Multicomponent Pathogen-Mimicking Nanoparticles Induce Intestinal Immune Responses against Paratuberculosis.

Given the worldwide problem posed by enteric pathogens, the discovery of safe and efficient intestinal adjuvants combined with novel antigen delivery techniques is essential to the design of mucosal vaccines. In this work, we designed poly (lactic-co-glycolic acid) (PLGA)-based nanoparticles (NPs) to codeliver all-trans retinoic acid (atRA), novel antigens, and CpG. To address the insolubility of the intestinal adjuvant atRA, we utilized PLGA to encapsulate atRA and form a "nanocapsid" with polydopamine. By leveraging polydopamine, we adsorbed the water-soluble antigens and the TLR9 agonist CpG onto the NPs' surface, resulting in the pathogen-mimicking PLPCa NPs. In this study, the novel fusion protein (HBf), consisting of the Mycobacterium avium subspecies paratuberculosis antigens HBHA, Ag85B, and Bfra, was coloaded onto the NPs. In vitro, PLPCa NPs were shown to promote the activation and maturation of bone marrow-derived dendritic cells. Additionally, we found that PLPCa NPs created an immune-rich microenvironment at the injection site following intramuscular administration. From the results, the PLPCa NPs induced strong IgA levels in the gut in addition to enhancing powerful systemic immune responses. Consequently, significant declines in the bacterial burden and inflammatory score were noted in PLPCa NPs-treated mice. In summary, PLPCa can serve as a novel and safe vaccine delivery platform against gut pathogens, such as paratuberculosis, capable of activating both systemic and intestinal immunity.

Layer-by-layer nanoparticle encapsulating all-trans retinoic acid and CpG as a mucosal adjuvant targeting colorectal cancer.

Colorectal cancer (CRC) ranks among the most prevalent cancers globally, demanding innovative therapeutic strategies. Immunotherapy, a promising avenue, employs cancer vaccines to activate the immune system against tumors. However, conventional approaches fall short of eliciting robust responses within the gastrointestinal (GI) tract, where CRC originates. Harnessing the potential of all-trans retinoic acid (ATRA) and cytosine-phosphorothioate-guanine (CpG), we developed layered nanoparticles using a layer-by-layer assembly method to co-deliver these agents. ATRA, crucial for gut immunity, was efficiently encapsulated alongside CpG within these nanoparticles. Administering these ATRA@CpG-NPs, combined with ovalbumin peptide (OVA), effectively inhibited orthotopic CRC growth in mice. Our approach leveraged the inherent benefits of ATRA and CpG, demonstrating superior efficacy in activating dendritic cells, imprinting T cells with gut-homing receptors, and inhibiting tumor growth. This mucosal adjuvant presents a promising strategy for CRC immunotherapy, showcasing the potential for targeting gut-associated immune responses in combating colorectal malignancies.

Conformationally Defined Rexinoids for the Prevention of Inflammation and Nonmelanoma Skin Cancers.

Compound 1 is a potent rexinoid that is highly effective in cancer chemoprevention but elevates serum triglycerides. In an effort to separate the lipid toxicity from the anticancer activity of 1, we synthesized four new analogs of rexinoid 1, of which three rexinoids did not elevate serum triglycerides. Rexinoids 3 and 4 are twice as potent as rexinoid 1 in binding to Retinoid X receptor (RXR). All-trans retinoic acid (ATRA) plays a key role in maintaining skin homeostasis, and rexinoids 3-6 are highly effective in upregulating the genes responsible for the biosynthesis of ATRA. Inflammation plays a key role in skin cancer, and rexinoids 3 and 4 are highly effective in diminishing LPS-induced inflammation. Rexinoids 3 and 4 are highly effective in preventing UVB-induced nonmelanoma skin cancer (NMSC) without displaying any overt toxicities. Biophysical studies of rexinoids 3 and 5 bound to hRXRα-ligand binding domain (LBD) reveal important conformational and dynamical differences in the ligand binding domain.

Biomolecular Electron Controller Composed of Nanobiohybrid with Electrically Released Complex for Spatiotemporal Control of Neuronal Differentiation.

In vitro spatiotemporal control of cell differentiation is a critical issue in several biomedical fields such as stem cell therapy and regenerative medicine, as it enables the generation of heterogeneous tissue structures similar to those of their native counterparts. However, the simultaneous control of both spatial and temporal cell differentiation poses important challenges, and therefore no previous studies have achieved this goal. Here, the authors develop a cell differentiation biomolecular electron controller ("Biomoletron") composed of recombinant proteins, DNA, Au nanoparticles, peptides, and an electrically released complex with retinoic acid (RA) to spatiotemporally control SH-SY5Y cell differentiation. RA is only released from the Biomoletron when the complex is electrically stimulated, thus demonstrating the temporal control of SH-SY5Y cell differentiation. Furthermore, by introducing a patterned Au substrate that allows controlling the area where the Biomoletron is immobilized, spatiotemporal differentiation of the SH-SY5Y cell is successfully achieved. Therefore, the proposed Biomoletron-mediated differentiation method provides a promising strategy for spatiotemporal cell differentiation control with applications in regenerative medicine and cell therapy.

Co-delivery of doxorubicin and siRNA by all-trans retinoic acid conjugated chitosan-based nanocarriers for multiple synergistic antitumor efficacy.

To achieve the co-delivery of doxorubicin (DOX) and small interfering RNA (siRNA) targeting B-cell lymphoma 2 (siBcl-2), lactose acid (LA) and all-trans retinoic acid (ATRA) double grafted N,N,N-trimethyl chitosan (TMC) nanoparticles (GTA NPs) were developed. The relative viability of QGY-7703 cells was decreased to 81.3% when the concentration of GTA NPs was 0.1 mg/mL, but no toxicity to normal cells was observed, indicating that the GTA NPs selectively inhibited the proliferation of tumor cells. With DOX loaded into the hydrophobic core and siRNA condensed onto the hydrophilic shell, GTA/DOX/siRNA NPs were prepared. The GTA/DOX/siRNA NPs possessed high cellular uptake via receptor-mediated endocytosis. Owing to multiple cooperative antitumor effects of DOX, siBcl-2, and GTA NPs, GTA/DOX/siRNA NPs had superior in vitro and in vivo antitumor efficiency to other formulations. These findings provide a guideline for the combined applications of multiple synergistic antitumor manners.

All-trans retinoic acid inhibits HCV replication by downregulating core levels via E6AP-mediated proteasomal degradation.

Here, we found that all-trans retinoic acid (ATRA), the most biologically active metabolite of vitamin A, strengthens the anti-viral defense mechanism of E6-associated protein (E6AP) that downregulates hepatitis C virus (HCV) Core levels via ubiquitin-dependent proteasomal degradation. For this effect, ATRA downregulated both protein and enzyme activity levels of DNA methyltransferase 1 and 3b and activated E6AP expression via promoter hypomethylation in HepG2 cells but not in Hep3B cells, in which p53 was absent. Ectopic p53 expression but not E6AP overexpression restored the ability of ATRA to downregulate HCV Core levels in Hep3B cells, suggesting a direct role of p53 in the E6AP-mediated ubiquitination of HCV Core. ATRA also downregulated HCV Core levels during HCV infection in Huh7D cells to inhibit virus replication, providing theoretical basis for the clinical application of ATRA against HCV infection.

Efficacy assessments of tretinoin-loaded nano lipid carriers in acne vulgaris: a double blind, split-face randomized clinical study.

Here, we assessed the efficacy and safety of Nano lipid carrier (NLC) drug delivery system containing tretinoin (NLC-TRE) in comparison with the conventional 0.05% tretinoin cream (TRE cream) in mild to moderate acne vulgaris. A stable and appropriate NLC-TRE formulation was prepared using a high-pressure homogenizer and particle characterization and physicochemical properties were evaluated under accelerated conditions. Efficacy assessment was performed via a split-face clinical study, by comparing the number of acne lesions, porphyrin production and skin biophysical parameters in both sides of the face randomly treated with NLC-TRE and TRE cream. Plasma concentration of tretinoin after topical application of NLC-TRE was measured for primary safety evaluation. We acquired a stable, spherical nanoparticles with particle size of 118.5 nm, PI equal to 0.485 and ZP of - 44.7 mV. The rate of decrease of acne lesions was significantly higher in NLC- TRE side (p value < 0.001). The size and intensity of porphyrin production in pilosebaceous follicles were significantly reduced only on NLC-TRE side (p value < 0.01). The plasma concentration of the tretinoin, after 8 weeks' application remained lower than the toxic levels. The NLC-TRE formula provides better efficiency and good loading capacity of TRE in the drug delivery system.

Design and Optimization of Cationic Nanocapsules for Topical Delivery of Tretinoin: Application of the Box-Behnken Design, In Vitro Evaluation, and Ex Vivo Skin Deposition Study.

Cationic nanocapsules represent a promising approach for topical delivery purposes. We elaborated on a novel formulation based on the cationic nanocapsules to enhance the pharmacodynamic efficacy, user compliance, and photostability of tretinoin (TTN). To achieve this goal, TTN nanocapsules were prepared by the nanoprecipitation method. In order to statistically optimize formulation variables, a Box-Behnken design, using Design-Expert software, was employed. Three independent variables were evaluated: total weight of the cationic acrylic polymer (X 1), oil volume (X 2), and TTN amount (X 3). The particle size and encapsulation efficiency percent (EE%) were selected as dependent variables. The optimal formulation demonstrated spherical morphology under scanning electron microscopy (SEM), optimum particle size of 116.3 nm, and high EE% of 83.2%. TTN-loaded nanocapsules improved photostability compared to its methanolic solution. The in vitro release study data showed that tretinoin was released in a sustained manner compared to the free drug. The ex vivo skin permeation study demonstrated that greater drug deposition into the epidermal region rather than the deep skin was observed with a gel containing TTN-loaded nanocapsules than that of drug solution, respectively. The skin irritation test revealed that the nanoencapsulation of the drug decreased its irritancy compared to the free drug. These results revealed the promising potential of cationic nanocapsules for topical delivery of tretinoin.

Polyplexes of retinoic acid: an in vitro study of complex nanostructures against colorectal cancer cell line (HCT-15).

Despite recent advances in the treatment of human colon cancer, the chemotherapeutic efficacy against colon cancer is still unsatisfactory. The complexity in colorectal cancer treatment leads to new research in combination therapy to overcome multidrug resistance in cancer and increase apoptosis. The objective of the present research work was to develop polyplexes for co-delivery of plasmid DNA with retinoic acid against colorectal cancer cell line (HCT-15). Plain polyplexes were prepared using chitosan and hyaluronic acid solution (0.1% w/v), whereas retinoic acid polyplexes were prepared using ethanol: water (1:9 v/v) system. The particle size was observed in the order of chitosan solution > blank polyplex > retinoic acid-loaded polyplex. Encapsulation efficiency of retinoic acid was found to be 81.51 ± 4.33% for retinoic acid-loaded polyplex formulation. The drug release was observed to be in a controlled pattern with 72.23 ± 1.32% release of retenoic acid from polyplex formulation. Cell line studies of the formulation displayed better cell inhibition and low cytotoxicity for the retinoic acid-loaded polyplexes in comparison to pure retinoic acid, thus demonstrating better potential action against colorectal cancer cell line HCT-15. Retinoic acid-loaded polyplexes indicated higher potential for the delivery of the active whereas the cell line studies displayed the efficacy of the formulation against colorectal cancer cell line HCT-15.

Induction Therapy of Retinoic Acid with a Temozolomide-Loaded Gold Nanoparticle-Associated Ultrasound Effect on Glioblastoma Cancer Stem-Like Colonies.

Glioblastoma multiforme (GBM) is the most aggressive glioma. The treatment response is always low, and the condition is typically rapidly fatal. The undifferentiated and self-renewal characteristics of cancer stem cells (CSCs) have been reported, and their potential contribution may cause tumor initiation, recurrence, metastasis, and therapeutic resistance. In particular, glioblastoma stem-like cells exhibit highly invasive properties and drug resistance, serving as a model for the development of novel therapeutic strategies. Induction therapy provides an alternative therapeutic strategy to eliminate the stem cell properties of CSCs and enhance therapeutic sensitivity. The differentiated cells may lose their self-renewal ability, downregulate stem cell-related genes and drug resistance genes, and enhance anticancer drug sensitivity. Therefore, the purpose of this study is to establish a niche for glioblastoma stem-like cell selection as a platform and facilitate the assessment of differentiation therapy on GBM cancer stem-like colonies by retinoic acid (RA) with temozolomide (TMZ)-loaded gold nanoparticles (GNPs) associated with low-intensity ultrasound (LIUS). Herein, a hyaluronic acid-based material system was used to isolate GBM cancer stem-like colonies. Colony formation, size determination, stem cell-related marker expression, and GBM cancer stem-like cell marker expression with the culture period were identified. The effect of TMZ on GBM stem-like colonies on HA-based material systems was also determined, and the results revealed that drug resistance was highly enhanced in GBM colonies compared with that in the control cell population. In addition, GBM colonies also exhibited a significant increase in breast cancer resistance protein expression, which is consistent with the drug resistance effect. Furthermore, several factors, including LIUS, RA, and GNPs, were used to determine the possibility of induction therapy. RA with TMZ-loaded GNP-associated LIUS stimulation exhibited a significant and synergistic effect on the differentiation effect and drug sensitivity enhancement. The GBM cancer stem-like colony system presents an opportunity for the development of new therapeutic strategies, and this study provides an alternative differentiation therapy for malignant tumors.

Clickable Vitamins as a New Tool to Track Vitamin A and Retinoic Acid in Immune Cells.

The vitamin A derivative, retinoid acid (RA) is key player in guiding adaptive mucosal immune responses. However, data on the uptake and metabolism of vitamin A within human immune cells has remained largely elusive because retinoids are small, lipophilic molecules which are difficult to detect. To overcome this problem and to be able to study the effect of vitamin A metabolism in human immune cell subsets, we have synthesized novel bio-orthogonal retinoid-based probes (clickable probes), which are structurally and functionally indistinguishable from vitamin A. The probes contain a functional group (an alkyne) to conjugate to a fluorogenic dye to monitor retinoid molecules in real-time in immune cells. We demonstrate, by using flow cytometry and microscopy, that multiple immune cells have the capacity to internalize retinoids to varying degrees, including human monocyte-derived dendritic cells (DCs) and naïve B lymphocytes. We observed that naïve B cells lack the enzymatic machinery to produce RA, but use exogenous retinoic acid to enhance CD38 expression. Furthermore, we showed that human DCs metabolize retinal into retinoic acid, which in co-culture with naïve B cells led to of the induction of CD38 expression. These data demonstrate that in humans, DCs can serve as an exogenous source of RA for naïve B cells. Taken together, through the use of clickable vitamins our data provide valuable insight in the mechanism of vitamin A metabolism and its importance for human adaptive immunity.

Transcriptional drug repositioning and cheminformatics approach for differentiation therapy of leukaemia cells.

Differentiation therapy is attracting increasing interest in cancer as it can be more specific than conventional chemotherapy approaches, and it has offered new treatment options for some cancer types, such as treating acute promyelocytic leukaemia (APL) by retinoic acid. However, there is a pressing need to identify additional molecules which act in this way, both in leukaemia and other cancer types. In this work, we hence developed a novel transcriptional drug repositioning approach, based on both bioinformatics and cheminformatics components, that enables selecting such compounds in a more informed manner. We have validated the approach for leukaemia cells, and retrospectively retinoic acid was successfully identified using our method. Prospectively, the anti-parasitic compound fenbendazole was tested in leukaemia cells, and we were able to show that it can induce the differentiation of leukaemia cells to granulocytes in low concentrations of 0.1 µM and within as short a time period as 3 days. This work hence provides a systematic and validated approach for identifying small molecules for differentiation therapy in cancer.

Overview of all-trans-retinoic acid (ATRA) and its analogues: Structures, activities, and mechanisms in acute promyelocytic leukaemia.

All-trans-retinoic acid (ATRA) is effective for preventing cancer and treating skin diseases and acute promyelocytic leukaemia (APL). These pharmacological effects of ATRA are mainly mediated by retinoid X receptors (RXRs) and retinoic acid receptors (RARs). This article provides a comprehensive overview of the clinical progress on and the molecular mechanisms of ATRA in the treatment of APL. ATRA can promote the transcriptional activation of differentiation-related genes and regulate autophagy by inhibiting mTOR, which results in anti-APL effects. In detail, the structures, pharmacological effects, and clinical studies of 68 types of ATRA analogues are described. These compounds have excellent antitumour therapeutic potential and could be used as lead compounds for further development and research.

Superparamagnetic iron oxide-gold nanoparticles conjugated with porous coordination cages: Towards controlled drug release for non-invasive neuroregeneration.

This paper reports a smart intracellular nanocarrier for sustainable and controlled drug release in non-invasive neuroregeneration. The nanocarrier is composed by superparamagnetic iron oxide-gold (SPIO-Au) core-shell nanoparticles (NPs) conjugated with porous coordination cages (PCCs) through the thiol-containing molecules as bridges. The negatively charged PCC-2 and positively charged PCC-3 are compared for intracellular targeting. Both types result in intracellular targeting via direct penetration across cellular membranes. However, the pyrene (Py)-PEG-SH bridge enabled functionalization of SPIO-Au NPs with PCC-3 exhibits higher interaction with PC-12 neuron-like cells, compared with the rhodamine B (RhB)-PEG-SH bridge enabled case and the stand-alone SPIO-Au NPs. With neglectable toxicities to PC-12 cells, the proposed SPIO-Au-RhB(Py)-PCC-2(3) nanocarriers exhibit effective drug loading capacity of retinoic acid (RA) at 13.505 µg/mg of RA/NPs within 24 h. A controlled release of RA is achieved by using a low-intensity 525 nm LED light (100% compared to 40% for control group within 96 h).

Arrest in the Progression of Type 1 Diabetes at the Mid-Stage of Insulitic Autoimmunity Using an Autoantigen-Decorated All-trans Retinoic Acid and Transforming Growth Factor Beta-1 Single Microparticle Formulation.

Type 1 diabetes (T1D) is a disorder of impaired glucoregulation due to lymphocyte-driven pancreatic autoimmunity. Mobilizing dendritic cells (DC) in vivo to acquire tolerogenic activity is an attractive therapeutic approach as it results in multiple and overlapping immunosuppressive mechanisms. Delivery of agents that can achieve this, in the form of micro/nanoparticles, has successfully prevented a number of autoimmune conditions in vivo. Most of these formulations, however, do not establish multiple layers of immunoregulation. all-trans retinoic acid (RA) together with transforming growth factor beta 1 (TGFß1), in contrast, has been shown to promote such mechanisms. When delivered in separate nanoparticle vehicles, they successfully prevent the progression of early-onset T1D autoimmunity in vivo. Herein, we show that the approach can be simplified into a single microparticle formulation of RA + TGFß1 with surface decoration with the T1D-relevant insulin autoantigen. We show that the onset of hyperglycemia is prevented when administered into non-obese diabetic mice that are at the mid-stage of active islet-selective autoimmunity. Unexpectedly, the preventive effects do not seem to be mediated by increased numbers of regulatory T-lymphocytes inside the pancreatic lymph nodes, at least following acute administration of microparticles. Instead, we observed a mild increase in the frequency of regulatory B-lymphocytes inside the mesenteric lymph nodes. These data suggest additional and potentially-novel mechanisms that RA and TGFß1 could be modulating to prevent progression of mid-stage autoimmunity to overt T1D. Our data further strengthen the rationale to develop RA+TGFß1-based micro/nanoparticle "vaccines" as possible treatments of pre-symptomatic and new-onset T1D autoimmunity.

The effects of all-trans retinoic acid on immune cells and its formulation design for vaccines.

As one of the most important metabolites of vitamin A, all-trans retinoic acid (RA) plays a crucial role in regulating immune responses. RA has been shown to promote the differentiation of naïve T and B cells and perform diverse functions in the presence of different cytokines. RA also induces gut tropic lymphocytes through upregulating the expression of chemokine (C-C motif) receptor 9 (CCR9) and α4ß7 integrin. In addition, RA promotes the expression of the enzyme retinal dehydrogenase (RALDH) on dendritic cells, which in turn strengthens the ability to synthesize RA. Due to the insolubility of RA, proper formulation design can maximize its ability to improve immune responses for vaccines. Recent studies have developed some formulations co-loading RA and antigen, which can effectively imprint lymphocytes gut homing properties and induce intestine immune responses as well as systemic responses through parenteral administration, providing a promising direction for the protection against mucosal infections. Here, we review the mechanism and effects of RA on lymphocyte differentiation and gut homing, and recent progress of RA delivery systems to improve mucosal immune responses.

Substituted diaryl ether compounds as retinoic acid-related orphan Receptor-γt (RORγt) agonists.

The discovery of a series of substituted diarylether compounds as retinoic acid related orphan receptor γt (RORγt) agonists is described. Compound 1 was identified from deck mining as a RORγt agonist. Hit-to-lead optimization led to the identification of lead compound 5, which possesses improved potency (10x). Extensive SAR exploration led to the identification of a potent and selective compound 22, that demonstrated an improved pharmacokinetic profile and a dose-dependent pharmacodynamic response. However, when dosed in a MC38 syngeneic tumor model, no evidence of efficacy was observed. ©2020 Elsevier Science Ltd. All rights reserved.

Retinoid Regulation of Ocular Surface Innate Inflammation.

Corneal and conjunctival inflammation and dry eye develop in systemic vitamin A deficiency (VAD). The objective of this study was to investigate the lacrimal ocular surface retinoid axis, particularly immunomodulatory effects of retinoic acid (RA) and change in conjunctival myeloid cell number and phenotype in VAD. We discovered that ocular surface epithelial and myeloid cells express retinoid receptors. Both all trans- and 9-cis-RA suppressed production of dry eye relevant inflammatory mediators [interleukin(IL)-1ß, IL-12, regulated upon activation, normal T cell expressed and secreted (RANTES)] by myeloid cells. Systemic VAD was associated with significant goblet cell loss and an increased number of CD45+ immune cells in the conjunctiva. MHCII-CD11b+ classical monocytes were significantly increased in the conjunctiva of VAD C57BL/6 and RXR-α mutated Pinkie strains. RNA seq revealed significantly increased expression of innate immune/inflammatory genes in the Pinkie conjunctiva. These findings indicate that retinoids are essential for maintaining a healthy, well-lubricated ocular surface and have immunomodulatory effects in the conjunctiva that are mediated in part via RXR-α signaling. Perturbation of the homeostatic retinoid axis could potentiate inflammation on the ocular surface.

Lung Cancer Combination Treatment: Evaluation of the Synergistic Effect of Cisplatin Prodrug, Vinorelbine and Retinoic Acid When Co-Encapsulated in a Multi-Layered Nano-Platform.

PURPOSE: Lung cancer remains the leading cancer-associated deaths worldwide. Cisplatin (CIS) was often used in combination with other drugs for the treatment of non-small cell lung cancer (NSCLC). Prodrug is an effective strategy to improve the efficiency of drugs and reduce the toxicity. The aim of this study was to prepare and characterize CIS prodrug, vinorelbine (VNR), and all-trans retinoic acid (ATRA) co-delivered multi-layered nano-platform, evaluating their antitumor activity in vitro and in vivo. METHODS: Cisplatin prodrug (CISP) was synthesized. A multi-layered nano-platform contained CISP, VNR and ATRA were prepared and named CISP/VNR/ATRA MLNP. The physicochemical properties of CISP/VNR/ATRA MLNP were investigated. In vitro cytotoxicity against CIS-resistant NSCLC cells (A549/CIS cells) and Human normal lung epithelial cells (BEAS-2B cells) was investigated, and in vivo anti-tumor efficiency was evaluated on mice bearing A549/CIS cells xenografts. RESULTS: CISP/VNR/ATRA MLNP were spherical particles with particle size and zeta potential of 158 nm and 12.3 mV. CISP/VNR/ATRA MLNP (81.36%) was uptake by cancer cells in vitro. CISP/VNR/ATRA MLNP could significantly inhibit the in vivo antitumor growth and suspended the tumor volume from 1440 mm3 to 220 mm3. CONCLUSION: It could be concluded that the CISP/VNR/ATRA MLNP may be used as a promising system for lung cancer combination treatment.

Retinoic Acid-Platinum (II) Complex [RT-Pt(II)] Protects Against Rheumatoid Arthritis in Mice via MEK/Nuclear Factor kappa B (NF-κB) Pathway Downregulation.

BACKGROUND Rheumatoid arthritis (RA) is an inflammatory disorder that is present in approximately 1% of the world's population. This study was aimed to investigate the effect of retinoic acid-platinum (II) complex [RT-Pt(II)] on rheumatoid arthritis (RA) and to explore the mechanism involved. MATERIAL AND METHODS MH7A cell viability was determined by MTT assay and apoptosis was assessed using FACSCalibur flow cytometry. RT-PCR and Western blot assays were used for assessment of mRNA and proteins levels. RESULTS Treatment of rheumatoid arthritis with RT-Pt(II) significantly reduced the levels of IL­1ß, IL-6, IL-8, MMP-1, and MMP-13 in synovial fluid of mice in a dose-dependent manner. The expression of iNOS and COX-2 mRNA and protein in rheumatoid arthritis rats was also significantly inhibited by treatment with RT-Pt(II). The TNF-alpha-induced proliferation of MH7A cells was alleviated by RT-Pt(II) treatment in a concentration-dependent manner. Moreover, RT-Pt(II) treatment induced apoptosis and caused arrest of cell cycle in MH7A cells. The activation of MEK/NF-kappaB pathway was downregulated by RT-Pt(II) treatment in MH7A cells. CONCLUSIONS In summary, the present study demonstrated that RT-Pt(II) inhibits TNF-alpha-induced inflammatory response, suppresses cell viability, and induces apoptosis in rheumatoid arthritis synovial cells. Moreover, RT-Pt(II) exhibited its effect through targeting the MEK/NF-kappaB pathway. Therefore, RT-Pt(II) can be used for the development of treatments for rheumatoid arthritis.