Small-Molecule-Mediated Stabilization of PP2A Modulates the Homologous Recombination Pathway and Potentiates DNA Damage-Induced Cell Death.

High-grade serous carcinoma (HGSC) is the most common and lethal ovarian cancer subtype. PARP inhibitors (PARPi) have become the mainstay of HGSC-targeted therapy, given that these tumors are driven by a high degree of genomic instability (GI) and homologous recombination (HR) defects. Nonetheless, approximately 30% of patients initially respond to treatment, ultimately relapsing with resistant disease. Thus, despite recent advances in drug development and an increased understanding of genetic alterations driving HGSC progression, mortality has not declined, highlighting the need for novel therapies. Using a small-molecule activator of protein phosphatase 2A (PP2A; SMAP-061), we investigated the mechanism by which PP2A stabilization induces apoptosis in patient-derived HGSC cells and xenograft (PDX) models alone or in combination with PARPi. We uncovered that PP2A genes essential for cellular transformation (B56α, B56γ, and PR72) and basal phosphatase activity (PP2A-A and -C) are heterozygously lost in the majority of HGSC. Moreover, loss of these PP2A genes correlates with worse overall patient survival. We show that SMAP-061-induced stabilization of PP2A inhibits the HR output by targeting RAD51, leading to chronic accumulation of DNA damage and ultimately apoptosis. Furthermore, combination of SMAP-061 and PARPi leads to enhanced apoptosis in both HR-proficient and HR-deficient HGSC cells and PDX models. Our studies identify PP2A as a novel regulator of HR and indicate PP2A modulators as a therapeutic therapy for HGSC. In summary, our findings further emphasize the potential of PP2A modulators to overcome PARPi insensitivity, given that targeting RAD51 presents benefits in overcoming PARPi resistance driven by BRCA1/2 mutation reversions.

AZGP1 autoantibody predicts survival and histone deacetylase inhibitors increase expression in lung adenocarcinoma.

INTRODUCTION: The importance of alpha-2-glycoprotein 1, zinc (AZGP1) in lung adenocarcinoma (AD) remains largely unknown. Analysis of serum autoantibodies to tumor antigens combined with gene expression profiling of primary tumors may provide insight into the mechanisms underlying lung carcinogenesis and identify new AD biomarkers. METHODS: T7 phage cDNA libraries were used to identify AZGP1 autoantibodies in the serum of 473 patients (192 ADs, 192 matched controls, and 89 additional ADs for confirmation of findings). AZGP1 mRNA expression was examined in 86 ADs and 10 control lung tissue samples using oligonucleotide microarrays. AZGP1 protein expression was studied in 230 tissue samples (222 ADs; 8 controls) with immunohistochemistry. Kaplan-Meier analyses were used to correlate circulating autoantibody and tissue mRNA production with survival. AD cell lines A549 and SKLU1 were treated with 5-aza-2;-deoxycytidine (5-AZA) and trichostatin A (TSA) to examine the role of promoter methylation and histone deacetylation in the expression of AZGP1. Real-time polymerase chain reaction was used to quantify the effects of treatment. RESULTS: In patients with AD, AZGP1 autoantibodies were observed in 40% of serum samples. Autoantibody production correlated with improved overall 5-year survival (p = 0.002) and improved survival in those with stage I to II disease (p = 0.008). A verification analysis was performed for the survival benefit and found similar results with p values of 0.02 and 0.036, respectively. Although abundant mRNA expression was found in a subset of tumors, mRNA expression did not correlate with prognosis. In normal lung, AZGP1 mRNA and protein expression were low or absent, whereas in AD they were highly expressed in 31.3% and 42.8% of samples, respectively. To determine whether AZGP1 expression in this subset of tumors might be affected by epigenetic mechanisms, low AZGP1-expressing A549 and SKLU1 AD cell lines were treated with TSA and 5-AZA. A 713-fold and 169-fold increase in mRNA expression were noted on treatment with TSA, respectively. Treatment with 5-AZA had minimal effect on AZGP1 mRNA expression. CONCLUSIONS: The presence of AZGP1 serum autoantibody may be used as a prognostic marker in patients with AD. Furthermore, up-regulation of AZGP1 mRNA in AD may be affected by chromatin remodeling by means of histone acetylation.