Niclosamide Research Guide: Properties, Uses & Handling

Niclosamide is a salicylanilide-class anthelmintic compound with well-established antiparasitic activity and emerging research applications as a multi-pathway signaling inhibitor targeting Wnt, mTORC1, STAT3, and NF-κB pathways.

CAS Number

50-65-7

Molecular Formula

C₁₃H₈Cl₂N₂O₄

Molecular Weight

327.12 g/mol

Appearance

Yellow to light yellow crystalline powder

Solubility

Poorly soluble in water (<0.1 mg/mL); soluble in DMSO and ethanol

Recommended Storage

Store at room temperature (15–25 °C), protected from light and moisture

Background and Mechanism of Action

Niclosamide (CAS 50-65-7) is a halogenated salicylanilide that has been used clinically as an oral anthelmintic for decades, primarily against cestode (tapeworm) infections. Its primary antiparasitic mechanism involves uncoupling of mitochondrial oxidative phosphorylation in susceptible parasites, leading to disruption of ATP synthesis and parasite death.

Beyond its classical antiparasitic role, niclosamide has attracted substantial research interest as a pleiotropic small-molecule modulator. Published research suggests it can modulate multiple oncogenic and inflammatory signaling cascades, including Wnt/β-catenin, STAT3, mTORC1, and NF-κB pathways. These properties have prompted investigation in preclinical models of cancer, viral infection, and metabolic disease. Researchers should note that most such applications remain at the in vitro or early preclinical stage, and mechanistic details may vary by cell type and concentration.

Physicochemical Properties and Solubility

Niclosamide has a molecular formula of C₁₃H₈Cl₂N₂O₄ and a molecular weight of approximately 327.12 g/mol. It presents as a yellow to light yellow crystalline powder at room temperature. Its physicochemical profile is dominated by low aqueous solubility, which is a critical consideration for assay design.

• Water: Practically insoluble (reported <0.1 mg/mL at physiological pH); aqueous solubility increases under alkaline conditions.
• DMSO: Niclosamide is soluble in DMSO, typically at concentrations suitable for preparing concentrated stock solutions (e.g., ≥10 mM). Warm gently if precipitation occurs.
• Ethanol: Soluble; useful as an alternative vehicle when DMSO is incompatible with downstream assays.

When preparing working solutions, prepare a concentrated DMSO stock and dilute into aqueous buffer immediately before use. Keep the final DMSO concentration ≤0.1% v/v in cell-based assays to minimise solvent cytotoxicity, and include matched solvent controls in all experiments.

Storage, Stability, and Handling

Storage conditions: Store niclosamide at room temperature (15–25 °C) in a tightly sealed container, protected from light and moisture. Under these conditions the solid compound is expected to be stable for at least 2 years from the date of manufacture. Verify expiry date on the Certificate of Analysis (CoA) supplied with each lot.

Stock solution stability: DMSO stock solutions should be prepared under dry conditions to prevent water absorption and compound degradation. Aliquot stocks into single-use volumes to avoid repeated freeze-thaw cycles. Store DMSO stocks at −20 °C and use within the manufacturer's recommended timeframe. Confirm solution stability by LC-MS or HPLC if long-term storage is required.

Safety and handling: Niclosamide is intended for research use only and is not for human or veterinary therapeutic use. Wear appropriate personal protective equipment (PPE) including gloves, lab coat, and eye protection. Avoid inhalation of dust. Consult the Safety Data Sheet (SDS) for full hazard information before use. Dispose of waste according to applicable local regulations.

Research Applications and Experimental Considerations

Niclosamide has been investigated across a range of preclinical research areas. The following represent common applications for which researchers procure this reagent:

• Cancer biology: Used to study Wnt/β-catenin, STAT3, and mTORC1 signaling inhibition in cancer cell lines. Typically applied at low micromolar concentrations in vitro, though optimal concentrations must be determined empirically for each model system.
• Antiviral research: Explored as a broad-spectrum antiviral agent in cell-based infection models; mechanistic basis under active investigation.
• Metabolic research: Investigated as a modulator of mitochondrial function and energy metabolism.
• Autophagy studies: Reported to affect autophagic flux in certain cell models.

Key experimental considerations: Due to its low aqueous solubility and potential for non-specific cytotoxicity at higher concentrations, rigorous dose–response profiling and appropriate vehicle controls are essential. Always include cell viability assays alongside functional readouts to distinguish specific pharmacological effects from cytotoxicity. Cross-validate findings using orthogonal methods (e.g., genetic knockdown of the purported target) where feasible.

Frequently asked questions

What is the best solvent for preparing a niclosamide stock solution?

DMSO is the most commonly used solvent for niclosamide stock preparation, typically yielding clear solutions at concentrations of 10 mM or higher. Ethanol can be used as an alternative. Aqueous buffers alone are not suitable due to the compound's very low water solubility. Always dilute into the final aqueous medium immediately before use and include a solvent-only control in assays.

How should niclosamide be stored to maintain stability?

The solid compound should be stored at room temperature (15–25 °C) in a sealed container away from light and moisture. DMSO stock solutions should be aliquoted and stored at −20 °C to prevent degradation from repeated freeze-thaw cycles. Always check the lot-specific Certificate of Analysis for confirmed expiry information.

Is niclosamide suitable for in vivo studies, and what formulation challenges exist?

Niclosamide has been used in preclinical in vivo studies, but its poor aqueous solubility and low oral bioavailability present significant formulation challenges. Researchers have employed strategies such as nano-formulations, PEG-based vehicles, or cyclodextrin complexation to improve delivery. Any in vivo use requires careful formulation development and ethical approval; consult the relevant literature for formulation precedents specific to your model.

What controls should be included when using niclosamide in cell-based assays?

At minimum, include a vehicle control (matching DMSO or ethanol concentration), a positive control for the pathway or endpoint being measured, and a cell viability assay run in parallel. Because niclosamide can be cytotoxic at higher concentrations, dose–response experiments spanning a wide concentration range are strongly recommended to establish a window of specific pharmacological activity separate from non-specific toxicity.

References

1. Andrews P. Niclosamide as a drug for tapeworm infections. Acta Trop. 1979;36(2):125-131.
2. Chen W, et al. Identification of niclosamide as a new small-molecule inhibitor of the STAT3 signaling pathway. ACS Med Chem Lett. 2012;3(4):288-293.
3. Osada T, et al. Antihelminthic niclosamide inhibits Wnt/Frizzled1 signaling. Anticancer Res. 2011;31(6):2061-2065.
4. Arend RC, et al. Inhibition of Wnt/β-catenin pathway by niclosamide: a therapeutic target for ovarian cancer. Gynecol Oncol. 2014;134(1):112-120.

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