Fibroblast heterogeneity in solid tumors: From single cell analysis to whole-body imaging

Insights into lung cancer diagnosis and clinical management using [18F]F-fibroblast activation protein inhibitor (FAPI)-42 positron emission tomography/computed tomography (PET/CT)

PURPOSE

Accurate diagnosis and staging of lung cancer are critical for optimal clinical management. Fibroblast activation protein inhibitor (FAPI) imaging has emerged as a promising modality with superior detection capabilities for lung cancer. We hypothesized that [1⁸F]FAPI-42 PET/CT would enhance diagnosis, TNM staging, and influence oncologic management in patients with suspected or confirmed lung cancer.

METHODS

In this retrospective study, 155 patients with clinically suspected or confirmed lung cancer underwent both conventional imaging and [1⁸F]FAPI-42 PET/CT scans within a one-week interval, without any intervening treatment. Lesions were visually assessed and categorized to evaluate the diagnostic capability of [18F]FAPI-42 PET/CT. Tracer activity was quantified using maximum standardized uptake values (SUVmax) and tumor-to-background ratios. TNM staging was independently determined by a board-certified radiologist or nuclear medicine physician using both imaging modalities, and discrepancies were assessed. Changes in TNM staging were documented and evaluated for their impact on clinical management.

RESULTS

Of the 155 patients, 99 were evaluated for primary lesion diagnosis and staging. Pathological examination confirmed malignant tumors in 87 patients and benign tumors in 12. The diagnostic sensitivity and positive predictive value of [18F]FAPI-42 PET/CT for detecting primary lung tumors were 96.77% and 92.78%, respectively. Malignant lesions exhibited significantly higher SUVmax compared to benign lesions (5.2 vs. 1.5, P = 0.0002), with an area under the ROC curve of 0.87. In total, 1,556 malignant lesions were identified among patients with lung cancer, and [18F]FAPI-42 PET/CT demonstrated a diagnostic accuracy of 95.50%. However, its sensitivity for detecting adrenal metastases was lower at 33.33%, with a specificity of 100% and an accuracy of 53.85%. The use of [18F]FAPI-42 PET/CT resulted in changes in TNM staging for 46% of patients, leading to upstaging in 58 patients and downstaging in 5. These staging adjustments directly impacted clinical management in 34 patients, prompting modifications in treatment plans.

CONCLUSION

[18F]FAPI-42 PET/CT is a promising modality for lung cancer diagnosis and staging, demonstrating high sensitivity and specificity. Its use significantly altered TNM staging in nearly half of the patients, directly impacting oncologic management and treatment planning. However, its limited sensitivity for detecting adrenal metastases underscores the need for additional imaging techniques.

Fibroblast activation protein peptide-targeted NIR-I/II fluorescence imaging for stable and functional detection of hepatocellular carcinoma

PURPOSE

Cancer-associated fibroblasts (CAFs) are the primary stromal component of the tumor microenvironment in hepatocellular carcinoma (HCC), affecting tumor progression and post-resection recurrence. Fibroblast activation protein (FAP) is a key biomarker of CAFs. However, there is limited evidence on using FAP as a target in near-infrared (NIR) fluorescence imaging for HCC. Thus, this study aims to develop a novel NIR fluorescent imaging strategy targeting FAP+ CAFs in HCC.

METHODS

The ICG-FAP-TATA probe was synthesized by conjugating a novel cyclization anti-FAP peptide with an indocyanine green derivative (ICG-NH2) as fluorophore, capable for NIR window I (NIR-I, 700-900 nm) and II (NIR-II, 1000-1700 nm) imaging. Its efficacy in lesion localization and other potential applications was evaluated.

RESULTS

In vivo imaging of subcutaneous HCC models revealed that ICG-FAP-TATA specifically targeted FAP+ CAFs in the stroma and detected differences in CAFs loading within lesions. The fluorescence intensity/tumor-to-background ratio (TBR) positively correlated with FAP expression (R2 > 0.8, p < 0.05). Ex vivo incubation of tumor tissues with ICG-FAP-TATA provided stable fluorescence imaging of tumors in subcutaneous and orthotopic HCC models, including different cell line co-culture systems (LM3-luc, MHCC97H-luc, HepG2-luc + LX2), and various liver backgrounds (healthy/fibrotic) (n = 5 per group). TBR of the tumor mice models was higher for NIR-II than NIR-I imaging (3.89 ± 1.27 vs. 2.64 ± 0.64, p < 0.05). Moreover, NIR-I/II imaging of fresh tissues from seven patients with HCC undergoing surgery incubated with ICG-FAP-TATA visually provided the spatial distribution heterogeneity of CAFs. The targeted fluorescence was relatively enriched more in the blood flow direction and at the tumor edge, both of which were associated with tumor metastasis (all p < 0.05).

CONCLUSION

This study presents a rapid and effective method for detecting HCC lesions, locating FAP+ CAFs, and visualizing high-risk areas for tumor metastasis at the macroscopic level. It offers a new promising approach with translational potential for imaging HCC.

68 Ga-FAPI PET/CT Depicted Non-FDG-Avid Malignant Peritoneal Mesothelioma

ABSTRACT

Malignant peritoneal mesothelioma (MPM) is a rare and aggressive malignancy of mesothelial cells in the peritoneum. Herein, we describe the 68 Ga-FAPI and 18 F-FDG PET/CT findings of MPM in a 41-year-old man. In the present case, the primary and metastatic tumors showed intense 68 Ga-FAPI accumulation but no significantly increased 18 F-FDG uptake. This case demonstrates that 68 Ga-FAPI PET/CT might be used as a helpful tool for evaluating MPM staging.

A heterodimeric radioligand labeled with gallium-68 targeting fibroblast activation protein

BACKGROUND

Fibroblast activation protein (FAP) targeting radiotracers have emerged as promising agents for cancer imaging and therapy. Recent advancements have focused on optimizing these agents for better tumor targeting and enhanced theranostic efficacy. In this study, we introduced a novel heterodimeric radioligand labeled with gallium-68, which targets FAP. We aimed to evaluate its in vitro and in vivo performance, comparing its efficacy with monomeric FAPI derivatives.

RESULTS

The heterodimeric ligand BiFAPI was synthesized by conjugating a cyclic peptide with a quinoline-based motif via a DOTA chelator. [68 Ga]Ga-BiFAPI demonstrated high radiochemical purity (> 95%) and exceptional stability in physiological conditions, as well as in both PBS and serum. In vitro studies revealed that the binding affinity of BiFAPI was comparable to that of FAP2286 and FAPI-04. Notably, [68 Ga]Ga-BiFAPI exhibited superior cellular uptake, with rapid internalization and slower efflux rates. Micro-PET/CT imaging in tumor-bearing mice demonstrated significantly higher tumor uptake than [68 Ga]Ga-FAP2286 and [68 Ga]Ga-FAPI-04. Co-injection with a FAP inhibitor reduced tumor uptake, confirming the tracer's FAP specificity. In vitro autoradiography, immunohistochemistry, and Western blotting confirmed the correlation between radioactive tracer accumulation and FAP-positive regions. Biodistribution studies revealed high tumor-to-blood ratios and rapid clearance from non-target tissues, further supporting the tracer's favorable pharmacokinetics.

CONCLUSION

[68 Ga]Ga-BiFAPI demonstrated superior tumor-targeting properties, higher tumor uptake, and favorable pharmacokinetics compared to [68 Ga]Ga-FAP2286 and [68 Ga]Ga-FAPI-04. Its promising performance in preclinical models positioned it as a potentially valuable agent for FAP-targeted PET imaging and cancer theranostics.

Cancer-Associated Fibroblasts as the "Architect" of the Lung Cancer Immune Microenvironment: Multidimensional Roles and Synergistic Regulation with Radiotherapy

Cancer-associated fibroblasts (CAFs), as the "architect" of the immune microenvironment in lung cancer, play a multidimensional role in tumor progression and immune regulation. In this review, we summarize the heterogeneity of the origin and the molecular phenotype of CAFs in lung cancer, and explore the complex interactions between CAFs and multiple components of the tumor microenvironment, including the regulatory relationships with innate immune cells (e.g., tumor-associated macrophages, tumor-associated neutrophils), adaptive immune cells (e.g., T cells), and extracellular matrix (ECM). CAFs significantly influence tumor progression and immunomodulation through the secretion of cytokines, remodeling of the ECM, and the regulation of immune cell function significantly affects the immune escape and treatment resistance of tumors. In addition, this review also deeply explored the synergistic regulatory relationship between CAF and radiotherapy, revealing the key role of CAF in radiotherapy-induced remodeling of the immune microenvironment, which provides a new perspective for optimizing the comprehensive treatment strategy of lung cancer. By comprehensively analyzing the multidimensional roles of CAF and its interaction with radiotherapy, this review aims to provide a theoretical basis for the precise regulation of the immune microenvironment and clinical treatment of lung cancer.

Dual-Time Point 68 Ga-FAPI-04 PET/CT Improves Tumor Delineation and Cervical Lymph Node Metastasis Identification in Patients With Head and Neck Squamous Cell Carcinoma

PURPOSE

The purpose of this study was to evaluate the benefit of dual-time point 68 Ga-FAPI-04 PET/CT in staging head and neck squamous cell carcinoma (HNSCC).

PATIENTS AND METHODS

Sixty-nine treatment-naive patients with HNSCC were enrolled. Each patient underwent whole-body 68 Ga-FAPI-04 PET/CT at approximately 30 minutes postinjection and a delayed scan in head and neck region at 2 hours. Radiotracer uptake (SUV max ), tumor-to-background ratio, change in SUV max (∆SUV max ), retention index, diagnostic performance, and staging were explored. Histopathology was the reference standard.

RESULTS

Primary tumors showed similar average SUV max between early (17.89) and delayed scans (17.86, P = 0.241). However, the tumor-to-background ratios of delayed imaging were all significantly higher than those of early imaging (all P < 0.001). In 38 patients who underwent neck dissection, metastatic lymph nodes showed higher mean SUV max on delayed imaging than on early imaging (early 10.53 ± 5.98 vs delayed 11.71 ± 6.36, P < 0.001), whereas nonmetastatic lymph nodes showed the opposite result (early 3.51 ± 0.51 vs delayed 2.58 ± 0.63, P = 0.002). The mean ∆SUV max and retention index of metastatic and nonmetastatic lymph nodes were 1.19 versus -0.93 and 12.79% versus -26.55%, respectively. N staging was correctly altered in 3 (3/38) patients based on delayed images.

CONCLUSIONS

Delayed 68 Ga-FAPI-04 PET/CT can effectively acquire high-contrast images, better tumor delineation, and detect hidden lesions near or within the tissues influenced by physiological uptake for HNSCC. In addition, dual-time point imaging adds diagnostic value for the differentiation of metastatic from nonmetastatic lymph nodes.

Tumor-Targeted Catalytic Immunotherapy

Cancer immunotherapy holds significant promise for improving cancer treatment efficacy; however, the low response rate remains a considerable challenge. To overcome this limitation, advanced catalytic materials offer potential in augmenting catalytic immunotherapy by modulating the immunosuppressive tumor microenvironment (TME) through precise biochemical reactions. Achieving optimal targeting precision and therapeutic efficacy necessitates a thorough understanding of the properties and underlying mechanisms of tumor-targeted catalytic materials. This review provides a comprehensive and systematic overview of recent advancements in tumor-targeted catalytic materials and their critical role in enhancing catalytic immunotherapy. It highlights the types of catalytic reactions, the construction strategies of catalytic materials, and their fundamental mechanisms for tumor targeting, including passive, bioactive, stimuli-responsive, and biomimetic targeting approaches. Furthermore, this review outlines various tumor-specific targeting strategies, encompassing tumor tissue, tumor cell, exogenous stimuli-responsive, TME-responsive, and cellular TME targeting strategies. Finally, the discussion addresses the challenges and future perspectives for transitioning catalytic materials into clinical applications, offering insights that pave the way for next-generation cancer therapies and provide substantial benefits to patients in clinical settings.

Advancements in molecular imaging probes for precision diagnosis and treatment of prostate cancer

Prostate cancer is the second most common cancer in men, accounting for 14.1% of new cancer cases in 2020. The aggressiveness of prostate cancer is highly variable, depending on its grade and stage at the time of diagnosis. Despite recent advances in prostate cancer treatment, some patients still experience recurrence or even progression after undergoing radical treatment. Accurate initial staging and monitoring for recurrence determine patient management, which in turn affect patient prognosis and survival. Classical imaging has limitations in the diagnosis and treatment of prostate cancer, but the use of novel molecular probes has improved the detection rate, specificity, and accuracy of prostate cancer detection. Molecular probe-based imaging modalities allow the visualization and quantitative measurement of biological processes at the molecular and cellular levels in living systems. An increased understanding of tumor biology of prostate cancer and the discovery of new tumor biomarkers have allowed the exploration of additional molecular probe targets. The development of novel ligands and advances in nano-based delivery technologies have accelerated the research and development of molecular probes. Here, we summarize the use of molecular probes in positron emission tomography (PET), single-photon emission computed tomography (SPECT), magnetic resonance imaging (MRI), optical imaging, and ultrasound imaging, and provide a brief overview of important target molecules in prostate cancer.

Spatial expression of fibroblast activation protein-α in clear cell renal cell carcinomas revealed by multiplex immunoprofiling analysis of the tumor microenvironment

Clear cell renal cell carcinoma (ccRCC) is one of the most challenging neoplasms because of its phenotypic variability and intratumoral heterogeneity. Because of its variability, ccRCC is a good test bench for the application of new technological approaches to unveiling its intricacies. Multiplex immunofluorescence (mIF) is an emerging method that enables the simultaneous and detailed assessment of tumor and stromal cell subpopulations in a single tissue section. This novel approach represents a promising step forward for analyzing the microenvironmental cell composition and distribution across the tumor and understanding its possible interactions with tumor cells. This study provides the first characterization of the spatial distribution of fibroblast activation protein-α (FAP)-expressing cancer-associated fibroblasts (FAP + CAFs) in conjunction with lymphoid (CD4 + , CD8 + , CD4 + FOXP3 + , and CD20 +) and myeloid (CD68 +) cells in tissue sections from ccRCC in their early phases of evolution (n = 88). Both the tumor center and periphery were analyzed with mIF. FAP + CAFs and tumor-infiltrating lymphocytes (TILs) were significantly concentrated at the tumor periphery. Additionally, elevated percentages of FAP + CAFs were correlated with larger tumors and synchronous metastases. Increased levels of CD68 +  and CD4 + FOXP3 +  cells (above the 75th percentile) were linked to worse cancer-specific survival (CSS) in patients with ccRCC. Furthermore, significant correlations emerged among FAP + CAFs, TILs, and CD68 +  cells, and the co-occurrence of elevated FAP + CAFs, T-cytotoxic (CD8 +), T-regulatory (CD4 + FOXP3 +) cells, and macrophages (CD68 +) at the tumor center were independently associated with worse CSS. These findings suggest that FAP + CAFs contribute to the aggressiveness of ccRCC, and their role is potentially mediated by their ability to foster an immunosuppressive environment within the renal tumor microenvironment.

Exploration the feasibility and additional value of [18F]FDG/[68Ga]Ga-FAPI-04 dual-low-activity-tracer one-stop total-body PET imaging at 34 min post-injection of [68Ga]Ga-FAPI-04

OBJECTIVES

To validate the feasibility of one-stop 2-[18F]fluoro-2-deoxy-D-glucose ([18F]FDG) and [68Ga]Ga-fibroblast activation protein inhibitor-04 ([68Ga]Ga-FAPI-04) dual-low-activity-tracer positron emission tomography/computed tomography (PET/CT) at 34 min post-injection of [68Ga]Ga-FAPI-04 and explore its additional value.

METHODS

Thirty pairs of patients with suspected malignancies who underwent dual-tracer imaging were enrolled in this retrospective study. The images were reconstructed at 34-39 and 50-60 min after additional injection of [68Ga]Ga-FAPI-04 (in one-stop FDG-FAPI PET/CT, named PETFDG, PETD34-39, and PETD50-60; in the 2-day protocol, named PETFDG', PETF34-39, and PETF50-60, respectively). Tumour-to-normal ratios (TNR) of lesions in PETFDG, PETD34-39, and PETD50-60 and TNR of lesions in PETF34-39 and PETF50-60 were evaluated separately. To evaluate the potential added value of one-stop FDG-FAPI PET/CT over the 2-day protocol, TNRs of PETFDG, PETD34-39, and PETD50-60 were compared with PETF34-39. The lesion detectability of the two imaging protocols was evaluated by chi-square test.

RESULTS

Comparing FAPI-weighted PET (PETD34-39 and PETD50-60) and single-tracer imaging (PETFDG) in one-stop FDG-FAPI PET/CT, TNRs of FAPI-weighted PET were higher than those of PETFDG. PETD34-39 and PETD50-60 showed similar performance in lesion detectability and TNRs (all P > 0.05). In the 2-day protocol, there are no statistically significant differences in TNRs of all lesions at PETF34-39 and PETF50-60. Comparing one-stop FDG-FAPI PET/CT with the 2-day protocol, TNRs of PETF34-39 were significantly higher than those of PETFDG but lower than those of PETD34-39 and PETD50-60. Lesion detectability in the one-stop FDG-FAPI PET/CT was higher than that in the 2-day protocol. The average radiation dose in one-stop FDG-FAPI PET/CT was significantly lower than that in the 2-day protocol (P<0.001).

CONCLUSION

One-stop FDG-FAPI PET/CT at 34 min could provide sufficient information to meet clinical diagnosis and showed better lesion detectability than that in the 2-day protocol.

Lipid imaging mass spectrometry: Towards a new molecular histology

Lipid research is attracting greater attention, as these molecules are key components to understand cell metabolism and the connection between genotype and phenotype. The study of lipids has also been fueled by the development of new and powerful technologies, able to identify an increasing number of species in a single run and at decreasing concentrations. One of such key developments has been the image techniques that enable the visualization of lipid distribution over a tissue with cell resolution. Thanks to the spatial information reported by such techniques, it is possible to associate a lipidome trait to individual cells, in fixed metabolic stages, which greatly facilitates understanding the metabolic changes associated to diverse pathological conditions, such as cancer. Furthermore, the image of lipids is becoming a kind of new molecular histology that has great chances to make an impact in the diagnostic units of the hospitals. Here, we examine the current state of the technology and analyze what the next steps to bring it into the diagnosis units should be. To illustrate the potential and challenges of this technology, we present a case study on clear cell renal cell carcinoma, a good model for analyzing malignant tumors due to their significant cellular and molecular heterogeneity.

Comparison of 68Ga-FAPI-04 and 18F-FDG PET/CT in diagnosing ovarian cancer

PURPOSE

This study assesses the diagnostic performance of 68Ga-FAPI-04 PET/CT compared to 18F-FDG PET/CT in primary, recurrent, and metastatic ovarian cancer.

METHODS

Seventy-nine ovarian cancer patients who performed 68Ga-FAPI-04 and 18F-FDG PET/CT were recruited. The target-to-background ratio (TBR), maximum standardized uptake value (SUVmax), the number of positive lesions, visual assessment, the peritoneal cancer index (PCI) score, staging/restaging, and treatment strategies were compared from the corresponding PET/CT. Additionally, we analyzed and contrasted the diagnostic efficacy in both scans.

RESULTS

Among all patients, 6 were assessed for initial assessment and 73 for recurrence and metastasis detection. For all lesions, 68Ga-FAPI-04 PET/CT demonstrated greater TBR than 18F-FDG PET/CT. 68Ga-FAPI-04 PET/CT demonstrated higher sensitivity for peritoneal metastases including patient-based and lesion-based analysis (95.00% vs. 83.33%, P = 0.065; 90.16% vs. 60.66%, P < 0.001) and a higher PCI score [median PCI: 6 (4, 12) vs. 4 (2, 8), P < 0.001]. According to the visual assessment, 68Ga-FAPI-04 PET revealed larger extent metastases in 55.93% (33/59) of the patients with peritoneal metastases. 68Ga-FAPI-04 was upstaged in 7 patients (8.86%, 7/79) and discrepancies in both scans caused treatment strategies to change in 11 patients (13.92%, 11/79).

CONCLUSION

68Ga-FAPI-04 PET/CT outperforms 18F-FDG PET/CT in identifying metastases and can be a potential supplement for managing ovarian cancer patients.

FAP-α is an effective tool to evaluate stroma invasion of lung adenocarcinoma

The main difficulty in the diagnosis of atypical in situ adenocarcinoma lies in the distinction between true and false stromal invasion. Moreover, how to identify local alveolar wall collapse in situ lung adenocarcinoma and how to identify whether the trapped adenoid structure around scar is an invasion component have become the key points for accurate diagnosis of lung adenocarcinoma. In the present study, we detected 40 cases of lung adenocarcinoma in situ and 40 cases of invasive adenocarcinoma by using immunohistochemical techniques. We found FAP-α had not immunreactivity in the stroma of adenocarcinoma in situ. However, it stained in the stroma of invasive areas in lung adenocarcinoma. FAP-α staining pattern could represent hyperplastic myofibroblast and demonstrated the true invasion of stroma. This study provides strong evidence that FAP-α is an effective tool to evaluate the presence or absence of stroma invasion of lung adenocarcinoma. Our findings will contribute to the accurate diagnosis of lung invasive adenocarcinoma.

Multiple roles of p53 in cancer development: Regulation of tumor microenvironment, m6A modification and diverse cell death mechanisms

BACKGROUND

The protein p53, encoded by the most frequently mutated gene TP53 in human cancers, has diverse functions in tumor suppression. As a best known transcription factor, p53 can regulate various fundamental cellular responses, ranging from the cell-cycle arrest, DNA repair, senescence to the programmed cell death (PCD), which includes autophagy, apoptosis, ferroptosis, cuproptosis, pyroptosis and disulfidoptosis. Accumulating evidence has indicated that the tumor microenvironment (TME), N6-methyladenosine (m6A) modification and diverse PCD are important for the progression, proliferation and metastases of cancers.

AIM OF REVIEW

This paper aims to systematically and comprehensively summarize the multiple roles of p53 in the development of cancers from the regulation of TME, m6A Modification and diverse PCD.

KEY SCIENTIFIC CONCEPTS OF REVIEW

TME, a crucial local homeostasis environment, influences every step of tumorigenesis and metastasis. m6A, the most prevalent and abundant endogenous modification in eukaryotic RNAs, plays an essential role in various biological processes, containing the progression of cancers. Additionally, PCD is an evolutionarily conserved mechanism of cell suicide and a common process in living organisms. Some forms of PCD contribute to the occurrence and development of cancer. However, the complex roles of p53 within the TME, m6A modification and diverse PCD mechanisms are still not completely understood. Presently, the function roles of p53 including the wild-type and mutant p53 in different context are summarized. Additionally, the interaction between the cancer immunity, cancer cell death and RNA m6A methylation and the p53 regulation during the development and progress of cancers were discussed. Moreover, the key molecular mechanisms by which p53 participates in the regulation of TME, m6A and diverse PCD are also explored. All the findings will facilitate the development of novel therapeutic approaches.

[64Cu]Cu-FAP-NOX, a N-oxalyl modified cyclic peptide for FAP PET imaging with a flexible imaging time window

BACKGROUND

The aim of the present study was to develop a novel 64Cu-labeled cyclic peptide ([64Cu]Cu-FAP-NOX) that targets fibroblast activation protein (FAP) and may offer advantages in terms of image contrast, imaging time window, and low uptake in normal tissues.

METHODS

The novel cyclic peptide featuring with a N-oxalyl modified tail was constructed and conjugated to NOTA for 64Cu labeling. Biochemical and cellular assays were performed with A549.hFAP cells. The performance of [64Cu]Cu-FAP-NOX was compared to that of two established tracers ([64Cu]Cu-FAPI-04 and [68Ga]Ga-FAP-2286) and three different NOTA-conjugates in HEK-293T.hFAP xenograft mice using micro-PET imaging. Ex vivo biodistribution studies were performed to confirm the FAP specificity and to validate the PET data. Furthermore, a first-in-human study of this novel tracer was conducted on one patient with lung cancer.

RESULTS

Compared to [64Cu]Cu-FAPI-04, [64Cu]Cu-FAP-NOX demonstrated faster and higher rates of cellular uptake and internalization in A549.hFAP cells, but lower rates of cellular efflux. All six radiotracers were rapidly taken up by the tumor within the first 4 h post-injection. However, [64Cu]Cu-FAP-NOX had more intense tumor accumulation and slower washout from the target. The ratios of the tumor to normal tissue (including kidneys and muscles) increased significantly over time, with [64Cu]Cu-FAP-NOX reaching the highest ratio among all tracers. In the patient, [64Cu]Cu-FAP-NOX PET showed a comparable result to FDG PET in the primary malignant lesion while exhibiting higher uptake in pleural metastases, consistent with elevated FAP expression as confirmed by immunohistochemistry.

CONCLUSION

[64Cu]Cu-FAP-NOX is a promising FAP-targeted tracer with a highly flexible imaging time window, as evidenced by preclinical evaluation encompassing biodistribution and micro-PET studies, along with a successful patient application. Furthermore, [64Cu]Cu-FAP-NOX showed enhanced image contrast and favorable pharmacokinetic properties for FAP PET imaging, warranting translation into large cohort studies.

Preclinical evaluation and first-in-human study of [18F]AlF-FAP-NUR for PET imaging cancer-associated fibroblasts

BACKGROUND

Fibroblast activation protein (FAP) has gained attention as a promising molecular target with potential utility for cancer diagnosis and therapy. [68Ga]Ga-labeled FAP-targeting peptides have been successfully applied to positron emission tomography (PET) imaging of various tumor types. To meet the applicable demand for peptide-based FAP tracers with high patient throughput, we herein report the radiosynthesis, preclinical evaluation, and the first-in-human imaging of a novel [18F]F-labeled FAP-targeting peptide.

RESULTS

[18F]AlF-FAP-NUR was automatedly prepared within 45 min with a non-decay corrected radiochemical yield of 18.73 ± 4.25% (n = 3). Compared to [68Ga]Ga-FAP-2286, the [18F]F-labeled peptide demonstrated more rapid, higher levels of cellular uptake and internalization, and lower levels of cellular efflux in HT1080-FAP cells. Micro-PET imaging and biodistribution studies conducted on xenograft mice models revealed a similar distribution pattern between the two tracers. However, [18F]AlF-FAP-NUR demonstrated significantly higher tumor-specific uptake resulting in improved Tumor-Background Ratios (TBRs). In the patients, a significant accumulation of [18F]AlF-FAP-NUR was found in the primary tumor. High uptake of the tracer within the bladder indicated that its major route of excretion was through urine.

CONCLUSIONS

Based on the physical imaging properties and longer half-life of [18F]F, [18F]AlF-FAP-NUR exhibited promising characteristics such as enhanced tumor-specific accumulation and elevated TBRs, which made it a viable candidate for further clinical investigation.

TRIAL REGISTRATION

www.Chictr.org.cn , ChiCTR2300076976 Retrospectively registered 25 October 2023. at, URL: https://www.chictr.org.cn/showproj.html?proj=206753 .

Development of an FAP-Targeted PET Probe Based on a Novel Quinolinium Molecular Scaffold

Fibroblast activation protein (FAP) has recently gained significant attention as a promising tumor biomarker for both diagnosis and therapeutic applications. A series of radiopharmaceuticals based on fibroblast activation protein inhibitors (FAPIs) have been developed and translated into the clinic. Though some of them such as radiolabeled FAPI-04 probes have achieved favorable in vivo imaging performance, further improvement is still highly desired for obtaining radiopharmaceuticals with a high theranostics potential. In this study, we innovatively designed an FAPI ligand SMIC-3002 by changing the core quinoline motif of FAPI-04 to the quinolinium scaffold. The engineered molecule was further radiolabeled with 68Ga to generate a positron emission tomography (PET) probe, [68Ga]Ga-SMIC-3002, which was then evaluated in vitro and in vivo. [68Ga]Ga-SMIC-3002 demonstrated high in vitro stability, nanomolar affinity for FAP (8 nM for protein, 23 nM for U87MG cells), and specific uptake in FAP-expressing tumors, with a tumor/muscle ratio of 19.1 and a tumor uptake of 1.48 ± 0.03 ID/g% at 0.5 h in U87MG tumor-bearing mice. In summary, the quinolinium scaffold can be successfully used for the development of the FAP-targeted tracer. [68Ga]Ga-SMIC-3002 not only shows high potential for clinical translation but also offers insights into designing a new generation of FAPI tracers.

Cancer-associated fibroblasts mediate resistance to anti-EGFR therapies in cancer

Over the last decade, epidermal growth factor receptor (EGFR)-targeted therapies have transformed the treatment landscape for patients with advanced solid tumors. Despite these advances, resistance to anti-EGFR therapies is still a significant clinical challenge. While cell-autonomous mechanisms of resistance are well-documented, they do not fully elucidate the complexity of drug resistance. Cancer-associated fibroblasts (CAFs), key mediators within the tumor microenvironment (TME), have emerged as pivotal players in cancer progression and chemoresistance. Recent evidence implicates CAFs in resistance to anti-EGFR therapies, suggesting they may undermine treatment efficacy. This review synthesizes current data, highlighting the critical role of CAFs in resistance pathogenesis and summarizing recent therapeutic strategies targeting CAFs. We underscore the challenges and advocate for the exploration of CAFs as a potential dual-targeted approach.

PRRX1-OLR1 axis supports CAFs-mediated lung cancer progression and immune suppression

OBJECTIVE

To investigate the mechanism by which cancer-associated fibroblasts (CAFs) affect the growth and immune evasion of lung cancer cells.

METHODS

Initially, datasets comparing CAFs with normal fibroblasts were downloaded from the GEO dataset GSE48397. Genes with the most significant differential expression were selected and validated using clinical data. Subsequently, CAFs were isolated, and the selected genes were knocked down in CAFs. Co-culture experiments were conducted with H1299 or A549 cells to analyze changes in lung cancer cell growth, migration, and immune evasion in vitro and in vivo. To further elucidate the upstream regulatory mechanism, relevant ChIP-seq data were downloaded from the GEO database, and the regulatory relationships were validated through ChIP-qPCR and luciferase reporter assays.

RESULTS

OLR1 was significantly overexpressed in CAFs and strongly correlated with adverse prognosis in lung cancer patients. Knockdown of OLR1 markedly inhibited CAFs' support for the growth and immune evasion of lung cancer cells in vitro and in vivo. ChIP-seq results demonstrated that PRRX1 can promote OLR1 expression by recruiting H3K27ac and H3K4me3, thereby activating CAFs. Knockdown of PRRX1 significantly inhibited CAFs' function, while further overexpression of OLR1 restored CAFs' support for lung cancer cell growth, migration, and immune evasion.

CONCLUSION

PRRX1 promotes OLR1 expression by recruiting H3K27ac and H3K4me3, activating CAFs, and thereby promoting the growth, migration, and immune evasion of lung cancer cells.

[68Ga]Ga-FAP-2286, a novel promising theragnostic approach for PET/CT imaging in patients with various type of metastatic cancers

BACKGROUND

Fibroblast activation protein (FAP) has emerged as a promising target for diagnosis and therapeutic intervention due to high expression and accumulation in the stromal compartments of a variety of malignant tumors. FAP-2286 utilizes cyclic peptides with FAP-binding characteristics to enhance the retention of the imaging agent within tumors, in contrast to the small-molecule FAP inhibitors (FAPI) like FAPI-04/46. The aim of this study was to quantify the tumor uptake of [68Ga] Gallium-FAP-2286 within primary solid tumors, adjacent excised tissues, and metastatic lesions.

METHODS

In this prospective study, 21 patients (average age 51.9) with various diagnoses of remaining and metastatic cancers participated. Among them, six had metastatic sarcoma, and 14 had adenocarcinoma, including eight breast, two rectum, two lung, two pancreas, and one thyroid cases. The patients underwent a [68Ga]Ga-FAP-2286 PET/CT scan. An hour post-administration of [68Ga]Ga-FAP-2286, a visual assessment of whole body scans and semi-quantification of the PET/CT results were carried out. The standardized uptake values (SUV)max of [68Ga]Ga-FAP-2286 in tumor lesions and the tumor-to-background ratio (TBR) were then calculated.

RESULTS

The vital signs of the patients, such as heart rate, blood pressure, and temperature, were observed before, during, and after the diagnostic procedure during the 4-h follow-up. All individuals underwent the [68Ga]Ga-FAP-2286 PET/CT scans without any signs of drug-associated pharmacological effects. The PET/CT scans displayed substantial absorption of [68Ga]Ga-FAP-2286 in tumor lesions in all patients (100% (21/21)). Irrespective of the tumors' origins (epithelial or mesothelium) and whether they exhibited local recurrence, distant recurrence, or metastatic lesions, the PET/CT scans revealed the uptake of [68Ga]Ga-FAP-2286 in these lesions.

CONCLUSION

Overall, these data suggest that [68Ga]Ga-FAP-2286 is a promising FAP derivative for efficient metastatic cancer diagnosis and being considered as a potential compound for therapeutic application in patients with advanced metastatic cancers.

Peptidic heterodimer-based radiotracer targeting fibroblast activation protein and integrin αvβ3

PURPOSE

Several studies have demonstrated the advantages of heterodimers over their corresponding monomers due to the multivalency effect. This effect leads to an increased number of effective targeted receptors and, consequently, improved tumor uptake. Fibroblast activation protein (FAP) and integrin αvβ3 are found to be overexpressed in different components of the tumor microenvironment. In our pursuit of enhancing tumor uptake and retention, we designed and developed a novel peptidic heterodimer that synergistically targets both FAP and integrin αvβ3.

METHODS

FAP-RGD was synthesized from FAP-2286 and c(RGDfK) through a multi-step organic synthesis. The dual receptor binding property of 68Ga-FAP-RGD was investigated by cell uptake and competitive binding assays. Preclinical pharmacokinetics were determined in HT1080-FAP and U87MG tumor models using micro-positron emission tomography/computed tomography (micro-PET/CT) and biodistribution studies. The antitumor efficacy of 177Lu-FAP-RGD was assessed in U87MG tumor models. The radiation exposure and clinical diagnostic performance of 68 Ga-FAP-RGD were evaluated in healthy volunteers and cancer patients.

RESULTS

Bi-specific radiotracer 68Ga-FAP-RGD exhibited high binding affinity for both FAP and integrin αvβ3. In comparison to 68Ga-FAP-2286 and 68Ga-RGDfK, 68Ga-FAP-RGD displayed enhanced tumor uptake and longer tumor retention time in preclinical models. 177Lu-FAP-RGD could efficiently suppress the growth of U87MG tumor in vivo when applied at an activity of 18.5 and 29.6 MBq. The effective dose of 68Ga-FAP-RGD was 1.06 × 10-2 mSv/MBq. 68Ga-FAP-RGD demonstrated low background activity and stable accumulation in most neoplastic lesions up to 3 h.

CONCLUSION

Taking the advantages of multivalency effect, the bi-specific radiotracer 68Ga-FAP-RGD showed superior tumor uptake and retention compared to its corresponding monomers. Preclinical studies with 68Ga- or 177Lu-labeled FAP-RGD showed favorable image contrast and effective antitumor responses. Despite the excellent performance of 68Ga-FAP-RGD in clinical diagnosis, experimental efforts are currently underway to optimize the structure of FAP-RGD to increase its potential for clinical application in endoradiotherapy.

The hidden messengers: cancer associated fibroblasts-derived exosomal miRNAs as key regulators of cancer malignancy

Cancer-associated fibroblasts (CAFs), a class of stromal cells in the tumor microenvironment (TME), play a key role in controlling cancer cell invasion and metastasis, immune evasion, angiogenesis, and resistance to chemotherapy. CAFs mediate their activities by secreting soluble chemicals, releasing exosomes, and altering the extracellular matrix (ECM). Exosomes contain various biomolecules, such as nucleic acids, lipids, and proteins. microRNA (miRNA), a 22-26 nucleotide non-coding RNA, can regulate the cellular transcription processes. Studies have shown that miRNA-loaded exosomes secreted by CAFs engage in various regulatory communication networks with other TME constituents. This study focused on the roles of CAF-derived exosomal miRNAs in generating cancer malignant characteristics, including immune modulation, tumor growth, migration and invasion, epithelial-mesenchymal transition (EMT), and treatment resistance. This study thoroughly examines miRNA's dual regulatory roles in promoting and suppressing cancer. Thus, changes in the CAF-derived exosomal miRNAs can be used as biomarkers for the diagnosis and prognosis of patients, and their specificity can be used to develop newer therapies. This review also discusses the pressing problems that require immediate attention, aiming to inspire researchers to explore more novel avenues in this field.

Diagnostic yield of FAP-guided positron emission tomography in thyroid cancer: a systematic review

Background

Several recent studies have proposed the possible application of positron emission tomography/computed tomography (PET/CT) administering radiolabelled fibroblast-activation protein (FAP) inhibitors for various forms of thyroid cancer (TC), including differentiated TC (DTC), and medullary TC (MTC).

Methods

The authors conducted an extensive literature search of original studies examining the effectiveness of FAP-guided PET/CT in patients with TC. The papers included were original publications exploring the use of FAP-targeted molecular imaging in restaging metastatic DTC and MTC patients.

Results

A total of 6 studies concerning the diagnostic yield of FAP-targeted PET/CT in TC (274 patients, of which 247 DTC and 27 MTC) were included in this systematic review. The included articles reported high values of FAP-targeted PET/CT detection rates in TC, ranging from 81 to 100% in different anatomical sites and overall superior to the comparative imaging method.

Conclusion

Although there are promising results, the existing literature on the diagnostic accuracy of FAP-guided PET in this context is still quite limited. To thoroughly evaluate its potential significance in TC patients, it is needed to conduct prospective randomized multicentric trials.

Beyond Small Molecules: Antibodies and Peptides for Fibroblast Activation Protein Targeting Radiopharmaceuticals

Fibroblast activation protein (FAP) is a serine protease characterized by its high expression in cancer-associated fibroblasts (CAFs) and near absence in adult normal tissues and benign lesions. This unique expression pattern positions FAP as a prospective biomarker for targeted tumor radiodiagnosis and therapy. The advent of FAP-based radiotheranostics is anticipated to revolutionize cancer management. Among various types of FAP ligands, peptides and antibodies have shown advantages over small molecules, exemplifying prolonged tumor retention in human volunteers. Within its scope, this review summarizes the recent research progress of the FAP radiopharmaceuticals based on antibodies and peptides in tumor imaging and therapy. Additionally, it incorporates insights from recent studies, providing valuable perspectives on the clinical utility of FAP-targeted radiopharmaceuticals.

Residual ANTXR1+ myofibroblasts after chemotherapy inhibit anti-tumor immunity via YAP1 signaling pathway

Although cancer-associated fibroblast (CAF) heterogeneity is well-established, the impact of chemotherapy on CAF populations remains poorly understood. Here we address this question in high-grade serous ovarian cancer (HGSOC), in which we previously identified 4 CAF populations. While the global content in stroma increases in HGSOC after chemotherapy, the proportion of FAP+ CAF (also called CAF-S1) decreases. Still, maintenance of high residual CAF-S1 content after chemotherapy is associated with reduced CD8+ T lymphocyte density and poor patient prognosis, emphasizing the importance of CAF-S1 reduction upon treatment. Single cell analysis, spatial transcriptomics and immunohistochemistry reveal that the content in the ECM-producing ANTXR1+ CAF-S1 cluster (ECM-myCAF) is the most affected by chemotherapy. Moreover, functional assays demonstrate that ECM-myCAF isolated from HGSOC reduce CD8+ T-cell cytotoxicity through a Yes Associated Protein 1 (YAP1)-dependent mechanism. Thus, efficient inhibition after treatment of YAP1-signaling pathway in the ECM-myCAF cluster could enhance CD8+ T-cell cytotoxicity. Altogether, these data pave the way for therapy targeting YAP1 in ECM-myCAF in HGSOC.

WNT-dependent interaction between inflammatory fibroblasts and FOLR2+ macrophages promotes fibrosis in chronic kidney disease

Chronic kidney disease (CKD) is a public health problem driven by myofibroblast accumulation, leading to interstitial fibrosis. Heterogeneity is a recently recognized characteristic in kidney fibroblasts in CKD, but the role of different populations is still unclear. Here, we characterize a proinflammatory fibroblast population (named CXCL-iFibro), which corresponds to an early state of myofibroblast differentiation in CKD. We demonstrate that CXCL-iFibro co-localize with macrophages in the kidney and participate in their attraction, accumulation, and switch into FOLR2+ macrophages from early CKD stages on. In vitro, macrophages promote the switch of CXCL-iFibro into ECM-secreting myofibroblasts through a WNT/β-catenin-dependent pathway, thereby suggesting a reciprocal crosstalk between these populations of fibroblasts and macrophages. Finally, the detection of CXCL-iFibro at early stages of CKD is predictive of poor patient prognosis, which shows that the CXCL-iFibro population is an early player in CKD progression and demonstrates the clinical relevance of our findings.

Cancer-Associated Fibroblast Heterogeneity in Malignancy with Focus on Oral Squamous Cell Carcinoma

Oral squamous cell carcinoma (OSCC) remains an understudied and significant global cancer killer and dismal survival rates have not changed in decades. A better understanding of the molecular basis of OSCC progression and metastasis is needed to develop new approaches for treating this disease. The supportive network surrounding cancer tumor cells known as the tumor microenvironment (TME) has gained increasing interest lately since it performs essential protumorigenic functions. Cancer-associated fibroblasts (CAFs) are one of the main cell types in the TME and are known to play a key role in influencing the biological behavior of tumors. CAFs present a heterogeneity both in phenotype as well as functions, leading to the suggestion of different CAF subtypes in several cancer forms. The task to subtype CAFs in OSCC has, however, just begun, and there is today no united way of subtyping CAFs in this disease. This review aims to define the features of CAFs and to summarize CAF subtype research in malignancy with focus on OSCC including aspects as disease prognosis and therapeutic opportunities.

Characterizing Normal Variant [68Ga]Ga-FAPI-46 Uptake in the Epididymis

The biodistribution of fibroblast activation protein inhibitor (FAPI) PET tracers includes the kidneys, bladder, uterus, breast, muscles, and bone marrow. We describe its occasional uptake patterns in the epididymis. Methods: Epididymal [68Ga]Ga-FAPI-46 uptake was retrospectively analyzed in 55 PET/CT studies of 55 men. Uptake intensity (SUV), pattern (diffuse, focal, or multifocal), laterality, and location (epididymal head with or without body/tail) were analyzed. Electronic medical records were reviewed to determine the presence of epididymis-related disease. Results: Epididymal [68Ga]Ga-FAPI-46 uptake was observed in 8 of 55 (15%) subjects, with bilateral epididymal head uptake in all cases and epididymal body/tail uptake in 6 of 8 (75%) cases, 5 of 6 (83%) bilaterally and 1 of 6 (17%) unilaterally. The average SUVmax was greater in the epididymal heads than in the epididymal bodies/tails, with an SUVmax of 4.1 versus 3.0 (P < 0.001). No subject had epididymal disease related to the uptake. Conclusion: [68Ga]Ga-FAPI-46 uptake in the epididymis occurs occasionally and does not appear related to epididymal disease.

Hypoxia as a potential inducer of immune tolerance, tumor plasticity and a driver of tumor mutational burden: Impact on cancer immunotherapy

In cancer patients, immune cells are often functionally compromised due to the immunosuppressive features of the tumor microenvironment (TME) which contribute to the failures in cancer therapies. Clinical and experimental evidence indicates that developing tumors adapt to the immunological environment and create a local microenvironment that impairs immune function by inducing immune tolerance and invasion. In this context, microenvironmental hypoxia, which is an established hallmark of solid tumors, significantly contributes to tumor aggressiveness and therapy resistance through the induction of tumor plasticity/heterogeneity and, more importantly, through the differentiation and expansion of immune-suppressive stromal cells. We and others have provided evidence indicating that hypoxia also drives genomic instability in cancer cells and interferes with DNA damage response and repair suggesting that hypoxia could be a potential driver of tumor mutational burden. Here, we reviewed the current knowledge on how hypoxic stress in the TME impacts tumor angiogenesis, heterogeneity, plasticity, and immune resistance, with a special interest in tumor immunogenicity and hypoxia targeting. An integrated understanding of the complexity of the effect of hypoxia on the immune and microenvironmental components could lead to the identification of better adapted and more effective combinational strategies in cancer immunotherapy. Clearly, the discovery and validation of therapeutic targets derived from the hypoxic tumor microenvironment is of major importance and the identification of critical hypoxia-associated pathways could generate targets that are undeniably attractive for combined cancer immunotherapy approaches.

Development and Characterization of Novel FAP-Targeted Theranostic Pairs: A Bench-to-Bedside Study

Fibroblast activation protein (FAP) is among the most popular targets in nuclear medicine imaging and cancer theranostics. Several small-molecule moieties (FAPI-04, FAPI-46, etc.) are used for developing FAP-targeted theranostic agents. Nonetheless, the circulation time of FAP inhibitors is relatively short, resulting in rapid clearance via kidneys, low tumor uptake, and associated unsatisfactory treatment efficacy. To address the existing drawbacks, we engineered 3 peptides named FD1, FD2, and FD3 with different circulation times through solid-phase peptide synthesis. All the 3 reported peptides bind to human and murine FAP with single-digit nanomolar affinity measured by surface plasmon resonance. The diagnostic and therapeutic potential of the agents labeled with 68Ga and 177Lu was assessed in several tumor models exhibiting different levels of FAP expression. While radiolabeled FD1 was rapidly excreted from kidneys, radiolabeled FD2/FD3 have significantly prolonged circulation, increased tumor uptake, and decreased kidney accumulation. Our findings indicated that [68Ga]Ga-DOTA-FD1 positron emission tomography (PET) effectively detected FAP dynamics, whereas [177Lu]Lu-DOTA-FD2 and [177Lu]Lu-DOTA-FD3 exhibited remarkable therapeutic efficacy in FAP-overexpressing tumor models, including pancreatic cancer cell models characterized by abundant stroma. Moreover, a pilot translational investigation demonstrated that [68Ga]Ga-DOTA-FD1 had the capability to identify both primary and metastatic tumors with precision and distinction. In summary, we developed [68Ga]Ga-DOTA-FD1 for same-day PET imaging of FAP dynamics and [177Lu]Lu-DOTA-FD2 and [177Lu]Lu-DOTA-FD3 for effective radioligand therapy of FAP-overexpressing tumors.

Define cancer-associated fibroblasts (CAFs) in the tumor microenvironment: new opportunities in cancer immunotherapy and advances in clinical trials

Despite centuries since the discovery and study of cancer, cancer is still a lethal and intractable health issue worldwide. Cancer-associated fibroblasts (CAFs) have gained much attention as a pivotal component of the tumor microenvironment. The versatility and sophisticated mechanisms of CAFs in facilitating cancer progression have been elucidated extensively, including promoting cancer angiogenesis and metastasis, inducing drug resistance, reshaping the extracellular matrix, and developing an immunosuppressive microenvironment. Owing to their robust tumor-promoting function, CAFs are considered a promising target for oncotherapy. However, CAFs are a highly heterogeneous group of cells. Some subpopulations exert an inhibitory role in tumor growth, which implies that CAF-targeting approaches must be more precise and individualized. This review comprehensively summarize the origin, phenotypical, and functional heterogeneity of CAFs. More importantly, we underscore advances in strategies and clinical trials to target CAF in various cancers, and we also summarize progressions of CAF in cancer immunotherapy.

The role of immunosuppressive myofibroblasts in the aging process and age-related diseases

Tissue-resident fibroblasts are mesenchymal cells which control the structural integrity of the extracellular matrix (ECM). Fibroblasts possess a remarkable plasticity to allow them to adapt to the changes in the microenvironment and thus maintain tissue homeostasis. Several stresses, also those associated with the aging process, convert quiescent fibroblasts into myofibroblasts which not only display fibrogenic properties but also act as immune regulators cooperating both with tissue-resident immune cells and those immune cells recruited into affected tissues. TGF-β cytokine and reactive oxygen species (ROS) are major inducers of myofibroblast differentiation in pathological conditions either from quiescent fibroblasts or via transdifferentiation from certain other cell types, e.g., macrophages, adipocytes, pericytes, and endothelial cells. Intriguingly, TGF-β and ROS are also important signaling mediators between immunosuppressive cells, such as MDSCs, Tregs, and M2 macrophages. It seems that in pathological states, myofibroblasts are able to interact with the immunosuppressive network. There is clear evidence that a low-grade chronic inflammatory state in aging tissues is counteracted by activation of compensatory immunosuppression. Interestingly, common enhancers of the aging process, such as oxidative stress, loss of DNA integrity, and inflammatory insults, are inducers of myofibroblasts, whereas anti-aging treatments with metformin and rapamycin suppress the differentiation of myofibroblasts and thus prevent age-related tissue fibrosis. I will examine the reciprocal interactions between myofibroblasts and immunosuppressive cells within aging tissues. It seems that the differentiation of myofibroblasts with age-related harmful stresses enhances the activity of the immunosuppressive network which promotes tissue fibrosis and degeneration in elderly individuals.

Comparison of Baseline 68Ga-FAPI and 18F-FDG PET/CT for Prediction of Response and Clinical Outcome in Patients with Unresectable Hepatocellular Carcinoma Treated with PD-1 Inhibitor and Lenvatinib

Fibroblast activation protein contributes to immunosuppression and resistance to immunotherapies. This study aimed to compare baseline 68Ga-labeled fibroblast activation protein inhibitor (68Ga-FAPI) PET/CT and 18F-FDG PET/CT in response and survival prediction in unresectable hepatocellular carcinoma (uHCC) patients treated with the combination of programmed cell death 1 (PD-1) inhibitor and lenvatinib. Methods: In this prospective cohort study, 22 patients with uHCC who underwent baseline 18F-FDG and 68Ga-FAPI PET/CT and soon began taking a combination of PD-1 inhibitor and lenvatinib were recruited. Semiquantitative indices of baseline PET/CT were measured as 18F-FDG SUVmax, metabolic tumor volume, total lesion glycolysis, 68Ga-FAPI SUVmax, 68Ga-FAPI-avid tumor volume (FTV), and total lesion fibroblast activation protein expression (TLF). The primary endpoint was durable or nondurable clinical benefit after treatment, and the secondary endpoints were progression-free survival (PFS) and overall survival (OS). Results: The overall response rate of the combination therapy was 41% (9/22). Fifty percent of patients had durable clinical benefit. Median PFS and OS were 4.8 and 14.4 mo, respectively. Patients with nondurable clinical benefit showed a significantly higher FTV and TLF than those with durable clinical benefit, whereas 18F-FDG parameters overlapped. A higher 68Ga-FAPI-avid tumor burden (FTV > 230.46 cm3 or TLF > 961.74 SUVbody weight⋅cm3) predicted both shorter PFS (4.0 vs. 13.5 mo, P = 0.016) and shorter OS (7.8 mo vs. not reached, P = 0.030). Patients with a higher metabolic tumor burden (metabolic tumor volume > 206.80 cm3 or total lesion glycolysis > 693.53 SUVbody weight⋅cm3) showed a shorter OS although the difference did not reach statistical significance (P = 0.085). In multivariate analysis, a higher 68Ga-FAPI-avid tumor burden (hazard ratio [HR], 3.88 [95% CI, 1.26-12.01]; P = 0.020) and macrovascular invasion (HR, 4.00 [95% CI, 1.06-15.14]; P = 0.039) independently predicted a shorter PFS, whereas a higher 68Ga-FAPI-avid tumor burden (HR, 5.92 [95% CI, 1.19-29.42]; P = 0.035) and bone metastases (HR, 5.88 [95% CI, 1.33-25.93]; P = 0.022) independently predicted a shorter OS. Conclusion: Volumetric indices on baseline 68Ga-FAPI PET/CT were potentially independent prognostic factors to predict durable clinical benefit, PFS, and OS in uHCC patients treated with a combination of PD-1 and lenvatinib. Baseline 68Ga-FAPI PET/CT may facilitate uHCC patient selection before combination therapy.

Fibroblast Activation Protein-α (FAP) Identifies Stromal Invasion in Colorectal Neoplasia

The increasing detection of colorectal adenomas and early adenocarcinomas (ADCs) in the context of nationwide screening programs has led to a significant increase in the incidence of inconclusive diagnoses in which histopathologic analysis of endoscopic biopsies does not allow pathologists to provide a reliable diagnosis of stromal invasion. The objective of this study was to analyze the discriminative capacity of the immunohistochemical expression of fibroblast activation protein-α (FAP) in distinguishing colorectal adenomas with low-grade dysplasia (LGD) and high-grade dysplasia (HGD) from invasive intestinal-type ADCs. The study analyzed the first endoscopic biopsies from a series of patients classified as inconclusive or conclusive for stromal invasion based on the pathologic report. In total, 30 ADCs, 52 HGDs, and 15 LGDs were included in the study. FAP expression was detected in 23/30 ADCs and was negative in all adenomas with either LGD or HGD features (100% specificity and 76.7% sensitivity, area under the curve=0.883, CI=0.79-0.98). Considering these findings, we conclude that FAP is a potentially useful tool for helping pathologists identify invasive lesions in colorectal endoscopic biopsies, avoiding unnecessary biopsy repetitions.

A radiohybrid theranostics ligand labeled with fluorine-18 and lutetium-177 for fibroblast activation protein-targeted imaging and radionuclide therapy

PURPOSE

A series of radiotracers targeting fibroblast activation protein (FAP) with great pharmacokinetics have been developed for cancer diagnosis and therapy. Nevertheless, the use of dominant PET tracers, gallium-68-labeled FAPI derivatives, was limited by the short nuclide half-life and production scale, and the therapeutic tracers exhibited rapid clearance and insufficient tumor retention. In this study, we developed a FAP targeting ligand, LuFL, containing organosilicon-based fluoride acceptor (SiFA) and DOTAGA chelator, capable of labeling fluorine-18 and lutetium-177 in one molecular with simple and highly efficient labeling procedure, to achieve cancer theranostics.

METHODS

The precursor LuFL (20) and [natLu]Lu-LuFL (21) were successfully synthesized and labeled with fluorine-18 and lutetium-177 using a simple procedure. A series of cellular assays were performed to characterize the binding affinity and FAP specificity. PET imaging, SPECT imaging, and biodistribution studies were conducted to evaluate pharmacokinetics in HT-1080-FAP tumor-bearing nude mice. A comparison study of [177Lu]Lu-LuFL ([177Lu]21) and [177Lu]Lu-FAPI-04 was carried out in HT-1080-FAP xenografts to determine the cancer therapeutic efficacy.

RESULTS

LuFL (20) and [natLu]Lu-LuFL (21) demonstrated excellent binding affinity towards FAP (IC50: 2.29 ± 1.12 nM and 2.53 ± 1.87 nM), compared to that of FAPI-04 (IC50: 6.69 ± 0.88 nM). In vitro cellular studies showed that 18F-/177Lu-labeled 21 displayed high specific uptake and internalization in HT-1080-FAP cells. Micro-PET, SPECT imaging and biodistribution studies with [18F]/[177Lu]21 revealed higher tumor uptake and longer tumor retention than those of [68 Ga]/[177Lu]Ga/Lu-FAPI-04. The radionuclide therapy studies showed significantly greater inhibition of tumor growth for the [177Lu]21 group, than for the control group and the [177Lu]Lu-FAPI-04 group.

CONCLUSION

The novel FAPI-based radiotracer containing SiFA and DOTAGA was developed as a theranostics radiopharmaceutical with simple and short labeling process, and showed promising properties including higher cellular uptake, better FAP binding affinity, higher tumor uptake and prolong retention compared to FAPI-04. Preliminary experiments with 18F- and 177Lu-labeled 21 showed promising tumor imaging properties and favorable anti-tumor efficacy.

68 Ga-FAPI PET/CT Detection of Non-FDG-Avid Poorly Differentiated Adenocarcinoma of the Trachea

ABSTRACT

Primary tracheal adenocarcinoma is relatively rare in clinical practice. We describe the 68 Ga-FAPI-04 and 18 F-FDG PET/CT findings of primary poorly differentiated tracheal adenocarcinoma in a 48-year-old woman. In the present case, the tumor showed increased 68 Ga-FAPI uptake but not significant 18 F-FDG activity.

What is new in cancer-associated fibroblast biomarkers?

The tumor microenvironment is one of the important drivers of tumor development. Cancer-associated fibroblasts (CAFs) are a major component of the tumor stroma and actively participate in tumor development, invasion, metastasis, drug resistance, and other biological behaviors. CAFs are a highly heterogeneous group of cells, a reflection of the diversity of their origin, biomarkers, and functions. The diversity of CAF origin determines the complexity of CAF biomarkers, and CAF subpopulations expressing different biomarkers may play contrasting roles in tumor progression. In this review, we provide an overview of these emerging CAF biomarkers and the biological functions that they suggest, which may give a better understanding of the relationship between CAFs and tumor cells and be of great significance for breakthroughs in precision targeted therapy for tumors. Video Abstract.

Usefulness of [68Ga]FAPI-04 and [18F]FDG PET/CT for the detection of primary tumour and metastatic lesions in gastrointestinal carcinoma: a comparative study

OBJECTIVE

To assess and compare the diagnostic performance of gallium-68-labelled fibroblast activation protein inhibitor ([⁶⁸Ga]FAPI-04) and fluorine-18 fluorodeoxyglucose ([¹⁸F]FDG) positron emission tomography/computed tomography (PET/CT) in gastrointestinal cancer.

METHODS

Fifty-one patients who underwent both [¹⁸F]FDG and [⁶⁸Ga]FAPI-04 PET/CT for initial staging or restaging were enrolled. Histopathological findings, typical radiological appearances, and clinical imaging follow-up were used as the reference standard. The diagnostic performance of the two tracers was calculated and compared. The maximum standardised uptake value (SUVmax), mean SUV (SUVmean), tumour-to-mediastinal blood pool ratio (TBR), and tumour-to-liver ratio (TLR) of primary and metastatic lesions were measured and compared between two imaging modalities.

RESULTS

In patient-based analysis, [⁶⁸Ga]FAPI-04 showed much better diagnostic sensitivity than [¹⁸F]FDG in detecting primary tumour (94.44% [17/18] vs. 61.11% [11/18]), postoperative recurrence and metastases (95.65% [22/23] vs. 69.57% [16/23]), and peritoneal carcinomatosis (100% [28/28] vs. 60.71% [17/28]) (all p < 0.05). In lesion-based analysis, [⁶⁸Ga]FAPI-04 showed higher sensitivity than [¹⁸F]FDG for detecting lymph node metastases. In peritoneal carcinomatosis, the median SUVmax (12.12 vs. 7.18) and SUVmean (6.84 vs. 4.11) with [⁶⁸Ga]FAPI-04 were significantly higher than those with [¹⁸F]FDG (all p < 0.005). The TBR and TLR of [⁶⁸Ga]FAPI-04 were significantly higher than those of [¹⁸F]FDG for detecting primary tumour, lymph node, liver, and peritoneal metastases (all p < 0.005). Therapeutic management changed in 13 patients according to [⁶⁸Ga]FAPI-04 PET/CT compared with conventional imaging.

CONCLUSIONS

[⁶⁸Ga]FAPI-04 is superior to [¹⁸F]FDG PET/CT for detecting primary tumour, postoperative recurrence and metastasis, and peritoneal carcinomatosis in gastrointestinal cancer.

KEY POINTS

• [⁶⁸Ga]FAPI-04 PET/CT showed significantly higher sensitivity than [¹⁸F]FDG PET/CT in the detection of primary tumour and postoperative recurrence and metastasis in patients with gastrointestinal carcinoma. • [⁶⁸Ga]FAPI-04 PET/CT had obvious advantages over [¹⁸F]FDG PET/CT in the detection of peritoneal carcinomatosis from gastrointestinal carcinoma with a much higher FAPI uptake value, TBR, and TLR. • Although the median SUVmax and SUVmean of [⁶⁸Ga]FAPI-04 were similar to those of [¹⁸F]FDG for the primary tumour, lymph node metastases, and liver metastases in gastrointestinal carcinoma, the TBR and TLR of the SUVmax and SUVmean were significantly higher on [⁶⁸Ga]FAPI-04 PET/CT, causing the lesions to be displayed more clearly.

Fibroblasts as Turned Agents in Cancer Progression

Differentiated epithelial cells reside in the homeostatic microenvironment of the native organ stroma. The stroma supports their normal function, their G0 differentiated state, and their expansion/contraction through the various stages of the life cycle and physiologic functions of the host. When malignant transformation begins, the microenvironment tries to suppress and eliminate the transformed cells, while cancer cells, in turn, try to resist these suppressive efforts. The tumor microenvironment encompasses a large variety of cell types recruited by the tumor to perform different functions, among which fibroblasts are the most abundant. The dynamics of the mutual relationship change as the sides undertake an epic battle for control of the other. In the process, the cancer "wounds" the microenvironment through a variety of mechanisms and attracts distant mesenchymal stem cells to change their function from one attempting to suppress the cancer, to one that supports its growth, survival, and metastasis. Analogous reciprocal interactions occur as well between disseminated cancer cells and the metastatic microenvironment, where the microenvironment attempts to eliminate cancer cells or suppress their proliferation. However, the altered microenvironmental cells acquire novel characteristics that support malignant progression. Investigations have attempted to use these traits as targets of novel therapeutic approaches.

Fibroblast Activation Protein Inhibitor Theranostics

Fibroblast activation protein (FAP)-radioligand therapy might be effective in some patients without being curative. FAP-radioligands deliver ionizing radiation directly to FAP⁺ cancer-associated fibroblasts and, in some cancers, to FAP⁺ tumor cells; in addition, they indirectly irradiate FAP^- cells in tumor tissue via cross-fire and bystander effects. Here, we discuss the potential to improve FAP-radioligand therapy through interfering with DNA damage repair, immunotherapy, and co-targeting cancer-associated fibroblasts. As the molecular and cellular effects of FAP-radioligands on the tumor and its microenvironment have not been investigated yet, we call for future research to close this gap in knowledge, which prevents the development of more effective FAP-radioligand therapies.

An Update of G-Protein-Coupled Receptor Signaling and Its Deregulation in Gastric Carcinogenesis

G-protein-coupled receptors (GPCRs) belong to a cell surface receptor superfamily responding to a wide range of external signals. The binding of extracellular ligands to GPCRs activates a heterotrimeric G protein and triggers the production of numerous secondary messengers, which transduce the extracellular signals into cellular responses. GPCR signaling is crucial and imperative for maintaining normal tissue homeostasis. High-throughput sequencing analyses revealed the occurrence of the genetic aberrations of GPCRs and G proteins in multiple malignancies. The altered GPCRs/G proteins serve as valuable biomarkers for early diagnosis, prognostic prediction, and pharmacological targets. Furthermore, the dysregulation of GPCR signaling contributes to tumor initiation and development. In this review, we have summarized the research progress of GPCRs and highlighted their mechanisms in gastric cancer (GC). The aberrant activation of GPCRs promotes GC cell proliferation and metastasis, remodels the tumor microenvironment, and boosts immune escape. Through deep investigation, novel therapeutic strategies for targeting GPCR activation have been developed, and the final aim is to eliminate GPCR-driven gastric carcinogenesis.

Advances in PET/CT Imaging for Breast Cancer Patients and Beyond

Breast cancer is the most common cancer in women around the world and the fifth leading cause of cancer-related death [...].

Modulation of the antitumor immune response by cancer-associated fibroblasts: mechanisms and targeting strategies to hamper their immunosuppressive functions

Cancer-associated fibroblasts (CAFs) are highly heterogeneous players that shape the tumor microenvironment and influence tumor progression, metastasis formation, and response to conventional therapies. During the past years, some CAFs subsets have also been involved in the modulation of immune cell functions, affecting the efficacy of both innate and adaptive anti-tumor immune responses. Consequently, the implication of these stromal cells in the response to immunotherapeutic strategies raised major concerns. In this review, current knowledge of CAFs origins and heterogeneity in the tumor stroma, as well as their effects on several immune cell populations that explain their immunosuppressive capabilities are summarized. The current development of therapeutic strategies for targeting this population and their implication in the field of cancer immunotherapy is also highlighted.

Integrative pan-cancer analysis and clinical characterization of the N7-methylguanosine (m7G) RNA modification regulators in human cancers

Background: RNA modification is one of the epigenetic mechanisms that regulates post-transcriptional gene expression, and abnormal RNA modifications have been reported to play important roles in tumorigenesis. N7-methylguanosine (m7G) is an essential modification at the 5′ cap of human mRNA. However, a systematic and pan-cancer analysis of the clinical relevance of m7G related regulatory genes is still lacking.

Methods: We used univariate Cox model and Kaplan-Meier analysis to generate the forest plot of OS, PFI, DSS and identified the correlation between the altered expression of m7G regulators and patient survival in 33 cancer types from the TCGA and GTEx databases. Then, the “estimate” R-package, ssGSEA and CIBERSORT were used to depict the pan-cancer immune landscape. Through Spearman’s correlation test, we analyzed the correlation between m7G regulators and the tumor microenvironment (TME), immune subtype, and drug sensitivity of the tumors, which was further validated in NSCLC. We also assessed the changes in the expression of m7G related regulatory genes in NSCLC with regards to the genetic and transcriptional aspects and evaluated the correlation of METTL1 and WDR4 expression with TMB, MSI and immunotherapy in pan-cancer.

Results: High expression of most of the m7G regulators was significantly associated with worse prognosis. Correlation analyses revealed that the expression of majority of the m7G regulators was correlated with tumor immune infiltration and tumor stem cell scores. Drug sensitivity analysis showed that the expression of CYFP1,2 was closely related to drug sensitivity for various anticancer agents (p &lt; 0.001). Analysis of the pan-cancer immune subtype revealed significant differences in the expression of m7G regulators between different immune subtypes (p &lt; 0.001). Additionally, the types and proportions of mutations in METTL1 and WDR4 and their relevance to immunotherapy were further described.

Conclusion: Our study is the first to evaluate the correlation between the altered expression of m7G regulators and patient survival, the degree of immune infiltration, TME and drug sensitivity in pan-cancer datasets.

m7G regulator-mediated molecular subtypes and tumor microenvironment in kidney renal clear cell carcinoma

Background: RNA methylation modification plays an important role in immune regulation. m7G RNA methylation is an emerging research hotspot in the RNA methylation field. However, its role in the tumor immune microenvironment of kidney renal clear cell carcinoma (KIRC) is still unclear.

Methods: We analyzed the expression profiles of 29 m7G regulators in KIRC, integrated multiple datasets to identify a novel m7G regulator-mediated molecular subtype, and developed the m7G score. We evaluated the immune tumor microenvironments in m7G clusters and analyzed the correlation of the m7G score with immune cells and drug sensitivity. We tested the predictive power of the m7G score for prognosis of patients with KIRC and verified the predictive accuracy of the m7G score by using the GSE40912 and E-MTAB-1980 datasets. The genes used to develop the m7G score were verified by qRT-PCR. Finally, we experimentally analyzed the effects of WDR4 knockdown on KIRC proliferation, migration, invasion, and drug sensitivity.

Results: We identified three m7G clusters. The expression of m7G regulators was higher in cluster C than in other clusters. m7G cluster C was related to immune activation, low tumor purity, good prognosis, and low m7G score. Cluster B was related to drug metabolism, high tumor purity, poor survival, and high m7G score. Cluster A was related to purine metabolism. The m7G score can well-predict the prognosis of patients with KIRC, and its prediction accuracy based on the m7G score nomogram was very high. Patients with high m7G scores were more sensitive to rapamycin, gefitinib, sunitinib, and vinblastine than other patients. Knocking down WDR4 can inhibit the proliferation, migration, and invasion of 786-0 and Caki-1 cells and increase sensitivity to sorafenib and sunitinib.

Conclusion: We proposed a novel molecular subtype related to m7G modification and revealed the immune cell infiltration characteristics of different subtypes. The developed m7G score can well-predict the prognosis of patients with KIRC, and our research provides a basis for personalized treatment of patients with KIRC.

Integrated analysis of fibroblasts molecular features in papillary thyroid cancer combining single-cell and bulk RNA sequencing technology

BACKGROUND

Papillary thyroid cancer (PTC) is the most common pathological type of thyroid cancer with a high incidence globally. Increasing evidence reported that fibroblasts infiltration in cancer was correlated with prognostic outcomes. However, fibroblasts related study in thyroid cancer remains deficient.

METHODS

Single-cell sequencing data of PTC were analyzed by Seurat R package to explore the ecosystem in PTC and identify fibroblasts cluster. The expression profiles and prognostic values of fibroblast related genes were assessed in TCGA dataset. A fibrosis score model was established for prognosis prediction in thyroid cancer patients. Differentially expressed genes and functional enrichment between high and low fibrosis score groups in TCGA dataset were screened. The correlation of immune cells infiltration and fibrosis score in thyroid cancer patients was explored. Expression levels and prognostic values of key fibroblast related factor were validated in clinical tissues another PTC cohort.

RESULTS

Fibroblasts were highly infiltrated in PTC and could interact with other type of cells by single-cell data analysis. 34 fibroblast related terms were differentially expressed in thyroid tumor tissues. COX regression analysis suggested that the constructed fibrosis score model was an independent prognostic predictor for thyroid cancer patients (HR = 5.17, 95%CI 2.31-11.56, P = 6.36E-05). Patients with low fibrosis scores were associated with a significantly better overall survival (OS) than those with high fibrosis scores in TCGA dataset (P = 7.659E-04). Specific immune cells infiltration levels were positively correlated with fibrosis score, including monocytes, M1 macrophages and eosinophils.

CONCLUSION

Our research demonstrated a comprehensive horizon of fibroblasts features in thyroid cancer microenvironment, which may provide potential value for thyroid cancer treatment.