Data from Pharmacologic Inhibition of Jak2–Stat5 Signaling By Jak2 Inhibitor AZD1480 Potently Suppresses Growth of Both Primary and Castrate-Resistant Prostate Cancer

Abstract

<div>Abstract<p><b>Purpose:</b> Progression of prostate cancer to the lethal castrate-resistant stage coincides with loss of responsiveness to androgen deprivation and requires development of novel therapies. We previously provided proof-of-concept that Stat5a/b is a therapeutic target protein for prostate cancer. Here, we show that pharmacologic targeting of Jak2-dependent Stat5a/b signaling by the Jak2 inhibitor AZD1480 blocks castrate-resistant growth of prostate cancer.</p><p><b>Experimental Design:</b> Efficacy of AZD1480 in disrupting Jak2–Stat5a/b signaling and decreasing prostate cancer cell viability was evaluated in prostate cancer cells. A unique prostate cancer xenograft mouse model (CWR22Pc), which mimics prostate cancer clinical progression in patients, was used to assess <i>in vivo</i> responsiveness of primary and castrate-resistant prostate cancer (CRPC) to AZD1480. Patient-derived clinical prostate cancers, grown <i>ex vivo</i> in organ explant cultures, were tested for responsiveness to AZD1480.</p><p><b>Results:</b> AZD1480 robustly inhibited Stat5a/b phosphorylation, dimerization, nuclear translocation, DNA binding, and transcriptional activity in prostate cancer cells. AZD1480 reduced prostate cancer cell viability sustained by Jak2–Stat5a/b signaling through induction of apoptosis, which was rescued by constitutively active Stat5a/b. In mice, pharmacologic targeting of Stat5a/b by AZD1480 potently blocked growth of primary androgen-dependent as well as recurrent castrate-resistant CWR22Pc xenograft tumors, and prolonged survival of tumor-bearing mice versus vehicle or docetaxel-treated mice. Finally, nine of 12 clinical prostate cancers responded to AZD1480 by extensive apoptotic epithelial cell loss, concurrent with reduced levels of nuclear Stat5a/b.</p><p><b>Conclusions:</b> We report the first evidence for efficacy of pharmacologic targeting of Stat5a/b as a strategy to inhibit castrate-resistant growth of prostate cancer, supporting further clinical development of Stat5a/b inhibitors as therapy for advanced prostate cancer. <i>Clin Cancer Res; 19(20); 5658–74. ©2013 AACR</i>.</p></div>