Bleomycin

Bleomycin is a glycopeptide antibiotic antineoplastic agent derived from *Streptomyces verticillus*. **Key Clinical Uses:** * Adjunctive treatment for lymphomas, squamous cell carcinomas (SCC), teratomas, and nonfunctional thyroid tumors in dogs and cats. * **Electrochemotherapy (ECT):** Bleomycin is highly effective when combined with intralesional electropermeabilization, significantly increasing intracellular drug concentrations for localized tumors (e.g., feline nasal planum SCC, canine mast cell tumors). **Toxicity Profile:** Unlike many traditional chemotherapeutics, bleomycin is generally **sparing to the bone marrow**. However, it carries significant risks of **pulmonary fibrosis** and dermatologic toxicity. This unique toxicity profile occurs because the lungs and skin lack the enzyme *bleomycin hydrolase*, which normally inactivates the drug in other tissues.

กลไกการออกฤทธิ์: Bleomycin acts primarily by inducing **single- and double-strand DNA breaks**. * **Mechanism:** The drug possesses a DNA-binding domain and an iron-binding domain. It binds to DNA and chelates intracellular **Fe²⁺** (ferrous iron). * **Oxidative Cleavage:** The Bleomycin-Fe²⁺ complex reacts with oxygen to generate highly reactive oxygen species (ROS), such as superoxide and hydroxyl radicals → oxidative cleavage of the DNA phosphodiester backbone. * **Cell Cycle:** It is considered cell-cycle phase-specific, primarily arresting cells in the **G2 and M phases**. * **Resistance:** Mediated by decreased cellular uptake, increased DNA repair mechanisms, or increased cellular expression of **bleomycin hydrolase** (the enzyme responsible for its degradation).

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