Inhibition of prostate cancer cell growth, motility and ability to alter monocyte/macrophage lineage commitment by a novel TRAF6 inhibitor


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Denise Giovana Carrasco Gonzalez1,Ryan T. Bishop2,Antonio Maurizi3,Silvia Marino4,Anna Sparatore5,Mattia Capulli3,Aymen I. Idris1
1University of Sheffield,2Moffitt Cancer Centre,3University of L’Aquila,4Indiana University,5University of Milano

Abstract

Background

The pro-inflammatory TRAF6 signalling pathway plays a key role in prostate cancer, immunity and bone remodelling. However, the role of TRAF6 in the ability of prostate cancer cells to grow, metastasise and influence the differentiation of uncommitted monocyte/macrophage into tumour-associated macrophage (M2) and bone-specific macrophages (osteoclasts) remains unknown.

Method

Results

Here, we show that TRAF6 is highly expressed in a panel of human and mouse prostate cancer cells including the osteotropic human PC3 and C42-B4 and mouse RM1-BM, and pharmacological inhibition of TRAF6 using the verified TRAF6 inhibitor 6877002 and its novel congeners FSAS1 – FSAS8 suppressed cell growth in a dose and time-dependent manner (IC50<2μM). The most potent congener FSAS3 enhanced the ability of uncommitted monocyte/macrophages (M0) to differentiate into classically-activated macrophages (M1) rather than tumour-associated M2, as assessed by flow cytometry. Additionally, FSAS3 reduced the ability of the uncommitted M0 macrophage to form bone-resorbing TRAP-positive osteoclasts in the presence and absence of tumour-derived factors from human PC3 prostate cancer cells (30% reduction, p<0.05). FSAS3 treatment had no effects on the ability of M1 to reduce the viability of human PC3 prostate cancer cells or the viability of the uncommitted M0 – thus excluding cytotoxic effects of this compound on macrophages. Additionally, conditioned medium from M2 macrophage – but not M0 and M1 phenotype - enhanced PC3 proliferation, wound-healing cell migration and transwell invasion and these effects were significantly inhibited by FSAS3 (20% reduction, p<0.05). Mechanistically, FSAS3 reduced IκB phosphorylation induced by RANKL and macrophage-derived factors in PC3 cells, indicative of NFκB inhibition.

Conclusion

These findings identify FSAS3 and its derivatives as a novel class of anti-cancer and antiresorptive agents which may be of value in the treatment of prostate cancer. In vivo studies to test the effects of FSAS3, alone and in combination with chemotherapeutic agents, on the initiation and progression of prostate cancer-associated bone disease are ongoing.