Figure 1. Modified 5-HT₄R agonists activate the 5-HT₄R and are minimally absorbed.

A. Data from CHO cells engineered to over-express the 5-HT₄R, and investigated in a cAMP assay. The compounds were potent agonists, with EC₅₀ concentrations of 1.1 nM (5HT4-LA1) and 18.8 nM (5HT4-LA2), as compared to an EC₅₀ of 3.6 nM for 5-HT. B. Mean concentration of 5HT4-LA1 and 5HT4-LA2 after PO administration, in mg/mL or mg/g, in log scale, respectively. Graph shows mean concentration of drug over time (12 hours for 5HT4-LA1 and 8 hours for 5HT4-LA2) in fasted male B6 mice. Drug concentrations for both compounds are significantly higher in colon content versus plasma (P<0.0001). Colon content indicates drug concentrations in chyme fluid; colon tissue indicates drug concentrations in homogenized whole murine colon; colon washings are concentrations from washed colonic mucosa. High levels of drug are detectible as early as 0.5 hours in the colon, with peak concentrations at 4-hour time point. Negligible plasma concentrations are detected from 0.5–2 hours for 5HT4-LA1, but drug is not detectible thereafter. 5HT4-LA2 is only detectible in plasma at the 4-hour time point at a negligible dose. Plasma concentrations were measured at all time points. Data represented as N=3 animals per time point with mean ± standard deviation (SD).