DNA damage as a potential target in canine lymphoma treatment: a comparative transcriptomic evaluation of olaparib effects in two lymphoid cell lines

Introduction: Olaparib is a poly ADP-ribose polymerase inhibitor (PARPi), targeting DNA damage response. It is indicated for cancers harboring BRCA1/2 mutations. However, several evidences show that sensitivity to PARPis could be driven by other factors impairing the DNA repair mechanism. As different hematological malignancies carry this kind of defects, this study aims to evaluate the transcriptional effects of olaparib in two canine cell lines, CLBL1 and GL1, derived from diffuse large B-cell lymphoma and acute B-cell leukemia, respectively. Materials and Methods: A whole-transcriptome analysis was carried out in CLBL1 and GL1 cells to evaluate the transcriptional effects of 25 and 50 µM olaparib after 24 hours of exposure. Total RNA was extracted using TRIzol and Qiagen RNeasy Mini Kit. After the assessment of RNA concentration and quality, cDNA libraries were constructed and sequenced using a 150 pb paired-end approach on Illumina platform. Reads were counted, checked for quality and trimmed using validated pipelines. Finally, reads were pseudo-aligned (Kallisto) building the index on Canis Familiaris reference genome (Ensembl). Kallisto outputs were imported in Rstudio with Tximport package; EdgeR and clusterProfiler were used to identify differentially expressed genes (DEGs; False Discovery Rate<0.05 and Fold Change>1.5) and carry out the functional enrichment analysis, respectively. Results: More than 25 million raw reads were obtained for each sample, resulting in a mean mapping percentage of 79%. In both cell lines, olaparib 50 µM produced more DEGs than olaparib 25 µM (707 vs 99 for GL1; 234 vs 180 for CLBL1). When looking at DEGs and enriched GO terms, the main biological processes modulated by olaparib in CLBL1 cells were stress (e.g. ATF3, CEBPB), immune/inflammatory response (e.g. TNFSF4, TNFRSF18) and apoptosis (e.g. BAX, TP53INP1). Olaparib seemed to interact with the immune response also in GL1 cells (e.g. IL10, CD276, IL2RA, IL6), but it also triggered a different cell death process, i.e. pyroptosis, as shown by the modulation of GSDME, GSDMD, and IL18 genes. Conclusions: Olaparib showed different transcriptional effects in chosen cell lines, interacting with immune checkpoints, stress sensors, and interfering with cell proliferation, cytokine production and causing different types of cell death. Considering that canine lymphoma is a serious concern in veterinary oncology, as well as a good model for its human counterpart, this study represents a step forward in the investigation of new therapeutic approaches and the identification of potential chemoresistance mechanisms.