The Pharmacology of Androgens Neil A. Clipstone, Ph.D.

TESTOSTERONE Physiological effects of testosterone Male Sex Organs Sex organ development Sperm production Prostate growth Erectile function Puberty Development & maintenance of secondary sexual characteristics Muscle Muscle mass Muscle strength Bone Marrow Red blood cell production TESTOSTERONE Bone Bone density Maintenance Epiphyseal closure Skin Growth of facial & body hair Collagen growth Androgenic alopecia CNS Sex drive Sense of well being Confidence Cognition & memory

Testosterone Mechanism of action Testosterone is a direct agonist of the Androgen receptor (AR) AR is an androgen-dependent nuclear transcription factor of the steroid hormone family AR binds to the Hormone response element (HRE) in androgen target genes AR recruits tissue-specific transcriptional cofactors and promotes androgen-specific patterns of gene expression SHBG AR HRE Testosterone-target gene 1. Testosterone binds AR in the cytosol 2. AR undergoes conformational change and forms dimers 3. AR dimers translocate into the nucleus and bind to target promoters 4. Promoter-bound, ligand-activated AR receptors recruit transcriptional co-factors and modulate target gene expression Testosterone Bound to + Transcriptional co-factor

Promote spermatogenesis Regulation of testosterone synthesis & secretion Testes Testosterone FSH + LH GnRH Negative feedback Inhibin Pulsatile LH FSH Leydig cell Sertoli cell Testosterone Androgen-binding protein ABP-Testosterone + other FSH-induced proteins Promote spermatogenesis Systemic testosterone responses

(INACTIVE METABOLITES) Hypothalamus/Skin/Bone Testosterone Biosynthesis & Metabolism Cholesterol Pregnenolone Progesterone Androstenedione Dehydroepi androsterone (DEHA) Androstenediol Testosterone 17b HSD 3b HSD Side chain cleavage enzyme HSD- Hydroxysteroid dehydrogenase Testes Skin/Liver/Bone Urogenital tissue Dihydrotestosterone (~10x > potent) PERIPHERAL TISSUES 5a-reductase Testosterone Estradiol Phase I/ Phase II Liver Andosterone Etiocholanolone (INACTIVE METABOLITES) Aromatase (CYP19A1) Liver/Adipose Hypothalamus/Skin/Bone

Direct and Indirect effects of Testosterone 5a-reductase Aromatase (CYP19A1) Dihydrotestosterone Estradiol AR AR ER External genitalia: - Differentiation during puberty - Maturation during puberty - Prostate size & Development Hair Follicles: Increased facial & body hair growth during puberty Male pattern baldness Internal genitalia - Wolffian development during gestation - Spermatogenesis Skeletal Muscle: - Increased mass & strength Libido Sexual Function Erythropoiesis Bone Growth Bone: - Epiphyseal closure - Increased density Libido Sexual Function Reduced Body Mass

Testosterone preparations Ester moiety cleaved by tissue esterases following administration to yield active testosterone More lipophilic Formulation for Transdermal Delivery Avoids first pass effect Testosterone ethanate cypionate Long acting Esterification Testosterone Parenteral administration (e.g. IM) Oral administration Methyltestosterone 17a Alkylation - Orally bioavailable - Less androgenic than testosterone - Increased hepatotoxicity Rapidly orally absorbed Low oral bioavailability High first pass metabolism 17a alkylation inhibits hepatic catabolism

Testosterone indications and therapeutic uses Male hypogonadism Primary Disease of testes - Sperm & testosterone < normal - LH & FSH > normal (no negative feedback) Secondary Hypothalamus/ - Sperm & Testosterone < normal Pituitary Disease - LH & FSH < normal Symptoms: In utero - ambiguous sexual organ development - micropenis at birth Prepubertal - failure to undergo complete puberty Adult - energy & libido - infertility - muscle mass, bone density & sexual hair

Treatment: - Testosterone replacement therapy adolescents at the time of puberty in symptomatic adult men Note: Treatment of older men with age-related declines in testosterone levels, but no overt hypogonadal symptoms or underlying hypothalamic/pituitary or testicular disease is controversial. Goal of treatment: - to restore testosterone levels to the normal range Serum testosterone levels are monitored for clinical efficacy Clinical Benefit: - development/maintenance of secondary sexual characteristics - libido (mediated in part by estradiol) - muscle strength - fat-free mass (mediated in part by estradiol) - bone density (mediated by estradiol) - improved mood & cognition (+/-)

Adverse effects: - Acne - Increased risk of prostate cancer/benign prostatic hyperplasia - Worsening of sleep apnea - Increased cardiovascular disease risk (HDL & LDL) - Increased risk of venous thromboembolic disease - Erythrocytosis – increase in red cell mass (increased risk of VTE) - Hepatic dysfunction (- 17a alkylated derivatives) - Suppression of spermatogenesis inhibition of LH production results in reduction of high level endogenous local testicular testosterone known to be required for sperm production Contraindications: - Pre-existing Prostate cancer - High levels of PSA in men at high risk for prostate cancer - Untreated sleep apnea

Androgen abuse as a performance enhancing drug Androgens and related compounds are used by athletes (both professional & recreational) at supraphysiological levels (100-200X) to boost athletic performance & physical appearance Rationale: Androgens known to increase - muscle mass - strength - fat-free mass Types of compounds used: Exogenous & synthetic testosterone (readily detected by drug testing) Androgen precursors e.g. andorstenedione & dehydroepiandrosterone (DHEA) - often present in dietary supplements - non androgenic in men (do not elevate testosterone)- but do increase estrogen levels - low affinity AR binding- act as partial agonists to block effects of testosterone in vivo rHCG – to stimulate endogenous testosterone production Aromatase inhibitors - to boost testosterone by preventing in vivo conversion to estradiol Synthetic Selective Androgen Receptor Modulators (designer drugs) - nonsteroidal molecules that selectively activate AR in muscle & bone

Adverse Effects: Cardiovascular - Coronary heart disease, cardiomyopathy, erythrocytosis, coagulation abnormalities, dyslipidemia & hypertension Tendon rupture Neuropsychiatric - mood disorders, increased aggression/violence Liver (17a derivatives)- cholestasis, hepatitis, hepatic neoplasms Men - hypogonadism, reduced testicular volume, suppression of spermatogenesis (can be prolonged in the case of chronic use) - gynecomastia (tamoxifen & aromatase inhibitors taken to prevent) - increased risk of benign prostatic hypertrophy and prostate cancer Women - acne, hirsutism, male pattern baldness, clitoromegealy - deepening of the voice (irreversible) - Irregular menstrual cycle

The role of androgens in prostate cancer development GnRH Pharmacological Interventions: Androgen deprivation Androgen synthesis inhibitors Androgen receptor antagonists Pulsatile FSH + LH Testes Testosterone AR 5a-Reductase Dihydrotestosterone

Androgen deprivation therapy for the treatment of advanced prostate cancer Rationale: Androgens stimulate prostate cancer growth Goal: Reduction of serum testosterone to castration levels - palliative not curative (sometime combined with chemotherapy) - results in tumor responses in 80-90% of patients Approach: Suppression of the Hypothalamic/Pituitary-gonadal axis to inhibit pituitary production of gonadotropins and reduce testicular production of testosterone - Historically ADT was achieved using estrogen therapy to suppress FSH & LH GnRH agonists- Leuprolide, Goserlin, Buserelin, Triptorelin & Naferelin - sustained GnRH signaling inhibits pituitary release of FSH & LH to decrease endogenous testosterone production - initial flare of GnRH can also cause a cancer flare GnRH antagonist- Degarelix - GnRH antagonist prevent GnRH signal from stimulating FSH & LH

Adverse Effects of Androgen Deprivation Therapy: Sexual dysfunction Osteoporosis & bone fractures Vasomotor responses (hot flashes) Loss of lean body mass & increased fat mass Fatigue Anemia (>90%) Gynecomastia Decreased penis and testicular size Emotional & cognitive changes Cardiovascular & metabolic abnormalities

Androgen synthesis inhibitor for treatment of Prostate cancer: Abiraterone MOA: Abiraterone inhibits the synthesis of testosterone - an irreversible inhibitor of CYP17A1 (aka 17a hydoxylase and 17,20 lyase) - Sequential enzymes involved in androgen biosynthesis - Inhibition of androgen production reduces androgen-dependent tumor growth Clinical Use: Used in combination with either GnRH Agonist/Antagonist to prevent compensatory upregulation of the HPG axis Adverse Effects: Adrenocorticol insufficiency (ameliorated by co-administered prednisone) Mineralocorticoid excess (fluid retention and hypokalemia) Hepatotoxicity (potentially severe) Cholesterol Pregnenolone Progesterone Androstenedione Dehydroepi androsterone (DEHA) Androstenediol Testosterone 17b HSD 3b HSD Side chain cleavage enzyme 17a-OH pregnenolone 17a-OH progesterone CYP17A1

Adverse Effects: Abiraterone Adrenocorticol insufficiency & mineralocorticoid excess Cholesterol Pregnenolone Progesterone Androstenedione Dehydroepi androsterone (DEHA) Androstenediol Testosterone 17b HSD 3b HSD Side chain cleavage enzyme 17a-OH pregnenolone 17a-OH progesterone CYP17A1 ALDOSTERONE (MINERALOCORTICOID) CORTISOL Prevented by co-administered PREDNISONE Cortisol deficiency

Androgen Receptor Antagonists for the treatment of Prostate Cancer First Generation: Flutamide, Bicalutamide, Nilutamide Second Generation: Enzalutamide (8x >potent) Description: Non steroidal selective antagonists of the androgen receptor MOA: Blocks the action of testosterone and dihydrotestosterone at the AR Indications: Treatment of advanced prostate cancer - not used as monotherapy because inhibiting testosterone results in an increase in LH leading to enhanced endogenous testosterone synthesis - used in combination with either GnRH agonist or GnRH antagonist attenuates the effect of initial GnRH agonist induced flare Flutamide also used for treatment of hyperandrogenism in women e.g. PCOS- acne, hirsutism, androgenic alopecia

Adverse Effects of Androgen Receptor Antagonists: Men - typical effects of androgen deprivation e.g. sexual dysfunction, gynecomastia, vasomotor responses etc Women - generally well tolerated Rare side affects associated with either sex First Gen associated with serious hepatotoxicity (including deaths) Enzalutamide associated with increased seizures (~1%) - crosses the BBB and inhibits the GABAA receptor

Additional Pharmacotherapy Indications

The role of dihydrotestosterone in the development of male pattern baldness (10X > Potent) 5a-Reductase DHT

Inhibitors of 5a-Reductase Finasteride & Dutasteride Description: Finasteride & Dutasteride are inhibitors of 5a reductase, the enzyme involved in the conversion of testosterone to the more potent dihydrotestosterone MOA: Finasteride & Dutasteride reduce serum levels of dihydrotestoseterone Indications: Male pattern hair loss, Benign Prostatic Hyperplasia (BPH) & Female Hirsutism Adverse Effects: Male sexual dysfunction, gynecomastia & depression Contraindications: Pregnancy (due to birth defects) Testosterone Dihydrotestosterone (10x > potent) 5a-reductase Finasteride

Spironolactone Description: Antagonist/very weak partial agonist of the androgen receptor Also a Mineralocorticoid Receptor antagonist - used as a diuretic to treat heart failure, nephrotic syndrome, ascites, essential HTN, hypokelemia etc MOA: Antagonist/very weak partial agonist of the androgen receptor - antagonizes androgenic responses in the presence of high levels of androgen Indications (as AR antagonist) : Treatment of women with acne, hirsutism or androgenic alopecia (Hyperandrogenism) Adverse Effects: menstrual irregularities, breast tenderness, orthostatic hypotension Contraindications: Males with prostate cancer- due to its partial agonist activity

Hormonal Therapy for treatment of Transgender Individuals

GENDER CONFIRMING SURGERY Transgender Female: Male-to-Female Transgender Male: Female-to-Male GOAL INITIAL THERAPY MAINTENANCE Suppress male secondary sex characteristics Induce female physical changes: Elimination of facial hair growth Induction of breast development Promote female fat/muscle distribution Maintain hormone levels in normal female range Suppress female secondary sex characteristics Induce male physical changes: Stop Menses Promote virilization Promote male pattern sexual hair Promote male physical body contours Maintain hormone levels in normal male range Antiandrogen- GnRH agonist (e.g. leuprolide) - spironolactone suppress Testosterone production & allows reduced estrogen dosing to avoid side effects Estrogen therapy- transdermal estradiol - oral estradiol ester Androgen therapy- Testosterone ethanate Suppresses estrogen production Promotes male characteristics Due to fewer side effects high dose testosterone can be used Discontinue Antiandrogen therapy Maintain Estrogen to protect against Sex hormone deficiency conditions e.g. osteoporosis Maintain testosterone to protect against GENDER CONFIRMING SURGERY

Summary Material

Testosterone INDICATIONS MOA Adverse Effects Misc. Androgen Receptor Male hypogonadism Direct agonism of the AR To restore testosterone to the normal level Contraindications: Prostate cancer High level of PSA Untreated sleep apnea Androgen Receptor Antagonists Flutamide Bicalutamide Nlutamide Enzalutamide Treatment of advanced Used in combination with androgen deprivation therapy (e.g. GnRH agonist/antagonist) Flutamide also used For treatment of hyperandrogenism in women Directly inhibits action of testosterone and Dihydrotestosterone at the AR Men- typical effects Of androgen deprivation e.g. sexual dysfunction, gynecomastia , vasomotor responses Rare side effects: 1st Gen- Hepatotoxicity 2nd Gen-increased seizure risk Abiraterone Hormone-resistant prostate cancer Not responding to androgen deprivation therapy Inhibition of CYP17A1 Inhibits synthesis of testosterone (also effects corisol, but not aldosterone) Spironolactone Treatment of women with acne, hirsutism, or androgenic alopecia Antagonist/ weak partial agonist of AR Also mineralocorticoid receptor antagonist- used as diuretic to treat HF Menstrual irregularities Breast tenderness Orthostatic HTN Contraindication: Should not be used in men with Acne Increased risk prostate cancer Increased risk BPH Worsening of sleep apnea Erythrocytosis Increased risk VTE Increased risk CVD Hepatic dysfunction Suppression of spermatogenesis Adrenocorticol insufficiency Mineralocorticoid excess 5a-reductase Inhibitors Finasteride Dutasteride BPH Male pattern baldness Female hirsutism Inhibits peripheral conversion of testosterone to dihydrotestosterone Male sexual dysfunction Pregnancy