Formestane

Formestane, formerly sold under the brand name Lentaron among others, is a steroidal, selective aromatase inhibitor which is used in the treatment of estrogen receptor-positive breast cancer in postmenopausal women.^[1] The drug is not active orally, and was available only as an intramuscular depot injection. Formestane was not approved by the United States FDA and the injectable form that was used in Europe in the past has been withdrawn from the market.^[2] Formestane is an analogue of androstenedione.

Formestane

Clinical data
Trade names	Lentaron, others
Other names	4-Hydroxyandrost-4-ene-3,17-dione
AHFS/Drugs.com	International Drug Names
Routes of administration	Intramuscular injection
Drug class	Aromatase inhibitor; Antiestrogen
ATC code	L02BG02 (WHO)
Identifiers
IUPAC name (8R,9S,10R,13S,14S)-4-hydroxy-10,13-dimethyl-2,6,7,8,9,11,12,14,15,16-decahydro-1H-cyclopenta[a]phenanthrene-3,17-dione
CAS Number	566-48-3 Y
PubChem CID	11273
ChemSpider	10799 Y
UNII	PUB9T8T355
KEGG	D07260 Y
ChEBI	CHEBI:75172 N
ChEMBL	ChEMBL132530 Y
CompTox Dashboard (EPA)	DTXSID3034113
ECHA InfoCard	100.153.838
Chemical and physical data
Formula	C19H26O3
Molar mass	302.414 g·mol−1
3D model (JSmol)	Interactive image
SMILES O=C4C(/O)=C3/CC[C@@H]2[C@H](CC[C@@]1(C(=O)CC[C@H]12)C)[C@@]3(C)CC4
InChI InChI=1S/C19H26O3/c1-18-10-8-15(20)17(22)14(18)4-3-11-12-5-6-16(21)19(12,2)9-7-13(11)18/h11-13,22H,3-10H2,1-2H3/t11-,12-,13-,18+,19-/m0/s1 Y Key:OSVMTWJCGUFAOD-KZQROQTASA-N Y
NY (what is this?)  (verify)

Formestane is often used to suppress the production of estrogens from anabolic steroids or prohormones. It also acts as a prohormone to 4-hydroxytestosterone, an active steroid which displays weak androgenic activity in addition to acting as a weak aromatase inhibitor.^[3]

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Pharmacodynamics of aromatase inhibitors

Generation	Medication	Dosage	% inhibitiona	Classb	IC50c
First	Testolactone	250 mg 4x/day p.o.	?	Type I	?
		100 mg 3x/week i.m.	?
	Rogletimide	200 mg 2x/day p.o. 400 mg 2x/day p.o. 800 mg 2x/day p.o.	50.6% 63.5% 73.8%	Type II	?
	Aminoglutethimide	250 mg mg 4x/day p.o.	90.6%	Type II	4,500 nM
Second	Formestane	125 mg 1x/day p.o. 125 mg 2x/day p.o. 250 mg 1x/day p.o.	72.3% 70.0% 57.3%	Type I	30 nM
		250 mg 1x/2 weeks i.m. 500 mg 1x/2 weeks i.m. 500 mg 1x/1 week i.m.	84.8% 91.9% 92.5%
	Fadrozole	1 mg 1x/day p.o. 2 mg 2x/day p.o.	82.4% 92.6%	Type II	?
Third	Exemestane	25 mg 1x/day p.o.	97.9%	Type I	15 nM
	Anastrozole	1 mg 1x/day p.o. 10 mg 1x/day p.o.	96.7–97.3% 98.1%	Type II	10 nM
	Letrozole	0.5 mg 1x/day p.o. 2.5 mg 1x/day p.o.	98.4% 98.9%–>99.1%	Type II	2.5 nM
Footnotes: a = In postmenopausal women. b = Type I: Steroidal, irreversible (substrate-binding site). Type II: Nonsteroidal, reversible (binding to and interference with the cytochrome P450 heme moiety). c = In breast cancer homogenates. Sources: See template.