Study guide: Classical Anticancer Agents Overview

Cancer Chemotherapy Revision Sheet

1. 📌 Essentials

• Classical anticancer agents target specific phases of the cell cycle, mainly S-phase.
• Main drug classes: antimetabolites, alkylating agents, cytotoxic antibiotics, plant alkaloids/microtubule inhibitors.
• Folate antagonists (e.g., methotrexate) inhibit DHFR, blocking purine and thymidylate synthesis.
• Alkylating agents form covalent DNA crosslinks, causing DNA damage and apoptosis.
• Resistance mechanisms include decreased drug uptake, increased DNA repair, and P-glycoprotein-mediated efflux.
• Tumor growth stages: A (dividing), B (resting but capable), C (non-dividing).
• Topoisomerases manage DNA supercoiling; targeted by specific antibiotics.
• Microtubule inhibitors arrest mitosis at metaphase.
• P-glycoprotein (P-gp) is a key efflux transporter mediating multidrug resistance.
• Chemotherapy's limited selectivity causes collateral damage to normal proliferating cells.

2. 🧩 Key Structures & Components

• Folate pathway — essential for nucleotide synthesis.
• DNA crosslinks — caused by alkylating agents.
• Topoisomerases I & II — enzymes managing DNA supercoiling.
• Microtubules — composed of tubulin, critical for mitosis.
• P-glycoprotein (P-gp) — efflux pump reducing intracellular drug levels.
• DNA — primary target for alkylating agents and antibiotics.
• Cell cycle phases — S-phase (DNA synthesis), M-phase (mitosis).

3. 🔬 Functions, Mechanisms & Relationships

• Antimetabolites inhibit nucleotide synthesis, arresting cells in S-phase.
• Alkylating agents form DNA crosslinks, preventing replication and transcription.
• Cytotoxic antibiotics intercalate DNA and inhibit topoisomerase II, causing DNA breaks.
• Microtubule inhibitors disrupt spindle formation, arresting cells at metaphase.
• Resistance mechanisms include reduced drug uptake, increased DNA repair, and efflux via P-gp.
• Topoisomerases relieve DNA supercoiling; inhibitors cause DNA strand breaks.
• P-gp actively exports drugs, decreasing intracellular concentrations, leading to multidrug resistance.

4. 📊 Comparative Table

5. 🗂️ Hierarchical Diagram (ASCII)

Cancer Chemotherapy
 ├─ Antimetabolites
 │    ├─ Folate antagonists (e.g., methotrexate)
 │    └─ Nucleic acid inhibitors (e.g., 5-FU)
 ├─ Alkylating Agents
 │    ├─ Nitrogen mustards
 │    ├─ Nitrosoureas
 │    └─ Platinum compounds
 ├─ Cytotoxic Antibiotics
 │    └─ Doxorubicin, daunorubicin
 └─ Microtubule Inhibitors
      ├─ Vinca alkaloids
      └─ Taxanes

6. ⚠️ High-Yield Pitfalls & Confusions

• Confusing methotrexate (DHFR inhibitor) with 5-FU (thymidylate synthase inhibitor).
• Mistaking alkylating agents for antibiotics; different mechanisms.
• Overlooking the role of P-gp in multidrug resistance.
• Assuming all DNA crosslinkers are equally effective; some cross the BBB (e.g., nitrosoureas).
• Confusing topoisomerase I (single-strand breaks) with topoisomerase II (double-strand breaks).
• Believing chemotherapy is highly selective; it affects proliferating normal cells too.
• Ignoring resistance mechanisms as a cause of treatment failure.

7. ✅ Final Exam Checklist

• Know the main classes of classical anticancer drugs and their mechanisms.
• Understand the cell cycle phases targeted by each drug class.
• Be able to describe how alkylating agents damage DNA.
• Recognize the role of topoisomerases and their inhibitors.
• Distinguish between microtubule inhibitors: Vinca alkaloids vs. taxanes.
• Comprehend the mechanisms of multidrug resistance, especially P-gp.
• Recall key drugs: methotrexate, 5-FU, cyclophosphamide, cisplatin, doxorubicin, vincristine, paclitaxel.
• Understand tumor growth stages and their implications for therapy.
• Be aware of common toxicities: cardiotoxicity (doxorubicin), nephrotoxicity (cisplatin), myelosuppression.
• Recognize the importance of combining chemotherapy with surgery or radiotherapy.
• Know the limitations of classical agents: lack of selectivity, resistance development.
• Understand DNA repair pathways involved in resistance.
• Be familiar with the blood-brain barrier crossing by nitrosoureas.
• Know the hierarchy of microtubule dynamics affected by inhibitors.
• Understand the hierarchical organization of drug targets and resistance mechanisms.

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