Cell-based assays:Layout 1 14/1/10 19:58 Page 77
Assays
that. You can either do multiple assays in parallel, Martin Valler: On multiple levels of optimisation,
or you can go to multiplexing where you’ve got the behaviour of compounds, the behaviour of
assay systems that can be run on the same cells, DMSO, incubation times, signal levels, the readout
which have different components in them. modality itself, the switch between readers to get
the second readout. On multiple levels, in our
Arthur Christopoulos: Let me ask, how common is hands, it hardly ever works. It’s not easy to do a
one versus the other? I suspect that multiplex is not multiplex assay. It takes twice as long in develop-
that common? ment, and the screening is generally quicker than
the development process.
Guido Zaman: Multiplexing I think it’s not always
easy, because you have different kinetics of the Guido Zaman: We didn’t spend too much time on
assays, sometimes you have in the same cell line it because we didn’t think we could gain too much
you have different DMSO sensitivity, for instance, time with it.
we have done beta arrestin cyclically in one cell
line that had a different DMSO sensitivity... Kevin Pfleger: Maybe someone else needs to do the
because you use a second line, it’s not essential to development, and then you guys...
do it multiplexed. You can do it separately. There
are many examples of screens, primary screens that Martin Valler: Yes, that’s also a wish, that some-
other companies do, where you use multiplexing, body can develop to your target for you.
and have the second signal as the internal control.
David Marks: In automated systems, we sometimes
David Marks: We’re not doing multiplexing. We run two parallel assays at the same time, instead of
find that trying to do multiplexing is too compli- running a multiplex assay, or duplex assay.
cated in terms of assay development, and making
sure that you don’t have interference against one Richard Eglen: One of the things to your point that
and the other. I say it’s simpler to run two assays. Arthur mentioned about imaging that data that’s
emerging, we’re seeing people look at imaging as a
Martin Valler: Same with us. The assay develop- precursor to a lot what we’ve talked about. The
ment has to be optimised enough for one readout. field of HCS at induced pluripotent stem cells, to
To optimise for two, there’s a danger maybe you find small molecules that control the differentia-
miss something in the middle. tion then as a prelude to finding authentic cell
types. It seems to be rapidly emerging, and that’s
Arthur Christopoulos: What about high content? where small molecules, stem cells, and imaging are
Do you guys do high content work? coming right together. And I think that will evolve
into science to help provide cell types that may
Guido Zaman: Yes, also on a smaller scale, and answer some of the points we’ve made here today,
particularly now we have these alternatives which where you are now in a series of cell lines that have
are compatible with HCS technology. It’s not nec- authentic human relevance in reproducible fashion
essary anymore to look at beta arrestin with high that may answer some of these questions. There’s
content. clearly a couple of years before that happens, the
question is finding these things and controlling
Kevin Pfleger: So the reason you’re not doing mul- their state of differentiation. Now that may be an
tiplexing at the moment is that the compatibility of activity best done in a series of university labs, or
the assays isn’t very good. If you could get good in big pharma, I don’t know, but it’s clearly some-
compatibility of assays to multiplex, is that some- thing that’s going on.
thing you’d want to do?
Richard Eglen: Just a general question mainly to
Guido Zaman: Yes, if somebody has developed it you guys in pharma. Do the compounds come
as such, yes. And I know from the literature that from general libraries? Or from enriched, substruc-
R&D companies have completed a screen on two tural searched libraries? Is there a chemistry virtu-
readouts at the same time. al screening step before dive into it?
Kevin Pfleger: So essentially you need assays that are David Marks: It depends on what kind of family
not cytotoxic, and not affecting your cells too much, class you’re talking about. With GPCRs, I don’t
and therefore don’t interfere with the other assay. think anybody really has a good idea how to make
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