In vitro and In vivo Radiation Sensitization of Human Tumor Cells by a Novel Checkpoint Kinase Inhibitor, AZD7762

Abstract

Purpose: Inhibition of checkpoint kinase 1 has been shown to enhance the cytotoxicity of DNAdamaging targeted chemotherapy through cell cycle checkpoint abrogation and impaired DNA damage repair. A novel checkpoint kinase 1/2 inhibitor, AZD7762, was evaluated for potential enhancement of radiosensitivity for human tumor cells in vitro and in vivo xenografts.Experimental Design: Survival of both p53 wild-type and mutant human cell lines was evaluated by clonogenic assay. Dose modification factors (DMF) were determined from survival curves (ratio of radiation doses for control versus drug treated at 10% survival). Flow cytometry, Western blot, and radiationinduced tumor regrowth delay assays were conducted.Results: AZD7762 treatment enhanced the radiosensitivity of p53-mutated tumor cell lines (DMFs ranging from 1.6-1.7) to a greater extent than for p53 wild-type tumor lines (DMFs ranging from 1.1-1.2). AZD7762 treatment alone exhibited little cytotoxicity to any of the cell lines and did not enhance the radiosensitivity of normal human fibroblasts (1522). AZD7762 treatment abrogated radiationinduced G 2 delay, inhibited radiation damage repair (assessed by γ-H2AX), and suppressed radiationinduced cyclin B expression. HT29 xenografts exposed to five daily radiation fractions and to two daily AZD7762 doses exhibited significant radiation enhancement compared with radiation alone.Conclusions: AZD7762 effectively enhanced the radiosensitivity of mutated p53 tumor cell lines and HT29 xenografts and was without untoward toxicity when administered alone or in combination with radiation. The results of this study support combining AZD7762 with radiation in clinical trials. Clin Cancer Res; 16(7); 2076-84. ©2010 AACR.

The Checkpoint Kinase Inhibitor AZD7762 Potentiates Chemotherapy-Induced Apoptosis of p53-Mutated Multiple Myeloma Cells

“…Chk1 inhibitors are known to predominantly sensitize p53-deficient cancer cells to DNA damage (12,29,30). KMS-12-BM and KMS-12-PE cells harbor only one copy of p53, and RPMI-8226 and U266B1 cells each have distinct p53 mutations (data not shown).…”

Identification of Preferred Chemotherapeutics for Combining with a CHK1 Inhibitor

“…A critical function of CHK1 is to phosphorylate a number of downstream targets (including CDC25A) to prevent cell-cycle progression into mitosis (1). Numerous CHK1 small-molecule inhibitors have been identified (5), and used to verify the essential role of CHK1 in maintaining the G 2 checkpoint response following DNA damage (6)(7)(8)(9).…”

“…Many of the studies describing CHK1 inhibitors have used a limited number of chemotherapeutics including gemcitabine (6,(13)(14)(15)(16)(17), 13,[16][17][18], camptothecin (13,18,19), cytarabine (16), cisplatin/carboplatin (16), hydroxyurea (14,16), topotecan (6), or ionizing radiation (8,(19)(20)(21). As these agents span different classes of DNA-damaging agents, it suggests that a CHK1 inhibitor may have broad utility.…”

Selective radiosensitization of p53 mutant pancreatic cancer cells by combined inhibition of Chk1 and PARP1

“…Abrogation of the G 2 checkpoint (by Chk1 inhibition and other strategies) has been shown to preferentially sensitize p53 mutant tumor cells to chemotherapy and radiation. [10][11][12][13][14][15][16][17] The prevailing model for tumor cell selectivity of Chk1 inhibition is that tumor cells harbor aberrations in other DNA damage response machinery (i.e., p53, p16, Rb) and, thus, do not G 1 arrest in response to DNA damage leading to selective sensitization of tumor cells by Chk1 inhibition, while normal cells are protected from Chk1 inhibition by their other intact checkpoints (i.e., p53-mediated G 1 arrest).…”

“…In the case of Chk1 inhibitors, the role of p53 in tumor cell selectivity has been extensively explored. The prevailing model 11,14,15,[33][34][35] suggests that p53 mutant tumor cells, unable to arrest in G 1 in response to DNA damage, will rely entirely on the G 2 checkpoint. Thus, abrogation of the G 2 checkpoint by Chk1 inhibition will have a significantly greater impact on p53 mutant cancer cells than it would in normal cells (with an intact p53-mediated G 1 checkpoint).…”