Abstract 5081: The IGF axis regulates hepatic stellate cell recruitment and activation during colorectal carcinoma liver metastasis
Authors: Fernandez Maria C. , Rayes Roni F. , Xu Jun , Kisseleva Tatiana , Yakar Shoshana , Brodt Pnina 
Published: August 2015

Abstract
Background: The hepatic stellate cells (HSC) play a major role in orchestrating the liver's fibrogenic (wounding) response and have been identified as an important player in the prometastatic microenvironment in the liver. Here we analyzed the role of the IGF axis in the recruitment and activation of HSC during the early stages of colorectal carcinoma (CRC) liver metastasis.
Methods: Murine CRC MC-38 cells were inoculated via the intrasplenic/portal route into female mice with a conditional liver IGF-1 deletion (iLID), induced by a single tamoxifen (Tx) injection 2 days or 3 weeks earlier. Vehicle (sunflower oil) injected iLID mice or Tx - injected wild type mice were used as controls. Experimental liver fibrosis was achieved by repeated carbon tetrachloride (CCl4) administration. The stromal response of the liver was analyzed using immunohistochemistry with emphasis on HSC recruitment and activation. In addition, in vitro assays were utilized to explore the role of IGF-1 in HSC activation.
Results: In iLID mice treated with Tx, a 75% reduction in circulating IGF-1 levels could be observed within 24 hr and it persisted for the duration of the experiments. When injected with MC-38 cells, 3 weeks post Tx injection, these mice developed significantly fewer liver metastases than non-treated controls, while no reduction in the number of metastases was seen in WT mice injected with Tx or in oil-injected iLID controls. Interestingly, we observed that Tx treatment 48 hr prior to tumor injection, failed to reduce liver metastasis in iLID mice, although their circulating IGF-1 levels were markedly reduced, suggesting that the loss of direct paracrine IGF-1 effects on the tumor cells was not sufficient to inhibit tumor growth in the liver and that other effects on the hepatic microenvironment were at play. Analysis of HSC recruitment and activation subsequently revealed a significant reduction in HSC activation around micrometastases as compared to controls. This was evident as early as 3 days post tumor inoculation, persisted for the duration of the experimental period (16-18 days) and corresponded with reduced IGF-1 receptor and Akt activation in these cells. In vitro studies confirmed that IGF-1 could directly activate isolated HSC and rescue them from serum-depletion induced apoptosis. Finally, in iLID mice with sustained IGF-1 depletion, a significant reduction in HSC-mediated collagen deposition was observed following continuous treatment with CCl4, confirming the role of IGF-1 in HSC activation in a second tumor-free model.
Conclusion: Our results show that a sustained reduction in circulating IGF-1 levels altered HSC recruitment and activation to tumor sites and reduced tumor cell growth in the liver. We identify IGF-1 as a regulator of HSC function and the response of the microenvironment to invading cancer cells, thereby affecting metastatic expansion.
Supported by CIHR Grant MOP 81201 (to PB) and MICRTP Fellowship (to MCF).
Note: This abstract was not presented at the meeting.
Citation Format: Maria C. Fernandez, Roni F. Rayes, Jun Xu, Tatiana Kisseleva, Shoshana Yakar, Pnina Brodt. The IGF axis regulates hepatic stellate cell recruitment and activation during colorectal carcinoma liver metastasis. [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 5081. doi:10.1158/1538-7445.AM2015-5081