What is the impact of CSCs on treatment?
Current treatments target cancer because the drugs act on cells that are actively dividing. Most of these drugs function by inducing the death (via apoptosis) of the cancer cells. Cancer stem cells carry mutations that lead to cancer, but they do not necessarily divide quickly. This relatively inactive state would allow them to avoid the effects of cancer treatments which would explain the all too frequent recurrences of cancers. CSCs also efficiently repair DNA damage and avoid apoptosis making them hard targets for today's drugs. This evasion of treatment could be likened to a weed in a garden. Cancer stem cells are like the roots of the weed and the majority of the tumor mass is the leaves and stem of the weed. Removing the visible part of the weed appears to kill it, but the roots underground soon sprout another stem and the weed lives on.(1)
Why is it difficult to target CSCs?
The problems encountered when clinicians treat cancer are also seen when purified CSCs are treated with anti-cancer drugs. Because normal stem cells and CSCs are very similar, it is difficult to kill CSCs and leave normal stem cells unharmed. Drug resistance is another major obstacle in treating both cancer and CSCs. Stem cells tend to have high levels of particular cellular pumps (i.e. the multiple drug resistance protein, MDR) that are able to eject cancer drugs from the cells making the drugs ineffective. Stem cells are also harder to kill than normal cells because they have an ability to block the signals that drugs like chemotherapy cause to lead to death (apoptosis). An excess of antiapoptotic proteins helps stem cells avoid the effects of cancer treatments.(1)
Learn more about MDR and drug resistance.
Learn more about cancer cell death (apoptosis).
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