Tế bào gốc ung thư trong kháng thuốc và sàng lọc thuốc: Chúng tôi có thể khai thác các Paradigm ung thư Tế bào gốc trong Tìm kiếm Đại lý kháng u mới? | Cancer Stem Cells in Drug Resistance and Drug Screening Can We Exploit the Cancer Stem Cell Paradigm in Search for New Antitumor Agents 427 3. Properties of stem cells and CSCs similarities and differences One of the issues concerning CSCs that needs clarification is which properties are shared between normal stem cells and cancer stem cells. This is particularly important for potential therapies directed toward CSCs that should spare normal stem cells. CSCs are defined to have three features i represent a minor population of a tumor typically of all cells but may be as high as 25 - see previous section ii have the property of self-renewal iii are the only cells within the tumor which are capable of immortal growth and production of the tumor in vivo. It follows that tumor cell population is composed of relatively rare CSCs and committed or differentiated non-CSC tumor cells with possibly limited life span. Important properties of normal stem cells include self-renewal as well as pluripotency i. e. the ability of stem cells to differentiate to many functionally distinct cell types. In addition to that stem cells are characterized by their very limited proliferation potential as stem cells cells divide only occasionally and in response to very specific intra- and extracellular signals. Some of these stem cell features cannot directly be applied to CSCs. Most of the available literature data show that CSCs proliferate quite rapidly although doubling times are frequently much slower compared to the non-stem tumor population Ropolo et al. 2009 Ishimoto et al. 2010 . An extreme case can be leukemia stem cells which are commonly dormant but can be induced to proliferate by specific cytokines or anticancer agents such as arsenic oxide Essers Trumpp 2010 Thomas Cannas 2010 . Secondly one of the features of stem cells is their ability to produce more differentiated cell progeny. Accordingly cells of many tumor types are able to differentiate reversibly or irreversibly
