3β-hydroxyandrost-5-en-17-one acetate

Endpoint summary

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

basic toxicokinetics in vivo

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

other information

Justification for type of information:

Data from the supporting substance Dehydroepiandrosterone is used to cover this endpoint. The justification for read across is attached in IUCLID Section 13.

Reason / purpose for cross-reference:

read-across source

Type:

absorption

Results:

Assuming the bioavailability obtained by the subcutaneous route to be 100%, it was estimated based on relative pharmacodynamic responses that the potencies of DHEA in rats by the percutaneous and oral routes were approximately 33% and 3%, respectively.

Details on absorption:

MALE RAT RESULTS
- DHEA administered percutaneously by twice daily application for 7 days to the dorsal skin of the rat stimulated an increase in ventral prostate weight with approximately one third the potency of the compound given by subcutaneous injection. The doses required to achieve a 50% reversal of the inhi bitory effect of orchiectomy were approximately 3 and 1 mg respectively. - By the oral route, DHEA had only 10-15% of the activity of the compound given percutaneously.
- Similar ratios of activity were obtained when dorsal prostate and seminal vesicle weight were used as parameters of androgenic activity.

FEMALE RAT RESULTS
- When examined on an estrogen-sensitive parameter, namely uterine weight in ovariectomized rats, the stimulatory effect of DHEA was much less potent than its androgenic activity measured in the male animal, a 50% reversal of the inhibitory effect of ovariectomy on uterine weight being observed at the 3 and 30 mg doses of DHEA administered by the subcutaneous and percutaneous routes.

These results are considered relevant for Dehydroepiandrosterone acetate. Justification for this read across approach is included in IUCLID section 13.

Conclusions:

No reliable toxicokinetics study is available for Dehydroepiandrosterone acetate. Therefore, reliable data from the supporting substance Dehydroepiandrosterone (DHEA) is used to cover this endpoint. DHEA was administered percutaneously by twice daily application for 7 days to the dorsal skin of orchiectomized (ORCH) male and ovariectomized (OVX) female Sprague Dawley rats to compare the bioavailability of DHEA after percutaneous and oral administration. The subcutaneous route of administration was used as a reference of maximal bioavailability. The animals were sacrified 7 days after the start of treatment. Uteri, ventral prostates, dorsal prostates and seminal vesicles were excised and weighed. Blood samples were collected and serum was frozen at -20 °C until assayed for the most relevant steroids. Based on changes in parameters of androgenic and estrogenic action, namely ventral prostate, dorsal prostate, seminal vesicle and uterine weight, the results showed that the bioavailability of DHEA administered by the percutaneous route was approximately one-third of that observed after subcutaneous administration and significantly more than that obtained by the oral route.  Assuming the bioavailability obtained by the subcutaneous route to be 100%, it was estimated based on relative pharmacodynamic responses that the potencies of DHEA in rats by the percutaneous and oral routes were approximately 33% and 3%, respectively. The same is assumed for Dehydroepiandrosterone acetate. Justification for this read across approach is included in IUCLID section 13.

Reference 2

Endpoint:

basic toxicokinetics in vivo

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

other information

Justification for type of information:

Data from the supporting substance Dehydroepiandrosterone is used to cover this endpoint. The justification for read across is attached in IUCLID Section 13.

Reason / purpose for cross-reference:

read-across source

Type:

absorption

Results:

Following a 50-mg DHEA PO dose, systemic availability was only 3.1 ± 0.4%. This result is considered relevant for Dehydroepiandrosterone acetate. Justification for this read across approach is included in IUCLID section 13.

Type:

metabolism

Results:

The major circulating metabolites of DHEA in the OVX DEX-suppressed cynomolgus female monkey were DHEA-Sulfate, androsterone glucuronide, and androstane-3α,17β-diol-glucuronide. This result is considered relevant for Dehydroepiandrosterone acetate.

Details on absorption:

Following PO administration of 50 mg of DHEA, systemic availability (F) of DHEA measured according to the AUC 0-24 h values was only 3.1 ± 0.4% of that measured after IV administration. This result is considered relevant for Dehydroepiandrosterone acetate. Justification for this read across approach is included in IUCLID section 13.

Test no.:

#2

Toxicokinetic parameters:

C(time):

Remarks:

DHEA iv (10 mg): Concentration DHEA at time 0 hr (C0) 15527 ± 700 nmol/liter

Test no.:

#2

Toxicokinetic parameters:

Cmax:

Remarks:

DHEA: DHEA PO (50 mg) 455 ± 83 nmol/liter

Test no.:

#2

Toxicokinetic parameters:

half-life 1st:

Remarks:

Terminal half-life of DHEA (t 1/2): DHEA iv (10 mg) 4.5 ± 0.3 h

Test no.:

#2

Toxicokinetic parameters:

half-life 1st:

Remarks:

Terminal half-life of DHEA (t 1/2): DHEA PO (50 mg) 4.3 ± 0.2 h

Test no.:

#2

Toxicokinetic parameters:

other:

Remarks:

Metabolic Clearance Rate (MCR) of DHEA: DHEA iv (10 mg) 99.9 ± 9.1 liter/d

Test no.:

#2

Toxicokinetic parameters:

Tmax:

Remarks:

DHEA: DHEA PO (50 mg) 0.7 ± 0.05 h

Test no.:

#2

Toxicokinetic parameters:

AUC:

Remarks:

(0->24 h) DHEA: DHEA iv (10 mg) 8871 ± 808 nmol/liter·h

Test no.:

#2

Toxicokinetic parameters:

AUC:

Remarks:

(0->24 h) DHEA: DHEA PO (50 mg) 1162 ± 76 nmol/liter·h

Metabolites identified:

yes

Details on metabolites:

The major circulating metabolites of DHEA were DHEA-Sulfate, androsterone glucuronide, and androstane-3α,17β-diol-glucuronide after single IV and single PO administration. The conversion ratios of androst-5-ene-3β,17β-diol, testosterone, dihydrotestosterone, and androstenedione were, in comparison, small. No transformation to estrogens could be detected in the circulation after either IV or PO DHEA administration. These results are considered relevant for Dehydroepiandrosterone acetate. Justification for this read across approach is included in IUCLID section 13.

Conclusions:

No reliable toxicokinetics study is available for Dehydroepiandrosterone acetate. Therefore, reliable data from the supporting substance Dehydroepiandrosterone (DHEA) is used to cover this endpoint. The pharmacokinetics of dehydroepiandrosterone (DHEA) administered orally (PO), intravenously (IV), and during a continuous IV infusion (12 hours) was studied in ovariectomized (OVX) cynomolgus monkeys under suppression of adrenal DHEA secretion with dexamethasone (DEX). The OVX DEX-suppressed cynomolgus monkey model also was used to investigate the effect of the various routes of administration of DHEA on circulating androgens, estrogens and their conjugated metabolites. This animal model was chosen to simulate postmenopausal women.  After a single 10 mg IV dose of DHEA to OVX DEX-suppressed cynomolgus monkeys, the metabolic clearance rate and terminal half-life of DHEA were 99.9 liter/day and 4.5 hours, respectively. Following PO administration of 50 mg of DHEA to OVX DEX-suppressed monkeys, systemic availability of DHEA measured according to the AUC 0-24 h values was only 3.1 ± 0.4% of that measured after IV administration.  The major circulating metabolites of DHEA were DHEA-Sulfate, androsterone glucuronide, and androstane-3α,17β-diol-glucuronide after single IV and single PO administration. The conversion ratios of androst-5-ene-3β,17β-diol, testosterone, dihydrotestosterone, and androstenedione were, in comparison, small. No transformation to estrogens could be detected in the circulation after either IV or PO DHEA administration. The same is assumed for Dehydroepiandrosterone acetate. Justification for this read across approach is included in IUCLID section 13.

Reference 3

Endpoint:

basic toxicokinetics in vivo

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

other information

Justification for type of information:

Data from the supporting substance Dehydroepiandrosterone is used to cover this endpoint. The justification for read across is attached in IUCLID Section 13.

Reason / purpose for cross-reference:

read-across source

Specific details on test material used for the study:

No specific information

Radiolabelling:

no

Species:

other: Human

Details on species / strain selection:

Human study volunteers, both sexes, aged 15-73

Sex:

male/female

Route of administration:

oral: unspecified

Vehicle:

unchanged (no vehicle)

Dose / conc.:

50 other: mg/day

Remarks:

Most commonn dose

Dose / conc.:

2 250 other: mg/day

Remarks:

Highest dose used

Details on dosing and sampling:

Doses ranged from 50 mg/day to 2,250 mg/day, 50 mg/day was used most often.

Statistics:

Logarithmic regression was used.

Metabolites identified:

yes

Remarks:

DHEA-S

Bioaccessibility (or Bioavailability) testing results:

Bioaccessibility testing results
Doses above 50 mg/day result in levels that are at or above the upper limit of normal for healthy young adults. At doses above 300 mg/day the increment of serum DHEA and DHEA-S appears to reach a plateau.

Conclusions:

No reliable toxicokinetics study is available for Dehydroepiandrosterone acetate. Therefore, reliable data from the supporting substance Dehydroepiandrosterone (DHEA) is used to cover this endpoint. Serum levels of DHEA and DHEA-S increase with increasing doses. Doses above 50 mg/day result in levels that are at or above the upper limit of normal for healthy young adults. At doses above 300 mg/day the increment of serum DHEA and DHEA-S appears to reach a plateau.
Those wanting to use supplemental DHEA might consider that doses of 300 mg/day are maximal; they clearly result in supraphysiologic concentrations and above this level doses may have increased side effects without significantly increasing the effective level of serum hormone.

Description of key information

Based on physicochemical and toxicological parameters, a qualitative assessment of the toxicokinetic behaviour of the supporting substance DHEA and the target substance T008506 is performed.

Key value for chemical safety assessment

Bioaccumulation potential:

no bioaccumulation potential

Absorption rate - oral (%):

50

Absorption rate - dermal (%):

50

Absorption rate - inhalation (%):

100

Additional information

T008506 (CAS number 853-23-6; EC number 212-714-1; prasterone acetate; 3β-hydroxyandrost-5-en-17-one acetate), is a white solid compound with a moderate molecular weight (330.47 g/mole), a low particle size (mass median diameter 9.060 µm), a very low water solubility (below limit of detection 0.05 mg/L at 20 °C), a high log Pow (5.1 at 20 °C) and a very low vapour pressure (1.1 x10^-6Pa at 25°C).

No experimental data (animal or human studies) on the toxicokinetic behaviour of the target substance T008506 is available. A read-across evaluation was developed to fill data gaps (according to scenario 2 of ECHA’s RAAF, 2017) with dehydroepiandrosterone (DHEA, prasterone) as the source substance. The justification for this read-across approach is included in IUCLID section 13. This read-across evaluation with DHEA as source substance is considered a prediction based on a worst-case approach.

DHEA (CAS number 53-43-0; EC number 200-175-5; prasterone; 3β-hydroxyandrost-5-en-17-one), is a white solid compound with a moderate molecular weight (288.4 g/mole), a very low water solubility (17.5 mg/L at 20 °C and pH 5.44), a high log Pow (3.03 at 20 °C) and a very low vapour pressure (<0.01 Pa at 25°C). No data is available on the particle size (mass median diameter).

The source substance DHEA is an active pharmaceutical ingredient (API). The target substance, prasterone acetate, is the final intermediate in the manufacturing of DHEA. DHEA is a steroid hormone, endogenous to both men and women and naturally synthesized by the zona reticularis of the adrenal cortex in response to adrenocorticotropic hormone.

DHEA has several uses, including nutritional supplement, adrenal exhaustion, systemic lupus erythematosus, enhancing sexual desire and function, improving mental function, treating infertility and hormone replacement therapy. It has both estrogen- and testosterone-like pharmacologicactivity. It is also a potent sigma-1 agonist and is considered a neurosteroid. It is occasionally used for muscle-building or performance-enhancing by athletes.Normal endogenous plasma concentrations of DHEA are generally in the range of 2 to 4 ng/ml in healthy men; values in women are slightly higher.

The backbone of both substances is adehydroepiandrosterone group, which is a polycyclic compound containing a hydroxyl- and an aldehyde group for DHEA. In the target substance prasterone acetate, the hydroxyl group is substituted by an acetate ester.

Based on its chemical similarity, comparable properties are expected for DHEA and prasterone acetate in both human and the environment. Acetate is a common anion in biological systems and might be degraded in these systems or under environmental or physiological conditions.

The data present in this dossier are based on physico-chemical and toxicological parameters and will allow a qualitative assessment of the toxicokinetic behavior of DHEA and thus also of T008506.

Pharmacokinetics of DHEA

The following publications on the pharmacokinetic behavior and bioavailability of DHEA are considered relevant:

·        DHEA was administered percutaneously by twice daily application for 7 days to the dorsal skin of orchiectomized (ORCH) male and ovariectomized (OVX) female Sprague Dawley rats to compare the bioavailability of DHEA after percutaneous and oral administration (Labrie et al., 1996). The subcutaneous route of administration was used as a reference of maximal bioavailability. The animals were sacrificed 7 days after the start of treatment. Uteri, ventral prostates, dorsal prostates and seminal vesicles were excised and weighed. Blood samples were collected, and serum was frozen at -20 °C until assayed for the most relevant steroids. Based on changes in parameters of androgenic and estrogenic action, namely ventral prostate, dorsal prostate, seminal vesicle and uterine weight, the results showed that the bioavailability of DHEA administered by the percutaneous route was approximately one-third of that observed after subcutaneous administration and significantly more than that obtained by the oral route.  Assuming the bioavailability obtained by the subcutaneous route to be 100%, it was estimated based on relative pharmacodynamic responses that the potencies of DHEA in rats by the percutaneous and oral routes were approximately 33% and 3%, respectively.

·        The pharmacokinetics of DHEA administered orally (PO), intravenously (IV), and during a continuous IV infusion (12 hours) was studied in ovariectomized (OVX) cynomolgus monkeys under suppression of adrenal DHEA secretion with dexamethasone (DEX) (Leblanc et al., 2003). The OVX DEX-suppressed cynomolgus monkey model also was used to investigate the effect of the various routes of administration of DHEA on circulating androgens, estrogens and their conjugated metabolites. This animal model was chosen to simulate postmenopausal women.  After a single 10 mg IV dose of DHEA to OVX DEX-suppressed cynomolgus monkeys, the metabolic clearance rate and terminal half-life of DHEA were 99.9 liter/day and 4.5 hours, respectively. Following PO administration of 50 mg of DHEA to OVX DEX-suppressed monkeys, systemic availability of DHEA measured according to the AUC 0-24 h values was only 3.1 ± 0.4% of that measured after IV administration. The major circulating metabolites of DHEA were DHEA-Sulfate, androsterone glucuronide, and androstane-3α,17β-diol-glucuronide after single IV and single PO administration. The conversion ratios of androst-5-ene-3β,17β-diol, testosterone, dihydrotestosterone, and androstenedione were, in comparison, small. No transformation to estrogens could be detected in the circulation after either IV or PO DHEA administration. The same is assumed for T008506.

·        Data from 18 published articles was summarized to describe the relationship between the administered dose of DHEA and the resulting serum level of DHEA and DHEA-sulfate in humans (Tummala and Svec, 1999). Serum levels of DHEA and DHEA-S increase with increasing doses. Doses above 50 mg/day result in levels that are at or above upper limit of normal for healthy young adults. At doses above 300 mg/day the increment of serum DHEA and DHEA-S appears to reach a plateau. Those wanting to use supplemental DHEA might consider that doses of 300 mg/day are maximal; they clearly result in supraphysiological concentrations and above this level doses may have increased side effects without significantly increasing the effective level of serum hormone.

 

Clinical pharmacokinetics

·        DHEA is well absorbed orally, but there are no reports of its oral bioavailability in humans. DHEA shows a low oral bioavailability in the rat, however, and, assuming the bioavailability obtained by the subcutaneous route to be 100%, it was estimated based on relative pharmacodynamic responses that the potencies (“bioavailabilities”) of DHEA by the percutaneous and oral routes were approximately 33% and 3%, respectively. In cynomolgus monkeys, the oral bioavailability was calculated to be 3.1%. Therefore, given the low oral bioavailability in two species, it is a reasonable assumption that it will also be low (< 10%) in humans.

·        DHEA however is converted to several active metabolites, including androstenedione, testosterone, estrone, estradiol and estriol. The elimination half-life of prasterone is 5-12 hours. Renal excretion amounts for 51-73% of the elimination of prasterone and its metabolites. Tmax is 1.5-2 hours after oral administration. AUC and Cmax values did not change significantly with multiple versus single 200 mg/day doses, indicating that it does not bioaccumulate with time and that there is relatively low interindividual patient variability.

 

Absorption

Both T008506 and DHEA have high log Pow values >0 (5.1 and 3.03 at 20 °C, resp.) and molecular weights below 500, what makes them favourable for absorption. Nevertheless, a substance with such a log P value can be poorly soluble in lipids and hence not readily absorbed with their low water solubility.

 

Oral/GI absorption:

Assuming that the extent of water solubility and partitioning approximate the bioavailability of a substance, it is expected that T008506 (prasterone acetate) and DHEA will be taken up by the body in a similar way, and that DHEA represents the worst-case scenario here. Any difference in absorption is possibly due to the difference in the molecular weight; substances with a low molecular weight are expected to be absorbed more easily compared to high molecular weight compounds. DHEA is expected to be absorbed more easily. In addition, a lower exposure of T008506 due to lower vapour pressure and a lower solubility supports the hypothesis that T008506 renders the lowest risk. Furthermore, the very low water solubility of the substance would lead to restricted dissolution into the gastrointestinal fluids and consequently restricted absorption through passive diffusion. It is generally assumed that the absorption along the gastrointestinal tract predominantly takes place in the small intestine since it has a very large surface area and the longest transit time.

No effects on mortality, body weight or gross pathology were observed following a single dose up to 2000 mg/kg of T008506 in an acute oral toxicity study with outbred female Wistar mice (OECD 423; van Sas, 2018). Clinical signs (hunched posture, uncoordinated movements and piloerection) were observed in the first 2 days after administration but disappeared. The LD50 in female rat was determined to be greater than 5000 mg/kg.

No long-term toxicity data is available on prasterone acetate. It is however expected that the repeated dose toxicity and the reproductive toxicity of the target substance prasterone acetate will be similar (or of lesser toxicity compared) to that of DHEA.

·        Data from one repeated dosing study with prasterone acetate was available. An LOEL of 6000 mg/kg was established after 6, 11 or 15 weeks of dosing via diet of Sprague-Dawley rats This study is considered supporting as one only dose level was administered via diet. This route of administration implies more uncertainties on the actual exposure levels and no dose-effect relationships could be established. The fact that no adverse effects were observed supports however the hypothesis that the target substance prasterone acetate holds no to very minor toxicological potential.

·        An LOAEL value of 30 mg/kg was established for DHEA after a 28-day oral repeated dose exposure in male and female rats (30 to 300 mg/kg bw/day; oral gavage).

·        Male and female Sprague-Dawley rats were dosed with DHEA during 6 months via oral gavage; an LOAEL of 10 mg/kg/d was established in the female animals (NOAEL = 10 mg/kg/d for male animals).

·        A chronic toxicity study in cynomolgus monkey was performed: animals were dosed with DHEA during one year via oral gavage. In this study an NOAEL of 10 mg/kg/d was established, as only effects related to pharmacological activity were observed. This study is considered the key study.

 

Based on the physicochemical properties and the results of acute and repeated dose toxicity studies, theoralabsorption factor is set to50%.

 

Respiratory absorption:

Given its low volatility (vapour pressure was 1.1 x10^-6Pa at 25°C), the availability of T008506 for inhalation as a vapour is limited. Due to the small particle size (MMAD 9.06 µm), it is expected that the solid particles have the potential to be inhaled and reach the alveolar region of the respiratory tract. Moderate lipophilic substances (-1<log P<4) have the potential to be absorbed directly across the respiratory tract epithelium by passive diffusion. However, due to its very low water solubility, the rate at which the particles dissolve into the mucus will limit the amount that could be absorbed directly when reaching the respiratory system. Poorly water-soluble dusts, such as T008506, depositing in the nasopharyngeal region could be coughed or sneezed out of the body or swallowed, while poorly water-soluble dusts depositing in the trachea-bronchial region would mainly be cleared from the lungs by the mucocilliary mechanism and swallowed. Nevertheless, a small amount can be taken up by phagocytosis and transported to the blood through the lymphatic system. Poorly water-soluble dusts depositing in the alveolar region would mainly be engulfed by alveolar macrophages which will either translocate particles to the ciliated airways or carry particles into the pulmonary interstitium and lymphoid tissues.

Based on the physicochemical properties, therespiratoryabsorption factor is set to100%.

 

Dermal absorption:

T008506 is a solid substance and therefore not readily taken up by the skin in comparison to liquid products. As the product is a solid, it will have to dissolve into the surface moisture of the skin before uptake can take place. This is also not probable considering the very low solubility of T008506. A molecular weight <100 would favour dermal uptake and >500 may be too large. For T008506 with a molecular weight of 330.47 g/mole, dermal uptake might be possible.

It is expected that, given its lipophilic character (log Pow = 5.1) the penetration of T008506 into the lipid rich environment of the stratum corneum will be favoured. Log Kow values between 1 and 4 favour dermal absorption (values between 2 and 3 are optimal) particularly if water solubility is high, which is not the case when it comes to the solubility of T008506. Therefore, the dermal uptake is expected to be low since the substance is not soluble enough in water to partition further from the stratum corneum into the epidermis.

 

Based on the physicochemical properties and the results of toxicity studies, thedermalabsorption factor is set to50%.

Distribution

The very low water solubility of T008506 will limit its distribution through the body by aqueous channels and pores. Since the substance is expected to be lipophilic it will distribute into the cells leading to a higher intracellular concentration in comparison to the extracellular concentration particularly in fatty tissues.

 

Accumulation

Based on the physicochemical properties of T008506 (very low water solubility, high partition coefficient), no accumulation is expected within the lungs, bones or stratum corneum. Since T008506 is a moderately lipophilic substance, it might concentrate in adipose tissue and may accumulate depending on the exposure conditions. Daily exposure to T008506 (log Kow around 4 or higher) could result in a build-up of the substance within the body. Highly lipophilic substances (log P between 4 and 6) that come into contact with the skin can readily penetrate the lipid rich stratum corneum but are not well absorbed systematically. Although they may persist in the stratum corneum, they will eventually be cleared as the stratum corneum is sloughed off.

 

Metabolism

Based on the structure, T008506 might undergo phase I biotransformation reactions such as (aromatic) hydroxylation, nitroreduction or oxidative deamination followed by conjugation reactions (phase II) such as glucuronidation (by the enzyme glucuronosyltransferase) and sulfation (by the enzyme sulfotransferase). The Phase II conjugation reactions largely increase the water solubility and hydrophilic character of the product. Metabolism mainly takes place in the liver, causing route specific presystemic (or first pass) effects, especially after oral intake. Other metabolic changes may take place in the gastrointestinal (GI) flora or within the GI tract epithelia (mainly in the small intestine), respiratory tract epithelia (in the nasal cavity, trachea-bronchial mucosa and alveoli and skin), etc.

 

Excretion

The water soluble conjugated metabolites of T008506 from Phase II biotransformation will be excreted from the systemic circulation through the urine. Most of them will have been filtered out from the blood by the kidneys, though a small amount can enter the urine directly by passive diffusion. There is also the potential for re-absorption into the systemic circulation across the tubular epithelium. Another route of excretion of conjugated derivatives (such as glucuronides) is the bile. The excretion via the bile is highly influenced by hepatic function since metabolites formed in the liver may be excreted directly into the bile without entering the bloodstream. Products in the bile pass through the intestine before excretion in the faeces and can thus undergo enterohepatic recycling which will prolong their half-life.

 

References

Labrie C, Flamand M, Bélanger A, Labrie F (1996) High bioavailability of dehydroepiandrosterone administered percutaneously in the rat. J Endocrinol 150: S107-S118

Leblanc M, Labrie C, Bélanger A, Candas B, Labrie F (2003) Bioavailability and pharmacokinetics of dehydroepiandrosterone in the cynomolgus monkey. J Clin Endocrinol Metab 88(9): 4293-4302

Tummala and Svec (1999) Correlation between the administered dose of DHEA and serum levels of DHEA and DHEA-S in human volunteers: analysis of published data. Clin biochem 32 (5) 355-361