Invitrogen this week announced that it has exclusively licensed cell-proliferation assays from Harvard University, a move designed to add to the company’s portfolio of Click-iT intellectual property.
The technology, which is based on work done by Barry Sharpless’ lab at the Scripps Research Institute, enables users to attach an azide to one binding partner and attach an alkyne to another binding partner, which could in turn bring those two partners together via a catalyst, Vicki Singer, science advisor for Invitrogen’s cell-analysis business unit, told CBA News this week.
“That is the fundamental nature of Click-iT chemistry because azides and alkynes do not react with anything otherwise,” Singer explained, adding that they are considered bioorthogonal because they do not usually react with other biological moieties.
“If you put an azide tag on one molecule and an alkyne tag on another molecule in the presence of this catalyst, only those two molecules among every single entity in a sample will interact with one another and bind,” she said.
Singer said that Invitrogen is currently exploring what the market needs, and that in the future, the company plans to focus more on its Click-iT portfolio.
“The way I like to think of it is that we have done a lot of work over the last decade on developing fluorescent dyes,” she explained. “Now we are shifting some of that emphasis to reactivity. How does one attach that label? How does one have the cell help attach the label?”
The Click-iT EdU kit, based on the technology that Invitrogen licensed from Harvard, can be used to assess DNA replication or DNA synthesis, said Adrian Salic, an assistant professor of cell biology at Harvard Medical School.
Salic, who along with Tim Mitchison invented the technology, said that the assay kit can be used to measure cell proliferation. He mentioned that bromodeoxyuridine, or BrdU, has been used for this purpose for the last 30 years or so.
“The advantages of this new method are its ease of use and the fact that the whole experiment running time is significantly shortened from hours to minutes,” said Salic.
It has a number of other advantages for basic research, such as the ability to examine, quite quickly, large specimens that would require processing such as histological sectioning using BrdU, Salic said.
Singer said that researchers using an antibody and BrdU have to feed the cell the precursor for the bromine label, and then they have to take that cell, fix it, and treat it with acid to denature the DNA, so that an antibody can then detect it.
“What happens when the cell is treated with acid is that many of the antigens or epitopes that investigators may want to learn about are damaged,” Singer said. She added that with the Click-iT chemistry, treating the cell with acid is unnecessary, because the tag is not hidden inside of the DNA helix, so it can be detected without denaturing the DNA.
Multitasking Made Easy
That means that “investigators can look at additional biomarkers of interest in parallel with cell proliferation,” said Singer. For example, they can look at histone modification or the modification of other kinds of proteins at the same time they are looking at cell proliferation, she said.
Singer said that the ability to examine cell proliferation and other biomarkers simultaneously is something that most investigators would like to do.
“The advantages of this new method are its ease of use and the fact that the whole experiment running time is significantly shortened from hours to minutes.”
Last year, Invitrogen released the first of its Click-iT products, which are assay kits for the detection of glycoproteins. She said that she and her colleagues believe that if they found a way to incorporate either an azide or an alkyne into a sugar residue on a protein, then they might have a method for detecting all of the proteins modified with that sugar in a cell or in vitro.
“We then asked ourselves about other biological moieties, such as nucleic acids or amino acids, that [Invitrogen customers] would want to look at,” Singer said.
Researchers could feed the cell a precursor for whatever that biological moiety is that is labeled with an azide or an alkyne, and an enzyme that is in the cell will attach it wherever they want it attached.
Singer said that earlier this fall, Invitrogen released the Click-iT AHA (L-azidohomoalanine) kit for the detection of nascent protein synthesis. The AHA kit is fast, sensitive, non-toxic, and replaces radioactivity (35S-methionine) for the detection of nascent protein, she said. In addition, it can be analyzed in cells in situ or in gels or blots.
Many major pharmaceutical companies are buying the Click-iT kits, said Singer. Biotechs and research labs are using them as well. She declined to say specifically which companies, however.
“Invitrogen launched the high-content screening tools earlier in the fall, and they were beta-tested at several biotechs and pharmaceutical companies,” Singer said, although she declined to elaborate further.
“Any biological entity that is produced in a cell is a viable target,” said Singer. All that is necessary is an ezymatic method of incorporating the azide or alkyne into a precursor to that moiety.
“One could imagine RNA or a lipid precursor, for example,” she said. “Certainly lipid modifications are of interest, and one can imagine almost any kind of protein modification.”