Eflornithine: Difference between revisions

{{Short description|Chemical compound}}

{{Use dmy dates|date=February 2024}}

{{cs1 config |name-list-style=vanc |display-authors=6}}

{{Infobox drug

| verifiedrevid = 458957274

| image = Eflornithine.svg

| width = 200

| alt =

| caption =

| tradename = Vaniqa, Iwilfin, others

| synonyms = α-difluoromethylornithine or DFMO

| DailyMedID = Eflornithine

| pregnancy_category =

| routes_of_administration = [[Intravenous therapy|intravenous]], [[Topical administration|topical]]

| ATC_prefix = D11

| ATC_suffix = AX16

| ATC_supplemental = {{ATC|P01|CX03}}, {{ATC|L01|XX79}}

| legal_US = Rx-only

| legal_US_comment = <ref name="Vaniqa FDA label">{{cite web | title=Vaniqa- eflornithine hydrochloride cream | website=DailyMed | date=Sep 18, 2012 | url=https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=a2c3d206-b893-4f65-a2f6-c11fa9a0e486 | access-date=Feb 26, 2024}}</ref><ref name="Iwilfin FDA label">{{cite web | title=Iwilfin- eflornithine hydrochloride tablet | website=DailyMed | date=Dec 21, 2023 | url=https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=6716d8cc-66e6-4cee-935c-ccb85ed984f5 | access-date=Feb 26, 2024}}</ref>

| bioavailability = 100% (Intravenous)<br />Negligible (topical)

| metabolism = Not metabolized

| excretion = [[Kidney]]

| IUPHAR_ligand = 5176

| CAS_number_Ref = {{cascite|changed|??}}

| CAS_number = 70052-12-9

| DrugBank_Ref = {{drugbankcite|changed|drugbank}}

| DrugBank = DB06243

| UNII_Ref = {{fdacite|correct|FDA}}

| KEGG_Ref = {{keggcite|correct|kegg}}

| ChEBI_Ref = {{ebicite|correct|EBI}}

| ChEMBL = 830

<!--Chemical data-->

| IUPAC_name = (''RS'')-2,5-Diamino-2-(difluoromethyl)pentanoic acid

<!-- Definition and medical uses -->

'''Eflornithine''', sold under the brand name '''Vaniqa''' among others, is a [[medication]] used to treat [[African trypanosomiasis]] (sleeping sickness) and [[hirsutism|excessive hair growth]] on the face in women.<ref name="Vaniqa FDA label" /><ref name=WHO2015E>{{cite web |url=https://www.who.int/medicines/publications/essentialmedicines/EML2015_8-May-15.pdf |title=19th WHO Model List of Essential Medicines (April 2015) |date=April 2015 |access-date=May 10, 2015 |publisher=WHO |url-status=live |archive-url=https://web.archive.org/web/20150513043105/http://www.who.int/medicines/publications/essentialmedicines/EML2015_8-May-15.pdf |archive-date=May 13, 2015 }}</ref><ref name=AHFS2016>{{cite web|title=Eflornithine|url=https://www.drugs.com/monograph/eflornithine.html|publisher=The American Society of Health-System Pharmacists|access-date=28 November 2016|url-status=live|archive-url=https://web.archive.org/web/20161220223444/https://www.drugs.com/monograph/eflornithine.html|archive-date=20 December 2016}}</ref> Specifically it is used for the second stage of sleeping sickness caused by ''[[T. b. gambiense]]'' and may be used with [[nifurtimox]].<ref name=WHO2015E/><ref name=CDC2016>{{cite web|title=CDC - African Trypanosomiasis - Resources for Health Professionals|url=https://www.cdc.gov/parasites/sleepingsickness/health_professionals/|website=U.S. [[Centers for Disease Control and Prevention]] (CDC) |access-date=6 December 2016|date=10 August 2016|url-status=live|archive-url=https://web.archive.org/web/20161128180459/http://www.cdc.gov/parasites/sleepingsickness/health_professionals/|archive-date=28 November 2016}}</ref> It is taken [[intravenously]] (injection into a vein) or [[topically]].<ref name=WHO2015E/><ref name=AHFS2016/> It is an [[ornithine decarboxylase]] inhibitor.<ref name="Iwilfin FDA label" />

<!-- Side effects and mechanisms -->

Common side effects when applied as a cream include rash, redness, and burning.<ref name=AHFS2016/> Side effects of the injectable form include [[bone marrow suppression]], vomiting, and [[seizures]].<ref name=CDC2016/> It is unclear if it is safe to use during [[pregnancy]] or [[breastfeeding]].<ref name=CDC2016/> It is recommended typically for children over the age of 12.<ref name=CDC2016/>

<!-- History, society and culture -->

Eflornithine was developed in the 1970s and came into medical use in 1990.<ref>{{cite book| vauthors = Steverding D | chapter = Sleeping Sickness and Nagana Disease Caused by Trypanosoma brucei | veditors = Marcondes CB |title=Arthropod Borne Diseases |date=2016 |publisher=Springer |isbn=9783319138848 |page=292| chapter-url = https://books.google.com/books?id=Qs55DQAAQBAJ&pg=PA292|url-status=live|archive-url=https://web.archive.org/web/20170910144448/https://books.google.com/books?id=Qs55DQAAQBAJ&pg=PA292|archive-date=2017-09-10}}</ref> It is on the [[WHO Model List of Essential Medicines|World Health Organization's List of Essential Medicines]].<ref name="WHO23rd">{{cite book | vauthors = ((World Health Organization)) | title = The selection and use of essential medicines 2023: web annex A: World Health Organization model list of essential medicines: 23rd list (2023) | year = 2023 | hdl = 10665/371090 | author-link = World Health Organization | publisher = World Health Organization | location = Geneva | id = WHO/MHP/HPS/EML/2023.02 | hdl-access=free }}</ref> In the United States the injectable form can be obtained from the US [[Centers for Disease Control and Prevention]].<ref name=CDC2016/> In regions of the world where the disease is common eflornithine is provided for free by the [[World Health Organization]].<ref name=WHO2016>{{cite web|title=Trypanosomiasis, human African (sleeping sickness)|url=https://www.who.int/mediacentre/factsheets/fs259/en/|website=World Health Organization|access-date=7 December 2016|date=February 2016|url-status=live|archive-url=https://web.archive.org/web/20161204153318/http://www.who.int/mediacentre/factsheets/fs259/en/|archive-date=4 December 2016}}</ref>

{{TOC limit|3}}

==Medical uses==

===Sleeping sickness===

Sleeping sickness, or trypanosomiasis, is treated with [[pentamidine]] or [[suramin]] (depending on subspecies of parasite) delivered by intramuscular injection in the first phase of the disease, and with [[melarsoprol]] and eflornithine intravenous injection in the second phase of the disease. Efornithine is commonly given in combination with [[nifurtimox]], which reduces the treatment time to 7 days of eflornithine infusions plus 10 days of oral nifurtimox tablets.<ref>{{cite journal | vauthors = Babokhov P, Sanyaolu AO, Oyibo WA, Fagbenro-Beyioku AF, Iriemenam NC | title = A current analysis of chemotherapy strategies for the treatment of human African trypanosomiasis | journal = Pathogens and Global Health | volume = 107 | issue = 5 | pages = 242–252 | date = July 2013 | pmid = 23916333 | pmc = 4001453 | doi = 10.1179/2047773213Y.0000000105 }}</ref>

Eflornithine is also effective in combination with other drugs, such as melarsoprol and nifurtimox. A study in 2005 compared the safety of eflornithine alone to melarsoprol and found eflornithine to be more effective and safe in treating second-stage sleeping sickness ''Trypanosoma brucei gambiense''.<ref name="Priotto2">{{cite journal | vauthors = Priotto G, Fogg C, Balasegaram M, Erphas O, Louga A, Checchi F, Ghabri S, Piola P | title = Three drug combinations for late-stage Trypanosoma brucei gambiense sleeping sickness: a randomized clinical trial in Uganda | journal = PLOS Clinical Trials | volume = 1 | issue = 8 | pages = e39 | date = December 2006 | pmid = 17160135 | pmc = 1687208 | doi = 10.1371/journal.pctr.0010039 | doi-access = free }}</ref> Eflornithine is not effective in the treatment of ''Trypanosoma brucei rhodesiense'' due to the parasite's low sensitivity to the drug. Instead, melarsoprol is used to treat ''Trypanosoma brucei rhodesiense''.<ref name = "Lute_2013">{{cite journal | vauthors = Lutje V, Seixas J, Kennedy A | title = Chemotherapy for second-stage human African trypanosomiasis | journal = The Cochrane Database of Systematic Reviews | volume = 2013 | issue = 6 | pages = CD006201 | date = June 2013 | pmid = 23807762 | pmc = 6532745 | doi = 10.1002/14651858.cd006201.pub3 }}</ref> Another randomized control trial in Uganda compared the efficacy of various combinations of these drugs and found that the nifurtimox-eflornithine combination was the most promising first-line theory regimen.<ref>{{cite journal | vauthors = Chappuis F, Udayraj N, Stietenroth K, Meussen A, Bovier PA | title = Eflornithine is safer than melarsoprol for the treatment of second-stage Trypanosoma brucei gambiense human African trypanosomiasis | journal = Clinical Infectious Diseases | volume = 41 | issue = 5 | pages = 748–751 | date = September 2005 | pmid = 16080099 | doi = 10.1086/432576 | doi-access = free }}</ref>

A randomized control trial was conducted in Congo, Côte d'Ivoire, the Democratic Republic of the Congo, and Uganda to determine if a 7-day intravenous regimen was as efficient as the standard 14-day regimen for new and relapsing cases. The results showed that the shortened regimen was efficacious in relapse cases, but was inferior to the standard regimen for new cases of the disease.<ref name="Vincent_2010">{{cite journal | vauthors = Vincent IM, Creek D, Watson DG, Kamleh MA, Woods DJ, Wong PE, Burchmore RJ, Barrett MP | title = A molecular mechanism for eflornithine resistance in African trypanosomes | journal = PLOS Pathogens | volume = 6 | issue = 11 | pages = e1001204 | date = November 2010 | pmid = 21124824 | pmc = 2991269 | doi = 10.1371/journal.ppat.1001204 | doi-access = free }}</ref>

[[Nifurtimox-eflornithine combination treatment]] (NECT) is an effective regimen for the treatment of second stage gambiense [[African trypanosomiasis]].<ref>{{Cite web | url =https://www.who.int/trypanosomiasis_african/research/combination_treatment/en/ | archive-url =https://web.archive.org/web/20141021143836/http://www.who.int/trypanosomiasis_african/research/combination_treatment/en/ | url-status =dead | archive-date =October 21, 2014 | title = Nifurtimox-eflornithine combination treatment for sleeping sickness (human African trypanosomiasis): WHO wraps up training of key health care personnel | publisher = World Health Organization | date = March 23, 2010}}</ref><ref name=cdrwww>{{cite journal | vauthors = Franco JR, Simarro PP, Diarra A, Ruiz-Postigo JA, Samo M, Jannin JG | title = Monitoring the use of nifurtimox-eflornithine combination therapy (NECT) in the treatment of second stage gambiense human African trypanosomiasis | journal = Research and Reports in Tropical Medicine | volume = 3 | pages = 93–101 | year = 2012 | pmid = 30100776 | pmc = 6067772 | doi = 10.2147/RRTM.S34399 | doi-access = free }}</ref>

====Trypanosome resistance====

After its introduction to the market in the 1980s, eflornithine has replaced melarsoprol as the first line medication against Human African trypanosomiasis (HAT) due to its reduced toxicity to the host.<ref name="Vincent_2010" /> ''Trypanosoma brucei'' resistant to eflornithine was reported as early as the mid-1980s.<ref name="Vincent_2010" />

The gene TbAAT6, conserved in the genome of Trypanosomes, is believed to be responsible for the transmembrane transporter that brings eflornithine into the cell.<ref>{{cite journal | vauthors = Sayé M, Miranda MR, di Girolamo F, de los Milagros Cámara M, Pereira CA | title = Proline modulates the Trypanosoma cruzi resistance to reactive oxygen species and drugs through a novel D, L-proline transporter | journal = PLOS ONE | volume = 9 | issue = 3 | pages = e92028 | year = 2014 | pmid = 24637744 | pmc = 3956872 | doi = 10.1371/journal.pone.0092028 | bibcode = 2014PLoSO...992028S | doi-access = free }}</ref> The loss of this gene due to specific mutations causes resistance to eflornithine in several trypanosomes.<ref name="pmid17618313">{{cite journal | vauthors = Barrett MP, Boykin DW, Brun R, Tidwell RR | title = Human African trypanosomiasis: pharmacological re-engagement with a neglected disease | journal = British Journal of Pharmacology | volume = 152 | issue = 8 | pages = 1155–71 | date = December 2007 | pmid = 17618313 | pmc = 2441931 | doi = 10.1038/sj.bjp.0707354 }}</ref> If eflornithine is prescribed to a patient with Human African trypanosomiasis caused by a trypanosome that contains a mutated or ineffective TbAAT6 gene, then the medication will be ineffective against the disease. Resistance to eflornithine has increased the use of melarsoprol despite its toxicity, which has been linked to the deaths of 5% of recipient HAT patients.<ref name="Vincent_2010" />

===Excess facial hair in women===

The topical cream is indicated for treatment of facial [[hirsutism]] in women.<ref name="Vaniqa FDA label" /><ref name="NHS and UKMi New Medicines Profile">{{cite web |url=http://www.ukmi.nhs.uk/NewMaterial/html/docs/EflornithineNMP0504b.pdf |title=NHS and UKMi New Medicines Profile |url-status=dead |archive-url=https://web.archive.org/web/20100215120040/http://www.ukmi.nhs.uk/NewMaterial/html/docs/EflornithineNMP0504b.pdf |archive-date=2010-02-15 }}</ref> It is the only topical prescription treatment that slows the growth of facial hair.<ref name="BalfourMcClellan2001">{{cite journal | vauthors = Balfour JA, McClellan K | title = Topical eflornithine | journal = American Journal of Clinical Dermatology | volume = 2 | issue = 3 | pages = 197–201; discussion 202 | date = June 2001 | pmid = 11705097 | doi = 10.2165/00128071-200102030-00009 | s2cid = 26181011 }}</ref> In clinical studies with Vaniqa, 81% percent of women showed clinical improvement after twelve months of treatment.<ref name="longterm">{{cite conference | vauthors = Schrode K, Huber F, Staszak J | conference = 58th Annual Meeting American Academy of Dermatology | collaboration = The Eflornithine Study Group |title=Evaluation of the long-term safety of eflornithine 15% cream in the treatment of women with excessive facial hair, Poster 294 | date = March 2000 | location = San Francisco; USA}}</ref> Positive results were seen after eight weeks.<ref name="apple">{{cite conference | vauthors = Schrode K, Huber F, Staszak J, Altman DJ, Shander D, Morton J | collaboration = The Eflornithine Study Group |title=Randomized, double-blind, vehicle-controlled safety and efficacy evaluation of eflornithine 15% cream in the treatment of women with excessive facial hair. Poster 291 | conference = 58th Annual Meeting of the Academy of Dermatology | date = March 2000 | location = San Francisco; USA }}</ref> However, discontinuation of the cream caused regrowth of hair back to baseline levels within 8 weeks.<ref>{{cite journal | vauthors = Wolf JE, Shander D, Huber F, Jackson J, Lin CS, Mathes BM, Schrode K | title = Randomized, double-blind clinical evaluation of the efficacy and safety of topical eflornithine HCl 13.9% cream in the treatment of women with facial hair | journal = International Journal of Dermatology | volume = 46 | issue = 1 | pages = 94–98 | date = January 2007 | pmid = 17214730 | doi = 10.1111/j.1365-4632.2006.03079.x | s2cid = 10795478 }}</ref>

Vaniqa treatment significantly reduces the psychological burden of facial hirsutism.<ref name="Jackson _2007">{{cite journal | vauthors = Jackson J, Caro JJ, Caro G, Garfield F, Huber F, Zhou W, Lin CS, Shander D, Schrode K | title = The effect of eflornithine 13.9% cream on the bother and discomfort due to hirsutism | journal = International Journal of Dermatology | volume = 46 | issue = 9 | pages = 976–81 | date = September 2007 | pmid = 17822506 | doi = 10.1111/j.1365-4632.2007.03270.x | s2cid = 25986442 | collaboration = flornithine HCl Study Group }}</ref>

=== Neuroblastoma ===

In the US, eflornithine is [[indicated]] to reduce the risk of relapse in people with high-risk neuroblastoma.<ref name="Iwilfin FDA label" />

==Contraindications==

===Topical===

Topical use is contraindicated in people hypersensitive to eflornithine or to any of the excipients.<ref name="emc.medicines.org.uk">{{cite web |url=http://www.emc.medicines.org.uk/medicine/21243/SPC/Vaniqa+11.5%+cream |title=Vaniqa Summary of Product Characteristics 2008 |url-status=dead |archive-url=https://web.archive.org/web/20091205163254/http://emc.medicines.org.uk/medicine/21243/SPC/Vaniqa+11.5%25+cream/ |archive-date=2009-12-05 }}</ref>

Throughout clinical trials, data from a limited number of exposed pregnancies indicate that there is no clinical evidence that treatment with Vaniqa adversely affects pregnant women or fetuses.<ref name="emc.medicines.org.uk"/>

===Oral administration===

When taken orally the risk-benefit should be assessed in people with impaired renal function or pre-existing hematologic abnormalities, as well as those with eighth-cranial-nerve impairment.<ref name="Ornidyl Drug Information">{{cite web|url=https://www.drugs.com/mmx/ornidyl.html |title=Ornidyl Drug Information |url-status=dead |archive-url=https://web.archive.org/web/20110607070234/http://www.drugs.com/mmx/ornidyl.html |archive-date=2011-06-07 }}</ref>

Adequate and well-controlled studies with eflornithine have not been performed regarding pregnancy in humans. Eflornithine should only be used during pregnancy if the potential benefit outweighs the potential risk to the fetus. However, since African trypanosomiasis has a high mortality rate if left untreated, treatment with eflornithine may justify any potential risk to the fetus.<ref name="Ornidyl Drug Information"/>

==Side effects==

Eflornithine is not genotoxic; no tumour-inducing effects have been observed in [[carcinogen]]icity studies, including one photocarcinogenicity study.<ref>{{cite journal | vauthors = Malhotra B, Noveck R, Behr D, Palmisano M | title = Percutaneous absorption and pharmacokinetics of eflornithine HCl 13.9% cream in women with unwanted facial hair | journal = Journal of Clinical Pharmacology | volume = 41 | issue = 9 | pages = 972–978 | date = September 2001 | pmid = 11549102 | doi = 10.1177/00912700122010951 | url = http://onlinelibrary.wiley.com/doi/10.1177/009127000104100907/abstract | url-status = live | archive-url = https://web.archive.org/web/20161112021229/http://onlinelibrary.wiley.com/doi/10.1177/009127000104100907/abstract | archive-date = 2016-11-12 }}</ref> No [[Teratology|teratogenic]] effects have been detected.<ref name=":0">{{cite book |title=Vaniqa Product Monograph | url = https://pdf.hres.ca/dpd_pm/00031219.PDF | date = 8 July 2015 | publisher = Cipher Pharmaceuticals Inc. | via = Drug and Health Product Register, Canada }}</ref>

===Topical ===

The topical form of elflornithine is sold under the brand name Vaniqa. The most frequently reported side effect is [[acne]] (7–14%). Other side effects commonly (> 1%) reported are skin problems, such as skin reactions from in-growing hair, hair loss, burning, stinging or tingling sensations, dry skin, itching, redness or rash.<ref name="vaniqa.com"/>

===Intravenous ===

The intravenous dosage form of eflornithine is sold under the brand name Ornidyl. Most side effects related to systemic use through injection are transient and reversible by discontinuing the drug or decreasing the dose. Hematologic abnormalities occur frequently, ranging from 10 to 55%. These abnormalities are dose-related and are usually reversible. [[Thrombocytopenia]] is thought to be due to a production defect rather than to peripheral destruction. [[Seizures]] were seen in approximately 8% of patients, but may be related to the disease state rather than the drug. Reversible hearing loss has occurred in 30–70% of patients receiving long-term therapy (more than 4–8 weeks of therapy or a total dose of >300&nbsp;grams); high-frequency hearing is lost first, followed by middle- and low-frequency hearing. Because treatment for African trypanosomiasis is short-term, patients are unlikely to experience hearing loss.<ref name="vaniqa.com" />

== Interactions ==

===Topical===

No interaction studies with the topical form have been performed.<ref name="emc.medicines.org.uk"/>

==Mechanism of action==

===Description===

Eflornithine is a "[[Suicide inhibition|suicide inhibitor]]," irreversibly binding to [[ornithine decarboxylase]] (ODC) and preventing the natural substrate ornithine from accessing the active site (Figure 1). Within the active site of ODC, eflornithine undergoes [[decarboxylation]] with the aid of cofactor pyridoxal 5'-phosphate (PLP). Because of its additional difluoromethyl group in comparison to ornithine, eflornithine is able to bind to a neighboring Cys-360 residue, permanently remaining fixated within the active site.<ref name=":0" />

During the reaction, eflornithine's decarboxylation mechanism is analogous to that of ornithine in the active site, where [[transamination]] occurs with PLP followed by decarboxylation. During the event of decarboxylation, the fluoride atoms attached to the additional methyl group pull the resulting negative charge from the release of carbon dioxide, causing a fluoride ion to be released. In the natural substrate of ODC, the ring of PLP accepts the electrons that result from the release of CO₂.{{cn|date=December 2022}}

The remaining [[fluoride]] atom that resides attached to the additional methyl group creates an electrophilic carbon that is attacked by the nearby thiol group of Cys-360, allowing eflornithine to remain permanently attached to the enzyme following the release of the second fluoride atom and transimination.

===Evidence===

The reaction mechanism of ''[[Trypanosoma brucei]]''{{'s}} ODC with ornithine was characterized by UV-VIS spectroscopy in order to identify unique intermediates that occurred during the reaction. The specific method of multiwavelength stopped-flow spectroscopy utilized monochromatic light and fluorescence to identify five specific intermediates due to changes in absorbance measurements.<ref name=name>{{cite journal | vauthors = Brooks HB, Phillips MA | title = Characterization of the reaction mechanism for Trypanosoma brucei ornithine decarboxylase by multiwavelength stopped-flow spectroscopy | journal = Biochemistry | volume = 36 | issue = 49 | pages = 15147–15155 | date = December 1997 | pmid = 9398243 | doi = 10.1021/bi971652b }}</ref> The steady-state turnover number, k_cat, of ODC was calculated to be 0.5&nbsp;s^&minus;1 at 4&nbsp;°C.<ref name=name/> From this characterization, the rate-limiting step was determined to be the release of the product putrescine from ODC's reaction with ornithine.

In studying the hypothetical reaction mechanism for eflornithine, information collected from radioactive peptide and eflornithine mapping, high pressure liquid [[chromatography]], and gas phase peptide sequencing suggested that Lys-69 and Cys-360 are covalently bound to eflornithine in ''T. brucei'' ODC's active site.<ref name=mech>{{cite journal | vauthors = Poulin R, Lu L, Ackermann B, Bey P, Pegg AE | title = Mechanism of the irreversible inactivation of mouse ornithine decarboxylase by alpha-difluoromethylornithine. Characterization of sequences at the inhibitor and coenzyme binding sites | journal = The Journal of Biological Chemistry | volume = 267 | issue = 1 | pages = 150–158 | date = January 1992 | pmid = 1730582 | doi = 10.1016/S0021-9258(18)48472-4 | doi-access = free }}</ref> Utilizing fast-atom bombardment mass spectrometry (FAB-MS), the structural conformation of eflornithine following its interaction with ODC was determined to be (''S'')-((2-(1-pyrroline-methyl) cysteine, a cyclic imine adduct. Presence of this particular product was supported by the possibility to further reduce the end product to (''S'')-((2-pyrrole) methyl) cysteine in the presence of [[sodium borohydride|NaBH₄]] and oxidize the end product to (''S'')-((2-pyrrolidine) methyl) cysteine (Figure 2).<ref name=mech/>

===Active site===

Eflornithine's suicide inhibition of ODC physically blocks the natural substrate ornithine from accessing the active site of the enzyme (Figure 3).<ref name=":0" /> There are two distinct active sites formed by the [[homodimerization]] of ornithine decarboxylase. The size of the opening to the active site is approximately 13.6 Å. When these openings to the active site are blocked, there are no other ways through which ornithine can enter the active site. During the intermediate stage of eflornithine with PLP, its position near Cys-360 allows an interaction to occur. As the phosphate of PLP is stabilized by Arg 277 and a Gly-rich loop (235-237), the difluoromethyl group of eflornithine is able to interact and remain fixated to both Cys-360 and PLP prior to transimination.

As shown in the figure, the pyrroline ring interferes with ornithine's entry (Figure 4). Eflornithine will remain permanently bound in this position to Cys-360. As ODC has two active sites, two eflornithine molecules are required to completely inhibit ODC from ornithine decarboxylation.

<gallery widths="200px" heights="200px" >

File:Ornithine and Eflornithine Comparison Structures.tiff|Figure 1<br>(A) 3D structure of L-Ornithine (B) 3D structure of Eflornithine. This molecule is similar to the structure of L-Ornithine, but its alpha-difluoromethyl group allows interaction with Cys-360 in the active site

File:Eflornithine Reaction Mechansim.png|Eflornithine ODC reaction mechanism

File:DFMO inhibitor product evidence.svg|Figure 2 <br>Experimental Evidence for Eflornithine End Product<ref name=mech/>

File:Eflornithine in the Active Site.png|Figure 3 <br>Active Site of ODC Formed by Homodimerization (Green and White Surface Structures) (A) Ornithine in the Active Site of ODC, Cys-360 highlighted in yellow (B) Product of Eflornithine Decarboxylation bound to Cys 360 (highlighted in yellow). The pyrroline ring blocks ornithine from entering the active site<ref>{{cite journal | vauthors = Grishin NV, Osterman AL, Brooks HB, Phillips MA, Goldsmith EJ | title = X-ray structure of ornithine decarboxylase from Trypanosoma brucei: the native structure and the structure in complex with alpha-difluoromethylornithine | journal = Biochemistry | volume = 38 | issue = 46 | pages = 15174–15184 | date = November 1999 | pmid = 10563800 | doi = 10.1021/bi9915115 }}</ref>

</gallery>

==History==

Eflornithine was initially developed for cancer treatment at Merrell Dow Research Institute in the late 1970s, but was found to be ineffective in treating malignancies. However, it was discovered to be highly effective in reducing hair growth,<ref name="Wolf">{{cite journal | vauthors = Wolf JE, Shander D, Huber F, Jackson J, Lin CS, Mathes BM, Schrode K | title = Randomized, double-blind clinical evaluation of the efficacy and safety of topical eflornithine HCl 13.9% cream in the treatment of women with facial hair | journal = International Journal of Dermatology | volume = 46 | issue = 1 | pages = 94–98 | date = January 2007 | pmid = 17214730 | doi = 10.1111/j.1365-4632.2006.03079.x | s2cid = 10795478 }}</ref> as well as in the treatment of [[African trypanosomiasis]] (sleeping sickness),<ref name="Pepin_1987">{{cite journal | vauthors = Pepin J, Milord F, Guern C, Schechter PJ | title = Difluoromethylornithine for arseno-resistant Trypanosoma brucei gambiense sleeping sickness | journal = Lancet | volume = 2 | issue = 8573 | pages = 1431–1433 | date = December 1987 | pmid = 2891995 | doi = 10.1016/S0140-6736(87)91131-7 | s2cid = 41019313 }}</ref> especially the West African form (Trypanosoma brucei gambiense).

===Hirsutism===

In the 1980s, Gillette was awarded a patent for the discovery that topical application of eflornithine HCl cream inhibits hair growth. In the 1990s, Gillette conducted dose-ranging studies with eflornithine in hirsute women that demonstrated that the drug slows the rate of facial hair growth. Gillette then filed a patent for the formulation of eflornithine cream. In July 2000, the U.S. [[Food and Drug Administration]] (FDA) granted a [[New Drug Application]] for Vaniqa. The following year, the European Commission issued its Marketing Authorisation.{{cn|date=December 2022}}

===Sleeping sickness treatment===

The drug was registered for the treatment of gambiense sleeping sickness on November 28, 1990.<ref name = "Lute_2013" /> However, in 1995 Aventis (now Sanofi-Aventis) stopped producing the drug, whose main market was African countries, because it did not make a profit.<ref name="MSF">{{cite web|url=http://www.msf.org/article/supply-sleeping-sickness-drugs-confirmed|title=Supply of sleeping sickness drugs confirmed | date = 3 May 2001 | work = Médecins Sans Frontières |url-status=live|archive-url=https://web.archive.org/web/20150921203626/http://www.msf.org/article/supply-sleeping-sickness-drugs-confirmed|archive-date=2015-09-21}}</ref>

In 2001, Aventis and the WHO formed a five-year partnership, during which more than 320,000 vials of pentamidine, over 420,000 vials of melarsoprol, and over 200,000 bottles of eflornithine were produced by Aventis, to be given to the WHO and distributed by the association [[Médecins sans Frontières]] (also known as Doctors Without Borders)<ref name="en.sanofi-aventis.com">{{cite web|url=http://en.sanofi-aventis.com/binaries/brochure_aam_en_tcm28-18133.pdf|title=Sanofi-Aventis Access to Medicines Brochure|url-status=live|archive-url=https://web.archive.org/web/20081114211421/http://en.sanofi-aventis.com/binaries/brochure_aam_en_tcm28-18133.pdf|archive-date=2008-11-14}}</ref><ref>{{cite web |url=http://www.ifpma.org/Health/other_infect/health_sleep.aspx |title=IFPMA Health Initiatives: Sleeping Sickness |url-status=dead |archive-url=https://web.archive.org/web/20060829033157/http://www.ifpma.org/Health/other_infect/health_sleep.aspx |archive-date=2006-08-29 }}</ref> in countries where sleeping sickness is endemic.

According to Médecins sans Frontières, this only happened after "years of international pressure," and coinciding with the period when media attention was generated because of the launch of another eflornithine-based product (Vaniqa, for the prevention of facial-hair in women),<ref name="MSF"/> while its life-saving formulation (for sleeping sickness) was not being produced.

From 2001 (when production was restarted) through 2006, 14 million diagnoses were made. This greatly contributed to stemming the spread of sleeping sickness, and to saving nearly 110,000 lives.{{cn|date=December 2022}}

==Society and culture==

[[File:EflornithineBottle.jpg|thumb|VIal of eflornithine]]

===Available forms===

Vaniqa is a cream, which is white to off-white in colour. It is supplied in tubes of 30 g and 60 g in Europe.<ref name="vaniqa.com">{{cite web|url=http://www.vaniqa.com/files/Vaniqa_Prescription_Info.pdf|title=Vaniqa US Patient Information Leaflet|url-status=live|archive-url=https://web.archive.org/web/20100215071210/http://www.vaniqa.com/files/Vaniqa_Prescription_Info.pdf|archive-date=2010-02-15}}</ref> Vaniqa contains 15% w/w eflornithine hydrochloride monohydrate, corresponding to 11.5% w/w anhydrous eflornithine (EU), respectively 13.9% w/w anhydrous eflornithine hydrochloride (U.S.), in a cream for topical administration.{{cn|date=December 2022}}

Ornidyl, intended for injection, was supplied in the strength of 200&nbsp;mg eflornithine hydrochloride per ml.<ref>{{cite web|url=http://drugs-about.com/drugs-o/ornidyl.html|title=Ornidyl facts|url-status=live|archive-url=https://web.archive.org/web/20110720160205/http://drugs-about.com/drugs-o/ornidyl.html|archive-date=2011-07-20}}</ref>

===Market===

Vaniqa, granted marketing approval by the US FDA, as well as by the European Commission<ref name="Vaniqa Training Programme Module 5">{{cite report |title=Vaniqa Training Programme Module 5}}</ref> among others, is currently the only topical prescription treatment that slows the growth of facial hair.<ref name="BalfourMcClellan2001"/> Besides being a non-mechanical and non-cosmetic treatment, it is the only non-hormonal and non-systemic prescription option available for women with facial hirsutism.<ref name="NHS and UKMi New Medicines Profile"/> Vaniqa is marketed by Almirall in Europe, SkinMedica in the US, Triton in Canada, Medison in Israel, and Menarini in Australia.<ref name="Vaniqa Training Programme Module 5"/>

Ornidyl, the injectable form of eflornithine hydrochloride, is licensed by Sanofi-Aventis, but is currently discontinued in the US.<ref>{{Cite web|url=http://www.accessdata.fda.gov/scripts/cder/drugsatfda/index.cfm?fuseaction=Search.DrugDetails|title=Drugs@FDA: FDA Approved Drug Products|website=www.accessdata.fda.gov|access-date=2016-11-17|url-status=live|archive-url=https://web.archive.org/web/20140813131107/http://www.accessdata.fda.gov/scripts/cder/drugsatfda/index.cfm?fuseaction=Search.DrugDetails|archive-date=2014-08-13}}</ref>

== Research ==

===Chemo preventative therapy===

It has been noted that [[ornithine decarboxylase]] (ODC) exhibits high activity in tumor cells, promoting cell growth and division, while absence of ODC activity leads to depletion of [[putrescine]], causing impairment of RNA and DNA synthesis. Typically, drugs that inhibit cell growth are considered candidates for cancer therapy, so eflornithine was naturally believed to have potential utility as an anti-cancer agent. By inhibiting ODC, eflornithine inhibits cell growth and division of both cancerous and noncancerous cells.{{cn|date=December 2022}}

However, several clinical trials demonstrated minor results.<ref name="Raul_2007">{{cite journal | vauthors = Raul F | title = Revival of 2-(difluoromethyl)ornithine (DFMO), an inhibitor of polyamine biosynthesis, as a cancer chemopreventive agent | journal = Biochemical Society Transactions | volume = 35 | issue = Pt 2 | pages = 353–5 | date = April 2007 | pmid = 17371277 | doi = 10.1042/BST0350353 }}</ref> It was found that inhibition of ODC by eflornithine does not kill proliferating cells, making eflornithine ineffective as a chemotherapeutic agent. The inhibition of the formation of [[polyamine]]s by ODC activity can be ameliorated by dietary and bacterial means because high concentrations are found in cheese, red meat, and some intestinal bacteria, providing reserves if ODC is inhibited.<ref name="Gerner, Eugene W." /> Although the role of polyamines in carcinogenesis is still unclear, polyamine synthesis has been supported to be more of a causative agent rather than an associative effect in cancer.<ref name="Raul_2007" />

Other studies have suggested that eflornithine can still aid in some chemoprevention by lowering polyamine levels in colorectal mucosa, with additional strong preclinical evidence available for application of eflornithine in colorectal and skin carcinogenesis.<ref name="Raul_2007" /><ref name="Gerner, Eugene W.">{{cite journal | vauthors = Gerner EW, Meyskens FL | title = Polyamines and cancer: old molecules, new understanding | journal = Nature Reviews. Cancer | volume = 4 | issue = 10 | pages = 781–792 | date = October 2004 | pmid = 15510159 | doi = 10.1038/nrc1454 | s2cid = 37647479 | url = https://www.escholarship.org/uc/item/1sc3c2gj }}</ref> This has made eflornithine a supported chemopreventive therapy specifically for colon cancer in combination with other medications. Several additional studies have found that eflornithine in combination with other compounds decreases the carcinogen concentrations of ethylnitrosourea, dimethylhydrazine, azoxymethane, methylnitrosourea, and hydroxybutylnitrosamine in the brain, spinal cord, intestine, mammary gland, and urinary bladder.<ref name="Gerner, Eugene W." />

==Veterinary uses==

Eflornithine is effective in [[mouse|mice]].<ref name="Klug-et-al-2016">{{cite journal | vauthors = Klug DM, Gelb MH, Pollastri MP | title = Repurposing strategies for tropical disease drug discovery | journal = Bioorganic & Medicinal Chemistry Letters | volume = 26 | issue = 11 | pages = 2569–2576 | date = June 2016 | pmid = 27080183 | pmc = 4853260 | doi = 10.1016/j.bmcl.2016.03.103 | publisher = [[Elsevier]] }} [[NIH Manuscript Submission|NIHMS]] 777366.</ref><ref name="Brun-et-al-2010">{{cite journal | vauthors = Büscher P, Cecchi G, Jamonneau V, Priotto G | title = Human African trypanosomiasis | journal = Lancet | volume = 390 | issue = 10110 | pages = 2397–2409 | date = November 2017 | pmid = 28673422 | doi = 10.1016/s0140-6736(09)60829-1 | publisher = [[Elsevier]] | s2cid = 4853616 }}</ref> Bacchi et al. 1980 found the drug to be curative in ''[[Trypanosoma brucei brucei|T. b. brucei]]'' infection of mouse and it is generally without toxicity.<ref name="Klug-et-al-2016" /> Klug et al. 2016<ref name="Klug-et-al-2016" /> are of the opinion that this demonstrates good promise for oral treatment. However although Jansson et al. 2008 also effectively treated mice with it they found the [[pharmacokinetics]] of oral administration in [[rat]]s very negative.<ref name="Brun-et-al-2010" /> Brun et al. 2010<ref name="Brun-et-al-2010" /> are of the opinion that Jansson's results have killed the prospects for oral treatment.

{{-}}

== References ==

{{Reflist}}

== External links ==

* {{Commonscatinline|Eflornithine}}

* {{ClinicalTrialsGov|NCT02395666|Preventative Trial of Difluoromethylornithine (DFMO) in High Risk Patients With Neuroblastoma That is in Remission}}

* {{ClinicalTrialsGov|NCT02679144|Neuroblastoma Maintenance Therapy Trial (NMTT)}}

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