Biología del Cáncer Robert Weinberg presentacion capitulos 12 - 16

Notas del editor

• #3: Es un término utilizado para enfermedades en el que células anormales se dividen sin control y que pueden invadir tejidos adyacentes. Las células cancerígenas también pueden esparcirse a otras partes del cuerpo a través de la sangre y el Sistema linfático.
• #4: La integridad estructural y por lo tanto baja mutabilidad de ADN depende de un conjunto amplio y complejo de los mecanismos biológicos y bioquímicos que trabajan para garantizar que las mutaciones somáticas se acumulan en los tejidos a precios muy bajos.
• #5: - cada célula madre (azul) se divide sólo de vez en cuando para generar una nueva hija de células madre y una hija de tránsito de amplificación. Las células tránsito de amplificación (verde) se someten a repetidos ciclos de crecimiento y división, expandiendose de manera exponencial. Las células altamente diferenciadas, estan en contacto directo con diversos agentes tóxicos, por lo que cualquier alelos mutantes que se presentan en estas células se perderán más pronto o más tarde, del tejido. Esto significa que los genomas de las células madre están protegidos a través de dos mecanismos: las células madre rara vez se dividen, y están protegidos anatómicamente de influencias nocivas, potencialmente mutagénicos
• #6: las células madre están incrustados profundamente dentro de las criptas (Figura 12.2A). está protegido de los contenidos mutagénicos de la luz intestinal por una gruesa capa de moco secretado por las células de la cripta. Este moco, que se forma a partir de proteínas altamente glicosiladas denominadas mucinas, crea una barrera similar a la gelatina que impide que el contenido de la luz intestinal de penetrar profundamente en la cripta (por ejemplo, véase la Figura 12.2B) e ilustra todavía otra estrategia mediante la cual las mutaciones pueden se reduce al mínimo en los genomas de las células madre: la evolución ha creado mecanismos por los que las células madre son anatómicamente protegidos de la acción de las toxinas, incluidas sustancias cancerígenas.
• #7: • las bases mal incorporadas generadas por errores en la replicación del ADN pueden contribuir a la carga de mutaciones acumuladas. El número de estas alteraciones se llevan a cabo por las bajas tasas de error de ADN polimerasas, junto con una serie de proteínas de corrección de errores, como los que participan en la reparación de desajuste. Defectos hereditarios en las proteínas de reparación de genes puede conducir a una mayor susceptibilidad a ciertos tipos de cáncer, el cáncer de colon sin poliposis hereditario particular. Corrección por las polimerasas de ADN Un número de polimerasas de ADN tiene una capacidad de corrección de pruebas que les permite minimizar el número de bases que están mal incorporados y retenidos en la hebra recientemente sintetizada. Por lo tanto, como una ADN polimerasa extiende una hebra naciente (azul oscuro) en un 5'-a-3 '(que se mueve hacia la derecha), se utilizará el existente 3'-OH de la hebra naciente como cebador para la elongación adicional (luz azul) Sin embargo, si una base ha sido mal incorporados (tercera dibujo), la ADN polimerasa, que está continuamente buscando hacia atrás para comprobar si se ha incorporado las bases correctas en la cadena de ADN en crecimiento, se puede degradar en un 3'-a-5 '(hacia la izquierda) en dirección a la hebra recientemente alargado (cuarta imagen) y nos comprometemos una vez más a sintetizar este tramo de la cadena naciente (dibujo inferior).
• #9: Genomas celulares están bajo ataque continuo por una variedad de moléculas químicamente reactivas, muchos de ellos se derivan de el proceso celular de la fosforilación oxidativa y las especies reactivas de oxígeno resultantes que se generan como subproductos de este proceso. Genomas de células también pueden sufrir alteraciones químicas espontáneas, que afectan a las bases de ADN a una velocidad baja pero significativa.
• #13: Además, el ADN genómico de las células puede ser atacado por moléculas mutagénicos de origen extranjero. Estos xenobioticos y sus derivados químicamente reactivos pueden provenir de contaminantes y, en mucha mayor medida, de los productos alimenticios de consumo habitual.
• #14: Cuando el ADN purificado se irradia con 254 ~ fotones nm, el 71% de los fotoproductos resultantes formados son los dímeros de pirimidina ciclobutano (EPD, A), mientras que el 24% son de la pirimidina (6 ~ 4) pirimidinona (6 ~ 4 PP) fotoproductos Estas estructuras son relativamente estables y deben ser removidos por la transcripción reparación y reparación genómica global (que se describe en la Sección 128) de acoplamiento.
• #16: Aflatoxin and liver carcinogenesis (A) The fungal toxin aflatoxin B 1 (AFB 1) is made by a mold that grows on peanuts and grains that have been stored improperly, notably those stored in areas of high rainfall and humidity. Within the Jiangsu province of eastern China, the incidence of hepatocellular carcinoma (HCC) cases (brown dots) is 8-fold higher in the very humid southeastern Qidong peninsula (arrow) than in the northwestern parts of the province.
• #17: (A) The 10 heterocyclic amines (HCAs) whose structures are shown here are the most common HCAs to which humans are exposed. This class of compounds derives its name from the fact that each of them is composed of multiple fused rings, which are generally formed from both carbon and nitrogen that bear one or more exocyclic amine groups protruding from the ring structure. HCAs arise through cooking various foods, notably red meats, at high temperature. PhlP has been estimated to constitute two-thirds of the total dietary intake of HCAs among Americans. (B) The oxidation of the exocyclic amine of PhlP (2-amino-l-methyl-6phenylimidazo (4,5-bl pyridine; pink) by CYP1A2, a cytochrome P-450, leads to the highly reactive compound N-OH-PhIP (red) It can react with the 8-C of deoxyguanosine (green)
• #18: Las células despliegan una amplia variedad de enzimas para llevar a cabo la tarea muy difícil de restaurar la estructura de ADN normal.
• #19: ( A) El 0 6 Posición de guanosina es especialmente vulnerable a la alquilación por agentes como etilnitrosourea ( ENU ) . A diferencia de muchas enzimas de reparación del ADN , que responden a las bases alteradas por la escisión de ellos o de nucleótidos que contiene la totalidad de ellos a partir del ADN , la enzima 06 - metilguanina - ADN metiltransferasa [ MGMT ; también conocido como ADN 06 - alquilguanina alquiltransferasa ( AGT ) ] restaura una alteración guanosina a su estructura normal . Se hace mediante la eliminación del grupo alquilo del átomo de 0 6 de la guanina . En ausencia de dicha reparación, la guanosina alquilado a menudo conduce a una - a - A G mutación transición ( D ) peróxidos de lípidos altamente reactivos , que son comunes en los tejidos inflamados , pueden atacar y modificar adenina ( que se muestra aquí ) , así como otras bases de ADN ( no se muestra ) . La enzima AlkB de bacterias puede eliminar los aductos resultantes , así como aductos de metilo más simples , tales como los que se muestran en la Figura 12.14C ; homólogos de AlkB se supone que actúan de manera similar en las células humanas . . . . . . . . . En biología, un aducto es un complejo que se forma cuando un compuesto químico se une a una molécula biológica, como ADN o proteínas.
• #20: Base- and nucleotideexcision repair (A) Base-excision repair (BER) is achieved by enzymes that recognize chemically altered bases having minimal helix-distorting effect. These DNA glycosylase enzymes cleave the glycosyl bond linking the altered base (purple) and the deoxyribose. The base-free deoxyribosylphosphate is then excised by an enzyme-apurinid apyrimidinic endonuclease (APE)specialized to remove base-free sugars. The resulting single nucleotide gap is then filled by DNA polymerase ~ and sealed by a DNA ligase.
• #21: (B) Nucleotide excision repair (NER) is accomplished by enzymes that recognize bulky, helixdistorting lesions and cleave the flanking oligonucleotide sequences at sites approximately 24 nucleotides (nt) on the 5' side and about 5 nucleotides on the 3' side. The resulting approximately 29-nt single-strand gap in the DNA is then filled by DNA polymerase 8 or E, acting together with PCNA (proliferating-cell nuclear antigen) and RPA (single-strand DNA-binding protein), and finally is sealed by a DNA ligase. The chevrons represent deoxyribose nucleotides; in all cases they are pointing in a 5'-to-3' direction .
• #23: La xerodermia pigmentosa es un trastorno recesivo autosómico, lo cual quiere decir que uno tiene que tener dos copias de un gen anormal para que la enfermedad o el rasgo se manifieste. La luz ultravioleta, como la que se encuentra en la luz solar, daña el material genético (ADN) en las células de la piel, pero normalmente el cuerpo repara este daño. Sin embargo, en personas que sufren de xerodermia pigmentosa, el cuerpo no repara este daño. Como resultado, la piel se vuelve muy delgada y aparecen parches de variados colores (pigmentación moteada)
• #24: El síndrome de Lynch o cáncer colorrectal hereditario no asociado a poliposis, en inglés HNPCC, es una condición hereditaria que incrementa la probabilidad de presentar cáncer de colon y cáncer de recto 
• #28: • In carcinomas, these cell types can be separated into the neoplastic epithelial cells and recruited stromal cells, which include fibroblasts, myofibroblasts, and macro phages, as well as the various cell types that participate in the construction of the tumor-associated vasculature, specifically endothelial cells, pericytes, and smooth muscle cells.
• #33: Factor de crecimiento derivadode plaquetas Factor de crecimiento de unión a heparina tipo egf
• #34: A) microvasos se pueden estudiar usando al menos tres tipos de microscopía . Microscopía de inmunofluorescencia ( izquierda ) de los capilares en una tráquea de ratón normal ( utilizando un anticuerpo que reconoce el antígeno específico de la célula endotelial CD31 ) revela una red bien organizada de los vasos . A nivel de microscopía electrónica de barrido (centro) , un capilar se ve a parecerse a un tubo de paredes lisas cilíndricas w ith pericitos unidos aquí y allá a su superficie ( flechas). En la micrografía de transmisión (a la derecha ) , una sección de un capilar revela que su pared se construye por el citoplasma plegada de una célula endotelial
• #35: Esta micrografía de inmunofluorescencia resuelve los pericitos y células endoteliales . Normalmente , los pericitos y células musculares lisas (tanto rojo anaranjado ) de la capa exterior de los tubos de las células endoteliales ( verde) , que forma normalmente estructurados vénulas y arteriolas ( panel izquierdo) . En estos recipientes , la cobertura de las células endoteliales por los pericitos y células musculares lisas es a menudo tan completa que es difícil de visualizar las células endoteliales se encuentran debajo de los pericitos . En contraste , en los capilares ( panel de la derecha ) , los pericitos son más escasamente dispuestos , pero no obstante son estrechamente asociadas a las células endoteliales que forman los capilares
• #37: Macrophages playa major role in releasing mitogenic factors for carcinoma cells as well as reorganizing the tumor stroma in order to facilitate angiogenesis and, in some tumors, carcinoma cell invasiveness.
• #44: This bar graph reveals that as the diameter of an initially diagnosed primary breast cancer increases, the probability increases that distant . metastases will arise in a patient's body.
• #46: cervix
• #49: Mientras que el venosa sistemas de la mayoría de los tejidos drenan hacia la derecha lado del corazón y, posteriormente, en el lechos capilares de los pulmones, las venas drenando el bazo y el intestino son organizado de manera diferente, ya que vacía directamente en el hígado a través del portal circulación. (Después de pasar a través de la hígado, la sangre venosa es sólo entonces enviado de regreso al corazón.) En consecuencia, un gran número de metástasis de células de carcinoma colorrectal están atrapados en los lechos capilares del hígado a segundos de abandonar el colon.
• #52: La principal diferencia entre la inmunidad celular y la inmunidad humoral son los efectores que en ella intervienen. En la inmunidad celular los mediadores son células, principalmente linfocitos T, en cambio, en la inmunidad humoral son los anticuerpos. Sin embargo cabe destacar que no es posible hablar de estos dos tipos de respuesta inmunitaria de forma totalmente independiente. Las células participan en la iniciación de las respuestas con anticuerpos y los anticuerpos constituyen un nexo imprescindible en algunas reacciones mediadas por células. A grandes rasgos decimos que la inmunidad celular actúa contra microorganismos intracelulares. Su proceso de actuación se basa en que las células presentadoras de antígenos procesan y presentan dichos antígenos en su membrana mediante el Complejo Mayor de Histocompatibilidad (CMH). Los linfocitos T citotóxicos (CD8+) reaccionan con el CMH I y los linfocitos T colaboradores o helper (CD4+) con el CMH II que son reconocidos por el receptor T que dichos linfocitos presentan en su membrana. Será entonces cuando los linfocitos T activarán toda la cascada de señales y reacciones que harán frente a la infección. En cambio la inmunidad humoral actúa contra microorganismos extracelulares. En primer lugar las células B reconocen el antígeno y son activadas por la acción de los linfocitos T. Ésto produce la expansión clonal de los linfocitos B encargados de segregar anticuerpos, principalmente IgM, y dependiendo del estímulo IgG, IgA o IgE. Los anticuerpos liberados se fijan a los antígenos o microorganismos y los desactivan. También atraen a fagocitos a la zona para ayudar a destruir a más microorganismos. Hay que recordar que después de producirse este tipo de respuesta inmunitaria quedarán como remanentes los linfocitos B de memoria, que son los que facilitarán que la respuesta secundaria sea más rápida.
• #53: Las IgG se dividen en dos regiones funcionales. Una región está diseñado para reconocer y unirse a moléculas de antígeno. Porque las moléculas de IgG en el plasma pueden reconocer una esencialmente ilimitada número de antígenos, las moléculas de IgG tienen una diversidad comparable de estructuras en sus porciones de unión a antígeno, que se llaman su dominios variables (rojo), para reconocer esta diversidad El resto de la IgG molécula se denomina su región constante (azul) y es invariante entre todas las moléculas de IgG de una subclase dada, por ejemplo, todas las moléculas de IgG 1. Una IgG molécula como un todo es un heterotetrámero compuesto de dos (L) cadenas ligeras y dos (H) cadenas pesadas. Dos -Reconociendo antígeno independiente y vinculante Se muestran los bolsillos (arriba a la izquierda, arriba a la derecha), cada uno compuesto de una H y una cadena L de dominio N-terminal (formas cóncavas).
• #54: Neutralization by antibody molecules (A) Virus particles (red) can become coated by antibody molecules (blue) developed by the immune system of an infected host. This coating neutralizes (inactivates) the infectivity of the particles by blocking their adsorption to host cells . (B) Similarly, a bacterium displaying certain surface antigens (red) can also be prevented from adhering to host cells (A) antibody prevents viral adsorption (B) antibody prevents bacterial adherence by bound antibody molecules.
• #55: The coating of a bacterium (red) by antibody molecules (yellow) may provoke a macrophage to use specialized receptors on its surface, termed Fc receptors (green), to recognize and bind the constant regions of the antibody molecules (which are not involved in antigen recognition; see Figure 15.1). This often results in the phagocytosis of the antibodycoated bacterium and its eventual destruction in Iysoso mes within the cytoplasm of the macrophage.
• #56: A mammalian cell (gray) becomes coated by antibody molecules (blue) that recognize and bind antigens (red) on its surface. A type of lymphocyte termed a natural killer (NK) cell then uses its Fc cell surface receptors (green) to bind the constant reg ions of the coating antibody molecules. This binding results in activation of the N K cell, which proceeds to destroy the targeted cell, using cytotoxic granules (purple dots), whose contents it introduces into the targeted cell, to do so. Sheep red blood cells were treated with an antibody that recognizes an antigen displayed on their surface. As seen in th is scanning electron micrograph, a large number of them have become adsorbed to a macrophage via the Fc receptors on the surface of the latter
• #57: Cytotoxic T lymphocytes The cellular arm of the immune response results in the formation of cytotoxic cells, such as cytotoxic T cells (T c's, CTLs) that are able to recognize and kill other cells displaying certain antigens on their surface. (A) CTLs develop antibody-like molecules on their surface termed T-cell receptors (TCRs). A diverse array of TCRs are developed during the development of the immune system, paralleling the development of a diverse repertoire of soluble antibodies. Each CTL displays a particular antigen-recognizing TCR.
• #58: Seen here is a CTL (upper right, 1st panel) that has already used its TCR to recognize and bind to a target cell (diagonally below it to the left). The cytotoxic granules within this CTL (red spot) begin over a period of minutes to migrate toward the point of contact between the killer and its victim. By 40 minutes, the contents of these granules (such as granzymes) have been introduced into the target cell, which has already advanced into apoptosis and begun to disintegrate.
• #59: Here we see a drawing of specialized phagocytic cells (i.e., Langerhans cells, yellow) residing in the skin, which take up antigens (red dots) by phagocytosis and then migrate to the lymph nodes (light blue), w here they mature into dendritic cells. In the lymph nodes, these cells confront T cells (dark blue circles), to which they present antigens; this results in the functional activation of the T cells and the subsequent mounting of a specific immune response against cells and viruses that display these antigens.
• #60: Antigen processing by antigen-presenting cells After phagocytes, notably dendritic cells and macrophages, have internalized potential antigenic particles (red oblongs), these are fragmented into oligopeptides (red dots) by proteolysis. The resulting oligopeptides are then loaded onto MHC class II molecules in the endoplasmic reticulum, which then move to the cell surface, allowing the MHC class II molecules to display the oligopeptide fragments on their surface and present the oligopeptide fragments to T cells in the lymph nodes.
• #62: Complement-mediated killing (A) Antigen-antibody complexes (red spheres) formed by the binding of antibody molecules to cell surface antigens (left) can attract complement proteins present in the plasma (yellow, green, purple) and induce them to form complexes that lead, through a series of steps, to the formation by other complement proteins of channels in the plasma membrane of the cell (right) at a site adjacent to w here the antigen-antibody complexes initially formed . (B) The resulting channels, seen here in this electron micrograph, destroy the integrity of the barrier functions of the plasma membrane and lead rapidly to cell death.
• #63: Display of intracellular antigens by MHC class I molecules Almost all cell types throughout the body, including cancer cells, routinely divert A portion of their recently synthesized proteins to the antigen-presenting machinery. (A) Some of the recently synthesized proteins in the cytosol are diverted to proteasomes (purple, yellow), in which they are broken down into oligopeptides (red dots); resulting oligopeptides are then introduced into the endoplasmic reticulum, w here they may encounter MHC class I molecules yellow) that bind them relatively tightly. This will cause the mul ti-protein complexes to move via membranous vesicles to the cell surface, w here these protein complexes serve to display to the immune system fragments of the proteins that are being synthesized within the cell. The overall process of displaying these antigens is similar to that undertaken by MHC class II molecules; however, MHC class II antigen presentation is the speciality of "professional antigen-presenting cells", such as macrophages, dendritic cells, and B cells, while MHC class I presentation is undertaken routinely by almost all cell types in the body. (B) A broad spectrum of oligopeptide fragments deriving from a large number of cellular proteins (here represented as four distinct protein species) are displayed simultaneously by cells using their MHC class I proteins
• #64: Activation of cytotoxic T cells by helper T cells In addition to inducing B cells to make antibody molecules, helper T celis (TH) of a second subtype (blue) can activate the precursors of cytotoxic T celis (light red, bottom) to become active cytotoxic T cells (termed Tc 's or CTLs, red) that can use their T-cell receptors (TCRs) to recognize and bind antigens presented on the surfaces of many cell types throughout the body by MHC class I molecules. This recognition results in attack on the antigen-displaying cell (gray, top), as shown by the micrographs of Figure 15.4B. The Tc 's often use cytotoxic granules (black dots) containing perforin and granzymes to kill targeted cells
• #65: An alternative mechanism of killing cells that have been targeted for destruction depends on the display of FasL (orange) by the T c (top, pink). FasL, which is a trimer, then engages the Fas receptor (brown) displayed by the targeted cell (bottom cell, gray) and triggers receptor trimerization and resulting activation of the ext rin sic apoptotic cascade in the targeted cell via the sequential activation of caspases 8 and 3
• #67: This SEM reveal s the initial attack of an NK cell (left panel, smaller cell) on a leukemia cell. Sixty minutes later, the NK cell has caused extensive damage to the plasma membrane of the leukemia cell, which has fragmented and rolled up its plasma membrane in response to this attack (right panel).
• #73: Macrophages can be activated by diverse signals, such as interferon-y (IFN-y) and bacterial lipopolysaccharide (LPS), the latter being used as an adjuvant to potentiate the immune response. Once activated, they can function to present antigen to helper T (TH) cells and to trigger tumor cell killing by antibody-dependent cellular cytotoxicity (ADCC) Acting in the opposite direction, hypoxia as well as a variety of physiologic signals released by tumors activate the macrophages and cause them to further tumor progression.
• #76: Immunoevasion through suppression of MHC class I expression Cancer cells will often dow n-regulate expression of the MHC class I molecules, osten sibly in order to avoid recognition and attack by cellular components of the adaptive immune response. In this immunohistochemical staining, cells of a human col orectal tumor are visualize d. They have been immunostained with an antibody that recognizes a human MHC class I molecule-HLA-A. As seen here, the cells in the lower part of the tumor strongly express HLA-A, w hile the cells in the upper part of the tumor have partially or totally lost HLA-A expression.
• #77: Regulation of NK function by the NKG2D receptor (A) The NKG2D receptor displayed by NK cells binds a number of ligands that are expressed by other cell types suffering certain physiologic stresses, notably the stresses caused by viral infection and neoplastic transformation, Shown here is an assembly of various alternative ligands of NKG2D that have been identified in human and murine cells, For example, MICA and MICB are normally expressed only by certain epithelial cells suffering certain types of cell-physiologic stress,
• #78: The molecular structure of the complex between NKG2D and its MICA ligand is shown here. The two subunits of the NKG2D receptor are shown above (blue, purple) as they might be displayed on the surface of an NK cell. The structure of the three subdomains of the ectodomain of MICA (beige, red, green) is shown as it might be displayed on the surface of a cancer cell.
• #82: Statistics of cancer mortality over the past three quarters of a century: the lay of the land. The statistics compiled in the United States on the age-adjusted death rates from various types of cancer reveal two different long-term trends. (A) Mortality from several major killers has declined significantly since 1930. This is due to changes in food storage practices and possibly Helicobacter pylori infection rates, in the case of stomach cancer, and to screening, in the cases of cervical and colorectal cancers.
• #83: (B) A number of major sources of cancer-related death have proven resistant to most forms of traditional Therapy, especially when these tumors progress to a highly malignant metastatic stage.
• #85: Breast cancer incidence vs. mortality in the United States The age-adjusted incidence of breast cancer has been increasing steadily over the past several decades, while mortality from this disease wa s quite constant until the end of the twentieth century, when it began to decline. Most of the increase in incidence appears to be attributable to increasing screening, but a small proportion of it may be due to real changes in the rate at which the disease strikes because of changes in reproductive practices, nutrition, and so forth.
• #86: High-resolution noninvasive imaging of human tissues The development of magnetic resonance imaging (MRI) has enabled increasingly higher-resolution, noninvasive visualization of living tissues. MRI now allows breast tumors of very small size (several mm diameter) to be detected and, as shown here, makes it possible to view the progress of antitumor therapy-in this case chemotherapy with an anthracycline cytotoxic agent-in exquisite detail. Widespread use of such highly sensitive imaging techniques is likely to result in further increases in the incidence rate of breast cancer.
• #87: Expression arrays were used to analyze the gene expression of a group of 295 primary breast cancers diagnosed In women of less than 53 years of age, The group included patients with metastatic cells in their axillary lymph nodes as well as patients whose lymph nodes were free of cancer cells, Bioinformatics analyses of these tumors were then employed to choose a set of 70 '"prognosis genes '" whose expression could be used to stratify these breast cancer patients (arrayed along vertical axis), whose clinical course had been followed for a mean time of 7 years, The expression leve ls of these 70 genes (arrayed along horizontal axis, names not given) together with information about the patients' clinical history w as then used to set a threshold that separated tumors that had a "good expression signature" from tumors that had a "poor expression signature,"
• #88: The fact that the PMBLs and the ABCs show high constitutive levels of NF-KB activity suggests t hat they may be particularly susceptible to disruption of this signaling pathway by inhibition of the upstream activator of NF-KB, IKB kinase (IKK; see Figure 6.29) This is borne out by experiments in which MLX105, a pharmacologic inhibitor of IKK, was applied to cell lines derived from the three types of lymphoma and indeed showed differential effects on these three cell populations growing in vitro.
• #89: Chemotherapy and mitotic catastrophe Many chemotherapeutic drugs may damage the chromosomes of cancer cells. Because the cancer cells lack key G2/M checkpoint controls, they may advance into mitosis without having repaired the chromosomal damage. This may cause them to enter into "mitotic catastrophe" that results in aneuploidy, polyploidy, formation of micronuclei, and the eventual death of these cells. Seen here are the effects of low doses (50 ng/ml) of doxorubicin, a widely used chemotherapeutic drug, on Huh-7 human hepatoma cells. Over a period of 9 days, the nuclei of these cells grow larger or smaller and many eventually fragment into micronuclei, each of which carries a small number of chromosomes; this leads eventually to cell death, often by apoptosis.
• #90: Inhibition of tumor growth by targeting downstream signaling elements As indicated in this diagram, signaling from receptors such as the EGF (HER1) and HER2/Neu receptors can be blocked in a number of ways. The ectodomains of the receptors can be targeted by monoclonal antibodies such as Herceptin. Moreover, the tyrosine kinase signal-emitting domains of these receptors can be targeted by a variety of low-molecular weight compounds. In addition, however, a number of drugs have been developed that target proteins functioning as components of downstream signaling pathways, including those that inhibit Ras (through inhibition of its post-translational maturation involving farnesylation), as well as Raf and MEK (through inhibition of their serine/threonine kinase catalytic functions), and mTOR (through inhibition of the formation of functional signaling complexes between mTOR and cell cycle associated partner proteins).
• #92: Multiple contacts between drugs and their targets (A) The chemical structure of Gleevec, which was developed to inhibit the tyrosine kinase activity of the Bcr-Abl fusion protein active in chronic myelogenous leukemia (CML), was the result of optimizing the structure of a precursor compound to w hich certain side chains were added w hile others were removed in order to improve drug binding to the catalytic cleft of the Abl tyrosine kinase domain. (B) The cata lytic cleft of the Abl kinase is found between its N- and C-terminal lobes, shown here as green ribbon structures. A spacefilling model (with van der Waals radii) of a Gleevec molecule is shown in dark blue, while the "activation loop" of Abl, which normally blocks access to substrates by the catalytic cleft, is shown in light blue. (This activation loop swings out of the way when the kinase shifts into its active configuration.)
• #93: The healthy effects claimed to come from drinking black and green teas have been ascribed to a number of the constituents of the tea leaves, some of which induce apoptosis in tumor cells at very low concentrations. Epigallocatechin gallate (EGCG; stick figure) extracted from green tea binds the important anti-apoptotic protein 8c1 -Xt with an inhibitory constant (Ki) of 490 nM and BcI-2 w ith a Ki of 335 nM. (The values of these constants reflect the concentrations at which 50% of the activity of these proteins 's inhibited; values in the submicromolar range are indicative of high potency.) A combination of three technologies-nuclear magnetic resonance (NMR) binding assays, fluorescence polarization assays, and computational docking-was used to derive this image, v"nlcn shows the docking of EGCG in three adjacent hydrophobic pockets of Bcl-XL (yellow ar,o green), whose molecular surfaces are shown here and labeled Pl, P2, and P3. These pockeo iO<Jether constitute a hydrophobic domain that Bcl-XL, which is overexpressed in many cancer cells, uses to bind and neutralize pro-apoptotic BH3-only proteins
• #94: The small molecule ICG-OO1 (left) inhibits the association of the b-catenin-Tcf/ Lef complex with the transcriptional co-activator CBP. The transcription factor complex is responsible for inducing, among other genes, expression of the gene encoding survivin, a key inhibitor of apoptosis. As seen here, expression of surviving (green, yellow immunofluorescence, both right panels) that is normally present in SW480 human colon carcinoma cells (arrows) is strongly reduced by the presence of ICG-001; tubulin (red) is used in both cases as a counterstain. The concentration of ICG001 used in this experiment causes an approximately 6-fold reduction in the activity of the survivin gene promoter
• #95: Tarceva and the inhibition of the EGF receptor kinase domain This space-filling model of the catalytic cleft of the EGF receptor tyrosine kinase (TK) domain, derived by X-ray crystallography, shows how the drug Tarceva (stick figure) fits snugly within the ATP-binding cavity of the cleft and in this way inhibits receptor signaling. The three-dimensional complementarity between drug and targeted protein is necessary for drug binding but not sufficient, as specific bonding, largely achieved through the formation of hydrogen bonds (not shown), must occur between the drug molecule and amino acids lining the drug-binding pocket A water molecule (behind, below) that is hydrogen-bonded to the Tarceva molecule is also shown.
• #96: Effects of kinase inhibitors on a wide spectrum of protein kinases The individual responses to various kinase inhibitors of an array of 156 distinct tyrosine and serine/threonine kinases have been tested by measuring the binding affinities of each inhibitor for each of these kinases. This test depends on the fact that almost all kinase inhibitors bind to the ATP-binding sites of targeted enzymes. (A) A cDNA encoding the kinase domain of a protein is cloned into a bacteriophage vector so that some of the phage capsid (coat) proteins (green) are synthesized as fusion proteins with the kinase (purple). An ATP analog that is known to bind the ATP-binding sites of many kinases (red) is then immobilized by being linked to microbeads (light blue). This allows phage particles to become linked via the fusion proteins in their capsids to the ATP analog on the beads. The assay then measures the ability of a test compound (e.g., a candidate tyrosine kinase inhibitor, yellow) to compete with the immobilized ATP analog (red), thereby blocking association of the phage to the bead. A reduction in binding of the phage to the beads, as revealed by the number of phage particles released from the beads (using a phage plaque assay or a polymerase chain reaction for the phage DNA) then indicates the binding affinity of the test compound for the kinase present in the fusion protein, as represented by its displacement constant, Kd, i.e, the concentration at which 50% of the phage is displaced from the beads. In the remaining panels, each kinase that showed a Kd of less than 1 microM is indicated by a red circle whose diameter varies inversely with the Kd (binding constant affinity) and whose position is dictated by the location of the kinase on the kinome tree
• #98: Pharmacokinetics and pharmacodynamics of Gleevec The pharmacokinetics of a drug represent the kinetics of its accumulation in and disappearance from the plasma, which in turn are presumed to provide a good ind ication of the drug concentrations that tumor cells experience in a laboratory animal or a patient under therapy. The plasma level of the drug Gleevec, plotted on a logarithmic scale (left ordinate), fluctuates dramatically following injection of the drug into a mouse (blue curve). Its concentration is indicated here as a multiple of the drug concentration known to inhibit the firing of the tyrosine kinase of the Kit receptor by 50% (i.e, the ICso of this agent). (The tyrosine kinase domain of the Kit growth factor receptor is also a target of inhibition by Gleevec.) As seen here, the amount of phosphotyrosine associated with the Kit receptor (a reflection of Kit tyrosine kinase activity) expressed by eng rafted human mast cell leukemia cells (red curve), which was initially set as 100%, is reduced to «1 % of preexisting levels within an hour after drug injection but rebounds within 8 hours as the concentration of the drug declines in the plasma.
• #99: Measurements of pharmacodynamics such as these, taken together with studies of pharmacokinetics and toxicity, define the therapeutic window in w hich a drug should be given-the range of concentrations that are efficacious without creating an unacceptable level of toxic side effect s.
• #100: Gemcitabine as a treatment for pancreatic cancer This Kaplan-Meier plot illustrates the high mortality exacted by pancreatic cancer. Patients treated with gemcitabine (GEM) lived slightly longer than did those treated with 5-fluorouracil (5-FU)-the standard of treatment in the 1990s. Both of these agents are pyrimidine derivatives whose cytotoxicity derives from their ability to inhibit DNA synthesis, in part through misincorporation into the DNA. (5·FU also interferes with pyrimidine biosynthesis.) As is apparent, gemcitabine treatment offered only a modest increase in patient survival in this study reported in 1997, but nevertheless this effect sufficed to allow its approval by the u.s. Food and Drug Administration.
• #102: Multi-drug resistance and the P-glycoprotein The MDRI gene encodes P-glycoprotein, a protein that is often present at elevated levels in cancer cells being treated with various types of chemotherapy. P-glycoprotein, whose structu re IS shown here, is a 170-kD ATP-dependent transmembrane protein that can pump a wide variety of drug molecules out of cells. It is a member of a large family of mammalian transporter molecules, of which 49 have been discovered until now Its actions appear to be responsible for the acquisition of drug resistance by a variety of human tumor types under treatment with low-molecula r-weight chemotherapeutic drugs.
• #104: Role of tumor stem cells in the response to anti-cancer treatments While the evidence is still fragmentary, it appears that in many tumors, a small proportion of the neoplastic cell population is composed of self-renewing tumor stem cells (gray). These spawn the bulk of the cancer cells in tumors (pink), which have many of the properties of normal progenitor or transit-amplifying cells. If, as is the case with Gleevec, an anti-cancer therapy results in the depletion of the neoplastic transit-amplifying cells without eliminating the tumor stem cells, then the latter can regenerate the tumor soon after that therapy is halted.
• #105: Targets for future cáncer drug development A survey of the cancer literature conducted in 2004 revealed at least 291 genes that have been implicated as contributing causally to hu man cancers. Of these, 260 are known to be present as somatically mutated alleles in human cancer cell genomes . However, the great bulk of the latter are somatICally mutated in the genomes of mesenchymal tumors (leukemias, lymphomas, and sarcomas), leaving only 77 genes that are mutant in the far more common tumors of the remaining types. Given the number of kinase genes present in the human genome, 6 kinases were expected to be among the 291 cancer-associated genes, whereas 27 were actually present in this list. Conversely, the more numerous G-protein-coupled receptors (GPCRs) were expected to yield at least 8 cancerassociated genes, but only 1 was present.