APE1 Redox Activity Research Articles

APX2009 sensitizes hypoxic breast cancer cells to doxorubicin by increasing its accumulation and caspase-3/7-mediated apoptosis.

The association of targeted therapy with chemotherapy is encouraged to increase the treatment efficiency, especially in hypoxic triple-negative breast cancer. The APE1 redox activity has stood out as a potential tumor target. However, the effect of the association of the APE1 redox inhibitors with doxorubicin in hypoxia still needs to be evidenced. Therefore, our objective was to investigate the effect of the APX2009 (APE1 inhibitor) on the sensitization of breast cancer cells to doxorubicin in normoxia and hypoxia. The WST-1 assay was used to evaluate cell viability after APX2009 and doxorubicin application under normoxia and hypoxia conditions in the MCF-7 and MDA-MB-231 cells. Apoptosis was analyzed by annexin assay and detection of caspases-3/7 activity by luminescence-based assay. The clinical association between APE1 inhibition signature and doxorubicin sensitivity was evaluated by bioinformatics analyses. MDA-MB-231 and MCF-7 cell lines were more sensitive to APX2009 in normoxia than in hypoxia. Co-treatment with APX2009 and doxorubicin in hypoxia further decreased the viability of triple-negative MDA-MB-231 cells than treatment alone, which was accompanied by doxorubicin intracellular accumulation, and increase of apoptotic cells percentage, and caspases-3/7 activity. Moderate association was found between APE1 inhibition signature and doxorubicin sensitivity in the hypoxic basal subtype. The findings suggest that APX2009 sensitizes the MDA-MB-231 cells to doxorubicin in hypoxia by doxorubicin intracellular accumulation and caspases-3/7-mediated apoptosis.

Abstract 3964: APE1 protects SMAD3 against ROC1 ubiquitin mediated degradation in esophageal adenocarcinoma cells

Abstract Background: The incidence of esophageal adenocarcinoma (EAC) has increased more than six-fold over the past three decades and continues to rise in the Western world. The 5-year survival rate for EAC patients is less than 20% which underscores the need to better understand the underlying mechanisms to identify new therapeutic approaches. This study aimed at investigating the potential role of APE1 in regulating SMAD3 and promoting EAC progression. Methods and Results: Western blot data showed that APE1 and SMAD3 were highly expressed in EAC cell lines. APE1 silencing reduced SMAD3 nuclear expression and downregulated its downstream targets SERPINE1 and c-myc. These results were confirmed by immunofluorescence staining showing loss of nuclear accumulation of SMAD3 after APE1 knockdown. Mechanistically, immunoprecipitation and proximity ligation assays revealed a direct binding between APE1 and SMAD3 in the nucleus. Further investigation showed that APE1 binds to the C-terminal MH2 domain of SMAD3, and this binding protects SMAD3 from ubiquitin mediated proteasomal degradation by blocking its interaction with the RING finger protein, ROC1. Interestingly, APE1-redox-specific inhibition (APX2009) downregulated SMAD3 expression and the APE1 redox-deficient mutant (C65A) disrupted APE1-SMAD3 binding indicating that this regulation depends on APE1 redox activity. Conclusion: Our findings establish a role of APE1 in regulating SMAD3 in EAC. These findings provide a potential therapeutic approach for the treatment of EAC by the pharmacological inhibition of APE1. Citation Format: Farah Ballout, Heng Lu, Dunfa Peng, Wael El-Rifai. APE1 protects SMAD3 against ROC1 ubiquitin mediated degradation in esophageal adenocarcinoma cells. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3964.

Abstract 2366: Inhibition of Ref-1/APE1 redox activity with APX3330 enhances Ref-1/APE1 protein unfolded conformation in human PDAC cells

Abstract Ref-1/APE1 (Redox factor-1, Ref-1; Apurinic/apyrimidinic endonuclease 1, APE1) is a redox signaling enzyme that biochemically converts several transcription factors (TFs), such as NF-kB, STAT3, HIF-1α from an oxidized to a reduced state, allowing TFs to bind DNA and activate various biological responses such as cell growth and inflammation. Ref-1 and its transcriptional targets are highly active in Pancreatic Ductal Adenocarcinoma (PDAC) which often presents with tumor metastasis and therapy resistance. The redox activity of Ref-1 is determined by the redox status of the relevant cysteine residues (Cys), particularly Cys residue 65 (C65), which is critical among seven Cys residues for Ref-1’s redox activity. Using CRISPR editing in PDAC cells, we changed the C65 to Ala (C65A) in Ref-1 to evaluate the effects of loss of Ref-1 redox activity on cell signaling pathways and how Ref-1 activity regulates critical transcription factors. Using Ref-1 redox inhibitor, APX3330, we previously investigated interactions between Ref-1 and APX3330 in a cell-free system in which Ref-1 underwent conformational changes in the presence of APX3330. This resulted in complete exposure of all seven Cys residues causing oxidation of the Ref-1 protein and redox signaling inactivity. However, how these events translate in the cell has not been completely established. Using a gel-based mobility shift assay, we examined the redox-modified Cys residues of Ref-1 in response to APX3330 in PDAC cell lines over time. We observed a gradual increase in labeling of Cys in Ref-1 following APX3330 treatment between 10min to 6h which returned to control levels at 48h in both wild-type control (Cas9) and C65A-expressing cells. This reduction in the redox status of Ref-1 was likely due to unfolding alteration like the cell-free system. To confirm this, both cell lines were treated with N-ethylmaleimide (NEM) prior to cell lysing, which blocks free thiols in the protein. We detected dramatic decreases in reduced forms of Ref-1 after APX3330 treatment (between 10min-6h) in both cell lines, demonstrating that C65 is not essential for the unfolded conformational changes of Ref-1. However, C65A-Ref-1 protein demonstrated a distinctly different redox pattern upon APX3330 treatment in comparison to WT Ref-1 in the Cas9 control line. C65A-expressing cells also had reduced mitochondrial function compared to Cas9 control PDAC cells. In vivo studies demonstrated significant reduction in tumor size, weight, and growth in C65A PDAC cells compared to the Cas9 control lines, further demonstrating the critical role of C65 in the Ref-1 redox signaling and downstream pathways including metabolism and proliferation. In conclusion, we demonstrate direct interactions between Ref-1 and APX3330 in PDAC cells and subsequent biological results confirm a critical involvement of Ref-1-C65 in the redox signaling and tumor phenotype. Citation Format: Mahmut Mijit, Olivia Babb, Silpa Gampala, Randall Wireman, Millie M. Georgiadis, Melissa L. Fishel, Mark R. Kelley. Inhibition of Ref-1/APE1 redox activity with APX3330 enhances Ref-1/APE1 protein unfolded conformation in human PDAC cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2366.

Abstract LB-396: Bile reflux-induced APE1 mediates activation of EGFR-STAT3 in barret's and esophageal adenocarcinoma cells

Abstract Background: Barrett's esophagus (BE) is a premalignant condition where columnar metaplasia replaces the stratified squamous epithelium of the distal esophagus and is regarded as the main risk factor for esophageal adenocarcinoma (EAC). BE develops as a consequence of chronic gastroesophageal reflux disease (GERD), where acid and bile salts abnormally refluxate from the stomach into the distal region of esophagus. APE1/REF-1 is a multifunctional protein that plays an essential role in DNA repair activity and in redox-dependent transcriptional regulation. STAT3 signaling has been implicated in regulating cell survival, angiogenesis, and metastasis. EGFR is well known to facilitate the tyrosine phosphorylation of STAT3 and initiates downstream signaling cascades that facilitate proliferation, tumorigenesis, metastasis, and chemo resistance. In this study, we investigated the role of APE1 in activation of STAT3 in response to acidic bile salts (ABS) in EAC. Methodology: Non-neoplastic Barrett's (CPA, BAR10T and CPB) and esophageal adenocarcinoma (OE33, FLO-1) cells were exposed to acidic bile salts (pH4.0 and 5.5, 100 and 200uM) for 20 minutes. The mRNA and protein expression levels of APE-1, STAT3 and target genes were evaluated by real time PCR and immunoblotting. STAT3 transcription activity was studied by luciferase reporter assay. Immunofluorescence and cytoplasmic-nuclear fractionation were used to examine localization of APE-1, EGFR and STAT3 after exposure to acidic bile salts. Results: We demonstrate that APE1 is constitutively overexpressed in EAC whereas its expression is induced in non-neoplastic BE in response to ABS. Using overexpression and shRNA knockdown of APE1, we found that APE1 is required for phosphorylation, nuclear localization, and transcription activation of STAT3. By using APE1 redox-specific mutant (C65A) and APE1 redox inhibitor (E3330), we demonstrate that APE1 activates STAT3 in a redox-dependent manner. By using pharmacologic inhibitors and genetic knockdown systems, we found that EGFR is a required link between APE1 and STAT3. Phosphorylation of EGFR (Y1068) was directly associated with APE1 levels and redox function. By using co-immunoprecipitation and proximity ligation assays, we found that APE1 coexists and interacts with the EGFR-STAT3 protein complex. Consistent with these findings, we demonstrated a significant induction in the mRNA expression levels of STAT3 target genes (IL-6, IL-17A, BCL-xL, Survivin and c-Myc) in BE and EAC cells, following ABS treatment. ChIP assays indicated that ABS-treatment enhances binding of STAT3 to the promoter of its target genes, Survivin and BCL-xL, following ABS treatment. Inhibition of APE1/REF-1 redox activity using E3330 abrogated STAT3 DNA binding and transcriptional activity. In summary, our results provide evidence that bile reflux induced APE1 is involved in the activation of EGFR-STAT3 signaling axis in BE and EAC. Conclusion: The redox activity of APE1 mediates EGFR- STAT3 activation as a survival mechanism in response to acidic bile salts and oxidative stress. Constitutive activation of APE1 in EAC may present a therapeutic opportunity to targeting redox vulnerabilities in cancer cells. Citation Format: Ajaz A. Bhat, Heng Lu, Mohammad Suotto, Chen Zheng, Dunfa Peng, Mohammad Haris, Abbes Belkhiri, Wael El-Rifai. Bile reflux-induced APE1 mediates activation of EGFR-STAT3 in barret's and esophageal adenocarcinoma cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr LB-396.

APE1/Ref-1 redox function contributes to inflammatory pain sensitization

Inflammatory pain is a complex and multifactorial disorder. Apurinic/apyrimidinic endonuclease 1 (APE1), also called Redox Factor-1 (Ref-1), is constitutively expressed in the central nervous system and regulates various cellular functions including oxidative stress. In the present study, we investigated APE1 modulation and associated pain behavior changes in the complete Freund's adjuvant (CFA) model of inflammatory pain in rats. In addition we tested the anti-inflammatory effects of E3330, a selective inhibitor of APE1-redox activity, in CFA pain condition.We demonstrate that APE1 expression and subcellular distribution are significantly altered in rats at 4 days post CFA injection. We observed around 30% reduction in the overall APE1 mRNA and protein levels. Interestingly, our data point to an increased nuclear accumulation in the inflamed group as compared to the sham group. E3330 inhibitor injection in CFA rats normalized APE1 mRNA expression and changed its distribution toward cytosolic accumulation. Furthermore, intrathecal injection of E3330 decreased inflammation (i.e. reduced IL-6 expression) and alleviated pain, as assessed by measuring the paw withdrawal threshold with the von Frey test. In conclusion, our data indicate that changes in APE1 expression and sub-cellular distribution are implicated in inflammatory pain mechanisms mediated by APE1 redox functions. Further studies are required to elucidate the exact function of APE1 in inflammatory pain processes.

Inhibition of Ape1 Redox Activity Promotes Odonto/osteogenic Differentiation of Dental Papilla Cells.

Dentinogenesis is the formation of dentin, a substance that forms the majority of teeth, and this process is performed by odontoblasts. Dental papilla cells (DPCs), as the progenitor cells of odontoblasts, undergo the odontogenic differentiation regulated by multiple cytokines and paracrine signal molecules. Ape1 is a perfect paradigm of the function complexity of a biological macromolecule with two major functional regions for DNA repair and redox regulation, respectively. To date, it remains unclear whether Ape1 can regulate the dentinogenesis in DPCs. In the present study, we firstly examed the spatio-temporal expression of Ape1 during tooth germ developmental process, and found the Ape1 expression was initially high and then gradually reduced along with the tooth development. Secondly, the osteo/odontogenic differentiation capacity of DPCs was up-regulated when treated with either Ape1-shRNA or E3330 (a specific inhibitor of the Ape1 redox function), respectively. Moreover, we found that the canonical Wnt signaling pathway was activated in this process, and E3330 reinforced-osteo/odontogenic differentiation capacity was suppressed by Dickkopf1 (DKK1), a potent antagonist of canonical Wnt signaling pathway. Taken together, we for the first time showed that inhibition of Ape1 redox regulation could promote the osteo/odontogenic differentiation capacity of DPCs via canonical Wnt signaling pathway.

Ape1 regulates WNT/β-catenin signaling through its redox functional domain in pancreatic cancer cells.

Apurinic/apyrimidinic endonuclease 1/redox factor-1 (Ape1/Ref-1, Ape1) is a multifunctional protein that is upregulated in human pancreatic cancer. Ape1 redox domain plays an essential role in regulating the effects of reactive oxygen species (ROS) generated during physiological metabolism and pathological stress. In the present study, we explored whether Ape1 and ROS affect WNT/β-catenin signaling. We used E3330, a small molecule inhibitor of the redox activity of Ape1, and a siRNA approach to knock down Ape1, in two human pancreatic cancer cell lines. Inhibition of Ape1 resulted in growth suppression of pancreatic cancer cells, increased ROS levels, upregulation of β-catenin and c-myc and downregulation of cyclin D1. Consistent with these data, overexpression of Ape1 in pancreatic cancer cells reduced ROS and c-myc levels and increased cyclin D1 levels. Moreover, treatment of pancreatic cancer cells with H2O2 to induce oxidative stress resulted in upregulated ROS levels, decreased Ape1 at both the mRNA and protein level, and alterations in WNT/β-catenin pathway components. Finally, treatment of pancreatic cancer cells with the WNT/β-catenin inhibitor IWR-1 resulted in growth inhibition, which was greatly enhanced when combined with E3330 treatment. In summary, our results demonstrate that ROS is an important intracellular messenger that can modulate WNT/β‑catenin signaling. The present study provides interesting new insight into crosstalk between the redox function of Ape1 and WNT/β-catenin signaling in cancer cells. Furthermore, our data show that the combination of Ape1 and WNT inhibitors enhanced the inhibition of pancreatic cell proliferation. These results provide a promising novel therapeutic strategy for treating pancreatic cancer in future.

Functional analysis of tanshinone IIA that blocks the redox function of human apurinic/apyrimidinic endonuclease 1/redox factor-1.

Apurinic/apyrimidinic endonuclease 1/redox factor-1 (APE1/Ref-1) is a multifunctional protein possessing both DNA repair and redox regulatory activities. It has been shown that blocking redox function leads to genotoxic, antiangiogenic, cytostatic, and proapoptotic effects in cells. Therefore, the selective inhibitors against APE1’s redox function can be served as potential pharmaceutical candidates in cancer therapeutics. In the present study, we identified the biological specificity of the Chinese herbal compound tanshinone IIA (T2A) in blocking the redox function of APE1. Using dual polarization interferometry, the direct interaction between APE1 and T2A was observed with a KD value at subnanomolar level. In addition, we showed that T2A significantly compromised the growth of human cervical cancer and colon cancer cells. Furthermore, the growth-inhibitory or proapoptotic effect of T2A was diminished in APE1 knockdown or redox-deficient cells, suggesting that the cytostatic effect of T2A might be specifically through inhibiting the redox function of APE1. Finally, T2A pretreatment enhanced the cytotoxicity of ionizing radiation or other chemotherapeutic agents in human cervical cancer and colon cancer cell lines. The data presented herein suggest T2A as a promising bioactive inhibitor of APE1 redox activity.

APE1 promotes antioxidant capacity by regulating Nrf-2 function through a redox-dependent mechanism

APE1 is a multifunctional protein that has recently been implicated in protecting cells from oxidative stress. In the current study, we confirmed that APE1׳s effect on cellular antioxidant capacity is related to its redox activity through the use of an APE1 functional mutant, and we investigated the mechanism through which this multifunctional protein affects the function of the transcription factor Nrf-2 in regulating oxidative stress-induced genes. Using a pair of mutants for both the redox activity and the acetylation-regulated activity of APE1, in vitro assays showed that the redox activity of APE1 is crucial for its nuclear association with Nrf-2 and subsequent activation of Nrf-2׳s transcription of several downstream genes during oxidative challenge. Important oxidative stress genes are affected by APE1 redox activity, including Hmox1, Gstm1, and Txnrd1. In addition, utilizing human non-small-cell lung cancer sample tissue as well as a nude mouse xenograft model, we determined that APE1 expression levels are inversely correlated to oxidative stress in vivo. These findings indicated that interference with these crucial functions of APE1 shows promise in preventing resistance to certain radiotherapies and that further research is necessary to understand APE1׳s complex roles in regulating both the basal redox status and the oxidative stress state of the cellular environment.

Specific Inhibition of the Redox Activity of Ape1/Ref-1 by E3330 Blocks Tnf-Α-Induced Activation of Il-8 Production in Liver Cancer Cell Lines

APE1/Ref-1 is a main regulator of cellular response to oxidative stress via DNA-repair function and co-activating activity on the NF-κB transcription factor. APE1 is central in controlling the oxidative stress-based inflammatory processes through modulation of cytokines expression and its overexpression is responsible for the onset of chemoresistance in different tumors including hepatic cancer. We examined the functional role of APE1 overexpression during hepatic cell damage related to fatty acid accumulation and the role of the redox function of APE1 in the inflammatory process. HepG2 cells were stably transfected with functional and non-functional APE1 encoding plasmids and the protective effect of APE1 overexpression toward genotoxic compounds or FAs accumulation, was tested. JHH6 cells were stimulated with TNF-α in the presence or absence of E3330, an APE1 redox inhibitor. IL-8 promoter activity was assessed by a luciferase reporter assay, gene expression by Real-Time PCR and cytokines (IL-6, IL-8, IL-12) levels measured by ELISA. APE1 over-expression did not prevent cytotoxicity induced by lipid accumulation. E3330 treatment prevented the functional activation of NF-κB via the alteration of APE1 subcellular trafficking and reduced IL-6 and IL-8 expression induced by TNF-α and FAs accumulation through blockage of the redox-mediated activation of NF-κB. APE1 overexpression observed in hepatic cancer cells may reflect an adaptive response to cell damage and may be responsible for further cell resistance to chemotherapy and for the onset of inflammatory response. The efficacy of the inhibition of APE1 redox activity in blocking TNF-α and FAs induced inflammatory response opens new perspectives for treatment of inflammatory-based liver diseases.

Characterization of the Redox Activity and Disulfide Bond Formation in Apurinic/Apyrimidinic Endonuclease

Apurinic/apyrimidinic endonuclease (APE1) is an unusual nuclear redox factor in which the redox-active cysteines identified to date, C65 and C93, are surface inaccessible residues whose activities may be influenced by partial unfolding of APE1. To assess the role of the five remaining cysteines in APE1's redox activity, double-cysteine mutants were analyzed, excluding C65A, which is redox-inactive as a single mutant. C93A/C99A APE1 was found to be redox-inactive, whereas other double-cysteine mutants retained the same redox activity as that observed for C93A APE1. To determine whether these three cysteines, C65, C93, and C99, were sufficient for redox activity, all other cysteines were substituted with alanine, and this protein was shown to be fully redox-active. Mutants with impaired redox activity failed to stimulate cell proliferation, establishing an important role for APE1's redox activity in cell growth. Disulfide bond formation upon oxidation of APE1 was analyzed by proteolysis of the protein followed by mass spectrometry analysis. Within 5 min of exposure to hydrogen peroxide, a single disulfide bond formed between C65 and C138 followed by the formation of three additional disulfide bonds within 15 min; 10 total disulfide bonds formed within 1 h. A single mixed-disulfide bond involving C99 of APE1 was observed for the reaction of oxidized APE1 with thioredoxin (TRX). Disulfide-bonded APE1 or APE1-TRX species were further characterized by size exclusion chromatography and found to form large complexes. Taken together, our data suggest that APE1 is a unique redox factor with properties distinct from those of other redox factors.

The repair function of the multifunctional DNA repair/redox protein APE1 is neuroprotective after ionizing radiation

Although exposure to ionizing radiation (IR) can produce significant neurotoxicity, the mechanisms mediating this toxicity remain to be determined. Previous studies using neurons isolated from the central nervous system show that IR produces reactive oxygen species and oxidative DNA damage in those cells. Because the base excision DNA repair pathway repairs single-base modifications caused by ROS, we asked whether manipulating this pathway by altering APE1 expression would affect radiation-induced neurotoxicity. In cultures of adult hippocampal and sensory neurons, IR produces DNA damage as measured by phosphorylation of histone H2A.X and results in dose-dependent cell death. In isolated sensory neurons, we demonstrate for the first time that radiation decreases the capsaicin-evoked release of the neuropeptide CGRP. Reducing APE1 expression in cultured cells augments IR-induced neurotoxicity, whereas overexpressing APE1 is neuroprotective. Using lentiviral constructs with a neuronal specific promoter that selectively expresses APE1s different functions in neurons, we show that selective expression of the DNA repair competent (redox inactive) APE1 constructs in sensory neurons resurrects cell survival and neuronal function, whereas use of DNA-repair deficient (redox active) constructs is not protective. Use of an APE1 redox-specific inhibitor, APX3330, also facilitates neuronal protection against IR-induced toxicity. These results demonstrate for the first time that the repair function of APE1 is required to protect both hippocampal and DRG neuronal cultures—specifically neuronal cells—from IR-induced damage, while the redox activity of APE1 does not appear to be involved.

Interactions of Apurinic/Apyrimidinic Endonuclease with a Redox Inhibitor: Evidence for an Alternate Conformation of the Enzyme

Apurinic/apyrimidinic endonuclease (APE1) is an essential base excision repair protein that also functions as a reduction and oxidation (redox) factor in mammals. Through a thiol-based mechanism, APE1 reduces a number of important transcription factors, including AP-1, p53, NF-κB, and HIF-1α. What is known about the mechanism to date is that the buried residues Cys 65 and Cys 93 are critical for APE1's redox activity. To further detail the redox mechanism, we developed a chemical footprinting-mass spectrometric assay using N-ethylmaleimide (NEM), an irreversible Cys modifier, to characterize the interaction of the redox inhibitor, E3330, with APE1. When APE1 was incubated with E3330, two NEM-modified products were observed, one with two and a second with seven added NEMs; this latter product corresponds to a fully modified APE1. In a similar control reaction without E3330, only the +2NEM product was observed in which the two solvent-accessible Cys residues, C99 and C138, were modified by NEM. Through hydrogen-deuterium amide exchange with analysis by mass spectrometry, we found that the +7NEM-modified species incorporates approximately 40 more deuterium atoms than the native protein, which exchanges nearly identically as the +2NEM product, suggesting that APE1 can be trapped in a partially unfolded state. E3330 was also found to increase the extent of disulfide bond formation involving redox critical Cys residues in APE1 as assessed by liquid chromatography and tandem mass spectrometry, suggesting a basis for its inhibitory effects on APE1's redox activity. Collectively, our results suggest that APE1 adopts a partially unfolded state, which we propose is the redox active form of the enzyme.

Subcellular localization of apurinic endonuclease 1 promotes lung tumor aggressiveness via NF-κB activation

Apurinic endonuclease 1 (Ape1) is not only involved in base excision repair, but also activates some transcriptional factors through its redox activity. However, which subcellular localization of Ape1 is involved in the activation of transcriptional factor remains unclear. We first observed that Cox-2 expression was associated with cytoplasmic Ape1 expression in lung tumors and cancer cell lines. We thus hypothesize that nuclear factor (NF)-kappaB is activated by cytoplasmic Ape1 to cause Cox-2 expression. Herein, we generated cytoplasmic and nuclear Ape1 in Ape1-knockdown lung cancer cells by exogenous expression of Ape1 containing various deletions and/or mutations of the nuclear localization sequence. It was observed that cytoplasmic Ape1, but not nuclear Ape1, induced Cox-2 expression through NF-kappaB activation. NF-kappaB activation by cytoplasmic Ape1 was diminished by the Ape1 redox activity inhibitor resveratrol. Cells expressing cytoplasmic Ape1 exhibited tumor progression and metastasis in vitro and in vivo as xenografts, but cells expressing nuclear Ape1 did not. Patients with tumors containing elevated cytoplasmic Ape1 had a poor prognosis and a 3.722-fold risk of tumor recurrence and/or metastasis. Cytoplasmic Ape1 could therefore enhance lung tumor malignancy through NF-kappaB activation, suggesting that combination of cisplatin and specific redox inhibitor could improve chemotherapeutic response in patients with tumors containing elevated cytoplasmic Ape1.

Design and Synthesis of Novel Quinone Inhibitors Targeted to the Redox Function of Apurinic/Apyrimidinic Endonuclease 1/Redox Enhancing Factor-1 (Ape1/Ref-1)

The multifunctional enzyme apurinic endonuclease 1/redox enhancing factor 1 (Ape1/ref-1) maintains genetic fidelity through the repair of apurinic sites and regulates transcription through redox-dependent activation of transcription factors. Ape1 can therefore serve as a therapeutic target in either a DNA repair or transcriptional context. Inhibitors of the redox function can be used as either therapeutics or novel tools for separating the two functions for in vitro study. Presently there exist only a few compounds that have been reported to inhibit Ape1 redox activity; here we describe a series of quinones that exhibit micromolar inhibition of the redox function of Ape1. Benzoquinone and naphthoquinone analogues of the Ape1-inhibitor E3330 were designed and synthesized to explore structural effects on redox function and inhibition of cell growth. Most of the naphthoquinones were low micromolar inhibitors of Ape1 redox activity, and the most potent analogues inhibited tumor cell growth with IC(50) values in the 10-20 microM range.

Potentiation of Melphalan-Induced Cytotoxicity through Targeting of the Base Excision Repair Pathway in Multiple Myeloma.

Melphalan (M) is an active agent against multiple myeloma (MM). One of the obstacles with M treatment is the patient's ability to tolerate side effects such as mucositis and pancytopenia. This is especially true for those patients >70 years of age. We hypothesize that potentiation of M-induced cytotoxicity is possible in MM with agents that target, and therefore further imbalance, multiple DNA repair pathways. A key protein in the Base Excision Repair (BER) pathway, Apurinic/apyrimidinic endonuclease/ redox factor (APE1/Ref-1 or APE1) plays a major role in the repair of damage caused by chemotherapeutic agents including M and Temozolomide (TMZ), interacts with a number of transcription factors (HIF1-a, p53, AP1, NFkB, etc) to regulate their function through oxidation/reduction (redox) signaling, and is overexpressed in refractory/relapsed MM cells. Furthermore, a reduction in APE1 protein sensitizes MM cells to melphalan indicating that inhibition of this protein may have therapeutic potential in MM. In order to decipher the importance of APE1's redox and repair functions in MM cells' response to DNA damage via melphalan and TMZ, we have available to us small molecule APE1 inhibitors that affect only the repair activity or only the redox activity of APE1. The mechanism of action of MLP is primarily via monoadduct leading to DNA interstrand cross-link (ICL) formation which is processed by the Nucleotide Excision Repair (NER) pathway. MLP also causes N7methyl-G and N3methyl-A adduct formation which are repaired by the BER pathway. For these studies, we treated RPMI 8226 cells with several chemotherapeutic agents:1.M;2.TMZ, which creates primarily N7methyl-G and N3methyl-A adducts;3.Methoxyamine (MX), which has been shown to inhibit further processing by the BER pathway; and4.a small molecule which blocks the redox function of APE1. Our purpose was to overwhelm the DNA repair pathways by causing the accumulation of DNA repair intermediates and inducing apoptosis.M-induced cytotoxicity is enhanced by TMZ (CI=0.08), MX (CI=0.89), and E3330 (CI=0.06), and this effect was synergistic as determined by CalcuSyn software which generates median effect and combinational index (CI) values, with CI<1 indicative of synergy. Using MX to inhibit APE1 in combination with TMZ results in an increase in DNA damage and an increase in apoptosis in 8226 cells. Furthermore, the combination of the redox inhibitor + MX which blocks both functions of APE1 also results in an increase in apoptosis in the MM cells. Further studies include the addition of M to these combinations that are demonstrating an increase in efficacy in MM cells. These results indicate that using these DNA repair-targeted agents in addition to MLP may be a feasible way to increase the effect of the M on MM cells. The potential advantages to patients would be that they would be able to tolerate more treatments and that the combination treatments would be more effective than treatment with M alone. We anticipate that effective modulation of M and/or TMZ will overcome resistance without compromising efficacy and help to alleviate some of the side effects patients have to endure with melphalan treatment. This may be particularly advantageous to the more elderly patients.

Ape1 regulates hematopoietic differentiation of embryonic stem cells through its redox functional domain

AbstractApe1 is a molecule with dual functions in DNA repair and redox regulation of transcription factors. In Ape1-deficient mice, embryos do not survive beyond embryonic day 9, indicating that this molecule is required for normal embryo development. Currently, direct evidence of the role of Ape1 in regulating hematopoiesis is lacking. We used the embryonic stem (ES) cell differentiation system and an siRNA approach to knockdown Ape1 gene expression to test the role of Ape1 in hematopoiesis. Hemangioblast development from ES cells was reduced 2- to 3-fold when Ape1 gene expression was knocked down by Ape1-specific siRNA, as was primitive and definitive hematopoiesis. Impaired hematopoiesis was not associated with increased apoptosis in siRNA-treated cells. To begin to explore the mechanism whereby Ape1 regulates hematopoiesis, we found that inhibition of the redox activity of Ape1 with E3330, a specific Ape1 redox inhibitor, but not Ape1 DNA repair activity, which was blocked using the small molecule methoxyamine, affected cytokine-mediated hemangioblast development in vitro. In summary, these data indicate Ape1 is required in normal embryonic hematopoiesis and that the redox function, but not the repair endonuclease activity, of Ape1 is critical in normal embryonic hematopoietic development.