Mitoxantrone in combination with an inhibitor of DNA‐dependent protein kinase: a potential therapy for high risk B‐cell chronic lymphocytic leukaemia

Abstract

SummaryDefects in the DNA damage response pathway [e.g. del(17p)] are associated with drug-resistant B-cell chronic lymphocytic leukaemia (CLL). We previously demonstrated that over-expression of DNA-dependent protein kinase (DNA-PK) correlates with chemo-resistance and that inhibition of DNA-PK sensitizes CLL cells to chemotherapeutics. Here, we investigated expression of DNA-PK and other proteins that impact on drug resistance, and evaluated the effects of a DNA-PK inhibitor (NU7441) on mitoxantroneinduced cytotoxicity in CLL cells. NU7441 sensitized cells from 42/49 CLL samples to mitoxantrone, with sensitization ranging from 2-to 200-fold Co-culture of CLL cells in conditioned stromal medium increased chemoresistance but did not reduce sensitization by NU7441. Mitoxantrone treatment induced cH2AX foci and NU7441 increased their longevity (24 h). NU7441 prevented mitoxantrone-induced autophosphorylation of the DNA-PK catalytic subunit (DNA-PKcs) at Ser 2056, confirming that DNA-PK participates in repair of mitoxantrone-induced DNA damage. del(17p) cases were more resistant to mitoxantrone than del(13q) cases, but were resensitized (7-16 fold) by co-incubation with NU7441. Expression of DNA-PKcs, Ku80, P-glycoprotein and topoisomerase IIb were significantly higher in del(17p) cases. PRKDC mRNA levels correlated with DNA-PKcs protein expression, which predicted shorter survival. These data confirm the potential of DNA-PK as a therapeutic target in poor prognosis CLL.

Combined inhibition of PI3K-related DNA damage response kinases and mTORC1 induces apoptosis in MYC-driven B-cell lymphomas

“…The potential for on-target interactions between DDR inhibition and coadministered conventional DNAdamaging cytotoxic modalities requires investigation. Antagonism of the DDR may sensitize it to sequentially scheduled chemotherapy 48 or radiotherapy. 39,40 Additionally, p53-independent BMF induction by BEZ235 could be beneficial in combination with corticosteroids (which also induce BMF 29 ), potentially abrogating glucocorticoid resistance.…”

“…To further define the relative importance of these kinases in apoptotic responses, we used a panel of inhibitors that selectively inhibited different BEZ235 targets ( Figure 1; Table 1). Specifically, BEZ235 was compared with BKM120 (PI3K-selective inhibitor 46 ), KU63794 (ATP-competitive mTORC1/2 inhibitor 47 ), KU55933 (ATM inhibitor), and KU57788 (DNA-PK inhibitor 48 ). Although these inhibitors have an affinity for their respective targets in the nanomolar concentration range (Table 1), none recapitulated the apoptotic response observed with BEZ235 ( Figure 5A).…”

DNA Damage Response/Signaling and Genome (In)Stability as the New Reliable Biological Parameters Defining Clinical Feature of CLL

“…In consequence, use of wortmanin, an inhibitor of PI3-Kinases along with DNA-PKcs (which is PI3-K like kinase), was able to potentialize cytotoxic effect of chlorambucil in CLL cells (Christodoulopoulos et al, 1998). Also, a DNA-PKcs specific inhibitor Nu7441 combined with drugs inducing DNA DSBs has been pointed as a potential therapy for high risk CLL (Elliott et al, 2011). After genotoxic stress and first cell division, structural chromosomal aberrations (dicentric, acentric or ring chromosomes) occurred more frequently in resistant than in sensitive CLL cells (Blaise et al, 2001), suggesting an accelerated but certainly unfaithful DNA repair.…”

Inhibition de la réparation des cassures double-brin de l'ADN: quel intérêt en radiothérapie et pharmacologie antitumorale?

“…Les criblages sont réalisés in vitro sur la base de l'activité de phosphorylation du complexe car le manque de résolution des structures ne permet pas une approche in silico. Les molécules sélectionnées montrent une efficacité sur des cellules leucé-miques (LLC) traitées par le chlorambucile (Veuger et al 2003 ;Willmore et al 2008) ou la mithoxantrone (Elliott et al 2011). De plus, ces inhibiteurs conduisent à une action synergique avec l'irinotécan, un inhibiteur de la topoisomérase I dans le traitement in vitro de cellules tumorales coliques (Davidson et al 2011).…”