Development of a high-throughput TR-FRET screening assay for LAG-3/FGL1 interaction

Finding the partner: FRET and beyond

Given the importance of aberrant protein-protein interactions (PPIs) in disease, the recent drug discovery focuses on targeting the altered PPIs to treat the disease. In this context, identifying the atypical PPIs underlying the disease is critical for the development of diagnostics and therapeutics. Various biochemical, biophysical, and genetic methods have been reported to study PPIs. Here, we are giving a short account of those techniques with more emphasis on Förster resonance energy transfer (FRET), which can be used to monitor macromolecular interactions in live cells. Besides the basics of FRET, we explain the modifications of its application, like Single molecule FRET (smFRET), Fluorescence Lifetime Imaging Microscopy-FRET (FLIM-FRET), and photoswitching FRET. While smFRET is extensively used for evaluating the biology of nucleic acids and also to develop diagnostics, FLIM-FRET is widely exploited to study the PPIs underlying neurological disorders and cancer. Photoswitching FRET is a relatively newer technique and it has tremendous potential to unravel the significance of different PPIs. Besides these modifications, there are several advancements in the field by introducing new fluorophores. Identification of lanthanide chelates, quantum dots, and other nanoparticle fluorophores has revolutionized the applications of FRET in diagnostics and basic biology. Yet, these methods can be employed to study the interactions of only two molecules. Since the majority of the PPIs are multimeric complexes, we still need to improve our technologies to study these interactions in live cells in real-time.

Structure-Based Rational Design of Constrained Peptides as TIM-3 Inhibitors

Blocking the immunosuppressive function of T-cell immunoglobulin mucin-3 (TIM-3) is an established therapeutic strategy to maximize the efficacy of immune checkpoint inhibitors for cancer immunotherapy. Currently, effective inhibition of TIM-3 interactions relies on monoclonal antibodies (mAbs), which come with drawbacks such as immunogenicity risk, limited tumor penetration, and high manufacturing costs. Guided by the X-ray cocrystal structures of TIM-3 with mAbs, we report an in silico structure-based rational design of constrained peptides as potent TIM-3 inhibitors. The top cyclic peptide from our study (P2) binds TIM-3 with a K D value of 166.3 ± 12.1 nM as determined by surface plasmon resonance (SPR) screening. Remarkably, P2 efficiently inhibits key TIM-3 interactions with natural TIM-3 ligands at submicromolar concentrations in a panel of cell-free and cell-based assays. The capacity of P2 to reverse immunosuppression in T-cell/cancer cell cocultures, coupled with favorable in vitro pharmacokinetic properties, highlights the potential of P2 for further evaluation in preclinical models of immuno-oncology.

Design of cyclic peptides as novel inhibitors of ICOS/ICOSL interaction

Compared to small molecules and antibodies, cyclic peptides exhibit unique biochemical and therapeutic attributes in the realm of pharmaceutical applications. The interaction between the inducible costimulator (ICOS) and its ligand (ICOSL) plays a key role in T-cell differentiation and activation. ICOS/ICOSL inhibition results in a reduction in the promotion of immunosuppressive regulatory T cells (Tregs) in both hematologic malignancies and solid tumors. Herein, we implement the computational cPEPmatch approach to design the first examples of cyclic peptides that inhibit ICOS/ICOSL interaction. The top cyclic peptide from our approach possessed an IC50 value of 1.87 ± 0.15 μM as an ICOS/ICOSL inhibitor and exhibited excellent in vitro pharmacokinetic properties as a drug candidate. Our work will lay the groundwork for future endeavors in cancer drug discovery, with the goal of developing cyclic peptides that target the ICOS/ICOSL interaction.

Small Molecule Immunomodulators as Next-Generation Therapeutics for Glioblastoma

Glioblastoma (GBM), the most aggressive astrocytic glioma, remains a therapeutic challenge despite multimodal approaches. Immunotherapy holds promise, but its efficacy is hindered by the highly immunosuppressive GBM microenvironment. This review underscores the urgent need to comprehend the intricate interactions between glioma and immune cells, shaping the immunosuppressive tumor microenvironment (TME) in GBM. Immunotherapeutic advancements have shown limited success, prompting exploration of immunomodulatory approaches targeting tumor-associated macrophages (TAMs) and microglia, constituting a substantial portion of the GBM TME. Converting protumor M2-like TAMs to antitumor M1-like phenotypes emerges as a potential therapeutic strategy for GBM. The blood-brain barrier (BBB) poses an additional challenge to successful immunotherapy, restricting drug delivery to GBM TME. Research efforts to enhance BBB permeability have mainly focused on small molecules, which can traverse the BBB more effectively than biologics. Despite over 200 clinical trials for GBM, studies on small molecule immunomodulators within the GBM TME are scarce. Developing small molecules with optimal brain penetration and selectivity against immunomodulatory pathways presents a promising avenue for combination therapies in GBM. This comprehensive review discusses various immunomodulatory pathways in GBM progression with a focus on immune checkpoints and TAM-related targets. The exploration of such molecules, with the capacity to selectively target key immunomodulatory pathways and penetrate the BBB, holds the key to unlocking new combination therapy approaches for GBM.

Inhibitors of Immune Checkpoints: Small Molecule- and Peptide-Based Approaches

The revolutionary progress in cancer immunotherapy, particularly the advent of immune checkpoint inhibitors, marks a significant milestone in the fight against malignancies. However, the majority of clinically employed immune checkpoint inhibitors are monoclonal antibodies (mAbs) with several limitations, such as poor oral bioavailability and immune-related adverse effects (irAEs). Another major limitation is the restriction of the efficacy of mAbs to a subset of cancer patients, which triggered extensive research efforts to identify alternative approaches in targeting immune checkpoints aiming to overcome the restricted efficacy of mAbs. This comprehensive review aims to explore the cutting-edge developments in targeting immune checkpoints, focusing on both small molecule- and peptide-based approaches. By delving into drug discovery platforms, we provide insights into the diverse strategies employed to identify and optimize small molecules and peptides as inhibitors of immune checkpoints. In addition, we discuss recent advances in nanomaterials as drug carriers, providing a basis for the development of small molecule- and peptide-based platforms for cancer immunotherapy. Ongoing research focused on the discovery of small molecules and peptide-inspired agents targeting immune checkpoints paves the way for developing orally bioavailable agents as the next-generation cancer immunotherapies.

Discovery of ICOS-Targeted Small Molecules Using Pharmacophore-Based Screening

There are currently no small molecules clinically approved as immune checkpoint modulators. Besides possessing oral bioavailability, cell-penetrating capabilities and enhanced tumor penetration compared to monoclonal antibodies (mAbs), small molecules are amenable to pharmacokinetic optimization, which allows adopting flexible dosage regimens that may avoid immune-related adverse events associated with mAbs. The interaction of inducible co-stimulator (ICOS) with its ligand (ICOS-L) plays key roles in T-cell differentiation and activation of T-cell to B-cell functions. This study represents the development and validation of a virtual screening strategy to identify small molecules that bind a novel druggable binding pocket in human ICOS. We used a lipophilic canyon in the apo-structure of ICOS and the ICOS/ICOS-L interface individually as templates for molecular dynamics simulation to generate 3D pharmacophores subsequently used for virtual screening campaigns. Our strategy was successful finding a first-in-class small molecule ICOS binder (5P, KD value=108.08±26.76 μM) and validating biophysical screening platforms for ICOS-targeted small molecules. We anticipate that future structural optimization of 5P will result in the discovery of high affinity chemical ligands for ICOS.

Discovery of Small-Molecule TIM-3 Inhibitors for Acute Myeloid Leukemia Using Pharmacophore-Based Virtual Screening

T-cell immunoglobulin and mucin domain 3 (TIM-3) is a negative immune checkpoint that represents a promising target for cancer immunotherapy. Although encouraging results have been observed for TIM-3 inhibition in the context of acute myeloid leukemia (AML), targeting TIM-3 is currently restricted to monoclonal antibodies (mAbs). To fill this gap, we implemented a pharmacophore-based screening approach to identify small-molecule TIM-3 inhibitors. Our approach resulted in the identification of hit compounds with TIM-3 binding affinity. Subsequently, we used the structure-activity relationship (SAR) by a catalog approach to identify compound A-41 with submicromolar TIM-3 binding affinity. Remarkably, A-41 demonstrated the ability to block TIM-3 interactions with key ligands and inhibited the immunosuppressive function of TIM-3 using an in vitro coculture assay. This work will pave the way for future drug discovery efforts aiming at the development of small-molecule inhibitors TIM-3 for AML.