Castration-mediated IL-8 promotes myeloid infiltration and prostate cancer progression

Drake and colleagues demonstrate that castration in prostate cancer models promotes IL-8 secretion and immunosuppressive myeloid-derived suppressor cell migration, and that inhibiting this axis in combination with checkpoint blockade can mitigate tumor progression. Unlike several other tumor types, prostate cancer rarely responds to immune checkpoint blockade (ICB). To define tumor cell intrinsic factors that contribute to prostate cancer progression and resistance to ICB, we analyzed prostate cancer epithelial cells from castration-sensitive and -resistant samples using implanted tumors, cell lines, transgenic models and human tissue. We found that castration resulted in increased expression of interleukin-8 (IL-8) and its probable murine homolog Cxcl15 in prostate epithelial cells. We showed that these chemokines drove subsequent intratumoral infiltration of tumor-promoting polymorphonuclear myeloid-derived suppressor cells (PMN-MDSCs), which was largely abrogated when IL-8 signaling was blocked genetically or pharmacologically. Targeting IL-8 signaling in combination with ICB delayed the onset of castration resistance and increased the density of polyfunctional CD8 T cells in tumors. Our findings establish a novel mechanism by which castration mediates IL-8 secretion and subsequent PMN-MDSC infiltration, and highlight blockade of the IL-8/CXCR2 axis as a potential therapeutic intervention.

Automated summary

Castration increases IL-8 expression in prostate epithelial cells, leading to infiltration of tumor-promoting PMN-MDSCs, which can be mitigated by blocking IL-8 signaling. Targeting IL-8 signaling in combination with ICB delays castration resistance and increases polyfunctional CD8 T cell density in tumors.