Small cell lung cancer (SCLC) is one of the most aggressive forms of lung cancer with a 5-year survival rate of less than 10%. Despite the initial high response rate to the frontline platinum based chemotherapy, relapse is common and rapid. The clinical activity of PARP inhibitors has shown good correlation with platinum sensitivity in breast and ovarian cancers. Thus, there is good rationale to test PARP inhibitors in SCLC. BGB-290 is a novel PARP-1/2 inhibitor, which is currently under clinical investigation in solid tumors. In this study, we evaluated the in vitro and in vivo activities of BGB-290, and its combination activity with chemotherapies in patient biopsy derived SCLC xenograft models.

In the biochemical assays, BGB-290 demonstrated great potency for PARP1/2 (IC50 = 0.83 and 0.11 nM, respectively) and high selectivity over other PARP enzymes. The DNA-trapping activity of BGB-290 was measured in a fluorescence polarization (FP) binding assay. BGB-290 showed potent DNA-trapping activity with IC50 of 13 nM. In the cellular assays, BGB-290 inhibited intracellular PAR formation with an IC50 of 0.24 nM. Tumor cell lines with homologous recombination defects were profoundly sensitive to BGB-290. Oral administration of BGB-290 resulted in time-dependent and dose-dependent inhibition of PARylation in MDA-MB-436 (BRCA1 mutant) breast cancer xenograft, correlating well with the tumor drug concentrations. Compared to olaparib, BGB-290 induced PAR inhibition was more sustained. Consistent with this finding, BGB-290 demonstrated excellent anti-tumor activity in this model, over 10-fold more potent than olaparib.

In a panel of 7 SCLC cell lines tested, 3 of them were sensitive to BGB-290. SCLC primary tumor models were established in house using patient biopsy samples obtained from Beijing Cancer Hospital. The anti-tumor activities of BGB-290 as single agent or in combination with etoposide/carboplatin (E/C) were evaluated in 8 SCLC primary tumor models. BGB-290 showed weak single agent activity in these models. Six of the 8 models (75%) were sensitive to E/C treatment, consistent with the clinical response observed in these patients. Addition of BGB-290 as concomitant treatment or maintenance therapy significantly prolonged the response duration in these chemo-sensitive models. In the two chemo-insensitive models, BGB-290 and E/C combo was less effective. Addition of BGB-290 to the chemo regiment was well-tolerated throughout the study.

In conclusion, BGB-290 is a potent and selective inhibitor of PARP1/2. It is highly active both in vitro and in vivo in BRCA mutant tumors. BGB-290 has also demonstrated good combination activity with chemotherapeutics in patient biopsy derived SCLC models, supporting further investigation in the clinic.

Citation Format: Zhiyu Tang, Ye Liu, Qin Zhen, Bo Ren, Hexiang Wang, Zhenyan Shi, Wenfeng Gong, Yong Liu, Xing Wang, Yajuan Gao, Fenglong Yu, Yiyuan Wu, Bing Jiang, Xuebing Sun, Min Wei, Changyou Zhou, Lusong Luo, Zhengxiang Li, Jiangyong Yu, Jun Zhao, Jie Wang, Lai Wang. BGB-290: A highly potent and specific PARP1/2 inhibitor potentiates anti-tumor activity of chemotherapeutics in patient biopsy derived SCLC models. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1653. doi:10.1158/1538-7445.AM2015-1653