Abstract
Resistance to drugs targeting the androgen receptor (AR) signaling axis remains an important challenge in the treatment of prostate cancer patients. Activation of alternative growth pathways is one mechanism used by cancer cells to proliferate despite treatment, conferring drug resistance. Through a kinome-centered CRISPR-Cas9 screen in CWR-R1 prostate cancer cells, we identified activated BRAF signaling as a determinant for enzalutamide resistance. Combined pharmaceutical targeting of AR and MAPK signaling resulted in strong synergistic inhibition of cell proliferation. The association between BRAF activation and enzalutamide resistance was confirmed in two metastatic prostate cancer patients harboring activating mutations in the BRAF gene, as both patients were unresponsive to enzalutamide. Our findings suggest that co-targeting of the MAPK and AR pathways may be effective in patients with an activated MAPK pathway, particularly in patients harboring oncogenic BRAF mutations. These results warrant further investigation of the response to AR inhibitors in BRAF-mutated prostate tumors in clinical settings.
Highlights
Prostate cancer is the second most common cancer diagnosed in men, accounting for over 350,000 cancer-related deaths worldwide each y ear[1]
Resistance to androgen receptor (AR) inhibitors commonly arises during therapy, and primary resistance occurs in 10–20% of patients[3,12]
We found that genetic knockout of the BRAF gene resulted in increased sensitivity to enzalutamide in CWR-R1 cells
Summary
Prostate cancer is the second most common cancer diagnosed in men, accounting for over 350,000 cancer-related deaths worldwide each y ear[1]. New compounds have been introduced clinically that target the AR signaling axis resulting in tumor regression These include drugs such as abiraterone, which blocks biosynthesis of androgen precursor molecules, and enzalutamide, which functions through antagonistic binding of AR. Acquired resistance to enzalutamide has been the focus of intense research, and several mechanisms have been described These resistance mechanisms include activation of other signaling pathways such as the PI3K pathway[8], NF-κB signaling[9] and glucocorticoid receptor (GR) o verexpression[10,11]. We found that inhibition of BRAF, or downstream MAPK components MEK and ERK, enhanced enzalutamide sensitivity in prostate cancer cells harboring a mutation in the activating kinase domain of the BRAF gene. Our findings suggest therapeutic potential for co-inhibition of the MAPK and AR pathways in BRAF-mutated prostate cancers
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