Moving toward a new horizon for the aldose reductase inhibitor epalrestat to treat drug-resistant cancer

Polyol pathway-generated fructose is indispensable for growth and survival of non-small cell lung cancer

Despite recent treatment advances, non-small cell lung cancer (NSCLC) remains one of the leading causes of cancer-related deaths worldwide, and therefore it necessitates the exploration of new therapy options. One commonly shared feature of malignant cells is their ability to hijack metabolic pathways to confer survival or proliferation. In this study, we highlight the importance of the polyol pathway (PP) in NSCLC metabolism. This pathway is solely responsible for metabolizing glucose to fructose based on the enzymatic activity of aldose reductase (AKR1B1) and sorbitol dehydrogenase (SORD). Via genetic and pharmacological manipulations, we reveal that PP activity is indispensable for NSCLC growth and survival in vitro and in murine xenograft models. Mechanistically, PP deficiency provokes multifactorial deficits, ranging from energetic breakdown and DNA damage, that ultimately trigger the induction of apoptosis. At the molecular level, this process is driven by pro-apoptotic JNK signaling and concomitant upregulation of the transcription factors c-Jun and ATF3. Moreover, we show that fructose, the PP end-product, as well as other non-glycolytic hexoses confer survival to cancer cells and resistance against chemotherapy via sustained NF-κB activity as well as an oxidative switch in metabolism. Given the detrimental consequence of PP gene targeting on growth and survival, we propose PP pathway interference as a viable therapeutic approach against NSCLC.

Novel bis-pocket binding aldose reductase inhibitors sensitize MCF-7/ADR cells to doxorubicin in a dual-role manner

Multidrug resistance (MDR) represents a bottleneck in the treatment of breast cancer. Although the potential of aldose reductase inhibitors (ARIs) as sensitizers against MDR has been explored in recent decades, the intrinsic mechanism still needs to be elucidated, and promising agents in the clinic need to be developed. In this study, three novel ARIs (5a-c), characterized by bis-pocket binding, were designed and synthesized. Inhibitory activity is positively correlated with antioxidation and benefits from rigid spacers. Only 5a with less activities in inhibition and antioxidation was demonstrated as a stronger sensitizer against doxorubicin (DOX)-resistant MCF-7 cells (MCF-7/ADR) than epalrestat (EPA). Either 5a or EPA may decrease GSH abundance and increase ROS, Fe2+, and lipid peroxidation levels. The restorative effects of both ARIs may be blocked by N-acetyl cysteine (NAC). These data suggest that both 5a and EPA may restore the sensitivity of MCF-7/ADR cells to DOX by increasing ferroptosis activity. Furthermore, the inhibition of AKR1B1 by 5a, as well as by EPA, dramatically decreased both p-STAT3 and SLC7A11 expression. Gene knockdown of AKR1B1 has the same effects as AKR1B1 inhibition. This evidence indicates that both ARIs can suppress MCF-7/ADR cell growth via the upregulation of ferroptosis activity via the AKR1B1/STAT3/SLC7A11 axis. Additionally, 5a was found to increase the accumulation of intramolecular DOX by inhibiting ABCB1, but EPA did not. These results support that 5a is a promising sensitizing agent against multidrug resistance in breast cancer.

Insights into tumor-derived exosome inhibition in cancer therapy

Exosomes are critical mediators of cell-to-cell communication in physiological and pathological processes, due to their ability to deliver a variety of bioactive molecules. Tumor-derived exosomes (TDEs), in particular, carry carcinogenic molecules that contribute to tumor progression, metastasis, immune escape, and drug resistance. Thus, TDE inhibition has emerged as a promising strategy to combat cancer. In this review, we discuss the key mechanisms of TDE biogenesis and secretion, emphasizing their implications in tumorigenesis and cancer progression. Moreover, we provide an overview of small-molecule TDE inhibitors that target specific biogenesis and/or secretion pathways, highlighting their potential use in cancer treatment. Lastly, we present the existing obstacles and propose corresponding remedies for the future development of TDE inhibitors.

Epalrestat Alleviates Reactive Oxygen Species and Endoplasmic Reticulum Stress by Maintaining Glycosylation in IMS32 Schwann Cells Under Exposure to Galactosemic Conditions

Aldose reductase (AR), a rate-limiting enzyme in the polyol pathway, mediates the conversion of several substrates, including glucose and galactose. In rodents, galactosemia induced by galactose feeding has been shown to develop peripheral nerve lesions resembling diabetic peripheral neuropathy. However, the mechanisms by which AR-mediated responses elicited Schwan cell lesions under galactosemic conditions remain unresolved. To investigate this, we examined the mechanism of high-galactose-induced damage mediated by AR using AR inhibitors such as ranirestat and epalrestat. The exposure of IMS32 Schwann cells under high-galactose conditions led to galactitol accumulation, the increased production of reactive oxygen species (ROS), endoplasmic reticulum (ER) stress, impaired mitochondrial morphology and membrane potential, decreased glycolysis, and aberrant glycosylation. Under these experimental conditions, ranirestat inhibited intracellular galactitol in a dose-dependent manner, whereas epalrestat failed to inhibit it. Interestingly, even at low concentrations where epalrestat did not inhibit AR activity, it prevented increased ROS production, ER stress, decreased glycolysis, and aberrant RCA120-binding glycosylation; however, no effect of ranirestat on the glycosylation was observed. Epalrestat and ranirestat did not recover mitochondrial morphology. These findings suggest that ER stress is induced by aberrant glycosylation under galactosemic conditions and that epalrestat may be effective in maintaining proper glycosylation in Schwann cells in these conditions.

In Search for Inhibitors of Human Aldo-Keto Reductase 1B10 (AKR1B10) as Novel Agents to Fight Cancer and Chemoresistance: Current State-of-the-Art and Prospects

Aldo-keto reductase 1B10 (AKR1B10) is a human enzyme that catalyzes the NADPH-dependent reduction of several different carbonyl compounds to the corresponding alcohols. Under physiological conditions, AKR1B10 is expressed mainly in the gastrointestinal tract, where it can detoxify reactive carbonyl compounds derived from dietary sources and xenobiotics. AKR1B10 is highly expressed in several cancers and precancerous conditions, proving to be crucially implicated in carcinogenesis and to function as a prognostic indicator of tumor development. Moreover, AKR1B10 up-regulation is strictly related to acquired resistance to known anticancer drugs. High levels of this enzyme are also correlated to the pathogenesis of noncancerous diseases, such as skin pathologies and COVID-19 complications. Therefore, in the last two decades, AKR1B10 has attracted interest as a novel target for agents able to fight both cancer and chemoresistance, and here, it is explored from a medicinal chemistry perspective.

Rational design and synthesis of novel N-benzylindole-based epalrestat analogs as selective aldose reductase inhibitors: An unexpected discovery of a new glucose-lowering agent (AK-4) acting as a mitochondrial uncoupler

Diabetes mellitus is one of the most frequent metabolic diseases associated with hyperglycemia. Although antidiabetic drugs reduce hyperglycemia, diabetic patients suffer from abnormal fluctuations in blood glucose levels leading to the onset of long-term complications. Aldose reductase inhibitors are considered a promising strategy for regulating the occurrence of diabetic-specific comorbidities. So far, epalrestat is the only drug being approved in Asian countries. In this paper, we ground our research in discovering novel epalrestat analogs that prevent chronic complications and normalize hyperglycemia. Herein, we describe the rational design and synthesis of four novel 4-thiazolidinone acetic acid derivatives (AK-1-4) being evaluated for their efficacy against aldose reductase from rat lenses and their specificity over the homologous enzyme from rat kidneys. AK-1-4 were also tested against human recombinant protein tyrosine phosphatase 1B as a key target in insulin sensitization and towards the closely related T-cell-derived enzyme. Docking analyses suggested possible binding modes on examined targets. The promising inhibitory profile of AK-4 sparked our interest in exploring its effect on the insulin-receptor signaling pathway and its ability to stimulate glucose uptake under ex vivo conditions. We further investigated the ability of AK-4 to target mitochondria acting as an uncoupling agent and impairing mitochondrial membrane potential. Herein, we report for the first time a new glucose-lowering agent (AK-4) that can combine alleviation for chronic diabetic complications without off-target adverse effects and antihyperglycemic efficacy through controlled mitochondrial uncoupling activity. Pharmacokinetic and toxicity studies in silico revealed optimal properties of AK-4 for oral administration without potential side effects.

AKR1B10 and digestive tumors development: a review

Aldo-keto reductase family 1 member B10 (AKR1B10) is a member of the AKR1B subfamily. It is mainly found in cytoplasm, and it is typically expressed in the stomach and intestines. Given that its expression is low or absent in other tissues, AKR1B10 is a potential diagnostic and therapeutic biomarker for various digestive system diseases. Here, we review recent research progress on AKR1B10 in digestive system tumors such as hepatocellular carcinoma, gastric carcinoma, colorectal carcinoma, pancreatic carcinoma, oral squamous cell carcinoma, laryngeal squamous cell carcinoma, cholangiocarcinoma, and nasopharyngeal carcinoma, over the last 5 years. We also discuss the current trends and future research directions for AKR1B10 in both oncological and non-oncological diseases to provide a scientific reference for further exploration of this gene.

Aldose reductase with quinolone antibiotics interaction: In vitro and in silico approach of its relationship with diabetic complications

Aldose reductase (AR, EC1.1.1.21), a member of the aldo-keto reductase family, is critically implicated in the pathogenesis of chronic complications associated with diabetes mellitus, including neuropathy, nephropathy, and retinopathy. Hyperglycemia-induced AR overactivity results in intracellular sorbitol accumulation, NADPH depletion, and oxidative stress. Consequently, AR is recognized as a key mediator of oxidative and inflammatory signaling pathways involved in diverse human pathologies such as cardiovascular diseases, inflammatory disorders, and cancer. This has sparked renewed interest in developing novel AR inhibitors (ARIs) with enhanced therapeutic profiles. In this study, we evaluated the inhibitory potential of five quinolone antibiotics-gatifloxacin, lomefloxacin, nalidixic acid, norfloxacin, and sparfloxacin-as ARIs relevant to various physiological and pathological conditions. Through comprehensive in vitro and in silico analyses, we explored these antibiotics' binding interactions and affinities within the AR active site. Our findings reveal that these quinolones moderately inhibit AR at micromolar concentrations, with inhibition constants (KIs) ranging from 1.03 ± 0.13 μM to 4.12 ± 0.51 μM, compared to the reference drug epalrestat (KI of 0.85 ± 0.06 μM). The combined in vitro and in silico results underscore significant interactions between these drugs and AR, suggesting their potential as therapeutic agents against the aforementioned pathological conditions. Furthermore, these insights will aid in optimizing clinical dosing regimens and mitigating unexpected drug-drug interactions when these antibiotics are co-administered with other treatments.

Esterase-Responsive Fluorogenic Prodrugs of Aldose Reductase Inhibitor Epalrestat: An Innovative Strategy toward Enhanced Anticancer Activity

In addition to the conventional chemotherapeutic drugs, potent inhibitors of key enzymes that are differentially overexpressed in cancer cells and associated with its progression are often considered as the drugs of choice for treating cancer. Aldose reductase (AR), which is primarily associated with complications of diabetes, is known to be closely related to the development of cancer and drug resistance. Epalrestat (EPA), an FDA-approved drug, is a potent inhibitor of AR and exhibits anticancer activity. However, its poor pharmacokinetic properties limit its bioavailability and therapeutic benefits. We report herein the first examples of esterase-responsive turn-on fluorogenic prodrugs for the sustained release of EPA to cancer cells with a turn-on fluorescence readout. Carboxylesterases are known to be overexpressed in several organ-specific cancer cells and help in selective uncaging of drug from the prodrugs. The prodrugs were synthesized using a multistep organic synthesis and successfully characterized. Absorption and emission spectroscopic studies indicated successful activation of the prodrugs in the presence of porcine liver esterase (PLE) under physiological condition. HPLC studies revealed a simultaneous release of both the drug and the fluorophore from the prodrugs over time with mechanistic insights. While the inhibitory potential of EPA released from the prodrugs toward the enzyme AR was validated in the aqueous medium, the anticancer activity of the prodrugs was studied in a representative cervical cancer cell line. Interestingly, our results revealed that the development of the prodrugs can significantly enhance the anticancer potential of EPA. Finally, the drug uncaging process from the prodrugs by the intracellular esterases was studied in the cellular medium by measuring the turn-on fluorescence using fluorescence microscopy. Therefore, the present study highlights the rational development of the fluorogenic prodrugs of EPA, which will help enhance its anticancer potential with better therapeutic potential.

Targeting AKR1B10 by Drug Repurposing with Epalrestat Overcomes Chemoresistance in Non-Small Cell Lung Cancer Patient-Derived Tumor Organoids

PURPOSE

Systemic treatments given to patients with non-small cell lung cancer (NSCLC) are often ineffective due to drug resistance. In the present study, we investigated patient-derived tumor organoids (PDTO) and matched tumor tissues from surgically treated patients with NSCLC to identify drug repurposing targets to overcome resistance toward standard-of-care platinum-based doublet chemotherapy.

EXPERIMENTAL DESIGN

PDTOs were established from 10 prospectively enrolled patients with non-metastatic NSCLC from resected tumors. PDTOs were compared with matched tumor tissues by histopathology/immunohistochemistry, whole exome sequencing, and transcriptome sequencing. PDTO growths and drug responses were determined by measuring 3D tumoroid volumes, cell viability, and proliferation/apoptosis. Differential gene expression analysis identified drug-repurposing targets. Validations were performed with internal/external data sets of patients with NSCLC. NSCLC cell lines were used for aldo-keto reductase 1B10 (AKR1B10) knockdown studies and xenograft models to determine the intratumoral bioavailability of epalrestat.

RESULTS

PDTOs retained histomorphology and pathological biomarker expression, mutational/transcriptomic signatures, and cellular heterogeneity of the matched tumor tissues. Five (50%) PDTOs were chemoresistant toward carboplatin/paclitaxel. Chemoresistant PDTOs and matched tumor tissues demonstrated overexpression of AKR1B10. Epalrestat, an orally available AKR1B10 inhibitor in clinical use for diabetic polyneuropathy, was repurposed to overcome chemoresistance of PDTOs. In vivo efficacy of epalrestat to overcome drug resistance corresponded to intratumoral epalrestat levels.

CONCLUSIONS

PDTOs are efficient preclinical models recapitulating the tumor characteristics and are suitable for drug testing. AKR1B10 can be targeted by repurposing epalrestat to overcome chemoresistance in NSCLC. Epalrestat has the potential to advance to clinical trials in patients with drug-resistant NSCLC due to favorable toxicity, pharmacological profile, and bioavailability.

Decoding selectivity: computational insights into AKR1B1 and AKR1B10 inhibition

Understanding selectivity mechanisms of inhibitors towards highly homologous proteins is of paramount importance in the design of selective candidates. Human aldo-keto reductases (AKRs) pertain to a superfamily of monomeric oxidoreductases, which serve as NADPH-dependent cytosolic enzymes to catalyze the reduction of carbonyl groups to primary and secondary alcohols using electrons from NADPH. Among AKRs, AKR1B1 is emerging as a promising target for cancer treatment and diabetes, despite its high structural similarity with AKR1B10, which leads to severe adverse events. Therefore, it is crucial to understand the selectivity mechanisms of AKR1B1 and AKR1B10 to discover safe anticancer candidates with optimal therapeutic efficacy. In this study, multiple computational strategies, including sequence alignment, structural comparison, Protein Contacts Atlas analysis, molecular docking, molecular dynamics simulation, MM-GBSA calculation, alanine scanning mutagenesis and pharmacophore modeling analysis were employed to comprehensively understand the selectivity mechanisms of AKR1B1/10 inhibition based on selective inhibitor lidorestat and HAHE. This study would provide substantial evidence in the design of potent and highly selective AKR1B1/10 inhibitors in future.

Repurposing of Chronically Used Drugs in Cancer Therapy: A Chance to Grasp

Despite the advancement in drug discovery for cancer therapy, drug repurposing remains an exceptional opportunistic strategy. This approach offers many advantages (faster, safer, and cheaper drugs) typically needed to overcome increased challenges, i.e., side effects, resistance, and costs associated with cancer therapy. However, not all drug classes suit a patient's condition or long-time use. For that, repurposing chronically used medications is more appealing. This review highlights the importance of repurposing anti-diabetic and anti-hypertensive drugs in the global fight against human malignancies. Extensive searches of all available evidence (up to 30 March 2023) on the anti-cancer activities of anti-diabetic and anti-hypertensive agents are obtained from multiple resources (PubMed, Google Scholar, ClinicalTrials.gov, Drug Bank database, ReDo database, and the National Institutes of Health). Interestingly, more than 92 clinical trials are evaluating the anti-cancer activity of 14 anti-diabetic and anti-hypertensive drugs against more than 15 cancer types. Moreover, some of these agents have reached Phase IV evaluations, suggesting promising official release as anti-cancer medications. This comprehensive review provides current updates on different anti-diabetic and anti-hypertensive classes possessing anti-cancer activities with the available evidence about their mechanism(s) and stage of development and evaluation. Hence, it serves researchers and clinicians interested in anti-cancer drug discovery and cancer management.

Bioinformatics Analysis Reveals the Vital Role of AKR1B1 in Immune Infiltration and Clinical Outcomes of Gastric Cancer

Infiltrated immune cells are an important constitute of tumor microenvironment, which exert complex effects on gastric cancer (GC) pathogenesis and progression. By using weighted gene co-expression network analysis, integrating the data from The Cancer Genome Atlas-stomach adenocarcinoma and GSE62254, we identify Aldo-Keto Reductase Family 1 Member B (AKR1B1) as a hub gene for immune regulation in GC. Notably, AKR1B1 is associated with higher immune infiltration and worse histologic grade of GC. In addition, AKR1B1 is an independent factor for predicting the survival rate of GC patients. In vitro experiments further demonstrated that AKR1B1-overexpressed THP-1-derived macrophages promoted the proliferation and migration of GC cells. Taken together, AKR1B1 plays an important role in GC progression by regulating immune microenvironment, which could be a biomarker for predicting GC prognosis as well as a potential therapeutic target for GC treatment.

Novel acetic acid derivatives containing quinazolin-4(3H)-one ring: Synthesis, in vitro, and in silico evaluation of potent aldose reductase inhibitors

Aldose reductase (AR) is a crucial enzyme of the polyol pathway through which glucose is metabolized under conditions of hyperglycemia related to diabetes. A series of novel acetic acid derivatives containing quinazolin-4(3H)-one ring (1-22) was synthesized and tested for in vitro AR inhibitory effect. All the target compounds exhibited nanomolar activity against the target enzyme, and all compounds displayed higher activity as compared to the reference drug epalrestat. Among them, Compound 19, named 2-(4-[(2-[(4-methylpiperazin-1-yl)methyl]-4-oxoquinazolin-3(4H)-ylimino)methyl]phenoxy)acetic acid, displayed the strongest inhibitory effect with a KI value of 61.20 ± 10.18 nM. Additionally, these compounds were investigated for activity against L929, nontumoral fibroblast cells, and MCF-7, breast cancer cells using the MTT assay. Compounds 16 and 19 showed lower toxicity against the normal L929 cells. The synthesized compounds' (1-22) absorption, distribution, metabolism, and excretion properties were also evaluated. Molecular docking simulations were used to look into the possible binding mechanisms of these inhibitors against AR.

The Aldose Reductase Inhibitor Epalrestat Maintains Blood-Brain Barrier Integrity by Enhancing Endothelial Cell Function during Cerebral Ischemia

Excessive activation of aldose reductase (AR) in the brain is a risk factor for aggravating cerebral ischemia injury. Epalrestat is the only AR inhibitor with proven safety and efficacy, which is used in the clinical treatment of diabetic neuropathy. However, the molecular mechanisms underlying the neuroprotection of epalrestat remain unknown in the ischemic brain. Recent studies have found that blood-brain barrier (BBB) damage was mainly caused by increased apoptosis and autophagy of brain microvascular endothelial cells (BMVECs) and decreased expression of tight junction proteins. Thus, we hypothesized that the protective effect of epalrestat is mainly related to regulating the survival of BMVECs and tight junction protein levels after cerebral ischemia. To test this hypothesis, a mouse model of cerebral ischemia was established by permanent middle cerebral artery ligation (pMCAL), and the mice were treated with epalrestat or saline as a control. Epalrestat reduced the ischemic volume, enhanced BBB function, and improved the neurobehavior after cerebral ischemia. In vitro studies revealed that epalrestat increased the expression of tight junction proteins, and reduced the levels of cleaved-caspase3 and LC3 proteins in mouse BMVECs (bEnd.3 cells) exposed to oxygen-glucose deprivation (OGD). In addition, bicalutamide (an AKT inhibitor) and rapamycin (an mTOR inhibitor) increased the epalrestat-induced reduction in apoptosis and autophagy related protein levels in bEnd.3 cells with OGD treatment. Our findings suggest that epalrestat improves BBB function, which may be accomplished by reducing AR activation, promoting tight junction proteins expression, and upregulating AKT/mTOR signaling pathway to inhibit apoptosis and autophagy in BMVECs.