Inhibition of noncanonical Wnt pathway overcomes enzalutamide resistance in castration-resistant prostate cancer

Because androgen receptor (AR) signaling is essential for prostate cancer (PCa) initiation and progression, castration is the main approach for treatment. Unfortunately, patients tend to enter a stage called castration-resistant prostate cancer (CRPC) despite the initial response to castration. For various reasons, AR signaling is reactivated in CRPC. As such, AR signaling inhibitors, such as enzalutamide, has been approved by the Food and Drug Administration to treat CRPC in the clinic. However, the limited success of these new drugs suggests an immediate unmet need to understand the underlying mechanisms for resistance so novel targets can be identified to enhance their efficacy.

An unbiased bioinformatics analysis was performed with the existing human patient dataset and RNA-seq results of in-house PCa cell lines to identify new targets to overcome enzalutamide resistance. Cell viability and growth were detected by 3-(4,5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide and colony formation assay. Cell invasion and migration were detected by transwell assay. Protein levels were detected by Western blot or immunofluorescence.

We found that the noncanonical Wnt signaling was activated in enzalutamide-resistant PCa cells and that the activation of noncanonical Wnt signaling was correlated with AR expression and disease progression. This was validated by the elevated expression of noncanonical Wnt pathway members such as Wnt5a, RhoA, and ROCK in enzalutamide-resistant PCa cells in comparison to their enzalutamide-sensitive counterparts. And, both Y27632, an inhibitor of ROCK, and depletion of ROCK enhanced the efficacy of enzalutamide in enzalutamide-resistant PCa cells. Of significance, a combination of Y27632 and enzalutamide inhibited 22RV1-derived xenograft tumor growth synergistically. Finally, ROCK depletion plus enzalutamide treatment inhibited invasion and migration of enzalutamide-resistant PCa cells via inhibition of epithelial-mesenchymal transition.

The noncanonical Wnt pathway is activated in enzalutamide-resistant PCa and inhibition of noncanonical Wnt pathway overcomes enzalutamide resistance and enhances its efficacy in CRPC.