Background
Rapamycin is a natural macrolide immunosuppressant that activates mTORC1. Seco rapamycin (sodium salt) is a nonenzyme-dependent degradation product of rapamycin resulting from ester hydration followed by dehydration.1 It has less than 4% of the potency of rapamycin in a thymocyte proliferation assay.1 Rapamycin quickly degrades to two ring-opened products, including seco rapamycin, in the cytoplasm or in homogenates of Caco-2 cells.2 Like rapamycin, seco rapamycin is secreted from cells by P-glycoprotein and metabolized to a common dihydro species.3 While seco rapamycin poorly activates mTOR, it mimics rapamycin in its ability to inhibit the proteasome.4
1.Wang, C.P., Chan, K.W., Schiksnis, R.A., et al.High performance liquid chromatographic isolation, spectroscopic characterization, and immunosuppressive activities of two rapamycin degradation productsJ. Liq. Chromatogr.17(16)3383-3392(1994)
2.Paine, M.F., Leung, L.Y., Lim, H.K., et al.Identification of a novel route of extraction of sirolimus in human small intestine: Roles of metabolism and secretionJ. Pharmacol. Exp. Ther.301(1)174-186(2002)
3.Paine, M.F., Leung, L.Y., and Watkins, P.B.New insights into drug absorption: Studies with sirolimusTher. Drug Monit.26(5)463-467(2004)
4.Osmulski, P.A., and Gaczynska, M.Rapamycin allosterically inhibits the proteasomeMol. Pharmacol.84(1)104-113(2013)
Protocol
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Cell experiment:
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To determine whether the Sirolimus metabolite M2 is formed from the degradation product Seco Rapamycin, duplicate Caco-2 cell cultures are dosed apically or basolaterally with 20 μM Seco Rapamycin and incubated for 4 h. To determine whether Seco Rapamycin is a substrate for P-gp, duplicate cultures are incubated with 0.5 μM LY335979 in the same manner for Sirolimus. For comparison, a parallel set of cultures is incubated similarly with 20 μM Sirolimus, but dosed apically only. M2 formation is also examined in human jejunal mucosal and liver homogenates and Caco-2 homogenates by incubating each preparation, in duplicate, with 20 μM Seco Rapamycin in the same manner for Sirolimus. For comparison, a parallel set of incubations containing 20 μM Sirolimus is also performed. To determine whether a high dose of Ketoconazole (100 μM) inhibits the formation of M2, parallel experiments with Caco-2 cells and the various homogenates are performed in a similar manner, only Ketoconazole (dissolved as a 100-fold concentration solution in ethanol) is included in the incubation medium/mixtures[1].
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参考文献:
[1]. Paine MF, et al. Identification of a novel route of extraction of sirolimus in human small intestine: roles ofmetabolism and secretion. J Pharmacol Exp Ther. 2002 Apr;301(1):174-86.
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