Treatment of experimental adjuvant arthritis with a novel folate receptor-targeted folic acid-aminopterin conjugate

Tumor-specific activation of folate receptor beta enables reprogramming of immune cells in the tumor microenvironment

Folate receptors can perform folate transport, cell adhesion, and/or transcription factor functions. The beta isoform of the folate receptor (FRβ) has attracted considerable attention as a biomarker for immunosuppressive macrophages and myeloid-derived suppressor cells, however, its role in immunosuppression remains uncharacterized. We demonstrate here that FRβ cannot bind folate on healthy tissue macrophages, but does bind folate after macrophage incubation in anti-inflammatory cytokines or cancer cell-conditioned media. We further show that FRβ becomes functionally active following macrophage infiltration into solid tumors, and we exploit this tumor-induced activation to target a toll-like receptor 7 agonist specifically to immunosuppressive myeloid cells in solid tumors without altering myeloid cells in healthy tissues. We then use single-cell RNA-seq to characterize the changes in gene expression induced by the targeted repolarization of tumor-associated macrophages and finally show that their repolarization not only changes their own phenotype, but also induces a proinflammatory shift in all other immune cells of the same tumor mass, leading to potent suppression of tumor growth. Because this selective reprogramming of tumor myeloid cells is accompanied by no systemic toxicity, we propose that it should constitute a safe method to reprogram the tumor microenvironment.

Targeting folate receptor beta on monocytes/macrophages renders rapid inflammation resolution independent of root causes

Provoked by sterile/nonsterile insults, prolonged monocyte mobilization and uncontrolled monocyte/macrophage activation can pose imminent or impending harm to the affected organs. Curiously, folate receptor beta (FRβ), with subnanomolar affinity for the vitamin folic acid (FA), is upregulated during immune activation in hematopoietic cells of the myeloid lineage. This phenomenon has inspired a strong interest in exploring FRβ-directed diagnostics/therapeutics. Previously, we have reported that FA-targeted aminopterin (AMT) therapy can modulate macrophage function and effectively treat animal models of inflammation. Our current investigation of a lead compound (EC2319) leads to discovery of a highly FR-specific mechanism of action independent of the root causes against inflammatory monocytes. We further show that EC2319 suppresses interleukin-6/interleukin-1β release by FRβ⁺ monocytes in a triple co-culture leukemic model of cytokine release syndrome with anti-CD19 chimeric antigen receptor T cells. Because of its chemical stability and metabolically activated linker, EC2319 demonstrates favorable pharmacokinetic characteristics and cross-species translatability to support future pre-clinical and clinical development.

•

Functional folate receptor beta is transiently expressed on inflammatory monocytes

•

EC2319 is an enhancement of traditional dihydrofolate reductase inhibitors

•

EC2319 anti-monocyte activity correlates with local/systemic therapeutic benefit

•

EC2319 inhibition of cytokine release suggests emergency use for hyperinflammation

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.

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.

Theranostic Agents in Musculoskeletal Disorders

Theranostic-based strategies, combining therapeutic and diagnostic properties of a single agent, have gained enormous attention in the past few years. Today, various multifunctional theranostic modalities have been examined, using different bioactive targeting, for the detection, quantifying, and monitoring of therapy response in different pathologies. Herein we review the newly emerging approaches in theranostic nanomedicine for the detection and therapy for musculoskeletal disorders to provide valuable insights for developing more efficient agents for clinical use. Some potential preclinical applications of radionuclide nanotheranostic agents are described in rheumatoid arthritis, osteoarthrosis, multiple myeloma, and neoplastic diseases.

Ultrasound-targeted microbubble destruction augmented synergistic therapy of rheumatoid arthritis via targeted liposomes

Rheumatoid arthritis (RA) can lead to joint destruction and deformity, which is a significant cause of the loss of the young and middle-aged labor force. However, the treatment of RA is still filled with challenges. Though dexamethasone, one of the glucocorticoids, is commonly used in the treatment of RA, its clinical use is limited because of the required high-dose and long-term use, unsatisfactory therapeutic effects, and various side-effects. Ultrasound-targeted microbubble destruction (UTMD) can augment the ultrasonic cavitation effects and trigger drug release from targeted nanocarriers in the synovial cavity, which makes it a more effective synergistic treatment strategy for RA. In this work, we aim to utilize the UTMD effect to augment the synergistic therapy of RA by using polyethylene glycol (PEG)-modified folate (FA)-conjugated liposomes (LPs) loaded with dexamethasone sodium phosphate (DexSP) (DexSP@LPs-PEG-FA). The UTMD-mediated DexSP@LPs-PEG-FA for targeted delivery of DexSP including a synergistic ultrasonic cavitation effect and drug therapy were investigated through in vitro RAW264.7 cell experiments and in vivo collagen-induced arthritis SD rat model animal experiments. The results show the DexSP release from targeted liposomes was improved under the UTMD effect. Likewise, the folate-conjugated liposomes displayed targeting association to RAW264.7 cells. Together with the application of ultrasound and microbubbles, liposomes-delivered DexSP potently reduced joints swelling, bone erosion, and inflammation in both joints and serum with a low dose. These results demonstrated that UTMD-mediated folate-conjugated liposomes are not only a promising method for targeted synergistic treatment of RA but also may show high potential for serving as nanomedicines for many other biomedical fields.

Efficacy and tolerability of folate-aminopterin therapy in a rat focal model of multiple sclerosis

BACKGROUND

Activated macrophages in the experimental model of multiple sclerosis (MS) express folate receptor-β (FR-β), representing a promising target for the treatment of MS. Here, we both evaluated the efficacy of a novel folate-aminopterin construct (EC2319) in a rat focal model of multiple sclerosis (MS) and investigated the utility of ⁶⁸Ga-labeled 1,4,7-triazacyclononane-1,4,7-triacetic acid-conjugated folate (⁶⁸Ga-FOL) for assessing inflammatory lesions. In addition, we investigated whether FR-β is expressed in the brain of patients with MS.

METHODS

Focal delayed-type hypersensitivity experimental autoimmune encephalomyelitis (fDTH-EAE) was induced in 40 Lewis rats; 20 healthy Lewis rats were used as controls. Rats were divided into six groups according to the duration of disease (control, acute, or chronic) and intervention (vehicle versus EC2319). ⁶⁸Ga-FOL analyses, histology, and immunofluorescence of the brain were performed to evaluate the efficacy of subcutaneously administered EC2319 on lesion development. Immunofluorescence was used to assess FR-β expression in postmortem brain samples from 5 patients with MS and 5 healthy controls.

RESULTS

Immunofluorescence and histological analyses revealed significant reductions in FR-β expression (P < 0.05) and lesion size (P < 0.01), as well as improved inducible nitric oxide synthase/mannose receptor C type 1 ratios (P < 0.01) in macrophages and microglia during the chronic but not acute phase of fDTH-EAE in EC2319-treated rats. The uptake of IV-injected ⁶⁸Ga-FOL in the brain was low and did not differ between the groups, but the in vitro binding of ⁶⁸Ga-FOL was significantly lower in EC2319-treated rats (P < 0.01). FR-β positivity was observed in chronically active lesions and in normal-appearing white matter in MS brain samples.

CONCLUSIONS

EC2319 was well tolerated and attenuated inflammation and lesion development in a rat model of a chronic progressive form of MS. Human MS patients have FR-β-positive cells in chronically active plaques, which suggests that these results may have translational relevance.

Detecting Functional and Accessible Folate Receptor Expression in Cancer and Polycystic Kidneys

Folate-based small molecule drug conjugates (SMDCs) are currently under development and have shown promising preclinical and clinical results against various cancers and polycystic kidney disease. Two requisites for response to a folate-based SMDC are (i) folate receptor alpha (FRα) protein is expressed in the diseased tissues, and (ii) FRα in those tissues is accessible and functionally competent to bind systemically administered SMDCs. Here we report on the development of a small molecule reporter conjugate (SMRC), called EC2220, which is composed of a folate ligand for FRα binding, a multilysine containing linker that can cross-link to FRα in the presence of formaldehyde fixation, and a small hapten (fluorescein) used for immunohistochemical detection. Data show that EC2220 produces a far greater IHC signal in FRα-positive tissues over that produced with EC17, a folate-fluorescein SMRC that is released from the formaldehyde-denatured FRα protein. Furthermore, the extent of the EC2220 IHC signal was proportional to the level of FRα expression. This EC2220-based assay was qualified both in vitro and in vivo using normal tissue, cancer tissue, and polycystic kidneys. Overall, EC2220 is a sensitive and effective reagent for evaluating functional and accessible receptor expression in vitro and in vivo.

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.

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.

Folate-dactolisib conjugates for targeting tubular cells in polycystic kidneys

The aim of the present study was to develop folic acid (FA) conjugates which can deliver the kinase inhibitor dactolisib to the kidneys via folate receptor-mediated uptake in tubular epithelial cells. Dactolisib is a dual inhibitor of phosphatidylinositol 3-kinase (PI3K) and mammalian target of rapamycin (mTOR) and is considered an attractive agent for treatment of polycystic kidney disease. The ethylenediamine platinum(II) linker, herein called Lx, was employed to couple dactolisib via coordination chemistry to thiol-containing FA-spacer adducts to yield FA-Lx-dactolisib conjugates. The dye lissamine was coupled via similar linker chemistry to folate to yield fluorescent FA-Lx-lissamine conjugates. Three different spacers (PEG₅-Cys, PEG₂₇-Cys or an Asp-Arg-Asp-Asp-Cys peptide spacer) were used to compare the influence of hydrophilicity and charged groups in the spacer on interaction with target cells and in vivo organ distribution of the final conjugates. The purity and identity of the final products were confirmed by UPLC and LC-MS analysis, respectively. FA-Lx-dactolisib conjugates were stable in serum and culture medium, while dactolisib was released from the conjugates in the presence of glutathione. All three type of conjugates were internalized efficiently by HK-2 cells and uptake could be blocked by an excess of folic acid in the medium, demonstrating FR mediated uptake. FA-Lx-dactolisib conjugates showed nanomolar inhibition of the PI3K pathway (Akt phosphorylation) and mTOR pathway (S6 phosphorylation) in cultured kidney epithelial cells (HK-2 cells). After intraperitoneal administration, all three types conjugates accumulated extensively in kidneys of iKsp-Pkd1^del mice with polycystic kidney disease. In conclusion, folate conjugates were successfully prepared by platinum(II) coordination chemistry and accumulated in a target-specific manner in kidney cells and polycystic kidneys. The folate conjugate of dactolisib thus may have potential for targeted therapy of polycystic kidney disease.

Novel solid-phase strategy for the synthesis of ligand-targeted fluorescent-labelled chelating peptide conjugates as a theranostic tool for cancer

In this article, we have successfully designed and demonstrated a novel continuous process for assembling targeting ligands, peptidic spacers, fluorescent tags and a chelating core for the attachment of cytotoxic molecules, radiotracers, nanomaterials in a standard Fmoc solid-phase peptide synthesis in high yield and purity. The differentially protected Fmoc-Lys-(Tfa)-OH plays a vital role in attaching fluorescent tags while growing the peptide chain in an uninterrupted manner. The methodology is versatile for solid-phase resins that are sensitive to mild and strong acidic conditions when acid-sensitive side chain amino protecting groups such as Trt (chlorotrityl), Mtt (4-methyltrityl), Mmt (4-methoxytrityl) are employed to synthesise the ligand targeted fluorescent tagged bioconjugates. Using this methodology, DUPA rhodamine B conjugate (DUPA = 2-[3-(1,3-dicarboxypropyl)ureido]pentanedioic acid), targeting prostate specific membrane antigen (PSMA) expressed on prostate, breast, bladder and brain cancers and pteroate rhodamine B, targeting folate receptor positive cancers such as ovarian, lung, endometrium as well as inflammatory diseases have been synthesized. In vitro studies using LNCaP (PSMA +ve), PC-3 (PSMA −ve, FR −ve) and CHO-β (FR +ve) cell lines and their respective competition experiments demonstrate the specificity of the newly synthesized bioconstructs for future application in fluorescent guided intra-operative imaging.

In Vivo Evaluation of Ligand Targeted Drug Conjugates for Cancer Therapy

The development of small molecule ligand-targeted therapeutics is currently of paramount importance for treatment of cancer due to their potential to reduce system toxicity and increase potency of a delivered chemotherapeutic drug. The main aim of a targeted drug-delivery technique is to release the drug cargo selectively into tumor tissues, avoiding off-site toxicity to healthy tissues and organs during chemotherapy. In this strategy, a chemotherapeutic drug is conjugated to a homing ligand, which has high affinity for proteins over-expressed on cancer cells, via a peptide linker and a self-immolative segment that facilitates intracellular release of drug cargo. During development of targeted drug conjugates, preclinical evaluation in tumor models of small animals like mice adds valuable data on the clinical performance of the drug. This article contains a set of protocols for implantation of tumor, determination of optimum dosage required for effective treatment, and estimation of maximum tolerated dose required for any visible side effects during treatment of cancer in tumor models of mice. © 2018 by John Wiley & Sons, Inc.

Preparation of Ligand-Targeted Drug Conjugates for Cancer Therapy and Their Evaluation In Vitro

Present treatment strategies focus on minimizing unwanted toxicity to healthy cells during chemotherapeutic treatment. This is achieved by developing strategies to selectively deliver drugs to malignant cells over-expressing specific protein biomarkers. The drugs are attached via a self-immolative linker to a small molecule homing ligand having affinity for protein biomarkers over-expressed during disease states. Several such targeting-ligand drug conjugates have now reached preclinical and clinical trials, and this article aims to show a general methodology to prepare the same. Using solid-phase peptide synthesis (SPPS) methodology, the targeting ligand is covalently linked to a peptide spacer having appropriate hydrophobic and hydrophilic amino acids. The targeting ligand-attached peptide spacer is next conjugated with the required drug molecule through a cleavable disulfide bond in a solution-phase reaction. This protocol further elucidates the step-by-step procedures to be followed for complete evaluation of newly synthesized ligand-targeted drug conjugates in vitro. © 2018 by John Wiley & Sons, Inc.

Diethylaminoethyl- chitosan as an efficient carrier for siRNA delivery: Improving the condensation process and the nanoparticles properties

Chitosan has been indicated as a promising carrier for the preparation of small interfering RNA (siRNA) delivery systems due to its remarkable properties. However, its weak interactions with siRNA molecules makes the condensation of siRNA molecules into nanoparticles difficult. In this work, a non-viral gene delivery system based on diethylaminoethyl chitosan (DEAE-CH) derivatives of varied Mw (25-230 kDa) having a low degree of substitution of 15% was investigated. The presence of secondary and tertiary amino groups strengthened the interaction of siRNA and DEAE-CH derivatives of higher Mw (130 kDa to 230 kDa) and provided the preparation of spherical nanoparticles at low charge ratios (N/P 2 to 3) with low polydispersities (0.15 to 0.2) in physiological ionic strength. Nanoparticles prepared with all derivatives exhibited remarkable silencing efficiencies (80% to 90%) on different cell lines (HeLa, MG-63, OV-3) by adjusting the charge ratios. A selected PEG-folic acid labeled derivative (FA-PEG-DEAE15-CH₂₃₀) was synthesized and its nanoparticles completely inhibited the mRNA expression level of TNF-α in RAW 264.7 macrophages. The study demonstrates that the insertion of DEAE groups provides improved physical properties to chitosan-siRNA nanoparticles and holds potential for in vivo applications.

FolamiRs: Ligand-targeted, vehicle-free delivery of microRNAs for the treatment of cancer

MicroRNAs are small RNAs that negatively regulate gene expression posttranscriptionally. Because changes in microRNA expression can promote or maintain disease states, microRNA-based therapeutics are being evaluated extensively. Unfortunately, the therapeutic potential of microRNA replacement is limited by deficient delivery vehicles. In this work, microRNAs are delivered in the absence of a protective vehicle. The method relies on direct attachment of microRNAs to folate (FolamiR), which mediates delivery of the conjugated microRNA into cells that overexpress the folate receptor. We show that the tumor-suppressive FolamiR, FolamiR-34a, is quickly taken up both by triple-negative breast cancer cells in vitro and in vivo and by tumors in an autochthonous model of lung cancer and slows their progression. This method delivers microRNAs directly to tumors in vivo without the use of toxic vehicles, representing an advance in the development of nontoxic, cancer-targeted therapeutics.

New Mechanism for Release of Endosomal Contents: Osmotic Lysis via Nigericin-Mediated K+/H+ Exchange

Although peptides, antibodies/antibody fragments, siRNAs, antisense DNAs, enzymes, and aptamers are all under development as possible therapeutic agents, the breadth of their applications has been severely compromised by their inability to reach intracellular targets. Thus, while macromolecules can often enter cells by receptor-mediated endocytosis, their missions frequently fail due to an inability to escape their entrapping endosomes. In this paper, we describe a general method for promoting release of any biologic material from any entrapping endosome. The strategy relies on the fact that all nascent endosomes contain extracellular (Na⁺-enriched) medium, but are surrounded by intracellular (K⁺-enriched) fluid in the cytoplasm. Osmotic swelling and rupture of endosomes will therefore be facilitated if the flow of K⁺ down its concentration gradient from the cytosol into the endosome can be facilitated without allowing downhill flow of Na⁺ from the endosome into the cytosol. While any K⁺ selective ionophore can promote the K⁺ specific influx, the ideal K⁺ ionophore will also exchange influxed K⁺ for an osmotically inactive proton (H⁺) in order to prevent buildup of an electrical potential that would rapidly halt K⁺ influx. The only ionophore that catalyzes this exchange of K⁺ for H⁺ efficiently is nigericin. We demonstrate here that ligand-targeted delivery of nigericin into endosomes that contain an otherwise impermeable fluorescent dye can augment release of the dye into the cell cytosol via swelling/bursting of the entrapping endosomes. We further show that nigericin-facilitated escape of a folate-targeted luciferase siRNA conjugate from its entrapping endosomes promotes rapid suppression of the intended luciferase reporter gene. Taken together, we propose that ionophore-catalyzed entry of K⁺ into endosomal compartments can promote the release of otherwise impermeable contents from their encapsulating endosomes.

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.

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.

Enhanced Anti-Inflammatory Efficacy Through Targeting to Macrophages: Synthesis and In Vitro Evaluation of Folate-Glycine-Celecoxib

As an effective COX-2 inhibitor, celecoxib is widely used in anti-inflammation therapy. However, it may cause cardiovascular risks and renal adverse effects. In the present study, we aimed to construct a celecoxib prodrug with enhanced anti-inflammatory efficacy and reduced adverse effects using folate in order to target activated macrophages. Folate-glycine-celecoxib was synthesized and identified by ¹H-NMR, MS, and FTIR analyses. The cytotoxicity of folate-glycine-celecoxib was tested on murine macrophage cells (RAW264.7) using thiazolyl blue tetrazolium bromide. Cellular uptake studies were employed to determine targeting ability toward folate receptors via flow cytometry and confocal microscopy. Anti-inflammatory efficacy of folate-glycine-celecoxib was investigated by measuring the concentration of LPS-induced nitric oxide (NO). Folate-glycine-celecoxib exhibited lower cytotoxicity than conventional celecoxib, and this conjugate could be targetedly transported into RAW264.7 cells through binding with folate receptors on cell surface. Through targeting to RAW264.7 cells, folate-glycine-celecoxib exhibited better effects than equimolar celecoxib in NO inhibition, suggesting greater anti-inflammatory activity. These findings demonstrated that the prodrug folate-glycine-celecoxib had potential to treat inflammatory disease with low cytotoxicity and high targeting ability.

Direct in vivo evidence of activated macrophages in human osteoarthritis

OBJECTIVE

Through binding to folate receptor-β (FR-β), the new (99m)Tc-EC20 (Etarfolatide) imaging technique detects activated but not resting macrophages in vivo. The goal of this study was to investigate macrophage-related inflammation in osteoarthritis (OA).

METHODS

Twenty-five individuals (50 knees) with symptomatic OA of at least one knee underwent SPECT-CT imaging of both knees and planar imaging of the whole body after injection of Etarfolatide. Scans and knee radiographs were scored blinded to clinical information including knee and other joint site pain severity. Measures of association controlled for age, gender, body mass index (BMI) and employed repeated measures to adjust for correlation between knees.

DESIGN

Activated macrophages were present in the majority (76%) of knees. The quantity of knee-related macrophages was significantly associated with knee pain severity (R = 0.60, P < 0.0001) and radiographic knee OA severity including joint space narrowing (R = 0.68, P = 0.007), and osteophyte (R = 0.66, P = 0.001). Macrophages were also localized to joints commonly affected by OA including hand finger joints (12%), thumb bases (28%), shoulders (26%), great toes (18%) and ankles (12%). The presence of joint pain at fingers, wrists, ankles and great toes was significantly positively associated with presence of activated macrophages at these sites (P < 0.0001-0.04).

CONCLUSIONS

This study provides the first direct in vivo evidence for macrophage involvement in OA in a substantial proportion of human knees. The association of quantity of activated macrophages with radiographic knee OA severity and joint symptoms suggests that drugs targeting macrophages and macrophage-associated inflammatory pathways may have the potential to be both symptom and structure modifying.

Etanercept improves endothelial function via pleiotropic effects in rat adjuvant-induced arthritis

OBJECTIVES

To determine the effect of etanercept on endothelial dysfunction and on traditional cardiovascular (CV) risk factors in the adjuvant-induced arthritis (AIA) rat model.

METHODS

At the first signs of arthritis, etanercept (10 mg/kg/3 days, s.c.) or saline was administered for 3 weeks in AIA rats. Body weights and arthritis scores were monitored daily. Endothelial function was studied in aortic rings relaxed with acetylcholine (Ach) with or without inhibitors of nitric oxide synthase (NOS), cyclo-oxygenase (COX-2), arginase, endothelium-derived hyperpolarizing factor and superoxide anions (O2 (-)°) production. Aortic expression of endothelial nitic oxide synthase (eNOS), Ser1177-phospho-eNOS, COX-2, arginase-2, p22(phox) and p47(phox) was evaluated by western blotting analysis. Blood pressure, heart rate and blood levels of triglycerides, cholesterol and glucose were measured.

RESULTS

Etanercept significantly reduced arthritis score (P < 0.001). It improved Ach-induced relaxation (P < 0.05) as a result of increased NOS activity, decreased COX-2/arginase activities and decreased O2 (-)° production. These functional effects relied on increased eNOS expression and phosphorylation, and decreased COX-2, arginase-2 and p22(phox) expressions. No correlation was found between arthritis score and Ach-induced relaxation. The treatment did not change triglycerides, cholesterol and glucose levels, but significantly increased systolic blood pressure and heart rate (P < 0.05).

CONCLUSION

Our data demonstrated that efficient dosage of etanercept on inflammatory symptoms improved endothelial function in AIA. This beneficial effect on endothelial function is disconnected from its impact on CV risk factors and relates to pleiotropic effects of etanercept on endothelial pathways. These results suggest that etanercept could be a good choice for patients with rheumatoid arthritis at high risk of CV events.

Comparison of nanoparticle penetration into solid tumors and sites of inflammation: studies using targeted and nontargeted liposomes

AIM

The vast majority of nanomedicine research is focused on the use of nanoparticles for the diagnosis and treatment of cancer. However, the dense extracellular matrix of solid tumors restricts nanoparticle penetration, raising the question of whether the best applications of nanomedicines lie in oncology.

MATERIALS & METHODS

In this study, the uptake of folate-conjugated liposomes was compared between folate receptor-expressing tumors and folate receptor+ inflammatory lesions within the same mouse.

RESULTS

We demonstrate here that both folate-targeted and nontargeted liposomes accumulate more readily at sites of inflammation than in solid tumors.

CONCLUSION

These data suggest that nanosized imaging and therapeutic agents may be better suited for the treatment and diagnosis of inflammatory/autoimmune diseases than cancer.

Rational Design of Targeted Next-Generation Carriers for Drug and Vaccine Delivery

Pattern recognition receptors on innate immune cells play an important role in guiding how cells interact with the rest of the organism and in determining the direction of the downstream immune response. Recent advances have elucidated the structure and function of these receptors, providing new opportunities for developing targeted drugs and vaccines to treat infections, cancers, and neurological disorders. C-type lectin receptors, Toll-like receptors, and folate receptors have attracted interest for their ability to endocytose their ligands or initiate signaling pathways that influence the immune response. Several novel technologies are being developed to engage these receptors, including recombinant antibodies, adoptive immunotherapy, and chemically modified antigens and drug delivery vehicles. These active targeting technologies will help address current challenges facing drug and vaccine delivery and lead to new tools to treat human diseases.

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.

Gene Expression Profiling in Peripheral Blood Cells and Synovial Membranes of Patients with Psoriatic Arthritis

Background

Psoriatic arthritis (PsA) is an inflammatory arthritis whose pathogenesis is poorly understood; it is characterized by bone erosions and new bone formation. The diagnosis of PsA is mainly clinical and diagnostic biomarkers are not yet available. The aim of this work was to clarify some aspects of the disease pathogenesis and to identify specific gene signatures in paired peripheral blood cells (PBC) and synovial biopsies of patients with PsA. Moreover, we tried to identify biomarkers that can be used in clinical practice.

Methods

PBC and synovial biopsies of 10 patients with PsA were used to study gene expression using Affymetrix arrays. The expression values were validated by Q-PCR, FACS analysis and by the detection of soluble mediators.

Results

Synovial biopsies of patients showed a modulation of approximately 200 genes when compared to the biopsies of healthy donors. Among the differentially expressed genes we observed the upregulation of Th17 related genes and of type I interferon (IFN) inducible genes. FACS analysis confirmed the Th17 polarization. Moreover, the synovial trascriptome shows gene clusters (bone remodeling, angiogenesis and inflammation) involved in the pathogenesis of PsA. Interestingly 90 genes are modulated in both compartments (PBC and synovium) suggesting that signature pathways in PBC mirror those of the inflamed synovium. Finally the osteoactivin gene was upregulared in both PBC and synovial biopsies and this finding was confirmed by the detection of high levels of osteoactivin in PsA sera but not in other inflammatory arthritides.

Conclusions

We describe the first analysis of the trancriptome in paired synovial tissue and PBC of patients with PsA. This study strengthens the hypothesis that PsA is of autoimmune origin since the coactivity of IFN and Th17 pathways is typical of autoimmunity. Finally these findings have allowed the identification of a possible disease biomarker, osteoactivin, easily detectable in PsA serum.

Development of optical probes for in vivo imaging of polarized macrophages during foreign body reactions

Plasticity of macrophage (MΦ) phenotypes exist in a spectrum from classically activated (M1) cells, to alternatively activated (M2) cells, contributing to both the normal healing of tissues and the pathogenesis of implant failure. Here, folate- and mannose-based optical probes were fabricated to simultaneously determine the degree of MΦ polarization. In vitro tests show the ability of these probes to specifically target M1 and M2 cells. In an in vivo murine model, they were able to distinguish between the M1-dominated inflammatory response to infection and the M2-dominated regenerative response to particle implants. Finally, the probes were used to assess the inflammatory/regenerative properties of biomaterial implants. Our results show that these probes can be used to monitor and quantify the dynamic processes of MΦ polarization and their role in cellular responses in real time.

Myeloid cell microsomal prostaglandin E synthase-1 fosters atherogenesis in mice

Microsomal prostaglandin E synthase-1 (mPGES-1) in myeloid and vascular cells differentially regulates the response to vascular injury, reflecting distinct effects of mPGES-1-derived PGE2 in these cell types on discrete cellular components of the vasculature. The cell selective roles of mPGES-1 in atherogenesis are unknown. Mice lacking mPGES-1 conditionally in myeloid cells (Mac-mPGES-1-KOs), vascular smooth muscle cells (VSMC-mPGES-1-KOs), or endothelial cells (EC-mPGES-1-KOs) were crossed into hyperlipidemic low-density lipoprotein receptor-deficient animals. En face aortic lesion analysis revealed markedly reduced atherogenesis in Mac-mPGES-1-KOs, which was concomitant with a reduction in oxidative stress, reflective of reduced macrophage infiltration, less lesional expression of inducible nitric oxide synthase (iNOS), and lower aortic expression of NADPH oxidases and proinflammatory cytokines. Reduced oxidative stress was reflected systemically by a decline in urinary 8,12-iso-iPF2α-VI. In contrast to exaggeration of the response to vascular injury, deletion of mPGES-1 in VSMCs, ECs, or both had no detectable phenotypic impact on atherogenesis. Macrophage foam cell formation and cholesterol efflux, together with plasma cholesterol and triglycerides, were unchanged as a function of genotype. In conclusion, myeloid cell mPGES-1 promotes atherogenesis in hyperlipidemic mice, coincident with iNOS-mediated oxidative stress. By contrast, mPGES-1 in vascular cells does not detectably influence atherogenesis in mice. This strengthens the therapeutic rationale for targeting macrophage mPGES-1 in inflammatory cardiovascular diseases.

Folate-functionalized dendrimers for targeting Chlamydia-infected tissues in a mouse model of reactive arthritis

Chlamydia trachomatis is an intracellular human pathogen that causes a sexually transmitted disease which may result in an inflammatory arthritis designated Chlamydia-induced reactive arthritis (ReA). The arthritis develops after dissemination of infected cells from the initial site of chlamydial infection. During Chlamydia-associated ReA, the organism may enter into a persistent infection state making treatment with antibiotics a challenge. We hypothesize that folate receptors (FR), which are overexpressed in Chlamydia-infected cells, and the associated inflammation would allow folate-targeted nanodevices to better treat infections. To investigate this, we developed a folate-PAMAM dendrimer-Cy5.5 conjugate (D-FA-Cy5.5), where Cy5.5 is used as the near-IR imaging agent. Uptake of D-FA-Cy5.5 upon systemic administration was assessed and compared to non-folate conjugated controls (D-Cy5.5), using a mouse model of Chlamydia-induced ReA, and near-IR imaging. Our results suggested that there was a higher concentration of folate-based nanodevice in sites of infection and inflammation compared to that of the control nanodevice. The folate-conjugated nanodevices localized to infected paws and genital tracts (major sites of inflammation and infection) at 3-4 fold higher concentrations than were dendrimer alone, suggesting that the overexpression of folate receptors in infected and inflamed tissues enables higher dendrimer uptake. There was an increase in uptake into thymus, spleen, and lung, but no significant differences in the uptake of the folate nanodevices in other organs including kidney and heart, indicating the 'relative specificity' of the D-FA-Cy5.5 conjugate nanodevices. These results suggest that folate targeting dendrimers are able to deliver drugs to attenuate infection and associated inflammation in Chlamydia-induced ReA.

Folate receptor-targeted aminopterin therapy is highly effective and specific in experimental models of autoimmune uveitis and autoimmune encephalomyelitis

EC0746 is a rationally designed anti-inflammatory drug conjugate consisting of a modified folic acid-based ligand linked to a γ-hydrazide analog of aminopterin. In this report, EC0746's effectiveness was evaluated against experimental retinal S-antigen (PDSAg) induced autoimmune uveitis (EAU) and myelin-basic-protein induced autoimmune encephalomyelitis (EAE). In both models, functional FR-β was detected on activated macrophages in local (retinal or central-nervous-system, respectively) and systemic (peritoneal cavity) sites of inflammation. In myelin-rich regions of EAE rats, an increased uptake of (99m)Tc-EC20 (etarfolatide; a FR-specific radioimaging agent) was also observed. EC0746 treatment at disease onset suppressed the clinical severity of both EAU and EAE, and it strongly attenuated progressive histopathological changes in the affected organs. In all parameters assessed, EC0746 activity was completely blocked by a benign folate competitor, suggesting that these therapeutic outcomes were specifically FR-β mediated. EC0746 may emerge as a useful macrophage-modulating agent for treating inflammatory episodes of organ-specific autoimmunity.

Prospects in folate receptor-targeted radionuclide therapy

Targeted radionuclide therapy is based on systemic application of particle-emitting radiopharmaceuticals which are directed toward a specific tumor-associated target. Accumulation of the radiopharmaceutical in targeted cancer cells results in high doses of absorbed radiation energy whereas toxicity to non-targeted healthy tissue is limited. This strategy has found widespread application in the palliative treatment of neuroendocrine tumors using somatostatin-based radiopeptides. The folate receptor (FR) has been identified as a target associated with a variety of frequent tumor types (e.g., ovarian, lung, brain, renal, and colorectal cancer). In healthy organs and tissue FR-expression is restricted to only a few sites such as for instance the kidneys. This demonstrates why FR-targeting is an attractive strategy for the development of new therapy concepts. Due to its high FR-binding affinity (K_D < 10⁻⁹ M) the vitamin folic acid has emerged as an almost ideal targeting agent. Therefore, a variety of folic acid radioconjugates for nuclear imaging have been developed. However, in spite of the large number of cancer patients who could benefit of a folate-based radionuclide therapy, a therapeutic concept with folate radioconjugates has not yet been envisaged for clinical application. The reason is the generally high accumulation of folate radioconjugates in the kidneys where emission of particle-radiation may result in damage to the renal tissue. Therefore, the design of more sophisticated folate radioconjugates providing improved tissue distribution profiles are needed. This review article summarizes recent developments with regard to a therapeutic application of folate radioconjugates. A new construct of a folate radioconjugate and an application protocol which makes use of a pharmacological interaction allowed the first preclinical therapy experiments with radiofolates. These results raise hope for future application of such new concepts also in the clinic.

Folate-based radiotracers for PET imaging--update and perspectives

The folate receptor (FR) is expressed in many tumor types, among those ovarian and lung cancer. Due to the high FR affinity of folic acid, it has been used for targeting of FR-positive tumors, allowing specific delivery of attached probes to the malignant tissue. Therefore, nuclear imaging of FR-positive cancer is of clinical interest for selecting patients who could benefit from innovative therapy concepts based on FR-targeting. Positron emission computed tomography (PET) has become an established technique in clinical routine because it provides an increased spatial resolution and higher sensitivity compared to single photon emission computed tomography (SPECT). Therefore, it is of critical importance to develop folate radiotracers suitable for PET imaging. This review article updates on the design, preparation and pre-clinical investigation of folate derivatives for radiolabeling with radioisotopes for PET. Among those the most relevant radionuclides so far are fluorine-18 (t_1/2: 110 min, E_avβ⁺: 250 keV) and gallium-68 (t_1/2: 68 min, E_av β⁺: 830 keV). Recent results obtained with new PET isotopes such as terbium-152 (t_1/2: 17.5 h, Eβ⁺: 470 keV) or scandium-44 (t_1/2: 3.97 h, E_av β⁺: 632 keV) are also presented and discussed. Current endeavors for clinical implementation of PET agents open new perspectives for identification of FR-positive malignancies in patients.

Use of folate-conjugated imaging agents to target alternatively activated macrophages in a murine model of asthma

Pro-inflammatory macrophages play a prominent role in such autoimmune diseases as rheumatoid arthritis, Crohn's disease, psoriasis, sarcoidosis, and atherosclerosis. Because pro-inflammatory macrophages have also been shown to overexpress a receptor for the vitamin folic acid (i.e., folate receptor beta; FR-β), folate-linked drugs have been explored for use in imaging and treatment of these same diseases. To determine whether allergic inflammatory disorders might be similarly targeted with folate-linked drugs, we have examined the characteristics of macrophages that are prominent in the pathogenesis of asthma. We report here that macrophages from the lungs of mice with experimental allergic asthma express FR-β. We further document that these FR-β(+) macrophages coexpress markers of alternatively activated (M2-type) macrophages, including the mannose receptor and arginase-1. Finally, we demonstrate that folate-conjugated fluorescent dyes and radioimaging agents can be specifically targeted to these asthmatic lung macrophages, with little uptake by macrophages present in healthy lung tissue. These data suggest strategies for the development of novel diagnostic agents for the imaging of asthma and other diseases involving alternatively activated macrophages.

Effects of the Janus kinase inhibitor CP-690550 (tofacitinib) in a rat model of oxazolone-induced chronic dermatitis

The effect of CP-690550 (tofacitinib), a new Janus kinase (JAK) inhibitor, was evaluated in chronic allergic dermatitis. Allergic contact dermatitis was induced in rat ears by repeated application of oxazolone. This dermatitis was accompanied by sustained ear swelling and marked epidermal hyperplasia. In the induced ear, a lot of inflammatory cells infiltrated into the dermis site and the amounts of interferon (IFN)-γ, tumor necrosis factor (TNF)-α, and interleukin (IL)-22 were elevated. Orally administered CP-690550 significantly suppressed ear swelling as well as epidermal thickening, and the effect at 10 mg/kg was comparable to that of cyclosporin A and etanercept. These results suggest a great potential of CP-690550, a JAK inhibitor, as a treatment for chronic dermatitis featuring epidermal hyperplasia (in the pathogenesis of which IFN-γ, TNF-α and IL-22 play a role) such as psoriasis and chronic atopic dermatitis.

Evaluation of the novel folate receptor ligand [18F]fluoro-PEG-folate for macrophage targeting in a rat model of arthritis

INTRODUCTION

Detection of (subclinical) synovitis is relevant for both early diagnosis and monitoring of therapy of rheumatoid arthritis (RA). Previously, the potential of imaging (sub)clinical arthritis was demonstrated by targeting the translocator protein in activated macrophages using (R)-[11C]PK11195 and positron emission tomography (PET). Images, however, also showed significant peri-articular background activity. The folate receptor (FR)-β is a potential alternative target for imaging activated macrophages. Therefore, the PET tracer [18F]fluoro-PEG-folate was synthesized and evaluated in both in vitro and ex vivo studies using a methylated BSA induced arthritis model.

METHODS

[18F]fluoro-PEG-folate was synthesized in a two-step procedure. Relative binding affinities of non-radioactive fluoro-PEG-folate, folic acid and naturally circulating 5-methyltetrahydrofolate (5-Me-THF) to FR were determined using KB cells with high expression of FR. Both in vivo [18F]fluoro-PEG-folate PET and ex vivo tissue distribution studies were performed in arthritic and normal rats and results were compared with those of the established macrophage tracer (R)-[11C]PK11195.

RESULTS

[18F]fluoro-PEG-folate was synthesized with a purity >97%, a yield of 300 to 1,700 MBq and a specific activity between 40 and 70 GBq/µmol. Relative in vitro binding affinity for FR of F-PEG-folate was 1.8-fold lower than that of folic acid, but 3-fold higher than that of 5-Me-THF. In the rat model, [18F]fluoro-PEG-folate uptake in arthritic knees was increased compared with both contralateral knees and knees of normal rats. Uptake in arthritic knees could be blocked by an excess of glucosamine-folate, consistent with [18F]fluoro-PEG-folate being specifically bound to FR. Arthritic knee-to-bone and arthritic knee-to-blood ratios of [18F]fluoro-PEG-folate were increased compared with those of (R)-[11C]PK11195. Reduction of 5-Me-THF levels in rat plasma to those mimicking human levels increased absolute [18F]fluoro-PEG-folate uptake in arthritic joints, but without improving target-to-background ratios.

CONCLUSIONS

The novel PET tracer [18F]fluoro-PEG-folate, designed to target FR on activated macrophages provided improved contrast in a rat model of arthritis compared with the accepted macrophage tracer (R)-[11C]PK11195. These results warrant further exploration of [18F]fluoro-PEG-folate as a putative PET tracer for imaging (sub)clinical arthritis in RA patients.

Radiosynthesis and preclinical evaluation of 3'-Aza-2'-[(18)F]fluorofolic acid: a novel PET radiotracer for folate receptor targeting

The folate receptor (FR) has been identified as a valuable target for the imaging of cancer and activated macrophages, involved in inflammatory and autoimmune diseases via positron emission tomography (PET). Therefore, conjugates of folic acid have been synthesized by coupling of a radiolabeled prosthetic group to the glutamate part of folic acid (pendent approach). In this work, we present a novel class of folates, where the phenyl ring of folic acid was isosterically replaced by a pyridine moiety for direct labeling with [(18)F]fluoride (integrated approach). 3'-Azafolic acid and its 2'-halogenated derivatives (2'-chloro and 2'-fluoro) were evaluated in vitro to determine their binding affinity. 3'-Aza-2'-[(18)F]fluorofolic acid ([(18)F]6) was obtained, starting from N(2)-acetyl-3'-aza-2'-chlorofolic acid di-tert-butylester (2), in a maximum decay corrected radiochemical yield of about 9% in ≥98% radiochemical purity and high specific activities of 35-127 GBq/μmol. Binding affinity to the FR was high (IC(50) = 0.8 ± 0.2 nM), and the radiotracer was stable in human plasma over 4 h at 37 °C. No degradation or defluorination was detected after incubation of the radiotracer for 1 h at 37 °C with human and murine liver microsomes and human S9-fraction. In vivo PET imaging and biodistribution studies with mice demonstrated a high and specific uptake in FR-positive KB tumor xenografts (12.59 ± 1.77% ID/g, 90 min p.i.). A high and specific accumulation of radioactivity was observed in the kidneys (57.33 ± 8.40% ID/g, 90 min p.i.) and salivary glands (14.09 ± 0.93% ID/g, 90 min p.i.), which are known to express the FR and nonspecific uptake found in the liver (10.31 ± 2.37% ID/g, 90 min p.i.). Preinjection of folic acid resulted in a >85% reduced uptake of [(18)F]6 in FR-positive tissues (xenografts, kidneys, and salivary glands). Furthermore, no radioactive metabolites were detected in the blood, urine, or tumor tissue, 30 min p.i. These characteristics indicate that this new (18)F-labeled 3'-azafolate is an appropriate tool for imaging FR-positive (malignant) tissue.

Folate-conjugated rapamycin slows progression of polycystic kidney disease

Activation of the mammalian target of rapamycin (mTOR) signaling pathway is aberrant in autosomal-dominant polycystic kidney disease (ADPKD). The mTOR inhibitors, such as rapamycin, ameliorate PKD in rodent models, but clinical trials have not shown benefit, possibly as a result of low tissue concentrations of rapamycin at clinically tolerable doses. To overcome this limitation, we synthesized a folate-conjugated form of rapamycin (FC-rapa) that is taken up by folate receptor-mediated endocytosis and cleaved intracellularly to reconstitute the active drug. We found that renal cyst-lining cells highly express the folate receptor in ADPKD and mouse models. In vitro, FC-rapa inhibited mTOR activity in a dose- and folate receptor-dependent manner. Treatment of a PKD mouse model with FC-rapa inhibited mTOR in the target tissue, strongly attenuated proliferation and growth of renal cysts and preserved renal function. Furthermore, FC-rapa inhibited mTOR activity in the kidney but not in other organs. In summary, these results suggest that targeting the kidney using FC-rapa may overcome the significant side effects and lack of renal efficacy observed in clinical trials with mTOR inhibitors in ADPKD.