Abstract P5-06-04: The PARP inhibitor niraparib demonstrated activity in patient-derived triple-negative breast cancer xenograft models with high homologous recombination deficiency (HRD) score

Triple negative breast cancer (TNBC), which comprises 15% of all breast cancers, has a poor prognosis and currently lacks effective treatment. TNBCs are highly proliferative, genomically unstable and share molecular characteristics with that of BRCA1/2 mutation driven breast cancer. Poly(ADP-ribose) polymerase-1 (PARP) is a key DNA repair enzyme that mediates single strand break (SSB) repair through the base excision repair (BER) pathway. PARP inhibitors have been demonstrated to selectively kill tumor cells that harbor BRCA1 and BRCA2 mutations. In addition, pre-clinical and preliminary clinical data suggest that PARP inhibitors are selectively cytotoxic for tumors with homologous recombination repair deficiency caused by dysfunction of genes other than BRCA1 or BRCA2. Niraparib is a potent, orally active PARP inhibitor that is being evaluated in Phase 3 clinical studies for ovarian cancer and BRCA related breast cancer. Previously, we demonstrated that a subset of basal breast cancer (BBC) patient-derived xenograft (PDX) models responded robustly to single agent niraparib treatment. To understand the selectivity observed, the samples from a collection of 37 BBC PDX models have been subjected to homologous recombination deficiency (HRD) analysis. HRD analysis is a DNA-based assay that is capable of detecting homologous recombination deficiency independent of its etiology. Genome-wide SNP data was generated from a custom Agilent SureSelect XT capture followed by sequencing on an Illumina HiSeq2500. SNP data was analyzed using three algorithms (LOH, TAI and LST scores), and the final HRD score is the sum of the LOH+TAI+LAST scores. Niraparib’s antitumor activity was investigated in patient derived BBC models with various HRD scores. The correlation between niraparib efficacy, HRD score and BRCA deficiency will be discussed. Citation Format: Yan Wang, Stefano Cairo, Olivier Deas, Anne-Renee Hartman, Joshua Jones, Alexander Gutin, Jerry Lanchbury, Zaina Sangale, Cara Solimeno, Jean-Gabriel Judde, Kirsten Timms, Keith Wilcoxen. The PARP inhibitor niraparib demonstrated activity in patient-derived triple-negative breast cancer xenograft models with high homologous recombination deficiency (HRD) score [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P5-06-04.