Mice were treated with a single dose of compound (2.5 mg/kg IP), and tissues were harvested at various time points and analyzed for PGE2 levels with an ELISA assay. Compared to untreated controls (t = 0 h),
the inhibitors (+)-1, (+)-12q, and (+)-44c doubled the PGE2 levels within the bone marrow within 3 h of treatment. Levels decreased by 6 h before returning to baseline by 12h. By contrast, (+)-
32 was less effective than the other 3 analogs under these conditions. Several aspects of these results are noteworthy. First,
we observed similar 2-fold elevation of PGE2 levels in the colon, lung and liver (see Figure S1). Second, this magnitude of PGE2 elevation appears maximal, as tissue PGE2 levels are consistently 2-fold higher in the 15-PGDH knockout mouse compared to wild-type littermates. Third, the pharmacological effects of (+)-
1, (+)-
12q and (+)-
44c last much longer than the pharmacokinetic half-lives might predict. For example, plasma levels of (+)-
12q drop below 10 nM within 3 h after an IP dose of 2.5 mg/kg body weight. Nonetheless, tissue PGE2 levels remain elevated at 3h. Since (+)-
12q is a tight binding inhibitor of 15-PGDH (Kiapp=0.06 nM), we suspect that it remains bound to the enzyme even after being cleared from the plasma. The levels of PGE2 continue to increase while the 15-PGDH is substantially inhibited, and likely return to normal as more enzyme is synthesized.
