*6.2. Lymph Node Metastasis*

Tumor necrotic factor (TNF) is negatively regulated by androgen/AR signaling, and androgen/AR signaling blockade induces TNF mRNA in prostatic stroma [56]. We observed that human prostate cancer cells (PC-3, DU145, LNCaP, and LNCaP-SF) express both TNFα and CCR7 and that low concentrations of TNFα can induce CCR7 expression in prostate cancer cells through phosphorylation of extracellular signal-regulated kinases in an autocrine manner [57]. CCL21, a ligand of CCR7 that is secreted by fibroblastic reticular cells in lymph nodes and is abundant in the T-cell zone of the lymph node [58], was found to promote prostate cancer cell migration via protein kinase p38 phosphorylation [57]. These results sugges<sup>t</sup> that TNFα induces CCR7 expression and that the CCL21-CCR7 axis is capable of increasing the metastatic potential of prostate cancer cells during lymph node metastasis. In combination with ADT, the CCL21-CCR7 axis may, therefore, prove a superior target compared with single androgen/AR signaling-targeted therapy for treatment of patients with prostate cancer and lymph node metastasis.

### *6.3. Resistance to Taxanes*

Understanding the underlying mechanisms behind chemoresistance and disease progression in patients with prostate cancer is important in order to develop novel treatment strategies. In particular, cabazitaxel resistance is a considerable challenge in CRPC patients as cabazitaxel is often administered as a last resort [59]. The mechanism through which cabazitaxel resistance develops is still unclear, however. We previously established a cabazitaxel-resistant prostate cancer cell line, DU145-TxR/CxR, from a paclitaxel-resistant cell line, DU145-TxR [60]. The cDNA microarray analysis revealed that CCL2 expression was upregulated in both DU145-TxR and DU145-TxR/CxR cells, compared with control DU145 cells. Furthermore, the secreted CCL2 protein level in DU145-TxR and DU145-TxR/CxR cells was observed to be higher than in the parental DU145 cells [61]. Stimulation of DU145 cells with CCL2 increased proliferation during cabazitaxel treatment, while CCR2 antagonist suppressed the proliferation of DU145-TxR and DU145-TxR/CxR cells during cabazitaxel treatment [61]. The CCL2-CCR2 axis was found to reduce apoptosis through inhibition of caspase-3 and poly(ADP-ribose) polymerase (PARP), indicating that CCL2 is potentially a key contributor to cabazitaxel resistance in prostate cancer cells [61]. Inhibition of the CCL2-CCR2 axis may provide a potential therapeutic strategy against both chemosensitive CRPC and chemoresistant CRPC.
