Background: Metastatic prostate cancer is either inherently resistant to chemotherapy or rapidly acquires this phenotype after chemotherapy exposure. In this study, we identified a docetaxel-induced resistance mechanism centered on CCL2.
Methods: We compared the gene expression profiles in individual human prostate cancer specimens before and after exposure to chemotherapy collected from previously untreated patients who participated in a clinical trial of preoperative chemotherapy. Subsequently, we used the gain- and loss-of-function approach in vitro to identify a potential mechanism underlying chemotherapy resistance.
Results: Among the molecular signatures associated with treatment, several genes that regulate the inflammatory response and chemokine activity were upregulated including a significant increase in transcripts encoding the CC chemokine CCL2. Docetaxel increased CCL2 expression in prostate cancer cell lines in vitro. CCL2-specific siRNA inhibited LNCaP and LAPC4 cell proliferation and enhanced the growth inhibitory effect of low-dose docetaxel. In contrast, overexpression of CCL2 or recombinant CCL2 protein stimulated prostate cancer cell proliferation and rescued cells from docetaxel-induced cytotoxicity. This protective effect of CCL2 was associated with activation of the ERK/MAP kinase and PI3K/AKT, inhibition of docetaxel-induced Bcl2 phosphorylation at serine 70, phosphorylation of Bad, and activation of caspase-3. The addition of a PI3K/AKT inhibitor Ly294002 reversed the CCL2 protection and was additive to docetaxel-induced toxicity.
Conclusion: These results support a mechanism of chemotherapy resistance mediated by cellular stress responses involving the induction of CCL2 expression and suggest that inhibiting CCL2 activity could enhance therapeutic responses to taxane-based therapy.
Prostate 70: 433-442, 2010. (c) 2009 Wiley-Liss, Inc.