Polyploidization can occur naturally in organs such as the liver, where it can be an advantage, allowing liver cells to tolerate high levels of exposure to the toxic molecules processed by the liver as part of its function. However, this polyploidy can also be an origin of carcinogenesis, and these cancers are frequently resistant to anti-cancer drugs.

Using a human liver cell line, the team showed that the occurrence of polyploidy did not always lead to the process called “senescence”, by which cells stop dividing. The presence of DNA damage caused difficulties when cells divided, thus increasing the likelihood of mistakes arising and polyploidization developing. At the same time, the presence of polyploidization increased the amount of DNA damage that occurred, because of the stress the extra genomic material placed on the process of cell division.

However, the team also discovered that polyploid cells can tolerate a greater amount of DNA damage than diploid cells. As diploid cells accumulate damage, they eventually stop cell division and begin to show a phenotype known as the senescence-associated secretory phenotype, or SASP. It took a greater level of DNA damage for polyploid cells to show growth arrest or SASP.

“As polyploid cells contain more copies of the genetic information than diploid cells, any DNA damage that accumulates is less likely to occur in all of the copies of any essential gene, allowing the cells to survive for longer,” explains the lead author of the study Kazuki Hayashi.

The study also provides an answer as to why cancers derived from polyploid cells are frequently resistant to anti-cancer drug treatments. Some chemotherapy drugs damage cellular DNA to stop cell growth. They target cancer cells because they are growing and dividing much faster than healthy cells.

“The higher tolerance of polyploid cells to DNA damage explains why these cells show resistance to these DNA-damaging agents, inhibiting the treatment of these cancers,” explains Tomonori Matsumoto, senior author.

Now that the details of this close link between polyploidy and DNA damage have been revealed, this will aid in overcoming the drug resistance shown by polyploid cancer cells and pave the way for novel treatments for these cancers.