Platinum compounds

Mechanism of Action - Platinum Power Play

• Alkylating-like agents; are prodrugs activated by aquation (hydrolysis) in the low-chloride intracellular environment.
• Covalently bind the N7 position of guanine & adenine.
• Forms intrastrand (~90%) and interstrand DNA cross-links, distorting the DNA helix.
• Inhibits DNA synthesis & replication, triggering apoptosis.

⭐ Resistance emerges via ↑DNA repair, ↓drug uptake, or inactivation by glutathione.

The Platinum Trio - Cisplatin, Carboplatin, Oxaliplatin

• Mechanism of Action: Function as alkylating-like agents. They create intra-strand and inter-strand DNA cross-links, primarily at the N7 position of guanine, leading to inhibition of DNA synthesis and cell apoptosis.

📌 Mnemonic: Think of the toxicities:

• Cisplatin: Cranial nerve VIII (ototoxicity) & Chemoprotectant for kidneys (nephrotoxicity).
• Carboplatin: Affects Carb-loading cells in the bone marrow (myelosuppression).
• Oxaliplatin: An Ox in the cold gets numb nerves (cold-induced neuropathy).

Adverse Effects - The Price of Platinum

• Shared Toxicity: All platinum agents are myelosuppressive and can trigger hypersensitivity reactions, particularly after multiple cycles of therapy.

• Cisplatin:

  • ⚠️ Nephrotoxicity is the primary dose-limiting toxicity. Minimized with aggressive pre-hydration (chloride diuresis) and the cytoprotective agent amifostine.
  • Significant ototoxicity (tinnitus, high-frequency hearing loss) and peripheral sensory neuropathy.
  • 📌 Mnemonic: Cis-"plat-in" splats the kidneys and ears.

• Carboplatin:

  • Myelosuppression, particularly thrombocytopenia (↓ platelets), is the dose-limiting toxicity.
  • Dosing is calculated using the Calvert formula, which targets a specific AUC based on GFR.

• Oxaliplatin:

  • Neurotoxicity is dose-limiting, presenting in two forms:
    • Acute: Pharyngolaryngeal dysesthesia, often triggered by exposure to cold.
    • Chronic: Cumulative, dose-dependent "stocking-glove" sensory neuropathy.

⭐ Oxaliplatin's unique acute, cold-sensitive neuropathy is caused by its metabolites affecting voltage-gated sodium channel function.

Clinical Use & Resistance - Where They Shine

• Key Indications (Solid Tumors):
  • Cisplatin: Curative for testicular cancer; also used for bladder, ovary, and lung cancers.
  • Carboplatin: Ovarian cancer; an option when cisplatin's toxicity is a major concern.
  • Oxaliplatin: Colorectal cancer, notably as a component of the FOLFOX regimen.
• Primary Resistance Mechanisms:
  • Reduced intracellular accumulation (↓ CTR1 transporter influx, ↑ ATP7A/B efflux).
  • Increased inactivation by thiol-containing molecules like glutathione (GSH).
  • Enhanced DNA repair (↑ Nucleotide Excision Repair).

⭐ Acquired resistance to cisplatin does not always confer cross-resistance to other platinum agents; oxaliplatin may retain activity.

High‑Yield Points - ⚡ Biggest Takeaways

• Platinum compounds (cisplatin, carboplatin) form DNA cross-links at the N7 of guanine, inhibiting DNA synthesis.
• Key uses include solid tumors like testicular, ovarian, bladder, and lung cancers.
• Cisplatin’s major dose-limiting toxicities are nephrotoxicity and ototoxicity; co-administer amifostine for protection.
• Carboplatin causes significant myelosuppression, particularly thrombocytopenia.
• Oxaliplatin is associated with a unique cold-exacerbated peripheral neuropathy.
• Resistance can emerge from increased DNA repair or inactivation by glutathione.