A single inactivating amino acid change in the SARS-CoV-2 NSP3 Mac1 domain attenuates viral replication and pathogenesis in vivo

Despite unprecedented efforts, our therapeutic arsenal against SARS-CoV-2 remains limited. The conserved macrodomain 1 (Mac1) in NSP3 is an enzyme exhibiting ADP-ribosylhydrolase activity and a possible drug target. To determine the therapeutic potential of Mac1 inhibition, we generated recombinant viruses and replicons encoding a catalytically inactive NSP3 Mac1 domain by mutating a critical asparagine in the active site. While substitution to alanine (N40A) reduced catalytic activity by ~10-fold, mutations to aspartic acid (N40D) reduced activity by ~100-fold relative to wildtype. Importantly, the N40A mutation rendered Mac1 unstable in vitro and lowered expression levels in bacterial and mammalian cells. When incorporated into SARS-CoV-2 molecular clones, the N40D mutant only modestly affected viral fitness in immortalized cell lines, but reduced viral replication in human airway organoids by 10-fold. In mice, N40D replicated at >1000-fold lower levels compared to the wildtype virus while inducing a robust interferon response; all animals infected with the mutant virus survived infection and showed no signs of lung pathology. Our data validate the SARS-CoV-2 NSP3 Mac1 domain as a critical viral pathogenesis factor and a promising target to develop antivirals.

Resistance to ATR Inhibitors Is Mediated by Loss of the Nonsense-Mediated Decay Factor UPF2

Significance:

Loss of NMD proteins promotes resistance to ATR inhibitors in gastric cancer cells, which may provide a combination of therapeutic targets and biomarkers to improve the clinical utility of these drugs.

High-throughput oncogene mutation profiling shows demographic differences in BRAF mutation rates among melanoma patients

Because of advances in targeted therapies, the clinical evaluation of cutaneous melanoma is increasingly based on a combination of traditional histopathology and molecular pathology. Therefore, it is necessary to expand our knowledge of the molecular events that accompany the development and progression of melanoma to optimize clinical management. The central objective of this study was to increase our knowledge of the mutational events that complement melanoma progression. High-throughput genotyping was adapted to query 159 known single nucleotide mutations in 33 cancer-related genes across two melanoma cohorts from Ireland (n=94) and Belgium (n=60). Results were correlated with various clinicopathological characteristics. A total of 23 mutations in 12 genes were identified, that is--BRAF, NRAS, MET, PHLPP2, PIK3R1, IDH1, KIT, STK11, CTNNB1, JAK2, ALK, and GNAS. Unexpectedly, we discovered significant differences in BRAF, MET, and PIK3R1 mutations between the cohorts. That is, cases from Ireland showed significantly lower (P<0.001) BRAF(V600E) mutation rates (19%) compared with the mutation frequency observed in Belgian patients (43%). Moreover, MET mutations were detected in 12% of Irish cases, whereas none of the Belgian patients harbored these mutations, and Irish patients significantly more often (P=0.027) had PIK3R1-mutant (33%) melanoma versus 17% of Belgian cases. The low incidence of BRAF(V600E)(-) mutant melanoma among Irish patients was confirmed in five independent Irish cohorts, and in total, only 165 of 689 (24%) Irish cases carried mutant BRAF(V600E). Together, our data show that melanoma-driving mutations vary by demographic area, which has important implications for the clinical management of this disease.

Abstract P5-07-09: Adenanthin, a new peroxiredoxin inhibitor, induces a switch between estrogen receptor alpha-mediated and Src/Akt-driven signaling in breast cancer cells

Increasing evidence indicates that oxidative stress is involved in the progression of estrogen receptor (ER)-positive breast cancer. A moderate increase in cellular oxidants contributes to the genomic instability and to the change in cellular growth pattern, which in turn can facilitate progressive transformation of normal cells into cancer cells. Accordingly, the oxidative stress-related gene expression signature has been suggested to correlate with therapy resistance and poorer outcome in breast cancer. Therefore, it is crucial to determine the antioxidant defense mechanisms that are utilized by breast cancer cells to regulate oxidative stress.

Peroxiredoxin 1 (PRDX1) is one of the most prevalent hydrogen peroxide scavenging enzymes in mammalian cells. Our recent studies indicated that PRDX1 is an independent biomarker of favorable prognosis in ER-positive breast cancer. Our results indicate the mechanistic link between PRDX1 and ERα in breast cancer and suggest a role for PRDX1 in mammary carcinogenesis. We provide a molecular explanation for this phenomenon in the current project.

To evaluate the importance of PRDX1 activity in ER-positive breast cancer, we have used adenanthin, a newly described PRDX1/2 inhibitor. In our studies, we have shown that adenanthin strongly inhibits metabolism of exogenous hydrogen peroxide by breast cancer cells. This phenomenon is accompanied by a shift from H2O2-degrading PRDX1 dimers into enzymatically inactive monomers and by a dramatic decrease of ERα protein presence in the cells. Moreover, we have observed that incubation of ER-positive breast cancer cells with adenanthin leads to a marked increase in phosphorylation status of proteins associated with Src-Akt-driven signaling in breast cancer. Thus, our results suggest that PRDX1 can play an important role in controlling the switch between estrogen receptor- and growth factor-driven signaling in breast cancer.

In summary, in our studies we describe for the first time molecular consequences of rapid dysfunction of PRDX-related system in ER-positive breast cancer. The deeper knowledge on the mechanisms of PRDX1 functioning can change our understanding of the events leading to the progression of ER-positive breast cancer and provide new opportunities for pharmacological interventions in this disease, especially in the context of recent observations connecting the oxidative stress and resistance to endocrine therapy.

Citation Format: Malgorzata Bajor, Agata O Zych, Patrick C O'Leary, Anna Czekalska, William M Gallagher, Jakub Golab, Radoslaw Zagozdzon. Adenanthin, a new peroxiredoxin inhibitor, induces a switch between estrogen receptor alpha-mediated and Src/Akt-driven signaling in breast cancer cells [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P5-07-09.

Peroxiredoxin-1 protects estrogen receptor α from oxidative stress-induced suppression and is a protein biomarker of favorable prognosis in breast cancer

INTRODUCTION

Peroxiredoxin-1 (PRDX1) is a multifunctional protein, acting as a hydrogen peroxide (H2O2) scavenger, molecular chaperone and immune modulator. Although differential PRDX1 expression has been described in many tumors, the potential role of PRDX1 in breast cancer remains highly ambiguous. Using a comprehensive antibody-based proteomics approach, we interrogated PRDX1 protein as a putative biomarker in estrogen receptor (ER)-positive breast cancer.

METHODS

An anti-PRDX1 antibody was validated in breast cancer cell lines using immunoblotting, immunohistochemistry and reverse phase protein array (RPPA) technology. PRDX1 protein expression was evaluated in two independent breast cancer cohorts, represented on a screening RPPA (n = 712) and a validation tissue microarray (n = 498). In vitro assays were performed exploring the functional contribution of PRDX1, with oxidative stress conditions mimicked via treatment with H2O2, peroxynitrite, or adenanthin, a PRDX1/2 inhibitor.

RESULTS

In ER-positive cases, high PRDX1 protein expression is a biomarker of improved prognosis across both cohorts. In the validation cohort, high PRDX1 expression was an independent predictor of improved relapse-free survival (hazard ratio (HR) = 0.62, 95% confidence interval (CI) = 0.40 to 0.96, P = 0.032), breast cancer-specific survival (HR = 0.44, 95% CI = 0.24 to 0.79, P = 0.006) and overall survival (HR = 0.61, 95% CI = 0.44 to 0.85, P = 0.004). RPPA screening of cancer signaling proteins showed that ERα protein was upregulated in PRDX1 high tumors. Exogenous H2O2 treatment decreased ERα protein levels in ER-positive cells. PRDX1 knockdown further sensitized cells to H2O2- and peroxynitrite-mediated effects, whilst PRDX1 overexpression protected against this response. Inhibition of PRDX1/2 antioxidant activity with adenanthin dramatically reduced ERα levels in breast cancer cells.

CONCLUSIONS

PRDX1 is shown to be an independent predictor of improved outcomes in ER-positive breast cancer. Through its antioxidant function, PRDX1 may prevent oxidative stress-mediated ERα loss, thereby potentially contributing to maintenance of an ER-positive phenotype in mammary tumors. These results for the first time imply a close connection between biological activity of PRDX1 and regulation of estrogen-mediated signaling in breast cancer.

Abstract A10: Peroxiredoxin-1 and oxidative stress: Controlling the balance between oncogenic and endocrine signalling in estrogen receptor-positive breast cancer

Introduction: Peroxiredoxin-1 (PRDX1) is a multifunctional protein, acting as a hydrogen peroxide (H2O2) scavenger, molecular chaperone and immune mediator. Differential expression of PRDX1 has been described in many tumor types, including lung and ovarian carcinoma. Despite the wealth of knowledge about PRDX1 functionality, its role in human breast cancer has not been fully elucidated. Preclinical studies suggest that PRDX1 may be protective against oncogene-induced mammary carcinogenesis, indicating that it may be an important biomarker. In this study, we describe PRDX1 as a robust prognostic biomarker in estrogen receptor α (ER)-positive breast cancer and propose a molecular mechanism which explains this observation.

Materials and Methods: The anti-PRDX1 antibody was validated in breast cancer cell lines using Western blotting, immunohistochemistry and reverse phase protein array (RPPA) technology following exogenous overexpression or shRNA-mediated knockdown of PRDX1. PRDX1 protein expression was evaluated using two independent breast cancer cohorts: a 512 patient tissue microarray (TMA) and a 712 patient RPPA cohort. Increase in cellular content of H2O2 was accomplished via treatment of cell lines with exogenous (H2O2) or activation of oncogenic pathways (611CTF-HER2 overexpression). Western blotting and RPPA were used to assess changes in ERα and oncogenic signaling proteins in cell lines and a third breast cancer cohort, consisting of 410 patients.

Results: High expression of PRDX1 protein was associated with a favorable outcome in ER-positive, but not ER-negative breast cancer cases across both cohorts (evaluable data for 975 patients total; log-rank p-value: TMA=0.022; RPPA=0.002). Exogenous treatment with (H2O2) or induction of oncogenic signaling suppressed ERα protein and stimulated phosphorylation/activation of Akt kinase in ER-positive cell lines. Knockdown of PRDX1 further sensitized the cells to the (H2O2)-mediated effect whilst overexpression protects against it. These observations were further validated in an additional cohort of ER-positive tumor samples, where PRDX1 protein levels correlated with ERα (positive) and pAkt-473 protein expression (negative).

Conclusions: Our findings provide robust evidence of the importance of PRDX1 as a biomarker of favorable prognosis in ER-positive breast cancer. We suggest that PRDX1 acts as a shielding mechanism for ERα protein by counteracting (H2O2)-mediated suppression of this molecule in ER-positive tumors, and suppressing phosphorylation of Akt kinase under these oxidative stress conditions. This strongly implies that (H2O2) and PRDX1 are important role players in the crosstalk between oncogenic (e.g. HER2- or PI3K-induced) and ER-driven signaling pathways in breast cancer. Understanding the mechanisms underlying the regulation of oxidative stress response in ER-positive breast cancer can allow for better tailoring the management of this disease.

Longitudinal study of serum thyroid hormone levels during normal pregnancy

We undertook a prospective longitudinal study of thyroid function in 60 normal pregnant women and measured serum concentrations of T4, triiodothyronine (T3), T-uptake, thyroxine binding globulin (TBG), free thyroxine index (FTI), free T4, albumin and thyrotropin (TSH). From these data we established reference ranges for each of these analytes for each trimester and examined the inter-relationships between laboratory measurements of thyroid function tests. We observed significant increases in serum concentrations of thyrotropin and decreases in free T4, assays commonly used as first line investigations of thyroid activity during pregnancy. However, the 95th centile intervals for both analytes remained within the reference range for nonpregnant women.

Effects of insulin-like growth factors and binding protein 1 on bovine granulosa cell division in anchorage-independent culture

Granulosa cells can exhibit the properties of stem cells and tumour cells. Contact with neighbouring cells does not inhibit their replication in vivo and they can divide in vitro while embedded in agar and thus without anchorage on a substratum. By culturing granulosa cells without anchorage, those cells that do not require anchorage, and thus exhibit at least one property of stem cells, divide. The effects of insulin-like growth factors (IGFs) and insulin-like growth factor binding protein 1 (IGFBP-1) on the replication of such cells was investigated by isolating granulosa cells from follicles (3-5 mm diameter) from cyclic cows and culturing them in soft agar-methylcellulose solution. Cell division was measured as [3H]thymidine incorporation into DNA, total DNA, or as the amount of the nuclear La antigen. This antigen is involved in RNA synthesis and is expressed ubiquitously; here it was used to estimate the number of cells indirectly. Both IGF-I (100 ng ml-1) and IGF-II (100 ng ml-1) and their respective analogues, as well as insulin, all at the same concentration, significantly increased DNA synthesis as determined by [3H]thymidine incorporation (n = 5). An increase in the number of cells in the presence of IGF-I was also confirmed by DNA measurement (P < 0.05, n = 5) and by western immunoblotting analyses of La antigen (n = 3). IGFBP-1 significantly inhibited cell division stimulated by IGF-I (P < 0.001) and IGF-II (P < 0.001), but not that stimulated by the analogue, LR3IGF-I, which has low affinity for IGFBPs. Other factors also known to affect IGF synthesis or effectiveness (FSH, oestradiol, growth hormone) did not appear to influence division of granulosa cells when cultured under anchorage-independent conditions, while dibutyryl cAMP significantly inhibited cell division (P < 0.01, n = 5). In conclusion, IGFs have a role to play in stimulating division of stem-cell-like granulosa cells during follicular development and IGFBP-1 can specifically inhibit the mitogenic effects of IGFs.

Effect of asthma treatment on urinary growth hormone excretion in children

We measured growth hormone (GH) concentrations in first morning urine samples in 110 prepubertal children to determine whether asthma therapies affected GH secretion. The children with asthma were assigned to two groups depending on their asthma treatments: 1) 16 children with a history of asthma, currently not on any treatment, and 2) asthmatics taking inhaled corticosteroids (n = 37), short-term oral corticosteroids (n = 15), or long-term non-corticosteroidal therapies (n = 19). Results obtained from these children were compared with a control group of healthy prepubertal children (n = 23) without previous or current symptoms of asthma. Five consecutive urine samples were collected from each child, and GH concentrations (corrected for urine creatinine) were determined by an enzyme immunoassay. The mean (+/- SD) urine GH concentration determined in the control group (23 healthy prepubertal children) was 15.6 +/- 8.7 ng/L (1.88 +/- 1.29 ng GH/mmol creatinine). The mean (+/- SD) urine GH concentrations in overnight samples were similar in untreated asthmatics (14.1 +/- 6.1 ng/L) and in the treatment groups (14.1 +/- 7.7 ng/L, inhaled corticosteroids; 16.5 +/- 11.7 ng/L, oral corticosteroids; 15.9 +/- 9.8 ng/L, long-term non-corticosteroidal therapies). Irrespective of the manner of expression of urine GH (ng/L) or after correction for urine creatinine concentration (ng GH/mmol), no significant differences were found in the GH excretion among any of the groups. In this study, the intra-individual coefficient of variation for urine GH, expressed as ng/L, ranged between 11 and 87% (median, 32%). When the urine GH was expressed as ng GH/mmol creatinine, the coefficient of variation ranged between 12 and 92% (median, 35%), accounting for approximately 60% of the inter-individual coefficient of variation (mean CV, 56%) and 47% when the urine GH is expressed as ng GH/mmol creatinine. We were unable to determine any short-term differences in urine GH excretion between non-asthmatic children and asthmatics treated with inhaled corticosteroids, oral corticosteroids, or bronchodilators. Our results suggest that there is not an adverse effect of current corticosteroid therapies for childhood asthma on GH secretion.

Elevated mid-trimester hCG and maternal lupus anticoagulant

An association is described between women with lupus anticoagulant and abnormal prenatal serum screening results. Three cases of positive second-trimester serum screening for Down syndrome, with karyotypically normal fetuses, in women demonstrated to have lupus anticoagulant are presented. Serum screening positivity was principally due to a disproportionately elevated maternal serum human chorionic gonadotrophin (hCG) level. In each case, early, severe intrauterine growth restriction was documented, with only one fetus surviving the neonatal period. As maternal lupus anticoagulant may have a profoundly adverse effect on the course of pregnancy, we suggest that an elevated hCG level on prenatal screening prompt consideration of maternal lupus anticoagulant testing if ultrasonography demonstrates an otherwise normal singleton gestation and the fetal karyotype is normal.

Serum insulin-like growth factor binding protein-1 in pregnant women: decreased concentrations following an oral glucose load

Serum concentrations of insulin-like growth factor binding protein-1 (IGFBP-1) were measured in men and in non-pregnant and pregnant women. Peak serum IGFBP-1 levels occurred mid-gestation followed by a slight decline towards term. Women with gestational diabetes had higher serum IGFBP-1 concentrations than apparently healthy women at comparable gestation. Following administration of an oral glucose load, serum IGFBP-1 concentrations were decreased within 2 h in men and in pregnant women while IGF-I levels remained constant. These results suggested that IGFBP-1 regulates IGF-I activity in pregnancy in a similar manner to that in the non-pregnant state.

Inhibin secretion is influenced by Leydig cells: evidence from studies using the cytotoxin ethane dimethane sulphonate (EDS)

Adult male rats given a single intraperitoneal injection of the Leydig cell cytotoxin ethane dimethane sulphonate (EDS) show a significant decrease in testosterone from 7 to 14 days, and elevation of serum FSH and LH levels commencing 7 days after treatment, returning to normal at 28 days for LH and 49 days for FSH. A significant rise in serum inhibin levels was seen at day 14 after EDS treatment with levels returning to normal at day 49. In a second series of experiments, silastic implants of testosterone, either 2.5 cm or 22.5 cm in length, were introduced subcutaneously into adult male rats which were treated with EDS 10 days later. Both doses of testosterone suppressed basal LH levels but did not significantly change FSH levels. The rise in FSH and LH levels seen in normal rats after EDS treatment did not occur in either group of testosterone-implanted rats. However, serum inhibin levels rose significantly in both groups after EDS treatment, suggesting that the rise in serum inhibin levels was not due to stimulation arising from the increase in FSH levels after EDS treatment. The data suggest that the rise in serum inhibin levels after EDS treatment is linked to destruction of the Leydig cells through mechanisms that require further investigation.

Alterations in mitogenic and steroidogenic activities in rat testicular interstitial fluid after administration of ethane dimethane sulphonate

A single dose of EDS was given to mature male rats and interstitial fluid (IF) was collected to determine the potency of mitogenic and steroidogenic activities therein. The potency of the factor stimulating testosterone secretion in vitro by Percoll-purified Leydig cells was significantly elevated 2 weeks after EDS, whilst the potency of mitogenic activities (stimulation of DNA synthesis by BALB/c 3T3 cells) was not elevated until 4 weeks after EDS treatment. This study suggests that two separate factors, one with mitogenic and the other steroidogenic activity, may be involved in the response of Leydig cells after EDS administration. The mitogenic factor may play a role in Leydig cell regeneration whereas the testosterone-stimulating factor may be involved in testicular testosterone homeostasis.

Effects of ethane dimethane sulphonate (EDS) on seminiferous tubule function in rats

The effects of a single injection of ethane dimethane sulphonate (EDS) on aspects of seminiferous tubule function were assessed over a period of 49 days. Ethane dimethane sulphonate, which is known to cause destruction of Leydig cells, reduced the levels of testosterone in both serum and testicular interstitial fluid for 21 days, after which recovery occurred. The low testosterone levels were associated with elevated serum levels of LH and FSH. Daily sperm production was decreased from 14 to 42 days post-EDS but returned to control levels at 49 days. The production of seminiferous tubule fluid, measured after unilateral efferent duct ligation, decreased significantly at 7 and 14 days but then recovered. The testicular content of androgen binding protein (ABP) was decreased from 14 to 28 days but returned to normal thereafter. These results demonstrate significant effects on seminiferous tubule function, which may be due to the decrease in testosterone or be associated with a direct effect of EDS.

Evaluation of testicular hCG binding in unilaterally cryptorchid rats following administration of ethane dimethane sulphonate (EDS)

Administration of ethane dimethane sulphonate (EDS) (75 mg/kg) to unilaterally cryptorchid rats, results in a rapid decline in serum testosterone levels and a marked reduction in hCG binding to homogenates of scrotal and cryptorchid testes, consistent with the destruction of Leydig cells within the testes as shown by morphological and morphometric analysis. Between 3 and 7 days after EDS, serum LH and FSH levels rise, LH to levels found in castrate rats. hCG binding begins to recover in scrotal testes, reaching 32% of control values 28 days after EDS. However, the recovery of hCG binding to cryptorchid testes is more rapid, reaching 51% of control levels by 21 days which coincides with the re-establishment of serum testosterone to normal levels. Since a different rate of recovery is observed for hCG binding to scrotal and cryptorchid testes, and both testes are exposed to the same circulating levels of LH and FSH, the likely stimulus for recovery of hCG binding and regeneration of Leydig cells is intratesticular in origin. This supports the concept that local factors, released following damage to the seminiferous epithelium by cryptorchidism, play a role in the differentiation and growth of Leydig cells within the testis.

The effects of ethylene dimethane sulphonate (EDS) on rat Leydig cells: evidence to support a connective tissue origin of Leydig cells

Ethylene dimethane sulphonate (DS) administered to adult male rats in a single dose of 75 mg/kg body weight results in a rapid destruction of Leydig cells which, in turn, is associated with a marked decline in levels of serum testosterone. For 24-72 h after treatment with EDS (post-EDS) the Leydig cells undergo degenerative changes consisting of chromatin condensation and cytoplasmic vacuolation, and testicular macrophages progressively remove Leydig cells from the intertubular tissue by phagocytosis. This results in the total absence of Leydig cells on Days 7-14 and the absence of any detectable specific 125I-hCG binding to testis homogenates. Associated with the low levels of serum testosterone, levels of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) in serum rise, LH to levels found in castrate rats. Morphometric and 125I-hCG binding studies indicate that a new generation of Leydig cells develop from Day 21 and reach control levels by Day 49. Morphologic observations suggest that the Leydig cells arise by differentiation from a pool of connective tissue cells that includes fibroblasts, lymphatic endothelial cells and pericytes. The new Leydig cells, which appear around Day 21 post-EDS, have the features of fetal Leydig cells. The latter appear to transform into Leydig cells typical of normal adult rats between 35-49 days post-EDS. The differentiation of new Leydig cells is associated with a reestablishment of normal levels of testosterone 21 days post-EDS. Serum LH and FSH return to normal at 28 days and 49 days respectively.