American Association for Cancer Research
00085472can122440-sup-fig1.pdf (125.35 kB)

Supplementary Figure 1 from Trastuzumab-Resistant Cells Rely on a HER2-PI3K-FoxO-Survivin Axis and Are Sensitive to PI3K Inhibitors

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journal contribution
posted on 2023-03-30, 21:53 authored by Anindita Chakrabarty, Neil E. Bhola, Cammie Sutton, Ritwik Ghosh, María Gabriela Kuba, Bhuvanesh Dave, Jenny C. Chang, Carlos L. Arteaga

PDF file - 125K, Inhibition of trastuzumab-resistant cells by RNAi of p110 alpha and beta



The antibody trastuzumab is approved for treatment of patients with HER2 (ERBB2)-overexpressing breast cancer. A significant fraction of these tumors are either intrinsically resistant or acquire resistance rendering the drug ineffective. The development of resistance has been attributed to failure of the antibody to inhibit phosphoinositide 3-kinase (PI3K), which is activated by the HER2 network. Herein, we examined the effects of PI3K blockade in trastuzumab-resistant breast cancer cell lines. Treatment with the pan-PI3K inhibitor XL147 and trastuzumab reduced proliferation and pAKT levels, triggering apoptosis of trastuzumab-resistant cells. Compared with XL147 alone, the combination exhibited a superior antitumor effect against trastuzumab-resistant tumor xenografts. Furthermore, treatment with XL147 and trastuzumab reduced the cancer stem-cell (CSC) fraction within trastuzumab-resistant cells both in vitro and in vivo. These effects were associated with FoxO-mediated inhibition of transcription of the antiapoptosis gene survivin (BIRC5) and the CSC-associated cytokine interleukin-8. RNA interference–mediated or pharmacologic inhibition of survivin restored sensitivity to trastuzumab in resistant cells. In a cohort of patients with HER2-overexpressing breast cancer treated with trastuzumab, higher pretreatment tumor levels of survivin RNA correlated with poor response to therapy. Together, our results suggest that survivin blockade is required for therapeutic responses to trastuzumab and that by combining trastuzumab and PI3K inhibitors, CSCs can be reduced within HER2+ tumors, potentially preventing acquired resistance to anti-HER2 therapy. Cancer Res; 73(3); 1190–200. ©2012 AACR.