Abstract LB-013: The immunomodulatory effect of JAK inhibitors enhances metastasis by impairing antitumor immunity in preclinical models of breast cancer
Authors: Hynes Nancy E. , Bottos Alessia , Gill Jason , Radimerski Thomas , Tzankov Alexander , Wodnar-Filipowicz Aleksandra 
Published: August 2015

The JAK-STAT pathway is an attractive therapeutic target in breast cancer due to its frequent activation. Clinical trials testing JAK inhibitors in breast cancer are ongoing, making it important to understand the effect of this therapeutic approach on metastasis. While it is recognized that tumor growth in primary and metastatic sites is influenced by the local environment, little is known about the effect of targeted therapies on metastases or on host cells interacting with tumor cells at distant locations. Our goal was to determine the effect of JAK inhibitors on breast cancer in the bone environment, a common site of metastasis. Using patient biopsies and preclinical models of breast cancer metastasis, we demonstrate that the JAK-STAT pathway is active in bone metastasis, both in the cancer cells and in the tumor environment. To study the effect of JAK inhibitors, we established preclinical models of bone metastatic tumors, taking advantage of the bone tropism when injected via the intracardiac route, of the breast cancer cell lines, human MDA-MB231 scp1833 and mouse EO771. In vivo, in both models, STAT3 was active and treatment with the JAK1-JAK2 inhibitor ruxolitinib decreased pSTAT3 levels in primary tumors and in bone metastases. Unexpectedly, blocking the pathway with ruxolitinib, or with the JAK2 inhibitor BSK805, enhanced the metastatic burden in both models. To investigate the effect of JAK inhibition on tumor cell dissemination from the primary site, we employed the 4T1.2 model, which spontaneously metastasizes from the mammary tumor to the bone and the lungs. As seen with the other models, there was a significant increase in tumor cell numbers in the bone and in the lungs in response to JAK inhibitor treatment. To understand the mechanism underlying the increase in metastatic load, we considered the host immune system as a potential bystander target of the JAK inhibitors. Indeed, in response to JAK inhibitor treatment we observed a major reduction in the NK cell population. The effect of JAK inhibitors on NK cells was systemic since they were also reduced in the bone marrow and in the peripheral blood of tumor-bearing mice. To mechanistically explain the impact of JAK inhibitors on NK cells, we used the NK cell line, NK-92. Upon treatment of NK-92 cells with JAK inhibitors, activation of multiple STATs decreased and cell proliferation was strongly inhibited. In cytotoxic assays, treatment with JAK inhibitors significantly decreased the killing ability of NK-92 cells against carcinoma cells. To test the in vivo relevance of NK cells in metastatic growth we used NSG mice, which are devoid of NK cell activity. Remarkably, in contrast to the results obtained with 4T1.2 mammary tumors grown in immunocompetent hosts, no increase in bone or lung metastases was observed in tumor-bearing NSG hosts treated with ruxolitinib, providing strong evidence that JAK inhibition increases metastasis by interfering with NK cell mediated anti-tumor innate immunity. These results suggest that the immunomodulatory effect of JAK inhibitors in breast cancer patients undergoing clinical trials should be monitored. Moreover, our work highlights the importance of evaluating the effect of targeted therapy on cell populations in the tumor environment in order to predict and overcame bystander effects that might impact on therapy response.

Citation Format: Nancy E. Hynes, Alessia Bottos, Jason Gill, Thomas Radimerski, Alexander Tzankov, Aleksandra Wodnar-Filipowicz. The immunomodulatory effect of JAK inhibitors enhances metastasis by impairing antitumor immunity in preclinical models of breast cancer. [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 LB-013. doi:10.1158/1538-7445.AM2015-LB-013