Mechanism of Action
Membrane and Intracellular Targets
Unlike most AMPs, indolicidin does not strictly lyse bacterial membranes. Instead, it permeabilizes membranes at low concentrations and translocates intracellularly, where it inhibits DNA synthesis by binding DNA. At higher concentrations membrane disruption dominates. This dual mechanism contributes to bacteriostatic activity at lower concentrations and bactericidal activity at higher concentrations.
HIV Integrase Inhibition
Indolicidin inhibits HIV-1 integrase in vitro with IC50 values in the low micromolar range. The mechanism involves binding to the active site metal cofactor and blocking strand transfer reactions. Tryptophan residues are critical for integrase binding, and removal of tryptophan residues abolishes antiviral activity while preserving some antimicrobial effects.
Research Summary
MX-594AN Phase II for Acne
Phase II (Completed)MX-594AN, a modified indolicidin analog formulated as a topical gel, completed Phase II trials for acne vulgaris. Results showed meaningful reduction in inflammatory lesion counts. Development was discontinued by NovaBay Pharmaceuticals due to strategic priorities rather than safety concerns, leaving an opportunity for further clinical development of this class.
Antifungal Properties
PreclinicalIndolicidin shows antifungal activity against Candida species and Cryptococcus neoformans. Combined with antimicrobial activity, this broad-spectrum profile has generated interest for topical use in mixed infections. Structural optimization to reduce mammalian cell cytotoxicity while maintaining antifungal potency is an active research area.
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Research Protocols
| Goal | Dose | Frequency | Route |
|---|---|---|---|
| Antimicrobial (in vitro) | 2-16 ug/mL MIC | Single exposure | Direct application |
| Topical acne | 0.5-2% gel (clinical) | Twice daily | Topical |
MX-594AN clinical dosing from Phase II trial protocol. No approved formulation available.
Interactions
Safety Profile
Hemolytic activity and cytotoxicity to mammalian cells at concentrations close to MIC values is a limitation. The therapeutic window for topical use is broader than for systemic use. MX-594AN showed acceptable local tolerability in Phase II. No systemic human dosing data.
References
- [1]Selsted ME, et al. (1992). Indolicidin, a novel bactericidal tridecapeptide amide from neutrophils. J Biol Chem, 267(7), 4292-4295.
- [2]Rozek A, et al. (2000). The antibiotic and anticancer activity of indolicidin. Biopolymers, 55(1), 74-82.