Cell-based assays:Layout 1 14/1/10 19:58 Page 74
Assays
Martin Valler: Those sort of efforts will certainly where one potentiates multiple pathways, we’ve
be supported by the structural biology, the struc- got another one that potentiates these pathways
tural studies of binding. It’s not going to be but inhibits those pathways in the same receptor,
overnight, but stepwise, people are going to come in the same cell type. What does an enhancer of
forward and say, this class of compound, will inter- ERK, and an inhibitor of calcium mean? I don’t
act with this residue, and we can do pharmaco know, but I’m going to stick them in a model, and
modeling on this class of compounds, and we I’m talking about receptors so we’re looking for
know this receptor is involved, and this class is neuropathic pain. We’re going to stick it in the
somewhere else, and on that basis you could sepa- animal and find out. We have clusters, we just
rate potential mutual agonism, inverse agonism, have to find out how the signals work. I can’t get
allosteric modulation... beyond that. But I couldn’t have gotten there with-
out the cell based assays in the first place. And
David Marks: But ultimately, you still need the cell multiple cell-based assays. I’d love to see one mul-
based assay to tell you that. Without the cell based tiplex, whether it’s high content, or however
assay, you have all the binding assays, all the struc- they’re going to do it, when you see everything
tures you want, you still don’t know what the going up or down.
interactions give you.
Kevin Pfleger: Just to throw an idea out there –
Martin Valler: In the ideal case, you just go, you how does physiology work? Do we, are we really
just put all the one million, two million compounds looking at receptor systems that have evolved over
straight into some inflammation model in some millions of years, where you hit it with an endoge-
animal, it’s not realistic is it? nous agonist, and you get a cascade? Or do we
have such intricate evolution where you hit it with
Richard Eglen: Do you think where people are a ligand, there is a cascade, but there’s also an
with dimerisation, is where people screening for opposite effect. Because then you can get home-
allosteric modulation was ten years ago, it’s a ostasis. So you’re looking at different pathways,
reflection of the maturity of the field of knowledge which actually in the body, give you this balance.
in the way in which you do it? There were clearly And then in pathologies, you can actually get an
allosteric modulators known since the Fifties, at upset of that balance. And you need to re-set that
GPCRs, it’s just that as the field developed, they modulation. So if you’re just hitting it with a
became legitimate targets for new avenues of drug sledgehammer, and you block the receptor, and just
discovery, and then all the molecules that had this shut it down, maybe you’re actually removing the
mode of action assigned to them. Because I think body’s own homeostatic side to its evolved func-
now, screening for allosteric modulators of tion.
GPCRs in a cell based assay is even a legitimate
activity in HTS. Richard Eglen: I think that’s a very good point. We
see an increased amount of cell based assays using
Arthur Christopoulos: There are two compounds primary cells, or even induced pluripotent stem
that have made it to the clinic on the basis of cells, because people are looking for doing the
allosteric modulators. I’m not following all the tri- screening in the situation that mimics the disease,
als, but I know of at least 14 from various Phase II- and not do screening in normal tissue, because of
plus trials. Yes, that’s a legitimate approach, that point. Now that point I made about kinases is
though there are still significant challenges. exactly where kinases have gone. People want to
do screening in cell types from tumors that have
Richard Eglen: I’m just thinking about your point the kinase receptor mutation.
about assigning large clusters of compounds to
modes of action. I think that was one of the Arthur Christopoulos: That makes sense. If you
approaches, to screen compounds that had a par- can take a diseased tissue from the patient, and
ticular mode of action, subsequently assign a screen on that, that’s your ideal, right?
mechanism.
Kevin Pfleger: I mean you want a drug, ideally, that
Arthur Christopoulos: We’re doing that now on a somebody who has normal physiology can take,
small scale. We’ve got allosteric ligands that now and it won’t do anything. But if they’ve got a dis-
engender stimulus bias in endogenous agonist of ease, like cancer, they take it and they have a ben-
the GPCR... And we’ve got examples of things eficial effect.
74 Drug Discovery World Winter 2009/10
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84 |
Page 85 |
Page 86 |
Page 87 |
Page 88