Recombinant drugs complications

As in the case of chemical inhibition, a lack of specificity can complicate the interpretation of antibody inhibition experiments. A lack of specificity and the nonspecific effects outlined above likely account for the majority of cases where the sum of the inhibitory effects of a panel of inhibitory antibodies adds up to greater than 100%. Another potential problem stems from the fact that many antibodies do not completely inhibit the activity of a microsomal CYP enzyme or the corresponding recombinant CYP enzyme. If an antibody inhibits the metabolism of a marker substrate by 80%, and if the same antibody inhibits the metabolism of drug candidate by 80%, there is uncertainty as to whether the inhibited enzyme contributes 80% or 100% to the metabolism of the drug candidate. This may seem like a trivial difference, but it has a... 

Cytochrome b5 affects the kinetics of drug metabolism by certain CYP enzymes hence, coexpression of this microsomal hemoprotein (together with NADPH-CYP reductase) can affect the catalytic efficiency of certain recombinant CYP enzymes (76,109). For example, the presence of cytochrome b5 tends to increase Fmax for reactions catalyzed by CYP3 A4, whereas it tends to decrease Km for reactions catalyzed by CYP2E1. In both cases, cytochrome b5 increases Vmax/Km, which is a measure of in vitro intrinsic clearance. The fact that some commercially available recombinant CYP enzymes are expressed with cytochrome b5 while others are not complicates the interpretation of results of studies performed with recombinant human CYP enzymes. 

The choice of assay type in a drug discovery campaign is complicated. Are you seeking an agonist, an antagonist, or a selective modulator What tools (cell lines, recombinant proteins, small molecule probes, etc.) are at your disposal How many compounds do you want to profile What are your cost and time constraints Each of these issues can modify your determination of the optimal assay for your particular project. 

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