Molecular oxygen sensing and PHD-inhibition: implications for colorectal cancer growth

缺氧诱导因子（Hypoxia-inducible factors，HIF）是缺氧适应性反应中的转录主调节因子，通过改变与肿瘤细胞存活、增殖、代谢、血管生成和转移有关的多种靶基因的表达来影响肿瘤的生长。HIF脯氨酰羟化酶（PHD 1、PHD 2和PHD 3）是调节HIF活性的分子氧传感器。由于这些PHD酶可以应用药理学抑制剂抑制，因此它们是潜在的治疗靶点。具体而言，目前的见解表明，PHD抑制可能会改善肝切除术后的肝功能，这是结肠直肠肝转移临床管理的基石。在第一个资助期间获得的数据显示，与健康肠粘膜相比，PHD 3（而不是PHD 1或PHD 2）的表达在人类结直肠癌标本中下调，并且PHD 3的低肿瘤表达与远处转移的频率增加相关。因此，功能遗传学分析显示，PHD 3在结直肠癌细胞中的过表达减弱了各种小鼠结肠肿瘤模型中的肿瘤生长和转移。独立于其在癌细胞本身中的功能，PHD 3在人结直肠癌组织的基质巨噬细胞中表达。事实上，遗传功能丧失研究表明，PHD 3的丧失特异性诱导巨噬细胞的成熟和促炎激活。综上所述，这些发现表明，肿瘤细胞中PHD 3表达的丧失发挥肿瘤抑制作用，而其在先天免疫细胞中的表达可能独立地调节肿瘤相关巨噬细胞的促炎和肿瘤抑制作用。在第二个资助期，我们建议进一步阐明PHD 3在结肠癌细胞和肿瘤相关巨噬细胞中的双重功能，以及它们对结直肠癌进展的协调作用。此外，为了评估这些见解如何转化为药物PHD抑制在结直肠癌患者中的潜在应用，我们将评估药物PHD抑制对结直肠肝转移扩大的影响，特别是在手术肝切除的情况下。

Hypoxia-inducible factors (HIFs) are transcriptional master regulators in the adaptive response to oxygen deprivation (hypoxia), and affect cancer growth by altering the expression of numerous target genes involved in tumor cell survival, proliferation, metabolism, angiogenesis and metastasis. HIF prolyl hydroxylase enzymes (PHD1, PHD2 and PHD3) are molecular oxygen sensors regulating the activity of HIFs. Since these PHD enzymes can be inhibited applying pharmacological inhibitors, they are potential therapeutic targets. Specifically, current insight suggests that PHD-inhibition may improve liver function following major hepatectomy, which represents a cornerstone in the clinical management of colorectal liver metastases. Data obtained during the first funding period revealed that expression of PHD3 (but not of PHD1 or PHD2) is down-regulated in human colorectal cancer specimens compared to healthy gut mucosa, and that low tumor-expression of PHD3 correlates with increased frequency of distant metastases. Consistently, functional genetic analyses revealed that over-expression of PHD3 in colorectal cancer cells attenuates tumor growth and metastasis in various mouse colon tumor models. Independently from its function in the cancer cells themselves, PHD3 was expressed in stromal macrophages of human colorectal cancer tissues. Indeed, genetic loss of function studies revealed that loss of PHD3 specifically induces the maturation and pro-inflammatory activation of macrophages. Taken together, these findings suggest that loss of PHD3-expression in tumor cells exerts tumor-suppressive effects, whereas its expression in innate immune cells may independently regulate proinflammatory and tumor-suppressive effects of tumor-associated macrophages. In the second funding period, we propose to further elucidate the suspected dual functions for PHD3 in colon cancer cells and tumor-associated macrophages, and their coordinate effects on colorectal cancer progression. Furthermore, in order to assess how these insights translate to potential applications of pharmacologic PHD-inhibition in colorectal cancer patients, we will assess the effects of pharmacologic PHD-inhibition on the expansion of colorectal liver metastases, particularly in the setting of surgical liver resection.