YPD-30, a prodrug of YPD-29B, is an oral small-molecule inhibitor targeting PD-L1 for the treatment of human cancer

Exploring the interaction mechanism between the programmed death-ligand 1 protein and scutellarin via multi-spectroscopy and computer simulation

The programmed death-ligand 1 (PD-L1) protein plays a key role in immune responses. Scutellarin (SCU), as a flavonoid, has a variety of bioactivities. In this study, the human PD-L1 was obtained by expression and purification, and the interaction mechanisms between PD-L1 and SCU were revealed through multi-spectroscopy and computer simulation. Fluorescence data indicated that the quenching of PD-L1 by SCU was mainly static quenching, and primarily driven by hydrogen bonding and van der Waals forces. The binding constant (Ka) was decreased from 2.05 ± 0.55 × 104 L·mol-1 to 0.28 ± 0.08 × 104 L·mol-1 with increasing temperature. Meanwhile, the changes in the microenvironment of PD-L1 were revealed by the synchronous and the 3D fluorescence data. In addition, the melting temperature of PD-L1 increased by 1.67 °C after binding with SCU. Moreover, the circular dichroism data showed that SCU changed the secondary structure of PD-L1 by increasing α-helix content and decreasing β-sheet content. Furthermore, the binding modes between SCU and PD-L1 and the key residues involved in the interaction were revealed by molecular docking and molecular dynamics. These findings supported SCU as an alternative ICB therapeutic strategy and provided evidence for computer-based drug design strategies.

In silico-driven identification of Pranlukast as a Stabilizer of PD-L1 Homodimers

INTRODUCTION

Programmed cell death protein 1 (PD-1) and programmed cell death ligand 1 (PD-L1) are critical immune checkpoints in cancer biology. Multiple small-molecule drugs have been developed as inhibitors of the PD-1/PD-L1 axis. Those drugs promote the formation of PD-L1 homodimers, causing their stabilization, internalization, and subsequent degradation. Drug repurposing is a strategy that expedites the clinical translation by identifying new effects of drugs with clinical use. Herein, we aimed to repurpose drugs as inductors of PD-L1 homodimerization and, therefore, as potential inhibitors of PD-L1.

METHODS

We generated a hybrid pharmacophore model by analyzing the structures of reported ligands that induce PD-L1 homodimerization and their target-binding mode. Pharmacophore-matching compounds were selected from a chemical library of Food and Drug Administration (FDA)-approved drugs. Their binding modes to PDL1 homodimers were assessed by molecular docking and the stability of the complexes and the corresponding binding energies were evaluated by molecular dynamics (MD) simulations. Finally, the activity of one drug as promoter of PD-L1 homodimerization was assessed in protein crosslinking assays.

RESULTS

We identified 12 pharmacophore-matching compounds, but only 4 reproduced the binding mode of the reference inhibitors. Further characterization by MD showed that pranlukast, an antagonist of leukotriene receptors that is used to treat asthma, generated stable and energy-favorable interactions with PD-L1 homodimers and induced homodimerization of recombinant PD-L1.

CONCLUSION

Our results suggest that pranlukast inhibits the PD-1/PD-L1 axis, meriting its repurposing as an antitumor drug.

In Vivo Antitumor Activity of the PD-1/PD-L1 Inhibitor SCL-1 in Various Mouse Tumor Models

BACKGROUND/AIM

Immune checkpoint blockade has achieved great success as a targeted immunotherapy for solid cancers. However, small molecules that inhibit programmed death 1/programmed death ligand 1 (PD-1/PD-L1) binding are still being developed and have several advantages, such as high bioavailability. Previously, we reported a novel PD-1/PD-L1-inhibiting small compound, SCL-1, which showed potent antitumor effects on PD-L1+ tumors. These effects were dependent on CD8+ T-cell infiltration and PD-L1 expression on tumors. The present study investigated the in vivo antitumor activity of SCL-1 in various mouse syngeneic tumor models.

MATERIALS AND METHODS

Twelve syngeneic mice models of tumors, such as colon, breast, bladder, kidney, pancreatic, non-small cell lung cancers, melanoma, and lymphomas, were used for in vivo experiments. Tumor mutation burden (TMB) was analyzed by whole exome sequencing (WES) using reference DNA from mouse blood. The proportion of CD8+ T-cells infiltrating tumors before and after treatment was assessed using flow cytometry and immunohistochemistry (IHC).

RESULTS

SCL-1 had a markedly greater antitumor effect (11 sensitive tumors and 1 resistant tumor among the 12 tumor types) than the anti-mouse PD-1 antibody (8 sensitive tumors and 4 resistant tumors). In addition, the tumor growth inhibition rate (%) was more closely associated with TMB in the SCL-1 group than in the anti-PD-1 antibody group. Furthermore, in vivo experiments using PD-L1 gene knockout and lymphocyte-depletion technologies demonstrated that the antitumor activity of SCL-1 was dependent on CD8+ T-cell infiltration and PD-L1 expression in tumors.

CONCLUSION

SCL-1 has great potential as an oral immunotherapy that targets immune checkpoint molecules in cancer treatment.

Development of small molecule drugs targeting immune checkpoints

Immune checkpoint inhibitors (ICIs) are used to relieve and refuel anti-tumor immunity by blocking the interaction, transcription, and translation of co-inhibitory immune checkpoints or degrading co-inhibitory immune checkpoints. Thousands of small molecule drugs or biological materials, especially antibody-based ICIs, are actively being studied and antibodies are currently widely used. Limitations, such as anti-tumor efficacy, poor membrane permeability, and unneglected tolerance issues of antibody-based ICIs, remain evident but are thought to be overcome by small molecule drugs. Recent structural studies have broadened the scope of candidate immune checkpoint molecules, as well as innovative chemical inhibitors. By way of comparison, small molecule drug-based ICIs represent superior oral bioavailability and favorable pharmacokinetic features. Several ongoing clinical trials are exploring the synergetic effect of ICIs and other therapeutic strategies based on multiple ICI functions, including immune regulation, anti-angiogenesis, and cell cycle regulation. In this review we summarized the current progression of small molecule ICIs and the mechanism underlying immune checkpoint proteins, which will lay the foundation for further exploration.

Reducing PD-L1 Expression by Degraders and Downregulators as a Novel Strategy to Target the PD-1/PD-L1 Pathway

Targeting the programmed cell death protein-1 (PD-1)/programmed cell death-ligand 1 (PD-L1) pathway has evolved into one of the most promising strategies for tumor immunotherapy. Thus far, multiple monoclonal antibody drugs have been approved for treating a variety of tumors, while the development of small-molecule PD-1/PD-L1 inhibitors has lagged far behind, with only a few small-molecule inhibitors entering clinical trials. In addition to antibody drugs and small-molecule inhibitors, reducing the expression levels of PD-L1 has attracted extensive research interest as another promising strategy to target the PD-1/PD-L1 pathway. Herein, we analyze the structures and mechanisms of molecules that reduce PD-L1 expression and classify them as degraders and downregulators according to whether they directly bind to PD-L1. Moreover, we discuss the potential prospects for developing PD-L1-targeting drugs based on these molecules. It is hoped that this perspective will provide profound insights into the discovery of potent antitumor immunity drugs.

Progress in small-molecule inhibitors targeting PD-L1

PD-L1 is a transmembrane protein overexpressed by tumor cells. It binds to PD-1 on the surface of T-cells, suppresses T-cell activity and hinders the immune response against cancer. Clinically, several monoclonal antibodies targeting PD-1/PD-L1 have achieved significant success in cancer immunotherapy. Nevertheless, their disadvantages, such as unchecked immune responses, high cost and long half-life, stimulated pharmacologists to develop small-molecule inhibitors targeting PD-1/PD-L1. After a batch of excellent inhibitors with a biphenyl core structure were firstly reported by BMS, more and more researchers focused on small-molecule inhibitors targeting PD-L1 rather than PD-1. Numerous small-molecule inhibitors were extensively designed and synthesized in the past few years. In this paper, the structural characteristics of PD-L1 and complexes of PD-L1 with its inhibitors are elaborated and small molecule inhibitors developed in the last decade are summarized as well. This paper aims to provide insights into further designing and synthesis of small molecule inhibitors targeting PD-L1.

Targeting PD-1/PD-L-1 immune checkpoint inhibition for cancer immunotherapy: success and challenges

The programmed death-1 receptor (PD-1) acts as a T-cell brake, and its interaction with ligand-1 (PD-L-1) interferes with signal transduction of the T-cell receptor. This leads to suppression of T-cell survival, proliferation, and activity in the tumor microenvironment resulting in compromised anticancer immunity. PD-1/PD-L-1 interaction blockade shown remarkable clinical success in various cancer immunotherapies. To date, most PD-1/PD-L-1 blockers approved for clinical use are monoclonal antibodies (mAbs); however, their therapeutic use are limited owing to poor clinical responses in a proportion of patients. mAbs also displayed low tumor penetration, steep production costs, and incidences of immune-related side effects. This strongly indicates the importance of developing novel inhibitors as cancer immunotherapeutic agents. Recently, advancements in the small molecule-based inhibitors (SMIs) that directly block the PD-1/PD-L-1 axis gained attention from the scientific community involved in cancer research. SMIs demonstrated certain advantages over mAbs, including longer half-lives, low cost, greater cell penetration, and possibility of oral administration. Currently, several SMIs are in development pipeline as potential therapeutics for cancer immunotherapy. To develop new SMIs, a wide range of structural scaffolds have been explored with excellent outcomes; biphenyl-based scaffolds are most studied. In this review, we analyzed the development of mAbs and SMIs targeting PD-1/PD-L-1 axis for cancer treatment. Altogether, the present review delves into the problems related to mAbs use and a detailed discussion on the development and current status of SMIs. This article may provide a comprehensive guide to medicinal chemists regarding the potential structural scaffolds required for PD-1/PD-L-1 interaction inhibition.

The regulatory relationship between NAMPT and PD-L1 in cancer and identification of a dual-targeting inhibitor

Cancer is a heterogeneous disease. Although both tumor metabolism and tumor immune microenvironment are recognized as driving factors in tumorigenesis, the relationship between them is still not well-known, and potential combined targeting approaches remain to be identified. Here, we demonstrated a negative correlation between the expression of NAMPT, an NAD+ metabolism enzyme, and PD-L1 expression in various cancer cell lines. A clinical study showed that a NAMPTHigh PD-L1Low expression pattern predicts poor prognosis in patients with various cancers. In addition, pharmacological inhibition of NAMPT results in the transcription upregulation of PD-L1 by SIRT-mediated acetylation change of NF-κB p65, and blocking PD-L1 would induce NAMPT expression through a HIF-1-dependent glycolysis pathway. Based on these findings, we designed and synthesized a dual NAMPT/PD-L1 targeting compound, LZFPN-90, which inhibits cell growth in a NAMPT-dependent manner and blocks the cell cycle, subsequently inducing apoptosis. Under co-culture conditions, LZFPN-90 treatment contributes to the proliferation and activation of T cells and blocks the growth of cancer cells. Using mice bearing genetically manipulated tumors, we confirmed that LZFPN-90 exerted target-dependent antitumor activities, affecting metabolic processes and the immune system. In conclusion, our results demonstrate the relevance of NAD+-related metabolic processes in antitumor immunity and suggest that co-targeting NAD+ metabolism and PD-L1 represents a promising therapeutic approach.

Challenges Coexist with Opportunities: Spatial Heterogeneity Expression of PD-L1 in Cancer Therapy

Cancer immunotherapy using anti-programmed death-ligand 1 (PD-L1) antibodies has been used in various clinical applications and achieved certain results. However, such limitations as autoimmunity, tumor hyperprogression, and overall low patient response rate impede its further clinical application. Mounting evidence has revealed that PD-L1 is not only present in tumor cell membrane but also in cytoplasm, exosome, or even nucleus. Among these, the dynamic and spatial heterogeneous expression of PD-L1 in tumors is mainly responsible for the unsatisfactory efficacy of PD-L1 antibodies. Hence, numerous studies focus on inhibiting or degrading PD-L1 to improve immune response, while a comprehensive understanding of the molecular mechanisms underlying spatial heterogeneity of PD-L1 can fundamentally transform the current status of PD-L1 antibodies in clinical development. Herein, the concept of spatial heterogeneous expression of PD-L1 is creatively introduced, encompassing the structure and biological functions of various kinds of PD-L1 (including mPD-L1, cPD-L1, nPD-L1, and exoPD-L1). Then an in-depth analysis of the regulatory mechanisms and potential therapeutic targets of PD-L1 is provided, seeking to offer a solid basis for future investigation. Moreover, the current status of agents is summarized, especially small molecular modulators development directed at these new targets, offering a novel perspective on potential PD-L1 therapeutics strategies.

Novel 4-Arylindolines Containing a Pyrido[3,2-d]pyrimidine Moiety as the Programmed Cell Death-1/Programmed Cell Death-Ligand 1 Interaction Inhibitors for Tumor Immunotherapy

A series of pyrido[3,2-d]pyrimidine-containing 4-arylindolines were identified as potent inhibitors of the programmed cell death-1 (PD-1)/programmed cell death-ligand 1 (PD-L1) interaction by structural optimization of a 4-arylindoline precursor reported previously. Among them, compound N11 was the most promising inhibitor, showing an IC50 value of 6.3 nM against the PD-1/PD-L1 interaction at the biochemical level. In in vitro T-cell tumor co-culture models, N11 significantly promoted T-cell proliferation, activation, and infiltration into tumor spheres, demonstrating that it possessed excellent immunomodulatory activity. In addition, N11 exhibited favorable in vivo antitumor activity in an LLC/PD-L1 tumor-bearing mouse model. Flow cytometry analysis verified that the in vivo antitumor efficacy of N11 was dependent on the activation of the immune microenvironment. These findings suggest that N11 can serve as a new starting point for the future development of small-molecule antitumor immunomodulators targeting the PD-1/PD-L1 axis.

Identification of CBPA as a New Inhibitor of PD-1/PD-L1 Interaction

Targeting of the PD-1/PD-L1 immunologic checkpoint is believed to have provided a real breakthrough in the field of cancer therapy in recent years. Due to the intrinsic limitations of antibodies, the discovery of small-molecule inhibitors blocking PD-1/PD-L1 interaction has gradually opened valuable new avenues in the past decades. In an effort to discover new PD-L1 small molecular inhibitors, we carried out a structure-based virtual screening strategy to rapidly identify the candidate compounds. Ultimately, CBPA was identified as a PD-L1 inhibitor with a KD value at the micromolar level. It exhibited effective PD-1/PD-L1 blocking activity and T-cell-reinvigoration potency in cell-based assays. CBPA could dose-dependently elevate secretion levels of IFN-γ and TNF-α in primary CD4+ T cells in vitro. Notably, CBPA exhibited significant in vivo antitumor efficacy in two different mouse tumor models (a MC38 colon adenocarcinoma model and a melanoma B16F10 tumor model) without the induction of observable liver or renal toxicity. Moreover, analyses of the CBPA-treated mice further showed remarkably increased levels of tumor-infiltrating CD4+ and CD8+ T cells and cytokine secretion in the tumor microenvironment. A molecular docking study suggested that CBPA embedded relatively well into the hydrophobic cleft formed by dimeric PD-L1, occluding the PD-1 interaction surface of PD-L1. This study suggests that CBPA could work as a hit compound for the further design of potent inhibitors targeting the PD-1/PD-L1 pathway in cancer immunotherapy.

A Potential Off-Target Effect of the Wnt/β-Catenin Inhibitor KYA1797K: PD-L1 Binding and Checkpoint Inhibition

Introduction

The quest for small molecule inhibitors of the PD-1/PD-L1 checkpoint continues in parallel to the extensive development of monoclonal antibodies directed against this immune checkpoint. Drug screening strategies are being set up to identify novel PD-L1 inhibitors.

Methods

A virtual screening based on molecular docking with the PD-L1 protein dimer has been performed to identify a new binder. Binding of the identified ligand to PD-L1 has been validated experimentally using a microscale thermophoresis (MST) assay. The cellular effect of the compound was evidenced using a fluorescence resonance energy transfer (FRET) assay based on activation of tyrosine phosphatase SHP-2.

Results

We have identified the potent Wnt/β-catenin inhibitor KYA1797K as a weak PD-L1 binder. Molecular docking suggested that the compound can bind to the interface of a PD-L1 dimer, with a geometry superimposable to that of the reference PD-L1 inhibitor BMS-202. The atypical 2-thioxo-4-thiazolidinone motif of KYA1797K, derived from the natural product rhodanine, plays a major role in the interaction with PD-L1. Binding of KYA1797K to recombinant hPD-L1 was validated experimentally, using MST. The drug was found to bind modestly but effectively to hPD-L1. The FRET assay confirmed the weak capacity of KYA1797K to interfere with the activation of SHP-2 upon its interaction with human PD-1.

Discussion

Collectively, the data show that KYA1797K could function as a weak modulator of the PD-1/PD-L1 checkpoint. This effect may contribute, at least partially, to the reported capacity of the β-catenin inhibitor to downregulate PD-L1 in cancer cells. The work also underlines the interest to further consider the rhodanine moiety as a chemical motif for the design of new PD-L1 binders.

Novel nitric oxide-releasing derivatives of pyranocarbazole as antitumor agents: Design, synthesis, biological evaluation, and nitric oxide release studies

In this study, a series of novel furoxan-based nitric oxide (NO) releasing derivatives of pyranocarbazole alkaloids were designed, synthesized, and biologically evaluated against human cancer cell lines. The derivatives showed considerable antiproliferative activities (IC50 = 0.05-7.55 μM) and most compounds showed higher activity in MDA-MB-231 than H460 and HeLa. Especially, the most active derivative 7a (IC50 = 0.05 μM) against MDA-MB-231 was about 60 times stronger than lead compound, as well as equivalent to positive control taxol, and produced high levels of NO in MDA-MB-231. Furthermore, 7a could significantly inhibit the growth of MDA-MB-231 tumors in vivo with low toxicity and the PI3K/Akt signaling pathway. These results indicated that compound 7a could be a promising lead for further studies.

Immunotherapy and Targeted Therapy in the Management of Oral Cancers

Oral cancers (OCs), being one of the frequent malignancies in the head and neck region, need prompt diagnosis and treatment. Apart from basic therapeutic modalities, immunotherapy has now been utilized as a novel approach to combat the disease. With the comprehension of the strategies adopted by cancer cells to evade the immune elimination by the body's immune system, targeted immunotherapies have now become the core area of research. The immune expression of epidermal growth factor receptor (EGFR), programmed cell death protein ligand-1 (PDL-1), etc., are enhanced in OC and have been associated with evasion of the immune system. Targeted immunotherapies now include monoclonal antibodies targeting EGFR like cetuximab and panitumumab, programmed cell death-1 (PD-1) inhibitors like pembrolizumab, cemiplimab, and nivolumab, and PD-L1 inhibitors like atezolizumab, avelumab, and durvalumab. Targeted immunotherapies like chimeric antigen receptor T-cell treatment and small molecule inhibitors are in several clinical trials tried as monotherapy and adjuvant immunotherapy and have shown promising results. Other immunothera-peutic approaches such as cytokines like interferons or interleukins, vaccines, and gene therapy have also been an area of research for the management of OC. However, the cautious selection of appropriate patients with specific immune characteristics as a candidate for immunotherapeutic agents is a crucial component of targeted immunotherapy. This article elaborates on the immune contexture of oral cancer cells, the mechanism of immune evasion by cancer cells, targets for immunotherapies, existent immunotherapeutic agents, and prospects in the field of immunotherapy.