Neoplasia 5 Dr. Hiba Wazeer Al Zou’bi

3- Evasion of Cell death Extrinsic pathway: through binding of receptors as CD95 (Fas) to its ligand (FasL) ultimately activating several CASPASES → Apoptosis. – Some tumors have ↓levels of CD95 → ↓ Apoptosis Intrinsic pathway: Mutations in genes of BCL-2 (Antiapoptosis) - Activated by t. (18;14) - Follicular B cell Lymphoma

4-Limitless replicative potential(Telomeres) Specialized structures at the end of chromosomes which are shortened after each division Shortening is prevented by TELOMERASE Majority of cancers  telomerase

5- Genomic instability due to defective DNA Repair Genes 1- Nucleotide excision repair genes Damage by U-V light: Defective in Xeroderma Pigmentosum 2-Mismatch repair genes: repair errors in pairing of nucleotides during cell division (Spell Checkers) - Defective in: ( HNPCC) (Hereditary Nonpolyposis Colonic Ca.) - HNPCC shows: Microsatellite Instability (MSI): changes in length of short tandem repeating sequences throughout the genome.

3- Homologous Recombination: - Syndromes involving defects in the homologous recombination DNA repair system : Bloom syndrome, ataxia-telangiectasia, and Fanconi anemia— characterized by hypersensitivity to DNA-damaging agents, such as ionizing radiation. - BRCA1 and BRCA2, mutated in 50% of familial breast cancers.

6- Development of sustained angiogenesis - Tumors cannot enlarge beyond 1 to 2 mm in diameter unless they are vascularized. Effects of vascularization: 1. It supplies needed nutrients and oxygen 2. Is required for tumor metastasis 3. Newly formed endothelial cells secret growth factors  vascular density = Poor prognosis

Angiogenic Factors: 1. Hypoxia-Inducible Factor (HIF-1  )  Induce transcription of VEGF 2. VEGF : increases the expression of ligands that activate the Notch signaling pathway, which regulates the branching and density of the new vessels. 3. Proteases from tumor or stroma can release the angiogenic basic FGF stored in the ECM

Anti- Angiogenesis: 1. Thrombospondin1(TSP-1) produced by stromal fibroblasts and induced by P53, so Inactivation of P53  Angiogenesis 2. VHL protein (Tumor supressor gene) in normoxic state destroys HIF-1   No VEGF -In hypoxic conditions, such as in a tumor that has reached a critical size, the lack of oxygen prevents HIF-1  recognition by VHL. -Germ line mutation of VHL  von Hippel-Lindau Syndrome  hereditary renal CA, hemangiomas in CNS, renal cyst. 3. Angiogenesis inhibitors

7- Ability to invade & metastasize Occurs in two phases: 1- Invasion of extracellular matrix 2- Vascular dissemination and homing of tumor cells

1- Mechanism of invasion of ECM: 1- Detachment of tumor cells - E-cadherin function is lost in almost all epithelial cancers, either: by mutational inactivation of E-cadherin genes by activation of β-catenin genes or by inappropriate expression of the SNAIL and TWIST transcription factors, which suppress E-cadherin expression. 2- Degradation of ECM by proteases : Matrix Metalloproteinase (MMPs): Cathepsin D, Type IV collagenase

3- Attachment of tumor cells to extracellular matrix 4- Locomotion: - Potentiated and directed by tumor derived cytokines e.g. Autocrine motility factor - Stromal cells produce paracrine effectors of cell motility e.g. HGF

2- Vascular dissemination and homing: Extravasation of free tumor cells or tumor emboli involves adhesion to the vascular endothelium, followed by egress through the basement membrane into the organ parenchyma by mechanisms similar to those involved in invasion. The site of extravasation and the organ distribution of metastases generally can be predicted by the location of the primary tumor and its vascular or lymphatic drainage In many cases, the natural pathways of drainage do not readily explain the distribution of metastases (Tropism) probably due to activation of adhesion or chemokine receptors whose ligands are expressed by endothelial cells at the metastatic site.

8- Reprogramming Energy Metabolism Even in the presence of ample oxygen, cancer cells shift their glucose metabolism away from the oxygen-hungry but efficient mitochondria to glycolysis ( Warburg effect, aerobic glycolysis) Aerobic glycolysis is less efficient than mitochondrial oxidative phosphorylation, producing 2 molecules of ATP per molecule of glucose, versus 36. But tumors that adopt aerobic glycolysis, such as Burkitt lymphoma, are the most rapidly growing of human cancers.

In rapidly growing cells glucose is the primary source of the carbons that are used for synthesis of lipids (needed for membrane assembly) as well as other metabolites needed for nucleic acid synthesis. This pattern of glucose carbon use is achieved by shunting pyruvate toward biosynthetic pathways at the expense of the oxidative phosphorylation pathway and ATP generation. The “glucose hunger” of such tumors is used to visualize tumors by positron emission tomography (PET) scanning, in which the patient is injected with 18F-fluorodeoxyglucose, a nonmetabolizable derivative of glucose. Most tumors are PET-positive.

9- Evasion of the Immune System The ability of tumors to evade destruction by the immune system. Will be discussed in the next lecture.

10- Tumor-Promoting Inflammation as Enabler of Malignancy 1- Persistent chronic inflammation in response to microbial infections or as part of an autoimmune reaction. -In chronic tissue injury, there is a compensatory proliferation of cells in an attempt to repair the damage aided by growth factors, cytokines, chemokines, and other bioactive substances -Persistent cell replication and reduced apoptosis place the cells at risk of acquiring mutations in one or more of the genes involved in carcinogenesis. -In addition, inflammatory cells such as neutrophils can contribute to carcinogenesis by secretion of reactive ROS, which in turn can inflict additional DNA damage in rapidly dividing cells. -Increased risk of cancer in patients affected by Barrett esophagus, ulcerative colitis, H. pylori gastritis, hepatitis B and C, and chronic pancreatitis.

2- When inflammation occurs in response to tumors. Virtually every tumor contains cells of the immune system. Inflammatory reaction represents an attempt by the host to destroy the tumor, but these cells can exert tumor-promoting activity by producing growth factors and inflicting additional DNA damage