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Ligand-independent CXCR7 Activation of MAPK Signaling leads to Prostate Cancer Enzalutamide Resistance

ABSTRACT: The standard of care for patients with advanced form of prostate cancer, castration-resistant, now includes enzalutamide, a second generation antiandrogen. However, most of the treated patients will develop resistance to enzalutamide based therapy in around a year, succumbing to lethal disease. Investigating the transcriptome of enzalutamide-resistant prostate cancer cell lines, we identified CXCR7 as one of the most upregulated genes suggesting its role in advanced prostate cancer. CXCR7, known as an atypical G-coupled receptor, is engaged in many physiological and pathological processes. Here we show that in prostate cancer CXCR7 is tightly regulated by androgen receptor (AR), which directly binds to CXCR7 gene promoter and enhancer and represses its transcription. In turn, CXCR7 in prostate cancer reduces enzalutamide toxicity and promotes cell survival and invasiveness. We identified that CXCR7 forms an integral complex with ARRB2 and activates ERK1/2, eliciting pro-survival MAPK pathway. Enzalutamide treatment combined with MAPKK specific inhibitor, trametinib, reversed enzalutamide resistance in prostate cancer in vitro and in vivo. Taken together our findings highlight the critical role of CXCR7 in enzalutamide-resistant prostate cancer and open an avenue for developing novel anti-CXCR7 therapies to improve survival in patients with advanced prostate cancer.

ORGANISM(S): Homo sapiens

PROVIDER: GSE104935 | GEO | 2019/04/06

REPOSITORIES: GEO

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Project description:Background. Androgen receptor splice variant-7 (AR-V7) is a truncated form of the androgen receptor protein which lacks the ligand-binding domain, the target of enzalutamide and abiraterone, but remains constitutively active as a transcription factor. We hypothesized that detection of AR-V7 in circulating tumor cells (CTCs) from men with advanced prostate cancer would be associated with resistance to enzalutamide and abiraterone. Methods. We used quantitative reverse-transcription polymerase-chain-reaction (qRT-PCR) to interrogate CTCs for the presence or absence of AR-V7 from prospectively enrolled patients with metastatic castration-resistant prostate cancer initiating treatment with either enzalutamide or abiraterone. We examined associations between AR-V7 status and PSA response rates, PSA-progression-free-survival (PSA-PFS), clinical/radiographic-progression-free-survival (PFS), and overall survival (OS). Multivariable Cox regression analyses were performed to determine the independent effect of AR-V7 status on clinical outcomes. Results. Thirty-one enzalutamide-treated patients and thirty-one abiraterone-treated patients were enrolled, of which 38.7% and 19.4% had detectable AR-V7 from CTCs, respectively. Among men receiving enzalutamide, AR-V7–positive patients had inferior PSA response rates (0% vs 52.6%, P=0.004), PSA-PFS (median: 1.4 vs 6.0 months, P<0.001), PFS (median: 2.1 vs 6.1 months, P<0.001), and OS (median: 5.5 months vs not reached, P=0.002) compared to AR-V7–negative patients. Similarly, among men receiving abiraterone, AR-V7–positive patients had inferior PSA response rates (0% vs 68.0%, P=0.004), PSA-PFS (median: 1.3 months vs not reached, P<0.001), PFS (median: 2.3 months vs not reached, P<0.001), and OS (median: 10.6 months vs not reached, P=0.006). The negative prognostic impact of AR-V7 was maintained after adjusting for full-length-AR expression. Conclusions. Detection of AR-V7 in CTCs from patients with castration-resistant prostate cancer is associated with resistance to enzalutamide and abiraterone. A total of four metastatic castration-resistant prostate tumor samples from four patients were subjected to RNA-seq. Two samples were positive for androgen receptor splice variant 7 and the other two were negative for this variant.

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Ligand-independent CXCR7 Activation of MAPK Signaling leads to Prostate Cancer Enzalutamide Resistance

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