Oxidative stress and androgen receptor signaling in the development and progression of castration-resistant prostate cancer

Gene polymorphisms in antioxidant enzymes correlate with the efficacy of androgen-deprivation therapy for prostate cancer with implications of oxidative stress

Background

Oxidative stress mitigated by antioxidant enzymes is thought to be involved in the progression to castration-resistant prostate cancer (CRPC) during androgen-deprivation therapy (ADT). This study investigated the association between genetic variations in antioxidant enzymes and the efficacy of ADT as well as its biological background.

Patients and methods

The non-synonymous or promoter-locating polymorphisms of antioxidant enzymes were examined as well as the time to CRPC progression and overall survival in 104 and 92 patients treated with ADT for metastatic and non-metastatic prostate cancer, respectively. In addition, intracellular reactive oxygen species and expression levels of antioxidant enzymes were examined in castration-resistant and enzalutamide-resistant cells.

Results

In metastatic prostate cancer, the AG/GG allele in GSTM3 rs7483 and CT/TT allele in CAT rs564250 were associated with a significantly lower risk of progression to CRPC and all-cause death compared with homozygotes of the major AA allele (hazard ratio [HR]; [95% confidence interval (CI)], 0.55 [0.34-0.86], P = 0.0086) and CC allele (HR; [95% CI], 0.48 [0.24-0.88], P = 0.016), respectively. On multivariate analyses, only GSTM3 rs7483 was associated with significant progression risk (AG/GG versus AA; HR; [95% CI], 0.45 [0.25-0.79], P = 0.0047) even after Bonferroni adjustment. In non-metastatic prostate cancer, the AG/GG allele in GSTM3 rs7483 was associated with a significantly lower risk of progression to CRPC (HR; [95% CI], 0.35 [0.10-0.93], P = 0.034) and all-cause death (HR; [95% CI], 0.26 [0.041-0.96], P = 0.043) compared with the AA allele. Intracellular reactive oxygen species levels were increased, accompanied with augmented GSTM3 expression in both castration-resistant and enzalutamide-resistant cells.

Conclusions

Differential activity of antioxidant enzymes caused by the polymorphism in GSTM3 may contribute to resistance to hormonal therapy through oxidative stress. The GSTM3 rs7483 polymorphism may be a promising biomarker for prostate cancer patients treated with ADT.

Thioredoxin-1 protects against androgen receptor-induced redox vulnerability in castration-resistant prostate cancer

Androgen deprivation (AD) therapy failure leads to terminal and incurable castration-resistant prostate cancer (CRPC). We show that the redox-protective protein thioredoxin-1 (TRX1) increases with prostate cancer progression and in androgen-deprived CRPC cells, suggesting that CRPC possesses an enhanced dependency on TRX1. TRX1 inhibition via shRNA or a phase I-approved inhibitor, PX-12 (untested in prostate cancer), impedes the growth of CRPC cells to a greater extent than their androgen-dependent counterparts. TRX1 inhibition elevates reactive oxygen species (ROS), p53 levels and cell death in androgen-deprived CRPC cells. Unexpectedly, TRX1 inhibition also elevates androgen receptor (AR) levels under AD, and AR depletion mitigates both TRX1 inhibition-mediated ROS production and cell death, suggesting that AD-resistant AR expression in CRPC induces redox vulnerability. In vivo TRX1 inhibition via shRNA or PX-12 reverses the castration-resistant phenotype of CRPC cells, significantly inhibiting tumor formation under systemic AD. Thus, TRX1 is an actionable CRPC therapeutic target through its protection against AR-induced redox stress.

Proteomics analyses of prostate cancer cells reveal cellular pathways associated with androgen resistance

While significant advances have been made in the diagnosis and treatment of prostate cancer, each year tens of thousands of men still die from prostate cancer in the United States. Thus, greater understanding of cellular pathways and molecular basis of prostate cancer progression in the development of androgen resistance is needed to treat these lethal phenotypes. To dissect the mechanism of androgen resistance, we utilize a proteomics approach to study the development of androgen resistance in LNCaP prostate cancer cells. Our results showed the predominant involvement of metabolic pathways that were elevated in androgen resistance phenotype. We further found the amplification of PI3K/AKT pathway and the overexpression of proteasome proteins while the mitochondrial oxidation phosphorylation was severely hampered in castration-resistant LNCaP-95 cells compared to LNCaP cells. Interestingly, we also found the induction of Dicer, a cytoplasmic endoribonuclease microRNA regulator in the androgen-ablated LNCaP-95 prostate cancer cells. We verified some of these data by orthogonal methods including Western blot analysis and in castrated animal xenograft studies. To our knowledge, this is the first report showing induced expression of proteasome proteins in androgen ablation prostate cancer cells. If validated in clinical studies, the findings will have significant implications in understanding the complexity of biochemical recurrence in prostate cancer.

Procyanidin B2 3,3″-di-O-gallate induces oxidative stress-mediated cell death in prostate cancer cells via inhibiting MAP kinase phosphatase activity and activating ERK1/2 and AMPK

Neoplastic cells exhibit higher oxidative stress compared to normal cells; however, antioxidants based clinical trials have mostly failed. Another attractive therapeutic approach is to further increase the oxidative stress in cancer cells leading to cell death. Herein, we show that Procyanidin B2 3,3″-di-O-gallate (B2G2), the most active constituent of grape seed extract, treatment causes cell death in human prostate cancer (PCa) cells (LNCaP and 22Rv1) via increasing the reactive oxygen species (ROS) generation. Mechanistically, B2G2 treatment decreased the mitochondrial electron transport chain complex III activity leading to enhanced mitochondrial superoxide generation and decreased ATP production in LNCaP cells. Additional molecular studies revealed that B2G2-induced cell death was mediated mainly through ROS-induced sustained activation of ERK1/2, which was due to inhibition of MAP kinase phosphatase (MKP) activity as over-expression of MKP3 in LNCaP cells conferred significant protection against B2G2-induced cell death. Along with ERK1/2, AMP-activated protein kinase α (AMPKα) was also activated by B2G2 treatment, and pre-treatment with AMPKα inhibitor compound C significantly reversed the cytotoxic effects of B2G2 in LNCaP cells. Furthermore, pre-treatment of MKP3 over-expressing LNCaP cells with compound C further reduced the B2G2-induced cell death, suggesting the involvement of AMPKα along with MKP3 and ERK1/2 in the biological effects of B2G2. Together, these results for the first time identified that oxidative stress and MKP3 inhibition play a critical role in B2G2-induced cell death in PCa cells through sustained activation of both ERK1/2 and AMPKα. These results offer a unique opportunity to control this deadly malignancy through B2G2 use.

Multimodal actions of the phytochemical sulforaphane suppress both AR and AR-V7 in 22Rv1 cells: Advocating a potent pharmaceutical combination against castration-resistant prostate cancer

Prostate cancer (PCa) cells expressing full-length androgen receptor (AR-FL) are susceptible to androgen deprivation therapy (ADT). However, outgrowth of castration-resistant prostate cancer (CRPC) can occur due to the expression of constitutively active (ligand-independent) AR splice variants, particularly AR-V7. We previously demonstrated that sulforaphane (SFN), an isothiocyanate phytochemical, can decrease AR-FL levels in the PCa cell lines, LNCaP and C4-2B. Here, we examined the efficacy of SFN in targeting both AR-FL and AR-V7 in the CRPC cell line, CWR22Rv1 (22Rv1). MTT cell viability, wound-heal assay, and colony forming unit (CFU) measurements revealed that 22Rv1 cells are resistant to the anti-androgen, enzalutamide (ENZ). However, co-exposure to SFN sensitized these cells to the potent anticancer effects of ENZ (P<0.05). Immunoblot analyses showed that SFN (5–20 µM) rapidly decreases both AR-FL and AR-V7 levels, and immunofluorescence microscopy (IFM) depicted decreased AR in both cytoplasm and nucleus with SFN treatment. SFN increased both ubiquitination and proteasomal activity in 22Rv1 cells. Studies using a protein synthesis inhibitor (cycloheximide) or a proteasomal inhibitor (MG132) indicated that SFN increases both ubiquitin-mediated aggregation and subsequent proteasomal-degradation of AR proteins. Previous studies reported that SFN inhibits the chaperone activity of heat-shock protein 90 (Hsp90) and induces the nuclear factor erythroid-2-like 2 (Nrf2) transcription factor. Therefore, we investigated whether the Hsp90 inhibitor, ganetespib (G) or the Nrf2 activator, bardoxolone methyl (BM) can similarly suppress AR levels in 22Rv1 cells. Low doses of G and BM, alone or in combination, decreased both AR-FL and AR-V7 levels, and combined exposure to G+BM sensitized 22Rv1 cells to ENZ. Therefore, adjunct treatment with the phytochemical SFN or a safe pharmaceutical combination of G+BM may be effective against CRPC cells, especially those expressing AR-V7.

Redox theory of aging: implications for health and disease

Genetics ultimately defines an individual, yet the phenotype of an adult is extensively determined by the sequence of lifelong exposures, termed the exposome. The redox theory of aging recognizes that animals evolved within an oxygen-rich environment, which created a critical redox interface between an organism and its environment. Advances in redox biology show that redox elements are present throughout metabolic and structural systems and operate as functional networks to support the genome in adaptation to environmental resources and challenges during lifespan. These principles emphasize that physical and functional phenotypes of an adult are determined by gene-environment interactions from early life onward. The principles highlight the critical nature of cumulative exposure memories in defining changes in resilience progressively during life. Both plasma glutathione and cysteine systems become oxidized with aging, and the recent finding that cystine to glutathione ratio in human plasma predicts death in coronary artery disease (CAD) patients suggests this could provide a way to measure resilience of redox networks in aging and disease. The emerging concepts of cumulative gene-environment interactions warrant focused efforts to elucidate central mechanisms by which exposure memory governs health and etiology, onset and progression of disease.

Gene Polymorphism-related Individual and Interracial Differences in the Outcomes of Androgen Deprivation Therapy for Prostate Cancer

Among patients with prostate cancer, the prognosis after androgen deprivation therapy differs significantly among individuals and among races; however, the reasons underlying these differences are poorly understood. Several single nucleotide polymorphisms in genes associated with prostate cancer progression or castration resistance might serve as the host factor that influences prognosis and, thus, accounts for these individual and racial gaps in treatment outcomes. Accordingly, single nucleotide polymorphisms associated with treatment outcomes could be used as predictive and/or prognostic biomarkers for patient stratification and to identify personalized treatment and follow-up protocols. The present review has summarized the genetic polymorphisms that have been reported to associate with androgen deprivation therapy outcomes among patients with prostate cancer and compared the allele frequencies among different ethnic groups.

Endostatin inhibits androgen-independent prostate cancer growth by suppressing nuclear receptor-mediated oxidative stress

Androgen-deprivation therapy has been identified to induce oxidative stress in prostate cancer (PCa), leading to reactivation of androgen receptor (AR) signaling in a hormone-refractory manner. Thus, antioxidant therapies have gained attention as adjuvants for castration-resistant PCa. Here, we report for the first time that human endostatin (ES) prevents androgen-independent growth phenotype in PCa cells through its molecular targeting of AR and glucocorticoid receptor (GR) and downstream pro-oxidant signaling. This reversal after ES treatment significantly decreased PCa cell proliferation through down-regulation of GR and up-regulation of manganese superoxide dismutase and reduced glutathione levels. Proteome and biochemical analyses of ES-treated PCa cells further indicated a significant up-regulation of enzymes in the major reactive oxygen species (ROS) scavenging machinery, including catalase, glutathione synthetase, glutathione reductase, NADPH-cytochrome P450 reductase, biliverdin reductase, and thioredoxin reductase, resulting in a concomitant reduction of intracellular ROS. ES further augmented the antioxidant system through up-regulation of glucose influx, the pentose phosphate pathway, and NAD salvaging pathways. This shift in cancer cell redox homeostasis by ES significantly decreased the effect of protumorigenic oxidative machinery on androgen-independent PCa growth, suggesting that ES can suppress GR-induced resistant phenotype upon AR antagonism and that the dual targeting action of ES on AR and GR can be further translated to PCa therapy.-Lee, J. H., Kang, M., Wang, H., Naik, G., Mobley, J. A., Sonpavde, G., Garvey, W. T., Darley-Usmar, V. M., Ponnazhagan, S. Endostatin inhibits androgen-independent prostate cancer growth by suppressing nuclear receptor-mediated oxidative stress.

Stimulation of cellular senescent processes, including secretory phenotypes and anti-oxidant responses, after androgen deprivation therapy in human prostate cancer

Endocrine resistance is a major problem in prostate cancer. Recent studies suggest that cellular plasticity plays a key role in therapy resistance. Yet little is known about the cellular changes of human prostate cancer after androgen deprivation therapy (ADT). In this study, we investigated cellular senescence, senescence-associated secretory phenotypes (SASPs), and anti-oxidant responses. Hormone ablation upregulated senescence-associated (SA)-β-Gal activity in prostate glands, as well as the expressions of p27^KIP1 and p53, in a mouse castration model. In line with this, the expressions of p21^CIP1 and p27^KIP1 were significantly more upregulated in human non-pathological prostatic glands after ADT than in untreated specimens. In a study of SASP markers, the expressions of IL6 and IL8 were also more upregulated in human non-pathological prostatic glands after ADT than in untreated specimens. IL6, IL8, and MMP2 were expressed more strongly in human prostate cancer specimens resected after ADT than in untreated tumors. Of note, treatment with the anti-oxidant reagent NAC significantly suppressed SA-β-Gal activity in androgen-sensitive human prostate cancer LNCaP cells. In immunohistochemical analyses on anti-oxidant response genes, NRF2 and NQO1 were more upregulated after hormone ablation in human prostate gland and carcinoma specimens after ADT than in untreated specimens or in murine prostate glands after castration. Taken together, these findings suggest that ADT induces cellular senescence processes accompanied by secretory phenotypes and anti-oxidant responses in prostate. These cellular changes may be attractive targets for preventing endocrine resistance in prostate cancer.

Low β₂-adrenergic receptor level may promote development of castration resistant prostate cancer and altered steroid metabolism

The underlying mechanisms responsible for the development of castration-resistant prostate cancer (CRPC) in patients who have undergone androgen deprivation therapy are not fully understood. This is the first study to address whether β₂-adrenergic receptor (ADRB2)- mediated signaling may affect CRPC progression in vivo. By immunohistochemical analyses, we observed that low levels of ADRB2 is associated with a more rapid development of CRPC in a Norwegian patient cohort. To elucidate mechanisms by which ADRB2 may affect CRPC development, we stably transfected LNCaP cells with shRNAs to mimic low and high expression of ADRB2. Two UDP-glucuronosyltransferases, UGT2B15 and UGT2B17, involved in phase II metabolism of androgens, were strongly downregulated in two LNCaP shADRB2 cell lines. The low-ADRB2 LNCaP cell lines displayed lowered glucuronidation activities towards androgens than high-ADRB2 cells. Furthermore, increased levels of testosterone and enhanced androgen responsiveness were observed in LNCaP cells expressing low level of ADRB2. Interestingly, these cells grew faster than high-ADRB2 LNCaP cells, and sustained their low glucuronidation activity in castrated NOD/SCID mice. ADRB2 immunohistochemical staining intensity correlated with UGT2B15 staining intensity in independent TMA studies and with UGT2B17 in one TMA study. Similar to ADRB2, we show that low levels of UGT2B15 are associated with a more rapid CRPC progression. We propose a novel mechanism by which ADRB2 may affect the development of CRPC through downregulation of UGT2B15 and UGT2B17.

Sex-specific hippocampal 5-hydroxymethylcytosine is disrupted in response to acute stress

Environmental stress is among the most important contributors to increased susceptibility to develop psychiatric disorders. While it is well known that acute environmental stress alters gene expression, the molecular mechanisms underlying these changes remain largely unknown. 5-hydroxymethylcytosine (5hmC) is a novel environmentally sensitive epigenetic modification that is highly enriched in neurons and is associated with active neuronal transcription. Recently, we reported a genome-wide disruption of hippocampal 5hmC in male mice following acute stress that was correlated to altered transcript levels of genes in known stress related pathways. Since sex-specific endocrine mechanisms respond to environmental stimulus by altering the neuronal epigenome, we examined the genome-wide profile of hippocampal 5hmC in female mice following exposure to acute stress and identified 363 differentially hydroxymethylated regions (DhMRs) linked to known (e.g., Nr3c1 and Ntrk2) and potentially novel genes associated with stress response and psychiatric disorders. Integration of hippocampal expression data from the same female mice found stress-related hydroxymethylation correlated to altered transcript levels. Finally, characterization of stress-induced sex-specific 5hmC profiles in the hippocampus revealed 778 sex-specific acute stress-induced DhMRs some of which were correlated to altered transcript levels that produce sex-specific isoforms in response to stress. Together, the alterations in 5hmC presented here provide a possible molecular mechanism for the adaptive sex-specific response to stress that may augment the design of novel therapeutic agents that will have optimal effectiveness in each sex.

Sulforaphane increases the efficacy of anti-androgens by rapidly decreasing androgen receptor levels in prostate cancer cells

Prostate cancer (PCa) cells utilize androgen for their growth. Hence, androgen deprivation therapy (ADT) using anti-androgens, e.g. bicalutamide (BIC) and enzalutamide (ENZ), is a mainstay of treatment. However, the outgrowth of castration resistant PCa (CRPC) cells remains a significant problem. These CRPC cells express androgen receptor (AR) and utilize the intratumoral androgen towards their continued growth and invasion. Sulforaphane (SFN), a naturally occurring isothiocyanate found in cruciferous vegetables, can decrease AR protein levels. In the present study, we tested the combined efficacy of anti-androgens and SFN in suppressing PCa cell growth, motility and clonogenic ability. Both androgen-dependent (LNCaP) and androgen-independent (C4-2B) cells were used to monitor the effects of BIC and ENZ, alone and in combination with SFN. Co-exposure to SFN significantly (p<0.005) enhanced the anti-proliferative effects of anti-androgens and downregulated expression of the AR-responsive gene, prostate specific antigen (PSA) (p<0.05). Exposure to SFN decreased AR protein levels in a time- and dose-dependent manner with almost no AR detected at 24 h with 15 µM SFN (p<0.005). This rapid and potent AR suppression by SFN occurred by both AR protein degradation, as suggested by cycloheximide (CHX) co-exposure studies, and by suppression of AR gene expression, as evident from quantitative RT-PCR experiments. Pre-exposure to SFN also reduced R1881-stimulated nuclear localization of AR, and combined treatment with SFN and anti-androgens abrogated the mitogenic effects of this AR-agonist (p<0.005). Wound-healing assays revealed that co-exposure to SFN and anti-androgens can significantly (p<0.005) reduce PCa cell migration. In addition, long-term exposures (14 days) to much lower concentrations of these agents, SFN (0.2 µM), BIC (1 µM) and/or ENZ (0.4 µM) significantly (p<0.005) decreased the number of colony forming units (CFUs). These findings clearly suggest that SFN may be used as a promising adjunct agent to augment the efficacy of anti-androgens against aggressive PCa cells.

Role of protein S in castration-resistant prostate cancer-like cells

Understanding how castration-resistant prostate cancer (CRPC) cells survive the androgen-deprivation condition is crucial for treatment of this advanced prostate cancer (PCa). Here, we reported for the first time the up-regulation of protein S (PROS), an anticoagulant plasma glycoprotein with multiple biological functions, in androgen-insensitive PCa cells and in experimentally induced castration-resistant PCa cells. Overexpression of exogenous PROS in LNCaP cells reduced androgen deprivation-induced apoptosis and enhanced anchorage-dependent clonogenic ability under androgen deprivation condition. Reciprocally, PROS1 knockdown inhibited cell invasiveness and migration, caused the growth inhibition of castration-resistant tumor xenograft under androgen-depleted conditions, and potentiated Taxol (a widely prescribed anti-neoplastic agent)-mediated cell death in PC3 cells. Furthermore, PROS overexpression significantly stimulated AKT activation but failed to evoke oxidative stress in LNCaP cells under normal condition, suggesting that the malignance-promoting effects of the above-mentioned pathway may occur in the order of oxidative stress/PROS/AKT. The potential mechanism may be due to control of oxidative stress-elicited activation of PI3K-AKT-mTOR pathway. Taken together, our gain-of-function, loss-of-function analyses suggest that PROS may facilitate cell proliferation and promote castration resistance in human castration-resistant PCa-like cells via its apoptosis-regulating property. Future study emphasizing on delineating how PROS regulate cellular processes controlling transformation during the development of castration resistance should open new doors for the development of novel therapeutic targets for CRPC.

Equol inhibits prostate cancer growth through degradation of androgen receptor by S-phase kinase-associated protein 2

Chemopreventive and potential therapeutic effects of soy isoflavones have been shown to be effective in numerous preclinical studies as well as clinical studies in prostate cancer. Although the inhibition of androgen receptor signaling has been supposed as one mechanism underlying their effects, the precise mechanism of androgen receptor inhibition remains unclear. Thus, this study aimed to clarify their mechanism. Among soy isoflavones, equol suppressed androgen receptor as well as prostate-specific antigen expression most potently in androgen-dependent LNCaP cells. However, the inhibitory effect on androgen receptor expression and activity was less prominent in castration-resistant CxR and 22Rv1 cells. Consistently, cell proliferation was suppressed and cellular apoptosis was induced by equol in LNCaP cells, but less so in CxR and 22Rv1 cells. We revealed that the proteasome pathway through S-phase kinase-associated protein 2 (Skp2) was responsible for androgen receptor suppression. Taken together, soy isoflavones, especially equol, appear to be promising as chemopreventive and therapeutic agents for prostate cancer based on the fact that equol augments Skp2-mediated androgen receptor degradation. Moreover, because Skp2 expression was indicated to be crucial for the effect of soy isoflavones, soy isoflavones may be applicable for precancerous and cancerous prostates.

A multicenter phase 1/2a dose-escalation study of the antioxidant moiety of vitamin E 2,2,5,7,8-pentamethyl-6-chromanol (APC-100) in men with advanced prostate cancer

BACKGROUND

A phase 1/2a dose escalation study of APC-100 (2,2,5,7,8-Pentamethyl-6-chromanol) was conducted to determine maximum tolerated dose (MTD), recommended phase 2 dose, toxicities and efficacy in men with castrate-resistant prostate cancer (CRPC).

METHODS

This open label phase 1/2a study utilizes a time-to-event reassessment method (TITE-CRM) design. Patients in cohorts of 3 were treated with escalating doses of APC-100 (900 mg-2400 mg) orally once daily continuously. Cycles were 28 days.

RESULTS

Twenty patients with CRPC were enrolled in the dose escalation cohort. One possible DLT (elevated ALT) was seen at dose level 1. No other DLTs were seen and no dose reductions were required. Most frequent AEs included nausea (grade 1 in 6 patients) and elevated transaminases (grade 1-3 in 5 patients). After enrolment of 20 patients the MTD was not reached, however the maximal feasible dose was exceeded due to the number of capsules ingested. Five of the 20 patients had stable disease as their best response. The median progression free survival (PFS) for the cohort was 2.8 months (range 1-8).

CONCLUSIONS

APC-100 is a novel agent with dual mechanism of action functioning both as potent antioxidant as well as antiandrogen. No detectable APC-100 was found in the plasma at dose level 5 (2100 mg) and it was felt that maximal feasibility was nearly reached. APC-100 is being reformulated as a tablet to allow further dose escalation. Once a recommended phase 2 dose is established, future studies in prostate cancer chemoprevention should be conducted.

LEDGF/p75 Overexpression Attenuates Oxidative Stress-Induced Necrosis and Upregulates the Oxidoreductase ERP57/PDIA3/GRP58 in Prostate Cancer

Prostate cancer (PCa) mortality is driven by highly aggressive tumors characterized by metastasis and resistance to therapy, and this aggressiveness is mediated by numerous factors, including activation of stress survival pathways in the pro-inflammatory tumor microenvironment. LEDGF/p75, also known as the DFS70 autoantigen, is a stress transcription co-activator implicated in cancer, HIV-AIDS, and autoimmunity. This protein is targeted by autoantibodies in certain subsets of patients with PCa and inflammatory conditions, as well as in some apparently healthy individuals. LEDGF/p75 is overexpressed in PCa and other cancers, and promotes resistance to chemotherapy-induced cell death via the transactivation of survival proteins. We report in this study that overexpression of LEDGF/p75 in PCa cells attenuates oxidative stress-induced necrosis but not staurosporine-induced apoptosis. This finding was consistent with the observation that while LEDGF/p75 was robustly cleaved in apoptotic cells into a p65 fragment that lacks stress survival activity, it remained relatively intact in necrotic cells. Overexpression of LEDGF/p75 in PCa cells led to the upregulation of transcript and protein levels of the thiol-oxidoreductase ERp57 (also known as GRP58 and PDIA3), whereas its depletion led to ERp57 transcript downregulation. Chromatin immunoprecipitation and transcription reporter assays showed LEDGF/p75 binding to and transactivating the ERp57 promoter, respectively. Immunohistochemical analysis revealed significantly elevated co-expression of these two proteins in clinical prostate tumor tissues. Our results suggest that LEDGF/p75 is not an inhibitor of apoptosis but rather an antagonist of oxidative stress-induced necrosis, and that its overexpression in PCa leads to ERp57 upregulation. These findings are of significance in clarifying the role of the LEDGF/p75 stress survival pathway in PCa.

Crosstalk between epithelial-mesenchymal transition and castration resistance mediated by Twist1/AR signaling in prostate cancer

Although invasive and metastatic progression via the epithelial-mesenchymal transition (EMT) and acquisition of resistance to castration are both critical steps in prostate cancer, the molecular mechanism of this interaction remains unclear. In this study, we aimed to elucidate the interaction of signaling between castration resistance and EMT, and to apply this information to the development of a novel therapeutic concept using transforming growth factor-β (TGF-β) inhibitor SB525334 combined with androgen-deprivation therapy against prostate cancer using an in vivo model. This study revealed that an EMT inducer (TGF-β) induced full-length androgen receptor (AR) and AR variant expression. In addition, a highly invasive clone showed augmented full-length AR and AR variant expression as well as acquisition of castration resistance. Conversely, full-length AR and AR as well as Twist1 and mesenchymal molecules variant expression were up-regulated in castration-resistant LNCaP xenograft. Finally, TGF-β inhibitor suppressed Twist1 and AR expression as well as prostate cancer growth combined with castration. Taken together, these results demonstrate that Twist1/AR signaling was augmented in castration resistant as well as mesenchymal-phenotype prostate cancer, indicating the molecular mechanism of mutual and functional crosstalk between EMT and castration resistance, which may play a crucial role in prostate carcinogenesis and progression.

Plk1 inhibition enhances the efficacy of androgen signaling blockade in castration-resistant prostate cancer

Prostate cancer is thought to be driven by oxidative stress, lipid metabolism, androgen receptor (AR) signaling, and activation of the PI3K-AKT-mTOR pathway, but it is uncertain how they may become coordinated during progression to castration-resistant disease that remains incurable. The mitotic kinase polo-like kinase 1 (Plk1) is elevated in prostate cancer, where its expression is linked to tumor grade. Notably, Plk1 signaling and lipid metabolism were identified recently as two of the top five most upregulated pathways in a mouse xenograft model of human prostate cancer. Herein, we show that oxidative stress activates both the PI3K-AKT-mTOR pathway and AR signaling in a Plk1-dependent manner in prostate cells. Inhibition of the PI3K-AKT-mTOR pathway prevented oxidative stress-induced activation of AR signaling. Plk1 modulation also affected cholesteryl ester accumulation in prostate cancer via the SREBP pathway. Finally, Plk1 inhibition enhanced cellular responses to androgen signaling inhibitors (ASI) and overcame ASI resistance in both cultured prostate cancer cells and patient-derived tumor xenografts. Given that activation of AR signaling and the PI3K-AKT-mTOR pathway is sufficient to elevate SREBP-dependent expression of key lipid biosynthesis enzymes in castration-resistant prostate cancer (CRPC), our findings argued that Plk1 activation was responsible for coordinating and driving these processes to promote and sustain the development of this advanced stage of disease. Overall, our results offer a strong mechanistic rationale to evaluate Plk1 inhibitors in combination drug trials to enhance the efficacy of ASIs in CRPC.

Expression of reactive oxygen species-related proteins according to androgen and HER-2 status in estrogen receptor-negative breast cancer

OBJECTIVE

The purpose of the current study is to understand the clinicopathological implications of redox proteins in association with androgen receptor (AR) and HER-2 status in estrogen receptor (ER)-negative breast cancers through evaluation of the expression patterns of redox proteins, such as catalase, thioredoxin reductase (TxNR), glutathione S-transferase π (GSTπ), thioredoxin interacting protein (TxNIP), and manganese superoxide dismutase (MnSOD).

METHODS

Two hundred cases of ER-negative breast cancer samples were collected as a tissue microarray. Immunohistochemical staining was done for redox-related proteins, after which the resulting data set was organized by AR and HER-2 status.

RESULTS

The redox proteins that had a significant association with AR and HER-2 status were tumoral catalase (p < 0.001) and stromal GSTπ (p < 0.001). Tumoral catalase was least expressed in the AR-/HER-2- group, while stromal GSTπ was least expressed in both the AR+/HER-2- and the AR-/HER-2- groups. Stromal GSTπ was highly expressed in HER-2 positive groups (p < 0.001). Stromal GSTπ negativity and tumoral MnSOD positivity were associated with a shorter disease-free survival (p = 0.041 and p = 0.007, respectively) in univariate analysis.

CONCLUSION

ER-negative breast cancers showed different expressions of redox-related proteins according to AR and HER-2 status. Catalase expression was high in AR-negative groups, while stromal GSTπ expression was high in HER-2-positive groups.

PMA induces androgen receptor downregulation and cellular apoptosis in prostate cancer cells

Phorbol 12-myristate 13-acetate (PMA) induces cellular apoptosis in prostate cancer cells, the growth of which is governed by androgen/androgen receptor (AR) signaling, but the mechanism by which PMA exerts this effect remains unknown. Therefore, in this study, we investigated the mechanistic action of PMA in prostate cancer cells with regard to AR. We showed that PMA decreased E2F1 as well as AR expression in androgen-dependent prostate cancer LNCaP cells. Furthermore, PMA activated JNK and p53 signaling, resulting in the induction of cellular apoptosis. In LNCaP cells, androgen deprivation and a novel anti-androgen enzalutamide (MDV3100) augmented cellular apoptosis induced by PMA. Moreover, castration-resistant prostate cancer (CRPC) C4-2 cells were more sensitive to PMA compared with LNCaP cells and were sensitized to PMA by enzalutamide. Finally, the expression of PKC, E2F1, and AR was diminished in PMA-resistant cells, indicating that the gain of independence from PKC, E2F1, and AR functions leads to PMA resistance. In conclusion, PMA exerted its anti-cancer effects via the activation of pro-apoptotic JNK/p53 and inhibition of pro-proliferative E2F1/AR in prostate cancer cells including CRPC cells. The therapeutic effects of PMA were augmented by androgen deletion and enzalutamide in androgen-dependent prostate cancer cells, as well as by enzalutamide in castration-resistant cells. Taken together, PMA derivatives may be promising therapeutic agents for treating prostate cancer patients including CRPC patients.

Targeting androgen receptor and JunD interaction for prevention of prostate cancer progression

BACKGROUND

Multiple studies show that reactive oxygen species (ROS) play a major role in prostate cancer (PCa) development and progression. Previously, we reported an induction of Spermidine/Spermine N(1) -Acetyl Transferase (SSAT) by androgen-activated androgen receptor (AR)-JunD protein complex that leads to over-production of ROS in PCa cells. In our current research, we identify small molecules that specifically block AR-JunD in this ROS-generating metabolic pathway.

METHODS

A high throughput assay based on Gaussia Luciferase reconstitution was used to identify inhibitors of the AR-JunD interaction. Selected hits were further screened using a fluorescence polarization competitor assay to eliminate those that bind to the AR Ligand Binding Domain (LBD), in order to identify molecules that specifically target events downstream to androgen activation of AR. Eleven molecules were selected for studies on their efficacy against ROS generation and growth of cultured human PCa cells by DCFH dye-oxidation assay and DNA fluorescence assay, respectively. In situ Proximity Ligation Assay (PLA), SSAT promoter-luciferase reporter assay, and western blotting of apoptosis and cell cycle markers were used to study mechanism of action of the lead compound.

RESULTS

Selected lead compound GWARJD10 with EC(50) 10 μM against ROS production was shown to block AR-JunD interaction in situ as well as block androgen-induced SSAT gene expression at IC(50) 5 μM. This compound had no effect on apoptosis markers, but reduced cyclin D1 protein level.

CONCLUSIONS

Inhibitor of AR-JunD interaction, GWARJD10 shows promise for prevention of progression of PCa at an early stage of the disease by blocking growth and ROS production.

Redox-mediated and ionizing-radiation-induced inflammatory mediators in prostate cancer development and treatment

SIGNIFICANCE

Radiation therapy is widely used for treatment of prostate cancer. Radiation can directly damage biologically important molecules; however, most effects of radiation-mediated cell killing are derived from the generated free radicals that alter cellular redox status. Multiple proinflammatory mediators can also influence redox status in irradiated cells and the surrounding microenvironment, thereby affecting prostate cancer progression and radiotherapy efficiency.

RECENT ADVANCES

Ionizing radiation (IR)-generated oxidative stress can regulate and be regulated by the production of proinflammatory mediators. Depending on the type and stage of the prostate cancer cells, these proinflammatory mediators may lead to different biological consequences ranging from cell death to development of radioresistance.

CRITICAL ISSUES

Tumors are heterogeneous and dynamic communication occurs between stromal and prostate cancer cells, and complicated redox-regulated mechanisms exist in the tumor microenvironment. Thus, antioxidant and anti-inflammatory strategies should be carefully evaluated for each patient at different stages of the disease to maximize therapeutic benefits while minimizing unintended side effects.

FUTURE DIRECTIONS

Compared with normal cells, tumor cells are usually under higher oxidative stress and secrete more proinflammatory mediators. Thus, redox status is often less adaptive in tumor cells than in their normal counterparts. This difference can be exploited in a search for new cancer therapeutics and treatment regimes that selectively activate cell death pathways in tumor cells with minimal unintended consequences in terms of chemo- and radio-resistance in tumor cells and toxicity in normal tissues.

Glyoxalase 1-419C>A variant is associated with oxidative stress: implications in prostate cancer progression

Glyoxalase 1 is a scavenging enzyme of potent precursors in reactive oxygen species formation and is involved in the occurrence and progression of human malignancies. Glyoxalase I A111E polymorphism has been suggested to influence its enzymatic activity. The present study was aimed at investigating the association of this polymorphism with oxidative stress and its implications in prostate cancer progression or survival. The polymorphism was genotyped in human differently aggressive and invasive prostate cancer cell lines, in 571 prostate cancer or 588 benign prostatic hyperplasia patients, and 580 healthy subjects by Polymerase Chain Reaction/Restriction Fragment Length Polymorphism. Glyoxalase 1 activity, the pro-oxidant Glyoxalase 1-related Argpyrimidine and oxidative stress biomarkers were evaluated by biochemical analyses. Glyoxalase 1 polymorphism was associated with an increase in Glyoxalase 1-related pro-oxidant Argpyrimidine and oxidative stress levels and cancer progression. The mutant A allele conferred a modest risk of prostate cancer, a marked risk of prostate cancer progression and a lower survival time, compared to the wild C allele. The results of our exploratory study point out a significant role for Glyoxalase 1 in prostate cancer progression, providing an additional candidate for risk assessment in prostate cancer patients and an independent prognostic factor for survival. Finally, we provided evidence of the biological plausibility of Glyoxalase 1 polymorphism, either alone or in combination with other ones, all related to oxidative stress control that represents a key event in PCa development and progression.

8-hydroxy-2'-deoxyguanosine in colorectal adenocarcinoma--is it a result of oxidative stress?

BACKGROUND

8-hydroxy-2'-deoxyguanosine (8-OHdG) is one of the most abundant oxidatively modified lesions in DNA and is a marker of the oxidative stress. 8-OHdG is a mutagenic lesion and it can mispair with adenine, causing G:C→T: A transversion. Our task was to determine the 8-OHdG level in patients with colorectal adenocarcinoma directly in tumor tissues and corresponding normal mucosa.

MATERIAL/METHODS

Samples of tumor tissues and corresponding normal mucosa of 47 patients undergoing surgery for colorectal cancer were analyzed. DNA was isolated from both tumor and normal tissues. Then, DNA was hydrolyzed to nucleotides using nuclease P1 and alkaline phosphatase. The 8-OHdG and 2'-dG (2'-deoxyguanosine) were determined in hydrolysates by high-performance liquid chromatography (HPLC) with electrochemical (EC) and UV detector.

RESULTS

The levels of 8-OHdG in colorectal adenocarcinoma tissues were higher than in corresponding normal mucosa. No significant differences were shown in 8-OHdG levels in the cancerous and cancer-free tissues between age and sex and stages A/B and C/D of Duke's classification.

CONCLUSIONS

8-OHdG reflects the local oxidative stress in colon adenocarcinoma tissue together with ageing processes, but not the intensity of tumorigenesis itself. Because of many factors that could influence the oxidative modification of DNA bases, its role as a diagnostic and/or prognostic factor in colon adenocarcinoma seems to be limited.

Selective targeting of the cysteine proteome by thioredoxin and glutathione redox systems

Thioredoxin (Trx) and GSH are the major thiol antioxidants protecting cells from oxidative stress-induced cytotoxicity. Redox states of Trx and GSH have been used as indicators of oxidative stress. Accumulating studies suggest that Trx and GSH redox systems regulate cell signaling and metabolic pathways differently and independently during diverse stressful conditions. In the current study, we used a mass spectrometry-based redox proteomics approach to test responses of the cysteine (Cys) proteome to selective disruption of the Trx- and GSH-dependent systems. Auranofin (ARF) was used to inhibit Trx reductase without detectable oxidation of the GSH/GSSG couple, and buthionine sulfoximine (BSO) was used to deplete GSH without detectable oxidation of Trx1. Results for 606 Cys-containing peptides (peptidyl Cys) showed that 36% were oxidized more than 1.3-fold by ARF, whereas BSO-induced oxidation of peptidyl Cys was only 10%. Mean fold oxidation of these peptides was also higher by ARF than BSO treatment. Analysis of potential functional pathways showed that ARF oxidized peptides associated with glycolysis, cytoskeleton remodeling, translation and cell adhesion. Of 60 peptidyl Cys oxidized due to depletion of GSH, 41 were also oxidized by ARF and included proteins of translation and cell adhesion but not glycolysis or cytoskeletal remodeling. Studies to test functional correlates showed that pyruvate kinase activity and lactate levels were decreased with ARF but not BSO, confirming the effects on glycolysis-associated proteins are sensitive to oxidation by ARF. These data show that the Trx system regulates a broader range of proteins than the GSH system, support distinct function of Trx and GSH in cellular redox control, and show for the first time in mammalian cells selective targeting peptidyl Cys and biological pathways due to deficient function of the Trx system.

Prostate cancer and physical activity: adaptive response to oxidative stress

Prostate cancer is the most common form of cancer affecting men in the Western world. Its relative incidence increases exponentially with age and a steady increase is observed with extended life span. A sedentary lifestyle represents an important risk factor and a decrease in prostate cancer prevalence is associated with exercise. However, the molecular mechanisms involved in this process remain unknown. We hypothesize that reactive oxygen species generated by physical exercise are a key regulatory factor in prostate cancer prevention. Aging is correlated with increased oxidative stress (OS), which in turn provides a favorable environment for tumorigenesis. Running training is known to enhance the antioxidant defense system, reducing oxidative stress. In this context, the decrease in OS induced by exercise may delay the development of prostate cancer. This review focuses on oxidative stress-based mechanisms leading to prostate cancer sensitization to exercise, which could have some impact on the development of novel cancer therapeutic strategies.

Dissecting Major Signaling Pathways throughout the Development of Prostate Cancer

Prostate cancer (PCa) is one of the most common malignancies found in males. The development of PCa involves several mutations in prostate epithelial cells, usually linked to developmental changes, such as enhanced resistance to apoptotic death, constitutive proliferation, and, in some cases, to differentiation into an androgen deprivation-resistant phenotype, leading to the appearance of castration-resistant PCa (CRPCa), which leads to a poor prognosis in patients. In this review, we summarize recent findings concerning the main deregulations into signaling pathways that will lead to the development of PCa and/or CRPCa. Key mutations in some pathway molecules are often linked to a higher prevalence of PCa, by directly affecting the respective cascade and, in some cases, by deregulating a cross-talk node or junction along the pathways. We also discuss the possible environmental and nonenvironmental inducers for these mutations, as well as the potential therapeutic strategies targeting these signaling pathways. A better understanding of how some risk factors induce deregulation of these signaling pathways, as well as how these deregulated pathways affect the development of PCa and CRPCa, will further help in the development of new treatments and prevention strategies for this disease.

Oxidative stress and the ageing endocrine system

Ageing is a process characterized by a progressive decline in cellular function, organismal fitness and increased risk of age-related diseases and death. Several hundred theories have attempted to explain this phenomenon. One of the most popular is the 'oxidative stress theory', originally termed the 'free radical theory'. The endocrine system seems to have a role in the modulation of oxidative stress; however, much less is known about the role that oxidative stress might have in the ageing of the endocrine system and the induction of age-related endocrine diseases. This Review outlines the interactions between hormones and oxidative metabolism and the potential effects of oxidative stress on ageing of endocrine organs. Many different mechanisms that link oxidative stress and ageing are discussed, all of which converge on the induction or regulation of inflammation. All these mechanisms, including cell senescence, mitochondrial dysfunction and microRNA dysregulation, as well as inflammation itself, could be targets of future studies aimed at clarifying the effects of oxidative stress on ageing of endocrine glands.

Androgen deprivation induces senescence characteristics in prostate cancer cells in vitro and in vivo

BACKGROUND

The treatment of non-localized prostate cancer involves androgen deprivation (AD) therapy which results in tumor regression. Apoptosis has been implicated in the tumor response to AD, but constitutes a small fraction of the total tumor at any time. Cellular senescence is a response to sub-lethal stress in which cells are persistently growth arrested and develop distinct morphological and biochemical characteristics. The occurrence of senescence in prostate tumor tissue after AD therapy has not previously been investigated.

METHODS

Phenotypic and molecular characteristics of senescence were examined in models of androgen-sensitive prostate cancer after AD and compared with androgen-intact controls.

RESULTS

In vitro in LNCaP cells, AD induced elevated senescence-associated β-galactosidase (SA-β-gal) staining, decreased proliferation, and increased flow cytometric side scatter while minimally affecting cell viability. The increased expression of the senescence-related proteins Glb1, the cyclin-dependent kinase inhibitor p27(Kip1) and chromatin-regulating heterochromatin protein 1γ (HP1γ) were detected in LNCaP cells after AD in vitro by immunoblot and immunofluorescence microscopy. In mice bearing LuCaP xenograft tumors in vivo, surgical castration similarly increased SA-β-gal staining, increased expression of p27(Kip1) and HP1γ, and decreased expression of the proliferation marker KI-67, with minimal induction of apoptosis identified by detection of cleaved caspase 3 and TUNEL. Immunohistochemical analysis of human prostate tumors removed after AD shows similar induction of Glb1, HP1γ and decreased KI-67.

CONCLUSIONS

We conclude that AD induces characteristics consistent with cellular senescence in androgen-sensitive prostate cancer cells. This finding may explain incomplete tumor regression in response to AD.

Pro-survival and anti-apoptotic properties of androgen receptor signaling by oxidative stress promote treatment resistance in prostate cancer

Oxidative stress caused by an increase in reactive oxygen species levels or a decrease in cellular antioxidant capacity can evoke the modulation of various cellular events including androgen receptor (AR) signaling via direct or indirect interactions. In this review, we summarize the mechanisms of AR activation by oxidative stress including: i) AR overexpression; ii) AR activation by AR co-regulators or intracellular signal transduction pathways; iii) generation of AR mutations or splice variants; and iv) de novo androgen synthesis. AR signaling augmented by oxidative stress appears to contribute to pro-survival and anti-apoptotic effects in prostate cancer cells in response to androgen deprivation therapy. In addition, AR signaling suppresses anti-survival and pro-apoptotic effects in prostate cancer cells in response to various cytotoxic and tumor-suppressive interventions including taxanes and radiation through the modulation of βIII-tubulin and ataxia telangiectasia-mutated kinase expression respectively. Taken together, AR signaling appears to render prostate cancer cells refractory to various therapeutic interventions including castration, taxanes, and radiation, indicating that AR signaling is a comprehensive resistant factor and crucial target for prostate cancer treatment.

Prostaglandin 15d-PGJ(2) inhibits androgen receptor signaling in prostate cancer cells

Androgen signaling, in particular overexpression of the androgen receptor (AR), is critical for the growth and progression of prostate cancer. Because the AR is amenable to targeting by small-molecule inhibitors, it remains the major druggable target for the advanced disease. Inflammation has also been implicated in the cancerous growth in the prostate. Here we show that 15-deoxy-Δ(12,14)-prostaglandin J(2) (15d-PGJ(2)), an endogenously produced antiinflammatory prostaglandin, targets the AR and acts as a potent AR inhibitor, rapidly repressing AR target genes, such as FKBP51 and TMPRSS2 in prostate cancer cells. However, exposure of prostate cancer cells to 15d-PGJ(2) does not simply evoke a general inhibition of nuclear receptor activity or transcription because under the same conditions, peroxisome proliferator-activated receptor-γ is activated by 15d-PGJ(2). Moreover, 15d-PGJ(2) rapidly triggers modifications of AR by small ubiquitin-related modifier-2/3 (SUMO-2/3), which may modulate the repressing effect of 15d-PGJ(2) on AR-dependent transcription. Chromatin immunoprecipitation assays indicate that the inhibitory effect of 15d-PGJ(2) on FKBP51 and TMPRSS2 expression occurs in parallel with the inhibition of the AR binding to the regulatory regions of these genes. However, the DNA-binding activity is not the only AR function targeted by 15d-PGJ(2) because the prostaglandin also blunted the androgen-dependent interaction between the AR amino and carboxy termini. In conclusion, our results identify 15d-PGJ(2) as a potent and direct inhibitor of androgen signaling, suggesting novel possibilities in restricting the AR activity in prostate cancer cells.

Androgen deprivation by flutamide modulates uPAR, MMP-9 expressions, lipid profile, and oxidative stress: amelioration by daidzein

The growth and development of prostate gland is governed by testosterone. Testosterone helps in maintaining the adipose tissue stores of the body. It is well documented that with advancing age there has been a gradual decline in testosterone levels. Our aim was to study the protective role of daidzein on flutamide-induced androgen deprivation on matrix degrading genes, lipid profile and oxidative stress in Wistar rats. Sub-chronic (60 days) flutamide (30 mg/kg b.wt) administration resulted in marked increase in expressions of matrix degrading genes [matrix metalloproteases 9 and urokinase plasminogen activation receptor]. Additionally, it increased the levels of low density lipoproteins, total cholesterol, triglycerides, and lowered the levels of high density lipoproteins and endogenous antioxidant levels. Oral administration of daidzein (20 and 60 mg/kg b.wt) restituted the levels to normal. Daidzein administration resulted in amelioration of the prostate atrophy, degeneracy and invasiveness induced by flutamide. Our findings suggest that the daidzein may be given as dietary supplement to patients who are on androgen deprivation therapy, to minimize the adverse effects related to it and also retarding susceptibility of patients to cardiovascular diseases.

Lipids and prostate cancer

The role of lipid metabolism has gained particular interest in prostate cancer research. A large body of literature has outlined the unique upregulation of de novo lipid synthesis in prostate cancer. Concordant with this lipogenic phenotype is a metabolic shift, in which cancer cells use alternative enzymes and pathways to facilitate the production of fatty acids. These newly synthesized lipids may support a number of cellular processes to promote cancer cell proliferation and survival. Hence, de novo lipogenesis is under intense investigation as a therapeutic target. Epidemiologic studies suggest dietary fat may also contribute to prostate cancer; however, whether dietary lipids and de novo synthesized lipids are differentially metabolized remains unclear. Here, we highlight the lipogenic nature of prostate cancer, especially the promotion of de novo lipid synthesis, and the significance of various dietary lipids in prostate cancer development and progression.

Antioxidants for prostate cancer chemoprevention: challenges and opportunities

Extensive research has led to the firm conclusion that antioxidants protect cells from damage caused by oxidative stress and its associated pathological conditions including inflammation. It has also been established that inflammation is a precursor in neoplastic transformation of the prostate. Although, a vast body of experimental and clinical evidence shows efficacy of antioxidants as preventive strategies for prostate cancer, there is a lack of consistent agreement in outcomes especially from recent large-scale randomized clinical trials. Despite these concerns, our understanding of the preventive mechanisms as well as clinical efficacy and safety data indicate that novel antioxidant therapeutics still hold great promise for prostate cancer chemoprevention. We propose that for effective use of antioxidants for prostate cancer prevention, further high impact translational research is needed with special attention on selecting those patients who will benefit from such intervention. Therefore, it is important to validate predictive biomarkers from successful trials and combine this with knowledge of preclinical characterization of antioxidants (and combinations) that will eventually facilitate the development of 'personalized prostate cancer chemoprevention'. In this review, we briefly describe some common and emerging antioxidants that have shown benefits in preclinical and clinical settings. Above all, we focus on summarizing the progress we made thus far in prostate cancer chemoprevention using antioxidants, the heightened interest and challenges in the future.