Intro to hormone dependent cancers: breast and prostate Flashcards
What is a hormone?
A chemical messenger that is made up of specialist cells (usually in endocrine gland) and is released into the bloodstream to have an effect in another part of the body
- can be chemical, peptides or proteins
In which organs are hormones produced in?
Endocrine organs.
- Brain there is pineal gland, hypothalamus, pituitary gland
- Thorax, there is thyroid and thymus glands
- Abdomen - pancreas, kidneys, adrenal glands
- Stomach and digestive system
- Male - testest
- female - ovaries and uterus
Hormones are grouped into 3 main classes
Steroids - lipid soluble, small molecules e.g testosterone
Peptides/protein hormones - insulin
Modified amino acids / amine hormones - adrenaline
What are all steroid hormones synthesised from?
What is the basic structure they have?
Cholesterol which is ingested or synthesised within body
Basic 4-ring steroid backbone structure
How are steroids synthesised?
Starting with cholesterol
Cholesterol converted to bi-synthetic precursors and hormones in adrenal cortex
Adrenal cortex secretes primary hormones - corticosteroids and mineralocorticoids
and secretes androgenic and estrogenic precursors released into blood stream - less potent form of final hormone
take up into gonadal tissues (ovaries and testes), metabolised to form fully active hormones like androgens and estrogens
testosterone may be metabolised again into more potent form in some tissues like prostate
What are sex hormones responsible for?
Sexual dismorphism between males and females, development of secondary sexual characteristics (e.g growth spurt, body hair, gonadal development, voice change)
Steroid hormones work systemically, they have effect on several tissues
Females: oestrogen controls menstrual cycle and breast tissue development, fertility and reproductive organ development, secondary sexual characteristics – body hair etc
Males testosterone controls reproductive and supportive organs (prostate), development of sexual characteristics in men e.g deepening of voice, body hair
Which are the top most common cancers in the UK?
Breast and prostate cancer.
Tissues strongly controlled by steroid hormones, hormone dependent
when breast/prostate cancer occurs steroid hormones can still influence how cells grow and function - how disease develops and progresses
can be exploited for treatment of cancers
Describe the steroid hormone receptor mechanism
- Steroid hormones cross into cell cytoplasm, bind to their receptor
- Binding to the receptor causes conformational change in nuclear receptor, causing it to become activated (and dissociate from any cytoplasmic chaperon proteins, some nuclear receptor dimerise at this point)
- Nuclear receptor then translocates into nucleus
- Nuclear receptors bind to specific DNA sequences called steroid response elements located in the promoters of steroid responsive genes
- Steroid responsive genes switched on and upregulated
What are the three main parts of the domain structure of a nuclear receptor?
Highly specific ligand binding domain (LBD) - each individual receptor binds specific steroid molecules with high affinity and specificity
DNA binding domain (DBD). Binds specific DNA sequences with high degree of specificity
Activation function domain (AF1 and 2). Recruits gene activation machinery, some receptors have a secondary AF2 domain towards the C-terminal.
Describe the steps in ligand activated transcription factors when activated
- Ligand binding to the ligand binding site causes a shift in an a-helix, activating the receptor
- Receptor dimerises, moves into the nucleus from cytoplasm, binds to specific DNA sequences
- Receptor then recruits DNA modifying enzymes e.g histone deacetylases, other transcription factors and RNA pol to promoters of hormone responsive genes - to inititae gene transcription
What domains do the DNA binding domain contain? What is it essential for?
DNA binding domain contains 2 zinc finger domains.
Essential for sequence specific DNA binding.
Sequence contains 4 cysteine residues that can bind to zinc atom and form zinc finger domain.
Holds amino acid backbone together and forms zinc finger domains required for specific DNA binding
What is the specific DNA sequences that nuclear receptors bind to called?
What part of the receptors domain helps to recognise them?
Hormone response elements, found in promoters of hormone responsive genes.
Many are palindromic.
Normally 6 DNA bases separated by 3 spacer DNA bases, then another 6 DNA bases repeated again / palindromic repeat.
Receptors zinc finger domains help recognise these sequences.
Are nuclear receptors similar in structure?
Have high homology in the DNA binding domain and a structure which is activated by ligand binding
differ in ligand binding domains and in N-terminal activation domains
Breast tissue is responsive to oestrogen
Describe the breast and what it is composed of
Aprocrine gland, produces milk
Composed of glands and ducts which produce fatty breast milk
milk producing part of breast is organised into 15-20 sections - lobes
within each lobe is smaller structure, lobules, where milk is produced
milk travels through tiny tubes, ducts, which come together into larger ducts and eventually exist skin in nipple
Wha does exocrine gland do?
Secretes substances out onto a surface or cavity via a ductal structure
What does endocrine glands do?
Secrete substances directly into bloodstream
What type of gland is an apocrine gland?
Specialised exocrine gland in which part of a cell’s cytoplasm breaks off, releasing the contents.
Mammary epithelium consists of two cell compartments
Luminal – form a single layer of polarised 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
myoepithelial (basal) on outside, luminal face in towards lumen.
What are the two major phases in mammary gland development?
Hormone-independent from embryonic development up to puberty
Hormone-dependent thereafter during puberty, menstrual cycle and pregnancy
What does estrogen do in adults?
Estrogen drives expression of genes involved in cellular proliferation and differentiation.
In adults allows for maintenace of mammary gland tissue + primes tissue for effects of progesterone during pregnancy for milk production
What does progesterone cause in the breast?
Progesterone receptor gene switched on by oestrogen receptor.
Progesterone increases branching of the ducts (estrogen determines growth of ducts)
Prolonged progesterone receptor activity (e.g during pregnancy) leads to more side branched and lactogenic differentiation (with prolactine hormone)
What is the aetiology of breast cancer?
Age
Genes implicated
Age - risk increases with age, most diagnosed after 50
Genetic mutations in BRCA1 and 2, inherting these genetic changes = higher risk of breast and ovarian cancer
Reproductive system - early onset of menstrual cycle before 12 and menopause after 55, exposed to hormones longer
previous treatment using radiation therapy - higher risk
Not physically active, overweight
Taking hormones, oral contraceptives increase risk
first pregnancy after 30, not breastfeeding
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), surrounded by glandular, fibrous and fatty tissues
Cancer cells develop within the ducts of the breast but remain within the ducts (in situ), it is called DCIS.
What is lobular breast carcinoma in situ (LCIS)
Lobular carcinoma in situ (LCIS) , uncommon condition in which abnormal cells form in the milk glands (lobules) in breast
LCIS isn’t cancer.
Being diagnosed with LCIS indicates that there could be an increased risk of developing breast cancer
Majority of breast cancer arises from which cells?
Luminal cells, express estrogen receptor.
Luminal epithelial cells are inside lumen
Sit on layer of basal myoepithelial cells that are in contact with basement membrane.
What is the difference between ER positive and negative ER breast cancers?
Majority are ER positive - good prognosis
ER negative - poor prognosis
ER negative breast cancers can’t be treated hormonally and patients given more conventional therapies
ER negative breast cancers develop from other cells like basal cells
Breast cancer subtypes
Why can progesterone receptor be used as an indicator of estrogen acitvity?
Because it is estrogen dependent gene.
Progesterone target for cancer therapy in some subtypes, may reduce cell growth.
Why is ER targeted in breast cancer treatment?
Mammary gland is estrogen sensitive and dependent
Estrogen key driver of breast cancer growth
Therefore can be used for treatment, switch off ER signalling and cancer growth
- ER targetting is Achilles heel of breast cancer
What is the normal action of estrogen?
Estrogen binds to receptor at ligand binding site
Estrogen receptor dimerses, translocates into nucleus
binds DNA and recruits in proteins for gene transcription e.g co-activators, chromatin modifiers, RNA polymerase.
Activation domains, AF1 and AF2 activated, triggering gene activation, drives cell growth and cancer growth forward.
How is estrogen action inhibited?
competitively blocking estrogen binding to receptor - and degrading ER protein.
No ER signal = no breast cancer cell growth
How does fulvestrant (faslodex) work?
Analogue of estradiol
Completely inhibits binding of estradiol to ER, binding affinity that is 89% that of estradiol
Binding to ER impairs receptor dimerisation
receptor translocation into nucleus (nucleo-cytoplasmic shuttling) and blocks it from working / blocks nuclear localisation of receptor
fulvestrant-ER complex transcriptionally inactive because AF1/2 disabled
fulvestrant-ER complex unstable, results in accelerated degradation of ER protein
= no estrogen receptor activity and gene transcription
How does tamoxifen work as a treatment for breast cancer?
Binds to ligand gated binding site, causes ER to become partially active
Binding causes conformation change in the ER, causing only one of the activation domains to become active, AF1.
AF2 domain not active.
ER remains partially inactive. Stops ER activity within breast tissue and cancer cells
However doesn’t stop ER activity in other tissues like liver and uterus
Mechanism is highly complicated, may be due to types of coactivators present in those tissue types
What does the aromatase enzyme do in the ovaries?
When ovaries aren’t functional in postmenopausal women, estrogen can come from peripheral conversion of androgens via aromatase enzyme.
present in multiple organs - adipose tissue, brain, blood vessels, skin, bone, breast tissue
What are the types of aromatase inhibitors?
Type 1 like exemestane (aromasin)
- androgen analogues, bind irreversibly to aromatase
Type 2 like anastrozole (Arimidex)
- contains functional group within ring structure
- binds heme iron of cytochrome P450, interfering with hydroxylation reactions
What is the main function of the prostate?
Produce prostatic fluid which creates semen when mixed with sperm produced by testes.
Prostate gland under bladder, an exocrine gland composed of glandular tissue
What type of gland is the prostate gland?
Specialised exocrine gland called apocrine gland (and merocrine)
Apocrine gland is specialised exocrine gland in which part of the cell’s cytoplasm breaks off releasing the contents
What phases can prostate development be separated into?
Hormone independent from embryonic development up to puberty
enlargement during puberty
Hormone dependent maintenance therafter in adulthood
Reactivation of prostate gland in old age - leads to hyperplasia and prostate cancer
What prostate abnormalities can occur?
Inflammation e.g due to infection
- Prostatitis linked to infertility
Dysregulated growth of prostate
- Benign: prostate hyperplasia (BPH)
- Malignant: prostate cancer
What are the symptoms of prostate cancer?
Frequent trips to urinate
Poor urinary stream
Urgent need to urinate
Lower back pain
Hesitancy whilst urinating
Blood in the urine (Rare)
tumour pass of prostate cancer squeezes and presses urethra, puts pressure on bladder
In what cells does prostate cancer start?
Luminal epithelial cells.
Hypoproliferate to form prostate intraepithelial neoplasia / PIN
became invasive adenocarcinoma
prostate cancer grows and divides rapidly, filling lumen, then begins to inavde outward from prostate
How is prostate cancer detected?
- Digital rectal examination (DRE)
- PSA test, if prostate is damaged or overgrown, the prostate specific antigen can escape into the blood where it can be measured with an immune test - blood sample, antibody based assay
- Ultrasound - to detect tumour outside prostate capsule
What are the different stages and grading of prostate cancer?
T1: small, localised tumour – lowest on scale
T2: palpable tumour by digital rectal exam
TNM – t for tumour, n is for number of lymph nodes involved in cancer, M for if cancer has metastasised or not
T3: escape from prostate gland, tumour is larger, grows outside of prostate gland
T4: local spread to pelvic region, tumour grown outside of prostate and involves other surrounding organs
What is the grading for N+ tumour in lymph nodes?
N0 = no cancer cells found in any lymph nodes
N1 = 1 positive lymph node <2cm across
N2 = >1 positive lymph node or 1 between 2-5cm across
N3 = Any positive lymph node >5cm across
What is the metastasis grading for prostate cancer?
M1a = Non-regional lymph nodes
M1b = Bone
M1c = other sites
What is the gleason grading system?
The Gleason grading system is used to help evaluate the prognosis of 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 worse prognosis
How is prostate cancer treated?
Watchful waiting - low grade tumour, older patients , tumour may never advance enough to be any concern to them.
Radical prostatectomy – stage T1 or T2 (confined to prostate gland)
Radical radiotherapy - external up to T3 (spread past capsule). Internal implants (brachytherapy) for T1/2
Hormone therapy +/- prostatectomy or radical radiotherapy for metastatic prostate cancer
What are the risk factors of prostate cancer?
Age - rare in men younger than 40, risk rises after 50
Race/ethnicity - more in african-american men and carribean men. less in asian america, latino men
Geography - common in north america, austrial, north-western europe. less common in asia, africa, central and south america - due to lifestyle difference
Family history - having father or brother with prostate cancer more than double’s risk of developing disease
Gene changes/inherited - inherited BRCA1/2 gene muations linked to increase breast/ovarian cancer also increases risk of prostate cancer. Lynch syndrome.
General risks - diet, obesity (lower risk of low grade cancer, higher risk of aggressive cancer), chemical exposures, inflammation of prosate
What genes are associated with prostate cancer?
BRCA1 mutations and PTen loss.
PTen is a phosphatase that antagonises the phosphatidylinositol 3-kinase signalling pathway.
PTen is the only known 3’ phosphatase counteracting the P13K/AKT pathway (that normally leads to cell growth).
Loss of PTen results in increased growth factor signalling – inappropriate cell growth and proliferation
What does TMPRSS2-ERD fusion cause?
Present in 40-80% of prostate cancers
promoter of the gene is fused with proto-oncogene ERG, strong proliferation signal driven by testosterone
AR now drives proto-oncogene ERG, leads to inappropriate gene activation
What hormone is growth and development of prostate gland dependent on?
Describe androgen receptor signalling
Androgens, most common is testosterone.
AR located in cytoplasm
testosterone converted to more potent agonist as it crosses into prostate, dihydrotestosterone, by 5-a-reductase then binds to AR with high affinity
AR activated, dimerised.
AR translocates into nucleus where it binds to androgen response elements (Specific DNA sequences in promoter regions of androgen target genes)
Recruits in gene transcription machinery + coactivators needed for expression of target gene
Leads to target protein generation and cell growth
What agent inhibits the enzymes needed to produce androgens in the body?
Abiraterone inhibits two main enzymes.
Has similar structure to cholesterol and steroid intermediates
In prostate cancer can swich off production of adrenal androgens, reduces overalll level of testosterone in body
How is hormone production controlled?
Gonadotrophin releasing hormone secreted from hypothalamus targets pituitary to release LH and FSH.
Circulate in blood, reach target tissue the testes, stimulating them to produce more testosterone.
Hypothalamus will then be sensitive to circulating testosterone hormone
Stop production of LH and FSH if testosterone levels are sufficient.
If not hypothalamus secretes more hormones.
How can the feedback loop of testosterone production be intercepted?
Goserelin – super agonist
Abarelix – antagonist
Shut down the hypothalamus to pituitary and testes signalling, reducing testosterone production.
Overall the actions of superagonists and antagonists are similar – they depress testosterone production in the testes
How do competitive androgen antagonists inhibit DHT binding to AR?
Competitive androgen antagonists. Compete with testosterone for the ligand binding site on the AR, causing it to not fold or be completely active.
- Bicalutamide.
- Enzalutamide
- Flutamide
- Nilutamide
All compete with testosterone for the ligand binding site within the androgen receptor.
in the presence of androgen antagonist , it binds to ligand binding site and stops H12 from folding over, keeping the receptor inactive.
Why do hormone therapies stop working?
Patient relapses with hormone refractory cancers.
Cancer cells develop mechanisms to overcome hormonal starvation.
Resistance mechanisms quickly selected for, cancers adapt to low levels of hormones.
some advanced tumours synthesis own steroid hormones, leads to autocrine stimulation.
Explain ligand binding site mutations
Some receptors for steroids acquire ligand binding site mutations, makes the binding sites less specific for the hormone.
Receptor is said to be promiscuous.
so if you target testosterone for prostate cancer, ligand binding site mutations in receptor may allow it to bind estrogen or cortisol, allowing cells to grow.
Explain receptor amplification
how cancer adapts resistance to hormonal therapies
Signal amplification and increased sensitivity to low hormone levels.
Steroid receptors themselves or genes expressing them are amplified, causes increased amount of receptor in the cell.
Leads to signal amplification from low hormone level.
Explain receptor phosphorylation / activation in absence of ligand
Cross over with other signal pathways e.g growth factors can phosphorylate and activate receptors nappropriately in the absence of ligand– prevalent for breast cancer
In the absence of hormone steroid receptor can bind to DNA and activate target genes.
Explain how androgen receptor transcript variants can be activated in the absence of ligands
Generaton of variants of nuclear receptor
some types of prostate cancer the AR can be expressed as a shorter, transcript variant, ARV7.
A truncated version of AR without C terminus in ligand binding domain.
Active without ligand in prostate cancer.
Can bind to DNA and trigger target gene activation without a ligand being present in the cell.
Explain receptor cofactor amplification
Cofactors recruited by hormone receptor to DNA to help activate target genes.
Cofactor amplification can amplify the signal from steroid receptors in response to a low level of steroid hormone.
Antagonists become agonists via LBD mutations
How can antagonists used for prostate cancer treatment become potent activators of mutant AR?
AR can acquire mutations in its ligand binding domain, allow antagonists to function as an agonist.
Antagonist fits in ligand binding domain and activates receptor.
Antagonists used for prostate cancer treatment can become potent activators of a mutant androgen receptor.
So sometimes patients can benefit with having therapy withdrawn.
