Abstract 716: Targeting Mek-Erk pathway abrogates hypoxia-mediated lapatinib resistance in ErbB2-positive breast cancer cells

Abstract

Abstract Overexpression/amplification of the tyrosine kinase ErbB2 is often observed in breast cancers. ErbB2 expression activates EGFR signaling pathway promoting tumorigenesis. Breast cancer ErbB2-positive patients are treated with lapatinib, a dual EGFR/ERBB2 inhibitor. Despite lapatinib clinical efficacy, acquired resistance has been reported and its mechanism is poorly understood. Another factor that is associated with mammary tumors is hypoxia. Hypoxia stabilizes hypoxia inducible factor 1 (HIF-1), a transcription factor that regulates cell growth, proliferation and survival. As a result, hypoxic tumors are often chemoresistant. Here, we show that hypoxia decreases lapatinib-mediated growth inhibition and apoptosis in three-dimensional cultures. In agreement with this data, hypoxia also promotes activation of signaling pathways downstream from ErbB2/EGFR including AKT and ERK in the presence of lapatinib. This protective effect depends on HIF-1 and can be abrogated by HIF-1 RNAi. Moreover stable overexpression HIF-1 in ErbB2-expressing cells under normoxic conditions is sufficient to rescue cell proliferation and survival and maintain ERK and AKT signaling in the presence of lapatinib. We also show that activation of ERK signaling is required for hypoxia-mediated lapatinib resistance and inhibition of MEK (a kinase upstream of Erk) reverses hypoxia protective effect on ErbB2-expressing cells. One potential mechanism of how hypoxia/HIF-1 may lead to activation of ERK pathway is via regulation of dual-specificity phosphatase 2 (DUSP2). DUSP2 is a negative regulator of ERK pathway. Here we demonstrate that cells exposed to hypoxia have decreased levels of DUSP2 and it correlate with increased activation of Erk signaling. Moreover, reducing DUSP2 expression alone in ErbB2-positive breast cancer cells is sufficient to reduce lapatinib-mediated effects. And DUSP2 overexpression abrogates hypoxia-mediated protective effect on ErbB2-expressing cells treated with lapatinib. All these data suggests that targeting MEK-Erk signaling pathway may reverse hypoxia mediated lapatinib resistance and might be a viable option for lapatinib resistant ErbB2-posive tumors. Indeed, a combination of lapatinib and an FDA approved MEK inhibitor trametinib abrogates hypoxia protective effect on cell growth inhibition and apoptosis in three dimensional (3D) cultures. Thus targeting MEK/ERK pathway in hypoxic breast cancer may improve an anti-ErbB2 therapy in breast cancer. Citation Format: Sergey Karakashev, Mauricio Reginato. Targeting Mek-Erk pathway abrogates hypoxia-mediated lapatinib resistance in ErbB2-positive breast cancer cells. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 716. doi:10.1158/1538-7445.AM2015-716