1- the question or problem you’re trying to solve. If you’re studying a particular disease state then the more closely the cell line exemplifies this disease the better.
2- Target tissue
3- Species: Non-human and non-primate cell lines
4-Functional characteristics: What is the purpose of your experiments?
5- Growth conditions and characteristics: What are your requirements with respect to growth rate, saturation density, cloning efficiency, and the ability to grow in suspension?
I think the literature search constitutes a major part of this decision. If there are some anticancer effects of this extract on certain cell lines, it gives you a clue about it. However, extract has many components and includes their interaction and combining effects. Without trying it on the certain cancer lines, it is challenging to estimate its certain effects. My suggestion is that you’d better use trial and error method with the light of previous studies.
I think it can be used in in vitro studies, just as extracts are used in in vivo studies. Because the aim here is to show synergistic effects. However, if you want to work on the active substance in the extract, you should first go to isolation methods
I think all your answers are very useful but still why this substance do its anticancer activity better for some tissues than others or why without literatures assistance select one tissue to work on ...