Estrogen receptor and its modulators

estrogen, its receptors, synthesis and actions

1. 1 Estrogen Receptor and its Modulators Presenter Dr C. Handique PGT, Dept of Pharmacology

2. Introduction Estrogens are the primary female sex hormones in the body with numerous physiological functions. The word estrogen is derived from Greek word “ oistrus ” literally meaning “ verve or inspiration ” and the suffix “ -gen ” meaning “ producer of ” . The therapeutic uses of estrogen largely represents the extension of their physiological activities. 2

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4. 4 1900 Hormonal nature of ovarian control of female reproductive system was established by Knauer . 1929 The active principle estradiol was obtained in pure form. 1960 Jensen and his colleagues demonstrated presence of intracellular receptor ER α in target tissues. 1996 The second recepor for estrogen was identified and termed as ER β . 1923 Allen & Doisy devised an bioassay for alcoholic ovarian extract base on vaginal smear of rat. 1926 Loewe & Lange found that a sex hormone varied in urine of women throughout the menstrual cycle.

5. Structure of Estrogen Receptor 5

6. 6 ESR1 on chromosome 6 codes for ER α . Present in Uterus, vagina & ovaries Mammary glad Hypothalamus Endothelial cell Vascular smooth muscle ESR2 on chromosome 14 codes for ER β Present in Prostrate Ovaries Lung Brain Bone Vasculature ER α ER β Estrogen receptor are super family of nuclear receptor

7. Mechanism of action The estrogen receptor is analogous to other steroid receptors. Agonist binding to the ligand binding domain brings about receptor dimerization and its interaction with “ Estrogen Response Element”. Gene transcription is promoted through certain coactivator proteins. On binding an estrogen antagonist the receptor assumes a different conformation and interacts with other corepressor proteins inhibiting gene transcription. 7

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9. Mechanism of action 9

10. Upon binding of estrogen (E) to an inactive estrogen receptor, the receptor is activated. Two receptor- ligand monomers dimerize and bind to the estrogen response element (ERE). Once bound to the ERE, the ER uses AF-1 and AF-2 to stimulate transcription from the promoter. Coactivators such as RIP140, CBP and SRC-1 bind to and link the hormone receptor with the general transcription factors (GTFs) and RNA polymerase of the transcription machinery to alter gene transcription. 10

11. Biosynthesis of estrogens 11 Steroidal estrogens arise from androstenedione or testosterone by the aromatization of the A ring. The enzyme catalyzing the reaction is Aromatase (CYP 19) enzyme.

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13. Action of estrogen Developmental Action 13 Neuroendocrine Control of Menstrual Cycle Metabolic Actions

14. DEVELOPMENTAL ACTION In Girls , Estrogens are responsible for development of pubertal changes and secondary sexual characteristics. They cause the growth and development of uterus, vagina and fallopian tubes as well as also contribute to breast enlargement. They contribute to the molding of the body contours and are responsible for the pubertal growth spurt of the long bones and epiphyseal closure 14

15. In Males , Estrogen plays important developmental role in males as well. In boys estrogen deficiency diminishes pubertal growth spurt. Its deficiency delays skeletal maturation and epiphyseal closure so that linear growth continues into adulthood. 15

16. Neuro endocrine control of menstrual cycle Hypothalamus fires at intervals that coincides with the GnRH release. GnRH interacts with its receptor on pituitary gonadotropes to cause release of LH and FSH. FSH and LH regulates the growth and maturation of graafian follicle in the ovary. The ovarian production of estrogen and progesterone which exerts negative feedback regulation on hypothalamus and pituitary. 16

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19. Metabolic effects Estrogens are anabolic in nature It promotes fusion of epiphysis both in boys and girls. It is important in maintaining the bone mass It promotes positive calcium balance It increases the HDL:LDL ratio. The blood coagulability is also increased. 19

20. The drugs which modulate the functions of estrogen receptor are as follows The other group of drugs include 20 Estrogen preparations Anti estrogens SERMs Aromatase inhbitors

21. 21 Estrogen receptor signaling pathway ER α ER β Ligands Estradiol SERMS Antiestrogen Ligand - ER three dimensional conformation Co regulatory factors ( Response element ) ERE Other REs Other REs Transcription AGONISTIC AGONISTIC/ ANTAGONISTIC PURE ANTAGONISTIC

22. Natural estrogens There are 3 major naturally occuring estrogen in the body They are estradiol , estrone and estriol Estradiol is synthesized in the graafian follicle, corpus luteum and placenta All the three forms are active and circulate in blood. 22

23. 23 Estradiol Most potent Predominat estrogen during the reproductive years Estriol Weakest of the three estrogens Pedominant estrogen during pregnancy Estrone Predominant estrogen during menopause

24. Estrogen preprations Natural Steroidal Estrogen - Estradiol , Estrone , Estriol Synthetic Steroidal Estrogen – Ethinyl estradiol Mestranol , Tibolone Synthetic Nonsteroidal Estrogen – Hexesterol , Diethylstilbesterol , Dienesterol Conjugated Estrogens – mixture of sodium estrone sulfate and sodium equiline sulfate 24

25. Estrogen : therapeutic use Post menopausal hormonal therapy As contraceptives Primary ovarian failure Dysfunctional uterine bleeding Acne Carcinoma prostrate Dysmenorrhea Delayed puberty in girls Senile vaginitis 25

26. Hormone replacement therapy The 5 common symptoms associated with menopause are osteoporosis, vasomotor disorders, cardiovascular problems, urogenital atrophy and psychological disturbances. 26 Osteoporosis HRT restore calcium balance and prevents further bone loss Accelertated bone loss on cessation of HRT Not the best choice, bisphosphonates are DOC Vasomotor symptoms Respond promptly to HRT Most common- hot flushes HRT to be stopped once vasomotor symptoms abate

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28. 28 CVS Events Improved HDL:LDL ratio with HRT, but Increased risk of venous Thromoembolism Increased risk of MI No secondary prophylaxis of CAD Urogenital atrophy Arrest genital atrophic changes Vulval urinary problem resolves Topical application possible

29. HRT generally includes the administration of estrogen and progestin combinations. It is given for the shortest possible duration and smallest effective dose. It increases the risk of breast cancer, gallstones, migraine and venous thromboembolism . REGIMEN Conjugated estrogens at a dose of 0.625mg/day is used either Cyclically(3 weeks treatment & 1 wk gap) OR, Continuously A progestin is added for the last 10-12 days each month. 29

30. Primary ovarian failure Treatment started with small doses of estrogen in cyclical pattern. Dysfunctional uterine bleeding Here estrogens have an adjuvant value. Acne Estrogen benefits by supressing ovarian production of androgen by inhibiting Gn release from pituitary Dysmenorrhea Estrogen benefit by inhibiting ovulation & decreasing PG synthesis in endometrium . 30

31. As contraceptive Estrogen is used in combination of progesterone in combined pill Used as combined pill, phased pill and emergency (post coital) pill. Ethinylestradiol (20- 50ug) Senile vaginitis Topical estrogen therapy preferred Estrogens change vaginal cytology to premenopausal form Carcinoma prostrate Estrogens are palliative They help by suppressing androgen production 31

32. Anti estrogens – clomiphene citrate It acts as a pure antagonist in all the human tissues. It binds to both the estrogen receptors . It has got two isomers- Zuclomiphene ( cis ) Enclompiphene (trans) P/K Well absorbed orally Deposited in adipose tissue Long half life of 6 days Largely metabolized and excreted in bile 32

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35. Indication Infertility due to failure of ovulation To aid in invitro fertilization Oligozoospermia Adverse Effects Polycystic ovaries Multiple pregnancy Hot flushes Gastric upset Vertigo Allergic dermatitis 35

36. Antiestrogen - fulvestrant It is a 7 α alkylamide derivative of estradiol and interacts with both the estrogen receptor. It is also known as “Selective Estrogen Receptor Down-regulator” MOA- It inhibits the estrogen receptor (ER) dimerization so that ER interaction with the DNA is prevented and thus enhances the receptor degradation The ER is down regulated and there is complete supression of ER responsive gene action. 36

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38. P/K Absorption is slow Plasma concentration reaches maximal in 7 days an maintained for a month . Numerous metabolites are formed invivo Mainly eliminated (90%) in faeces . Indication Tamoxifen Resistant Breast Cancer Administered as 250mg monthly i.m injections in the buttock 38

39. Selective estrogen receptor modulators SERMs are the compounds which exert estrogenic as well as anti-estrogenic actions in a tissue selective manner. The pharmacological goal of these drugs is to produce beneficial estrogenic effect in certain tissues ( like bone, brain and liver ) while producing antagonistic activity in tissues such as breast and endometrium where estrogenic action ( e.g carcinogenesis) may be harmful. 39

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41. Tamoxifen citrate Tamoxifen is a non steroidal compound. It acts as an Antagonist – breast carcinoma cells and blood vessels Agonist – uterus, bone, liver, pituitary Estrogenic actions Decrease in total and LDL cholesterol Improvement in bone mass Stimulation of endometrial proliferation Increase risk of deep vein thrombosis 41

42. Antiestrogenic action Inhibition of human breast cancer cells Hot flushes P/K Effective orally. Plasma half life - Biphasic (10 hours and 7 days) Some of its metabolites are more potent anti estrogens (4- hydroxy tamoxifen ) Excreted - bile 42

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45. Indication Primary breast carcinoma ( both early and advanced) Metastatic breast carcinoma Male breast carcinoma Male infertility Some other uses are McCune Albright’s Syndrome Gynnaecomastia 45

46. Side Effects Hot flushes Vaginal bleeding and discharge Menstrual irregularities Increased risk of venous thromboembolism Increased risk of uterine cancer DOLOXIFEN and TOREMIFENE are other SERMs in clinical use with the similar pharmacological indications , property and toxicity. 46

47. Raloxifene It is a non steroidal compound binding to both the estrogen receptor with high affinity. It acts as an Estrogen agonist – Bone & Cardiovascular system Estrogen antagonist – Endometrium & Breast In Post Menopausal women Prevents bone loss Reduces LDL cholesterol but there is no increase in HDL and TG 47

48. Raloxifene significantly reduces the risk of ER+ve breast cancer. It doesn’t stimulate uterine proliferation and there is no increase in risk of endometrial carcinoma. However, it doesn’t alleviate the post menopausal vasomotor symptoms : rather hot flushes may be induced in some women. P/K Well absorbed orally Extensive first pass metabolism Half life- 28 hours Excreted - faeces 48

49. Side effects Hot flushes, leg cramps, vaginal bleeding and increased risk of deep vein thrombosis. Use It is approved as a second line agent for the prevention and treatment of osteoporosis. Dose is 60mg/day 49

50. Aromatase inhibitors These are the group of drugs which inhibit the estrogen synthesis. Aromatization of the “A” ring of the testosterone and androstenedione is the final step in the production of estrogens. This group of drugs come into play as locally produced estrogens appear to play an important role in the development of breast cancer. Both steroidal and non steroidal agents are available. 50

51. Steroidal or the type 1 , agents are substrate analogs that act as suicide inhibitor to inhibit aromatase enzyme irreversibly. Example- formestane , exmestane Non steroidal or the type II agents interact reversibly with the heme group of CYPs Example – anastrozole , letrozole , vorozole 51

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54. Letrozole Orally active 100% bioavaialbility Slow metabolism Large Volume of distibution Half life – 40 hours Anastrozole More potent than letrozole Accumulates in the body Peak effect after 7-10 days 54

55. One of the first generation aromatase inhibitor is aminoglutethimide . However its use is limited by its lack of selectivity and side effects like sedation. Exmestane Steroidal compound Type I inhibitor of aromatase Administered orally Well tolerated 55

56. They inhibit the production of estrogen in all tissues. They are contraindicated in pre-menopausal women. They are more effective in delaying recurrence of early stage breast cancer and continue to exert prophylactic effect beyond 5 years. They are effective in tamoxifen failure cases of advanced breast carcinoma. 56

57. Advantages No endometrial hyperplasia No predisposition to uterine cancer No effect on lipid profile No increase in thromboembolic risk Adverse effects Accelerates bone loss Predisposes to osteoporosis Predisposes to fracture Prdisposes the arthritic symptoms Hot flushes, nausea, dairrhea 57

58. Conclusion Estrogens are primary female sex hormones The discovery of the estrogen receptors marked an important step towards the development of various drugs. These drugs exert different effects depending upon the three dimensional conformation the receptor acquires after ligand binding. Further knowledge of such interactions can lead to discovery of other aspects that can be implemented towards human health. 58

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