Department of Chemical Engineering & Applied Chemistry, 200 College Street, Toronto, ON M5S 3E5, Canada.
BMC Cancer. 2012 Dec 5;12:579. doi: 10.1186/1471-2407-12-579.
Human tumour xenografts in immune compromised mice are widely used as cancer models because they are easy to reproduce and simple to use in a variety of pre-clinical assessments. Developments in nanomedicine have led to the use of tumour xenografts in testing nanoscale delivery devices, such as nanoparticles and polymer-drug conjugates, for targeting and efficacy via the enhanced permeability and retention (EPR) effect. For these results to be meaningful, the hyperpermeable vasculature and reduced lymphatic drainage associated with tumour pathophysiology must be replicated in the model. In pre-clinical breast cancer xenograft models, cells are commonly introduced via injection either orthotopically (mammary fat pad, MFP) or ectopically (subcutaneous, SC), and the organ environment experienced by the tumour cells has been shown to influence their behaviour.
To evaluate xenograft models of breast cancer in the context of EPR, both orthotopic MFP and ectopic SC injections of MDA-MB-231-H2N cells were given to NOD scid gamma (NSG) mice. Animals with matched tumours in two size categories were tested by injection of a high molecular weight dextran as a model nanocarrier. Tumours were collected and sectioned to assess dextran accumulation compared to liver tissue as a positive control. To understand the cellular basis of these observations, tumour sections were also immunostained for endothelial cells, basement membranes, pericytes, and lymphatic vessels.
SC tumours required longer development times to become size matched to MFP tumours, and also presented wide size variability and ulcerated skin lesions 6 weeks after cell injection. The 3 week MFP tumour model demonstrated greater dextran accumulation than the size matched 5 week SC tumour model (for P < 0.10). Immunostaining revealed greater vascular density and thinner basement membranes in the MFP tumour model 3 weeks after cell injection. Both the MFP and SC tumours showed evidence of insufficient lymphatic drainage, as many fluid-filled and collagen IV-lined spaces were observed, which likely contain excess interstitial fluid.
Dextran accumulation and immunostaining results suggest that small MFP tumours best replicate the vascular permeability required to observe the EPR effect in vivo. A more predictable growth profile and the absence of ulcerated skin lesions further point to the MFP model as a strong choice for long term treatment studies that initiate after a target tumour size has been reached.
免疫功能低下的小鼠中的人肿瘤异种移植物被广泛用作癌症模型，因为它们易于繁殖，并且易于在各种临床前评估中使用。纳米医学的发展导致了使用肿瘤异种移植物来测试纳米级递药装置，如纳米颗粒和聚合物-药物偶联物，通过增强的通透性和保留（EPR）效应进行靶向和疗效。为了使这些结果有意义，必须在模型中复制与肿瘤病理生理学相关的高通透性血管和减少的淋巴引流。在临床前乳腺癌异种移植物模型中，细胞通常通过注射（乳腺脂肪垫，MFP）或异位（皮下，SC）进行引入，并且肿瘤细胞所经历的器官环境已被证明会影响其行为。
为了在 EPR 背景下评估乳腺癌异种移植物模型，将 MDA-MB-231-H2N 细胞的原位 MFP 和异位 SC 注射均给予 NOD scid gamma（NSG）小鼠。将两种大小类别的匹配肿瘤的动物用高分子量葡聚糖作为模型纳米载体进行注射测试。收集肿瘤并切片，以评估与肝组织相比的葡聚糖积累情况，肝组织作为阳性对照。为了了解这些观察结果的细胞基础，还对肿瘤切片进行了内皮细胞、基膜、周细胞和淋巴管的免疫染色。
SC 肿瘤需要更长的时间才能达到与 MFP 肿瘤匹配的大小，并且在细胞注射后 6 周还表现出广泛的大小变异性和溃疡性皮肤病变。3 周的 MFP 肿瘤模型显示出比大小匹配的 5 周 SC 肿瘤模型更高的葡聚糖积累（P < 0.10）。细胞注射后 3 周，MFP 肿瘤模型中的血管密度更大，基膜更薄。MFP 和 SC 肿瘤均显示出淋巴引流不足的证据，因为观察到许多充满液体和胶原 IV 线的空间，其中可能含有过多的间质液。
葡聚糖积累和免疫染色结果表明，小的 MFP 肿瘤最能复制体内观察到 EPR 效应所需的血管通透性。更可预测的生长曲线和不存在溃疡性皮肤病变进一步指向 MFP 模型，因为它是在达到目标肿瘤大小后开始的长期治疗研究的理想选择。
