lecture 7: ethical issues: what's all the fuss?

Question 1

What do you reply when asked these questions:

• What are cancers?
• How do they occur?
• Where do they occur?
• What are the components of a tumour?
• Are all tumours malignant?
• How does a tumour metastasize?
• How are cancers treated?
• How does cancer actually kill a person?
• Most common cancers in Australia?

Answer 1

• cancer is uncontrolled cell division
• caused by mutations in genes that control cell death and cell proliferation
  
  • lack of function
  • gene doesn’t produce viable protein
  • e.g. an oncogene that no longer responds to signals that switch off cell division
• occur in all tissues
• components
  
  • cells
  • cancerous stem cells, transit cells, blood vessel cells
  • solid tumour might have necrotic tissue
• benign tumour doesn’t metastasise
• loses adhesion molecules etc to metastasise
• goes into the blood stream
• EMT (gain movement), MET (solid cancer, but can’t move)
• treated with chemotherapy (chemicals in the body that kill of rapidly dividing)
• radiation therapy
• cancer inhibits the function of something, getting bigger e.g. in brain, pressure, skull capacity etc
• strip normal cells of their nutrients, metabolism etc
• big killers: breast, prostate, lung, colorectal, brain, skin

Question 2

What is cancer formation and disease progression?

Answer 2

• carcinomas usually form as a consequence of genetic and epigentic changes taking place over many years
• disease progression:
  
  • these genetic and epigenetic changes lead to the developmnet of benign tumours
  • followed by development of malignant characterstics
  • e.g. changes in phenotype, proliferation rates and the ability to invade adjacent tissues (metastasize)
• malignant tumours are characterised by:
  
  • genome instability
  • contain many mutations and tumour heterogeneity
  • different cell populations which differ in number of mutations, state of differentiation and function
• carcinomas are a type of cancer that develops from epithelial cells
• specifically a carcinoma is a cancer that begins in a tissue that lines the inner or outer surfaces of an organ or the body
• carcinomas are the focus of this lecture
• metastasis, or metastatic disease, is the spread of cancer cells from one organ to another
• the new occurences of disease thus generated are referred to as metastases

Question 3

What are cancer stem cells?

Answer 3

• heterogeneity arise among cancer cells within the same tumour as a consequence of genetic change, environmental* dfferences (niche/microenvironment) and reversible changes in cell properties
• the cancer-stem cell model provides one explanation for the heterogeneity among cancer cells in a tumour
• cancer arises from tumour cells with stem cell properties - now called CSC
• CSC considered the only self-renewing cells that drive tumour growth, disease progression, recurrences and metastases
• controversial

Question 4

What are the characteristics of CSC?

Answer 4

• undergo asymmetric division
• form spheres in vitro that differentiate into different cell types
• initiate tumours in SCID mice that form tumours in secondary mice
• occur in low numbers, identified in some tumours, appear to be chemotherapy- and radiation therapy-resistant
• recapitulating gastrulation
• some issues still unresolved:
  
  • their origin is still debated (adult stem cels vs reprogramming of somatic cells)
  • marker profiles to clearly identify CSC is not established
  • it remains unclear what fraction of cancers follow the stem-cell model
  • not everyone agrees

Question 5

What is one model of the heterogeneous cell population in a tumour?

Answer 5

• cancer stem cell
  
  • quasi mesenchymal
  • high plasticity
• non-stem-like carcinoma cell
  
  • epithelial
  • some plasticity
• tumour-derived stromal cell
  
  • extreme mesenchymal
  • low plasticity (or locked)
  • TSC
• CSC can also give rise to tumour derived stromal cells (TSC) with no plasticity
• TSC enhance tumour growth via secreted factors or modifications to ECM
• CSC give rise to TSC via epithelial–mesenchymal transition (EMT)
• it is postulated that TSC and Non-stem-like-carcinoma cells can revert back to CSC

Question 6

What is the tumour niche?

Answer 6

contains:

• diverse stromal cells – fibroblasts & myofibroblasts (also known as mesenchymal cells), fat cells (adipocytes), & diverse immune system cells (macrophages, T cells, Neutrophils) (these are not TSC)
• vascular network
• secreted factors (e.g. hormones, growth factors, cytokines)
• extra cellular matrix (ECM) components

the formation of tumours (tumourigenicity) involves genetic changes in the tumour cells but also involves complex interactions between the tumour and the non-tumour stromal cells

• niches promote stemness, proliferation and apoptosis of normal tissue stem cells and CSC
• fluid filled environment
• matrix is not inert

Question 7

What is the proposed model of tumour recurrence and role of CSC?

Answer 7

• CSC is one possibility for why we have relapse
• however CSC explain this better than any other model out there
• cancers are subjected to cytotoxic therapy but it only affects TSC and non-stem like cancer cells
• CSC are chemo/radiotherpay resistant
• aggresive relapsed tumour
• still in niche, unperturbed
• two major issues still unresolved for cancer treatments
  
  • resistance to cytotoxic therapy
  • ability to form metastases

Question 8

Why is this CSC unaffected?

Answer 8

• asymmetric division and daughter cells with different fates
• one becomes more differentiated and the other is for self-renewal
• in ES or iPSC we treat them to make specialised cell for therapy, but not all change and some remain undifferentiated and this can lead to cancer in patient
• are the factors that cause CSC to remain resistant to cytotoxic drugs similar to those that cause some pluripotent stem cells to become resistant to differentiation in vitro?

Question 9

Why use specific inhibitors of CSC?

Answer 9

• decrease their capacity to survive conventional cytotoxic therapies and cause tumour recurrence
• CSCs self-renew and differentiate in a niche:
  
  • suggests we also need to understand the niche components and how they influence CSC

Question 10

What is the impact of stromal cells and secreted factors on CSC?

Answer 10

• one model of CSC formation:
  
  • stromal cell types (e.g. fibroblast, macrophage, adipocytes) influence the tumour cell by secreting factors that convert them into CSC

Question 11

What similarities do CSC share with normal tissue stem cells?

Answer 11

• undergo asymmetric division
• form spheres in vitro that differentiate into different cell types
• initiate tumours in SCID mice that form tumours in secondary mice
• CSC also share expression of pluripotency factors: Oct4, Sox2, and Nanog are expressed in many cancers

Question 12

What is a possible role of Nanog in CSC?

Answer 12

• Nanog expression has been found in many cancers
• where levels are high, prognosis is poor for ovarian, lung, colorectal and breast carcinomas
• nanog expression is higher in CSC than non-stem cancer cells for many carcinomas
• some studies show nanog promotes CSC characteristics
• nanog plays a role in the cancer signalling network
• p53 → Nanog → cyclin D1, GDF3 → tumour growth, cell cycle progression, cell proliferation
• SHH → nanog → E-Cad, FoxJ1, Slug → metastasis, EMT
• STAT3 → nanog → DKK1, Td1a → microenvironment, communication, immune evasion
• miRNAs → nanog → ABCB1, Akt, p53 → drug-resistance, anti-apoptosis

Question 13

What happened when EC-derived neurons were implanted in the brain of a stroke victim?

Answer 13

• did not form neoplasms
• were all ECs converted into neurons in vitro or did the niche influence the behaviour of all the grafted cells? what do you think?
• Nelson et al., (2002) Clonal Human (hNT) Neuron Grafts for Stroke Therapy Neuropathology in a patient 27 months after implantation
  
  • Although grafted cells may be promising therapy for stroke, survival of implanted neural cells in the brains of stroke patients has never been documented
  • human NT2N (hNT) neurons derived from the NTera2 (NT2) teratocarcinoma cell line were shown to remain postmitotic, retain a neuronal phenotype, survive > 1 year in host rodent brains and ameliorate motor and cognitive impairments in animal models of ischemic stroke
  • here we report the first postmortem brain findings of a phase I clinical stroke trial patient implanted with human hNT neurons adjacent to a lacunar infarct 27 months after surgery
  • neurofilament immunoreactive neurons were identified in the graft site, fluorescent in situ hybridisation revealed polyploidy in groups of cells at this site just like polyploid hNT neurons in vitro, and there was no evidence of a neoplasm
  • these findings indicate that implanted hNT neurons survive for > 2 years in the human brain without deleterious effects