Department of Medical Biophysics, University of Toronto, Toronto, ON, Canada.
BMC Cancer. 2009 Oct 6;9:356. doi: 10.1186/1471-2407-9-356.
Anti-cancer drugs access solid tumors via blood vessels, and must penetrate tumor tissue to reach all cancer cells. Previous studies have demonstrated steep gradients of decreasing doxorubicin fluorescence with increasing distance from blood vessels, such that many tumor cells are not exposed to drug. Studies using multilayered cell cultures show that increased P-glycoprotein (PgP) is associated with better penetration of doxorubicin, while PgP inhibitors decrease drug penetration in tumor tissue. Here we evaluate the effect of PgP expression on doxorubicin distribution in vivo.
Mice bearing tumor sublines with either high or low expression of PgP were treated with doxorubicin, with or without pre-treatment with the PgP inhibitors verapamil or PSC 833. The distribution of doxorubicin in relation to tumor blood vessels was quantified using immunofluorescence.
Our results indicate greater uptake of doxorubicin by cells near blood vessels in wild type as compared to PgP-overexpressing tumors, and pre-treatment with verapamil or PSC 833 increased uptake in PgP-overexpressing tumors. However, there were steeper gradients of decreasing doxorubicin fluorescence in wild-type tumors compared to PgP overexpressing tumors, and treatment of PgP overexpressing tumors with PgP inhibitors led to steeper gradients and greater heterogeneity in the distribution of doxorubicin.
PgP inhibitors increase uptake of doxorubicin in cells close to blood vessels, have little effect on drug uptake into cells at intermediate distances, and might have a paradoxical effect to decrease doxorubicin uptake into distal cells. This effect probably contributes to the limited success of PgP inhibitors in clinical trials.
抗癌药物通过血管进入实体肿瘤，必须穿透肿瘤组织才能到达所有癌细胞。先前的研究表明，阿霉素荧光强度随距血管距离的增加而呈梯度下降，因此许多肿瘤细胞未接触到药物。使用多层细胞培养的研究表明，增加 P-糖蛋白（PgP）与阿霉素更好的穿透有关，而 PgP 抑制剂则减少肿瘤组织中的药物穿透。在这里，我们评估 PgP 表达对体内阿霉素分布的影响。
用表达 PgP 水平较高或较低的肿瘤亚系小鼠进行阿霉素处理，同时或不预先用 PgP 抑制剂维拉帕米或 PSC 833 处理。使用免疫荧光定量分析阿霉素在肿瘤血管附近的分布。
我们的结果表明，与 PgP 过表达肿瘤相比，野生型肿瘤中靠近血管的细胞摄取阿霉素的量更大，用维拉帕米或 PSC 833 预处理可增加 PgP 过表达肿瘤中的摄取量。然而，与 PgP 过表达肿瘤相比，野生型肿瘤中阿霉素荧光强度的下降梯度更陡峭，并且用 PgP 抑制剂处理 PgP 过表达肿瘤会导致阿霉素分布的梯度更陡峭和异质性更大。
PgP 抑制剂增加了靠近血管的细胞中阿霉素的摄取量，对中间距离的细胞摄取药物几乎没有影响，并且可能对降低远端细胞中阿霉素的摄取有相反的作用。这种作用可能是 PgP 抑制剂在临床试验中效果有限的原因。
