A Genome-Wide Pooled shRNA Screen Identifies PPP2R2A as a Predictive Biomarker for the Response to ATR and CHK1 Inhibitors

FAM122A ensures cell cycle interphase progression and checkpoint control by inhibiting B55α/PP2A through helical motifs

The Ser/Thr protein phosphatase 2 A (PP2A) regulates the dephosphorylation of many phosphoproteins. Substrate recognition are mediated by B regulatory subunits. Here, we report the identification of a substrate conserved motif [RK]-V-x-x-[VI]-R in FAM122A, an inhibitor of B55α/PP2A. This motif is necessary for FAM122A binding to B55α, and computational structure prediction suggests the motif, which is helical, blocks substrate docking to the same site. In this model, FAM122A also spatially constrains substrate access by occluding the catalytic subunit. Consistently, FAM122A functions as a competitive inhibitor as it prevents substrate binding and dephosphorylation of CDK substrates by B55α/PP2A in cell lysates. FAM122A deficiency in human cell lines reduces the proliferation rate, cell cycle progression, and hinders G1/S and intra-S phase cell cycle checkpoints. FAM122A-KO in HEK293 cells attenuates CHK1 and CHK2 activation in response to replication stress. Overall, these data strongly suggest that FAM122A is a short helical motif (SHeM)-dependent, substrate-competitive inhibitor of B55α/PP2A that suppresses multiple functions of B55α in the DNA damage response and in timely progression through the cell cycle interphase.

PP2A B55α inhibits epithelial-mesenchymal transition via regulation of Slug expression in non-small cell lung cancer

PP2A B55α, encoded by PPP2R2A, acts as a regulatory subunit of the serine/threonine phosphatase PP2A. Despite a frequent loss of heterozygosity of PPP2R2A in cases of non-small cell lung cancer (NSCLC), research on PP2A B55α's functions remains limited and controversial. To investigate the biological roles of PP2A B55α, we conducted bulk RNA-sequencing to assess the impact of PPP2R2A knockdown using two shRNAs in a NSCLC cell line. Gene set enrichment analysis (GSEA) of the RNA-sequencing data revealed significant enrichment of the epithelial-mesenchymal transition (EMT) pathway, with SNAI2 (the gene encoding Slug) emerging as one of the top candidates. Our findings demonstrate that PP2A B55α suppresses EMT, as PPP2R2A deficiency through knockdown or homozygous or hemizygous depletion promotes EMT and metastatic behavior in NSCLC cells, as evidenced by changes in EMT biomarkers, invasion and migration abilities, as well as metastasis in a tail vein assay. Mechanistically, PP2A B55α inhibits EMT by downregulating SNAI2 expression via the GSK3β-β-catenin pathway. Importantly, PPP2R2A deficiency also slows cell proliferation by disrupting DNA replication, particularly in PPP2R2A-/- cells. Furthermore, PPP2R2A deficiency, especially PPP2R2A-/- cells, leads to an increase in the cancer stem cell population, which correlates with enhanced resistance to chemotherapy. Overall, the decrease in PP2A B55α levels due to hemizygous/homozygous depletion heightens EMT and the metastatic or stemness/drug resistance potential of NSCLC cells despite their proliferation disadvantage. Our study highlights the significance of PP2A B55α in EMT and metastasis and suggests that targeting EMT/stemness could be a potential therapeutic strategy for treating PPP2R2A-deficient NSCLC.

The thioredoxin system determines CHK1 inhibitor sensitivity via redox-mediated regulation of ribonucleotide reductase activity

Checkpoint kinase 1 (CHK1) is critical for cell survival under replication stress (RS). CHK1 inhibitors (CHK1i's) in combination with chemotherapy have shown promising results in preclinical studies but have displayed minimal efficacy with substantial toxicity in clinical trials. To explore combinatorial strategies that can overcome these limitations, we perform an unbiased high-throughput screen in a non-small cell lung cancer (NSCLC) cell line and identify thioredoxin1 (Trx1), a major component of the mammalian antioxidant-system, as a determinant of CHK1i sensitivity. We establish a role for redox recycling of RRM1, the larger subunit of ribonucleotide reductase (RNR), and a depletion of the deoxynucleotide pool in this Trx1-mediated CHK1i sensitivity. Further, the TrxR inhibitor auranofin, an approved anti-rheumatoid arthritis drug, shows a synergistic interaction with CHK1i via interruption of the deoxynucleotide pool. Together, we show a pharmacological combination to treat NSCLC that relies on a redox regulatory link between the Trx system and mammalian RNR activity.

Clinical translation for targeting DNA damage repair in non-small cell lung cancer: a review

Despite significant advancements in screening, diagnosis, and treatment of non-small cell lung cancer (NSCLC), it remains the primary cause of cancer-related deaths globally. DNA damage is caused by the exposure to exogenous and endogenous factors and the correct functioning of DNA damage repair (DDR) is essential to maintain of normal cell circulation. The presence of genomic instability, which results from defective DDR, is a critical characteristic of cancer. The changes promote the accumulation of mutations, which are implicated in cancer cells, but these may be exploited for anti-cancer therapies. NSCLC has a distinct genomic profile compared to other tumors, making precision medicine essential for targeting actionable gene mutations. Although various treatment options for NSCLC exist including chemotherapy, targeted therapy, and immunotherapy, drug resistance inevitably arises. The identification of deleterious DDR mutations in 49.6% of NSCLC patients has led to the development of novel target therapies that have the potential to improve patient outcomes. Synthetic lethal treatment using poly (ADP-ribose) polymerase (PARP) inhibitors is a breakthrough in biomarker-driven therapy. Additionally, promising new compounds targeting DDR, such as ATR, CHK1, CHK2, DNA-PK, and WEE1, had demonstrated great potential for tumor selectivity. In this review, we provide an overview of DDR pathways and discuss the clinical translation of DDR inhibitors in NSCLC, including their application as single agents or in combination with chemotherapy, radiotherapy, and immunotherapy.

Exploiting the DNA Damage Response for Prostate Cancer Therapy

Prostate cancers that progress despite androgen deprivation develop into castration-resistant prostate cancer, a fatal disease with few treatment options. In this review, we discuss the current understanding of prostate cancer subtypes and alterations in the DNA damage response (DDR) that can predispose to the development of prostate cancer and affect its progression. We identify barriers to conventional treatments, such as radiotherapy, and discuss the development of new therapies, many of which target the DDR or take advantage of recurring genetic alterations in the DDR. We place this in the context of advances in understanding the genetic variation and immune landscape of CRPC that could help guide their use in future treatment strategies. Finally, we discuss several new and emerging agents that may advance the treatment of lethal disease, highlighting selected clinical trials.

New horizons in lung cancer management through ATR/CHK1 pathway modulation

Lung cancer is the leading cause of cancer-related deaths worldwide. Molecular profiling has contributed to a new classification of lung cancer, driving advancements in research and therapy. The ataxia telangiectasia and rad3/checkpoint kinase 1 (ATR/CHK1) pathway plays a crucial role in maintaining genomic stability, and its activation has been linked to the development of lung cancer, drug resistance and poor prognosis. Clinical and preclinical studies have demonstrated promising results in targeting this pathway. ATR and CHK1 are proteins that collaborate to repair DNA damage caused by radiation or chemotherapy. ATR/CHK1 inhibitors are currently under investigation in preclinical and clinical trials. This article explores the ATR/CHK1 pathway and its potential for treating lung cancer.

FAM122A ensures cell cycle interphase progression and checkpoint control as a SLiM-dependent substrate-competitive inhibitor to the B55⍺/PP2A phosphatase

The Ser/Thr protein phosphatase 2A (PP2A) is a highly conserved collection of heterotrimeric holoenzymes responsible for the dephosphorylation of many regulated phosphoproteins. Substrate recognition and the integration of regulatory cues are mediated by B regulatory subunits that are complexed to the catalytic subunit (C) by a scaffold protein (A). PP2A/B55 substrate recruitment was thought to be mediated by charge-charge interactions between the surface of B55α and its substrates. Challenging this view, we recently discovered a conserved SLiM [ RK ]- V -x-x-[ VI ]- R in a range of proteins, including substrates such as the retinoblastoma-related protein p107 and TAU (Fowle et al. eLife 2021;10:e63181). Here we report the identification of this SLiM in FAM122A, an inhibitor of B55α/PP2A. This conserved SLiM is necessary for FAM122A binding to B55α in vitro and in cells. Computational structure prediction with AlphaFold2 predicts an interaction consistent with the mutational and biochemical data and supports a mechanism whereby FAM122A uses the 'SLiM' in the form of a short α-helix to dock to the B55α top groove. In this model, FAM122A spatially constrains substrate access by occluding the catalytic subunit with a second α-helix immediately adjacent to helix 1. Consistently, FAM122A functions as a competitive inhibitor as it prevents binding of substrates in in vitro competition assays and the dephosphorylation of CDK substrates by B55α/PP2A in cell lysates. Ablation of FAM122A in human cell lines reduces the rate of proliferation, progression through cell cycle transitions and abrogates G1/S and intra-S phase cell cycle checkpoints. FAM122A-KO in HEK293 cells results in attenuation of CHK1 and CHK2 activation in response to replication stress. Overall, these data strongly suggest that FAM122A is a 'SLiM'-dependent, substrate-competitive inhibitor of B55α/PP2A that suppresses multiple functions of B55α in the DNA damage response and in timely progression through the cell cycle interphase.

VPA mediates bidirectional regulation of cell cycle progression through the PPP2R2A-Chk1 signaling axis in response to HU

Cell cycle checkpoint kinases play a pivotal role in protecting against replicative stress. In this study, valproic acid (VPA), a histone deacetylase inhibitor (HDACi), was found to promote breast cancer MCF-7 cells to traverse into G2/M phase for catastrophic injury by promoting PPP2R2A (the B-regulatory subunit of Phosphatase PP2A) to facilitate the dephosphorylation of Chk1 at Ser317 and Ser345. By contrast, VPA protected normal 16HBE cells from HU toxicity through decreasing PPP2R2A expression and increasing Chk1 phosphorylation. The effect of VPA on PPP2R2A was at the post-transcription level through HDAC1/2. The in vitro results were affirmed in vivo. Patients with lower PPP2R2A expression and higher pChk1 expression showed significantly worse survival. PPP2R2A D197 and N181 are essential for PPP2R2A-Chk1 signaling and VPA-mediated bidirectional effect on augmenting HU-induced tumor cell death and protecting normal cells.

ATR Inhibitors in Platinum-Resistant Ovarian Cancer

Platinum-resistant ovarian cancer (PROC) is one of the deadliest types of epithelial ovarian cancer, and it is associated with a poor prognosis as the median overall survival (OS) is less than 12 months. Targeted therapy is a popular emerging treatment method. Several targeted therapies, including those using bevacizumab and poly (ADP-ribose) polymerase inhibitor (PARPi), have been used to treat PROC. Ataxia telangiectasia and RAD3-Related Protein Kinase inhibitors (ATRi) have attracted attention as a promising class of targeted drugs that can regulate the cell cycle and influence homologous recombination (HR) repair. In recent years, many preclinical and clinical studies have demonstrated the efficacy of ATRis in PROC. This review focuses on the anticancer mechanism of ATRis and the progress of research on ATRis for PROC.

Biased holoenzyme assembly of protein phosphatase 2A (PP2A): From cancer to small molecules

Protein phosphatase 2A (PP2A) is a family of serine threonine phosphatases responsible for regulating protein phosphorylation, thus opposing the activity of cellular kinases. PP2A is composed of a catalytic subunit (PP2A Cα/β) and scaffolding subunit (PP2A Aα/β) and various substrate-directing B regulatory subunits. PP2A biogenesis is regulated at multiple levels. For example, the sequestration of the free catalytic subunit during the process of biogenesis avoids promiscuous phosphatase activity. Posttranslational modifications of PP2A C direct PP2A heterotrimeric formation. Additionally, PP2A functions as a haploinsufficient tumor suppressor, where attenuated PP2A enzymatic activity creates a permissive environment for oncogenic transformation. Recent work studying PP2A in cancer showed that its role in tumorigenesis is more nuanced, with some holoenzymes being tumor suppressive, while others are required for oncogenic transformation. In cancer biology, PP2A function is modulated through various mechanisms including the displacement of specific B regulatory subunits by DNA tumor viral antigens, by recurrent mutations, and through loss of carboxymethyl-sensitive heterotrimeric complexes. In aggregate, these alterations bias PP2A activity away from its tumor suppressive functions and toward oncogenic ones. From a therapeutic perspective, molecular glues and disruptors present opportunities for both the selective stabilization of tumor-suppressive holoenzymes and disruption of holoenzymes that are pro-oncogenic. Collectively, these approaches represent an attractive cancer therapy for a wide range of tumor types. This review will discuss the mechanisms by which PP2A holoenzyme formation is dysregulated in cancer and the current therapies that are aimed at biasing heterotrimer formation of PP2A for the treatment of cancer.

Degradome-focused RNA interference screens to identify proteases important for breast cancer cell growth

Proteases are known to promote or impair breast cancer progression and metastasis. However, while a small number of the 588 human and 672 murine protease genes have been extensively studied, others were neglected. For an unbiased functional analysis of all genome-encoded proteases, i.e., the degradome, in breast cancer cell growth, we applied an inducible RNA interference library for protease-focused genetic screens. Importantly, these functional screens were performed in two phenotypically different murine breast cancer cell lines, including one stem cell-like cell line that showed phenotypic plasticity under changed nutrient and oxygen availability. Our unbiased genetic screens identified 252 protease genes involved in breast cancer cell growth that were further restricted to 100 hits by a selection process. Many of those hits were supported by literature, but some proteases were novel in their functional link to breast cancer. Interestingly, we discovered that the environmental conditions influence the degree of breast cancer cell dependency on certain proteases. For example, breast cancer stem cell-like cells were less susceptible to depletion of several mitochondrial proteases in hypoxic conditions. From the 100 hits, nine proteases were functionally validated in murine breast cancer cell lines using individual knockdown constructs, highlighting the high reliability of our screens. Specifically, we focused on mitochondrial processing peptidase (MPP) subunits alpha (Pmpca) and beta (Pmpcb) and discovered that MPP depletion led to a disadvantage in cell growth, which was linked to mitochondrial dysfunction.

A MYC-ZNF148-ID1/3 regulatory axis modulating cancer stem cell traits in aggressive breast cancer

The MYC proto-oncogene (MYC) is one of the most frequently overexpressed genes in breast cancer that drives cancer stem cell-like traits, resulting in aggressive disease progression and poor prognosis. In this study, we identified zinc finger transcription factor 148 (ZNF148, also called Zfp148 and ZBP-89) as a direct target of MYC. ZNF148 suppressed cell proliferation and migration and was transcriptionally repressed by MYC in breast cancer. Depletion of ZNF148 by short hairpin RNA (shRNA) and CRISPR/Cas9 increased triple-negative breast cancer (TNBC) cell proliferation and migration. Global transcriptome and chromatin occupancy analyses of ZNF148 revealed a central role in inhibiting cancer cell de-differentiation and migration. Mechanistically, we identified the Inhibitor of DNA binding 1 and 3 (ID1, ID3), drivers of cancer stemness and plasticity, as previously uncharacterized targets of transcriptional repression by ZNF148. Silencing of ZNF148 increased the stemness and tumorigenicity in TNBC cells. These findings uncover a previously unknown tumor suppressor role for ZNF148, and a transcriptional regulatory circuitry encompassing MYC, ZNF148, and ID1/3 in driving cancer stem cell traits in aggressive breast cancer.

Targeting Squalene Epoxidase Interrupts Homologous Recombination via the ER Stress Response and Promotes Radiotherapy Efficacy

Over 50% of all patients with cancer are treated with radiotherapy. However, radiotherapy is often insufficient as a monotherapy and requires a nontoxic radiosensitizer. Squalene epoxidase (SQLE) controls cholesterol biosynthesis by converting squalene to 2,3-oxidosqualene. Given that SQLE is frequently overexpressed in human cancer, this study investigated the importance of SQLE in breast cancer and non-small cell lung cancer (NSCLC), two cancers often treated with radiotherapy. SQLE-positive IHC staining was observed in 68% of breast cancer and 56% of NSCLC specimens versus 15% and 25% in normal breast and lung tissue, respectively. Importantly, SQLE expression was an independent predictor of poor prognosis, and pharmacologic inhibition of SQLE enhanced breast and lung cancer cell radiosensitivity. In addition, SQLE inhibition enhanced sensitivity to PARP inhibition. Inhibition of SQLE interrupted homologous recombination by suppressing ataxia-telangiectasia mutated (ATM) activity via the translational upregulation of wild-type p53-induced phosphatase (WIP1), regardless of the p53 status. SQLE inhibition and subsequent squalene accumulation promoted this upregulation by triggering the endoplasmic reticulum (ER) stress response. Collectively, these results identify a novel tumor-specific radiosensitizer by revealing unrecognized cross-talk between squalene metabolites, ER stress, and the DNA damage response. Although SQLE inhibitors have been used as antifungal agents in the clinic, they have not yet been used as antitumor agents. Repurposing existing SQLE-inhibiting drugs may provide new cancer treatments.

SIGNIFICANCE

Squalene epoxidase inhibitors are novel tumor-specific radiosensitizers that promote ER stress and suppress homologous recombination, providing a new potential therapeutic approach to enhance radiotherapy efficacy.

Targeting Ribonucleotide Reductase Induces Synthetic Lethality in PP2A-Deficient Uterine Serous Carcinoma

Uterine serous carcinoma (USC) is a highly aggressive endometrial cancer subtype with limited therapeutic options and a lack of targeted therapies. While mutations to PPP2R1A, which encodes the predominant protein phosphatase 2A (PP2A) scaffolding protein Aα, occur in 30% to 40% of USC cases, the clinical actionability of these mutations has not been studied. Using a high-throughput screening approach, we showed that mutations in Aα results in synthetic lethality following treatment with inhibitors of ribonucleotide reductase (RNR). In vivo, multiple models of Aα mutant uterine serous tumors were sensitive to clofarabine, an RNR inhibitor (RNRi). Aα-mutant cells displayed impaired checkpoint signaling upon RNRi treatment and subsequently accumulated more DNA damage than wild-type (WT) cells. Consistently, inhibition of PP2A activity using LB-100, a catalytic inhibitor, sensitized WT USC cells to RNRi. Analysis of The Cancer Genome Atlas data indicated that inactivation of PP2A, through loss of PP2A subunit expression, was prevalent in USC, with 88% of patients with USC harboring loss of at least one PP2A gene. In contrast, loss of PP2A subunit expression was rare in uterine endometrioid carcinomas. While RNRi are not routinely used for uterine cancers, a retrospective analysis of patients treated with gemcitabine as a second- or later-line therapy revealed a trend for improved outcomes in patients with USC treated with RNRi gemcitabine compared with patients with endometrioid histology. Overall, our data provide experimental evidence to support the use of ribonucleotide reductase inhibitors for the treatment of USC.

SIGNIFICANCE

A drug repurposing screen identifies synthetic lethal interactions in PP2A-deficient uterine serous carcinoma, providing potential therapeutic avenues for treating this deadly endometrial cancer.

A Novel Role for RNF126 in the Promotion of G2 Arrest via Interaction With 14-3-3σ

PURPOSE

Cell cycle checkpoints and DNA repair are important for cell survival after exogenous DNA damage. Both rapid blockage of G2 to M phase transition in the cell cycle and the maintenance of relatively slow G2 arrest are critical to protect cells from lethal ionizing radiation (IR). Checkpoint kinase 1 is pivotal in blocking the transition from G2 to M phases in response to IR. The 14-3-3σ protein is important for IR-induced G2 arrest maintenance in which p53-dependent 14-3-3σ transcription is involved. It has been demonstrated that Ring finger protein 126 (RNF126), an E3 ligase, is required to upregulate checkpoint kinase 1 expression. Thus, our goal was to study the role of RNF126 in the G2/M phase checkpoint.

METHODS AND MATERIALS

The transition from G2 to M phases and G2 accumulation in response to IR were determined by flow cytometry through staining with phospho-histone H3 (pS10) antibody and propidium iodide, respectively. The interaction of RNF126 and 14-3-3σ was determined by GST-pulldown and coimmunoprecipitation assays. The stability of RNF126 and 14-3-3σ was determined by cycloheximide-based stability assay and ubiquitination detection by coimmunoprecipitation. The sequestering of cyclin-dependent kinase 1 and cyclin B1 from the nucleus was determined by immunofluorescence staining.

RESULTS

RNF126 knockdown had no impact on the IR-induced transient blockage of G2 to M but impaired IR-induced G2 arrest maintenance in cells with or without wild-type p53. Mechanistically, RNF126 binds 14-3-3σ and prevents both proteins from ubiquitination-mediated degradation. Last, RNF126 is required for enforcing the cytoplasmic sequestration of cyclin B1 and cyclin-dependent kinase 1 proteins in response to IR.

CONCLUSIONS

RNF126 promotes G2 arrest via interaction with 14-3-3σ in response to IR. Our study revealed a novel role for RNF126 in promoting G2 arrest, providing a new target for cancer treatment.

PPP2R2A affects embryonic implantation by regulating the proliferation and apoptosis of Hu sheep endometrial stromal cells

Embryonic implantation is a complex reproductive physiological process in mammals. Although several endometrial proteins affecting embryonic implantation have been reported in the past, there are still potential endometrial proteins that have been neglected, and their specific regulatory mechanisms are unclear. This study demonstrated that protein phosphatase 2A regulatory subunit B55α (PPP2R2A) served as a novel regulator in medication of sheep embryonic implantation in vitro. Our results showed that sheep PPP2R2A encoded 447 amino acids and shared 91.74%-92.36% amino acid sequences with its orthologs compared with other species. Meanwhile, PPP2R2A was widely expressed in sheep uterine tissues, and it could regulate the expression levels of key regulators of embryonic implantation in endometrial stromal cells (ESCs). Knockdown of PPP2R2A significantly inhibited cell proliferation by blocking cell cycle transfer G0/G1 into S phase accompanied by downregulation of CDK2, CDK4, CCND1, CCNE1 and upregulation of P21. In contrast to PPP2R2A overexpression, PPP2R2A interference greatly promoted cell apoptosis and the expression of BAX, CASP3, CASP9 and BAX/BCL-2. Taken together, these results suggest that PPP2R2A, as a novel regulatory factor, affects embryonic implantation via regulating the proliferation and apoptosis of Hu sheep ESCs in vitro.

DNA damage repair in glioblastoma: current perspectives on its role in tumour progression, treatment resistance and PIKKing potential therapeutic targets

BACKGROUND

The aggressive, invasive and treatment resistant nature of glioblastoma makes it one of the most lethal cancers in humans. Total surgical resection is difficult, and a combination of radiation and chemotherapy is used to treat the remaining invasive cells beyond the tumour border by inducing DNA damage and activating cell death pathways in glioblastoma cells. Unfortunately, recurrence is common and a major hurdle in treatment, often met with a more aggressive and treatment resistant tumour. A mechanism of resistance is the response of DNA repair pathways upon treatment-induced DNA damage, which enact cell-cycle arrest and repair of DNA damage that would otherwise cause cell death in tumour cells.

CONCLUSIONS

In this review, we discuss the significance of DNA repair mechanisms in tumour formation, aggression and treatment resistance. We identify an underlying trend in the literature, wherein alterations in DNA repair pathways facilitate glioma progression, while established high-grade gliomas benefit from constitutively active DNA repair pathways in the repair of treatment-induced DNA damage. We also consider the clinical feasibility of inhibiting DNA repair in glioblastoma and current strategies of using DNA repair inhibitors as agents in combination with chemotherapy, radiation or immunotherapy. Finally, the importance of blood-brain barrier penetrance when designing novel small-molecule inhibitors is discussed.

Exosomal miR-136-5p Derived from Anlotinib-Resistant NSCLC Cells Confers Anlotinib Resistance in Non-Small Cell Lung Cancer Through Targeting PPP2R2A

Background

Anlotinib resistance is a challenge for advanced non-small cell lung cancer (NSCLC). Understanding the underlying mechanisms against anlotinib resistance is of great importance to improve prognosis and treatment of patients with advanced NSCLC.

Methods

RT-qPCR assay was used to assess the level of miR-136-5p in anlotinib-resistant NSCLC cells and exosomes derived from anlotinib-resistant NSCLC cells. In addition, miR-136-5p level in tumor tissues from patients who exhibited a poor response to anlotinib therapy and patients who were therapy naïve or patients who exhibited a positive response to anlotinib therapy was detected by RT-qPCR assay.

Results

In this study, we found that high levels of plasma exosomal miR-136-5p is correlated with clinically poor anlotinib response. In addition, anlotinib-resistant NSCLC cells promoted parental NSCLC cell proliferation via transferring functional miR-136-5p from anlotinib-resistant NSCLC cells to parental NSCLC cells via exosomes. Moreover, exosomal miR-136-5p could endow NSCLC cells with anlotinib resistance by targeting PPP2R2A, leading to the activation of Akt pathway. Furthermore, miR-136-5p antagomir packaging into anlotinib-resistant NSCLC cell-derived exosomes functionally restored NSCLC cell anlotinib sensitivity in vitro. Animal studies showed that A549/anlotinib cell-derived exosomal miR-136-5p agomir promoted A549 cell anlotinib resistance in vivo.

Conclusion

Collectively, these findings indicated that anlotinib-resistant NSCLC cell-derived exosomal miR-136-5p confers anlotinib resistance in NSCLC cells by targeting PPP2R2A, indicating miR-136-5p may act as a potential biomarker for anlotinib response in NSCLC.

Novel and Highly Potent ATR Inhibitor M4344 Kills Cancer Cells With Replication Stress, and Enhances the Chemotherapeutic Activity of Widely Used DNA Damaging Agents

Although several ATR inhibitors are in development, there are unresolved questions regarding their differential potency, molecular signatures of patients with cancer for predicting activity, and most effective therapeutic combinations. Here, we elucidate how to improve ATR-based chemotherapy with the newly developed ATR inhibitor, M4344 using in vitro and in vivo models. The potency of M4344 was compared with the clinically developed ATR inhibitors BAY1895344, berzosertib, and ceralasertib. The anticancer activity of M4344 was investigated as monotherapy and combination with clinical DNA damaging agents in multiple cancer cell lines, patient-derived tumor organoids, and mouse xenograft models. We also elucidated the anticancer mechanisms and potential biomarkers for M4344. We demonstrate that M4344 is highly potent among the clinically developed ATR inhibitors. Replication stress (RepStress) and neuroendocrine (NE) gene expression signatures are significantly associated with a response to M4344 treatment. M4344 kills cancer cells by inducing cellular catastrophe and DNA damage. M4344 is highly synergistic with a broad range of DNA-targeting anticancer agents. It significantly synergizes with topotecan and irinotecan in patient-derived tumor organoids and xenograft models. Taken together, M4344 is a promising and highly potent ATR inhibitor. It enhances the activity of clinical DNA damaging agents commonly used in cancer treatment including topoisomerase inhibitors, gemcitabine, cisplatin, and talazoparib. RepStress and NE gene expression signatures can be exploited as predictive markers for M4344.

Bioactive Compounds with Antiglioma Activity from Marine Species

The search for new chemical compounds with antitumor pharmacological activity is a necessary process for creating more effective drugs for each specific malignancy type. This review presents the outcomes of screening studies of natural compounds with high anti-glioma activity. Despite significant advances in cancer therapy, there are still some tumors currently considered completely incurable including brain gliomas. This review covers the main problems of the glioma chemotherapy including drug resistance, side effects of common anti-glioma drugs, and genetic diversity of brain tumors. The main emphasis is made on the characterization of natural compounds isolated from marine organisms because taxonomic diversity of organisms in seawaters significantly exceeds that of terrestrial species. Thus, we should expect greater chemical diversity of marine compounds and greater likelihood of finding effective molecules with antiglioma activity. The review covers at least 15 classes of organic compounds with their chemical formulas provided as well as semi-inhibitory concentrations, mechanisms of action, and pharmacokinetic profiles. In conclusion, the analysis of the taxonomic diversity of marine species containing bioactives with antiglioma activity is performed noting cytotoxicity indicators and to the tumor cells in comparison with similar indicators of antitumor agents approved for clinical use as antiglioblastoma chemotherapeutics.

Targeting c-Myc to overcome acquired resistance of EGFR mutant NSCLC cells to the third generation EGFR tyrosine kinase inhibitor, osimertinib

Osimertinib (AZD9291 or TAGRISSOTM) is a promising and approved third-generation epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor (TKI) for treating patients with advanced non-small cell lung cancer (NSCLC) harboring EGFR-activating mutations or the resistant T790M mutation. However, the inevitable emergence of acquired resistance limits its long-term efficacy. A fuller understanding of the mechanism of action of osimertinib and its linkage to acquired resistance will enable the development of more efficacious therapeutic strategies. Consequently, we have identified a novel connection between osimertinib or other EGFR TKI and c-Myc. Osimertinib rapidly and sustainably decreased c-Myc levels primarily via enhancing protein degradation in EGFR-mutant (EGFRm) NSCLC cell lines and xenograft tumors. c-Myc levels were substantially elevated in different EGFRm NSCLC cell lines with acquired resistance to osimertinib in comparison with their corresponding parental cell lines and could not be reduced any further by osimertinib. Consistently, c-Myc levels were elevated in the majority of EGFRm NSCLC tissues relapsed from EGFR-TKI treatment compared to their corresponding untreated baseline c-Myc levels. Suppression of c-Myc through knockdown or pharmacological targeting with BET inhibitors restored the response of resistant cell lines to osimertinib. These findings indicate that c-Myc modulation mediates the therapeutic efficacy of osimertinib and the development of osimertinib-acquired resistance. Furthermore, they establish c-Myc as a potential therapeutic target and warrant clinical testing of BET inhibition as a potential strategy to overcome acquired resistance to osimertinib or other EGFR inhibitors.

MYC-Induced Replicative Stress: A Double-Edged Sword for Cancer Development and Treatment

MYC is a transcription factor that controls the expression of a large fraction of cellular genes linked to cell cycle progression, metabolism and differentiation. MYC deregulation in tumors leads to its pervasive genome-wide binding of both promoters and distal regulatory regions, associated with selective transcriptional control of a large fraction of cellular genes. This pairs with alterations of cell cycle control which drive anticipated S-phase entry and reshape the DNA-replication landscape. Under these circumstances, the fine tuning of DNA replication and transcription becomes critical and may pose an intrinsic liability in MYC-overexpressing cancer cells. Here, we will review the current understanding of how MYC controls DNA and RNA synthesis, discuss evidence of replicative and transcriptional stress induced by MYC and summarize preclinical data supporting the therapeutic potential of triggering replicative stress in MYC-driven tumors.

Loss of the abasic site sensor HMCES is synthetic lethal with the activity of the APOBEC3A cytosine deaminase in cancer cells

Analysis of cancer mutagenic signatures provides information about the origin of mutations and can inform the use of clinical therapies, including immunotherapy. In particular, APOBEC3A (A3A) has emerged as a major driver of mutagenesis in cancer cells, and its expression results in DNA damage and susceptibility to treatment with inhibitors of the ATR and CHK1 checkpoint kinases. Here, we report the implementation of CRISPR/Cas-9 genetic screening to identify susceptibilities of multiple A3A-expressing lung adenocarcinoma (LUAD) cell lines. We identify HMCES, a protein recently linked to the protection of abasic sites, as a central protein for the tolerance of A3A expression. HMCES depletion results in synthetic lethality with A3A expression preferentially in a TP53-mutant background. Analysis of previous screening data reveals a strong association between A3A mutational signatures and sensitivity to HMCES loss and indicates that HMCES is specialized in protecting against a narrow spectrum of DNA damaging agents in addition to A3A. We experimentally show that both HMCES disruption and A3A expression increase susceptibility of cancer cells to ionizing radiation (IR), oxidative stress, and ATR inhibition, strategies that are often applied in tumor therapies. Overall, our results suggest that HMCES is an attractive target for selective treatment of A3A-expressing tumors.

The Valproate Mediates Radio-Bidirectional Regulation Through RFWD3-Dependent Ubiquitination on Rad51

Ionizing radiation (IR) can induce DNA double-strand breaks (DSBs) in tumor cells during radiotherapy (RT), but the efficiency of RT is limited because of the toxicity to normal cells. Locating an adjuvant treatment to alleviate damage in normal cells while sensitizing tumor cells to IR has attracted much attention. Here, using the 7,12-dimethylbenz[α]anthracene (DMBA)-induced malignant transformed MCF10A cells, we found that valproate (VPA), a histone deacetylase inhibitor (HDACi), radiosensitized transformed cells while alleviated IR-induced damage in normal cells at a safe dose (0.5 mM). We further demonstrated the decrease of homologous recombination (HR)-associated Rad51 in the transformed cells was related to the increase of its ubiquitination regulated by E3 ligase RFWD3 for the radiosensitization, which was opposite to normal cells, indicating that RFWD3-dependent ubiquitination on Rad51 was involved in the VPA-mediated radio-bidirectional effect. Through DMBA-transformed breast cancer rat model, VPA at 200 mg/kg radiosensitized tumor tissue cells by increasing RFWD3 and inhibited Rad51, while radioprotected normal tissue cells by decreasing RFWD3 and enhanced Rad51. In addition, we found high-level Rad51 was associated with tumorigenesis and poor prognosis in breast cancer patients. Our findings uncovered RFWD3-dependent Rad51 ubiquitination was the novel mechanism of VPA-mediated radio-bidirectional effect, VPA is a potential adjuvant treatment for tumor RT.