Introduction to Hormone-Dependent Cancers: Breast and Prostate Cancer Flashcards
What is a hormone?
A hormone is a chemical messenger that is made by specialist cells, usually within an endocrine gland, and it is released into the bloodstream to have an effect in another part of the body.
Hormones can be chemicals, peptides or proteins.
Places in the body where hormones are produced include: pineal gland hypothalamus pituitary gland thyroid gland thymus pancreas stomach adrenal cortex kidneys testes ovaries uterus
What 3 classes can hormones be grouped into?
They can be grouped into 3 main classes
Steroids – lipid soluble small molecule e.g. testosterone
Peptide / proteins e.g. insulin
Modified amino acids / amine hormones e.g. adrenaline
What are all steroid hormones synthesised from?
cholesterol which is either ingested or synthesised within the body (contains the basic 4 ringed steroid back bone structure which forms a part of all steroid hormones!)
Cholesterol is converted into pre-cursors and hormones in the adrenal cortex, which is positioned next to the kidney
Where are the main corticosteroids and mineralocorticoids synthesised? What other hormones can be released/what else happens?
What are some examples of steroid hormones?
Main corticosteroids and mineralocorticoids synthesised in the adrenal cortex
Androgenic and estrogenic precursors released into the bloodstream also from the adrenal cortex and reach the Gonadal tissues- Androgens and estrogens produced in target tissues e.g. testes and ovaries – then released into the bloodstream
examples of steroid hormones include: Androgen (testosterone) Estrogen (estradiol) Progestogen (progesterone) Corticosteroid (cortisol) Mineralocorticoid (aldosterone)
in brackets is an example of the group of hormones that is the name above the brackets
What are the sex hormones responsible for?
These are responsible for the sexual dimorphism between males and females,
the development of the secondary sexual characteristics e.g. the growth spurt during puberty, body hair, gonadal development, voice change, breast growth and accessory organs of the reproductive organs e.g. the prostate in men.
What effects do steroid hormones have on tissues?
Steroid hormones work systemically, having effects on several tissues
These effects are:
in females oestrogen controls the menstrual cycle, and breast tissue development, fertility, and reproductive organ development, secondary sexual characteristics - body hair etc.
in males testosterone controls reproductive and supportive organs (prostate), development of sexual characteristics in men e.g. deepening of the voice, body hair etc
What is the action of steroid hormones?
What is the mechanism of the receptor?
Once the steroid hormones enter the cells, they bind to receptors.
These receptors are known as nuclear receptors – as they have their effects in the nucleus, however they may be found in the cytoplasm or nucleus initially.
Steroid hormones are small lipophilic molecules, they can easily enter cells by passing through the plasma membrane.
Mechanism receptor:
Steroid hormones cross into the cell cytoplasm where they will bind to their receptor
Binding to the receptor causes a conformational change in the nuclear receptor, causing it to become activated (some nuclear receptor dimerise at this point)
Nuclear receptors then translocate into the nucleus
Nuclear receptors bind to specific DNA sequences called response elements located in the promoters of steroid responsive genes.
Steroid responsive genes are switched on and upregulated.
What does a nuclear receptor consist of?
1.Ligand binding domain (LBD)
Binds specific steroid molecules with high affinity
2.DNA binding domain (DBD)
Binds specific DNA sequences
3.Activation function domain (AF1 & 2)
Recruits gene activation machinery, some receptors have a secondary AF2 domain towards the C-terminal
When these receptors bind steroid hormones they are activated.
Thus they are called ligand-activated receptors
The binding of steroids to the ligand binding domain causes a physical restructuring of the polypeptide chains in the receptor, activating it
What happens when a ligand binds to a ligand binding site?
Ligand binding to the ligand binding site causes a shift in an a-helix, activating the receptor.
Receptor dimerises, moves into the nuceus and binds to specific DNA sequences
Receptor then recruits DNA modifying enzymes e.g. histone deacetylases, other transcription factors and RNA polymerase to promoters of hormone responsive genes.
What are the 2 Zinc finger domains found on the DNA binding domain?
The DNA binding domain contains 2 zinc fingers domains, which are essential for sequence specific DNA binding.
1.CI Zinc finger
Specific DNA
sequence binding
2.CII Zinc finger
Interaction with the
DNA phosphate backbone
What are hormone responsive genes and hormone response elements?
Many hundreds of genes may be upregulated by a steroid hormone receptor.
Some genes may be downregulated
Genes include functional tissue specific genes, cell cycle and proliferation genes, and genes involved in tissue development and differentiation.
Hormone Response Elements are specific DNA sequences found in the promoters of hormone responsive genes.
Many are palindromic
What do we know about the nuclear receptor (super)-family?
There are 48 nuclear receptor genes in humans
All share a common domain structure and are thought to arise from a common evolutionary ancestor.
They all share a structure that is activated by ligand binding.
How are steroid hormone receptors similar/different to each other- in which of the 3 parts do they share most in common/differ most?
Receptors have a high homology in the DNA binding domain, and differ in ligand binding domains, and differ significantly in N-terminal activation domains
What do we know about breasts, with regards to structure?
The breast is anapocrinegland that produces themilkused to feed an infant
The breast is composed of glands and ducts, which produce the fatty breast milk.
The milk-producing part of the breast is organized into 15 to 20 sections, called lobes.
Within each lobe are smaller structures, called lobules, where milk is produced.
The milk travels through a network of tiny tubes called ducts. The ducts connect and come together into larger ducts, which eventually exit the skin in the nipple.
What is the difference between an endocrine, exocrine and apocrine gland?
Exocrine glands – secrete substances out onto a surface or cavity, via a ductal structure.
Endocrine glands – secrete substances directly into the bloodstream
The breast:
Apocrine glands – are a specialised exocrine gland in which a part of the cells’ cytoplasm breaks off releasing the contents.
What 2 cell compartments does the mammary epithelium consist of?
The mammary epithelium consists of two cell compartments:
Luminal – form a single layer of polarized epithelium around the ductal lumen, luminal cells produce milk during lactation.
Basal – comprise of the cells that do not touch the lumen, basally oriented myoepithelial cells in contact with the basement membrane, have contractile function during lactation
Although oversimplified, this constitutes the main mammary gland cell types.
What are the 2 major phases that can be distinguished in mammary gland development?
What do we know about oestrogen and progesterone function in the normal breast?
Two major phases can be distinguished in mammary gland development:
hormone-independent from embryonic development up to puberty
hormone-dependent thereafter during puberty, menstrual cycle and pregnancy.
Estrogen, together with other hormones (e.g. growth hormone and cortisol) drives the expression of genes involved in cellular proliferation and differentiation
Hormone-dependent mammary gland development occurs after puberty and results in ductal elongation and triggers side branching.
In the adult estrogen allows for the maintenance of mammary gland tissue, and also primes the tissue for the effects of progesterone during pregnancy for milk production.
Estrogen is primarily involved in the initial growth of breast cancer
The progesterone receptor gene is switched on by the estrogen receptor
Progesterone increases the branching of the ducts
Prolonged progesterone receptor activity i.e. during pregnancy, leads to more side branching and lactogenic differentiation (together with prolactin hormone).
What is breast cancer?
Breast cancer occurs when abnormal cells in the breast begin to grow and divide in an uncontrolled way and eventually form a tumour.
Breast cancer starts in the breast tissue, most commonly in the cells that line the milk ducts of the breast.
1 in 8 women (approx.) may develop breast cancer in their lifetime.
The main risks are age, lifestyle (including smoking and obesity), and genetic familial factors.
Breast Cancer Aetiology
Age - The risk for breast cancer increases with age; most breast cancers are diagnosed after age 50.
Genetic mutations to certain genes, such as BRCA1 and BRCA2. Women who have inherited these genetic changes are at higher risk of breast and ovarian cancer.
Reproductive history. Early onset of menstrual cycle before 12yrs and starting menopause after 55yrs expose women longer to hormones.
Previous treatment using radiation therapy to the chest or breasts (e.g. treatment for lymphoma) before age 30 have a higher risk of getting breast cancer later in life.
Not being physically active increases the risk of breast cancer.
Being overweight or obese.
Taking hormones. Some forms of hormone replacement taken during menopause can raise risk for breast cancer when taken for more than five years. Certain oral contraceptives (birth control pills) also have been found to raise breast cancer risk.
Reproductive history. Having the first pregnancy after age 30, not breastfeeding, and never having a full-term pregnancy can raise breast cancer risk.
Drinking alcohol. Risk for breast cancer increases with more alcohol.
What is Ductal Breast Carcinoma in Situ (DCIS)?
Breasts are made up of lobules (milk-producing glands) and ducts (tubes that carry milk to the nipple), which are surrounded by glandular, fibrous and fatty tissue.
When cancer cells develop within the ducts of the breast but remain within the ducts (‘in situ’), it is called DCIS. The cancer cells have not yet developed the ability to spread outside these ducts into the surrounding breast tissue or to other parts of the body.
What is Lobular Breast Carcinoma in Situ (LCIS)?
Lobular carcinoma in situ (LCIS) is an uncommon condition in which abnormal cells form in the milk glands (lobules) in the breast.
LCIS isn’t cancer. But being diagnosed with LCIS indicates that there could be an increased risk of developing breast cancer.
What cells do the majority of breast cancers arise from?
What do these cells express and what are the majority of breast cancers? (in terms of breast cancer subtypes)
The majority of breast cancers arise from the luminal cells.
These cells express ER (estrogen receptor)
The majority of breast cancers are ER+ve and have a good prognosis, however the remainder are ER-ve and have a relatively poor prognosis.
ER-ve breast cancers cannot be treated ‘hormonally’ and patients are given more conventional therapies.
What do we know about breast cancer subtypes?
It is an oversimplification to classify breast cancer as either ER+ve or ER-ve.
There are several classifications of breast cancer – approx. 16-20 sub types have been identified based on molecular profiling and are beyond the scope of this module.
ER+ve/PR+ve breast cancer have a better prognosis
Progesterone receptor is in itself an indicator of estrogen activity, but progesterone is becoming a more interesting target for cancer therapy as in some subtypes it may reduce cell growth.
Targeting the Estrogen receptor in breast cancer
In the normal breast ER controls functions such as cell proliferation, development and differentiation in a highly controlled manner.
However, in breast cancer, the ER signalling pathway is subverted and becomes uncontrolled.
ER’s ability to bind DNA and open chromatin becomes hijacked and is used to transcribe many genes, non-coding RNAs and miRNAs.
ER then governs cancer cell proliferation, and controls and influences many hundreds of genes involved in metastasis, invasion and adhesion.
How can we inhibit estrogen action? Why would we do this?
NORMALLY:
Estrogen binds to its receptor at the ligand binding site, causing the estrogen receptor to dimerise and trabsolcate into the nucleus where it binds DNA and recruits coactivators. The two activation domains- AF1 and AF2 are activated and this activates the full gene activation to move cell growth forwards and therefore cell cancer growth forwards
Pharmaceutically competitively blocking estrogen binding to receptor – and degrading ER protein
No ER signalling = no breast cancer cell growth
So ER is present in breast cancer and helps to drive forward the growth of the cancer cells.
What is fulvestrant (Faslodex)?
Fulvestrant is an analogue of estradiol.
Fulvestrant competitively inhibits binding of estradiol to the ER, with a binding affinity that is 89% that of estradiol
Fulvestrant – ER binding impairs receptor dimerisation, and energy-dependent nucleo-cytoplasmic shuttling, thereby blocking nuclear localisation of the receptor.
Additionally, any fulvestrant – ER complex that enters the nucleus is transcriptionally inactive because both AF1 and AF2 are disabled.
The fulvestrant–ER complex is unstable, resulting in accelerated degradation of the ER protein.
How does Tamoxifen work?
Tamoxifen binds the ER at the ligand binding site.
Tamoxifen is a partial agonist but does not cause the full activation of ER.
It has a mixed activity – it activates ER in the uterus and liver, but acts as an antagonist in breast tissue.
Tamoxifen is a Selective Estrogen Receptor Modulator (SERM).
Tamoxifen bound ER does not fold properly and the AF2 domains do not function
Tamoxifen Bound ER:
Estradiol binds deep within a pocket in the receptor and is covered by a loop of protein chain, as shown in the upper illustration
This loop forms part of the activation signal that will stimulate growth in the cell (AF2).
Tamoxifen (in pink in the lower illustration) binds, the extra tail of the drug is too bulky and the receptor loop is not able to adopt its active conformation.
What do aromatase inhibitors do? What are the two types and what do they do?
When ovaries are no longer functional in postmenopausal women, potential sources of estrogens come from the peripheral conversion of androgens by the aromatase enzyme.
This enzyme is present in multiple organs including adipose tissue, brain, blood vessels, skin, bone, endometrium, and breast tissue.
Androgens are hormones such as testosterone, or adrenal androgens such as androstenedione
Type 1 inhibitors, like exemestane (Aromasin ©), are androgen analogues and bind irreversibly to aromatase, so they are also called “suicide inhibitors”. The duration of inhibitory effect is primarily dependent on the rate of de novo synthesis of aromatase.
Type 2 inhibitors, like anastrozole (Arimidex ©), contain a functional group within the ring structure that binds the heme iron of the cytochromeP450,interfering with the hydroxylation reactions.
Summarise the part of the lecture on breast cancer
Breast cancer is derived from a hormonally sensitive tissue, and remains responsive and reliant on estrogen for growth.
Blocking estrogen action via competitive inhibitors and reducing estrogen synthesis is an unique avenue that can be exploited to treat breast cancer.
In many cases anti-estrogen therapy is very useful, but 1/3 may develop endocrine resistance, and relapse within 5 years, after which conventional chemotherapy may be used (i.e. non hormonal)
What is the normal function of the prostate? What type of gland is the prostate gland?
The main function of the prostate is to produce prostatic fluid that creates semen when mixed with the sperm produced by the testes.
The prostate is an EXOCRINE GLAND (Exocrine glands – secrete substances out onto a surface or cavity, via a ductal structure)
What phases constitute prostate gland development?
Prostate gland development can be separated into phases :
hormone-independent from embryonic development up to puberty
enlargement during puberty
hormone-dependent maintenance thereafter in adulthood
And – reactivation of prostate growth in old age – leading to hyperplasia and prostate cancer
How can the prostate gland develop abnormally?
• Inflammation, e.g. due to infection
Prostatitis - linked to infertility
Dysregulated growth of prostate
eg Benign: Benign Prostatic Hyperplasia (BPH)
Malignant: Prostate Cancer
What are some symptoms of prostate cancer?
- frequent trips to urinate
- poor urinary stream
- urgent need to urinate
- hesitancy whilst urinating
- lower back pain
- blood in the urine (rare)
How can you detect prostate cancer?
1) Digital rectal examination (DRE)
2) PSA test
3) Ultrasound
What is used to help evaluate theprognosisof men using prostate biopsy samples?
TheGleason grading systemis used to help evaluate theprognosisof men using prostate biopsy samples.
The samples are examined by a clinical histologist.
Prostate cancer staging predicts prognosis and helps guide therapy.
Cancers with a higher Gleason score are more aggressive and have a worse prognosis.
What do some prostate cancer treatments include?
What is Active surveillance?
4 stages of prostate cancer:
1.“Watchful waiting”- Low grade tumour, older patients
Recommended for older men when it’s unlikely the cancer will affect their natural lifespan.
If the cancer is in its early stages and not causing symptoms, you may decide to delay treatment and wait to see if any symptoms of progressive cancer develop.
- Radical prostatectomy- Stage T1 or T2 (confined to prostate gland)
3.Radical radiotherapy-External up to T3 (spread past capsule)
Internal implants (brachytherapy) for T1/2
4.• Hormone therapy - ± prostatectomy or radical radiotherapy, also Metastatic prostate cancer
Active surveillance
Aims to avoid unnecessary treatment of harmless cancers while still providing timely treatment for men who need it.
Active surveillance involves having regular PSA tests, MRI scans and sometimes biopsies to ensure any signs of progression are found as early as possible.
What are some risk factors for prostate cancer?
Age:
Prostate cancer is rare in men younger than 40, but the chance of having prostate cancer rises rapidly after age 50. About 6 in 10 cases of prostate cancer are found in men older than 65.
Race/Ethnicity:
Prostate cancer develops more often in African-American men and in Caribbean men of African ancestry than in men of other races. And when it does develop in these men, they tend to be younger. Prostate cancer occurs less often in Asian-American and Hispanic/Latino men than in non-Hispanic whites.
The lifetime risk of being diagnosed with prostate cancer is 13.2-15.0% for White males, while in Black males it is significantly higher (23.5-37.2%), and in Asian males it is significantly lower (6.3-10.5%)
Geography:
Most common in North America, north-western Europe, Australia, and on Caribbean islands. It is less common in Asia, Africa, Central America, and South America.
More intensive screening for prostate cancer in some developed countries probably accounts for at least part of this difference, but other factors such as lifestyle differences (diet, etc.) are likely to be important. For example, Asian Americans have a lower risk of prostate cancer than white Americans, but their risk is higher than that of men of similar ethnic backgrounds living in Asia.
Family History:
Prostate cancer seems to run in some families, which suggests that in some cases there may be an inherited or genetic factor.
Most prostate cancers occur in men without a family history of it.
Having a father or brother with prostate cancer more than doubles a man’s risk of developing this disease. (The risk is higher for men who have a brother with the disease than for those who have a father with it.) The risk is much higher for men with several affected relatives, particularly if their relatives were young when the cancer was found.
Gene changes/inherited:
Several inherited gene changes seem to increase prostate cancer risk, but they probably account for only a small percentage of cases overall.
Inherited BRCA1 or BRCA2 gene mutations of the, which are linked to an increased risk of breast and ovarian cancers in some families, can also increase prostate cancer risk in men (especially mutations in BRCA2).
Men with Lynch syndrome (also known as hereditary non-polyposis colorectal cancer, or HNPCC), a condition caused by inherited gene changes, have an increased risk for a number of cancers, including prostate cancer.
Other general risk factors:
Diet - The exact role of diet in prostate cancer is not clear, but several factors have been studied. Men who eat a lot of dairy products appear to have a slightly higher chance of getting prostate cancer.
Obesity - Being obese does not seem to increase the overall risk of getting prostate cancer.
Some studies have found that obese men have a lower risk of getting a low-grade (slower growing) form of the disease, but a higher risk of getting more aggressive (faster growing) prostate cancer.
Chemical exposures - There is some evidence that firefighters can be exposed to chemicals that may increase their risk of prostate cancer. Chemical agents used during the wars may also increase risk. Hormonal mimicking agents in plastics and foodstuffs.
Inflammation of the prostate - Prostatitis (inflammation of the prostate gland) may be linked to an increased risk of prostate cancer.
Sexually transmitted infections - Researchers have looked to see if sexually transmitted infections (like gonorrhoea or chlamydia) might increase the risk of prostate cancer, because they can lead to inflammation of the prostate. So far, studies have not agreed, and no firm conclusions have been reached.
Also HPV infections may have a role.
What genes are associated with prostate cancer?
There are several genes associated with prostate cancer
e.g. BRCA1 mutations and PTen loss
What is PTEN?
PTEN is a phosphatase that antagonizes the phosphatidylinositol 3-kinase signalling pathway.
As PTEN is the only known 3′ phosphatase counteracting the PI3K/AKT pathway.
Loss of PTen results in increased growth factor signalling.
What is the most common androgen in the body and where is it produced?
The growth and development of the prostate gland is dependent upon the presence of androgens (male hormones).
The most common androgen is testosterone, a steroid hormone.
Testosterone is produced in the testes.
Where is Androgen receptor located?
AR is located in the cytoplasm associated with many chaperone proteins.
Testosterone is converted to a more potent agonist as it crosses into the prostate
Dihydrotestosterone (DHT) then binds the AR
Targeting AR in Prostate Cancer:
The prostate gland is an androgen sensitive and dependent tissue
Prostate cancer cells retain this sensitivity and dependency – androgens are a key driver of prostate cancer growth.
Therefore, this can be used as an inherent vulnerability that can be exploited for treatment.
Switch off AR signalling, switch off the the cancer growth.
AR targeting is the “Achilles Heel” of prostate cancer.
Inhibition of testosterone synthesis…
The adrenal gland derived androgens circulate in the blood, and are finally converted to testosterone in the testes.
Testosterone then circulates in the blood where it reaches end target organs e.g. prostate
The adrenal androgen production can be inhibited, thus depriving the testes of testosterone precursors.
GnRH (gonadotropin releasing hormone)
Goserelin – super agonist
Abarelix – antagonist
Overall the actions of superagonists and antagonists are similar – they depress testosterone production in the testes
Testosterone is converted in the prostate to a more potent androgen – dihydrotestosterone – which drives prostate growth and function
