Abstract B042: Differential effects of erbB3 and IGF-1R signaling on lapatinib resistance acquired by the erbB2-overexpressing breast cancer cells refractory to trastuzumab

Introduction: Resistance to erbB2-targeted therapy frequently occurs in the treatment of erbB2-overexpression breast cancer. We previously showed that the heterotrimerization of erbB2, erbB3, and IGF-1 receptor (IGF-1R) resulted in trastuzumab resistance. Enhanced activation of the downstream signaling, such as PI3K/Akt and Src, was related to the resistant phenotype. Specific knockdown of either erbB3 or IGF-1R significantly reversed the resistance, suggesting that both erbB3 and IGF-1R signaling contributed to trastuzumab resistance. However, it is not known whether the trastuzumab-resistant breast cancer cells are also refractory to lapatinib, another targeted therapeutic against erbB2. It remains unclear whether the erbB3 and IGF-1R signaling may differentially influence the lapatinib sensitivity. Material and Methods: Cell growth (MTS) assays were used to determine cell viability. Quantification of cells undergoing apoptosis was measured by a specific apoptotic ELISA. Western blot analyses were performed to assess the expression and activation of proteins. Lentiviral vector containing shRNA was used to specifically knockdown erbB3 or IGF-1R. Results: The acquired trastuzumab-resistant breast cancer cells (SKBR3-pool2 and BT474-HR20 derived from SKBR3 and BT474 cells, respectively) also showed cross-refractoriness to lapatinib. The IC50s of lapatinib in SKBR3 and SKBR3-pool2 cells were 0.043±0.003 μmol/L and 0.15±0.003 μmol/L, respectively. The IC50s of lapatinib in BT474 and BT474-HR20 cells were 0.054±0.009 μmol/L and 0.12±0.006 μmol/L ( p <0.05), respectively. These data suggest heterotrimerization of the erbB2, erbB3, and IGF-1R may also lead to lapatinib resistance. To further elucidate the role of erbB3 and IGF-1R in the lapatinib resistance, the lentiviral vectors containing specific shRNA were used. Specific knockdown of erbB3 in both SKBR3-pool2 and BT474-HR20 cells significantly overcame the resistant phenotype, and dramatically re-sensitized the cells to lapatinib-induced apoptosis. Meanwhile, inactivation of the downstream PI3K/Akt signaling was clearly detected. In contrast, specific knockdown of IGF-1R did not alter the cells' refractoriness to lapatinib treatment. While the levels of phosphorylated Src (P-Src) were reduced upon IGF-1R knockdown, the levels of P-Akt, however, remained unchanged. Conclusions: The erbB2-overexpressing breast cancer cells resistant to trastuzumab also show refractory to Lapatinib, which may be attributed to the heterotrimerization of erbB2, erbB3, and IGF-1R as well. Our data indicate that the erbB3 receptor plays an important role in both trastuzumab and lapatinib resistances mainly through activation of the PI3K/Akt signaling. However, the IGF-1R, via activation of the Src kinase, only leads to trastuzumab resistance without affecting the cells' sensitivity to lapatinib. To the best of our knowledge, this is the first report experimentally demonstrating that the erbB3 and IGF-1R signaling differentially regulates lapatinib sensitivity in trastuzumab-resistant breast cancer cells. These findings may facilitate the development of novel therapeutic regimens for breast cancer treatment. Citation Format: Hui Lyu, Jingcao Huang, Youngseok Lee, Bolin Liu. Differential effects of erbB3 and IGF-1R signaling on lapatinib resistance acquired by the erbB2-overexpressing breast cancer cells refractory to trastuzumab. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Breast Cancer Research: Genetics, Biology, and Clinical Applications; Oct 3-6, 2013; San Diego, CA. Philadelphia (PA): AACR; Mol Cancer Res 2013;11(10 Suppl):Abstract nr B042.