Structural analysis of rapamycin and related compounds using [M + Li]+ ions generated by liquid secondary ion mass spectrometry

Pharmacokinetics and metabolic disposition of sirolimus in healthy male volunteers after a single oral dose

The pharmacokinetics and metabolic disposition of sirolimus (rapamycin, Rapamune), a macrocyclic immunosuppressive agent for the prevention of allograft rejection in organ transplantation, were investigated in 6 healthy male volunteers after a single nominal 40-mg oral dose of the C-radiolabeled drug, with the added aim of assessing the potential role of sirolimus metabolites in the clinical pharmacology of the parent drug. The absorption of parent drug and derived materials was rapid (tmax 1.3 +/- 0.5 hours, mean +/- SD), and the elimination of sirolimus was slow (t(1/2) 60 +/- 10 hours, mean +/- SD) in whole blood. The high whole blood to plasma (B/P) concentration ratio of sirolimus (142 +/- 39) was consistent with its extensive partitioning into formed blood elements. The markedly lower B/P value based on radioactivity (2.7 +/- 0.4) suggested that drug-derived products partitioned into formed blood elements to a much lesser extent. Based on AUC0-144h values, unchanged sirolimus represented an average 35% of total radioactivity in whole blood. Drug-derived products in whole blood were characterized by HPLC, LC/MS, and LC/MS/MS as 41-O-demethyl, 7-O-demethyl, and several hydroxy, dihydroxy, hydroxy-demethyl and didemethyl sirolimus metabolites. The percentage distribution of sirolimus metabolites in whole blood ranged from 3%-10% at 1 hour to 6%-17% at 24 hours after drug administration. Based on their low immunosuppressive activities and relative abundance in whole blood of humans after sirolimus administration, metabolites of sirolimus do not appear to play a major role in the clinical pharmacology of the parent drug. A majority of the administered radioactivity (91.0 +/- 8.0%) was recovered from feces, and only 2.2% +/- 0.9% was renally excreted.

Multiple ion isolation applications in FT-ICR MS: exact-mass MSn internal calibration and purification/interrogation of protein-drug complexes

Two new applications using multiple ion isolations in the cell of a Fourier transform-ion cyclotron resonance mass spectrometer equipped with an electrospray ionization source are described. A procedure that uses multiple ion isolations of an analyte and calibrants for internal calibration at each stage in a MSn experiment, under high-resolution exact-mass conditions, for structural characterization/elucidation of angiotensin I and rapamycin is illustrated. Fragment ion mass accuracies < 1.0 ppm are demonstrated and routinely achieved. Purification of a mixture is illustrated by isolating multiple charge states of a protein-drug complex from residual protein for further MSn studies to elucidate the site of covalent drug bonding using IRMPD for a mixture of epidermal growth factor receptor (EGFr) protein and EGFr-drug complex. The procedure developed for multiple ion isolations is referred to as multi-CHEF, multiple correlated harmonic excitation fields, in which tailored waveforms are used to notch out multiple mass regions of a spectrum with minimal off-resonance excitation.

Identification of a new metabolite of macrolide immunosuppressant, like rapamycin and SDZ RAD, using high performance liquid chromatography and electrospray tandem mass spectrometry

Previously unknown metabolites from the two macrolide immunosuppressants rapamycin (sirolimus) and SDZ RAD [40-O-(2-hydroxyethyl)rapamycin] obtained after in vitro incubation with human liver microsomes have been purified. Structure elucidation was performed by nanoelectrospray ionization tandem mass spectrometry applying low energy collision activated dissociation. This ionization method is, as shown here, a powerful tool to determine metabolic pathways by analysis of even low abundance products. Product ion spectra of the isolated metabolites indicate a new kind of biotransformation reaction for rapamycin and SDZ RAD. The proposed metabolic pathway starts with an ester hydrolysis which leads to a ring-opened structure. A dehydration on C33-C34 and a supplementary hydrogenation at C33-C34 result in a structure similar to the ring-opened isomer with an single bond at C33-C34.