Silk fibroin hydrogel adhesive enables sealed-tight reconstruction of meniscus tears.

Despite orientationally variant tears of the meniscus, suture repair is the current clinical gold treatment. However, inaccessible tears in company with re-tears susceptibility remain unresolved. To extend meniscal repair tools from the perspective of adhesion and regeneration, we design a dual functional biologic-released bioadhesive (S-PIL10) comprised of methacrylated silk fibroin crosslinked with phenylboronic acid-ionic liquid loading with growth factor TGF-ß1, which integrates chemo-mechanical restoration with inner meniscal regeneration. Supramolecular interactions of ß-sheets and hydrogen bonds richened by phenylboronic acid-ionic liquid (PIL) result in enhanced wet adhesion, swelling resistance, and anti-fatigue capabilities, compared to neat silk fibroin gel. Besides, elimination of reactive oxygen species (ROS) by S-PIL10 further fortifies localized meniscus tear repair by affecting inflammatory microenvironment with dynamic borate ester bonds, and S-PIL10 continuously releases TGF-ß1 for cell recruitment and bridging of defect edge. In vivo rabbit models functionally evidence the seamless and dense reconstruction of torn meniscus, verifying that the concept of meniscus adhesive is feasible and providing a promising revolutionary strategy for preclinical research to repair meniscus tears.

A nano-composite hyaluronic acid-based hydrogel efficiently antibacterial and scavenges ROS for promoting infected diabetic wound healing.

Diabetic wound infection brings chronic pain to patients and the therapy remains a crucial challenge owing to the disruption of the internal microenvironment. Herein, we report a nano-composite hydrogel (ZnO@HN) based on ZnO nanoparticles and a photo-trigging hyaluronic acid which is modified by o-nitrobenzene (NB), to accelerate infected diabetic wound healing. The diameter of the prepared ZnO nanoparticle is about 50 nm. X-ray photoelectron spectroscopy (XPS) analysis reveals that the coordinate bond binds ZnO in the hydrogel, rather than simple physical restraint. ZnO@HN possesses efficient antioxidant capacity and it can scavenge DPPH about 40 % in 2 h and inhibit H2O2 >50 % in 8 h. The nano-composite hydrogel also exhibits satisfactory antibacterial capacity (58.35 % against E. coli and 64.03 % against S. aureus for 6 h). In vitro tests suggest that ZnO@HN is biocompatible and promotes cell proliferation. In vivo experiments reveal that the hydrogel can accelerate the formation of new blood vessels and hair follicles. Histological analysis exhibits decreased macrophages, increased myofibroblasts, downregulated TNF-α expression, and enhanced VEGFA expression during wound healing. In conclusion, ZnO@HN could be a promising candidate for treating intractable infected diabetic skin defection.

Discovery of (4-Pyrazolyl)-2-aminopyrimidines as Potent and Selective Inhibitors of Cyclin-Dependent Kinase 2.

CDK2 is a critical regulator of the cell cycle. For a variety of human cancers, the dysregulation of CDK2/cyclin E1 can lead to tumor growth and proliferation. Historically, early efforts to develop CDK2 inhibitors with clinical applications proved unsuccessful due to challenges in achieving selectivity over off-target CDK isoforms with associated toxicity. In this report, we describe the discovery of (4-pyrazolyl)-2-aminopyrimidines as a potent class of CDK2 inhibitors that display selectivity over CDKs 1, 4, 6, 7, and 9. SAR studies led to the identification of compound 17, a kinase selective and highly potent CDK2 inhibitor (IC50 = 0.29 nM). The evaluation of 17 in CCNE1-amplified mouse models shows the pharmacodynamic inhibition of CDK2, measured by reduced Rb phosphorylation, and antitumor activity.

Exploring the antibiotic potential of cultured 'unculturable' bacteria.

In response to the severe global antibiotic resistance crisis, this forum delves into 'unculturable' bacteria, believed to be a promising source of novel antibiotics. We propose remarkable drug discovery strategies that leverage these bacteria's diversity, aspiring to transform resistance management. The urgent call for new antibiotics accentuates the essentiality of further research.

Size- and Dose-Dependent Body-Wide Organ Transcriptomic Responses to Calcium Phosphate Nanomaterials.

Nanomaterials are widely used in clinical practice. There are potential risks of body-wide infiltration due to their small size; however, the body-wide reliable risk assessment of nanoparticle infiltration is not fully studied and established. In this study, we demonstrated the size- and dose-dependent body-wide organ transcriptomic responses to calcium phosphate nanomaterials in vivo. In a mice model, a calcium phosphate nanocluster (amorphous calcium phosphate, ACP, ∼1 nm in diameter) and its crystallization product (ACP-M, ∼10 nm in diameter) in a series of doses was administrated systematically; multiorgan transcriptomics were then performed with tissues of heart, liver, spleen, lung, kidney, and brain to investigate the systematic effect of dose and size of nanomaterials on the whole body. The results presented gene expression trajectories correlated with the dose of the nanomaterials and tissue-specific risk effects in all detected tissues. For the dose-dependent tissue-specific risk effects, lung tissue exhibited the most significant risk signatures related to apoptosis, cell proliferation, and cell stress. The spleen showed the second most significant risk signatures associated with immune response and DNA damage. For the size-dependent tissue-specific risk effects, ACP nanomaterials could increase most of the tissue-specific risk effects of nanomaterials in multiple organs than larger calcium phosphate nanoparticles. Finally, we used the size- and dose-dependent body-wide organ transcriptomic responses/risks to nanomaterials as the standards and built up a risk prediction model to evaluate the risk of the local nanomaterials delivery. Thus, our findings could provide a size- and dose- dependent risk assessment scale of nanoparticles in the transcriptomic level. It could be useful for risk assessment of nanomaterials in the future.

Core-Shell Au@Pd Bimetallic Nanozyme Mediated Mild Photothermal Therapy through Reactive Oxygen Species-Regulating Tumor Thermoresistance.

Mild photothermal therapy (mPTT), which circumvents the limitations of conventional photothermal therapy, is emerging and exhibits remarkable potential in clinical applications. Nevertheless, mPTT is not able to efficiently eradicate tumors because its therapeutic efficacy is dramatically diminished by stress-induced heat shock proteins (HSP). Herein, a core-shell structured Au@Pd (AP) bimetallic nanozyme was fabricated for reactive oxygen species (ROS) augmentation-induced mPTT. The nanocatalytic AP nanozymes with photothermal conversion performance harbor multienzymatic (catalase, oxidase, and peroxidase) activities to induce ROS storm formation. The generated ROS could suppress the heat-defense response of tumor cells by cleaving HSP. Overall, our work highlights a ROS-regulating strategy to counteract hyperthermia-associated resistance in mPTT.

Low-Temperature Photothermal Therapy Platform Based on Pd Nanozyme-Modified Hydrogenated TiO2.

In photothermal treatments (PTTs), normal tissues around cancerous tumors get injured by excessive heat, whereas damaged cancer cells are easily restored by stress-induced heat shock proteins (HSPs) at low temperatures. Therefore, to achieve a unique tumor microenvironment (TME), it is imperative to increase PTT efficiency and reduce normal tissue injury by adopting appropriate reactive oxygen species (ROS) and lipid peroxides (LPO) cross-linked with HSPs. In the present research, a potential strategy for mild photothermal treatments (mPTTs) was proposed by initiating localized catalytic chemical reactions in TME based on Pd nanozyme-modified hydrogenated TiO2 (H-TiO2@Pd). In vitro and in vivo evaluations demonstrated that H-TiO2@Pd had good peroxidase-like activities (POD), glutathione oxidase-like activities (GSHOx), and photodynamic properties and also satisfactory biocompatibility for 4T1 cells. Localized catalytic chemical reactions in H-TiO2@Pd significantly depleted GSH to downregulate the protein expression of GPX4 and promoted the accumulation of LPO and ROS, which consumed HSP70 or inhibited its function in 4T1 cells. Hence, the as-constructed low-temperature photothermal therapeutic platform based on Pd nanozyme-modified H-TiO2 can be a promising candidate to develop a safe and effective mPTT for cancer treatments.

Development of a novel 1-octen-3-ol-loaded agar/curdlan hydrogel for inhibiting peach fruit diseases.

Our previous study found that 1-octen-3-ol fumigation treatment could effectively induce the resistance of peach fruit diseases. However, 1-octen-3-ol is a liquid fumigant, which is not conducive to storage and application. Herein, the gel of 1 % agar compound with 1 % curdlan was used as a novel material for covering 1-octen-3-ol. The interaction of agar and curdlan was promoted by adding 1-octen-3-ol, leading to a higher thermostability compared to single-component antibacterial gels. Moreover, 1-octen-3-ol resulted in changes in the internal structure and mechanical properties of gel to form a pore-like structure, which is beneficial to the retention and release of 1-octen-3-ol. Additionally, the 2 % agar gel containing 1-octen-3-ol had the best inhibitory effect on the mycelial growth of Monilinia fructicola and Rhizopus stolonifer in vitro, and the compound hydrogel of 1 % agar and 1 % curdlan with 1-octen-3-ol could most effectively inhibit brown rot and soft rot caused by these two pathogens in vivo. Overall, the data indicated that the novel 1-octen-3-ol-loaded agar/curdlan hydrogels could effectively retain and release 1-octen-3-ol, and induce the resistance of peach fruit diseases.

Stage-specific and location-specific cartilage calcification in osteoarthritis development.

OBJECTIVES: This study investigated the stage-specific and location-specific deposition and characteristics of minerals in human osteoarthritis (OA) cartilages via multiple nano-analytical technologies. METHODS: Normal and OA cartilages were serially sectioned for micro-CT, scanning electron microscopy with energy dispersive X-ray spectroscopy, micro-Raman spectroscopy, focused ion beam scanning electron microscopy, high-resolution electron energy loss spectrometry with transmission electron microscopy, nanoindentation and atomic force microscopy to analyse the structural, compositional and mechanical properties of cartilage in OA progression. RESULTS: We found that OA progressed by both top-down calcification at the joint surface and bottom-up calcification at the osteochondral interface. The top-down calcification process started with spherical mineral particle formation in the joint surface during early-stage OA (OA-E), followed by fibre formation and densely packed material transformation deep into the cartilage during advanced-stage OA (OA-A). The bottom-up calcification in OA-E started when an excessive layer of calcified tissue formed above the original calcified cartilage, exhibiting a calcified sandwich structure. Over time, the original and upper layers of calcified cartilage fused, which thickened the calcified cartilage region and disrupted the cartilage structure. During OA-E, the calcified cartilage was hypermineralised, containing stiffer carbonated hydroxyapatite (HAp). During OA-A, it was hypomineralised and contained softer HAp. This discrepancy may be attributed to matrix vesicle nucleation during OA-E and carbonate cores during OA-A. CONCLUSIONS: This work refines our current understanding of the mechanism underlying OA progression and provides the foothold for potential therapeutic targeting strategies once the location-specific cartilage calcification features in OA are established.

Seamless and early gap healing of osteochondral defects by autologous mosaicplasty combined with bioactive supramolecular nanofiber-enabled gelatin methacryloyl (BSN-GelMA) hydrogel.

Autologous mosaicplasty is a common approach used to treat osteochondral defects in clinical practice. Gap integration between host and transplanted plugs requires bone tissue reservation and hyaline cartilage regeneration without uneven surface, graft necrosis and sclerosis. However, poor gap integration is a serious concern, which eventually leads to deterioration of joint function. To deal with such complications, this study has developed a strategy to effectively enhance integration of the gap region following mosaicplasty by applying injectable bioactive supramolecular nanofiber-enabled gelatin methacryloyl (GelMA) hydrogel (BSN-GelMA). A rabbit osteochondral defect model demonstrated that BSN-GelMA achieved seamless osteochondral healing in the gap region between plugs of osteochondral defects following mosaicplasty, as early as six weeks. Moreover, the International Cartilage Repair Society score, histology score, glycosaminoglycan content, subchondral bone volume, and collagen II expression were observed to be the highest in the gap region of BSN-GelMA treated group. This improved outcome was due to bio-interactive materials, which acted as tissue fillers to bridge the gap, prevent cartilage degeneration, and promote graft survival and migration of bone marrow mesenchymal stem cells by releasing bioactive supramolecular nanofibers from the GelMA hydrogel. This study provides a powerful and applicable approach to improve gap integration after autologous mosaicplasty. It is also a promising off-the-shelf bioactive material for cell-free in situ tissue regeneration.

Dynamic photoelectrical regulation of ECM protein and cellular behaviors.

Dynamic regulation of cell-extracellular matrix (ECM)-material interactions is crucial for various biomedical applications. In this study, a light-activated molecular switch for the modulation of cell attachment/detachment behaviors was established on monolayer graphene (Gr)/n-type Silicon substrates (Gr/Si). Initiated by light illumination at the Gr/Si interface, pre-adsorbed proteins (bovine serum albumin, ECM proteins collagen-1, and fibronectin) underwent protonation to achieve negative charge transfer to Gr films (n-doping) through π-π interactions. This n-doping process stimulated the conformational switches of ECM proteins. The structural alterations in these ECM interactors significantly reduced the specificity of the cell surface receptor-ligand interaction (e.g., integrin recognition), leading to dynamic regulation of cell adhesion and eventual cell detachment. RNA-sequencing results revealed that the detached bone marrow mesenchymal stromal cell sheets from the Gr/Si system manifested regulated immunoregulatory properties and enhanced osteogenic differentiation, implying their potential application in bone tissue regeneration. This work not only provides a fast and feasible method for controllable cells/cell sheets harvesting but also gives new insights into the understanding of cell-ECM-material communications.

Nitric oxide-mediated regulation of mitochondrial protective autophagy for enhanced chemodynamic therapy based on mesoporous Mo-doped Cu9S5 nanozymes.

The depletion of reactive oxygen species (ROS) by glutathione (GSH) and oxidative stress induced protective autophagy severely impaired the therapeutic effect of chemodynamic therapy (CDT). Therefore, how to construct a CDT treatment nanosystem with high yield and full utilization of ROS in tumor site is the main issue of CDT. Herein, a multifunctional cascade bioreactor based on mesoporous Mo-doped Cu9S5 (m-MCS) nanozymes loaded with L-Arginine (LA), abbreviated as m-MCS@LA, is constructed for realizing enhanced CDT promoted by ultrasound (US) triggered gas therapy. The m-MCS based on the catalytic performance of multivalent metal ions, which were served as nanozymes, exhibit enhanced Fenton-like and glutathione (GSH) peroxidase-like activities in comparison to Cu9S5 nanoparticles without Mo-doping. Once placed in tumor microenvironment (TME), the existence of redox couples (Cu+/Cu2+ and Mo4+/Mo6+) in m-MCS enabled it to react with hydrogen peroxide (H2O2) to generate ·OH for achieving CDT effect via Fenton-like reaction. Meanwhile, m-MCS could consume overexpressed GSH in tumor microenvironment (TME) to alleviate antioxidant capability for enhancing CDT effect. Moreover, m-MCS with mesoporous structure could be employed as the carrier to load natural nitric oxide (NO) donor LA. US as the excitation source with high tissue penetration can trigger m-MCS@LA to produce NO. As the gas transmitter with physiological functions, NO could play dual roles to kill cancer cells through gas therapy directly, and enhance CDT effect by inhibiting protective autophagy simultaneously. As a result, this US-triggered and NO-mediated synergetic cancer chemodynamic/gas therapy based on m-MCS@LA NPs can effectively eliminate primary tumor and achieved tumor-specific treatment, which provide a possible strategy for developing more effective CDT in future practical applications. STATEMENT OF SIGNIFICANCE: The depletion of reactive oxygen species (ROS) by glutathione (GSH) and oxidative stress induced protective autophagy severely impaired the therapeutic effect of chemodynamic therapy (CDT). Herein, a multifunctional cascade bioreactor based on mesoporous Mo-doped Cu9S5 (m-MCS) nanozymes loaded with L-Arginine (m-MCS@LA) is constructed for realizing enhanced CDT promoted by ultrasound (US) triggered gas therapy. The m-MCS with double redox couples presents the enhanced enzyme-like activities to perform cascade reactions for reducing GSH and generating ROS. LA loaded by m-MCS can produce NO triggered by US to inhibit the mitochondria protective autophagy for reactivating mitochondria involved apoptosis pathway. The US-triggered and NO-mediated CDT based on m-MCS@LA can effectively eliminate primary tumor through the high yield and full utilization of ROS.

GABA keeps nitric oxide in balance by regulating GSNOR to enhance disease resistance of harvested tomato against Botrytis cinerea.

Gamma-aminobutyric acid (GABA), a widely distributed metabolite in prokaryotes and eukaryotes, has many functions for plants in stress responses. In this study, hypotonic treatment with 10 mmol L-1 GABA in cherry tomato induced resistance to Botrytis cinerea with markedly lower disease incidence and lesion diameter, led to endogenous nitric oxide (NO) tansient accumulation before inoculation the pathogen then decrease after inoculation, and enhanced the content of arginine (Arg) and glutamic acid (Glu). The resistance of fruit treated with a NO scavenger, carboxy-2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO), was significantly reduced. Moreover, the enzyme activity and gene expression of S-nitrosoglutathione reductase (GSNOR) were enhanced following endogenous NO increased. The endogenous NO level was excessively high after treatment with a GSNOR scavenger, N6022, making the fruit more susceptible to pathogen. Similarly, after break down of SlGSNOR, fruit had much higher endogenous NO and lower disease resistance. However, overexpression of SlGSNOR exhibited opposite consequences. These results suggest that a suitable level of NO is beneficial for enhancing disease resistance, and GABA can help tomatoes maintain NO equilibrium by regulating GSNOR.

Identification of an Ultrathin Osteochondral Interface Tissue with Specific Nanostructure at the Human Knee Joint.

Cartilage adheres to subchondral bone via a specific osteochondral interface tissue where forces are transferred from soft cartilage to hard bone without conferring fatigue damage over a lifetime of load cycles. However, the fine structure and mechanical properties of the osteochondral interface tissue remain unclear. Here, we identified an ultrathin ∼20-30 µm graded calcified region with two-layered micronano structures of osteochondral interface tissue in the human knee joint, which exhibited characteristic biomolecular compositions and complex nanocrystals assembly. Results from finite element simulations revealed that within this region, an exponential increase of modulus (3 orders of magnitude) was conducive to force transmission. Nanoscale heterogeneity in the hydroxyapatite, coupled with enrichment of elastic-responsive protein-titin, which is usually present in muscle, endowed the osteochondral tissue with excellent mechanical properties. Collectively, these results provide novel insights into the potential design for high-performance interface materials for osteochondral interface regeneration.

In-cytoplasm mitochondrial transplantation for mesenchymal stem cells engineering and tissue regeneration.

Stem cell therapies are unsatisfactory due to poor cell survival and engraftment. Stem cell used for therapy must be properly "tuned" for a harsh in vivo environment. Herein, we report that transfer of exogenous mitochondria (mito) to adipose-derived mesenchymal stem cells (ADSCs) can effectively boost their energy levels, enabling efficient cell engraftment. Importantly, the entire process of exogeneous mitochondrial endocytosis is captured by high-content live-cell imaging. Mitochondrial transfer leads to acutely enhanced bioenergetics, with nearly 17% of higher adenosine 5'-triphosphate (ATP) levels in ADSCs treated with high mitochondrial dosage and further results in altered secretome profiles of ADSCs. Mitochondrial transfer also induced the expression of 334 mRNAs in ADSCs, which are mainly linked to signaling pathways associated with DNA replication and cell division. We hypothesize that increase in ATP and cyclin-dependent kinase 1 and 2 expression might be responsible for promoting enhanced proliferation, migration, and differentiation of ADSCs in vitro. More importantly, mito-transferred ADSCs display prolonged cell survival, engraftment and horizontal transfer of exogenous mitochondria to surrounding cells in a full-thickness skin defect rat model with improved skin repair compared with nontreated ADSCs. These results demonstrate that intracellular mitochondrial transplantation is a promising strategy to engineer stem cells for tissue regeneration.

Biomimetic Joint Paint for Efficient Cartilage Repair by Simultaneously Regulating Cartilage Degeneration and Regeneration in Pigs.

Irregular partial-thickness cartilage defect is a common pathogenesis of osteoarthritis (OA) with no available treatment in clinical practice. Currently, cartilage tissue engineering is only suitable for a limited area of full-thickness cartilage defect. Here, we design a biomimetic joint paint for the intractable partial-thickness cartilage defect repair. The joint paint, composed of a bridging layer of chondroitin sulfate and a surface layer of gelatin methacrylate with hyaluronic acid, can quickly and tightly adhere to the cartilage defect by light activation. Being treated by the joint paint, the group of rabbit and pig models with partial-thickness cartilage defects showed a restoration of a smooth cartilage surface and the preservation of normal glycosaminoglycan content, whereas the untreated control group exhibited serious progressive OA development. This paint treatment functions by prohibiting chondrocyte apoptosis, maintaining chondrocyte phenotype, and preserving the content of glycosaminoglycan in the partial-thickness cartilage defects. These findings illustrated that the biomimetic joint paint is an effective and revolutionary therapeutics for the patients with noncurable partial-thickness cartilage defects.

Advanced hydrogels for the repair of cartilage defects and regeneration.

Cartilage defects are one of the most common symptoms of osteoarthritis (OA), a degenerative disease that affects millions of people world-wide and places a significant socio-economic burden on society. Hydrogels, which are a class of biomaterials that are elastic, and display smooth surfaces while exhibiting high water content, are promising candidates for cartilage regeneration. In recent years, various kinds of hydrogels have been developed and applied for the repair of cartilage defects in vitro or in vivo, some of which are hopeful to enter clinical trials. In this review, recent research findings and developments of hydrogels for cartilage defects repair are summarized. We discuss the principle of cartilage regeneration, and outline the requirements that have to be fulfilled for the deployment of hydrogels for medical applications. We also highlight the development of advanced hydrogels with tailored properties for different kinds of cartilage defects to meet the requirements of cartilage tissue engineering and precision medicine.

Recent advances in light-induced cell sheet technology.

Various stimuli have been applied to harvest complete cell sheets, including temperature, magnetic, pH, and electrical stimuli. Cell sheet technology is a convenient and efficient approach with beneficial effects for tissue regeneration and cell therapy. Lights of different wavelengths, such as ultraviolet (UV), visible light, and near infrared ray (NIR) light, were confirmed to aid in fabricating a cell sheet. Changes in the wettability, potential, or water content of the culturing surfaces that occur under light illumination induce conformational changes in the adhesive proteins or collagens, which then leads to cell sheet detachment. However, the current approaches face several limitations, as few standards for safe light illumination have been proposed to date, and require a careful control of the wavelength, power, and irradiation time. Future studies should aim at generating new materials for culturing and releasing cell sheets rapidly and effectively.

Bioactive nanocomposite coatings under visible light illumination promoted surface-mediated gene delivery.

Gene delivery based on bioactive coatings on collagen has great potential for applications in bone repair. Meanwhile, controlled gene delivery at specific times/regions is essential for an efficient and complete bone reconstruction process. However, spatio-temporal regulation of gene release and delivery remains a great challenge. In this paper, we used visible light illumination to effectively regulate gene release and subsequent delivery into biological cells. A visible light responsive and bioactive nanocomposite coating (based on collagen/gold nanoparticles, e.g., Col/AuNPs) was prepared through hydrothermal and sol-gel processes and was used as a loading platform for complexes of enhanced green fluorescent protein and Lipofectamine2000 (LF/GFP). The results showed that the amount of immobilized LF/GFP was increased on Col/AuNPs and the release of pre-adsorbed LF/GFP was significantly enhanced in a spatio-temporal and controlled manner under visible light illumination. Moreover, the cellular intake of the released genes was improved, thus enhancing the gene expression efficiency of the cells. The mechanism of enhanced controlled gene delivery was attributed to the changes in collagen structures and rearrangement of cytoskeletal structures induced by the photothermal effect. The developed Col/AuNP composite coating is effective for both controlled surface-mediated gene delivery and gene-mediated bone repair.

Identification of pAKT as a pharmacodynamic marker for MER kinase in human melanoma G361 cells.

BACKGROUND: The MER signaling pathway represents an attractive therapeutic target for human cancers. Growth arrest-specific protein 6 (GAS6)-induced MER phosphorylation is often unstable and difficult to detect without pervanadate pretreatment in human cancer cells, posing a challenge for the development of selective MER kinase inhibitors. Here, we identified phosphorylated AKT (pAKT) as a specific pharmacodynamic marker for MER kinase inhibitors in human melanoma G361 cells. METHODS: The expression of MER, TYRO3, and AXL were profiled among multiple human cancer cells. To determine whether they play a role in the activation of pAKT, MER and TYRO3 were selectively depleted by small, interfering RNA knockdown. In addition, using AKT phosphorylation as a readout, a high-throughput cell-based assay was established in G361 cells for evaluation of the potency of potential inhibitors of MER pathway activation. RESULTS: We demonstrated that high levels of MER and TYRO3, but not AXL, were expressed in G361 cells. In these cells, pAKT was induced by GAS6 treatment, which could be reversed by AXL/MER inhibitors. We showed that GAS6-induced pAKT is only dependent on MER kinase, but not TYRO3, in G361 cells. Furthermore, we observed a correlation in potency between inhibition of pAKT in G361 cells and pMER in MER-overexpressing Ba/F3 cells by these inhibitors. CONCLUSIONS: In summary, we have demonstrated that GAS6-induced pAKT is a possible pharmacodynamic marker for the inhibition of MER kinase, and we have successfully developed a cell-based functional assay for screening small-molecule inhibitors of MER kinase for potential therapeutic utility in treating GAS6/MER-deregulated human cancers.