Preclinical Development The Checkpoint Kinase Inhibitor AZD 7762 Potentiates Chemotherapy-Induced Apoptosis of p 53-Mutated Multiple Myeloma Cells

DNA cross-linking agents are frequently used in the treatment of multiple myeloma–generating lesions, which activate checkpoint kinase 1 (Chk1), a critical transducer of the DNAdamage response. Chk1 activation promotes cell survival by regulating cell-cycle arrest andDNA repair following genotoxic stress. The ability of AZD7762, an ATP-competitive Chk1/2 inhibitor to increase the efficacy of the DNA-damaging agents bendamustine, melphalan, and doxorubicin was examined using four human myeloma cell lines, KMS-12BM,KMS-12-PE, RPMI-8226, andU266B1. The in vitro activity ofAZD7762 asmonotherapy and combinedwith alkylating agents and the "novel" drug bortezomib was evaluated by studying its effects on cytotoxicity, signaling, and apoptotic pathways. The Chk1/2 inhibitor AZD7762 potentiated the antiproliferative effects of bendamustine, melphalan, and doxorubicin but not bortezomib in multiple myeloma cell lines that were p53deficient. Increased gH2AXstaining in cells treatedwith bendamustine ormelphalanplusAZD7762 indicates a greater degree of DNA damage with combined therapy. Abrogation of the G2–M checkpoint by AZD7762 resulted in mitotic catastrophe with ensuing apoptosis evidenced by PARP and caspase-3 cleavage. In summary, the cytotoxic effects of bendamustine, melphalan and doxorubicin on p53-deficient multiple myeloma cell lines were enhanced by the coadministration of AZD7762. These data provide a rationale for testing these combinations in patients with relapsed and/or refractory multiple myeloma.Mol Cancer Ther; 11(8); 1781–8. 2012 AACR.