Hypoxic Tumor Kinase Signaling Mediated by STAT5A in Development of Castration-Resistant Prostate Cancer

In this study, we hypothesized that androgen-deprivation therapy (ADT) in prostate cancer, although initially efficient, induces changes in the tumor kinome, which subsequently promote development of castration-resistant (CR) disease. Recognizing the correlation between tumor hypoxia and poor prognosis in prostate cancer, we further hypothesized that such changes might be influenced by hypoxia. Microarrays with 144 kinase peptide substrates were applied to analyze CWR22 prostate carcinoma xenograft samples from ADT-naïve, androgen-deprived (AD), long-term AD (ADL), and CR disease stages. The impact of hypoxia was assessed by matching the xenograft kinase activity profiles with those acquired from hypoxic and normoxic prostate carcinoma cell cultures, whereas the clinical relevance was evaluated by analyzing prostatectomy tumor samples from patients with locally advanced disease, either in ADT-naïve or early CR disease stages. By using this novel peptide substrate microarray method we revealed high kinase activity mediated by signal transducer and activator of transcription 5A (STAT5A) in CR prostate cancer. Additionally, we uncovered high STAT5A kinase activity already in regressing ADL xenografts, before renewed CR growth was evidenced. Finally, since increased STAT5A kinase activity also was detected after exposing prostate carcinoma cells to hypoxia, we propose long-term ADT to induce tumor hypoxia and stimulate STAT5A kinase activity, subsequently leading to renewed CR tumor growth. Hence, the study detected STAT5A as a candidate to be further investigated for its potential as marker of advanced prostate cancer and as possible therapeutic target protein.

本研究提出假说：前列腺癌患者接受雄激素剥夺疗法（androgen-deprivation therapy, ADT）初期虽可获得良好疗效，但会诱导肿瘤激酶组发生改变，进而促进去势抵抗（castration-resistant, CR）性前列腺癌的发生发展。鉴于前列腺癌肿瘤缺氧与不良预后存在相关性，本研究进一步提出假说：上述激酶组改变可能受缺氧调控。本研究采用包含144种激酶肽底物的微阵列，对未经ADT治疗（ADT-naïve）、雄激素剥夺（androgen-deprived, AD）、长期雄激素剥夺（long-term AD, ADL）及去势抵抗性疾病阶段的CWR22前列腺癌异种移植样本开展激酶活性分析。通过将异种移植的激酶活性谱与缺氧培养及常氧培养的前列腺癌细胞系所得谱图进行比对，评估缺氧对激酶活性的影响；同时通过分析接受前列腺切除术的局部晚期前列腺癌患者（分为未经ADT治疗组与早期CR疾病组）的肿瘤样本，验证该研究发现的临床相关性。借助这一新型肽底物微阵列技术，本研究发现去势抵抗性前列腺癌中存在由信号转导与转录激活因子5A（signal transducer and activator of transcription 5A, STAT5A）介导的高激酶活性。此外，本研究还在正在消退的ADL异种移植样本中（即在观察到CR肿瘤复发前）即检测到STAT5A激酶活性升高。鉴于将前列腺癌细胞暴露于缺氧环境后同样可检测到STAT5A激酶活性升高，本研究提出：长期雄激素剥夺疗法可诱导肿瘤缺氧并激活STAT5A激酶活性，最终促使去势抵抗性肿瘤复发。综上，本研究将STAT5A鉴定为潜在的晚期前列腺癌预后标志物及治疗靶点，有待后续开展进一步研究。