Abstract 5126: Does genetic background in glioma influence the sensitivity of tumor cells to a PARP inhibitor in the presence of different DNA damaging agents
Authors: Carlson Jennifer H. , Leyland-Jones Brian , Martin David , De Pradip , Dey Nandini 
Published: May 2015

Abstract
Background: Upregulation of cellular signaling pathways for proliferation is one of the characteristic features of high-grade glioblastomas (GBM), the most common and lethal type of adult brain tumors. Common oncogenic alterations in GBM include a characteristic gain-of-function of growth-promoting EGFR gene, a functionally relevant activation of p21-RAS pathway or a loss-of-expression of growth-attenuating tumor suppressor PTEN gene. Here we tested the role of genetic backgrounds (RAS pathway upregulation and PTEN nullness) on the sensitivity of ABT888 in the presence of either temozolomide (TMZ) or carboplatin (C). Methods: We examined the anti-tumor effects of ABT888 using PTEN null U87MG cell line and a transgenic mouse model (12V-Ha-Ras transgenic mice) of human glioma expressing V12 RAS (Can. Res. 2001). LacZ, GFAP and PCNA-positive primary astrocytes (derivative astrocytes, passage 100) were used for the study. The effect of the drugs were tested by (1) soft agar colony growth (2) 3D- On-Top assay (3) cell cycle analyses (4) vascular mimicry (real time) and (5) Western blots in a dose and time dependent manner. Results: Expression of the transgene in 12V-Ha-Ras mice (tail biopsy of mice from which derivative glioma cells cultures were established) and in the derivative glioma cells (established from the transgene-expressing mice) at different passages were confirmed by genotyping. Testing for astrocytic marker GFAP by ICC (&gt;95% GFAP positive at passage 10 and onwards). Both U87MG glioma cells and astrocytoma cells from 12V-Ha-Ras mice were positive for GFAP and PCNA. Our results show that (1) the combination of ABT888 plus TMZ is additive in reducing soft agar colony growth in both U87MG and V12RAS astrocytes (2) ABT888 sensitized both U87MG and V12RAS astrocytes to TMZ in 3D On-Top assay, (3) in both U87MG and V12RAS astrocytes the largest amount of G0 was observed following the combination of ABT888 plus C at 72 hours (4) ABT888 plus C as well as ABT888 plus TMZ blocked vascular mimicry in both U87MG and V12RAS astrocytes and (5) at 72 hours PTEN null U87MG cells exhibited an increase in pro-apoptotic cl-PARP and a decrease in anti-apoptotic MCL-1 following both combination treatments, an effect not observed in V12RAS astrocytes. At 48 hours the TMZ induced increase in PAR is blocked by ABT888, an effect more pronounced in U87MG cells. Conclusion: The data demonstrate that ABT888 sensitizes the effect of TMZ in PTEN null glioma cells. The functional link between tumor suppressor, PTEN and the sensitization of PARP inhibitor is being currently worked out utilizing glioma cells expressing PTEN to specifically address the role of PTEN nullness in the context of ABT888 in combination with TMZ, the results of which will be presented at the meeting.
Citation Format: Jennifer H. Carlson, Brian Leyland-Jones, David Martin, Pradip De, Nandini Dey. Does genetic background in glioma influence the sensitivity of tumor cells to a PARP inhibitor in the presence of different DNA damaging agents. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 5126. doi:10.1158/1538-7445.AM2014-5126