Ficha de revisão: 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

Item	Key Features	Notes / Differences
Antimetabolites	Inhibit nucleotide synthesis; S-phase specific	e.g., methotrexate, 5-FU
Alkylating agents	Form DNA crosslinks; cause DNA damage	e.g., cyclophosphamide, cisplatin
Cytotoxic antibiotics	Intercalate DNA, inhibit topoisomerase II	e.g., doxorubicin
Microtubule inhibitors	Arrest mitosis by disrupting tubulin	Vinca alkaloids vs. taxanes
Resistance	Decreased drug uptake, increased repair, P-gp efflux	Major cause of therapy failure

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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