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Cell Biology of Cancer Wilma Lingle, PhD Experimental Pathology Mayo Clinic Biology of Breast Cancer Neoplastic Transformation Normal Cancer Basement membrane (basal lamina) • Basement membrane is an extracellular matrix located: – around muscle and fat cells – under epithelial tissues (skin, lining of gut) – under endothelial lining of blood vessels • Basement membrane functions include: – providing mechanical support for attached cells, – generating signals that maintain cell survival, – separating adjacent tissues – acting as barrier to some macromolecules Differentiation and cancer Tissue specificity Tumor formation (differentiated (dedifferentiation) state) Invasion - Metastasis 1. Oncogenes 2. Tumor suppressors 3. Therapeutic targets 4. Cellular and biochemical mechanisms of chemical or genetic carcinogenesis What Is A Tumor Suppressor Gene? Narrow definition: A gene that encodes a protein that normally functions to control cell division (Knudson, 1993). Broader definition: A gene that encodes a protein that normally functions to suppress the expression of traits associated with the malignant phenotype. Functions of cellular proto-oncogenes 1. Secreted Growth Factors 2. Growth Factor Receptors 4. Nuclear Proteins: Transcription 3. Cytoplasmic Factors Signal Transduction Proteins Cell Growth Genes Chromosome changes in cancer Cancer karyotype Stable karyotype Tumor Suppressor Genes Encode Proteins that Suppress the Expression of Traits Associated With the Malignant Phenotype. “The malignant phenotype” is a spectrum of traits commonly associated with tumorigenesis: •Increased cellular proliferation. •Decreased apoptosis. •Increased cellular motility and invasive ability. •Decreased contact inhibition. •Decreased dependence on growth factors. How Do Tumor Suppressor Genes Fail? Tumor suppressor genes function normally to repress the expression of traits associated with the malignant phenotype. Why and how do tumor suppressor genes lose this repressive function during tumorigenesis? Tumor suppressor genes become inactivated during tumorigenesis. The loss of function of tumor suppressor proteins facilitates tumorigenesis. Interphase Prophase Metaphase Anaphase Cell Cycle Checkpoints • Regulate progression through the cell cycle insuring that each step takes place only once and in the right sequence • There are three major checkpoints: G1/S (where most cancer-related defects occur) G2/M Spindle checkpoint Cancer Evolution • Deregulation Of Cell Cycle • Centrosome Defects • Phenotypic Heterogeneity • Selection Of Aggressive Cancer Cells • Molecular Targeted Therapy To Delay Chemo-resistance And Metastasis Errors in Mitosis • Centrosomes • Kinetochores • Telomeres Errors in Mitosis No cell is an island Cells are continuously responding to signals from the endogenous and exogenous environment. Signal input dictates disparate cellular outcomes Biology of Breast Cancer Proliferative Signaling Pathways EGFR P*EGFR Other RTKs PI3K RAS/RAF STAT1/3 AKT ERK1/2 P*AKT P*ERK1/2 P*STAT1/3 cell proliferation survival The Epidermal Growth Factor Family of Tyrosine Kinase Receptors GF GF GF P P EGFRs EGFRs EGFRs EGFRs EGFRs EGFRs P P P P The EGFR Family Members can form Homodimers or Heterodimers GF GF GF P P P P P P EGFR EGFR HER2 HER2 HER2 EGFR P P P P P P P P P P P P Mechanisms to Inhibit EGFR Activity GF X GF GF MAB X P X P HER2 HER2 HER2 EGFR EGFRs EGFRs SMI X P SMI X X P P More than 40% of BC Patients Relapse within 5 years of diagnosis • Inadequate surgeries or treatment • Drug resistance • Evolution of tumor cells resistant to initial treatment How can response to EGFR Therapies be monitored? Assessing Circulating Tumor Cells to Monitor Response Traditionally, BC patients are followed only by frequent mammograms and manual breast exams, making it difficult to monitor response to therapy. But - invasive cancers shed malignant cells into the bloodstream. We propose to collect these cells before treatment and at intervals after treatment in order to monitor the patient’s response. Assessing Circulating Tumor Cells to Monitor Response EGFR-Targeted Therapies Our Hypotheses: Patients with initial good response will have: • a high baseline ratio of P-EGFR to EGFR • significant baseline levels of P-AKT and P-ERK1/2 - indicating that activation of the EGFR pathway is involved in the primary tumor. Patients with continued good response will have: • a lower follow-up ratio of P-EGFR to EGFR - indicating inhibited activation of EGFR. Assessing Circulating Tumor Cells to Monitor Response EGFR-Targeted Therapies Our Hypotheses (cont): Patients with continued good response will also have: • diminished P-AKT and P-ERK1/2 at follow-up - indicating that other activators of proliferation are not present. Patients with failure to maintain response will have: • an increase in P-AKT and P-ERK1/2 in the absence of P-EGFR at follow-up - indicating that proliferation is being stimulated by another receptor tyrosine kinase. These patients are no longer benefiting from treatment; their treatment should be changed.
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