Targeting DNA repair with aphidicolin sensitizes primary chronic lymphocytic leukemia cells to purine analogs

// Eliza Starczewska 1 , Maxime Beyaert 1 , Lucienne Michaux 2 , Marie-Christiane Vekemans 2 , Pascale Saussoy 3 , Vanesa Bol 4 , Ainhoa Arana Echarri 1 , Caroline Smal 1 , Eric Van Den Neste 1, 2 , Francoise Bontemps 1 1 de Duve Institute, Universite Catholique de Louvain, B-1200 Brussels, Belgium 2 Department of Hematology, Cliniques Universitaires Saint-Luc, Universite Catholique de Louvain, B-1200 Brussels, Belgium 3 Service de Biologie Clinique, Cliniques Universitaires Saint-Luc, Universite Catholique de Louvain, B-1200 Brussels, Belgium 4 Center for Molecular Imaging, Radiotherapy and Oncology, Institut de Recherche Experimentale et Clinique (IREC), Universite Catholique de Louvain, B-1200 Brussels, Belgium Correspondence to: Francoise Bontemps, email: francoise.bontemps@uclouvain.be Keywords: chronic lymphocytic leukemia, DNA damage, fludarabine, aphidicolin, γH2AX Received: March 09, 2016      Accepted: May 04, 2016      Published: May 20, 2016 ABSTRACT Purine analogs are among the most effective chemotherapeutic drugs for the treatment of chronic lymphocytic leukemia (CLL). However, chemoresistance and toxicity limit their clinical use. Here, we report that the DNA polymerase inhibitor aphidicolin, which displayed negligible cytotoxicity as a single agent in primary CLL cells, markedly synergizes with fludarabine and cladribine via enhanced apoptosis. Importantly, synergy was recorded regardless of CLL prognostic markers. At the molecular level, aphidicolin enhanced purine analog-induced phosphorylation of p53 and accumulation of γH2AX, consistent with increase in DNA damage. In addition, aphidicolin delayed γH2AX disappearance that arises after removal of purine analogs, suggesting that aphidicolin causes an increase in DNA damage by impeding DNA damage repair. Similarly, aphidicolin inhibited UV-induced DNA repair known to occur primarily through the nucleotide excision repair (NER) pathway. Finally, we showed that fludarabine induced nuclear import of XPA, an indispensable factor for NER, and that XPA silencing sensitized cell lines to undergo apoptosis in response to fludarabine. Together, our data indicate that aphidicolin potentiates the cytotoxicity of purine analogs by inhibiting a DNA repair pathway that involves DNA polymerases, most likely NER, and provide a rationale for manipulating it to therapeutic advantage.