Canonical vs. non-canonical E-selectin ligands on solid human tumor cells differentially determine their E-selectin binding affinity: Functional and molecular implications for a novel anti-adhesive and anti-metastatic strategy

e -选择素（在血管内皮细胞上）和碳水化合物e -选择素配体（在循环肿瘤细胞上）之间的凝集素-聚糖相互作用是肺转移形成的一个重要步骤，因为它介导CTC从血流粘附到血管内皮，从而先于CTC外渗。外渗同时使ctc避开了循环中存在的不利条件。因此，阻断粘连是一种诱人的治疗方法。e -选择素在内皮细胞上的表达取决于促炎细胞因子环境，这在生理上允许白细胞特异性地外渗到炎症组织中。癌症中的这种促炎环境被认为是通过细胞因子的系统性释放产生的。促炎转录因子必须由蛋白酶体激活。可以阻断这种激活的原型蛋白酶体抑制剂是硼替佐米（BZM）。BZM已经用于临床治疗多发性骨髓瘤患者。在此背景下，我们的初步工作表明，BZM在体外和原位实验中实际上降低了肿瘤细胞的内皮粘附，并在原理验证实验中降低了肿瘤细胞在体内的转移形成。然而，BZM的功效取决于肿瘤细胞表面各自表达的e -选择素配体。我们分析了人类肿瘤可以使用规范或非规范的e -选择素配体进行内皮粘附，这决定了它们的e -选择素结合亲和力和内皮粘附对额外cam的潜在需求。只有表达低亲和力、非典型e -选择素配体的肿瘤细胞对BZM敏感，而表达高亲和力、典型e -选择素配体的肿瘤细胞对BZM敏感。首先，有必要分析BZM在体内对其他异种移植肿瘤是否表现出不同的抗转移效果。其次，由于BZM不仅可以下调e -选择素，还可以下调ICAM-1和内皮趋化因子，因此需要更详细地阐明蛋白酶体抑制的抗粘附机制。第三，我们将确定观察到的BZM的抗转移作用是否实际上是由于损害CTC对肺微血管内皮的粘附（对于其他细胞系）。为此，我们将利用已建立的离体肺灌注模型，直接观察肿瘤细胞在小鼠肺微循环中的粘附情况。我们还将研究皮下原发性肿瘤的存在是否会促进CTC在远处的原位粘连。最后，我们将研究如何靶向bzm耐药、高e选择素仿射肿瘤的内皮粘附。因此，我们的目的是确定在bzm耐药细胞系中鉴定的糖蛋白载体和糖基转移酶在体外和原位粘附以及体内转移形成中的功能相关性。

The lectin-glycan interaction between E-selectin (on vascular endothelial cells, ECs) and carbohydrate E-selectin ligands (on circulating tumor cells, CTCs) is one important step of pulmonary metastasis formation as it mediates the adhesion of CTCs from the blood stream to vascular endothelium and hence precedes CTC extravasation. Extravasation concomitantly eludes CTCs from adverse conditions existing within the circulation. Hence, blocking adhesion displays a tempting therapeutic approach. E-selectin expression on ECs depends on a pro-inflammatory cytokine environment, which physiologically allows the extravasation of leukocytes specifically into inflamed tissues. This pro-inflammatory environment in cancer is thought to be generated through a systemic release of cytokines. The pro-inflammatory transcription factors have to be activated by the proteasome. The prototype proteasome inhibitor could block this activation is bortezomib (BZM). BZM is already in clinical use for treating multiple myeloma patients. On this background our preliminary work shows that BZM actually reduces endothelial adhesion of tumor cells in vitro and in situ and - in proof-of-principle experiments - their metastasis formation in vivo. However, the efficacy of BZM depends on the respective E-selectin ligands expressed at the tumor cell surface. We dissected that human tumors can use either canonical or non-canonical E-selectin ligands for endothelial adhesion and that this determines their E-selectin binding affinity and the potential requirement of additional CAMs for endothelial adhesion. Only tumor cells that express low affinity, non-canonical E-selectin ligands were susceptible to BZM, but not tumor cells that express high affinity, canonical E-selectin ligands. At first, it is necessary to analyze whether BZM shows divergent anti-metastatic efficacy on additional xenograft tumors in vivo. Secondly, the anti-adhesive mechanism of proteasome inhibition should be clarified in more detail since BZM was observed to down-regulate not only E-selectin, but also ICAM-1 and endothelial chemokines. Thirdly, we will determine whether the observed anti-metastatic effect of BZM is actually due to impairing CTC adhesion to pulmonary microvascular endothelium (for additional cell lines). For this purpose, we will use an established ex vivo lung perfusion model enabling us to directly observe tumor cell adhesion in the murine lung microcirculation. We will also investigate whether the presence of subcutaneous primary tumors promotes CTC adhesion at a distant site in situ. Finally, we will investigate how the endothelial adhesion of BZM-resistant, highly E-selectin-affine tumors can be targeted. Therefore, we aim to determine the functional relevance of the glycoprotein carriers and glycosyltransferases identified in BZM-resistant cell lines for their adhesion in vitro and in situ as well as metastasis formation in vivo.