Abstract 5131: Escape from breast cancer therapy, are neuropilins the key

Abstract

Abstract The anti-VEGF antibody Bevacizumab (Bz) inhibits VEGF binding to VEGF-R1/2 and increases progression free survival in breast cancer patients. However, eventually tumors escape treatment control and we hypothesize that this may be because Bz does not prevent VEGF from binding to its alternative receptors, the neuropilins (Np1 & Np2). Gene expression of VEGF165, VEGF165b and the VEGF receptors, VEGF-R1/2, Np1 and Np2 in human dermal microvascular endothelial cells (ECs) and three breast cancer cell lines (MCF7, MDA-MB-231 & MDA-MB-436) was assessed using standard PCR techniques and protein expression by Western blot. The effects of 4 different Np1 binding peptides and Bz were assessed on EC differentiation (Matrigel assay of tubule formation), migration (scratch assay) and proliferation (MTS assay). PCR revealed that VEGF and Np1/Np2 are expressed in ECs and all three breast cancer cell lines whereas VEGF-R1/2 are expressed in ECs and MDA-MB-436/231 cells only. These data were also confirmed by Western blot analysis. EC differentiation when measured as tubule number or branch points was significantly inhibited (p<0.005) by three Np1 binding peptides (p2, p7b & p10) whereas a fourth peptide (p1) had no effect. In contrast there was no significant effect on EC or breast cancer cell proliferation, although p10 caused a slight inhibition of MDA-MB-436 proliferation. Bz demonstrated a profound inhibition of EC tubule formation (Bz: 52.8± 7.2 vs. control: 76.3±1.4) but did not significantly inhibit EC or breast cancer proliferation. The effects of the peptides on migration was variable, with all four peptides having a slight inhibitory effect on EC migration, whereas only p1 and p7b slightly reduced MDA-MB-231 migration and only p10 reduced MDA-MB-436 migration. These data are currently being confirmed using the Boyden chamber, an alternative migration assay and combination studies of Bz with the most effective Np1 binding peptides are being performed These data show that endothelial and breast cancer cells express Np1/Np2 receptors, and one Np1 binding peptide (p10: GSGSTRPPRRRR) inhibits both EC differentiation and breast cancer cell proliferation, and potentially EC and breast cancer cell migration in vitro, suggesting that this peptide may have therapeutic potential for breast cancer treatment. In vivo studies are evaluating the response to Np1 inhibition (p10) alone and in combination with Bz on angiogenesis in a breast tumor model using subcutaneous implantation of either MDA-MB-231 or MDA-MB-436 cells. Supported by Breast Cancer Campaign Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 5131. doi:10.1158/1538-7445.AM2011-5131