cAMP-Mediated Autophagy Promotes Cell Survival via ROS-Induced Activation of PARP1: Implications for Treatment of Acute Lymphoblastic Leukemia

DNA-damaging therapy is the basis for treatment of most cancers, including B-cell precursor acute lymphoblastic leukemia (BCP-ALL, hereafter ALL). We have previously shown that cAMP-activating factors present in the bone marrow render ALL cells less sensitive to DNA damage-induced apoptosis, by enhancing autophagy and suppressing p53. To sensitize ALL cells to DNA-damaging therapy, we have searched for novel targets that may counteract the effects induced by cAMP signaling. In the current study, we have identified PARP1 as a potential target. We show that the PARP1 inhibitors olaparib or PJ34 inhibit cAMP-mediated autophagy and thereby potentiate the DNA-damaging treatment. Furthermore, we reveal that cAMP-mediated PARP1 activation is preceded by induction of reactive oxygen species (ROS) and results in depletion of nicotinamide adenine dinucleotide (NAD), both of which are autophagy-promoting events. Accordingly, we demonstrate that scavenging ROS by N-acetylcysteine and repleting NAD independently reduce DNA damage-induced autophagy. In addition, olaparib augmented the effect of DNA-damaging treatment in a human xenograft model of ALL in NOD-scidIL2Rgammanull mice. On the basis of the current findings, we suggest that PARP1 inhibitors may enhance the efficiency of conventional genotoxic therapies and thereby provide a novel treatment strategy for pediatric patients with ALL. PARP1 inhibitors augment the DNA damage-induced killing of ALL cells by limiting the opposing effects of cAMP-mediated autophagy, which involves ROS-induced PARP1 activation and depletion of cellular NAD levels.