Aspira Biosystems, an aspiring new player in the protein chip development field, recently won a Small Business Innovation Research grant totaling $108,000 from the National Institutes of Health.
This grant adds to the $2.95 million in venture funding the South San Francisco, Calif., startup has so far raised in its bid to bring a protein chip to market within a year.
The companys chief asset in its attempt to distinguish itself from the protein chip pack is its patent-pending ProteinPrint technology. ProteinPrint relies on a technique called molecular imprinting to produce capture agents. In this process, proprietary monomers are allowed to self-assemble around a protein of interest, forming a cavity, which is followed by cross linking.
Although the technology is not new, it did not lend itself to large biomolecules like proteins in the past.
We have made some very big changes to the traditional methods that have allowed us to work with proteins, said Casey Lynch, Aspiras president and co-founder. One of these changes, for example, was a switch from organic solvents to an aqueous system. Another change, which is in the works, is a move from producing protein capture molecules against peptides representing the C-terminal regions of proteins to producing them against surface-expressed domains.
This technology possesses a key potential advantage over those used in other protein chip platforms: The polymer cavities could alleviate the need for specific antibodies, of which there is an acute shortage.
Many chip makers are looking at arraying antibodies and are having a lot of frustrations because there are not enough, said Lynch. The problem is not really making an array, the problem is getting good capture agents.
The polymer cavities, according to Lynch, serve as good capture agents, because they selectively bind to the target proteins, and bind more weakly to proteins differing in just one amino acid near their C-terminus. Lynch said that 80 to 90 percent of all proteins are unique by at least one amino acid in that region. Cross reactivity will be a problem within certain families of proteins that are highly homologous, she said, but often these are expressed in different tissues.
With regard to affinities, Aspiras polymers seem to compare favorably to antibodies and their mimetics: Ours are in the nanomolar range, said Lynch. However, unlike monoclonal antibodies, imprinted polymers are expected to be heterogeneous, displaying a range of affinities.
Another advantage of Aspiras capture agents, Lynch said, is their short production time, currently three to four weeks instead of six months for an antibody. Compared to phage antibodies, which also only take a few weeks to produce, the library size does not present a problem. Ours is essentially an unlimited library, said Lynch.
In the absence of published data, however, some express doubts about the technology. Knowing the little I do about imprinting and properties of polymers and the type of interactions you can get from them, I find it difficult to believe that they are going to be competitive with antibodies or with the various antibody mimetics, like phage antibodies, said Gavin MacBeath, who develops protein microarrays at the Bauer Center for Genomics Research at Harvard University. However, without seeing data, I cannot really comment on it.
Kenneth Shea, professor of chemistry at the University of California, Irvine and a member of Aspiras scientific advisory board, cautioned: It is quite likely that [imprinted polymers] would never achieve the exquisite fidelity that an antibody might. But a run of C-terminal amino acids would probably [be] sufficient information to discriminate between many different types of proteins, he said.
There are no publications about the technology yet, according to Lynch, but Aspira is hoping to embark on academic collaborations soon.