Chronic inflammation and African ancestry are implicated in prostate cancer aggressiveness, and inflammation-related genes are more highly expressed in prostate cancer in African American men. IL8 secretion is also implicated in prostate cancer progression and castration resistance. We used RNA in situ hybridization to localize IL1β, IL6, IL8, and IL10 mRNA in low- and high-grade prostate cancer from African American and European American men. IL8 was the most abundantly expressed and the only interleukin detected in tumor cells. We further interrogated IL8 expression in primary and metastatic prostate cancer tissue microarrays and both androgen-dependent and castration-resistant patient-derived xenografts (PDX). IL8 was significantly increased in both tumor and benign regions of higher grade cases (ISUP Grade Group 4-5), but there was no difference between races. We determined that IL8 expression in prostate cancer cell lines, distant metastases, and PDX lines was associated with androgen receptor (AR) loss, but not castration resistance. Reciprocal IL8 and AR expression was also observed in high IL8-expressing atrophy lesions with simultaneous AR downregulation. Finally, we show that IL8 is likely repressed by AR binding to the IL8 promoter and is inducible in prostate cancer cells stimulated with lipopolysaccharide only in cells with AR loss. Likewise, AR knockdown in androgen-dependent cells induced IL8 expression, further demonstrating that AR represses IL8 expression. In conclusion, IL8 expression in the tumor microenvironment is associated with aggressive prostate cancer and with AR loss in metastatic disease. IMPLICATIONS: IL8 expression is repressed by AR and is associated with prostate cancer aggressiveness and AR loss in metastatic disease.
©2019 American Association for Cancer Research.