Abstract P6-02-08: Novel flavonoid Anto-028 shows promising antitumor activity in preclinical models of breast cancer

Abstract

Abstract New drugs are required to treat both endocrine resistant and triple negative breast cancers (TNBC). Among new structures being investigated are flavonoids, which are natural polyphenolic compounds with antitumor properties. Clinical trials are underway to assess their application as chemopreventatives and as sensitisers to chemotherapy. Among flavonoids, myricetin has shown particular promise, inducing cell cycle arrest and mitochondrial-dependent apoptosis in cancer cell line models. In this study we evaluated a novel series of myricetin-derived flavonoids with improved antioxidant and mitochondrial targeting properties. We hypothesised that these compounds might have potential in breast cancer management and in particular to treat estrogen receptor positive (ER+) tumors, in which estrogen controls tumor growth at least partially through oxidative stress-related mitochondrial signalling. We first assessed the effect of 8 flavonoids on 4 breast cancer cell lines (MDA-MB-231, BT-549, MCF-7 and HBL-100) and 3 MCF-7-derived cell lines with reduced sensitivity to endocrine therapy (LCC-1/LCC-2/LCC-9). The novel flavonoids were designed to assess the involvement of redox potential and mitochondrial targeting through selective structure-activity changes. Anto-028 was the most potent compound identified with 4 to 140-fold lower IC50 values than myricetin, as shown by sulforhodamine B (SRB) assays applied to assess antiproliferative effects. Although endocrine-resistant cell lines were less sensitive, Anto-028 exerted a strong, ER-independent antiproliferative effect on both ER+ and TNBC cell lines, with IC50 values in the low micromolar range. Treatment for 8 hours exerted dose-dependent reduction in cell viability and induction of cytotoxicity and apoptosis, with a 2 to 5-fold increase in caspase activation, as detected by luminescence-based plate assays. The involvement of reactive oxygen species (ROS) regulation in these effects was demonstrated by plate-based assays and microscopic detection of fluorescent probes for mitochondrial hydrogen peroxide and superoxide. Results indicated that different species of ROS are sequentially generated by treatment with a range of concentrations of Anto-028, suggesting a possible biphasic effect of the drug at different concentrations. Experiments in mice implanted with subcutaneous MDA-MB-231 xenografts showed that Anto-028 can significantly inhibit tumour growth in vivo with associated changes in percentage of viable areas within the xenografts (from 56% in controls to 37% in mice treated with 25mg/kg/day of Anto-028) and reduced Ki67 proliferation index (from 60% in controls to 36% in treated xenografts). Current studies are assessing combinatorial effects with TRAIL and chemotherapy which have produced synergistic effects in ovarian cancer models, with nanomolar concentrations of Anto-028 sensitising resistant cells to induce strong, significant antiproliferative effects. In conclusion, Anto-028 is a novel flavonoid with promising antitumor activity in preclinical models of breast cancer. Citation Format: Carlos Martinez-Perez, Carol Ward, Peter Mullen, Graeme Cook, Donald McPhail, Arran K Turnbull, David J Harrison, Simon P Langdon. Novel flavonoid Anto-028 shows promising antitumor activity in preclinical models of breast cancer [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 P6-02-08.