Multiwell optogenetics for enhanced cell-based assays

Many environmental toxicants can activate estrogen receptor α (ERα), disrupting normal endocrine function. While these activities are predicted across in silico, in vitro, and in vivo models, translating active concentrations between these systems remains challenging. We hypothesized that cellular uptake and the resulting free intracellular toxicant concentration could bridge this gap. Using cell-free (hER) and cell-based (ERα-CALUX cells) estrogen assays, we tested this hypothesis by determination of the free intracellular concentration available for binding to the intracellularly located ERα. Predictive modeling identified three classes of estrogenic chemicals from the ToxCast collection: bisphenols, parabens, and phthalates. Experimental data confirmed potency differences of up to 100-fold between the cell-free and cell-based models. Cellular toxicokinetic (TK) parameters, including cellular uptake and intracellular binding, were determined using computational and experimental methods. Incorporating experimental TK parameters significantly improved the correlation between ERα activities in the cell-free and cellular models (from r = 0.6230, P = 0.0989 without corrections to r = 0.8869, P = 0.0033 after corrections), and bridged the gap between the cell free and cell based assays. Both computational and experimental TK parameters varied widely across chemical classes and compounds. Correcting active concentrations for free intracellular levels enhanced assay correlations, with experimentally derived corrections showing the strongest improvement with r = 0.8869 (compared to the in silico derived corrections with r = 0.811). Our findings highlight the critical role of free intracellular concentration in determining the biological activity of estrogenic toxicants and emphasize its importance in accurately assessing their endocrine-disrupting potential.

Discovery of diminazene as a dual inhibitor of SARS-CoV-2 human host proteases TMPRSS2 and furin using cell-based assays.

The two organic anion transporting polypeptides (OATPs) 1B1 and 1B3 are expressed at the sinusoidal membrane of hepatocytes. They have a broad and overlapping substrate specificity and transport many endobiotics and drugs. Specific inhibitors are required to determine the contribution of each OATP to the hepatocellular uptake of common substrates. We have developed a cell-based high-throughput assay to screen chemical libraries in order to identify such inhibitors for OATP1B1 and OATP1B3. We have used OATP1B1- or OATP1B3-expressing Chinese Hamster Ovary cells on 96-well plates and determined uptake of fluorescein-methotrexate (FMTX). We validated the assay with known inhibitors and screened the well characterized Prestwick library of 1120 drugs. Along with several known OATP inhibitors including rifampicin, cyclosporine A and mifepristone we identified some new inhibitors. For inhibitors that seemed to be able to distinguish between OATP1B1- and OATP1B3-mediated FMTX uptake IC50 values were determined. Estropipate (estrone-3-sulfate stabilized with piperazine) was the most selective OATP1B1 inhibitor (IC50 = 0.06 μM vs. 19.3 μM for OATP1B3). Ursolic acid was the most selective OATP1B3 inhibitor (IC50 = 2.3 μM vs. 12.5 μM for OATP1B1). In conclusion, this cell-based assay should allow us to identify even more specific inhibitors by screening larger chemical libraries.

Experimental validation of a parenteral permitted daily exposure value for cleaning-induced degradants from recombinant therapeutic proteins with in vitro immunogenicity assays

Serological markers of Nuromyelitis Optica (NMO), an autoimmune disorder of the central nervous system, are autoantibodies targeting the astrocytic water channel aquaporin-4 (AQP4). We have previously demonstrated that the main epitopes for these autoantibodies (AQP4-IgG) are generated by the supramolecular arrangement of AQP4 tetramers into an Orthogonal Array of Particles (OAPs). Many tests have been developed to detect AQP4-IgG in patient sera but several procedural issues affect OAP assembly and consequently test sensitivity. To date, the protein based ELISA test shows the lowest sensitivity while representing a valid alternative to the more sensitive cell based assay (CBA), which, however, shows economic, technical and interpretation problems. Here we have developed a high perfomance ELISA in which native OAPs are used as the molecular target. To this aim a native size exclusion chromatography method has been developed to isolate integral, highly pure and AQP4-IgG-recognized OAPs from rat brain. These OAPs were immobilized and oriented on a plastic plate by a sandwich approach and 139 human sera were tested, including 67 sera from NMO patients. The OAP-ELISA showed a 99% specificity and a higher sensitivity (91%) compared to the CBA test. A comparative analysis revealed an end-point titer three orders of magnitude higher than the commercial ELISA and six times higher than our in-house CBA test. We show that CNS-extracted OAPs are crucial elements in order to perform an efficient AQP4-IgG test and the OAP-ELISA developed represents a valid alternative to the CBA currently used.

Botulinum neurotoxins (BoNTs) are the most potent human toxins known and the causative agent of botulism, and are widely used as valuable pharmaceuticals. The BoNTs are modular proteins consisting of a heavy chain and a light chain linked by a disulfide bond. Intoxication of neuronal cells by BoNTs is a multi-step process including specific cell binding, endocytosis, conformational change in the endosome, translocation of the enzymatic light chain into the cells cytosol, and SNARE target cleavage. The quantitative and reliable potency determination of fully functional BoNTs produced as active pharmaceutical ingredient (API) requires an assay that considers all steps in the intoxication pathway. The in vivo mouse bioassay has for years been the 'gold standard' assay used for this purpose, but it requires the use of large numbers of mice and thus causes associated costs and ethical concerns. Cell-based assays are currently the only in vitro alternative that detect fully functional BoNTs in a single assay and have been utilized for years for research purposes. Within the last 5years, several cell-based BoNT detection assays have been developed that are able to quantitatively determine BoNT potency with similar or greater sensitivity than the mouse bioassay. These assays now offer an alternative method for BoNT potency determination. Such quantitative and reliable BoNT potency determination is a crucial step in basic research, in the development of pharmaceutical BoNTs, and in the quantitative detection of neutralizing antibodies.

The outbreak of COVID-19 caused by SARS-CoV-2 has resulted in more than 50 million confirmed cases and over 1 million deaths worldwide as of November 2020. Currently, there are no effective antivirals approved by the Food and Drug Administration to contain this pandemic except the antiviral agent remdesivir. In addition, the trimeric spike protein on the viral surface is highly glycosylated and almost 200,000 variants with mutations at more than 1,000 positions in its 1,273 amino acid sequence were reported, posing a major challenge in the development of antibodies and vaccines. It is therefore urgently needed to have alternative and timely treatments for the disease. In this study, we used a cell-based infection assay to screen more than 3,000 agents used in humans and animals, including 2,855 small molecules and 190 traditional herbal medicines, and identified 15 active small molecules in concentrations ranging from 0.1 nM to 50 μM. Two enzymatic assays, along with molecular modeling, were then developed to confirm those targeting the virus 3CL protease and the RNA-dependent RNA polymerase. Several water extracts of herbal medicines were active in the cell-based assay and could be further developed as plant-derived anti-SARS-CoV-2 agents. Some of the active compounds identified in the screen were further tested in vivo, and it was found that mefloquine, nelfinavir, and extracts of Ganoderma lucidum (RF3), Perilla frutescens, and Mentha haplocalyx were effective in a challenge study using hamsters as disease model.

Identification of Novel Human High-Density Lipoprotein Receptor Up-regulators Using a Cell-Based High-Throughput Screening Assay

Detection of Phospholipidosis Induction: A Cell-Based Assay in High-Throughput and High-Content Format

Drug-induced hepatotoxicity is a major problem in drug development, and reactive metabolites generated by cytochrome P450s are suggested to be one of the causes. CYP2C9 is one of the major enzymes in hepatic drug metabolism. In the present study, we developed a highly sensitive cell-based screening system for CYP2C9-mediated metabolic activation using an adenovirus vector expressing CYP2C9 (AdCYP2C9). Human hepatocarcinoma HepG2 cells infected with our constructed AdCYP2C9 for 2 days at multiplicity of infection 10 showed significantly higher diclofenac 4'-hydroxylase activity than human hepatocytes. AdCYP2C9-infected cells were treated with several hepatotoxic drugs, resulting in a significant increase in cytotoxicity by treatment with losartan, benzbromarone, and tienilic acid. Metabolic activation of losartan by CYP2C9 has never been reported, although the metabolic activations of benzbromarone and tienilic acid have been reported. To identify the reactive metabolites of losartan, the semicarbazide adducts of losartan were investigated by liquid chromatography-tandem mass spectrometry. Two CYP2C9-specific semicarbazide adducts of losartan (S1 and S2) were detected. S2 adduct formation suggested that a reactive metabolite was produced from the aldehyde metabolite E3179, but a possible metabolite from S1 adduct formation was not produced via E3179. In conclusion, a highly sensitive cell-based assay to evaluate CYP2C9-mediated metabolic activation was established, and we found for the first time that CYP2C9 is involved in the metabolic activation of losartan. This cell-based assay system would be useful for evaluating drug-induced cytotoxicity caused by human CYP2C9.

Tobacco metabolites play a crucial role in shaping the sensory experience of tobacco products, such as cigarettes. Bitter metabolites in tobacco not only serve as protective agents in plants, but also significantly influence the overall flavor profile of cigarettes. In this study, we employed an integrated approach combining chemical profiling, cell-based calcium imaging assays, and molecular docking studies to identify key bitter compounds in cigarette smoke and explore the molecular mechanisms underlying their bitterness. We analyzed 22 commercial cigarette brands, revealing notable variability in bitterness perception. GC-MS analysis identified 88 compounds in mainstream cigarette smoke (MCS), with pyridines, esters, and phenols being the most prevalent. Using a TAS2R14-Gα16gust44-HEK293T cell-based assay, we objectively measured bitterness and identified nicotine, succinimide, and scopoletin as key bitter compounds through correlation analysis. Molecular docking studies provided detailed insights into the interactions of these compounds with the TAS2R14 receptor, highlighting significant hydrogen bonding and hydrophobic interactions. This integrated methodology not only identifies key contributors to cigarette bitterness but also enhances our understanding of the molecular basis of bitterness perception in tobacco. These findings pave the way for future studies to further elucidate the complex interactions of bitter compounds. This understanding of the links between tobacco bitterness and consumption holds significant implications for public health and tobacco control initiatives.Supplementary InformationThe online version contains supplementary material available at 10.1038/s41598-025-16488-2.

Development and validation of cell-based luciferase reporter gene assays for measuring neutralizing anti-drug antibodies against interferon beta

Background: There is an increasing demand for effective combinatory agents to improve upon PD-1/PD-L1-based therapeutics. One combinatory target axis is the adenosine metabolism pathway that consists of three major players, including CD39, CD73 and A2AR. Inhibition of any of these targets have shown enhanced preclinical efficacy in combination with PD-1/PD-L1 inhibitors. CD39 is an ectonucleotidase which degrades extracellular ATP to adenosine monophosphate (AMP). This is considered a rate-limiting step for the further degradation to adenosine by CD73. Adenosine is an immunosuppressive metabolite that can suppress NK and T cells. Blockade of CD39-mediated degradation of ATP to AMP may therefore recover anti-tumor immunity through preventing the enrichment of adenosine in the tumor microenvironment. Method: Two anti-CD39 VHH molecules were generated, named Ye-37 and Ye-46, which bind to two different epitopes on CD39. Binding experiments were carried out by bio-layer interferometry. Cell binding experiments were tested on CD39-overexpression cell lines by flow cytometry. Cellular CD39 enzymatic inhibition experiments were tested using an MOLP-8 cell line and PBMC via a luminescence-based assay. Soluble CD39 enzymatic tests were carried out on recombinant CD39 protein using a similar method. T cell proliferation assays were performed and observed on CD4+ or CD8+ T cell populations. In vivo efficacy studies were tested in B-NDG B2M-KO mice that were injected subcutaneously with A375-CD39+ tumor cells and human PBMC. An anti-PD1 x CD39 bispecific antibody was then generated by fusing the anti-CD39 biparatopic antibody to the C-terminus of an anti-PD1 IgG and tested using similar methods. Results: Two candidates, Ye-37 and Ye-46, were selected for their functional activity that recognize non-overlapping epitopes on CD39. The combination of Ye-37 and Ye-46 shows high potency in cell-based and soluble CD39 assays in blocking CD39 activity. Two biparatopic molecules were generated by fusing the biparatopic unit to the N- or C-termini of Fc (46-37-Fc and Fc-37-46) and showed similar activity to the combination. In vivo, we showed single-agent control of tumor growth and potentiation of tumor-growth inhibition when combined with anti-CD73 antibodies. An anti-PD1 x CD39 bispecific was generated and showed potent inhibition of PD-1/PD-L1 interactions by cell-based assays. Potent anti-tumor efficacy was shown, which was as effective as the combination of anti-PD1 plus anti-CD39 antibodies. Conclusion: Potent anti-CD39 and anti-PD1 x CD39 therapeutic candidates have been generated with promising activity as a combinatory or single agent, respectively. As such, we plan to file for clinical trial authorization of these programs by 2022. Citation Format: Zhenqing Zhang, Yunli Jia, Xiaoniu Miao, Weifeng Huang, Chao Wang, Zhijun Yuan, Wenchao Jiang, Liandi Chen, Zhiyuan Li, Andy Tsun. A highly potent anti-CD39 biparatopic antibody and bispecific for cancer therapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5528.

Cancer has become the silent killer in less-developed countries and the most significant cause of morbidity worldwide. The accessible and frequently used treatments include surgery, radiotherapy, chemotherapy, and immunotherapy. Chemotherapeutic drugs traditionally involve using plant-based medications either in the form of isolated compounds or as scaffolds for synthetic drugs. To launch a drug in the market, it has to pass through several intricate steps. The multidrug resistance in cancers calls for novel drug discovery and development. Every year anticancer potential of several plant-based compounds and extracts is reported but only a few advances to clinical trials. The false-positive or negative results impact the progress of the cell-based anticancer assays. There are several cell-based assays but the widely used include MTT, MTS, and XTT. In this article, we have discussed various pitfalls and workable solutions.

Formation of anti-drug antibodies (ADA) and, in particular, neutralizing antibodies (NAb), is a major risk to the development of biotherapeutics. Cell-based assays, which can reflect the mechanistic interactions among the drug, target, and NAb, are often most suitable for the detection of NAb. We report the development and validation of cell-based platform assays for a class of incretin molecules. An affinity capture elution step was employed to improve drug tolerance of a cell-based cyclic adenosine monophosphate (cAMP) assay. Assay conditions and procedures, including acid elution, cell density, and TAG labeled cAMP (cAMP-TAG) incubation time and concentration, were thoroughly optimized. Delta percent (Δ%) Neutralization was used to reduce assay variability during validation and sample analysis. This platform method has been applied to several incretin molecules and has demonstrated desired sensitivity, drug tolerance, and robustness.