Co-inhibition of pol θ and HR genes efficiently synergize with cisplatin to suppress cisplatin-resistant lung cancer cells survival

Polθ: emerging synthetic lethal partner in homologous recombination-deficient tumors

The most remarkable finding in synthetic lethality (SL) is the hypersensitivity to PARP inhibitors (PARPis) of the tumors harboring defects in genes involved in homologous repair (HR) such as BRCA1/2. Despite initial responsiveness to PARPi, the penetrance of the synthetic lethal interactions between BRCA1/2 genes and PARPi is incomplete. Thus, a significant proportion of HR-defective tumors experience intrinsic or acquired resistance, representing a key challenge of clinical research. An expanded concept of SL is opening new ways and includes novel forms of genetic interactions, investigating not only traditional SL of pairs genes but also SL between biological pathways that regulate the same essential survival cell function. In this context, recent research showed that HR and theta-mediated end-joining (TMEJ) pathways exhibit SL. DNA polymerase theta (Polθ) is encoded by the POLQ gene and is a key component of the TMEJ, an essential backup pathway, intrinsically mutagenic, to repair resected double-strand breaks (DSBs) when the non-homologous end joining (NHEJ) and HR are impaired. Polθ is broadly expressed in normal tissues, overexpressed in several cancers, and typically associated with poor outcomes and shorter relapse-free survival. Notably, HR-deficient tumor cells present the characteristic mutational signatures of the error-prone TMEJ pathway. According to this observation, the loss of HR proteins, such as BRCA1 or BRCA2, contributes to increasing the TMEJ-specific genomic profile, suggesting synthetic lethal interactions between loss of the POLQ and HR genes, and resulting in the emerging interest for Polθ as a potential therapeutic target in BRCA1/2-associated tumors.This review summarizes the converging roles of the POLQ and HR genes in DNA DSB repair, the early-stage clinical trials using Polθ inhibitor to treat HR-defective tumors and to overcome BRCA-reversion mutations responsible for therapeutic resistance, and the novel pleiotropic effects of Polθ, paving the way for the development of unexplored synthetic lethality strategies.

Targeting the DNA damage response in cancer

DNA damage response (DDR) pathway is the coordinated cellular network dealing with the identification, signaling, and repair of DNA damage. It tightly regulates cell cycle progression and promotes DNA repair to minimize DNA damage to daughter cells. Key proteins involved in DDR are frequently mutated/inactivated in human cancers and promote genomic instability, a recognized hallmark of cancer. Besides being an intrinsic property of tumors, DDR also represents a unique therapeutic opportunity. Indeed, inhibition of DDR is expected to delay repair, causing persistent unrepaired breaks, to interfere with cell cycle progression, and to sensitize cancer cells to several DNA-damaging agents, such as radiotherapy and chemotherapy. In addition, DDR defects in cancer cells have been shown to render these cells more dependent on the remaining pathways, which could be targeted very specifically (synthetic lethal approach). Research over the past two decades has led to the synthesis and testing of hundreds of small inhibitors against key DDR proteins, some of which have shown antitumor activity in human cancers. In parallel, the search for synthetic lethality interaction is broadening the use of DDR inhibitors. In this review, we discuss the state-of-art of ataxia-telangiectasia mutated, ataxia-telangiectasia-and-Rad3-related protein, checkpoint kinase 1, Wee1 and Polθ inhibitors, highlighting the results obtained in the ongoing clinical trials both in monotherapy and in combination with chemotherapy and radiotherapy.

Structural basis for a Polθ helicase small-molecule inhibitor revealed by cryo-EM

DNA polymerase theta (Polθ) is a DNA helicase-polymerase protein that facilitates DNA repair and is synthetic lethal with homology-directed repair (HDR) factors. Thus, Polθ is a promising precision oncology drug-target in HDR-deficient cancers. Here, we characterize the binding and mechanism of action of a Polθ helicase (Polθ-hel) small-molecule inhibitor (AB25583) using cryo-EM. AB25583 exhibits 6 nM IC50 against Polθ-hel, selectively kills BRCA1/2-deficient cells, and acts synergistically with olaparib in cancer cells harboring pathogenic BRCA1/2 mutations. Cryo-EM uncovers predominantly dimeric Polθ-hel:AB25583 complex structures at 3.0-3.2 Å. The structures reveal a binding-pocket deep inside the helicase central-channel, which underscores the high specificity and potency of AB25583. The cryo-EM structures in conjunction with biochemical data indicate that AB25583 inhibits the ATPase activity of Polθ-hel helicase via an allosteric mechanism. These detailed structural data and insights about AB25583 inhibition pave the way for accelerating drug development targeting Polθ-hel in HDR-deficient cancers.

Discovery of a small-molecule inhibitor that traps Polθ on DNA and synergizes with PARP inhibitors

The DNA damage response (DDR) protein DNA Polymerase θ (Polθ) is synthetic lethal with homologous recombination (HR) factors and is therefore a promising drug target in BRCA1/2 mutant cancers. We discover an allosteric Polθ inhibitor (Polθi) class with 4-6 nM IC50 that selectively kills HR-deficient cells and acts synergistically with PARP inhibitors (PARPi) in multiple genetic backgrounds. X-ray crystallography and biochemistry reveal that Polθi selectively inhibits Polθ polymerase (Polθ-pol) in the closed conformation on B-form DNA/DNA via an induced fit mechanism. In contrast, Polθi fails to inhibit Polθ-pol catalytic activity on A-form DNA/RNA in which the enzyme binds in the open configuration. Remarkably, Polθi binding to the Polθ-pol:DNA/DNA closed complex traps the polymerase on DNA for more than forty minutes which elucidates the inhibitory mechanism of action. These data reveal a unique small-molecule DNA polymerase:DNA trapping mechanism that induces synthetic lethality in HR-deficient cells and potentiates the activity of PARPi.

Discovery of 3-hydroxymethyl-azetidine derivatives as potent polymerase theta inhibitors

Inhibition of the low fidelity DNA polymerase Theta (Polθ) is emerging as an attractive, synthetic-lethal antitumor strategy in BRCA-deficient tumors. Here we report the AI-enabled development of 3-hydroxymethyl-azetidine derivatives as a novel class of Polθ inhibitors featuring central scaffolding rings. Structure-based drug design first identified A7 as a lead compound, which was further optimized to the more potent derivative B3 and the metabolically stable deuterated compound C1. C1 exhibited significant antiproliferative properties in DNA repair-compromised cells and demonstrated favorable pharmacokinetics, showcasing that 3-hydroxymethyl-azetidine is an effective bio-isostere of pyrrolidin-3-ol and emphasizing the potential of AI in medicinal chemistry for precise molecular modifications.

Role of Translesion DNA Synthesis in the Metabolism of Replication-associated Nascent Strand Gaps

Translesion DNA synthesis (TLS) is a DNA damage tolerance pathway utilized by cells to overcome lesions encountered throughout DNA replication. During replication stress, cancer cells show increased dependency on TLS proteins for cellular survival and chemoresistance. TLS proteins have been described to be involved in various DNA repair pathways. One of the major emerging roles of TLS is single-stranded DNA (ssDNA) gap-filling, primarily after the repriming activity of PrimPol upon encountering a lesion. Conversely, suppression of ssDNA gap accumulation by TLS is considered to represent a mechanism for cancer cells to evade the toxicity of chemotherapeutic agents, specifically in BRCA-deficient cells. Thus, TLS inhibition is emerging as a potential treatment regimen for DNA repair-deficient tumors.

Freedom to err: The expanding cellular functions of translesion DNA polymerases

Translesion synthesis (TLS) DNA polymerases were originally described as error-prone enzymes involved in the bypass of DNA lesions. However, extensive research over the past few decades has revealed that these enzymes play pivotal roles not only in lesion bypass, but also in a myriad of other cellular processes. Such processes include DNA replication, DNA repair, epigenetics, immune signaling, and even viral infection. This review discusses the wide range of functions exhibited by TLS polymerases, including their underlying biochemical mechanisms and associated mutagenicity. Given their multitasking ability to alleviate replication stress, TLS polymerases represent a cellular dependency and a critical vulnerability of cancer cells. Hence, this review also highlights current and emerging strategies for targeting TLS polymerases in cancer therapy.

Small Molecules Targeting DNA Polymerase Theta (POLθ) as Promising Synthetic Lethal Agents for Precision Cancer Therapy

Synthetic lethality (SL) is an innovative strategy in targeted anticancer therapy that exploits tumor genetic vulnerabilities. This topic has come to the forefront in recent years, as witnessed by the increased number of publications since 2007. The first proof of concept for the effectiveness of SL was provided by the approval of poly(ADP-ribose)polymerase inhibitors, which exploit a SL interaction in BRCA-deficient cells, although their use is limited by resistance. Searching for additional SL interactions involving BRCA mutations, the DNA polymerase theta (POLθ) emerged as an exciting target. This review summarizes, for the first time, the POLθ polymerase and helicase inhibitors reported to date. Compounds are described focusing on chemical structure and biological activity. With the aim to enable further drug discovery efforts in interrogating POLθ as a target, we propose a plausible pharmacophore model for POLθ-pol inhibitors and provide a structural analysis of the known POLθ ligand binding sites.

Fanconi anemia-associated chromosomal radial formation is dependent on POLθ-mediated alternative end joining

Activation of the Fanconi anemia (FA) pathway after treatment with mitomycin C (MMC) is essential for preventing chromosome translocations termed "radials." When replication forks stall at MMC-induced interstrand crosslinks (ICLs), the FA pathway is activated to orchestrate ICL unhooking and repair of the DNA break intermediates. However, in FA-deficient cells, how ICL-associated breaks are resolved in a manner that leads to radials is unclear. Here, we demonstrate that MMC-induced radials are dependent on DNA polymerase theta (POLθ)-mediated alternative end joining (A-EJ). Specifically, we show that radials observed in FANCD2^-/- cells are dependent on POLθ and DNA ligase III and occur independently of classical non-homologous end joining. Furthermore, treatment of FANCD2^-/- cells with POLθ inhibitors abolishes radials and leads to the accumulation of breaks co-localizing with common fragile sites. Uniformly, these observations implicate A-EJ in radial formation and provide mechanistic insights into the treatment of FA pathway-deficient cancers with POLθ inhibitors.

DNA Repair and Therapeutic Strategies in Cancer Stem Cells

First-line cancer treatments successfully eradicate the differentiated tumour mass but are comparatively ineffective against cancer stem cells (CSCs), a self-renewing subpopulation thought to be responsible for tumour initiation, metastasis, heterogeneity, and recurrence. CSCs are thus presented as the principal target for elimination during cancer treatment. However, CSCs are challenging to drug target because of numerous intrinsic and extrinsic mechanisms of drug resistance. One such mechanism that remains relatively understudied is the DNA damage response (DDR). CSCs are presumed to possess properties that enable enhanced DNA repair efficiency relative to their highly proliferative bulk progeny, facilitating improved repair of double-strand breaks induced by radiotherapy and most chemotherapeutics. This can occur through multiple mechanisms, including increased expression and splicing fidelity of DNA repair genes, robust activation of cell cycle checkpoints, and elevated homologous recombination-mediated DNA repair. Herein, we summarise the current knowledge concerning improved genome integrity in non-transformed stem cells and CSCs, discuss therapeutic opportunities within the DDR for re-sensitising CSCs to genotoxic stressors, and consider the challenges posed regarding unbiased identification of novel DDR-directed strategies in CSCs. A better understanding of the DDR mediating chemo/radioresistance mechanisms in CSCs could lead to novel therapeutic approaches, thereby enhancing treatment efficacy in cancer patients.

Multifaceted Nature of DNA Polymerase θ

DNA polymerase θ belongs to the A family of DNA polymerases and plays a key role in DNA repair and damage tolerance, including double-strand break repair and DNA translesion synthesis. Pol θ is often overexpressed in cancer cells and promotes their resistance to chemotherapeutic agents. In this review, we discuss unique biochemical properties and structural features of Pol θ, its multiple roles in protection of genome stability and the potential of Pol θ as a target for cancer treatment.

Polθ Inhibition: An Anticancer Therapy for HR-Deficient Tumours

DNA polymerase theta (Polθ)-mediated end joining (TMEJ) is, along with homologous recombination (HR) and non-homologous end-joining (NHEJ), one of the most important mechanisms repairing potentially lethal DNA double-strand breaks (DSBs). Polθ is becoming a new target in cancer research because it demonstrates numerous synthetically lethal interactions with other DNA repair mechanisms, e.g., those involving PARP1, BRCA1/2, DNA-PK, ATR. Inhibition of Polθ could be achieved with different methods, such as RNA interference (RNAi), CRISPR/Cas9 technology, or using small molecule inhibitors. In the context of this topic, RNAi and CRISPR/Cas9 are still more often applied in the research itself rather than clinical usage, different than small molecule inhibitors. Several Polθ inhibitors have been already generated, and two of them, novobiocin (NVB) and ART812 derivative, are being tested in clinical trials against HR-deficient tumors. In this review, we describe the significance of Polθ and the Polθ-mediated TMEJ pathway. In addition, we summarize the current state of knowledge about Polθ inhibitors and emphasize the promising role of Polθ as a therapeutic target.

Identification of , an Orally Bioavailable Compound that Inhibits the DNA Polymerase Activity of Polθ

DNA polymerase theta (Polθ) is an attractive synthetic lethal target for drug discovery, predicted to be efficacious against breast and ovarian cancers harboring BRCA-mutant alleles. Here, we describe our hit-to-lead efforts in search of a selective inhibitor of human Polθ (encoded by POLQ). A high-throughput screening campaign of 350,000 compounds identified an 11 micromolar hit, giving rise to the N2-substituted fused pyrazolo series, which was validated by biophysical methods. Structure-based drug design efforts along with optimization of cellular potency and ADME ultimately led to the identification of RP-6685: a potent, selective, and orally bioavailable Polθ inhibitor that showed in vivo efficacy in an HCT116 BRCA2-/- mouse tumor xenograft model.

Replication Stress: A Review of Novel Targets to Enhance Radiosensitivity-From Bench to Clinic

DNA replication is a process fundamental in all living organisms in which deregulation, known as replication stress, often leads to genomic instability, a hallmark of cancer. Most malignant tumors sustain persistent proliferation and tolerate replication stress via increasing reliance to the replication stress response. So whilst replication stress induces genomic instability and tumorigenesis, the replication stress response exhibits a unique cancer-specific vulnerability that can be targeted to induce catastrophic cell proliferation. Radiation therapy, most used in cancer treatment, induces a plethora of DNA lesions that affect DNA integrity and, in-turn, DNA replication. Owing to radiation dose limitations for specific organs and tumor tissue resistance, the therapeutic window is narrow. Thus, a means to eliminate or reduce tumor radioresistance is urgently needed. Current research trends have highlighted the potential of combining replication stress regulators with radiation therapy to capitalize on the high replication stress of tumors. Here, we review the current body of evidence regarding the role of replication stress in tumor progression and discuss potential means of enhancing tumor radiosensitivity by targeting the replication stress response. We offer new insights into the possibility of combining radiation therapy with replication stress drugs for clinical use.

Synthetic Lethality Targeting Polθ

Research studies regarding synthetic lethality (SL) in human cells are primarily motivated by the potential of this phenomenon to be an effective, but at the same time, safe to the patient's anti-cancer chemotherapy. Among the factors that are targets for the induction of the synthetic lethality effect, those involved in DNA repair seem to be the most relevant. Specifically, when mutation in one of the canonical DNA double-strand break (DSB) repair pathways occurs, which is a frequent event in cancer cells, the alternative pathways may be a promising target for the elimination of abnormal cells. Currently, inhibiting RAD52 and/or PARP1 in the tumor cells that are deficient in the canonical repair pathways has been the potential target for inducing the effect of synthetic lethality. Unfortunately, the development of resistance to commonly used PARP1 inhibitors (PARPi) represents the greatest obstacle to working out a successful treatment protocol. DNA polymerase theta (Polθ), encoded by the POLQ gene, plays a key role in an alternative DSB repair pathway-theta-mediated end joining (TMEJ). Thus, it is a promising target in the treatment of tumors harboring deficiencies in homologous recombination repair (HRR), where its inhibition can induce SL. In this review, the authors discuss the current state of knowledge on Polθ as a potential target for synthetic lethality-based anticancer therapies.

WHO grading system for invasive pulmonary lung adenocarcinoma reveals distinct molecular signature: An analysis from the cancer genome atlas database

Lung adenocarcinoma grading has gained interest in the past years. Recently a three-tier tumor grading was proposed showing that it is related to patients' prognosis. Nevertheless, the underlying molecular basis of this morphological grading remains partly unknown. The aim of our work is to take advantage of The Cancer Genome Atlas lung adenocarcinoma (TCGA_LUAD) cohort to describe the molecular data associated to tumor grading. We performed a study on publicly available data of the TCGA database first by assessing a tumor grade on downloadable tumor slides. Secondly we analyzed the molecular features of each tumor grade group. Our work was performed on a study group of 449 patients. We show that aneuploidy score was significantly different between grade 2 and grade 3 groups with different chromosomal imbalance (p < 0.001). SCGB1A1 mRNA expression was higher in grade 2 (p = 0.0179) whereas NUP155, CHFR, POLQ and CDC7 have a higher expression in grade 3 (p = 0.0189, 0.0427, 0.0427 and 0.427 respectively). GZMB and KRT80 have a higher methylation of DNA in grade 2 (p = 0.0201 and 0.0359 respectively). MT1G, CLEC12B and NDUFA7 have a higher methylation of DNA in grade 3 (p < 0.001, 0.0246 and 0.0359 respectively). We showed that the number of activated pathways is different between grade 2 and grade 3 patients (p = 0.004). We showed that differentially expressed genes by mRNA analysis and DNA methylation analysis involve several genes implied in chemoresistance. This could suggest that grade 3 lung adenocarcinoma might be more resistant to chemotherapy.

Simultaneous nanocarrier-mediated delivery of siRNAs and chemotherapeutic agents in cancer therapy and diagnosis: Recent advances

Recently, investigations have revealed that RNA interference (RNAi) has a remarkable potential to decrease cancer burden by downregulating genes. Among various RNAi molecules, small interfering RNA (siRNA) has been more attractive for this goal and is able to silence a target pathological path and promote the degradation of a certain mRNA, resulting in either gain or loss of function of proteins. Moreover, therapeutic siRNAs have exhibited low side effects compared to other therapeutic molecular candidates. Nevertheless, siRNA delivery has its own limitations including quick degradation in circulation, ineffective internalization and low passive uptake by cells, possible toxicity against off-target sites, and inducing unfavorable immune responses. Therefore, delivery tools must be able to specifically direct siRNAs to their target locations without inflicting detrimental effects on other sites. To conquer the mentioned problems, nanocarrier-mediated delivery of siRNAs, using inorganic nanoparticles (NPs), polymers, and lipids, has been developed as a biocompatible delivery approach. In this review, we have discussed recent advances in the siRNA delivery methods that employ nanoparticles, lipids, and polymers, as well as the inorganic-based co-delivery systems used to deliver siRNAs and anticancer agents to target cells.

Genome-wide CRISPR screens reveal cyclin C as synthetic survival target of BRCA2

Poly (ADP-ribose) polymerase inhibitor (PARPi)-based therapies initially reduce tumor burden but eventually lead to acquired resistance in cancer patients with BRCA1 or BRCA2 mutation. To understand the potential PARPi resistance mechanisms, we performed whole-genome CRISPR screens to discover genetic alterations that change the gene essentiality in cells with inducible depletion of BRCA2. We identified that several RNA Polymerase II transcription Mediator complex components, especially Cyclin C (CCNC) as synthetic survival targets upon BRCA2 loss. Total mRNA sequencing demonstrated that loss of CCNC could activate the transforming growth factor (TGF)-beta signaling pathway and extracellular matrix (ECM)-receptor interaction pathway, however the inhibition of these pathways could not reverse cell survival in BRCA2 depleted CCNC-knockout cells, indicating that the activation of these pathways is not required for the resistance. Moreover, we showed that the improved survival is not due to restoration of homologous recombination repair although decreased DNA damage signaling was observed. Interestingly, loss of CCNC could restore replication fork stability in BRCA2 deficient cells, which may contribute to PARPi resistance. Taken together, our data reveal CCNC as a critical genetic determinant upon BRCA2 loss of function, which may help the development of novel therapeutic strategies that overcome PARPi resistance.

DNA Polymerase θ: A Cancer Drug Target with Reverse Transcriptase Activity

The emergence of precision medicine from the development of Poly (ADP-ribose) polymerase (PARP) inhibitors that preferentially kill cells defective in homologous recombination has sparked wide interest in identifying and characterizing additional DNA repair enzymes that are synthetic lethal with HR factors. DNA polymerase theta (Polθ) is a validated anti-cancer drug target that is synthetic lethal with HR factors and other DNA repair proteins and confers cellular resistance to various genotoxic cancer therapies. Since its initial characterization as a helicase-polymerase fusion protein in 2003, many exciting and unexpected activities of Polθ in microhomology-mediated end-joining (MMEJ) and translesion synthesis (TLS) have been discovered. Here, we provide a short review of Polθ's DNA repair activities and its potential as a drug target and highlight a recent report that reveals Polθ as a naturally occurring reverse transcriptase (RT) in mammalian cells.

Targeting the replication stress response through synthetic lethal strategies in cancer medicine

The replication stress response (RSR) involves a downstream kinase cascade comprising ataxia telangiectasia-mutated (ATM), ATM and rad3-related (ATR), checkpoint kinases 1 and 2 (CHK1/2), and WEE1-like protein kinase (WEE1), which cooperate to arrest the cell cycle, protect stalled forks, and allow time for replication fork repair. In the presence of elevated replicative stress, cancers are increasingly dependent on RSR to maintain genomic integrity. An increasing number of drug candidates targeting key RSR nodes, as monotherapy through synthetic lethality, or through rational combinations with immune checkpoint inhibitors and targeted therapies, are demonstrating promising efficacy in early phase trials. RSR targeting is also showing potential in reversing PARP inhibitor resistance, an important area of unmet clinical need. In this review, we introduce the concept of targeting the RSR, detail the current landscape of monotherapy and combination strategies, and discuss emerging therapeutic approaches, such as targeting Polθ.

Depletion of DNA Polymerase Theta Inhibits Tumor Growth and Promotes Genome Instability through the cGAS-STING-ISG Pathway in Esophageal Squamous Cell Carcinoma

Simple Summary

DNA polymerase theta, encoded by the human POLQ gene, is upregulated in several cancers and is associated with poor clinical outcomes. The importance of POLQ, however, has yet to be elucidated in esophageal cancer. In this study, we explored the functional impacts of POLQ and looked into its underlying mechanisms. POLQ was overexpressed in esophageal squamous cell carcinoma (ESCC) tumors associated with unfavorable prognosis and contributed to malignant phenotypes by promoting genome stability, suggesting that targeting polymerase theta may provide a potential therapeutic approach for improving ESCC management.

Abstract

Overexpression of the specialized DNA polymerase theta (POLQ) is frequent in breast, colon and lung cancers and has been correlated with unfavorable clinical outcomes. Here, we aimed to determine the importance and functional role of POLQ in esophageal squamous cell carcinoma (ESCC). Integrated analysis of four RNA-seq datasets showed POLQ was predominantly upregulated in ESCC tumors. High expression of POLQ was also observed in a cohort of 25 Hong Kong ESCC patients and negatively correlated with ESCC patient survival. POLQ knockout (KO) ESCC cells were sensitized to multiple genotoxic agents. Both rH2AX foci staining and the comet assay indicated a higher level of genomic instability in POLQ-depleted cells. Double KO of POLQ and FANCD2, known to promote POLQ recruitment at sites of damage, significantly impaired cell proliferation both in vitro and in vivo, as compared to either single POLQ or FANCD2 KOs. A significantly increased number of micronuclei was observed in POLQ and/or FANCD2 KO ESCC cells. Loss of POLQ and/or FANCD2 also resulted in the activation of cGAS and upregulation of interferon-stimulated genes (ISGs). Our results suggest that high abundance of POLQ in ESCC contributes to the malignant phenotype through genome instability and activation of the cGAS pathway.

Celastrol acts synergistically with afatinib to suppress non-small cell lung cancer cell proliferation by inducing paraptosis

Non-small cell lung cancer (NSCLC) with wild-type epidermal growth factor receptor (EGFR) is intrinsic resistance to EGFR-tyrosine kinase inhibitors (TKIs), such as afatinib. Celastrol, a natural compound with antitumor activity, was reported to induce paraptosis in cancer cells. In this study, intrinsic EGFR-TKI-resistant NSCLC cell lines H23 (EGFR wild-type and KRAS mutation) and H292 (EGFR wild-type and overexpression) were used to test whether celastrol could overcome primary afatinib resistance through paraptosis induction. The synergistic effect of celastrol and afatinib on survival inhibition of the NSCLC cells was evaluated by CCK-8 assay and isobologram analysis. The paraptosis and its modulation were assessed by light and electron microscopy, Western blot analysis, and immunofluorescence. Xenografts models were established to investigate the inhibitory effect of celastrol plus afatinib on the growth of the NSCLC tumors in vivo. Results showed that celastrol acted synergistically with afatinib to suppress the survival of H23 and H292 cells by inducing paraptosis characterized by extensive cytoplasmic vacuolation. This process was independent of apoptosis and not associated with autophagy induction. Afatinib plus celastrol-induced cytoplasmic vacuolation was preceded by endoplasmic reticulum stress and unfolded protein response. Accumulation of intracellular reactive oxygen species and mitochondrial Ca2+ overload may be initiating factors of celastrol/afatinib-induced paraptosis and subsequent cell death. Furthermore, Celastrol and afatinib synergistically suppressed the growth of H23 cell xenograft tumors in vivo. The data indicate that a combination of afatinib and celastrol may be a promising therapeutic strategy to surmount intrinsic afatinib resistance in NSCLC cells.

Shaping the BRCAness mutational landscape by alternative double-strand break repair, replication stress and mitotic aberrancies

Tumours with mutations in the BRCA1/BRCA2 genes have impaired double-stranded DNA break repair, compromised replication fork protection and increased sensitivity to replication blocking agents, a phenotype collectively known as 'BRCAness'. Tumours with a BRCAness phenotype become dependent on alternative repair pathways that are error-prone and introduce specific patterns of somatic mutations across the genome. The increasing availability of next-generation sequencing data of tumour samples has enabled identification of distinct mutational signatures associated with BRCAness. These signatures reveal that alternative repair pathways, including Polymerase θ-mediated alternative end-joining and RAD52-mediated single strand annealing are active in BRCA1/2-deficient tumours, pointing towards potential therapeutic targets in these tumours. Additionally, insight into the mutations and consequences of unrepaired DNA lesions may also aid in the identification of BRCA-like tumours lacking BRCA1/BRCA2 gene inactivation. This is clinically relevant, as these tumours respond favourably to treatment with DNA-damaging agents, including PARP inhibitors or cisplatin, which have been successfully used to treat patients with BRCA1/2-defective tumours. In this review, we aim to provide insight in the origins of the mutational landscape associated with BRCAness by exploring the molecular biology of alternative DNA repair pathways, which may represent actionable therapeutic targets in in these cells.

Targeting the DNA Repair Enzyme Polymerase θ in Cancer Therapy

Targeted cancer therapies represent a milestone towards personalized treatment as they function via inhibition of cancer-specific alterations. Polymerase θ (POLQ), an error-prone translesion polymerase, also involved in DNA double-strand break (DSB) repair, is often upregulated in cancer. POLQ is synthetic lethal with various DNA repair genes, including known cancer drivers such as BRCA1/2, making it essential in homologous recombination-deficient cancers. Thus, POLQ represents a promising target in cancer therapy and efforts for the development of POLQ inhibitors are actively underway with first clinical trials due to start in 2021. This review summarizes the journey of POLQ from a backup DNA repair enzyme to a promising therapeutic target for cancer treatment.

New small-molecule compound Hu-17 inhibits estrogen biosynthesis by aromatase in human ovarian granulosa cancer cells

Estrogen-dependent cancers (breast, endometrial, and ovarian) are among the leading causes of morbidity and mortality in women worldwide. Aromatase is the main enzyme that catalyzes the biosynthesis of estrogen, which drives proliferation, and antiestrogens can inhibit the growth of these estrogen-dependent cancers. Hu-17, an aromatase inhibitor, is a novel small-molecule compound that suppresses viability of and promotes apoptosis in ovarian cancer cells. Therefore, this study aimed to predict targets of Hu-17 and assess its intracellular signaling in ovarian cancer cells. Using the Similarity Ensemble Approach software to predict the potential mechanism of Hu-17 and combining phospho-proteome arrays with western blot analysis, we observed that Hu-17 could inhibit the ERK pathway, resulting in reduced estrogen synthesis in KGN cells, a cell line derived from a patient with invasive ovarian granulosa cell carcinoma. Hu-17 reduced the expression of CYP19A1 mRNA, responsible for producing aromatase, by suppressing the phosphorylation of cAMP response element binding-1. Hu-17 also accelerated aromatase protein degradation but had no effect on aromatase activity. Therefore, Hu-17 could serve as a potential treatment for estrogen-dependent cancers albeit further investigation is warranted.

BRCA1-associated structural variations are a consequence of polymerase theta-mediated end-joining

Failure to preserve the integrity of the genome is a hallmark of cancer. Recent studies have revealed that loss of the capacity to repair DNA breaks via homologous recombination (HR) results in a mutational profile termed BRCAness. The enzymatic activity that repairs HR substrates in BRCA-deficient conditions to produce this profile is currently unknown. We here show that the mutational landscape of BRCA1 deficiency in C. elegans closely resembles that of BRCA1-deficient tumours. We identify polymerase theta-mediated end-joining (TMEJ) to be responsible: knocking out polq-1 suppresses the accumulation of deletions and tandem duplications in brc-1 and brd-1 animals. We find no additional back-up repair in HR and TMEJ compromised animals; non-homologous end-joining does not affect BRCAness. The notion that TMEJ acts as an alternative to HR, promoting the genome alteration of HR-deficient cells, supports the idea that polymerase theta is a promising therapeutic target for HR-deficient tumours.

Participation of the ATR/CHK1 pathway in replicative stress targeted therapy of high-grade ovarian cancer

Ovarian cancer is one of the most lethal gynecologic malignancies reported throughout the world. The initial, standard-of-care, adjuvant chemotherapy in epithelial ovarian cancer is usually a platinum drug, such as cisplatin or carboplatin, combined with a taxane. However, despite surgical removal of the tumor and initial high response rates to first-line chemotherapy, around 80% of women will develop cancer recurrence. Effective strategies, including chemotherapy and new research models, are necessary to improve the prognosis. The replication stress response (RSR) is characteristic of the development of tumors, including ovarian cancer. Hence, RSR pathway and DNA repair proteins have emerged as a new area for anticancer drug development. Although clinical trials have shown poly (ADP-ribose) polymerase inhibitors (PARPi) response rates of around 40% in women who carry a mutation in the BRCA1/2 genes, PARPi is responsible for tumor suppression, but not for complete tumor regression. Recent reports suggest that cells with impaired homologous recombination (HR) activities due to mutations in TP53 gene or specific DNA repair proteins are specifically sensitive to ataxia telangiectasia and Rad3-related protein (ATR) inhibitors. Replication stress activates DNA repair checkpoint proteins (ATR, CHK1), which prevent further DNA damage. This review describes the use of DNA repair checkpoint inhibitors as single agents and strategies combining these inhibitors with DNA-damaging compounds for ovarian cancer therapy, as well as the new platforms used for optimizing ovarian cancer therapy.

Application of curcumin and its derivatives in tumor multidrug resistance

Malignant tumor endangers seriously the health of all mankind. Multidrug resistance (MDR) is one of the main causes of clinical tumor chemotherapy failure. Curcumin (CUR) has not only antitumor activity but also reversing tumor MDR effect. CUR reverses tumor MDR via regulating related signal pathways or corresponding expressed proteins or gene. When combined with chemotherapeutic agents, CUR can be a chemotherapeutic sensitive agent to enhance chemotherapy efficacy and weaken tumor MDR. On the other hand, to improve the MDR reversal effect of CUR, its derivatives have been extensively studied. Therefore, this article mainly focuses on reviewing the application of CUR and its derivatives in MDR and its mechanism of reversing MDR.

LncRNA-ATB Promotes Cisplatin Resistance in Lung Adenocarcinoma Cells by Targeting the miR-200a/β-Catenin Pathway

Introduction

Lung adenocarcinoma (LUAD), which is associated with high morbidity and mortality, is prone to cisplatin resistance, resulting in poor patient prognosis. Long non-coding RNAs (lncRNAs) have complex biological functions in a variety of tumors. Elucidating the underlying molecular mechanisms between lncRNA and cisplatin resistance in LUAD is expected to enable identification of new targets for drug development.

Methods

Cell proliferation was measured by CCK-8 assay and cell apoptosis was detected using flow cytometry analysis. Luciferase reporter assay was conducted to determine the interaction between lncRNA and MicroRNA. Gene expression was evaluated by Real-Time Quantitative Reverse Transcription Polymerase Chain Reaction and Western blot analysis.

Results

Long non-coding RNA activated by TGF-β (lncRNA-ATB) was shown to be significantly up-regulated in A549 cells resistant to cisplatin/cis-dichlorodiammineplatinum (II) (cis-DDP) (A549/CDDP cells), compared with corresponding levels in parental A549 cells. Overexpression of lncRNA-ATB significantly elevated cisplatin resistance in LUAD cell lines (A549 and H1975 cells), and this was associated with activation of apoptosis-related genes. Conversely, silencing of lncRNA-ATB decreased cisplatin resistance in LUAD cells. Mechanistically, lncRNA-ATB increased expression of β-catenin by directly binding to MicroRNA-200a (miR-200a), thereby promoting cell survival and cisplatin resistance. Transfection with a miR-200a mimic or treatment with the β-catenin downstream pathway inhibitor IWR-1 could reverse the phenotypes induced by lncRNA-ATB overexpression.

Conclusion

In summary, this study revealed that lncRNA-ATB is dramatically up-regulated in cisplatin-resistant LUAD cell lines, and that lncRNA-ATB facilitates cell survival by targeting the miR-200a/β-catenin pathway in these cells.

Securing the Payload, Finding the Cell, and Avoiding the Endosome: Peptide-Targeted, Fusogenic Porous Silicon Nanoparticles for Delivery of siRNA

Despite the promise of ribonucleic acid interference therapeutics, the delivery of oligonucleotides selectively to diseased tissues in the body, and specifically to the cellular location in the tissues needed to provide optimal therapeutic outcome, remains a significant challenge. Here, key material properties and biological mechanisms for delivery of short interfering RNAs (siRNAs) to effectively silence target-specific cells in vivo are identified. Using porous silicon nanoparticles as the siRNA host, tumor-targeting peptides for selective tissue homing, and fusogenic lipid coatings to induce fusion with the plasma membrane, it is shown that the uptake mechanism can be engineered to be independent of common receptor-mediated endocytosis pathways. Two examples of the potential broad clinical applicability of this concept in a mouse xenograft model of ovarian cancer peritoneal carcinomatosis are provided: silencing the Rev3l subunit of polymerase Pol ζ to impair DNA repair in combination with cisplatin; and reprogramming tumor-associated macrophages into a proinflammatory state.

Inhibition of ATM reverses EMT and decreases metastatic potential of cisplatin-resistant lung cancer cells through JAK/STAT3/PD-L1 pathway

Background

The cisplatin-resistance is still a main course for chemotherapy failure of lung cancer patients. Cisplatin-resistant cancer cells own higher malignance and exhibited increased metastatic ability, but the mechanism is not clear. In this study, we investigated the effects of Ataxia Telangiectasia Mutated (ATM) on lung cancer metastasis.

Materials and methods

Cisplatin-resistant A549CisR and H157CisR cell line were generated by long-term treating parental A549 and H157 cells (A549P and H157P) with cisplatin. Cell growth, cell migration and cell invasion were determined. Gene expressions were determined by Western Blot and qPCR. Tumor metastasis was investigated using a xenograft mouse model.

Results

The IC50 of the cisplatin-resistant cells (A549CisR and H157CisR cells) to cisplatin was 6–8 higher than parental cells. The A549CisR and H157CisR cells expressed lower level of E-cadherin and higher levels of N-cadherin, Vimentin and Snail compared to the parental A549P and H157P cells, and exhibited stronger capabilities of metastatic potential compared to the parental cells. The ATM expression was upregulated in A549CisR and H157CisR cells and cisplatin treatment also upregulated expression of ATM in parental cells, The inhibition of ATM by using specific ATM inhibitor CP466722 or knock-down ATM by siRNA suppressed Epithelial-to-Mesenchymal transition (EMT) and metastatic potential of A549CisR and H157CisR cells. These data suggest that ATM mediates the cisplatin-resistance in lung cancer cells. Expressions of JAK_1,2,、 STAT₃ 、PD-L1 and ATM were increased in A549CisR and H157CisR cells and could by induced by cisplatin in parental lung cancer cells. Interestedly, ATM upregulated PD-L1 expression via JAK_1,2/STAT₃ pathway and inhibition of ATM decreased JAK/STAT3 signaling and decreased PD-L1 expression. The treatment of PD-L1 neutralizing Ab reduced EMT and cell invasion. Inhibition of JAK_1,2/STAT₃ signaling by specific inhibitors suppressed ATM-induced PD-L1 expression, EMT and cell invasion. Importantly, inhibition of ATM suppressed EMT and tumor metastasis in cisplatin-resistant lung cancer cells in an orthotopic xenograft mouse model.

Conclusions

Our results show that ATM regulates PD-L1 expression through activation of JAK/STAT3 signaling in cisplatin-resistant cells. Overexpression of ATM contributes to cisplatin-resistance in lung cancer cells. Inhibition of ATM reversed EMT and inhibited cell invasion and tumor metastasis. Thus, ATM may be a potential target for the treatment of cisplatin-resistant lung cancer.

Electronic supplementary material

The online version of this article (10.1186/s13046-019-1161-8) contains supplementary material, which is available to authorized users.

In vitro apoptosis-induction, antiproliferative and BSA binding studies of a oxidovanadium(V) complex

In our ongoing efforts to develop novel trace metal complexes with therapeutically interesting properties, a neutral mono nuclear oxidomethoxidovanadium(V) complex, [V^VO(OCH₃)(hpdbal-sbdt)] (1) and a μ-O bridged dinuclear oxidovanadium(V) complex, [{V^VO(hpdbal-sbdt)}₂μ-O] (2) [H₂hpdbal-sbdt (I) is a tridentate and dibasic ONS^2- donor ligand obtained through the Schiff base reaction of 2-hydroxy-5-(phenyldiazenyl)benzaldehyde (Hhpdbal) and S-benzyldithiocarbazate (Hsbdt)] have been synthesized and characterized by various analytical techniques such as TGA, EDS, ATR-IR, UV-Vis, CV, ¹H NMR, ¹³C NMR and ⁵¹V NMR. Single-crystal X-ray diffraction analysis of 1 confirms the coordination of phenolate oxygen, imine nitrogen and thioenolate sulfur of the ligand to the vanadium center with a distorted tetragonal-pyramidal geometry. The compound 2 triggered apoptotic and reproductive death of the cancer cells in vitro with 76% and 62% growth inhibition of human breast adenocarcinoma (MCF-7) and human lung carcinoma cells (A549) respectively. The compound 2 was found to be sufficiently stable over a wide window of physiological pH. The complex 2 was studied further for its interaction with a drug carrier protein BSA with the aid of spectroscopic techniques viz. fluorescence, temperature controlled UV-vis and deconvoluted IR techniques.

Phytochemicals: Current strategy to sensitize cancer cells to cisplatin

Cisplatin-based chemotherapeutic regimens are the most frequently used adjuvant treatments for many types of cancer. However, the development of chemoresistance to cisplatin results in treatment failure. Despite the significant developments in understanding the mechanisms of cisplatin resistance, effective strategies to enhance the chemosensitivity of cisplatin are lacking. Phytochemicals are naturally occurring plant-based compounds that can augment the anti-cancer activity of cisplatin, with minimal side effects. Notably, some novel phytochemicals, such as curcumin, not only increase the efficacy of cisplatin but also decrease toxicity induced by cisplatin. However, the exact mechanisms underlying this process remain unclear. In this review, we discussed the progress made in utilizing phytochemicals to enhance the anti-cancer efficacy of cisplatin. We also presented some ideal phytochemicals as novel agents for counteracting cisplatin-induced organ damage.

YM155 sensitizes non-small cell lung cancer cells to EGFR-tyrosine kinase inhibitors through the mechanism of autophagy induction

Resistance to epidermal growth factor receptor-tyrosine kinase inhibitors (EGFR-TKIs), such as erlotinib and gefitinib, is a major clinical problem in the treatment of patients with non-small cell lung cancer (NSCLC). YM155 is a survivin small molecule inhibitor and has been demonstrated to induce cancer cell apoptosis and autophagy. EGFR-TKIs have been known to induce cancer cell autophagy. In this study, we showed that YM155 markedly enhanced the sensitivity of erlotinib to EGFR-TKI resistant NSCLC cell lines H1650 (EGFR exon 19 deletion and PTEN loss) and A549 (EGFR wild type and KRAS mutation) through inducing autophagy-dependent apoptosis and autophagic cell death. The effects of YM155 combined with erlotinib on apoptosis and autophagy inductions were more obvious than those of YM155 in combination with survivin knockdown by siRNA transfection, suggesting that YM155 induced autophagy and apoptosis in the NSCLC cells partially depend on survivin downregulation. Meanwhile, we found that the AKT/mTOR pathway is involved in modulation of survivin downregulation and autophagy induction caused by YM155. In addition, YM155 can induce DNA damage in H1650 and A549 cell lines. Moreover, combining erlotinib further augmented DNA damage by YM155, which were retarded by autophagy inhibitor 3MA, or knockdown of autophagy-related protein Beclin 1, revealing that YM155 induced DNA damage is autophagy-dependent. Similar results were also observed in vivo xenograft experiments. Therefore, combination of YM155 and erlotinib offers a promising therapeutic strategy in NSCLC with EGFR-TKI resistant phenotype.

Co-inhibition of Pol η and ATR sensitizes cisplatin-resistant non-small cell lung cancer cells to cisplatin by impeding DNA damage repair

For the majority of patients with advanced non-small cell lung cancer (NSCLC), the standard of care remains platinum-based chemotherapy. However, cisplatin resistance is a big obstacle to the treatment, and elucidation of its mechanism is warranted. In this study, we showed that there was no difference in intracellular uptake of cisplatin or the removal of platinum-DNA adducts between a cisplatin-resistant NSCLC cell line (A549/DR) and a cisplatin-sensitive NSCLC cell line (A549). However, the capacity to repair DNA interstrand crosslinks (ICLs) and double-strand breaks (DSBs) was significantly enhanced in the A549/DR cell line compared to 3 cisplatin-sensitive cell lines. We found that the protein and mRNA expression levels of Pol η, a Y-family translesion synthesis (TLS) polymerase, were markedly increased upon cisplatin exposure in A549/DR cells compared with A549 cells. Furthermore, intracellular co-localization of Pol η and proliferation cell nuclear antigen (PCNA) induced by cisplatin or cisplatin plus gemcitabine treatment was inhibited by depleting ataxia telangiectasia mutated and Rad-3-related (ATR). Pol η depletion by siRNA sensitized A549/DR cells to cisplatin; co-depletion of Pol η and ATR further increased A549/DR cell death induced by cisplatin or cisplatin plus gemcitabine compared to depletion of Pol η or ATR alone, concomitant with inhibition of DNA ICL and DSB repair and accumulation of DNA damage. No additional sensitization effect of co-depleting Pol η and ATR was observed in A549 cells. These results demonstrate that co-inhibition of Pol η and ATR reverses the drug resistance of cisplatin-resistant NSCLC cells by blocking the repair of DNA ICLs and DSBs induced by cisplatin or cisplatin plus gemcitabine.

Gemcitabine resistance mediated by ribonucleotide reductase M2 in lung squamous cell carcinoma is reversed by GW8510 through autophagy induction

Although chemotherapeutic regimen containing gemcitabine is the first-line therapy for advanced lung squamous cell carcinoma (LSCC), gemcitabine resistance remains an important clinical problem. Some studies suggest that overexpressions of ribonucleotide reductase (RNR) subunit M2 (RRM2) may be involved in gemcitabine resistance. We used a novel RRM2 inhibitor, GW8510, as a gemcitabine sensitization agent to investigate the therapeutic utility in reversing gemcitabine resistance in LSCC. Results showed that the expressions of RRM2 were increased in gemcitabine intrinsic resistant LSCC cells upon gemcitabine treatment. GW8510 not only suppressed LSCC cell survival, but also sensitized gemcitabine-resistant cells to gemcitabine through autophagy induction mediated by RRM2 down-regulation along with decrease in dNTP levels. The combination of GW8510 and gemcitabine produced a synergistic effect on killing LSCC cells. The synergism of the two agents was impeded by addition of autophagy inhibitors chloroquine (CQ) or bafilomycin A1 (Baf A1), or knockdown of the autophagy gene, Bcl-2-interacting protein 1 (BECN1). Moreover, GW8510-caused LSCC cell sensitization to gemcitabine through autophagy induction was parallel with impairment of DNA double-strand break (DSB) repair and marked increase in cell apoptosis, revealing a cross-talk between autophagy and DNA damage repair, and an interplay between autophagy and apoptosis. Finally, gemcitabine sensitization mediated by autophagy induction through GW8510-caused RRM2 down-regulation was demonstrated in vivo in gemcitabine-resistant LSCC tumor xenograft, further indicating that the sensitization is dependent on autophagy activation. In conclusion, GW8510 can reverse gemcitabine resistance in LSCC cells through RRM2 downregulation-mediated autophagy induction, and GW850 may be a promising therapeutic agent against LSCC as it combined with gemcitabine.

A hypothesis-driven approach identifies CDK4 and CDK6 inhibitors as candidate drugs for treatments of adrenocortical carcinomas

High proliferation rate and high mutation density are both indicators of poor prognosis in adrenocortical carcinomas. We performed a hypothesis-driven association study between clinical features in adrenocortical carcinomas and the expression levels of 136 genes involved in DNA metabolism and G1/S phase transition. In 79 samples downloaded from The Cancer Genome Atlas portal, high Cyclin Dependent Kinase 6 (CDK6) mRNA levels gave the most significant association with shorter time to relapse and poorer survival of patients. A hierarchical clustering approach assembled most tumors with high levels of CDK6 mRNA into one group. These tumors tend to cumulate mutations activating the Wnt/β-catenin pathway and show reduced MIR506 expression. Actually, the level of MIR506 RNA is inversely correlated with the levels of both CDK6 and CTNNB1 (encoding β-catenin). Together these results indicate that high CDK6 expression is found in aggressive tumors with activated Wnt/β-catenin pathway. Thus we tested the impact of Food and Drug Administration-approved CDK4 and CDK6 inhibitors, namely palbociclib and ribociclib, on SW-13 and NCI-H295R cells. While both drugs reduced viability and induced senescence in SW-13 cells, only palbociclib was effective on the retinoblastoma protein (pRB)-negative NCI-H295R cells, by inducing apoptosis. In NCI-H295R cells, palbociclib induced an increase of the active form of Glycogen Synthase Kinase 3β (GSK3β) responsible for the reduced amount of active β-catenin, and altered the amount of AXIN2 mRNA. Taken together, these data underline the impact of CDK4 and CDK6 inhibitors in treating adrenocortical carcinomas.

Mutational signatures of non-homologous and polymerase theta-mediated end-joining in embryonic stem cells

Cells employ potentially mutagenic DNA repair mechanisms to avoid the detrimental effects of chromosome breaks on cell survival. While classical non-homologous end-joining (cNHEJ) is largely error-free, alternative end-joining pathways have been described that are intrinsically mutagenic. Which end-joining mechanisms operate in germ and embryonic cells and thus contribute to heritable mutations found in congenital diseases is, however, still largely elusive. Here, we determined the genetic requirements for the repair of CRISPR/Cas9-induced chromosomal breaks of different configurations, and establish the mutational consequences. We find that cNHEJ and polymerase theta-mediated end-joining (TMEJ) act both parallel and redundant in mouse embryonic stem cells and account for virtually all end-joining activity. Surprisingly, mutagenic repair by polymerase theta (Pol θ, encoded by the Polq gene) is most prevalent for blunt double-strand breaks (DSBs), while cNHEJ dictates mutagenic repair of DSBs with protruding ends, in which the cNHEJ polymerases lambda and mu play minor roles. We conclude that cNHEJ-dependent repair of DSBs with protruding ends can explain de novo formation of tandem duplications in mammalian genomes.

Suppression of the FA pathway combined with CHK1 inhibitor hypersensitize lung cancer cells to gemcitabine

The combination of platinum and gemcitabine is one of the standard regimens in the treatment of advanced lung squamous carcinoma (LSC). Resistance to gemcitabine is main barrier to the successful treatment of LSC. In this study, we showed that suppression of the Fanconi anemia (FA) pathway increased the sensitivity of two LSC cell lines SK-MES-1 and KLN205 to gemcitabine. Moreover, we found that the CHK1 pathway and the FA pathway are functionally compensatory in the repair of DNA damage in the LSC cell lines. Inactivation of one of the two pathways led to DNA damage, triggering compensatory activation of other pathway. Furthermore, we demonstrated that FANCD2 depletion combined with CHK1 inhibitor MK-8776 significantly potentiated the cytotoxicity of gemcitabine to the two LSC cell lines, compared to individual FANCD2 depletion or MK-8776 treatment. The enhanced effect of gemcitabine-chemosensitization was accompanied by loss of DNA repair function and accumulation of DNA single strand breaks and double strand breaks, in parallel with obvious increase of caspase-3 dependent apoptosis. Our results indicate that the enhancement effect of FANCD2 depletion combined with CHK1 inhibitor in sensitizing the LCS cells to gemcitabine supports the FA pathway and CHK1 as two therapeutic targets for improvement of anti-tumor regimens in treatment of LSC.

Differential expression profile analysis of PSTK-regulated mRNAs in podocytes

This study aimed to elucidate the precise mechanisms underlying the protective effects of phosphoseryl-tRNA kinase (PSTK) against cisplatin-induced podocyte injury. PSTK overexpression and knockdown vectors were generated and transfected into murine podocyte cells-5. PSTK levels were measured, and transcriptome sequencing was conducted. Differential expression analysis was performed to identify messenger RNAs (mRNAs) that were positively and negatively correlated with PSTK. We selected 10 candidate genes identified via real-time quantitative polymerase chain reaction and Western blot analysis for further analysis. As expected, PSTK levels were significantly higher in PSTK-overexpressing podocytes and significantly lower in PSTK-knockdown podocytes. PSTK overexpression resulted in the upregulation of 122 genes and downregulation of 372 genes in podocytes. On the other hand, PSTK knockdown resulted in the upregulation of 231 genes and downregulation of 445 genes. Furthermore, the analysis revealed that 11 genes were positively correlated with PSTK, whereas 20 genes were negatively correlated with PSTK. The obtained PSTK-regulated genes were primarily involved in molecular function, biological process, and cellular component, as well as the angiogenesis pathway. The Wnt family member 10A levels were significantly higher after PSTK overexpression, but were significantly lower after PSTK knockdown. In addition, Na+/K+ ATPase subunit α-2 and matrix metalloproteinase 9 levels were significantly downregulated after PSTK overexpression, but significantly upregulated upon PSTK knockdown. Cell proliferation was significantly increased upon PSTK overexpression, but significantly decreased upon PSTK suppression. The results of this study not only identified several significant PSTK-regulated genes for further validation, but also provided insights into the mechanisms underlying the protective effects of PSTK on podocytes.

Cisplatin-enriching cancer stem cells confer multidrug resistance in non-small cell lung cancer via enhancing TRIB1/HDAC activity

Chemotherapeutic agents are generally used as a frontline therapy for non-small cell lung cancer (NSCLC). However, resistance to chemotherapy arises rapidly in NSCLC, and the reasons for chemotherapy resistance have not been fully determined. Here, we found cisplatin, but not paclitaxel and doxorubicin, induced the enrichment of cancer stem cell (CSC) and conferred multidrug resistance in NSCLC cell lines. In vivo study confirmed drug-resistant tumors displayed the enhanced expressions of CSC transcription factors. Mechanistically, cisplatin treatment resulted in C/EBP-β-dependent increasing of TRIB1. The crucial role of TRIB1 in cisplatin-induced enrichment of CSC and drug resistance was verified by knockdown TRIB1. Interestingly, cisplatin treatment also contributed to the increasement of HDAC, the interaction of TRIB1 with HDAC, and inactivation of p53. Similarly, the silencing of HDAC led to reduction of cisplatin-induced CSC, and combined knockdown of HDAC and TRIB1 exhibited enhanced effect. Additionally, the combination of HDAC inhibitor and cisplatin showed a reinforced antitumor action in NSCLC cell lines with TRIB1-dependent manner and remarkably shrink tumors in xenograft models. Moreover, cisplatin-treated NSCLC patients with high levels of TRIB1 exhibited a significantly poorer prognosis. Our findings illustrate a novel perspective in the evolution of chemotherapy resistance and provide a promising approach for the treatment of patients with NSCLC.

Emerging therapeutic agents for lung cancer

Lung cancer continues to be the most common cause of cancer-related mortality worldwide. Recent advances in molecular diagnostics and immunotherapeutics have propelled the rapid development of novel treatment agents across all cancer subtypes, including lung cancer. Additionally, more pharmaceutical therapies for lung cancer have been approved by the US Food and Drug Administration in the last 5 years than in previous two decades. These drugs have ushered in a new era of lung cancer managements that have promising efficacy and safety and also provide treatment opportunities to patients who otherwise would have no conventional chemotherapy available. In this review, we summarize recent advances in lung cancer therapeutics with a specific focus on first in-human or early-phase I/II clinical trials. These drugs either offer better alternatives to drugs in their class or are a completely new class of drugs with novel mechanisms of action. We have divided our discussion into targeted agents, immunotherapies, and antibody drug conjugates for small cell lung cancer (SCLC) and non-small-cell lung cancer (NSCLC). We briefly review the emerging agents and ongoing clinical studies. We have attempted to provide the most current review on emerging therapeutic agents on horizon for lung cancer.