Selective expression of folate receptor beta and its possible role in methotrexate transport in synovial macrophages from patients with rheumatoid arthritis

Defining and targeting macrophage heterogeneity in the mammary gland and breast cancer

INTRODUCTION

Macrophages are innate immune cells that are associated with extensive phenotypic and functional plasticity and contribute to normal development, tissue homeostasis, and diseases such as cancer. In this review, we discuss the heterogeneity of tissue resident macrophages in the normal mammary gland and tumor-associated macrophages in breast cancer. Tissue resident macrophages are required for mammary gland development, where they have been implicated in promoting extracellular matrix remodeling, apoptotic clearance, and cellular crosstalk. In the context of cancer, tumor-associated macrophages are key drivers of growth and metastasis via their ability to promote matrix remodeling, angiogenesis, lymphangiogenesis, and immunosuppression.

METHOD

We identified and summarized studies in Pubmed that describe the phenotypic and functional heterogeneity of macrophages and the implications of targeting individual subsets, specifically in the context of mammary gland development and breast cancer. We also identified and summarized recent studies using single-cell RNA sequencing to identify and describe macrophage subsets in human breast cancer samples.

RESULTS

Advances in single-cell RNA sequencing technologies have yielded nuances in macrophage heterogeneity, with numerous macrophage subsets identified in both the normal mammary gland and breast cancer tissue. Macrophage subsets contribute to mammary gland development and breast cancer progression in differing ways, and emerging studies highlight a role for spatial localization in modulating their phenotype and function.

CONCLUSION

Understanding macrophage heterogeneity and the unique functions of each subset in both normal mammary gland development and breast cancer progression may lead to more promising targets for the treatment of breast cancer.

Targeted treatment of gouty arthritis by biomineralized metallic nanozyme-mediated oxidative stress-mitigating nanotherapy

Gouty arthritis is characterized by chronic deposition of monosodium urate (MSU) crystals in the joints and other tissues, resulting in the production of excess reactive oxygen species (ROS) and proinflammatory cytokines that intensify synovial inflammation. This condition is mainly associated with inflammatory M1 macrophage activation and oxidative stress production. Hence, gout symptoms can often be resolved by eliminating M1 macrophage activation and scavenging oxidative stress in the inflamed areas. Herein, we developed M1-macrophage-targeting biomineralized metallic nanozymes (FALNZs) that deplete oxidative stress and reduce the M1 macrophage levels to mitigate gouty arthritis. Intra-articular injection of the FALNZs targets inflammatory macrophages and suppresses ROS levels in joints with MSU-crystal-induced arthritis. In addition, the FALNZs alleviate joint swelling, inflammatory cytokine production, and pathological features of the joints. Overall, the proposed therapeutic approach is biocompatible and is an effective ROS scavenger for the treatment of gouty pathogenesis.

Insights about the ability of folate based supramolecular gels to act as targeted therapeutic agents

With the aim to obtain targeted chemotherapeutic agents, imidazolium and ammonium-based folate salts were synthesized. Their photophysical behavior was investigated both in buffer and buffer/DMSO solution as well as in solid phase, performing UV-vis and fluorescence investigations. Properties of the aggregates were also analyzed by dynamic light scattering. Gelation ability of the salts was analyzed in biocompatible solvents, and gel phases obtained were characterized by determining critical gelation concentrations and gel-solution transition temperatures. Insights about gelator interactions in the tridimensional network were also gained performing ATR-FTIR investigation. Properties of soft materials were further analyzed performing rheology measurements, scanning electron microscopy, fluorescence and resonance light scattering investigations. Antiproliferative activity of organic salts was tested towards two breast cancer cell lines, expressing different levels of folate receptor, namely MDA-MB-231 and MCF-7, and a normal epithelial cell line, like h-TER T-RPE-1, by using MTT assay. Dichlodihydrofluorescein acetate test was performed to verify the role of oxidative stress in cell death. Finally, antiproliferative activity was also evaluated in gel phase, to verify if salts were able to retain biological activity also after the entrapment in the gelatinous network. Results collected evidence that folate based organic salts were able to behave as targeted chemotherapeutic agents both in solution and gel phase, showing uptake mechanism and selectivity indexes that depend on both cancer cell line nature and salt structure.

Oral liposomes encapsulating ginsenoside compound K for rheumatoid arthritis therapy

Ginsenoside compound K (GCK) can efficiently treat rheumatoid arthritis (RA) due to its immune and anti-inflammatory functions. However, GCK exists some shortcomings such as poor aqueous solubility, low permeability to the intestinal cell membrane, and serious P-gp efflux, thus limiting its application. In order to solve these problems, a folic acid-targeted drug delivery system based on liposomes (FA-LP-GCK) was developed. The prepared FA-LP-GCK had a uniform size distribution and spherical structure, the particle size was 249.13 ± 1.40 nm. Meanwhile, they had high encapsulation efficiency (93.33 ± 0.05 %). FA-LP-GCK also presented good stability in artificial gastric juice, so they can be absorbed into the intestine and enter the blood circulation. The activated RAW 264.7 cells were chosen to evaluate the cytotoxicity and cellular uptake capacity of FA-LP-GCK. FA-LP-GCK showed stronger growth inhibition and cellular uptake ability against activated macrophages. Finally, the efficacy of FA-LP-GCK in vivo was evaluated in the adjuvant arthritis rat model. The results showed that FA-LP-GCK can significantly reduce joint swelling. Furthermore, it can significantly inhibit the expression of pro-inflammatory cytokines and improve synovial hyperplasia of joints and pathological changes in the spleen. Therefore, FA-LP-GCK may be a potential therapeutic approach for RA.

Methotrexate Provokes Disparate Folate Metabolism Gene Expression and Alternative Splicing in Ex Vivo Monocytes and GM-CSF- and M-CSF-Polarized Macrophages

Macrophages constitute important immune cell targets of the antifolate methotrexate (MTX) in autoimmune diseases, including rheumatoid arthritis. Regulation of folate/MTX metabolism remains poorly understood upon pro-inflammatory (M1-type/GM-CSF-polarized) and anti-inflammatory (M2-type/M-CSF-polarized) macrophages. MTX activity strictly relies on the folylpolyglutamate synthetase (FPGS) dependent intracellular conversion and hence retention to MTX-polyglutamate (MTX-PG) forms. Here, we determined FPGS pre-mRNA splicing, FPGS enzyme activity and MTX-polyglutamylation in human monocyte-derived M1- and M2-macrophages exposed to 50 nmol/L MTX ex vivo. Moreover, RNA-sequencing analysis was used to investigate global splicing profiles and differential gene expression in monocytic and MTX-exposed macrophages. Monocytes displayed six-eight-fold higher ratios of alternatively-spliced/wild type FPGS transcripts than M1- and M2-macrophages. These ratios were inversely associated with a six-ten-fold increase in FPGS activity in M1- and M2-macrophages versus monocytes. Total MTX-PG accumulation was four-fold higher in M1- versus M2-macrophages. Differential splicing after MTX-exposure was particularly apparent in M2-macrophages for histone methylation/modification genes. MTX predominantly induced differential gene expression in M1-macrophages, involving folate metabolic pathway genes, signaling pathways, chemokines/cytokines and energy metabolism. Collectively, macrophage polarization-related differences in folate/MTX metabolism and downstream pathways at the level of pre-mRNA splicing and gene expression may account for variable accumulation of MTX-PGs, hence possibly impacting MTX treatment efficacy.

Macrophage-Driven Inflammation in Metabolic Osteoarthritis: Implications for Biomarker and Therapy Development

Osteoarthritis (OA) is a common and debilitating joint disorder that leads to progressive joint breakdown and loss of articular cartilage. Accompanied by a state of low-grade inflammation, its etiology extends beyond that of a wear-and-tear disease, and the immune system might have a role in its initiation and progression. Obesity, which is directly associated with an increased incidence of OA, alters adipokine release, increases pro-inflammatory macrophage activity, and affects joint immune regulation. Studying inflammatory macrophage expression and strategies to inhibit inflammatory macrophage phenotype polarization might provide insights into disease pathogenesis and therapeutic applications. In pre-clinical studies, the detection of OA in its initial stages was shown to be possible using imaging techniques such as SPECT-CT, and advances are made to detect OA through blood-based biomarker analysis. In this review, obesity-induced osteoarthritis and its mechanisms in inducing joint degeneration are summarized, along with an analysis of the current developments in patient imaging and biomarker use for diagnostic and therapeutic strategies.

Nanotechnology-enabled immunoengineering approaches to advance therapeutic applications

Immunotherapy has reached clinical success in the last decade, with the emergence of new and effective treatments such as checkpoint blockade therapy and CAR T-cell therapy that have drastically improved patient outcomes. Still, these therapies can be improved to limit off-target effects, mitigate systemic toxicities, and increase overall efficacies. Nanoscale engineering offers strategies that enable researchers to attain these goals through the manipulation of immune cell functions, such as enhancing immunity against cancers and pathogens, controlling the site of immune response, and promoting tolerance via the delivery of small molecule drugs or biologics. By tuning the properties of the nanomaterials, such as size, shape, charge, and surface chemistry, different types of immune cells can be targeted and engineered, such as dendritic cells for immunization, or T cells for promoting adaptive immunity. Researchers have come to better understand the critical role the immune system plays in the progression of pathologies besides cancer, and developing nanoengineering approaches that seek to harness the potential of immune cell activities can lead to favorable outcomes for the treatment of injuries and diseases.

Folate Receptor Beta for Macrophage Imaging in Rheumatoid Arthritis

Non-invasive imaging modalities constitute an increasingly important tool in diagnostic and therapy response monitoring of patients with autoimmune diseases, including rheumatoid arthritis (RA). In particular, macrophage imaging with positron emission tomography (PET) using novel radiotracers based on differential expression of plasma membrane proteins and functioning of cellular processes may be suited for this. Over the past decade, selective expression of folate receptor β (FRβ), a glycosylphosphatidylinositol-anchored plasma membrane protein, on myeloid cells has emerged as an attractive target for macrophage imaging by exploiting the high binding affinity of folate-based PET tracers. This work discusses molecular, biochemical and functional properties of FRβ, describes the preclinical development of a folate-PET tracer and the evaluation of this tracer in a translational model of arthritis for diagnostics and therapy-response monitoring, and finally the first clinical application of the folate-PET tracer in RA patients with active disease. Consequently, folate-based PET tracers hold great promise for macrophage imaging in a variety of (chronic) inflammatory (autoimmune) diseases beyond RA.

Folate Conjugated Polyethylene Glycol Probe for Tumor-Targeted Drug Delivery of 5-Fluorouracil

A targeted delivery system is primarily intended to carry a potent anticancer drug to specific tumor sites within the bodily tissues. In the present study, a carrier system has been designed using folic acid (FA), bis-amine polyethylene glycol (PEG), and an anticancer drug, 5-fluorouracil (5-FU). FA and PEG were joined via an amide bond, and the resulting FA-PEG-NH₂ was coupled to 5-FU producing folate-polyethylene glycol conjugated 5-fluorouracil (FA-PEG-5-FU). Spectroscopic techniques (UV-Vis, ¹HNMR, FTIR, and HPLC) were used for the characterization of products. Prodrug (FA-PEG-5-FU) was analyzed for drug release profile (in vitro) up to 10 days and compared to a standard anticancer drug (5-FU). Folate conjugate was also analyzed to study its folate receptors (FR) mediated transport and in vitro cytotoxicity assays using HeLa cancer cells/Vero cells, respectively, and antitumor activity in tumor-bearing mice models. Folate conjugate showed steady drug release patterns and improved uptake in the HeLa cancer cells than Vero cells. Folate conjugate treated mice group showed smaller tumor volumes; specifically after the 15th day post-treatment, tumor sizes were decreased significantly compared to the standard drug group (5-FU). Molecular docking findings demonstrated importance of Trp138, Trp140, and Lys136 in the stabilization of flexible loop flanking the active site. The folic acid conjugated probe has shown the potential of targeted drug delivery and sustained release of anticancer drug to tumor lesions with intact antitumor efficacy.

Folate Transport and One-Carbon Metabolism in Targeted Therapies of Epithelial Ovarian Cancer

New therapies are urgently needed for epithelial ovarian cancer (EOC), the most lethal gynecologic malignancy. To identify new approaches for targeting EOC, metabolic vulnerabilities must be discovered and strategies for the selective delivery of therapeutic agents must be established. Folate receptor (FR) α and the proton-coupled folate transporter (PCFT) are expressed in the majority of EOCs. FRβ is expressed on tumor-associated macrophages, a major infiltrating immune population in EOC. One-carbon (C1) metabolism is partitioned between the cytosol and mitochondria and is important for the synthesis of nucleotides, amino acids, glutathione, and other critical metabolites. Novel inhibitors are being developed with the potential for therapeutic targeting of tumors via FRs and the PCFT, as well as for inhibiting C1 metabolism. In this review, we summarize these exciting new developments in targeted therapies for both tumors and the tumor microenvironment in EOC.

Targeted delivery of mPGES-1 inhibitors to macrophages via the folate receptor-β for inflammatory pain

Activated macrophages overexpress the folate receptor β (FR-β) that can be used for targeted delivery of drugs conjugated to folic acid. FR-expressing macrophages contribute to arthritis progression by secreting prostaglandin E₂ (PGE₂). Non-steroidal anti-inflammatory drugs (NSAIDs) block PGs and thromboxane by inhibiting the cyclooxygenase (COX) enzymes and are used for chronic pain and inflammation despite their well-known toxicity. New NSAIDs target an enzyme downstream of COXs, microsomal prostaglandin E synthase-1 (mPGES-1). Inhibition of mPGES-1 in inflammatory macrophages promises to retain NSAID efficacy while limiting toxicity. We conjugated a potent mPGES-1 inhibitor, MK-7285, to folate, but the construct released the drug inefficiently. Folate conjugation to the primary alcohol of MK-7285 improved the construct's stability and the release of free drug. Surprisingly, the drug-folate conjugate potentiated PGE₂ in FR-positive KB cells, and reduced PGE₂ in macrophages independently of the FR. Folate conjugation of NSAIDs is not an optimal strategy for targeting of macrophages.

Role of folate-conjugated glycol-chitosan nanoparticles in modulating the activated macrophages to ameliorate inflammatory arthritis: in vitro and in vivo activities

Activated macrophages are the primary targets in rheumatoid arthritis (RA) management. So, we report efficacious, dual-functional Methotrexate (MTX) loaded folate-conjugated pH-responsive glycol-chitosan nanoparticles (MFGCN) prepared by nano-precipitation and zero-order cross-linking reaction for targeting inflamed arthritic tissue. Physical characterization by DLS, SEM and TEM indicated a spherical, smooth morphology with a diameter ~ 300 nm. ¹H NMR and FTIR indicated folic acid conjugation to GC by zero-order cross-linkers. In vitro release kinetics in PBS showed pH-responsive and sustained release behaviour of MFGCN. Enhanced cellular uptake and cytotoxicity of MFGCN in LPS(+)RAW and activated peritoneal macrophages (Mϕ) were observed when compared to LPS(-)RAW cells. MFGCN-induced mitochondrial membrane potential (MMP) perturbations indicated apoptosis. Oxidative stress was evident by significant increase in ROS and RNS, 4 h post incubation with MFGCN. Negligible hemolysis by FGCN and MFGCN on rat RBC's indicated biocompatibility. In vivo biodistribution of MFGCN in adjuvant-induced arthritis (AIA) rats indicated RA targetability. Prolonged blood circulation coupled with higher concentrations of ^99mTc-MFGCN at the arthritic site was observed post 24 h of injection. The gamma scintigraphic image confirmed accumulation of radiolabelled MFGCN in arthritic paw when compared to the non-inflamed paw, confirming the selective uptake of ^99mTc-MFGCN by folate-overexpressing macrophages in the arthritic synovium thereby proving its targeted efficacy and theranostic potential. In AIA rats, MFGCN lowers arthritic signs, improves antioxidant response and decreases pro-inflammatory cytokines, suggesting its potential in targeting activated macrophages of synovium. Graphical abstract.

A Role for Folate in Microbiome-Linked Control of Autoimmunity

The microbiome exerts considerable control over immune homeostasis and influences susceptibility to autoimmune and autoinflammatory disease (AD/AID) such as inflammatory bowel disease (IBD), multiple sclerosis (MS), type 1 diabetes (T1D), psoriasis, and uveitis. In part, this is due to direct effects of the microbiome on gastrointestinal (GI) physiology and nutrient transport, but also to indirect effects on immunoregulatory controls, including induction and stabilization of T regulatory cells (T _reg). Secreted bacterial metabolites such as short-chain fatty acids (SCFA) are under intense investigation as mediators of these effects. In contrast, folate (vitamin B9), an essential micronutrient, has attracted less attention, possibly because it exerts global physiological effects which are difficult to differentiate from specific effects on the immune system. Here, we review the role of folate in AD/AID with some emphasis on sight-threatening autoimmune uveitis. Since folate is required for the generation and maintenance of T _{reg ,} we propose that one mechanism for microbiome-based control of AD/AID is via folate-dependent induction of GI tract T _{reg ,} particularly colonic T _reg, via anergic T cells (T _an). Hence, folate supplementation has potential prophylactic and/or therapeutic benefit in AID/AD.

CAR-T cell-mediated depletion of immunosuppressive tumor-associated macrophages promotes endogenous antitumor immunity and augments adoptive immunotherapy

The immunosuppressive tumor microenvironment (TME) represents a major barrier for effective immunotherapy. Tumor-associated macrophages (TAMs) are highly heterogeneous and plastic cell components of the TME which can either promote tumor progression (M2-like) or boost antitumor immunity (M1-like). Here, we demonstrate that a subset of TAMs that express folate receptor β (FRβ) possess an immunosuppressive M2-like profile. In syngeneic tumor mouse models, chimeric antigen receptor (CAR)-T cell-mediated selective elimination of FRβ⁺ TAMs in the TME results in an enrichment of pro-inflammatory monocytes, an influx of endogenous tumor-specific CD8⁺ T cells, delayed tumor progression, and prolonged survival. Preconditioning of the TME with FRβ-specific CAR-T cells also improves the effectiveness of tumor-directed anti-mesothelin CAR-T cells, while simultaneous co-administration of both CAR products does not. These results highlight the pro-tumor role of FRβ⁺ TAMs in the TME and the therapeutic implications of TAM-depleting agents as preparative adjuncts to conventional immunotherapies that directly target tumor antigens.

Perspectives of Methotrexate-Based Radioagents for Application in Nuclear Medicine

Methotrexate is a gold standard among disease modifying antirheumatic drugs and is also extensively used clinically in combination with oncological therapies. Thus, it is not surprising that nuclear medicine found an interest in methotrexate in the search for diagnostic and therapeutic solutions. Numerous folate-related radiopharmaceuticals have been proposed for nuclear medicine purposes; however, methotrexate radioagents represent only a minority. This imbalance results from the fact that methotrexate has significantly weaker affinity for folate receptors than folic acid. Nevertheless, radiolabeled methotrexate agents utilized as a tool for early detection and imaging of inflammation in rheumatoid arthritis patients gave promising results. Similarly, the use of multimodal MTX-release nanosystems may find potential applications in radiosynovectomy and theranostic approaches in folate receptor positive cancers.

Biomedical and Pharmacological Uses of Fluorescein Isothiocyanate Chitosan-Based Nanocarriers

Chitosan-based nanocarriers (ChNCs) are considered suitable drug carriers due to their ability to encapsulate a variety of drugs and cross biological barriers to deliver the cargo to their target site. Fluorescein isothiocyanate-labeled chitosan-based NCs (FITC@ChNCs) are used extensively in biomedical and pharmacological applications. The main advantage of using FITC@ChNCs consists of the ability to track their fate both intra and extracellularly. This journey is strictly dependent on the physico-chemical properties of the carrier and the cell types under investigation. Other applications make use of fluorescent ChNCs in cell labeling for the detection of disorders in vivo and controlling of living cells in situ. This review describes the use of FITC@ChNCs in the various applications with a focus on understanding their usefulness in labeled drug-delivery systems.

Trigger-responsive engineered-nanocarriers and image-guided theranostics for rheumatoid arthritis

Rheumatoid Arthritis (RA), one of the leading causes of disability due to progressive autoimmune destruction of synovial joints, affects ∼1% of the global population. Standard therapy helps in reducing inflammation and delaying the progression of RA but is limited by non-responsiveness on long-term use and several side-effects. The conventional nanocarriers (CNCs), to some extent, minimize toxicity associated with free drug administration while improving the therapeutic efficacy. However, the uncontrolled release of the encapsulated drug even at off-targeted organs limits the application of CNCs. To overcome these challenges, trigger-responsive engineered nanocarriers (ENCs) have been recently explored for RA treatment. Unlike CNCs, ENCs enable precise control over on-demand drug release due to endogenous triggers in arthritic paws like pH, enzyme level, oxidative stress, or exogenously applied triggers like near-infrared light, magnetic field, ultrasonic waves, etc. As the trigger is selectively applied to the inflamed joint, it potentially reduces toxicity at off-target locations. Moreover, ENCs have been strategically coupled with imaging probe(s) for simultaneous monitoring of ENCs inside the body and facilitate an 'image-guided-co-trigger' for site-specific action in arthritic paws. In this review, the progress made in recently emerging 'trigger-responsive' and 'image-guided theranostics' ENCs for RA treatment has been explored with emphasis on the design strategies, mechanism, current status, challenges, and translational perspectives.

Folate Receptor β (FRβ) Expression in Tissue-Resident and Tumor-Associated Macrophages Associates with and Depends on the Expression of PU.1

As macrophages exhibit a huge functional plasticity under homeostasis and pathological conditions, they have become a therapeutic target for chronic inflammatory diseases. Hence, the identification of macrophage subset-specific markers is a requisite for the development of macrophage-directed therapeutic interventions. In this regard, the macrophage-specific Folate Receptor β (FRβ, encoded by the FOLR2 gene) has been already validated as a target for molecular delivery in cancer as well as in macrophage-targeting therapeutic strategies for chronic inflammatory pathologies. We now show that the transcriptome of human macrophages from healthy and inflamed tissues (tumor; rheumatoid arthritis, RA) share a significant over-representation of the “anti-inflammatory gene set”, which defines the gene profile of M-CSF-dependent IL-10-producing human macrophages (M-MØ). More specifically, FOLR2 expression has been found to strongly correlate with the expression of M-MØ-specific genes in tissue-resident macrophages, tumor-associated macrophages (TAM) and macrophages from inflamed synovium, and also correlates with the presence of the PU.1 transcription factor. In fact, PU.1-binding elements are found upstream of the first exon of FOLR2 and most M-MØ-specific- and TAM-specific genes. The functional relevance of PU.1 binding was demonstrated through analysis of the proximal regulatory region of the FOLR2 gene, whose activity was dependent on a cluster of PU.1-binding sequences. Further, siRNA-mediated knockdown established the importance of PU.1 for FOLR2 gene expression in myeloid cells. Therefore, we provide evidence that FRβ marks tissue-resident macrophages as well as macrophages within inflamed tissues, and its expression is dependent on PU.1.

Design, synthesis and biological evaluation of novel pyrrolo[2,3-d]pyrimidine as tumor-targeting agents with selectivity for tumor uptake by high affinity folate receptors over the reduced folate carrier

Tumor-targeted 6-substituted pyrrolo[2,3-d]pyrimidine benzoyl compounds based on 2 were isosterically modified at the 4-carbon bridge by replacing the vicinal (C11) carbon by heteroatoms N (4), O (5) or S (6), or with an N-substituted formyl (7), trifluoroacetyl (8) or acetyl (9). Replacement with sulfur (6) afforded the most potent KB tumor cell inhibitor, ~6-fold better than the parent 2. In addition, 6 retained tumor transport selectivity via folate receptor (FR) α and -β over the ubiquitous reduced folate carrier (RFC). FRα-mediated cell inhibition for 6 was generally equivalent to 2, while the FRβ-mediated activity was improved by 16-fold over 2. N (4) and O (5) substitutions afforded similar tumor cell inhibitions as 2, with selectivity for FRα and -β over RFC. The N-substituted analogs 7-9 also preserved transport selectivity for FRα and -β over RFC. For FRα-expressing CHO cells, potencies were in the order of 8 > 7 > 9. Whereas 8 and 9 showed similar results with FRβ-expressing CHO cells, 7 was ~16-fold more active than 2. By nucleoside rescue experiments, all the compounds inhibited de novo purine biosynthesis, likely at the step catalyzed by glycinamide ribonucleotide formyltransferase. Thus, heteroatom replacements of the CH₂ in the bridge of 2 afford analogs with increased tumor cell inhibition that could provide advantages over 2, as well as tumor transport selectivity over clinically used antifolates including methotrexate and pemetrexed.

Tissue-Specific Delivery of Oligonucleotides

From the initial discovery of short-interfering RNA (siRNA) and antisense oligonucleotides for specific gene knockdown at the posttranscriptional level to the current CRISPR-Cas9 system offering gene editing at the genomic level, oligonucleotides, in addition to their biological functions in storing and conveying genetic information, provide the most prominent solutions to targeted gene therapies. Nonetheless, looking into the future of curing cancer and acute diseases, researchers are only cautiously optimistic as the cellular delivery of these polyanionic biomacromolecules is still the biggest hurdle for their therapeutic realization. To overcome the delivery obstacle, oligonucleotides have been encapsulated within or conjugated with delivery vehicles for enhanced membrane penetration, improved payload, and tissue-specific delivery. Such delivery systems include but not limited to virus-based vehicles, gold-nanoparticle vehicles, formulated liposomes, and synthetic polymers. In this chapter, delivery challenges imposed by biological barriers are briefly discussed; followed by recent advances in tissue-specific oligonucleotide delivery utilizing both viral and nonviral delivery vectors, discussing their advantages, and how judicious design and formulation could improve and expand their potential as delivery vehicles.

Investigating the Potential of Conjugated Selenium Redox Folic Acid as a Treatment for Triple Negative Breast Cancer

Previous studies have demonstrated that redox selenium compounds arrest cancer cell viability in vitro through their pro-oxidative activity by generating superoxide (O₂^•−). Currently, there are no efficacious treatment options for women with Triple Negative Breast Cancer (TNBC). However, the association between the over-expression of the Folate Receptor Alpha (FRA) in TNBC and other cancer cells, has led to the possibility that TNBCs might be treated by targeting the FRA with redox selenium covalent Folic Acid conjugates. The present study reports the synthesis of the redox active vitamer, Selenofolate, generating superoxide. Superoxide (O₂^•−) catalytic generation by Selenofolate was assessed by an in vitro chemiluminescence (CL) assay and by a Dihydroethidium (DHE) in vivo assay. Cytotoxicity of Selenofolate was assessed against the TNBC cell line MDA-MB-468 and an immortalized, mammary epithelial cell line, HME50-5E. Cytotoxicity of Selenofolate was compared to Folic Acid and sodium selenite, in a time and dose dependent manner. Selenofolate and selenite treatments resulted in greater inhibition of MDA-MB-468 cell proliferation than HME50-5E as evaluated by Trypan Blue exclusion, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) metabolic assay and Annexin V apoptosis assays. Folate receptor alpha (FRA) protein expression was assessed by Western blotting, with the experimental results showing that redox active Selenofolate and selenite, but not Folic Acid, was cytotoxic to MDA-MB-468 cells in vitro, suggesting a possible clinical option for treating TNBC and other cancers over-expressing FRA.

First in man study of [18F]fluoro-PEG-folate PET: a novel macrophage imaging technique to visualize rheumatoid arthritis

Non-invasive imaging of arthritis activity in rheumatoid arthritis (RA) patients using macrophage PET holds promise for early diagnosis and therapeutic response monitoring. Previously obtained results with macrophage tracer (R)-[¹¹C]PK11195 were encouraging, but the imaging signal could be further improved by reduction of background uptake. Recently, the novel macrophage tracer [¹⁸F]fluoro-PEG-folate was developed. This tracer showed excellent targeting of the folate receptor β on activated macrophages in synovial tissue in a preclinical arthritic rat model. We performed three substudies to investigate the biodistribution, potential for imaging arthritis and kinetic properties of [18F]fluoro-PEG-folate in RA patients. Firstly, biodistribution demonstrated fast clearance of [¹⁸F]fluoro-PEG-folate from heart and blood vessels and no dose limiting uptake in organs. Secondly, [¹⁸F]fluoro-PEG-folate showed uptake in arthritic joints with significantly lower background and hence significantly higher target-to-background ratios as compared to reference macrophage tracer (R)-[¹¹C]PK11195. Lastly, dynamic scanning demonstrated fast tracer uptake in affected joints, reaching a plateau after 1 minute, co-existing with a rapid blood clearance. In conclusion, this first in man study demonstrates the potential of [¹⁸F]fluoro-PEG-folate to image arthritis activity in RA with favourable imaging characteristics of rapid clearance and low background uptake, that allow for detection of inflammatory activity in the whole body.

Receptor targeting drug delivery strategies and prospects in the treatment of rheumatoid arthritis

Rheumatoid arthritis (RA), a chronic inflammatory disease, is characterized by cartilage damage, bone tissue destruction, morphological changes in synovial fluids, and synovial joint inflammation. The inflamed synovial tissue has potential for passive and active targeting because of enhanced permeability and retention effect and the existence of RA synovial macrophages and fibroblasts that selectively express surface receptors such as folate receptor β, CD44 and integrin αVβ. Although there are numerous interventions in RA treatment, they are not safe and effective. Therefore, it is important to develop new drug or drug delivery systems that specifically targets inflamed/swollen joints but attenuates other possible damages to healthy tissues. Recently some receptors such as toll-like receptors (TLRs), the nucleotide-binding oligomerization domain-like receptors, and Fc-γ receptor have been identified in synovial tissue and immune cells that are involved in induction or suppression of arthritis. Analysis of the TLR pathway has moreover suggested new insights into the pathogenesis of RA. In the present paper, we have reviewed drug delivery strategies based on receptor targeting with novel ligand-anchored carriers exploiting CD44, folate and integrin αVβ as well as TLRs expressed on synovial monocytes and macrophages and antigen presenting cells, for possible active targeting in RA. TLRs could not only open a new horizon for developing new drugs but also their antagonists or humanized monoclonal antibodies that block TLRS specially TLR4 and TLR9 signaling could be used as targeting agents to antigen presenting cells and dendritic cells. As a conclusion, common conventional receptors and multifunctional ligands that arte involved in targeting receptors or developing nanocarriers with appropriate ligands for TLRs can provide profoundly targeting drug delivery systems for the effective treatment of RA.

Nanomedicine - advantages for their use in rheumatoid arthritis theranostics

Rheumatoid arthritis (RA) is an autoimmune disease accompanies with synovial inflammation and progressive bone destruction. Currently, anti-rheumatic drugs need high dose and frequent use for a long-term, which lead to serious side effect and low patient compliance. To overcome above problems and improve clinical efficacy, nano-technology with targeting ability, sustained release and so forth, has been proposed on RA treatment and already achieved success in RA animal models. In this review, authors summarize and illustrate representative nanomedicine targeting to RA states, which is achieved either through passive or active targeting with high affinity to the receptors that are over-expressed in macrophages or angiogenesis. In particular, authors highlight the new strategies to promote the efficacy of nanoscale treatments through phototherapy and the addition of contrast elements for theranostic application. The described advances may pave the way to better understanding and designing the novel nanomedicine and multifunctional nano-system on efficient RA treatment.

KA, Su Z, Guissi NEI, Xiao Y, Zong L, Ping Q. Folate Receptor-Targeting and Reactive Oxygen Species-Responsive Liposomal Formulation of Methotrexate for Treatment of Rheumatoid Arthritis

Multifunctional nanomedicines with active targeting and stimuli-responsive drug release function utilizing pathophysiological features of the disease are regarded as an effective strategy for treatment of rheumatoid arthritis (RA). Under the inflammatory environment of RA, activated macrophages revealed increased expression of folate receptor and elevated intracellular reactive oxygen species (ROS) level. In this study, we successfully conjugated folate to polyethylene glycol 100 monostearate as film-forming material and further prepared methotrexate (MTX) and catalase (CAT) co-encapsulated liposomes, herein, shortened to FOL-MTX&CAT-L, that could actively target to activated macrophages. Thereafter, elevated intracellular hydrogen peroxide, the main source of ROS, diffused into liposomes and encapsulated CAT catalyzed the decomposition of hydrogen peroxide into oxygen and water. Continuous oxygen-generation inside liposomes would eventually disorganize its structure and release the encapsulated MTX. We characterized the in vitro drug release, cellular uptake and cytotoxicity studies as well as in vivo pharmacokinetics, biodistribution, therapeutic efficacy and safety studies of FOL-MTX&CAT-L. In vitro results revealed that FOL-MTX&CAT-L possessed sufficient ROS-sensitive drug release, displayed an improved cellular uptake through folate-mediated endocytosis and exhibited a higher cytotoxic effect on activated RAW264.7 cells. Moreover, in vivo results showed prolonged blood circulation time of PEGylated liposomes, enhanced accumulation of MTX in inflamed joints of collagen-induced arthritis (CIA) mice, reinforced therapeutic efficacy and minimal toxicity toward major organs. These results imply that FOL-MTX&CAT-L may be used as an effective nanomedicine system for RA treatment.

Optical Molecular Imaging of Inflammatory Cells in Interventional Medicine-An Emerging Strategy

The optical molecular imaging of inflammation is an emerging strategy for interventional medicine and diagnostics. The host's inflammatory response and adaptation to acute and chronic diseases provides unique signatures that have the potential to guide interventions. Thus, there are emerging a suite of molecular imaging and sensing approaches for a variety of targets in this area. This review will focus on two key cellular orchestrators that dominate this area, neutrophils and macrophages, with recent developments in molecular probes and approaches discussed.

Formulation Strategies for Folate-Targeted Liposomes and Their Biomedical Applications

The folate receptor (FR) is a tumor-associated antigen that can bind with folic acid (FA) and its conjugates with high affinity and ingests the bound molecules inside the cell via the endocytic mechanism. A wide variety of payloads can be delivered to FR-overexpressed cells using folate as the ligand, ranging from small drug molecules to large DNA-containing macromolecules. A broad range of folate attached liposomes have been proven to be highly effective as the targeted delivery system. For the rational design of folate-targeted liposomes, an intense conceptual understanding combining chemical and biomedical points of view is necessary because of the interdisciplinary nature of the field. The fabrication of the folate-conjugated liposomes basically involves the attachment of FA with phospholipids, cholesterol or peptides before liposomal formulation. The present review aims to provide detailed information about the design and fabrication of folate-conjugated liposomes using FA attached uncleavable/cleavable phospholipids, cholesterol or peptides. Advances in the area of folate-targeted liposomes and their biomedical applications have also been discussed.

Hybrid micelles containing methotrexate-conjugated polymer and co-loaded with microRNA-124 for rheumatoid arthritis therapy

Purpose: Methotrexate (MTX) is a first-line drug for rheumatoid arthritis (RA)therapy. However, MTX monotherapy often results in irreversible joint damage due to its slow onset of action and long duration. microRNA-124 (miR-124) has shown direct bone protection activity against RA. A co-delivery system for MTX and microRNA combination may provide therapeutic synergy. Methods: Methotrexate-conjugated polymer hybrid micelles (M-PHMs) were prepared by self-assembly of two functional amphiphilic polymers (MTX-PEI-LA and mPEG-LA) at an optimized weight ratio. Incorporation of microRNA was achieved through electrostatic interactions between microRNA and cationic polymer MTX-PEI-LA. Cellular uptake, endosome escape, biodistribution, and therapeutic efficacy of M-PHMs/miR-124 complexes were investigated and evaluated in RAW264.7 cells and a rat adjuvant-induced arthritis (AIA) model. Results: M-PHMs/miR-124 complexes exhibited folate receptor-mediated uptake in activated RAW264.7 cells. miR-124 was able to escape from the endosome and down-regulate nuclear factor of activated T cells cytoplasmic1 (NFATc1). M-PHMs/miR-124 complexes accumulated in inflamed joints of AIA rats and showed superior therapeutic efficacy through both anti-inflammatory effect and direct bone protective effect. Combination of miR-124 and MTX in these micelles induced disease remission. Conclusions: M-PHMs/miR-124 was highly effective against RA through therapeutic synergy. Additional studies are warranted to further investigate its therapeutic potential and delineate its mechanisms of action.

Depletion of activated macrophages with a folate receptor-beta-specific antibody improves symptoms in mouse models of rheumatoid arthritis

Objectives

Most therapies for autoimmune and inflammatory diseases either neutralize or suppress production of inflammatory cytokines produced by activated macrophages (e.g., TNFα, IL-1, IL-6, IL-17, GM-CSF). However, no approved therapies directly target this activated subset of macrophages.

Methods

First, we undertook to examine whether the folate receptor beta (FR-β) positive subpopulation of macrophages, which marks the inflammatory subset in animal models of rheumatoid arthritis, might constitute the prominent population of macrophages in inflamed lesions in humans. Next, we utilized anti-FR-β monoclonal antibodies capable of mediating antibody-dependent cell cytotoxicity (ADCC) to treat animal models of rheumatoid arthritis and peritonitis.

Results

Human tissue samples of rheumatoid arthritis, Crohn’s disease, ulcerative colitis, idiopathic pulmonary fibrosis, nonspecific interstitial pneumonia, chronic obstructive pulmonary disease, systemic lupus erythematosus, psoriasis, and scleroderma are all characterized by dramatic accumulation of macrophages that express FR-β, a protein not expressed on resting macrophages or any other healthy tissues. A monoclonal antibody to FR-β accumulates specifically in inflamed lesions of murine inflammatory disease models and successfully treats such models of rheumatoid arthritis and peritonitis. More importantly, elimination of FR-β-positive macrophages upon treatment with an anti-FR-β monoclonal antibody promotes the departure of other immune cells, including T cells, B cells, neutrophils, and dendritic cells from the inflamed lesions.

Conclusions

These data suggest that specific elimination of FR-β-expressing macrophages may constitute a highly specific therapy for multiple autoimmune and inflammatory diseases and that a recently developed human anti-human FR-β monoclonal antibody (m909) might contribute to suppression of this subpopulation of macrophages.

Electronic supplementary material

The online version of this article (10.1186/s13075-019-1912-0) contains supplementary material, which is available to authorized users.

Folic acid deficiency and vision: a review

Folic acid (FA), also termed folate, is an essential vitamin for health at all ages since it participates in the biosynthesis of nucleotides, amino acids, neurotransmitters, and certain vitamins. It is therefore crucial for rapidly growing tissues such as those of the fetus. It is becoming clear that FA deficiency and impaired folate pathways are implicated in many diseases of both early life and old age. FA can be transported into the cell by the folate receptor, the reduced folate transporter, and proton-coupled folate transporter. Folate transport proteins are present in certain eye tissues, which explains why FA plays an important role in eye development. The purpose of this literature review is to investigate the evidence relating FA deficiency to eye diseases.

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.

Tissue Engineering Therapies Based on Folic Acid and Other Vitamin B Derivatives. Functional Mechanisms and Current Applications in Regenerative Medicine

B-vitamins are a group of soluble vitamins which are cofactors of some of the enzymes involved in the metabolic pathways of carbohydrates, fats and proteins. These compounds participate in a number of functions as cardiovascular, brain or nervous systems. Folic acid is described as an accessible and multifunctional niche component that can be used safely, even combined with other compounds, which gives it high versatility. Also, due to its non-toxicity and great stability, folic acid has attracted much attention from researchers in the biomedical and bioengineering area, with an increasing number of works directed at using folic acid and its derivatives in tissue engineering therapies as well as regenerative medicine. Thus, this review provides an updated discussion about the most relevant advances achieved during the last five years, where folic acid and other vitamins B have been used as key bioactive compounds for enhancing the effectiveness of biomaterials' performance and biological functions for the regeneration of tissues and organs.

Hyaluronic Acid-Based Optical Probe for the Diagnosis of Human Osteoarthritic Cartilage

Osteoarthritis is typically caused by cartilage injury, followed by localized inflammatory responses and tissue deterioration. Early treatment of osteoarthritis is often impossible due to the lack of diagnostic options. Recent studies have supported that different imaging probes can be used for arthritis detection in mice. However, none of these diagnostic tools have been tested on human articular cartilage. To fill this gap, an optical imaging probe was developed to target activated macrophages and the accumulation of imaging probes on tissue was used to assess the severity of human osteoarthritis. Methods: The probe was fabricated using hyaluronic acid (HA) particles conjugated with near-infrared dye and folic acid (FA). The ability of the FA-HA probes to detect activated macrophages and quantify cartilage injury was evaluated using a cell culture model in vitro and human osteoarthritic cartilage explants ex vivo. Results: Our cell study results supported that the FA-HA probes are cell compatible (up to 0.5mg/mL) and can detect activated macrophages in 30 minutes. Using human articular cartilage, we verified the existence of activated macrophages on osteoarthritic cartilage with highly up-regulated expression of folate receptors (~13 folds by comparison with healthy control). In addition, we found that FA-HA probes had higher binding amounts (~3 folds) to osteoarthritic tissue than healthy ones. Histological analyses confirmed that there was a strong linear relationship (R=0.933) between the fluorescent intensity of tissue-associated probe and the extent of folate receptors on osteoarthritic cartilage. Finally, the co-localization of the imaging probe, folate receptors and cartilage degeneration on the tissue sections indicated the extraordinary accuracy and efficiency of this osteoarthritis diagnostic probe. Conclusions: Our results support the probe as an effective diagnostic tool to detect the area and severity of osteoarthritic human articular cartilage.

Imaging of Folate Receptor Expressing Macrophages in the Rat Groove Model of Osteoarthritis: Using a New DOTA-Folate Conjugate

Objective To evaluate the presence and localization of folate receptor expressing macrophages in the rat groove model of osteoarthritis and determine the suitability of a new folate conjugate with albumin-binding entity (cm09) for in vivo SPECT (single-photon emission computed tomography) analysis. Design In male Wistar rats, local cartilage damage was induced in addition to a standard ( n = 10) or high-fat diet ( n = 6). After 12 weeks, ¹¹¹In labeled folate conjugates were administered, and SPECT/CT (computed tomography) imaging was performed after 24 hours. Subsequently, osteoarthritis severity and folate receptor expression were assessed using (immuno)-histological sections. Results In vivo SPECT/CT imaging of the new folate conjugate (cm09) was as useful as a folate conjugate without albumin-binding entity in the groove model of osteoarthritis with less renal accumulation. Induction of cartilage damage on a standard diet resulted in no effect on the amount of folate receptor expressing macrophages compared with the contralateral sham operated joints. In contrast, inducing cartilage damage in the high-fat diet group resulted in 28.4% increase of folate receptor expression as compared with the nondamaged control joints. Folate receptor expressing cells were predominantly present in the synovial lining and in subchondral bone as confirmed by immunohistochemistry. Conclusions Folate receptor expression, and thus macrophage activation, can clearly be demonstrated in vivo, in small animal models of osteoarthritis using the new ¹¹¹In-folate conjugate with specific binding to the folate receptor. Increased macrophage activity only plays a role in the groove model of osteoarthritis when applied in a high-fat diet induced dysmetabolic condition, which is in line with the higher inflammatory state of that specific model.

Imaging and Methotrexate Response Monitoring of Systemic Inflammation in Arthritic Rats Employing the Macrophage PET Tracer [18F]Fluoro-PEG-Folate

Background

In rheumatoid arthritis, articular inflammation is a hallmark of disease, while the involvement of extra-articular tissues is less well defined. Here, we examined the feasibility of PET imaging with the macrophage tracer [¹⁸F]fluoro-PEG-folate, targeting folate receptor β (FRβ), to monitor systemic inflammatory disease in liver and spleen of arthritic rats before and after methotrexate (MTX) treatment.

Methods

[¹⁸F]Fluoro-PEG-folate PET scans (60 min) were acquired in saline- and MTX-treated (1 mg/kg, 4x) arthritic rats, followed by tissue resection and radiotracer distribution analysis. Liver and spleen tissues were stained for ED1/ED2-macrophage markers and FRβ expression.

Results

[¹⁸F]Fluoro-PEG-folate PET and ex vivo tissue distribution studies revealed a significant (p < 0.01) 2-fold lower tracer uptake in both liver and spleen of MTX-treated arthritic rats. Consistently, ED1- and ED2-positive macrophages were significantly (p < 0.01) decreased in liver (4-fold) and spleen (3-fold) of MTX-treated compared with saline-treated rats. Additionally, FRβ-positive macrophages were also significantly reduced in liver (5-fold, p < 0.005) and spleen (3-fold, p < 0.01) of MTX- versus saline-treated rats.

Conclusions

MTX treatment reduced activated macrophages in liver and spleen, as markers for systemic inflammation in these organs. Macrophage PET imaging with [¹⁸F]fluoro-PEG-folate holds promise for detection of systemic inflammation in RA as well as therapy (MTX) response monitoring.

Recent progress in dendrimer-based nanomedicine development

Dendrimers offer well-defined nanoarchitectures with spherical shape, high degree of molecular uniformity, and multiple surface functionalities. Such unique structural properties of dendrimers have created many applications for drug and gene delivery, nanomedicine, diagnostics, and biomedical engineering. Dendrimers are not only capable of delivering drugs or diagnostic agents to desired sites by encapsulating or conjugating them to the periphery, but also have therapeutic efficacy in their own. When compared to traditional polymers for drug delivery, dendrimers have distinct advantages, such as high drug-loading capacity at the surface terminal for conjugation or interior space for encapsulation, size control with well-defined numbers of peripheries, and multivalency for conjugation to drugs, targeting moieties, molecular sensors, and biopolymers. This review focuses on recent applications of dendrimers for the development of dendrimer-based nanomedicines for cancer, inflammation, and viral infection. Although dendrimer-based nanomedicines still face some challenges including scale-up production and well-characterization, several dendrimer-based drug candidates are expected to enter clinical development phase in the near future.

Modulating the immune system through nanotechnology

Nowadays, nanotechnology-based modulation of the immune system is presented as a cutting-edge strategy, which may lead to significant improvements in the treatment of severe diseases. In particular, efforts have been focused on the development of nanotechnology-based vaccines, which could be used for immunization or generation of tolerance. In this review, we highlight how different immune responses can be elicited by tuning nanosystems properties. In addition, we discuss specific formulation approaches designed for the development of anti-infectious and anti-autoimmune vaccines, as well as those intended to prevent the formation of antibodies against biologicals.

Targeted delivery of nucleic acids into xenograft tumors mediated by novel folate-equipped liposomes

Folate receptors (FR) are cellular markers highly expressed in various cancer cells. Here, we report on the synthesis of a novel folate-containing lipoconjugate (FC) built of 1,2-di-O-ditetradecyl-rac-glycerol and folic acid connected via a PEG spacer, and the evaluation of the FC as a targeting component of liposomal formulations for nucleic acid (NA) delivery into FR expressing tumor cells. FR-targeting liposomes, based on polycationic lipid 1,26-bis(cholest-5-en-3β-yloxycarbonylamino)-7,11,16,20-tetraazahexacosan tetrahydrochloride (2X3), lipid helper dioleoylphosphatidylethanolamine (DOPE) and novel FC, formed small compact particles in solution with diameters of 60 ± 22 nm, and were not toxic to cells. Complexes of NAs with the liposomes were prepared at various nitrogen to phosphate ratios (N/P) to optimize liposome/cell interactions. We showed that FR-mediated delivery of different nucleic acids mediated by 2X3-DOPE/FC liposomes occurs in vitro at low N/P (1/1 and 2/1); under these conditions FC-containing liposomes display 3-4-fold higher transfection efficiency in comparison with conventional formulation. Lipoplexes formed at N/P 1/1 by targeted liposomes and cargo (Cy7-labeled siRNA targeting MDR1 mRNA) in vivo efficiently accumulate in tumor (∼15-18% of total amount), and kidneys (71%), and were retained there for more than 24 h, causing efficient downregulation of p-glycoprotein expression (to 40% of control) in tumors. Thus, FC containing liposomes provide effective targeted delivery of nucleic acids into tumor cells in vitro and in xenograft tumors in vivo.

Folate-conjugated liposomes target and deliver therapeutics to immune cells in a rat model of rheumatoid arthritis

AIM

We endeavored to create a folate-targeted liposome (Fol-liposome) that could selectively target areas of inflammation.

MATERIALS & METHODS

Fol-liposomes were prepared with encapsulated DiD fluorophore or betamethasone (BM) to image and treat an adjuvant-induced rat model of rheumatoid arthritis.

RESULTS

Fol-liposomes selectively accumulated in arthritic rat paws to a greater extent than nontargeted liposomes. When these Fol-liposomes were used to encapsulate BM and administered to arthritic rats, animals exhibited less paw swelling, lower arthritis scores, a reduction in bone erosion, less splenomegaly and better maintenance of body weight when compared with nontreated or nontargeted BM-containing liposome groups.

CONCLUSION

Fol-liposomes can selectively deliver imaging and therapeutic agents to sites of inflammation in a rat model of rheumatoid arthritis.

In-vivo monitoring of anti-folate therapy in arthritic rats using [18F]fluoro-PEG-folate and positron emission tomography

Background

Folate receptor β (FRβ) is involved in facilitating cellular uptake of folates and anti-folates (such as methotrexate (MTX)). In rheumatoid arthritis, FRβ is expressed on synovial macrophages and recently has been explored as a biomarker for imaging in arthritic rats using the folate-based positron emission tomography (PET) tracer [¹⁸F]fluoro-PEG-folate. The purpose of this study was to examine whether this folate tracer can also be used to monitor therapeutic efficacy of MTX in arthritic rats.

Methods

Arthritic rats received either no treatment or MTX therapy (1 mg/kg, either 2× or 4×). Healthy rats did not receive any arthritic induction or therapy. [¹⁸F]fluoro-PEG-folate PET-CT scans (60 min) were performed before and after MTX therapy. Following PET, the ex-vivo tissue distribution of radioactivity was determined in excised knees and multiple tissues. Synovial macrophage infiltration in knee sections was quantified by immunohistochemistry using ED1 and ED2 antibodies.

Results

PET scans clearly visualized increased uptake of [¹⁸F]fluoro-PEG-folate in arthritic knees compared with contralateral knees. Significantly lower standard uptake values (1.5-fold, p < 0.01) were observed in arthritic knees of both MTX-treated groups after therapy, approximating the levels seen in healthy rats. Consistently, ex-vivo tissue distribution demonstrated a 2–4-fold lower tracer uptake in the arthritic knee of 2× and 4× MTX-treated rats, respectively, compared with control rats. These results were corroborated with significantly reduced (2–4-fold, p < 0.01) ED1-positive and ED2-positive synovial macrophages in arthritic knees of the MTX-treated rats compared with those of the control rats.

Conclusion

This study in arthritic rats underscores the potential and usefulness of [¹⁸F]fluoro-PEG-folate PET as a therapeutic monitoring tool of MTX therapy and potentially other anti-folate treatment of arthritis.

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.

Optimization of Folate-Targeted Immunotherapy for the Treatment of Experimental Arthritis

Folate-targeted immunotherapy constitutes a powerful method for the treatment of established arthritis in multiple animal models of the disease. The therapy involves immunization of the animal against a hapten to induce anti-hapten antibodies, followed by injection with a folate-hapten conjugate to decorate the surface of folate receptor-positive (activated) macrophages with the antigenic hapten. The hapten-marked macrophages are then recognized by the anti-hapten antibodies and eliminated by immune mechanisms, leading to attenuation of disease symptoms. In the following paper, we optimize the therapy for elimination of inflammatory macrophages and suppression of rheumatoid arthritis symptoms. We also demonstrate a tight correlation between folate receptor-positive macrophage abundance in the liver and inflammation of affected joints. The results suggest that therapies that reduce folate receptor-positive macrophage populations in the body should constitute effective treatments for rheumatoid arthritis.