Florida Atlantic University College of Engineering & Computer Science The 6 Hallmarks of Cancer And Related Assays/Therapies.

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1 Florida Atlantic University College of Engineering & Computer Science The 6 Hallmarks of Cancer And Related Assays/Therapies Alberto Haces July 24 th 2012

2 Cancer Hallmarks Acquired functional capabilities that allow cancer cells to survive, proliferate, and disseminate. - Sustained Proliferative signaling - Evading growth suppressors - Resisting cell death - Inducing angiogenesis - Enabling replicative immortality - Activating invasion and metastasis

3 DEFINITIONS - Gene: DNA message that codes for a protein or for rrna, trna. - Protein: gene product. Example, p53 is a gene and p21 is its protein (or TP53 protein). - Regulator : a protein that controls another. - Effector: small molecule that acts upon the regulator. Example, lactose and lac Repressor

4 Intracellular signaling networks are reprogrammed to regulate the hallmark abilities within cancer cells

5 Sustaining proliferative signaling Normal cells carefully control the production and release of growth promoting signals and instruct entry into and progression through the cell growth-and-division cycle: homeostasis Cancer cells, by deregulating the signals, become masters of their own destinies. The enabling signals are conveyed in large part by growth factors that bind cell surface receptors, typically containing intracellular tyrosine kinase domains. The latter proceed to emit signals via branched intracellular signaling pathways that regulate cell growth and proliferation. Examples of these pathways are: Ras and Myc mediated pathways that, when mutated become oncogenic proteins. Mutations can be found either upstream (at the receptors level) or downstream (internal pathways). Alternatively, cancer cells may produce growth factors ligands themselves, to which they can respond via the expression of cognate receptors. Or they may send signals to stimulate normal cells within the supporting tumor-associated stroma, which reciprocate by supplying the cancer cells with various growth factors.

6 Examples: Ras (GTPase) and Myc (TF) Example 1

7 Receptors types: Tyrosine kinases

8 . Example of GPCR (large)

9 Evading growth suppressors: Tumors supressors And contact inhibition Tumor suppressors are proteins that negatively regulate cell proliferation. Through gain and loss of function experiments in mice, dozens of them have been identified. The two prototypical suppressors are RB (Retinoblastoma- associated) and the TP53 proteins. The RB protein integrates signals from diverse extracellular and intracellular sources and, in response, decides whether or not a cell should proceed to its growth-anddivision cycle. In contrast, the TP53 protein receives inputs from stress and abnormality sensors within the cell: if the degree of damage to the genome is excessive, or the growth-promoting signals, glucose, oxygen are suboptimal,the protein can halt cell division until these conditions have been normalized. Nevertheless, these proteins seem to be part of a larger network of protection: chimeric mice populated throughout their bodies with individual cells lacking a functional RB gene are surprisingly free of proliferative abnormalities.a year a go I is a good is a Similarly, TP53 null mice develop normally, show largely proper cell and tissue homeostasis, and again develop abnormalities later in life, in the form of leukemias. TGF-b is best known for its antiproliferative effects, and evasion by cancer cells of these effects is now appreciated to be far more elaborate than simple shutdown of its signaling circuitry. In many latestage tumors, TGF-b signaling is redirected away from suppressing cell proliferation and is found instead to activate a cellular program, termed the epithelial-tomesenchymal transition (EMT), that confers on cancer cells traits associated with highgrade malignancy.

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11 Contact inhibition: normal cell-to cell contacts formed in two-dimensional culture operate to suppress further cell proliferation, such contact inhibition is abolished in various types of cancer cells in culture. One mechanism involves the product of the NF2 gene, long implicated as a tumor suppressor because its loss triggers a form of human neurofibromatosis. Merlin, the cytoplasmicnf2 gene product, orchestrates contact inhibition via couplingcell-surface adhesion molecules (e.g., E- cadherin) to transmembrane receptor tyrosine kinases (e.g., the EGF receptor). In so doing, Merlin strengthens the adhesivity of cadherin-mediated cell-to-cell attachments. Additionally, by sequestering growth factor receptors, Merlin limits their ability to efficiently emit mitogenic

12 Resisting Cell Death Programmed cell death by apoptosis serves as a natural barrier to cancer development. The apoptotic machinery is composed of both upstream regulators and downstream effector components. The regulators, in turn, are divided into two major circuits, one receiving and processing extracellular death-inducing signals (the extrinsic apoptotic program, involving for example the Fas ligand/fas receptor), and the other sensing and integrating a variety of signals of intracellular origin (the intrinsic program). Each culminates in activation of a normally latent protease (caspases 8 and 9, respectively), which proceeds to initiate a cascade of proteolysis involving effector caspases responsible for the execution phase of apoptosis, in which the cell is progressively disassembled and then consumed, both by its neighbors and by professional phagocytic cells. The archetype Bcl-2 is an inhibitor of apoptosis, acting in large part by binding to and thereby suppressing two proapoptotic triggering proteins (Bax and Bak); the latter are embedded in the mitochondrial outer membrane. When relieved of inhibition by their antiapoptotic relatives, Bax and Bak disrupt the integrity of the outer mitochondrial membrane, causing the release of proapoptotic signaling proteins, the most important of which is cytochrome c. The released cytochrome c activates, in turn, a cascade of caspases that act via their proteolytic activities to induce the multiple cellular changes associated with the apoptotic program

13 Apoptosis mechanism

14 Tumor cells evade apoptosis Tumor cells evolve a variety of strategies to limit or circumvent apoptosis. Most common is the loss of TP53 tumor suppressor function, which eliminates this critical damage sensor from the apoptosis-inducing circuitry. Alternatively, tumors may achieve similar ends by increasing expression of antiapoptotic regulators(bcl-2, BclxL) or of survival signals (Igf1/2), by downregulating proapoptotic factors (Bax, Bim, Puma), or by short-circuiting the extrinsic ligand-induced death pathway. The multiplicity of apoptosis-avoiding mechanisms presumably reflects the diversity of apoptosis-inducing signals that cancer cell populations encounter during their evolution to the malignant state.

15 Enabling Replicative Immortality Normal cells divide about times (Hayflick rule) before they become senescent and die by apoptosis. In contrast, cancer cells divide forever: they are immortalized! In order for normal cells to become immortalized (cancerous), they must overcome two distinct barriers to proliferation: senescence, a typically irreversible entrance into a nonproliferative but viable state, and crisis, which involves cell death. Accordingly, when cells are propagated in culture, repeated cycles of cell division lead first to induction of senescence and then, for those cells that succeed in circumventing this barrier, to a crisis phase, in which the great majority of cells in the population die. On rare occasion, cells emerge from a population in crisis and exhibit unlimited replicative potential. This transition has been termed immortalization,a trait that most established cell lines possess by virtue of their ability to proliferate in culture without evidence of either Senescence. Hela cells were the line that was derived from cervical cancer cells taken on February 8, 1951 from Henrietta Lacks, a patient who eventually died of her cancer on October 4, 1951.

16 Telomerase absence is needed for genotype unstability andcancer development. Telomeres, eukaryotic chromosomes endings, are composed of multiple tandem hexanucleotide repeats, shorten progressively in nonimmortalized cells propagated in culture, eventually losing the ability to protect the ends of chromosomal DNAs from end-to-end fusions; such fusions generate unstable dicentric chromosomes whose resolution results in a scrambling of karyotype that threatens cell viability. Accordingly, the length of telomeric DNA in a cell dictates how many successive cell generations its progeny can pass through before telomeres are largely eroded and have consequently lost their protective functions, triggering entrance into crisis. Telomerase, the specialized DNA polymerase that adds telomere repeat segments to the ends of telomeric DNA, is almost absent in nonimmortalized cells but expressed at functionally significant levels in the vast majority (90%) of spontaneously immortalized cells, including human cancer cells. There is now evidence that clones of incipient cancer cells often experience telomere loss-induced crisis relatively early during the course of multistep tumor progression due to their inability to express significant levels of telomerase. Thus, extensively eroded telomeres have been documented in premalignant growths. which has also revealed the end-to-end chromosomal fusions that signal telomere failure and crisis. Specially if p53 is absent as well.

17 Inducing angiogenesis Tumors require sustenance in the form of nutrients and oxygen as well as an ability to evacuate metabolic wastes and carbon dioxide. The tumor-associated neovasculature, generated by the process of permanent angiogenesis, addresses these needs. Permanent angiogenesis ( as opposed to transient wound healing, estrus, etc) requires switches that are governed by countervailing factors that either induce or oppose angiogenesis. Some of these angiogenic regulators are signaling proteins that bind to stimulatory or inhibitory cellsurface receptors displayed by vascular endothelial cells. The well-known prototypes of angiogenesis inducers and inhibitors are vascular endothelial growth factor-a (VEGF-A) and thrombospondin- 1 (TSP-1), respectively. VEGF gene expression can by upregulated both by hypoxia and by oncogene signaling. Additionally, VEGF ligands can be sequestered in the extracellular matrix in latent forms that are subject to release and activation by extracellular matrix-degrading proteases (e.g., MMP-9). In addition, other proangiogenic signals, such as members of the fibroblast growth factor (FGF) family, have been implicated in sustaining tumor angiogenesis when their expression is chronically upregulated

18 Anti-angiogenesis therapy. Judah Folkman

19 OTHER SMALL MOLECULES ANTIANGIOGENESIS AGENTS