Characterization of Aminobenzylphenols as Protein Disulfide Isomerase Inhibitors in Glioblastoma Cell Lines

Visualization of ferroptosis in brain diseases and ferroptosis-inducing nanomedicine for glioma

A remarkable body of new data establishes that many degenerative brain diseases and some acute injury situations in the brain may be associated with ferroptosis. In recent years, ferroptosis has also attracted great interest in the cancer research community, partly because it is a unique mode of cell death distinct from other forms and thus has great therapeutic potential for brain cancer. Glioblastoma is a highly aggressive and fatal human cancer, accounting for 60% of all primary brain tumors. Despite the development of various pharmacological and surgical modalities, the survival rates of high-grade gliomas have remained poor over the past few decades. Recent evidence has revealed that ferroptosis is involved in tumor initiation, progression, and metastasis, and manipulating ferroptosis could offer a novel strategy for glioma management. Nanoparticles have been exploited as multifunctional platforms that can cross the blood-brain barrier and deliver therapeutic agents to the brain to address the pressing need for accurate visualization of ferroptosis and glioma treatment. To create efficient and durable ferroptosis inducers, many researchers have engineered nanocomposites to induce a more effective ferroptosis for therapy. In this review, we present the mechanism of ferroptosis and outline the current strategies of imaging and nanotherapy of ferroptosis in brain diseases, especially glioma. We aim to provide up-to-date information on ferroptosis and emphasize the potential clinical implications of ferroptosis for glioma diagnosis and treatment. However, regulation of ferroptosis in vivo remains challenging due to a lack of compounds.

First-in-Class NADH/Ubiquinone Oxidoreductase Core Subunit S7 (NDUFS7) Antagonist for the Treatment of Pancreatic Cancer

Pancreatic cancer cells adapt to nutrient-scarce metabolic conditions by increasing their oxidative phosphorylation reserve to survive. Here, we present a first-in-class small-molecule NDUFS7 antagonist that inhibits oxidative phosphorylation (OXPHOS) for the treatment of pancreatic cancer. The lead compound, DX2-201, suppresses the proliferation of a panel of cell lines, and a metabolically stable analogue, DX3-213B, shows significant efficacy in a syngeneic model of pancreatic cancer. Exome sequencing of six out of six clones resistant to DX2-201 revealed a pV91M mutation in NDUFS7, providing direct evidence of its drug-binding site. In combination studies, DX2-201 showed synergy with multiple metabolic modulators, select OXPHOS inhibitors, and PARP inhibitors. Importantly, a combination with 2-deoxyglucose overcomes drug resistance in vivo. This study demonstrates that an efficacious treatment for pancreatic cancer can be achieved through inhibition of OXPHOS and direct binding to NDUFS7, providing a novel therapeutic strategy for this hard-to-treat cancer.

Inhibition of Protein Disulfide Isomerase (PDIA1) Leads to Proteasome-Mediated Degradation of Ubiquitin-like PHD and RING Finger Domain-Containing Protein 1 (UHRF1) and Increased Sensitivity of Glioblastoma Cells to Topoisomerase II Inhibitors

Glioblastoma (GBM) is the most aggressive brain tumor, and the prognosis remains poor with current available treatments. PDIA1 is considered a promising therapeutic target in GBM. In this study, we demonstrate that targeting PDIA1 results in increased GBM cell death by topoisomerase II (Top-II) inhibitors resulting in proteasome-mediated degradation of the oncogenic protein UHRF1. Combination of the PDIA1 inhibitor, bepristat-2a, produces strong synergy with doxorubicin, etoposide, and mitoxantrone in GBM and other cancer cell lines. Our bioinformatics analysis of multiple datasets revealed downregulation of UHRF1, upon PDIA1 inhibition. In addition, PDIA1 inhibition results in proteasome-mediated degradation of UHRF1 protein. Interestingly, treatment of GBM cells with bepristat-2a results in increased apoptosis and resistance to ferroptosis. Our findings emphasize the importance of PDIA1 as a therapeutic target in GBM and present a promising new therapeutic approach using Top-II inhibitors for GBM treatment.

Dual Targeting of MDM4 and FTH1 by MMRi71 for Induced Protein Degradation and p53-Independent Apoptosis in Leukemia Cells

MDM2 and MDM4 are cancer drug targets validated in multiple models for p53-based cancer therapies. The RING domains of MDM2 and non-p53-binder MDM2 splice isoforms form RING domain heterodimer polyubiquitin E3 ligases with MDM4, which regulate p53 stability in vivo and promote tumorigenesis independent of p53. Despite the importance of the MDM2 RING domain in p53 regulation and cancer development, small molecule inhibitors targeting the E3 ligase activity of MDM2-MDM4 are poorly explored. Here, we describe the synthesis and characterization of quinolinol derivatives for the identification of analogs that are capable of targeting the MDM2-MDM4 heterodimer E3 ligase and inducing apoptosis in cells. The structure-activity-relationship (SAR) study identified structural moieties critical for the inhibitory effects toward MDM2-MDM4 E3 ligase, the targeted degradation of MDM4 and FTH1 in cells, and anti-proliferation activity. Lead optimization led to the development of compound MMRi71 with improved activity. In addition to accumulating p53 proteins in wt-p53 bearing cancer cells as expected of any MDM2 inhibitors, MMRi71 effectively kills p53-null leukemia cells, an activity that conventional MDM2-p53 disrupting inhibitors lack. This study provides a prototype structure for developing MDM4/FTH1 dual-targeting inhibitors as potential cancer therapeutics.

The amino acid transporter SLC7A11-mediated crosstalk implicated in cancer therapy and the tumor microenvironment

The solute carrier family 7 member 11 (SLC7A11), an amino acid transporter protein is frequently overexpressed in human malignancies. The expression and activity of SLC7A11 is finely regulated by oncogenes and tumor suppressors in tumor cells through various mechanisms and is highly specific for cystine and glutamate. Cystine is mainly transported intracellularly by SLC7A11 in the tumor microenvironment (TME) and is involved in GSH synthesis, which leads to ferroptosis resistance in tumor cells and promotes tumorigenesis and progression. The downregulation of SLC7A11 presents a unique drug discovery opportunity for ferroptosis-related diseases. Experimental work has shown that the combination of targeting SLC7A11 and tumor immunotherapy triggers ferroptosis more potently. Moreover, immunotargeting of SLC7A11 increases the chemosensitivity of cancer stem cells to doxorubicin, suggesting that it may act as an adjuvant to chemotherapy. Thus, SLC7A11 could be a promising target to overcome resistance mechanisms in conventional cancer treatments. This review provides an overview of the regulatory network of SLC7A11 in the TME and progress in the development of SLC7A11 inhibitors. In addition, we summarize the cytotoxic effects of blocking SLC7A11 in cancer cells, cancer stem cells and immune cells.

Non-innocuous Consequences of Metabolic Oxidation of Alkyls on Arenes

Reactive metabolite (RM) formation is widely accepted as playing a pivotal role in causing adverse idiosyncratic drug reactions, with most attention paid to drug-induced liver injury. Mechanisms of RM formation are determined by the drug's properties in relation to human enzymes transforming the drug. This Perspective focuses on enzymatic oxidation of alkyl groups on aromatics leading to quinone methides and benzylic alcohol sulfates as RMs, a topic that has not received very much attention. Unlike previous overviews, we will include in our Perspective several fulvene-like methides such as 3-methyleneindole. We also speculate that a few older drugs may form non-reported methides of this class. In addition, we report a few guiding DFT calculations of changes in free energy on going from a benzylic alcohol to the corresponding methide. Particularly facile reactions of 2-aminothiazole-5-methanol and 4-aminobenzyl alcohol are noted.

Glioblastoma: Current Status, Emerging Targets, and Recent Advances

Glioblastoma (GBM) is a highly malignant brain tumor characterized by a heterogeneous population of genetically unstable and highly infiltrative cells that are resistant to chemotherapy. Although substantial efforts have been invested in the field of anti-GBM drug discovery in the past decade, success has primarily been confined to the preclinical level, and clinical studies have often been hampered due to efficacy-, selectivity-, or physicochemical property-related issues. Thus, expansion of the list of molecular targets coupled with a pragmatic design of new small-molecule inhibitors with central nervous system (CNS)-penetrating ability is required to steer the wheels of anti-GBM drug discovery endeavors. This Perspective presents various aspects of drug discovery (challenges in GBM drug discovery and delivery, therapeutic targets, and agents under clinical investigation). The comprehensively covered sections include the recent medicinal chemistry campaigns embarked upon to validate the potential of numerous enzymes/proteins/receptors as therapeutic targets in GBM.

Identifying Interaction Partners of Yeast Protein Disulfide Isomerases Using a Small Thiol-Reactive Cross-Linker: Implications for Secretory Pathway Proteostasis

Protein disulfide isomerases (PDIs) function in forming the correct disulfide bonds in client proteins, thereby aiding the folding of proteins that enter the secretory pathway. Recently, several PDIs have been identified as targets of organic electrophiles, yet the client proteins of specific PDIs remain largely undefined. Here, we report that PDIs expressed in Saccharomyces cerevisiae are targets of divinyl sulfone (DVSF) and other thiol-reactive protein cross-linkers. Using DVSF, we identified the interaction partners that were cross-linked to Pdi1 and Eug1, finding that both proteins form cross-linked complexes with other PDIs, as well as vacuolar hydrolases, proteins involved in cell wall biosynthesis and maintenance, and many ER proteostasis factors involved ER stress signaling and ER-associated protein degradation (ERAD). The latter discovery prompted us to examine the effects of DVSF on ER quality control, where we found that DVSF inhibits the degradation of the ERAD substrate CPY*, in addition to covalently modifying Ire1 and blocking the activation of the unfolded protein response. Our results reveal that DVSF targets many proteins within the ER proteostasis network and suggest that these proteins may be suitable targets for covalent therapeutic development in the future.

Roles of Protein Disulfide Isomerase in Breast Cancer

Simple Summary

Triple-negative breast cancer (TNBC) is the most aggressive subtype of breast cancer and has a poor prognosis and higher recurrence rate due to ineffective therapy. Even with newly approved therapeutics, only limited TNBC patients could have benefited from the regimens. Protein disulfide isomerase (PDI) has been of great interest as a potential therapeutic target for cancers due to its impacts on tumor progression, metastasis, and clinical outcomes. Here, we discuss the roles of PDI members in breast cancers such as TNBC and the PDI inhibitors studied in breast cancer research.

Abstract

Protein disulfide isomerase (PDI) is the endoplasmic reticulum (ER)’s most abundant and essential enzyme and serves as the primary catalyst for protein folding. Due to its apparent role in supporting the rapid proliferation of cancer cells, the selective blockade of PDI results in apoptosis through sustained activation of UPR pathways. The functions of PDI, especially in cancers, have been extensively studied over a decade, and recent research has explored the use of PDI inhibitors in the treatment of cancers but with focus areas of other cancers, such as brain or ovarian cancer. In this review, we discuss the roles of PDI members in breast cancer and PDI inhibitors used in breast cancer research. Additionally, a few PDI members may be suggested as potential molecular targets for highly metastatic breast cancers, such as TNBC, that require more attention in future research.

Thiol Isomerases Orchestrate Thrombosis and Hemostasis

Significance: Since protein disulfide isomerase (PDI) was first described in 1963, researchers have shown conclusively that PDI and sibling proteins are quintessential for thrombus formation. PDI, endoplasmic reticulum protein (ERp)5, ERp57, and ERp72 are released from platelets and vascular cells and interact with integrin αIIbβ3 on the outer surface of platelets. Recent Advances: At the cell surface they influence protein folding and function, propagating thrombosis and maintaining hemostasis. TMX1, which is a transmembrane thiol isomerase, is the first family member shown to negatively regulate platelets. Targets of thiol isomerases have been identified, including integrin α2β1, Von Willebrand Factor, GpIbα, nicotinamide adenine dinucleotide phosphate oxidase (Nox)-1, Nox-2, and tissue factor, all of which are pro-thrombotic, and several of which are on the cell surface. In spite of this, PDI can paradoxically catalyze the delivery of nitric oxide to platelets, which decrease thrombus formation. Critical Issues: Although the overall effect of PDI is to positively regulate platelet activation, it is still unclear how thiol isomerases function in pro-thrombotic states, such as obesity, diabetes, and cancer. In parallel, there has been a surge in the development of novel thiol isomerase inhibitors, which display selectivity, potency and modulate thrombosis and hemostasis. The availability of selective thiol isomerase inhibitors has culminated in clinical trials, with promising outcomes for the prevention of cancer-associated thrombosis. Future Directions: Altogether, thiol isomerases are perceived as an orchestrating force that regulates thrombus development. In the current review, we will explore the history of PDI in cardiovascular biology, detail known mechanisms of action, and summarize known thiol isomerase inhibitors.

ERO1-PDI Redox Signaling in Health and Disease

Significance: Protein disulfide isomerase (PDI) and endoplasmic reticulum oxidoreductase 1 (ERO1) are crucial for oxidative protein folding in the endoplasmic reticulum (ER). These enzymes are frequently overexpressed and secreted, and they contribute to the pathology of neurodegenerative, cardiovascular, and metabolic diseases. Recent Advances: Tissue-specific knockout mouse models and pharmacologic inhibitors have been developed to advance our understanding of the cell-specific functions of PDI and ERO1. In addition to their roles in protecting cells from the unfolded protein response and oxidative stress, recent studies have revealed that PDI and ERO1 also function outside of the cells. Critical Issues: Despite the well-known contributions of PDI and ERO1 to specific disease pathology, the detailed molecular and cellular mechanisms underlying these activities remain to be elucidated. Further, although PDI and ERO1 inhibitors have been identified, the results from previous studies require careful evaluation, as many of these agents are not selective and may have significant cytotoxicity. Future Directions: The functions of PDI and ERO1 in the ER have been extensively studied. Additional studies will be required to define their functions outside the ER.

Discovery of penipanoid C-inspired 2-(3,4,5-trimethoxybenzoyl)quinazolin-4(3H)-one derivatives as potential anticancer agents by inhibiting cell proliferation and inducing apoptosis in hepatocellular carcinoma cells

Hepatocellular carcinoma (HCC) is the most common form of liver cancer and the fourth leading cause of cancer-related death worldwide. First-line drugs such as sorafenib provide only a modest benefit to HCC patients. In this study, the gram-scale synthesis of 2-benzoylquinazolin-4(3H)-one skeleton was achieved successfully via the I₂/DMSO catalytic system. A series of penipanoid C-inspired 2-(3,4,5-trimethoxybenzoyl)quinazolin-4(3H)-one derivatives was synthesized and evaluated for their cytotoxic activities against four cancer cell lines, HepG2, Bel-7402, A549, and U251. Among these compounds, 4a was the most effective one with IC₅₀ values of 1.22 μM and 1.71 μM against HepG2 and Bel-7402 cells, respectively. Mechanistic studies showed that 4a inhibited hepatocellular carcinoma cell proliferation via arresting cell cycle. Additionally, 4a induced HepG2 cells apoptosis by inducing reactive oxygen species production and elevating the expression of apoptosis-related proteins. More importantly, 4a displayed significant in vivo anticancer effects in the HepG2 xenograft models. This suggests that 4a is a promising lead compound with the potential to be developed as a chemotherapy agent for hepatocellular carcinoma.

Crosstalk between endoplasmic reticulum stress and oxidative stress: Focus on protein disulfide isomerase and endoplasmic reticulum oxidase 1

Cellular stress and inflammation, establishing as disease pathology, have reached great heights in the last few decades. Stress conditions such as hyperglycemia, hyperlipidemia and lipoproteins are known to disturb proteostasis resulting in the accumulation of unfolded or misfolded proteins, alteration in calcium homeostasis culminating in unfolded protein response. Protein disulfide isomerase and endoplasmic reticulum oxidase-1 are the key players in protein folding. The protein folding process assisted by endoplasmic reticulum oxidase-1 results in the production of reactive oxygen species in the lumen of the endoplasmic reticulum. Production of reactive oxygen species beyond the quenching capacity of the antioxidant systems perturbs ER homeostasis. Endoplasmic reticulum stress also induces the production of cytokines leading to inflammatory responses. This has been proven to be the major causative factor for various pathophysiological states compared to other cellular triggers in diseases, which further manifests to increased oxidative stress, mitochondrial dysfunction, and altered inflammatory responses, deleterious to cellular physiology and homeostasis. Numerous studies have drawn correlations between the progression of several diseases in association with endoplasmic reticulum stress, redox protein folding, oxidative stress and inflammatory responses. This review aims to provide an insight into the role of protein disulfide isomerase and endoplasmic reticulum oxidase-1 in endoplasmic reticulum stress, unfolded protein response, mitochondrial dysfunction, and inflammatory responses, which exacerbate the progression of various diseases.