Hallmarks: Oncogenes

• Mutations can affect several areas of the central dogma process

• - Central Dogma process: DNA → RNA → Proteins

• Mutations in Promoter = may not transcribe RNA

• Mutations in Structure = truncated protein loses “off switch”

• Mutations can result in several DNA variations

• - Mutations

• - Amplification: increased amount of gene

• - Chromosomal translocation: one part of gene goes to different part

• Ex. Mutation changes protein structure so that it is always on

• Ex. Amplification increasing the copy number of the gene so there are more of the protein and when stimulated create overwhelming response to grow

• Ex. Chromosomal translocation- creates new “fusion protein”

• Transitions: DNA mutations whereby a purine (A or G) is exchanged for another purine or a pyrimidine (C or T) is exchanged for another pyrimidine. Can be silent or can change amino acid during translation

• Translocation: DNA mutations whereby the part of one chromosome is transferred to or exchanged for another part of a different chromosome

• Transversion: mutations whereby a purine is exchanged for a pyrimidine or vice versa

• Insertions: additional base pair is added

• Deletions: can be at base pair level or at whole gene level

• - Ex. Deletion of Rb

• Amplification: can be at base pair level or at whole gene level

• - Ex. Amplification of HER2/Neu

Hallmark- Sustaining Proliferative Signaling

• Signal to proliferative and divide

• Similar to a gas pedal

• i.e. oncogenes

• Normal cells require mitogenic growth signals to move from a quiescent (not dividing) to a proliferative state

• Oncogenes act by mimicking growth stimulating pathways

• Oncogenes: genes whose products are capable of transforming a normal cell into a cancer cell

• Oncogenes result from the mutation of normal genes (proto-oncogenes)

• Mutations: changes in the base of DNA, which may include transitions, transversions, deletions, amplification, insertions, or translocations

• Oncogene addiction: is the dependence of a cancer cell on a specific oncogene for its maintenance

Common Oncogenes:

• Src

• Ras

• Myc

• Bcr-Abl

• Her 2/Neu

Scr

• Scr: key mediatory involved in many key pathways

Ras

• Robert Weinberg, PhD - Later 1970s - MIT

• Determine if cancer-causing genes could be transferred directly from cancer cells to normal cells

  • Bypass RSV introducing the cancer genes

• Cancer cell DNA should make normal cells proliferate

• DNA binds to calcium phosphate to form tiny white particles

• Particles are ingested by cells, and would therefore ingest DNA bound to it

• Cells that ingested and incorporated cancer DNA- grow uncontrollably?

• Chiaho Shih: Grad student in Weinburg’s lab

• Transferred mouse cancer cell to DNA to normal cells- grew in foci (clumps) → Cancer!

• Next moved to confirm in human cells

• It worked- Normal cells began to proliferate more from the DNA from human cancer cells

• Weinburg’s lab now racing to isolate and identify the first human oncogene (native from a cancer cells- not a virus)

• 3 groups isolated the same gene- Weinburg (MIT), Mariano Barbacid (NCI), and Michael Wigler (Cold Spring Harbor NY) and published findings

• All 3 groups had isolated same gene → Ras

• Had also been discovered in virus before (“Ras” - rat sarcoma)

• Ras in normal cells (like Src) was tightly regulated

• Mutated Ras was hyperactive and always on

• This was first “native” human oncogene discovered

Myc

• Originally discovered as v-myc oncogene

  • Virus causes Myelocytomatosis (Myc) (leukemia and sarcoma) in chickens

• Myc is a transcription factor, binds to regions of the DNA to promote transcription (make RNA, which then will be translated to protein)

• Human Myc is consistenly altered by chromosomal translocation in:

  • Burkitt lymphoma (B-cell lymphoma)

  • Multiple myeloma (Plasma cell cancer)

• Myc is one of the most highly amplified oncogenes in several human cancers (colon, lung, stomach, cervix)

• Mouse genetics- could introduce exogenous (outside) genes into mouse embryo- “transgenic mice” (getting genes externally)

• First one attempted- c-Myc

  • Philip Leder and Timothy Stewart- Harvard

• Overexpressed Myc only in breast mammary cells, to specifically study overexpression of Myc and if it resulted in breast cancer

• Called this mouse OncoMouse- 1988 patented- first animal to be patented

• OncoMouse (c-Myc) only developed small breast tumors and not in every mouse

• Leder created another OncoMouse

  • Activated 2 oncogenes: Ras and c-myc

  • Multiple tumors sprouted within months

  • Cancer had artificially been created in an animal, through altering endogenous innate genes

Normal cells

• Normal cells grow as monolayer(one layer)

  • Contact inhibition prevents overgrowth - aka if comes in contact with other cells, it will stop growing

Cancer cells

• No contact inhibition, continue to grow, form clumps or foci

• Can grow in low serum

• Adopt round morphology, rather than flat extended

• Can grow without attaching to a surface- “anchorage independence”

Bcr-Abl

• Philadelphia Chromosome

  • 1959; Peter Nowell and David Hungerford in Philadelphia

  • Studied CML- Chronic Myeloid Leukemia

  • One chromosome (one copy of 22nd) had it’s “head lopped off” - shortened

    • Shortened chromosome 22- Philadelphia Chromosome

• Janet Rowley- 1972

  • Found the missing head of 22

    • Had attached to the tip of ch 9

    • Piece of 9 attached to 22

  • Chromosomal Translocation- flip flop transposition of 2 pieces of chromosome

• Organized chromosomal chaos

• Fusion of 2 genes on/from different chromosomes

• CML translocation

• Unique fusion protein: Oncogene

• Would be known as Bcr-Abl

• Oncogene Fusion Protein:

  • BCR- breakpoint cluster region protein (BCR)

  • ABL- ABL kinase

• BCR-ABL Fusion Protein:

  • Bcr-Abl- new fusion protein made from the new gene mutation/translocation

  • Bcr-Abl constitutively active kinase

• Drug that targets Bcr-Abl

  • Gleevec (imatinib)

• Deep remissions for CML patients- Gleevec was a success but have to keep taking drug. 10 year survival 83%

• First targeted molecular therapy for cancer

Her2/Neu

• Lakshmi Charan Padhy- 1982 postdoc in Weinberg’s lab (MIT)

• Isolated oncogene from rat tumor- neuroblastoma

  • called the oncogene “neu”

• 1984- Researchers discovered the human homolog of neu gene

  • Human EGF Receptor (HER)- “Her2”

• Her2 member of EGFR family of recpetors

• Previously, most oncogenes encoded proteins that were inside the cell

  • Ras, Myc, Src, Bcr-Abl all intracellular proteins

• Her2 has extracellular domain

  • Large fragment hangs outside

• Dennis Slamon- found that Her2 was increased in ~20% breast cancer samples

  • Her2 positive (more aggressive)

  • Her2 negative

• Genentech developed antibody drug to target outside domain of Her2

  • Tratuzumab- Herceptin

    • Herceptin- Her2 intercept and inhibitor

Hallmarks: Tumor Suppressors

Hallmark- Evading Growth Suppressors

• Loss of proteins or functions that would normally stop or suppress the signal to divide

• Brake pedals

• i.e. Tumor Suppressor

Tumor Suppressor Genes

• Tumor suppressor genes: genes whose products perform functions that inhibit tumor formation

• Loss or mutation (usually both copies) of these genes leads to tumor formation

• Genes in which a germline mutation predisposed individuals to cancer

• There are exceptions to this rule

• Regulate and monitor cell cycle progression

  • Prevent cells from undergoing mitosis unless needed

• Regulate processes to repair DNA damage

  • Assist proteins in repair of DNA damage or editing errors

• If tumor suppressors are deleted or mutated, then the cell can freely enter mitosis and DNA damage goes unfixed

Two-Hit Hypothesis

• Alfred Knudson- 1970s

• Studied retinoblastoma for hereditary cancer model and noticed different speeds of developing the cancer

• Inherited- only one genetic change required. Already had one mutation

• Sporadic- required 2 genetic changes

• “Two-Hit Hypothesis”: need mutation in both copied for cancer

• Why are 2 hits needed for Rb, but only 1 for src?

• Src activated division- Oncogene

• Rb “suppresses” cell division

  • Opposite of Src the “anti-oncogene”

  • Recessive in nature- need 2 hits to develop cancer

• Analogy:

• Each cell has 2 gas pedals and 2 break pedals

  • Activate 1 gas pedal and car will increase

  • Removing 1 brake pedal, the car can still brake with other (backup)

    • Need to lose both brake pedals to develop cancer

• Mutations activate oncogenes to be more active

• Mutations in suppressors, lose their power to stop division

Rb Function

• Rb protein is a gatekeeper for cell division

• Rb is resting state, sequesters a protein called E2F unless activated by signal to release

• During normal proliferation, Rb will be phosphorylated and release E2F

• E2F will bind to DNA and control expression of genes that progress cell from G1 to S phase- for proliferation

• Rb normally binds and hold E2F, but if there is no Rb (cancer) then E2F is free to start proliferative signal

• Rb is also mutated in lung, bone, esophageal, breast, and bladder cancer

Hereditary Cancers and Syndromes

• Two-hit model explains the mechanism behind conditions that predispose individuals to an increased risk of cancer

• Individuals inherit one mutated tumor suppressor allele and may acquire a second somatic mutation over time

• These individuals have a “head start” towards a cancer phenotype in the accumulation of mutations

• Lynch Syndrome

• Li-Fraumeni Syndrome

• BRACA1/2 Mutations

• Lynch syndrome:

  • also known as hereditary non-polyposis colorectal cancer (HNPCC)

  • Colon cancer that occurs at a younger age, especially before age 50

  • A family history (early onset) of other cancers, including endometrial, ovarian, kidney, stomach, small intestine cancer, live, sweat gland cancer (sebaceous carcinoma) and other cancers

  • Mutations in genes that affect DNA repair

  • Genes: MLH1, MSH2, MSH6, PMS2, and EPCAM

  • Not everyone with Lynch Syndrome will get cancer

  • Estimated that roughly 1 in 300 people have Lynch Syndrome

• Li-Fraumeni Syndrome:

  • Predisposed to increase risk of bone and visceral sarcomas, breast cancer, leukemias, and brain tumors

  • Age <45 years and children

  • 50% risk of developing cancer by age 40, and up to a 90% chance by age 60\

  • Relatively rare: 1 in 5,000 to 1 in 20,000 families

  • Approximately 70% of families with LFS will have a mutation in the TP53 gene

  • TP53- “Guardian of the Genome”

  • TP53- gene; p53 protein

• BRCA 1 / 2 mutations:

  • BRCA1 (BReast CAncer gene 1)

  • BRCA2 (BReast CAncer gene2 )

  • Predisposed to breast, ovarian, pancreatic and prostate cancer

  • Mutations are rare in general population (<1%)

  • About 70 % of breast cancers diagnosed in people with an inherited BRCA1 have the triple-negative subtype

  • Risk: About 13% of women (1 in 8 women) in the general population will develop breast cancer sometime during their lives

  • By contrast, 55%-72% (BRCA1 variant) and 45%-69% (BRCA2 variant) will develop breast cancer by 70-80 years of age

  • About 1.2% of women in the general population develop ovarian cancer sometime during their lives

  • By contrast, 39%-44% (BRCA1 variant) and 11%-17% (BRCA2 variant) will develop ovarian cancer by 70-80 years of age

  • 12% of men with advanced prostate cancer carry a BRCA mutation

  • Men with a mutation in their BRCA gene have 3 to 8 times increased risk of developing prostate cancer

  • Involved in DNA repair

  • BRCA1 and BRCA2 help RAD51 protein get to nucleus

    • Helps repair broken or damaged DNA

  • Loss of BRCA1/2 cannot help repair damaged DNA

Hallmarks- Immortality and Resisting Death

Hallmark- Enabling Replicative Immortality

• Immortality- being able to divide indefinitely

• Normal cells have an autonomous program that allows for a finite number of replication cycles

• Cancer cells have unlimited replication

• Self-renewal= the process whereby a stem cell (or progenitor cell) gives rise to daughter cell with equivalent developmental problems

• Cells in culture typically only undergo a certain number of doublings before they stop dividing and enter senescence

• Senescence= irreversible cell cycle arrest (i.e. retirement)

• From senex= Latin “old” or “to grow old”

Telomeres

• Telomeres: repeated DNA sequences and associated proteins that are located at the end of chromosomes

• The telomeres shorten upon each round of cell division

• A natural and physical clock/molecular counter to allow only a certain number of cell division/DNA replication

• Telomeres protect the ends of chromosomes from digestion by nuclear enzymes and prevent induction of DNA repair

• Telomeres are composed of several thousand repeats of the sequence TTAGGG

• Telomeres shorten by 100-200 bases with each round of DNA replication, due to the limits of DNA polymerases during DNA replication

• When each chromosome reaches a threshold length, cells enter senescence. Also known as “Hayflick Limit”

• Multiple reports indicate that telomeres protecting the ends of chromosomes are centrally involved in the capability for unlimited proliferation

• The length of telomeric DNA in a cell dictates how many cell generations its progeny can pass through before telomeres are largely eroded and have consequently lost their protective functions, triggering entrance into crisis and or senescence

• Telomerase: an enzyme that extends and maintains telomere length

• Activity is preserved in stem cell populations and hematopoietic lineages (immune cells)

• Telomerase: a ribonucleoprotein contaning:

  • Telomerase Reverse Transcriptase (TERT)

  • Telomerase RNA Template (TERC)

• The TERC contains 11 complementary base pairs to the TAGGG repeats and acts as a template for the TERT to add new repeats

• TERT uses an RNA template (TERC) to synthesize single-stranded TTAGGG repeats

TERT in Cancer

• By extending telomeric DNA, telomerase is able to counter the progressive telomere loss that would otherwise occur

• Reactivation of TERT (telomerase reverser transcriptase) in cancer cells mediated immortalization via telomere extension

  • Turning back the clock

• Telomerase activity is elevated in 90% of cancers

• Telomerase expression in cancer:

  • Early-stage cancers do not express significant levels of telomerase

  • Malignant tumors (advanced stage) have high telomerase

• TERT expression increases with malignancy and grading

• TERT Promoter Mutations (TPMs) are the most common variants observed

• TPMs constitute the most common non-coding driver mutation in cancer

• Mutually exclusive point mutations in the TERT promoter generate de novo binding sites for ETS transcription factors in ~15-25% of tumors

• 85% of cutaneous melanomas harbor TERT promoter mutations (TPMs)

• TPMs are associated with elevated TERT expression and worse overall survival in many cancer including glioblastoma, cutaneous melanoma, and meningioma

• Acquired mutations in the TERT promoter increase TERT expression and are observed in ~75% of glioblastomas

• Other mechanisms that promote TERT expression in cancer include TERT gene amplification, chromosomal rearrangement, and promoter hypermethylation

  • These are relatively rare compared to promoter mutations

• c-MYC, a known oncogene commonly overexpresses in cancers, binds to TERT promoter resulting in another method of increased TERT expression

TERT Promoter Mutations

• Mutations occur mostly at 2 sites:

  • C228T and C250T

• Creates novel binding site for transcription factors

• Transcription factors bind, turn on RNA transcription, which then gets translated to more TERT protein to go and elongate telomeres

Summary of Immortality Hallmark

• Cancer cells have acquired mechanisms for unlimited replication potential

• Cancer cells maintain telomere length, which normally degrades after each cell division in normal cells

• Telomerase, enzyme that maintains telomere length is activated in 90% of cancers, mostly due to promoter mutations increasing protein expression

• This increase in telomerase activity is primarily responsible for the acquired immortality of cancer cells

Hallmark-Resisting Cell Death

• Resisting cell death

• Apoptosis: programmed cell death

• Self-destruct signal

Apoptosis

• The term “apoptosis” comes from Greek

  • “apo” = “separation” + “ptosis” = ”falling off”

• Generally (or visually) seen as the falling off of leaves from trees

• Highly regulated programmed cell death

• Normally control cell numbers and gets rid of damaged cells

• Organized and regulated self destruct signal

• Examples

  • Skin peeling from sunburn- damages DNA and cell undergoes programmed cell death

  • Developing embryo- webbed fingers/toes- excess is removed

  • Endometrium during menstruation

  • Lining of gut, skin and lung replaced daily

  • Tadpole losing tail

• Compartmentalizes cell pieces into smaller pieces to allow other cells to phagocytose the debris

• Necrosis= cell death from trauma or insult; cell lysis, spill contents, membranes become leaky and more “sloppy” than apoptosis

• Two Main Pathways of Apoptosis:

  • Extrinsic usually from external signals or from other cells that are dying

  • Intrinsic usually from internal cell stress

• Both activate Caspases= proteases that cleave and break down proteins at aspartate residues (scissors)

• Extrinsic Pathway- external signals received to start apoptosis

• Death receptor pathway

• Ligands:

  • TNF (Tumor necrosis factor)

  • Fas

  • TRAIL (Tumor necrosis factor-related apoptosis-inducing ligand)

• Caspases target many proteins, actin (break down cytoskeleton) and DNAse (breakdown DNA)

• Intrinsic Pathway: Internal signals such as DNA damage or oxidative stress start apoptosis

• Bcl-2 family of proteins on mitochondria (25 types)

• Balance of good to bad Bcl-2 proteins flips switch to start spoptosis

• Bcl—2, Bcl-xL: anti-apoptotic

• Baz, Bak: pro-apoptotic

• Intrinsic Pathway-

  • Balance of good to bad Bcl-2 proteins flips switch to start apoptosis

  • Bcl-2: anti-apoptotic (survival)

  • Bax: pro-apoptotic (death)

  • Bcl-2 family members (anti-apoptotic; survival) proteins bind to the proapoptotic members to prevent activation

Apoptosis and Cancer

• Bcl-2 highly expressed in cancers (B-cell lymphoma example)

• Caspase 8 deficiency via gene alterations, deletions and methylation (decreases expression)

• p53 activates Bax- pro-apoptotic; but if p53 is mutates or loss, no activation of Bax

• Bax mutated in over 50% of some colon cancer subtypes

Hallmarks: Angiogenesis and Metastasis

Hallmark- Inducing Angiogenesis

• Angiogenesis- creation of new blood vessels

• Cancer cells need oxygen from blood vessels

• They recruit and grow their own blood supply

Angiogenesis

• Angiogenesis = the process of forming new blood vessels from pre-existing ones

• Greek angeion =”case, capsule, vessel of the body” + “genesis” = creation

• Normally occurs during embryogenesis, would healing, and uterine female reproductive cycle

• First described in cancer by Dr. Judah Folkman, 1971

• Occurs by the growth and migration of endothelial cells called “sprouting”

• Secreted factors entice vessels to grow towards the tumor

The Angiogenic Switch

• Angiogenesis is a balance of angiogenic inhibitors and activators

• Increase in activators promotes the angiogenic switch to “on”

• Activator = VEGF

• Inhibitor =Angiostatin

Angiogenic Inducers

• VEGF = Vascular Endothelial Growth Factor

  • Endothelial Cell= Blood vessel cell

• VEGF is the star player - main activator

  • Ligands: VEGF (A-D)

  • Receptors: VEGFR (1,2,3)

• VEGFA and VEGFR2 is main signaling pathway for angiogenesis

• VEGFA is secreted by tumor cells

Angiogenic Inhibitors

• Endogenous inhibitors- normally found in the body

• Plasminogen cleaved to release angiogenic Angiostatin

• Angiostatin binds to receptors on surface of endothelial cells to prevent angiogenesis

Angiogenesis in Cancer

• Cells must be within 100-200 um of a blood vessel (the diffusion limit of oxygen) in order to receive essential oxygen and nutrients

• Cells in a tumor core that do not receive sufficient oxygen and nutrients die by necrosis

• Vasculature in cancer is unlike normal angiogenesis

  • Leaky

  • Tortuous

  • Disorganized (i.e. haphazardly constructed)

  • Inadequate flow

  • Provides direct entry, allowing cells easy access to the circulation

• How do cancer cells induce angiogenesis?

• 1. Cells growing too fast, make a larger mass and create areas of hypoxia

• 2) Oncogene Activation:

  • EGFR (epidermal growth factor receptor), Src, and Ras all activate VEGF

• 3) Loss of Tumor Suppressors:

  • VHL (von Hippel Lindau) loss in cancer causes increased HIF-1α activity

  • p53 normally induces Thrombospondin, which is an angiogenesis inhibitor; so, loss of p53 means no TSP, so loss of inhibitor of angiogenesis

Angiogenic Switch

• What causes the balance to tip? → Hypoxia

• As the tumor grows, it creates areas of hypoxia

• Hypoxia (low oxygen) activates HIF-1α accumulation

  • HIF1α = hypoxia inducible factor

  • HIF1α is a transcription factor = goes into nucleus and turns on VEGF gene

• Cancer cells can sense low oxygen, and start secreting VEGF to signal EC to grow towards them

Process of Angiogenic Sprouting

• VEGF binding induces formation of an endothelial cell “tip cell” at forefront of sprout

• Behind the tip cell, proliferating stalk cells extend the sprouting vessel

• Growing sprout moves along a VEGF gradient. When two tip cells meet they fuse and allow for a connected lumen, allowing blood to flow

Other Angiogenic Mechanisms

• Vascular mimicry

  • Tumor cells organize themselves to form vessel like channels

  • Or leaky vessels just flow through matrix of tumor bed

• Vasculogenesis

  • Recruitment of endothelial progenitor cells from the bone marrow

  • After reaching the tumor, they differentiate and contribute to the tumor neovasculature (new blood vessels)

  • 40% of tumor endothelial cells are from circulating endothelial progenitor cells from bone marrow

Hallmark- Invasion and Metastasis

• Activating Invasion and Metastasis

• Escaping the primary mass, migrating to distant site and starting second tumor mass

• Primary cause of cancer mortality

Metastasis

• Metastasis = the ability to dissociate, disseminate and colonize discontinuous secondary sites

• Metastasis remains the cause of 90% of deaths from solid tumors

• Cure more likely for cancers when diagnosis occurs before cells have spread beyond the tissue of origin

• First recorded 1580s

• Greek= “meta” - change, alteration, result of change and “stasis” - state of equilibrium

  • Also = “beyond stillness”

• Refers to the process and the outcome

• This is critical part of cancer, since it is usually the secondary mass that causes the most clinical problem and or mortality

• Metastatic cells are behaviorally, genetically and biochemically distinct from the cells still at the primary site

• Metastasis is accomplished through entire series of sequential steps, called the metastatic cascade

• Metastasis occurs not only through bloodstream, but also along nerves, along basal (under) side of endothelial cells (blood vessels), lymphatic system and interstitium and peritoneal cavity

• 1889 Stephen Paget proposed the “seed and soil” hypothesis to explain the organs that are afflicted with disseminated cancer

  • Seed = Cancer Cells

  • Soil = Organ/site and environment

• 1975 Irwin Bross proposed the metastatic cascade to define the sequential events needed for metastasis success

Metastasis - Seed and Soil

• Seed and Soil Hypothesis

  • Seed = Cancer Cells

  • Soil = other organs and environments

• Not all cancer cells that escape the primary mass will form tumors

• Not all sites will foster growth of escaped cancer cells

• Certain cancers have a predisposition to metastasize to certain organs

• Metastasis is not random

• For example: Melanoma, Breast and Lung cancers tend to metastasize to the Brain

• Bone most common site for breast and prostate cancers

The Metastatic Cascade

1. Developing a Metastatic Cell

   • The cell acquires more malignant oncogene activation, changing the behavior

2. Motility and Invasion

   • The cell acquires the means to break down the basement membrane (e.g. collagen) and begins to migrate

   • EMT = epithelial to mesenchymal transition

   • Migration = movement/motility

   • Invasion = breaks down, destroys or digests the basement membrane to pave the path through

3. Intravasation

   • The cell intravasates (invades/enters) into the blood supply, lymphatic supply or other means to escape the primary mass

4. Dissemination and Transport

   • The cell has entered the circulation (or other) and has to survive interactions with other cells and a new environment

   • Single cells that have entered the vasculature typically roll along the endothelium

5. Cellular Arrest, Vascular Adhesion and Extravasation

   • The cell has reached a stopping point, adheres to the vessel wall and extravasates (exists) into the new tissue

6. Colonization

   • The cell interacts with premetastatic niches that are permissive for proliferative and colonization for secondary sites

   • Colonization is dependent upon a combination of tumor cell and tissue-specific factors

Conclusions

• Tumors have acquired mechanisms to recruit their own blood supply termed angiogenesis

• VEGF is the key activator for angiogenesis

• Other mechanisms include vascular mimicry and vasculogenesis, recruiting cells from the bone marrow to form new vessels

• Metastasis is the major cause of clinical mortality for cancer patients

• Metastasis behavior is described by the seed and soil hypothesis

• Metastasis is a complex process of several steps (metastatic cascade) that facilitates successful colonization and growth of the metastatic tumor

Hallmarks: Emerging and Enabling

Deregulating Cellular Energetics

• i.e. Altered Cellular Metablism

• Adjustments of energy metabolism are made in order to fuel cell growth and division

• Cellular Respiration in Normal Cells

• Aerobic conditions (oxygen present) cells process glucose to make ATP through oxidative phosphorylation

• Anaerobic conditions (low oxygen) cell shifts to glycolysis

• Even in the presence of oxygen cancer cells utilize glycolysis, termed “aerobic glycolysis”

• For both normal and low oxygen, cancer cells use glycolysis

• Also called The Warburg Effect

• “Aerobic glycolysis” is inefficient

• Cancer cells must compensate for the 18-fold lower efficiency of ATP production by upregulating glucose transporters, notably GLUT1, which increases glucose import into the cell

• Aerobic Glycolysis has been shown to be associated with activated oncogenes (e.g., RAS, MYC) and mutant tumor suppressors (e.g., TP53)

• Ras and hypoxia can independently increase the levels of the HIF1α transcription factor, which in turn upregulates glycolysis as well

Genome Instability and Mutation

• Enabling Characteristic

• Genome Instability and mutation

• Continual increase in numbers of mutations

• Bert Vogelstein, Johns Hopkins 1988

  • Determined how many genetic changes were required to initiate cancer

• Cancer is a progressive disease and can often see pre-cancerous lesions at start

• Studies progression in colon cancer from human samples

  • Series of 4 human cancer genes (oncogenes and suppressors)

  • Assessed each stage of cancer for activation or inactivation of those 4 genes in his patient samples

• Confirmed that there is a genetic progression of cancer

• Genetic progression mirror clinical histological progression

  • Benign neoplasia (few mutations)

  • Full time malignancy (numerous mutations)

• Time: 1 mutation → +1 mutation → +1 mutation …

• “mutant cells beget mutant cells”

• Cancer genome analysis from patients

  • Individual samples of breast and colon had 50-80 mutated genes per patient

  • Brain tumor patients had 40-50 mutations per sample

• Heterogeneity of mutations is problematic - every patient’s cancer genome is unique

• How do we know which mutations to target or are important?

• Mutations in cancer come in two forms:

• Passive: as cancer cell divides, accumulate mutations because of accidents in DNA replication

  • Bystander or passenger mutations

  • No impact on behavior - just on for the ride but still show up in sequencing analysis

• Active: Driver mutations - not passive players

  • Directly influence growth and behavior of the cancer cells

• Example: Breast cancer - 100 mutations in one patient sample

  • only ~10 may be actually contributing to growth and survival of the tumor

  • The rest are just gene copy errors and passive

• Vogelstein’s cancer mutation landscape map

• Driver mutations → Key oncogenes and tumor suppressor that recur in sample after sample - patterns emerge (mountains/peaks)

Avoiding Immune Destruction

• Emerging Hallmark

• Avoiding Immune Destruction

• Escaping immune cell surveillance

• Immune System

  • Adaptive Immune Cells

    • T-cells (CD4 and CD8)

    • B-cells

• Innate Immune Cells

  • Macrophages

  • Dendritic Cells

  • Natural Killer Cells

Immune System

• Complex system of cells and proteins that defend the body against infection

• Infection can be pathogens or any entity that is “non self” i.e. cancer cells

• Most originate in bone marrow

Innate Immune System

• Macrophages

• Dendritic Cells (DCs)

• Can phagocytose pathogens, bacteria and even tumor cells

• DCs usually are stationary in tissues; Macrophages can move between tissues and blood

Avoiding Immune Destruction

• Cells and tissues are constantly monitored by an alert immune system, which is responsible for recognizing and eliminating cancer

  • Referred to as “immunoediting”

• Tumors that have managed to avoid detection by the immune system have escaped elimination

• Immunosuppressed individuals have increased risk for cancer

  • e.g. HIV patients develop Kasposi’s sarcoma

  • e.g. Organ transport recipient developing cancer from donor (rare)

• Mouse tumors grow faster in immunodeficient mice

  • Mice lack T-cells so cannot reject tumor

• Human tumors can be grown in mice that are immunodeficient

  • Athymic nude mice - no thymus, so no T-cells

  • SCID mice (severe combined immuno-deficient) - No B or T cells

Tumor Promoting Inflammation

• Enabling Characteristic

• Tumor-promoting inflammation

• Immune cells that do respond accidentally help the growth

• Tumor-associated inflammatory response has the paradoxical effect of enhancing tumorigenesis and progression

• i.e. Immune cells secrete factors that turn off the immune response when the immune cells arrive

  • Ex: macrophages are recruited to the tumor,, but when arriving are met with cytokines from the tumor such as Il-10 that then turn off the macrophage

  • CD8 and CD4 cells are present in the tumor, but are “exhausted” and not doing their job

• Immune cells are present in the tumor, but the immune cells are suppressed

• Ex: macrophages and microglia (resident brain macrophages) make up 30-50% of the total cells in glioblastoma (brain tumors)

  • Those cells aren’t attacking the tumor, and instead are secreting cytokines to assist growth and turn off T-cells

Hallmarks- New Dimensions

• 4 new hallmarks in 2022

  • Unlocking phenotypic plasticity

  • Nonmutational epigenetic reprogramming

  • Polymorphic microbiomes

  • Senescent cells

• Unlocking phenotypic plasticity

• Nonmutational epigenetic reprogramming

• Adding epigenetic tags such as methylation to a gene promoter to turn off it’s expression

• No change in DNA sequence, but genes (oncogenes or suppressors) are being manipulated by these epigenetic tags

• Polymorphic Microbes

• Senescent cells

• Technically not all tumor cells are actively dividing all the time

  • Some cells are in a state of senescence- suspended growth and proliferation

• These cells can re-enter cell cycle and divide at any time

• These cells are also resistant to many chemotherapies, which target actively dividing cells

Conclusion

• Cancer cells display altered cellular energetics (i.e. altered metabolism) and undergo aerobic glycolysis for energy

• Genomic instability is the increasing number of mutations found in the tumor that assist in malignancy

• Avoiding immune destruction is achieved by increasing to immune cell attacks and results in escape and growth of the tumor

• Immune cells when infiltrating the tumor, assist by secreting inflammatory cytokines that accidentally assist in the growth of the tumor

• 4 New Hallmarks - new dimensions- highlight the ever evolving understand oof cancer biology and reveal new targets for potential therapies

Ras- 1st oncogene from human cancer cells

• Map kinase

• GTPase

• Rat Sarcoma

Bcr-Abl- chromosome translocation, use Gleevec to treat, Philadelphia chromosome

Her2/Neu- receptor(can see it on the surface), Herceptin/Tratuzamab, common in breast cancer, also seen in stomach cancer

Src- Sarcoma(tumors of muscle or bones), very first oncogene

Myc- Transcription Factor, OncoMouse