Clinical data | |
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Other names | 5α-DHNET; 5α-Dihydro-NET; Dihydronorethisterone; Dihydronorethindrone; DHNET; 17α-Ethynyl-5α-dihydro-19-nortestosterone; 17α-Ethynyl-5α-estran-17β-ol-3-one; STS-737; NSC-85401; 19-Nor-5α,17α-pregn-20-yn-17-ol-3-one |
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CAS Number | |
PubChem CID | |
ChemSpider | |
UNII | |
ChEMBL | |
CompTox Dashboard ( EPA) | |
Chemical and physical data | |
Formula | C20H28O2 |
Molar mass | 300.442 g·mol−1 |
3D model ( JSmol) | |
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5α-Dihydronorethisterone (5α-DHNET, dihydronorethisterone, 17α-ethynyl-5α-dihydro-19-nortestosterone, or 17α-ethynyl-5α-estran-17β-ol-3-one) is a major active metabolite of norethisterone (norethindrone). [1] [2] [3] [4] Norethisterone is a progestin with additional weak androgenic and estrogenic activity. [1] 5α-DHNET is formed from norethisterone by 5α-reductase in the liver and other tissues. [1] [2] [3] [4]
Unlike norethisterone which is purely progestogenic, 5α-DHNET has been found to possess both progestogenic and marked antiprogestogenic activity, showing a profile of progestogenic activity like that of a selective progesterone receptor modulator (SPRM). [4] Moreover, the affinity of 5α-DHNET for the progesterone receptor (PR) is greatly reduced relative to that of norethisterone at only 25% of that of progesterone (versus 150% for norethisterone). [1]
5α-DHNET shows higher affinity for the androgen receptor (AR) compared to norethisterone with approximately 27% of the affinity of the potent androgen metribolone (versus 15% for norethisterone). [1] However, although 5α-DHNET has higher affinity for the AR than does norethisterone, it has significantly diminished and in fact almost abolished androgenic activity in comparison to norethisterone in rodent bioassays. [2] [5] Similar findings were observed for ethisterone (17α-ethynyltestosterone) and its 5α-reduced metabolite, whereas 5α-reduction enhanced both the AR affinity and androgenic potency of testosterone and nandrolone (19-nortestosterone) in rodent bioassays. [5] As such, it appears that the C17α ethynyl group of norethisterone is responsible for its loss of androgenicity upon 5α-reduction. [5] Instead of androgenic activity, 5α-DHNET has been reported to possess some antiandrogenic activity. [6]
Norethisterone and 5α-DHNET have been found to act as weak irreversible aromatase inhibitors (Ki = 1.7 μM and 9.0 μM, respectively). [7] However, the concentrations required are probably too high to be clinically relevant at typical dosages of norethisterone. [1] 5α-DHNET specifically has been assessed and found to be selective in its inhibition of aromatase, and does not affect other steroidogenesis enzymes such as cholesterol side-chain cleavage enzyme (P450scc), 17α-hydroxylase/ 17,20-lyase, 21-hydroxylase, or 11β-hydroxylase. [7] Since it is not aromatized (and hence cannot be transformed into an estrogenic metabolite), unlike norethisterone, 5α-DHNET has been proposed as a potential therapeutic agent in the treatment of estrogen receptor (ER)-positive breast cancer. [7]
Compound | Typea | PR | AR | ER | GR | MR | SHBG | CBG |
---|---|---|---|---|---|---|---|---|
Norethisterone | – | 67–75 | 15 | 0 | 0–1 | 0–3 | 16 | 0 |
5α-Dihydronorethisterone | Metabolite | 25 | 27 | 0 | 0 | ? | ? | ? |
3α,5α-Tetrahydronorethisterone | Metabolite | 1 | 0 | 0–1 | 0 | ? | ? | ? |
3α,5β-Tetrahydronorethisterone | Metabolite | ? | 0 | 0 | ? | ? | ? | ? |
3β,5α-Tetrahydronorethisterone | Metabolite | 1 | 0 | 0–8 | 0 | ? | ? | ? |
Ethinylestradiol | Metabolite | 15–25 | 1–3 | 112 | 1–3 | 0 | 0.18 | 0 |
Norethisterone acetate | Prodrug | 20 | 5 | 1 | 0 | 0 | ? | ? |
Norethisterone enanthate | Prodrug | ? | ? | ? | ? | ? | ? | ? |
Noretynodrel | Prodrug | 6 | 0 | 2 | 0 | 0 | 0 | 0 |
Etynodiol | Prodrug | 1 | 0 | 11–18 | 0 | ? | ? | ? |
Etynodiol diacetate | Prodrug | 1 | 0 | 0 | 0 | 0 | ? | ? |
Lynestrenol | Prodrug | 1 | 1 | 3 | 0 | 0 | ? | ? |
Notes: Values are percentages (%). Reference ligands (100%) were promegestone for the PR , metribolone for the AR , estradiol for the ER , dexamethasone for the GR , aldosterone for the MR , dihydrotestosterone for SHBG , and cortisol for CBG . Footnotes: a = Active or inactive metabolite, prodrug, or neither of norethisterone. Sources: See template. |
Many synthetic steroids with high myotrophic activity exhibit myotrophic–androgenic dissociation, since, due to changes introduced in the structure of ring A, they will probably not be substrates for the 5α-reductases [85]. 5α-Reduction does not always amplify the androgenic potency in spite of high RBA of androgens to the AR. This is the case for norethisterone (Fig. 1, 34), a synthetic 19-nor-17α-ethynyl testosterone derivative, which also undergoes enzyme-mediated 5α-reduction and exerts potent androgenic effects in target organs. 5α-Reduced norethisterone displays a higher AR binding but shows a significantly lower androgenic potency than unchanged norethisterone [102,103].
Clinical data | |
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Other names | 5α-DHNET; 5α-Dihydro-NET; Dihydronorethisterone; Dihydronorethindrone; DHNET; 17α-Ethynyl-5α-dihydro-19-nortestosterone; 17α-Ethynyl-5α-estran-17β-ol-3-one; STS-737; NSC-85401; 19-Nor-5α,17α-pregn-20-yn-17-ol-3-one |
Identifiers | |
| |
CAS Number | |
PubChem CID | |
ChemSpider | |
UNII | |
ChEMBL | |
CompTox Dashboard ( EPA) | |
Chemical and physical data | |
Formula | C20H28O2 |
Molar mass | 300.442 g·mol−1 |
3D model ( JSmol) | |
| |
|
5α-Dihydronorethisterone (5α-DHNET, dihydronorethisterone, 17α-ethynyl-5α-dihydro-19-nortestosterone, or 17α-ethynyl-5α-estran-17β-ol-3-one) is a major active metabolite of norethisterone (norethindrone). [1] [2] [3] [4] Norethisterone is a progestin with additional weak androgenic and estrogenic activity. [1] 5α-DHNET is formed from norethisterone by 5α-reductase in the liver and other tissues. [1] [2] [3] [4]
Unlike norethisterone which is purely progestogenic, 5α-DHNET has been found to possess both progestogenic and marked antiprogestogenic activity, showing a profile of progestogenic activity like that of a selective progesterone receptor modulator (SPRM). [4] Moreover, the affinity of 5α-DHNET for the progesterone receptor (PR) is greatly reduced relative to that of norethisterone at only 25% of that of progesterone (versus 150% for norethisterone). [1]
5α-DHNET shows higher affinity for the androgen receptor (AR) compared to norethisterone with approximately 27% of the affinity of the potent androgen metribolone (versus 15% for norethisterone). [1] However, although 5α-DHNET has higher affinity for the AR than does norethisterone, it has significantly diminished and in fact almost abolished androgenic activity in comparison to norethisterone in rodent bioassays. [2] [5] Similar findings were observed for ethisterone (17α-ethynyltestosterone) and its 5α-reduced metabolite, whereas 5α-reduction enhanced both the AR affinity and androgenic potency of testosterone and nandrolone (19-nortestosterone) in rodent bioassays. [5] As such, it appears that the C17α ethynyl group of norethisterone is responsible for its loss of androgenicity upon 5α-reduction. [5] Instead of androgenic activity, 5α-DHNET has been reported to possess some antiandrogenic activity. [6]
Norethisterone and 5α-DHNET have been found to act as weak irreversible aromatase inhibitors (Ki = 1.7 μM and 9.0 μM, respectively). [7] However, the concentrations required are probably too high to be clinically relevant at typical dosages of norethisterone. [1] 5α-DHNET specifically has been assessed and found to be selective in its inhibition of aromatase, and does not affect other steroidogenesis enzymes such as cholesterol side-chain cleavage enzyme (P450scc), 17α-hydroxylase/ 17,20-lyase, 21-hydroxylase, or 11β-hydroxylase. [7] Since it is not aromatized (and hence cannot be transformed into an estrogenic metabolite), unlike norethisterone, 5α-DHNET has been proposed as a potential therapeutic agent in the treatment of estrogen receptor (ER)-positive breast cancer. [7]
Compound | Typea | PR | AR | ER | GR | MR | SHBG | CBG |
---|---|---|---|---|---|---|---|---|
Norethisterone | – | 67–75 | 15 | 0 | 0–1 | 0–3 | 16 | 0 |
5α-Dihydronorethisterone | Metabolite | 25 | 27 | 0 | 0 | ? | ? | ? |
3α,5α-Tetrahydronorethisterone | Metabolite | 1 | 0 | 0–1 | 0 | ? | ? | ? |
3α,5β-Tetrahydronorethisterone | Metabolite | ? | 0 | 0 | ? | ? | ? | ? |
3β,5α-Tetrahydronorethisterone | Metabolite | 1 | 0 | 0–8 | 0 | ? | ? | ? |
Ethinylestradiol | Metabolite | 15–25 | 1–3 | 112 | 1–3 | 0 | 0.18 | 0 |
Norethisterone acetate | Prodrug | 20 | 5 | 1 | 0 | 0 | ? | ? |
Norethisterone enanthate | Prodrug | ? | ? | ? | ? | ? | ? | ? |
Noretynodrel | Prodrug | 6 | 0 | 2 | 0 | 0 | 0 | 0 |
Etynodiol | Prodrug | 1 | 0 | 11–18 | 0 | ? | ? | ? |
Etynodiol diacetate | Prodrug | 1 | 0 | 0 | 0 | 0 | ? | ? |
Lynestrenol | Prodrug | 1 | 1 | 3 | 0 | 0 | ? | ? |
Notes: Values are percentages (%). Reference ligands (100%) were promegestone for the PR , metribolone for the AR , estradiol for the ER , dexamethasone for the GR , aldosterone for the MR , dihydrotestosterone for SHBG , and cortisol for CBG . Footnotes: a = Active or inactive metabolite, prodrug, or neither of norethisterone. Sources: See template. |
Many synthetic steroids with high myotrophic activity exhibit myotrophic–androgenic dissociation, since, due to changes introduced in the structure of ring A, they will probably not be substrates for the 5α-reductases [85]. 5α-Reduction does not always amplify the androgenic potency in spite of high RBA of androgens to the AR. This is the case for norethisterone (Fig. 1, 34), a synthetic 19-nor-17α-ethynyl testosterone derivative, which also undergoes enzyme-mediated 5α-reduction and exerts potent androgenic effects in target organs. 5α-Reduced norethisterone displays a higher AR binding but shows a significantly lower androgenic potency than unchanged norethisterone [102,103].