The subject of this study was the determination of the major urinary and biliary metabolites of [14C]-ZD6126 following i.v. administration to female and male bile duct cannulated rats at 10 mg/kg and 20 mg/kg, respectively, and male bile duct cannulated dogs at 6 mg/kg by HPLC–NMR spectroscopy.
ZD6126 is a phosphorylated pro-drug, which is rapidly hydrolysed to the active metabolite, ZD6126 phenol. The results presented here demonstrate that [14C]-ZD6126 phenol is subsequently metabolised extensively by male dogs and both, male and female rats.
Recovery of the dose in bile and urine was determined utilising the radiolabel, revealing biliary excretion as the major route of excretion (93%) in dog, with the majority of the radioactivity recovered in both biofluids in the first 6 h.
In the rat, greater than 92% recovery was obtained within the first 24 h. The major route of excretion was via the bile 51–93% within the first 12 h. The administered phosphorylated pro-drug was not observed in any of the excreta samples.
Metabolite profiles of bile and urine samples were determined by high performance liquid chromatography with radiochemical detection (HPLC–RAD), which revealed a number of radiolabelled components in each of the biofluids. The individual metabolites were subsequently identified by HPLC–NMR spectroscopy and HPLC–MS.
In the male dog, the major component in urine and bile was the [14C]-ZD6126 phenol glucuronide, which accounted for 3% and 77% of the dose, respectively. [14C]-ZD6126 phenol was observed in urine at 1% of dose, but was not observed in bile. A sulphate conjugate of demethylated [14C]-ZD6126 phenol was identified in bile by HPLC–NMR and confirmed by HPLC–MS.
In the rat, the bile contained two major radiolabelled components. One was identified as the [14C]-ZD6126 phenol glucuronide, the other as a glucuronide conjugate of demethylated [14C]-ZD6126 phenol.
However, a marked difference in the proportions of these two components was observed between male and female rats, either due to a sex difference in metabolism or a difference in dose level. The glucuronide conjugate of the demethylated [14C]-ZD6126 phenol was present at higher concentration in the bile of male rats (4–34%), while the phenol glucuronide was present at higher concentration in the bile of female rats (8–70%) over a 0–6 h collection period.
A third component was only observed in the bile samples (0–6 h and 6–12 h) of male rats. This was identified as being the same sulphate conjugate of demethylated [14C]-ZD6126 phenol as the one observed in dog bile.
The rat urines contained two main metabolites in greatly varying concentrations, namely the demethylated [14C]-ZD6126 phenol glucuronide and the glucuronide of [14C]-ZD6126 phenol. Again, the differences in relative amounts between male and female rats were observed, the major metabolite in the urines from male rats being the demethylated [14C]-ZD6126 phenol (0–17% in 0–24 h), whilst the phenol glucuronide, accounting for 0.5–50% of the dose over 0–24 h, was the major metabolite in females.
Methanolic extracts of the pooled biofluid samples were submitted for HPLC–NMR for the quick identification of the major metabolites. Following a single injection of the equivalent of 6–28 ml of the biofluids directly onto the HPLC-column with minimal sample preparation, the metabolites could be largely successfully isolated. Despite severe column overloading, the major metabolites of [14C]-ZD6126 could be positively identified, and the results are presented in this paper.