Versluis A J, van Geel P J, Oppelaar H, van Berkel T J, Bijsterbosch M K
Division of Biopharmaceutics, Leiden/Amsterdam Center for Drug Research, University of Leiden, The Netherlands.
Br J Cancer. 1996 Aug;74(4):525-32. doi: 10.1038/bjc.1996.396.
Selective delivery of cytotoxic anti-neoplastic drugs can diminish the severe side-effects associated with these drugs. Many malignant tumours express high levels of low-density lipoprotein (LDL) receptors on their membranes. Therefore, LDL may be used as a carrier to obtain selective delivery of anti-neoplastic drugs to tumours. The present study was performed to investigate the feasibility of the murine B16 tumour/mouse model for the evaluation of LDL-mediated tumour therapy. LDL binds with high affinity to LDL receptors on cultured B16 cells (Kd, 5.9 +/- 2.3 micrograms ml-1; Bmax 206 +/- 23 ng LDL mg-1 cell protein). After binding and internalisation, LDL was very efficiently degraded: 724 +/- 19 ng LDL mg-1 cell protein h-1. Chloroquine and ammonium chloride completely inhibited the degradation of LDL by the B16 cells, indicating involvement of lysosomes. LDL receptors were down-regulated by 70% after preincubation of B16 cells with 300 micrograms ml-1 LDL, indicating that their expression is regulated by intracellular cholesterol. To evaluate the uptake of LDL by the B16 tumour in vivo, tissue distribution studies were performed in C57/B1 mice inoculated with B16 tumours. For these experiments, LDL was radiolabelled with tyramine cellobiose, a non-degradable label, which is retained in cells after uptake. At 24 h after injection of LDL, the liver, adrenals and the spleen were found to be the major organs involved in LDL uptake, with tissue-serum (T/S) ratios of 0.82 +/- 0.08, 1.17 +/- 0.20 and 0.69 +/- 0.08 respectively. Of all the other tissues, the tumour showed the highest uptake of LDL (T/S ratio of 0.40 +/- 0.07). A large part of the LDL uptake was receptor mediated, as the uptake of methylated LDL was much lower. Although the LDL uptake by the liver, spleen and adrenals is higher than that by the tumour, the LDL receptor-mediated uptake by these organs may be selectively down-regulated by methods that do not affect the expression of LDL receptors on tumour cells. It is concluded that the B16 tumour-bearing mouse constitutes a good model to evaluate the effectiveness of LDL-mediated delivery of cytotoxic (pro)drugs to tumours in vivo.
细胞毒性抗肿瘤药物的选择性递送可减少与这些药物相关的严重副作用。许多恶性肿瘤在其细胞膜上表达高水平的低密度脂蛋白（LDL）受体。因此，LDL可作为载体，用于将抗肿瘤药物选择性递送至肿瘤。本研究旨在探讨小鼠B16肿瘤/小鼠模型用于评估LDL介导的肿瘤治疗的可行性。LDL以高亲和力与培养的B16细胞上的LDL受体结合（解离常数Kd，5.9±2.3微克/毫升；最大结合量Bmax，206±23纳克LDL/毫克细胞蛋白）。结合并内化后，LDL被非常有效地降解：724±19纳克LDL/毫克细胞蛋白·小时-1。氯喹和氯化铵完全抑制了B16细胞对LDL的降解，表明溶酶体参与其中。用300微克/毫升LDL预孵育B16细胞后，LDL受体下调了70%，表明其表达受细胞内胆固醇调节。为了评估B16肿瘤在体内对LDL的摄取，对接种了B16肿瘤的C57/B1小鼠进行了组织分布研究。对于这些实验，LDL用纤维二糖酪胺进行放射性标记，这是一种不可降解的标记物，摄取后保留在细胞中。注射LDL后24小时，发现肝脏、肾上腺和脾脏是参与LDL摄取的主要器官，组织-血清（T/S）比值分别为0.82±0.08、1.17±0.20和0.69±0.08。在所有其他组织中，肿瘤显示出最高的LDL摄取（T/S比值为0.40±0.07）。大部分LDL摄取是由受体介导的，因为甲基化LDL的摄取要低得多。尽管肝脏、脾脏和肾上腺对LDL的摄取高于肿瘤，但这些器官中由LDL受体介导的摄取可通过不影响肿瘤细胞上LDL受体表达的方法选择性下调。结论是，携带B16肿瘤的小鼠构成了一个良好的模型，可用于评估LDL介导的细胞毒性（前体）药物在体内递送至肿瘤的有效性。
