DNA Intercalation and New Targets in Cancer Therapy

Targeting DNA Topoisomerases in Cancer Chemotherapy

• Topoisomerase II (TOP2) is targeted by several anticancer drugs.

• Mechanism of action:

  • Drugs trap the covalent TOP2-DNA complex, leading to DNA strand breaks.

  • Inhibiting repair pathways enhances drug efficacy.

• Examples of TOP2 inhibitors:

  • Doxorubicin – intercalates DNA and inhibits TOP2, leading to double-strand breaks.

  • Mitoxantrone – similar mechanism but lower cardiotoxicity.

• Side effects and challenges:

  • Cardiotoxicity limits anthracycline use.

  • Drug-induced DNA translocations can lead to secondary malignancies.

  • Resistance develops through enhanced DNA repair.

DNA Intercalation and Its Role in Cancer Therapy

• Intercalators are small molecules that insert between DNA base pairs, disrupting transcription and replication.

• Examples of intercalators:

  • Doxorubicin – intercalates and stabilizes TOP2-DNA cleavage complex.

  • Mitoxantrone – intercalates DNA, inhibits replication.

  • Aclarubicin – disrupts DNA structure and function.

• Pluramycin Mechanism:

  • Binds to TATA-binding protein (TBP), immobilizing it on DNA.

  • Alkylation is enhanced when TBP binds to the TATA box, disrupting transcription.

DNA Recognition and Targeting

• G-quadruplexes in gene promoters are promising targets for cancer therapy.

• Compounds that interact with G-quadruplexes:

  • Perylene derivatives – stabilize G-quadruplexes, preventing DNA replication.

  • Cationic porphyrins – sequester G-quadruplexes, interfering with transcription.

• Potential therapeutic strategies:

  • Inhibiting helicases that unwind G-quadruplexes.

  • Enhancing formation of G-quadruplex structures to block oncogene transcription.

Telomerase as a Target for Cancer Therapy

• Telomerase function:

  • Adds repetitive DNA sequences (TTAGGG) to telomeres, maintaining chromosome integrity.

  • Overexpressed in 90% of cancers, making it a therapeutic target.

• G-quadruplex stabilizers as telomerase inhibitors:

  • Telomestatin – stabilizes telomeric G-quadruplexes, preventing elongation.

  • TMPyP4 – disrupts telomerase activity by inducing quadruplex formation.

• Challenges:

  • Targeting telomerase without affecting normal stem cells.

  • Resistance due to alternative lengthening of telomeres (ALT) pathways.

Summary – DNA Repair and Chemotherapy Resistance

• DNA repair mechanisms counteract chemotherapy-induced damage.

• Common DNA repair pathways:

  • Base excision repair (BER) – fixes single-strand breaks.

  • Nucleotide excision repair (NER) – removes bulky DNA adducts.

  • Homologous recombination (HR) and non-homologous end joining (NHEJ) – repair double-strand breaks.

• Clinical Implications:

  • Resistance develops when cancer cells upregulate DNA repair pathways.

  • Combining DNA-damaging agents with repair inhibitors enhances efficacy.

  • Example: PARP inhibitors for BRCA-mutant cancers.

Drug Table

Key Takeaways

• DNA intercalation is a major strategy for disrupting cancer cell replication.

• TOP2 inhibitors like doxorubicin trap cleavage complexes, leading to DNA breaks.

• G-quadruplex stabilizers target telomerase, preventing chromosome elongation.

• DNA repair inhibitors can enhance the effectiveness of chemotherapy.

• Combination therapy is crucial to overcoming resistance mechanisms in cancer.

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