Shockley T R, Lin K, Sung C, Nagy J A, Tompkins R G, Dedrick R L, Dvorak H F, Yarmush M L
Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge 02139.
Cancer Res. 1992 Jan 15;52(2):357-66.
The time-dependent (5 min-72 h) localization of 3 radiolabeled anti-melanoma monoclonal antibodies (MAbs 436, IND1, and 9.2.27) was studied in paired label experiments in small (4-12 mg) s.c. human melanoma xenografts (SK-MEL-2 and M21) in athymic nude mice. MAb 436 recognizes a Mr 125,000 cell surface melanoma-associated glycoprotein antigen (125 kDa-MAA); MAbs IND1 and 9.2.27 recognize a high molecular weight melanoma-associated antigen, but with equilibrium association constants differing by 2 orders of magnitude (10(8)-10(10) M-1). The two tumors were found to differ in their antigen expression levels and in both interstitial and vascular volumes. Accumulation of MAbs in both tumors was determined primarily by antigen expression levels and also by physiological factors such as vascular permeability and vascular volume; at the dose administered (20 micrograms/mouse), differences in MAb affinity among specific MAbs had minimal effect on accumulation. Quantitative flow cytometry measurements showed that antigen expression in vivo differed from that of cultured tumor cells. In vivo, expression of the Mr 125,000 MAA decreased by a factor of about 2.5 in both tumors. In contrast, the in vivo expression of the high molecular weight MAA decreased in M21 tumors but increased by 2.0-3.5-fold in SK-MEL-2 tumors. Data were analyzed using a three-compartment pharmacokinetic model (C. Sung et al., Cancer Res., 52:377-384, 1992) to provide plasma-to-tissue transport constants (k), the interstitial fluid flow rate (L), and estimates of the in vivo interstitial MAb binding site concentration (B0). For all MAbs, the plasma-to-tissue transport constants were consistently greater for M21 tumors (0.44-0.85 microliter/min/g) than for SK-MEL-2 tumors (0.28-0.66 microliter/min/g), and values of k for both tumors were approximately 1 order of magnitude greater than those for skeletal muscle (0.06-0.08 microliter/min/g). The model-estimated binding site concentration of melanoma-specific antibodies was 15-70 times lower than that predicted by experimental measurements of tumor antigen concentrations. Factors that may contribute to this discrepancy include inaccessibility of tumor cell binding sites to MAb and MAb catabolism. In summary, these results indicate that, for the MAb dose used in this study, variables pertaining to the tumor target (i.e., antigen expression levels, vascular volume, and vascular permeability) are the most important for determining MAb accumulation in tumors.
在无胸腺裸鼠体内的小型（4 - 12毫克）皮下人黑色素瘤异种移植瘤（SK - MEL - 2和M21）中，通过配对标记实验研究了3种放射性标记的抗黑色素瘤单克隆抗体（单克隆抗体436、IND1和9.2.27）随时间（5分钟至72小时）的定位情况。单克隆抗体436识别一种分子量为125,000的细胞表面黑色素瘤相关糖蛋白抗原（125 kDa - MAA）；单克隆抗体IND1和9.2.27识别一种高分子量黑色素瘤相关抗原，但平衡缔合常数相差2个数量级（10⁸ - 10¹⁰ M⁻¹）。发现这两种肿瘤在抗原表达水平以及间质和血管体积方面存在差异。两种肿瘤中抗体的积累主要由抗原表达水平决定，也受血管通透性和血管体积等生理因素影响；在给药剂量（20微克/小鼠）下，特定单克隆抗体之间亲和力的差异对积累的影响最小。定量流式细胞术测量表明，体内抗原表达与培养的肿瘤细胞不同。在体内，两种肿瘤中分子量为125,000的MAA表达均下降约2.5倍。相比之下，高分子量MAA在M21肿瘤中的体内表达下降，但在SK - MEL - 2肿瘤中增加了2.0 - 3.5倍。使用三室药代动力学模型（C. Sung等人，《癌症研究》，52:377 - 384，1992）分析数据，以提供血浆到组织的转运常数（k）、间质液流速（L）以及体内间质单克隆抗体结合位点浓度（B0）的估计值。对于所有单克隆抗体，M21肿瘤（0.44 - 0.85微升/分钟/克）的血浆到组织转运常数始终高于SK - MEL - 2肿瘤（0.28 - 0.66微升/分钟/克），并且两种肿瘤的k值比骨骼肌（0.06 - 0.08微升/分钟/克）大约高1个数量级。模型估计的黑色素瘤特异性抗体结合位点浓度比肿瘤抗原浓度的实验测量预测值低15 - 70倍。可能导致这种差异的因素包括肿瘤细胞结合位点对单克隆抗体不可及以及单克隆抗体分解代谢。总之，这些结果表明，对于本研究中使用的单克隆抗体剂量，与肿瘤靶点相关的变量（即抗原表达水平、血管体积和血管通透性）对于确定单克隆抗体在肿瘤中的积累最为重要。
