Targeting the Ataxia Telangiectasia Mutated-null phenotype in chronic lymphocytic leukemia with pro-oxidants

Abstract

© F e r r a t a S t o r t i F o u n d a t i o n(ROS) production or reduced antioxidant capacity. A principle antioxidant pathway is regulated by the redox sensitive transcription factor, NF-E2 p45-related factor-2 (NRF2/NFE2L2). In unstressed cells, low levels of NRF2 are maintained through interaction with Kelch-like ECHassociated protein 1 (KEAP1), an adapter for the E3 ubiquitin ligase Cullin 3 (CUL3) that directs NRF2 for proteasomal degradation. 13 Modification of redox and electrophile sensitive cysteine residues inhibits the substrate adaptor activity of KEAP1 allowing NRF2 accumulation. The interaction of KEAP1 with NRF2 is further modulated by phosphorylation of NRF2 at serine 40 by protein kinase C (PKC).14 Within the nucleus, NRF2 forms heterodimers with v-maf musculoaponeurotic fibrosarcoma oncogene homolog (MAF) proteins (MAF-F, G and K) and binds to antioxidant response elements (AREs) in the promoters of target genes such as those required for glutathione synthesis and its own promoter. 15 This activity is regulated by the transcriptional repressor BTB and CNC homology 1 transcription factor (BACH1) which competes for the MAF binding partners and for binding to gene promoters. 16 In addition, genetic models suggest that binding of Nrf-2 and its activity are regulated by the ATM substrate, Brca1. 17The most compelling evidence for the role of ATM in redox homeostasis comes from studies of the human radiosensitivity syndrome, Ataxia Telangiectasia (A-T), where both ATM alleles are inactivated. Cells from these patients display increased oxidative stress as a consequence of elevated levels of ROS, increased oxidized/reduced glutathione (GSSG/GSH) ratio, diminished capacity to scavenge ROS and mitochondrial dysfunction. 12,18 Furthermore, ATM is directly activated by oxidative stress 19 and can exert antioxidant activity through regulation of the pentose-phosphate pathway. 20 Recent evidence suggests that ATM might regulate oxidative stress through NRF2. Namely, Nrf2 target gene expression was decreased in Atm-/-murine osteoblasts and this was rescued by the ectopic expression of PKC delta (PKCδ). 21 In this study, we tested the hypothesis that ATM-null CLLs have an intrinsic defect in their antioxidant defenses that might be exploited to induce synthetic lethality of tumor cells by escalating oxidative stress. We show that compared to ATM-wild type (wt) CLL, ATM-null CLL tumors exhibited defective NRF2-dependent antioxidant transcriptional responses, decreased antioxidant capacity, elevated mitochondrial ROS, and increased sensitivity to pro-oxidants both in vitro and in vivo. Furthermore, we demonstrate that pro-oxidant treatment bypassed the need for a functional DRR and induced cell death via a p53-and caspase-independent mechanism involving apoptosis inducing factor (AIF). Methods Patients' samples and cell linesChronic lymphocytic leukemia samples were obtained from Birmingham and Bournemouth Hospitals (Online Supplementary Table S1). These were comprised of 3 CLLs with monoallelic ATM...

USP7 inhibition alters homologous recombination repair and targets CLL cells independently of ATM/p53 functional status

“…This in turn can induce DNA fragmentation as previously reported. 36,55 It has been demonstrated that the USP7 inhibitor P5019 also inhibits USP47 with a comparable EC 50 to USP7. 56 Although the potential off-target effects of HBX19818 have not been thoroughly tested, in this study we demonstrate that many of the cellular phenotypes resulting from USP7 inhibition with HBX19818 can be recapitulated by knocking down USP7 with siRNA.…”

Derivatisation of parthenolide to address chemoresistant chronic lymphocytic leukaemia

“… 6 PTL ( 1 ) demonstrates effective and selective anti-CLL activity in vitro , 7 and through its pro-oxidant activity, can target CLL cells independently of their p53 status. 8 Furthermore, co-authors of this report 9 are among those who have shown that ATM-deficiency disrupts redox homeostasis, increasing further the sensitivity of this DDR-defective subtype of CLL to PTL. 10 In addition to inducing oxidative stress, PTL has been shown to target tumour cells by suppressing pro-survival and proliferation signalling through the NF-κB pathway, 11 by inhibiting JAK–STAT kinase activity and thereby preventing STAT-mediated transcription of anti-apoptotic genes and by inhibiting DNMT1 and HDACs leading to activation of epigenetically silenced tumour suppressor genes.…”

“…16 u PTL has been shown to induce oxidative stress in cancer cells, 17 and recently DMAPT ( 2a ) was confirmed to induce oxidative stress in CLL cells. 9 There are a number of reports on the use and derivatisation of PTL, with a view to addressing various cancer types, 16z , 18 but the only PTL derivative to be applied to CLL remains compound 2a . 19 Previous studies have used molecular docking to investigate 1 and 2a which have suggested that interaction with IKKβ is a plausible mechanism for their action against haematological and solid tumours.…”

mda-7/IL-24 Induces Cell Death in Neuroblastoma through a Novel Mechanism Involving AIF and ATM

“…Taken together, our results suggest that ATM and AIF are functionally related in a positive feedback loop in which they regulate each other in neuroblastoma cells following Ad.5/3- CTV infection (Fig 7). Another recent study reported that treatment with pro-oxidant resulted in caspase-independent, AIF-dependent apoptosis in ATM-null primary CLL tumors (50). These results from others and us suggest that ATM and AIF can work independently or together to induce caspase-independent cell death.…”