# Estradiol stearate

Estradiol stearate (E2-17-St), also known as estradiol octadecanoate and sold under the brand name Depofollan, is a naturally occurring estrogen and an estrogen ester – specifically, the C17β stearate ester of estradiol. It occurs in the body as a very long-lasting metabolite and prohormone of estradiol. The compound is one of the components that collectively constitute lipoidal estradiol, another of which is estradiol palmitate. It is extremely lipophilic and hydrophobic. Estradiol stearate has no affinity for the estrogen receptor, requiring transformation into estradiol via esterases for its estrogenic activity. The compound does not bind to sex hormone-binding globulin or α-fetoprotein, instead being transported by lipoproteins such as high-density lipoprotein and low-density lipoprotein.
Estradiol stearate has a prolonged duration of action relative to estradiol regardless of whether it is given by intravenous injection or subcutaneous injection. This is in contrast to short-chain fatty acid esters of estradiol, such as estradiol benzoate, which do not show a prolonged duration with intravenous injection. When administered by intravenous injection in rodents, estradiol stearate has a greatly increased terminal half-life relative to estradiol (6 hours vs. 2 minutes). Estradiol stearate also had a half-life that was 60% longer than that of estradiol arachidonate, despite similar ester chain lengths. In contrast to the long-chain esters, the half-lives of short-chain estradiol esters such as estradiol acetate and estradiol hexanoate were the same as that of estradiol. As such, whereas short-chain estradiol esters are rapidly hydrolyzed, long-chain estradiol esters like estradiol stearate are resistant to metabolism. Thus, the prolongation of effect of short-chain estradiol esters is purely due to their increased lipophilicity and slow release from the injected depot, whereas the prolonged duration of long-chain estradiol esters is due both to this property and to their resistance to metabolism. Estradiol stearate is susceptible to first-pass metabolism in the liver, and hence has much greater potency by subcutaneous injection than by oral administration.
In addition to its endogenous role, estradiol stearate was previously available as a pharmaceutical drug for use via depot intramuscular injection. The medication was introduced between 1938 and 1941 under the brand name Depofollan. It has been used to treat prostate cancer. Estradiol stearate is a long-acting estrogen and is said to have been the first long-acting estrogen used in medicine, although it was never widely employed. It was reported to have a duration of more than one month. The medication was provided as an oil solution in ampoules containing 15 mg estradiol stearate. It was manufactured by Chinoin, a Hungarian pharmaceutical company. The compound was studied by Karl Miescher in 1938 and was patented by Miescher and Chinoin in 1939 and 1941, respectively. A similar clinically used long-acting estradiol ester is estradiol undecylate, which has 11 carbon atoms instead of the 18 carbon atoms in estradiol stearate.
vte Affinities and estrogenic potencies of estrogen esters and ethers at the estrogen receptors :
| Estrogen | Other names | RBATooltip Relative binding affinity (%)$^a$ | REP (%)$^b$ | REP (%)$^b$ |
| Estrogen | Other names | ER | ERα | ERβ |
| Estradiol | E2 | 100 | 100 | 100 |
| Estradiol 3-sulfate | E2S; E2-3S | ? | 0.02 | 0.04 |
| Estradiol 3-glucuronide | E2-3G | ? | 0.02 | 0.09 |
| Estradiol 17β-glucuronide | E2-17G | ? | 0.002 | 0.0002 |
| Estradiol benzoate | EB; Estradiol 3-benzoate | 10 | 1.1 | 0.52 |
| Estradiol 17β-acetate | E2-17A | 31–45 | 24 | ? |
| Estradiol diacetate | EDA; Estradiol 3,17β-diacetate | ? | 0.79 | ? |
| Estradiol propionate | EP; Estradiol 17β-propionate | 19–26 | 2.6 | ? |
| Estradiol valerate | EV; Estradiol 17β-valerate | 2–11 | 0.04–21 | ? |
| Estradiol cypionate | EC; Estradiol 17β-cypionate | ?$^c$ | 4.0 | ? |
| Estradiol palmitate | Estradiol 17β-palmitate | 0 | ? | ? |
| Estradiol stearate | Estradiol 17β-stearate | 0 | ? | ? |
| Estrone | E1; 17-Ketoestradiol | 11 | 5.3–38 | 14 |
| Estrone sulfate | E1S; Estrone 3-sulfate | 2 | 0.004 | 0.002 |
| Estrone glucuronide | E1G; Estrone 3-glucuronide | ? | <0.001 | 0.0006 |
| Ethinylestradiol | EE; 17α-Ethynylestradiol | 100 | 17–150 | 129 |
| Mestranol | EE 3-methyl ether | 1 | 1.3–8.2 | 0.16 |
| Quinestrol | EE 3-cyclopentyl ether | ? | 0.37 | ? |
| Footnotes: $^a$ = Relative binding affinities (RBAs) were determined via in-vitro displacement of labeled estradiol from estrogen receptors (ERs) generally of rodent uterine cytosol. Estrogen esters are variably hydrolyzed into estrogens in these systems (shorter ester chain length -> greater rate of hydrolysis) and the ER RBAs of the esters decrease strongly when hydrolysis is prevented. $^b$ = Relative estrogenic potencies (REPs) were calculated from half-maximal effective concentrations (EC$_{50}$) that were determined via in-vitro β‐galactosidase (β-gal) and green fluorescent protein (GFP) production assays in yeast expressing human ERα and human ERβ. Both mammalian cells and yeast have the capacity to hydrolyze estrogen esters. $^c$ = The affinities of estradiol cypionate for the ERs are similar to those of estradiol valerate and estradiol benzoate (figure). Sources: See template page. |||||
vte Structural properties of selected estradiol esters :
| Estrogen | Structure | Ester(s) | Ester(s) | Ester(s) | Ester(s) | Relative mol. weight | Relative E2 content$^b$ | log P$^c$ |
| Estrogen | Structure | Position(s) | Moiet(ies) | Type | Length$^a$ | Relative mol. weight | Relative E2 content$^b$ | log P$^c$ |
| Estradiol | | – | – | – | – | 1.00 | 1.00 | 4.0 |
| Estradiol acetate | | C3 | Ethanoic acid | Straight-chain fatty acid | 2 | 1.15 | 0.87 | 4.2 |
| Estradiol benzoate | | C3 | Benzoic acid | Aromatic fatty acid | – (~4–5) | 1.38 | 0.72 | 4.7 |
| Estradiol dipropionate | | C3, C17β | Propanoic acid (×2) | Straight-chain fatty acid | 3 (×2) | 1.41 | 0.71 | 4.9 |
| Estradiol valerate | | C17β | Pentanoic acid | Straight-chain fatty acid | 5 | 1.31 | 0.76 | 5.6–6.3 |
| Estradiol benzoate butyrate | | C3, C17β | Benzoic acid, butyric acid | Mixed fatty acid | – (~6, 2) | 1.64 | 0.61 | 6.3 |
| Estradiol cypionate | | C17β | Cyclopentylpropanoic acid | Cyclic fatty acid | – (~6) | 1.46 | 0.69 | 6.9 |
| Estradiol enanthate | | C17β | Heptanoic acid | Straight-chain fatty acid | 7 | 1.41 | 0.71 | 6.7–7.3 |
| Estradiol dienanthate | | C3, C17β | Heptanoic acid (×2) | Straight-chain fatty acid | 7 (×2) | 1.82 | 0.55 | 8.1–10.4 |
| Estradiol undecylate | | C17β | Undecanoic acid | Straight-chain fatty acid | 11 | 1.62 | 0.62 | 9.2–9.8 |
| Estradiol stearate | | C17β | Octadecanoic acid | Straight-chain fatty acid | 18 | 1.98 | 0.51 | 12.2–12.4 |
| Estradiol distearate | | C3, C17β | Octadecanoic acid (×2) | Straight-chain fatty acid | 18 (×2) | 2.96 | 0.34 | 20.2 |
| Estradiol sulfate | | C3 | Sulfuric acid | Water-soluble conjugate | – | 1.29 | 0.77 | 0.3–3.8 |
| Estradiol glucuronide | | C17β | Glucuronic acid | Water-soluble conjugate | – | 1.65 | 0.61 | 2.1–2.7 |
| Estramustine phosphate$^d$ | | C3, C17β | Normustine, phosphoric acid | Water-soluble conjugate | – | 1.91 | 0.52 | 2.9–5.0 |
| Polyestradiol phosphate$^e$ | | C3–C17β | Phosphoric acid | Water-soluble conjugate | – | 1.23$^f$ | 0.81$^f$ | 2.9$^g$ |
| Footnotes: $^a$ = Length of ester in carbon atoms for straight-chain fatty acids or approximate length of ester in carbon atoms for aromatic or cyclic fatty acids. $^b$ = Relative estradiol content by weight (i.e., relative estrogenic exposure). $^c$ = Experimental or predicted octanol/water partition coefficient (i.e., lipophilicity/hydrophobicity). Retrieved from PubChem, ChemSpider, and DrugBank. $^d$ = Also known as estradiol normustine phosphate. $^e$ = Polymer of estradiol phosphate (~13 repeat units). $^f$ = Relative molecular weight or estradiol content per repeat unit. $^g$ = log P of repeat unit (i.e., estradiol phosphate). Sources: See individual articles. |||||||||