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

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

Folate receptor overexpression induces toxicity in a diet-dependent manner in C. elegans

Folate receptor (FR) alpha (FOLR1) and beta (FOLR2) are membrane-anchored folate transporters that are expressed at low levels in normal tissues, while their expression is strongly increased in several cancers. Intriguingly, although the function of these receptors in, for example, development and cancer has been studied intensively, their role in aging is still unknown. To address this, we utilized Caenorhabditis elegans, in which FOLR-1 is the sole ortholog of folate receptors. We found that the loss of FOLR-1 does not affect reproduction, physical condition, proteostasis or lifespan, indicating that it is not required for folate transport to maintain health. Interestingly, we found that FOLR-1 is detectably expressed only in uterine-vulval cells, and that the histone-binding protein LIN-53 inhibits its expression in other tissues. Furthermore, whereas knockdown of lin-53 is known to shorten lifespan, we found that the loss of FOLR-1 partially rescues this phenotype, suggesting that elevated folr-1 expression is detrimental for health. Indeed, our data demonstrate that overexpression of folr-1 is toxic, and that this phenotype is dependent on diet. Altogether, this work could serve as a basis for further studies to elucidate the organismal effects of abnormal FR expression in diseases such as cancer.

microRNA-622 upregulates cell cycle process by targeting FOLR2 to promote CRC proliferation

BACKGROUND

Epigenetic alterations contribute greatly to the development and progression of colorectal cancer, and effect of aberrant miR-622 expression is still controversial. This study aimed to discover miR-622 regulation in CRC proliferation.

METHODS

miR-622 expression and prognosis were analyzed in clinical CRC samples from Nanfang Hospital. miR-622 regulation on cell cycle and tumor proliferation was discovered, and FOLR2 was screened as functional target of miR-622 using bioinformatics analysis, which was validated via dual luciferase assay and gain-of-function and loss-of-function experiments both in vitro and in vivo.

RESULTS

miR-622 overexpression in CRC indicated unfavorable prognosis and it regulated cell cycle to promote tumor growth both in vitro and in vivo. FOLR2 is a specific, functional target of miR-622, which negatively correlates with signature genes in cell cycle process to promote CRC proliferation.

CONCLUSIONS

miR-622 upregulates cell cycle process by targeting FOLR2 to promote CRC proliferation, proposing a novel mechanism and treatment target in CRC epigenetic regulation of miR-622.

Recent Advances in Folates and Autoantibodies against Folate Receptors in Early Pregnancy and Miscarriage

Though firstly identified in cerebral folate deficiency, autoantibodies against folate receptors (FRAbs) have been implicated in pregnancy complications such as miscarriage; however, the underlying mechanism needs to be further elaborated. FRAbs can be produced via sensitization mediated by folate-binding protein as well as gene mutation, aberrant modulation, or degradation of folate receptors (FRs). FRAbs may interfere with folate internalization and metabolism through blocking or binding with FRs. Interestingly, different types of FRs are expressed on trophoblast cells, decidual epithelium or stroma, and macrophages at the maternal-fetal interface, implying FRAbs may be involved in the critical events necessary for a successful pregnancy. Thus, we propose that FRAbs may disturb pregnancy establishment and maintenance by modulating trophoblastic biofunctions, placental development, decidualization, and decidua homeostasis as well as the functions of FOLR2+ macrophages. In light of these findings, FRAbs may be a critical factor in pathological pregnancy, and deserve careful consideration in therapies involving folic acid supplementation for pregnancy complications.

Single-cell RNA sequencing reveals unique monocyte-derived interstitial macrophage subsets during lipopolysaccharide-induced acute lung inflammation

Interstitial macrophages (IMs) reside in the lung tissue surrounding key structures including airways, vessels, and alveoli. Recent work has described IM heterogeneity during homeostasis, however, there are limited data on IMs during inflammation. We sought to characterize IM origin, subsets, and transcriptomic profiles during homeostasis and lipopolysaccharide (LPS) induced acute lung inflammation. During homeostasis, we used three complementary methods, spectral flow cytometry, single-cell RNA-sequencing, and gene regulatory network enrichment, to demonstrate that IMs can be divided into two core subsets distinguished by surface and transcriptional expression of folate receptor β (Folr2/FRβ). These subsets inhabited distinct niches within the lung interstitium. Within FRβ+ IMs we identified a subpopulation marked by coexpression of LYVE1. During acute LPS-induced inflammation, lung IM numbers expand. Lineage tracing revealed IM expansion was due to recruitment of monocyte-derived IMs. At the peak of inflammation, recruited IMs were comprised two unique subsets defined by expression of genes associated with interferon signaling and glycolytic pathways. As recruited IMs matured, they adopted the overall transcriptional state of FRβ- resident IMs but retained expression in several origin-specific genes, such as IL-1β. FRβ+ IMs were of near-pure resident origin. Taken together our data show that during LPS-induced inflammation, there are distinct populations of IMs that likely have unique functions. FRΒ+ IMs comprise a stable, resident population, whereas FRβ- ΙΜs represent a mixed population of resident and recruited IMs.

A Novel Treatment for Glomerular Disease: Targeting the Activated Macrophage Folate Receptor with a Trojan Horse Therapy in Rats

Since activated macrophages express a functional folate receptor β (FRβ), targeting this macrophage population with folate-linked drugs could increase selectivity to treat inflammatory diseases. Using a macrophage-mediated anti-glomerular basement membrane (anti-GBM) glomerulonephritis (GN) in WKY rats, we investigated the effect of a novel folic acid-aminopterin (AMT) conjugate (EC2319) designed to intracellularly deliver AMT via the FR. We found that treatment with EC2319 significantly attenuated kidney injury and preserved renal function. Kidney protection with EC2319 was blocked by a folate competitor, indicating that its mechanism of action was specifically FRβ-mediated. Notably, treatment with methotrexate (MTX), another folic acid antagonist related to AMT, did not protect from kidney damage. EC2319 reduced glomerular and interstitial macrophage infiltration and decreased M1 macrophage recruitment but not M2 macrophages. The expression of CCL2 and the pro-fibrotic cytokine TGF-β were also reduced in nephritic glomeruli with EC2319 treatment. In EC2319-treated rats, there was a significant decrease in the deposition of collagens. In nephritic kidneys, FRβ was expressed on periglomerular macrophages and macrophages present in the crescents, but its expression was not observed in normal kidneys. These data indicate that selectively targeting the activated macrophage population could represent a novel means for treating anti-GBM GN and other acute crescentic glomerulonephritis.

Folate Receptor Beta Designates Immunosuppressive Tumor-Associated Myeloid Cells That Can Be Reprogrammed with Folate-Targeted Drugs

Although immunotherapies of tumors have demonstrated promise for altering the progression of malignancies, immunotherapies have been limited by an immunosuppressive tumor microenvironment (TME) that prevents infiltrating immune cells from performing their anticancer functions. Prominent among immunosuppressive cells are myeloid-derived suppressor cells (MDSC) and tumor-associated macrophages (TAM) that inhibit T cells via release of immunosuppressive cytokines and engagement of checkpoint receptors. Here, we explore the properties of MDSCs and TAMs from freshly isolated mouse and human tumors and find that an immunosuppressive subset of these cells can be distinguished from the nonimmunosuppressive population by its upregulation of folate receptor beta (FRβ) within the TME and its restriction to the TME. This FRβ+ subpopulation could be selectively targeted with folate-linked drugs. Delivery of a folate-targeted TLR7 agonist to these cells (i) reduced their immunosuppressive function, (ii) increased CD8+ T-cell infiltration, (iii) enhanced M1/M2 macrophage ratios, (iv) inhibited tumor growth, (v) blocked tumor metastasis, and (vi) improved overall survival without demonstrable toxicity. These data reveal a broadly applicable strategy across tumor types for reprogramming MDSCs and TAMs into antitumorigenic immune cells using a drug that would otherwise be too toxic to administer systemically. The data also establish FRβ as the first marker that distinguishes immunosuppressive from nonimmunosuppressive subsets of MDSCs and TAMs. Because all solid tumors accumulate MDSCs and TAMs, a general strategy to both identify and reprogram these cells should be broadly applied in the characterization and treatment of multiple tumors. SIGNIFICANCE: FRβ serves as both a means to identify and target MDSCs and TAMs within the tumor, allowing for delivery of immunomodulatory compounds to tumor myeloid cells in a variety of cancers.

Folate receptor-beta expression as a diagnostic target in human & rodent nonalcoholic steatohepatitis

INTRODUCTION

Nonalcoholic steatohepatitis (NASH) afflicts 20-36% of individuals with nonalcoholic fatty liver disease (NAFLD). A lipotoxic hepatic environment, altered innate immune signaling and inflammation are defining features of progression to NASH. Activated resident liver macrophages express folate receptor beta (FR-β) which may be an indicator of progression from steatosis to NASH. The goals of this study were to characterize FR-β protein expression in human NAFLD and rodent models of NASH, and demonstrate liver targeting of an FR-β imaging agent to the liver of a rodent NASH model using FR-β.

METHODS

Rat liver lysates from methionine choline deficient (MCD) fed rats, high fat diet (HFD) and methionine choline sufficient (MC+) rat controls were analyzed for hepatic FR-β protein. The FR-β-targeted agent, Etarfolatide was injected into MCD and MC + -fed C57BL/6 mice for efficient FastSPECT hepatic imaging. Additionally, FR-β expression across the stages of human NAFLD from normal to NASH was assessed.

RESULTS

FastSPECT images show targeting of Etarfolatide to the liver of mice fed 8 weeks of MCD diet but not control-fed mice. The MCD rat model exhibited significantly increased protein expression of hepatic FR-β in contrast to HFD or normal samples. Similarly human liver samples categorized as NASH Fatty or NASH Not Fatty showed elevated FR-β protein when compared to normal liver. FR-β transcript expression levels were elevated across both NASH Fatty and NASH Not Fatty samples.

CONCLUSION

The findings in this study indicate that FR-β expression in NASH may be harnessed to target agents directly to the liver.

The folate receptor β as a macrophage-mediated imaging and therapeutic target in rheumatoid arthritis

Macrophages play a key role in the pathophysiology of rheumatoid arthritis (RA). Notably, positive correlations have been reported between synovial macrophage infiltration and disease activity as well as therapy outcome in RA patients. Hence, macrophages can serve as an important target for both imaging disease activity and drug delivery in RA. Folate receptor β (FRβ) is a glycosylphosphatidyl (GPI)-anchored plasma membrane protein being expressed on myeloid cells and activated macrophages. FRβ harbors a nanomolar binding affinity for folic acid allowing this receptor to be exploited for RA disease imaging (e.g., folate-conjugated PET tracers) and therapeutic targeting (e.g., folate antagonists and folate-conjugated drugs). This review provides an overview of these emerging applications in RA by summarizing and discussing properties of FRβ, expression of FRβ in relation to macrophage polarization, FRβ-targeted in vivo imaging modalities, and FRβ-directed drug targeting.

A Folate-Conjugated Dual-Modal Fluorescent Magnetic Resonance Imaging Contrast Agent that Targets Activated Macrophages In Vitro and In Vivo

Mucin-1 (MUC1), a transmembrane glycoprotein is aberrantly expressed on ∼90% of breast cancer and is an excellent target for nanoparticulate targeted imaging. In this study, the development of a dye-doped NIR emitting mesoporous silica nanoparticles platform conjugated to tumor-specific MUC1 antibody (ab-tMUC1-NIR-MSN) for in vivo optical detection of breast adenocarcinoma tissue is reported. The structural properties, the in vitro and in vivo performance of this nanoparticle-based probe were evaluated. In vitro studies showed that the MSN-based optical imaging nanoprobe is non-cytotoxic and targets efficiently mammary cancer cells overexpressing human tMUC1 protein. In vivo experiments with female C57BL/6 mice indicated that this platform accumulates mainly in the liver and did not induce short-term toxicity. In addition, we demonstrated that the ab-tMUC1-NIR-MSN nanoprobe specifically detects mammary gland tumors overexpressing human tMUC1 in a human MUC1 transgenic mouse model.

Smart Human-Serum-Albumin-As2 O3 Nanodrug with Self-Amplified Folate Receptor-Targeting Ability for Chronic Myeloid Leukemia Treatment

Arsenic trioxide (ATO, As2 O3 ) is currently used to treat acute promyelocytic leukemia. However, expanding its use to include high-dose treatment of other cancers is severely hampered by serious side effects on healthy organs. To address these limitations, we loaded ATO onto folate (FA)-labeled human serum albumin (HSA) pretreated with glutathione (GSH) based on the low pH- and GSH-sensitive arsenic-sulfur bond, and we termed the resulting smart nanodrug as FA-HSA-ATO. FA-HSA-ATO could specifically recognize folate receptor-β-positive (FRβ+) chronic myeloid leukemia (CML) cells, resulting in more intracellular accumulation of ATO. Furthermore, the nanodrug could upregulate FRβ expression in CML cancer cells and xenograft tumor model, facilitating even more recruitment and uptake of FRβ-targeting drugs. In vitro and in vivo experiments indicate that the nanodrug significantly alleviates side effects and improves therapeutic efficacy of ATO on CML and xenograft tumor model.

Neutral PEGylated liposomal formulation for efficient folate-mediated delivery of MCL1 siRNA to activated macrophages

Cationic liposomes are efficient vectors for systemic delivery of therapeutic small interfering RNA (siRNA), taking advantage of RNA interference (RNAi), a naturally occurring gene-silencing mechanism in mammalian cells. However, toxicity at high concentrations, short circulating half-lives and lack of specificity restrict their successful application in a wider scale. The purpose of this study was to evaluate the efficiency of neutral liposomes containing polyethylene glycol (PEG) to encapsulate siRNA in their aqueous core. This formulation will reduce drastically the toxicity associated to cationic liposomes by bringing surface charge to almost zero, increasing stealth degree and therefore circulation time. In this study, we evaluate the efficiency of folate-targeted liposomes for specific delivery of siRNA to activated macrophages, key effector cells in rheumatoid arthritis (RA) pathology which specifically express folate receptor β (FRβ). Myeloid cell leukaemia-1 (Mcl-1) is a protein essential for synovial macrophage survival, since Mcl-1 suppression results in the induction of apoptosis. The effect of MCL1 siRNA incorporated in liposomal formulation was assessed in primary human macrophages and successful inhibition of Mcl-1 expression was achieved. Here we show that the neutral liposomal derived from DOPE (1,2-dioleoyl-sn-glycero-3-phosphoethanolamine) formulation developed is efficient to encapsulate MCL1 siRNA and silencing gene expression in activated human macrophages.

Folate receptor targeted three-layered micelles and hydrogels for gene delivery to activated macrophages

New folic acid (FA) coupled three layered micelles (3LM) were designed to encapsulate DNA, and their application as delivery system that specifically targets activated macrophages was investigated for new treatment options in rheumatoid arthritis (RA). FA coupled poly(l-lactide)-b-poly(ethylene glycol) (FA-PEG-PLLA) was synthesized via the NHS-ester activated/amine coupling method. Fluorescein labeled folic acid was used for flow cytometric detection of the expression of functional folic receptor β in LPS-activated and resting macrophages. FA coupled 3LM were formulated in a two-step procedure and characterized regarding hydrodynamic diameters and zeta potentials. The presence of the targeting ligand was shown not to increase the size of the 3LM compared to their non-targeted counterparts. Targeted and non-targeted 3LM were used in vitro to optimize uptake conditions in the RAW 264.7 macrophage cell line. The amount of FA coupled polymer in the final formulation was found to be optimal at 75% FA-PEG-PLLA and 25% PLLA-PEG-PLLA. Subsequently, transgene expression in vitro in RAW 264.7 cells and ex vivo in primary activated and resting mouse macrophages was determined as a function of FR-mediated internalization of 3LM encapsulating GFP expressing plasmid. FR-overexpressing activated cells, as successfully identified by internalization of FA-fluorescein, showed significantly higher GFP expression in vitro and ex vivo than resting macrophages with only a basal level of FR expression. Lastly, injectable hydrogels as depot formulation were formed by stereocomplexation, and their degradation, DNA release profiles, and dissociation into intact 3LM were found to be beneficial for potential in vivo application. Our findings confirm that FA-3LM are taken up by activated macrophages via folate receptor mediated endocytosis and that their hydrogels release intact 3LM for efficient transfection of primary macrophages. Therefore, FA-3LM could become a promising delivery system for receptor-mediated drug or gene delivery and novel therapy for rheumatoid arthritis in an in situ forming gel formulation.

Antiinflammatory Activity of a Novel Folic Acid Targeted Conjugate of the mTOR Inhibitor Everolimus

Folate receptor (FR)-β has been identified as a promising target for antimacrophage and antiinflammatory therapies. In the present study, we investigated EC0565, a folic acid-derivative of everolimus, as a FR-specific inhibitor of the mammalian target of rapamycin (mTOR). Because of its amphiphilic nature, EC0565 was first evaluated for water solubility, critical micelle formation, stability in culture and FR-binding specificity. Using FR-expressing macrophages, the effect of EC0565 on mTOR signaling and cellular proliferation was studied. The pharmacokinetics, metabolism and bioavailability of EC0565 were studied in normal rats. The in vivo activity of EC0565 was assessed in rats with adjuvant arthritis, a "macrophage-rich" model with close resemblance to rheumatoid arthritis. EC0565 forms micellar aggregates in physiological buffers and demonstrates good water solubility as well as strong multivalent FR-binding capacity. EC0565 inhibited mTOR signaling in rat macrophages at nanomolar concentrations and induced G0/G1 cell cycle arrest in serum-starved RAW264.7 cells. Subcutaneously administered EC0565 in rats displayed good bioavailability and a relatively long half-life (~12 h). When given at 250 nmol/kg, EC0565 selectively inhibited proliferating cell nuclear antigen expression in thioglycollate-stimulated rat peritoneal cells. With limited dosing regimens, the antiarthritic activity of EC0565 was found superior to that of etanercept, everolimus and a nontargeted everolimus analog. The in vivo activity of EC0565 was also comparable to that of a folate-targeted aminopterin. Folate-targeted mTOR inhibition may be an effective way of suppressing activated macrophages in sites of inflammation, especially in nutrient-deprived conditions, such as in the arthritic joints. Further investigation and improvement upon the physical and biochemical properties of EC0565 are warranted.

Folate receptor–targeted single-photon emission computed tomography/computed tomography to detect activated macrophages in atherosclerosis: can it distinguish vulnerable from stable atherosclerotic plaques?

The need for noninvasive imaging to distinguish stable from vulnerable atherosclerotic plaques is evident. Activated macrophages play a role in atherosclerosis and express folate receptor folate receptor β (FR-β). The feasibility of folate targeting to detect atherosclerosis was demonstrated in human and mouse plaques, and it was suggested that molecular imaging of FR-β through folate conjugates might be a specific marker for plaque vulnerability. However, these studies did not allow differentiation between stable and vulnerable atherosclerotic plaques. We investigated the feasibility of a folate-based radiopharmaceutical (111)In-EC0800) with high-resolution animal single-photon emission computed tomography/computed tomography (SPECT/CT) to differentiate between stable and vulnerable atherosclerotic plaques in apolipoprotein E(−/−) mice in which we can induce plaques with the characteristics of stable and vulnerable plaques by placing a flow-modifying cast around the common carotid artery. Both plaques showed (111)In-EC0800 uptake, with higher uptake in the vulnerable plaque. However, the vulnerable plaque was larger than the stable plaque. Therefore, we determined tracer uptake per plaque volume and demonstrated higher accumulation of (111)In-EC0800 in the stable plaque normalized to plaque volume. Our data show that (111)In-EC0800 is not a clear-cut marker for the detection of vulnerable plaques but detects both stable and vulnerable atherosclerotic plaques in a mouse model of atherosclerosis.

Depletion of folate receptor β-expressing macrophages alleviates bleomycin-induced experimental skin fibrosis

OBJECTIVES

Folate receptor β (FRβ)-expressing macrophages have been identified as activated macrophages. Here, we investigated the infiltration of FRβ-expressing macrophages in a murine model of bleomycin (BLM)-induced skin fibrosis and assessed the antifibrotic effects of depletion of FRβ-expressing macrophages in this model using a recombinant immunotoxin to FRβ.

METHODS

A recombinant immunotoxin (anti-FRβ-PE38) was prepared by conjugating the Fv portion of the anti-mouse FRβ heavy chain with truncated Pseudomonas exotoxin A (VH-PE38) and the Fv portion of the anti-mouse FRβ light chain. BLM-induced skin fibrosis mice were intravenously treated with either anti-FRβ-PE38 or VH-PE38 as a control protein. Skin fibrosis was evaluated by the change of skin thickness and hydroxyproline content on Day 29. The TGFβ1 mRNA levels in the treated skin were assessed by quantitative real-time RT-PCR on Day 9.

RESULTS

Numbers of FRβ-expressing macrophages increased in BLM-injected skin. Anti-FRβ-PE38 treatment led to a dramatic reduction in the number of FRβ-expressing macrophages. Additionally, skin thickness and hydroxyproline content, were markedly reduced. TGFβ1 mRNA levels were also down-regulated after the treatment. TGFβ1 expression was enriched in FRβ-expressing macrophages compared with FRβ-negative macrophages.

CONCLUSION

These results indicated that anti-FRβ-PE38 treatment efficiently depleted FRβ-expressing macrophages and consequently alleviated BLM-induced skin fibrosis.

Imaging atherosclerotic plaque inflammation via folate receptor targeting using a novel 18F-folate radiotracer

Folate receptor β (FR-β) is overexpressed on activated, but not resting, macrophages involved in a variety of inflammatory and autoimmune diseases. A pivotal step in atherogenesis is the subendothelial accumulation of macrophages. In nascent lesions, they coordinate the scavenging of lipids and cellular debris to define the likelihood of plaque inflammation and eventually rupture. In this study, we determined the presence of FR-β-expressing macrophages in atherosclerotic lesions by the use of a fluorine-18-labeled folate-based radiotracer. Human endarterectomized specimens were used to measure gene expression levels of FR-β and CD68. Increased FR-β and CD68 levels were found in atherosclerotic plaques compared to normal artery walls by quantitative real-time polymerase chain reaction. Western blotting and immunohistochemistry demonstrated prominent FR-β protein levels in plaques. FR-β-positive cells colocalized with activated macrophages (CD68) in plaque tissue. Carotid sections incubated with 3'-aza-2'-[18F]fluorofolic acid displayed increased accumulation in atherosclerotic plaques through in vitro autoradiography. Specific binding of the radiotracer correlated with FR-β-expressing macrophages. These results demonstrate high FR-β expression in atherosclerotic lesions of human carotid tissue correlating with CD68-positive macrophages. Areas of high 3'-aza-2'-[18F]fluorofolic acid binding within the lesions represented FR-β-expressing macrophages. Selectively targeting FR-β-positive macrophages through folate-based radiopharmaceuticals may be useful for noninvasive imaging of plaque inflammation.

Methotrexate transport mechanisms: the basis for targeted drug delivery and ß-folate-receptor-specific treatment

Methotrexate (MTX) plays a pivotal role in the treatment of rheumatoid arthritis (RA). The transport mechanisms with which MTX reaches is target after application are an important part of MTX pharmacology and its concentration in target tissue such as RA synovial membrane might strongly influence the effectiveness of the drug. Physiological plasma protein binding of MTX to albumin is important for the distribution of MTX in the body and relative high concentrations of the drug are found in the liver. However, targeted drug delivery into inflamed joints and increased anti-arthritic efficiency can be obtained by covalent coupling of MTX ex-vivo to human serum albumin (MTX-HSA) or in-vivo to endogenous albumin mediated through the MTX-pro-drug AWO54. High expression of the folate receptor β (FR-β) on synovial macrophages of RA patients and its capacity to mediate binding and uptake of MTX has been demonstrated. To further improve drug treatment of RA, FR-β specific drugs have been developed and were characterised for their therapeutic potency in synovial inflammation. Therefore, different approaches to improve folate inhibitory and FR-β specific therapy of RA beyond MTX are in development and will be described.