Abstract 5178: Determinants of response to temozolomide in an exceptionally sensitive patient derived model
Authors: el Touny Lara H. , Connelly John , Hose Curtis , Monks Anne , Burkett Mark W. , Harris Erik , Delosh Rene’ M. , Laudeman Julie , Ogle Chad , Reinhart Russell , Selby Michael , Silvers Thomas , Evans David , Newton Dianne , Stockwin Luke , Hollingshead Melinda , Parchment Ralph , Doroshow James H. , Teicher Beverly , Rapisarda Annamaria 
Published: July 2016

Abstract
Application of precision medicine to cancer treatment utilizes cutting-edge genomic sequencing techniques to identify specific mutations in tumors that can be matched to targeted therapies designed to treat those abnormalities. To complement NCI-MPACT, an ongoing molecular profiling-based clinical trial (NCT01827384), we used cell lines developed from several patient-derived xenograft (PDX) models to examine response to, and potential biomarkers for, the regimens of the 4-arm MPACT trial: veliparib (VLP)/temozolomide (TMZ), AZD1775/carboplatin, everolimus and trametinib. In vitro sensitivity of the PDX-derived cell lines to clinically achievable concentrations of these MPACT drugs (combinations and single agents) was examined in classic 2D cultures (monolayer on plastic) and 3D cultures (spheroids generated in ultra-low attachment culture plates). Responses in 2D and 3D cultures were similar after 7 days of drug exposure. Moreover, adding VLP (1.7μM or 5μM) in combination with TMZ did not enhance TMZ cytotoxicity. A bladder cancer cell line developed from a PDX model (BLX) showed exceptional sensitivity to TMZ (IC50 ∼ 3-5μM) compared to a lung cancer cell line (also produced from a PDX; LUX) which was insensitive (IC50 &gt;40 μM). Loss of MGMT expression in glioma and possibly in colorectal carcinoma is considered a predictive biomarker for response to alkylating agents, such as dacarbazine and TMZ. Indeed, we could not detect MGMT protein expression in BLX, while MGMT was present at high levels in LUX. To elucidate unique determinants of BLX hypersensitivity to TMZ beyond MGMT expression, we examined DNA damage responses elicited in this model. Under both 2D and 3D conditions, exposure to TMZ (13 and 40μM) for various times (4, 8, 12, 24, 48, 72 and 96 hrs) induced γH2AX after 24 hr, while PARP1 cleavage was induced as early as 48 hrs after drug addition indicating the onset of apoptosis. TMZ activated ATR and ATM signaling pathways especially at the later time points, paralleling the pharmacodynamics of PARP cleavage. Moreover, concordant with the sensitivity profiles, signaling activation in 2D and 3D conditions was similar. In contrast, none of these pathways were activated in the TMZ non-responsive LUX model. Cell line models developed from PDXs with intermediate MGMT expression are being evaluated.
A key to success of personalized medicine in oncology will be the identification of genomic determinants that predict which individual cases will show exceptional responses to particular treatments, and our data suggest that PDX cell line models may be valuable for elucidating molecular and genetic characteristics of response to specific drugs and for the identification of predictive biomarkers.
Funded by NCI Contract No. HHSN261200800001E. This research was supported, in part, by the Developmental Therapeutics Program in the Division of Cancer Treatment and Diagnosis of the National Cancer Institute.
Citation Format: Lara H. el Touny, John Connelly, Curtis Hose, Anne Monks, Mark W. Burkett, Erik Harris, Rene’ M. Delosh, Julie Laudeman, Chad Ogle, Russell Reinhart, Michael Selby, Thomas Silvers, David Evans, Dianne Newton, Luke Stockwin, Melinda Hollingshead, Ralph Parchment, James H. Doroshow, Beverly Teicher, Annamaria Rapisarda. Determinants of response to temozolomide in an exceptionally sensitive patient derived model. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 5178.