PARP-inhibitors (PARPi) are an integral part of ovarian cancer treatment. However, overcoming acquired PARPi resistance or increasing the benefit of PARPi in patients without homologous recombination Show more
PARP-inhibitors (PARPi) are an integral part of ovarian cancer treatment. However, overcoming acquired PARPi resistance or increasing the benefit of PARPi in patients without homologous recombination deficiency (HRD) remains an unmet clinical need. We sought to identify genetic modulators of PARPi response, guiding pharmacological PARPi sensitization. CRISPR-Cas9 mediated loss-of-function screen with a focused sgRNA library revealed that DNA-demethylases JMJD1B/JMJD1C, targetable by the small inhibitor methylstat, promote PARPi resistance. Methylstat synergistically interacted with olaparib, and (re-)sensitized ovarian cancer cells to PARPi treatment, surpassing the efficacy of common demethylase inhibitors. Genetic knockout of JMJD1B and/or JMJD1C phenocopied the effect of methylstat in an additive manner. Validation studies revealed methylstat to be a universal PARPi-sensitizing drug, effective, regardless of PARPi resistance status or BRCA1 mutational background. Methylstat modulated clonal cancer dynamics by mitigating positive selection of PARPi-resistant or BRCA1-proficient cells under olaparib treatment. Using a model of PARPi-induced cellular toxicity, we showed that methylstat impairs cellular DNA repair, indicated by an increased susceptibility of ovarian cancer cells to olaparib-induced DNA double strand breaks after methylstat exposure. This study proposes the histone demethylase inhibitor methylstat as an epigenetic drug for overcoming PARPi-resistance or for increasing efficacy of PARPi beyond HRD in ovarian cancer patients. Show less
Arteries and veins show marked differences in their anatomy, physiology and genetic expression pattern. In this study, we analyzed impact of overexpression or downregulation of arterial marker gene He Show more
Arteries and veins show marked differences in their anatomy, physiology and genetic expression pattern. In this study, we analyzed impact of overexpression or downregulation of arterial marker gene Hey2 and venous marker gene COUP-TFII in human venous and arterial endothelial cells on genes involved in arteriovenous differentiation. Lentiviral overexpression of venous marker gene COUP-TFII in arterial endothelial cells led to downregulation of NICD4, arterial marker gene Hey2 and EphrinB2. Downregulation of Hey2 could be mediated by direct binding of COUP-TFII to Hey2 promoter as shown by ChIP, EMSA and promoter analysis. Downregulation of Hey2 by shRNA causes downregulation of EphrinB2 expression. Overexpression of arterial marker Hey2 in venous endothelial cells did not change expression pattern of COUP-TFII. Downregulation of venous marker gene COUP-TFII in venous endothelial cells resulted in upregulation of VEGF-A, Dll4 and EphrinB2 expression. Our data support an important role of Hey2 and COUP-TFII in arteriovenous differentiation of human endothelial cells. Show less