Abstract P4-08-04: Abcc10 status affects proliferation, metastases and tumor sensitivity

Abstract

Abstract Background: It has been proposed that therapy-induced overexpression of ATP-binding cassette (ABC) drug efflux pumps promotes resistance in many drug-treated cancers. While early studies focused on overexpression and activity of the P-glycoprotein (Pgp) pump, a structurally distinct group of ABC efflux pumps, known as the Multidrug Resistance Proteins (MRPs;ABCCs), have been gaining increasing attention as alternative sources of resistance. There are 9 ABCC family members (ABCC1-6, 10–12), and we have previously shown that ABCC10 is unique because it confers resistance to a wide variety of anticancer agents including taxanes, vinca alkaloids and nucleoside-based analogs (Hopper-Borge et al, 2004, Hopper-Borge et al, 2009). Importantly we have shown that Abcc10 null mice are sensitized to taxanes (Hopper-Borge et al, Cancer Research, 2011). This is the first transporter whose loss results in in vivo tissue sensitivity to taxanes. Methods & Results: We recently bred a PyVmT mammary tumor model to our Abcc10 gene disrupted mice to investigate Abcc10's in vivo activities regarding breast cancer resistance mechanisms. We have observed that Abcc10+/+ (WT) status limits the rate of tumorigenesis (p = 0.020) and that WT tumors are more metastatic compared to Abcc10−/− (KO), (p = 0.0489). To better understand the potential resistance mechanisms in this model we determined the expression levels of relevant transporters with qRT-PCR and found no significant differences between WT and KO. The PI3K-AKT-mTOR, a major signaling pathway involved in breast cancer progression has been connected to ABCCs (Tazzari, et al, 2007), and we observed upregulation of AKT in KO versus WT mammary tumor cell lines via western analyses. Therefore, we decided to ask if Abcc10 status affects proliferation, attachment, and/or migration (CyQuant, Invitrogen and xCELLigence, Roche). We showed that WT cell lines grow 3 times slower compared to KO. For migration kinetic we observed that KO cell lines were more active compared to WT. To determine the impact of Abcc10 loss in vivo we injected SCID mice with 3 WT or KO mammary tumor derived cell lines and treated tumors with docetaxel or vehicle. Tumors derived from WT and KO mice were both responsive to docetaxel (WT, p = 0.003 and KO, p = 0.001). However, over 21 days, the WT tumors were reduced by 50% compared to KO reduction of 86%. Kaplan-Meier survival analysis of treated/untreated SCID mice reveals that Abcc10 status is related to a poorer prognosis (KO p < 0.0001, WT p = 0.0648). Conclusion: Here we show that Abcc10 status limits tumorigenesis (proliferation, attachment, migration) of MMTV-PyVmT mammary tumor model and Abcc10+/+ tumors are more metastatic compared to KO tumors. Thus Abcc10 may be involved in breast cancer development and progression. mRNA expression analysis of ABC transporters in mammary tumors derived cell lines reveals that other transporters do not compensate for Abcc10 loss. In vivo experiments show that treatment with docetaxel is more effective for KO tumors compared to WT tumors, suggesting Abcc10 is a breast cancer resistance factor. Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P4-08-04.