Abstract

<div>Abstract<p><b>Purpose:</b> Androgen deprivation therapy (ADT), including enzalutamide, induces resistance in prostate cancer; ADT resistance is associated with neuroendocrine differentiation (NED) and tumor-associated macrophages (TAM). This study aimed to investigate the association between enzalutamide-induced NED and TAMs and its mechanism.</p><p><b>Experimental Design:</b> The association between enzalutamide-induced NED and TAMs was investigated by IHC using prostate cancer tissues, enzalutamide-resistant mouse xenografts, and a coculture system. The underlying mechanisms were assessed using <i>in vitro</i> cytokine antibody arrays, ELISAs, chromatin immunoprecipitation, and other methods. An orthotopic prostate cancer mouse model was established to evaluate the <i>in vivo</i> effects of combined IL6 receptor (IL6R) and high mobility group box 1 (HMGB1) inhibition on enzalutamide resistance.</p><p><b>Results:</b> High CD163 expression was observed in ADT-treated prostate cancer or castration-resistant prostate cancer (CRPC) tissues with high levels of neuron-specific enolase (NSE) and chromogranin A (CHGA) and in enzalutamide-resistant xenografts, indicating the crucial roles of NED and TAMs in enzalutamide resistance. Specifically, enzalutamide-induced HMGB1 expression facilitated TAM recruitment and polarization and drove NED via β-catenin stabilization. HMGB1-activated TAMs secreted IL6 to augment enzalutamide-induced NED and directly promote HMGB1 transcription via STAT3. Finally, inhibition of the IL6/STAT3 pathway by tocilizumab combined with HMGB1 knockdown inhibited enzalutamide-induced resistance in an orthotopic prostate cancer mouse model.</p><p><b>Conclusions:</b> Enzalutamide elevates HMGB1 levels, which recruits and activates TAMs. Moreover, IL6 secreted by HMGB1-activated TAMs facilitates the enzalutamide-induced NED of prostate cancer, forming a positive feedback loop between NED in prostate cancer and TAMs. The combined inhibition of IL6R and HMGB1 may serve as a new treatment for enzalutamide resistance in patients with advanced or metastatic prostate cancer. <i>Clin Cancer Res; 24(3); 708–23. ©2017 AACR</i>.</p></div>

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