The application of the fibroblast activation protein α-targeted immunotherapy strategy

Biomimetic "nano-spears" for CAFs-targeting: splintered three "shields" with enhanced cisplatin anti-TNBC efficiency

The treatment dilemma of triple-negative breast cancer (TNBC) revolves around drug resistance and metastasis. Cancer-associated fibroblasts (CAFs) contribute to cisplatin (Cis) resistance and further metastasis in TNBC, making TNBC a difficult-to-treat disease. The dense stromal barrier which restricts drug delivery, invasive phenotype of tumor cells, and immunosuppressive tumor microenvironment (TME) induced by CAFs serve as three "shields" for TNBC against Cis therapy. Here, we designed a silybin-loaded biomimetic nanoparticle coated with anisamide-modified red blood cell membrane (ARm@SNP) as a "nanospear" for CAFs-targeting, which could shatter the "shields" and significantly exhibit inhibitory effect on 4T1 cells in combination with Cis both in vitro and in vivo. The ARm@SNP/Cis elicited 4T1 tumor growth arrest and destroyed three "shields" as follows: disintegrating the stromal barrier by inhibiting blood vessels growth and the expression of fibronectin; decreasing 4T1 cell invasion and metastasis by affecting the TGF-β/Twist/EMT pathway which impeded EMT activation; reversing the immunosuppressive microenvironment by increasing the activity and infiltration of immunocompetent cells. Based on CAFs-targeting, ARm@SNP reversed the resistance of Cis, remodeled the TME and inhibited invasion and metastasis while significantly improving the therapeutic effect of Cis on 4T1 tumor-bearing mice, providing a promising approach for treating intractable TNBC.

Value of Semi-Quantitative Parameters of 68Ga-FAPI-04 PET/CT in Primary Malignant and Benign Diseases: A Comparison with 18F-FDG

Objectives: We aimed to compare the value of the semiquantitative parameters of 68Ga-labeled FAP inhibitor (68Ga-FAPI)-04 positron emission tomography/computed tomography (PET/CT) and 18F-fluorodeoxyglucose (18F-FDG) in diagnosing primary malignant and benign diseases. Materials and Methods: 18F-FDG and 68Ga-FAPI-04 PET/CT images of 80 patients were compared. Semiquantitative parameters, including maximum standardized uptake value (SUVmax), mean SUV (SUVmean), peak SUV (SUVpeak), peak SUV by lean body mass (SULpeak), metabolic tumor volume (or tumor volume of FAPI; FAPI-TV), and TLG (or total lesion activity of FAPI; FAPI-TLA), were automatically obtained using the IntelliSpace Portal image processing workstation with a threshold of 40% SUVmax. The liver blood pool was measured as the background, and the tumor-to-background ratio (TBRliver) was calculated. Results: In all malignant lesions, FAPI-TV and FAPI-TLA were higher in 68Ga-FAPI-04 PET/CT than in 18F-FDG. In the subgroup analysis, 68Ga-FAPI-04 had higher FAPI-TV and FAPI-TLA and lower SUVmax than 18F-FDG had in group A, including gynecological tumor, esophageal, and colorectal cancers. However, six semiquantitative parameters were higher in group B (the other malignant tumors). For the benign diseases, SUVmax, SUVmean, SUVpeak, and SULpeak were lower in 68Ga-FAPI-04 PET/CT than in 18F-FDG. 68Ga-FAPI-04 PET/CT showed a lower liver background and a higher TBRliver than 18F-FDG did. 68Ga-FAPI-04 PET/CT had higher accuracy, sensitivity, and specificity than 18F-FDG had. Conclusion: More accurate semiquantitative parameters and lower abdominal background in 68Ga-FAPI-04 PET/CT make it more competitive in the differential diagnosis of malignant and benign diseases than in 18F-FDG.

Impact of STAT-signaling pathway on cancer-associated fibroblasts in colorectal cancer and its role in immunosuppression

Colorectal cancer (CRC) remains one of the most commonly diagnosed and deadliest types of cancer worldwide. CRC displays a desmoplastic reaction (DR) that has been inversely associated with poor prognosis; less DR is associated with a better prognosis. This reaction generates excessive connective tissue, in which cancer-associated fibroblasts (CAFs) are critical cells that form a part of the tumor microenvironment. CAFs are directly involved in tumorigenesis through different mechanisms. However, their role in immunosuppression in CRC is not well understood, and the precise role of signal transducers and activators of transcription (STATs) in mediating CAF activity in CRC remains unclear. Among the myriad chemical and biological factors that affect CAFs, different cytokines mediate their function by activating STAT signaling pathways. Thus, the harmful effects of CAFs in favoring tumor growth and invasion may be modulated using STAT inhibitors. Here, we analyze the impact of different STATs on CAF activity and their immunoregulatory role.

Quarter Century Positron Emission Tomography/Computed Tomography Transformation of Oncology: Head and Neck Cancer

During the last 2 decades, f-18 fluorodeoxyglucose positron emission tomography/computed tomography (18F FDG PET/CT) has transformed the clinical head and neck cancer imaging for patient management and predicting survival outcomes. It is now widely used for staging, radiotherapy planning, posttherapy assessment, and for detecting recurrence in head and neck cancers and is widely included in NCCN and other evidence based clinical practice guidelines. Future Directions would include evaluating the potential value of FAPI PET/CT for head and neck cancers, opportunity to use volumetric and tumor heterogeneity parameters and deploying AI in diagnostic and therapeutic assessments.

Nano-drug delivery system targeting FAP for the combined treatment of oral leukoplakia

Oral leukoplakia (OLK) has received much attention due to its potential risk of malignant transformation. Studies have shown that when drug therapy is combined with photothermal therapy (PTT), not only can the cytotoxicity of the drug be enhanced, but also the heat energy can be used to kill the lesion cells, so we can combine drug therapy with PTT to enhance the therapeutic effect on OLK. However, with certain drawbacks due to its lack of targeting, fibroblast activating protein (FAP) has become an attractive target for OLK combination therapy. In this study, we used NGO-PEG loaded with FAP-targeting peptide (F-TP) and celecoxib (CXB) to construct a nano-drug delivery system CGPF for targeting OLK with high FAP expression and confirmed the biocompatibility and therapeutic efficacy of CGPF by in vitro and in vivo experiments. Overall, the novel nano-drug delivery system CGPF proposed in this study showed a very significant potential for the combination therapy of OLK.

Role of cancer-associated fibroblasts in colorectal cancer and their potential as therapeutic targets

Cancer-associated fibroblasts (CAFs) are mesenchymal cells in the tumor microenvironment (TME). CAFs are the most abundant cellular components in the TME of solid tumors. They affect the progression and course of chemotherapy and radiotherapy in various types of tumors including colorectal cancer (CRC). CAFs can promote tumor proliferation, invasion, and metastasis; protect tumor cells from immune surveillance; and resist tumor cell apoptosis caused by chemotherapy, resulting in drug resistance to chemotherapy. In recent years, researchers have become increasingly interested CAF functions and have conducted extensive research. However, compared to other types of malignancies, our understanding of the interaction between CRC cells and CAFs remains limited. Therefore, we searched the relevant literature published in the past 10 years, and reviewed the origin, biological characteristics, heterogeneity, role in the TME, and potential therapeutic targets of CAFs, to aid future research on CAFs and tumors.

Tumor-derived systems as novel biomedical tools-turning the enemy into an ally

Cancer is a complex illness that presents significant challenges in its understanding and treatment. The classic definition, "a group of diseases characterized by the uncontrolled growth and spread of abnormal cells in the body," fails to convey the intricate interaction between the many entities involved in cancer. Recent advancements in the field of cancer research have shed light on the role played by individual cancer cells and the tumor microenvironment as a whole in tumor development and progression. This breakthrough enables the utilization of the tumor and its components as biological tools, opening new possibilities. This article delves deeply into the concept of "tumor-derived systems", an umbrella term for tools sourced from the tumor that aid in combatting it. It includes cancer cell membrane-coated nanoparticles (for tumor theranostics), extracellular vesicles (for tumor diagnosis/therapy), tumor cell lysates (for cancer vaccine development), and engineered cancer cells/organoids (for cancer research). This review seeks to offer a complete overview of the tumor-derived materials that are utilized in cancer research, as well as their current stages of development and implementation. It is aimed primarily at researchers working at the interface of cancer biology and biomedical engineering, and it provides vital insights into this fast-growing topic.

Fibroblast diversity and plasticity in the tumor microenvironment: roles in immunity and relevant therapies

Cancer-associated fibroblasts (CAFs), enriched in the tumor stroma, have received increasing attention because of their multifaceted effects on tumorigenesis, development, metastasis, and treatment resistance in malignancies. CAFs contributed to suppressive microenvironment via different mechanisms, while CAFs also exerted some antitumor effects. Therefore, CAFs have been considered promising therapeutic targets for their remarkable roles in malignant tumors. However, patients with malignancies failed to benefit from current CAFs-targeted drugs in many clinical trials, which suggests that further in-depth investigation into CAFs is necessary. Here, we summarize and outline the heterogeneity and plasticity of CAFs mainly by exploring their origin and activation, highlighting the regulation of CAFs in the tumor microenvironment during tumor evolution, as well as the critical roles performed by CAFs in tumor immunity. In addition, we summarize the current immunotherapies targeting CAFs, and conclude with a brief overview of some prospects for the future of CAFs research in the end. Video Abstract.

Targeting fibroblast activation protein (FAP): advances in CAR-T cell, antibody, and vaccine in cancer immunotherapy

Fibroblast activation protein (FAP) is a serine protease with dual enzymatic activities overexpressed in cancer-associated fibroblasts (CAFs) in several tumor types, while its expression in healthy adult tissues is scarce. FAP overexpression on CAFs is associated with poor prognosis and plays an important role in tumor development, progression, and invasion. Therefore, FAP is considered a robust therapeutic target for cancer therapy. Here, we try to review and highlight the recent advances in immunotherapies for FAP targeting including the anti-FAP antibodies and immunoconjugates, FAP chimeric antigen receptor (CAR)-T cell, and various FAP vaccines in a preclinical and clinical setting. Subsequently, a discussion on the challenges and prospects associated with the development and translation of effective and safe therapies for targeting and depletion of FAP is provided. We proposed that new CAR-T cell engineering strategies and nanotechnology-based systems as well as advanced functional biomaterials can be used to improve the efficiency and safety of CAR-T cells and vaccines against FAP for more personalized immunotherapy. This review emphasizes the immune targeting of FAP as an emerging stromal candidate and one of the crucial elements in immunotherapy and shows the potential for improvement of current cancer therapy. A summary of different immunotherapy approaches to target fibroblast activation protein (FAP) for cancer therapy.

Imaging Recommendations for Theranostic PET-CT in Oncology

We in this article have presented a review of the guideline recommendations on theranostic positron emission tomography-computed tomography (PET-CT) imaging which will be helpful to assist practitioners in providing appropriate patient care. Multiple guidelines by different societies and medical associations provide standards for diagnosis, imaging, and treatment of cancer patients. They have generated a number of recommendations related to 68Ga-DOTATATE and 68Ga-PSMA-11 PET-CT, which are the classical examples of theranostic PET-CT imaging in current practice.

Targeting cancer-associated fibroblasts: Challenges, opportunities and future directions

Cancer-associated fibroblasts (CAFs) are a common cell in the tumour microenvironment with diverse tumour-promoting functions. Their presence in tumours is commonly associated with poor prognosis making them attractive therapeutic targets, particularly in the context of immunotherapy where CAFs have been shown to promote resistance to checkpoint blockade. Previous attempts to inhibit CAFs clinically have not been successful, however, in part due to a lack of understanding of CAF heterogeneity and function, with some fibroblast populations potentially being tumour suppressive. Recent single-cell transcriptomic studies have advanced our understanding of fibroblast phenotypes in normal tissues and cancers, allowing for a more precise characterisation of CAF subsets and providing opportunities to develop new therapies. Here we review recent advances in the field, focusing on the evolving area of therapeutic CAF targeting.

Epitope-based minigene vaccine targeting fibroblast activation protein α induces specific immune responses and anti-tumor effects in 4 T1 murine breast cancer model

Fibroblast activation protein (FAPα) is a tumor stromal antigen expressed by cancer-associated fibroblasts (CAFs) in more than 90 % of malignant epithelial carcinomas. FAPα-based immunotherapy has been reported and showed that FAPα-specific immune response can remold immune microenvironment and contribute to tumor regression. Many FAPα-based vaccines have been investigated in preclinical trials, which can elicit strong and durable cytolytic T lymphocytes (CTL) with good safety. However, epitope-based FAPα vaccines are rarely reported. To break tolerance against self-antigens, analogue epitopes with modified peptides at the anchor residues are typically used to improve epitope immunogenicity. To investigate the feasibility of a FAPα epitope-based vaccine for cancer immunotherapy in vivo, we conducted a preclinical study to identify a homologous CTL epitope of human and mouse FAPα and obtained its analogue epitope in BALB/c mice, and explored the anti-tumor activity of their minigene vaccines in 4 T1 tumor-bearing mice. By using in silico epitope prediction tools and immunogenicity assays, immunodominant epitope FAP.291 (YYFSWLTWV) and its analogue epitope FAP.291I9 (YYFSWLTWI) were identified. The FAP.291-based epitope minigene vaccine successfully stimulated CTLs targeting CAFs and exhibited anti-tumor activity in a 4 T1 murine breast cancer model. Furthermore, although the analogue epitope FAP.291I9 enhanced FAP.291-specific immune responses, improvement of anti-tumor immunity effects was not observed. Check of immunosuppressive factors revealed that the high levels of IL-10, IL-13, myeloid-derived suppressor cells and iNOS induced by FAP.291I9 increased, which considered the main cause of the failure of the analogue epitope-based vaccine. Thus, we demonstrated for the first time that the FAP.291 minigene vaccine could induce mouse CTLs and also function as a tumor regression antigen, providing the basis for future studies of FAPα epitope-based vaccines. This study may also be valuable for further improvement of the immunogenicity of analogue epitope vaccines.

Metabolic reprogramming and crosstalk of cancer-related fibroblasts and immune cells in the tumor microenvironment

It is notorious that cancer cells alter their metabolism to adjust to harsh environments of hypoxia and nutritional starvation. Metabolic reprogramming most often occurs in the tumor microenvironment (TME). TME is defined as the cellular environment in which the tumor resides. This includes surrounding blood vessels, fibroblasts, immune cells, signaling molecules and the extracellular matrix (ECM). It is increasingly recognized that cancer cells, fibroblasts and immune cells within TME can regulate tumor progression through metabolic reprogramming. As the most significant proportion of cells among all the stromal cells that constitute TME, cancer-associated fibroblasts (CAFs) are closely associated with tumorigenesis and progression. Multitudinous studies have shown that CAFs participate in and promote tumor metabolic reprogramming and exert regulatory effects via the dysregulation of metabolic pathways. Previous studies have demonstrated that curbing the substance exchange between CAFs and tumor cells can dramatically restrain tumor growth. Emerging studies suggest that CAFs within the TME have emerged as important determinants of metabolic reprogramming. Metabolic reprogramming also occurs in the metabolic pattern of immune cells. In the meanwhile, immune cell phenotype and functions are metabolically regulated. Notably, immune cell functions influenced by metabolic programs may ultimately lead to alterations in tumor immunity. Despite the fact that multiple previous researches have been devoted to studying the interplays between different cells in the tumor microenvironment, the complicated relationship between CAFs and immune cells and implications of metabolic reprogramming remains unknown and requires further investigation. In this review, we discuss our current comprehension of metabolic reprogramming of CAFs and immune cells (mainly glucose, amino acid, and lipid metabolism) and crosstalk between them that induces immune responses, and we also highlight their contributions to tumorigenesis and progression. Furthermore, we underscore potential therapeutic opportunities arising from metabolism dysregulation and metabolic crosstalk, focusing on strategies targeting CAFs and immune cell metabolic crosstalk in cancer immunotherapy.

Automated synthesis of [68Ga]Ga-FAPI-46 without pre-purification of the generator eluate on three common synthesis modules and two generator types

Background

The recent development of quinoline-based radiotracers, which act as fibroblast activation protein inhibitors (FAPIs), has shown promising preclinical and clinical advantages. [⁶⁸Ga]Ga-FAPI-46 is a new radiotracer for in vivo detection of the fibroblast activation protein by positron emission tomography (PET). Recently, the automated synthesis of [⁶⁸Ga]Ga-FAPI-46 was reported based on pre-concentration and purification of the generator eluate by using a cation exchange-cartridge.

Our aim was to simplify the synthesis and shorten the automated synthesis of [⁶⁸Ga]Ga-FAPI-46 to make it accessible and thus even more attractive to a broader clinical and scientific community.

Results

We developed and evaluated the GMP compliant automatic synthesis of [⁶⁸Ga]Ga-FAPI-46 using two different ⁶⁸Ge/⁶⁸Ga generators (an Eckert & Ziegler, GalliaPharm generator, 1.85 GBq/50 mCi and an iThemba generator, 1.85 GBq/50 mCi) Somerset West, South Africa) and three different commercial and customized systems: the EasyOne module from Trasis; the GaSy module from Synthra with a customized synthesis template and a customized single use cassette. Additionally, the automatic synthesis of [⁶⁸Ga]Ga-FAPI-46 was established on a GallElut synthesis module from Scintomics with fixed tubing.

Conclusions

Independent of the synthesis modules or the generators employed we were able to complete the synthesis of [⁶⁸Ga]Ga-FAPI-46 in 12 min including the process of purification and formulation. In all cases, the final products showed more than 99.5% chemical purity and the radiochemical yield reached around 92.5% (decay corrected). All quality control parameters (e.g. sterility, stability and radiochemical purity) were conform to the European Pharmacopoeia.

Targeting the tumor biophysical microenvironment to reduce resistance to immunotherapy

Immunotherapy based on immune checkpoint inhibitors has evolved into a new pillar of cancer treatment in clinics, but dealing with treatment resistance (either primary or acquired) is a major challenge. The tumor microenvironment (TME) has a substantial impact on the pathological behaviors and treatment response of many cancers. The biophysical clues in TME have recently been considered as important characteristics of cancer. Furthermore, there is mounting evidence that biophysical cues in TME play important roles in each step of the cascade of cancer immunotherapy that synergistically contribute to immunotherapy resistance. In this review, we summarize five main biophysical cues in TME that affect resistance to immunotherapy: extracellular matrix (ECM) structure, ECM stiffness, tumor interstitial fluid pressure (IFP), solid stress, and vascular shear stress. First, the biophysical factors involved in anti-tumor immunity and therapeutic antibody delivery processes are reviewed. Then, the causes of these five biophysical cues and how they contribute to immunotherapy resistance are discussed. Finally, the latest treatment strategies that aim to improve immunotherapy efficacy by targeting these biophysical cues are shared. This review highlights the biophysical cues that lead to immunotherapy resistance, also supplements their importance in related technologies for studying TME biophysical cues in vitro and therapeutic strategies targeting biophysical cues to improve the effects of immunotherapy.

FAPI-PET/CT in Cancer Imaging: A Potential Novel Molecule of the Century

Fibroblast activation protein (FAP), a type II transmembrane serine protease, is highly expressed in more than 90% of epithelial tumors and is closely associated with various tumor invasion, metastasis, and prognosis. Using FAP as a target, various FAP inhibitors (FAPIs) have been developed, most of which have nanomolar levels of FAP affinity and high selectivity and are used for positron emission tomography (PET) imaging of different tumors. We have conducted a systematic review of the available data; summarized the biological principles of FAPIs for PET imaging, the synthesis model, and metabolic characteristics of the radiotracer; and compared the respective values of FAPIs and the current mainstream tracer ¹⁸F-Fludeoxyglucose (¹⁸F-FDG) in the clinical management of tumor and non-tumor lesions. Available research evidence indicates that FAPIs are a molecular imaging tool complementary to ¹⁸F-FDG and are expected to be the new molecule of the century with better imaging effects than ¹⁸F-FDG in a variety of cancers, including gastrointestinal tumors, liver tumors, breast tumors, and nasopharyngeal carcinoma.

Modeling Pancreatic Cancer with Patient-Derived Organoids Integrating Cancer-Associated Fibroblasts

Simple Summary

Pancreatic cancer tissue is resistant to anticancer drugs because of its complex microenvironment. Cancer-associated fibroblasts (CAFs) are an important source of extracellular matrix components, which alter the physical and chemical properties of pancreatic tissue, thus impairing effective intratumoral drug delivery and resulting in resistance to conventional chemotherapy. In this study, we developed a novel CAF-integrated pancreatic cancer organoid (CIPCO) model that can mimic the tumor microenvironment and confirmed that the gene expression and pathological characteristics of CIPCO are similar to those of human cancer tissue. The organoid model could serve as a preclinical model for developing individualized therapies.

Abstract

Pancreatic cancer is a devastating disease and is highly resistant to anticancer drugs because of its complex microenvironment. Cancer-associated fibroblasts (CAFs) are an important source of extracellular matrix (ECM) components, which alter the physical and chemical properties of pancreatic tissue, thus impairing effective intratumoral drug delivery and resulting in resistance to conventional chemotherapy. The objective of this study was to develop a new cancer organoid model, including a fibrous tumor microenvironment (TME) using CAFs. The CAF-integrated pancreatic cancer organoid (CIPCO) model developed in this study histologically mimicked human pancreatic cancer and included ECM production by CAFs. The cancer cell–CAF interaction in the CIPCO promoted epithelial–mesenchymal transition of cancer cells, which was reversed by CAF inhibition using all-trans retinoic acid. Deposition of newly synthesized collagen I in the CIPCO disturbed the delivery of gemcitabine to cancer cells, and treatment with collagenase increased the cytotoxic effect of gemcitabine. This model may lead to the development of next-generation cancer organoid models recapitulating the fibrous TME.

Fibroblast activation protein alpha: Comprehensive detection methods for drug target and tumor marker

Fibroblast activation protein alpha (FAP-α, EC3.4.2. B28), a type II transmembrane proteolytic enzyme for the serine protease peptidase family. It is underexpressed in normal tissues but increased significantly in disease states, especially in neoplasm, which is a potential biomarker to turmor diagnosis. The inhibition of FAP-α activity will retard tumor formation, which is expected to be a promising tumor therapeutic target. At present, although the FAP-α expression detection methods has diversification, a superlative detection means is necessary for the clinical diagnosis. This review covers the discovery and the latest advances in FAP-α, as well as the future research prospects. The tissue distribution, structural characteristics, small-molecule ligands and structure-activity relationship of major inhibitors of FAP-α were summarized in this review. Furthermore, a variety of detection methods including traditional detection methods and emerging probes detection were classified and compared, and the design strategy and kinetic parameters of these FAP-α probe substrates were summarized. In addition, these comprehensive information provides a series of practical and reliable assays for the optimal design principles of FAP-α probes, promoting the application of FAP-α as a disease marker in diagnosis, and a drug target in drug design.

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.

Theranostics – present and future

Theragnostics in nuclear medicine constitute an essential element of precision medicine. This notion integrates radionuclide diagnostics procedures and radionuclide therapies using appropriate radiopharmaceutics and treatment targeting specific biological pathways or receptors. The term theragnostics should also include another aspect of treatment: not only whether a given radioisotopic drug can be used, but also in what dose it ought to be used. Theragnostic procedures also allow predicting the effects of treatment based on the assessment of specific receptor density or the metabolic profile of neoplastic cells. The future of theragnostics depends not only on the use of new radiopharmaceuticals, but also on new gamma cameras. Modern theragnostics already require unambiguous pharmacokinetic and pharmacodynamic measurements based on absolute values. Only dynamic studies provide such a possibility. The introduction of the dynamic total-body PET-CT will enable this type of measurements characterizing metabolic processes and receptor expression on the basis of Patlak plot.

FAPI-04 Uptake in Healthy Tissues of Cancer Patients in 68Ga-FAPI-04 PET/CT Imaging

Objective

The aim of this study is to investigate the uptake of ⁶⁸Ga-FAPI-04 in normal tissues and calculate standardized uptake values (SUVs) for various organs in the body.

Methods

A total of 49 patients who underwent ⁶⁸Ga-FAPI-04 PET/CT were included in our study. The following organs were identified on CT images: brain, parotid, and submandibular glands, palatine tonsils, thyroid, lymph nodes (if present), breasts, lungs, thymus, left ventricle walls, mediastinal blood pool, vertebral bone marrow, liver, spleen, pancreas, stomach, small and large intestines, adrenal glands, kidneys, uterus, testes, and prostate. Median, minimum, and maximum values (max) and average (avg) values of standard uptake value (SUV) of tissues and organs were calculated.

Results

The accumulation of ⁶⁸Ga-FAPI in normal organs showed variations. The cerebral/cerebellar cortex exhibited no ⁶⁸Ga-FAPI uptake, while the scalp showed low uptake. Low uptake was also observed in the lung parenchyma, esophagus, left ventricle walls, nipple, and glandular breast tissue. In the abdominopelvic area, the pancreas exhibited low uptake, which was higher in the tail region. Low uptake was observed in the renal cortex. Intense ⁶⁸Ga-FAPI uptake was observed throughout the uterus, which was higher in the corpus. There was no uptake of ⁶⁸Ga-FAPI in the bone cortex and medulla.

Conclusion

We determined the physiological uptake and SUVmax of FAPI-04 in different tissues and organs and created a guide for researchers.

First-In-Human Results on the Biodistribution, Pharmacokinetics, and Dosimetry of [177Lu]Lu-DOTA.SA.FAPi and [177Lu]Lu-DOTAGA.(SA.FAPi)2

Recently, great interest has been gained regarding fibroblast activation protein (FAP) as an excellent target for theranostics. Several FAP inhibitor molecules such as [68Ga]Ga-labelled FAPI-02, 04, 46, and DOTA.SA.FAPi have been introduced and are highly promising molecular targets from the imaging point of view. FAP inhibitors introduced via bifunctional DOTA and DOTAGA chelators offer the possibility to complex Lutetium-177 due to an additional coordination site, and are suitable for theranostic applications owing to the increased tumor accumulation and prolonged tumor retention time. However, for therapeutic applications, very little has been accomplished, mainly due to residence times of the compounds. In an attempt to develop a promising therapeutic radiopharmaceutical, the present study aimed to evaluate and compare the biodistribution, pharmacokinetics, and dosimetry of [177Lu]Lu-DOTA.SA.FAPi, and [177Lu]Lu-DOTAGA.(SA.FAPi)2 in patients with various cancers. The FAPi agents, [177Lu]Lu-DOTA.SA.FAPi and [177Lu]Lu-DOTAGA.(SA.FAPi)2, were administered in two different groups of patients. Three patients (mean age-50 years) were treated with a median cumulative activity of 2.96 GBq (IQR: 2.2-3 GBq) [177Lu]Lu-DOTA.SA.FAPi and seven (mean age-51 years) were treated with 1.48 GBq (IQR: 0.6-1.5) of [177Lu]Lu-DOTAGA.(SA.FAPi)2. Patients in both the groups underwent serial imaging whole-body planar and SPECT/CT scans that were acquired between 1 h and 168 h post-injection (p.i.). The residence time and absorbed dose estimate in the source organs and tumor were calculated using OLINDA/EXM 2.2 software. Time versus activity graphs were plotted to determine the effective half-life (Te) in the whole body and lesions for both the radiotracers. Physiological uptake of [177Lu]Lu-DOTA.SA.FAPi was observed in the kidneys, colon, pancreas, liver, gall bladder, oral mucosa, lacrimal glands, and urinary bladder contents. Physiological biodistribution of [177Lu]Lu-DOTAGA.(SA.FAPi)2 involved liver, gall bladder, colon, pancreas, kidneys, and urinary bladder contents, lacrimal glands, oral mucosa, and salivary glands. In the [177Lu]Lu-DOTA.SA.FAPi group, the highest absorbed doses were noted in the kidneys (0.618 ± 0.015 Gy/GBq), followed by the colon (right colon: 0.472 Gy/GBq and left colon: 0.430 Gy/GBq). In the [177Lu]Lu-DOTAGA.(SA.FAPi)2 group, the colon received the highest absorbed dose (right colon: 1.160 Gy/GBq and left colon: 2.870 Gy/GBq), and demonstrated a significantly higher mean absorbed dose than [177Lu]Lu-DOTA.SA.FAPi (p < 0.011). [177Lu]Lu-DOTAGA.(SA.FAPi)2 had significantly longer median whole-body Te compared to that of [177Lu]Lu-DOTA.SA.FAPi [46.2 h (IQR: 38.5-70.1) vs. 23.1 h (IQR: 17.8-31.5); p-0.0167]. The Te of tumor lesions was significantly higher for [177Lu]Lu-DOTAGA.(SA.FAPi)2 compared to [177Lu]Lu-DOTA.SA.FAPi [86.6 h (IQR: 34.3-94.6) vs. 14 h (IQR: 12.8-15.5); p-0.0004]. The median absorbed doses to the lesions were 0.603 (IQR: 0.230-1.810) Gy/GBq and 6.70 (IQR: 3.40-49) Gy/GBq dose per cycle in the [177Lu]Lu-DOTA.SA.FAPi, and [177Lu]Lu-DOTAGA.(SA.FAPi)2 groups, respectively. The first clinical dosimetry study demonstrated significantly higher tumor absorbed doses with [177Lu]Lu-DOTAGA.(SA.FAPi)2 compared to [177Lu]Lu-DOTA.SA.FAPi. [177Lu]Lu-DOTAGA.(SA.FAPi)2 is safe and unveiled new frontiers to treat various end-stage cancer patients with a theranostic approach.

Crosstalk between cancer-associated fibroblasts and immune cells in the tumor microenvironment: new findings and future perspectives

Cancer-associated fibroblasts (CAFs), a stromal cell population with cell-of-origin, phenotypic and functional heterogeneity, are the most essential components of the tumor microenvironment (TME). Through multiple pathways, activated CAFs can promote tumor growth, angiogenesis, invasion and metastasis, along with extracellular matrix (ECM) remodeling and even chemoresistance. Numerous previous studies have confirmed the critical role of the interaction between CAFs and tumor cells in tumorigenesis and development. However, recently, the mutual effects of CAFs and the tumor immune microenvironment (TIME) have been identified as another key factor in promoting tumor progression. The TIME mainly consists of distinct immune cell populations in tumor islets and is highly associated with the antitumor immunological state in the TME. CAFs interact with tumor-infiltrating immune cells as well as other immune components within the TIME via the secretion of various cytokines, growth factors, chemokines, exosomes and other effector molecules, consequently shaping an immunosuppressive TME that enables cancer cells to evade surveillance of the immune system. In-depth studies of CAFs and immune microenvironment interactions, particularly the complicated mechanisms connecting CAFs with immune cells, might provide novel strategies for subsequent targeted immunotherapies. Herein, we shed light on recent advances regarding the direct and indirect crosstalk between CAFs and infiltrating immune cells and further summarize the possible immunoinhibitory mechanisms induced by CAFs in the TME. In addition, we present current related CAF-targeting immunotherapies and briefly describe some future perspectives on CAF research in the end.

New Frontiers in Cancer Imaging and Therapy Based on Radiolabeled Fibroblast Activation Protein Inhibitors: A Rational Review and Current Progress

Over the past decade, the tumor microenvironment (TME) has become a new paradigm of cancer diagnosis and therapy due to its unique biological features, mainly the interconnection between cancer and stromal cells. Within the TME, cancer-associated fibroblasts (CAFs) demonstrate as one of the most critical stromal cells that regulate tumor cell growth, progression, immunosuppression, and metastasis. CAFs are identified by various biomarkers that are expressed on their surfaces, such as fibroblast activation protein (FAP), which could be utilized as a useful target for diagnostic imaging and treatment. One of the advantages of targeting FAP-expressing CAFs is the absence of FAP expression in quiescent fibroblasts, leading to a controlled targetability of diagnostic and therapeutic compounds to the malignant tumor stromal area using radiolabeled FAP-based ligands. FAP-based radiopharmaceuticals have been investigated strenuously for the visualization of malignancies and delivery of theranostic radiopharmaceuticals to the TME. This review provides an overview of the state of the art in TME compositions, particularly CAFs and FAP, and their roles in cancer biology. Moreover, relevant reports on radiolabeled FAP inhibitors until the year 2021 are highlighted-as well as the current limitations, challenges, and requirements for those radiolabeled FAP inhibitors in clinical translation.

Broadening Drug Design and Targets to Tumor Microenvironment? Cancer-Associated Fibroblast Marker Expression in Cancers and Relevance for Survival Outcomes

Solid tumors have complex biology and structure comprising cancer cells, stromal cells, and the extracellular matrix. While most therapeutics target the cancer cells, recent data suggest that cancer cell behavior and response to treatment are markedly influenced by the tumor microenvironment (TME). In particular, the cancer-associated fibroblasts (CAFs) are the most abundant stromal cells, and play a significant contextual role in shaping tumor initiation, progression, and metastasis. CAFs have therefore emerged as part of the next-generation cancer drug design and discovery innovation strategy. We report here new findings on differential expression and prognostic significance of CAF markers in several cancers. We utilized two publicly available resources: The Cancer Genomic Atlas and Gene Expression Profiling Interactive Analysis. We examined the expression of CAF markers, ACTA2, S100A4, platelet-derived growth factor receptor-beta [PDGFR-β], CD10, and fibroblast activation protein-alpha (FAP-α), in tumor tissues versus the adjacent normal tissues. We found that CAF markers were differentially expressed in various different tumors such as colon, breast, and esophageal cancers and melanoma. No CAF marker is expressed in the same pattern in all cancers, however. Importantly, we report that patients with colon adenocarcinoma and esophageal carcinoma expressing high FAP-α and CD10, respectively, had significantly shorter overall survival, compared with those with low levels of these CAF markers (p < 0.05). We call for continued research on TME biology and clinical evaluation of the CAF markers ACTA2, S100A4, PDGFR-β, CD10, and FAP-α in relation to prognosis of solid cancers in large population samples. An effective cancer drug design and discovery roadmap in the 21st century ought to be broadly framed, and include molecular targets informed by both cancer cell and TME variations.

Cancer-associated cells release citrate to support tumour metastatic progression

Citrate is important for lipid synthesis and epigenetic regulation in addition to ATP production. We have previously reported that cancer cells import extracellular citrate via the pmCiC transporter to support their metabolism. Here, we show for the first time that citrate is supplied to cancer by cancer-associated stroma (CAS) and also that citrate synthesis and release is one of the latter's major metabolic tasks. Citrate release from CAS is controlled by cancer cells through cross-cellular communication. The availability of citrate from CAS regulated the cytokine profile, metabolism and features of cellular invasion. Moreover, citrate released by CAS is involved in inducing cancer progression especially enhancing invasiveness and organ colonisation. In line with the in vitro observations, we show that depriving cancer cells of citrate using gluconate, a specific inhibitor of pmCiC, significantly reduced the growth and metastatic spread of human pancreatic cancer cells in vivo and muted stromal activation and angiogenesis. We conclude that citrate is supplied to tumour cells by CAS and citrate uptake plays a significant role in cancer metastatic progression.

Simultaneous Targeting Tumor Cells and Cancer-Associated Fibroblasts with a Paclitaxel-Hyaluronan Bioconjugate: In Vitro Evaluation in Non-Melanoma Skin Cancer

BACKGROUND

Cancer-associated fibroblasts (CAFs) facilitate many aspects of cancer development by providing a structural framework rich in bioactive compounds. There are emerging studies proposing a combination of conventional anti-cancer therapies directed against neoplastic cells to molecules targeting tumor microenvironments.

METHODS

The study evaluated the pharmacological properties of the anti-tumor agent paclitaxel conjugated to hyaluronic acid (HA) regarding non-melanoma skin cancer (NMSC) and the surrounding fibroblasts. This molecule, named Oncofid-P20 (Onco-P20), preferentially targets cells expressing high levels of CD44, the natural ligand of HA.

RESULTS

Consistent with paclitaxel's mechanism of action involving interference with the breakdown of microtubules during cell division, highly sensitive carcinoma cells rapidly underwent apoptotic cell death. Interestingly, less sensitive cells, such as dermal fibroblasts, resisted the Onco-P20 treatment and experienced a prolonged growth arrest characterized by morphological change and significant modification of the gene expression profile. Onco-P20-treated fibroblasts exhibited reduced growth factor production, downmodulation of the Wnt signaling pathway, and the acquisition of a marked pro-inflammatory profile. Independently of direct exposure to taxol, in the presence of Onco-P20-treated fibroblasts or in their conditioned medium, carcinoma cells had a reduced proliferation rate. Similar to NHF, fibroblasts isolated from skin cancer lesions or from adjacent tissue acquired anti-neoplastic activity under Onco-P20 treatment.

CONCLUSION

Collectively, our data demonstrate that Onco-P20, exerting both a direct and an NHF-mediated indirect effect on carcinoma cells, is a candidate for an innovative therapy alternative to surgery for the treatment of NMSC.

Understanding the Immune-Stroma Microenvironment in B Cell Malignancies for Effective Immunotherapy

Cancers, including lymphomas, develop in complex tissue environments where malignant cells actively promote the creation of a pro-tumoral niche that suppresses effective anti-tumor effector T cell responses. Research is revealing that the tumor microenvironment (TME) differs between different types of lymphoma, covering inflamed environments, as exemplified by Hodgkin lymphoma, to non-inflamed TMEs as seen in chronic lymphocytic leukemia (CLL) or diffuse-large B-cell lymphoma (DLBCL). In this review we consider how T cells and interferon-driven inflammatory signaling contribute to the regulation of anti-tumor immune responses, as well as sensitivity to anti-PD-1 immune checkpoint blockade immunotherapy. We discuss tumor intrinsic and extrinsic mechanisms critical to anti-tumor immune responses, as well as sensitivity to immunotherapies, before adding an additional layer of complexity within the TME: the immunoregulatory role of non-hematopoietic stromal cells that co-evolve with tumors. Studying the intricate interactions between the immune-stroma lymphoma TME should help to design next-generation immunotherapies and combination treatment strategies to overcome complex TME-driven immune suppression.

Altered Tissue and Plasma Levels of Fibroblast Activation Protein-α (FAP) in Renal Tumours

Simple Summary

Malignant epithelial tumour’s behaviour in the kidney has traditionally been analysed attending to different prognostic parameters focussed on the proliferating neoplastic cell. This is the case of renal cell carcinoma (RCC), in which a large tumour diameter, high histological grade, and the presence of necrosis, among other factors, have been related with a high risk of distant metastasis and, therefore, worse survival. Recently, several elements of the tumour microenviroment, such as cancer-associated fibroblasts (CAFs), are being studied in order to develop more accurate diagnostic and therapeutic approaches. We present data that support that the fibroblast activation protein-α (FAP), a CAF biomarker, provides interesting information both in tumour tissues and in plasma from patients with RCC.

Abstract

(1) Background: Renal cell carcinoma (RCC) is a heterogeneous and complex disease with only partial response to therapy, high incidence of metastasis and recurrences, and scarce reliable biomarkers indicative of progression and survival. Cancer-associated fibroblasts (CAFs) play an important role supporting and promoting renal cancer progression. (2) Methods: In this study, we analysed fibroblast activation protein-α (FAP) immunohistochemical expression and its soluble isoform (sFAP) in tumour tissues and plasma from 128 patients with renal tumours. (3) Results: FAP is expressed in the cell surface of CAFs of the tumour centre and infiltrating front from clear cell renal cell carcinomas (CCRCC, n = 89), papillary renal cell carcinomas (PRCC, n = 21), and chromophobe renal cell carcinomas (ChRCC, n = 8), but not in the benign tumour renal oncocytoma (RO, n = 10). A high expression of FAP and low levels sFAP are significantly associated with high tumour diameter, high grade, and high pT stage, lymph node invasion, development of early metastases, and worse 5-year cancer specific survival of CCRCC patients. (4) Conclusions: These findings corroborate the potential usefulness of FAP immunohistochemistry and plasma sFAP as a biomarker of CCRCC progression and point to CAF-related proteins as promising immunohistochemical biomarkers for the differential diagnosis of ChRCC and RO.

Breast Tumor Cell Invasion and Pro-Invasive Activity of Cancer-Associated Fibroblasts Co-Targeted by Novel Urokinase-Derived Decapeptides

Among peritumoral cells, cancer-associated fibroblasts (CAFs) are major facilitators of tumor progression. This study describes the effects of two urokinase-derived, novel decapeptides, denoted as Pep 1 and its cyclic derivative Pep 2. In a mouse model of tumor dissemination, using HT1080 fibrosarcoma cells, Pep 2 reduced the number and size of lung metastases. Specific binding of fluoresceinated Pep 2 to HT1080 and telomerase immortalised fibroblasts (TIF) cell surfaces was enhanced by αv overexpression or abolished by excess vitronectin, anti-αv antibodies or silencing of ITGAV αv gene, identifying αv-integrin as the Pep 2 molecular target. In 3D-organotypic assays, peptide-exposed TIFs and primary CAFs from breast carcinoma patients both exhibited a markedly reduced pro-invasive ability of either HT1080 fibrosarcoma or MDA-MB-231 mammary carcinoma cells, respectively. Furthermore, TIFs, either exposed to Pep 2, or silenced for αv integrin, were impaired in their ability to chemoattract cancer cells and to contract collagen matrices, exhibiting reduced α-smooth muscle actin (α-SMA) levels. Finally, peptide exposure of αv-expressing primary CAFs led to the downregulation of α-SMA protein and to a dramatic reduction of their pro-invasive capability. In conclusion, the ability of the novel decapeptides to interfere with tumor cell invasion directly and through the down-modulation of CAF phenotype suggests their use as lead compounds for co-targeting anti-cancer strategies.

Heterogeneity of cancer-associated fibroblasts: Opportunities for precision medicine

Despite marked development in cancer therapies during recent decades, the prognosis for advanced cancer remains poor. The conventional tumor-cell-centric view of cancer can only explain part of cancer progression, and thus a thorough understanding of the tumor microenvironment (TME) is crucial. Among cells within the TME, cancer-associated fibroblasts (CAFs) are attracting attention as a target for cancer therapy. However, CAFs present a heterogeneous population of cells and more detailed classification of CAFs and investigation of functions of each subset is needed to develop novel CAF-targeted therapies. In this context, application of newly developed approaches to single-cell analysis has already made an impact on our understanding of the heterogeneity of CAFs. Here, we review the recent literature on CAF heterogeneity and function, and discuss the possibility of novel therapies targeting CAF subsets.

Targeting fibroblast activation protein (FAP): next generation PET radiotracers using squaramide coupled bifunctional DOTA and DATA5m chelators

Background

Fibroblast activation protein (FAP) is a proline selective serine protease that is overexpressed in tumor stroma and in lesions of many other diseases that are characterized by tissue remodeling. In 2014, a most potent FAP-inhibitor (referred to as UAMC1110) with low nanomolar FAP-affinity and high selectivity toward related enzymes such as prolyl oligopeptidase (PREP) and the dipeptidyl-peptidases (DPPs): DPP4, DPP8/9 and DPP2 were developed. This inhibitor has been adopted recently by other groups to create radiopharmaceuticals by coupling bifunctional chelator-linker systems. Here, we report squaric acid (SA) containing bifunctional DATA^5m and DOTA chelators based on UAMC1110 as pharmacophor. The novel radiopharmaceuticals DOTA.SA.FAPi and DATA^5m.SA.FAPi with their non-radioactive derivatives were characterized for in vitro inhibitory efficiency to FAP and PREP, respectively and radiochemical investigated with gallium-68. Further, first proof-of-concept in vivo animal study followed by ex vivo biodistribution were determined with [⁶⁸Ga]Ga-DOTA.SA.FAPi.

Results

[⁶⁸Ga]Ga-DOTA.SA.FAPi and [⁶⁸Ga]Ga-DATA^5m.SA.FAPi showed high complexation > 97% radiochemical yields after already 10 min and high stability over a period of 2 h. Affinity to FAP of DOTA.SA.FAPi and DATA^5m.SA.FAPi and its ^natGa and ^natLu-labeled derivatives were excellent resulting in low nanomolar IC₅₀ values of 0.7–1.4 nM. Additionally, all five compounds showed low affinity for the related protease PREP (high IC₅₀ with 1.7–8.7 μM). First proof-of-principle in vivo PET-imaging animal studies of the [⁶⁸Ga]Ga-DOTA.SA.FAPi precursor in a HT-29 human colorectal cancer xenograft mouse model indicated promising results with high accumulation in tumor (SUV_mean of 0.75) and low background signal. Ex vivo biodistribution showed highest uptake in tumor (5.2%ID/g) at 60 min post injection with overall low uptake in healthy tissues.

Conclusion

In this work, novel PET radiotracers targeting fibroblast activation protein were synthesized and biochemically investigated. Critical substructures of the novel compounds are a squaramide linker unit derived from the basic motif of squaric acid, DOTA and DATA^5m bifunctional chelators and a FAP-targeting moiety. In conclusion, these new FAP-ligands appear promising, both for further research and development as well as for first human application.

Identification of genes associated with gastric cancer survival and construction of a nomogram to improve risk stratification for patients with gastric cancer

The present study aimed to identify genes associated with gastric cancer survival and improve risk stratification for patients with gastric cancer. Transcriptomic and clinicopathological data from 443 gastric cancer samples were retrieved from The Cancer Genome Atlas database. The DESeq R package was applied to screen for differentially expressed genes between Tumor-Node-Metastasis (TNM) stage (I vs. IV) and histological grade (G3 vs. G1 and G2). A total of seven genes were common to both comparisons; spondin 1 (SPON1); thrombospondin 4 (THBS4); Sushi, Von Willebrand factor type A, EGF and pentraxin domain containing 1 (SVEP1); prickle planar cell polarity protein 1 (PRICKLE1); ATP binding cassette subfamily A member 8 (ABCA8); Slit guidance ligand 2 (SLIT2); and EGF containing fibulin extracellular matrix protein 1 (EFEMP1), were selected as candidate survival-associated genes for further analysis. The prognostic value of these genes was assessed according to a literature review and Kaplan-Meier survival analysis. In addition, a multivariate Cox regression analysis revealed PRICKLE1 expression to be an independent prognostic factor for patients with gastric cancer. Furthermore, a predictive nomogram was generated using PRICKLE1 expression, patient age and TNM stage to assess overall survival (OS) rate at 1, 3 and 5 years, with an internal concordance index of 0.65. External validation was conducted in an independent cohort of 59 patients with gastric cancer, and high consistency between the predicted and observed results for OS was exhibited. Overall, the current findings suggest that PRICKLE1 expression may serve as an independent prognostic factor that can be integrated with age and TNM stage in a nomogram able to predict OS rate in patients with gastric cancer.

Future of Theranostics: An Outlook on Precision Oncology in Nuclear Medicine

Molecular alterations in malignant disease result in the expression or upregulations of various targets that can be used for imaging and treatment with radiopharmaceuticals. This theranostic principle has acquired greater importance in personalized medicine in recent years, particularly in oncology, where advanced tumors can be treated effectively with low side effects. Since the pioneering use of ¹³¹I in differentiated thyroid cancer in the 1940s, remarkable achievements in nuclear medicine endoradiotherapy have been demonstrated, mainly in the treatment of neuroendocrine neoplasms by using ¹⁷⁷Lu-labeled somatostatin analogs or in the treatment of advanced prostate cancer using prostate-specific membrane antigen-directed radionuclide therapy. Besides that, this review focuses on promising novel radiopharmaceuticals and describes their preclinical and clinical status. Radiolabeled antibodies, such as ¹³¹I-omburtamab directed against the B7-H3 protein on the surface of neuroblastoma cells; HuMab-5B1, a ⁸⁹Zr/¹⁷⁷Lu-labeled antibody for the treatment of CA19-9-expressing malignancies; and ¹⁷⁷Lu-lilotomab, a CD37 antibody for the treatment of B-cell lymphomas, are being highlighted. The neurotensin receptor ligand ¹¹¹In/¹⁷⁷Lu-3B-227 has demonstrated high potential in imaging and therapy for several malignancies (e.g., pancreatic adenocarcinomas). Targeting of the fibroblast activation protein is currently being explored for different tumor entities using PET imaging with the fibroblast activation protein inhibitor (FAPI) ⁶⁸Ga-FAPI-04, and the first therapeutic applications of ⁹⁰Y-FAPI-04 have been applied. After 2 decades of rapid development in theranostics, a variety of new targets are available for further clinical investigation.

Antifibrotic therapy to normalize the tumor microenvironment

Most tumors develop abnormal fibrotic regions consisting of fibroblasts, immune cells, and a dense extracellular matrix (ECM) immersed in a viscous interstitial fluid, and an abundant fibrotic tumor microenvironment (TME) is associated with poor outcome of treatment. It has been hypothesized that the treatment of cancer may be improved by interventions aiming to normalize this TME. The approaches used in attempts to normalize the fibrotic TME can be categorized into three strategies of targeted antifibrotic therapy: targeting of components of the ECM, targeting of the producers of the ECM components-the activated cancer-associated fibroblasts (CAFs), and targeting of the signaling pathways activating CAFs. To target the ECM, enzymes against components of the ECM have been used, including collagenase, relaxin, hyaluronidase, and lyxyl oxidase. Targeting of CAFs have been investigated by using agents aiming to eliminate or reprogram CAFs. CAFs are activated primarily by transforming growth factor-β (TGF-β), hedgehog, or focal adhesion kinase signaling, and several agents have been used to target these signaling pathways, including angiotensin II receptor I blockers (e.g., losartan) to inhibit the TGF-β pathway. Taken together, these studies have revealed that antifibrotic therapy is a two-edged sword: while some studies suggest enhanced response to treatment after antifibrotic therapy, others suggest that antifibrotic therapy may lead to increased tumor growth, metastasis, and impaired outcome of treatment. There are several possible explanations of these conflicting observations. Most importantly, tumors contain different subpopulations of CAFs, and while some subpopulations may promote tumor growth and metastasis, others may inhibit malignant progression. Furthermore, the outcome of antifibrotic therapy may depend on stage of disease, duration of treatment, treatment-induced activation of alternative profibrotic signaling pathways, and treatment-induced recruitment of tumor-supporting immune cells. Nevertheless, losartan-induced suppression of TGF-β signaling appears to be a particularly promising strategy. Losartan is a widely prescribed antihypertensive drug and highly advantageous therapeutic effects have been observed after losartan treatment of pancreatic cancer. However, improved understanding of the mechanisms governing the development of fibrosis in tumors is needed before safe antifibrotic treatments can be established.

Altered expression of fibroblast activation protein-α (FAP) in colorectal adenoma-carcinoma sequence and in lymph node and liver metastases

Colorectal cancer (CRC) is a major health problem in elderly people because of its high incidence and high mortality rate. Despite early screening programs, more than half of CRC patients are diagnosed at advanced stages. Fibroblast activation protein-α (FAP) expression in cancer-associated fibroblasts (CAFs) has been associated with a higher risk of metastases and poor survival. Here, we have analyzed the immunohistochemical expression of FAP in 41 adenoma-carcinoma sequences. In addition, FAP expression was analyzed individually and in combination with β-catenin (BCAT), CD44 and Cyclin-D1 expression in primary tumors and in their corresponding lymph node and liver metastases (n=294). Finally, soluble FAP (sFAP) levels in plasma from CRC patients (n=127) were also analyzed by ELISA. FAP was expressed only in CRC tissue and its expression level was found to be higher in tumors exhibiting deeper local invasion and poorer cancer cell differentiation. FAP and concomitant nuclear BCAT expression in cancer cells at the infiltrating front of primary tumors and in lymph node metastases was independently associated with 5- and 10-year cancer specific and disease-free survival. Moreover, lower sFAP levels correlated with poorer survival. These findings support the potential importance of FAP as a biomarker of CRC development and progression.

Targeting the Tumor Microenvironment with Fluorescence-Activatable Bispecific Endoglin/Fibroblast Activation Protein Targeting Liposomes

Liposomes are biocompatible nanocarriers with promising features for targeted delivery of contrast agents and drugs into the tumor microenvironment, for imaging and therapy purposes. Liposome-based simultaneous targeting of tumor associated fibroblast and the vasculature is promising, but the heterogeneity of tumors entails a thorough validation of suitable markers for targeted delivery. Thus, we elucidated the potential of bispecific liposomes targeting the fibroblast activation protein (FAP) on tumor stromal fibroblasts, together with endoglin which is overexpressed on tumor neovascular cells and some neoplastic cells. Fluorescence-quenched liposomes were prepared by hydrating a lipid film with a high concentration of the self-quenching near-infrared fluorescent dye, DY-676-COOH, to enable fluorescence detection exclusively upon liposomal degradation and subsequent activation. A non-quenched green fluorescent phospholipid was embedded in the liposomal surface to fluorescence-track intact liposomes. FAP- and murine endoglin-specific single chain antibody fragments were coupled to the liposomal surface, and the liposomal potentials validated in tumor cells and mice models. The bispecific liposomes revealed strong fluorescence quenching, activatability, and selectivity for target cells and delivered the encapsulated dye selectively into tumor vessels and tumor associated fibroblasts in xenografted mice models and enabled their fluorescence imaging. Furthermore, detection of swollen lymph nodes during intra-operative simulations was possible. Thus, the bispecific liposomes have potentials for targeted delivery into the tumor microenvironment and for image-guided surgery.

Cancer associated fibroblasts: role in breast cancer and potential as therapeutic targets

Introduction: Cancer associated fibroblasts (CAFs) are the largest population of stromal cells in breast tumors. Emerging evidence has suggested that CAFs are important players not only in fostering tumor growth and spread but also in altering the tumor response to therapeutic agents. On the basis of these observations, huge efforts have been made to exploit CAFs as potential targets for breast cancer therapy.Areas covered: The current understanding of the hallmarks and biology of CAFs, their multilayered interplay with various cell populations of breast tumor microenvironment toward cancer initiation, progression, metastasis and resistance to anticancer therapies are discussed. In addition, a comprehensive overview of the CAFs-based molecular druggable targets in breast tumors is provided. The most relevant literature, in particular the studies retrieved in Medline in the last 10 years, served for this purpose.Expert opinion: The interest on CAFs as a target to fight breast cancer has becoming a hot topic for drug discovery. Indeed, several CAFs-targeted approaches are emerging as appealing therapeutic strategies in breast cancer. At pre-clinical level, this research field is speedily advancing toward the assessment of successful tactics targeting CAFs in breast cancer. Therefore, anti-CAFs therapies may display an intriguing potential to be exploited in clinical studies.

Fibroblast Activation Protein (FAP) Overexpression Induces Epithelial-Mesenchymal Transition (EMT) in Oral Squamous Cell Carcinoma by Down-Regulating Dipeptidyl Peptidase 9 (DPP9)

Purpose

Fibroblast activation protein (FAP) acts as a tumor promoter via epithelial–mesenchymal transition (EMT) in human oral squamous cell carcinoma (OSCC). The present study was designed to investigate the FAP targeting proteins and explore the precise mechanism by which FAP promotes EMT in OSCC.

Patients and Methods

Proteins interacting with FAP were found and filtered by immunoprecipitation-mass spectrometry (IP-MS). Both DPP9 protein and mRNA were examined in 90 paired OSCC samples and matched normal tissue. DPP9 knockdown was conducted to determine its function in OSCC in vitro and in vivo.

Results

Dipeptidyl peptidase 9 (DPP9) was identified as interacting with FAP intracellularly by IP-MS. The levels of both DPP9 protein and mRNA were down-regulated in OSCC tissue. Lower DPP9 expression was correlated with unfavorable survival rates of OSCC patients. DPP9 knockdown accelerates the proliferation of OSCC cells in vitro and in vivo. Overexpression of FAP leads to a reduction in DPP9 expression. Likewise, DPP9 overexpression reverses the proliferation, migration, invasion and EMT induced by FAP during OSCC.

Conclusion

Our study finds that FAP promotes EMT of OSCC by down-regulating DPP9 in a non-enzymatic manner. FAP-DPP9 pathway could be a potential therapeutic target of OSCC.

Design and Development of 99mTc-Labeled FAPI Tracers for SPECT Imaging and 188Re Therapy

Most epithelial tumors recruit fibroblasts and other nonmalignant cells and activate them into cancer-associated fibroblasts. This often leads to overexpression of the membrane serine protease fibroblast-activating protein (FAP). It has already been shown that DOTA-bearing FAP inhibitors (FAPIs) generate high-contrast images with PET/CT scans. Since SPECT is a lower-cost and more widely available alternative to PET, ^99mTc-labeled FAPIs represent attractive tracers for imaging applications in a larger number of patients. Furthermore, the chemically homologous nuclide ¹⁸⁸Re is available from generators, which allows FAP-targeted endoradiotherapy. Methods: For the preparation of ^99mTc-tricarbonyl complexes, a chelator was selected whose carboxylic acids can easily be converted into various derivatives in the finished product, enabling a platform strategy based on the original tracer. The obtained ^99mTc complexes were investigated in vitro by binding and competition experiments on FAP-transfected HT-1080 (HT-1080-FAP) or on mouse FAP-expressing (HEK-muFAP) and CD26-expressing (HEKCD26) HEK cells and characterized by planar scintigraphy and organ distribution studies in tumor-bearing mice. Furthermore, a first-in-humans application was done on 2 patients with ovarian and pancreatic cancer, respectively. Results: ^99mTc-FAPI-19 showed specific binding to recombinant FAP-expressing cells with high affinity. Unfortunately, liver accumulation, biliary excretion, and no tumor uptake were observed on planar scintigraphy for a HT-1080-FAP-xenotransplanted mouse. To improve the pharmacokinetic properties, hydrophilic amino acids were attached to the chelator moiety of the compound. The resulting ^99mTc-labeled FAPI tracers revealed excellent binding properties (≤45% binding; >95% internalization), high affinity (half-maximal inhibitory concentration, 6.4-12.7 nM), and significant tumor uptake (≤5.4% injected dose per gram of tissue) in biodistribution studies. The lead candidate ^99mTc-FAPI-34 was applied for diagnostic scintigraphy and SPECT of patients with metastasized ovarian and pancreatic cancer for follow-up to therapy with ⁹⁰Y-FAPI-46. ^99mTc-FAPI-34 accumulated in the tumor lesions, as also shown on PET/CT imaging using ⁶⁸Ga-FAPI-46. Conclusion: ^99mTc-FAPI-34 represents a powerful tracer for diagnostic scintigraphy, especially when PET imaging is not available. Additionally, the chelator used in this compound allows labeling with the therapeutic nuclide ¹⁸⁸Re, which is planned for the near future.

[Cancer-associated fibroblasts and their significance in tumor progression]

Carcinogenesis and tumor progression are not caused not only by malignant epithelial cells, but also by the tumor stroma around cancer stem cells which performs regulatory, nutritional and 'framework' functions. It is represented by mesenchymal cells of various types predominantly by cancer-associated fibroblasts (CAF). αSMA, FAP-1, desmin, podoplanin, neuron-glial antigen 2 (NG2), PDGFR-α and -β are used for CAF identification but there is no universal markers due to the plasticity of the cell population that underlies the subpopulation division CAF. CAF subpopulations are not described for many tumor types. Recently, evidence has accumulated that CAFs mediate many adverse processes in the tumor, including can support stromal inflammation and cause fibrosis. By forming a niche in cancer stem cells, CAFs mediate chemoresistance and the appearance of dormant metastases. The study of the role of CAF will allow not only to form a fundamentally new understanding of the mechanisms of carcinogenesis, but also to create new diagnostic and therapeutic targets for treating tumors.

Fibroblasts Fuel Immune Escape in the Tumor Microenvironment

Immune escape is central to the persistence of most, if not all, solid tumors and poses a critical obstacle to successful cancer (immuno)therapy. Cancer-associated fibroblasts (CAFs) constitute the most prevalent, yet heterogeneous, component of the tumor stroma, where they 'cool down' the immune microenvironment. The central role played by CAFs, both as a physical barrier and source of immunosuppressive molecules, sets them as a target to enhance immunotherapy of cancer. We outline the current understanding of how CAFs fuel immune escape, as well as their potential clinical applications. Whether these therapeutics really have clinically significant activity remains to be seen, but the outlook is positive.

Impact of Cancer-Associated Fibroblast on the Radiation-Response of Solid Xenograft Tumors

Increasing evidence indicates that the heterogeneous tumor stroma supports therapy resistance at multiple levels. Fibroblasts, particularly cancer-associated fibroblasts (CAFs) are critical components of the tumor stroma. However, the impact of CAFs on the outcome of radiotherapy (RT) is poorly understood. Here, we investigated if and how fibroblasts/CAFs modulate the radiation response of malignant tumors by altering cancer cell radiosensitivity or radioresistance in vitro and in vivo. The influence of fibroblasts on cancer cell proliferation, cell death induction and long-term survival after RT was studied using different sets of fibroblasts and cancer cells in an indirect co-culture (2D) system to analyse potential paracrine interactions or a 3D model to study direct interactions. Paracrine signals from embryonic NIH-3T3 fibroblasts promoted MPR31.4 prostate and Py8119 breast cancer cell proliferation. Indirect co-culture with L929 skin fibroblasts induced higher levels of apoptosis in irradiated MPR31.4 cells, while they promoted proliferation of irradiated Py8119 cells. In addition, NIH-3T3 fibroblasts promoted long-term clonogenic survival of both tumor cell types upon irradiation in the 3D co-culture system when compared to non-irradiated controls. Also in vivo, co-implantation of cancer cells and fibroblasts resulted in different effects depending on the respective cell combinations used: co-implantation of MPR31.4 cells with NIH-3T3 fibroblasts or of Py8119 cells with L929 fibroblasts led to increased tumor growth and reduced radiation-induced tumor growth delay when compared to the respective tumors without co-implanted fibroblasts. Taken together, the impact of fibroblasts on cancer cell behavior and radiation sensitivity largely depended on the respective cell types used as they either exerted a pro-tumorigenic and radioresistance-promoting effect, an anti-tumorigenic effect, or no effect. We conclude that the plasticity of fibroblasts allows for such a broad spectrum of activities by the same fibroblast and that this plasticity is at least in part mediated by cancer cell-induced fibroblast activation toward CAFs.

The propensity of invasive circulating tumor cells (iCTCs) in metastatic progression and therapeutic responsiveness

Circulating tumor cells (CTCs) are important clinical indicators of metastatic progression and treatment efficacy. However, because of their low number and heterogeneity, reliable patient-derived CTC models are not readily available. We report here the isolation and characterization of the invasive population of CTCs, iCTCs, from blood of 10 patients with epithelial ovarian cancer (EOC) and one pancreatic cancer patient based on the avidity of tumor cells toward an artificial collagen-based adhesion matrix (CAM), in comparison with tumor progenitor (TP) cells isolated from tumor cell lines, tumors and ascites from EOC patients. CAM-avid cells identified to be iCTCs were indistinguishable with TP cells using either functional CAM uptake or surface markers (seprase and CD44). In addition, iCTCs were characterized using peritoneal and spontaneous metastasis models in vivo to evaluate their metastatic propensity and therapeutic response. TP cells and iCTCs had a doubling time of about 34-42 hours. TP cells were rare (<3.5%) in most patient-derived specimens, however, iCTCs emigrated into blood, at a high frequency, 64.2% (n = 49). Approximately 500 patient-derived iCTCs recapitulated formation of iCTCs in mouse blood and formed micrometastases in the liver and/or lung, a degree of metastatic spread equivalent to the inoculation of 5 × 105 bulk tumor cells isolated from ascites and tumors. iCTCs were shown to be novel therapeutic targets for blocking metastasis using the reduced formation of iCTCs and micrometastases by RNAi, peptides, and monoclonal antibodies against seprase.

Comparisons of cancer-associated fibroblasts in the intratumoral stroma and invasive front in colorectal cancer

The aim of this study was to evaluate the cytomorphologic maturity and molecular activation of cancer-associated fibroblasts (CAFs) in the intratumoral stroma and invasive front in colorectal cancer and understand how they affect cancer invasion and long-term oncological outcomes.The cytomorphologic maturity of and α-smooth muscle actin (α-SMA), fibroblast activation protein α (FAPα), and fibroblast-specific protein 1 (FSP-1) expression in CAFs in the intratumoral stroma (CAF) and the invasive front (CAF) of colorectal cancer tissues were compared (n = 147). The correlations between CAF maturation, molecular activity markers, and cancer invasion were evaluated by network analysis. Overall survival and systemic recurrence were analyzed to assess the oncological effects of CAF properties.The cytomorphologic maturation rate was comparable between CAF and CAF. The presence of mature CAFs was related to epidermal growth factor receptor overexpression in cancer cells. Expression rates of α-SMA (96.6%-98.0%) and FAPα (18.6%-22.9%) were similar between CAF and CAF. FSP-1 expression was more frequent in CAF than in CAF (66.4% vs 58.2%, P = .038). There was a significant decrease in FSP-1 expression in CAF and CAF in higher stages. The infiltrating growth pattern of the tumor was more frequent in the immature CAF. In colorectal cancer with perineural invasion and lymph node metastasis, FSP-1 expression in CAF was significantly lower. On multivariate analysis using the Cox proportional hazards model, immature CAF was found to be an independent prognostic factor of overall survival. In non-metastatic (stage I-III) colorectal cancer patients, CAF maturity was not a prognostic factor for systemic recurrence.Cytomorphologic maturity and molecular activation markers were similar between CAFs in the intratumoral stroma and invasive front of colorectal cancer.

Hypoxia as a barrier to immunotherapy in pancreatic adenocarcinoma

Pancreatic ductal adenocarcinoma (PDA) is a lethal disease with limited response to cytotoxic chemoradiotherapy, as well as newer immunotherapies. The PDA tumor microenvironment contains infiltrating immune cells including cytotoxic T cells; however, there is an overall immunosuppressive milieu. Hypoxia is a known element of the solid tumor microenvironment and may promote tumor survival. Through various mechanisms including, but not limited to, those mediated by HIF-1α, hypoxia also leads to increased tumor proliferation and metabolic changes. Furthermore, epithelial to mesenchymal transition is promoted through several pathways, including NOTCH and c-MET, regulated by hypoxia. Hypoxia-promoted changes also contribute to the immunosuppressive phenotype seen in many different cell types within the microenvironment and thereby may inhibit an effective immune system response to PDA. Pancreatic stellate cells (PSCs) and myofibroblasts appear to contribute to the recruitment of myeloid derived suppressor cells (MDSCs) and B cells in PDA via cytokines increased due to hypoxia. PSCs also increase collagen secretion in response to HIF-1α, which promotes a fibrotic stroma that alters T cell homing and migration. In hypoxic environments, B cells contribute to cytotoxic T cell exhaustion and produce chemokines to attract more immunosuppressive regulatory T cells. MDSCs inhibit T cell metabolism by hoarding key amino acids, modulate T cell homing by cleaving L-selectin, and prevent T cell activation by increasing PD-L1 expression. Immunosuppressive M2 phenotype macrophages promote T cell anergy via increased nitric oxide (NO) and decreased arginine in hypoxia. Increased numbers of regulatory T cells are seen in hypoxia which prevent effector T cell activation through cytokine production and increased CTLA-4. Effective immunotherapy for pancreatic adenocarcinoma and other solid tumors will need to help counteract the immunosuppressive nature of hypoxia-induced changes in the tumor microenvironment. Promising studies will look at combination therapies involving checkpoint inhibitors, chemokine inhibitors, and possible targeting of hypoxia. While no model is perfect, assuring that models incorporate the effects of hypoxia on cancer cells, stromal cells, and effector immune cells will be crucial in developing successful therapies.

Identification of Novel Natural Substrates of Fibroblast Activation Protein-alpha by Differential Degradomics and Proteomics

Fibroblast activation protein-alpha (FAP) is a cell-surface transmembrane-anchored dimeric protease. This unique, constitutively active serine protease has both dipeptidyl aminopeptidase and endopeptidase activities and can hydrolyze the post-proline bond. FAP expression is very low in adult organs but is upregulated by activated fibroblasts in sites of tissue remodeling, including fibrosis, atherosclerosis, arthritis and tumors. To identify the endogenous substrates of FAP, we immortalized primary mouse embryonic fibroblasts (MEFs) from FAP gene knockout embryos and then stably transduced them to express either enzymatically active or inactive FAP. The MEF secretomes were then analyzed using degradomic and proteomic techniques. Terminal amine isotopic labeling of substrates (TAILS)-based degradomics identified cleavage sites in collagens, many other extracellular matrix (ECM) and associated proteins, and lysyl oxidase-like-1, CXCL-5, CSF-1, and C1qT6, that were confirmed in vitro In addition, differential metabolic labeling coupled with quantitative proteomic analysis also implicated FAP in ECM-cell interactions, as well as with coagulation, metabolism and wound healing associated proteins. Plasma from FAP-deficient mice exhibited slower than wild-type clotting times. This study provides a significant expansion of the substrate repertoire of FAP and provides insight into the physiological and potential pathological roles of this enigmatic protease.

Elevation of Stromal-Derived Mediators of Inflammation Promote Prostate Cancer Progression in African-American Men

Progress in prostate cancer racial disparity research has been hampered by a lack of appropriate research tools and better understanding of the tumor biology. Recent gene expression studies suggest that the tumor microenvironment (TME) may contribute to racially disparate clinical outcomes in prostate cancer. Analysis of the prostate TME has shown increased reactive stroma associated with chronic inflammatory infiltrates in African-American (AA) compared with European-American (EA) patients with prostate cancer. To better understand stromal drivers of changes in TME, we isolated prostate fibroblasts (PrF) from AA (PrF^-AA) and EA (PrF^-EA) prostate cancer tissues and studied their functional characteristics. PrF^-AA showed increased growth response to androgens FGF2 and platelet-derived growth factor. Compared with PrF^-EA, conditioned media from PrF^-AA significantly enhanced the proliferation and motility of prostate cancer cell lines. Expression of markers associated with myofibroblast activation (αSMA, vimentin, and tenascin-C) was elevated in PrF^-AA In vivo tumorigenicity of an AA patient-derived prostatic epithelial cell line E006AA was significantly increased in the presence of PrF^-AA compared with PrF^-EA, and RNA-seq data and cytokine array analysis identified a panel of potential proinflammatory paracrine mediators (BDNF, CHI3L1, DPPIV, FGF7, IL18BP, IL6, and VEGF) to be enriched in PrF^-AA E006AA cell lines showed increased responsiveness to BDNF ligand compared with EA-derived LNCaP and C4-2B cells. Addition of a TrkB-specific antagonist significantly reduced the protumorigenic effects induced by PrF^-AA compared with PrF^-EA These findings suggest that fibroblasts in the TME of AA patients may contribute to the health disparity observed in the incidence and progression of prostate cancer tumors.Significance: These findings suggest that stromal cells in the tumor microenvironment of African-American men promote progression of prostate cancer by increasing levels of a specific set of pro-inflammatory molecules compared with European-American men.Graphical Abstract: http://cancerres.aacrjournals.org/content/canres/78/21/6134/F1.large.jpg Cancer Res; 78(21); 6134-45. ©2018 AACR.

Role of Alpha-Smooth Muscle Actin and Fibroblast Activation Protein Alpha in Ovarian Neoplasms

BACKGROUND/AIMS

Studies show that tumor growth is not just determined by the presence of malignant cells, since interactions between cancer cells and stromal microenvironment have important impacts on the cancer growth and progression. Cancer-associated fibroblasts play a prominent role in this process. The aims of the study were to investigate 2 cancer-associated fibroblasts markers, alpha-smooth muscle actin (α-SMA), and fibroblast activation protein alpha (FAP) in the stromal microenvironment of benign and malignant ovarian epithelial neoplasms, and to relate their tissue expression with prognostic factors in ovarian cancer.

METHODS

α-SMA and FAP were evaluated by immunohistochemistry in malignant (n = 28) and benign (n = 28) ovarian neoplasms. Fisher's exact test was used with a significance level lower than 0.05.

RESULTS

FAP immunostaining was stronger in ovarian cancer when compared to benign neoplasms (p = 0.0366). There was no significant difference in relation to α-SMA expression between malignant and benign ovarian neoplasms as well as prognostic factors. In ovarian cancer, FAP stainings 2/3 was significantly related to histological grades 2 and 3 (p = 0.0183).

CONCLUSION

FAP immunostaining is more intense in malignant neoplasms than in benign ovarian neoplasms, as well as in moderately differentiated and undifferentiated ovarian carcinomas compared to well-differentiated neoplasms, thus indicating that it can be used as a marker of worse prognosis.

Cancer associated fibroblasts tailored tumor microenvironment of therapy resistance in gastrointestinal cancers

Gastrointestinal cancers (GI), are a group of highly aggressive malignancies with heavy cancer-related mortalities. Even if continued development of therapy methods, therapy resistance has been a great obstruction for cancer treatment and thereby inevitably leads to depressed final mortality. Peritumoral cancer associated fibroblasts (CAFs), a versatile population assisting cancer cells to build a facilitated tumor microenvironment (TME), has been demonstrated exerting a promotion influence on cancer proliferation, migration, invasion, metastasis, and also therapy resistance. In this review, we provide an update progress in describing how CAFs mediate therapy resistance in GI by various means, meanwhile highlight the crosstalk between CAFs and cancer cells and present some vital signaling pathways activated by CAFs in this resistant process. Furthermore, we discuss the current advances in adopting novel drugs against CAFs and how the knowledge contributing to improved therapy efficacy in clinical practice. In sum, CAFs create a therapy-resistant TME in several aspects of GI progression, although some key problems about distinguishing CAFs subpopulations and controversial issues on pleiotropic CAFs in medication need to be solved for subsequent clinical application. Predictably, targeting therapy-resistant CAFs is a promising adjunctive treatment to benefit GI patients.