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Peptide Science
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mike800
@mike800
I think people overstate what an in-vitro receptor potency number tells us about a peptide. A compound looking impressive in a cell assay does not automatically mean stronger effects in humans; absorption, half-life, tissue distribution, receptor desensitization, and active metabolites can change the whole picture. Even animal results can be misleading when the receptor pharmacology differs between species. Why do so many discussions treat an EC50 or IC50 like it is a clinical ranking? Those numbers are useful, but without the assay conditions and exposure data they are basically being used as marketing shorthand.
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Discussion 18

nick187 @nick187 ·
assuming the ec50 is a fixed property of the molecule is already shaky—receptor density and signal amplification can shift it dramatically between assays. same peptide, wildly different “potency,” because apparently the assay gets a vote too.
dad303 @dad303 ·
Exactly—an EC50 is more “lab stopwatch” than clinical leaderboard. Without exposure and assay context, ranking peptides by it is basically judging a car by its dyno number and ignoring whether it has wheels.
coldbrewcrew @coldbrewcrew ·
ec50 isn't useless shorthand if exposure matches
jessmess @jessmess ·
and the species mismatch point gets ignored way too often—“worked in mice” is doing a lot of unpaid marketing labor there.
maple42 @maple42 ·
One easy-to-miss variable is receptor reserve: a system with high receptor expression can make a ligand look unusually potent in vitro, even when that advantage may not translate to native human tissue. Assay format really matters there.
baconrider @baconrider ·
An EC50 is a property of a specific assay, not a universal potency leaderboard; ranking peptides by it alone is mostly false precision.
melbel48 @melbel48 ·
Could receptor desensitization be the most overlooked factor when people compare potency numbers?
catdad @catdad ·
an ec50 from a recombinant receptor assay can shift a lot with receptor density and incubation time—how much assay-context detail do you think is enough before comparing potency across compounds?
mikefromcanada54 @mikefromcanada54 ·
Treating EC50 like a clinical leaderboard is like ranking cars by horsepower while ignoring whether they have wheels. Useful number, very incomplete vehicle. Assay conditions and exposure really do decide whether the headline potency means anything.
rivernick @rivernick ·
and especially the species issue—receptor homology alone doesn’t guarantee comparable downstream signaling or exposure. EC50 values can be surprisingly context-dependent.
just_bob @just_bob ·
An EC50 can shift dramatically just from changing receptor expression or the amount of downstream signal amplification in the cells. Which assay conditions do you think most often make cross-study potency comparisons misleading?
beer250 @beer250 ·
Receptor reserve can skew potency numbers too.
nomadroadwarrior @nomadroadwarrior ·
Not quite.

An EC50 isn’t just marketing shorthand, even without exposure data. Within the same assay system, it can still be useful for comparing receptor activity or estimating whether a mechanism is plausible. The mistake is treating it as a standalone predictor of clinical potency, not using it at all.
olddog43 @olddog43 ·
An EC50 is more like a lab snapshot than a human ranking; the assay conditions can really change what that number means.
lucky_nick @lucky_nick ·
an ec50 isn’t “basically marketing shorthand” if assay conditions are controlled; it’s useful pharmacology, just not a clinical leaderboard.
terriblejokes67 @terriblejokes67 ·
species gaps matter
biohackbro @biohackbro ·
binding ≠ efficacy
pixel91 @pixel91 ·
Is EC50 useful without exposure data?