Chambers A F, MacDonald I C, Schmidt E E, Morris V L, Groom A C
Department of Oncology, University of Western Ontario, London, Canada.
Cancer Metastasis Rev. 1998;17(3):263-9. doi: 10.1023/a:1006136428254.
Preclinical in vivo studies of agents targeted against metastasis have to date been based primarily on end-point assays. Such assays can determine whether a treatment affects the number or size of metastases in an organ at a given time, but are poorly suited to determining how and at what stage in the process the treatment affected the end point. High resolution in vivo videomicroscopy permits direct observation of the process of metastasis as it occurs in living animals over time. Studies based on this technique and a cell accounting procedure we have devised, have shown that early steps in the metastatic process (survival in the circulation, extravasation) contribute relatively little to cell loss and metastatic inefficiency. Steps that occur after extravasation appear to be primarily responsible for the significant losses that result in metastatic inefficiency, and these steps may represent good targets for the design of new antimetastatic therapies. Matrix metalloproteinases have been implicated functionally in metastasis, and are viewed as an appropriate target in the development of inhibitors of metastasis. Using both endogenous and synthetic exogenous metalloproteinase inhibitors, we have shown that the inhibition of metastasis which these agents produce is not due to inhibition of cell extravasation from the circulation into the tissue, but to reduction of angiogenesis within metastases. A similar conclusion was reached concerning the mechanism of action, on metastasis, of carboxyamidotriazole, an inhibitor of calcium-mediated signal transduction which is currently in Phase II single agent clinical trials. In vivo videomicroscopy of sequential steps in metastasis, coupled with methods that allow precise quantification of cell loss at specific steps in the metastatic process, as well as standard histological assessment at stages identified as crucial, allow characterization of the details of metastasis as an ongoing process. This provides a powerful complement to end-point assays, for it allows mechanistic information to be obtained from in vivo experiments, an approach which provides better understanding of how and when a drug may function in vivo to inhibit metastasis.
迄今为止，针对转移的靶向药物的临床前体内研究主要基于终点测定法。此类测定法可以确定一种治疗方法在给定时间是否会影响器官中转移灶的数量或大小，但不太适合确定该治疗方法是如何以及在过程的哪个阶段影响终点的。高分辨率体内视频显微镜术能够随着时间推移在活体动物中直接观察转移过程。基于这项技术以及我们设计的细胞计数程序所开展的研究表明，转移过程的早期步骤（在循环中的存活、外渗）对细胞损失和转移效率低下的影响相对较小。外渗后发生的步骤似乎是导致转移效率低下的显著损失的主要原因，这些步骤可能是设计新型抗转移疗法的良好靶点。基质金属蛋白酶在功能上与转移有关，被视为转移抑制剂开发中的合适靶点。使用内源性和合成外源性金属蛋白酶抑制剂，我们已经表明，这些药物所产生的转移抑制作用并非由于抑制细胞从循环进入组织的外渗，而是由于减少转移灶内的血管生成。对于目前正处于II期单药临床试验阶段的钙介导信号转导抑制剂羧甲脒三唑对转移的作用机制，也得出了类似的结论。对转移过程中连续步骤进行体内视频显微镜观察，再结合能够精确量化转移过程中特定步骤细胞损失的方法，以及在确定为关键阶段进行标准组织学评估，能够将转移过程的细节表征为一个持续进行的过程。这为终点测定法提供了有力补充，因为它能够从体内实验中获取机制信息，这种方法有助于更好地理解药物在体内如何以及何时发挥作用来抑制转移。
