Inhibition of GFAT1 in lung cancer cells destabilizes PD-L1 protein

Emerging therapeutic frontiers in cancer: insights into posttranslational modifications of PD-1/PD-L1 and regulatory pathways

The interaction between programmed cell death ligand 1 (PD-L1), which is expressed on the surface of tumor cells, and programmed cell death 1 (PD-1), which is expressed on T cells, impedes the effective activation of tumor antigen-specific T cells, resulting in the evasion of tumor cells from immune-mediated killing. Blocking the PD-1/PD-L1 signaling pathway has been shown to be effective in preventing tumor immune evasion. PD-1/PD-L1 blocking antibodies have garnered significant attention in recent years within the field of tumor treatments, given the aforementioned mechanism. Furthermore, clinical research has substantiated the efficacy and safety of this immunotherapy across various tumors, offering renewed optimism for patients. However, challenges persist in anti-PD-1/PD-L1 therapies, marked by limited indications and the emergence of drug resistance. Consequently, identifying additional regulatory pathways and molecules associated with PD-1/PD-L1 and implementing judicious combined treatments are imperative for addressing the intricacies of tumor immune mechanisms. This review briefly outlines the structure of the PD-1/PD-L1 molecule, emphasizing the posttranslational modification regulatory mechanisms and related targets. Additionally, a comprehensive overview on the clinical research landscape concerning PD-1/PD-L1 post-translational modifications combined with PD-1/PD-L1 blocking antibodies to enhance outcomes for a broader spectrum of patients is presented based on foundational research.

Recent advances and mechanisms of action of PD-L1 degraders as potential therapeutic agents

PD-L1 is an important immune checkpoint protein that can bind to T cells' PD-1 receptor, thereby promoting immune escape from tumors. In recent years, many researchers have developed strategies to degrade PD-L1 to improve the effect of immunotherapy. The study of degrading PD-L1 provides new opportunities for immunotherapy. Here, we mainly summarize and review the current active molecules and mechanisms that mediate the degradation of immature and mature PD-L1 during the post-translational modification stages, involving PD-L1 phosphorylation, glycosylation, palmitoylation, ubiquitination, and the autophagy-lysosomal process. This review expects that by degrading PD-L1 protein, we will not only gain a better understanding of oncogenic mechanisms involving tumor PD-L1 protein but also provide a new way to improve immunotherapy.

Nutlin-3a induces KRAS mutant/p53 wild type lung cancer specific methuosis-like cell death that is dependent on GFPT2

BACKGROUND

Oncogenic KRAS mutation, the most frequent mutation in non-small cell lung cancer (NSCLC), is an aggressiveness risk factor and leads to the metabolic reprogramming of cancer cells by promoting glucose, glutamine, and fatty acid absorption and glycolysis. Lately, sotorasib was approved by the FDA as a first-in-class KRAS-G12C inhibitor. However, sotorasib still has a derivative barrier, which is not effective for other KRAS mutation types, except for G12C. Additionally, resistance to sotorasib is likely to develop, demanding the need for alternative therapeutic strategies.

METHODS

KRAS mutant, and wildtype NSCLC cells were used in vitro cell analyses. Cell viability, proliferation, and death were measured by MTT, cell counting, colony analyses, and annexin V staining for FACS. Cell tracker dyes were used to investigate cell morphology, which was examined by holotomograpy, and confocal microscopes. RNA sequencing was performed to identify key target molecule or pathway, which was confirmed by qRT-PCR, western blotting, and metabolite analyses by UHPLC-MS/MS. Zebrafish and mouse xenograft model were used for in vivo analysis.

RESULTS

In this study, we found that nutlin-3a, an MDM2 antagonist, inhibited the KRAS-PI3K/Akt-mTOR pathway and disrupted the fusion of both autophagosomes and macropinosomes with lysosomes. This further elucidated non-apoptotic and catastrophic macropinocytosis associated methuosis-like cell death, which was found to be dependent on GFPT2 of the hexosamine biosynthetic pathway, specifically in KRAS mutant /p53 wild type NSCLC cells.

CONCLUSION

These results indicate the potential of nutlin-3a as an alternative agent for treating KRAS mutant/p53 wild type NSCLC cells.

Current knowledge and potential intervention of hexosamine biosynthesis pathway in lung cancer

Lung cancer is a highly prevalent malignancy characterized by significant metabolic alterations. Understanding the metabolic rewiring in lung cancer is crucial for the development of effective therapeutic strategies. The hexosamine biosynthesis pathway (HBP) is a metabolic pathway that plays a vital role in cellular metabolism and has been implicated in various cancers, including lung cancer. Abnormal activation of HBP is involved in the proliferation, progression, metastasis, and drug resistance of tumor cells. In this review, we will discuss the function and regulation of metabolic enzymes related to HBP in lung cancer. Furthermore, the implications of targeting the HBP for lung cancer treatment are also discussed, along with the challenges and future directions in this field. This review provides a comprehensive understanding of the role and intervention of HBP in lung cancer. Future research focusing on the HBP in lung cancer is essential to uncover novel treatment strategies and improve patient outcomes.

Regulation of post-translational modification of PD-L1 and advances in tumor immunotherapy

The immune checkpoint molecules programmed cell death receptor 1 (PD-1) and programmed death ligand 1 (PD-L1) are one of the most promising targets for tumor immunotherapy. PD-L1 is overexpressed on the surface of tumor cells and inhibits T cell activation upon binding to PD⁃1 on the surface of T cells, resulting in tumor immune escape. The therapeutic strategy of targeting PD-1/PD-L1 involves blocking this binding and restoring the tumor-killing effect of immune cells. However, in clinical settings, a relatively low proportion of cancer patients have responded well to PD-1/PD-L1 blockade, and clinical outcomes have reached a bottleneck and no substantial progress has been made. In recent years, PD-L1 post-translation modifications (PTMs) have gradually become a hot topic in the field of PD-L1 research, which will provide new insights to improve the efficacy of current anti-PD-1/PD-L1 therapies. Here, we summarized and discussed multiple PTMs of PD-L1, including glycosylation, ubiquitination, phosphorylation, acetylation and palmitoylation, with a major emphasis on mechanism-based therapeutic strategies (including relevant enzymes and targets that are already in clinical use and that may become drugs in the future). We also summarized the latest research progress of PTMs of PD-L1/PD-1 in regulating immunotherapy. The review provided novel strategies and directions for tumor immunotherapy research based on the PTMs of PD-L1/PD-1.

The Hexosamine Biosynthesis Pathway: Regulation and Function

The hexosamine biosynthesis pathway (HBP) produces uridine diphosphate-N-acetyl glucosamine, UDP-GlcNAc, which is a key metabolite that is used for N- or O-linked glycosylation, a co- or post-translational modification, respectively, that modulates protein activity and expression. The production of hexosamines can occur via de novo or salvage mechanisms that are catalyzed by metabolic enzymes. Nutrients including glutamine, glucose, acetyl-CoA, and UTP are utilized by the HBP. Together with availability of these nutrients, signaling molecules that respond to environmental signals, such as mTOR, AMPK, and stress-regulated transcription factors, modulate the HBP. This review discusses the regulation of GFAT, the key enzyme of the de novo HBP, as well as other metabolic enzymes that catalyze the reactions to produce UDP-GlcNAc. We also examine the contribution of the salvage mechanisms in the HBP and how dietary supplementation of the salvage metabolites glucosamine and N-acetylglucosamine could reprogram metabolism and have therapeutic potential. We elaborate on how UDP-GlcNAc is utilized for N-glycosylation of membrane and secretory proteins and how the HBP is reprogrammed during nutrient fluctuations to maintain proteostasis. We also consider how O-GlcNAcylation is coupled to nutrient availability and how this modification modulates cell signaling. We summarize how deregulation of protein N-glycosylation and O-GlcNAcylation can lead to diseases including cancer, diabetes, immunodeficiencies, and congenital disorders of glycosylation. We review the current pharmacological strategies to inhibit GFAT and other enzymes involved in the HBP or glycosylation and how engineered prodrugs could have better therapeutic efficacy for the treatment of diseases related to HBP deregulation.

Dysregulation of hexosamine biosynthetic pathway wiring metabolic signaling circuits in cancer

Metabolite sensing, a fundamental biological process, plays a key role in metabolic signaling circuit rewiring. Hexosamine biosynthetic pathway (HBP) is a glucose metabolic pathway essential for the synthesis of uridine diphosphate N-acetylglucosamine (UDP-GlcNAc), which senses key nutrients and integrally maintains cellular homeostasis. UDP-GlcNAc dynamically regulates protein N-glycosylation and O-linked-N-acetylglucosamine modification (O-GlcNAcylation). Dysregulated HBP flux leads to abnormal protein glycosylation, and contributes to cancer development and progression by affecting protein function and cellular signaling. Furthermore, O-GlcNAcylation regulates cellular signaling pathways, and its alteration is linked to various cancer characteristics. Additionally, recent findings have suggested a close association between HBP stimulation and cancer stemness; an elevated HBP flux promotes cancer cell conversion to cancer stem cells and enhances chemotherapy resistance via downstream signal activation. In this review, we highlight the prominent roles of HBP in metabolic signaling and summarize the recent advances in HBP and its downstream signaling, relevant to cancer.

Differential effects of glucose and N-acetylglucosamine on genome instability

Aberrant sugar metabolism is linked to an increased risk of pancreatic cancer. Previously, we found that high glucose induces genome instability and de novo oncogenic KRAS mutation preferentially in pancreatic cells through dysregulation of O-GlcNAcylation. Increasing O-GlcNAcylation by extrinsically supplying N-acetyl-D-glucosamine (GlcNAc) causes genome instability in all kinds of cell types regardless of pancreatic origin. Since many people consume excessive amount of sugar (glucose, fructose, and sucrose) in daily life, whether high sugar consumption directly causes genome instability in animals remains to be elucidated. In this communication, we show that excess sugar in the daily drink increases DNA damage and protein O-GlcNAcylation preferentially in pancreatic tissue but not in other kinds of tissue of mice. The effect of high sugar on the pancreatic tissue may be attributed to the intrinsic ratio of GFAT and PFK activity, a limiting factor that dictates UDP-GlcNAc levels. On the other hand, GlcNAc universally induces DNA damage in all six organs examined. Either inhibiting O-GlcNAcylation or supplementing dNTP pool diminishes the induced DNA damage in these organs, indicating that the mechanism of action is similar to that of high glucose treatment in pancreatic cells. Taken together, these results suggest the potential hazards of high sugar drinks and high glucosamine intake to genomic instability and possibly cancer initiation.

Therapeutic Potential of Glutamine Pathway in Lung Cancer

Cancer cells tend to obtain the substances needed for their development depending on altering metabolic characteristics. Among the reorganized metabolic pathways, Glutamine pathway, reprogrammed to be involved in the physiological process including energy supply, biosynthesis and redox homeostasis, occupies an irreplaceable role in tumor cells and has become a hot topic in recent years. Lung cancer currently maintains a high morbidity and mortality rate among all types of tumors and has been a health challenge that researchers have longed to overcome. Therefore, this study aimed to clarify the essential role of glutamine pathway played in the metabolism of lung cancer and its potential therapeutic value in the interventions of lung cancer.

MiR-145 modulates the radiosensitivity of non-small cell lung cancer cells by suppression of TMOD3

Radioresistance is a major problem encountered in the treatment of non-small cell lung cancer (NSCLC). Aberrant microRNA (miRNA) expression contributes to multiple cancer‑associated signaling pathways, and profoundly influences effects of radiotherapy (RT) in cancers. MicroRNA-145-5p (miR-145) is recognized as a tumor suppresser in NSCLC. However, the roles of miR-145 during radiotherapy of NSCLC are largely unknown. The present study aimed to investigate the function and underlying mechanism of miR-145 in modulation of radiosensitivity in NSCLC. We generated radioresistant H460 and A549 subclones, named H460R and A549R, respectively, and found that irradiation (IR) could suppress the expression levels of miR-145 in radioresistant NSCLC cells. Furthermore, overexpression of miR-145 could sensitize radioresistant NSCLC cells to IR, while knockdown of miR-145 in NSCLC cells acted the converse manner. Mechanically, miR-145 was able to directly target 3'UTR of tropomodulin 3 (TMOD3) mRNA and decrease the expression of TMOD3 at the levels of mRNA and protein. Additionally, we confirmed that miR-145 could enhance the radiosensitivity of radioresistant NSCLC cells by targeting TMOD3 in vitro and in vivo, and could be used as a target in clinical treatment of NSCLC. Collectively, restoration of miR-145 expression increases the radiosensitivity of radioresistant NSCLC cells by suppression of TMOD3, and miR-145 can act as a new radiosensitizer for NSCLC therapy.