Stable Fibroblast Growth Factor 2 Dimers with High Pro-Survival and Mitogenic Potential

Disulfide bridge-dependent dimerization triggers FGF2 membrane translocation into the extracellular space

Fibroblast growth factor 2 (FGF2) exits cells by direct translocation across the plasma membrane, a type I pathway of unconventional protein secretion. This process is initiated by phosphatidylinositol-4,5-bisphosphate (PI(4,5)P2)-dependent formation of highly dynamic FGF2 oligomers at the inner plasma membrane leaflet, inducing the formation of lipidic membrane pores. Cell surface heparan sulfate chains linked to glypican-1 (GPC1) capture FGF2 at the outer plasma membrane leaflet, completing FGF2 membrane translocation into the extracellular space. While the basic steps of this pathway are well understood, the molecular mechanism by which FGF2 oligomerizes on membrane surfaces remains unclear. In the current study, we demonstrate the initial step of this process to depend on C95-C95 disulfide-bridge-mediated FGF2 dimerization on membrane surfaces, producing the building blocks for higher FGF2 oligomers that drive the formation of membrane pores. We find FGF2 with a C95A substitution to be defective in oligomerization, pore formation, and membrane translocation. Consistently, we demonstrate a C95A variant of FGF2 to be characterized by a severe secretion phenotype. By contrast, while also important for efficient FGF2 secretion from cells, a second cysteine residue on the molecular surface of FGF2 (C77) is not involved in FGF2 oligomerization. Rather, we find C77 to be part of the interaction interface through which FGF2 binds to the α1 subunit of the Na,K-ATPase, the landing platform for FGF2 at the inner plasma membrane leaflet. Using cross-linking mass spectrometry, atomistic molecular dynamics simulations combined with a machine learning analysis and cryo-electron tomography, we propose a mechanism by which disulfide-bridged FGF2 dimers bind with high avidity to PI(4,5)P2 on membrane surfaces. We further propose a tight coupling between FGF2 secretion and the formation of ternary signaling complexes on cell surfaces, hypothesizing that C95-C95-bridged FGF2 dimers are functioning as the molecular units triggering autocrine and paracrine FGF2 signaling.

Targeting HER2 and FGFR-positive cancer cells with a bispecific cytotoxic conjugate combining anti-HER2 Affibody and FGF2

Breast cancer remains a significant global health challenge, necessitating the development of effective targeted therapies. This study aimed to create bispecific targeting molecules against HER2 and FGFR1, two receptors known to play crucial roles in breast cancer progression. By combining the high-affinity Affibody ZHER2:2891 and a modified, stable form of fibroblast growth factor 2 (FGF2), we successfully generated bispecific proteins capable of simultaneously recognizing HER2 and FGFR1. Two variants were designed: AfHER2-sFGF2 with a shorter linker and AfHER2-lFGF2 with a longer linker between the HER2 and FGFR1-recognizing proteins. Both proteins exhibited selective binding to HER2 and FGFR1, with AfHER2-lFGF2 demonstrating simultaneous binding to both receptors. AfHER2-lFGF2 exhibited superior internalization compared to FGF2 in FGFR-positive cells and significantly increased internalization compared to AfHER2 in HER2-positive cells. To enhance their therapeutic potential, highly potent cytotoxic agent MMAE was conjugated to the targeting proteins, resulting in protein-drug conjugates. The bispecific AfHER2-lFGF2-vcMMAE conjugate demonstrated exceptional cytotoxic activity against HER2-positive, FGFR-positive, and dual-positive cancer cell lines that was significantly higher compared to monospecific conjugates. These data indicate the beneficial effect of simultaneous targeting of HER2 and FGFR1 in precise anticancer medicine and contribute valuable insights into the design and potential of bispecific targeting molecules for breast cancer treatment.

A framework to validate fluorescently labeled DNA-binding proteins for single-molecule experiments

Due to the enhanced labeling capability of maleimide-based fluorescent probes, lysine-cysteine-lysine (KCK) tags are frequently added to proteins for visualization. In this study, we employed an in vitro single-molecule DNA flow-stretching assay as a sensitive way to assess the impact of the KCK tag on the property of DNA-binding proteins. Using Bacillus subtilis ParB as an example, we show that, although no noticeable changes were detected by in vivo fluorescence imaging and chromatin immunoprecipitation (ChIP) assays, the KCK tag substantially altered ParB's DNA compaction rates and its response to nucleotide binding and to the presence of the specific sequence (parS) on the DNA. While it is typically assumed that short peptide tags minimally perturb protein function, our results urge researchers to carefully validate the use of tags for protein labeling. Our comprehensive analysis can be expanded and used as a guide to assess the impacts of other tags on DNA-binding proteins in single-molecule assays.

A precise design strategy for a cell-derived extracellular matrix based on CRISPR/Cas9 for regulating neural stem cell function

The extracellular matrix (ECM) is a natural microenvironment pivotal for stem cell survival, as well as proliferation, differentiation and metastasis, composed of a variety of biological molecular complexes secreted by resident cells in tissues and organs. Heparan sulfate proteoglycan (HSPG) is a type of ECM protein that contains one or more covalently attached heparan sulfate chains. Heparan sulphate chains have high affinity with growth factors, chemokines and morphogens, acting as cytokine-binding domains of great importance in development and normal physiology. Herein, we constructed endogenous HSPG2 overexpression in mouse embryonic fibroblasts based on the CRISPR/Cas9 synergistic activation mediator system and then fabricated a cell-derived HSPG2 functional ECM (ECMHSPG2). The ECMHSPG2 is capable of enriching basic fibroblast growth factor (bFGF), which binds more strongly than the negative control ECM. With a growing bFGF concentration, ECMHSPG2 could better maintain neural stem cell (NSCs) stemness and promote NSC proliferation and differentiation in culture. These findings provide a precise design strategy for producing a specific cell-derived ECM for biomaterials in research and regenerative medicine.

Dual-Warhead Conjugate Based on Fibroblast Growth Factor 2 Dimer Loaded with α-Amanitin and Monomethyl Auristatin E Exhibits Superior Cytotoxicity towards Cancer Cells Overproducing Fibroblast Growth Factor Receptor 1

Targeting fibroblast growth factor receptor 1 (FGFR1) is a promising therapeutic strategy for various cancers associated with alterations in the FGFR1 gene. In this study, we developed a highly cytotoxic bioconjugate based on fibroblast growth factor 2 (FGF2), which is a natural ligand of this receptor, and two potent cytotoxic drugs-α-amanitin and monomethyl auristatin E-with completely independent mechanistic modes of action. Utilizing recombinant DNA technology, we produced an FGF2 N- to C-end dimer that exhibited superior internalization capacity in FGFR1-positive cells. The drugs were site-specifically attached to the targeting protein using SnoopLigase- and evolved sortase A-mediated ligations. The resulting dimeric dual-warhead conjugate selectively binds to the FGFR1 and utilizes receptor-mediated endocytosis to enter the cells. Moreover, our results demonstrate that the developed conjugate exhibits about 10-fold higher cytotoxic potency against FGFR1-positive cell lines than an equimolar mixture of single-warhead conjugates. The diversified mode of action of the dual-warhead conjugate may help to overcome the potential acquired resistance of FGFR1-overproducing cancer cells to single cytotoxic drugs.

Using DNA flow-stretching assay as a tool to validate the tagging of DNA-binding proteins for single-molecule experiments

Due to the enhanced labeling capability of maleimide-based fluorescent probes, lysine-cysteine-lysine (KCK) tags are frequently added to proteins for visualization. In this study, we employed in vitro single-molecule DNA flow-stretching assay as a sensitive way to assess the impact of the KCK-tag on the property of DNA-binding proteins. Using Bacillus subtilis ParB as an example, we show that, although no noticeable changes were detected by in vivo fluorescence imaging and chromatin immunoprecipitation (ChIP) assays, the KCK-tag substantially altered ParB's DNA compaction rates, its response to nucleotide binding and to the presence of the specific sequence (parS) on the DNA. While it is typically assumed that short peptide tags minimally perturb protein function, our results urge researchers to carefully validate the use of tags for protein labeling. Our comprehensive analysis can be expanded and used as a guide to assess the impacts of other tags on DNA-binding proteins in single-molecule assays.

A Beefy-R culture medium: Replacing albumin with rapeseed protein isolates

The development of cost-effective serum-free media is essential for the economic viability of cultured meat. A key challenge facing this goal is the high-cost of recombinant albumin which is necessary in many serum-free media formulations, including a recently developed serum-free medium for bovine satellite cell (BSC) culture termed Beefy-9. Here we alter Beefy-9 by replacing recombinant albumin with rapeseed protein isolate (RPI), a bulk-protein solution obtained from agricultural waste through alkali extraction (pH 12.5), isoelectric protein precipitation (pH 4.5), dissolution of physiologically soluble proteins (pH 7.2), and concentration of proteins through 3 kDa ultrafiltration. This new medium, termed Beefy-R, was then used to culture BSCs over four passages, during which cells grew with an average doubling time of 26.6 h, showing improved growth compared with Beefy-9. In Beefy-R, BSCs maintained cell phenotype and myogenicity. Together, these results offer an effective, low-cost, and sustainable alternative to albumin for serum-free culture of muscle stem cells, thereby addressing a key hurdle facing cultured meat production.

Cyclic and dimeric fibroblast growth factor 2 variants with high biomedical potential

Fibroblast growth factor 2 (FGF2) is a pleiotropic protein engaged in the regulation of key cellular processes in a wide spectrum of cells. FGF2 is an important object of basic research as well as a molecule used in regenerative medicine, in vitro cell culture maintenance, and as an anticancer drug carrier. However, the unsatisfactory stability and pleiotropic activities of the wild-type FGF2 largely limit its use as a medical product. To overcome these limitations, we have designed a set of FGF2-based macromolecules via sortase A-mediated cyclization and oligomerization. We obtained heparin-switchable FGF2 variants with enhanced stability and improved ability to stimulate cell proliferation and migration. We have shown that stimulation of glucose uptake by adipocytes is modulated by the architecture of FGF2 oligomers. Moreover, we used hyper-stable FGF2 variants for the construction of highly effective drug carriers for selective killing of FGFR1-overproducing cancer cells. The strategy for FGF2 engineering presented in this work provides novel insights into the design of growth factor variants for regenerative and anti-cancer precise medicine.

Comparison of 68Ga-FAPI and 18F-FDG PET/CT in the Evaluation of Patients With Newly Diagnosed Non-Small Cell Lung Cancer

Purpose

Several studies have demonstrated that ⁶⁸Ga-FAPI PET/CT shows high intratumoral tracer uptake and low normal tissue uptake, allowing for excellent visualization of cancer. The purpose of this study was to compare the ability of ⁶⁸Ga-FAPI and ¹⁸F-FDG PET/CT for the evaluation of newly diagnosed NSCLC.

Materials and Methods

A prospective analysis of 28 individuals with histopathologically newly confirmed NSCLC that underwent ⁶⁸Ga-FAPI and ¹⁸F-FDG PET/CT was conducted. The performance of two imaging modalities was compared based upon visual assessment, rates of cancer detection, and semi-quantitative parameters (target-to-background ratio [TBR], maximum standard uptake value [SUVmax]) for both primary tumors and metastases.

Results

In total, this study enrolled 28 participants (13 male, 15 female; median age: 60.5 years, range: 34 – 78 years. <u>For primary tumors, ⁶⁸Ga-FAPI and ¹⁸F-FDG PET/CT have similar detection performance (28 vs. 27). However, ⁶⁸Ga-FAPI PET/CT was found to more effectively evaluate most metastases as compared to ¹⁸F-FDG PET/CT. ⁶⁸Ga-FAPI PET/CT detecting more metastases present within the lymph nodes (53 vs. 49), pleura (8 vs. 7), liver (4 vs. 1), and bone (41 vs. 35).</u> The SUVmax and TBR values for ⁶⁸Ga-FAPI were substantially superior to those for ¹⁸F-FDG in lymph node, pleural, and bone metastases. While the SUVmax for these two imaging approaches was comparable for hepatic metastases, ⁶⁸Ga-FAPI exhibited a significantly higher TBR in relation to that of ¹⁸F-FDG. In addition, ⁶⁸Ga-FAPI PET/CT demonstrates excellent N (80% [8/10]) and M (92.9% [26/28]) staging accuracy in NSCLC patients.

Conclusions

⁶⁸Ga-FAPI PET/CT as an examination modality is excellent for evaluation of newly diagnosed NSCLC. ⁶⁸Ga-FAPI PET/CT improves the detection rates of most metastases and facilitating the superior staging of patients with newly diagnosed NSCLC, relative to that achieved by ¹⁸F-FDG PET/CT.

New developments in the biology of fibroblast growth factors

The fibroblast growth factor (FGF) family is composed of 18 secreted signaling proteins consisting of canonical FGFs and endocrine FGFs that activate four receptor tyrosine kinases (FGFRs 1-4) and four intracellular proteins (intracellular FGFs or iFGFs) that primarily function to regulate the activity of voltage-gated sodium channels and other molecules. The canonical FGFs, endocrine FGFs, and iFGFs have been reviewed extensively by us and others. In this review, we briefly summarize past reviews and then focus on new developments in the FGF field since our last review in 2015. Some of the highlights in the past 6 years include the use of optogenetic tools, viral vectors, and inducible transgenes to experimentally modulate FGF signaling, the clinical use of small molecule FGFR inhibitors, an expanded understanding of endocrine FGF signaling, functions for FGF signaling in stem cell pluripotency and differentiation, roles for FGF signaling in tissue homeostasis and regeneration, a continuing elaboration of mechanisms of FGF signaling in development, and an expanding appreciation of roles for FGF signaling in neuropsychiatric diseases. This article is categorized under: Cardiovascular Diseases > Molecular and Cellular Physiology Neurological Diseases > Molecular and Cellular Physiology Congenital Diseases > Stem Cells and Development Cancer > Stem Cells and Development.

Strategies to Modulate the Redifferentiation of Chondrocytes

Because of the low self-healing capacity of articular cartilage, cartilage injuries and degenerations triggered by various diseases are almost irreversible. Previous studies have suggested that human chondrocytes cultured in vitro tend to dedifferentiate during the cell-amplification phase and lose the physiological properties and functions of the cartilage itself, which is currently a critical limitation in the cultivation of cartilage for tissue engineering. Recently, numerous studies have focused on the modulation of chondrocyte redifferentiation. Researchers discovered the effect of various conditions (extracellular environment, cell sources, growth factors and redifferentiation inducers, and gene silencing and overexpression) on the redifferentiation of chondrocytes during the in vitro expansion of cells, and obtained cartilage tissue cultured in vitro that exhibited physiological characteristics and functions that were similar to those of human cartilage tissue. Encouragingly, several studies reported positive results regarding the modulation of the redifferentiation of chondrocytes in specific conditions. Here, the various factors and conditions that modulate the redifferentiation of chondrocytes, as well as their limitations and potential applications and challenges are reviewed. We expect to inspire research in the field of cartilage repair toward the future treatment of arthropathy.

Fibroblast Growth Factor 2 Conjugated with Monomethyl Auristatin E Inhibits Tumor Growth in a Mouse Model

Worldwide, cancer is the second leading cause of death. Regardless of the continuous progress in medicine, we still do not have a fully effective anti-cancer therapy. Therefore, the search for new targeted anti-cancer drugs is still an unmet need. Here, we present novel protein–drug conjugates that inhibit tumor growth in a mouse model of human breast cancer. We developed conjugates based on fibroblast growth factor (FGF2) with improved biophysical and biological properties for the efficient killing of cancer cells overproducing fibroblast growth factor receptor 1 (FGFR1). We used hydrophilic and biocompatible PEG4 or PEG27 molecules as a spacer between FGF2 and the toxic agent monomethyl auristatin E. All conjugates exhibited a cytotoxic effect on FGFR1-positive cancer cell lines. The conjugate with the highest hydrodynamic size (42 kDa) and cytotoxicity was found to efficiently inhibit tumor growth in a mouse model of human breast cancer.

Sequence sensitivity and pH dependence of maleimide conjugated N-terminal cysteine peptides to thiazine rearrangement

Thiazine formation during the conjugation of N‐terminal cysteine peptides to maleimides is an underreported side reaction in the peptide literature. When the conjugation was performed at neutral and basic pH, we observed the thiazine isomer as a significant by‐product. Nuclear magnetic resonance (NMR) spectroscopy confirmed the structure of the six‐membered thiazine and ultra‐high performance liquid chromatography (UHPLC) combined with tandem mass spectrometry (MS/MS) allowed for facile, unambiguous detection due to a unique thiazine mass fragment. Furthermore, substitution of various amino acids adjacent to the N‐terminal cysteine in a tripeptide model system resulted in different rates of thiazine formation, albeit within the same order of magnitude. We also determined that varying the N‐substitution of the maleimide affects the thiazine conversion rate. Altogether, our findings suggest that thiazine rearrangement for N‐terminal cysteine‐maleimide adducts is a general side reaction that is applicable to other peptide or protein systems. Performing the conjugation reaction under acidic conditions or avoiding the use of an N‐terminal cysteine with a free amino group prevents the formation of the thiazine impurity.

Dissecting biological activities of fibroblast growth factor receptors by the coiled-coil-mediated oligomerization of FGF1

Fibroblast growth factor receptors (FGFRs) are integral membrane proteins involved in various biological processes including proliferation, migration and apoptosis. There are a number of regulatory mechanisms of FGFR signaling, which tightly control the specificity and duration of transmitted signals. The effect of the FGFRs spatial distribution in the plasma membrane on receptor-dependent functions is still largely unknown. We have demonstrated that oligomerization of FGF1 with coiled-coil motifs largely improves FGF1 affinity for FGFRs and heparin. Set of developed FGF1 oligomers evoked prolonged activation of FGFR1 and receptor-downstream signaling pathways, as compared to the wild type FGF1. The majority of obtained oligomeric FGF1 variants showed increased stability, enhanced mitogenic activity and largely improved internalization via FGFR1-dependent endocytosis. Importantly, FGF1 oligomers with the highest oligomeric state exhibited reduced ability to stimulate FGFR-dependent glucose uptake, while at the same time remained hyperactive in the induction of cell proliferation. Our data implicate that oligomerization of FGF1 alters the biological activity of the FGF/GFR1 signaling system. Furthermore, developed FGF1 oligomers, due to improved stability and proliferative potential, can be applied in the regenerative medicine or as drug delivery vehicles in the ADC approach against FGFR1-overproducing cancers.