DNA Damage & Repair Cancer

Page 1: Introduction to DNA Damage and Cancer

Abstract

  • DNA damage is a crucial factor in cancer development and progression.

  • DNA lesions can cause mutations leading to genomic instability, which is a key contributor to cancer.

  • Understanding DNA repair pathways is essential for therapeutic interventions.

Introduction

  • DNA damage can alter nucleotide sequences and lead to dysfunctional proteins.

  • Sources of DNA damage can be endogenous (such as reactive oxygen species) or exogenous (like ionizing radiation).

  • DNA damaging agents can be classified into clastogens (which cause chromosomal breaks) and aneugens (which lead to aneuploidy).

  • Genotoxic agents disrupt covalent bonds in DNA, affecting replication and transcription integrity.

Page 2: Types of DNA Damage

Overview of DNA Lesions

  • DNA lesions affect a large number of cells, with estimates between 10,000 to 1,000,000 lesions per cell daily.

  • Ionizing radiation is a significant source of DNA damage, causing direct and indirect effects.

  • Reactive oxygen species also play a role in initiating DNA damage.

Severity of DNA Damage

  • Double strand breaks (DSBs) are the most severe and can cause mutations or cell death if not repaired properly.

  • The type and complexity of DNA damage vary with radiation doses.

Page 3: DNA Damage Response (DDR)

Mechanisms of DDR

  • DNA repair pathways are encoded by proteins that detect and correct DNA alterations.

  • The presence of DNA damage activates a response involving signal transducers and effector proteins.

  • Checkpoints are critical in determining whether to repair damage or trigger apoptosis.

Page 4: DNA Repair Proteins and Checkpoints

Role of DDR Proteins

  • Proteins such as ATM and ATR are key regulators of DDR and maintain genomic stability.

  • Components like CHK1 and CHK2 work alongside ATM/ATR to inhibit DNA repair.

  • Checkpoints in the progression of the cell cycle ensure repair processes complete before further cell division.

Page 5: Cancer Treatment Strategies

Cancer Therapies and DNA Damage

  • Radiotherapy and chemotherapy are designed to induce DNA damage in cancer cells.

  • Resistance to treatment may arise from defects in DDR mechanisms.

  • Inhibitors targeting DDR pathways show promise in increasing the effectiveness of traditional therapies.

Page 6: DNA Repair Mechanisms

Overview of DNA Repair Pathways

  • Different mechanisms exist for repairing various types of DNA damage, including direct repair, base excision repair, nucleotide excision repair, mismatch repair, and others.

  • Each repair pathway is specialized for specific types of lesions and involves various enzymes.

Page 7: Direct Repair Mechanism

Direct Repair Overview

  • Direct repair involves specific enzymes that reverse chemical damage without the need for a template.

  • Key enzymes include O6-methylguanine-DNA methyltransferase (MGMT) and ALKBH dioxygenases.

Page 8: Base Excision Repair (BER)

Function of BER

  • Base excision repair corrects small, non-helix-distorting base lesions through two pathways (short and long patch).

  • Key proteins in BER include DNA glycosylases, AP endonuclease, DNA polymerase, and ligase.

Page 9: Nucleotide Excision Repair (NER)

NER Processes

  • NER repairs bulky DNA lesions caused by environmental factors like UV light and chemical mutagens.

  • NER is divided into global genomic NER and transcription-coupled NER, each focusing on distinct aspects of DNA.

Page 10: Mismatch Repair (MMR)

Importance of MMR

  • MMR corrects errors made during DNA replication and prevents permanent mutations.

  • Defects in MMR are linked to various cancers due to increased mutation rates.

Page 11: Double Strand Break Repair Mechanisms

NHEJ and HR

  • Non-Homologous End Joining (NHEJ) and Homologous Recombination Repair (HR) are crucial for resolving double strand breaks.

  • NHEJ directly ligates broken ends, while HR requires a homologous template.

Page 12: Mechanisms of NHEJ and HR

Differences in NHEJ and HR

  • NHEJ operates throughout the cell cycle and is especially important in response to ionizing radiation.

  • HR provides an accurate repair option for DSBs, mainly functioning in the S and G2 phases.

Page 13: Role of Cell Cycle in DNA Repair

Checkpoints in the Cell Cycle

  • Checkpoints in the G1/S and G2/M phases regulate cell cycle progression and prevent the division of damaged cells.

Page 14: Chemotherapy and Radiation Effects

Mechanisms of Cancer Treatment

  • Chemotherapy and radiotherapy aim to induce DNA damage in cancerous cells, facilitating cell apoptosis.

  • Both treatment modalities can lead to long-term effects and toxicities on normal cells.

Page 15: Potential Biomarkers

Role of Micronuclei and Other Biomarkers

  • Micronuclei and other nuclear anomalies serve as indicators of DNA damage and chromosomal instability.

Page 16: Clonal Evolution in Cancer

Understanding Clonal Evolution

  • Clonal evolution contributes to tumor heterogeneity and treatment resistance through the accumulation of mutations.

Page 17: Concluding Remarks

Significance of DNA Damage in Cancer

  • Understanding DNA damage and repair pathways is vital for cancer diagnosis, therapy, and monitoring response to treatments.

Detailed Notes on DNA Damage and Cancer

DNA Damage and Cancer

  • Abstract: DNA damage is a critical factor in cancer development. It causes mutations and genomic instability.

  • Sources of Damage: Can be endogenous (e.g., reactive oxygen species) or exogenous (e.g., ionizing radiation).

  • Types of Damage: Clastogens cause chromosomal breaks; aneugens lead to aneuploidy.

DNA Damage Overview

  • Prevalence: Each cell can experience 10,000 to 1,000,000 DNA lesions daily.

  • Major Factors: Ionizing radiation and reactive oxygen species.

  • Severity: Double strand breaks (DSBs) are the most serious, risking mutations or cell death.

DNA Damage Response (DDR)

  • Mechanisms: Involves proteins that detect and correct DNA damage, activated responses, and checkpoints to ensure repair or trigger apoptosis.

Key Repair Proteins and Checkpoints

  • Roles: ATM, ATR, CHK1, and CHK2 regulate DDR, maintaining genomic stability, and inhibiting further cell division until repair is complete.

Cancer Treatment Strategies

  • Therapies: Radiotherapy and chemotherapy are designed to intentionally induce DNA damage in cancer cells.

  • Resistance: Can arise from defects in DDR.

  • Innovations: Inhibitors targeting DDR pathways enhance traditional treatment efficacy.

DNA Repair Mechanisms

  • Repair Pathways: Includes direct repair, base excision repair (BER), nucleotide excision repair (NER), and mismatch repair (MMR).

  • Direct Repair: Enzymes like MGMT reverse chemical damage directly.

  • BER: Repairs small base lesions through short and long patch pathways.

  • NER: Targets bulky lesions caused by environmental agents.

  • MMR: Fixes replication errors, preventing mutations.

  • Double Strand Break Repair: Non-Homologous End Joining (NHEJ) and Homologous Recombination (HR) provide mechanisms for DSB resolution.

Role of Cell Cycle in Repair

  • Checkpoints: G1/S and G2/M checkpoints prevent division of cells with DNA damage.

Treatment Mechanisms

  • Chemotherapy & Radiotherapy: Aim to cause DNA damage, promoting apoptosis while potentially affecting normal cells.

Biomarkers

  • Micronuclei & Anomalies: Serve as indicators of DNA damage and chromosomal instability related to cancer.

Clonal Evolution in Cancer

  • Significance: Clonal evolution contributes to tumor heterogeneity and treatment resistance via mutation accumulation.

Conclusion

  • Understanding DNA damage and repair mechanisms is crucial for advancing cancer diagnosis and therapy.