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The following message was posted to: PharmPK
Dear
Ester molecules gets hydrolysed by plasma esterase and
converts into acid. We did the linearity using the
esterase inhibitor (paraxoan). Usually for protein
binding, we use ultrafitration method. for these type
of drug, how to assess the protein binding. Is there
any way to assess the molecule protein binding apart
from radiolabelling the drug, as ester drug converts
immediately to acid in plasma. Please tell me how
assess the protein binding of these type of molecule.
regards
shivakumar
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Dear Shivakumar,
One option is to measure the ester's binding to the major serum drug
binding proteins (HSA and AGP), and then estimate the percent bound.
This can be done in the absence of the esterases. I'd be happy to send
you a poster on this assay technique (a disclaimer: my lab offers this
assay as a fee-for-service).
Thanks,
Adrian Sheldon
Charles River Labs (In Vitro ADMET)
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The following message was posted to: PharmPK
Hi
I thought that serum albumin had some esterase activity ?
Dave
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David, you're correct. Serum albumin (from multiple species) indeed
has some esterase activity toward various substrates. The extent of
activity directed toward a particular ester-containing compound can
vary, so should be tested on a case-by-case basis to determine how
significant the issue is (re. making SA protein binding measurements).
Adrian
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The following message was posted to: PharmPK
Thanks for your inputs with regard to my prevoius
questions. Here is one more!
How does one rank compounds based on (human) plasma
protein binding data during the discovery phase? Which
is better - low or moderate or highly bound. Any
refrence will be highly appreciated.
Thanks,
Cali
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Dear Cali,
There are several experimental approaches for quickly ranking protein
binding for early discovery (screening/lead optimization) needs, such as
fluorescent probe assays, equilibrium dialysis in 96 well device, or
ultracentrifugation. They each have pros and cons. For screening, it's
important to avoid the limitations of equilibrium dialysis (poor
recovery, not reaching equilibrium, poor performance of some plate-based
devices such as the Harvard plate, etc.), and while ultrafiltration is
relatively fast it is prone to NSB problems and MS interference from
extractables. My lab has established a fluorescence-based discovery
assay which provides Kds for specific binding sites on HSA and AGP, and
works well as long as the compounds have good solubility and don't
interfere.
If you send me your email address, I can send some technical info and a
presentation we gave at a conference earlier this year.
Thanks,
Adrian
Adrian Sheldon, Ph.D
In Vitro ADMET
Charles River Labs (a CRO)
Worcester, MA
Adrian.sheldon.-a-.us.crl.com
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Hi.
I would think this depends on the target receptor of the drug and
also how quick an effect is desired. If you're looking for an
instantaneous response, you'd be after something with low affinity
for plasma proteins. As far as a ranking system goes, I'm not aware
of any reference.
Anand
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Copyright 1995-2010 David W. A. Bourne (david@boomer.org)