Screening and Preclinical Evaluation of Novel Radiolabeled Anti-Fibroblast Activation Protein-α Recombinant Antibodies

Background: Fibroblast activation protein-α (FAPα) is selectively overexpressed in tumor-associated fibroblasts in more than 90% of epithelial tumors, and may be a good target for anticancer treatment, for example, using an anti-FAPα recombinant antibody (rAb) labeled with radionuclides. In the present report, the radiolabeling and preclinical evaluation of novel anti-FAPα rAbs were investigated. Materials and Methods: Two novel anti-FAPα VHHs (AMS002-1 and AMS002-2) with high binding affinity to FAPα were selected from an antibody phage library. The anti-FAPα VHHs were then fused with the Fc fragment of human IgG4 to create two VHH-Fc rAbs. The VHH-Fc rAbs were radiolabeled with 89Zr and 177Lu. The radiolabeled products were evaluated by radioligand-binding assays using FAPα-expressing cells. The biodistribution and tumor-targeting properties were investigated by small-animal PET/CT. AMS002-1-Fc, which showed promising tumor-targeting properties in 89Zr-microPET imaging, was radiolabeled with 177Lu for efficacy study on HT1080 tumor-bearing mice and monitored with SPECT/CT imaging. Results: The two VHH-Fc rAbs with good affinity with KD values in low nanomolar range were identified. Both PET/CT imaging with 89Zr-AMS002-1-Fc rAb and SPECT/CT imaging with 177Lu-AMS002-1-Fc rAb demonstrated highest tumor uptakes at 72 h p.i. and long tumor retention in the preclinical models. Furthermore, ex vivo biodistribution analysis revealed high tumor uptake of 89Zr-AMS002-1-Fc at 48 h p.i. with the value of 6.91% ± 2.08% ID/g. Finally, radioimmunotherapy with 177Lu-AMS002-1-Fc rAb delayed the tumor growth without significant weight loss in mice with HT1080 xenografts. The tumor size of untreated control group was 2.59 times larger compared with the treatment group with 177Lu-AMS002-1-Fc at day 29. Conclusion: 89Zr/177Lu-AMS002-1-Fc represent a pair of promising radiopharmaceuticals for theranostics on FAPα-expressing tumors.

Dendritic cells infected with recombinant adenoviral vector encoding mouse fibroblast activation protein-α and human livin α exert an antitumor effect against Lewis lung carcinoma in mice

BACKGROUND

Fibroblast activation protein-α (FAP) and livin α are considered as cancer-associated fibroblasts (CAFs) and tumor-specific targets, respectively, for immunogenic tumor vaccines. This study is designed to decipher the antitumor effect of double-gene modified dendritic cells (DCs) on Lewis lung carcinoma (LLC).

METHODS

By encoding mouse FAP cDNA and human livin α (i.e., hlivin α) cDNA into recombinant adenoviral vector (rAd), rAd-FAP, rAd-hlivin α, and rAd-FAP/hlivin α were constructed, which were then transduced into mouse DCs. LLC-bearinig mice were immunized with the infected DCs (5 × 105 cells/mouse), followed by calculation of tumor volume and survival rate. The identification of CAFs from mouse LLC as well as the determination on expressions of FAP and livin α, was accomplished by western blot. Cytotoxic T lymphocyte assay was harnessed to assess the effect of the infected DCs on inducing splenic lymphocytes to lyse CAFs.

RESULTS

DCs were successfully transduced with rAd-FAP/hlivin α in vitro. FAP was highly expressed in CAFs. CAFs were positive for α-SMA and negative for CD45 and CD31. Livin α level was upregulated in mouse LLC. Immunization with rAd-FAP/hlivin α-transduced DCs suppressed LLC volume and improved the survival of tumor-bearing mice. Immunization with rAd-FAP/hlivin α-transduced DCs enhanced the cytotoxic effect of splenic lymphocytes on LLC tumor-derived CAFs.

CONCLUSION

Injection with rAd-FAP/hlivin α-transduced DCs promotes immune-enhanced tumor microenvironment by decreasing CAFs and suppresses tumor growth in LLC mouse models.

Evaluating near-infrared photoimmunotherapy for targeting fibroblast activation protein-α expressing cells in vitro and in vivo

Photoimmunotherapy (PIT), carried out using an Ab conjugated to the near infrared dye IRDye700DX, is achieving significant success in target-specific elimination of cells. Fibroblast activation protein alpha (FAP-α) is an important target in cancer because of its expression by cancer-associated fibroblasts (CAFs) as well as by some cancer cells. Cancer-associated fibroblasts that express FAP-α have protumorigenic and immune suppressive functions. Using immunohistochemistry of human breast cancer tissue microarrays, we identified an increase of FAP-α⁺  CAFs in invasive breast cancer tissue compared to adjacent normal tissue. We found FAP-α expression increased in fibroblasts cocultured with cancer cells. In proof-of-principle studies, we engineered human FAP-α overexpressing MDA-MB-231 and HT-1080 cancer cells and murine FAP-α overexpressing NIH-3T3 fibroblasts to evaluate several anti-FAP-α Abs and selected AF3715 based on its high binding affinity with both human and mouse FAP-α. After conjugation of AF3715 with the phthalocyanine dye IR700, the resultant Ab conjugate, FAP-α-IR700, was evaluated in cells and tumors for its specificity and effectiveness in eliminating FAP-α expressing cell populations with PIT. Fibroblast activation protein-α-IR700-PIT resulted in effective FAP-α-specific cell killing in the engineered cancer cells and in two patient-derived CAFs in a dose-dependent manner. Following an intravenous injection, FAP-α-IR700 retention was three-fold higher than IgG-IR700 in FAP-α overexpressing tumors, and two-fold higher compared to WT tumors. Fibroblast activation protein-α-IR700-PIT resulted in significant growth inhibition of tumors derived from FAP-α overexpressing human cancer cells. A reduction of endogenous FAP-α⁺  murine CAFs was identified at 7 days after FAP-α-IR700-PIT. Fibroblast activation protein-α-targeted near infrared PIT presents a promising strategy to eliminate FAP-α⁺  CAFs.

Ultrasensitive Fibroblast Activation Protein-α-Activated Fluorogenic Probe Enables Selective Imaging and Killing of Melanoma In Vivo

Melanoma is a malignant cancer with a high risk of metastasis and continued increase in death rates over the past decades, and its prognosis is highly related to the disease's stage, while early detection and treatment of melanoma are significant to the improvement of its therapy outcome. Different from the traditional methods for disease diagnosis, enzyme-activated fluorescent probes were developed rapidly due to their high sensitivity and temporal-spatial ratio and have been widely applied in tumor detection, surgical navigation, and cancer-related research. Fibroblast activation protein-α (FAPα), a serine-type cell surface protease that plays important roles in cell invasion and extracellular matrix degradation, is widely involved in tumor progression such as malignant melanoma, so developing a FAPα activity-based molecular tool would be of great potential for the early diagnosis and therapy of melanoma. However, few fluorescent probes targeting FAPα have been applied in melanoma-related studies, and thus, the construction of FAPα activity-based fluorescent probes for melanoma detection is in urgent need. By incorporating the selective recognition unit with a red-emission fluorophore, cresyl violet, we herein report an ultrasensitive (limit of detection = 5.3 ng/mL) fluorogenic probe for FAPα activity sensing, named CV-FAP; the acquired probe showed a significantly higher binding affinity (15.7-fold) and overall catalytic efficiency (2.6-fold) when compared with those of the best reported FAPα probes. The good performance of CV-FAP made it possible to discriminate malignant melanoma cells and tumor-bearing mice from normal cells and mice with high contrast. More importantly, CV-FAP showed significant antitumor activity toward melanoma in cultured cells and tumor-bearing nude mice (over 95% inhibited tumor growth) with good safety, which made it an ideal theranostic agent for melanoma.

Fibroblast Activation Protein-α Responsive Peptide Assembling Prodrug Nanoparticles for Remodeling the Immunosuppressive Microenvironment and Boosting Cancer Immunotherapy

Checkpoint blockade immunotherapy has broad application prospects in the clinical treatment of malignant tumors. However, the low response rate of the checkpoint blockade is due to low tumor immunogenicity and immunosuppression within the tumor microenvironment. Herein, the authors design an amphiphilic bifunctional PD-1/PD-L1 peptide antagonist PCP, and co-deliver doxorubicin (DOX) and R848 through co-assembly of a multi-agent prodrug (PCP@R848/DOX), which can be specifically cleaved by fibroblast activation protein-α (FAP-α) in the tumor stroma. Upon reaching the tumor tissue, the PCP@R848/DOX prodrug nanostructure is disassembled by FAP-α. The localized release of DOX and R848 triggers immunogenic cell death (ICD) and reprograms tumor-associated macrophages (TAMs) to elicit antitumor immunity. Furthermore, sustained release of PD-1 or PD-L1 peptide antagonists mediates the PD-L1 pathway blockade for further propagated activation of cytotoxic T lymphocytes. Notably, a tumor microenvironment activatable prodrug nanoparticle is presented for triple-modality cancer therapy that functions by simultaneously activating ICD and altering the phenotype of TAMs when combined with PD-1 blockade therapy, which efficiently elicits a strong systemic antitumor immune response. This strategy may emerge as a new paradigm in the treatment of cancer by combination immunotherapy.

Fibroblast Activation Protein-α as a Target in the Bench-to-Bedside Diagnosis and Treatment of Tumors: A Narrative Review

Fibroblast activation protein-α (FAP) is a type II integral serine protease that is specifically expressed by activated fibroblasts. Cancer-associated fibroblasts (CAFs) in the tumor stroma have an abundant and stable expression of FAP, which plays an important role in promoting tumor growth, invasion, metastasis, and immunosuppression. For example, in females with a high incidence of breast cancer, CAFs account for 50–70% of the cells in the tumor’s microenvironment. CAF overexpression of FAP promotes tumor development and metastasis by influencing extracellular matrix remodeling, intracellular signaling, angiogenesis, epithelial-to-mesenchymal transition, and immunosuppression. This review discusses the basic biological characteristics of FAP and its applications in the diagnosis and treatment of various cancers. We review the emerging basic and clinical research data regarding the use of nanomaterials that target FAP.

Fibroblast Activation Protein-α Expressing Fibroblasts Promote Lymph Node Metastasis in Esophageal Squamous Cell Carcinoma

Background and Objectives

Esophageal squamous cell carcinoma (ESCC) remains one of the most common malignancies in China and has a high metastasis rate and poor prognosis. Fibroblast activation protein-α (FAP-α) is a serine peptidase the expression of which in cancer-associated fibroblasts has been associated with a higher risk of metastases and poor survival. This study aimed to analyze the correlation of FAP-α expression with the lymph node metastasis and prognostic significance in ESCC.

Methods

FAP-α expression was examined in 121 resected ESCC specimens and 10 adjacent normal tissue using immunohistochemistry. FAP-α expression was scored in the stromal fibroblasts adjacent to neoplastic nests. A chi-square test was used to analyze the correlation between FAP-α expression in tumors stromal and lymph node metastasis of ESCC. The association between FAP-α expression and prognosis was evaluated using univariable and multivariable statistical modeling.

Results

FAP-α expression was absent in the benign controls. FAP-α expression was evident in the stromal 37% (45/121) of ESCC. Expression of FAP-α level is significantly associated with lymph node metastasis (p=0.023), but it is not correlated to age, gender, and tumor location in ESCC patients. Stromal FAP-α expression was significantly associated with poor survival in univariable (HR 2.009; 95% CI 1.259–3.205; p=0.003) and multivariable analysis (HR 1.833; 95% CI 1.144–2.937; p=0.012).

Conclusion

FAP-α may be an important regulator in lymph node metastasis of ESCC and may provide a novel therapeutic target in ESCC.

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Oxytocin Inhibition of Metastatic Colorectal Cancer by Suppressing the Expression of Fibroblast Activation Protein-α

Oxytocin (OXT) and its receptor (OXTR) are present in the gastrointestinal system and are involved in gastrointestinal tumorigenesis. However, the effect of OXTR signaling on the development of colorectal cancer (CRC) and its underlying mechanisms remain unexplored. To address these issues, we first examined the expressions of OXT, OXTR, and several cancer-associated proteins using colon “tissue chips” from a spectrum of malignant progression of the colon, which included normal colon tissue, chronic colitis, colorectal adenoma, and colorectal adenocarcinoma (CAC). The results showed that the expressions of OXT and OXTR decreased gradually with the malignant progression of the disease. Stimulation of CAC tissues with OXT increased OXTR expression while down-regulated FAPα and CCL-2 protein expressions in a concentration- and time-dependent manner. Moreover, cell invasion experiment showed that OXT treatment reduced the invasion ability of colon cancer cells and blocking OXTR with atosiban blocked OXT-reduced invasion ability of human colon cancer cell lines Ls174T and SW480. The results indicate that OXT has the potential to inhibit CRC development via down-regulating the immunosuppressive proteins FAPα and CCL-2. When the OXTR signaling is weakened, colon tissues may transform to CRC. These findings also highlight the possibility of applying OXT to inhibit CRC development directly.

Transformable Peptide Nanocarriers for Expeditious Drug Release and Effective Cancer Therapy via Cancer-Associated Fibroblast Activation

A novel cleavable amphiphilic peptide (CAP) was designed to be specifically responsive to fibroblast activation protein-α (FAP-α), a protease specifically expressed on the surface of cancer-associated fibroblasts. The CAP self-assembled into fiber-like nanostructures in solution, while the presence of hydrophobic chemotherapeutic drugs readily transformed the assemblies into drug-loaded spherical nanoparticles. The disassembly of these nanoparticles (CAP-NPs) upon FAP-α cleavage resulted in rapid and efficient release of the encapsulated drugs specifically at tumor sites. This Transformers-like drug delivery strategy could allow them to disrupt the stromal barrier and enhance local drug accumulation. Therapeutic results suggested that drug-loaded CAP-NPs hold promising tumor specificity and therapeutic efficacy for various solid tumor models, confirming its potential utility and versatility in antitumor therapy.

The stromal compartments in pancreatic cancer: are there any therapeutic targets?

Pancreatic ductal adenocarcinoma (PDAC) is characterised by an abundant stromal response also known as a desmoplastic reaction. Pancreatic Stellate Cells have been identified as playing a key role in pancreatic cancer desmoplasia. There is accumulating evidence that the stroma contributes to tumour progression and to the low therapeutic response of PDAC patients. In this review we described the main actors of the desmoplastic reaction within PDAC and novel therapeutic approaches that are being tested to block the detrimental function of the stroma.

Tumor fibroblast specific activation of a hybrid ferritin nanocage-based optical probe for tumor microenvironment imaging

Ferritin-based FAP-α-responsive fluorescence nanoprobes could be activated immediately as they penetrate the tumor blood vessels and come across the FAP-α molecules on the membrane of CAFs in the tumor microenvironment instead of reaching a certain depth into tumor tissue to interact with tumor cells. This probe may become a promising nanomaterial for highly specific and sensitive tumor imaging through responding to the enzymes in the tumor microenvironment.