Identifying and targeting the genetic determinants of immune suppression and immunotherapy failure in prostate cancer. - PROJECT SUMMARY The goal of this project is to determine the mechanisms by which interferon gamma (IFNg) signaling promotes tumor growth and immune suppression to drive neuroendocrine prostate cancer (NEPC) progression and resistance to immune checkpoint blockade (ICB) therapies. Following hormone therapy failure, some patients develop an aggressive subtype of prostate cancer known as NEPC that is lacking in effective treatment options. Though most prostate cancers are defined by a “cold” tumor microenvironment (TME) lacking T cells that mediate anti-tumor immunity and are necessary for immunotherapy responses, it was recently shown that a subset of NEPC patient tumors are “inflamed” with T cells and have heightened expression of interferon gamma (IFNg) signatures. As IFNg is associated with activation of adaptive immunity and better ICB outcomes, this suggests that NEPC patients may potentially benefit from immunotherapy. To determine the impact of IFNg on tumor- immune interactions in situ, I developed a novel mouse model of NEPC through in vivo electroporation of CRISPR constructs targeting three tumor suppressor genes, Pten, p53, and Rb1 (PtPRb), commonly disrupted in NEPC patients. Despite PtPRb NEPC tumors recapitulating the inflamed TME of human NEPC with enhanced IFNg signaling and a significant influx of CD8+ T cells, paradoxically, mice failed to respond and even had worse survival following anti-PD-1 ICB. Inhibiting Nuclear Factor kappa B (NFkB) signaling downstream of IFNg in NEPC cell lines in vitro or blocking the IFNg receptor (IFNGR1) in NEPC tumors in vivo not only inhibited tumor growth and prolonged survival, but also reduced the numbers of macrophages that highly infiltrate NEPC tumors and can suppress T cell and immunotherapy responses. Based on these preliminary results, our central hypothesis is that IFNg signaling contributes directly to tumor growth and macrophage dysfunction, and that targeting it will activate immunotherapy responses in NEPC. In Aim 1, we will test whether IFNg signaling directly contributes to NEPC viability and growth signaling. Genetic and pharmacological approaches will be used inhibit different upstream and downstream IFNg signaling regulators in murine NEPC tumor cells and human NEPC organoids to investigate their role in driving growth factor signaling and growth phenotypes in vitro and in vivo. In Aim 2, we will test whether IFNg drives macrophage-mediated immune suppression and immunotherapy resistance. The impact of IFNGR1 KO on macrophage polarization, phenotypes, and T cell interactions will be assessed in vitro by tumor-immune co-culture assays and in vivo in murine NEPC tumor models by multiplexed error-robust fluorescence in situ hybridization (MERFISH) spatial transcriptomics. Finally, we will evaluate the effects of macrophage or IFNGR1 blockade on tumor and immune responses and anti-PD-1 ICB outcomes in our preclinical NEPC animal models. Ultimately, this work will not only unveil new tumor intrinsic and extrinsic mechanisms by which IFNg signaling drives NEPC progression, but also advance novel strategies targeting IFNg regulators to enhance immunotherapy outcomes in this aggressive disease.
