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Can someone please tell me the difference and importance of doing a
metabolite study of any drug using human cDNA-expressed P450 screening and
microsomes?
Thanks
Ananda
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Using cDNA expressed cytochrome P450s allows you to assign the generation of
a particular metabolite to a specific isoform of cytochrome P450.
Microsomes can be used to generate the same information by using cytochrome
P450 isoform specific inhibitors (chemical or immunological). It is also
possible to use a series of microsome samples to correlate the specific
cytochrome P450 isoform content with metabolite production (correlation
analysis). Microsome analysis is generally not as clean since chemical
inhibitors may not be entirely specific and specific inhibitory antibodies
are expensive and may not be available for all isoforms.
Charlie Fisher, Ph.D.
Senior Scientist/Prodject Director
In vitro Metabolism
CEDRA Corporation
http://www.cedracorp.com
cfisher.at.cedracorp.com
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Dear Ananda,
The use of cDNA expressed P450's and human liver microsomes depends
upon the type of study you are dealing with. If its for identifying
the enzymes responsible for the metabolism of the drug, the simplest
approach would be to go for recombinants and alternatively microsomes
can be used with chemical inhibitors and antibodies. However, for
P450 inhibtion studies it is always better to have data from human
liver microsomes because the IC 50's and Ki would be more pertinent,
if its obtained from microsomes, since sometimes you would get
different results from microsomes and cDNA's.
Another important aspect is that you can obtain microsome samples
with low, mid or high activity of the enzyme you are interested in.
This will help you to investigate if the enzyme in question is still
the major contributor for the metabolism of the drug in the real life
situation where you would encounter subjects having various p450
activities.
Regards,
Azher M. Hussain, Ph.D
Post Doctoral Researcher
P450 Inhibition
Xenotech, LLC
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Copyright 1995-2010 David W. A. Bourne (david@boomer.org)