BIOL473 - Steroids

What were the two common usages of progesterone agonists in animals?

Lengthening cycles to synchronize groups of animals and preventing estrus behaviours

What are the two human usages of progestin agonists?

1. Preventing ovulation (contraception with or without estrogen)

2. Post-menopausal hormone replacement (combined with estrogen)

What is RU-486 (mifepristone)?

Emergency contraceptive / abortifacent

Why was RU-486 such a controversial drug when it was released?

After testing was approved by French government but the creator wanted to stop distribution in response to protests → french government ordered him to keep distributing it (in the interests of public health)

What happened to mifepristone when it was approved in canada?

Became a two step drug regime marketed as “mifegymiso” → mifepristone (one pill) and misoprostol (PGE agonist) 1-2 days later

What were the requirements of taking the mifegymiso pill?

• ultrasound required beforehand to make sure the pregnancy was not ectopic or further along than 49 days

• Return visit with doctor to ensure abortion was complete

• Doctor required special training

How has coverage changed between 2016 to now?

2016 → provincial drug plans would not cover abortion pills in Canada, cost $300-450

2025 → covered by all provincial drug plans and dispensed by all health professionals, no ultrasound needed and gestational limit extended to 63 days

What are the two common uses of estrogen agonists?

1. Oral contraceptives (combined with progestin)

2. Post-menopausal hormone replacement (also typically with progestin)

What is considered a “natural” estrogen hormone?

Anything produced by humans or plants (phytoestrogens too?)

Define bioidentical hormones

Exact copies of endogenous human hormones (not synthetic or non-human)

Provide examples of bio-identical and non-bioidentical hormones

Bioidentical = estradiol, estriol, and progesterone

Non-bioidentical = ethinyl estradiol, equine estrogens (from horses)

Are bioidentical hormones natural?

Not necessarily → many bioidentical hormones are synthesized (not natural) but non-bioidentical hormones can be from natural sources (phytoestrogens)

What are the two main clinical anabolic androgen agonists steroid (AAS) applications?

1. Male hypogonadism

2. Cancer-associated wasting / AIDS / burns

What is the main use of anabolic androgenic steroids (AAS)?

Athletes taken lead to levels 40x higher than typical medical uses!

Why is the effects of the extremely high doses difficult to interpret?

Steroid receptors are structurally related, so high doses can interact with different receptors or the steroids can be transformed into others (androgens → estrogens)

What are the two common side effects of anabolic androgenic steroids?

Compromises endogenous synthesis, leading to:

• decreased tropic hormones (FSH and LH)

• Atrophy of steroidogenic gland (testes decrease in size!)

What are two side effects seen in anabolic androgenic steroids seen by bioconversions?

DHT → enhanced androgenic effects

Estradiol → estrogen effects!

How are stanozolol and methyl testosterone different as anabolic steroids?

Stanozolol is a non-convertible anabolic steroid, meaning it cannot be aromatized to estrogen!

Methyltestosterone however can be aromatized to estrogen and cause other effects

How do stanozolol and 5a reduced astructures differ in terms of androgenic effects?

Stanozolol cannot be reduced so it has a less androgenic effect compared to the anabolic effects, while 5a reduced structures can be converted to DHT to amplify androgenic effects (like in the prostate)

Why are the two derivatives of gestrinone (a progestin) important?

If converted to THG → will degrade quickly in urine and has an equal potency to DHT (used in doping scandals because it leaves urine quickly!)

If converted to trenbolone → 2x as potent as testosterone!

What two characteristics of tumor cells are targeted therapies for breast cancer based on? Which is most important for endocrine therapies?

ER+ and PR+? (Estrogen and progesterone receptors) → estrogen receptors are most important!

What are the two therapies possible if tumor cells are expressing estrogen receptors?

1. Block estrogen synthesis (i.e. aromatase inhibitors)

2. Block estrogen action (at the level of the receptor)

When are aromatase inhibitors commonly used?

In post-menopausal women when estrogen is coming only from peripheral sources (not ovaries) since it won’t affect fertility(?)

What are the two types of receptor level inhibitors?

SERMs → selective estrogen receptor modulators

SERDs → selective estrogen receptor degraders

Compare the functions of SERMs and SERDs

SERMs → mimic estrogen action in certain tissues (agonists) while opposite it in others (antagonist)

SERDs → bind to the estrogen receptor, reduce dimerization, and promote degradation via proteasomes

Tamoxifen and Raloxifene are both SERMs with different targets, compare them

Tamoxifen → antagonist for breast, agonist for bone and uterus

Raloxifene → antagonist for breast and uterus, agonist for bone

Where are the consequential effects of using Tamoxifen vs Raloxifene?

Both antagonize estrogen receptors in the breast (--) and agonize estrogen receptors in the bone (++) BUT:

Tamoxifen → agonizes estrogen in the uterus (++)

Raloxifene → antagonizes estrogen in the uterus (--)

Compare the medical applications of tamoxifen vs Raloxifene

TAM → effective treatment for all stages of hormone-responsive breast cancer and used as a preventative for high-risk women

RAL → previously approved for prevention and treatment of osteoporosis but also approved for breast cancer (more recently)

What is the risk of using TAM vs RAL?

TAM increases the risk of endometrial hyperplasia / uterine cancer (uterus agonist), while RL does not (not a uterus agonist)

How are estrogen agonists and antagonists different in terms of their function at the level of the receptor?

Agonist → binds to the receptor and induces all the usual post-receptor effects (“mimics”)

Antagonist → binds to the receptor but does NOT have biological effects (“blocker”)

What two ways does an activated ER receptor interact with DNA?

1. ‘Classic mechanism’

2. ‘Tethering’

Compare the classic mechanism and tethering

Classic → binds directly to EREs of target genes and interacts directly with coregulatory proteins and RNA polymerase (DIRECT)

Tethering → interacts with DNA-bound TF’s in a way that stabilizes the DNA binding of the TF and recruits coactivators to the complex

What is the risk of the tethered mechanism?

They tend to be associated with proto-oncogenes!

How do Raloxifene and tamoxifen differ from expected activity when considering both transcriptional mechanisms?

Raloxifene represses gene expression in both mammary and uterine cells in both pathways, and recruit corepressors (never any difference in activity

HOWEVER

Tamoxifen represses gene expression in mammary and uterine cells in the classical mechanism BUT NOT with tethered genes in uterine cells (recruits coactivators!)

What 3 factors determine a SERMs activity in different tissues?

1. Shape of ligand + shape of ER ligand combination

2. How the ER-ligand complex interacts with genes

3. Which co-regulatory molecules are present/recruited

To summarize: what is the overall interaction of tamoxifen between mammary and endometrial cells in both pathways?

Mammary cells → ‘classic’ genes are blocked, ‘tethered’ genes are blocked

Endometrial cells → ‘classic’ genes are blocked, ‘tethered’ genes are activated

What is ER-ESR1?

A mutant form of ER that arises in metastatic breast cancer that is constitutively active!

How does ER-ESR1 change the therapy type used? Why?

SERDs must be used instead because SERMs are no longer effective

How do SERDs prevent ER-ESR1 from becoming a problem?

They bind to ER-ESR1 and degrade it in the proteasome when used in high doses

How prevalent is prostate cancer?

The most frequently diagnosed malignancy in males and the second leading f cause of death in men (in western countries)

Why are androgens the focus for controlling prostate cancer and not other measures?

Metastatic prostate cancers respond poorly to typical anti-mitotic used in other cancers, so withdrawal of androgens (or blockage) are optimal

Why are prostate cancers dangerous if they progress too far?

They become androgen-independent as a result of the reactivation of ARs?

What is CRPC?

Castration-resistant prostate cancer → meaning the cancer will continue regardless of if androgens are present or not

What are the two main suggested strategies to shut down androgen production in the treatment of metastatic prostate cancers?

1. GnRH antagonists and agonists (chemical castration)

2. Androgen synthesis inhibitors (5a-reductive or 17a hydroxylase)

What happens if 17a-hydroxylase is inhibited?

There is no testosterone, DHT, or estradiol production (only preg, prog, aldo) → but also no cortisol! (Need supplements!)

What are the two methods used to block AR signalling in prostate cancers?

First and second generation androgen blockers

Compare first and second generations androgen receptor blockers

1st generation → competes for androgen binding

2nd generation → blocks multiple stages of AR-mediated transcription

Why are second generation blockers better?

They have higher affinity and are able to target aberrant AR signalling

How effective are 17a-hydroxylasse (Abiraterone) inhibitors?

Survival increased by 3.9 months and could even be used in breast cancers!

What 3 steps do 2nd gen blockers interfere at?

1. Nuclear translocation (entering nucleus)

2. DNA binding

3. coactivator recruitment

Where do both 1st and 2nd gen blockers bind?

To the ligand-binding domain of the androgen receptor (antagonist) to compete with androgens

What are the 4 min mechanisms implicated in castration-resistant prostate cancer?

1. Over-expression of AR

2. Gain of function AR mutations

3. Over-expression of coactivators

4. Expression of steroidogenic enzymes within tumour cells (intracrine)

What are the 3 main future directions in treatment of prostate/breast cancer

1. Steroid synthesis (more potent inhibitors of enzymes)

2. Steroid action (higher affinity blockers or blockers that recognize aberrant forms of receptor)

3. Personalized treatments (known receptor mutations to treat more accurately?)