Abstract 1622: Efficacy of mitotic spindle directed therapies in orthotopic models of human breast cancer

Abstract Aim: Stathmin is one of the key regulators of the mitotic spindle and the microtubule cytoskeleton. Stathmin is expressed at high levels in breast cancer (BC) & its overexpression is linked to BC progression. Thus, stathmin provides an attractive molecule to target in therapies that disrupt the mitotic apparatus. We previously showed that stathmin inhibition could suppress the malignant phenotype of BC cells in vitro. Here, we asked whether inhibition of stathmin could suppress BC growth in orthotopic models. Methods: We used MDA-MB-231 BC cells, which are highly invasive and tumorigenic when injected orthotopically in the mammary fat pad (m.f.p). To target stathmin, we developed a bicistronic adenoviral vector (Ad. Rz. GFP) that coexpresses green fluorescent protein (GFP) & a ribozyme (Rz) that selectively degrades stathmin mRNA. Results & Discussion: We first examined the effects of ex vivo gene transfer of anti-stathmin ribozyme on tumorigenicity of MDA-MB-231 cells in nude mice. Nine mice were divided into three groups of three mice each. Group I was injected orthotopically with 5×106 uninfected MDA-MB-231 cells in m.f.p in two pairs of mammary gland. Similarly Group II & group III mice were injected orthotopically in two pairs of mammary gland with 5×106 MDA-MB-231 cells that were pre-infected with control Ad.GFP (moi 100) & Ad. Rz. GFP (moi 100) adenovirus, respectively. After 6-8 weeks, group I & group II mice formed tumors at all four injection sites that ranged from 0.4 to 1.0 cm in size. In contrast, the group III mice that were injected with cells infected with the anti-stathmin adenovirus failed to form tumors at any of the injection sites. We also examined the therapeutic efficacy of the anti-stathmin adenovirus in pre-established tumors derived from MDA-MB-231 cells. Nine animals bearing established orthotopic MDA-MB-231 xenografts were divided into three groups of 3 mice each. We initiated treatment by intratumoral injections after the mice developed tumors about 0.3-0.4 cm in size. Group 1 was injected with PBS, group II with the control Ad.GFP virus (108 viral particles, once/week, for a total of 3 injections) & group III with the anti-stathmin adenovirus (108 viral particles, once/week, for a total of 3 injections). The animals were then closely monitored for the rate of tumor growth for 60 days. Nearly 62 % of the tumors injected with the anti-stathmin adenovirus regressed completely & 38% stopped growing throughout the period of close observation. In contrast, tumors that were injected with PBS or the control adenovirus continued to grow & reached large sizes. This data demonstrates that anti-stathmin therapy can mediate profound anti-tumorigenic effects in vivo. Since anti-tumor drugs like taxol that is widely used against BC also exert its effect through the mitotic pathway, anti-stathmin therapy may be combined with taxol to provide synergistic anti-tumor effects. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1622.