Abrine, an IDO1 inhibitor, suppresses the immune escape and enhances the immunotherapy of anti-PD-1 antibody in hepatocellular carcinoma

Tumor cells evade the immune surveillance by up-regulating surface expression of PD-L1, which interacts with PD-1 on T cells to elicit the immune checkpoint response 1,2 . Anti-PD-1 antibodies have shown remarkable promise in treating tumors, including metastatic melanoma 2–4 . However, patient response rate is low 4,5 . A better understanding of PD-L1-mediated immune evasion is needed to predict patient response and improve treatment efficacy. Here we report that metastatic melanoma releases a high level of extracellular vesicles (EVs), mostly in the form of exosomes, that carry PD-L1 on their surface. Interferon-γ (IFN-γ) up-regulates PD-L1 on these vesicles, which suppresses the function of CD8 T cells and facilitates tumor growth. In patients with metastatic melanoma, the level of circulating exosomal PD-L1 positively correlates with that of IFN-γ, and changes during the course of anti-PD-1 therapy. The magnitudes of the early on-treatment increase in circulating exosomal PD-L1, as an indicator of the adaptive response of the tumor cells to T cell re-invigoration, stratifies clinical responders from non-responders. Our study unveils a mechanism by which tumor cells systemically suppress the immune system, and provides a rationale for the application of exosomal PD-L1 as a predictor for anti-PD-1 therapy. Show more

N6-methyladenosine (m6A) is considered the most common, abundant, and conserved internal transcript modification, especially in eukaryotic messenger RNA (mRNA). m6A is installed by m6A methyltransferases (METTL3/14, WTAP, RBM15/15B, VIRMA and ZC3H13, termed “writers”), removed by demethylases (FTO, ALKBH5, and ALKBH3, termed “erasers”), and recognized by m6A-binding proteins (YTHDC1/2, YTHDF1/2/3, IGF2BP1/2/3, HNRNP, and eIF3, termed “readers”). Accumulating evidence suggests that m6A RNA methylation greatly impacts RNA metabolism and is involved in the pathogenesis of many kinds of diseases, including cancers. In this review, we focus on the physiological functions of m6A modification and its related regulators, as well as on the potential biological roles of these elements in human tumors. Show more

Thermal shift assays are used to study thermal stabilization of proteins upon ligand binding. Such assays have been used extensively on purified proteins in the drug discovery industry and in academia to detect interactions. Recently, we published a proof-of-principle study describing the implementation of thermal shift assays in a cellular format, which we call the cellular thermal shift assay (CETSA). The method allows studies of target engagement of drug candidates in a cellular context, herein exemplified with experimental data on the human kinases p38α and ERK1/2. The assay involves treatment of cells with a compound of interest, heating to denature and precipitate proteins, cell lysis, and the separation of cell debris and aggregates from the soluble protein fraction. Whereas unbound proteins denature and precipitate at elevated temperatures, ligand-bound proteins remain in solution. We describe two procedures for detecting the stabilized protein in the soluble fraction of the samples. One approach involves sample workup and detection using quantitative western blotting, whereas the second is performed directly in solution and relies on the induced proximity of two target-directed antibodies upon binding to soluble protein. The latter protocol has been optimized to allow an increased throughput, as potential applications require large numbers of samples. Both approaches can be completed in a day. Show more