Synergistic targeting and resistance to PARP inhibition in DNA damage repair-deficient pancreatic cancer

Abstract

ObjectiveATM serine/threonine kinase (ATM) is the most frequently mutated DNA damage response gene, involved in homologous recombination (HR), in pancreatic ductal adenocarcinoma (PDAC).DesignCombinational synergy screening was performed to endeavour a genotype-tailored targeted therapy.ResultsSynergy was found on inhibition of PARP, ATR and DNA-PKcs (PAD) leading to synthetic lethality in ATM-deficient murine and human PDAC. Mechanistically, PAD-induced PARP trapping, replication fork stalling and mitosis defects leading to P53-mediated apoptosis. Most importantly, chemical inhibition of ATM sensitises human PDAC cells toward PAD with long-term tumour control in vivo. Finally, we anticipated and elucidated PARP inhibitor resistance within the ATM-null background via whole exome sequencing. Arising cells were aneuploid, underwent epithelial-mesenchymal-transition and acquired multidrug resistance (MDR) due to upregulation of drug transporters and a bypass within the DNA repair machinery. These functional observations were mirrored in copy number variations affecting a region on chromosome 5 comprising several of the upregulated MDR genes. Using these findings, we ultimately propose alternative strategies to overcome the resistance.ConclusionAnalysis of the molecular susceptibilities triggered by ATM deficiency in PDAC allow elaboration of an efficient mutation-specific combinational therapeutic approach that can be also implemented in a genotype-independent manner by ATM inhibition.

Maintenance Therapy for ATM-Deficient Pancreatic Cancer by Multiple DNA Damage Response Interferences after Platinum-Based Chemotherapy

“…Indeed, others and we found ATR (HR repair) and DNA-PKcs (non-homologous end joining, NHEJ) as corroborating pathways to ATM-signaling in PDAC [13,20,21]. In a recently published study, we showed that PARP, ATR, and DNA-PK inhibitors (PAD) act synergistically on ATM-deficient cells, leading to a lethal accumulation of DNA damage and, thus, demonstrating PAD treatment is a valuable approach that can be exploited to target ATM-mutant human PDACs effectively [13]. Consequently, we tested a putative synthetically lethal therapeutic option by multi-DDR interference (mDDRi) with PAD in a maintenance therapy setting after platinum-based induction therapy in analogy to the POLO trial for efficacy in ATM-deficient PDAC.…”

“…Thus, concepts that target compensatory, mainly HR-related pathways against PARP inhibition in an ATM-deficient PDAC appear reasonable [19]. Indeed, others and we found ATR (HR repair) and DNA-PKcs (non-homologous end joining, NHEJ) as corroborating pathways to ATM-signaling in PDAC [13,20,21]. In a recently published study, we showed that PARP, ATR, and DNA-PK inhibitors (PAD) act synergistically on ATM-deficient cells, leading to a lethal accumulation of DNA damage and, thus, demonstrating PAD treatment is a valuable approach that can be exploited to target ATM-mutant human PDACs effectively [13].…”

“…Based on previous findings and conducted dosage titrations [13], we established a synergistically operating therapy approach with the maximal possible HR and NHEJ inhibition in ATM-deficient murine PDAC cells. In this context, synergism between PARP, ATR, and DNA-PKcs inhibitors allowed the substantial lowering of single drug dosages while maintaining a highly potent cytotoxic effect [13].…”

“…Based on previous findings and conducted dosage titrations [13], we established a synergistically operating therapy approach with the maximal possible HR and NHEJ inhibition in ATM-deficient murine PDAC cells. In this context, synergism between PARP, ATR, and DNA-PKcs inhibitors allowed the substantial lowering of single drug dosages while maintaining a highly potent cytotoxic effect [13]. We referred to this approach comprising the inhibition of PARP (olaparib), ATR (VE-822), and DNA-PKcs (CC-115) as multi-DDR interference (mDDRi) and applied the latter regimen in a maintenance therapy setting following induction with the standard of care regimen FOLFIRINOX in a preclinical trial setting in analogy to the POLO trial.…”

“…4%, the ATM serine/threonine kinase (ATM) is the most frequently mutated DDR gene in sporadic PDAC, before the BRCA1 and BRCA2 genes [12]. ATM acts as a crucial enzyme in HR, its deficiency representing a bona fide HR-defective PDAC model for preclinical studies [13]. We could previously show that impaired ATM expression associates with a poor prognosis in human PDAC.…”