Back to the Top
Does anyone know how to quantitatively evaluate the metabolic contribution of a designated CYP450 isoforms such as CYP3A4 to a certain compound without knowing or having its metabolites using in vitro assay? Can you give me some useful literatures? What I understand is we can incubate the compound at low concentrations such as 1 uM with human liver microsomes for several different times (The substrate depletion method) with or without adding selective monoclonal antibody to completely inhibit a certain CYP isoforms and then we can get two kinds of in vitro intrinsic clearances (CLint and CLint'). Then the contribution=1-CLint'/CLint, if CLint is got without inhibiting CYP enzyme and CLint' is got with adding antibody. Is it right? Any suggestions are appreciated. Thanks!
Jian
Back to the Top
Dear Jian,
This is the method which we follow in our lab but using specific inhibitors rather than antibodies (which is most accurate way of doing this experiment).
But in some cases inhibition of primary pathway,activates secondary pathway and as a result you will get artifact clearance.
e.g. if a molecule is substrate of two CYPs; 3A4 and 2D6.
In this situation molecule will under go phase-I metabolism via CYP 3A4 and CYP2D6 and both will contribute for total clearance
Now if you are inhibiting CYP 3A4 it means more amount of drug will be available for CYP2D6 now in comparison to previous case so clearance contributed by CYP2D6 will be increased which will give you false positive result.
Regards,
Rahul Vats
Back to the Top
Dear Rahul:
Many thanks for your advise. I have a question that why chemical inhibitor is more suitable than antibody? What I understand is antibody has better selectivity and will be more accurate to evaluate the contribution.
Jian
Back to the Top
Dear Jian,
As I mentioned that antibodies are better choice than chemical inhibitors.
Regards,
Rahul Vats
Back to the Top
The following message was posted to: PharmPK
Thanks to Rahul and Jian,
It is very good topic. I have the same question, what rahul asked,
Please give the answer for that question with logics. Please refer any
literature on same.
Thanks and Regards,
K.N.Purna chandra rao
Research Associate
PREMAS Biotech Pvt. Ltd.
Plot No. 77, Sector 4,
IMT Manesar.
Gurgaon-122050Haryana,
Want to post a follow-up message on this topic?
If this link does not work with your browser send a follow-up message to PharmPK@boomer.org with "CYP contribution" as the subject | Support PharmPK by using the |
Copyright 1995-2011 David W. A. Bourne (david@boomer.org)