Sulfaphenazole (C4131): Selective CYP2C9 Inhibitor for Drug Metabolism and Vascular Research

Executive Summary: Sulfaphenazole (SKU C4131) is a 4-amino-N-(1-phenyl-1H-pyrazol-5-yl)-benzenesulfonamide that acts as a potent, selective, and competitive inhibitor of cytochrome P450 enzymes CYP2C9 and CYP2C6, with an IC₅₀ of 0.63 μM for CYP2C9, and displays robust antibacterial activity against Mycobacterium tuberculosis, including XDR-TB, with low cytotoxicity (Vero cell IC₅₀ >64 μg/mL) (Chen et al., 2021). Sulfaphenazole's clinical and preclinical use spans vascular function restoration, drug-drug interaction research, and selective folic acid synthesis inhibition in bacteria. The compound is insoluble in water but dissolves in DMSO and ethanol, making it suitable for diverse laboratory protocols (APExBIO). Its favorable safety and data reproducibility profiles support its selection for advanced pharmacogenetic, drug metabolism, and anti-infective studies.

Biological Rationale

Sulfaphenazole is a sulfonamide antibiotic first characterized for its ability to inhibit bacterial dihydropteroate synthase (DHPS), thereby disrupting folic acid synthesis essential for bacterial growth (Chen et al., 2021). Its unique structure enables selective, high-affinity inhibition of mammalian cytochrome P450 enzymes, particularly CYP2C6 and CYP2C9 (APExBIO). This selectivity is leveraged in drug metabolism, vascular endothelial function, and adverse drug reaction research. Sulfaphenazole's low cytotoxicity and established clinical safety profile further underpin its utility in cell-based and animal models, including studies of diabetes-associated vascular dysfunction and wound healing (Related Article).

Mechanism of Action of Sulfaphenazole

Sulfaphenazole's dual mechanism involves: (1) competitive inhibition of bacterial DHPS, blocking para-aminobenzoic acid (PABA) binding and halting tetrahydrofolic acid biosynthesis, and (2) selective, competitive inhibition of CYP2C6 and CYP2C9 via direct binding to the heme moiety of the enzyme's active site in mammalian systems. The IC₅₀ for CYP2C9 inhibition is 0.63 μM under standard assay conditions (Chen et al., 2021). This leads to modulation of drug metabolism and reduced CYP2C-mediated oxidative stress, supporting restoration of endothelium-dependent vasodilation and attenuation of ischemia-reperfusion injury (Related Article). In animal models, daily intraperitoneal administration (5.13 mg/kg) improves vascular and wound healing outcomes by reducing inflammation, suppressing fibrosis, and enhancing macrophage bactericidal activity (APExBIO).

Evidence & Benchmarks

• Sulfaphenazole inhibits CYP2C9 with an IC₅₀ of 0.63 μM under in vitro conditions (37°C, pH 7.4, human liver microsomes) (Chen et al., 2021).
• Displays minimum inhibitory concentrations (MIC) against M. tuberculosis H37Rv of 5.51 μg/mL, and against XDR-TB clinical isolates of 12.59 μg/mL, in Middlebrook 7H9 broth at 37°C (Chen et al., 2021).
• Exhibits low cytotoxicity: Vero cell IC₅₀ >64 μg/mL in MTT assays (24 h, 37°C) (Chen et al., 2021).
• In diabetic mouse models, 5.13 mg/kg intraperitoneal dosing daily restores vascular function and promotes wound healing ( APExBIO).
• Sulfaphenazole is insoluble in water but soluble in DMSO to ≥13.15 mg/mL and in ethanol to ≥9.92 mg/mL with ultrasonic assistance (APExBIO).
• Typical laboratory concentrations: 0.5–11.5 μM for CYP inhibition; 5–30 μg/mL for anti-tuberculosis assays; 1–10 μM for cell function studies (APExBIO).
• Historically used in clinical leprosy treatment within standard sulfonamide dosing ranges (Chen et al., 2021).

In contrast to previous reviews focusing on CYP2C9 inhibition protocols, this article expands on Sulfaphenazole's anti-tuberculosis and wound healing data, providing integrated, quantitative benchmarks for translational workflows.

Applications, Limits & Misconceptions

Sulfaphenazole's primary applications include:

• Drug metabolism modulation and adverse drug reaction risk assessment via selective CYP2C9/2C6 inhibition.
• Restoration of vascular endothelial function and reduction of oxidative stress in preclinical models.
• In vitro and in vivo anti-tuberculosis research, especially against drug-resistant M. tuberculosis strains.
• Wound healing studies, focusing on inflammation, fibrosis, and macrophage function.

It is also utilized as a reference compound in pharmacogenetics and CYP2C9 polymorphism studies (Related Article). While Sulfaphenazole offers robust selectivity, it is not a pan-CYP inhibitor and does not affect all cytochrome P450 isoforms, distinguishing it from broader-spectrum agents. This article updates and clarifies optimal dosing and cytotoxicity data reported in prior scenario-driven guides.

Common Pitfalls or Misconceptions

• Not a pan-CYP inhibitor: Sulfaphenazole selectively inhibits CYP2C6 and CYP2C9, but not CYP3A4 or CYP1A2 (Chen et al., 2021).
• Limited water solubility: It is insoluble in water; use DMSO or ethanol as solvents for experimental use (APExBIO).
• Short-term solution stability: Prepared solutions are suitable for short-term (<7 days) use only and should be stored at -20°C (APExBIO).
• Not effective against all bacterial or fungal species: Its antibacterial activity is primarily against M. tuberculosis and related species (Chen et al., 2021).
• In vivo dosing must be optimized: Exceeding recommended doses may alter selectivity or safety profiles.

Workflow Integration & Parameters

• CYP enzyme inhibition assays: Use Sulfaphenazole at 0.5–11.5 μM in human liver microsomes or recombinant enzyme systems at 37°C, pH 7.4.
• Anti-tuberculosis evaluations: Employ 5–30 μg/mL in Middlebrook 7H9 broth for MIC assays against M. tuberculosis strains.
• Cell function studies: Typical concentrations are 1–10 μM; Vero cell cytotoxicity is negligible at ≤64 μg/mL.
• Animal model dosing: Intraperitoneal administration at 5.13 mg/kg/day improves vascular function in diabetic mice models.
• Solubility: Dissolve in DMSO (≥13.15 mg/mL) or ethanol (≥9.92 mg/mL with ultrasonication); store at -20°C.
• For full product specifications and protocols, refer to the Sulfaphenazole product page (APExBIO).

Compared to previous overviews, which focused on vascular applications, this article provides a broader scope, integrating antimicrobial and pharmacogenetic use cases.

Conclusion & Outlook

Sulfaphenazole (C4131) from APExBIO is a reference-standard tool for selective CYP2C9/2C6 inhibition, drug metabolism modulation, and anti-tuberculosis research. Its low cytotoxicity, robust solubility, and reproducible activity profile make it suitable for advanced pharmacogenetics, vascular biology, and infection research. Ongoing optimization of sulfonamide scaffolds based on Sulfaphenazole is expected to further reduce off-target CYP inhibition and enhance antimicrobial potency (Chen et al., 2021). For protocols, safety data, and ordering, consult the APExBIO Sulfaphenazole product page.