Cell-based assays:Layout 1 14/1/10 19:58 Page 75
Assays
Guido Zaman: But you were also probably also refer- series of molecules, we actually screen at the cell-
ring to the mechanism of receptor desensitisation. based level, on the different species as well, that we
intend on moving to an animal model.
Arthur Christopoulos: We have an allosteric mod-
ulator that potentiates just about every pathway David Marks: Yes, we do the same thing as well.
we looked at, but it potentiates internalisation bet-
ter. So now the question is, when you take this Martin Valler: Because otherwise you could end up
modulator into an animal, and you see a lack of in with a compound that’s basically good, but just not
vivo efficacy, is that because it’s switching things developing, because your validated animal models
off better than it’s switching things on? So that’s a just don’t work.
new headache to consider.
Richard Eglen: So do you think then there’s a case
Guido Zaman: And do you study that in primary to take receptor pharmacology back 20 years, and
cells? if I look at the holistic approach, that is, either
look at changes in the cell phenotype, as a response
Arthur Christopoulos: We do. We’ve done it in both. to a pathway, or look at some cellular change
many of the label free technologies are directed
Guido Zaman: Do you think it will make a differ- at... and to hell with the pathway, tell me what the
ence in the end? cell does, and combine all these different mecha-
nisms...
Arthur Christopoulos: I don’t know, because this is
still a relatively new issue in some regard, because David Marks: But the problem is you have to fig-
on top of this – not the one I just mentioned – but ure out how each class of molecules is going to
we also have species of variance in the allosteric work. You’re going to end up by finding a lot of
pockets. And so now the next question is, if you different things, that may not be acting on the
find a compound from whatever cell based screen- receptor, maybe somewhere else, and how are you
ing you use, then you’ve got to take it into a pre- going to figure that out?
clinical animal model, and if it fails in the preclini-
cal animal model again, is it because the target or Arthur Christopoulos: No matter what you have to
the compound’s wrong? Or is it because they’re validate the target.
right, but because the pocket in the species is dif-
ferent, and we’ve found that too, with the same Richard Eglen: I think it’s emerging. Let me give
modulator. you some examples. We are working with groups
that are looking for HIV infection and they’re
Guido Zaman: Even without allosteric modulators, doing this... with human cells, disease-relevant
with even [autosteric], we have species differences. cells, and they screen for changes in the cell phe-
notype. And they have then defined six or seven
Arthur Christopoulos: Yes, and that’s been very different cell phenotypes, and then defined to those
well known, and I think a lot of people have for- discrete mechanisms of action. And then they’ve
gotten that the same thing could apply to an gone off to their chemists and done SARs around
allosteric site, if not even more so because it does- mechanisms of action on each of these phenotypes.
n’t have the pressure to conserve?]. So how many But they did such a broad net on the initial screen,
in vivo models have failed not because the com- they found all of these leads, and the challenge was
pounds aren’t good, but because of lack of activity. to ascribe them to a mode of action for the SAR, so
So if we seduce the animal with a little bit more of it wasn’t finding the leads that was the problem, it
an agonist, all of a sudden we see activity. So to me was the chemistry of the follow up activity for the
that says the compound can work, provided there’s therapeutic.
enough tone, and provided it’s the right sort of
agonist. Because the problem with allosterics of David Marks: What I was saying earlier is that
course, is that if you change the agonist from the we’ve done a small screen using a label free type
autosteric site, you change the natural allosteric approach, compared to a FLIPR approach, and we
direction. That’s called probe dependence. That’s found that there’s only a one percent overlap of the
another headache. So all these things are converg- hits. So you could take that to mean that with the
ing, happening at the same time. So our approach label free approach you find a lot of other things
now, whenever we are serious about a target, or a but we don’t know how it works.
Drug Discovery World Winter 2009/10 75
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