Diisopromine as a non-labelled CYP3A4 substrate: Implications for breath test development

Area of Science:

• Pharmacology
• Drug Metabolism
• Biochemistry

Background:

• Breath tests require specific substrates yielding volatile metabolites for predicting patient drug response.
• Tolterodine is a known CYP3A4 substrate producing a volatile metabolite, but diisopromine's structural differences may offer advantages.

Purpose of the Study:

• To evaluate diisopromine as a potential substrate for CYP assays.
• To compare diisopromine's biotransformation with tolterodine and assess its suitability for drug response prediction.

Main Methods:

• Utilized mass spectrometry (PTR-ToF-MS, LC-MS) to identify volatile and non-volatile metabolites.
• Employed a design of experiments to optimize reaction conditions for diisopromine metabolism.
• Investigated diisopromine specificity across different CYP isoforms (CYP3A4, CYP2D6, CYP2C9) using HepG2 cell clones.

Main Results:

• Diisopromine demonstrated 1.5 times higher N-dealkylation and 1.4 times higher acetone production than tolterodine.
• Metabolism of diisopromine was predominantly mediated by CYP3A4, with minor contributions from CYP2D6 and CYP2C9.
• Diisopromine exhibited significantly lower cellular toxicity (TC50 ~1000 μM) compared to tolterodine.

Conclusions:

• Diisopromine's structural modification enhances biotransformation efficiency and reduces toxicity.
• Its favorable metabolic profile supports its potential development for non-invasive CYP assays.
• This facilitates patient-specific drug response prediction.