CBIO5: Hormones and cancer Flashcards
Define hormone
Hormones are naturally occurring substances produced in specific parts of our bodies and act as chemical messengers. They travel through the blood to control functions of other tissues and organs
What hormones are released from these glands? Pineal Hypothalamus Pituitary Thyroid Parathyroid Thymus Adrenal cortex Kidney Pancreas Testes Ovary Uterus
Pineal: melatonin Hypothalamus: dopamine Pituitary: vasopressin Thyroid: calcitonin Parathyroid: PTH Thymus: thymopoietin Adrenal cortex: adrenaline Kidney: erythropoietin Pancreas: insulin Testes: androgen Ovary: oestrogen Uterus: prolactin
What are the three classes of hormones?
peptide/protein hormones (e.g. insulin), amine hormones (e.g. adrenaline) and steroid hormones
Where are all steroid hormones derived from?
Cholesterol
What are the different steroid hormone classes?
Androgens, oestrogens, progestins, glucocorticoids and mineralocorticoids
How do steroid hormones bring about their action on cells?
Act directly on intracellular receptors due to their lipophilicity: steroid hormones enter cells through the lipid-rich plasma membrane and then bind to so-called nuclear receptors. Nuclear receptors are transcription factors that regulate gene expression and hence protein production.
How many nuclear receptors are there in humans?
48
The subset of nuclear receptors that mediate steroid hormone signalling are called what?
Steroid receptors
Breast and prostate cancers are examples of what type of cancers?
Hormone-dependent / Endocrine cancers
What pharmaceuticals can increase the risk of breast/ovarian cancer?
- combined menopausal hormone therapy
- oestrogen-only therapy slightly increases the risk of endometrial cancer
What is Diethylstilbestrol (DES)?
A synthetic oestrogen that was given to some pregnant women during in the 1940s-70s to prevent miscarriages
What do 1) early onset puberty, 2) late menopause, 3) late or no first pregnancy have in common?
Increased breast cancer risk as they are all factors that increase exposure to oestrogen cycles
What does insulin increase the risk of?
Pancreatic, liver, kidney, stomach and respiratory cancers
What does insulin-like growth factors (IGFs) increase the risk of?
Prostate, breast and bowel cancers
What are the key differences between oestrogens and androgens?
Oestrogens (e.g. oestradiol/estradiol) are produced in ovaries and are required for development of female secondary sex characteristics. Androgens (e.g. testosterone) are mainly produced by the testes and are responsible for the development of male secondary sex characteristics. However, note that males and females each have both androgens and oestrogens – it is the ratio that is different.
What is the production of oestrogen and androgen regulated by? what is this hormone regulated by?
uteinizing hormone (LH) produced by the anterior pituitary gland. LH secretion is in turn regulated by gonadotropin-releasing hormone (GnRH)
what does de novo mean?
where cholesterol in synthesised in the liver: the synthesis process begins with cholesterol being taken into the steroid-producing cells
What are oestrogens and androgens responsible for?
Female and male secondary sex characteristics
What does LH induce the production of in Leydig cells in the testes and granulosa cells in the ovaries?
pregnenolone
What is pregnenolone converted into?
dehydroepiandrosterone (DHEA)
What is dehydroepiandrosterone (DHEA) converted into? (men)
two intermediates: androstenediol and androstenedione
In men, testosterone circulates in the blood bound to what?
serum sex hormone binding globulin (SHBG) and albumin
Free-form testosterone enters prostate cells where it is converted into what by what enzyme?
dihydrotestosterone (DHT) via 5alpha-reductase
Where other than the testis and ovaries is androgen produced?
Adrenal glands
What is dehydroepiandrosterone (DHEA) converted into? (women)
How does this occur?
Into oestrogens: oestrone, 17beta-oestradiol (E2) and oestriol. Androstenedione is aromatized and oxidised in this process
What is the main circulating oestrogen during reproductive years?
E2
What is the main circulating oestrogen during pregnancy?
Oestriol
What is the main circulating oestrogen during menopause?
Oestrone
From where can E2 be directly syntheised?
Testosterone
What is the feedback loop for testosterone and oestrogen?
Testosterone and the oestrogens negatively feedback onto pituitary LH and hypothalamic GnRH levels
Where is GnRH produced?
Hypothalamus
Where is the receptor for GnRH?
In the anterior pituitary
What does GnRH stimulate the release of?
LH/FSH
What does LH/FSH do?
Stimulates testosterone production from the interstitial cells of the testis; FSH stimulates oestrogen production from the ovary (FSH and LH have additional roles in the testis and ovary also)
What is a homodimer
A pair of the same molecule
What are response elements?
Oestrogen receptors (ERs) and androgen receptors (AR) bind as homodimers to specific DNA sites, known as response elements
Describe the structure of response elements for oestrogen and androgen
These consist of two 6-nucleotide sequences (which can vary slightly in sequence) separated by 3 unconserved nucleotides
What is the base sequence for Oestrogen and Androgen response elements?
EREs: 5’-(A/G)GGTCAnnnTGACC(T/C)-3’
AREs: 5’-GG(A/T)ACAnnnTGTTCT-3’
The 3 unconserved nucleotides are represented as n
What are the oestrogen receptors called?
ERα and ERβ, encoded by two distinct genes, ESR1 and ESR2, respectively
What are the three functional domains or ARs and ERs?
- N-terminal transcriptional regulation domain (with AF-1)
- DNA-binding domain (DBD)
- Ligand-binding domain (LBD with AF-2)
In the absence of a ligand, what is the AR doing?
Cytoplasmic and bound to receptor-associated proteins
When a ligand binds to AR, explain what happens
A conformational change in the LBD and the displacement of the receptor-associated proteins. This exposes the nuclear localisation signal (NLS) and promotes the binding of importins and microtubule-associated motor proteins which facilitates the translocation of the ligand-receptor complex into the nucleus.
How does ER compare to AR with regards to cytoplasmic/nuclear property?
ER is partially nuclear even in the absence of ligand
What is required for receptor dimerisation and ERE & ARE binding?
Ligand binding to ER/AR
What regulates the ability of the ligands (oestrogen/testosterone) to transactivate the target gene?
coregulators such as: coactivators and corepressors
Explain the mechanism for how ER-alpha causes transcription (ERE dependent)
In the nucleus, ER-alpha interacts with EREs and recruits coactivators such as steroid receptor coactivators e.g. SRC-1 in the p160 family, which then recruit CREB binding protein in the p300 family which has intrinsic histone acetyltransferase (HAT) activity. This histone acetylation near the ERE opens up the chromatin and facilitates RNA polymerase II transcription. RNA polymerase II is then phosphorylated by coactivators to form an elongation-competent form
How does ERE-independent signalling occur?
Wherein ER does not bind to the DNA itself, but interacts with transcription factors such as SP1 and AP1
What type of glands are the breast and prostate? What does this mean?
Exocrine: they secrete substances outside of the body via ducts
Where do 90% of breast and prostate cancers occur?
Luminal epithelial layer
How are 90% of breast and prostate cancers diagnosed?
Loss in the basal cell layer
Briefly describe the structure of the breast and the prostate glands
The breast and the prostate both consist of several branching glands and secrete fluids out of the body via the nipple or urethra
Can you list the three structural domains of oestrogen receptor and androgen receptor?
N-terminal, DNA-binding domain (DBD), Ligand-binding domain (LBD)
What is the difference between and exocrine gland and an endocrine gland?
An exocrine gland secretes substances to the outside of the body via one or more ducts, whereas an endocrine gland secretes substances that are retained in the body – normally these substances (for example hormones) are secreted directly into the blood.
There is evidence that when they are present in the same cells the action of ERβ can actually _____ that of ERα
oppose
What is oestrogen responsible for in women?
growth and development of the uterus, fallopian tubes, vagina and breasts, shaping body contours and the pubertal growth spurt in long bones and epiphyseal closure
What is oestrogen responsible for in men?
growth spurt, skeletal maturation and epiphyseal closure
Explain the 5 steps of the menstrual cycle
- GnRH is released from the hypothalamus
- LH and FSH secretion from anterior pituitary stimulated
- FSH and LH stimulates growth and maturation of ovarian follicles and FSH stimulates oestrogen release
- LH induces ovulation and transforms the granulosa into the corpus luteum which is an actively secreting gland
- Ovaries produce oestrogen and progesterone which negatively feedback onto hypothalamus and pituitary.
Which organs express buth ERbeta and ERalpha?
Bones, breasts, cardiovascular system, testes/ovary
1 in how many women will be diagnosed with breast cancer at some time in their life?
1 in 8
What % of cancers diagnosed in women are breast?
31%
What are the four stages involved in breast cancer?
1) ductal or lobular hyperproliferation
2) evolution into carcinoma in situ
3) invasive carcinoma
4) metastatic disease
What are the risk factors for breast cancer?
1) Age (4/5 above 50)
2) Family history (first-degree female relative doubles risk)
3) Genetics (5-10% of bc)
4) Radiation exposure (to face or chest before age of 30)
5) Being overweight
6) Early menstruation (before 12)
7) HRT/combined pill
What are the symptoms of breast cancer?
- New lump or mass in breast tissue
- Swelling of all or part of a breast
- Skin irritation or dimpling
Breast or nipple pain - Nipple retraction
- Nipple discharge (other than breast milk)
- Redness, flaking, or thickening of the nipple or breast tissue
What are normal breast ducts composed of?
Basement membrane and a layer each of luminal epithelial and basal epithelial, also known as myoepithelial, cells
Where are the twoareas that uncontrolled proliferation can occur in?
ductal (in ducts) or lobular (in lobules)
What does hyperplasia mean?
Enlargement of tissue due to increased cell division
What % of BC are ERalpha+
70-80%
What happens to ERbeta expression levels in tumour cells?
decreased
If the BC is ERalpha+ what does this mean about it?
Hormone-dependent
histopathological sub-classification of invasive ductal carcinoma most commonly depends on what?
The expression of ER, PR and HER2 but sometimes consider HER1 and cytokeratins for further classifications
ER+ breast cancers are classified as luminal cancers which are divided into what?
- Luminal A – HER2-
* Luminal B – HER2+
ER- cancers are ______ or ______ subtypes
HER2-enriched
triple-negative
What are the genes that familial mutations are associated with breast cancers?
What do these genes do?
- BRCA1 and BRCA2 – key roles in DNA repair and cell cycle
- ATM – gene underlying ataxia-telangiectasia
- BARD1 – regulates cell apoptosis
How are reast cancers detected?
screening (e.g. mammography, MRI) and diagnostic tests (e.g. biopsies) and monitoring tests are used to assess the effect of the treatment
Originally, how were ER+ cancers treated?
oophorectomy until drugs modulating the oestrogen receptor were developed
What drugs have been developed to treat ER+ BC?
- Synthetic steroidal and non-steroidal oestrogens
- Anti-oestrogens (antagonists)
- Non-ER-modulating drugs (aromatase inhibitors)
- Selective oestrogen receptor modulator (SERM)
- Selective oestrogen down-regulator (SERD)
Give an example of a SERM and SERD
- Tamoxifen (SERM)
- Fulvestrant (SERD)
How does Tamoxifen work?
It’s an antagonist in mammary tissue, induces conformational changes in the ER, but stimulates cholesterol metabolism, bone density and cell proliferation in the endometrium. This was the first targeted anti-cancer therapy for ER+ breast cancer and can reduce the risk of developing breast cancer in high-risk women
What are the side effects of Tamoxifen?
Hot flushes, bone pain, nausea and fatigue, loss of libido, headache, and increased risk of endometrial cancer
How does Fulvestrant work?
It prevents ER dimerisation as well as promotes ER degradation and reduces ER expression. It is used to treat advanced and metastatic ER+ breast cancer
What are the side effects of Fulvestrant
Nausea, vomiting, appetite loss, joint and muscle pain and hot flushes
For pre-menopausal women with ER+ BC what treatment is offered? Why?
usually administered Tamoxifen with additional GnRH super-agonists, which inhibit oestrogen secretion by suppressing FSH and LH. This is because ovarian oestrogen secretion is the major oestrogen source
For post-menopausal women with ER+ BC what treatment is offered? Why?
Aromatase inhibitors (Type I and type II) prevent the conversion of androgens to oestrogens in all tissues Post-menopausal women generate most of their oestrogen from androgen precursors from the adrenal glands which are made into oestrogen peripherally – such as in the adipose
What are the two types of Aromatase inhibitors?
- Type I steroidal inhibitor – exemestane
* Type II non-steroidal inhibitor – anastrozole and letrozole
How do Type I aromatase inhibitors work?
Type I agents act as irreversible suicide inhibitors
How doe type II aromatase inhibitors work?
Type II agents are reversible and bind to the haem group in aromatase
By what two pathways can tamoxifen resistance work?
1) Intrinsic – ER+ or ER- tumour cells with enhanced pre-existing survival pathways
2) Acquired – ER+ tumour cells become tamoxifen resistant through clonal selection
Name the 4 resistance mechanisms that can be observed in BC cells
- ER coactivator and corepressor expression
- Growth factor signalling
- Androgen receptor expression
- ER mutation
What is HER2 encoded by?
ERBB2
What drives the conversion of androstenedione to oestrogens?
Aromatisation (of the ‘A’ ring) of testosterone and androstenedione is the final step in the production of oestrogens
Where are Aromatase inhibitors expressed?
Endoplasmatic reticulum of oestrogen producing cells
How does resistance by growth factor signalling work?
HER2 and MAPK pathway activation provide survival and proliferation signals independent of ER: These pathways can be activated by overexpression of the receptors or their cognate ligands. Pathway activation can also occur through deregulation of downstream signalling molecules (example: activating mutation in PI3K or loss of expression of PTEN tumour suppressor)
How does resistance by androgen receptor work?
AR stimulates division in the absence of ER (substitute): AR is expressed in 80-90% of ER+ breast cancers
How does resistance by ER mutation work?
Constitutive activation of ER even in oestradiol absence following ESR1 mutations
How does resistance by coactivation and co-repression work?
Overexpression of coactivators (AIB1) and downregulation of corepressors (NCoR) results in Tamoxifen resistance
What two ducts are stabilised by androgens?
Müllerian duct and Wolffian duct
What other hormone does the Wolffian duct require to form?
of testosterone secreted from the Leydig cells (at 9 weeks)
What is dihydrotestosterone (DHT)?
a more potent androgen
What does DHT driv?
prostate development as well as masculinisation (virilisation) of the external genitalia
What is the mullerian duct and how is it repressed in males?
the precursor of the female internal reproductive system, by AMH secreted from Sertoli cells
What is the prostatic utricle?
Remnant of Mullerian duct and forms an indentation in the prostatic urethra
What is the Wolffian duct?
the precursor of the male internal reproductive system
Where is the prostate found?
the base of the bladder and encircles the urethra. It is surrounded by a thick, fibrous capsule and its epithelium
What is the epithelium of the gut made up of? Describe these cells
- Luminal cells – tall, columnar cells which express cytokeratins 8 and 18, secretory proteins (e.g. PSA) and high levels of AR
- Basal cells – non-secretory cells which express cytokeratins 5, 14 and p53 with low to absent levels of AR
- Neuroendocrine cells – rarer cells which produce neuropeptides and other hormones
What is prostatic fluid?
An alkaline fluid to aid sperm survival and is made up of PSA, zinc, citrate, coagulative enzymes, proteases and polyamines
What are the 3 major morbidities associated with the prostate gland?
- Prostatic hyperplasia
- Prostate cancer
- Prostatitis (inflammation of prostate)
What are the risk factors of Prostate cancer?
- Aging
- Race – more common in Caucasians
- Family history
- Genetic risk
- Hormone levels in utero
What are the symptoms of prostate cancer?
- Frequent urination
- Poor urinary stream
- Urgent need to urinate
- Hesitant urination
- Lower back pain
- Blood in the urine
- Or asymptomatic
Most prostate cancers are what type? Originating where?
Adenocarcinomas originating in luminal epithelial cells and can be characterised by the absence of the basal cells
What is the steps of prostate adenocarcinoma?
Intraepithelial neoplasia (PIN), followed by invasive carcinoma and finally castration-resistance and metastasis. The stroma will be altered to support tumour growth.
How are prostate cancers classified?
using the histopathological Gleason grading system from 1 (normal morphology) to 5 (abnormal morphology with large sheets of epithelium and lost ducts).
What genes are associated with prostate cancer? How do they function?
- PTEN – inactivates anti-apoptotic proteins
- BRCA2
- ETS fusions – ETS transcription factors and androgen-regulated promoters translocate to produce androgen-driven expression of ETS
- NKX3.1 – demonstrates haploinsufficiency which initiates prostate carcinogenesis
- MYC – overexpression during PIN stage drives progression to invasive adenocarcinoma, genome instability and metastasis.
How can prostate cancers be detected?
digital rectal examination (DRE), PSA test using a blood-sample and antibody-based assay, and ultrasound
What does prostate specific antigen (PSA) do?
A component of prostatic fluid that normally remains within the ducts as its function is to clear the seminal vesicles clear by lysing seminal coagulate
What is the production of prostate specif antigen stimulated by?
androgens as it has several androgen-responsive elements in its gene promoter/enhancer regions
What are the specific AREs in the PSA gene?
- 170bp upstream of TSS – AGAACA-gca-AGTGCT
* 4000bp upstream of TSS – GGAACA-tat-TGTATC
What are normal serum levels of PSA are lower than?
4ng/mL
Why is there increased levels of prostate specif antigen in the blood serum of patients with prostate cancer?
When the barrier in the prostate is disrupted by mechanical disruptions or cell invasion, PSA can escape into the stroma which causes an increased PSA level in blood serum
Levels higher than 4ng/ml of PSA in blood serum is indicative of what?
carcinoma
What amount of PSA is found in advanced disease levels of prostate cancer?
100,000ng/mL. This is not the most accurate test and requires biopsy for confirmation of cancer
What is the standard care for prostate cancer?
Androgen-deprivation therapy (ADT) and seeks to block the androgen pathway
How does ADT seek to block the androgen pathway?
- Testicular ablation (i.e. castration)
- Pituitary down-regulators
- Anti-androgens
- Androgen synthesis inhibitors
Explain how pituitary down regulators block the androgen pathway?
goserelin acetate, buserelin, leuprolide acetate are GnRH agonists that cause an initial increase in LH and testosterone, but the pituitary-gonadal axis is eventually inhibited after 2 weeks. DHT levels are reduced by half, as adrenal androgens can also be converted into DHT
Explain how anti-androgens block the androgen pathway?
can be steroidal (CPA) which is non-specific or non-steroidal (enzalutamide) which are specific. These induce conformational changes in the AR which reduces its nuclear translocation ability and promotes corepressor binding to the ARE.
Explain how androgen synthesis inhibitors block the androgen pathway?
Abiraterone is an inhibitor of CYP17 that carries out 2 early steps in androgen synthesis. Knock-on effects on other steroid levels means that patients are required to take glucocorticoids to control blood pressure
Resistance o ADT can result in what?
castration-resistant prostate cancer (CRPC) or metastatic castration-resistant prostate cancer (mCRPC) and there is no effective treatment for this stage
List the resistance mechanisms to ADT
- Loss of ligand-specificity
- Alternative splice variants (AR-V)
- AR over-expression
- Alteration in co-factor levels
Explain loss of ligand-specificity as a mechanism for ADT resistance
when mutations in the AR-ligand binding domain which increases the sensitivity and decreases the specificity of ligand-binding. This causes inappropriate AR activation.
Explain alternative splice variants (AR-V) as a mechanism for ADT resistance
of the AR all lack the ligand-binding domain but contain the DNA-binding domain and AF-1, allowing them to be constitutively active
Explain AR overexpression as a mechanism for ADT resistance
through gene amplification or overexpression causes increased androgen sensitivity in low androgen levels
Explain alteration in cofactors levels as a mechanism for ADT resistance
can mediate hormone resistance. Increased coactivator levels increase androgen sensitivity whilst increased corepressor levels increase chromatin compaction and inhibit transcription. The ratio of coactivators to corepressors in the target tissue determines the outcome of hormonal treatment
Pros and cons of PSA test
Inaccurate
False positives
Requires diagnostic biopsy
Non-invasive
Quick/easy
Can just be used for screening
Correlates disease progression and treatment efficiency
What is active surveillance of prostate cancer
Not taking action on cancer tumour instead watching symptoms
