Abstract 3870: SLFN11 is a biomarker of sensitivity to PARP inhibition and chemotherapy in small cell lung cancer (SCLC)
Authors: Stewart C. Allison , Tong Pan , Cardnell Robert , Sen Triparna , Masrorpour Fatemah Mina , Fan Youhong , Wang Jing , Byers Lauren Averett 
Published: July 2016

Abstract
Small cell lung cancer (SCLC) is an aggressive disease that accounts for 14% of lung cancers. Very little progress has been made towards the treatment of SCLC in the past four decades and there are no established biomarkers to predict effective therapies for patients. In other cancers, SLFN11 plays an important role in sensitizing cancer cells to topoisomerase inhibitors, DNA synthesis inhibitors and alkylating agents. Previously, our lab identified an increase in poly (ADP-Ribose) polymerase 1 (PARP1), an enzyme involved in DNA damage repair, in SCLC patients and cell lines. PARP inhibitors demonstrate significant anti-tumor activity in cell line and animal models of SCLC and are currently being tested in clinical trials for SCLC patients. In Ewing sarcoma (EWS), SLFN11 has been proposed as a biomarker of PARP inhibitor response. Because both EWS and SCLC have high PARP levels and respond favorably to PARP inhibition, we hypothesized that SLFN11 may also be a biomarker for drug sensitivity in SCLC. Using SCLC patient tumors and a large panel of molecularly profiled SCLC cell lines, we investigated the expression of SLFN11 in SCLC and its association with in vitro sensitivity to PARP inhibition (olaparib) and chemotherapy. SLFN11 mRNA levels are significantly higher in SCLC patient tumors relative to normal lung tissue (P = 0.005). In a panel of 51 SCLC cell lines, higher SLFN11 protein expression correlates with both cisplatin (P&lt;0.001) and olaparib (PARP inhibitor; P = 0.05) sensitivity. In fact, SLFN11 is the top protein biomarker of cisplatin sensitivity in SCLC cell lines (of 171 proteins measured). Consistent with what has been shown for other cancer types, SLFN11 mRNA expression is also correlated with sensitivity to irinotecan (P = 0.005) and topotecan (P = 0.05) in SCLC, two drugs frequently used to treat this disease. Expression of other SLFN family members does not correlate with drug sensitivity. SLFN11 protein and mRNA levels are concordant (P&lt;0.001) and both demonstrate a bimodal expression pattern in SCLC cell lines which corresponds to cisplatin (protein, P&lt;0.001; mRNA, P = 0.005) and olaparib (mRNA, P = 0.05) sensitive (SLFN11 high) versus resistant (SLFN11 low) groups. In EWS, leukemia, colon, breast and prostate cancers, SLFN11 functions as an ETS transcription factor response gene. However, a panel of 26 ETS transcription factors did not correlate well with SLFN11 or PARP1 mRNA expression or cisplatin sensitivity, suggesting that SLFN11 expression may be regulated in a different manner in SCLC. In summary, SLFN11 is a predictor of sensitivity to chemotherapies routinely used in the treatment of SCLC, including alkylating agents (cisplatin) and topoisomerase inhibitors (irinotecan, topotecan). Moreover, SLFN11 predicts in vitro response to PARP inhibition, which may have important clinical implications given the ongoing clinical trials investigating PARP as a novel therapeutic target for SCLC.
Citation Format: C. Allison Stewart, Pan Tong, Robert Cardnell, Triparna Sen, Fatemah Mina Masrorpour, Youhong Fan, Jing Wang, Lauren Averett Byers. SLFN11 is a biomarker of sensitivity to PARP inhibition and chemotherapy in small cell lung cancer (SCLC). [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 3870.