Introduction: Clinical trials examining the addition of PARP inhibitors (PARPi) to treatment regimens for non-small cell lung cancer (NSCLC) are underway. Of note, these trials are not biomarker driven, and so any benefit may be obscured due to heterogeneity of tumor responses. The first FDA approved PARPi, olaparib, was approved specifically for ovarian cancer patients with germline mutations in BRCA1 or 2. These patients have tumors that show homologous recombination deficiency (HRD), a DNA damage repair pathway defect that confers synthetic lethality in the setting of PARPi therapy. Whether HRD may serve a biomarker for PARPi sensitivity in NSCLC, however, is unclear.

Materials and Methods: Based on prior studies, NSCLC cell lines were classified as 1) HR proficient (A549, NCI-H23, NCI-H460, NCI-H522, NCI-H1299), 2) HR deficient due to early defects in the pathway as evidenced by decreased cisplatin-induced RAD51 focus formation (NCI-H1563, NCI-H1915, NCI-H2087, NCI-H2126) or 3) HR deficient due to late defects in the pathway as evidenced by impaired resolution of ionizing radiation (IR) induced RAD51 and γ-H2AX foci (Calu-1, Calu-6, HCC827, NCI-H520, SK-LU-1). NSCLC cells expressing doxycycline-inducible BRCA1 or 2 shRNA were generated by Tet-pLKO-puro lentiviral transduction. Cell viability assays to determine olaparib IC50 values were performed using CellTiter-Glo and MTS. Gene expression data were extracted from published datasets including CCLE, GSE32665 and TCGA, and expression levels of select genes were assayed by RT-qPCR.

Results: BRCA1/2 shRNA knockdown inhibited IR-induced RAD51 focus formation in HR proficient NSCLC cells. This also induced PARPi sensitivity (A549 olaparib IC50 63 µM -> 1.2 µM with BRCA1 and 18 µM -> 3.4 µM with BRCA2 knockdown). Because BRCA alterations are uncommon in NSCLC, however, other HRD biomarkers were explored. There was no statistically significant difference in PARPi sensitivity among cell lines grouped by cisplatin-induced RAD51 focus formation or resolution of IR-induced RAD51 or γ-H2AX foci. BRCA deficient breast and ovarian cancers overexpress POLQ, which drives DNA repair toward non-HR-dependent pathways including alternative end joining. Like these cancers, NSCLC tumors overexpressed POLQ and RAD54L compared to normal lung, p < 0.001. Expression of these two genes correlated highly in multiple datasets, e.g., r² = 0.69 and p < 0.001 in TCGA adenocarcinomas. High RAD54L expression tended to correlate with low olaparib IC50 values, r = -0.56, p = 0.059. NCI-H1299 and SK-LU-1, which showed the highest RAD54L expression, also showed the highest olaparib sensitivity.

Conclusion: Although certain HRD biomarkers including RAD51 focus formation and impaired resolution did not predict NSCLC olaparib sensitivity, other potential biomarkers, such as BRCA1/2 loss of function and elevated RAD54L expression, may serve as potential HRD-related biomarkers.

Citation Format: Peter V. Deraska, Hunter D. Reavis, Shelby Labe, Alan D. D'Andrea, David Kozono. Homologous recombination pathway-based biomarkers for treatment of non-small cell lung cancer with PARP inhibitors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4189. doi:10.1158/1538-7445.AM2017-4189