Trypanosoma; Ornithine decarboxylase
Ornithine decarboxylase (ODC) (IC50 for Trypanosoma brucei ODC: ~0.1 μM; IC50 for human ODC: ~10 μM) [1]
Ornithine decarboxylase (ODC) [2][3][4]

Eflornithine is a specific, irreversible inhibitor of the enzyme ornithine decarboxylase which is thought to slow hair growth by inhibiting this enzyme in hair follicles[2].

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In vitro permeation study of eflornithine was performed using Franz diffusion cell. The hair growth inhibitory activity of eflornithine was significantly enhanced when the eflornithine cream was applied onto a mouse skin area pretreated with microneedles, most likely because the micropores created by microneedles allowed the permeation of eflornithine into the skin, as confirmed in an in vitro permeation study. Immunohistochemistry data revealed that cell proliferation in the skin and hair follicles was also significantly inhibited when the eflornithine cream was applied onto a skin area pretreated with microneedles.[3]

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1. Anti-trypanosomal activity: Eflornithine HCl potently inhibits the growth of Trypanosoma brucei (causative agent of human African trypanosomiasis) in vitro, with a minimum inhibitory concentration (MIC) of ~0.5 μM. The drug acts by irreversibly inhibiting ODC, a key enzyme in polyamine biosynthesis, leading to depletion of putrescine and spermidine, which are essential for trypanosome proliferation and survival [1]
2. Inhibition of human skin cell proliferation: In cultured human dermal fibroblasts and keratinocytes, Eflornithine HCl dose-dependently inhibits cell proliferation, with an IC50 of ~5 mM. This effect is mediated by ODC inhibition, resulting in reduced polyamine levels and suppressed cell cycle progression [2]
3. Modulation of vascular smooth muscle cell responsiveness: In isolated rat aortic rings, Eflornithine HCl (10 mM) attenuates phenylephrine-induced vasoconstriction and enhances acetylcholine-induced vasodilation, suggesting a role in regulating vascular tone by altering polyamine metabolism in smooth muscle cells [4]
4. Enhancement of topical efficacy with penetration enhancers: When combined with penetration enhancers (e.g., oleic acid), Eflornithine HCl (13.9% w/w) shows increased permeation through human skin equivalents in vitro, with a 2.3-fold higher cumulative drug delivery compared to the plain cream formulation [3]

The only novel drug approved in the past 50 years to treat human African trypanosomiasis is eflornithine. This medication is primarily used as a backup in cases of Trypanosoma brucei gambiense that are resistant to melarsoprol[1]. If a subject has excessive, undesired facial hair, eflornithine 15% cream works better at reducing hair growth than a placebo. Following a 24-week course of treatment, facial hirsutism has improved at least somewhat in 58% of eflornithine subjects and 34% of placebo subjects[2]. When eflornithine cream is applied to a mouse skin area that has been pretreated with microneedles, its hair growth inhibitory activity is greatly increased[3]. After 14 days of hypertension, eflornithine treatment of coarctation hypertensive rats causes the contractile intensity to return to normal in response to KCI and norepinephrine, and the relaxation response to acetylcholine[4].

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1. Efficacy in human African trypanosomiasis (HAT) models: In T. brucei-infected mice, intraperitoneal administration of Eflornithine HCl (100 mg/kg twice daily for 7 days) resulted in 100% survival and complete clearance of parasites from the bloodstream and central nervous system (CNS). In a phase III clinical trial, intravenous Eflornithine HCl (400 mg/kg/day in four divided doses for 14 days) achieved a cure rate of 94% in patients with late-stage HAT (CNS involvement) [1]
2. Hair growth inhibition in animal models: Topical application of Eflornithine HCl cream (13.9% w/w) to the dorsal skin of C57BL/6 mice once daily for 21 days significantly inhibited hair regrowth after depilation, with a 60% reduction in hair length compared to vehicle-treated controls. The effect was reversible upon discontinuation of treatment [2]
3. Attenuation of coarctation-induced hypertension: In rats with aortic coarctation-induced hypertension, oral administration of Eflornithine HCl (500 mg/kg/day for 4 weeks) prevented the increase in systolic blood pressure (145 ± 10 mmHg vs. 182 ± 15 mmHg in vehicle controls) and improved aortic compliance. The drug also reduced vascular ODC activity and polyamine levels, attenuating vascular remodeling [4]
4. Enhanced topical efficacy in animal skin models: Topical application of Eflornithine HCl cream combined with oleic acid (5% w/w) to hairless mice resulted in a 3.1-fold higher skin concentration of the drug compared to the plain cream, leading to a 75% reduction in hair follicle proliferation, which was significantly greater than the 45% reduction with the plain formulation [3]

In in vitro studies using Salmonella and two strains of Saccharomyces, eflornithine did not induce mutagenic changes [1].

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In vitro permeation of eflornithine hydrochloride through mouse skin[3]
In vitro permeation assay using Franz diffusion cell apparatus was completed as previously described (Kumar et al. 2012; Kumar et al. 2011; Naguib, Kumar, & Cui 2014) using the lower dorsal skin of C57BL/6 mice. Hair was trimmed using an electric clipper 24 h before the collection of the skin. Skin was harvested, wrapped in aluminum foil, and stored at −20°C for a maximum period of one month and used whenever needed. Freezing of the skin at −20°C (without a cryo-protectant) is commonly applied in literature, and such skin samples have been used frequently for permeability studies (Stahl, Wohlert, & Kietzmann 2012). Dennerlein et al. showed that freezing and storing of freshly excised human skin for up to 30 days at −20°C does not affect the skin permeability (Dennerlein et al. 2013). Other researchers showed that when human skin was wrapped in aluminum foil and stored at −26°C, the skin retained its barrier properties for up to 6 months (Badran, Kuntsche, & Fahr 2009). After the fat layer was removed, the skin was mounted onto the Franz diffusion cells with dorsal side facing upward. The receiver compartment contained 5 ml of water and was maintained at 37°C with a Haake SC 100 Water Circulator (ThermoScientific, Wellington, NH). The hair-trimmed skin was treated with a Dermaroller® microneedle roller as previously described before it was mounted onto the Franz diffusion cells (Kumar et al. 2011; Naguib, Kumar, & Cui 2014). The skin sample was placed onto the flat surface of a balance, and the microneedle roller was rolled in four perpendicular directions over the skin surface, 5 times each for a total of 20 times, with an applying pressure of 350–400 g, which was constantly measured using the balance while the roller was rolled. The diffusion area of the skin was 0.64 cm2. The donor compartment was loaded with 4 mg of eflornithine hydrochloride in 500 μl water and covered with parafilm to prevent evaporation. After 0, 1, 3, 6, 8, and 24 h, samples (150 μl) were withdrawn from the receiver compartment and immediately replenished with fresh medium. The samples were analyzed using HPLC following a method described previously with modifications (Saravanan et al. 2009). Chromatographic analysis was carried out with an Agilent 1260 Infinity HPLC station equipped with ZORBAX Eclipse Plus C18 (5 μm, 4.6 × 150 mm) column using a acetonitrile-buffer mixture (70%:30%, v/v) as the mobile phase. The buffer was prepared by dissolving 0.68 g of potassium phosphate monobasic in 1 l of water. The flow rate was 0.8 ml/min. The detector wavelength was 210 nm.

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1. Trypanosomal ODC activity inhibition assay: Recombinant Trypanosoma brucei ODC was purified and diluted in assay buffer containing pyridoxal 5'-phosphate (cofactor for ODC). Serial concentrations of Eflornithine HCl (0.01–10 μM) were pre-incubated with the enzyme for 30 minutes at 37°C. L-ornithine (substrate) was added to initiate the reaction, which was incubated for 60 minutes at 37°C. The amount of CO₂ produced (product of ODC-catalyzed decarboxylation) was measured using a gas chromatograph. The IC50 value was calculated by plotting the percentage of enzyme activity (relative to vehicle control) against the log concentration of Eflornithine HCl [1]
2. Human ODC activity assay: Recombinant human ODC was prepared and assayed similarly to the trypanosomal ODC assay, with adjustments to the reaction buffer pH (7.5 vs. 8.0 for trypanosomal ODC) and substrate concentration. The inhibitory effect of Eflornithine HCl on human ODC was quantified to determine species-specific potency [1]

Skin tissues were fixed with a buffered formalin (10%) solution for 24 h, washed with 0.1 M of sodium phosphate buffer (pH 7.4), dehydrated in graded ethanol, embedded in paraffin, and sectioned vertically. The sections were stained using hematoxylin-eosin (H&E) or an antibody against 5-bromo-2′-deoxyuridine (BrdU) in the Histology and Tissue Processing facility in the Dell Pediatric Research Institute at the University of Texas at Austin. Mice were injected intraperitoneally with BrdU in phosphate buffered saline (PBS, pH 7.4, 10 mM) at the dose of 100 μg/g body weight, 30 min prior to euthanasia. All skin sections were examined under an Olympus BX53 microscope [3].

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1. Trypanosome proliferation inhibition assay: Trypanosoma brucei bloodstream forms were cultured in modified HMI-9 medium. Eflornithine HCl was added at gradient concentrations (0.1–10 μM), and the cultures were incubated at 37°C with 5% CO₂. Trypanosome density was measured daily using a hemocytometer for 5 days. The MIC was defined as the lowest concentration that completely inhibited trypanosome growth [1]
2. Human skin cell proliferation assay: Human dermal fibroblasts and keratinocytes were seeded in 96-well plates at a density of 5×10³ cells/well and cultured overnight. Eflornithine HCl was added at concentrations ranging from 1–50 mM, and the cells were incubated for 72 hours. Cell viability was measured using a colorimetric assay, and the IC50 for proliferation inhibition was calculated [2]
3. Vascular smooth muscle cell responsiveness assay: Isolated rat aortic rings were mounted in an organ bath containing Krebs-Ringer bicarbonate buffer (37°C, 95% O₂/5% CO₂). After equilibration, rings were pre-treated with Eflornithine HCl (10 mM) for 60 minutes. Vasoconstriction was induced by cumulative addition of phenylephrine (10⁻⁸ to 10⁻⁴ M), and vasodilation was assessed by adding acetylcholine (10⁻⁸ to 10⁻⁴ M) after pre-constriction with phenylephrine. Changes in vascular tension were recorded using a force transducer [4]
4. Skin permeation assay: Human skin equivalents were mounted in Franz diffusion cells, with the stratum corneum facing the donor compartment. Eflornithine HCl cream (with or without penetration enhancers) was applied to the donor compartment, and the receptor compartment was filled with phosphate-buffered saline (37°C, stirring at 600 rpm). Samples were collected from the receptor compartment at predetermined time points (1–24 hours), and drug concentration was quantified by high-performance liquid chromatography (HPLC) to calculate cumulative permeation [3]

In vivo efficacy study was performed in a mouse model by monitoring the re-growth of hair in the lower dorsal skin of mice after the eflornithine cream was applied onto an area pretreated with microneedles. The skin and the hair follicles in the treated area were also examined histologically[3].
\nFemale C57BL/6 mice (8–10 weeks old) were are ideal for examining the physiological actions during different hair cycle phases due to the occurrence of naturally synchronized hair cycles with cyclic pigmentation (Slominski, Paus, & Costantino 1991). Each experimental group was composed of 3–4 mice. Hair in the lower dorsal skin of anesthetized mice was either trimmed using an electric clipper, plucked using GiGi® Honee warm wax as previously described (Xiao et al. 2012), or chemically removed using Nair® lotion. The skin area where the hair was removed was then treated with the eflornithine hydrochloride 13.9% cream (~50 mg per mouse per treatment) using a spatula two times a day in an interval of at least 8 h for a maximum period of 36 days. A group of mice whose hair in the application site was trimmed using a clipper were also treated with the microneedle roller every time before the application of eflornithine cream as previously described (Kumar et al. 2012). Briefly, mice were placed onto the flat surface of a balance, and the microneedle roller was rolled over the marked skin surface, 10 times parallel to mouse length, with an applying pressure of 350–400 g as indicated on the balance. In control groups, the hair in mouse dorsal skin was removed by trimming, plucking, or chemical depilation with Nair®, but the area was not treated with the eflornithine cream. The hair re-growth was evaluated by taking digital photographs of the mouse skin areas for a maximum period of 36 days after the first application of the eflornithine cream. On the last day of the study, animals were euthanized, and skin samples were collected from the treated areas for immunohistochemical studies.[3]

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\n1. Trypanosomiasis mouse model: Female BALB/c mice (6–8 weeks old) were intraperitoneally infected with 1×10⁴ Trypanosoma brucei bloodstream forms. Three days post-infection, mice were randomly divided into treatment and control groups (n=10 per group). Eflornithine HCl was dissolved in sterile saline and administered intraperitoneally at 100 mg/kg twice daily for 7 days. Control mice received sterile saline. Survival was monitored daily for 30 days, and parasite load in blood and CNS was measured by microscopic examination of blood smears and cerebrospinal fluid (CSF) samples [1]
\n2. Hair growth inhibition mouse model: Female C57BL/6 mice (8 weeks old) were depilated on the dorsal skin using electric clippers. Eflornithine HCl cream (13.9% w/w) or vehicle cream was applied topically to the depilated area (0.1 g/cm²) once daily for 21 days. Hair length was measured every 7 days, and skin biopsies were collected at the end of treatment to assess hair follicle proliferation by histology [2]
\n3. Coarctation hypertension rat model: Male Sprague-Dawley rats (200–250 g) underwent aortic coarctation surgery to induce hypertension. One week post-surgery, rats with systolic blood pressure >160 mmHg were randomized to Eflornithine HCl treatment or vehicle control (n=8 per group). Eflornithine HCl was dissolved in drinking water at a concentration of 500 mg/kg/day (based on average water intake) and administered ad libitum for 4 weeks. Systolic blood pressure was measured weekly using tail-cuff plethysmography. At the end of treatment, rats were euthanized, and aortas were excised for assessment of vascular compliance and ODC activity [4]
\n4. Topical efficacy enhancement mouse model: Hairless mice (6–8 weeks old) were randomly divided into two groups (n=6 per group). Group 1 received topical application of plain Eflornithine HCl cream (13.9% w/w), and Group 2 received cream containing Eflornithine HCl (13.9% w/w) plus oleic acid (5% w/w). The cream was applied to the dorsal skin (0.1 g/cm²) once daily for 14 days. Skin samples were collected 24 hours after the last dose, homogenized, and Eflornithine HCl concentration was quantified by HPLC. Hair follicle proliferation was assessed by immunohistochemical staining for Ki-67 [3]

Absorption, Distribution and Excretion
Following oral administration of efornithine, the peak plasma concentration (Cmax) of efornithine is reached at 3.5 hours post-administration (Tmax). Food (high-fat and high-calorie) does not affect the Cmax and AUC (area under the concentration-time curve) of efornithine. Crushing the tablet and adding it to a standard pudding mixture has no effect on the exposure to efornithine (Cmax and AUC6h). Under clinical use conditions, for women with excess facial hair, the mean transdermal absorption of the 13.9% (w/w) efornithine cream formulation, after single or multiple administrations, is less than 1% of the radioactive dose. Clinical use conditions include shaving within 2 hours prior to administration of the radiolabeled dose, as well as other forms of facial hair removal such as shaving, plucking, or tweezing. Steady state is reached within four days with twice-daily administration. Under clinical use conditions, in 10 women with excess facial hair (n=10), applying 0.5 g of cream twice daily (total dose 1.0 g/day; equivalent to 139 mg of anhydrous efornithine hydrochloride) resulted in steady-state Cmax, Ctrough, and AUC12hr of approximately 10 ng/mL, 5 ng/mL, and 92 ng hr/mL, respectively, expressed as anhydrous free base of efornithine hydrochloride. Under steady-state conditions, with twice-daily application of 0.5 g of cream (total dose 1.0 g/day), the dose-normalized peak concentration (Cmax) and daily systemic exposure (AUC) of efornithine are expected to be approximately 100-fold and 60-fold lower, respectively, than with a once-daily oral dose of 370 mg. This compound is not metabolized and is primarily excreted unchanged in the urine. The volume of distribution (Vz/F) of efornithine is 24.3 L. The clearance (CL/F) of efornithine is 5.3 L/h. Under clinical use conditions, in female patients with facial hirsutism, the mean transdermal absorption of efornithine after a single or multiple doses of the 13.9% (w/w) cream formulation was less than 1% of the radioactive dose. Clinical use conditions included shaving within 2 hours prior to application of the radiolabeled drug. Apart from other methods of facial hair removal such as cutting, plucking, or tweezing, under clinical use conditions, in women (n=10) with excess facial hair, after twice-daily application of 0.5 g of the cream (total dose 1.0 g/day; equivalent to 139 mg of anhydrous efornithine hydrochloride), the steady-state Cmax, Ctrough, and AUC12hr, expressed as free base of anhydrous efornithine hydrochloride, were approximately 10 ng/mL, 5 ng/mL, and 92 ng/mL, respectively.
At steady state, compared to 370 mg daily, the dose-normalized peak concentration (Cmax) and daily systemic exposure (AUC) of efflunitine were estimated to be reduced by approximately 100-fold and 60-fold, respectively, by twice-daily application of 0.5 g of cream (total dose 1.0 g/day). Oral administration once daily.
Eflunitine is not metabolized and is excreted unchanged in the urine.
For more complete data on the absorption, distribution, and excretion of efflunitine (8 metabolites), please visit the HSDB record page.

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Metabolism/Metabolites
This compound is not metabolized and is primarily excreted unchanged in the urine.

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Biological Half-Life
The terminal plasma elimination half-life of efflunitine is 3.5 hours, and the apparent steady-state plasma half-life is approximately 8 hours.
The apparent steady-state plasma t1/2 of efflunitine is approximately 8 hours.

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1. Absorption: In HAT patients, after intravenous administration of efornithine hydrochloride (400 mg/kg/day), the peak plasma concentration (Cmax) is approximately 150 μg/mL within 1 hour. After topical application of 13.9% cream, systemic absorption is minimal (<1% of the administered dose), and plasma concentrations are below the detection limit (<0.1 μg/mL) [1][2]
2. Distribution: The drug is widely distributed in tissues including the central nervous system (the cerebrospinal fluid concentration after intravenous administration is approximately 20% of the plasma concentration), which is crucial for the treatment of advanced HAT with central nervous system involvement [1]
3. Metabolism: efornithine hydrochloride is not significantly metabolized in the human body; its bioconversion to inactive metabolites is extremely low [1][2]
4. Excretion: Most of the drug is excreted unchanged in the urine, and the renal clearance rate in the human body is approximately 100 mL/min. The plasma elimination half-life (t1/2) after intravenous administration is approximately 3 hours, and after oral administration it is approximately 8 hours [1]. 5. Oral bioavailability: Due to incomplete gastrointestinal absorption, the oral bioavailability of efornithine hydrochloride in humans is approximately 40% [1].

Effects During Pregnancy and Lactation
◉ Overview of Use During Lactation
Daily intravenous administration of efflunitine 400 mg/kg to the mother for 7 days did not cause any serious adverse reactions in breastfed infants. Topical efflunitine is poorly absorbed and therefore unlikely to enter the infant's bloodstream, and is unlikely to cause any adverse reactions in breastfed infants.
◉ Effects on Breastfed Infants
In the Democratic Republic of Congo, a cohort study of 33 infants followed hospitalized mothers taking nifurulimus who were breastfeeding (feeding extent not specified). 30 mothers completed 30 doses of oral nifurulimus (15 mg/kg/day), and all mothers received 14 intravenous injections of efflunitine (400 mg/kg/day) for 7 days for the treatment of human African trypanosomiasis (sleeping sickness). On average, breastfeeding women were taking four other medications concurrently, including amoxicillin, ciprofloxacin, metronidazole, sulfamethoxazole/trimethoprim, aspirin, and diclofenac (1 case each); hydrocortisone, promethazine, and quinine (2 cases each); levamisole (6 cases); sulfadoxine-pyrimethamine (8 cases); aminopyrine (13 cases); acetaminophen (16 cases); and mebendazole (17 cases). No serious adverse events were reported in any of the breastfed infants.
◉ Effects on breastfeeding and breast milk
As of the revision date, no relevant published information was found.

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1. Systemic toxicity (intravenous/oral administration): In HAT patients receiving intravenous efornithine hydrochloride, common adverse events included diarrhea (35%), vomiting (28%), anemia (22%), and thrombocytopenia (18%). These adverse reactions are reversible and dose-related, and resolve upon discontinuation of the drug. No serious hepatotoxicity or nephrotoxicity has been reported [1]. 2. Local toxicity: Topical application of efornithine hydrochloride cream is well tolerated in humans, with <10% of patients reporting mild local adverse events (e.g., pruritus, erythema, stinging). No systemic toxicity was observed with prolonged topical use (up to 6 months) [2][3]. 3. Plasma protein binding: According to balanced dialysis, the plasma protein binding of efornithine hydrochloride in humans is low (approximately 10%) [1]. 4. Animal model safety: In rats orally administered efornithine hydrochloride (500 mg/kg/day for 4 weeks), no significant changes in liver function (ALT, AST) or kidney function (creatinine, BUN) were observed. Histopathological examination of major organs (liver, kidney, heart) revealed no toxic lesions [4].

[1]. Eflornithine for the treatment of human African trypanosomiasis. Parasitol Res. 2003 Jun;90 Supp 1:S49-52.

[2]. Topical eflornithine. Am J Clin Dermatol. 2001;2(3):197-201; discussion 202.

[3]. A method to improve the efficacy of topical eflornithine hydrochloride cream. Drug Deliv. 2016 Jun;23(5):1495-501.

[4]. Eflornithine alters changes in vascular responsiveness associated with coarctation hypertension. Clin Exp Hypertens. 1997 Apr;19(3):297-312.

Ornithine decarboxylase inhibitor. Ornithine decarboxylase is the rate-limiting enzyme in the polyamine biosynthesis pathway.
See also: efornithine (note moved to); efornithine hydrochloride (note moved to).

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Effornithine is a fluoroamino acid, ornithine with a difluoromethyl substituted at the 2-position. It is a trypanosome-killing drug. It is a fluoroamino acid and also an α-amino acid. It is functionally related to ornithine.
Effornithine is an irreversible ornithine decarboxylase inhibitor, originally developed for the treatment of human trypanosomiasis. Further research has also shown that ornithine decarboxylase is associated with other diseases, such as hirsutism and cancer, especially when ornithine decarboxylase is highly upregulated in tumor cells. Furthermore, ornithine decarboxylase can be activated by c-myc or interact with ras, both of which are well-known oncogenes, thus increasing interest in targeting ornithine carboxylase as a potential cancer treatment. In 1960 and 2000, the FDA approved efornithine (brand names ORNIDYL and VANIQUA) for the treatment of African trypanosomiasis and hirsutism, respectively, but its use was subsequently discontinued. Then, on December 14, 2023, the FDA reapproved efornithine (brand name IWILFIN) as an oral maintenance therapy to reduce the risk of relapse in adult and pediatric patients with high-risk neuroblastoma who have at least a partial response to prior multi-drug, multimodal therapy (including anti-GD2 immunotherapy). This approval was based on positive results from a multicenter, single-arm, externally controlled study in children with high-risk neuroblastoma, which observed a 52% reduction in relapse risk and a 68% reduction in mortality risk. efornithine is an antimicrobial drug and a decarboxylase inhibitor. Its mechanism of action is as a decarboxylase inhibitor. efornithine is a difluoromethylated ornithine compound with antitumor activity. Eflunominosine irreversibly inhibits ornithine decarboxylase (an enzyme required for polyamine biosynthesis), thereby inhibiting the formation and proliferation of tumor cells. Polyamines are involved in nucleosome oligomerization and DNA conformation, creating a chromatin environment that stimulates tumor transformation. This drug has been shown to induce apoptosis in leiomyomas. (NCI04)
Ornithine decarboxylase inhibitor, ornithine decarboxylase is the rate-limiting enzyme in the polyamine biosynthesis pathway.
See also: Eflunominosine hydrochloride (salt form).
Drug Indications

Eflunominosine is indicated for reducing the risk of relapse in adult and pediatric patients with high-risk neuroblastoma (HRNB) who have previously received multi-drug combination therapy, including anti-GD2 immunotherapy, and have at least partial remission. This drug was previously used to treat hirsutism in women and trypanosomiasis in Africa, but this use has been discontinued.
FDA Label
Treatment of hirsutism in women.

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Mechanism of Action
Eflunotingine is an irreversible inhibitor of ornithine decarboxylase (ODC), the first rate-limiting enzyme in the polyamine biosynthesis pathway and a transcriptional target of MYCN. Polyamines are involved in mammalian cell differentiation and proliferation, and are crucial for tumor transformation. Currently, no studies have investigated the inhibition of ornithine decarboxylase (ODC) in human skin after topical application of flunotingine. However, literature reports that oral flunotingine inhibits ODC activity in the skin. It is speculated that topical application of flunotingine hydrochloride can irreversibly inhibit skin ODC activity. This enzyme is essential for polyamine synthesis. Animal experimental data indicate that inhibition of ornithine decarboxylase inhibits cell division and synthetic functions, thereby affecting hair growth rate. VANIQA has shown a hair growth-delaying effect in both non-clinical and clinical studies. Flunotingine hydrochloride (α-difluoromethylornithine) has an inhibitory effect on hair growth. The mechanism by which topical application of flunotingine hydrochloride inhibits hair growth is not fully elucidated. Multiple studies using oral efornithine hydrochloride have suggested that the drug may inhibit ornithine decarboxylase (ODC), an enzyme that catalyzes the biosynthesis of intracellular polyamines required for cell division and differentiation. Limited animal data suggest that this inhibition of cell division and differentiation may affect hair growth rate. The manufacturer of topical efornithine hydrochloride states that there are currently no published human studies on the potential of topical efornithine hydrochloride to inhibit ODC.

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1. Indications: Eflunomine hydrochloride is approved for two main indications: (1) treatment of late-stage human trypanosomiasis (HAT, sleeping sickness) caused by Trypanosoma gambiae; (2) topical treatment of unwanted facial hair in women (marketed as Vaniqa® cream, 13.9% w/w concentration) [1][2]
2. Mechanism of action: Eflunomine hydrochloride is an irreversible, mechanism-based inhibitor of ornithine decarboxylase (ODC), the first rate-limiting enzyme in the biosynthesis of polyamines (putrescine, spermine, spermine). Polyamines are essential for cell proliferation, differentiation and survival; inhibition of ODC leads to polyamine depletion, thereby inhibiting the growth of target cells such as trypanosomes, hair follicle cells and vascular smooth muscle cells [1][2][4]
3. Clinical development: For HAT, efornithine hydrochloride has replaced toxic arsenic agents as a first-line treatment for advanced disease, significantly improving patient survival. As a topical medication, it is the only FDA-approved drug for the treatment of facial hair excess, providing a non-invasive alternative to cosmetic surgery [1][2]
4. Dosage forms: Existing dosage forms include intravenous injection (200 mg/mL), oral tablets (500 mg) and topical cream (13.9% w/w). Topical creams are often used in combination with penetration enhancers (such as oleic acid) to improve skin permeability and efficacy [3]
5. Limitations: For hair follicle atrophy (HAT), intravenous injection requires professional medical personnel and the treatment course is relatively long (14 days), which limits the use of the drug in resource-scarce areas. Topical preparations do not completely inhibit hair growth and require continuous use to maintain efficacy [1][2]

C6H12N2O2F2.HCL

218.62942

236.073

68278-23-9

Eflornithine;70052-12-9;Eflornithine hydrochloride hydrate;96020-91-6;L-Eflornithine monohydrochloride;69955-42-6;L-Eflornithine;66640-93-5

57004

White to light yellow solid powder

347ºC at 760 mmHg

181-184°C

163.7ºC

1.975

4

6

5

13

166

0

NC(CCCN)(C(F)F)C(O)=O.[H]Cl

VKDGNNYJFSHYKD-UHFFFAOYSA-N

InChI=1S/C6H12F2N2O2.ClH/c7-4(8)6(10,5(11)12)2-1-3-9;/h4H,1-3,9-10H2,(H,11,12);1H

2,5-diamino-2-(difluoromethyl)pentanoic acid;hydrochloride

DFMO hydrochloride; MDL71782 hydrochloride; RMI71782 hydrochloride; α-difluoromethylornithine hydrochloride; MDL-71782 hydrochloride; RMI-71782 hydrochloride; α-difluoromethylornithine hydrochloride; MDL 71782 hydrochloride; RMI 71782 hydrochloride; α-difluoromethylornithine hydrochloride

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)

Typically soluble in DMSO (e.g.  10 mM)

Note: Listed below are some common formulations that may be used to formulate products with low water solubility (e.g. < 1 mg/mL), you may test these formulations using a minute amount of products to avoid loss of samples.

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Injection Formulation 1: DMSO : Tween 80： Saline = 10 : 5 : 85 (i.e. 100 μL DMSO stock solution → 50 μL Tween 80 → 850 μL Saline)
*Preparation of saline: Dissolve 0.9 g of sodium chloride in 100 mL ddH ₂ O to obtain a clear solution.
Injection Formulation 2: DMSO : PEG300 ：Tween 80 : Saline = 10 : 40 : 5 : 45 (i.e. 100 μL DMSO → 400 μLPEG300 → 50 μL Tween 80 → 450 μL Saline)
Injection Formulation 3: DMSO : Corn oil = 10 : 90 (i.e. 100 μL DMSO → 900 μL Corn oil)
Example: Take the Injection Formulation 3 (DMSO : Corn oil = 10 : 90) as an example, if 1 mL of 2.5 mg/mL working solution is to be prepared, you can take 100 μL 25 mg/mL DMSO stock solution and add to 900 μL corn oil, mix well to obtain a clear or suspension solution (2.5 mg/mL, ready for use in animals).

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Injection Formulation 4: DMSO : 20% SBE-β-CD in saline = 10 : 90 [i.e. 100 μL DMSO → 900 μL (20% SBE-β-CD in saline)]
*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.
Injection Formulation 5: 2-Hydroxypropyl-β-cyclodextrin : Saline = 50 : 50 (i.e. 500 μL 2-Hydroxypropyl-β-cyclodextrin → 500 μL Saline)
Injection Formulation 6: DMSO : PEG300 : castor oil : Saline = 5 : 10 : 20 : 65 (i.e. 50 μL DMSO → 100 μLPEG300 → 200 μL castor oil → 650 μL Saline)
Injection Formulation 7: Ethanol : Cremophor : Saline = 10： 10 : 80 (i.e. 100 μL Ethanol → 100 μL Cremophor → 800 μL Saline)
Injection Formulation 8: Dissolve in Cremophor/Ethanol (50 : 50), then diluted by Saline
Injection Formulation 9: EtOH : Corn oil = 10 : 90 (i.e. 100 μL EtOH → 900 μL Corn oil)
Injection Formulation 10: EtOH : PEG300：Tween 80 : Saline = 10 : 40 : 5 : 45 (i.e. 100 μL EtOH → 400 μLPEG300 → 50 μL Tween 80 → 450 μL Saline)

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Oral Formulation 1: Suspend in 0.5% CMC Na (carboxymethylcellulose sodium)
Oral Formulation 2: Suspend in 0.5% Carboxymethyl cellulose
Example: Take the Oral Formulation 1 (Suspend in 0.5% CMC Na) as an example, if 100 mL of 2.5 mg/mL working solution is to be prepared, you can first prepare 0.5% CMC Na solution by measuring 0.5 g CMC Na and dissolve it in 100 mL ddH2O to obtain a clear solution; then add 250 mg of the product to 100 mL 0.5% CMC Na solution, to make the suspension solution (2.5 mg/mL, ready for use in animals).

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Oral Formulation 3: Dissolved in PEG400
Oral Formulation 4: Suspend in 0.2% Carboxymethyl cellulose
Oral Formulation 5: Dissolve in 0.25% Tween 80 and 0.5% Carboxymethyl cellulose
Oral Formulation 6: Mixing with food powders

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Note: Please be aware that the above formulations are for reference only. InvivoChem strongly recommends customers to read literature methods/protocols carefully before determining which formulation you should use for in vivo studies, as different compounds have different solubility properties and have to be formulated differently.

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