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Title:  Ovariectomized mouse model for human menopause

United States Patent:  6,583,334

Issued:  June 24, 2003

Inventors:  Haslam; Sandra Z. (Laingsburg, MI)

Assignee:  Board of Trustees operating Michigan State University (East Lansing, MI)

Appl. No.:  576838

Filed:  May 23, 2000

Abstract

A method for determining a response to a biologically active agent in ovariectomized lower test mammals is described. The mammals are divided into those which have an early time post ovariectomy and those which have a late time post ovariectomy and then each group is tested simultaneously with the agent. The method is used to simulate menopause in humans for the purpose of determining a positive or negative response and a possible treatment.

SUMMARY OF THE INVENTION

The present invention relates to a method for determining a response to a biologically active agent in lower laboratory test mammals which comprises:

(a) surgically ovariectomizing the lower mammal at a baseline time;

(b) dividing the ovariectomized lower mammals into at least two groups;

(c) treating a first of the groups of the ovariectomized mammals with the biologically active agent within a first period less than 21 days, from the baseline time;

(d) treating a second of the groups of the ovariectomized mammals with the biologically active agent with a second period of greater than about 35 days from the baseline time;

(e) comparing the results for the first and second groups of mammals to determine the response to biologically active agent.

In particular the present invention relates to mice as the test mammals. The invention approximates early and late menopause in humans.

The biologically active agent can be estrogen alone or in combination with progestin. These agents can be used alone or in combination with other agents which suppress or potentiate their activity. The method can also be used with other compounds which regulate biological activity in females including chemotherapeutic agents including SERMS as described in U.S. Pat. Nos. 5,994,370, 5,395,842, and 5,147,880.

The test mice can be normal or predisposed to a particular disease such as a tumor. All of this is well known to those skilled in the art.

The aim of the present invention is to particularly enable the identification of compounds which positively regulate the effects of estrogen and/or progesterone to prevent disease, such as breast tumors. It is particularly desirable to regulate negative results from estrogen in humans and the present invention enables the simulation of such regulation in a safe and effective manner.

DESCRIPTION OF PREFERRED EMBODIMENTS

Hormone replacement therapy (HRT) with estrogen alleviates menopausal symptoms and is effective in reducing osteoporosis and cardiovascular disease when taken in early postmenopause. Older, late postmenopausal women who never previously received HRT are also believed to benefit from estrogen treatment. On the other hand, increased lifetime exposure of the mammary gland to estrogen may increase the risk of breast cancer. The development of suitable experimental animal model systems can advance our understanding of the effects of estrogen and the timing of HRT on the postmenopausal breast. Toward this end, early and late postmenopausal states were induced in mice by short vs. long-term ovariectomy (1 vs. 5 wk) and the effects of 17.beta.-estradiol (E) on mammary gland morphology, cell proliferation and progesterone receptor (PR) levels were investigated. In late postmenopausal mice, E caused a pronounced enlargement of duct ends and a 6.5- and 4-fold greater mitogenic response in the duct end epithelium and adjacent stromal cells respectively, as compared to the response in early postmenopausal mice. Furthermore, after long-term, daily treatment with E, steady-state levels of proliferation remained 2-fold higher than that of similarly treated, early postmenopausal mice. E failed to increase mammary progesterone receptor (PR) levels in late postmenopausal, but not in early postmenopausal mice. Stimulation of duct ends by E and lack of PR-inducibility are characteristics of the immature pubertal mammary gland, and indicate that the late postmenopausal mammary gland resembled the immature state. In contrast, minimal E-induced proliferation and increased PR inducibility, characteristics of the adult, sexually mature mammary gland, were retained in early postmenopausal mice. The lack of difference in the numbers of estrogen receptor (ER) positive epithelial or stromal cells or in ER cellular concentration after short vs. long-term ovariectomy indicate that the observed greater efficacy of E is mediated at a step beyond receptor-ligand binding. This mouse model of experimentally induced early vs. late postmenopausal states should prove useful in better understanding alterations in hormone responsiveness and their implications for timing HRT on the human breast.

Results suggest that altered hormonal milieu and long-term deprivation of ovarian hormones, rather than advanced age are the major contributing factors to the observed differences in response to E alone HRT in the murine model. The purpose of the present study was to examine the proliferative effects of long-term combined treatment with E+P on the mammary gland in a murine model of early and late postmenopause.

Claim 1 of 23 Claims

I claim:

1. A method for determining a response to a biologically active agent in ovariectomized mice which comprises:

(a) surgically ovariectomizing the mice at a baseline time to establish menopause in the mice;

(b) monitoring the ovariectomized mice for serum estrogen after being ovariectomized and establishing a constant level of estrogen for the overiectomized mice;

(c) dividing the ovariectomized mice of step (b) into at least two groups;

(d) treating a first of the groups of the ovariectomized mice over time with the biologically active agent wherein the treating is initiated within a first period of time which is less than 21 days from the baseline time and which corresponds to early menopause in a human;

(e) treating a second of the groups of the ovariectomized mice over time with the biologically active agent wherein the treating is initiated within a second period of time which is greater than about 35 days from the baseline time and which corresponds to late menopause in a human; and

(f) comparing the results for the first and second groups of ovariectomized mice to determine the response to the biologically active agent.

 





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