Abstract 4648: A cell line screen identifies TSPYL5 as marker for resistance to HDAC inhibitor treatment.
Authors: Garrick Brett , Schwartz Erin , Ning Yuhong , Tang Lin , DiMarino Jorge , Trowe Torsten B. 
Published: August 2014

Abstract
Romidepsin is a class I selective HDAC inhibitor approved for the treatment of cutaneous T cell lymphoma (CTCL) and peripheral T cell lymphoma (PTCL) in the US. In contrast to the 30% response rate to romidepsin in these malignancies, only rare responses have been reported in solid tumor clinical trials. A molecular understanding of the basis for romidepsin's anti-tumor effects could lead to the development of predictive biomarkers to select patients who are most likely to benefit from this agent. As an initial step towards identifying candidate predictive biomarkers, we undertook an in vitro screen for romidepsin sensitivity in over 100 cell lines representing hematologic malignancies and eight different solid tumors. Here, we report the results of this screen and its use, in conjunction with gene expression profiling (GEP) to identify TSPYL5, a novel candidate biomarker, as a predictor of resistance to romidepsin.
A limitation of previously reported cell viability screens using romidepsin has been the use of prolonged incubation times which vastly exceed the clinical exposure of tumor cells to this agent. Moreover, earlier screens have based sensitivity on cell line EC50/IC50 values, suggesting that romidepsin is broadly active in solid tumors within a narrow range of sensitivities which is not consistent with clinical data in solid tumors. For our screen, we utilized a 6 hour drug exposure which is similar to the exposure of patients receiving the drug. Sensitivity to romidepsin treatment after 72 hours was assessed by Cell Titer Glo and was expressed as a composite score incorporating the IC50 and % growth inhibition or cell kill (S score).
As expected, based on clinical data, the most sensitive lines (lowest S scores) are derived from hematologic malignancies, including T cell lymphomas. Solid tumor cell lines exhibit a broad range of S scores. We compared the baseline GEP of sensitive and resistant lines to identify differentially expressed genes associated with sensitivity or resistance. Two genes strongly correlated with resistance were ABCB1, encoding a drug efflux pump implicated in resistance to romidepsin and TSPYL5, encoding a protein that modulates P53 stability via interaction with the USP7 deubiquitinase. Cell lines with readily detectable expression of TSPYL5 are resistant to treatment with romidepsin. We observed a similar relationship between TSPYL5 expression and resistance to panobinostat, a pan-HDAC inhibitor and in primary human tumor cells treated with romidepsin. Cell lines in which TSPYL5 was knocked down using shRNA show increased sensitivity to treatment. Our work identifies potentially novel applications for HDAC inhibitors in the treatment of certain solid malignancies. These data may be useful to guide clinical development or as a tool in further research aimed at understanding the mode of action of HDAC inhibitors.
Citation Format: Brett Garrick, Erin Schwartz, Yuhong Ning, Lin Tang, Jorge DiMarino, Torsten B. Trowe. A cell line screen identifies TSPYL5 as marker for resistance to HDAC inhibitor treatment. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4648. doi:10.1158/1538-7445.AM2013-4648