Breast Cancer and the ROS Story Study Notes

Definition: Breast cancer is a malignant neoplasm that arises from epithelial cells located in the breast ducts or lobules.
Characteristics:
- Uncontrolled cellular proliferation.
- Ability to invade surrounding tissues.
- Potential to metastasize to distant organs.
Prevalence: It is recognized as one of the most common cancers affecting women globally.

Breast cancer develops when the normal regulatory mechanisms of three systems become disrupted:
- Cell cycle control: The system that regulates cell division.
- DNA repair: Mechanisms that fix damaged DNA.
- Apoptosis: The programmed cell death pathway.
Disruption of these systems leads to several outcomes:
- Accumulation of mutations.
- Genomic instability.
- Progressive transformation of breast epithelial cells into cancerous cells.

Non-modifiable Risk Factors:
- Age: Risk increases with age.
- Female sex: Women are at higher risk than men.
- Genetic mutations: Specific mutations such as BRCA1 and BRCA2 (commonly referred to as Breast Cancer Gene 1 and Breast Cancer Gene 2).
Modifiable Risk Factors:
- Obesity: Excess body fat can increase risks.
- Alcohol consumption: Linked to breast cancer.
- Radiation exposure: Increased risk due to prior radiation treatment.
- Hormonal influences: Hormonal changes can augment risk.
Connection: Many risk factors are associated with increased oxidative stress, which links them to free radical damage.

Definition: Free radicals are atoms or molecules that contain unpaired electrons, making them highly reactive.
Major Biological Free Radicals: They primarily belong to the category of Reactive Oxygen Species (ROS), which include:
- Superoxide anion ($O_2^-$)
- Hydrogen peroxide ($H2O2$)
- Hydroxyl radical ($OH^-$)
Production: Most free radicals are produced in mitochondria during cellular respiration.

Definition: Oxidative stress occurs when the production of reactive oxygen species (ROS) exceeds the antioxidant defenses of the cell.
Consequences: This leads to damage in several key biological components:
- Deoxyribonucleic Acids (DNA)
- Proteins
- Lipids
Significance: Chronic oxidative stress is a significant molecular contributor to the process of carcinogenesis.

Mechanisms of Damage: Reactive oxygen species (ROS) cause:
- Oxidative DNA base damage, e.g., formation of 8-oxo-deoxyguanosine.
- Single-strand and double-strand DNA breaks.
- Mutations in tumor suppressor genes such as p53.
- Impairment of DNA repair mechanisms, particularly in genes like BRCA1 and BRCA2.
Outcome: These genetic alterations and damages initiate the process of malignant transformation.

Process: ROS attack polyunsaturated fatty acids (PUFAs) within cell membranes, resulting in the formation of by-products:
- Malondialdehyde (MDA)
- 4-Hydroxynonenal (4-HNE)
Consequences of By-products:
- Formation of DNA adducts, which can alter DNA structure and function.
- Promotion of mutagenesis, which can initiate tumorigenesis.
- Alterations of cellular signaling pathways affecting cell behavior.

Impact of ROS: Reactive oxygen species (ROS) oxidize regulatory proteins, leading to the activation of different signaling pathways that promote cancer progression:
- Mitogen-Activated Protein Kinase (MAPK) pathway: Involved in cell proliferation.
- Phosphoinositide 3-Kinase / Protein Kinase B (PI3K/Akt) pathway: Contributes to cell survival mechanisms.
- Nuclear Factor kappa B (NF-kB) pathway: Plays a crucial role in inflammation and prevention of apoptosis.

Mechanisms of Spread: Reactive Oxygen Species (ROS) contribute to tumor spread in several ways:
- Angiogenesis: By stabilizing Hypoxia-Inducible Factor-1 alpha (HIF-1), promoting the production of Vascular Endothelial Growth Factor (VEGF).
- Activation of Matrix Metalloproteinases (MMPs): Leads to the degradation of the extracellular matrix, facilitating metastasis.
- Enhanced invasion and metastasis: Increases the ability of cancer cells to invade surrounding tissues and organs.

Consequences of ROS Damage: Reactive oxygen species (ROS) can damage mitochondrial DNA and components of the electron transport chain, leading to:
- Increased production of ROS.
- Metabolic reprogramming of cancer cells.
- Resistance to apoptosis (programmed cell death).
Result: A self-perpetuating oxidative cycle develops, worsening cancer progression.

Moderate ROS Levels: Can support tumor growth and facilitate signaling pathways that promote cancer survival.
Excess ROS Levels: Trigger mitochondrial permeability and induce apoptosis, which can eliminate cancer cells.
Balance: Cancer cells often maintain a balance near the threshold of oxidative stress, which sustains both growth and survival mechanisms.

Mechanisms: Cells counteract ROS through various antioxidant systems, including:
- Superoxide Dismutase (SOD): Enzyme that converts superoxides (O2-) into less harmful hydrogen peroxide (H2O2).
- Catalase: A peroxisomal enzyme that rapidly converts hydrogen peroxide (H2O2) into water (H2O) and oxygen (O2) to protect cells from oxidative damage.
- Glutathione Peroxidase (GPx): Catalyzes the conversion of hydrogen peroxide (H2O2) to water (H2O) using reduced glutathione.
- Reduced Glutathione (GSH): A key antioxidant that aids in preventing DNA mutations and cellular damage.

Types of Antioxidants:
- Vitamin C (Ascorbic acid)
- Vitamin E (Tocopherol)
- Polyphenols (bioactive compounds found in plants)
- Diets rich in trace elements: Copper (Cu), Zinc (Zn), Manganese (Mn), and Selenium (Se).
Function: These dietary antioxidants can scavenge ROS and may help reduce cancer risk.
Caution: Excessive use of antioxidants during chemotherapy may reduce treatment efficacy.

Role of Free Radicals in Breast Cancer:
- Initiation of mutations within cellular DNA.
- Activation of oncogenic signaling pathways that drive cancer progression.
- Promotion of angiogenesis and metastasis, enhancing the spread of cancer.
Final Thoughts: Breast cancer involves a redox imbalance, where the controlled ROS signaling shifts into pathological oxidative stress, facilitating cancer development.