叶酸的摄取主要由叶酸受体(FR)β介导,由FOLR2基因编码,在粒细胞等骨髓免疫细胞中,单核细胞,尤其是在构成网状内皮系统(RES)并浸润肿瘤微环境的巨噬细胞中。由于骨髓免疫区室在肿瘤发生过程中动态变化,评估表达FRβ的骨髓细胞对肿瘤的浸润状态以更好地确定叶酸功能化药物递送系统的靶向功效至关重要。另一方面,RES的清除是用叶酸修饰的纳米颗粒的靶向功效的主要限制。因此,这项研究的目的是(i)确定在不同阶段浸润肿瘤的FRβ骨髓细胞的数量和亚型,(ii)比较荷瘤动物和健康动物不同器官中FRβ骨髓细胞的数量和亚型,(iii)测试原型叶酸官能化纳米颗粒的癌症靶向功效和生物分布是否与FRP+骨髓细胞的密度相关。这里,我们报道在小鼠乳腺癌模型中,在肿瘤发生的不同阶段,髓样细胞浸润增强,FRβ上调.巨噬细胞的CD206+亚群高表达FRβ,在荷瘤小鼠和健康小鼠中都很突出。在荷瘤小鼠中,所有骨髓细胞的数量,但尤其是粒细胞,在肿瘤中显著增加,肝脏,肺,脾,脾肾脏,淋巴结,腹膜腔,骨髓,心,和大脑。与巨噬细胞相比,粒细胞和单核细胞中FRβ水平适中。肿瘤微环境中FRβ+免疫细胞的密度与叶酸官能化的环糊精纳米颗粒的肿瘤靶向功效不直接相关。肺被确定为叶酸功能化纳米颗粒的优先积累位点,其中FRβ+CD206+巨噬细胞显著吞噬环糊精纳米颗粒。总之,我们的结果表明,肿瘤的形成增加了FR水平,改变了髓样免疫细胞在所有器官中的浸润和分布,这应该被认为是影响纳米颗粒给药靶向效果的主要因素.
Folate uptake is largely mediated by folate receptor (FR)β, encoded by FOLR2 gene, in myeloid immune cells such as granulocytes, monocytes, and especially in macrophages that constitute the reticuloendothelial system (RES) and infiltrate the tumor microenvironment. Since the myeloid immune compartment dynamically changes during tumorigenesis, it is critical to assess the infiltration status of the tumors by FRβ-expressing myeloid cells to better define the targeting efficacy of folate-functionalized drug delivery systems. On the other hand, clearance by RES is a major limitation for the targeting efficacy of nanoparticles decorated with folate. Therefore, the aims of this study are (i) to determine the amount and subtypes of FRβ+ myeloid cells infiltrating the tumors at different stages, (ii) to compare the amount and subtype of FRβ+ myeloid cells in distinct organs of tumor-bearing and healthy animals, (iii) to test if the cancer-targeting efficacy and biodistribution of a prototypic folate-functionalized nanoparticle associates with the density of FRβ+ myeloid cells. Here, we report that myeloid cell infiltration was enhanced and FRβ was upregulated at distinct stages of tumorigenesis in a mouse breast cancer model. The CD206+ subset of macrophages highly expressed FRβ, prominently both in tumor-bearing and healthy mice. In tumor-bearing mice, the amount of all myeloid cells, but particularly granulocytes, was remarkably increased in the tumor, liver, lungs, spleen, kidneys, lymph nodes, peritoneal cavity, bone marrow, heart, and brain. Compared with macrophages, the level of FRβ was moderate in granulocytes and monocytes. The density of FRβ+ immune cells in the tumor microenvironment was not directly associated with the tumor-targeting efficacy of the folate-functionalized
cyclodextrin nanoparticles. The lung was determined as a preferential site of accumulation for folate-functionalized nanoparticles, wherein FRβ+CD206+ macrophages significantly engulfed
cyclodextrin nanoparticles. In conclusion, our results demonstrate that the tumor formation augments the FR levels and alters the infiltration and distribution of myeloid immune cells in all organs which should be considered as a major factor influencing the targeting efficacy of nanoparticles for drug delivery.