Pharmacokinetics of the nonsteroidal steroid sulphatase inhibitor 667 COUMATE and its sequestration into red blood cells in rats

Abstract

Breast cancer is a major cause of mortality in Western countries and there is an urgent requirement for novel treatment strategies. The nonsteroidal sulphatase inhibitor 667 COUMATE inhibits hepatic steroid sulphatase and growth of oestrone sulphate stimulated tumours in the nitrosomethylurea-induced rat mammary model. Other compounds that contain an aryl sulphamate moiety, for example, oestrone-3-O-sulphamate, are sequestered into red blood cells (RBCs). The aims of this study were to determine the pharmacokinetics of 667 COUMATE and to investigate its sequestration into RBCs. We administered a single p.o. or i.v. dose (10 mg kg(-1)) of 667 COUMATE to rats and used a high-performance liquid chromatography method to measure the levels of the agent and its putative metabolites in plasma. 667 COUMATE had a bioavailability of 95% and could be detected in plasma for up to 8 h. Using two independent analytical methods, we demonstrated that 667 COUMATE is sequestered by RBCs both ex vivo and in vivo. Previous investigations have revealed that 667 COUMATE is rapidly degraded in plasma ex vivo. In this study, we demonstrate that 667 COUMATE is stabilised due to its sequestration into RBCs. In conclusion, the pharmacological efficacy and high oral bioavailability of 667 COUMATE may be partly a consequence of the ability of RBCs to both protect the agent from metabolic degradation and facilitate its transport to tissues. These data support the further clinical evaluation of this novel endocrine therapeutic agent.

Figure 1

Chemical structures of 3-Hydroxy-6-oxo-8,9,10,11-tetrahydro-7H-cyclohepta-[c] [1] benzopyran (667 COUMARIN) and 6-oxo-8,9,10,11-tetrahydro-7H-cyclohepta-[c] [1] benzopyran-3-O-sulphamate (667 COUMATE).

Figure 2

High-performance liquid chromatograms of diethyl ether extracts of rat plasma (A–C) or RBCs (D) 30 min after administration of (A) vehicle only, (B) 667 COUMATE i.v., (C) 667 COUMATE p.o. and (D) 667 COUMATE p.o. 7-Hydroxycoumarin, added as the internal standard, 667 COUMARIN and 667 COUMATE are denoted by 1, 2 and 3, respectively. For details of extraction and HPLC method, see Materials and Methods.

Figure 3

Plasma concentrations of 667 COUMATE after administration of a single p.o. or i.v. dose of 667 COUMATE to female Wistar rats. The values shown in the figure are the means of three animals±s.e.m.

Figure 4

Percentage uptake of 667 COUMATE by rat RBCs following incubation of the agent with whole rat blood maintained at 37°C on rollers. The coefficients of variation between samples were calculated to be less than 10%. For details of extraction of 667 COUMATE from whole blood, see Materials and Methods (means, n=6).

Figure 5

The ratio of 667 COUMATE/667 COUMARIN following incubation of 667 COUMATE (10 μg ml⁻¹) with whole blood or plasma. The coefficients of variation between samples were found to be less than 10% (means, n=6).