Core4: Molecular targets of drugs

🎯 High-yield / 要点：Drug targets are not only receptors. Main categories: receptors, enzymes, transporters, ion channels, nucleic acids, microbial targets, non-receptor effects, biologic/cell targets.

Main target classes / 主な標的

Target	Examples	High-yield point
Receptors	Intracellular receptors, ligand-gated channels, GPCRs, enzyme-linked receptors	Largest classic pharmacology category
Enzymes	COX, ACE, acetylcholinesterase, HMG-CoA reductase	Often inhibited by drugs
Transporters	SERT, NET, DAT, intestinal cholesterol transporter	Reuptake/absorption blockade changes concentration
Voltage-gated ion channels	Na⁺, K⁺, Ca²⁺ channels	Important in antiarrhythmics and neurologic drugs
Nucleic acids	DNA, RNA, siRNA	Common in anticancer/antiviral/targeted therapy
Microbial targets	Cell wall, protein synthesis, nucleic acid synthesis	Antibiotic targets
Non receptor-mediated	Bile acids, gastric acid, osmotic effects	Effect by binding/neutralizing/physical osmotic action
Others	Cytokines, CD20, tubulin	Biologics and cytotoxic drugs

Receptor subtypes / 受容体標的

• Intracellular receptors：thyroid hormone nuclear receptors; steroid cytoplasmic receptors.
• Ligand-gated ion channels：
  • Nicotinic ACh receptor: nicotine, choline esters, skeletal muscle relaxants.
  • GABA_A: benzodiazepines, barbiturates, propofol, some anticonvulsants.
  • 5-HT3: setrons; NMDA: ketamine; AMPA: topiramate; glycine: strychnine.
• GPCRs：
  • Gs：β-adrenergic, D1, glucagon, H₂, prostacyclin.
  • Gi：α₂, M₂, D₂, opioid, some serotonin receptors.
  • Gq：α₁, M₁/M₃/M₅, AT1, some serotonin receptors.
• Enzyme-linked receptors：tyrosine kinase receptors, TGF-β receptor, guanylate cyclase/ANP.

Remember / 覚え方

• Receptor–Enzyme–Transporter–Channel = core four.
• Antibiotics often target microbial cell wall/protein synthesis/nucleic acid synthesis.
• Antacids/osmotic laxatives work without classic receptors.