Progesterone Metabolites Regulate Breast Cell Tumors
Progesterone Metabolites Regulate Breast Cell Tumors
Introduction: Of the nearly 1.4 million new cases of breast cancer diagnosed each year, a large proportion is characterized as hormone receptor negative, lacking estrogen receptors (ER) and/or progesterone receptors (PR). Patients with receptor-negative tumors do not respond to current steroid hormone-based therapies and generally have significantly higher risk of recurrence and mortality compared with patients with tumors that are ER- and/or PR-positive. Previous in vitro studies had shown that the progesterone metabolites, 5α-dihydroprogesterone (5αP) and 3α-dihydroprogesterone (3αHP), respectively, exhibit procancer and anticancer effects on receptor-negative human breast cell lines. Here in vivo studies were conducted to investigate the ability of 5αP and 3αHP to control initiation, growth, and regression of ER/PR-negative human breast cell tumors.
Methods: ER/PR-negative human breast cells (MDA-MB-231) were implanted into mammary fat pads of immunosuppressed mice, and the effects of 5αP and 3αHP treatments on tumor initiation, growth, suppression/regression, and histopathology were assessed in five separate experiments. Specific radioimmunoassays and gas chromatography-mass spectrometry were used to measure 5αP, 3αHP, and progesterone in mouse serum and tumors.
Results: Onset and growth of ER/PR-negative human breast cell tumors were significantly stimulated by 5αP and inhibited by 3αHP. When both hormones were applied simultaneously, the stimulatory effects of 5αP were abrogated by the inhibitory effects of 3αHP and vice versa. Treatment with 3αHP subsequent to 5αP-induced tumor initiation resulted in suppression of further tumorigenesis and regression of existing tumors. The levels of 5αP in tumors, regardless of treatment, were about 10-fold higher than the levels of 3αHP, and the 5αP:3αHP ratios were about fivefold higher than in serum, indicating significant changes in endogenous synthesis of these hormones in tumorous breast tissues.
Conclusions: The studies showed that estrogen/progesterone-insensitive breast tumors are sensitive to, and controlled by, the progesterone metabolites 5αP and 3αHP. Tumorigenesis of ER/PR-negative breast cells is significantly enhanced by 5αP and suppressed by 3αHP, the outcome depending on the relative concentrations of these two hormones in the microenvironment in the breast regions. The findings show that the production of 5αP greatly exceeds that of 3αHP in ER/PR-negative tumors and that treatment with 3αHP can effectively block tumorigenesis and cause existing tumors to regress. The results provide the first hormonal theory to explain tumorigenesis of ER/PR-negative breast tissues and support the hypothesis that a high 3αHP-to-5αP concentration ratio in the microenvironment may foster normalcy in noncancerous breast regions. The findings suggest new diagnostics based on the relative levels of these hormones and new approaches to prevention and treatment of breast cancers based on regulating the levels and action mechanisms of anti- and pro-cancer progesterone metabolites.
Breast cancer is the most frequently diagnosed cancer and the leading cause of cancer death in women worldwide, with nearly 1.4 million new cases annually. Progesterone and estrogens have long been linked to breast cancer, and current understanding of the effective actions of these hormones implies the presence of receptors (ER and PR) in the target cells. However, a large proportion (about 30% to 60%) of breast tumors are ER and/or PR negative, and about 90% of normal proliferating breast epithelial cells are receptor negative. Patients with receptor-negative tumors generally show lack of response to adjuvant hormone therapy and have significantly higher risk of mortality compared with patients with tumors that are ER and/or PR positive. Overall, this means that for receptor-negative breast cancers, current explanations based on estrogen and progesterone actions and receptors are inadequate, and the related hormone-based therapies are ineffective. Here evidence is presented that the progesterone metabolites, 5α-pregnane-3,20-dione (5α-dihydroprogesterone; 5αP) and 4-pregnen-3α-ol-20-one (3α-dihydroprogesterone; 3αHP), can regulate ER/PR-negative breast cell tumor formation and growth as well as tumor regression and maintenance of normalcy.
Our previous in vitro studies had shown that breast tissues and cell lines readily convert progesterone to 5α-pregnanes, such as 5αP, and delta-4-pregnenes, such as 3αHP (Figure 1), and that tumorous breast tissues and tumorigenic breast cell lines produce higher levels of 5αP and lower levels of 3αHP than do normal breast tissues and nontumorigenic cell lines. The differences in progesterone metabolism between normal and tumorous breasts were observed in all breast tissue samples examined, regardless of the ages of the women, subtypes and grades of carcinomas, and whether the tissues were ER and PR positive and/or negative. The progesterone metabolism studies suggested that increases in 5αP and decreases in 3αHP production accompany the shift toward breast cell neoplasia and tumorigenicity.In vitro studies on five different human breast cell lines showed that cell proliferation and detachment are significantly increased by 5αP and decreased by 3αHP. The opposing in vitro effects of 5αP and 3αHP were observed in all breast cells studied: tumorigenic and nontumorigenic, estrogen-responsive and unresponsive, and ER/PR-positive and -negative cells.
(Enlarge Image)
Figure 1.
Conversion of progesterone to 3α-dihydroprogesterone (3αHP) and 5α-dihydroprogesterone (5αP). In vitro studies have shown that both ER/PR-positive and -negative human breast tissues and cell lines are able to convert progesterone to 3αHP and 5αP by the actions of 3α-hydroxysteroid oxidoreductase (3α-HSO) and 5α-reductase, respectively.
The objectives of the current studies were (a) to determine whether the progesterone metabolites, 5αP and 3αHP, have the ability to regulate in vivo induction and growth of ER/PR-negative human breast cancer cell tumors in mice, and (b) to determine the relative concentrations of 5αP and 3αHP in serum of tumorous and nontumorous mice and within tumors. The studies provide the first in vivo evidence that initiation and growth of ER/PR-negative human breast cell tumors are markedly stimulated by 5αP and suppressed by 3αHP, and that established 5αP-induced tumors can be regressed by treatment with 3αHP. Measurements of their levels indicate that the relative concentrations in the breast microenvironment of the progesterone metabolites determine whether ER/PR-negative cells are stimulated toward neoplasia and tumorigenesis or regulated to maintain a normal state.
Abstract and Introduction
Abstract
Introduction: Of the nearly 1.4 million new cases of breast cancer diagnosed each year, a large proportion is characterized as hormone receptor negative, lacking estrogen receptors (ER) and/or progesterone receptors (PR). Patients with receptor-negative tumors do not respond to current steroid hormone-based therapies and generally have significantly higher risk of recurrence and mortality compared with patients with tumors that are ER- and/or PR-positive. Previous in vitro studies had shown that the progesterone metabolites, 5α-dihydroprogesterone (5αP) and 3α-dihydroprogesterone (3αHP), respectively, exhibit procancer and anticancer effects on receptor-negative human breast cell lines. Here in vivo studies were conducted to investigate the ability of 5αP and 3αHP to control initiation, growth, and regression of ER/PR-negative human breast cell tumors.
Methods: ER/PR-negative human breast cells (MDA-MB-231) were implanted into mammary fat pads of immunosuppressed mice, and the effects of 5αP and 3αHP treatments on tumor initiation, growth, suppression/regression, and histopathology were assessed in five separate experiments. Specific radioimmunoassays and gas chromatography-mass spectrometry were used to measure 5αP, 3αHP, and progesterone in mouse serum and tumors.
Results: Onset and growth of ER/PR-negative human breast cell tumors were significantly stimulated by 5αP and inhibited by 3αHP. When both hormones were applied simultaneously, the stimulatory effects of 5αP were abrogated by the inhibitory effects of 3αHP and vice versa. Treatment with 3αHP subsequent to 5αP-induced tumor initiation resulted in suppression of further tumorigenesis and regression of existing tumors. The levels of 5αP in tumors, regardless of treatment, were about 10-fold higher than the levels of 3αHP, and the 5αP:3αHP ratios were about fivefold higher than in serum, indicating significant changes in endogenous synthesis of these hormones in tumorous breast tissues.
Conclusions: The studies showed that estrogen/progesterone-insensitive breast tumors are sensitive to, and controlled by, the progesterone metabolites 5αP and 3αHP. Tumorigenesis of ER/PR-negative breast cells is significantly enhanced by 5αP and suppressed by 3αHP, the outcome depending on the relative concentrations of these two hormones in the microenvironment in the breast regions. The findings show that the production of 5αP greatly exceeds that of 3αHP in ER/PR-negative tumors and that treatment with 3αHP can effectively block tumorigenesis and cause existing tumors to regress. The results provide the first hormonal theory to explain tumorigenesis of ER/PR-negative breast tissues and support the hypothesis that a high 3αHP-to-5αP concentration ratio in the microenvironment may foster normalcy in noncancerous breast regions. The findings suggest new diagnostics based on the relative levels of these hormones and new approaches to prevention and treatment of breast cancers based on regulating the levels and action mechanisms of anti- and pro-cancer progesterone metabolites.
Introduction
Breast cancer is the most frequently diagnosed cancer and the leading cause of cancer death in women worldwide, with nearly 1.4 million new cases annually. Progesterone and estrogens have long been linked to breast cancer, and current understanding of the effective actions of these hormones implies the presence of receptors (ER and PR) in the target cells. However, a large proportion (about 30% to 60%) of breast tumors are ER and/or PR negative, and about 90% of normal proliferating breast epithelial cells are receptor negative. Patients with receptor-negative tumors generally show lack of response to adjuvant hormone therapy and have significantly higher risk of mortality compared with patients with tumors that are ER and/or PR positive. Overall, this means that for receptor-negative breast cancers, current explanations based on estrogen and progesterone actions and receptors are inadequate, and the related hormone-based therapies are ineffective. Here evidence is presented that the progesterone metabolites, 5α-pregnane-3,20-dione (5α-dihydroprogesterone; 5αP) and 4-pregnen-3α-ol-20-one (3α-dihydroprogesterone; 3αHP), can regulate ER/PR-negative breast cell tumor formation and growth as well as tumor regression and maintenance of normalcy.
Our previous in vitro studies had shown that breast tissues and cell lines readily convert progesterone to 5α-pregnanes, such as 5αP, and delta-4-pregnenes, such as 3αHP (Figure 1), and that tumorous breast tissues and tumorigenic breast cell lines produce higher levels of 5αP and lower levels of 3αHP than do normal breast tissues and nontumorigenic cell lines. The differences in progesterone metabolism between normal and tumorous breasts were observed in all breast tissue samples examined, regardless of the ages of the women, subtypes and grades of carcinomas, and whether the tissues were ER and PR positive and/or negative. The progesterone metabolism studies suggested that increases in 5αP and decreases in 3αHP production accompany the shift toward breast cell neoplasia and tumorigenicity.In vitro studies on five different human breast cell lines showed that cell proliferation and detachment are significantly increased by 5αP and decreased by 3αHP. The opposing in vitro effects of 5αP and 3αHP were observed in all breast cells studied: tumorigenic and nontumorigenic, estrogen-responsive and unresponsive, and ER/PR-positive and -negative cells.
(Enlarge Image)
Figure 1.
Conversion of progesterone to 3α-dihydroprogesterone (3αHP) and 5α-dihydroprogesterone (5αP). In vitro studies have shown that both ER/PR-positive and -negative human breast tissues and cell lines are able to convert progesterone to 3αHP and 5αP by the actions of 3α-hydroxysteroid oxidoreductase (3α-HSO) and 5α-reductase, respectively.
The objectives of the current studies were (a) to determine whether the progesterone metabolites, 5αP and 3αHP, have the ability to regulate in vivo induction and growth of ER/PR-negative human breast cancer cell tumors in mice, and (b) to determine the relative concentrations of 5αP and 3αHP in serum of tumorous and nontumorous mice and within tumors. The studies provide the first in vivo evidence that initiation and growth of ER/PR-negative human breast cell tumors are markedly stimulated by 5αP and suppressed by 3αHP, and that established 5αP-induced tumors can be regressed by treatment with 3αHP. Measurements of their levels indicate that the relative concentrations in the breast microenvironment of the progesterone metabolites determine whether ER/PR-negative cells are stimulated toward neoplasia and tumorigenesis or regulated to maintain a normal state.
Source...