Abstract 3349: Crosstalk between Runx2 regulatory network and insulin-like growth factor receptor/Akt signaling pathway in bone metastasis of breast cancer

Proceedings: AACR Annual Meeting 2014; April 5-9, 2014; San Diego, CA The metastasis of breast cancer cells to bones is a leading cause of cancer-related deaths. The bone microenvironment presents a vital source of several growth factors that could promote survival and proliferation of metastatic cancer cells. The bone-derived insulin-like growth factor-1 (IGF-1) binds to insulin-like growth factor receptor (IGF-1R) to initiate intracellular signaling. The downstream signaling events in response to IGF-1R stimulation include activation of Phosphatidyl Inositol 3’ Kinase (PI3K) and Mitogen Activated Protein Kinase (MAPK) pathways. However, the inhibition of these signaling pathways has shown modest benefit in recent clinical trials necessitating the need to identify regulatory mechanisms to successfully block breast cancer-associated bone metastasis. The Runt-related transcription factor, Runx2, is required for normal bone development but is also aberrantly expressed at higher levels in invasive mammary epithelial cells and promotes invasive properties. Previously, we have identified a mechanism wherein Runx2 promotes survival of parental population of invasive breast cancer MDA-MB-231cells by promoting phosphorylation of serine/threonine kinase Akt (pAkt) via mammalian target of rapamycin complex-2 proteins. To determine the implications of Runx2-mediated pAkt regulation in bone metastasis of breast cancers, we harvested Runx2 knockdown or control MDA-MB-231 cells from bones 7 weeks post intracardiac injections in NOD/SCID mice. The gene and protein expression levels of IGF-1R/Akt pathway effectors in the bone seeking subpopulation were determined by real-time PCR and western blotting approaches. The bone-derived Runx2 knockdown cells showed increased IGF-1Rβ levels compared to controls. The Runx2 knockdown MDA-MB-231 cells showed an increase in pIGF1R-β and pAkt levels in response to IGF-1 stimulation that could be inhibited with IGF-1Rβ inhibitor OSI-906 (Linsitinib). However, despite inhibition of IGF-1R and Akt activity with OSI-906 treatment, no alterations were observed in growth or survival of bone-seeking cells. Interestingly, in contrast to IGF-1Rβ and pAkt, the Erk 1/2 levels were reduced in bone-derived Runx2 knockdown MDA-MB-231 cells compared to parental MDA-MB-231 cells. The treatment of cells with Erk 1/2 inhibitor PD184161 reduced cell proliferation and clonogenic potential. Furthermore, the Runx2 protein levels were also reduced in bone seeking subpopulation compared to parental MDA-MB-231cells. Taken together, our studies indicate Runx2-mediated suppression of IGF-1Rβ and Akt but upregulation of Erk signaling in bone seeking breast cancer cells compared to parental MDA-MB-231 cells. Our results suggest that the growth of bone metastatic cancer cells could be effectively blocked by inhibition of Runx2 and Erk pathway. Citation Format: Manish Tandon, Zujian Chen, Jitesh Pratap. Crosstalk between Runx2 regulatory network and insulin-like growth factor receptor/Akt signaling pathway in bone metastasis of breast cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3349. doi:10.1158/1538-7445.AM2014-3349