Receptors on a cell are more or less accessible for pharmaceuticals depending on their position in the cell membrane and the surrounding environment like carbohydrates etc. Under in-vivo conditions where a continuous flow rapidly transports the pharmaceuticals to and from the cell surface, the accessibility will impact the ability to bind.
With a label free cell based biosensor this can be measured, but with, for instance, flow cytometry, the necessary incubation times are too long to obtain meaningful data. Is anyone aware of other methods that enables receptor accessibility measurements?
Will simple competitive binding with different ligands help? This may give you relative (not absolute) data on receptor accessibility.
Dear Venil,
Thank you for your answer. Could you please elaborate on how the assay should be set up in order to obtain the accessibility?
Best regards
Teodor
Perhaps one can start with receptors bound with labelled or fluorescent tagged ligands of moderate affinity, and then add unlabelled competitor ligands (of high affinity). This should result in rapid loss of label or fluor. Are you making a distinction between receptor occupancy and accessibility? Perhaps, one has to model the possible competitive reactions in silico to distinguish between these 2 possibilites. There is a view that certain low-affinity interactions maybe very important also. Hope this helps!
Dear Venil,
Thank you!
Yes we do distinguish between occupancy and accessibility. We consider the occupancy is a function of for instance the target accessibility, association- and dissociation rate,
Best regards
Teodor
Thanks! I guess you have an equation that gives some weightage to these 3 parameters (target accessibility, association- and dissociation rate)? How much weightage per parameter? Different poses of the receptor drug complex wold be considered?? Regds. Venil
Good question, the equation would be fine, we need to work it out!
thanks
Teodor
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