Inhibitor-conjugated harmonic nanoparticles targeting fibroblast activation protein

FAP Targeting of Photosensitizer-Loaded Polymersomes for Increased Light-Activated Cell Killing

As current chemo- and photodynamic cancer therapies are associated with severe side effects due to a lack of specificity and to systemic toxicity, innovative solutions in terms of targeting and controlled functionality are in high demand. Here, we present the development of a polymersome nanocarrier equipped with targeting molecules and loaded with photosensitizers for efficient uptake and light-activated cell killing. Polymersomes were self-assembled in the presence of photosensitizers from a mixture of nonfunctionalized and functionalized PDMS-b-PMOXA diblock copolymers, the latter designed for coupling with targeting ligands. By encapsulation inside the polymersomes, the photosensitizer Rose Bengal was protected, and its uptake into cells was mediated by the nanocarrier. Inhibitor of fibroblast activation protein α (FAPi), a ligand for FAP, was attached to the polymersomes' surface and improved their uptake in MCF-7 breast cancer cells expressing relatively high levels of FAP on their surface. Once internalized by MCF-7, irradiation of Rose Bengal-loaded FAPi-polymersomes generated reactive oxygen species at levels high enough to induce cell death. By combining photosensitizer encapsulation and specific targeting, polymersomes represent ideal candidates as therapeutic nanocarriers in cancer treatment.

The Prognostic and therapeutic value and clinical implications of fibroblast activation protein-α as a novel biomarker in colorectal cancer

The identification of contributing factors leading to the development of Colorectal Cancer (CRC), as the third fatal malignancy, is crucial. Today, the tumor microenvironment has been shown to play a key role in CRC progression. Fibroblast-Activation Protein-α (FAP) is a type II transmembrane cell surface proteinase expressed on the surface of cancer-associated fibroblasts in tumor stroma. As an enzyme, FAP has di- and endoprolylpeptidase, endoprotease, and gelatinase/collagenase activities in the Tumor Microenvironment (TME). According to recent reports, FAP overexpression in CRC contributes to adverse clinical outcomes such as increased lymph node metastasis, tumor recurrence, and angiogenesis, as well as decreased overall survival. In this review, studies about the expression level of FAP and its associations with CRC patients' prognosis are reviewed. High expression levels of FAP and its association with clinicopathological factors have made as a potential target. In many studies, FAP has been evaluated as a therapeutic target and diagnostic factor into which the current review tries to provide a comprehensive insight. Video Abstract.

Regulation of Fibroblast Activation Protein-α Expression: Focus on Intracellular Protein Interactions

The prolyl-specific peptidase fibroblast activation protein-α (FAP-α) is expressed at very low or undetectable levels in nondiseased human tissues but is selectively induced in activated (myo)fibroblasts at sites of tissue remodeling in fibrogenic processes. In normal regenerative processes involving transient fibrosis FAP-α⁺(myo)fibroblasts disappear from injured tissues, replaced by cells with a normal FAP-α^- phenotype. In chronic uncontrolled pathological fibrosis FAP-α⁺(myo)fibroblasts permanently replace normal tissues. The mechanisms of regulation and elimination of FAP-α expression in(myo)fibroblasts are unknown. According to a yeast two-hybrid screen and protein databanks search, we propose that the intracellular (co)-chaperone BAG6/BAT3 can interact with FAP-α, mediated by the BAG6/BAT3 Pro-rich domain, inducing proteosomal degradation of FAP-α protein under tissue homeostasis. In this Perspective, we discuss our findings in the context of current knowledge on the regulation of FAP-α expression and comment potential therapeutic strategies for uncontrolled fibrosis, including small molecule degraders (PROTACs)-modified FAP-α targeted inhibitors.

Cell-specific drug targeting in the lung

Non-targeted drug delivery systems have several limitations including the decreased bioavailability of the drug, poor stability and rapid clearance in addition to off-target distribution. Cell-specific targeted delivery approaches promise to overcome some of these limitations and enhance therapeutic selectivity. In this review, we aim to discuss cell-specific targeted approachesin the lung at the biochemical and molecular levels. These approaches include;a) directly administered small molecule drugs with intracellular action; b) targeted biologics and synthetic hybrids with extracellular action; c) site activateddrugs; and d) delivery systems.We discuss the pharmaceutical and biochemical parameters that govern the fate of drug molecules at delivery sites while presenting an overview of relevant literature surrounding this area of research and current advancements.

A Novel Chemiluminescence Probe for Sensitive Detection of Fibroblast Activation Protein-Alpha In Vitro and in Living Systems

Fibroblast activation protein-alpha (FAPα) is a key modulator of the microenvironment in multiple pathologies and is becoming the next pan-cancer target for cancer diagnostics and therapeutics. Chemiluminescence (CL) luminophores are considered as one of the most sensitive families of probes for detection and imaging applications due to their high signal-to-noise ratio. Until now, however, no such effective CL probe was reported for FAPα detection. Herein, we developed a novel CL probe for the detection of endogenous FAPα activity by incorporating FAPα-specific dipeptide substrates (glycine-proline) to the improved Schaap's adamantylidene-dioxetane. In this manner, we designed three CL probes (CFCL, BFCL, and QFCL) with the dipeptide substrate blocked by N-terminal benzyloxycarbonyl, N-tert-butoxycarbonyl or N-quinoline-4-carboxylic acid, respectively, which was used as the masking group to restrain the chemiexcitation energy. Probe CFCL exhibited the optimal specificity for the discrimination of FAPα from dipeptidase IV and prolyl oligopeptidase, which was elucidated by molecular docking simulation. Upon FAPα cleavage, CFCL was turned on for the highly selective and sensitive detection of FAPα with a limit of detection of 0.785 ng/mL. Furthermore, the ability of CFCL to image FAPα was effectively demonstrated in vitro, including various biological samples (plasma and tissue preparations), and in living systems (tumor cells and tumor-bearing mice). Furthermore, this newly established probe could be easily extended to evaluate FAPα inhibitors. Overall, we anticipate that probe CFCL will offer a facile and cost-effective alternative in the early detection of pathologies, individual tailoring of drug therapy, and drug screening.

Molecular recognition of fibroblast activation protein for diagnostic and therapeutic applications

Fibroblast activation protein (FAP) is a non-classical serine protease expressed predominantly in conditions accompanied by tissue remodeling, particularly cancer. Due to its plasma membrane localization, FAP represents a promising molecular target for tumor imaging and treatment. The unique enzymatic activity of FAP facilitates development of diagnostic and therapeutic tools based on molecular recognition of FAP by substrates and small-molecule inhibitors, in addition to conventional antibody-based strategies. In this review, we provide background on the pathophysiological role of FAP and discuss its potential for diagnostic and therapeutic applications. Furthermore, we present a detailed analysis of the structural patterns crucial for substrate and inhibitor recognition by the FAP active site and determinants of selectivity over the related proteases dipeptidyl peptidase IV and prolyl endopeptidase. We also review published data on targeting of the tumor microenvironment with FAP antibodies, FAP-targeted prodrugs, activity-based probes and small-molecule inhibitors. We describe use of a recently developed, selective FAP inhibitor with low-nanomolar potency in inhibitor-based targeting strategies including synthetic antibody mimetics based on hydrophilic polymers and inhibitor conjugates for PET imaging. In conclusion, recent advances in understanding of the molecular structure and function of FAP have significantly contributed to the development of several tools with potential for translation into clinical practice.