Ornithine decarboxylase

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]

The only novel drug approved in the last fifty years for the treatment of human African trypanosomiasis is eflornithine. It is mostly used as a stand-by medication for Trypanosoma brucei gambiense infections that do not respond to melarsoprol [1]. When it came to decreasing the growth of facial hair in participants with excess hair, eflornithine 15% cream outperformed a placebo. Following a 24-week course of treatment, face hirsutism improved at least somewhat in 58% of eflornithine patients and 34% of placebo subjects [2]. When eflornithine cream was administered to mouse skin areas that had been microneedled beforehand, the hair growth inhibitory activity of eflornithine was markedly increased [3]. After 14 days of hypertension, eflornithine treatment of constrictive hypertensive rats led to the normalization of KCI and norepinephrine contractile strength as well as the relaxing of acetylcholine [4].

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.

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].

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].
Female 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]

Absorption, Distribution and Excretion
Following oral administrations of eflornithine, peak plasma concentrations of eflornithine (Cmax) were achieved (Tmax) 3.5 hours post-dosing. The Cmax and AUC (area under the concentration-time curve) of eflornithine were not affected by food (high fat and high calories). Administration of crushed tablets in a standard pudding admixture had no effect on eflornithine exposure (Cmax and AUC6h). The mean percutaneous absorption of eflornithine in women with unwanted facial hair, from a 13.9% w/w cream formulation, is < 1% of the radioactive dose, following either single or multiple doses under conditions of clinical use, that included shaving within 2 hours before radiolabeled dose application in addition to other forms of cutting or plucking and tweezing to remove facial hair. Steady state was reached within four days of twice-daily application. Following twice-daily application of 0.5 g of the cream (total dose 1.0 g/day; 139 mg as anhydrous eflornithine hydrochloride), under conditions of clinical use in women with unwanted facial hair (n=10), the steady-state Cmax, Ctrough and AUC12hr were approximately 10 ng/mL, 5 ng/mL, and 92 ng hr/mL, respectively, expressed in terms of the anhydrous free base of eflornithine hydrochloride. At steady state, the dose-normalized peak concentrations (Cmax) and the extent of daily systemic exposure (AUC) of eflornithine following twice-daily application of 0.5 g of the cream (total dose 1.0 g/day) is estimated to be approximately 100- and 60-fold lower, respectively, when compared to 370 mg/day once-daily oral doses.
This compound is not known to be metabolized and is primarily excreted unchanged in the urine.
Eflornithine volume of distribution (Vz/F) is 24.3 L.
The clearance (CL/F) of eflornithine is 5.3 L/h.
The mean percutaneous absorption of eflornithine in women with unwanted facial hair, from a 13.9% w/w cream formulation, is < 1% of the radioactive dose, following either single or multiple doses under conditions of clinical use, that included shaving within 2 hr before radiolabeled dose application in addition to other forms of cutting or plucking and tweezing to remove facial hair.
Following twice daily application of 0.5 g of the cream (total dose 1.0 g/day; 139 mg as anhydrous eflornithine hydrochloride), under conditions of clinical use in women with unwanted facial hair (n=10), the steady-state Cmax, Ctrough and AUC12hr were approximately 10 ng/mL, 5 ng/mL, and 92 nghr/mL, respectively, expressed in terms of the anhydrous free base of eflornithine hydrochloride.
At steady state, the dose-normalized peak concentrations (Cmax) and the extent of daily systemic exposure (AUC) of eflornithine following twice-daily application of 0.5 g of the cream (total dose 1.0 g/day) is estimated to be approximately 100- and 60-fold lower, respectively, when compared to 370 mg/day once-daily oral doses.
Eflornithine is not metabolized and is excreted unchanged in urine.
For more Absorption, Distribution and Excretion (Complete) data for Eflornithine (8 total), please visit the HSDB record page.

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

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

Effects During Pregnancy and Lactation
◉ Summary of Use during Lactation
Maternal intravenous eflornithine 400 mg/kg daily for 7 days did not cause any adverse serious effects in breastfed infants. After topical application, eflornithine is poorly absorbed so it is not likely to reach the bloodstream of the infant or cause any adverse effects in breastfed infants.
◉ Effects in Breastfed Infants
A cohort of 33 infants who were breastfed (extent not stated) by hospitalized mothers taking nifurtimox was followed in the Democratic Republic of the Congo. Thirty mothers took a full course of 30 doses of oral nifurtimox 15 mg/kg daily and all received 14 doses of intravenous eflornithine 400 mg/kg daily for 7 days for human African trypanosomiasis. (sleeping sickness). Nursing mothers also took a median of 4 other concomitant medications, including amoxicillin, ciprofloxacin, metronidazole, trimethoprim-sulfamethoxazole, aspirin, and diclofenac (1 patient each); hydrocortisone, promethazine and quinine (2 patients each); levamisole (6 patients); sulfadoxine-pyrimethamine (8 patients); dipyrone (13 patients); acetaminophen (16 patients); and mebendazole (17 patients). No serious adverse events were reported in any of the breastfed infants.
◉ Effects on Lactation and Breastmilk
Relevant published information was not found as of the revision date.

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Protein Binding
Eflornithine does not specifically bind to human plasma proteins.

[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.

Eflornithine is a fluoroamino acid that is ornithine substituted by a difluoromethyl group at position 2. It has a role as a trypanocidal drug. It is a fluoroamino acid and an alpha-amino acid. It is functionally related to an ornithine.
Eflornithine is an irreversible ornithine decarboxylase inhibitor originally developed as a treatment for human African trypanosomiasis. Further research has also implicated ornithine decarboxylase in other conditions like facial hirsutism and cancer, especially when ornithine decarboxylase is highly upregulated in tumor cells. Additionally, ornithine decarboxylase is activated by c-myc or interacts with ras, both very well-known oncogenes, thus increasing the interest in targeting ornithine carboxylase as a potential cancer treatment. In 1960 and 2000, the FDA approved eflornithine under the brand names ORNIDYL and VANIQUA for the treatment of African trypanosomiasis and hirsutism, respectively, but has since been discontinued. Subsequently, on December 14, 2023, the FDA approved eflornithine again but under the 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 demonstrated at least a partial response to prior multiagent, multimodality therapy, including anti-GD2 immunotherapy. This approval is based on positive results obtained from a multi-site, single-arm, externally controlled study of children with high-risk neuroblastoma, where a 52% reduction in the risk of relapse and a 68% reduction in the risk of death were observed.
Eflornithine is an Antiprotozoal and Decarboxylase Inhibitor. The mechanism of action of eflornithine is as a Decarboxylase Inhibitor.
Eflornithine is a difluoromethylated ornithine compound with antineoplastic activity. Eflornithine 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 neoplastic transformation of cells. This agent has been shown to induce apoptosis in leiomyoma cells. (NCI04)
An inhibitor of ornithine decarboxylase, the rate limiting enzyme of the polyamine biosynthetic pathway.
See also: Eflornithine Hydrochloride (has salt form).

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Drug Indication
Eflornithine is indicated to reduce the risk of relapse in adult and pediatric patients with high-risk neuroblastoma (HRNB) who have demonstrated at least a partial response to prior multiagent, multimodality therapy including anti-GD2 immunotherapy. It was also previously indicated for the treatment of female hirsutism and African trypanosomiasis but has since been discontinued.
FDA Label
Treatment of facial hirsutism in women.

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Mechanism of Action
Eflornithine is an irreversible inhibitor of the enzyme ornithine decarboxylase (ODC), the first and rate-limiting enzyme in the biosynthesis of polyamines and a transcriptional target of MYCN. Polyamines are involved in the differentiation and proliferation of mammalian cells and are important for neoplastic transformation.
There are no studies examining the inhibition of the enzyme ornithine decarboxylase (ODC) in human skin following the application of topical eflornithine. However, there are studies in the literature that report the inhibition of ODC activity in skin following oral eflornithine. It is postulated that topical eflornithine hydrochloride irreversibly inhibits skin ODC activity. This enzyme is necessary in the synthesis of polyamines. Animal data indicate that inhibition of ornithine decarboxylase inhibits cell division and synthetic functions, which affect the rate of hair growth. VANIQA has been shown to retard the rate of hair growth in non-clinical and clinical studies.
Eflornithine (alpha-difluoromethylornithine) hydrochloride has hair growth retarding properties. The mechanism(s) by which topically applied eflornithine hydrochloride reduces hair growth has not been fully elucidated. Results of several studies using oral eflornithine hydrochloride indicate 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 indicate that such inhibition of cell division and differentiation may affect the rate of hair growth. The manufacturer of topical eflornithine hydrochloride states that there are no published studies in humans on the ODC inhibitory potential of topical eflornithine hydrochloride.

C6H12F2N2O2

182.16848

182.087

C, 39.56; H, 6.64; F, 20.86; N, 15.38; O, 17.57

70052-12-9

Eflornithine hydrochloride hydrate;96020-91-6;L-Eflornithine monohydrochloride;69955-42-6;Eflornithine hydrochloride;68278-23-9;L-Eflornithine;66640-93-5; 70052-12-9; 70050-55-4 (R-isomer)

3009

White to light yellow solid

1.293g/cm3

347ºC at 760 mmHg

163.7ºC

1.173

3

6

5

12

166

0

NC(CCCN)(C(F)F)C(O)=O

VLCYCQAOQCDTCN-UHFFFAOYSA-N

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

2,5-diamino-2-(difluoromethyl)pentanoic acid.

CPP-1X; DFMO; MDL 71782; MDL-71782; EFLORNITHINE; 70052-12-9; dfmo; Difluoromethylornithine; Ornidyl; 2-(Difluoromethyl)ornithine; 2,5-diamino-2-(difluoromethyl)pentanoic acid; Eflornithinum; MDL71782; RMI71782; RMI-71782; RMI 71782; Difluoromethylornithine Eflornithine

2934.99.9001

Powder      -20°C    3 years

                     4°C     2 years

In solvent   -80°C    6 months

                  -20°C    1 month

Note: Please store this product in a sealed and protected environment, avoid exposure to moisture.

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

H2O : ~83.33 mg/mL (~457.43 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.)