Abstract 2657: Radiosensitization of pancreatic cancer cells by combined inhibition of Chk1 and PARP1 using AZD7762 and olaparib
Authors: Vance Sean M. , Maybuam Jonathan , Lawrence Theodore S. , Morgan Meredith A. 
Published: June 2012

Abstract
Small molecule inhibitors targeted to key DNA damage response/repair proteins, such as Chk1 (checkpoint kinase 1) and PARP1 (poly (ADP-ribose) polymerase-1) are being developed to sensitize tumor cells to chemo- and radio- therapy. We have recently shown that inhibition of HRR (homologous recombination repair) by the Chk1/2 inhibitor, AZD7762 (AstraZeneca) is a mechanism of radiosensitization in pancreatic cancer cells. Others have demonstrated that AZD7762 selectively sensitizes p53 mutant tumor cells. PARP inhibitors have demonstrated preferential efficacy as radiation sensitizers in cells with other DNA damage repair defects, including HRR. Thus, we hypothesized that inhibition of HRR (mediated by Chk1 via AZD7762) and PARP1 (via olaparib, AZD2281) would selectively sensitize p53 mutant pancreatic cancer cells to radiation. To test this hypothesis we assessed radiosensitization by clonogenic survival in two p53 mutant pancreatic cancer cell lines, MiaPaCa-2 and MPanc96. Cells were treated with AZD7762 (100nM) and/or olaparib (1uM) for 1 hour before radiation (0-8Gy), and for 23 hours after radiation, followed by processing for clonogenic survival. We verified that treatment with olaparib inhibited poly (ADP-ribose). We found that olaparib or AZD7762 alone produced similar magnitudes of radiosensitization in MiaPaCa-2 cells (1.5 ± 0.1 and 1.5 ± 0.01, respectively). However, the combination of olaparib and AZD7762 produced significantly greater radiosensitization than either agent alone (2.4 ± 0.1, P&lt;0.05), which appeared to be greater than additive. Similarly, in a second cell line, MPanc96, the combination of olaparib and AZD7762 produced significantly greater radiosensitization (3.0 ± 0.4, P&lt;0.05) than either olaparib (1.5 ± 0.1) or AZD7782 alone (2.0 ± 0.1). The combination of olaparib with AZD7762 produced minimal toxicity with clonogenic surviving fractions in MiaPaCa-2 cells of 1.1 ± 0.1 (olaparib), 0.8 ± 0.1 (AZD7762), and 0.7 ± 0.1 (olaparib + AZD7762) and in MPanc96 cells of &gt;1.0 ± 0.2 (olaparib), 0.5 ± 0.1 (AZD7762), and 0.6 ± 0.2 (olaparib + AZD7762). Radiosensitization by olaparib and AZD7762 was accompanied by an increase in γH2AX and S345 Chk1 suggesting that DNA damage was increased under these conditions. Taken together, these findings demonstrate that the combination of olaparib and AZD7762 induces profound radiosensitization of p53 mutant pancreatic cancer cell lines. Furthermore, these studies suggest that inhibition of HRR by Chk1 inhibitors may be a useful strategy for selectively inducing a BRAC1/2 deficient-like phenotype in p53 mutant tumor cells, thus resulting in synergistic radiosensitization when used in combination with PARP1 inhibition. Supported by R01CA78554.
Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2657. doi:10.1158/1538-7445.AM2011-2657