Galectin-3 Is Implicated in Tumor Progression and Resistance to Anti-androgen Drug Through Regulation of Androgen Receptor Signaling in Prostate Cancer.

BACKGROUND: Castration-resistant prostate cancer (CRPC)-related deaths are increasing worldwide. Therefore, clarification of the mechanisms of hormone-related tumor progression and resistance to anti-androgen drugs is useful in order to develop strategies for appropriate treatment of CRPC. Galectin-3 has been shown to be correlated with tumor progression in a variety of cancer types through the regulation of tumor proliferation, angiogenesis, and apoptosis.

MATERIALS AND METHODS: We examined tumor cell invasion and migration using the xCELLigence system. Control LNCaP and galectin-3-expressing LNCaP (LNCaP-Gal-3) cells were cultured with androgen-depleted medium with 5% charcoal-stripped serum. Cells were treated for 24 h with or without dihydrotestosterone alone or combined with MDV3100 and bicalutamide; gene profile was then analyzed by microarray analysis and mRNA expression was confirmed by quantitative real-time polymerase chain reaction (qRT-PCR). We evaluated tumor growth using spheroids and xenograft tumor growth in a mouse model.

RESULTS: In vitro, LNCaP-Gal-3 cells promoted both cell migration and invasion in an androgen-independent manner compared to control LNCaP cells. Galectin-3 also enhanced anchorage-independent growth and xenograft tumor growth even after castration. Importantly, galectin-3 greatly enhanced transcriptional activity of the androgen receptor (AR), especially on treatment with dihydrotestosterone. In microarray and qRT-PCR analyses, galectin-3 increased the expression of several AR-target genes, such as kallikrein-related peptidase 3 (KLK3), and transmembrane protease, serine 2 (TMPRSS2). These AR-target genes were not fully suppressed by anti-androgen drugs such as bicalutamide or MDV3100. Galectin-3 significantly inhibited the effect induced by anti-androgen drugs MDV3100 and bicalutamide, suggesting that galectin-3 may be involved in resistance to anti-androgen drug through enhancement of transcriptional activity of AR and expression of AR-related genes.

CONCLUSION: These results suggest that galectin-3 is a potential target molecule for future treatment of anti-androgen drug-resistant prostate cancer.