Abstract P3-07-15: Treatment with a Jumonji demethylase inhibitor JIB-04 sensitizes resistant breast cancer cells to chemotherapeutic drugs in an in vitro model of intrinsic resistance

We have recently developed a usable model of panresistance in triple-negative breast cancer. We have shown that only 0.01% cells survive a metabolic challenge involving lack of glutamine in culture medium of SUM149 triple-negative Inflammatory Breast Cancer cell line. These cells, designated as SUM149-MA for metabolic adaptability, are resistant to chemotherapeutic drugs, and they efficiently metastasize to multiple organs in nude mice. The MA cells can survive a variety of challenges in the metastasis process because of their embryo-like nature and high adaptability. Epigenetic state is a key player in cancer evolution. Therefore, a variety of compounds are being developed that would target epigenome for anticancer therapy. We believe that the identification of potentially effective epigenetic drugs can benefit from their evaluation in a usable system of panresistant cancer cells such as our model system of MA cells. This is particularly true for the compounds that may affect cellular adaptability upon a long treatment rather than affecting cell proliferation or apoptosis in a short period. In this study we evaluated JIB-04, a pan-inhibitor of Jumonji family of histone demethylases, for its ability to affect intrinsic resistance in MA cells. First, we found that MA cells are more resistant to JIB-04 treatment in a comparative evaluation with the parental SUM149 cells line. A treatment with 125-250 nM JIB-04 for 18-20 days killed all parental cells but not all MA cells; at least 20 MA cells survived and formed colonies after a 14-days recovery. Next, we asked whether JIB-04 treatment would affect the intrinsic resistance of MA cells, e.g., sensitize them to treatment with chemotherapeutic drugs. In order to assess the most resistant cells in population, these experiments involved treatment of MA cells with 125 nM JIB-04 for 10 days followed by a recovery in drug-free medium for 7 days; then we treated the cells with 5 nM paclitaxel or 100 nM doxorubicin for 6-8 days followed by a recovery for 1-12 days. We found that JIB-04 pre-treatment sensitized MA cells and the parental SUM149-Luc cell line to both these chemotherapeutic drugs as assessed by a dramatic drop in the number of colonies as compared to those obtained after treatment of control cells with the same chemotherapeutic drugs. To consider how our results may apply in the context of evolving disease in patients who are not taking chemotherapeutic drugs, we asked whether JIB-04 treatment would alter expression of surface molecules on resistant breast cancer cells such that they can be destroyed by immune system. In this regard, we specifically found that JIB-04 treatment increased the expression of PD-L1 in MA cells. Published results from a clinical study suggest that PD-L1 expression on breast cancer cells renders them responsive to various therapies, not just immune checkpoint blockade targeting PD-L1. In conclusion, our results suggest a novel approach for evaluating potential anticancer agents such as JIB-04 that would halt cancer evolution and prevent development of resistance to currently offered therapies. Supported by a State of Texas Grant for Rare and Aggressive Cancers. Citation Format: Singh B, Washburn LJ, Kinne HE, Milligan RD, Lucci A. Treatment with a Jumonji demethylase inhibitor JIB-04 sensitizes resistant breast cancer cells to chemotherapeutic drugs in an in vitro model of intrinsic resistance [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P3-07-15.