T. Wang1, C. Subramanian1, M. Cohen1 1University Of Michigan,General Surgery,Ann Arbor, MI, USA
Introduction: Breast cancer is the second leading cause of cancer-related death in women in the US. To date, use of immunotherapy has been difficult due to decreased mutational burden in breast cancer compared to other cancers such as melanoma. Hsp90 has been an exciting target for the development of anti-tumor agents, as multiple cancer signaling pathways can be disrupted simultaneously through Hsp90 inhibition; however, current Hsp90 inhibitors have significant immunosuppressive effects by decreasing dendritic cell maturation, antigen uptake, and tumor recognition by T cells. Recently our group has developed novel Hsp90 inhibitors that target only the carboxy-teminus (KU758) or are selective to the beta-isoform of Hsp90 (KUNB31). We hypothesize that these novel approaches to Hsp90 inhibition will have decreased immunosuppressive effects (due to their improved selectivity for client proteins) compared to traditional N-terminal inhibitors (17-AAG) and would be more ideal drugs for combination with immunotherapy.
Methods: Validated MCF7 (ER+) and MDA-MB-231 (triple neg) breast cancer cells were treated with 17-AAG, KU758, and KUNB31 for 30 hr. Dendritic cells (DC) were isolated from murine bone marrow and plated on a 96-well plate. The supernatant from the treated cells was then transferred to DCs for 24 hours. IL-6, TNA-α, and TGF-β secretion was measured by ELISA assay. SPSS software was used for statistical analysis and all experiments were repeated in triplicate.
Results: IL-6 secretion from DCs was decreased by exposure to 17-AAG treated MCF7 cells compared to untreated cells by 45.9% (p=0.05). Similar results were observed in exposure to 17-AAG treated MDA-MB-231 cells (52.6% decrease, p=0.001). In contrast, IL-6 levels were not significantly changed with exposure of DCs to both cell types treated with KU758 or KUNB31, except slightly at high concentrations >10uM of KUNB31 (decreased by 15.2%, p=0.13). In DCs exposed to Hsp90 inhibitor-treated MCF7 cells, there was decreased TNF-α expression with all drugs, but the greatest effect was noted with 17-AAG (decreased by 39.6%, p=0.07). TNF-α expression was significantly decreased by 81.9% (p=0.01) from DCs exposed to 17-AAG treated MDA-MB-231 cells. In contrast, no significant decrease in either TNF-α expression or TGF-β secretion was seen with KU758 and KUNB31 treatment. See Figure 1.
Conclusion: Compared to N-terminal inhibitors, our novel approach to Hsp90 inhibition may be better targets for combination with immunotherapy agents due to their lack of immunosuppressive effects. Additional studies in translational models are warranted to further validate this significant opportunity and support future clinical applications.
