Abstract 1327: IGF-I and insulin signaling enhances levels of choline kinase in breast cancer cells: Implications for developing noninvasive magnetic resonance spectroscopy of choline containing compounds as a biomarker of response to IGF1R targeted therapy.

Insulin-like growth factor I (IGF-I) and insulin signal through the type I IGF receptor (IGF1R) and insulin receptor (IR) respectively. Multiple drugs targeting IGF1R and IGF1R/IR are being tested in clinical trials. Biomarkers that enable the selection of patients with IGF driven tumors or the monitoring of response to this therapy have not yet been identified. Previously, we found that intratumoral total choline (tCho) metabolites decreased in MCF-7 xenograft tumors in mice twenty-four hours following administration of an inhibitory antibody against IGF1R. The tCho was measured by 1H magnetic resonance spectroscopy (MRS) and included three species of choline containing compounds, choline, phosphocholine (pCho), and glycerophosphocholine. These data suggested that noninvasive measurement of tCho may be a useful surrogate marker of response to IGF1R targeted therapy. The objective of the current study is to investigate whether there is a mechanistic link between IGF-I and insulin signaling and choline phospholipid metabolism to understand if decreased tCho levels could be a specific marker of inhibition of IGF signaling in cancer cells. In this study, we examined the effect of IGF-I and insulin signaling on levels of choline kinase (CK). CK is the enzyme that generates pCho, one of the species measured by MRS in our prior in vivo study. Estrogen receptor positive (ER+) human breast cancer cell lines (MCF-7, T47-D, ZR-75-1) and triple negative cells (MDA-MB-231, MDA-231-LM2 and MDA-MB-435A/LCC6) were treated with IGF-I or insulin for 10 minutes, 4h or 24h and levels of CK were examined. IGF-I and insulin signaling upregulated CK levels in ER+ breast cancer cells (MCF-7, T47-D, and ZR-75-1) but not in triple negative breast cancer cells (MDA-MB-231, MDA-231-LM2 and MDA-MB-435A/LCC6). In ER+ breast cancer cells, IGF-I and insulin activate the mitogen-activated protein kinase (MAPK) pathway. However, in triple negative breast cancer cells phosphorylation of p44/p42 MAPK are unaffected by IGF-I and insulin signaling or IGF1R inhibition. Inhibition of the MAPK pathway with U0126 blocked IGF-I and insulin induced upregulation of CK. These data suggest that IGF-I and insulin induce upregulation of CK via a MAPK dependent mechanism. We next investigated the effect of EM164, an inhibitory antibody against IGF1R, on IGF-I and insulin induced upregulation of CK. EM164 blocked IGF-I induced upregulation of CK but did not affect insulin induced upregulation of CK. These results provide molecular evidence for the observed decrease in intratumoral tCho after IGF1R inhibition in xenograft tumors. Our study is clinically significant as it provides evidence for developing decreased tCho, following IGF1R targeted drugs, as a specific biomarker for inhibition of IGF signaling. Citation Format: Huy T. Donguyen, Joseph C. Weber, Deepali Sachdev. IGF-I and insulin signaling enhances levels of choline kinase in breast cancer cells: Implications for developing noninvasive magnetic resonance spectroscopy of choline containing compounds as a biomarker of response to IGF1R targeted therapy. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1327. doi:10.1158/1538-7445.AM2013-1327