Drug Repurposing

Overview

Drug repurposing (also called drug repositioning) is the strategy of identifying new therapeutic uses for existing approved drugs. It dramatically accelerates the path from bench to bedside because safety, pharmacokinetics, and manufacturing are already established. In the WikiBiome context, drug repurposing is particularly powerful because many existing drugs have unrecognized microbiome effects or metal-modulating properties that map to disease signatures in ways their original developers never intended.

The convergence of pharmacomicrobiomics and metallomics creates a rich landscape for repurposing: a drug developed for one purpose may happen to restrict a critical metal cofactor, reshape the gut microbiome toward a healthier configuration, or disable a metal-dependent virulence factor in a pathogenic organism.

Paradigm Examples

Metformin: Diabetes Drug as Microbiome Modulator

metformin is the clearest example of a drug whose therapeutic effects are partly microbiome-mediated:

  • Originally developed as an antidiabetic agent
  • Increases akkermansia muciniphila abundance and short chain fatty acids production
  • Improves gut barrier function and reduces endotoxemia
  • Reduces vitamin B12 (cobalamin) absorption — a metallomics interaction (cobalt-containing vitamin)
  • Now being explored for cancer prevention, cardiovascular protection, and aging — all conditions with microbiome components

Disulfiram: Alcohol Deterrent as Metal Chelator and Antimicrobial

Disulfiram (Antabuse) exemplifies multi-target repurposing:

  • Original use: Alcohol deterrent (blocks aldehyde dehydrogenase)
  • Metal chelation: Active metabolite DDC chelates nickel (specific antidote for nickel carbonyl poisoning) and copper
  • Anticancer: Copper-DDC complex inhibits proteasome and NF-kB; being explored in pancreatic and breast cancer
  • Anti-parasitic: Activity against Giardia, Leishmania, Trypanosoma
  • Biofilm disruption: Disrupts candida albicans biofilms — connecting to inter kingdom metal shielding

Statins: Cholesterol Drugs as Microbiome and Immune Modulators

See statins for detailed treatment. Statins modulate bile acid metabolism, influence gut microbial composition, and have anti-inflammatory effects independent of cholesterol lowering.

Microbiome-Mediated Repurposing Opportunities

Antifungals in Bacterial Disease

Antifungal drugs that disrupt fungal-bacterial cooperation in biofilms:

  • Fluconazole disrupts candida albicans biofilm scaffolds that protect bacterial pathogens
  • Amphotericin B disrupts ergosterol in fungal membranes, collapsing inter kingdom metal shielding
  • These have implications for conditions where fungal-bacterial biofilms drive disease (IBD, CRC)

NSAIDs and Aspirin

  • Low-dose aspirin reduces CRC risk, partly through COX-2 inhibition and partly through microbiome modulation
  • NSAIDs alter gut microbial composition and increase intestinal permeability — a double-edged effect

Antidepressants

  • SSRIs (fluoxetine) have direct antimicrobial activity against gut bacteria
  • Tricyclics alter gut motility and microbiome composition
  • These microbiome effects may contribute to both therapeutic and adverse effects in neuropsychiatric conditions

Metal-Targeting Repurposing

Iron-Targeting Strategies

  • Deferasirox: Iron chelator being explored for antimicrobial activity by starving pathogens of iron (see metal chelation therapy)
  • Gallium compounds: Gallium mimics iron and is taken up by siderophore systems, poisoning iron-dependent enzymes (gallium)
  • Lactoferrin: Natural iron-binding protein with both antimicrobial and immune-modulatory effects

Zinc-Targeting Strategies

  • EDTA-based compounds: Zinc chelation to disable zinc metalloprotease virulence factors
  • Zinc ionophores: Compounds that deliver zinc into cells, enhancing intracellular antimicrobial defense

Nickel-Targeting Strategies

The Repurposing Pipeline in WikiBiome

Drug repurposing candidates in the WikiBiome framework are identified through a systematic process:

  1. Signature analysis: Identify the metal-dependent virulence factors driving a disease signature
  2. Metal restriction screen: Which existing drugs chelate, sequester, or compete with the required metal?
  3. Microbiome effect screen: Which existing drugs shift the microbiome toward the depleted-taxon profile needed for ecological restoration?
  4. Triangle validation: Does the drug have evidence for all three edges (I→f, I→D, f→D)?
  5. Safety assessment: Since the drug is already approved, human safety data exists

Challenges

  • Regulatory: Repurposed drugs often lack patent protection, reducing commercial incentive for clinical trials
  • Dosing: Optimal dose for microbiome modulation may differ from the approved indication
  • Off-target effects: Microbiome disruption by repurposed drugs may cause unexpected adverse effects
  • Individual variation: Microbiome-mediated drug effects vary 100-fold between individuals maddu 2025 microbiome drug interactions pharmacokinetic review

Open Questions

  • Can computational screening of drug-metal interactions identify repurposing candidates systematically?
  • Do drug-microbiome interactions explain why clinical trials for repurposed drugs sometimes fail (wrong patient microbiome)?
  • Which metal-chelating drugs have the best therapeutic index for antimicrobial metal restriction?
  • Can combination strategies (metal chelator + probiotic) achieve synergistic effects?

Cross-References

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