Targeting DNA repair pathways for cancer treatment: what's new?

Loss of the DNA Repair Gene RNase H2 Identifies a Unique Subset of DDR-Deficient Leiomyosarcomas

Targeting the DNA damage response (DDR) pathway is an emerging therapeutic approach for leiomyosarcoma (LMS), and loss of RNase H2, a DDR pathway member, is a potentially actionable alteration for DDR-targeted treatments. Therefore, we designed a protein- and genomic-based RNase H2 screening assay to determine its prevalence and prognostic significance. Using a selective RNase H2 antibody on a pan-tumor microarray (TMA), RNase H2 loss was more common in LMS (11.5%, 9/78) than across all tumors (3.8%, 32/843). In a separate LMS cohort, RNase H2 deficiency was confirmed in uterine LMS (U-LMS, 21%, 23/108) and soft-tissue LMS (ST-LMS; 30%, 39/102). In the TCGA database, RNASEH2B homozygous deletions (HomDels) were found in 6% (5/80) of LMS cases, with a higher proportion in U-LMS (15%; 4/27) compared with ST-LMS (2%; 1/53). Using the SNiPDx targeted-NGS sequencing assay to detect biallelic loss of function in select DDR-related genes, we found RNASEH2B HomDels in 54% (19/35) of U-LMS cases with RNase H2 loss by IHC, and 7% (3/43) HomDels in RNase H2 intact cases. No RNASEH2B HomDels were detected in ST-LMS. In U-LMS patient cohort (n = 109), no significant overall survival difference was seen in patients with RNase H2 loss versus intact, or RNASEH2B HomDel (n = 12) versus Non-HomDel (n = 37). The overall diagnostic accuracy, sensitivity, and specificity of RNase H2 IHC for detecting RNA-SEH2B HomDels in U-LMS was 76%, 93%, and 71%, respectively, and it is being developed for future predictive biomarker driven clinical trials targeting DDR in U-LMS.

Impact of DNA ligase 1 and IIIα interactions with APE1 and polβ on the efficiency of base excision repair pathway at the downstream steps

Base excision repair (BER) requires a tight coordination between the repair enzymes through protein-protein interactions and involves gap filling by DNA polymerase (pol) β and subsequent nick sealing by DNA ligase (LIG) 1 or LIGIIIα at the downstream steps. Apurinic/apyrimidinic-endonuclease 1 (APE1), by its exonuclease activity, proofreads 3' mismatches incorporated by polβ during BER. We previously reported that the interruptions in the functional interplay between polβ and the BER ligases result in faulty repair events. Yet, how the protein interactions of LIG1 and LIGIIIα could affect the repair pathway coordination during nick sealing at the final steps remains unknown. Here, we demonstrate that LIGIIIα interacts more tightly with polβ and APE1 than LIG1, and the N-terminal noncatalytic region of LIG1 as well as the catalytic core and BRCT domain of LIGIIIα mediate interactions with both proteins. Our results demonstrated less efficient nick sealing of polβ nucleotide insertion products in the absence of LIGIIIα zinc-finger domain and LIG1 N-terminal region. Furthermore, we showed a coordination between APE1 and LIG1/LIGIIIα during the removal of 3' mismatches from the nick repair intermediate on which both BER ligases can seal noncanonical ends or gap repair intermediate leading to products of single deletion mutagenesis. Overall results demonstrate the importance of functional coordination from gap filling by polβ coupled to nick sealing by LIG1/LIGIIIα in the presence of proofreading by APE1, which is mainly governed by protein-protein interactions and protein-DNA intermediate communications, to maintain repair efficiency at the downstream steps of the BER pathway.

Live-cell imaging of human apurinic/apyrimidinic endonuclease 1 in the nucleus and nucleolus using a chaperone@DNA probe

Human apurinic/apyrimidinic endonuclease 1 (APE1) plays crucial roles in repairing DNA damage and regulating RNA in the nucleus. However, direct visualization of nuclear APE1 in live cells remains challenging. Here, we report a chaperone@DNA probe for live-cell imaging of APE1 in the nucleus and nucleolus in real time. The probe is based on an assembly of phenylboronic acid modified avidin and biotin-labeled DNA containing an abasic site (named PB-ACP), which cleverly protects DNA from being nonspecifically destroyed while enabling targeted delivery of the probe to the nucleus. The PB-ACP construct specifically detects APE1 due to the high binding affinity of APE1 for both avidin and the abasic site in DNA. It is easy to prepare, biocompatible and allowing for long-term observation of APE1 activity. This molecular tool offers a powerful means to investigate the behavior of APE1 in the nuclei of various types of live cells, particularly for the development of improved cancer therapies targeting this protein.

Excavatolide C/cisplatin combination induces antiproliferation and drives apoptosis and DNA damage in bladder cancer cells

Excavatolide C (EXCC), a marine coral-derived compound, exhibits an antiproliferation effect on bladder cancer cells. The present study evaluated the improvement in the antiproliferation ability of EXCC by co-treatment with cisplatin in bladder cancer cells. EXCC/cisplatin (12.5 and 1 μg/mL) showed higher antiproliferation effects on bladder cancer cells than single treatments (EXCC or cisplatin alone) in the 48 h ATP assay. EXCC/cisplatin also enhanced the increase in subG1, annexin V-mediated apoptosis, and activation of poly (ADP-ribose) polymerase (PARP) and several caspases (caspases 3, 8, and 9) compared to the single treatments. Cellular and mitochondrial oxidative stress was enhanced with EXCC/cisplatin compared to the single treatments according to analyses of reactive oxygen species (ROS), mitochondrial superoxide, and mitochondrial membrane potential; in addition, cellular antioxidants, such as glutathione (GSH), and the mRNA expressions of antioxidant signaling genes (catalase and NFE2-like bZIP transcription factor 2) were downregulated. EXCC/cisplatin treatment produced more DNA damage than the single treatments, as indicated by γH2AX and 8-hydroxy-2'-deoxyguanosine levels. Moreover, several DNA repair genes for homologous recombination (HR) and non-homologous end joining (NHEJ) were downregulated in EXCC/cisplatin compared to others. The addition of the GSH precursor N-acetylcysteine, which has ROS scavenging activity, attenuated all EXCC/cisplatin-induced changes. Notably, EXCC/cisplatin showed lower antiproliferation, apoptosis, ROS induction, GSH depletion, and γH2AX DNA damage in normal cells than in bladder cancer cells. Therefore, the co-treatment of EXCC/cisplatin reduces the proliferation of bladder cancer cells via oxidative stress-mediated mechanisms with normal cell safety.

Natural products for combating multidrug resistance in cancer

Cancer cells frequently develop resistance to chemotherapeutic therapies and targeted drugs, which has been a significant challenge in cancer management. With the growing advances in technologies in isolation and identification of natural products, the potential of natural products in combating cancer multidrug resistance has received substantial attention. Importantly, natural products can impact multiple targets, which can be valuable in overcoming drug resistance from different perspectives. In the current review, we will describe the well-established mechanisms underlying multidrug resistance, and introduce natural products that could target these multidrug resistant mechanisms. Specifically, we will discuss natural compounds such as curcumin, resveratrol, baicalein, chrysin and more, and their potential roles in combating multidrug resistance. This review article aims to provide a systematic summary of recent advances of natural products in combating cancer drug resistance, and will provide rationales for novel drug discovery.

New Ref-1/APE1 targeted inhibitors demonstrating improved potency for clinical applications in multiple cancer types

AP endonuclease-1/Redox factor-1 (APE1/Ref-1 or Ref-1) is a multifunctional protein that is overexpressed in most aggressive cancers and impacts various cancer cell signaling pathways. Ref-1's redox activity plays a significant role in activating transcription factors (TFs) such as NFκB, HIF1α, STAT3 and AP-1, which are crucial contributors to the development of tumors and metastatic growth. Therefore, development of potent, selective inhibitors to target Ref-1 redox function is an appealing approach for therapeutic intervention. A first-generation compound, APX3330 successfully completed phase I clinical trial in adults with progressing solid tumors with favorable response rate, pharmacokinetics (PK), and minimal toxicity. These positive results prompted us to develop more potent analogs of APX3330 to effectively target Ref-1 in solid tumors. In this study, we present structure-activity relationship (SAR) identification and validation of lead compounds that exhibit a greater potency and a similar or better safety profile to APX3330. In order to triage and characterize the most potent and on-target second-generation Ref-1 redox inhibitors, we assayed for PK, mouse and human S9 fraction metabolic stability, in silico ADMET properties, ligand-based WaterLOGSY NMR measurements, pharmacodynamic markers, cell viability in multiple cancer cell types, and two distinct 3-dimensional (3D) cell killing assays (Tumor-Microenvironment on a Chip and 3D spheroid). To characterize the effects of Ref-1 inhibition in vivo, global proteomics was used following treatment with the top four analogs. This study identified and characterized more potent inhibitors of Ref-1 redox function (that outperformed APX3330 by 5-10-fold) with PK studies demonstrating efficacious doses for translation to clinic.

Impact of polβ/XRCC1 Interaction Variants on the Efficiency of Nick Sealing by DNA Ligase IIIα in the Base Excision Repair Pathway

Base excision repair (BER) requires a coordination from gap filling by DNA polymerase (pol) β to subsequent nick sealing by DNA ligase (LIG) IIIα at downstream steps of the repair pathway. X-ray cross-complementing protein 1 (XRCC1), a non-enzymatic scaffolding protein, forms repair complexes with polβ and LIGIIIα. Yet, the impact of the polβ mutations that affect XRCC1 interaction and protein stability on the repair pathway coordination during nick sealing by LIGIIIα remains unknown. Our results show that the polβ colon cancer-associated variant T304 exhibits a reduced interaction with XRCC1 and the mutations in the interaction interface of V303 loop (L301R/V303R/V306R) and at the lysine residues (K206A/K244A) that prevent ubiquitin-mediated degradation of the protein exhibit a diminished repair protein complex formation with XRCC1. Furthermore, we demonstrate no significant effect on gap and nick DNA binding affinity of wild-type polβ by these mutations. Finally, our results reveal that XRCC1 leads to an efficient channeling of nick repair products after nucleotide incorporation by polβ variants to LIGIIIα, which is compromised by the L301R/V303R/V306R and K206A/K244A mutations. Overall, our findings provide insight into how the mutations in the polβ/XRCC1 interface and the regions affecting protein stability could dictate accurate BER pathway coordination at the downstream steps involving nick sealing by LIGIIIα.

Targeting the COMMD4-H2B protein complex in lung cancer

BACKGROUND

Lung cancer is the biggest cause of cancer-related deaths worldwide. Non-small cell lung cancer (NSCLC) accounts for 85-90% of all lung cancers. Identification of novel therapeutic targets are required as drug resistance impairs chemotherapy effectiveness. COMMD4 is a potential NSCLC therapeutic target. The aims of this study were to investigate the COMMD4-H2B binding pose and develop a short H2B peptide that disrupts the COMMD4-H2B interaction and mimics COMMD4 siRNA depletion.

METHODS

Molecular modelling, in vitro binding and site-directed mutagenesis were used to identify the COMMD4-H2B binding pose and develop a H2B peptide to inhibit the COMMD4-H2B interaction. Cell viability, DNA repair and mitotic catastrophe assays were performed to determine whether this peptide can specially kill NSCLC cells.

RESULTS

Based on the COMMD4-H2B binding pose, we have identified a H2B peptide that inhibits COMMD4-H2B by directly binding to COMMD4 on its H2B binding binding site, both in vitro and in vivo. Treatment of NSCLC cell lines with this peptide resulted in increased sensitivity to ionising radiation, increased DNA double-strand breaks and induction of mitotic catastrophe in NSCLC cell lines.

CONCLUSIONS

Our data shows that COMMD4-H2B represents a novel potential NSCLC therapeutic target.

Usnic Acid Derivatives Inhibit DNA Repair Enzymes Tyrosyl-DNA Phosphodiesterases 1 and 2 and Act as Potential Anticancer Agents

Tyrosyl-DNA phosphodiesterase 1 and 2 (Tdp1 and Tdp2) are DNA repair enzymes that repair DNA damage caused by various agents, including anticancer drugs. Thus, these enzymes resist anticancer therapy and could be the reason for resistance to such widely used drugs such as topotecan and etoposide. In the present work, we found compounds capable of inhibiting both enzymes among derivatives of (-)-usnic acid. Both (+)- and (-)-enantiomers of compounds act equally effectively against Tdp1 with IC50 values in the range of 0.02-0.2 μM; only (-)-enantiomers inhibited Tdp2 with IC50 values in the range of 6-9 μM. Surprisingly, the compounds protect HEK293FT wild type cells from the cytotoxic effect of etoposide (CC50 3.0-3.9 μM in the presence of compounds and 2.4 μM the presence of DMSO) but potentiate it against Tdp2 knockout cells (CC50 1.2-1.6 μM in the presence of compounds against 2.3 μM in the presence of DMSO). We assume that the sensitizing effect of the compounds in the absence of Tdp2 is associated with the effective inhibition of Tdp1, which could take over the functions of Tdp2.

A review of the mechanisms of anti-cancer activities of some medicinal plants-biochemical perspectives

Cancer is a disease resulting in unbridled growth of cells due to dysregulation in the balance of cell populations. Various management procedures in handling cases of cancer are not without their adverse side effects on the normal cells. Medicinal plants/herbs have been in use in the management of various ailments, including cancer, for a long time. Medicinal plants have been credited with wide safety margins, cost effectiveness, availability and diverse activities. This study reviewed various mechanisms of anti-cancer activities of some medicinal plants from a biochemical perspective. The mechanisms of anti-cancer activities of plant compounds addressed in this article include induction of apoptosis, anti-angiogenic effects, anti-metastasis, inhibition of cell cycle, inhibition of DNA destruction and effects on key enzymes, cytotoxic and anti-oxidant effects. The anti-cancer activities of some of the plants involve more than one mechanism.

Veliparib (ABT-888), a PARP inhibitor potentiates the cytotoxic activity of 5-fluorouracil by inhibiting MMR pathway through deregulation of MSH6 in colorectal cancer stem cells

OBJECTIVE

Sensitization of mismatch repair (MMR)-deficient colorectal cancer (CRC) cells by 5-Fluorouracil (5-FU) is well-documented. But not much is known about the treatment of MMR-proficient CRC cancer stem cells (CRC-CSCs). Here, we investigated whether a PARP inhibitor (ABT-888) can enhance the 5-FU-mediated apoptosis in CRC-CSCs through MMR pathway inhibition.

METHODS

The anti-cancer action of 5-FU+ABT-888 combination in CRC-CSCs has been studied by using in vitro, ex vivo, and in vivo preclinical model systems.

RESULTS

5-FU caused DNA damage in CRC-CSCs, and ABT-888 enhanced the accumulation of DNA mismatches by downregulating the MMR pathway, triggering S-phase arrest, and finally apoptosis and cell death in 5-FU-pre-treated MMR-proficient-CRC-CSCs at much lower concentrations than their individual treatments. After 5-FU treatment, PARylated-PARP1 activated MMR pathway by interacting with MSH6. But, upon ABT-888 treatment in 5-FU-pre-exposed CSCs, PARylation was inhibited, as a result of which PARP1 could not interact with MSH6, and other MMR proteins were downregulated. The role of MSH6 in PARP1-mediated MMR activation, was confirmed by silencing MSH6 gene, which resulted in MMR pathway shutdown. Similar results were obtained in ex vivo and in vivo model systems.

CONCLUSIONS

5-FU+ABT-888 combination enhanced CRC-CSCs death by increasing DNA damage accumulation and simultaneously inhibiting the MMR pathway in MMR-proficient cells. But this study does not discuss whether the combination treatment will increase the sensitivity of MMR-deficient CSCs, for which further research will be performed in the future.

Recent advances in access to overcome cancer drug resistance by nanocarrier drug delivery system

Cancer is currently one of the most intractable diseases causing human death. Although the prognosis of tumor patients has been improved to a certain extent through various modern treatment methods, multidrug resistance (MDR) of tumor cells is still a major problem leading to clinical treatment failure. Chemotherapy resistance refers to the resistance of tumor cells and/or tissues to a drug, usually inherent or developed during treatment. Therefore, an urgent need to research the ideal drug delivery system to overcome the shortcoming of traditional chemotherapy. The rapid development of nanotechnology has brought us new enlightenments to solve this problem. The novel nanocarrier provides a considerably effective treatment to overcome the limitations of chemotherapy or other drugs resulting from systemic side effects such as resistance, high toxicity, lack of targeting, and off-target. Herein, we introduce several tumor MDR mechanisms and discuss novel nanoparticle technology applied to surmount cancer drug resistance. Nanomaterials contain liposomes, polymer conjugates, micelles, dendrimers, carbon-based, metal nanoparticles, and nucleotides which can be used to deliver chemotherapeutic drugs, photosensitizers, and small interfering RNA (siRNA). This review aims to elucidate the advantages of nanomedicine in overcoming cancer drug resistance and discuss the latest developments.

DNA repair pathways in breast cancer: from mechanisms to clinical applications

BACKGROUND

Breast cancer (BC) is a complex disease with various subtypes and genetic alterations that impact DNA repair pathways. Understanding these pathways is essential for developing effective treatments and improving patient outcomes.

AREA COVERED

This study investigates the significance of DNA repair pathways in breast cancer, specifically focusing on various pathways such as nucleotide excision repair, base excision repair, mismatch repair, homologous recombination repair, non-homologous end joining, fanconi anemia pathway, translesion synthesis, direct repair, and DNA damage tolerance. The study also examines the role of these pathways in breast cancer resistance and explores their potential as targets for cancer treatment.

CONCLUSION

Recent advances in targeted therapies have shown promise in exploiting DNA repair pathways for BC treatment. However, much research is needed to improve the efficacy of these therapies and identify new targets. Additionally, personalized treatments that target specific DNA repair pathways based on tumor subtype or genetic profile are being developed. Advances in genomics and imaging technologies can potentially improve patient stratification and identify biomarkers of treatment response. However, many challenges remain, including toxicity, resistance, and the need for more personalized treatments. Continued research and development in this field could significantly improve BC treatment.

Visualization and Comparison of the Level of Apurinic/Apyrimidinic Endonuclease 1 in Live Normal/Cancerous and Neuron Cells with a Fluorescent Nanoprobe

As a major apurinic/apyrimidinic endonuclease and a redox signaling protein in human cells, APE1 plays a crucial role in cellular function and survival. The relationship between alterations of APE1 expression and subcellular localization and the initiation, development and treatment of various cancers has received extensive attention. However, comparing the in-vivo activity of APE1 in normal and cancerous breast live cells remains challenging due to the low efficiency of commonly used liposome transfection methods in delivering DNA substrate probes into human normal breast epithelial cells (MCF-10A). In this work, we develop a DNA/RNA hybrid-based small magnetic fluorescent nanoprobe (25 ± 3 nm) that can be taken up by various live cells under magnetic transfection. The D₀/R-nanoprobe demonstrates an outstanding specificity toward APE1 and strong resistance to the cellular background interference. Using this nanoprobe, we are not only able to visualize the intracellular activity of APE1 in breast ductal carcinoma (MCF-7) live cells, but also demonstrate the APE1 activity in MCF-10A live cells for the first time. The method is then extended to observe the changes in APE1 levels in highly metabolically active neuroendocrine cells under normal conditions and severe attacks by reactive oxygen species in real-time. The fluorescent nanoprobe provides a useful tool for studying the dynamic changes of intracellular APE1 in normal or cancerous live cells. It also displays the potential for visible and controllable release of miRNA drugs within live cells for therapeutic purposes.

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.

NEIL3 promotes hepatoma epithelial-mesenchymal transition by activating the BRAF/MEK/ERK/TWIST signaling pathway

Hepatocellular carcinoma (HCC) is among the most prevalent visceral neoplasms. So far, reliable biomarkers for predicting HCC recurrence in patients undergoing surgery are far from adequate. In the aim of searching for genetic biomarkers involved in HCC development, we performed analyses of cDNA microarrays and found that the DNA repair gene NEIL3 was remarkably overexpressed in tumors. NEIL3 belongs to the Fpg/Nei protein superfamily, which contains DNA glycosylase activity required for the base excision repair for DNA lesions. Notably, the other Fpg/Nei family proteins NEIL1 and NEIL2, which have the same glycosylase activity as NEIL3, were not elevated in HCC; NEIL3 was specifically induced to participate in HCC development independently of its glycosylase activity. Using RNA-seq and invasion/migration assays, we found that NEIL3 elevated the expression of epithelial-mesenchymal transition (EMT) factors, including the E/N-cadherin switch and the transcription of MMP genes, and promoted the invasion, migration, and stemness phenotypes of HCC cells. Moreover, NEIL3 directly interacted with the key EMT player TWIST1 to enhance invasion and migration activities. In mouse orthotopic HCC studies, NEIL3 overexpression also caused a prominent E-cadherin decrease, tumor volume increase, and lung metastasis, indicating that NEIL3 led to EMT and tumor metastasis in mice. We further found that NEIL3 induced the transcription of MDR1 (ABCB1) and BRAF genes through the canonical E-box (CANNTG) promoter region, which the TWIST1 transcription factor recognizes and binds to, leading to the BRAF/MEK/ERK pathway-mediated cell proliferation as well as anti-cancer drug resistance, respectively. In the HCC cohort, the tumor NEIL3 level demonstrated a high positive correlation with disease-free and overall survival after surgery. In conclusion, NEIL3 activated the BRAF/MEK/ERK/TWIST pathway-mediated EMT and therapeutic resistances, leading to HCC progression. Targeted inhibition of NEIL3 in HCC individuals with NEIL3 induction is a promising therapeutic approach. © 2022 The Pathological Society of Great Britain and Ireland.

A nuclease-mimetic platinum nanozyme induces concurrent DNA platination and oxidative cleavage to overcome cancer drug resistance

Platinum (Pt) resistance in cancer almost inevitably occurs during clinical Pt-based chemotherapy. The spontaneous nucleotide-excision repair of cancer cells is a representative process that leads to Pt resistance, which involves the local DNA bending to facilitate the recruitment of nucleotide-excision repair proteins and subsequent elimination of Pt-DNA adducts. By exploiting the structural vulnerability of this process, we herein report a nuclease-mimetic Pt nanozyme that can target cancer cell nuclei and induce concurrent DNA platination and oxidative cleavage to overcome Pt drug resistance. We show that the Pt nanozyme, unlike cisplatin and conventional Pt nanoparticles, specifically induces the nanozyme-catalyzed cleavage of the formed Pt-DNA adducts by generating in situ reactive oxygen species, which impairs the damage recognition factors-induced DNA bending prerequisite for nucleotide-excision repair. The recruitment of downstream effectors of nucleotide-excision repair to DNA lesion sites, including xeroderma pigmentosum groups A and F, is disrupted by the Pt nanozyme in cisplatin-resistant cancer cells, allowing excessive accumulation of the Pt-DNA adducts for highly efficient cancer therapy. Our study highlights the potential benefits of applying enzymatic activities to the use of the Pt nanomedicines, providing a paradigm shift in DNA damaging chemotherapy.

Complementary anti-cancer pathways triggered by inhibition of sideroflexin 4 in ovarian cancer

DNA damaging agents are a mainstay of standard chemotherapy for ovarian cancer. Unfortunately, resistance to such DNA damaging agents frequently develops, often due to increased activity of DNA repair pathways. Sideroflexin 4 (SFXN4) is a little-studied inner mitochondrial membrane protein. Here we demonstrate that SFXN4 plays a role in synthesis of iron sulfur clusters (Fe-S) in ovarian cancer cells and ovarian cancer tumor-initiating cells, and that knockdown of SFXN4 inhibits Fe-S biogenesis in ovarian cancer cells. We demonstrate that this has two important consequences that may be useful in anti-cancer therapy. First, inhibition of Fe-S biogenesis triggers the accumulation of excess iron, leading to oxidative stress. Second, because enzymes critical to multiple DNA repair pathways require Fe-S clusters for their function, DNA repair enzymes and DNA repair itself are inhibited by reduction of SFXN4. Through this dual mechanism, SFXN4 inhibition heightens ovarian cancer cell sensitivity to DNA-damaging drugs and DNA repair inhibitors used in ovarian cancer therapy, such as cisplatin and PARP inhibitors. Sensitization is achieved even in drug resistant ovarian cancer cells. Further, knockout of SFXN4 decreases DNA repair and profoundly inhibits tumor growth in a mouse model of ovarian cancer metastasis. Collectively, these results suggest that SFXN4 may represent a new target in ovarian cancer therapy.

Olaparib enhances the Resveratrol-mediated apoptosis in breast cancer cells by inhibiting the homologous recombination repair pathway

Although sensitization of BRCA-mutated, homologous recombination (HR)-deficient breast cancer cells through PARP inhibitor is widely studied, not much is known about the treatment of BRCA-wild-type, HR-proficient breast cancer. Here, we aim to investigate whether a bioactive compound, Resveratrol (RES), can induce DNA double-strand breaks in HR-proficient breast cancer cells and Olaparib (OLA), a PARP inhibitor, can enhance the RES-mediated apoptosis by deregulating the HR repair pathway. The detailed mechanism of anti-cancer action of RES + OLA combination in breast cancer has been evaluated using in vitro, ex vivo, and in vivo preclinical model systems. OLA increased RES-mediated DNA damage, downregulated the HR pathway proteins, caused a late S/G2 cell cycle arrest, enhanced apoptosis and cell death in RES pre-treated breast cancer cells at much lower concentrations than their individual treatments. Direct measurement of HR pathway activity using a GFP plasmid-based assay demonstrated reduced HR efficiency in I-SceI endonuclease-transfected cells treated with OLA. Moreover, RES + OLA treatment also caused significant reduction in PARP1-mediated PARylation and efficiently trapped PARP1 at the DNA damage site. Upon RES treatment, PARylated PARP1 was found to interact with BRCA1, which then activated other HR pathway proteins. But after addition of OLA in RES pre-treated cells, PARP1 could not interact with BRCA1 due to inhibition of PARylation. This resulted in deregulation of HR pathway. To further confirm the role of BRCA1 in PARP1-mediated HR pathway activation, BRCA1 was knocked down that caused complete inhibition of HR pathway activity, and further enhanced apoptosis after RES + OLA treatment in BRCA1-silenced cells. In agreement with in vitro data, similar experimental results were obtained in ex vivo patient-derived breast cancer cells and in vivo xenograft mice. Thus, RES + OLA combination treatment enhanced breast cancer cell death by causing excessive DNA damage and also simultaneously inhibiting the HR pathway.

Exploring ABOBEC3A and APOBEC3B substrate specificity and their role in HPV positive head and neck cancer

APOBEC3 family members are cytidine deaminases catalyzing conversion of cytidine to uracil. Many studies have established a link between APOBEC3 expression and cancer development and progression, especially APOBEC3A (A3A) and APOBEC3B (A3B). Preclinical studies with human papillomavirus positive (HPV+) head and neck squamous cell carcinoma (HNSCC) and clinical trial specimens revealed induction of A3B, but not A3A expression after demethylation. We examined the kinetic features of the cytidine deaminase activity for full length A3B and found that longer substrates and a purine at −2 position favored by A3B, whereas A3A prefers shorter substrates and an adenine or thymine at −2 position. The importance and biological significance of A3B catalytic activity rather than A3A and a preference for purine at the −2 position was also established in HPV+ HNSCCs. Our study explored factors influencing formation of A3A and A3B-related cancer mutations that are essential for understanding APOBEC3-related carcinogenesis and facilitating drug discovery.

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A3B is upregulated after 5-AzaC treatment and related to 5-AzaC sensitivity in HPV+ HNSCC

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Full-length A3B prefers longer substrates and a purine at −2 site biochemically

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A3B also prefers a purine at −2 site in both HPV+ and HPV− HNSCC cells

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A3B signature at -2 site linked to poor patient survival in HPV+ HNSCC low smokers

Molecular Epidemiology in Amerindians of the Brazilian Amazon Reveals New Genetic Variants in DNA Repair Genes

Native American populations from the Brazilian Amazon have a low genetic diversity and a different genetic profile when compared to people from other continents. Despite this, few studies have been conducted in this group, and there is no description of their genetic data in the various currently existent international databases. The characterization of the genomic profile of a population not only has an impact in studies of population genetics, but also helps to advance diagnostic and therapeutic response studies, leading to the optimization of clinical applicability. Genetic variations in DNA repair genes have been associated with the modulation of susceptibility to various pathologies, as well as in their prognosis and therapy. This is the first study to investigate DNA repair genes in Amerindians from the Brazilian Amazon region. We investigated 13 important DNA repair genes in the exome of 63 Native Americans, comparing our results with those found in 5 continental populations, whose data are available in the Genome Aggregation Database. Our results showed that 57 variants already described in literature were differentially distributed in the Amerindian populations in relation to the continental populations, 7 of which have significant clinical relevance. In addition, 9 new variants were described, suggesting that they are unique to these populations. Our study reinforces the understanding that the Amazonian Native American population presents a unique genetic profile, and our findings may collaborate with the creation of public policies that optimize the quality of life of these groups as well as the Brazilian population, which presents a high degree of interethnic mixing with Amerindian groups.

Looking beyond the cytogenetics in haematological malignancies: decoding the role of tandem repeats in DNA repair genes

BACKGROUND

In cancer research, one of the most significant findings was to characterize the DNA repair deficiency as carcinogenic. Amongst the various repair mechanisms, mismatch repair (MMR) and direct reversal of DNA damage systems are designated as multilevel safeguards in the human genome. Defects in these elevate the rate of mutations and results in dire consequences like cancer. Of the several molecular signatures in human genome, tandem repeats (TRs) appear at various frequencies in the exonic, intronic, and regulatory regions of the DNA. Hypervariability among these repeats in the coding and non-coding regions of the genes is well characterized for solid tumours, but its significance in haematologic malignancies remains to be explored. The purpose of our study was to elucidate the role of nucleotide repeat instability in the coding and non-coding regions of 10 different repair genes in myeloid and lymphoid cell lines compared to the control samples.

METHODS AND RESULTS

We selected MMR deficient extensively studied microsatellite instable colorectal cancer (HCT116), and MMR proficient breast cancer (MCF-7) cells along with underemphasized haematologic cancer cell lines to decipher the hypermutability of tandem repeats. A statistically significant TR variation was observed for MSH2 and MSH6 genes in 4 and 3 of the 6 cell lines respectively. KG1 (AML) and Daudi (Burkitt's lymphoma) were found to have compromised DNA repair competency with highly unstable nucleotide repeats.

CONCLUSION

Taken together, the results suggest that mutable TRs in intronic and non-intronic regions of repair genes in blood cancer might have a tumorigenic role. Since this is a pilot study on cell lines, high throughput research in large cohorts can be undertaken to reveal novel diagnostic markers for unexplained blood cancer patients with normal karyotypes or otherwise with karyotypic defects.

Physapruin A Enhances DNA Damage and Inhibits DNA Repair to Suppress Oral Cancer Cell Proliferation

The selective antiproliferation to oral cancer cells of Physalis peruviana-derived physapruin A (PHA) is rarely reported. Either drug-induced apoptosis and DNA damage or DNA repair suppression may effectively inhibit cancer cell proliferation. This study examined the selective antiproliferation ability of PHA and explored detailed mechanisms of apoptosis, DNA damage, and repair. During an ATP assay, PHA provided high cytotoxicity to two oral cancer cell lines (CAL 27 and Ca9-22) but no cytotoxicity to two non-malignant oral cells (HGF-1 and SG). This selective antiproliferation of PHA was associated with the selective generation of reactive oxygen species (ROS) in oral cancer cells rather than in non-malignant oral cells, as detected by flow cytometry. Moreover, PHA induced other oxidative stresses in oral cancer cells, such as mitochondrial superoxide generation and mitochondrial membrane potential depletion. PHA also demonstrated selective apoptosis in oral cancer cells rather than non-malignant cells in annexin V/7-aminoactinmycin D and caspase 3/7 activity assays. In flow cytometry and immunofluorescence assays, PHA induced γH2AX expressions and increased the γH2AX foci number of DNA damages in oral cancer cells. In contrast, the mRNA expressions for DNA repair signaling, including homologous recombination (HR) and non-homologous end joining (NHEJ)-associated genes, were inhibited by PHA in oral cancer cells. Moreover, the PHA-induced changes were alleviated by the oxidative stress inhibitor N-acetylcysteine. Therefore, PHA generates selective antiproliferation, oxidative stress, and apoptosis associated with DNA damage induction and DNA repair suppression in oral cancer cells.

OGG1 Inhibition Triggers Synthetic Lethality and Enhances The Effect of PARP Inhibitor Olaparib in BRCA1-Deficient TNBC Cells

Background

PARP1 plays a critical role in the base excision repair (BER) pathway, and PARP1 inhibition leads to specific cell death, through a synthetic lethal interaction, in the context of BRCA1/2 deficiency. To date, up to five different PARP inhibitors (PARPi), have been approved, nevertheless, the acquisition of resistance to PARPi is common and there is increasing interest in enhancing responses and expand their use to other tumour types.

Methods

We hypothesized that other BER members could be additional synthetic lethal partners with mutated BRCA genes. To test this, we decided to evaluate the glycosylase OGG1 as a potential candidate, by treating BRCA1 proficient and deficient breast cancer cells with PARPi olaparib and the OGG1 inhibitor TH5478.

Results

Knocking out BRCA1 in triple-negative breast cancer cell lines causes hypersensitivity to the OGG1 inhibitor TH5487. Besides, TH5487 enhances the sensitivity to the PARP inhibitor olaparib, especially in the context of BRCA1 deficiency, reflecting an additive interaction.

Discussion

These results provide the first evidence that OGG1 inhibition is a promising new synthetic lethality strategy in BRCA1-deficient cells, and could lead to a new framework for the treatment of hereditary breast and ovarian cancer.

Mutational signatures are markers of drug sensitivity of cancer cells

Genomic analyses have revealed mutational footprints associated with DNA maintenance gone awry, or with mutagen exposures. Because cancer therapeutics often target DNA synthesis or repair, we asked if mutational signatures make useful markers of drug sensitivity. We detect mutational signatures in cancer cell line exomes (where matched healthy tissues are not available) by adjusting for the confounding germline mutation spectra across ancestries. We identify robust associations between various mutational signatures and drug activity across cancer cell lines; these are as numerous as associations with established genetic markers such as driver gene alterations. Signatures of prior exposures to DNA damaging agents – including chemotherapy – tend to associate with drug resistance, while signatures of deficiencies in DNA repair tend to predict sensitivity towards particular therapeutics. Replication analyses across independent drug and CRISPR genetic screening data sets reveal hundreds of robust associations, which are provided as a resource for drug repurposing guided by mutational signature markers.

Mutational signatures can reveal the impact of mutagenic processes in cancer, including exposure to therapy. Here, the authors develop an approach that can accurately predict drug responses in cancer using mutational signatures while simultaneously correcting for germline variants with an ancestry matching procedure.

Mechanisms of Resistance to Photodynamic Therapy (PDT) in Vulvar Cancer

Photodynamic therapy (PDT) is a valuable treatment method for vulvar intraepithelial neoplasia (VIN). It allows for the treatment of a multifocal disease with minimal tissue destruction. 5-Aminolevulinic acid (5-ALA) is the most commonly used prodrug, which is converted in the heme pathway to protoporphyrin IX (PpIX), an actual photosensitizer (PS). Unfortunately, not all patients treated with PDT undergo complete remission. The main cause of their failure is resistance to anticancer therapy. In many cancers, resistance to various anticancer treatments is correlated with increased activity of the DNA repair protein apurinic/apyrimidinic endonuclease 1 (APE1). Enhanced activity of drug pumps may also affect the effectiveness of therapy. To investigate whether multidrug resistance mechanisms underlie PDT resistance in VIN, porphyrins were isolated from sensitive and resistant vulvar cancer cells and their culture media. APE1 activity was measured, and survival assay after PDT combined with APE1 inhibitor was performed. Our results revealed that resistant cells accumulated and effluxed less porphyrins than sensitive cells, and in response to PDT, resistant cells increased APE1 activity. Moreover, PDT combined with inhibition of APE1 significantly decreased the survival of PDT-resistant cells. This means that resistance to PDT in vulvar cancer may be the result of alterations in the heme synthesis pathway. Moreover, increased APE1 activity may be essential for the repair of PDT-mediated DNA damage, and inhibition of APE1 activity may increase the efficacy of PDT.

The human AP-endonuclease 1 (APE1) is a DNA G-quadruplex structure binding protein and regulates KRAS expression in pancreatic ductal adenocarcinoma cells

Pancreatic ductal adenocarcinoma (PDAC), one of the most aggressive types of cancer, is characterized by aberrant activity of oncogenic KRAS. A nuclease-hypersensitive GC-rich region in KRAS promoter can fold into a four-stranded DNA secondary structure called G-quadruplex (G4), known to regulate KRAS expression. However, the factors that regulate stable G4 formation in the genome and KRAS expression in PDAC are largely unknown. Here, we show that APE1 (apurinic/apyrimidinic endonuclease 1), a multifunctional DNA repair enzyme, is a G4-binding protein, and loss of APE1 abrogates the formation of stable G4 structures in cells. Recombinant APE1 binds to KRAS promoter G4 structure with high affinity and promotes G4 folding in vitro. Knockdown of APE1 reduces MAZ transcription factor loading onto the KRAS promoter, thus reducing KRAS expression in PDAC cells. Moreover, downregulation of APE1 sensitizes PDAC cells to chemotherapeutic drugs in vitro and in vivo. We also demonstrate that PDAC patients' tissue samples have elevated levels of both APE1 and G4 DNA. Our findings unravel a critical role of APE1 in regulating stable G4 formation and KRAS expression in PDAC and highlight G4 structures as genomic features with potential application as a novel prognostic marker and therapeutic target in PDAC.

Decoding Cancer Variants of Unknown Significance for Helicase-Nuclease-RPA Complexes Orchestrating DNA Repair During Transcription and Replication

All tumors have DNA mutations, and a predictive understanding of those mutations could inform clinical treatments. However, 40% of the mutations are variants of unknown significance (VUS), with the challenge being to objectively predict whether a VUS is pathogenic and supports the tumor or whether it is benign. To objectively decode VUS, we mapped cancer sequence data and evolutionary trace (ET) scores onto crystallography and cryo-electron microscopy structures with variant impacts quantitated by evolutionary action (EA) measures. As tumors depend on helicases and nucleases to deal with transcription/replication stress, we targeted helicase–nuclease–RPA complexes: (1) XPB-XPD (within TFIIH), XPF-ERCC1, XPG, and RPA for transcription and nucleotide excision repair pathways and (2) BLM, EXO5, and RPA plus DNA2 for stalled replication fork restart. As validation, EA scoring predicts severe effects for most disease mutations, but disease mutants with low ET scores not only are likely destabilizing but also disrupt sophisticated allosteric mechanisms. For sites of disease mutations and VUS predicted to be severe, we found strong co-localization to ordered regions. Rare discrepancies highlighted the different survival requirements between disease and tumor mutations, as well as the value of examining proteins within complexes. In a genome-wide analysis of 33 cancer types, we found correlation between the number of mutations in each tumor and which pathways or functional processes in which the mutations occur, revealing different mutagenic routes to tumorigenesis. We also found upregulation of ancient genes including BLM, which supports a non-random and concerted cancer process: reversion to a unicellular, proliferation-uncontrolled, status by breaking multicellular constraints on cell division. Together, these genes and global analyses challenge the binary “driver” and “passenger” mutation paradigm, support a gradient impact as revealed by EA scoring from moderate to severe at a single gene level, and indicate reduced regulation as well as activity. The objective quantitative assessment of VUS scoring and gene overexpression in the context of functional interactions and pathways provides insights for biology, oncology, and precision medicine.

Carbonic Anhydrase IX Inhibitors as Candidates for Combination Therapy of Solid Tumors

Combination therapy is becoming imperative for the treatment of many cancers, as it provides a higher chance of avoiding drug resistance and tumor recurrence. Among the resistance-conferring factors, the tumor microenvironment plays a major role, and therefore, represents a viable target for adjuvant therapeutic agents. Thus, hypoxia and extracellular acidosis are known to select for the most aggressive and resilient phenotypes and build poorly responsive regions of the tumor mass. Carbonic anhydrase (CA, EC 4.2.1.1) IX isoform is a surficial zinc metalloenzyme that is proven to play a central role in regulating intra and extracellular pH, as well as modulating invasion and metastasis processes. With its strong association and distribution in various tumor tissues and well-known druggability, this protein holds great promise as a target to pharmacologically interfere with the tumor microenvironment by using drug combination regimens. In the present review, we summarized recent publications revealing the potential of CA IX inhibitors to intensify cancer chemotherapy and overcome drug resistance in preclinical settings.

Chlorine, chromium, proteins of oxidative stress and DNA repair pathways are related to prognosis in oral cancer

The comparison of chemical and histopathological data obtained from the analysis of excised tumor fragments oral squamous cell carcinoma (OSCC) with the demographic and clinical evolution data is an effective strategy scarcely explored in OSCC studies. The aim was to analyze OSCC tissues for protein expression of enzymes related to oxidative stress and DNA repair and trace elements as candidates as markers of tumor aggressiveness and prognosis. Tumor fragments from 78 OSCC patients that had undergone ablative surgery were qualitatively analyzed by synchrotron micro-X-ray fluorescence for trace elements. Protein expression of SOD-1, Trx, Ref-1 and OGG1/2 was performed by immunohistochemistry. Sociodemographic, clinical, and histopathological data were obtained from 4-year follow-up records. Disease relapse was highest in patients with the presence of chlorine and chromium and lowest in those with tumors with high OGG1/2 expression. High expression of SOD-1, Trx, and Ref-1 was determinant of the larger tumor. Presence of trace elements can be markers of disease prognosis. High expression of enzymes related to oxidative stress or to DNA repair can be either harmful by stimulating tumor growth or beneficial by diminishing relapse rates. Interference on these players may bring novel strategies for the therapeutic management of OSCC patients.

Synergistic radiosensitizing effect of BR101801, a specific DNA-dependent protein kinase inhibitor, in various human solid cancer cells and xenografts

DNA-dependent protein kinase (DNA-PK), an essential component of the non-homologous end-joining (NHEJ) repair pathway, plays an important role in DNA damage repair (DDR). Therefore, DNA-PK inhibition is a promising approach for overcoming radiotherapy or chemotherapy resistance in cancers. In this study, we demonstrated that BR101801, a potent DNA-PK inhibitor, acted as an effective radiosensitizer in various human solid cancer cells and an in vivo xenograft model. Overall, BR101801 strongly elevated ionizing radiation (IR)-induced genomic instability via induction of cell cycle G₂/M arrest, autophagic cell death, and impairment of DDR pathway in human solid cancer cells. Interestingly, BR101801 inhibited not only phosphorylation of DNA-PK catalytic subunit in NHEJ factors but also BRCA2 protein level in homologous recombination (HR) factors. In addition, combination BR101801 and IR suppressed tumor growth compared with IR alone by reducing phosphorylation of DNA-PK in human solid cancer xenografts. Our findings suggested that BR101801 is a selective DNA-PK inhibitor with a synergistic radiosensitizing effect in human solid cancers, providing evidence for clinical applications.

Non-canonical function of nuclear PTEN and its implication on tumorigenesis

Suppression of genomic instability is the key to prevent tumor development. PTEN is a unique tumor suppressor protein having both lipid and protein phosphatase activities. Interestingly though it is a cytoplasmic protein, but a significant pool of PTEN can also be localized in nucleus. The function of cytoplasmic PTEN is well defined and extensively studied in various literatures focusing mainly on the negative regulation of oncogenic PI-3Kinase-AKT pathway but functional regulation of nuclear PTEN is less defined and therefore it is a fascinating subject of research in cancer biology. Post-translation modulation of PTEN such as phosphorylation, sumorylation, acetylation and methylation also regulates its cellular localization, protein-protein association and catalytic function. Loss or mutation in PTEN is associated with the development of tumors in various tissues from the brain to prostate. Here we have summarized the role of nuclear PTEN and its epigenetic modulation in various DNA metabolic pathways, for example, DNA damage response, DNA repair, DNA replication, DNA segregation etc. Further, pathways involved in nuclear PTEN degradation are also discussed. Additionally, we also emphasize probable potential targets associated with PTEN pathway for chemotherapeutic purpose.

Melatonin: A smart molecule in the DNA repair system

DNA repair is an important pathway for the protection of DNA molecules from destruction. DNA damage can be produced by oxidative reactive nitrogen or oxygen species, irritation, alkylating agents, depurination and depyrimidination; in this regard, DNA repair pathways can neutralize the negative effects of these factors. Melatonin is a hormone secreted from the pineal gland with an antioxidant effect by binding to oxidative factors. In addition, the effect of melatonin on DNA repair pathways has been proven by the literature. DNA repair is carried out by several mechanisms, of which homologous recombination repair (HRR) and non-homologous end-joining (NHEJ) are of great importance. Because of the importance of DNA repair in DNA integrity and the anticancer effect of this pathway, we presented the effect of melatonin on DNA repair factors regarding previous studies conducted in this area.

Correlation analysis of RDM1 gene with immune infiltration and clinical prognosis of hepatocellular carcinoma

Purpose: Liver hepatocellular carcinoma (LIHC) is one of the most common primary malignant liver tumors worldwide. The RAD52 motif-containing protein 1 (RDM1) has been shown to play a role in mediating DNA damage repair and homologous recombination. The present study was designed to determine the expression of RDM1 and its prognostic value as well as its relationship with immune infiltration in LIHC patients.

Methods: Oncomine and Tumor Immunoassay Resource were used to assess the expression of RDM1. PrognoScan and Kaplan–Meier bioinformatics database were used to analyze the impact of clinical influencing factors on prognosis. Finally, the Tumor Immune Assessment Resource (TIMER) and Gene Expression Analysis Interactive Analysis (GEPIA) databases were used to detect the correlation between the expression of RDM1 and expression of marker genes related to immune infiltration. Immunohistochemistry (IHC) method was used to detect the expression level of RDM1 in 90 cases of hepatocellular carcinoma and adjacent normal liver tissues.

Results: RDM1 expression was up-regulated in most cancers. The expression of RDM1 was remarkably higher than that of the corresponding normal control genes in LIHC tissues. The increase in RDM1 messenger RNA (mRNA) expression was closely related to the decreases in overall survival (OS) and progression-free survival (PFS). Additionally, the increase in RDM1 mRNA expression was closely related to the infiltration levels of macrophages, CD8⁺ T cells and B cells and was positively correlated with a variety of immune markers in LIHC.

Conclusion: The findings of the present study demonstrate that RDM1 is a potentially valuable prognostic biomarker that can help determine the progression of cancer and is associated with immune cell infiltration in LIHC.

Inhibition of APE1/Ref-1 for Neovascular Eye Diseases: From Biology to Therapy

Proliferative diabetic retinopathy (PDR), neovascular age-related macular degeneration (nvAMD), retinopathy of prematurity (ROP) and other eye diseases are characterized by retinal and/or choroidal neovascularization, ultimately causing vision loss in millions of people worldwide. nvAMD and PDR are associated with aging and the number of those affected is expected to increase as the global median age and life expectancy continue to rise. With this increase in prevalence, the development of novel, orally bioavailable therapies for neovascular eye diseases that target multiple pathways is critical, since current anti-vascular endothelial growth factor (VEGF) treatments, delivered by intravitreal injection, are accompanied with tachyphylaxis, a high treatment burden and risk of complications. One potential target is apurinic/apyrimidinic endonuclease 1/reduction-oxidation factor 1 (APE1/Ref-1). The multifunctional protein APE1/Ref-1 may be targeted via inhibitors of its redox-regulating transcription factor activation activity to modulate angiogenesis, inflammation, oxidative stress response and cell cycle in neovascular eye disease; these inhibitors also have neuroprotective effects in other tissues. An APE1/Ref-1 small molecule inhibitor is already in clinical trials for cancer, PDR and diabetic macular edema. Efforts to develop further inhibitors are underway. APE1/Ref-1 is a novel candidate for therapeutically targeting neovascular eye diseases and alleviating the burden associated with anti-VEGF intravitreal injections.

Discovery of First-in-Class Dual PARP and EZH2 Inhibitors for Triple-Negative Breast Cancer with Wild-Type BRCA

PARP inhibitors have highly significant effects on BRCA mutant cells, allowing targeted therapy of triple-negative breast cancer (TNBC). However, some TBNC patients lack BRCA mutations. Recent studies have shown that EZH2 inhibitors can increase the sensitivity of wild-type BRCA cells to PARP inhibitors. We designed a series of dual PARP and EZH2 inhibitors, and the most promising compound, 5a, showed good inhibitory activity against PARP-1 and EZH2 and good inhibitory effects on MDA-MB-231 (IC₅₀ = 2.63 μM) and MDA-MB-468 (IC₅₀ = 0.41 μM) cells with wild-type BRCA. Compared with that of olaparib, the growth inhibitory activities against these two cell types increased by approximately 15- and 80-fold, respectively, which was even more effective than the combination of olaparib and tazemetostat/GSK126. 5a can induce autophagy death of tumor cells and cause less damage to normal cells. Therefore, 5a, as a first-in-class dual PARP and EZH2 inhibitor, is a potential anticancer drug candidate for the treatment of TNBC.

Ref-1 redox activity alters cancer cell metabolism in pancreatic cancer: exploiting this novel finding as a potential target

BACKGROUND

Pancreatic cancer is a complex disease with a desmoplastic stroma, extreme hypoxia, and inherent resistance to therapy. Understanding the signaling and adaptive response of such an aggressive cancer is key to making advances in therapeutic efficacy. Redox factor-1 (Ref-1), a redox signaling protein, regulates the conversion of several transcription factors (TFs), including HIF-1α, STAT3 and NFκB from an oxidized to reduced state leading to enhancement of their DNA binding. In our previously published work, knockdown of Ref-1 under normoxia resulted in altered gene expression patterns on pathways including EIF2, protein kinase A, and mTOR. In this study, single cell RNA sequencing (scRNA-seq) and proteomics were used to explore the effects of Ref-1 on metabolic pathways under hypoxia.

METHODS

scRNA-seq comparing pancreatic cancer cells expressing less than 20% of the Ref-1 protein was analyzed using left truncated mixture Gaussian model and validated using proteomics and qRT-PCR. The identified Ref-1's role in mitochondrial function was confirmed using mitochondrial function assays, qRT-PCR, western blotting and NADP assay. Further, the effect of Ref-1 redox function inhibition against pancreatic cancer metabolism was assayed using 3D co-culture in vitro and xenograft studies in vivo.

RESULTS

Distinct transcriptional variation in central metabolism, cell cycle, apoptosis, immune response, and genes downstream of a series of signaling pathways and transcriptional regulatory factors were identified in Ref-1 knockdown vs Scrambled control from the scRNA-seq data. Mitochondrial DEG subsets downregulated with Ref-1 knockdown were significantly reduced following Ref-1 redox inhibition and more dramatically in combination with Devimistat in vitro. Mitochondrial function assays demonstrated that Ref-1 knockdown and Ref-1 redox signaling inhibition decreased utilization of TCA cycle substrates and slowed the growth of pancreatic cancer co-culture spheroids. In Ref-1 knockdown cells, a higher flux rate of NADP + consuming reactions was observed suggesting the less availability of NADP + and a higher level of oxidative stress in these cells. In vivo xenograft studies demonstrated that tumor reduction was potent with Ref-1 redox inhibitor similar to Devimistat.

CONCLUSION

Ref-1 redox signaling inhibition conclusively alters cancer cell metabolism by causing TCA cycle dysfunction while also reducing the pancreatic tumor growth in vitro as well as in vivo.

Oncolytic Bovine Herpesvirus 1 Inhibits Human Lung Adenocarcinoma A549 Cell Proliferation and Tumor Growth by Inducing DNA Damage

Bovine herpesvirus 1 (BoHV-1) is a promising oncolytic virus with broad antitumor spectrum; however, its oncolytic effects on human lung adenocarcinoma in vivo have not been reported. In this study, we report that BoHV-1 can be used as an oncolytic virus for human lung adenocarcinoma, and elucidate the underlying mechanism of how BoHV-1 suppresses tumor cell proliferation and growth. First, we examined the oncolytic activities of BoHV-1 in human lung adenocarcinoma A549 cells. BoHV-1 infection reduced the protein levels of histone deacetylases (HDACs), including HDAC1-4 that are promising anti-tumor drug targets. Furthermore, the HDAC inhibitor Trichostatin A (TSA) promoted BoHV-1 infection and exacerbated DNA damage and cytopathology, suggesting a synergy between BoHV-1 and TSA. In the A549 tumor xenograft mouse model, we, for the first time, showed that BoHV-1 can infect tumor and suppressed tumor growth with a similar high efficacy as the treatment of TSA, and HDACs have potential effects on the virus replication. Taken together, our study demonstrates that BoHV-1 has oncolytic effects against human lung adenocarcinoma in vivo.

The scaffold protein XRCC1 stabilizes the formation of polβ/gap DNA and ligase IIIα/nick DNA complexes in base excision repair

The base excision repair (BER) pathway involves gap filling by DNA polymerase (pol) β and subsequent nick sealing by ligase IIIα. X-ray cross-complementing protein 1 (XRCC1), a nonenzymatic scaffold protein, assembles multiprotein complexes, although the mechanism by which XRCC1 orchestrates the final steps of coordinated BER remains incompletely defined. Here, using a combination of biochemical and biophysical approaches, we revealed that the polβ/XRCC1 complex increases the processivity of BER reactions after correct nucleotide insertion into gaps in DNA and enhances the handoff of nicked repair products to the final ligation step. Moreover, the mutagenic ligation of nicked repair intermediate following polβ 8-oxodGTP insertion is enhanced in the presence of XRCC1. Our results demonstrated a stabilizing effect of XRCC1 on the formation of polβ/dNTP/gap DNA and ligase IIIα/ATP/nick DNA catalytic ternary complexes. Real-time monitoring of protein–protein interactions and DNA-binding kinetics showed stronger binding of XRCC1 to polβ than to ligase IIIα or aprataxin, and higher affinity for nick DNA with undamaged or damaged ends than for one nucleotide gap repair intermediate. Finally, we demonstrated slight differences in stable polβ/XRCC1 complex formation, polβ and ligase IIIα protein interaction kinetics, and handoff process as a result of cancer-associated (P161L, R194W, R280H, R399Q, Y576S) and cerebellar ataxia-related (K431N) XRCC1 variants. Overall, our findings provide novel insights into the coordinating role of XRCC1 and the effect of its disease-associated variants on substrate-product channeling in multiprotein/DNA complexes for efficient BER.

The Cancer Prevention Project of Philadelphia: preliminary findings examining diversity among the African diaspora

Objective: Cancer mortality inequity among persons of African Ancestry is remarkable. Yet, Black inclusion in cancer biology research is sorely lacking and warrants urgent attention. Epidemiologic research linking African Ancestry and the African Diaspora to disease susceptibility and outcomes is critical for understanding the significant and troubling health disparities among Blacks. Therefore, in a cohort of diverse Blacks, this study examined differences in genetic ancestry informative markers (AIMs) in the DNA repair pathway and the cancer related biomarker 4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL).Methods: Participants completed a questionnaire and provided bio-specimens. AIMs in or around DNA repair pathway genes were analyzed to assess differences in minor allele frequency (MAF) across the 3 ethnic subgroups. NNAL concentration in urine was measured among current smokers.Results: To date the cohort includes 852 participants, 88.3% being Black. Of the 752 Blacks, 51.3% were US-born, 27.8% were Caribbean-born, and 19.6% were Africa-born. Current and former smokers represented 14.9% and 10.0%, respectively. US-born Blacks were more likely to be smokers and poor metabolizers of NNAL. Two-way hierarchical clustering revealed MAF of AIMs differed across the 3 ethnic subgroups.Conclusion: Our findings are consistent with the emerging literature demonstrating Black heterogeneity underscoring African Ancestry genetic subgroup differences - specifically relevant to cancer. Further investigations, with data harmonization and sharing, are urgently needed to begin to map African Ancestry cancer biomarkers as well as race, and race by place\region comparative biomarkers to inform cancer prevention and treatment in the era of precision medicine.

countfitteR: efficient selection of count distributions to assess DNA damage

Background

DNA double-strand breaks can be counted as discrete foci by imaging techniques. In personalized medicine and pharmacology, the analysis of counting data is relevant for numerous applications, e.g., for cancer and aging research and the evaluation of drug efficacy. By default, it is assumed to follow the Poisson distribution. This assumption, however, may lead to biased results and faulty conclusions in datasets with excess zero values (zero-inflation), a variance larger than the mean (overdispersion), or both. In such cases, the assumption of a Poisson distribution would skew the estimation of mean and variance, and other models like the negative binomial (NB), zero-inflated Poisson or zero-inflated NB distributions should be employed. The model chosen has an influence on the parameter estimation (mean value and confidence interval). Yet the choice of the suitable distribution model is not trivial.

Methods

To support, simplify and objectify this process, we have developed the countfitteR software as an R package. We used a Bayesian approach for distribution model selection and the shiny web application framework for interactive data analysis.

Results

We show the application of our software based on examples of DNA double-strand break count data from phenotypic imaging by multiplex fluorescence microscopy. In analyzing numerous datasets of molecular pharmacological markers (phosphorylated histone H2AX and p53 binding protein), countfitteR demonstrated an equal or superior statistical performance compared to the usually employed two-step procedure, with an overall power of up to 98%. In addition, it still gave information in cases with no result at all from the two-step procedure. In our data sample we found that the NB distribution was the most frequent, with the Poisson distribution taking second place.

Conclusions

countfitteR can perform an automated distribution model selection and thus support the data analysis and lead to objective statistically verifiable estimated values. Originally designed for the analysis of foci in biomedical image data, countfitteR can be used in a variety of areas where non-Poisson distributed counting data is prevalent.

Emerging Therapeutics for Patients with Triple-Negative Breast Cancer

PURPOSE OF REVIEW

Triple negative breast cancer (TNBC) accounts for approximately 10-15% of all breast cancers and it is associated with a poor prognosis. However, recent new effective treatment strategies have improved its outcomes. The aim of this review is to provide an overview on the emerging therapeutics for TNBC, describing both previously approved therapies that are currently being repurposed, as well as new target therapies that may improve patient outcomes.

RECENT FINDINGS

Emerging therapies are forthcoming in TNBC's treatment landscape, including new post-neoadjuvant chemotherapy strategies, PARP inhibitors, immune checkpoint inhibitors, and antibody-drug conjugates. Combination of different therapies such as AKT/PI3K/mTOR-inhibitors, other immunotherapeutic agents, CDK-inhibitors, antiandrogens, antiangiogenics, and histone deacetylase inhibitors is under clinical investigation. The treatment landscape for TNBC is gradually evolving towards a more personalized approach with promising expectations.

Non-Genomic Actions of Estrogens on the DNA Repair Pathways Are Associated With Chemotherapy Resistance in Breast Cancer

Estrogens have been implicated in the etiology of breast cancer for a long time. It has been stated that long-term exposure to estrogens is associated with a higher incidence of breast cancer, since estradiol (E₂) stimulates breast cell growth; however, its effect on DNA damage/repair is only starting to be investigated. Recent studies have documented that estrogens are able to modify the DNA damage response (DDR) and DNA repair mechanisms. On the other hand, it has been proposed that DDR machinery can be altered by estrogen signaling pathways, that can be related to cancer progression and chemoresistance. We have demonstrated that E₂ promotes c-Src activation and breast cancer cell motility, through a non-genomic pathway. This review discusses scientific evidence supporting this non-genomic mechanism where estrogen modifies the DNA repair pathways, and its relationship to potential causes of chemoresistance.

Whole Genome Interpretation for a Family of Five

Although best practices have emerged on how to analyse and interpret personal genomes, the utility of whole genome screening remains underdeveloped. A large amount of information can be gathered from various types of analyses via whole genome sequencing including pathogenicity screening, genetic risk scoring, fitness, nutrition, and pharmacogenomic analysis. We recognize different levels of confidence when assessing the validity of genetic markers and apply rigorous standards for evaluation of phenotype associations. We illustrate the application of this approach on a family of five. By applying analyses of whole genomes from different methodological perspectives, we are able to build a more comprehensive picture to assist decision making in preventative healthcare and well-being management. Our interpretation and reporting outputs provide input for a clinician to develop a healthcare plan for the individual, based on genetic and other healthcare data.

COMMD1, from the Repair of DNA Double Strand Breaks, to a Novel Anti-Cancer Therapeutic Target

Lung cancer has the highest incidence and mortality among all cancers, with non-small cell lung cancer (NSCLC) accounting for 85-90% of all lung cancers. Here we investigated the function of COMMD1 in the repair of DNA double strand breaks (DSBs) and as a prognostic and therapeutic target in NSCLC. COMMD1 function in DSB repair was investigated using reporter assays in COMMD1-siRNA-depleted cells. The role of COMMD1 in NSCLC was investigated using bioinformatic analysis, qRT-PCR and immunoblotting of control and NSCLC cells, tissue microarrays, cell viability and cell cycle experiments. DNA repair assays demonstrated that COMMD1 is required for the efficient repair of DSBs and reporter assays showed that COMMD1 functions in both non-homologous-end-joining and homologous recombination. Bioinformatic analysis showed that COMMD1 is upregulated in NSCLC, with high levels of COMMD1 associated with poor patient prognosis. COMMD1 mRNA and protein were upregulated across a panel of NSCLC cell lines and siRNA-mediated depletion of COMMD1 decreased cell proliferation and reduced cell viability of NSCLC, with enhanced death after exposure to DNA damaging-agents. Bioinformatic analyses demonstrated that COMMD1 levels positively correlate with the gene ontology DNA repair gene set enrichment signature in NSCLC. Taken together, COMMD1 functions in DSB repair, is a prognostic maker in NSCLC and is potentially a novel anti-cancer therapeutic target for NSCLC.

Sesquiterpene Alcohol Cedrol Chemosensitizes Human Cancer Cells and Suppresses Cell Proliferation by Destabilizing Plasma Membrane Lipid Rafts

Chemosensitization of cancer cells with small molecules may improve the therapeutic index of antitumoral agents by making tumor cells sensitive to the drug regimen and thus overcome the treatment resistance and side effects of single therapy. Cell membrane lipid rafts are known to transduce various signaling events in cell proliferation. Sensitizing cancer cells may cause modulation of membrane lipid rafts which may potentially be used in improving anticancer drug response. Cedrol, a natural sesquiterpene alcohol, was used to treat human leukemia K562 and colon cancer HT-29 cell lines, and effects were observed. Cedrol decreased the cell viability by inducing apoptosis in both cell lines by activation of pro-apoptosis protein BID and inhibition of anti-apoptosis proteins Bcl-X_L, Bcl-2, and XIAP. Cedrol activated the caspase-9-dependent mitochondrial intrinsic pathway of apoptosis. Furthermore, cedrol inhibited the levels of pAKT, pERK, and pmTOR proteins as well as nuclear and cytoplasmic levels of the p65 subunit of NF-κB. Cedrol caused redistribution of cholesterol and sphingomyelin contents from membrane lipid raft, which was confirmed by a combined additive effect with methyl-β-cyclodextrin (lipid raft-disrupting agent). Lipid raft destabilization by cedrol led to the increased production of ceramides and inhibition of membrane-bound NADPH oxidase 2 enzyme activity. Cholesterol/sphingomyelin-redistributing abilities of cedrol appear as a novel mechanism of growth inhibition of cancer cells. Cedrol can be classified as a natural lipid raft-disrupting agent with possibilities to be used in general studies involving membrane lipid raft modifications.

DNA double-strand breaks repair inhibitors potentiates the combined effect of VP-16 and CDDP in human colorectal adenocarcinoma (LoVo) cells

I.

BACKGROUND

A combination of etoposide (VP-16) and cisplatin (CDDP) is the standard treatment for certain colon cancers. These drugs promote the death of cancer cells via direct and indirect induction of the most lethal DNA lesions - DNA double-stand breaks. However, cancer cells can reverse the DNA damaging effect of anticancer drugs by triggering DNA repair processes. In eukaryotic cells, the main DNA repair pathway responsible for DNA double-stand breaks repair is non-homologous end-joining (NHEJ). Inhibitors of DNA repair are of special interest in cancer research as they could break the cellular resistance to DNA-damaging agents and increase the efficiency of standard cancer treatments. In this study, we investigated the effect of two NHEJ inhibitors, SCR7 and NU7441, on the cytotoxic mechanism of VP-16/CDDP in a LoVo human colorectal adenocarcinoma cell line. SCR7 blocks Ligase IV-mediated joining by interfering with its DNA binding, whereas NU7441 is a highly potent and selective DNA-PK inhibitor.II.

METHODS AND RESULTS

Both inhibitors synergistically increased the cytotoxicity of CDDP and VP-16 when combined, but the effect of SCR7 was more pronounced. SCR7 and NU7441 also significantly increased VP-16; CDDP induced DNA double-stand breaks level and delayed drug-induced DSB repair, as seen on the comet assay and measured using H2AX foci. We also observed changes in cell cycle distribution and enhanced apoptosis ratio in colorectal adenocarcinoma cells treated with DNA repair inhibitors and VP-16/CDDP.III.

CONCLUSIONS

Our data support the hypothesis that NHEJ inhibitors could be used in conjunction with standard therapy to provide effective clinical improvement and allow reduction in drug doses.

Exploiting DNA repair pathways for tumor sensitization, mitigation of resistance, and normal tissue protection in radiotherapy

More than half of cancer patients are treated with radiotherapy, which kills tumor cells by directly and indirectly inducing DNA damage, including cytotoxic DNA double-strand breaks (DSBs). Tumor cells respond to these threats by activating a complex signaling network termed the DNA damage response (DDR). The DDR arrests the cell cycle, upregulates DNA repair, and triggers apoptosis when damage is excessive. The DDR signaling and DNA repair pathways are fertile terrain for therapeutic intervention. This review highlights strategies to improve therapeutic gain by targeting DDR and DNA repair pathways to radiosensitize tumor cells, overcome intrinsic and acquired tumor radioresistance, and protect normal tissue. Many biological and environmental factors determine tumor and normal cell responses to ionizing radiation and genotoxic chemotherapeutics. These include cell type and cell cycle phase distribution; tissue/tumor microenvironment and oxygen levels; DNA damage load and quality; DNA repair capacity; and susceptibility to apoptosis or other active or passive cell death pathways. We provide an overview of radiobiological parameters associated with X-ray, proton, and carbon ion radiotherapy; DNA repair and DNA damage signaling pathways; and other factors that regulate tumor and normal cell responses to radiation. We then focus on recent studies exploiting DSB repair pathways to enhance radiotherapy therapeutic gain.