B (HER2-positive) & HER2-positive & triple-negative, yielding a sensitivity of 94% and specificity of 79%. CONCLUSION: The uptake of [18F]AlF-NOTA-FAPI-04 is significantly correlated with the molecular subtypes of breast cancer, and [18F]AlF-NOTA-FAPI-04 PET/CT is a potential tool for noninvasive identification of luminal A subtypes and guidance of FAP-targeted therapies.

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Background: Fibroblast Activation Protein (FAP)-targeted nanoparticles (NPs) are designed to accumulate in cancerous stroma. These NPs hold promise for imaging applications in cancer therapy. Objective: This systematic review aimed to comprehensively explore the use of FAP-targeting NPs for cancer diagnosis through different imaging modalities. Material and Methods: This systematic review followed the framework proposed by O'Malley and Arksey. Peer-reviewed studies were searched in the Scopus, Science Direct, PubMed, and Google Scholar databases. Eligible studies were selected, and data were extracted to investigate the FAP-targeting NPs in imaging. The Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guideline was also utilized to present the results. Results: Five studies met the specified inclusion criteria and were finally selected for analysis. The extracted data was classified into two categories: general and specific data. The general group indicated that most studies have been conducted in Mexico and have increased since 2022, and the specific group showed that colorectal cancer and Nude mice have received the most research attention. Furthermore, FAP-targeted NPs have demonstrated superior diagnostic imaging capabilities, even compared to specific methods for each cancer type. Also, they have been safe, with no toxicity. Conclusion: FAP-targeted NPs using different ligands, such as Fibroblast Activation Protein Inhibitor (FAPI), can accurately detect tumors and metastases, and outperform specific cancer peptides like PSMA in cancer diagnosis. They are also non-toxic and do not cause radiation damage to tissues. Therefore, FAP-targeted NPs have the potential to serve as a viable alternative to FAP-targeted radionuclides for cancer diagnosis.

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Canine idiopathic pulmonary fibrosis (CIPF) is a progressive fibrotic interstitial lung disease of unknown etiology, afflicting aging West Highland white terriers (WHWTs) and leading to progressive respiratory failure. Fibroblast activation protein (FAP), a protease overexpressed in many cancers, is upregulated in idiopathic pulmonary fibrosis in humans. The aim of this study was to investigate FAP as a marker of active fibrosis in lung biopsies from WHWTs affected with CIPF, as well as the potential of plasmatic FAP as a biomarker. After establishing a scoring system to evaluate the severity and activity of fibrosis on histopathological lung sections, anti-FAP immunohistochemistry was performed on healthy and CIPF samples. FAP expression was characterized using both visual and digital quantitative pathology software analyses and then correlated to fibrosis severity and activity. Levels of plasmatic FAP in WHWTs affected with CIPF were measured by enzyme-linked immunosorbent assay and compared with healthy dogs. Lung samples from 22 WHWTs affected with CIPF were collected. According to the fibrosis scoring system, they were classified as cases of mild (5), moderate (9) and severe (8) fibrosis and were attributed scores of fibrosis activity. Fifteen healthy lung samples were classified as non-fibrotic. Healthy lung samples were FAP-negative, whereas fibroblasts were FAP-positive in 20 CIPF samples. FAP immunohistochemical expression correlated mildly with fibrosis severity (p < 0.05; R 2 = 0.22) but highly with fibrosis activity scores (p < 0.001; R 2 = 0.68). Digital image analysis detected a higher percentage of FAP-positive cells in areas of active fibrosis (p < 0.001) and FAP-positive cells were distributed outside mature fibrosis lesions, clustered in active fibrosis areas or scattered within alveolar septa. On the other hand, plasmatic FAP was significantly lower in dogs affected with CIPF compared with healthy dogs (p < 0.01). In conclusion, this study provides a valuable histological scoring system to assess the severity and activity of fibrosis in CIPF. It demonstrates that FAP is a good cellular marker of fibrotic activity in CIPF, and thus constitutes a promising target to be exploited for diagnostic and therapeutic applications. Additionally, it suggests that plasmatic FAP, although non-specific, could be altered in CIPF.

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Introduction: This study investigates the role of Fibroblast Activation Protein (FAP)-positive cancer-associated fibroblasts (FAP+CAF) in shaping the tumor immune microenvironment, focusing on its association with immune cell functionality and cytokine expression patterns. Methods: Utilizing immunohistochemistry, we observed elevated FAP+CAF density in metastatic versus primary renal cell carcinoma (RCC) tumors, with higher FAP+CAF correlating with increased T cell infiltration in RCC, a unique phenomenon illustrating the complex interplay between tumor progression, FAP+CAF density, and immune response. Results: Analysis of immune cell subsets in FAP+CAF-rich stromal areas further revealed significant correlations between FAP+ stroma and various T cell types, particularly in RCC and non-small cell lung cancer (NSCLC). This was complemented by transcriptomic analyses, expanding the range of stromal and immune cell subsets interrogated, as well as to additional tumor types. This enabled evaluating the association of these subsets with tumor infiltration, tumor vascularization and other components of the tumor microenvironment. Our comprehensive study also encompassed cytokine, angiogenesis, and inflammation gene signatures across different cancer types, revealing heterogeneous cellular composition, cytokine expressions and angiogenic profiles. Through cytokine pathway profiling, we explored the relationship between FAP+CAF density and immune cell states, uncovering potential immunosuppressive circuits that limit anti-tumor activity in tumor-resident immune cells. Conclusions: These findings underscore the complexity of tumor biology and the necessity for personalized therapeutic and patient enrichment approaches. The insights gathered from FAP+CAF prevalence, immune infiltration, and gene signatures provide valuable perspectives on tumor microenvironments, aiding in future research and clinical strategy development.

Asunto(s)

Fibroblastos Asociados al Cáncer , Inmunoterapia , Serina Endopeptidasas , Microambiente Tumoral , Microambiente Tumoral/inmunología , Humanos , Fibroblastos Asociados al Cáncer/metabolismo , Fibroblastos Asociados al Cáncer/inmunología , Inmunoterapia/métodos , Serina Endopeptidasas/metabolismo , Serina Endopeptidasas/genética , Citocinas/metabolismo , Endopeptidasas , Proteínas de la Membrana/metabolismo , Proteínas de la Membrana/genética , Gelatinasas/metabolismo , Gelatinasas/genética , Linfocitos Infiltrantes de Tumor/inmunología , Linfocitos Infiltrantes de Tumor/metabolismo , Neoplasias Renales/inmunología , Neoplasias Renales/patología , Neoplasias Renales/terapia , Neoplasias Renales/metabolismo , Carcinoma de Células Renales/inmunología , Carcinoma de Células Renales/terapia , Carcinoma de Células Renales/patología , Carcinoma de Células Renales/metabolismo , Neoplasias Pulmonares/inmunología , Neoplasias Pulmonares/patología , Neoplasias Pulmonares/terapia , Neoplasias Pulmonares/metabolismo

RESUMEN

BACKGROUND: Cancer-associated fibroblasts have become a new target for therapy. Fibroblasts present within malignancies express the fibroblast activation protein (FAP). Inhibitors to FAP (FAPI) are small molecules recently developed as a theranostic agents for imaging and radiotherapy. All currently used FAPI rely on a linker-chelator complex attached to the 'inhibitor'. We describe a new automated method of the direct attachment of the radioisotope to the inhibitor, resulting in a >50% MW reduction with the hope of an improved tumor-to-background ratio and tumor uptake. METHODS: [18F]FluroFAPI was developed from a Sn precursor. This allowed for subsequent automated radioflourination. We obtained the biodistribution of [18F]FluroFAPI in rats, performed estimated human radiation dosimetry, and performed a 100× expected single dose toxicology analysis for eventual first-in-human experiments. RESULTS: The synthesis of the Sn precursor for FluorFAPI and the automated synthesis of [18F]FluroFAPI was demonstrated. [18F]FluroFAPI had favorable estimated human radiation dosimetry, and demonstrated no adverse effects when injected at a dose of 100× that planned for [18F]FluroFAPI. CONCLUSIONS: With the successful development of an automated synthesis of [18F]FluroFAPI, first-in-human testing can be planned with the hope of an improved tumor-to-background performance compared to other FAPI agents.