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Lecture Overview

  • Topic: Tumor Angiogenesis

  • Key Objectives: Understand blood vessel cell types, angiogenesis vs. vasculogenesis, tumor blood vessel differences, role of VEGF, and implications for cancer treatment.

Cell Types in Blood Vessels

  • Blood vessels are not solely comprised of endothelial cells.

  • Important components:

    • Endothelial cells: Form the walls of blood vessels.

    • Pericytes: Reinforce capillary structure, attached to the basement membrane.

    • Basement membrane: An extracellular matrix that provides support.

Origins of Blood Vessel Formation

  1. Angiogenesis: Formation of new blood vessels from existing ones.

    • Triggered by hypoxia (lack of oxygen).

    • Types of angiogenesis:

      • Sprouting Angiogenesis: New branches form from existing vessels due to signals from hypoxic tissues.

      • Branching Angiogenesis: A single blood vessel splits into two.

  2. Vasculogenesis: Development of blood vessels de novo from precursor cells called angioblasts.

    • Occurs during early embryonic development and is primarily driven by the presence of specific growth factors.

Tumor Angiogenesis

  • Tumor blood vessels are distinct from normal blood vessels:

    • Morphologically different (tortuous and leaky).

  • VEGF (Vascular Endothelial Growth Factor): Key player in promoting angiogenesis.

    • High levels of VEGF in tumors lead to abnormal, permeable vessels.

Angiogenic Switch in Tumors

  • Tumors can remain dormant without proper blood supply.

  • Angiogenesis contributes to nutrient and oxygen delivery, allowing tumor growth.

  • Prognosis: Increased angiogenesis is often correlated with worse prognosis in cancer patients.

Factors Influencing Angiogenesis

  • Many factors control the angiogenic process, including:

    • Growth factors (e.g., VEGF, FGF).

    • Inhibitors (e.g., thrombospondin, angiostatin).

  • The balance between activators and inhibitors dictates the angiogenic switch.

Tumor Vessel Characteristics vs. Normal Vessels

  • Normal vessels:

    • Organized, stable, and non-permeable.

    • Low interstitial pressure, uniform blood flow.

  • Tumor vessels:

    • Disorganized, leaky, located in hypoxic regions, and often have high interstitial pressure.

    • Facilitates tumor spread (metastasis) due to the leaky nature, allowing cancer cells to escape into the bloodstream.

Chemotherapy and Anti-Angiogenic Strategies

  • Current cancer treatments target angiogenesis to inhibit blood vessel formation in tumors.

  • Examples of drugs used: Avastin (a VEGF inhibitor), Thalidomide, and others.

  • Aim: Restore normal vascular structure, limit leakiness, and improve drug delivery to the tumor.

VEGF and Inflammation

  • VEGF not only promotes angiogenesis but also has roles in inflammation associated with tumors.

  • Interaction between tumor progression and inflammatory responses can exacerbate tumor growth.

Research on Angiogenesis

  • Studies often utilize animal models to explore tumor biology, angiogenesis, and treatment responses.

    • Conventionally use immune-deficient mice to assess tumor growth and treatment efficacy.

    • Patient-derived xenografts (PDX) are emerging tools for personalized treatment approaches.

Importance of Understanding Angiogenesis

  • Tumor angiogenesis is critical in cancer biology and therapy applications, emphasizing that effective cancer treatment must account for both the tumor characteristics and the surrounding microenvironment.


  • Topic: Tumor Angiogenesis

  • Key Objectives: Understand the various types of blood vessel cell types, distinguish between angiogenesis and vasculogenesis, recognize tumor blood vessel differences from normal blood vessels, comprehend the role of Vascular Endothelial Growth Factor (VEGF) in promoting angiogenesis, and explore the implications for cancer treatment, including anti-angiogenic therapies.

Cell Types in Blood Vessels

  • Blood vessels are complex structures that consist of multiple cell types, each performing critical roles.

    • Endothelial Cells: These cells form the innermost lining of blood vessels and are responsible for regulating the exchange of substances between blood and tissues. They control permeability and act as a barrier to potential toxins.

    • Pericytes: Located around capillary walls, pericytes provide structural support, regulate blood flow, and are involved in the angiogenic process, especially during vessel remodeling.

    • Basement Membrane: This extracellular matrix encases endothelial cells, providing mechanical support and influencing cell behavior, essential for vessel integrity and function.

Origins of Blood Vessel Formation

  1. Angiogenesis: The process of new blood vessel formation from pre-existing vessels, crucial for growth and repair in tissues.

    • Triggered by hypoxia, which indicates low oxygen levels, often found in rapidly growing tumors.

    • Types of angiogenesis include:

    • Sprouting Angiogenesis: In response to growth factors, new blood vessels sprout from existing ones. This occurs through endothelial cell proliferation and migration, driven by signals from hypoxic tissues.

    • Branching Angiogenesis: A single blood vessel branches off into two or more, facilitating enhanced blood supply to areas needing repair or growth.

  2. Vasculogenesis: The de novo formation of blood vessels from precursor cells called angioblasts, predominantly observed during embryonic development.

    • This process is guided by specific growth factors such as VEGF and fibroblast growth factor (FGF), essential for establishing the initial vascular network.

Tumor Angiogenesis

  • Tumor-associated blood vessels differ significantly from normal blood vessels:

    • Morphology: Tumor blood vessels exhibit a tortuous, chaotic structure characterized by increased permeability, leading to fluid leakage into the tumor microenvironment.

    • VEGF (Vascular Endothelial Growth Factor): A pivotal signaling protein that stimulates angiogenesis. Tumors often produce high levels of VEGF, exacerbating vessel abnormalities and promoting tumor progression.

Angiogenic Switch in Tumors

  • Tumors remain dormant until a sufficient blood supply is established, marking the "angiogenic switch."

  • Enhanced angiogenesis permits the delivery of necessary nutrients and oxygen, facilitating tumor growth and survival.

  • Prognosis: Increased levels of tumor angiogenesis correlate with poorer outcomes and prognosis in cancer patients, highlighting its role as a potential therapeutic target.

Factors Influencing Angiogenesis

  • Various factors govern the angiogenic process, including:

    • Growth Factors: Such as VEGF and FGF, which promote endothelial cell proliferation, migration, and survival.

    • Inhibitory Factors: Materials like thrombospondin and angiostatin that regulate and counterbalance the actions of growth factors, maintaining a homeostatic balance.

  • The dynamic interplay between factors that stimulate and inhibit angiogenesis is critical in deciding whether the angiogenic switch occurs.

Tumor Vessel Characteristics vs. Normal Vessels

  • Normal Vessels:

    • Exhibit an organized and stable structure with low permeability.

    • Maintain low interstitial pressure and uniform blood flow, which prevents abnormal fluid dynamics.

  • Tumor Vessels:

    • Display disorganization and excessive leakiness, often situated within hypoxic regions.

    • High interstitial pressure can facilitate cancer cell metastasis by allowing cells to enter the bloodstream more easily, complicating treatment efforts.

Chemotherapy and Anti-Angiogenic Strategies

  • Current cancer treatments focus on anti-angiogenic strategies to inhibit blood vessel formation within tumors, thus starving them of essential nutrients.

  • Notable drugs include Avastin (a VEGF inhibitor), Thalidomide, and others, designed to restore normal vascular architecture and enhance the effectiveness of traditional chemotherapy by improving drug delivery to tumors.

VEGF and Inflammation

  • Beyond angiogenesis, VEGF contributes to inflammatory processes in tumors, promoting an environment conducive to cancer progression.

  • The relationship between tumor development and inflammatory response underscores the complexity of cancer biology and the potential for targeting both pathways in treatments.

Research on Angiogenesis

  • Research in angiogenesis often employs animal models, particularly immune-deficient mice, to study tumor biology and therapeutic efficacy. These models allow the evaluation of tumor growth and response to treatments in a controlled environment.

  • Additionally, Patient-Derived Xenografts (PDX) have emerged as valuable tools for personalized medicine approaches, allowing for tailored therapeutic strategies based on individual tumor characteristics.

Importance of Understanding Angiogenesis

  • Understanding tumor angiogenesis is vital in the realm of cancer biology and therapeutic applications, emphasizing the necessity for treatments that consider both tumor behavior and the surrounding microenvironment for effective management of cancer.