The journal Science Translational Medicine has published an article questioning the results of more than 1,000 scientific studies of brain tumors. We are talking about experiments carried out with cells isolated from glioma 50 years ago. It turned out that these cells actually come from a completely different source.
Many medical and biotechnological research is carried out in cell cultures. They are initially obtained from cells isolated from human, animal and plant tissues. For example, HeLa is a cervical cancer cell line from a woman named Henrietta Lacks, who died in 1951. It is still used in pharmacology to test new types of drugs. Thanks to special enzymes, HeLa are virtually immortal and can divide as many times as they want, which is very reminiscent of organisms from science fiction films. Over the years, cancer cells have evolved, and some scientists even refer them to a new species.
Researchers often use the lines supplied by the ATCC (American Type Culture Collection) repository and other cell culture banks. In addition, various strains of microorganisms and biological products are stored in the refrigerators of these organizations. The ATCC collection includes more than 3000 human and animal cell lines, 1200 hybrids (hybrids of immune and cancer cells), 4000 plant and animal viruses, as well as protozoa, yeasts and fungi.
The U87MG line, perhaps one of the most commonly used cell cultures in scientific work, is cells isolated from human glioma. It is the most common brain tumor. Scientists seized U87MG from a 44-year-old patient and it has been stored at the ATCC ever since. In the PubMed scientific publications database, you can find more than 1,700 articles (200 of them in 2015) devoted to the research of this culture.
Researchers from a laboratory at Uppsala University in Sweden, after studying U87MG for a long time, wondered about the authenticity of the culture contained in the ATCC. In other words, the scientists suspected that the material that was originally isolated from the tumor, and the U87MG obtained by physicians and biologists from the repository, are cells from different sources. If this is true, the results of many scientific works will be at risk. These include trials of various drugs that inhibit the growth of glioma. It is hard to imagine how seriously such a mistake could have slowed down the search for a cure that could save people with brain tumors.
To find out the true origin of the line, scientists used an approach called DNA fingerprinting. The essence of the method lies in the fact that the sequence of nucleotides (building blocks of DNA) in the genome of each living organism is unique and can be used to establish genetic relationship. Scientists usually analyze short tandem repeats (also known as microsatellites) - small pieces of DNA (2-5 nucleotides long) that repeat one after another five to 50 times.
HeLa cells
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Image: National Institutes of Health
The researchers compared short tandem repeats in U87MG cell cultures held at Uppsala University (where the line was first isolated) and ATCC. It was found that 12 out of 14 repeats have differences, which indicates that the two versions of the glioma cell line do not have a common origin. The scientists further analyzed 19 other cell lines that were used in their laboratory for brain tumor research, and none of them matched the original U87MG.
Having thus proved that the commercial cell culture had nothing to do with the tumor from which it was allegedly isolated, biologists decided to determine the true source of the line. They examined databases that store information on various cancer cell lines. They wondered if other cultures have a similar gene expression profile. The latter is understood as the content in the cell of the products of active genes (such products are RNA molecules formed during the process of transcription). For this task, scientists used the Cancer Cell Line Encyclopedia (CCLE), which describes 1036 different lines isolated from tumors of the brain, breast, intestines and other tissues and organs.
Glioma
Image: Christaras A
It turned out that the cell line U87MG belonging to ATCC corresponds to the culture isolated from a tumor of the central nervous system. The confusion is likely due to cross-contamination with other biological material.
It is not the first time that scientists have faced the problem of misusing cell lines. Some medical and biological journals insist that the cultures used in published scientific papers be tested. Nature requires the authors to conduct DNA analysis. However, in some cases, as biologists have shown, it is necessary to have information about the genetic profile of the original tissue. Scientists are calling for a move away from commercial lines such as U87MG in favor of proven glioma cells grown under suitable conditions.
Alexander Enikeev