PD-L1, via its interactions with PD-1, constitutes the key immune checkpoint that allows cancer cells to escape immune surveillance. Targeting PD-1/PD-L1 with monoclonal antibodies (mAbs) led to spectacular success in clinical oncology. However, the inherent limitations of mAbs and increasing findings about the immune-related adverse events (iRAEs) prompted intense research in the field of small-molecule inhibitors of PD-L1. This review covers inhibitors of PD-L1 reported in patents published in the online databases of the World Intellectual Property Organization and European Patent Office in the 2022-2023 period. This review provides a landscape of available inhibitors, including their chemical structures, activity, and stage of development. Small-molecule inhibitors impairing PD-L1/PD-1 interaction represent an attractive alternative to mAbs. In recent years, the field of small-molecule and macrocyclic inhibitors targeting PD-L1 has grown rapidly. The majority (if not all) of small-molecule inhibitors developed recently, similarly to their predecessors, act through a dimerization mechanism of PD-L1, followed by its internalization into the cytosol. In contrast, macrocyclic peptides act purely through a competition mechanism as protein-protein interaction inhibitors. The ongoing clinical trials should ultimately reveal which strategy has real clinical potential and may complement or even replace mAbs-based therapies.

The PD-1/PD-L1 complex is an immune checkpoint responsible for regulating the natural immune response, but also allows tumors to escape immune surveillance. Inhibition of the PD-1/PD-L1 axis positively contributes to the efficacy of cancer treatment. The only available therapeutics targeting PD-1/PD-L1 are monoclonal antibody-based drugs, which have several limitations. Therefore, small molecule compounds are emerging as an attractive alternative that can potentially overcome the drawbacks of mAb-based therapy. In this article, we present a novel class of small molecule compounds based on the terphenyl scaffold that bind to PD-L1. The general architecture of the presented structures is characterized by axial symmetry and consists of three elements: an m-terphenyl core, an additional aromatic ring, and a solubilizing agent. Using molecular docking, we designed a series of final compounds, which were subsequently synthesized and tested in HTRF assay and NMR binding assay to evaluate their activity. In addition, we performed an in-depth analysis of the mutual arrangement of the phenyl rings of the terphenyl core within the binding pocket of PD-L1 and found several correlations between the plane angle values and the affinity of the compounds towards the protein.

Piptoporus betulinus is a fungus known for its medicinal properties. It possesses antimicrobial, anti-inflammatory, and anti-cancer activity. In this study, several tests were performed to evaluate the cytotoxic effect of the ethanolic extract of Piptoporus betulinus on two melanoma human cell lines, WM115 primary and A375 metastatic cell lines, as well as Hs27 human skin fibroblasts. The extract proved to affect cancer cells in a dose-dependent manner, and at the same time showed a low cytotoxicity towards the normal cells. The total phenolic content (TPC) was determined spectrophotometrically by the Folin-Ciocalteu method (F-C), and the potential antioxidant activity was measured by ferric-reducing antioxidant power (FRAP) assay. One of the active compounds in the extract is betulin. It was isolated and then its cytotoxic activity was compared to the results obtained from the Piptoporus betulinus extract. To further understand the mechanism of action of the extract’s anticancer activity, tests on model cell membranes were conducted. A model membrane of a melanoma cell was designed and consisted of 1,2-dimyristoyl-sn-glycero-3-phosphocholine, disialoganglioside-GD_1a and cholesterol: DMPC:GD_1a:chol (5:2:3 mole ratio). Changes in a Langmuir monolayer were observed and described based on Π-A_mol isotherm and compressibility modulus changes. LB lipid bilayers were deposited on a hydrophilic gold substrate and analyzed by IR and X-ray photoelectron spectroscopy. Our study provides new data on the effect of Piptoporus betulinus extract on melanoma cells and its impact on the model of melanoma plasma membranes.