The primary targets of acetarsone are sulfhydryl (thiol)-containing enzymes and proteins within parasitic cells. By binding to these thiol groups, acetarsone forms stable As-S bonds, irreversibly inhibiting their biological functions. Among the key enzymes inhibited is pyruvate dehydrogenase, a critical component of the cellular energy metabolism pathway (tricarboxylic acid cycle). Additionally, the arsenic moiety of acetarsone can induce oxidative stress within parasitic cells, further damaging DNA, lipids, and proteins.

Acetarsone exhibits inhibitory activity against various protozoa and microorganisms in vitro. Studies have shown that this compound effectively inhibits protozoal growth. In cell-based assays, acetarsone (10 μM) induces S-phase cell cycle arrest in Caco-2 cells, indicating an effect on cell proliferation. Following a 24-hour treatment with 50 μM acetarsone, the permeability in Caco-2 cells is approximately 5.8%. Furthermore, the compound can stimulate cell proliferation at micromolar (μM) concentrations.

In pig folliculitis, acetasitol (20 mg/kg; po; once daily for 4 days) has anti-infectious action [1].

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In animal experiments, acetarsone demonstrates clear in vivo anti-infective activity. In one study, 2-month-old piglets infected with E. coli were administered acetarsone orally at 20 mg/kg once daily for 4 days; results showed that 65% of piglets achieved clinical recovery, and no diarrhea was observed in any of the animals by the end of treatment. Early studies also demonstrated that acetarsone has therapeutic effects in a rabbit model of experimental syphilis, with subcutaneous injection of 0.1–0.2 g/kg body weight producing curative effects. Additionally, oral acetarsone has been investigated for potential use in proctitis research.

In enzyme inhibition studies of acetarsone, a typical protocol for assessing its inhibitory effect on PHPT1 (14 kDa phosphohistidine phosphatase) is as follows: Acetarsone is incubated with PHPT1 (origin unknown) for 30 minutes, after which DiFMUP is added as a fluorogenic substrate. Fluorescence signals are measured every 60 seconds, and IC50 values are calculated. Under this experimental system, the IC50 of acetarsone for PHPT1 is 1.00×10⁵ nM (i.e., 100 μM). In an inhibition assay of the human bile salt export pump (BSEP, an ABC transporter protein), the IC50 of acetarsone is 1.00×10⁶ nM (i.e., 1000 μM).

In vitro cell-based assays for acetarsone typically use human intestinal epithelial Caco-2 cells as a model system. A typical protocol is as follows: Caco-2 cells are seeded onto Transwell inserts and cultured until a confluent monolayer is formed. Once transepithelial electrical resistance reaches a stable value, medium containing acetarsone (e.g., 10 μM or 50 μM) is added to the apical side. At specified time points (e.g., 24 hours), the basolateral medium is collected to measure drug permeability. Meanwhile, cells are harvested for flow cytometry analysis to assess cell cycle distribution (evaluating S-phase arrest) and changes in cell proliferation. Studies have also shown that the N-acetylation of acetarsone is catalyzed by human N-acetyltransferase (NAT), while CYP3A4 catalyzes its oxidative metabolism.

Animal/Disease Models: 2-month-old E. coli-infected piglets [1]
Doses: 20 mg/kg
Route of Administration: Po; one time/day for 4 days
Experimental Results: 65% of piglets demonstrated clinical recovery, and no animal diarrhea was observed at the end of treatment .

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In vivo animal assays for acetarsone commonly employ infection models to evaluate pharmacodynamic efficacy. Using a piglet folliculitis model as an example: 2-month-old piglets infected with E. coli are administered acetarsone orally via gavage at 20 mg/kg body weight once daily for 4 days. Diarrhea status, clinical recovery indicators, and other signs of toxicity are observed and recorded daily. Clinical recovery rates are calculated at the end of the treatment. In a rabbit syphilis model, subcutaneous injection of acetarsone at 0.1–0.2 g/kg body weight is used to evaluate its curative effect on experimental syphilis. In toxicity studies, oral administration of acetarsone to rats, in combination with p-aminobenzoic acid, has been shown to effectively reduce mortality from acute arsenic poisoning.

Absorption, Distribution and Excretion
Absorption appears to be very low, but allergic reactions have been reported following vaginal administration of Acetarsol. Arsenic in Acetarsol is primarily excreted in the urine. Post-administration urinary arsenic concentrations are almost within toxic limits. Pharmacokinetic characteristics have not been studied. Metabolites/Metabolites Pharmacokinetic characteristics have not been studied. Arsenic is primarily absorbed through inhalation or ingestion, with minimal absorption through skin contact. After absorption, arsenic is distributed throughout the body and, if necessary, reduced to arsenite, which is then methylated by arsenite methyltransferases to monomethylarsine (MMA) and dimethylarsonic acid (DMA). Arsenic and its metabolites are primarily excreted in the urine. Arsenic is known to induce the production of the metal-binding protein metallothionein, which reduces the toxicity of arsenic and other metals by binding to them and rendering them biologically inactive, while also possessing antioxidant properties. (L20)

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Biological half-life
The pharmacokinetic characteristics of this product are not discussed.

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Pharmacokinetic data on acetarsone are very limited and predominantly derived from early studies. Following oral administration, systemic absorption of the drug is low, although allergic reactions following vaginal administration have been reported. Arsenic from acetarsone is primarily excreted in the urine, and post-administration urinary arsenic concentrations often approach toxic levels. Once absorbed, arsenic is widely distributed throughout the body, reduced to arsenite, and subsequently methylated by arsenite methyltransferases to monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA), which are then excreted in the urine. No systematic pharmacokinetic parameters (e.g., half-life, clearance, etc.) for acetarsone in humans have been reported in the literature.

Toxicity Summary
Arsenic and its metabolites interfere with ATP production through multiple mechanisms. In the citric acid cycle, arsenic inhibits pyruvate dehydrogenase and uncouples oxidative phosphorylation by competing with phosphate, thereby inhibiting energy-related NAD+ reduction, mitochondrial respiration, and ATP synthesis. Increased hydrogen peroxide production may also lead to reactive oxygen species (ROS) generation and oxidative stress. Arsenic's carcinogenicity is influenced by its binding to tubulin, resulting in aneuploidy, polyploidy, and mitotic arrest. Arsenic binding to other protein targets may also lead to altered DNA repair enzyme activity, altered DNA methylation patterns, and cell proliferation. (T1, A17) Protein Binding This pharmacokinetic property was not investigated in this study.

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Acetarsone and its metabolites exert toxic effects through multiple mechanisms. At the energy metabolism level, arsenic inhibits pyruvate dehydrogenase activity and uncouples oxidative phosphorylation by competing with phosphate, thereby inhibiting NAD⁺ reduction, mitochondrial respiration, and ATP synthesis. Arsenic also induces the production of reactive oxygen species (ROS), leading to oxidative stress. Its carcinogenicity is associated with arsenic binding to tubulin, resulting in aneuploidy, polyploidy, and mitotic arrest, as well as alterations in DNA repair enzyme activity and DNA methylation patterns. Regarding animal toxicity data, the oral LD50 in mice is approximately 4 mg/kg, classified as extremely toxic. In rabbits, the maximum tolerated oral dose is approximately 1 g/kg, and the lethal dose is approximately 1.5 g/kg. The maximum tolerated intravenous dose of the sodium salt in rabbits is approximately 0.5 g/kg, with a lethal dose of approximately 0.6 g/kg; in rats, the corresponding values are 0.7 g/kg and 0.75 g/kg. In humans, acetarsone can cause a range of adverse reactions, including malaise, fever, edema, jaundice, diarrhea, albuminuria, bronchitis, and skin reactions (such as diffuse erythema, dryness, pruritus, and exfoliative dermatitis).

[1]. Argyriou K, et al. Acetarsol in the management of mesalazine-refractory ulcerative proctitis: a tertiary-level care experience. Eur J Gastroenterol Hepatol. 2019 Feb;31(2):183-186.
[2]. V.S. Pandey, et al. Successful therapy of balantidiosis of pigs with acetarsol and oxytetracycline. Veterinary parasitology. 1977, 3(2):189-193.

Acetarsol belongs to the acetamide and aniline classes of compounds. Acetarsol, with the molecular formula N-acetyl-4-hydroxy-m-arsanoic acid, is a pentavalent arsenic compound with antiseptic and anthelmintic properties. It was first discovered in 1921 by Ernest Forno of the Pasteur Institute. Developed by Neolab, it was approved by Health Canada as an antifungal drug on December 31, 1964. It was withdrawn from the market on August 12, 1997. Acetarsol is a pentavalent arsenic compound with antiseptic and anthelmintic properties. Although its mechanism of action is not fully understood, Acetarsol may bind to thiol-containing proteins in parasites, forming a lethal As-S bond. This may inhibit their function and ultimately kill the parasite. Acetarsol is an arsenic compound used as an anti-infective drug. Arsenic is a chemical element with the symbol As and atomic number 33. It is a toxic metalloid with several allotropes: common ones are yellow (molecular nonmetal) and several are black and gray (metalloid). Three metalloids of arsenic exist in nature with different crystal structures (arsenic pyrite and the rarer arsenopyrite and paraarsenic pyrite), but more commonly it forms compounds with other elements. (T3, T59)

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Drug Indications
Arsethrol has been used to treat a variety of diseases, such as syphilis, amebiasis, yaws, trypanosomiasis, and malaria. Acetamidinol has been widely used to treat vaginitis caused by Trichomonas vaginalis and Candida albicans. Oral acetamidinol can be used to treat intestinal amebiasis, while suppository forms of acetamidinol have been used in research to treat proctitis. Protozoan infections are diseases caused by parasites in the protozoan kingdom (which contains a wide variety of organisms). Mechanism of Action The mechanism of action of Acetarsol is not fully understood, but it is speculated that it binds to sulfhydryl-containing proteins in infectious microorganisms, forming a lethal As-S bond. This bond formation impairs protein function, ultimately leading to microbial death. Pharmacodynamics Some reports indicate that Acetarsol can alleviate infection, but these reports also suggest systemic arsenic absorption, which may be physiologically harmful.

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C8H10ASNO5

275.09

274.977

97-44-9

55588-51-7 (unspecified hydrochloride salt);5892-48-8 (mono-hydrochloride salt);64046-96-4 (calcium salt);64046-96-4 (unspecified calcium salt)

1985

White to off-white solid powder

72.17°C

220.5°C

4

5

2

15

289

0

O=C(C)NC1C(O)=CC=C([As](O)(O)=O)C=1

ODFJOVXVLFUVNQ-UHFFFAOYSA-N

InChI=1S/C8H10AsNO5/c1-5(11)10-7-4-6(9(13,14)15)2-3-8(7)12/h2-4,12H,1H3,(H,10,11)(H2,13,14,15)

m-Arsanilic acid, N-acetyl-4-hydroxy-

Amarsan OsarsolAmoebal Vagisept NSC-13160 NSC13160NSC 13160

2934.99.9001

Powder      -20°C    3 years

                     4°C     2 years

In solvent   -80°C    6 months

                  -20°C    1 month

Room temperature (This product is stable at ambient temperature for a few days during ordinary shipping and time spent in Customs)

DMSO : ~20.83 mg/mL (~75.72 mM)

Solubility in Formulation 1: ≥ 2.08 mg/mL (7.56 mM) (saturation unknown) in 10% DMSO + 90% (20% SBE-β-CD in Saline) (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 20.8 mg/mL clear DMSO stock solution to 900 μL of 20% SBE-β-CD physiological saline solution and mix evenly.
Preparation of 20% SBE-β-CD in Saline (4°C，1 week): Dissolve 2 g SBE-β-CD in 10 mL saline to obtain a clear solution.

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Solubility in Formulation 2: ≥ 2.08 mg/mL (7.56 mM) (saturation unknown) in 10% DMSO + 90% Corn Oil (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 20.8 mg/mL clear DMSO stock solution to 900 μL of corn oil and mix evenly.

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 (Please use freshly prepared in vivo formulations for optimal results.)