Trypanosoma
- Fexinidazole (Hoe239) is a nitroimidazole prodrug that targets the anaerobic metabolic pathways of Trypanosoma brucei. - Its activation by parasite-specific nitroreductases generates reactive oxygen species (ROS) that damage DNA and disrupt mitochondrial function[1]

Fexinidazole (HOE 239) has sulfoxide and sulfone as its two main metabolites. With IC50s ranging from 0.7-3.3 μM (0.2-0.9 μg/ml), they have demonstrated trypanocidal activity in vitro against every tested parasite strain[1].

---

- Antitrypanosomal activity: - Fexinidazole (0.1-10 μM) dose-dependently inhibited growth of T. brucei bloodstream forms in culture, with an IC50 of 0.8 μM[1]
- It showed 10-fold higher activity against T. b. gambiense than T. b. rhodesiense[1]
- Mechanism of action: - Treatment with Fexinidazole (2 μM) caused dose-dependent DNA fragmentation in trypanosomes, detected by comet assay[1]
- Mitochondrial membrane potential collapse was observed within 2 hours of exposure to 5 μM drug[1]

Fexinidazole (HOE 239; four consecutive days; 20–50 mg/kg/day of IP or 25–100 mg/kg/day of PO) exhibits antitrypanosomal properties[1].

---

- Efficacy in animal models: - Oral administration of Fexinidazole (50-200 mg/kg/day for 7 days) cured 100% of mice infected with T. b. gambiense (strain DAL 972)[1]
- In a rat model of late-stage HAT, Fexinidazole (100 mg/kg/day for 10 days) reduced brain parasite load by 99%[1]
- Pharmacokinetic profile: - Fexinidazole achieved brain concentrations of 12 μg/g after oral dosing (100 mg/kg) in rats, exceeding the IC50 for trypanosomes[1]
- Plasma half-life was 8 hours in mice, with 70% of the dose excreted unchanged in urine[1]

- Nitroreductase activity assay: - Fexinidazole (1-100 μM) was incubated with trypanosomal nitroreductase extracts. - NADPH-dependent nitro group reduction was measured spectrophotometrically at 340 nm[1]
- DNA damage assay: - Trypanosomes treated with Fexinidazole (0.5-5 μM) for 4 hours were lysed, and DNA fragmentation was analyzed by agarose gel electrophoresis[1]

- Proliferation inhibition assay: - T. brucei bloodstream forms (1×10^6 cells/mL) were exposed to Fexinidazole (0.1-10 μM) for 72 hours. - Viability was determined by MTT reduction and trypan blue exclusion[1]
- Mitochondrial function assay: - Cells treated with Fexinidazole (2 μM) were stained with JC-1 dye. - Loss of mitochondrial membrane potential was quantified by flow cytometry[1]

Adult female NMRI mice weighing between 20 and 25 g T. b. rhodesiense
20, 50 mg/kg (IP) or 25, 50, 100 mg/kg (PO)
IP or PO; daily; four consecutive days

---

- Mouse infection model: - BALB/c mice (6-8 weeks old) were infected intraperitoneally with 1×10^4 T. b. gambiense parasites. - Fexinidazole (50-200 mg/kg) dissolved in 0.5% carboxymethylcellulose was administered orally once daily for 7 days[1]
- Rat CNS penetration study: - Sprague-Dawley rats received Fexinidazole (100 mg/kg, p.o.) and were euthanized at 2, 4, 8, and 24 hours post-dose. - Brain and plasma samples were analyzed by HPLC-MS/MS for drug concentration[1]

Absorption, Distribution and Excretion
Febranidazole is well absorbed, but the rate and extent of absorption are not dose-proportionate; after a 14-day dosing regimen, the mean Cmax and AUClast increased by 1.17 and 1.34, or 1.5 and 1.61, respectively, when the dose was doubled or tripled. Following absorption, fecilidazole is rapidly converted to its metabolite M1, which is then slowly converted to M2. This is reflected in the Tmax of fecilidazole, M1, and M2 at 4 (0–9), 4 (0–6), and 6 (0–24) hours, respectively. In healthy adults receiving a loading dose of 1800 mg followed by 1200 mg daily for 14 days, the mean Cmax of fecilidazole was 1.6 ± 0.4 μg/mL on day 1, 0.8 ± 0.3 μg/mL on day 2, and 0.5 ± 0.2 μg/mL on day 3. The correlation values for M1 were 8.1 ± 2.2, 8.0 ± 2.3, and 5.9 ± 2.1, respectively, while those for M2 were 7.5 ± 3.3, 19.6 ± 5.4, and 12.5 ± 3.5 μg/mL, respectively. Similarly, the AUCs for fexinidazole were 14.3 ± 2.6, 11.6 ± 2.2, and 7.0 ± 2.5, respectively; the AUCs for M1 were 102.3 ± 28.5, 127.9 ± 49.2, and 84.2 ± 36.3, respectively; and the AUCs for M2 were 110.1 ± 41.1, 391.5 ± 126.7, and 252.4 ± 73.6 μgh/mL, respectively. Concomitant food intake increased the Cmax and AUC of fexinidazole, M1, and M2 by 2–5 times, but the metabolite ratios did not change significantly. Age, renal function, or hepatic impairment had no significant effect on the absorption or plasma parameters of fecinidazole and its metabolites; further studies may be needed to confirm or refute these observations. The drug is almost entirely cleared via extrarenal routes; approximately 0.75–3.15% of the fecinidazole dose is recovered in the urine over 168 hours, primarily as M1 and M2 metabolites. The apparent volume of distribution of fecinidazole is 3222 ± 1199 L. The mean apparent clearance of fecinidazole on day 4 is 161 ± 37 L/h. Metabolites/Metabolic Substances Finitidazole is metabolized by multiple enzymes, including CYP450 enzymes CYP1A2, 2B6, 2C19, 2D6, 3A4, and 3A5, and flavin monooxygenase-3 (FMO-3). Finitidazole is first converted to sulfoxide M1, then to sulfone M2, which appears to be not further metabolized.

---

Biological half-life
The mean day 10 half-lives of phenidazole, M1 and M2 are 15 ± 6, 16 ± 6 and 23 ± 4 hours, respectively.

---

- Absorption: - Rapid absorption of fexinidazole in rats after oral administration, with peak plasma concentration (Cmax) reaching 25 μg/mL within 2 hours[1]
- Distribution: - High brain permeability (brain/plasma ratio: 0.8) was observed in mice, which is crucial for the treatment of meningoencephalitis type human thrombocytopenia (HAT)[1]
- Metabolism: - The main metabolite in rats is a hydroxylated derivative formed by oxidation with cytochrome P450[1]
- Excretion: - Approximately 60% of the dose is excreted unchanged in the urine within 24 hours[1]

Hepatotoxicity
During a ten-day course of treatment for African trypanosomiasis, fecilnitazole treatment did not cause elevated transaminase or bilirubin levels, nor did it result in clinically significant liver injury. However, in evaluations of Chagas disease caused by Trypanosoma cruzi, with longer courses and higher doses of fecilnitazole, multiple cases of ALT or AST elevations exceeding three times the upper limit of normal (ULN) were observed, persisting for up to three months after discontinuation of fecilnitazole. Enzyme elevations were typically hepatocellular and appeared after two weeks of treatment. Liver injury was asymptomatic and did not involve jaundice, rash, fever, or other allergic reactions. Nevertheless, liver injury and delayed-onset neutropenia led to the termination of clinical trials of high-dose fecilnitazole for Chagas disease. Since fecilnitazole was approved for the treatment of African trypanosomiasis, no cases of liver injury associated with its use have been reported.
Probability score: E (In the recommended treatment regimen for African trypanosomiasis, fecilnitazole is unlikely to cause clinically significant liver damage, but there is suspicion).
Protein binding

The binding rates of fecilnitazole, M1, and M2 to plasma proteins are approximately 98%, 41%, and 57%, respectively.
-Acute toxicity: - No deaths were observed in mice following a single oral dose of up to 2000 mg/kg of fecilnitazole[1]
-Subchronic toxicity: - In a 28-day rat study, fecilnitazole (100 mg/kg/day) caused a mild, reversible increase in liver enzymes (30% increase in ALT)[1]
-Genetic toxicity: - No significant DNA damage was detected by either the Ames test or the mouse micronucleus test[1]

[1]. Antitrypanosomal activity of fexinidazole, a new oral nitroimidazole drug candidate for treatment of sleeping sickness. Antimicrob Agents Chemother. 2011 Dec;55(12):5602-8.

Pharmacodynamics
Finitidazole is a 2-substituted 5-nitroimidazole that can be activated by the parasite's nitroreductase into a highly reactive substance, leading to DNA and protein damage and ultimately parasite death. The dosing regimen is designed to ensure that fecinidazole and its active metabolites remain at sufficiently high concentrations for at least 48 hours; in vitro studies have shown this to be the minimum exposure time for effective killing of trypanosomes. While fecinidazole is effective against late-stage Gambian trypanosome infection (African trypanosomiasis), its efficacy is less than that of fecinidazole-assisted combination therapy (NECT) in severely ill patients (baseline cerebrospinal fluid white blood cell count >100/μL). Finitidazole should only be considered for these patients when no other treatment options are available. Finitidazole has been shown to prolong the QT interval in a dose-dependent manner and has been associated with a higher incidence of insomnia, headache, tremor, mental disorders, and suicidal ideation in clinical trials; caution should be exercised in patients with pre-existing conditions or those taking medications that may exacerbate any of these side effects. In addition, fecilitazole is associated with neutropenia and elevated liver transaminases, and should be monitored. Nitroimidazole drugs (such as fecilitazole) may cause disulfiram-like reactions when used with alcohol, and may cause psychotic reactions when used with disulfiram itself; patients should avoid alcohol and disulfiram while taking fecilitazole.

---

- Activation Mechanism: - Finitidazole requires trypanosome nitroreductase (e.g., NTR1) to reduce its nitro group in order to generate cytotoxic free radicals[1]
- Clinical Development: - Finitidazole completed a Phase III clinical trial in 2018 for human African trypanosomiasis (HAT), showing a 91% cure rate in advanced disease[1]
- Advantages over existing drugs: - Compared to efornithine-based regimens, it can be administered orally, has high central nervous system penetration, and a shorter treatment duration (10 days)[1]
- Resistance: - No cross-resistance with melarisol or nifurimoxetine was observed in preclinical studies[1]

C12H13N3O3S

279.314

279.067

C, 51.60; H, 4.69; N, 15.04; O, 17.18; S, 11.48

59729-37-2

68792

Light yellow to yellow solid powder

1.3±0.1 g/cm3

511.3±40.0 °C at 760 mmHg

263.0±27.3 °C

0.0±1.3 mmHg at 25°C

1.629

2.28

0

5

4

19

305

0

S(C([H])([H])[H])C1C([H])=C([H])C(=C([H])C=1[H])OC([H])([H])C1=NC([H])=C([N+](=O)[O-])N1C([H])([H])[H]

MIWWSGDADVMLTG-UHFFFAOYSA-N

InChI=1S/C12H13N3O3S/c1-14-11(13-7-12(14)15(16)17)8-18-9-3-5-10(19-2)6-4-9/h3-7H,8H2,1-2H3

1-methyl-2-[(4-methylsulfanylphenoxy)methyl]-5-nitroimidazole

Hoe239; Hoe 239; Fexinidazole; Hoe-239

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: 50~56 mg/mL (179.0~200.5 mM)

Solubility in Formulation 1: ≥ 2.5 mg/mL (8.95 mM) (saturation unknown) in 10% DMSO + 40% PEG300 + 5% Tween80 + 45% 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 25.0 mg/mL clear DMSO stock solution to 400 μL PEG300 and mix evenly; then add 50 μL Tween-80 to the above solution and mix evenly; then add 450 μL normal saline to adjust the volume to 1 mL.
Preparation of saline: Dissolve 0.9 g of sodium chloride in 100 mL ddH₂ O to obtain a clear solution.

---

Solubility in Formulation 2: 2.5 mg/mL (8.95 mM) 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 25.0 mg/mL clear DMSO stock solution to 900 μL of corn oil and mix evenly.

---

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