PP4 inhibition stimulates anti-tumor immunity in ovarian cancer

Abstract Background Increased infiltration of T cells into ovarian tumors has been repeatedly shown to be predictive of enhanced patient survival. However, despite the evidence of an active immune response in OC, immune checkpoint blockade therapy has been ineffective. Recently studies have shown that deficiencies in the DNA damage response (DDR) can drive increased genomic instability and tumor immunogenicity. One target involved in the DDR that has the potential to be of therapeutic value is protein phosphatase 4 (PP4); however, the effect of PP4 deficiency on anti-tumor immunity remain unknown. Results Our results show that PP4 inhibition combined with carboplatin leads to increased carboplatin sensitivity, DNA damage, and micronuclei formation. Using a panel of ovarian cancer cells, we show that PP4 inhibition triggers inflammatory signaling via NFκB and STAT1 activation resulting in increased expression of pro-inflammatory cytokines including IFNβ1, CCL5, CXCL10, and IL-6. We further show that PP4 inhibition and carboplatin-induced STAT1 activation is significantly blunted upon STING knockdown in ovarian cancer cells. Moreover, using mouse ID8 ovarian cancer cell line and OT-I cells, we demonstrate that the combination of PP4 inhibition and carboplatin significantly increased CD8 T cell migration over carboplatin treatment alone. In addition, the same treatment resulted in enhanced NK cell-mediated tumor cell killing and T cell killing in an autologous human organoid model. Conclusions Our work has identified a role for PP4 inhibition in promoting anti-tumor immune activation. These findings provide the rationale for combining PP4 inhibitors with immunotherapy as a new approach in ovarian cancer treatment. Supported by DOD W81XWH2110489