Angiogenesis: Factors, Inhibitors & Tumors

• Angiogenesis is the formation of blood vessels from existing ones through sprouting, splitting, and remodeling
• Vasculogenesis involves the formation of new endothelial cells and tube formation from stem cells
• Pericytes are immune cells of the blood vessel that close pores on blood vessels
• Vascular endothelial growth factor (VEGF) is a specific growth factor for endothelial cells and a primary angiogenic factor

Angiogenic Factors and Inhibitors

• Activators include basic fibroblast growth factor, transforming growth factor alpha, tumor necrosis factor alpha, and adenosine (sugar associated with ATP)
• Inhibitors include angiostatin, endostatin, interferons, prolactin 16Kd fragment (promotes milk production), and protein 55 (p53)
• Natural angiogenic inhibitors include green tea, soy, and red wine

Tumors and Angiogenesis

• Sizeable tumors exist in hypoxic environments and usually contain more than 1 million tumor cells
• Soluble factors, like VEGF, promotes angiogenesis
• Tumors promote extracellular matrix remodeling and tip cell formation
• Blood vessels continue to grow in a tumor environment

Inflammation and Angiogenesis

• Inflammatory cells are present in the tumor microenvironment
• Tumor-associated macrophages (TAM) are present
• Mast cells release histamines, causing dilation of blood vessels
• Eosinophils release cytokines
• Neutrophils act as phagocytes
• Dendritic cells target T cells
• Inflammatory cells produce and release pro-angiogenic factors

Angiogenesis Requirements

• Requires IL-6 and IL-8 (chemokines) and matrix metalloproteinases 9 and 13

Angiogenic Cascade

• Begins with the initiation of angiogenic response
• Disruption of focal contacts occurs between adjacent endothelial cells, pericytes, and smooth muscle
• Endothelial cells migrate, proliferate, and form tubes
• Activated endothelial cells produce MMPs that degrade the ECM, enabling them to migrate away from the parent vessel
• Endothelial cells divide and organize into hollow tubes that mature into a network with the help of an adhesion factor like integrin alpha or beta
• Maturation of neovasculature requires stabilization via Angiotensin-1,-2 and their receptor Tie-2
• Anastomosis of developing buds forms intact capillary loops

Characteristics of Tumor Blood Vessels

• Precocious capillary sprouting is present
• Vessels are distorted and enlarged
• Erratic blood flow and microhemorrhaging occur
• Abnormal levels of endothelial cell proliferation and apoptosis are present
• Oxygen can diffuse through living tissue up to a distance of 0.2mm
• Angiogenesis is necessary for tumor expansion beyond 400um (or 1 million cells) of tumor size

Anti-Angiogenic Therapy

• Designed to prevent the formation of new blood vessels
• Uses cytostatic drugs rather than cytotoxic drugs
• Anti-VEGF monoclonal antibodies like Bevacizumab are humanized and precisely target VEGF
• Bevacizumab exerts multiple effects including inhibition of new vessel growth, regression of existing tumors, and antipermeability of surviving vasculature
• Small molecule tyrosine kinase inhibitors and mTOR inhibitors are used

Cancer Biomarkers

• A biomarker is a measurable characteristic identified using a variety of techniques to assess risk, diagnose, and track disease states

Biomarkers as Subcategories of Illness Indicators

• Physiological indicators include blood pressure, temperature, and breath sounds
• Molecular indicators include RBC count and cholesterol levels
• Imaging indicators include tumor mass and bone fractures

Biomarkers of Specific Categories

Susceptibility/Risk Biomarkers

• Assess patients' susceptibility to developing cancer in their lifetime
• Relate to patients who do not have cancer
• BRCA 1/2 mutations can be detected using saliva and blood samples

Diagnostic Biomarkers

• Used to make a diagnosis after a disease has been established
• Sensitivity is the ability to produce a positive test when positive
• Specificity is the ability to produce a negative test when negative

Monitoring Biomarkers

• Assess changes in disease progression throughout the course of treatment
• Repeated measurements can show if conditions are better, worse, or the same

Prostate Specific Antigen (PSA)

• High levels indicate cancer cells are present
• Low levels mean normal conditions

Prognostic Biomarkers

• Assess the current state/stage/severity of cancer to predict the progression of the disease
• The Gleason scale is prostate cancer-specific

Predictive Biomarkers

• Predict how patients will respond to different therapies
• HER2+ breast cancer is more responsive to certain treatments
• HER2 oncogene mutation

Responsive Biomarkers

• Show how the cancer is responding to treatment

Safety Biomarkers

• Monitor adverse effects as a result of treatment

Cancer and the Environment

• Inherent characteristics
• Intrinsic biological factors
  • Genetic predisposition
  • Inheritable disease
  • BRCA1/2

Natural Environment

• Consists of everything around us that is not human-made
• Includes natural disasters and climate change
• Also related to benzene and leukemia

Built Environment

• Human-made environment
• Includes infrastructure/parks
• Steel plants and leukemia

Social Environment

• Pertains to your place in society
• Socioeconomic status can increase cancer risk

Behavioral Environment

• Refers to interactions with the environment
• Includes smoking and sun tanning

Viral Oncogenesis

• Nearly 20% of all cancers worldwide are attributed to viruses

Oncogenic Viruses

• Viruses that produce tumors in their host and induce malignant transformation of cell cultures

  • DNA tumor virus
  • RNA tumor virus

• Both have the ability to integrate their own genome into that of the host cell

Transformation

• Introduction of inheritable changes in a cell, causing changes in the growth phenotype and immortalization

Transformation by a Virus

• Changes in the biologic functions of a cell resulting from regulation of the cell by viral genes that induce properties of neoplasia
  • Neoplasia is the formation or presence of a new, abnormal growth of tissue
  • A transformed cell is one taken up by a virus and now has altered properties

Cellular Proto-Oncogene

• Encode proteins that function in DNA replication
• Are not normally expressed in cells as they would multiply to repair damage
• Can be transformed into oncogenes only after being altered by a mutation or being activated by a promotor

Oncogenes

• Cellular genes that influence cell growth and differentiation
• Code for a protein that can be potentially transformed into a malignant cell

Viral Oncogenes

• Cellular oncogenes that become incorporated into the virus by recombination

Viruses and Cancer

• A virus can cause cancer by carrying an oncogene into a cell (immediate) or by activating a proto-oncogene as a promotor (immediate)

Retrovirus

• Can change RNA to DNA to integrate into the host cell

Viral Reverse Transcriptase

• A DNA-polymerase enzyme that transcribes RNA into DNA
• Indicates genetic information can travel from RNA to DNA rather than the opposite, which is normal
• Discovered by Howard Temin and David Baltimore

Cell Growth Transformation by Retroviruses

• Provirus is an innate virus that does not have full infection potential and is time-dependent
• A provirus integrates into the cellular genome as a normal part of the virus life cycle and is time-variable
• A provirus carries a captured cellular oncogene and is time-variable
• A provirus-coded protein activates cellular genes and can happen in real-time from ingestion, which has a link to meat consumption and cancer

Viruses Associated with Human Cancer

• DNA viruses
  • Papillomavirus: Targets endothelial cells (the body takes 52 years to rid itself of it)
    • Carcinoma of the uterine cervix
    • Benign warts
    • Vulvar, penile, and cervical cancers type 16 and 18
    • Laryngeal papillomatosis
  • Hepadnaviral family
    • Hepatitis-B virus: Liver cancer (hepatocellular carcinoma)
    • Hepatitis C
    • Hepatocellular carcinoma
  • Epstein-Barr virus
    • Burkitt's lymphoma
    • Nasopharyngeal carcinoma
    • B cell lymphoma
    • Oral hairy leukoplakia
  • Herpes simplex virus
    • HSV-1 causes cold sores
    • HSV-2 is sexually transmitted and is associated with cervical intraepithelial neoplasia and carcinoma of the uterine cervix

RNA viruses

• Retrovirus family
  • Human T-cell leukemia virus type 1 (HTLV-1)
    • Adult T-cell leukemia
    • Characterized by a proliferation of mutated CD4+ T-lymphocytes
    • Sexually transmitted and parenterally transmitted
    • Flower cells
  • Human immunodeficiency virus (HIV)
    • Kaposi sarcoma

Genital Warts

• Keratinized epithelial tissue
• Shares pathogenesis with cancer
• Has a neoplastic nature

HPV Vaccines

• Gardasil contains L protein of types 6, 11, 16, and 18
• Cervarix contains L protein of types 16 and 18
  • Type 16 and 18 cause cervix cancer
  • Type 6 and 11 cause genital warts

Antitumoral Components of the Innate Immune System

• Dendritic cells
• Neutrophils
• Macrophages release tumor necrosis factor gamma
• NK cells release perforin and granzyme causing apoptosis
• T cells recognize tumor antigens and activate NK cells
• B cells
• Complement targets a cell and creates a pore to allow for material flow and burst
• Transforming growth factor beta (TGF beta)
• Cytokines
  • Recruitment of IL-10 and IL-12
    • IL-10 is anti-inflammatory
    • IL-12 activates CTLs and NK cells
• Interferon gamma is critical for cancer identification