Recent advances in small molecule based cancer immunotherapy

Design, synthesis, and evaluation of antitumor activity of 2-arylmethoxy-4-(2-fluoromethyl-biphenyl-3-ylmethoxy) benzylamine derivatives as PD-1/PD-l1 inhibitors

A series of novel 2-arylmethoxy-4-(2-fluoromethyl-biphenyl-3-ylmethoxy) benzylamine derivatives was designed, synthesized, and evaluated for their antitumor effects as PD-1/PD-L1 inhibitors both in vitro and in vivo. Firstly, the ability of these compounds to block the PD-1/PD-L1 immune checkpoint was assessed using the homogeneous time-resolved fluorescence (HTRF) assay. Two of the compounds can strongly block the PD-1/PD-L1 interaction, with IC50 values of less than 10 nM, notably, compound HD10 exhibited significant clinical potential by inhibiting the PD-1/PD-L1 interaction with an IC50 value of 3.1 nM. Further microscale thermophoresis (MST) analysis demonstrated that HD10 had strong interaction with PD-L1 protein. Co-crystal structure (2.7 Å) analysis of HD10 in complex with the PD-L1 protein revealed a strong affinity between the compound and the target PD-L1 dimer. This provides a solid theoretical basis for further in vitro and in vivo studies. Next, a typical cell-based experiment demonstrated that HD10 could remarkably prevent the interaction of hPD-1 293 T cells from human recombinant PD-L1 protein, effectively restoring T cell function, and promoting IFN-γ secretion in a dose-dependent manner. Moreover, HD10 was effective in suppressing tumor growth (TGI = 57.31 %) in a PD-1/PD-L1 humanized mouse model without obvious toxicity. Flow cytometry, qPCR, and immunohistochemistry data suggested that HD10 inhibits tumor growth by activating the immune system in vivo. Based on these results, it seems likely that HD10 is a promising clinical candidate that should be further investigated.

Therapeutic Target Identification and Drug Discovery Driven by Chemical Proteomics

Throughout the human lifespan, from conception to the end of life, small molecules have an intrinsic relationship with numerous physiological processes. The investigation into small-molecule targets holds significant implications for pharmacological discovery. The determination of the action sites of small molecules provide clarity into the pharmacodynamics and toxicological mechanisms of small-molecule drugs, assisting in the elucidation of drug off-target effects and resistance mechanisms. Consequently, innovative methods to study small-molecule targets have proliferated in recent years, with chemical proteomics standing out as a vanguard development in chemical biology in the post-genomic age. Chemical proteomics can non-selectively identify unknown targets of compounds within complex biological matrices, with both probe and non-probe modalities enabling effective target identification. This review attempts to summarize methods and illustrative examples of small-molecule target identification via chemical proteomics. It delves deeply into the interactions between small molecules and human biology to provide pivotal directions and strategies for the discovery and comprehension of novel pharmaceuticals, as well as to improve the evaluation of drug safety.

Discovery of Small and Bifunctional Molecules Targeting PD-L1/CD73 for Cancer Dual Immunotherapy

In this work, a series of bifunctional PD-L1/CD73 (cluster of differentiation 73) small-molecule inhibitors were designed and synthesized. Among them, CC-5 showed the strongest PD-L1 inhibitory effects with an IC50 of 6 nM and potent anti-CD73 activity with an IC50 of 0.773 μM. The high PD-L1/CD73 inhibitory activity of CC-5 was further confirmed by SPR assays with KD of 182 nM for human PD-L1 and 101 nM for CD73, respectively. Importantly, CC-5 significantly suppressed tumor growth in a CT26 and B16-F10 tumor model with TGI of 64.3% and 39.6%, respectively. Immunohistochemical (IHC) and flow cytometry analysis of tumor-infiltrating lymphocytes (TILs) indicated that CC-5 exerted anticancer effects via activating the tumor immune microenvironment. Collectively, CC-5 represents the first dual PD-L1/CD73 inhibitor worthy of further research as a bifunctional immunotherapeutic agent.

Process Development of a Macrocyclic Peptide Inhibitor of PD-L1

This article outlines the process development leading to the manufacture of 800 g of BMS-986189, a macrocyclic peptide active pharmaceutical ingredient. Multiple N-methylated unnatural amino acids posed challenges to manufacturing due to the lability of the peptide to cleavage during global side chain deprotection and precipitation steps. These issues were exacerbated upon scale-up, resulting in severe yield loss and necessitating careful impurity identification, understanding the root cause of impurity formation, and process optimization to deliver a scalable synthesis. A systematic study of macrocyclization with its dependence on concentration and pH is presented. In addition, a side chain protected peptide synthesis is discussed where the macrocyclic protected peptide is extremely labile to hydrolysis. A computational study explains the root cause of the increased lability of macrocyclic peptide over linear peptide to hydrolysis. A process solution involving the use of labile protecting groups is discussed. Overall, the article highlights the advancements achieved to enable scalable synthesis of an unusually labile macrocyclic peptide by solid-phase peptide synthesis. The sustainability metric indicates the final preparative chromatography drives a significant fraction of a high process mass intensity (PMI).

Immunomodulatory Peptides for Tumor Treatment

Peptides exhibit various biological activities, including biorecognition, cell targeting, and tumor penetration, and can stimulate immune cells to elicit immune responses for tumor immunotherapy. Peptide self-assemblies and peptide-functionalized nanocarriers can reduce the effect of various biological barriers and the degradation by peptidases, enhancing the efficiency of peptide delivery and improving antitumor immune responses. To date, the design and development of peptides with various functionalities have been extensively reviewed for enhanced chemotherapy; however, peptide-mediated tumor immunotherapy using peptides acting on different immune cells, to the knowledge, has not yet been summarized. Thus, this work provides a review of this emerging subject of research, focusing on immunomodulatory anticancer peptides. This review introduces the role of peptides in the immunomodulation of innate and adaptive immune cells, followed by a link between peptides in the innate and adaptive immune systems. The peptides are discussed in detail, following a classification according to their effects on different innate and adaptive immune cells, as well as immune checkpoints. Subsequently, two delivery strategies for peptides as drugs are presented: peptide self-assemblies and peptide-functionalized nanocarriers. The concluding remarks regarding the challenges and potential solutions of peptides for tumor immunotherapy are presented.

Emerging potential approaches in alkaline phosphatase (ALP) activatable cancer theranostics

Alkaline phosphatase (ALP) is known as one of the most crucial members of the phosphatase family and encompasses the enormous ability to hydrolyze the phosphate group in various biomolecules; by this, it regulates several events in the pool of biological medium. Owing to its overexpression in various cancer cells, recently, its potential has evolved as a prominent biomarker in cancer research. In this article, we have underlined the recent advances (2019 onwards) of alkaline phosphatase in the arena of emerging cancer theranostics. Herein, we mainly focused on phosphate-locked molecular systems such as peptides, prodrugs, and aggregation-induced emission (AIE)-based molecules. When these theranostics encounter cancer cell-overexpressed ALP, it results in the hydrolysis of the phosphate group, which leads to the release of highly cytotoxic agents along with turn-on fluorophore/pre-existing fluorophore.

Targeted therapy, immunotherapy, and small molecules and peptidomimetics as emerging immunoregulatory agents for melanoma

Primary cutaneous melanoma is the most lethal of all skin neoplasms and its incidence is increasing. Clinical management of advanced melanoma in the last decade has been revolutionised by the availability of immunotherapies and targeted therapies, used alone and in combination. This article summarizes advances in the treatment of late-stage melanoma including use of protein kinase inhibitors, antibody-based immune checkpoint inhibitors, adoptive immunotherapy, vaccines and more recently, small molecules and peptidomimetics as emerging immunoregulatory agents.

Theranostic Fluorescent Probes

The ability to gain spatiotemporal information, and in some cases achieve spatiotemporal control, in the context of drug delivery makes theranostic fluorescent probes an attractive and intensely investigated research topic. This interest is reflected in the steep rise in publications on the topic that have appeared over the past decade. Theranostic fluorescent probes, in their various incarnations, generally comprise a fluorophore linked to a masked drug, in which the drug is released as the result of certain stimuli, with both intrinsic and extrinsic stimuli being reported. This release is then signaled by the emergence of a fluorescent signal. Importantly, the use of appropriate fluorophores has enabled not only this emerging fluorescence as a spatiotemporal marker for drug delivery but also has provided modalities useful in photodynamic, photothermal, and sonodynamic therapeutic applications. In this review we highlight recent work on theranostic fluorescent probes with a particular focus on probes that are activated in tumor microenvironments. We also summarize efforts to develop probes for other applications, such as neurodegenerative diseases and antibacterials. This review celebrates the diversity of designs reported to date, from discrete small-molecule systems to nanomaterials. Our aim is to provide insights into the potential clinical impact of this still-emerging research direction.

PROTAC-biomacromolecule conjugates for precise protein degradation in cancer therapy: A review

Proteolysis targeting chimera (PROTAC) technology is a promising new mode of targeted protein degradation with significant transformative implications for the clinical treatment of different diseases. Nevertheless, while this technology offers numerous advantages, on-target off-tumour toxicity in healthy cells remains a major challenge for clinical application in cancer therapy. Strategies are presently being explored to optimize degradation activity with cellular selectivity to minimize undesirable side effects. PROTAC-antibody conjugates and PROTAC-aptamer conjugates are unique innovations that combine PROTACs and biomacromolecules. These novel PROTAC-biomacromolecule conjugates (PBCs) can enhance the targetability of PROTACs and reduce their off-target side-effects. The combination of potent PROTACs and highly safe biomacromolecules will pioneer an emerging trend in targeted protein degradation. In our review, we have summarized recent advances in PBCs, discussed current challenges, and outlooked opportunities for future research in the field.

HDAC-targeting epigenetic modulators for cancer immunotherapy

HDAC inhibitors, which can inhibit the activity of HDAC enzymes, have been extensively studied in tumor immunotherapy and have shown potential therapeutic effects in cancer immunotherapy. To date, numerous small molecule HDAC inhibitors have been identified, but many of them suffer from limited clinical efficacy and serious toxicity. Hence, HDAC inhibitor-based combination therapies, and other HDAC modulators (e.g. PROTAC degraders, dual-acting agents) have attracted great attention with significant advancements achieved in the past few years due to their superior efficacy compared to single-target HDAC inhibitors. In this review, we overviewed the recent progress on HDAC-based drug discovery with a focus on HDAC inhibitor-based drug combination therapy and other HDAC-targeting strategies (e.g. selective HDAC inhibitors, HDAC-based dual-target inhibitors, and PROTAC HDAC degraders) for cancer immunotherapy. In addition, we also summarized the reported co-crystal structures of HDAC inhibitors in complex with their target proteins and the binding interactions. Finally, the challenges and future directions for HDAC-based drug discovery in cancer immunotherapy are also discussed in detail.

Forward or Backward: Lessons Learned from Small Molecule Drugs Approved by FDA from 2012 to 2022

At every juncture in history, the design and identification of new drugs pose significant challenges. To gain valuable insights for future drug development, we conducted a detailed analysis of New Molecular Entitiy (NME) approved by the Food and Drug Administration (FDA) from 2012 to 2022 and focused on the analysis of first-in-class (FIC) small-molecules from a perspective of a medicinal chemist. We compared the change of numbers between all the FDA-approved NMEs and FIC, which could be more visual to analyze the changing trend of FIC. To get a more visual change of molecular physical properties, we computed the annual average trends in molecular weight for FIC across various therapeutic fields. Furthermore, we consolidated essential information into three comprehensive databases, which covered the indications, canonical SMILES, structural formula, research and development (R&D) institutions, molecular weight, calculated LogP (CLogP), and route of administration on all the small-molecule pharmaceutical. Through the analysis of the database of 11 years of approvals, we forecast the development trend of NME approval in the future.

Effect of Fragment 1 on the Binding of Epigallocatechin Gallate to the PD-L1 Dimer Explored by Molecular Dynamics

Blocking the interaction between programmed cell death-1 (PD-1) and programmed cell death-ligand 1 (PD-L1) by directly targeting the PD-L1 dimer has emerged as a hot topic in the field of cancer immunotherapy. Epigallocatechin gallate (EGCG), a natural product, has been demonstrated binding to the PD-L1 dimer in our previous study, but has a weaker binding capacity, moreover, EGCG is located at the end of the binding pocket of the PD-L1 dimer. The inhibitor fragment 1 (FRA) lies at the other end. So, we proposed that the introduction of FRA might be able to improve the binding ability. To illuminate this issue, molecular dynamics (MD) simulation was performed in the present study. Binding free energy calculations show that the binding affinity is significantly increased by 17 kcal/mol upon the introduction of FRA. It may be due to the energy contributions of emerging key residues ATyr56, AMet115, BTyr123, AIle54 and the enhanced contributions of initial key residues ATyr123 and BVal68. Binding mode and non-bonded interaction results indicate that FRA_EGCG (EGCG in combination with FRA) binds to the C-, F- and G-sheet of the PD-L1 dimer. Importantly, the introduction of FRA mainly strengthened the nonpolar interactions. The free energy landscape and secondary structure results further show that FRA_EGCG can interact with the PD-L1 dimer more stably. These data demonstrated here provide the theoretical basis for screening two or more natural products with additive inhibitory effect on this pathway and therefore exerting more effective anticancer immunity.

Pathomorphological Manifestations and the Course of the Cervical Cancer Disease Determined by Variations in the TLR4 Gene

Cervical cancer (CC) is often associated with human papillomavirus (HPV). Chronic inflammation has been described as one of the triggers of cancer. The immune system fights diseases, including cancer. The genetic polymorphism of pathogen recognition receptors potentially influences the infectious process, development, and disease progression. Many candidate genes SNPs have been contradictory demonstrated to be associated with cervical cancer by association studies, GWAS. TLR4 gene activation can promote antitumor immunity. It can also result in immunosuppression and tumor growth. Our study aimed to investigate eight selected polymorphisms of the TLR4 gene (rs10759932, rs1927906, rs11536898, rs11536865, rs10983755, rs4986790, rs4986791, rs11536897) and to determine the impact of polymorphisms in genotypes and alleles on the pathomorphological characteristics and progression in a group of 172 cervical cancer subjects with stage I-IV. Genotyping was performed by RT-PCR assay. We detected that the CA genotype and A allele of rs11536898 were significantly more frequent in patients with metastases (p = 0.026; p = 0.008). The multivariate logistic regression analysis confirmed this link to be significant. The effect of rs10759932 and rs11536898 on progression-free survival (PFS) and overall survival (OS) has been identified as important. In univariate and multivariate Cox analyses, AA genotype of rs11536898 was a negative prognostic factor for PFS (p = 0.024; p = 0.057, respectively) and OS (p = 0.008; p = 0.042, respectively). Rs11536898 C allele predisposed for longer PFS (univariate and multivariate: p = 0.025; p = 0.048, respectively) and for better OS (univariate and multivariate: p = 0.010; p = 0.043). The worse prognostic factor of rs10759932 in a univariate and multivariate Cox analysis for survival was CC genotype: shorter PFS (p = 0.032) and increased risk of death (p = 0.048; p = 0.015, respectively). The T allele of rs10759932 increased longer PFS (univariate and multivariate: p = 0.048; p = 0.019, respectively) and longer OS (univariate and multivariate: p = 0.037; p = 0.009, respectively). Our study suggests that SNPs rs10759932 and rs11536898 may have the potential to be markers contributing to the assessment of the cervical cancer prognosis. Further studies, preferably with larger groups of different ethnic backgrounds, are needed to confirm the results of the current study.

Proteolysis-targeting chimeras in biotherapeutics: Current trends and future applications

The success of inhibitor-based therapeutics is largely constrained by the acquisition of therapeutic resistance, which is partially driven by the undruggable proteome. The emergence of proteolysis targeting chimera (PROTAC) technology, designed for degrading proteins involved in specific biological processes, might provide a novel framework for solving the above constraint. A heterobifunctional PROTAC molecule could structurally connect an E3 ubiquitin ligase ligand with a protein of interest (POI)-binding ligand by chemical linkers. Such technology would result in the degradation of the targeted protein via the ubiquitin-proteasome system (UPS), opening up a novel way of selectively inhibiting undruggable proteins. Herein, we will highlight the advantages of PROTAC technology and summarize the current understanding of the potential mechanisms involved in biotherapeutics, with a particular focus on its application and development where therapeutic benefits over classical small-molecule inhibitors have been achieved. Finally, we discuss how this technology can contribute to developing biotherapeutic drugs, such as antivirals against infectious diseases, for use in clinical practices.

In-vivo anticancer efficacy of self-targeted methotrexate-loaded polymeric nanoparticles in solid tumor-bearing rat

Here, cytotoxicity and antitumor efficacy against a chemically (N-methyl-N-nitrosourea) generated mammary tumor in rats were assessed using methotrexate-loaded chitosan nanoparticles (Meth-Cs-NPs). Meth-Cs-NPs intravenous administrated resulted in noticeably decreased tumor incidence, multiplicity, and weight. Further, kidney function tests for the treated groups resulted in noticeably decreased ALP (Meth-Cs-NPs; 244 ± 15, diseases control; 403 ± 14 U/L), Creatinine (Meth-Cs-NPs; 0.81 ± 0.05, diseases control; 2 ± 0.05 mg/dl), and Urea (Meth-Cs-NPs; 56.62 ± 5, diseases control; 113 ± 6 mg/dl) levels, close to a normal control group. Similarly, liver function tests showed significantly decreased serum biomarkers, SGPT (Meth-Cs-NPs; 40 ± 1.8, diseases control; 84 ± 1.9 U/L) and SGOT (Meth-Cs-NPs; 15 ± 2, diseases control; 55 ± 4 U/L) levels in treated groups as compared to the untreated group (diseases control). From the results, pro-inflammatory cytokines were also markedly reduced in the treated group such as, TNF-α (Meth-Cs-NPs; 17.31 ± 1.15, diseases control; 36.9 ± 5 pg/mL), IL-1β (Meth-Cs-NPs; 433.3 ± 66.5, diseases control; 1540 ± 131.1 pg/mL), and IL-6 (Meth-Cs-NPs; 1515 ± 53, diseases control; 2200.6 ± 69 pg/mL) levels. Whereas Meth-Cs-NPs not only helped in lowering tumor multiplicity rates but also decrease inflammation. The studies could be successfully performed in chemically induced mammary tumors due to their easy, quick tumor growth and low mortality rates in rat models. According to the current study, Meth-Cs-NPs have high treatment potency and represent a possible therapeutic alternative for breast cancer treatment.

Tunable Multivalent Platform for Immune Recruitment to Lower Antigen Expressing Cancers

Chemical immunotherapeutic strategies including Antibody Recruiting Molecules (ARMs - bivalent small molecules containing an antibody-binding domain (ABD) and a target-binding domain (TBD)) direct immune-mediated clearance of diseased cells. Anti-cancer ARM function relies on high tumor antigen valency, limiting function against lower antigen expressing tumors. To address this limitation, we report a tunable multivalent immune recruitment (MIR) platform to amplify/stabilize antibody recruitment to cells with lower antigen valencies. An initial set of polymeric ARMs (pARMs) were synthesized and screened to evaluate ABD/TBD copy number, ratio, and steric occlusion on specific immune induction. Most pARMs demonstrated simultaneous high avidity binding to anti-dinitrophenyl antibodies and prostate-specific membrane antigens on prostate cancer. Optimized pARMs mediated enhanced anti-cancer immune function against lower antigen expressing target cells compared to an analogous ARM.

Phenotypic screening platform identifies statins as enhancers of immune cell-induced cancer cell death

BACKGROUND

High-throughput screening (HTS) of small molecule drug libraries has greatly facilitated the discovery of new cancer drugs. However, most phenotypic screening platforms used in the field of oncology are based solely on cancer cell populations and do not allow for the identification of immunomodulatory agents.

METHODS

We developed a phenotypic screening platform based on a miniaturized co-culture system with human colorectal cancer- and immune cells, providing a model that recapitulates part of the tumor immune microenvironment (TIME) complexity while simultaneously being compatible with a simple image-based readout. Using this platform, we screened 1,280 small molecule drugs, all approved by the Food and Drug Administration (FDA), and identified statins as enhancers of immune cell-induced cancer cell death.

RESULTS

The lipophilic statin pitavastatin had the most potent anti-cancer effect. Further analysis demonstrated that pitavastatin treatment induced a pro-inflammatory cytokine profile as well as an overall pro-inflammatory gene expression profile in our tumor-immune model.

CONCLUSION

Our study provides an in vitro phenotypic screening approach for the identification of immunomodulatory agents and thus addresses a critical gap in the field of immuno-oncology. Our pilot screen identified statins, a drug family gaining increasing interest as repurposing candidates for cancer treatment, as enhancers of immune cell-induced cancer cell death. We speculate that the clinical benefits described for cancer patients receiving statins are not simply caused by a direct effect on the cancer cells but rather are dependent on the combined effect exerted on both cancer and immune cells.

Combined PARP inhibitors and small molecular inhibitors in solid tumor treatment (Review)

With the development of precision medicine, targeted therapy has attracted extensive attention. Poly(ADP‑ribose) polymerase inhibitors (PARPi) are critical clinical drugs designed to induce cell death and are major antitumor targeted agents. However, preclinical and clinical data have revealed the limitations of PARPi monotherapy. Therefore, their combination with other targeted drugs has become a research hotspot in tumor treatment. Recent studies have demonstrated the critical role of small molecular inhibitors in multiple haematological cancers and solid tumors via cellular signalling modulation, exhibiting potential as a combined pharmacotherapy. In the present review, studies focused on small molecular inhibitors targeting the homologous recombination pathway were summarized and clinical trials evaluating the safety and efficacy of combined treatment were discussed.

Small-Molecule PROTACs for Cancer Immunotherapy

Unsatisfactory physicochemical properties of macromolecular drugs seriously hinder their application in tumor immunotherapy. However, these problems can be effectively solved by small-molecule compounds. In the promising field of small-molecule drug development, proteolysis targeting chimera (PROTAC) offers a novel mode of action in the interactions between small molecules and therapeutic targets (mainly proteins). This revolutionary technology has shown considerable impact on several proteins related to tumor survival but is rarely exploited in proteins associated with immuno-oncology up until now. This review attempts to comprehensively summarize the well-studied and less-developed immunological targets available for PROTAC technology, as well as some targets to be explored, aiming to provide more options and opportunities for the development of small-molecule-based tumor immunotherapy. In addition, some novel directions that can magnify and broaden the protein degradation efficiency are mentioned to improve PROTAC design in the future.

PD-L1 Over-Expression Varies in Different Subtypes of Lung Cancer: Will This Affect Future Therapies?

Programmed death-ligand (PD-L) 1 and 2 are ligands of programmed cell death 1 (PD-1) receptor. They are members of the B7/CD28 ligand-receptor family and the most investigated inhibitory immune checkpoints at present. PD-L1 is the main effector in PD-1-reliant immunosuppression, as the PD-1/PD-L pathway is a key regulator for T-cell activation. Activation of T-cells warrants the upregulation of PD-1 and production of cytokines which also upregulate PD-L1 expression, creating a positive feedback mechanism that has an important role in the prevention of tissue destruction and development of autoimmunity. In the context of inadequate immune response, the prolonged antigen stimulation leads to chronic PD-1 upregulation and T-cell exhaustion. In lung cancer patients, PD-L1 expression levels have been of special interest since patients with non-small cell lung cancer (NSCLC) demonstrate higher levels of expression and tend to respond more favorably to the evolving PD-1 and PD-L1 inhibitors. The Food and Drug Administration (FDA) has approved the PD-1 inhibitor, pembrolizumab, alone as front-line single-agent therapy instead of chemotherapy in patients with NSCLC and PD-L1 ≥1% expression and chemoimmunotherapy regimens are available for lower stage disease. The National Comprehensive Cancer Network (NCCN) guidelines also delineate treatment by low and high expression of PD-L1 in NSCLC. Thus, studying PD-L1 overexpression levels in the different histological subtypes of lung cancer can affect our approach to treating these patients. There is an evolving role of immunotherapy in the other sub-types of lung cancer, especially small cell lung cancer (SCLC). In addition, within the NSCLC category, squamous cell carcinomas and non-G12C KRAS mutant NSCLC have no specific targetable therapies to date. Therefore, assessment of the PD-L1 expression level among these subtypes of lung cancer is required, since lung cancer is one of the few malignances wherein PD-L1 expression levels is so crucial in determining the role of immunotherapy. In this study, we compared PD-L1 expression in lung cancer according to the histological subtype of the tumor.

Computational discovery of small drug-like compounds as potential inhibitors of PD-1/PD-L1 interactions

The programmed cell death ligand protein 1 (PD-L1) is a strong immunosuppressive molecule that inactivates tumor-specific T cells by binding to the programmed cell death- 1 protein (PD-1). Cancer immunotherapy based on the monoclonal antibodies targeting the PD-1/PD-L1 pathway has demonstrated therapeutic responses without precedent over a wide range of cancers. However, the antibody-based immunotherapies have several limitations such as high production cost or the induction of severe immune-related adverse effects. Small-molecule inhibitors of the PD-1/PD-L1 pathway are a promising alternative or complementary therapeutic to antibodies. Currently, the field of developing anti-PD-1/PD-L1 small-molecule inhibitors is intensively explored. In the present study a pharmacophore model was generated based on previously developed compounds and their atomistic structures with the PD-L1 dimer. Structure-based affinity-based virtual screening of small-molecule inhibitors of the PD-1/PD-L1 pathway according to the pharmacophore model followed by a screening in terms of drug-likeness resulted in ten hit compounds of high affinity towards the PD-L1 dimer and the satisfaction to all of the drug-likeness rules. Molecular dynamics (MD) simulations showed that nine of ten compounds formed stable complexes with the PD-L1 dimer as evidenced by the analysis of MD trajectories. Molecular mechanics Poisson- Boltzmann surface area (MM-PBSA) calculation revealed very low binding energies (<-46 kcal/mol) for the interactions of these ligands with the PD-L1 dimer, suggesting that identified compounds may serve as good scaffolds for the design of novel agents of antitumor immunotherapy able to target the PD-1/PD-L1 interactionCommunicated by Ramaswamy H. Sarma.

A review on structurally diversified synthesized molecules as monoacylglycerol lipase inhibitors and their therapeutic uses

Monoacylglycerol is a metabolic key serine hydrolase, engaged in the regulation of signalling network system of endocannabinoids, which is associated with various physiological processes like pain, inflammation, feeding cognition and neurodegenerative diseases like Alzheimer, Parkinson's disease. The monoacylglycerol also found to act as a regulator and the free fatty acid provider in the proliferation of cancer cells, numerous aggressive tumours such as colorectal cancer, neuroblastoma and nasopharyngeal carcinoma. It also played an important role in increasing the concentration of specific lipids derived from free fatty acids like phosphatidic acid, lysophosphatidic acid, sphingosine-1-phosphate and prostaglandin E2. These signalling lipids are associated with cell proliferation, survival, tumour cell migration, contributing to tumour development, maturation and metastases. In the present study here, we are presenting a review on structurally diverse MAGL inhibitors, their development and their evaluation for different pharmacological activities.

pH-programmed responsive nanoplatform for synergistic cancer therapy based on single atom catalysts

The development of stimuli-responsive nanoplatform provides powerful tool for simultaneously enhancing the efficiency and accuracy of cancer therapies. Herein, we develop a pH-programmed responsive and synergistically theranostic nanoplatform based on CaCO₃ mineralized single atom iron nanoparticles (SAF NPs). Basically, the highly active site on SAF NPs nanoagent can trigger in-situ produce toxic •OH in tumor microenvironment (TME) that kill cancer cells for Fenton-reaction-based chemodynamic therapy (CDT). The porous structure of SAF NPs can serve as delivery platforms to package and programmed release chemotherapeutic drug doxorubicin (DOX) to enhance chemotherapy (CT) efficiency. The nanoplatform was simultaneously in-situ mineralized with CaCO₃ and A549 cell membrane (CM) which could avoid DOX leakage during transport in bloodstream and target homologous cancer cells. In addition, overload Ca²⁺ decomposed from CaCO₃ triggers mitochondrial dysfunction, induces cytoskeleton collapse and oxidative stress to formulate calcium ions interference therapy (CIT). With the combination of CDT, CT and CIT, the designed multi-synergetic nanoplatform exhibits excellent biocompatibility, specificity and tunable drug release behavior, which has a broad application prospect in tumor therapy.

Fused pyrrolo-pyridines and pyrrolo-(iso)quinoline as anticancer agents

This work emphasizes the synthesis strategies and antiproliferative related properties of fused pyrrolo-pyridine (including indolizine and azaindoles) and pyrrolo-(iso)quinoline derivatives recently reported in literature.

Pure drug nano-assemblies: A facile carrier-free nanoplatform for efficient cancer therapy

Nanoparticulate drug delivery systems (Nano-DDSs) have emerged as possible solution to the obstacles of anticancer drug delivery. However, the clinical outcomes and translation are restricted by several drawbacks, such as low drug loading, premature drug leakage and carrier-related toxicity. Recently, pure drug nano-assemblies (PDNAs), fabricated by the self-assembly or co-assembly of pure drug molecules, have attracted considerable attention. Their facile and reproducible preparation technique helps to remove the bottleneck of nanomedicines including quality control, scale-up production and clinical translation. Acting as both carriers and cargos, the carrier-free PDNAs have an ultra-high or even 100% drug loading. In addition, combination therapies based on PDNAs could possibly address the most intractable problems in cancer treatment, such as tumor metastasis and drug resistance. In the present review, the latest development of PDNAs for cancer treatment is overviewed. First, PDNAs are classified according to the composition of drug molecules, and the assembly mechanisms are discussed. Furthermore, the co-delivery of PDNAs for combination therapies is summarized, with special focus on the improvement of therapeutic outcomes. Finally, future prospects and challenges of PDNAs for efficient cancer therapy are spotlighted.

Multifunctional Nanosystems with Enhanced Cellular Uptake for Tumor Therapy

Rapid development of nanotechnology provides promising strategies in biomedicine, especially in tumor therapy. In particular, the cellular uptake of nanosystems is not only a basic premise to realize various biomedical applications, but also a fatal factor for determining the final therapeutic effect. Thus, a systematic and comprehensive summary is necessary to overview the recent research progress on the improvement of nanosystem cellular uptake for cancer treatment. According to the process of nanosystems entering the body, they can be classified into three categories. The first segment is to enhance the accumulation and permeation of nanosystems to tumor cells through extracellular microenvironment stimulation. The second segment is to improve cellular internalization from extracellular to intracellular via active targeting. The third segment is to enhance the intracellular retention of therapeutics by subcellular localization. The major factors in the delivery can be utilized to develop multifunctional nanosystems for strengthening the tumor therapy. Ultimately, the key challenges and prospective in the emerging research frontier are thoroughly outlined. This review is expected to provide inspiring ideas, promising strategies and potential pathways for developing advanced anticancer nanosystems in clinical practice.

Developments of CRBN-based PROTACs as potential therapeutic agents

Protease-targeted chimeras (PROTACs) are a new technology that is receiving much attention in the treatment of diseases. The mechanism is to inhibit protein function by hijacking the ubiquitin E3 ligase for protein degradation. Heterogeneous bifunctional PROTACs contain a ligand for recruiting E3 ligase, a linker, and another ligand to bind to the target protein for degradation. A variety of small-molecule PROTACs (CRBN, VHL, IAPs, MDM2, DCAF15, DCAF16, and RNF114-based PROTACs) have been identified so far. In particular, CRBN-based PROTACs (e.g., ARV-110 and ARV-471) have received more attention for their promising therapeutic intervention. To date, CRBN-based PRTOACs have been extensively explored worldwide and have excelled not only in cancer diseases but also in cardiovascular diseases, immune diseases, neurodegenerative diseases, and viral infections. In this review, we will provide a comprehensive update on the latest research progress in CRBN-based PRTOACs area. Following the criteria, such as disease area and drug target class, we will present the degradants in alphabetical order by target. We also provide our own perspective on the future prospects and potential challenges facing PROTACs.

Interfering with the Tumor-Immune Interface: Making Way for Triazine-Based Small Molecules as Novel PD-L1 Inhibitors

The inhibition of the PD-1/PD-L1 axis by monoclonal antibodies has achieved remarkable success in treating a growing number of cancers. However, a novel class of small organic molecules, with BMS-202 (1) as the lead, is emerging as direct PD-L1 inhibitors. Herein, we report a series of 2,4,6-tri- and 2,4-disubstituted 1,3,5-triazines, which were synthesized and assayed for their PD-L1 binding by NMR and homogeneous time-resolved fluorescence. Among them, compound 10 demonstrated to strongly bind with the PD-L1 protein and challenged it in a co-culture of PD-L1 expressing cancer cells (PC9 and HCC827 cells) and peripheral blood mononuclear cells enhanced antitumor immune activity of the latter. Compound 10 significantly increased interferon γ release and apoptotic induction of cancer cells, with low cytotoxicity in healthy cells when compared to 1, thus paving the way for subsequent preclinical optimization and medical applications.

Advances in Pancreatic Ductal Adenocarcinoma Treatment

Pancreatic Ductal Adenocarcinoma (PDAC) is one of the deadliest malignancies among all cancers. Despite curative intent, surgery and the use of standard cytotoxic chemotherapy and radiation therapy, PDAC remains treatment-resistant. In recent years, more contemporary treatment modalities such as immunotherapy via checkpoint inhibition have shown some promise in many other malignancies, yet PDAC still eludes an effective curative treatment. In investigating these phenomena, research has suggested that the significant desmoplastic and adaptive tumor microenvironment (TME) of PDAC promote the proliferation of immunosuppressive cells and act as major obstacles to treatment efficacy. In this review, we explore challenges associated with the treatment of PDAC, including its unique immunosuppressive TME. This review examines the role of surgery in PDAC, recent advances in surgical approaches and surgical optimization. We further focus on advances in immunotherapeutic approaches, including checkpoint inhibition, CD40 agonists, and discuss promising immune-based future strategies, such as therapeutic neoantigen cancer vaccines as means of overcoming the resistance mechanisms which underly the dense stroma and immune milieu of PDAC. We also explore unique signaling, TME and stromal targeting via novel small molecule inhibitors, which target KRAS, FAK, CCR2/CCR5, CXCR4, PARP and cancer-associated fibroblasts. This review also explores the most promising strategy for advancement in treatment of pancreatic cancer by reviewing contemporary combinatorial approaches in efforts to overcome the treatment refractory nature of PDAC.

Structure-activity relationship and biological evaluation of 12 N-substituted aloperine derivatives as PD-L1 down-regulatory agents through proteasome pathway

Twenty-nine 12 N-substituted aloperine derivatives were synthesized and screened for suppression on PD-L1 expression in H460 cells, as a continuation of our work. Systematic structural modifications led to the identification of compound 6b as the most active PD-L1 modulator. Compound 6b could significantly down-regulate both constitutive and inductive PD-L1 expression in NSCLC cells, and successively enhance the cytotoxicity of co-cultured T cells against tumor cells at the concentration of 20 μM. Also, it exhibited a moderate in vivo anticancer efficacy against Lewis tumor xenograft with a stable PK and safety profile. The mechanism study indicated that 6b mediated the degradation of PD-L1 through a proteasome pathway, rather than a lysosome route. These results provided the powerful information for cancer immunotherapy of aloperine derivatives with unique endocyclic skeleton by targeting PD-L1 to activate immune cells to kill cancer cells.

Rational Design of Original Fused-Cycle Selective Inhibitors of Tryptophan 2,3-Dioxygenase

Tryptophan 2,3-dioxygenase (TDO2) is a heme-containing enzyme constitutively expressed at high concentrations in the liver and responsible for l-tryptophan (l-Trp) homeostasis. Expression of TDO2 in cancer cells results in the inhibition of immune-mediated tumor rejection due to an enhancement of l-Trp catabolism via the kynurenine pathway. In the study herein, we disclose a new 6-(1H-indol-3-yl)-benzotriazole scaffold of TDO2 inhibitors developed through rational design, starting from existing inhibitors. Rigidification of the initial scaffold led to the synthesis of stable compounds displaying a nanomolar cellular potency and a better understanding of the structural modulations that can be accommodated inside the active site of hTDO2.

Co-delivery of IOX1 and doxorubicin for antibody-independent cancer chemo-immunotherapy

Anti-programmed cell death-1 (PD-1)/programmed cell death-ligand 1 (PD-L1) antibodies are currently used in the clinic to interupt the PD-1/PD-L1 immune checkpoint, which reverses T cell dysfunction/exhaustion and shows success in treating cancer. Here, we report a histone demethylase inhibitor, 5-carboxy-8-hydroxyquinoline (IOX1), which inhibits tumour histone demethylase Jumonji domain-containing 1A (JMJD1A) and thus downregulates its downstream β-catenin and subsequent PD-L1, providing an antibody-independent paradigm interrupting the PD-1/PD-L1 checkpoint. Synergistically, IOX1 inhibits cancer cells’ P-glycoproteins (P-gp) through the JMJD1A/β-catenin/P-gp pathway and greatly enhances doxorubicin (DOX)-induced immune-stimulatory immunogenic cell death. As a result, the IOX1 and DOX combination greatly promotes T cell infiltration and activity and significantly reduces tumour immunosuppressive factors. Their liposomal combination reduces the growth of various murine tumours, including subcutaneous, orthotopic, and lung metastasis tumours, and offers a long-term immunological memory function against tumour rechallenging. This work provides a small molecule-based potent cancer chemo-immunotherapy.

Some chemotherapeutic drugs, such as doxorubicin, induce immunogenic cell death (ICD) and promote anti-tumor immune responses. Here the authors report that the histone demethylase inhibitor 5-carboxy-8-hydroxyquinoline (IOX1) reduces the expression of PD-L1 in cancer cells and enhances doxorubicin-induced ICD, promoting T cell infiltration and reducing tumor growth in preclinical models.

If small molecules immunotherapy comes, can the prime be far behind?

Anti-cancer immunotherapy, which includes cellular immunotherapy, immune checkpoint inhibitors and cancer vaccines, has transformed the treatment strategies of several malignancies in the past decades. Immune checkpoints blockade (ICB) is the most commonly tested therapy and has the potential to induce a durable immune response in different types of cancers. However, all approved immune checkpoint inhibitors (ICIs) are monoclonal antibodies (mAbs), which are fraught with disadvantages including lack of oral bioavailability, prolonged tissue retention and poor membrane permeability. Therefore, the research focus has shifted to developing small molecule inhibitors to obviate the limitations of mAbs. Given the complexity of the tumor micro-environment (TME), the combination of ICIs with various small molecule agonists/inhibitors are currently being tested in clinical trials to improve treatment outcomes and prevent tumor recurrence. In this review, we have summarized the mechanisms and therapeutic potential of several molecular targets, along with the current status of small molecule inhibitors.

Systematic insight into the active constituents and mechanism of Guiqi Baizhu for the treatment of gastric cancer

Traditional Chinese medicine treatment of diseases has been recognized, but the material basis and mechanisms are not clear. In this study, target prediction of the antigastric cancer (GC) effect of Guiqi Baizhu (GQBZP) and the analysis of potential key compounds, key targets, and key pathways for the therapeutic effects against GC were carried out based on the method of network analysis and Kyoto Encyclopedia of Genes and Genomes enrichment. There were 33 proteins shared between GQBZP and GC, and 131 compounds of GQBZP had a high correlation with these proteins, indicating that the PI3K‐AKT signaling pathway might play a key role in GC. From these studies, we selected human epidermal growth factor receptor 2 (HER2) and programmed cell death 1‐ligand 1 (PD‐L1) for docking; the results showed that 385 and 189 compounds had high docking scores with HER2 and PD‐L1, respectively. Six compounds were selected for microscale thermophoresis (MST). Daidzein/quercetin and isorhamnetin/formononetin had the highest binding affinity for HER2 and PD‐L1, with K_d values of 3.7 μmol/L and 490, 667, and 355 nmol/L, respectively. Molecular dynamics simulation studies based on the docking complex structures as the initial conformation yielded the binding free energy between daidzein/quercetin with HER2 and isorhamnetin/formononetin with PD‐L1, calculated by molecular mechanics Poisson‐Boltzmann surface area, of −26.55, −14.18, −19.41, and −11.86 kcal/mol, respectively, and were consistent with the MST results. In vitro experiments showed that quercetin, daidzein, and isorhamnetin had potential antiproliferative effects in MKN‐45 cells. Enzyme activity assays showed that quercetin could inhibit the activity of HER2 with an IC₅₀ of 570.07 nmol/L. Our study provides a systematic investigation to explain the material basis and molecular mechanism of traditional Chinese medicine in treating diseases.

Discovery of novel CA-4 analogs as dual inhibitors of tubulin polymerization and PD-1/PD-L1 interaction for cancer treatment

A series of novel CA-4 analogs as dual inhibitors of tubulin polymerization and PD-1/PD-L1 were designed, synthesized and bio-evaluated. Among them, compound TP5 exhibited strongest inhibitory effects against five cancer cell lines with an IC50 value of 800 nM in HepG2 cells. In addition, mechanism studies revealed that TP5 could effectively inhibit tubulin polymerization, suppress HepG2 cells migration and colony formation, and cause cell arrest at G2/M phase and induce apoptosis. Furthermore, TP5 exhibited moderate anti-PD-1/PD-L1 activity with IC50 values of 48.76 μM in a homogenous time-resolved fluorescence (HTRF) assay. In vivo efficacy studies indicated that TP5 could significantly suppress tumor growth in an immune checkpoint humanized mouse model with a Tumor Growth Suppression (TGI) of 57.9% at 100 mg/kg without causing significant toxicity. Moreover, TP5 did not cause in vivo cardiotoxicity in BALB/c mice. These results suggest that the novel CA-4 analogs may serve as a starting point for developing more potent dual inhibitors of tubulin polymerization and PD-1/PD-L1.

UBE2S interacting with TRIM28 in the nucleus accelerates cell cycle by ubiquitination of p27 to promote hepatocellular carcinoma development

Genomic sequencing analysis of tumors provides potential molecular therapeutic targets for precision medicine. However, identifying a key driver gene or mutation that can be used for hepatocellular carcinoma (HCC) treatment remains difficult. Here, we performed whole-exome sequencing on genomic DNA obtained from six pairs of HCC and adjacent tissues and identified two novel somatic mutations of UBE2S (p. Gly57Ala and p. Lys63Asn). Predictions of the functional effects of the mutations showed that two amino-acid substitutions were potentially deleterious. Further, we observed that wild-type UBE2S, especially in the nucleus, was significantly higher in HCC tissues than that in adjacent tissues and closely related to the clinicopathological features of patients with HCC. Functional assays revealed that overexpression of UBE2S promoted the proliferation, invasion, metastasis, and G1/S phase transition of HCC cells in vitro, and promoted the tumor growth significantly in vivo. Mechanistically, UBE2S interacted with TRIM28 in the nucleus, both together enhanced the ubiquitination of p27 to facilitate its degradation and cell cycle progression. Most importantly, the small-molecule cephalomannine was found by a luciferase-based sensitive high-throughput screen (HTS) to inhibit UBE2S expression and significantly attenuate HCC progression in vitro and in vivo, which may represent a promising strategy for HCC therapy.

Small molecular drugs reshape tumor microenvironment to synergize with immunotherapy

Recently, immune checkpoint blockade (ICB), especially anti-programmed death 1 (anti-PD-1) and anti-programmed death-ligand 1 (anti-PD-L1) therapy, has become an increasingly appealing therapeutic strategy for cancer patients. However, only a small portion of patients responds to anti-PD treatment. Therefore, treatment strategies are urgently needed to reverse the ICB-resistant tumor microenvironment (TME). It has become clear that the TME has diminished innate sensing that is critical to activate adaptive immunity. In addition, tumor cells upregulate various immunosuppressive factors to diminish the immune response and resist immunotherapy. In this review, we briefly update the current small molecular drugs that could synergize with immunotherapy, especially anti-PD therapy. We will discuss the modes of action by those drugs including inducing innate sensing and limiting immunosuppressive factors in the TME.

Discovery of a new inhibitor targeting PD-L1 for cancer immunotherapy

Blockade of the PD-1/PD-L1 immunologic checkpoint using monoclonal antibodies has provided breakthrough therapies against cancer in the recent years. Nevertheless, intrinsic disadvantages of therapeutic antibodies may limit their applications. Thus, blocking of the PD-1/PD-L1 interaction by small molecules may be a promising alternative for cancer immunotherapy. We used a docking-based virtual screening strategy to rapidly identify new small molecular inhibitors targeting PD-L1. We demonstrated that a small molecule compound (N-[2-(aminocarbonyl)phenyl][1,1′-biphenyl]-4-carboxamide [APBC]) could effectively interrupt the PD-1/PD-L1 interaction by directly binding to PD-L1, presenting the K_D and IC₅₀ values at low-micromolar level. Molecular docking study revealed that APBC may have function through a PD-L1 dimer-locking mechanism, occluding the PD-1 interaction surface of PD-L1. We further confirmed the ligand blocking activity and T cell-reinvigoration potency of APBC using cell-based assays. APBC could dose-dependently elevate cytokine secretions of the primary T-lymphocytes that are cocultured with cancer cells. Importantly, APBC displayed superior antitumor efficacy in hPD-L1 knock-in B16F10-bearing mouse model without the induction of observable liver toxicity. Analyses on the APBC-treated mice further revealed drastically elevated levels of infiltrating CD4⁺ and CD8⁺ T cells, and inflammatory cytokines production in tumor microenvironment. The APBC compound could serve as a privileged scaffold in the design of improved PD pathway modulators, thus providing us promising drug candidates for tumor immunotherapy.

A theranostic probe of indoleamine 2,3-dioxygenase 1 (IDO1) for small molecule cancer immunotherapy

Discovering novel small molecules for cancer immunotherapy represents a promising but challenging strategy in future cancer treatment. Herein, we designed the first theranostic fluorescent probes to efficiently detect and inhibit the enzymatic activity of 2,3-dioxygenase 1 (IDO1). Probe 6b is a highly active IDO1 inhibitor (IC₅₀ = 12 nM, Cellular IC₅₀ = 10 nM), which can sensitively and specifically detect endogenous IDO1 in living cells. Furthermore, as a theranostic probe, 6b showed excellent in vivo antitumor efficacy in the CT26 xenograft mouse model as well. Therefore, it can be applied as a valuable chemical tool for better understanding the immunotherapy mechanism of IDO1 and improving the therapeutic efficiency.

Discovery of Novel and Highly Potent Resorcinol Dibenzyl Ether-Based PD-1/PD-L1 Inhibitors with Improved Drug-like and Pharmacokinetic Properties for Cancer Treatment

A series of programmed cell death-1 (PD-1)/programmed cell death ligand 1 (PD-L1) inhibitors based on the resorcinol diphenyl ether scaffold were discovered by incorporating hydrophilic moieties into the side chain and converting into the corresponding hydrochloride salt. Among these compounds, P18 showed the highest inhibitory activity against PD-1/PD-L1 with an IC50 value of 9.1 nM in a homogeneous time-resolved fluorescence binding assay. Besides, P18 promoted HepG2 cell death dose dependently in a HepG2/PD-L1 and Jurkat/PD-1 coculture cell model. Further, P18 demonstrated significantly higher water solubility (17.61 mg/mL) and improved pharmacokinetics (e.g., t1/2 of ∼20 h and oral bioavailability of 12%) than the previous analogues. Moreover, P18 was highly effective in suppressing tumor growth in an immune checkpoint humanized mouse model without apparent toxicity. Collectively, these results suggest that compound P18 represents a promising PD-1/PD-L1 inhibitor worthy of further investigation as a potential anticancer agent.

Structures/cytotoxicity/selectivity relationship of natural steroidal saponins against GSCs and primary mechanism of tribulosaponin A

Glioblastoma multiform (GBM) is the highly aggressive brain tumor with poor prognosis. Glioma stem cells (GSCs), small population of cancer cells that exist in GBM tissues, resistant to chemotherapy and radiotherapy and usually driving GBM recurrence, have been developed as effective therapeutic target. Steroidal saponins are one of important resources for anti-tumor agent and may be benefited to selectively clear GSCs. In this report, total of 97 natural steroidal saponins were investigated the relationship among structures/cytotoxicity/selectivity against GSCs, glioma cell lines and human untransformed cells, and revealed that tribulosaponin A was the most potent compound. Further investigation suggested that tribulosaponin A up-regulated the expression of NCF1 and NOX1 to accumulate ROS for triggering apoptosis in GSCs, but not in untransformed cells, and it was further supported by the assay that N-acetyl-l-cysteine (NAC) clearing ROS delayed GSCs apoptosis. Besides, tribulosaponin A damaged GSCs recapturing tumor spheres formation.

Small molecules targeting the innate immune cGAS‒STING‒TBK1 signaling pathway

Multiple cancer immunotherapies including chimeric antigen receptor T cell and immune checkpoint inhibitors (ICIs) have been successfully developed to treat various cancers by motivating the adaptive anti-tumor immunity. Particularly, the checkpoint blockade approach has achieved great clinic success as evidenced by several U.S. Food and Drug Administration (FDA)-approved anti-programmed death receptor 1/ligand 1 or anti-cytotoxic T lymphocyte associated protein 4 antibodies. However, the majority of cancers have low clinical response rates to these ICIs due to poor tumor immunogenicity. Indeed, the cyclic guanosine monophosphate-adenosine monophosphate synthase‒stimulator of interferon genes‒TANK-binding kinase 1 (cGAS‒STING‒TBK1) axis is now appreciated as the major signaling pathway in innate immune response across different species. Aberrant signaling of this pathway has been closely linked to multiple diseases, including auto-inflammation, virus infection and cancers. In this perspective, we provide an updated review on the latest progress on the development of small molecule modulators targeting the cGAS‒STING‒TBK1 signaling pathway and their preclinical and clinical use as a new immune stimulatory therapy. Meanwhile, highlights on the clinical candidates, limitations and challenges, as well as future directions in this field are also discussed. Further, small molecule inhibitors targeting this signaling axis and their potential therapeutic use for various indications are discussed as well.

Injectable Reactive Oxygen Species-Responsive SN38 Prodrug Scaffold with Checkpoint Inhibitors for Combined Chemoimmunotherapy

Chemotherapeutic agents have been widely used for cancer treatment in clinics. Aside from their direct cytotoxicity to cancer cells, some of them could activate the immune system of the host, contributing to the enhanced antitumor activity. Here, the reactive oxygen species (ROS)-responsive hydrogel, covalently cross-linked by phenylboronic acid-modified 7-ethyl-10-hydroxycamptothecin (SN38-SA-BA) with poly(vinyl alcohol) (PVA), is fabricated for topical delivery of anti-programmed cell death protein ligand 1 antibodies (aPDL1). In the presence of endogenous ROS, SN38-SA-BA will be oxidized and hydrolyzed, leading to the degradation of hydrogel and the release of initial free SN38 and encapsulated aPDL1. It is demonstrated that SN38 could elicit specific immune responses by triggering immunogenic cell death (ICD) of cancer cells, a distinct cell death pathway featured with the release of immunostimulatory damage-associated molecular patterns (DAMPs). Meanwhile, the released aPDL1 could bind to programmed cell death protein ligand 1 (PDL1) expressed on cancer cells to augment antitumor T cell responses. Thus, the ROS-responsive prodrug hydrogel loaded with aPDL1 could induce effective innate and adaptive antitumor immune responses after local injection, significantly inhibiting or even eliminating those tumors.

Neothalfine, a potent natural anti-tumor agent against metastatic colorectal cancer and its primary mechanism

Neothalfine is a natural bisbenzylisoquinoline alkaloid with the abundant resource in medicinal plants and has not been reported its anti-tumor efficacy. In the present study, the anti-tumor efficacy was investigated and it showed broad-spectrum activity against several cancer cell lines, especially metastatic colorectal cancer (HCT116, SW620, T84) with the IC₅₀ values of 7.2, 5.9, 8.2 nM, respectively, roughly equal to well-known anti-tumor agent docetaxel (4.0, 4.7, 2.7 nM) and nearly 1000 folds than CPT-11 (4.4, 5.1, 6.9 μM). Furthermore, neothalfine inhibited colorectal cell proliferation by resulting in cell cycle arrest at the G2/M phase and induced apoptosis through the dysfunction of mitochondria to trigger intrinsic apoptotic pathway by untargeted metabolomic method, mitochondrial membrane potential, and caspase-3/7 activity assay. Moreover, neothalfine damaged colorectal cancer clonal spheres expansion significantly at the concentration of 3.5 nM with nearly 1000 folds efficacy than CPT-11 (3.0 µM). The results supported that neothalfine might be an anti-tumor lead for further investigation.

Development of small molecule inhibitors/agonists targeting STING for disease

Cyclic guanosine monophosphate-adenosine monophosphate synthase (cGAS) -stimulator of interferon genes (STING) signaling pathway is the primary immune response pathway in the cytoplasm. Pharmacological regulation of the STING pathway has good characteristics in both structure and function, which plays a significant role in the immunotherapy of autoimmune diseases, autoinflammatory diseases, and cancer. In this review, we summarized the activation of STING signaling pathway, the STING-related diseases, the development principle and the latest progress of inhibitors and agonists targeting STING. Our review demonstrates that STING signal pathway is a promising drug target, providing effective clues and correct guidance for the discovery of novel small molecule inhibitors/agonists that targeted STING for cancer, autoimmune, and inflammatory diseases.

Partial Least-Squares Discriminant Analysis and Ensemble-Based Flexible Docking of PD-1/PD-L1 Inhibitors: A Pilot Study

Although mAbs targeting the programmed cell death protein 1 (PD-1)/programmed cell death ligand 1 (PD-L1) pathway have achieved remarkable therapeutic potential against multiple types of cancer, it is still of great interest for researchers to develop small-molecule PD-1/PD-L1 inhibitors without the mAb-related disadvantages of no oral bioavailability and poor solid tumor penetration. However, targeting the PD-1/PD-L1 pathway with small molecules is normally considered challenging because of the flat and large interaction surface of the PD-1/PD-L1 complex. In this paper, a total of 2558 PD-1/PD-L1 inhibitors were compiled from recent patents and literatures and then used for exploring the chemical space and structural features of PD-1/PD-L1 inhibitors by partial least-squares discriminant analysis. The results showed that intramolecular H bond, amphotericity indices, radius of gyration, nonbond electrostatic energy, fractional van der Waals surface area of H-bond donors, octanol-water partition coefficient, and molecular weight are the seven key features discriminating the PD-1/PD-L1 inhibitors from noninhibitors, with the prediction accuracy larger than 0.90. Based on the seven crystal structures of the PD-L1 dimer complexed with the patent Bristol Myers Squibb (BMS) inhibitors, the feasibility of molecular docking for this unconventional binding pocket was further investigated. The results showed that the ensemble-based flexible docking protocol can reproduce the near-native binding conformations of the BMS inhibitors with a strong correlation between the IC₅₀ values and ligand-receptor interaction energies (R = 0.81). In general, this paper delineates, for the first time, the characteristic features of the PD-1/PD-L1 inhibitors as well as a high-quality flexible docking strategy for the unconventional binding pocket of the PD-L1 dimer.

Modulation of the Innate Immune Response by Targeting Toll-like Receptors: A Perspective on Their Agonists and Antagonists

Toll-like receptors (TLRs) are a class of proteins that recognize pathogen-associated molecular patterns (PAMPs) and damaged-associated molecular patterns (DAMPs), and they are involved in the regulation of innate immune system. These transmembrane receptors, localized at the cellular or endosomal membrane, trigger inflammatory processes through either myeloid differentiation primary response 88 (MyD88) or TIR-domain-containing adapter-inducing interferon-β (TRIF) signaling pathways. In the last decades, extensive research has been performed on TLR modulators and their therapeutic implication under several pathological conditions, spanning from infections to cancer, from metabolic disorders to neurodegeneration and autoimmune diseases. This Perspective will highlight the recent discoveries in this field, emphasizing the role of TLRs in different diseases and the therapeutic effect of their natural and synthetic modulators, and it will discuss insights for the future exploitation of TLR modulators in human health.

Small molecules as antagonists of co-inhibitory pathways for cancer immunotherapy: a patent review (2018-2019)

INTRODUCTION

Therapeutic antibodies blocking co-inhibitory pathways do not attack tumor cells directly, but instead bind to their targeted proteins and mobilize the immune system to eradicate tumors. However, only a small fraction of patients with certain cancer types can benefit from the antibodies. Additionally, antibodies have shown serious immune-related adverse events in certain patients. Small-molecule antagonists may be a complementary and potentially synergistic approach to antibodies for patients with various cancers.

AREAS COVERED

The authors review the small molecules as antagonists of co-inhibitory pathway proteins, summarize their preliminary SARs, discuss biochemistry assays used in patents for the development of small molecules as novel antagonists.

EXPERT OPINION

The disclosed pharmacophores of small molecules as co-inhibitory pathway antagonists are represented by biphenyl derivatives, biaryl derivatives, teraryl derivatives, quateraryl derivatives, and oxadiazole/thiadiazole derivatives. However, these antagonists are still inferior to therapeutic antibodies in their inhibitory activities due to relatively flat of human co-inhibitory pathways proteins. Allosteric modulators may be an alternative approach. The more safety and efficacy evaluation trials of small-molecule antagonists targeting co-inhibitory pathways should be performed to demonstrate the proof-of-principle that small-molecule antagonists can result in sustained safety and antitumor response in the near future.