Expression Of DNA Damage Response Genes Research Articles

Acetylated KHSRP impairs DNA-damage-response-related mRNA decay and facilitates prostate cancer tumorigenesis.

Androgen-regulated DNA damage response (DDR) is one of the essential mechanisms in prostate cancer (PCa), a hormone-sensitive disease. The heterogeneous nuclear ribonucleoprotein K (hnRNPK)-homology splicing regulatory protein known as far upstream element-binding protein 2 (KHSRP) is an RNA-binding protein that can attach to AU-rich elements in the 3' untranslated region (3'-UTR) of messenger RNAs (mRNAs) tomediate mRNA decay and emerges as a critical regulator in the DDR to preserve genome integrity. Nevertheless, how KHSRP responds to androgen-regulated DDR in PCa development remains unclear. This study found that androgen can significantly induce acetylation of KHSRP, which intrinsically drives tumor growth in xenografted mice. Moreover, enhanced KHSRP acetylation upon androgen stimuli impedes KHSRP-regulated DDR gene expression, as seen by analyzing RNA sequencing (RNA-seq) and Gene Set Enrichment Analysis (GSEA) datasets. Additionally, NAD-dependent protein deacetylase sirtuin-7 (SIRT7) is a promising deacetylase of KHSRP, and androgen stimuli impairs its interaction with KHSRP to sustain the increased KHSRP acetylation level in PCa. We first report the acetylation of KHSRP induced by androgen, which interrupts the KHSRP-regulated mRNA decay of the DDR-related genes to promote the tumorigenesis of PCa. This study provides insight into KHSRP biology and potential therapeutic strategies for PCa treatment, particularly that of castration-resistant PCa.

Abstract A023: High glucose increases DNA damage and elevates the expression of multiple DDR genes

Abstract The DNA Damage Response (DDR) pathways sense DNA damage and coordinate robust DNA repair and bypass mechanisms. A series of repair proteins are recruited depending on the type of breaks and lesions to ensure overall survival. An increase in glucose levels was shown to induce genome instability, yet the links between DDR and glucose are still not well investigated. In this study, we aimed to identify dysregulation in the transcriptome of normal and cancerous breast cell lines upon changing glucose levels. We first performed bioinformatics analysis using a microarray dataset containing the triple-negative breast cancer (TNBC) MDA-MB-231 and the normal human mammary epithelium MCF10A cell lines grown in high glucose (HG) or in the presence of the glycolysis inhibitor 2-deoxyglucose (2DG). Interestingly, multiple DDR genes were significantly upregulated in both cell lines grown in HG. In the wet lab, we remarkably found that HG results in severe DNA damage to TNBC cells as observed using the comet assay. In addition, several DDR genes were confirmed to be upregulated using qPCR analysis in the same cell line. Our results propose a strong need for DDR pathways in the presence of HG to oppose the severe DNA damage induced in cells. Citation Format: Mai A. Rahmoon, Reem A. Elghaish, Aya A. Ibrahim, Zina Alaswad, Mohamed Z. Gad, Sherif F. El-Khamisy, Menattallah Elserafy. High glucose increases DNA damage and elevates the expression of multiple DDR genes [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: DNA Damage Repair: From Basic Science to Future Clinical Application; 2024 Jan 9-11; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2024;84(1 Suppl):Abstract nr A023.

MYC up-regulation confers vulnerability to dual inhibition of CDK12 and CDK13 in high-risk Group 3 medulloblastoma

BackgroundMedulloblastoma (MB) is the most common cerebellar malignancy during childhood. Among MB, MYC-amplified Group 3 tumors display the worst prognosis. MYC is an oncogenic transcription factor currently thought to be undruggable. Nevertheless, targeting MYC-dependent processes (i.e. transcription and RNA processing regulation) represents a promising approach.MethodsWe have tested the sensitivity of MYC-driven Group 3 MB cells to a pool of transcription and splicing inhibitors that display a wide spectrum of targets. Among them, we focus on THZ531, an inhibitor of the transcriptional cyclin-dependent kinases (CDK) 12 and 13. High-throughput RNA-sequencing analyses followed by bioinformatics and functional analyses were carried out to elucidate the molecular mechanism(s) underlying the susceptibility of Group 3 MB to CDK12/13 chemical inhibition. Data from International Cancer Genome Consortium (ICGC) and other public databases were mined to evaluate the functional relevance of the cellular pathway/s affected by the treatment with THZ531 in Group 3 MB patients.ResultsWe found that pharmacological inhibition of CDK12/13 is highly selective for MYC-high Group 3 MB cells with respect to MYC-low MB cells. We identified a subset of genes enriched in functional terms related to the DNA damage response (DDR) that are up-regulated in Group 3 MB and repressed by CDK12/13 inhibition. Accordingly, MYC- and CDK12/13-dependent higher expression of DDR genes in Group 3 MB cells limits the toxic effects of endogenous DNA lesions in these cells. More importantly, chemical inhibition of CDK12/13 impaired the DDR and induced irreparable DNA damage exclusively in MYC-high Group 3 MB cells. The augmented sensitivity of MYC-high MB cells to CDK12/13 inhibition relies on the higher elongation rate of the RNA polymerase II in DDR genes. Lastly, combined treatments with THZ531 and DNA damage-inducing agents synergically suppressed viability of MYC-high Group 3 MB cells.ConclusionsOur study demonstrates that CDK12/13 activity represents an exploitable vulnerability in MYC-high Group 3 MB and may pave the ground for new therapeutic approaches for this high-risk brain tumor.

Relationship between androgen biosynthesis linked to 3βHSD1 and resistance to radiotherapy: A germline biomarker for combined androgen blockade with radiation in high-risk prostate cancer.

e17084 Background: Around 50% of men with advanced prostate cancer (PCa) have at least one germline copy of the adrenal-permissive (1245C) HSD3B1 allele. This allele leads to higher levels of the steroid biosynthesis enzyme, 3β-hydroxysteroid dehydrogenase (3βHSD1). Inheriting this allele is linked to worse outcomes in men with advanced PCa. To determine if (1245C) HSD3B1 could be causing early resistance to combined androgen deprivation and radiotherapy in localized PCa, we studied its role in modulating radioresistance. Methods: PCa cell lines were used to investigate the reciprocal effects of 3βHSD1 knockdown and overexpression in intrinsically high and low 3βHSD1 lines, respectively. PCa xenografts were used to confirm the results in vivo. The connection between androgen receptor (AR) expression and elevated DNA Damage Response (DDR) gene expression was validated using transcriptomic data from 680 radical prostatectomy specimens The ability of enzalutamide, a non-steroidal anti-androgen, to restore radiosensitivity in 1245C expressing lines was interrogated in vitro and in vivo. Results: 1245C HSD3B1 expressing PCa lines displayed increased clonogenic survival after ionizing radiation. Effects were dependent on the 3βHSD1 substrate, DHEA, confirming intratumoral androgen metabolism was required for radioresistance. Resistant lines showed enhanced DNA double-strand break (DSB) repair and heightened DDR gene expression. PCa xenografts with 1245C HSD3B1 were similarly more resistant to radiation using murine models that faithfully mimic human adrenal physiology. A correlation between AR expression and increased DDR gene expression was confirmed in 680 patient samples. Enzalutamide pretreatment resulted in a decrease in DSB repair ability and re-sensitized 1245C HSD3B1 PCa cells to radiation. Conclusions: 1245C HSD3B1 fuels prostate cancer treatment resistance by elevating regional androgen biosynthesis from adrenal steroid precursors, leading to DDR gene overexpression and enhanced DNA DSB repair kinetics. This work supports clinical validation of biomarker informed selective intensification strategies, e.g., combined androgen blockade, for high-risk men with the 1245C HSD3B1 allele receiving curative intent radiotherapy.

Identification of DNA repair gene signature and potential molecular subtypes in hepatocellular carcinoma.

DNA repair is a critical factor in tumor progression as it impacts tumor mutational burden, genome stability, PD-L1 expression, immunotherapy response, and tumor-infiltrating lymphocytes (TILs). In this study, we present a prognostic model for hepatocellular carcinoma (HCC) that utilizes genes related to the DNA damage response (DDR). Patients were stratified based on their risk score, and groups with lower risk scores demonstrated better survival rates compared to those with higher risk scores. The prognostic model's accuracy in predicting 1-, 3-, and 5-year survival rates for HCC patients was analyzed using receiver operator curve analysis (ROC). Results showed good accuracy in predicting survival rates. Additionally, we evaluated the prognostic model's potential as an independent factor for HCC prognosis, along with tumor stage. Furthermore, nomogram was employed to determine the overall survival year of patients with HCC based on this independent factor. Gene set enrichment analysis (GSEA) revealed that in the high-risk group, apoptosis, cell cycle, MAPK, mTOR, and WNT cascades were highly enriched. We used training and validation datasets to identify potential molecular subtypes of HCC based on the expression of DDR genes. The two subtypes differed in terms of checkpoint receptors for immunity and immune cell filtration capacity.Collectively, our study identified potential biomarkers of HCC prognosis, providing novel insights into the molecular mechanisms underlying HCC.

DNA protein kinase promotes cellular senescence in dental follicle cells

ObjectiveShort telomeres and genomic DNA damage are causes of cellular senescence in dental follicle cells (DFCs). DesignThis study examined the role of the DNA damage response (DDR) during cellular senescence of DFCs by β-galactosidase activity and DNA damage by comet assay. Expression of genes/proteins was determined by Western Blots and reverse transcription-quantitative polymerase chain reaction, while glycolysis was enzymatically estimated. Cell cycle stages and reactive oxygen species (ROS) were investigated by flow cytometry. ResultsDuring the induction of cellular senescence gene expression of DDR genes were down-regulated, while DNA double-strand breaks occurred at the same time. Furthermore, inhibition of DNA protein kinase (DNA-PK) reduced senescence and ROS, both of which are associated with cellular senescence. In contrast, while these data suggest that inhibition of DDR is associated with the induction of cellular senescence, inhibition of DNA-PK did not result in renewal of DFCs, as inhibition resulted in typical features of depleted cells such as increased cell size and reduced cell proliferation rate. DNA-PK repression inhibited both osteogenic differentiation potential and glycolysis, which are typical features of cellular exhaustion. Moreover, DNA-PK affects cellular senescence via activation of AKT1 (protein kinase B). ConclusionOur results suggest that DNA-PK promotes cellular senescence, but DFCs may control the induction of cellular senescence via down-regulation of DDR genes. However, we also showed that inhibition of DNA-PK cannot renew senescent DFCs

DNA Damage Response Gene Signature as Potential Treatment Markers for Oral Squamous Cell Carcinoma.

Oral squamous cell carcinoma (OSCC) is a rapidly progressive cancer that often develops resistance against DNA damage inducers, such as radiotherapy and chemotherapy, which are still the standard of care regimens for this tumor. Thus, the identification of biomarkers capable of monitoring the clinical progression of OSCC and its responsiveness to therapy is strongly required. To meet this need, here we have employed Whole Genome Sequencing and RNA-seq data from a cohort of 316 patients retrieved from the TCGA Pan-Cancer Atlas to analyze the genomic and transcriptomic status of the DNA damage response (DDR) genes in OSCC. Then, we correlated the transcriptomic data with the clinical parameters of each patient. Finally, we relied on transcriptomic and drug sensitivity data from the CTRP v2 portal, performing Pearson's correlation analysis to identify putative vulnerabilities of OSCC cell lines correlated with DDR gene expression. Our results indicate that several DDR genes show a high frequency of genomic and transcriptomic alterations and that the expression of some of them correlates with OSCC grading and infection by the human papilloma virus. In addition, we have identified a signature of eight DDR genes (namely CCNB1, CCNB2, CDK2, CDK4, CHECK1, E2F1, FANCD2, and PRKDC) that could be predictive for OSCC response to the novel antitumor compounds sorafenib and tipifarnib-P1. Altogether, our data demonstrate that alterations in DDR genes could have an impact on the biology of OSCC. Moreover, here we propose a DDR gene signature whose expression could be predictive of OSCC responsiveness to therapy.

High Glucose Increases DNA Damage and Elevates the Expression of Multiple DDR Genes.

The DNA Damage Response (DDR) pathways sense DNA damage and coordinate robust DNA repair and bypass mechanisms. A series of repair proteins are recruited depending on the type of breaks and lesions to ensure overall survival. An increase in glucose levels was shown to induce genome instability, yet the links between DDR and glucose are still not well investigated. In this study, we aimed to identify dysregulation in the transcriptome of normal and cancerous breast cell lines upon changing glucose levels. We first performed bioinformatics analysis using a microarray dataset containing the triple-negative breast cancer (TNBC) MDA-MB-231 and the normal human mammary epithelium MCF10A cell lines grown in high glucose (HG) or in the presence of the glycolysis inhibitor 2-deoxyglucose (2DG). Interestingly, multiple DDR genes were significantly upregulated in both cell lines grown in HG. In the wet lab, we remarkably found that HG results in severe DNA damage to TNBC cells as observed using the comet assay. In addition, several DDR genes were confirmed to be upregulated using qPCR analysis in the same cell line. Our results propose a strong need for DDR pathways in the presence of HG to oppose the severe DNA damage induced in cells.

Abstract B028: CDK12/13 inhibition antagonizes resistance to KRASG12C inhibitors

Abstract Covalent inhibitors selectively targeting the KRASG12C mutation offer a promising new therapeutic opportunity for non-small cell lung cancer (NSCLC) patients, with partial or complete response observed in up to 40% of cancers harboring this lesion. As observed for other precision medicines targeting oncogenic drivers, resistance to these agents develops upon prolonged treatment. We have developed cell-based models of acquired resistance to the KRASG12C inhibitor sotorasib by serial passage of sotorasib-sensitive NSCLC cell lines in the presence of the drug. We have observed dynamic phosphorylation of the transcriptional elongation kinases CDK12 and CDK13 as well as hyperphosphorylation of a network of DNA damage response (DDR) proteins in sotorasib-resistant cell lines by phosphoproteomic profiling of resistant and sensitive cells. This is accompanied by elevated sensitivity to DDR pathway and CDK12/13 (e.g., SR-4835) inhibitors. Combined treatment of NSCLC cell lines with sotorasib and SR-4835 delays or prevents adaptation to sotorasib and the development of acquired resistance. Furthermore, gene expression profiling of SR-4835-treated cells reveals that CDK12/13 inhibition suppresses both DDR gene expression and metabolic pathways associated with resistance to sotorasib. This reflects synergy between SR-4835 and inhibitors targeting the DDR pathway in breast cancer cell lines and demonstrates that transcriptional elongation is a critical vulnerability for cells undergoing adaptation to KRASG12C inhibitors via DDR-dependent mechanisms. Citation Format: Yaakov E. Stern, Pompom Ghosh, Hannah L. Walker-Mimms, John W. Mosior, Denis Imbody, Hitendra S. Solanki, Andrii Monastyrskyi, Derek R. Duckett, Eric B. Haura. CDK12/13 inhibition antagonizes resistance to KRASG12C inhibitors. [abstract]. In: Proceedings of the AACR Special Conference: Cancer Epigenomics; 2022 Oct 6-8; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2022;82(23 Suppl_2):Abstract nr B028.

Abstract P1088: Polycystin-1 Protects Against Experimental Atrial Fibrillation

Atrial fibrillation (AF) is the most common cardiac arrhythmia with a 1 in 4 lifetime risk. AF impairs cardiac function and increases the risk of stroke and heart attack. Although this is a common and harmful disease, little is known about the molecular mechanisms driving this disease. We have previously demonstrated that the protein polycystin-1 (PC1) plays a role in atrial cardiomyocyte excitation-contraction coupling in ventricular cardiomyocytes. Interestingly, patients with mutations in PC1 encoding gene have increased rates of atrial arrhythmias, including atrial fibrillation. Here, we sought to study the role of PC1 in atrial cardiomyocyte function and atrial fibrillation inducibility. We performed intracardiac electrophysiology with burst pacing in two mouse models with impaired PC1 function: 1) a mouse model harboring R3277C mutation (RC/RC) known to cause autosomal polycystic kidney disease, and 2) cardiomyocyte-specific PC1 KO (CKO). We observed increased rates of atrial fibrillation inducibility in both RC/RC and PC1 CKO mice compared to their respective control littermates (76.9% in RC/RC and 81.8% in CKO vs 20.0% and 11.1% in their respective WT controls). To elucidate molecular mechanisms driving increased susceptibility to atrial fibrillation, we determined whether PC1 affects excitation-contraction coupling in atrial cardiomyocytes. Human induced pluripotent stem cells-derived atrial cardiomyocytes (hiPSC-aCM) were treated with control or PC1 siRNA. Action potentials and intracellular calcium were measured using Fluovolt and Fluo-4, respectively. PC1 ablation decreased action potential duration and calcium transient peak amplitude elicited by electrical stimulation in hiPSC-CM. Decreased calcium transient peaks were also observed in HL-1 atrial cell line treated with siRNA and adult atrial cardiomyocytes isolated from RC/RC mice compared to their control counterparts. Unexpectedly, RNA-sequencing revealed altered DNA Damage Response gene expression. DNA damage has been implicated in the pathogenesis of atrial fibrillation. Therefore, we studied whether tachypacing elicited DNA damage in hiPSC-aCM. We observed increased levels of H2AX phosphorylation (gamma H2AX) in hiPSC-aCM with reduced PC1 expression. Our data show that PC1 mutations increase atrial fibrillation inducibility in multiple mouse models, likely due to impaired DNA damage response and altered action potential and calcium handling.

A ten-gene DNA-damage response pathway gene expression signature predicts gemtuzumab ozogamicin response in pediatric AML patients treated on COGAAML0531 and AAML03P1 trials.

Gemtuzumab ozogamicin (GO) is an anti-CD33 monoclonal antibody linked to calicheamicin, a DNA damaging agent, and is a well-established therapeutic for treating acute myeloid leukemia (AML). In this study, we used LASSO regression modeling to develop a 10-gene DNA damage response gene expression score (CalDDR-GEx10) predictive of clinical outcome in pediatric AML patients treated with treatment regimen containing GO from the AAML03P1 and AAML0531 trials (ADE + GO arm, N = 301). When treated with ADE + GO, patients with a high CalDDR-GEx10 score had lower complete remission rates (62.8% vs. 85.5%, P = 1.7 7 * 10-5) and worse event-free survival (28.7% vs. 56.5% P = 4.08 * 10-8) compared to those with a low CalDDR-GEx10 score. However, the CalDDR-GEx10 score was not associated with clinical outcome in patients treated with standard chemotherapy alone (ADE, N = 242), implying the specificity of the CalDDR-GEx10 score to calicheamicin-induced DNA damage response. In multivariable models adjusted for risk group, FLT3-status, white blood cell count, and age, the CalDDR-GEx10 score remained a significant predictor of outcome in patients treated with ADE + GO. Our findings present a potential tool that can specifically assess response to calicheamicin-induced DNA damage preemptively via assessing diagnostic leukemic cell gene expression and guide clinical decisions related to treatment using GO.

Zinc Prevents DNA Damage in Normal Cells but Shows Genotoxic and Cytotoxic Effects in Acute Myeloid Leukemia Cells.

Genomic instability is prevented by the DNA damage response (DDR). Micronutrients, like zinc (Zn), are cofactors of DDR proteins, and micronutrient deficiencies have been related to increased cancer risk. Acute myeloid leukemia (AML) patients commonly present Zn deficiency. Moreover, reports point to DDR defects in AML. We studied the effects of Zn in DDR modulation in AML. Cell lines of AML (HEL) and normal human lymphocytes (IMC) were cultured in standard culture, Zn depletion, and supplementation (40 μM ZnSO4) conditions and exposed to hydrogen peroxide (H2O2) or ultraviolet (UV) radiation. Chromosomal damage, cell death, and nuclear division indexes (NDI) were assessed through cytokinesis-block micronucleus assay. The phosphorylated histone H2AX (yH2AX) expression was monitored at 0 h, 1 h, and 24 h after exposure. Expression of DDR genes was evaluated by quantitative real time polymerase chain reaction (qPCR). Zn supplementation increased the genotoxicity of H2O2 and UV radiation in AML cells, induced cytotoxic and antiproliferative effects, and led to persistent yH2AX activation. In contrast, in normal lymphocytes, supplementation decreased damage rates, while Zn depletion favored damage accumulation and impaired repair kinetics. Gene expression was not affected by Zn depletion or supplementation. Zn presented a dual role in the modulation of genome damage, preventing damage accumulation in normal cells and increasing genotoxicity and cytotoxicity in AML cells.

DNA damage response proteins in canine cancer as potential research targets in comparative oncology

The DNA damage response (DDR) is a complex signal transduction network that is activated when endogenous or exogenous genotoxins damage or interfere with the replication of genomic DNA. Under such conditions, the DDR promotes DNA repair and ensures accurate replication and division of the genome. High levels of genomic instability are frequently observed in cancers and can stem from germline loss‐of‐function mutations in certain DDR genes, such as BRCA1, BRCA2, and p53, that form the basis of human cancer predisposition syndromes. In addition, mutation and/or aberrant expression of multiple DDR genes are frequently observed in sporadic human cancers. As a result, the DDR is considered to represent a viable target for cancer therapy in humans and a variety of strategies are under investigation. Cancer is also a significant cause of mortality in dogs, a species that offers certain advantages for experimental oncology. Domestic dogs present numerous inbred lines, many of which display predisposition to specific forms of cancer and the study of which may provide insight into the biological basis of this susceptibility. In addition, clinical trials are possible in dogs and may lead to therapeutic insights that could ultimately be extended to humans. Here we review what is known specifically about the DDR in dogs and discuss how this knowledge could be extended and exploited to advance experimental oncology in this species.

DNA-PKc inhibition overcomes taxane resistance by promoting taxane-induced DNA damage in prostate cancer cells.

Overcoming taxane resistance remains a major clinical challenge in metastatic castrate-resistant prostate cancer (mCRPC). Loss of DNA repair proteins is associated with resistance to anti-microtubule agents. We propose that alterations in DNA damage response (DDR) pathway contribute to taxane resistance, and identification of these alterations may provide a potential therapeutic target to resensitize docetaxel-refractory mCRPC to taxane-based therapy. Alterations in DDR gene expression in our prostate cancer cell line model of docetaxel-resistance (DU145-DxR) derived from DU-145 cells were determined by DDR pathway-specific polymerase chain reaction array and immunoblotting. The PRKDC gene encoding DNA-PKc (DNA-dependent protein kinase catalytic unit), was noted to be overexpressed and evaluated for its role in docetaxel resistance. Cell viability and clonogenic survival of docetaxel-treated DU145-DxR cells were assessed after pharmacologic inhibition of DNA-PKc with three different inhibitors-NU7441, LTURM34, and M3814. Response to second-line cytotoxic agents, cabazitaxel and etoposide upon DNA-PKc inhibition was also tested. The impact of DNA-PKc upregulation on DNA damage repair was evaluated by comet assay and analysis of double-strand breaks marker, γH2AX and Rad51. Lastly, DNA-PKc inhibitor's effect on MDR1 activity was assessed by rhodamine 123 efflux assay. DDR pathway-specific gene profiling revealed significant upregulation of PRKDC and CDK7, and downregulation of MSH3 in DU145-DxR cells. Compared to parental DU145, DU145-DxR cells sustained significantly less DNA damage when exposed to etoposide and docetaxel. Pharmacologic inhibition of DNA-PKc, a component of NHEJ repair machinery, with all three inhibitors, significantly resensitized DU145-DxR cells to docetaxel. Furthermore, DNA-PKc inhibition also resensitized DU145-DxR to cabazitaxel and etoposide, which demonstrated cross-resistance. Inhibition of DNA-PKc led to increased DNA damage in etoposide- and docetaxel-treated DU145-DxR cells. Finally, DNA-PKc inhibition did not affect MDR1 activity, indicating that DNA-PKc inhibitors resensitized taxane-resistant cells via an MDR1-independent mechanism. This study supports a role of DDR genes, particularly, DNA-PKc in promoting resistance to taxanes in mCRPC. Targeting prostatic DNA-PKc may provide a novel strategy to restore taxane sensitivity in taxane-refractory mCRPC.

Abstract 1185: PRMT5 inhibition epigenetically regulates DNA damage response pathways in cancer cells and sensitizes to chemotherapy and PARP inhibition

Abstract Genetic defects of DNA damage response (DDR) pathways in cancer cells induce synthetic lethality with chemotherapy and PARP inhibitors. However, many patients with advanced cancers develop resistance to these therapies mainly due to circumvention and/or restoration of the inactivated DDR genes. In the present study, we demonstrate that pharmacological inhibition of PRMT5, the major type II protein arginine methyltransferase, epigenetically downregulates multiple genes involved in the DDR/DNA replication pathways, resulting in the sensitization of cancer cells to chemotherapy and PARP inhibition. Treatment with C220 or PRT543, potent and selective PRMT5 inhibitors, downregulates expression of DDR genes and/or proteins including BRCA1/2, ATM/ATR, CHK1/2, RAD51, POLD1/3, and PNKP in multiple types of cancer cells in vitro. Mechanistically, PRT543 promotes global alternative splicing (ΔPSI) changes, including intron retention and exon skipping. In particular, PRT543 significantly increases retained intron of POLD1 and PNKP genes, which are downstream of the spliceosome subunit SRSF1, a major protein substrate of PRMT5. Additionally, PRT543 increases intron retention of ATM and ATR genes. For BRCA1/2, CHK1/2 and RAD51, no changes in alternative splicing were observed, suggesting the involvement of other mechanisms such as the CLNS1A/H4R3me2s chromatin regulation pathway. The regulation of the DDR pathway by PRT543 is associated with increased DNA damage as determined by COMET and gamma H2AX analyses. Combining PRT543 with PARP inhibitors or DNA-alkylating agents demonstrates a potent synergistic interaction in both HR proficient and HR deficient cancer cell lines in vitro. Similar combination effects are observed in primary cultures of patient-derived breast cancer and high-grade serous ovarian cancer. Moreover, combination of PRT543 with PARP inhibition effectively inhibits the growth of HCC1569 CDX breast cancer in vivo. Further ex vivo and in vivo combination studies with PRT543 and PARP inhibitors or chemotherapy in genetically defined CDX and PDX models are ongoing. These studies not only reveal a novel mechanism of PRMT5 inhibition, but also suggest beneficial combination effects with other therapies, particularly in patients with tumors that are resistant to therapies that are dependent on DNA damage as their mechanism of action. PRT543 is currently under evaluation in a Phase I clinical trial in patients with advanced solid tumors and hematological malignancies (NCT03886831). Citation Format: Koichi Ito, Jack Carter, Venkat Thodima, Youyou Zhang, Monisha Sivakumar, Mu Xu, Neha Bhagwat, Joseph Rager, Jacob Spruance, Lin Zhang, Bruce Ruggeri, Peggy Scherle, Kris Vaddi. PRMT5 inhibition epigenetically regulates DNA damage response pathways in cancer cells and sensitizes to chemotherapy and PARP inhibition [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1185.

Altering mammalian transcription networking with ADAADi: An inhibitor of ATP-dependent chromatin remodeling

Active DNA-dependent ATPase A Domain inhibitor (ADAADi) is the only known inhibitor of ATP-dependent chromatin remodeling proteins that targets the ATPase domain of these proteins. The molecule is synthesized by aminoglycoside phosphotransferase enzyme in the presence of aminoglycosides. ADAADi interacts with ATP-dependent chromatin remodeling proteins through motif Ia present in the conserved helicase domain, and thus, can potentially inhibit all members of this family of proteins. We show that mammalian cells are sensitive to ADAADi but with variable responses in different cell lines. ADAADi can be generated from a wide variety of aminoglycosides; however, cells showed differential response to ADAADi generated from various aminoglycosides. Using HeLa and DU145 cells as model system we have explored the effect of ADAADi on cellular functions. We show that the transcriptional network of a cell type is altered when treated with sub-lethal concentration of ADAADi. Although ADAADi has no known effects on DNA chemical and structural integrity, expression of DNA-damage response genes was altered. The transcripts encoding for the pro-apoptotic proteins were found to be upregulated while the anti-apoptotic genes were found to be downregulated. This was accompanied by increased apoptosis leading us to hypothesize that the ADAADi treatment promotes apoptotic-type of cell death by upregulating the transcription of pro-apoptotic genes. ADAADi also inhibited migration of cells as well as their colony forming ability leading us to conclude that the compound has effective anti-tumor properties.

Modulation of plant DNA damage response gene expression during Agrobacterium infection

Agrobacterium T-DNA (transfer DNA) integration into the plant genome relies mostly on host proteins involved in the DNA damage repair pathways. However, conflicting results have been obtained using plants with mutated or down-regulated genes involved in these pathways. Here, we chose a different approach by following the expression of a series of genes, encoding proteins involved in the DNA damage response, during early stages of Agrobacterium infection in tobacco. First, we identified tobacco homologs of Arabidopsis genes induced upon DNA damage and demonstrated that their expression was activated by bleomycin, a DNA-break causing agent. Then, we showed that Agrobacterium infection induces the expression of several of these genes markers of the host DNA damage response, with different patterns of transcriptional response. This induction largely depends on Agrobacterium virulence factors, but not on the T-DNA, suggesting that the DNA damage response activation may rely on Agrobacterium-encoded virulence proteins. Our results suggest that Agrobacterium modulates the plant DNA damage response machinery, which might facilitate the integration of the bacterial T-DNA into the DNA breaks in the host genome.

Endometrial DNA damage response is modulated in endometriosis.

Is the DNA damage response (DDR) dysregulated in the eutopic endometrium of women with endometriosis? Endometrial expression of genes involved in DDR is modulated in women with endometriosis, compared to those without the disease. Ectopic endometriotic lesions are reported to harbour somatic mutations, thereby hinting at dysregulation of DDR and DNA repair pathways. However, it remains inconclusive whether the eutopic endometrium also manifests dysregulated DDR in endometriosis. For this case-control study conducted between 2015 and 2019, eutopic endometrial (E) samples (EE- from women with endometriosis, CE- from women without endometriosis) were collected in either mid-proliferative (EE-MP, n = 23; CE-MP, n = 17) or mid-secretory (EE-MS, n = 17; CE-MS, n = 9) phases of the menstrual cycle. This study compares: (i) DNA damage marker localization, (ii) expression of DDR genes and (iii) expression of DNA repair genes in eutopic endometrial samples from women with and without endometriosis. The study included (i) 40 women (aged 31.9 ± 0.81 years) with endometriosis and (ii) 26 control women (aged 31.4 ± 1.02 years) without endometriosis. Eutopic endometrial samples from the two groups were divided into different parts for histological analysis, immunohistochemistry, RNA extraction, protein extraction and comet assays. Eighty-four genes of relevance in the DNA damage signalling pathway were evaluated for their expression in eutopic endometrial samples, using RT2 Profiler PCR arrays. Validations of the expression of two GADD (Growth Arrest DNA Damage Inducible) proteins - GADD45A and GADD45G were carried out by immunoblotting. DNA damage was assessed by immunohistochemical localization of γ-H2AFX (a phosphorylated variant of histone H2AX) and 8-OHdG (8-hydroxy-2'-deoxyguanosine). RNA sequencing data from mid-proliferative (EE-MP, n = 4; CE-MP, n = 3) and mid-secretory phase (EE-MS and CE-MS, n = 4 each) endometrial samples were scanned to compare the expression status of all the genes implicated in human DNA repair. PCNA (Proliferating Cell Nuclear Antigen) expression was determined to assess endometrial proliferation. Residual DNA damage in primary endometrial cells was checked by comet assays. Public datasets were also scanned for the expression of DDR and DNA repair genes as our RNASeq data were limited by small sample size. All the comparisons were made between phase-matched endometrial samples from women with and without endometriosis. Endometrial expression of DDR genes and intensity of immunolocalized γ-H2AFX were significantly (P < 0.05) higher in EE, compared to CE samples. DDR proteins, especially those belonging to the GADD family, were found to be differentially abundant in EE, as compared to CE. These patterns were evident in both mid-proliferative and mid-secretory phases. Intriguingly, higher DDR was associated with increased cell proliferation in EE-MP, compared to CE-MP. Furthermore, among the differentially expressed transcripts (DETs) encoded by DNA repair genes, the majority showed up-regulation in EE-MP, compared to CE-MP. Interestingly, CE-MP and EE-MP had a comparable percentage (P > 0.05) of cells with residual DNA damage. However, unlike the mid-proliferative phase data, many DETs encoded by DNA repair genes were down-regulated in EE-MS, compared to CE-MS. An analysis of the phase-matched control and endometriosis samples included in the GSE51981 dataset available in the Gene Expression Omnibus database also revealed significant (P < 0.05) alterations in the expression of DDR and DNA repair genes in EE, compared to CE. N/A. The study was conducted on a limited number of endometrial samples. Also, the study does not reveal the causes underlying dysregulated DDR in the eutopic endometrium of women with endometriosis. Alterations in the expression of DDR and DNA repair genes indirectly suggest that eutopic endometrium, as compared to its healthy counterpart, encounters DNA damage-inducing stimuli, either of higher strength or for longer duration in endometriosis. It will be worthwhile to identify the nature of such stimuli and also explore the role of higher genomic insults and dysregulated DDR/DNA repair in the origin and/or progression of endometriosis. The study was supported by the Department of Biotechnology and Indian Council of Medical Research, Government of India. No conflict of interest is declared.

Acute Myeloid Leukaemia in Elderly: Expression Analysis of DNA Damage Response (DDR) and Anti-Apoptosis Genes Identify Novel Targets for Potential “Synergistic Lethality”

Background: Genetic instability and heterogeneity are fundamental to AML biology and pivotal to its prognosis. Acute myeloid leukaemia (AML) is most frequent in older adults (&amp;gt;60 years) and a significant majority are considered "treatment-naïve" given medical comorbidities, high-risk disease biology, and poor tolerance to chemotherapy. These patients receive low-intensity regimens, mostly hypomethylating agents due to impaired tolerance to induction chemotherapy, resulting in low overall survival. Thus, there is a critical need to develop targeted therapies capable of rapidly inducing a high rate of clinical response, with better tolerability and durable responses for these elderly AML patients. DNA damage response (DDR) is a specialized and highly orchestrated signalling cascade to maintain genetic stability and is closely linked to the cell cycle. The cell cycle checkpoints result in arrest and the resumption of cell cycle progression when DNA damage has been repaired. However, the DNA repair failure will direct cells towards cellular senescence or apoptosis. Hence, DDR and apoptosis are intricately related physiological processes. In AML, mutations in key regulators of gene expression and/or chromatin structure, such as p53, K-RAS, and isocitrate dehydrogenase 1 and 2 (IDH1/2) results in defective DDR. Defects in DDR are also age-related; therefore, resulting in an exponential increase in the incidence of cancer with age. The emerging treatment regimens for elderly AML are focusing on synergistic lethality using a combination of DDR inhibitors (PARP1) and/ or anti-apoptotic inhibitors (BCL2) in combination with low dose anthracycline and additional targeted therapies like (IDH2/DNTM etc.). However, the wider implication and influence of DDR genes either alone or in combination with anti-apoptotic genes remains uncharacterized in elderly AML. In this pilot study, we screened a large cohort of AML samples for mRNA expression for a series of DDR and apoptotic genes to investigate the age-related variation in expression of these molecules. We observed distinct differences in DDR and anti-apoptotic gene expression between elderly AML compared to paediatric patients. We anticipate, that these preliminary observations will pave the pathway for future comprehensive studies to expand the employment of synergistic lethality strategy for elderly AML patients. Methods: We employed RNA extracted from formalin-fixed paraffin-embedded (FFPE) diagnostic tissuesamples in 100 AML patients. Age defined the categorization of patients into three groups; a, &amp;lt;18 years (n=34); b,18-60 years (n=32) and c, &amp;gt;60 years (n=34). nCounter (NanoString Technologies) platform was used for the quantification of mRNA. Qlucore Omics Explorer software was employed with defined criteria (fold change &amp;gt;2.0; p&amp;lt;0.01 and q &amp;lt;0.05) for statistical analysis. Results:We noted that several DDR mediators (BRIP1, POLD1, XRCC4) are differentially up-regulated in the AML samples linked with elderly patient group, alongside anti-apoptotic genes (IDH2, IKBKB) when compared with samples from patient &amp;lt;18 years (Figure 1). Moreover, DDR effectors (BRCA1&amp; ATM) were up-regulated in the elderly cohort relative to paediatric AML samples, suggesting potential targets for treating elderly AML (Figure2). Conclusions:This pilot study identifies several additional and novel DDR targets; which can be exploited to enhance chemotherapeutic efficacy in "treatment fit" as well as "treatment naïve" elderly AML patients. Besides, we also report numerous novel anti-apoptotic molecules up-regulated in elderly AML. Taken together the preliminary data, presented here, expand the repertoire for targeted therapy in elderly AML with a specific focus on synergistic lethality. Disclosures No relevant conflicts of interest to declare.

Abstract B27: MT1-MMP targeting in melanoma brain metastasis

Abstract Background: Melanoma brain metastases contribute to morbidity and mortality of melanoma, and the treatment is limited due to its accessibility for drugs and also for surgical approaches. Radiotherapy is a widely used approach for disseminated metastatic foci in the brain. However, there is a gap in therapeutics since there are few to no alternatives to melanoma brain metastasis after the radiotherapy dose has been maximized. MT1-MMP is a metalloproteinase that has shown a direct correlation with metastasis and whose inhibition slows down the occurrence of metastasis and tumor growth. By microarray analysis, it has been found that inhibition of MT1-MMP downregulates the expression of DNA-damage response genes. Objective/Hypothesis: We hypothesize that the inhibition of MT1-MMP in combination with radiotherapy will enhance the tumor cell killing efficacy by means of preventing cells from responding to the DNA damage that is caused by radiation. Further, we hypothesize that the Integrin beta 1 pathway downstream of MT1-MMP is the mediator in the downregulation of DNA-damage response genes. Methods: We utilized melanoma cell lines, A375, WM-266-4-Luciferase, and K457, in which we introduced shMT1-MMP lentivirus with control shGFP. Cell culture assays compared the response of shMT1-MMP cells and shGFP cells in the presence of radiotherapy and the assays included comet assay, foci of gammaH2AX staining, clonogenic assay, and evaluation of radiotherapy response by Western blot. Furthermore, a nude mouse model was utilized in which WM-266-4-luciferase shMT1-MMP and control shGFP cells were inoculated by stereotactic injection. In vivo imaging system (IVIS) was utilized to follow up the tumors. Results: Ongoing experiments aim to look at the response of shMT1-MMP cells to radiotherapy compared to shGFP cells by DNA damage evaluation assays (Comet assay, gammaH2AX foci, DNA-damage response proteins by Western blot), downstream signaling of Integrin beta 1 pathway, and the survival of nude mice in shMT1-MMP inoculated tumors and their response to radiotherapy. Impact: This project has the potential to advance the current treatment of melanoma brain metastasis and also has the potential of advancing the understanding of the DNA-damage response in melanoma. Citation Format: Julia Escandon, Varsha Thakur, Barbara Bedogni. MT1-MMP targeting in melanoma brain metastasis [abstract]. In: Proceedings of the AACR Special Conference on Melanoma: From Biology to Target; 2019 Jan 15-18; Houston, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(19 Suppl):Abstract nr B27.