Abstract 3756: PARP inhibitor sensitivity in small cell lung cancer cell lines and patient-derived xenografts correlates with SLFN11 expression but not with structural homologous recombination deficiency

Poly-(ADP)-ribose polymerase (PARP) was identified as a potential novel therapeutic target for small cell lung cancer (SCLC) in two key proteomic studies. These findings led to the inclusion of a SCLC cohort in a Phase I study of talazoparib (BMN 673) - currently the most potent PARP inhibitor available - with promising efficacy signals. Identifying predictors of response to PARP inhibition would bring a needed therapeutic advance in this recalcitrant disease. PARP inhibition was first demonstrated to have marked efficacy in BRCA1/2 mutant cancers that are deficient in homologous recombination (HR). Large chromosomal structural alterations characteristic of these tumors can be quantitated by three correlated HR deficiency (HRD) metrics. We sought to determine if HRD would be a relevant predictive biomarker in SCLC. Thirty-six SCLC cell lines represented in the Cancer Cell Line Encyclopedia (CCLE) were interrogated for sensitivity to talazoparib, olaparib and cisplatin. We found significant correlation between these three pharmacologic agents and sought to determine response predictors. Three different HRD metrics were computed in these 36 SCLC cell lines using publically available CCLE Affymetrix SNP 6.0 array datasets. Surprisingly, none of these three measures of HRD were discriminatory for response to talazoparib in vitro. However, we found that after controlling for HRD and PARP1 target expression, expression of a single gene, SLFN11, was significantly correlated with talazoparib sensitivity as measured by the CCLE Affymetrix U133+2 arrays (q value = 0.008). After deriving SLFN11 knock-out SCLC cell lines by CRISPR/Cas9 gene editing, we found that loss of SLFN11 conferred resistance to talazoparib (IC50 >log difference) as compared to parental SLFN11 proficient cells. We then treated several SCLC patient-derived xenograft (PDX) models with talazoparib daily and found that SLFN11 expression in vivo was necessary but not sufficient for response. None of the SLFN11 low expressing PDXs responded to therapy, whereas 3/5 (60%) of SLFN11 high expressing PDXs demonstrated significant tumor growth inhibition of 54-75% after 21-28 days of daily treatment with talazoparib 0.3mg/kg. In conclusion, we demonstrate that SLFN11 expression is correlated with response to PARP inhibition in SCLC in vitro and in vivo. HRD structural aberration scores do not predict for in vitro PARP inhibitor sensitivity, however functional HR interrogation (such as RAD51 foci recruitment) may still be a relevant discriminator in addition to ongoing in vivo analysis. SLFN11 may be a pertinent predictive biomarker in SCLC for therapeutic response to PARP inhibition with considerable clinical implications. Citation Format: Benjamin H. Lok, Ying Feng, G. Karen Yu, Eric E. Gardner, Nadeem Riaz, Yuanbin (Kevin) Ru, Elisa de Stanchina, Simon N. Powell, Jerry Shen, John T. Poirier, Charles M. Rudin. PARP inhibitor sensitivity in small cell lung cancer cell lines and patient-derived xenografts correlates with SLFN11 expression but not with structural homologous recombination deficiency. [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 3756.