The Cancerous Cell: Characteristics and Mechanisms of Cancer Development

Learning Objectives and Overview

MICR2120/BIOC2301/3/5 John Ladbury SMCB j.e.ladbury@leeds.ac.ukGeneral characteristics of cancer How does a cell become CANCEROUS

• Cancer as a genetic disease
• Aberrant protein function and cancer
• The cell cycle and cancer
• Pathway activation in cancer

Cancer Statistics Worldwide

Worldwide: 19M people were diagnosed with cancer (2020) 10M people died of cancer (2020) Ushijima et al. Science (2021) 373 1474. Sung et al. CA Cancer. J. Clin. (2021) 71, 209.

Cancer Statistics United Kingdom

United Kingdom: 385 477 people were diagnosed with cancer (2017 -2019) 167 142 people died of cancer (2017 - 2019) Someone diagnosed with cancer every 2 minutes Someone dies of cancer every 4 minutes www.cancerresearchuk.org/health-professional/cancer-statistics-for -the-uk New cases of young peoples' cancers/year 2016-2018 - 2400 Peak age for young peoples' cancers 20 - 24 Trend for 25-49 year-olds' cancers +24% since 1990s.

Twenty Most Common Cancers in the UK: 2016 - 2018

Females Breast Lung Melanoma Skin Cancer Head and Neck Pancreas Leukaemia Uterus Cancer of Unknown Primary Stomach Myeloma Other Sites 10,000 20,000 30,000 40,000 50,000 60,000 Data from CRUK https://www.cancerresearchuk.org/health-professional/cancer-statistics/incidence

Common Cancers in Males

Males Prostate Bowel Non-Hodgkin Lymphoma Kidney Brain, Other CNS & Intracranial Tumours Bladder Oesophagus Ovary Liver Thyroid

Common Cancer Types in Human Tissue/Blood

Carcinoma

Carcinoma refers to a malignant neoplasm of epithelial origin or cancer of the internal or external lining of the body. Responsible for > 80% of cancer-related deaths in the high income/developed countries.

Sarcoma

Sarcoma refers to cancer that originates in supportive and connective tissues such as bones, tendons, cartilage, muscle, and fat. Responsible for ~1% of tumours

Myeloma

Myeloma is cancer that originates in the plasma cells of bone marrow. The plasma cells produce some of the proteins found in blood - abnormal plasma cells.

Leukemia

Leukemias ("liquid cancers" or "blood cancers") are cancers of the bone marrow (the site of blood cell production) - abnormal leukocytes.

Lymphoma

Lymphomas develop in the glands or nodes of the lymphatic system, a network of vessels, nodes, and organs (specifically the spleen, tonsils, and thymus) that purify bodily fluids and produce infection-fighting white blood cells, or lymphocytes.

Histopathology of Cancer Progression

Invasive cancer 1 Cell with mutation In situ cancer T Dysplasia Hyperplasia epithelia Basal cells/basal membrane stroma Amplified growth of epithelial cells - (benign) Cells become abnormal Cell organisation disrupted Nuclei noticeably enlarged Invasion of adjacent tissue - cancer i.e. malignant carcinoma

Hallmarks of Cancer

Key cellular functions that need to be in place for cancer to be sustained Self-sufficiency in growth signals Evading apoptosis Insensitivity to anti-growth signals Ability to survive stress and DNA damage Sustained angiogenesis Tissue invasion & metastasis Limitless replicative potential Hanahan & Weinberg (2000) Cell 100, 57-70 and (2011) Cell 144, 646-674.

How does a cell become CANCEROUS

Cancer as a Genetic Disease

. Most cancers derive from a SINGLE CELL (we will define the properties that are acquired by the cell to make it cancerous). . If a single cell is to give rise to a tumour it must pass on its abnormality to its progeny. . Thus, the development of a clone of cancer cells depends on genetic changes. . The tumour cells contain somatic mutations: they have one or more shared detectable abnormalities in their DNA sequence. . The number of 'driver' mutations is small, there are however a substantial number of 'passenger' mutations, e.g. 1000-10000/genome in IBD-exposed colon 1000-4000/genome in oesophagus.

Genetic Changes and Cancer

Genetic changes (mutations) are the cause of cancer - some are inherited (germline) but the majority are sporadic (somatic). - The current list of known cancer genes includes approximately 70 genes associated with germline mutations and 340 genes associated with somatic mutations Driver mutations in several genes (5-7) in a single cell are usually required to become cancerous. Cancers are genetically unstable

Examples of Mutations in Cancer

Examples of mutations occurring in cancer : -point mutations, e.g. RAS protein, Gly to Val (codon 12) -amplification (many copies of a gene): e.g. EGFR (growth factor receptor) MYC (transcription factor) -deletions particularly relevant to tumour suppressors -chromosomal re-arrangements, e.g. translocations - parts of one chromosome can be inserted into another chromosome putting it under the control of different regulatory elements

Single Mutation Insufficiency

A single mutation is not enough to change a normal cell into a cancerous cell. An estimated 1016 cell divisions occur in a human over the course of a lifetime. In this time every single gene is likely to have undergone mutation on about 1010 separate occasions in a human. Clearly if a mutation in a single gene were enough to convert a typical healthy cell into a cancer cell, we would not be a viable organism. Therefore, to produce a cancerous cell requires a substantial number of independent, rare genetic and epigenetic accidents to occur.

Evolution of Tumour Clones

Natural Selection Tx Ecosystem 1 Eco 4 Eco 2 recurrence Single 'founder' cell (stem or progenitor) confined diffuse Cells respond to each other Eco 3 Sub-clones with unique genotype / 'driver' mutations metastases Selective pressures allow some mutant subclones to expand while others become extinct or remain dormant. Therapeutic intervention (Tx) may destroy cancer clones and erode their habitats, but it can also inadvertently provide a potent selective pressure for the expansion of resistant variants. Ecosystems 1-4 (boxes) represent the different tissue ecosystems or habitats (environmental conditions/stress). Nature 481, 306 (2012)

Mutations and Clonal Expansion

Mutations and clonal expansion lead to tumour malignancy Non- functional passenger event not under selection Functional driver event under positive selection Tumour cell Subclone outcompetes neighbours and begins clonal sweep Non- functional event evolves neutrally Time Nature Reviews Cancer 21, 379 (2021)

Tumour Heterogeneity

Mutations and clonal expansion lead to tumour heterogeneity Fraction of population Tumor-propagating potential Survival Single Cell Chemotherapy resistance Proliferation Metastasis Time

Aberrant Protein Function and Cancer

Major Types of Genes/Proteins Involved in Cancer

• Oncogenes/oncoproteins - Stimulate cell growth Gain-of-function
• Tumour suppressor genes/proteins Suppress cell growth - negatively regulate cell cycle (hence NOT oncogenes) Loss-of-function
• Genes/proteins involved in DNA repair Recognise mis-matches in DNA and repairs them. Potential mutations are corrected. When not functioning increase in mutations.

Genetic Impact on Cancer

(A) dominant mutation (gain of function) single mutation event in proto-oncogene creates oncogene normal cell activating mutation enables oncogene to stimulate cell survival and proliferation (B) recessive mutation (loss of function) mutation event second mutation event inactivates tumor suppressor gene inactivates second gene copy normal cell no effect of mutation in one gene copy two inactivating mutations functionally eliminate the tumor suppressor gene, stimulating cell survival and proliferation Figure 20-47 Essential Cell Biology (@ Garland Science 2010)

Functions of Proto-Oncogenes

Proto-oncogenes are normal genes that help cells grow, whereas an oncogene is any gene that causes cancer. Proto-oncogenes become oncogenes Mutation of proto-oncogenes found in cancers Examples of proto-oncogenes

• Growth factors (e.g. platelet-derived growth factor, PDGF)
• Growth factor receptors (e.g. epidermal growth factor receptor, EGFR)
• Signal transducers (e.g. RAS-GTPase)
• Nuclear proto-oncogenes and transcription factors (e.g. c-MYC transcription factor)

Proto-oncogene Function in Cancer

proto-oncogene MUTATION IN CODING SEQUENCE GENE AMPLIFICATION CHROMOSOME REARRANGEMENT 1 or DNA RNA - I- III 1 protein -. ! : hyperactive protein made in normal amounts normal protein greatly overproduced nearby regulatory DNA sequence causes normal protein to be overproduced fusion to actively transcribed gene produces hyperactive fusion protein e.g. RAS e.g. MYC e.g. BCR-ABL DNA 1 RNA ! Retroviruses can acquire proto-oncogenes from the cellular genome and convert them to viral oncogenes Integration of viral genes - transform cells Figure 20-48 Essential Cell Biology (@ Garland Science 2010)

Tumour Suppressors

Mutation in a tumour suppressor gene causes a loss of gene function Recessive genes - sometimes inherited mutations Both copies of the tumour suppressor gene need to be inactivated by mutation to create a cancer cell Some DNA viruses (e.g. HPV) bind tumour suppressor gene products and inactivate or degrade them. e.g. papiloma virus Tumour suppressor proteins often function to down-regulate pathways that are involved in proliferative signalling e.g. Neurofibromin NF1 - RAS signalling see later. e.g. p53 - multifunctional tumour suppressor. Tumour suppressor cancer drivers are rarer, but very difficult to design therapeutics for.

Retinoblastoma - Caused by Mutation in a Tumour Suppressor Gene

Rb gene encodes for pRb protein that functions to prevent excessive cell proliferation by inhibiting cell cycle progression. pRb is inactivated by phosphorylation NORMAL, HEALTHY INDIVIDUAL HEREDITARY RETINOBLASTOMA x inherited mutant Rb gene x x xx x occasional cell inactivates one of its two good Rb genes occasional cell inactivates its only good Rb gene copy one good copy so tumour suppressor is expressed excessive cell proliferation leading to retinoblastoma the second copy of Rb is very rarely inactivated in the same line of cells tumour suppressor is non-functional or NOT expressed tumour suppressor is non- functional or NOT expressed excessive cell proliferation leading to retinoblastoma RESULT: NO TUMOR RESULT: MOST PEOPLE WITH INHERITED MUTATION DEVELOP MULTIPLE TUMORS IN BOTH EYES RESULT: ONLY ABOUT 1 IN 30,000 NORMAL PEOPLE DEVELOP ONE TUMOR IN ONE EYE Figure 20-30 Molecular Biology of the Cell (@ Garland Science 2008) NONHEREDITARY RETINOBLASTOMA = occasional cell inactivates one of its two good Rb genes + 1 *