DNA Damage Response Inhibitor Combinations Exert Synergistic Antitumor Activity in Aggressive B-Cell Lymphomas

Abstract

The DNA damage response (DDR) kinases ATR, Chk1, and Wee1 play vital roles in the response to replication stress and in maintaining cancer genomic stability. Inhibitors of these kinases are currently under clinical investigation. Mantle cell lymphoma (MCL) and diffuse large B-cell lymphoma (DLBCL) are aggressive lymphomas whose clinical outcome is still largely unsatisfactory. These cell lymphoma subtypes are highly dependent on both Chk1 and Wee1 for survival. We investigated the activity of the ATR inhibitor AZD6738 as single agent and in combination with either Chk1 (AZD6738) or Wee1 (AZD1775) inhibitors in several preclinical models of MCL and DLBCL. This study included preclinical <i>in vitro</i> activity screening on a large panel of cell lines, both as single agent and in combination, and validation experiments on <i>in vivo</i> models. Cellular and molecular mechanisms of the observed synergistic effect as well as pharmacodynamic analysis of <i>in vivo</i> samples were studied. AZD6738 exerted a strong synergistic cytotoxic effect in combination with both AZD7762 and AZD1775 in the 2 lymphoma subtypes regardless of their <i>TP53, MYC</i>, and <i>ATM</i> mutational status. These DDR inhibitor combinations, similarly to the Chk1/Wee1 inhibitor combination, caused a marked S-phase delay, with an increase in cyclin-dependent kinases (CDK) activity, increased DNA damage, and decreases in Wee1, MYC, and RRM2 protein levels. The synergistic <i>in vitro</i> activity translated to striking <i>in vivo</i> antitumor activity. DDR-DDR inhibitor combinations could potentially offer promising novel therapeutic strategies for patients with B-cell lymphoma.