Functional analysis of the involvement of apurinic/apyrimidinic endonuclease 1 in the resistance to melphalan in multiple myeloma

A review of synthetic strategy, SAR, docking, simulation studies, and mechanism of action of isoxazole derivatives as anticancer agents

Breast cancer (BC) is a global health concern and the leading cause of cancerous death among women across the world, BC has been characterized by fresh lump in the breast or underarm (armpit), thickened or swollen. Worldwide estimated 9.6 million deaths in 2018-2019. Numerous drugs have been approved by FDA for BC treatment but showed numerous adverse effects like bioavailability issues, selectivity issues, and toxicity issues. Therefore, there is an immediate need to develop new molecules that are non-toxic and more efficient for treating cancer. Isoxazole derivatives have gained popularity over the few years due to their effective antitumor potential. These derivatives work against cancer by inhibiting the thymidylate enzyme, inducing apoptosis, inhibiting tubulin polymerization, protein kinase inhibition, and aromatase inhibition. In this study, we have concentrated on the isoxazole derivative with structure-activity relationship study, various synthesis techniques, mechanism of action, docking, and simulation studies pertaining to BC receptors. Hence the development of isoxazole derivatives with improved therapeutic efficacy will inspire further progress in improving human health.Communicated by Ramaswamy H. Sarma.

DNA methylation-mediated inhibition of MGARP is involved in impaired progeny testosterone synthesis in mice exposed to DBP in utero

The dibutyl phthalate (DBP) has been detected in fetuses and infants and can cause damage to the reproductive system in adulthood, but the exact mechanism remains unclear. Here, we aim to investigate the effects of intrauterine DBP exposure on offspring reproductive function and explore possible mechanisms. SPF C57BL/6 pregnant mice were given DBP (0.5, 5, 75 mg/kg/d) or corn oil from day 5 to day 19 by gavage. After weaning, the pups were fed a standard diet for 5 weeks. In addition, TM3 Leydig cell cultures were used to study the relevant mechanisms in vitro. The results showed that intrauterine DBP exposure could reduce sperm density and sperm motility, cause testicular tissue damage, down-regulate serum T and LH levels, and up-regulate serum FSH levels at 75 mg/kg/d. Western blot and methylation detection revealed intrauterine exposure to DBP down-regulated testosterone synthesis-related proteins StAR, P450scc, 3β-HSD, PKA, and PKC expression, while up-regulated the levels of methyltransferase proteins expression and DNA 5-methylcytosine (5mC) in testicular tissue of mouse offspring at 75 mg/kg/d. Further detection found in utero 75 mg/kg/d DBP exposure down-regulated MGARP protein expression, and induced incomplete methylation of the MGARP gene. An in vitro analysis showed that MGARP inhibition is involved in an impaired testosterone synthesis in TM3 cells. Cell culture results suggest that MGARP down-regulation may be involved in impaired testosterone production in monobutyl phthalate-treated cells. The present study revealed that 75 mg/kg/d DBP exposure in utero resulted in testosterone synthesis disorders and reproductive function impairment in mouse offspring, and the mechanism may be related to DNA methylation-mediated down-regulation of MGARP in the testis.

Targeting the Interplay between HDACs and DNA Damage Repair for Myeloma Therapy

Multiple myeloma (MM) is a malignancy of terminally differentiated plasma cells, and accounts for 10% of all hematologic malignancies and 1% of all cancers. MM is characterized by genomic instability which results from DNA damage with certain genomic rearrangements being prognostic factors for the disease and patients’ clinical response. Following genotoxic stress, the evolutionary conserved DNA damage response (DDR) is activated and, in turn, coordinates DNA repair with cell-cycle events. However, the process of carcinogenesis cannot be attributed only to the genetic alterations, but also involves epigenetic processes. Regulation of expression and activity of key players in DNA repair and checkpoint proteins are essential and mediated partly by posttranslational modifications (PTM), such as acetylation. Crosstalk between different PTMs is important for regulation of DNA repair pathways. Acetylation, which is mediated by acetyltransferases (HAT) and histone deacetylases (HDAC), not only affects gene expression through its modulation of histone tails but also has recently been implicated in regulating non-histone proteins. Currently, several HDAC inhibitors (HDACi) have been developed both in pre-clinical and clinical studies, with some of them exhibiting significant anti-MM activities. Due to reversibility of epigenetic changes during the evolutionary process of myeloma genesis, the potency of epigenetic therapies seems to be of great importance. The aim of the present paper is the summary of all data on the role of HDACi in DDR, the interference with each DNA repair mechanism and the therapeutic implications of HDACi in MM.

DNA Damage Response in Multiple Myeloma: The Role of the Tumor Microenvironment

Multiple myeloma (MM) is an incurable plasma cell malignancy characterized by genomic instability. MM cells present various forms of genetic instability, including chromosomal instability, microsatellite instability, and base-pair alterations, as well as changes in chromosome number. The tumor microenvironment and an abnormal DNA repair function affect genetic instability in this disease. In addition, states of the tumor microenvironment itself, such as inflammation and hypoxia, influence the DNA damage response, which includes DNA repair mechanisms, cell cycle checkpoints, and apoptotic pathways. Unrepaired DNA damage in tumor cells has been shown to exacerbate genomic instability and aberrant features that enable MM progression and drug resistance. This review provides an overview of the DNA repair pathways, with a special focus on their function in MM, and discusses the role of the tumor microenvironment in governing DNA repair mechanisms.

Curcumin exerts protective effects against hypoxia‑reoxygenation injury via the enhancement of apurinic/apyrimidinic endonuclease 1 in SH‑SY5Y cells: Involvement of the PI3K/AKT pathway

Curcumin, a polyphenolic compound extracted from the plant Curcuma longa, has been reported to exert neuroprotective effects against cerebral ischemia reperfusion (I/R) injury. However, the mechanisms underlying these effects remain to be fully elucidated. Emerging evidence indicated that apurinic/apyrimidinic endonuclease 1 (APE1), a multifunctional enzyme, participates in neuronal survival against I/R injury. Therefore, the aim of the present study was to investigate whether curcumin alleviates oxygen-glucose deprivation/reper-fusion (OGD/R)-induced SH-SY5Y cell injury, which serves as an in vitro model of cerebral I/R injury, by regulating APE1. The results revealed that curcumin increased cell viability, decreased LDH activity, reduced apoptosis and caspase-3 activity, downregulated the pro-apoptotic protein Bax expression and upregulated the anti-apoptotic protein Bcl-2 expression in SH-SY5Y cells subjected to OGD/R. Simultaneously, curcumin eliminated the OGD/R-induced decreases in APE1 protein and mRNA expression, as well as 8-hydroxy-2′-deoxyguanosine (8-OHdG) level and AP sites in SH-SY5Y cells. However, APE1 knockdown by siRNA transfection markedly abrogated the protective effects of curcumin against OGD/R-induced cytotoxicity, apoptosis and oxidative stress, as illustrated by the decreases in reactive oxygen species production and NADPH oxidase 2 expression, and the increase in superoxide dismutase activity and glutathione levels in SH-SY5Y cells. Furthermore, curcumin mitigated the OGD/R-induced activation of phosphatidylinositol 3-kinase/protein kinase B (PI3K/AKT) signaling pathway. Treatment with LY294002, an inhibitor of PI3K/AKT pathway activity, attenuated the protective effects of curcumin on cytotoxicity and apoptosis, and reversed the curcumin-induced upregulation of APE1 protein expression in SH-SY5Y cells subjected to OGD/R. Taken together, these results demonstrated that curcumin protects SH-SY5Y cells against OGD/R injury by inhibiting apoptosis and oxidative stress, and via enhancing the APE1 level and activity, promoting PI3K/AKT pathway activation.

Prion protein deficiency impairs hematopoietic stem cell determination and sensitizes myeloid progenitors to irradiation

Highly conserved among species and expressed in various types of cells, numerous roles have been attributed to the cellular prion protein (PrPC). In hematopoiesis, PrPC regulates hematopoietic stem cell self-renewal but the mechanisms involved in this regulation are unknown. Here we show that PrPC regulates hematopoietic stem cell number during aging and their determination towards myeloid progenitors. Furthermore, PrPC protects myeloid progenitors against the cytotoxic effects of total body irradiation. This radioprotective effect was associated with increased cellular prion mRNA level and with stimulation of the DNA repair activity of the Apurinic/pyrimidinic endonuclease 1, a key enzyme of the base excision repair pathway. Altogether, these results show a previously unappreciated role of PrPC in adult hematopoiesis, and indicate that PrPC-mediated stimulation of BER activity might protect hematopoietic progenitors from the cytotoxic effects of total body irradiation.

miR-520g and miR-520h overcome bortezomib resistance in multiple myeloma via suppressing APE1

Background: Nowadays, microRNAs (miRNAs) attract much attention in regulating anticancer drug resistance in cancers including multiple myeloma (MM). Bortezomib is the first-line choice in MM treatment, and bortezomib resistance caused by aberrant DNA repair leads to the recurrence and therapeutic failure of MM. Objective: Our study aims to identify a miRNA that overcomes bortezomib resistance in MM. Methods: We established bortezomib-resistant MM cell lines, and screened several miRNAs that have aberrant expressions in MM cell lines. The expression of DNA-repair-related proteins were assessed by western blot, and cell viability was determined by the MTT assay in bortezomib-resistant cell lines. The binding between miRNAs and 3'-UTR of APE1 mRNA was confirmed by luciferase reporter assay. The mouse bortezomib-resistant xenograft was established to verify the therapeutic effect of miRNA overexpression. Results: miR-520g and miR-520h were significantly downregulated in bortezomib-resistant MM cell lines, and overexpression of miR-520g and miR-520h together inhibited expression of homologous recombination-related protein Rad51 and cell viability of bortezomib-resistant MM cells in vitro by binding with 3'-UTR of APE1 mRNA. Combined overexpression of miR-520g and miR-520h inhibited bortezomib-resistant MM tumor growth in vivo. Conclusion: Our findings demonstrated that combined overexpression of miR-520g and miR-520h overcomes bortezomib resistance in MM through inhibition of DNA repair, offering a promising therapeutic target for MM treatment.

Elevated level of acetylation of APE1 in tumor cells modulates DNA damage repair

Apurinic/apyrimidinic (AP) sites are frequently generated in the genome by spontaneous depurination/depyrimidination or after removal of oxidized/modified bases by DNA glycosylases during the base excision repair (BER) pathway. Unrepaired AP sites are mutagenic and block DNA replication and transcription. The primary enzyme to repair AP sites in mammalian cells is AP endonuclease (APE1), which plays a key role in this repair pathway. Although overexpression of APE1 in diverse cancer types and its association with chemotherapeutic resistance are well documented, alteration of posttranslational modification of APE1 and modulation of its functions during tumorigenesis are largely unknown. Here, we show that both classical histone deacetylase HDAC1 and NAD⁺-dependent deacetylase SIRT1 regulate acetylation level of APE1 and acetylation of APE1 enhances its AP-endonuclease activity both in vitro and in cells. Modulation of APE1 acetylation level in cells alters AP site repair capacity of the cell extracts in vitro. Primary tumor tissues of diverse cancer types have higher level of acetylated APE1 (AcAPE1) compared to adjacent non-tumor tissue and exhibit enhanced AP site repair capacity. Importantly, in the absence of APE1 acetylation, cells accumulate AP sites in the genome and show increased sensitivity to DNA damaging agents. Together, our study demonstrates that elevation of acetylation level of APE1 in tumor could be a novel mechanism by which cells handle the elevated levels of DNA damages in response to genotoxic stress and maintain sustained proliferation.

The metabolomic signature of hematologic malignancies

The ongoing accumulation of knowledge raises hopes that understanding tumor metabolism will provide new ways for predicting, diagnosing, and even treating cancers. Some metabolic biomarkers are at present routinely utilized to diagnose cancer and metabolic alterations of tumors are being confirmed as therapeutic targets. The growing utilization of metabolomics in clinical research may rapidly turn it into one of the most potent instruments used to detect and fight tumor. In fact, while the current state and trends of high throughput metabolomics profiling focus on the purpose of discovering biomarkers and hunting for metabolic mechanism, a prospective direction, namely reprogramming metabolomics, highlights the way to use metabolomics approach for the aim of treatment of disease by way of reconstruction of disturbed metabolic pathways. In this review, we present an ample summary of the current clinical appliances of metabolomics in hematological malignancies.

High-Throughput Phenotypic Screening of Human Astrocytes to Identify Compounds That Protect Against Oxidative Stress

Astrocytes are the predominant cell type in the nervous system and play a significant role in maintaining neuronal health and homeostasis. Recently, astrocyte dysfunction has been implicated in the pathogenesis of many neurodegenerative diseases, including Alzheimer's disease, Parkinson's disease, Huntington's disease, and amyotrophic lateral sclerosis. Astrocytes are thus an attractive new target for drug discovery for neurological disorders. Using astrocytes differentiated from human embryonic stem cells, we have developed an assay to identify compounds that protect against oxidative stress, a condition associated with many neurodegenerative diseases. This phenotypic oxidative stress assay has been optimized for high-throughput screening in a 1,536-well plate format. From a screen of approximately 4,100 bioactive tool compounds and approved drugs, we identified a set of 22 that acutely protect human astrocytes from the consequences of hydrogen peroxide-induced oxidative stress. Nine of these compounds were also found to be protective of induced pluripotent stem cell-differentiated astrocytes in a related assay. These compounds are thought to confer protection through hormesis, activating stress-response pathways and preconditioning astrocytes to handle subsequent exposure to hydrogen peroxide. In fact, four of these compounds were found to activate the antioxidant response element/nuclear factor-E2-related factor 2 pathway, a protective pathway induced by toxic insults. Our results demonstrate the relevancy and utility of using astrocytes differentiated from human stem cells as a disease model for drug discovery and development.

SIGNIFICANCE

Astrocytes play a key role in neurological diseases. Drug discovery efforts that target astrocytes can identify novel therapeutics. Human astrocytes are difficult to obtain and thus are challenging to use for high-throughput screening, which requires large numbers of cells. Using human embryonic stem cell-derived astrocytes and an optimized astrocyte differentiation protocol, it was possible to screen approximately 4,100 compounds in titration to identify 22 that are cytoprotective of astrocytes. This study is the largest-scale high-throughput screen conducted using human astrocytes, with a total of 17,536 data points collected in the primary screen. The results demonstrate the relevancy and utility of using astrocytes differentiated from human stem cells as a disease model for drug discovery and development.

Mitochondrial translocation of APE1 relies on the MIA pathway

APE1 is a multifunctional protein with a fundamental role in repairing nuclear and mitochondrial DNA lesions caused by oxidative and alkylating agents. Unfortunately, comprehensions of the mechanisms regulating APE1 intracellular trafficking are still fragmentary and contrasting. Recent data demonstrate that APE1 interacts with the mitochondrial import and assembly protein Mia40 suggesting the involvement of a redox-assisted mechanism, dependent on the disulfide transfer system, to be responsible of APE1 trafficking into the mitochondria. The MIA pathway is an import machinery that uses a redox system for cysteine enriched proteins to drive them in this compartment. It is composed by two main proteins: Mia40 is the oxidoreductase that catalyzes the formation of the disulfide bonds in the substrate, while ALR reoxidizes Mia40 after the import. In this study, we demonstrated that: (i) APE1 and Mia40 interact through disulfide bond formation; and (ii) Mia40 expression levels directly affect APE1's mitochondrial translocation and, consequently, play a role in the maintenance of mitochondrial DNA integrity. In summary, our data strongly support the hypothesis of a redox-assisted mechanism, dependent on Mia40, in controlling APE1 translocation into the mitochondrial inner membrane space and thus highlight the role of this protein transport pathway in the maintenance of mitochondrial DNA stability and cell survival.

Modulation of cell metabolic pathways and oxidative stress signaling contribute to acquired melphalan resistance in multiple myeloma cells

Alkylating agents are widely used chemotherapeutics in the treatment of many cancers, including leukemia, lymphoma, multiple myeloma, sarcoma, lung, breast and ovarian cancer. Melphalan is the most commonly used chemotherapeutic agent against multiple myeloma. However, despite a 70-80% initial response rate, virtually all patients eventually relapse due to the emergence of drug-resistant tumour cells. By using global proteomic and transcriptomic profiling on melphalan sensitive and resistant RPMI8226 cell lines followed by functional assays, we discovered changes in cellular processes and pathways not previously associated with melphalan resistance in multiple myeloma cells, including a metabolic switch conforming to the Warburg effect (aerobic glycolysis), and an elevated oxidative stress response mediated by VEGF/IL8-signaling. In addition, up-regulated aldo-keto reductase levels of the AKR1C family involved in prostaglandin synthesis contribute to the resistant phenotype. Finally, selected metabolic and oxidative stress response enzymes were targeted by inhibitors, several of which displayed a selective cytotoxicity against the melphalan-resistant cells and should be further explored to elucidate their potential to overcome melphalan resistance.