Abstract P5-19-03: Olaparib plus carboplatin in combination with vandetanib inhibited the growth of BRCA-wt triple negative breast tumors in mice: Outside BRCA-box
Authors: Dey N , Sun Y , De P , Leyland-Jones B 
Published: August 2014

Introduction: PARP inhibition has emerged as one of the most exciting and promising ‘targeted’ therapeutic strategies in the treatment of advanced triple negative breast cancer (TNBC) – the intended ‘target,’ being DNA repair (Anders CK, 2010). Although olaparib is known to have antitumor activity in BRCA-related TNBC cells, a limited number of preclinical and clinical studies have shown antitumor efficacy of olaparib in non-BRCA-related BC (Shimo T, 2012). Understanding the biology of TNBC cells has identified molecular targets including RTK(s), such as EGFR.

Purpose: Here we tested the combination of a PARP inhibitor, olaparib (O) (AstraZeneca) plus carboplatin (C) with the EGFR/VEGFR inhibitor, vandetanib (V) (AstraZeneca) in a BRCA-wt TNBC model.

Methods: Athymic mice bearing TNBC (BRCA-wt VEGFR expressing MDA-MB231& MDA-MB468 [EGFR amplified/overexpressed]) xenograft tumors (200 mm3) were treated with O plus C in combination with V (Arms: vehicle control 1, vehicle control 2, C+O, V, C+O+V). In vitro effects of V in combination with O plus C (or temozolomide) on clonogenic growth (3D on-TOP assay), proliferation (MTT and CelltiterGLO), apoptosis (Apoptosis Array), cell signaling marker(s) (Western Blot), and tumor cell phenotypes (fibronectin-directed migration, matrigel-invasion, and vascular mimicry) were investigated in a panel of five BRCA-wt and BRCA-mutated TNBC cell lines. The effects of V were tested on (a) cell signaling marker(s), (b) angiogenesis marker (HIF-1alpha), and (c) angiogenesis related phenotypes (vitronectin-directed migration, and cord formation) in HUVEC.

Results: (1) O plus C in combination with V caused a regression of the in vivo growth of established tumors by 50% which was evident in both the BRCA-wt TNBC models tested. Interestingly, a marked suppression of the progression of tumor-growth was observed in the O plus C arm. (2) In vitro, V alone (10 µM) inhibited baseline as well as EGF-induced phosphorylation of AKT (S473/T308), S6RP, 4EBP1 and ERK. (3) TNBC cells exhibited higher sensitivity to V in clonogenic assays when combined with a 10 µM fixed dose of O and C/temozolomide. (4) A combination of V with O plus C increased cleaved caspase-3, PARP cleavage, and pro-apoptotic signals, while inhibiting vascular mimicry, migration, and invasion in MDA-MB231, MDA-MB468, and SUM149 cells. (5) Treatment with V blocked cord formation, migration, EGF-induced HIF-1α accumulation, and phosphorylation of AKT, 4EBP1, and ERK in HUVEC.

Conclusion: A profound anti-tumor efficacy of O plus C in combination with V in BRCA-wt TNBC model can be explained by a significant anti-proliferative/pro-apoptotic and anti-migratory/anti-invasive actions of the drugs (alone or in combination), as observed both in tumor cells as well as in endothelial compartments. The combination of O plus C plus V merits further investigation in TNBC.

Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P5-19-03.