More Like this

1. Are there increases in CRISPR/Cas off-target effects in homologous recombination repair deficient Saccharomyces cerevisiae cells?

   Castillo, S ; Santoro, I ( January 2023 , Southeastern biology)

   CRISPR/Cas technology is increasingly being used as a common methodology in many cancer biology studies due to the ease and convenience of the technique. Precise editing of genomic DNA has been achieved upon repair of CRISPR-induced DNA double-strand breaks (DSBs) by homologous recombination (HR). HR repairs DNA DSBs with high fidelity and therefore, deficiencies in HR result in genome instability. These deficiencies have been demonstrated in many cancers. RAD51-dependent HR is a very important pathway for repairing DSBs. Previous studies have shown that genome editing using CRISPR technology relies on the repair of site-specific DNA DSBs induced by the RNA-guided Cas9 endonuclease. Furthermore, previous studies have shown that the efficiency of CRISPR-mediated HR can be improved by the stimulation of HR promoting factors, such as the RAD51 recombinase. Despite the ease and efficient use the CRISPR/Cas technology for genome editing, one limitation is the potential occurrence of associated off-target effects. If CRISPR technology is planned to be used to target cancer cells with defective HR capabilities, will off-target mutations be likely to occur? In order to answer this question, a system was developed in Saccharomyces cerevisiae using green fluorescent protein (GFP) as a reporter to identify off-target CRISPR-induced DSBs. This study set out to test the number of off-target DSBs that could be introduced by CRISPR-induced genome editing in a RAD51-deficient HR model. We were curious whether loss of RAD51-dependent HR would increase the abundance of off-target CRISPR-induced DSBs in mutant yeast strains as compared to those with a functioning HR-dependent DNA repair pathway. Preliminary findings using this system will be presented. 

   more » « less
2. Image Processing Pipeline to Compute Homologous Recombination Score

   https://doi.org/10.1145/3535694.3535704  

   Vundavilli, Haswanth ; Tumiati, Manuela ; Hautaniemi, Sampsa ; Datta, Aniruddha ; Kauppi, Liisa ( April 2022 , 12th International Conference on Biomedical Engineering and Technology (2022), Tokyo, Japan)

   DNA double-strand breaks (DSBs) occur frequently in eukaryotic cells, and the homologous recombination pathway (HR) is one of the major pathways required to repair these breaks. However, tumor cells that are able to repair DSBs are unlikely to die due to damage incurred by DNA damaging chemotherapies, such as platinum compounds. While platinum-based therapies have been effective in treating various cancers, they also carry harsh side effects, and thus ideally platinum should be used when the probability of treatment resistance is low. HR scores provide a measure for patients’ tumor’s HR capacity and have been shown to predict their chemotherapy response and long-term survival. Calculating this score manually from immunofluorescence microscopy images for each patient is error-prone and time-consuming. Herein, we propose an image processing pipeline that takes as input imaging data from three emission channels (representing nuclei, S-phase cells, and HR-mediated repair in a tumor slice) from an epifluorescence microscope and computes the HR score. Our open-source methodology forms a rationale to develop similar approaches in predicting chemotherapeutic responses and facilitating to make treatment decisions. 

   more » « less
3. Methylation of CpG Sites as Biomarkers Predictive of Drug-Specific Patient Survival in Cancer

   https://doi.org/10.1177/11769351221131124  

   Neary, Bridget ; Lin, Shuting ; Qiu, Peng ( January 2022 , Cancer Informatics)

   Background: Though the development of targeted cancer drugs continues to accelerate, doctors still lack reliable methods for predicting patient response to standard-of-care therapies for most cancers. DNA methylation has been implicated in tumor drug response and is a promising source of predictive biomarkers of drug efficacy, yet the relationship between drug efficacy and DNA methylation remains largely unexplored. Method: In this analysis, we performed log-rank survival analyses on patients grouped by cancer and drug exposure to find CpG sites where binary methylation status is associated with differential survival in patients treated with a specific drug but not in patients with the same cancer who were not exposed to that drug. We also clustered these drug-specific CpG sites based on co-methylation among patients to identify broader methylation patterns that may be related to drug efficacy, which we investigated for transcription factor binding site enrichment using gene set enrichment analysis. Results: We identified CpG sites that were drug-specific predictors of survival in 38 cancer-drug patient groups across 15 cancers and 20 drugs. These included 11 CpG sites with similar drug-specific survival effects in multiple cancers. We also identified 76 clusters of CpG sites with stronger associations with patient drug response, many of which contained CpG sites in gene promoters containing transcription factor binding sites. Conclusion: These findings are promising biomarkers of drug response for a variety of drugs and contribute to our understanding of drug-methylation interactions in cancer. Investigation and validation of these results could lead to the development of targeted co-therapies aimed at manipulating methylation in order to improve efficacy of commonly used therapies and could improve patient survival and quality of life by furthering the effort toward drug response prediction. 

   more » « less
4. Identifying gene expression patterns associated with drug-specific survival in cancer patients

   https://doi.org/10.1038/s41598-021-84211-y  

   Neary, Bridget ; Zhou, Jie ; Qiu, Peng ( December 2021 , Scientific Reports)

   null (Ed.)

   Abstract The ability to predict the efficacy of cancer treatments is a longstanding goal of precision medicine that requires improved understanding of molecular interactions with drugs and the discovery of biomarkers of drug response. Identifying genes whose expression influences drug sensitivity can help address both of these needs, elucidating the molecular pathways involved in drug efficacy and providing potential ways to predict new patients’ response to available therapies. In this study, we integrated cancer type, drug treatment, and survival data with RNA-seq gene expression data from The Cancer Genome Atlas to identify genes and gene sets whose expression levels in patient tumor biopsies are associated with drug-specific patient survival using a log-rank test comparing survival of patients with low vs. high expression for each gene. This analysis was successful in identifying thousands of such gene–drug relationships across 20 drugs in 14 cancers, several of which have been previously implicated in the respective drug’s efficacy. We then clustered significant genes based on their expression patterns across patients and defined gene sets that are more robust predictors of patient outcome, many of which were significantly enriched for target genes of one or more transcription factors, indicating several upstream regulatory mechanisms that may be involved in drug efficacy. We identified a large number of genes and gene sets that were potentially useful as transcript-level biomarkers for predicting drug-specific patient survival outcome. Our gene sets were robust predictors of drug-specific survival and our results included both novel and previously reported findings, suggesting that the drug-specific survival marker genes reported herein warrant further investigation for insights into drug mechanisms and for validation as biomarkers to aid cancer therapy decisions. 

   more » « less
5. Chromatin and other obstacles to base excision repair: potential roles in carcinogenesis

   https://doi.org/10.1093/mutage/gez029  

   Caffrey, Paul J ; Delaney, Sarah ( October 2019 , Mutagenesis)

   Abstract DNA is comprised of chemically reactive nucleobases that exist under a constant barrage from damaging agents. Failure to repair chemical modifications to these nucleobases can result in mutations that can cause various diseases, including cancer. Fortunately, the base excision repair (BER) pathway can repair modified nucleobases and prevent these deleterious mutations. However, this pathway can be hindered through several mechanisms. For instance, mutations to the enzymes in the BER pathway have been identified in cancers. Biochemical characterisation of these mutants has elucidated various mechanisms that inhibit their activity. Furthermore, the packaging of DNA into chromatin poses another obstacle to the ability of BER enzymes to function properly. Investigations of BER in the base unit of chromatin, the nucleosome core particle (NCP), have revealed that the NCP acts as a complex substrate for BER enzymes. The constituent proteins of the NCP, the histones, also have variants that can further impact the structure of the NCP and may modulate access of enzymes to the packaged DNA. These histone variants have also displayed significant clinical effects both in carcinogenesis and patient prognosis. This review focuses on the underlying molecular mechanisms that present obstacles to BER and the relationship of these obstacles to cancer. In addition, several chemotherapeutics induce DNA damage that can be repaired by the BER pathway and understanding obstacles to BER can inform how resistance and/or sensitivity to these therapies may occur. With the understanding of these molecular mechanisms, current chemotherapeutic treatment regiments may be improved, and future therapies developed. 

   more » « less