Comparison of Estetrol Exposure between Women and Mice to Model Preclinical Experiments and Anticipate Human Treatment

Abstract

Estetrol (E4) is a natural estrogen with promising therapeutic applications in humans. The European Medicines Agency and the Food and Drug Administration have approved the use of 15 mg E4/3 mg drospirenone for contraceptive indication. Phase III clinical trials with 15-20 mg E4 for the relief of climacteric complaints are currently running. Relevant data from preclinical animal models are needed to characterize the molecular mechanisms and the pharmacological effects of E4 and possibly to reveal new therapeutic applications and to anticipate potential adverse effects. Therefore, it is important to design experimental procedures in rodents that closely mimic or anticipate human E4 exposure. In this study, we compared the effects of E4 exposure after acute or chronic administration in women and mice. Women who received chronic E4 treatment per os at a dose of 15 mg once daily reached a steady state within 6 to 8 days, with a mean plasma concentration of 3.20 ng/mL. Importantly, with subcutaneous, intraperitoneal or oral administration of E4 in mice, a stable concentration over time that would mimic human pharmacokinetics could not be achieved. The use of osmotic minipumps continuously releasing E4 for several weeks provided an exposure profile mimicking chronic oral administration in women. Measurements of the circulating concentration of E4 in mice revealed that the mouse equivalent dose necessary to mimic human treatment does not fit with the allometric prediction. In conclusion, this study highlights the importance of precise definition of the most appropriate dose and route of administration to utilize when developing predictive preclinical animal models to mimic or anticipate specific human treatment.

Keywords: estetrol; exposure; human; mice; pharmacokinetics; route of administration.

Figure 1

Pharmacokinetics of single- and multiple-dose daily oral E4 treatment in women. (A) E4 blood concentration (logarithmic scale, mean ± SD) after a single oral administration of E4 (5, 15 or 45 mg) over time (hours). E4 concentrations (n = 9) were measured after 10, 20, 30, 45, 60, 75, 90, 105, 120 and 150 min and after 3, 4, 6, 8, 12, 16, 24, 36, 48, 72, 96, 120, 144 and 168 h. (B) E4 blood concentration (mean ± SD, ng/mL) after treatment with multiple daily oral doses of E4 (15 mg) over time (days). E4 concentrations were measured on days 1, 2, 4, 6, 8, 12 and 14 (n = 19).

Figure 2

Intravenous administration in mice. (A) Schematic treatment protocol of mice: ovariectomy at 4 weeks of age, E4 treatment at 6 weeks of age and blood sampling schedule after treatment. (B) Circulating E4 concentrations in blood over time (0 to 24 h) after intravenous injection of 7.5 µg (0.3 mg/kg) E4. Results are expressed in ng/mL as mean ± SD (n = 6). (C) Expression as a natural logarithm (Ln) of E4 concentrations (ng/mL) in blood over time (h), allowing for definition of the distribution and the elimination phases.

Figure 3

Pharmacokinetics of E4 in mice. E4 blood concentrations (0 to 24 h) after administration of 7.5 µg (0.3 mg/kg) through subcutaneous (s.c., (A)), intraperitoneal (i.p., (B)) or oral gavage (C) routes of administration over time (h). Results are expressed in ng/mL as mean ± SD (n = 6).

Figure 4

E4 blood plasma levels after Alzet^® osmotic minipump administration in mice. (A) Schematic treatment protocol in mice: ovariectomy at 4 weeks of age, starting of treatment at 6 weeks of age and blood sampling schedule after starting the treatment. (B) Circulating E4 concentrations in blood over time (week): after 24 h, 1 week, 3 weeks and 5 weeks of treatment delivered by Alzet^® osmotic minipumps (E4 diluted in PPG). Results are expressed in ng/mL as mean ± SD (n = 6). (C) Correlation between administered E4 dose and E4 blood circulating concentration. (D) Circulating E4 concentrations in blood over time (week): after 24 h, 1 week, 3 weeks and 5 weeks of treatment administered by Alzet^® osmotic minipumps (E4 = 0.3 mg/kg/day diluted in HP-β-CD or in PPG). Results are expressed in ng/mL as mean ± SD (n = 6).