Single, escalating dose pharmacokinetics, safety and food effects of a new oral androgen dimethandrolone undecanoate in man: a prototype oral male hormonal contraceptive

Authors

  • P. Surampudi,

    1. Division of Endocrinology, Department of Medicine, Harbor UCLA Medical center and Los Angeles Biomedical Research Institute, Torrance, CA, USA
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    • These authors contributed equally to the study.
  • S. T. Page,

    1. Division of Endocrinology, Department of Medicine, University of Washington, Seattle, WA, USA
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    • These authors contributed equally to the study.
  • R. S. Swerdloff,

    1. Division of Endocrinology, Department of Medicine, Harbor UCLA Medical center and Los Angeles Biomedical Research Institute, Torrance, CA, USA
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  • J. J. Nya-Ngatchou,

    1. Division of Endocrinology, Department of Medicine, University of Washington, Seattle, WA, USA
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  • P. Y. Liu,

    1. Division of Endocrinology, Department of Medicine, Harbor UCLA Medical center and Los Angeles Biomedical Research Institute, Torrance, CA, USA
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  • J. K. Amory,

    1. Division of Endocrinology, Department of Medicine, University of Washington, Seattle, WA, USA
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  • A. Leung,

    1. Division of Endocrinology, Department of Medicine, Harbor UCLA Medical center and Los Angeles Biomedical Research Institute, Torrance, CA, USA
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  • L. Hull,

    1. Division of Endocrinology, Department of Medicine, Harbor UCLA Medical center and Los Angeles Biomedical Research Institute, Torrance, CA, USA
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  • D. L. Blithe,

    1. Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, USA
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  • J. Woo,

    1. Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, USA
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  • W. J. Bremner,

    1. Division of Endocrinology, Department of Medicine, University of Washington, Seattle, WA, USA
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  • C. Wang

    Corresponding author
    1. Division of Endocrinology, Department of Medicine, Harbor UCLA Medical center and Los Angeles Biomedical Research Institute, Torrance, CA, USA
    • Correspondence:

      Christina Wang, Clinical and Translational Science Institute, Harbor-UCLA Medical Center, 1000 W. Carson St, Torrance, CA 90509, USA.

      E-mail: wang@labiomed.org

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Summary

The novel androgen, dimethandrolone (DMA) has both androgenic and progestational activities, properties that may maximize gonadotropin suppression. We assessed the pharmacokinetics of dimethandrolone undecanoate (DMAU), an orally bioavailable, longer acting ester of DMA, for male contraceptive development. Our objective was to examine the safety and pharmacokinetics of single, escalating doses of DMAU (powder in capsule formulation) administered orally with or without food in healthy men. We conducted a randomized, double-blind Phase 1 study. For each dose of DMAU (25–800 mg), 10 male volunteers received DMAU and two received placebo at two academic medical centres. DMAU was administered both fasting and after a high-fat meal (200–800 mg doses). Serial serum samples were collected over 24 h following each dose. DMAU was well tolerated without significant effects on vital signs, safety laboratory tests or electrocardiograms. When administered while fasting, serum DMA (active compound) was detectable in only 4/10 participants after the 800 mg dose. When administered with a 50% fat meal, serum DMA was detectable in all participants given 200 mg DMAU and showed a dose-incremental increase up to 800 mg, with peak levels 4–8 h after taking the dose. Serum gonadotropins and sex hormone concentrations were significantly suppressed 12 h after DMAU administration with food at doses above 200 mg. This first-in-man study demonstrated that a single, oral dose of DMAU up to 800 mg is safe. A high-fat meal markedly improved DMAU/DMA pharmacokinetics.

Introduction

Unplanned pregnancies increase the risk of maternal complications and foetal morbidity and mortality. Although many contraceptive options are available for women, few are available for men. Currently, male methods such as abstinence, coitus interruptus, or condoms are user dependent with very high long-term failure rates, whereas vasectomy is difficult to reverse (Trussell, 2009). Efforts are ongoing to develop a reversible male contraceptive that induces azoospermia or severe oligozoospermia.

Several contraceptive efficacy studies have shown that testosterone (T) ester injections or implants alone or in combination with a progestin such as depot medroxyprogesterone acetate are effective in preventing pregnancies in the female partner once sperm concentration is suppressed to very low levels (World Health Organization Task Force on Methods for the Regulation of Male Fertility, 1990, 1996; Gu et al., 2003, 2009; Turner et al., 2003). Thus, current male hormonal contraceptive development strategies have relied on combining T injections, patches, pellets, or gels with injectable, oral, or implant progestins formulations because the combination of an androgen with a progestin more effectively suppresses spermatogenesis than an androgen alone (Buchter et al., 1999; Meriggiola et al., 2003; Wang & Swerdloff, 2004; Liu et al., 2008; Page et al., 2008; Nieschlag, 2010). Oral progestins such as levonorgestrel are very effective in suppressing gonadotropins (Bebb et al., 1996; Anawalt et al., 2000). Oral T undecanoate (TU) in oil, the only safe oral formulation for long-term androgen delivery currently available, must be administered two to three times/day and, even when combined with a progestin, is not effective in suppressing spermatogenesis in most men (Nieschlag et al., 1978). An effective oral male contraceptive regimen has not yet been developed.

Dimethandrolone (DMA, 7α,11 β -methyl-19-nortestosterone) and its ester DMA undecanoate (DMAU) are being developed by the National Institute of Child Health and Human Development as an orally bioavailable male hormonal contraceptive. Like other 19-nortestosterone derivatives (e.g. levonorgestrel, etonogestrel and norethisterone), DMA has both androgen and progesterone receptor binding activity. The relative binding affinity of DMA to the AR is fourfold higher than T and to uterine progesterone receptors is about is about 0.4 that of progesterone (Attardi et al., 2006). The addition of an ester undecanoate in the 17α position to DMA forms DMAU, which exhibits an extended half-life. The cleavage of the ester undecanoate produces a biologically active unesterified DMA that is not converted by aromatase to oestrogenic products and thus in long-term studies oestrogen-dependent functions such as bone health and body fat have to be assessed (Attardi et al., 2008). DMA is also not 5α-reduced, properties that may spare stimulation of prostate growth compared to T (Attardi et al., 2010,2011). Oral DMAU also has the potential for use as androgen replacement therapy in hypogonadal men (Cook & Kepler, 2005). Although DMA is more potent than testosterone and may have less stimulating effect on the prostate, it is not aromatized. Given the known role of oestrogens in bone formation and prevention of bone resorption (Khosla & Bilezikian, 2003) and fat mass and sexual function in men (Finkelstein et al., 2013), the long-term use of DMAU in men has to be carefully monitored to ensure there is no oestrogen deficiency.

In vivo studies in castrated animals showed that oral DMA has the same potency as methyl T in stimulating ventral prostate weight but is 5 fold more potent in stimulating levator ani muscle weight (Attardi et al., 2006). Several preclinical studies with DMAU administered in an oral aqueous vehicle suspension in rats and rabbits showed that DMA suppresses gonadotropins, maintains androgenic effects and inhibits spermatogenesis to induce reversible infertility in rodents (Hild et al., 2007, 2010; Attardi et al., 2010, 2011). Unpublished toxicology studies administering oral doses of DMAU up to 125 mg/kg in rats, rabbits and monkeys did not reveal toxicological effects of DMAU/DMA even at these high doses (unpublished data from Bioqual Inc., Rockville, MD, USA). Based on these promising pre-clinical and toxicological studies, we conducted a double-blind, single dose, dose escalating phase 1 study of DMAU to assess the safety, tolerability and pharmacokinetics (PK) of DMAU (powder in capsule formulation equivalent to aqueous suspension administered in pre-clinical studies) and food effects on the bioavailability of DMAU/DMA after oral administration in men.

Research Participants and Methods

Research participants

Healthy male volunteers (18–50 years) with normal medical history, physical examination, blood count, clinical chemistries, liver function tests and electrocardiogram (EKG), and BMI <33 kg/m2, were recruited for the study. Men were excluded if they used hormonal therapy in the last 3 months, had elevated PSA levels (>2.5 ng/mL), disorders of the hypothalamus/pituitary/testis or desired fertility, or their partner was known to be pregnant or did not agree to use effective methods of contraception during the study. The participants were recruited and followed at the Harbor-UCLA Medical Center/Los Angeles Biomedical Research Institute (Harbor-UCLA/LABioMed) in Torrance, California and the University of Washington in Seattle, Washington. The study protocol was approved by the institutional review boards for both participating institutions. All participants provided written informed consent before any study procedures. The medical monitor (JW) and the investigators reviewed adverse events and safety data weekly with the provision that an external independent data safety monitoring board would be notified if and when a grade 3 adverse event occurred. This trial was registered at www.clinicaltrials.gov, National Clinical Trial Number NCT01382069.

Study medications

DMAU was synthesized by Evestra (San Antonio, TX, USA; synthesis method in Drug Master File 16641); micronization was carried out by Micron Technologies (Exton, PA, USA); and the active ingredient encapsulated as 25 mg powder in capsules by SRI International (Menlo Park, CA, USA). The placebo capsule contained all the other inactive components in the capsule, but no DMAU.

Study design

All participants were screened by a study physician to ensure that all inclusion and exclusion criteria were met. For each dose, 10 participants received DMAU and two received identical number of placebo capsules. The doses of DMAU that were administered fasting were 25, 50, 100, 200, 400 and 800 mg and DMAU 200, 400 and 800 mg doses were also administered immediately after a high-fat diet (>50% of fat, 800–900 calorie meal, with approximately 150, 250 and 500–600 calories from protein, carbohydrates and fat respectively) to determine the effect of food on the absorption of orally administered DMAU. There is a wash out period (7–14 days) between each dose. The end of study visit occurred approximately 14 days after the final dose.

All participants were admitted to the clinical research unit within the Clinical and Translational Science Institute at each site and were observed for 24 h with hourly vital signs monitoring following dosing. An EKG was performed 4–6 and 24 h after drug administration. Safety laboratory tests (complete blood count, clinical chemistry panel, liver function test and lipid profile) were checked at baseline and 24 h after each DMAU dose. Serum hormones [T, estradiol, 5α-dihydrotestosterone (DHT), LH, FSH and sex hormone binding globulin (SHBG)] were measured before drug administration (time zero) and at 12 and 24 h post administration. Blood samples were collected for measurement of DMA and DMAU concentrations at −0.5 before, 0, and 0.5, 1, 2, 4, 6, 8, 12, 18 and 24 h after oral administration of DMAU. The participants returned to the outpatient clinic research unit at least 7 days after the dose of DMAU for safety laboratory tests, adverse event reporting, and safety endpoints checks. If the participant had no adverse events or clinically significant abnormal laboratory tests, he was scheduled for the next dose. Halting rules were developed for this phase 1 safety and tolerability study. The dose escalation would be halted if two participants receiving DMAU at the same dose developed a grade 3 adverse event using parameters for clinical trials as recommended by the Food and Drug Administration.

Analytical methods

Safety laboratory tests were done at each study site's licensed Clinical Chemistry Laboratory. All hormones were measured by the licensed Endocrine and Metabolic Research Laboratory at Harbor-UCLA/LA Biomed using validated methods. SerumT, DHT and estradiol were measured by liquid chromatography–tandem mass spectrometry (LC-MS/MS) (Shiraishi et al., 2008; Rothman et al., 2011), serum LH, FSH and SHBG by sensitive fluoroimmunometric assays previously described (Swerdloff et al., 2000), and free T calculated by using a standard formula (Vermeulen et al., 1999). Serum DMA and DMAU were measured by LC-MS/MS developed for this study (see Supporting Information for details of the all the hormone measurement methods).

Statistical analyses

The primary endpoints of the trial were safety and tolerability of DMAU. Secondary endpoints included the 24-h pharmacokinetics (PK) of DMAU and DMA after oral dosing of DMAU as well as gonadotropin and T suppression. The number of men for this early stage clinical study was chosen to provide at least a 0.80 probability to detect a true incidence of grade 3 adverse events of 20% or more. Incidence of treatment-emergent adverse events was summarized. Summary statistics for serum DMA, DMAU and hormone levels were calculated using transformations to achieve normal statistical distributions or using alternative non-parametric statistics. The pharmacokinetic parameters for each full sampling day for DMAU were determined by non-compartmental methods and were primarily assessed using the area under the curve from 0–24 h (AUC0–24) of serum DMAU/DMA levels generated by the 10 blood sampling times over 24 h for each dose of DMAU and computed using the trapezoid method. Other PK parameters assessed included Cavg (average concentration over 24 h), Cmax (maximum concentration over 24 h) and Tmax (the time to reach Cmax). Mixed models incorporated repeated measurements within subjects using a compound symmetrical covariance structure were constructed to examine the effect of food, dose and the interaction of fasting nested within dose on AUC, Cavg, Cmax and Tmax for serum DMA, serum DMAU and the ratio of DMA to DMAU. To allow estimation of food effect (DMAU was only administered at doses of 200, 400 and 800 mg), and because doses <200 mg did not consistently result in detectable serum DMA concentrations, all analyses were restricted to doses of 200, 400 and 800 mg. The effect of oral DMAU treatment on serum T, DHT, estradiol, LH, FSH, calculated free T and SHBG collected at zero, 12 and 24 h, the dose (200, 400 and 800 mg), time (0, 12 and 24 h) and time nested within dose interaction was examined separately according to whether subjects were fed or fasting. Findings from main effects models are reported when interaction terms did not significantly contribute to the model. When a significant time effect was detected, then Bonferroni adjusted post hoc testing (baseline versus 12 h and baseline vs. 24 h) was performed across all dose levels, and then at each dose level. Post hoc testing of significant dose effects was analysed analogously. All analyses were performed using SAS version 9.3 (SAS Institute Inc., Cary, NC, USA), with two-tailed p < 0.05 construing statistical significance. Data are presented as mean ± SEM.

Results

Research participants' demographics and disposition

We enrolled 19 participants (2 Native Americans, 1 Hawaiian/Pacific Islander, 2 African Americans, 12 Whites and 2 others). Their mean age was 31.7 ± 2.3 years, height 176.0 ± 2.5 cm, weight 80.4 ± 3.3 kg and BMI 25.9 ± 0.7 kg/m2. Six completed all nine PK days, and the remaining 13 participants each contributed to some PK days. Participants who exited early for schedule conflicts or personal reasons were replaced at the time point when they exited the study. One participant was discontinued from the study because he had bradycardia (pulse rate as low as 38 beats/minute) during sleep after oral administration of DMAU 50 mg. This participant was an athlete with a resting heart rate in the low 50 sec. A subsequent evaluation showed that bradycardia to the same level also occurred during sleep without DMAU administration in this individual.

Safety and tolerability

DMAU capsules were well tolerated. There were no serious adverse events. One participant had a mean systolic BP of 141 and diastolic of 83 mmHg during his inpatient confinement after taking DMAU 800 mg while fasting. His baseline BP on that day was 146/96 mmHg. This was not considered a grade 1 adverse event (BP > 140 mmHg systolic or 90 mmHg diastolic). This participant likely has subclinical, labile hypertension as his screening BP was 135/85 mmHg. There were two mild cases of acne on the face that resolved while participants were continuing in the trial that were considered “probably related” to the study medications. Other adverse events were mild and considered unrelated to the study. There were no clinically significant changes in blood counts, chemistry panel, liver function tests, or lipid panel that were considered clinically significant throughout the study. Haemoglobin and haematocrit were not significantly different between baseline and at the end of the study. One participant had a transient elevation of aspartate aminotransferase (AST) to 111 IU/L (>twice upper limit of reference range) for no apparent reason four days after administration of DMAU 100 mg while fasting but on repeat testing before his dose of 200 mg was given his AST had normalized to 33 IU/L. Except for this single elevation of AST, this subject's liver enzymes stayed within the reference range during the remainder of the study. EKGs and QCT intervals in all participants showed no significant changes from baseline.

Pharmacokinetics of DMA and DMAU (Table 1)

When the participants were fasting, serum DMAU levels became detectable in all participants only when 200 mg of DMAU or more was administered. Concomitant high-fat meals increased the absorption of oral DMAU (200–800 mg) leading to significantly higher AUC, Cavg and Cmax in serum DMAU compared to fasting state (p < 0.0001, Table 1, Fig. 1A). Serum DMAU peaked at 4–6 h and then gradually decreased but did not reach baseline levels at 24 h. High-fat meal did not alter the time that the maximum concentration of DMAU in blood (p = 0.41) (Fig. 1A, Table 1). There was a significant DMAU dose (200–400 mg) incremental effect on serum DMAU levels (all p < 0.0002, Table 1).

Table 1. Pharmacokinetic parameters of serum DMAU and DMA after oral administration of a single dose of DMAU fasting and after a high-fat meal (conversion DMA 1 ng/mL = 3.29 nmol/L and DMAU 1 ng/mL = 2.12 nmol/L)
 200 mg400 mg800 mg
Fasting (n = 10)Fed (n = 10)Fasting (n = 10)Fed (n = 10)Fasting (n = 10)Fed (n = 10)
  1. DMAU, dimethandrolone undecanoate; DMA, dimethandrolone.

DMAU
AUC (ng/mL/24 h)78.9 ± 51.93152.6 ± 469.173.9 ± 24.36104.6 ± 1138.3823.8 ± 390.610346.1 ± 726.5
Cavg (ng/mL)3.3 ± 2.2131.4 ± 19.53.1 ± 1.0254.4 ± 47.434.3 ± 16.3431.1 ± 30.3
Cmax (ng/mL)16.9 ± 12.6854.9 ± 193.117.9 ± 7.71405.7 ± 283.6257.2 ± 128.82593.5 ± 177.4
Tmax (h)2.8 ± 0.95.8 ± 0.63.4 ± 0.96.2 ± 1.15.8 ± 0.56.0 ± 0.6
DMA
AUC (ng/mL/24 h)12.7 ± 0.466.7 ± 12.012.0 ± 0.0165.9 ± 24.221.1 ± 4.1269.1 ± 43.0
Cavg (ng/mL)0.5 ± 0.02.8 ± 0.50.5 ± 0.06.9 ± 1.00.9 ± 0.211.1 ± 1.8
Cmax (ng/mL)0.8 ± 0.212.5 ± 2.80.5 ± 0.027.7 ± 4.32.7 ± 1.152.3 ± 11.2
Tmax (h)1.2 ± 0.85.8 ± 0.50.0 ± 0.06.4 ± 1.03.6 ± 1.46.0 ± 0.6
Figure 1.

Serum dimethandrolone undecanoate (DMAU) (A) and dimethandrolone (DMA) (B) concentrations after oral administration of a single dose 200, 400 or 800 mg of DMAU after fasting (closed circles) or a high-fat meal (50% fat) (open circles). Note y axis is in log scale. (Conversion DMA 1 ng/mL = 3.29 nmol/L and DMAU 1 ng/mL = 2.12 nmol/L).

When the participants were fasting, serum DMA levels were just above the lower limit of quantification (LLOQ) in 4/10 participants when the highest dose tested (800 mg DMAU) was administered (Fig. 1B). In contrast, after a high-fat meal, serum DMA levels were detectable in all participants with DMAU dosed at 200 mg and above (Fig. 1B). Doses lower than 200 mg resulted in DMA concentrations that were undetectable or near the LLOQ (data not shown) even when DMAU was administered with food. The DMA concentration peaked between 4 and 8 h after administration of DMAU with food, after which time DMA concentrations declined but serum DMA remained detectable at 24 h after 400 and 800 mg doses (Fig. 1B). Compared to the fasting state, high-fat meal increased the absorption of oral DMAU leading to higher AUC, Cavg and Cmax in serum DMA (all p less than equal to 0.0001, Table 1), but did not alter the time to achieve the maximum serum concentration of DMA (p = 0.60). The three dose levels (200, 400 and 800 mg) of DMAU administered resulted in statistically different AUC, Cavg and Cmax of DMA overall (all p less than equal to 0.0002, Table 1), although the differences between the 400 and 800 mg doses were not statistically significant in the fed state. The DMA to DMAU ratios (conversion of DMAU to DMA) were 2.8 ± 0.6%, 3.6 ± 0.5% and 2.6 ± 0.4% in the fed state after 200, 400 and 800 mg dose respectively (p = 0.89) without a dose effect. The DMA: DMAU could not be calculated in the fasting state because DMA concentration was below LLOQ in many participants. There was no significant dose effect on the time to reach maximum concentrations of DMA (p = 0.96).

Serum LH, FSH, testosterone, free testosterone, estradiol, DHT and SHBG (Fig. 2)

Greater suppression of gonadotropins (LH and FSH) was detected with increasing doses of DMAU (p < 0.05 for each) in either the fed or fasting state, although post hoc testing revealed that the 400 and 800 mg dose levels were equivalent (Fig. 2A,B). A significant time effect was detected only in the fed state for LH across all dose levels (p < 0.0001), and also for FSH in the fed state across all dose levels (p < 0.0001). Post hoc testing show that blood concentrations of LH or FSH at either 12 or 24 h were different from baseline at each dose levels (Fig. 2A,B). All steroids (testosterone, free testosterone, estradiol and DHT) showed a significant time effect in the fed state (Fig. 2C–F). Blood concentrations of all these hormones at 12–24 h were generally significantly different from baseline when DMAU was administered with food (see Fig. 2C–F for specific significance levels). No dose or time effects were detected for SHBG (Fig. 2G). Time effects in these parameters in the fasting state were less consistent, as would be anticipated given the lower absorption of DMAU.

Figure 2.

Serum LH (A), FSH (B), T(C), free T (D), DHT (E) and estradiol (F) concentrations after administration of a single dose 200, 400 or 800 mg of dimethandrolone undecanoate (DMAU) (n = 10) or placebo after fasting (closed circles) or a high-fat meal (50% fat, open circles). The right panel shows hormone levels in two participants taking the same number of capsules as the active drug studied while fasting or after a high-fat meal on three occasions. Hormone concentrations at 12 or 24 h that were significantly different from baseline hormone concentration were marked with *p < 0.05 and **p < 0.001 at each dose level by mixed model analysis.

Discussion

This randomized, double-blind study assessed the safety and tolerability of single, escalating dose of DMAU and its potential to suppress gonadotropins and endogenous androgen production, properties critical for a male hormonal contraceptive. Single doses of DMAU up to 800 mg were well tolerated, safe and were not associated with any serious adverse events. Bioavailability of DMAU was markedly enhanced, nearly 80-fold, when DMAU was administered with a high-fat meal compared to administration while fasting. In this fed state, serum DMAU and DMA showed dose-incremental pharmacokinetics. Once the dose and formulation of DMAU have been determined, further studies on the amount of fat required in the diet for optimum absorption of DMAU will be examined. About 2–3% of DMAU in the serum was hydrolysed to the active compound DMA, which was detected in serum about 2 h after dosing of 200, 400 or 800 mg of DMAU with food but not with lower doses. DMA levels in the serum remained detectable 24 h after oral administration of 400 and 800 mg of DMAU with food suggesting that this formulation might be compatible with a daily dosing regimen.

As anticipated with androgen administration, mild acne was reported in two participants. There were no other adverse events that were attributable to DMAU administration. Haematocrit and haemoglobin, and white blood cell and platelet counts were not significantly affected by single doses of DMAU. There were no changes in clinical chemistries including liver enzymes in these studies when a single dose of DMAU was administered, given that methyl T and other orally active modified androgens may be associated with hepatotoxicty (Boyer et al., 1976; Murray-Lyon et al., 1977; Westaby et al., 1977). Further careful monitoring of liver function tests when DMAU is administered repeatedly over the longer term will be needed to confirm this finding.

In contrast to T, DMA does not require 5α-reductase activity for its androgenic action and is not converted to 5α-reduced products (Attardi et al., 2010, 2011). 5α-reductase type 2 is highly expressed within the prostate gland where this conversion may serve as a local androgen amplification step. A lack of conversion of DMA by 5α-reductase may render DMAU/DMA less stimulatory to the prostate than some androgens (Attardi et al., 2006). Unlike testosterone, DMA is not aromatized to oestrogenic metabolites (Attardi et al., 2008). The importance of oestrogens for bone formation and decrease in bone resorption in men has been shown in prior studies (Khosla et al., 2001; Khosla & Bilezikian, 2003). A recent study in healthy men whose hypothalamus–pituitary–testis axis was suppressed by a gonadotropin releasing hormone agonist, comparing testosterone administration with an aromatase inhibitor with testosterone alone showed that oestrogens are important for decreasing fat mass and contribute to maintenance of sexual function (Finkelstein et al., 2013). Studies in hypogonadal men administered aromatase inhibitor showed while serum testosterone was increased and serum estradiol was suppressed, spine bone mineral density was decreased when estradiol was suppressed to very low levels (Burnett-Bowie et al., 2009) but was unchanged when estradiol was kept at the lower limit of the reference range (Loves et al., 2013). Because endogenous production of oestrogens is suppressed by DMA administration, the long-term effects of this androgen on bone health, fat mass and other oestrogen-dependent processes will need to be carefully assessed in future longer term clinical trials of DMAU. Suppression of the hypothalamic–pituitary function resulting in oestrogen deficiency should be avoided.

Administration with a high-fat meal clearly improved the oral bioavailability of DMAU and DMA. Studies of TU in oleic acid, castor oil or as a Self-Emulsifying Drug Delivery System (SEDDS) formulations have demonstrated that administration of TU with a fatty meal compared to fasting increased serum T and DHT levels (Bagchus et al., 2003; Schnabel et al., 2007; Yin et al., 2012a,b;). In our study, peak levels of DMA were reached at 4–6 h after ingestion with food, similar to TU in oil or SEDDS administered with a high-fat diet (Yin et al., 2012a,b). TU is absorbed mainly through the intestinal lymphatics because the aliphatic undecanoate ester chain allows TU to travel with dietary lipids in the lymphatics (Horst et al., 1976; Shackleford et al., 2003). It is likely that DMAU, which has the same long chain fatty acid ester (undecanoate) is similarly absorbed via intestinal lymphatics, explaining the significant impact of concomitant fatty food intake on absorption of DMAU. The requirement of medications to be taken with food should not be an impediment for men as many common medications such as non-steroidal anti-inflammatory agents have to be taken with food.

Once absorbed into the body only about 2–3% of serum DMAU is available as serum DMA, the active compound. Oral TU in castor oil (Andriol Testocap; Organon [now Merck], Oss, the Netherlands), when administered to dogs, gave equivalent concentrations of TU and T measured in thoracic duct lymphatics suggesting complete hydrolysis of the TU to T in the systemic circulation (Shackleford et al., 2003). Oral TU administered as a SEDDS formulation with food resulted in serum concentrations of T was about 30 per cent of serum concentration of TU (Yin et al., 2012a,b). From these studies in dogs and men, the undecanoate moiety from oral TU in castor oil or SEDDS appears to release T from TU in the body rapidly and much more efficiently than DMAU conversion to DMA when DMAU is administered as a powder in capsules. The poor conversion of DMAU to DMA is likely because of either a lack of exposure to sufficient systemic esterase activity or to the inefficient hydrolysis of the undecanoate moiety. The latter may be owing to steric hindrance by the presence of additional methyl groups at the 7α and 11β position in DMAU, but not in TU (Attardi et al., 2008). Moreover, the current powder formulation of DMAU may not be the optimal formulation for delivering DMAU to the intestine. We are exploring DMAU formulated in castor oil or SEDDS with the goal of enhancing oral bioavailability. Given that DMA appears to be at least as androgenic as T in vitro and in vivo (Attardi et al., 2006), if bioavailability can be improved, it is possible that lower or less frequent doses of DMAU may be required to provide physiologic androgen action than are currently required for TU.

In this study, oral DMAU administration with food suppressed serum levels of LH, FSH, total and free T, estradiol and DHT concentration at 12 h compared to baseline values, and this persisted 24 h after dosing. Although single baseline samples for gonadotropins were drawn for each subject, our prior study showed that drawing three samples compared to one sample did not significantly affect the assessment of the suppression of gonadotropins by exogenous steroids (Roth et al., 2013). The suppression of LH and FSH was dependent on the dose of DMAU. Dose-dependent decreases in total and free T, and the metabolites (DHT and E2) were not consistently observed. The consistent suppression of sex steroids may not have been apparent because of low participant numbers or secondary to the fact that LH, despite being suppressed by DMAU, likely stayed within the normal range throughout most of the 24-h observation period. Our data suggest that DMAU/DMA can rapidly exert negative feedback on the hypothalamic–pituitary–testicular axis. This is likely because of the potent progestational effects of DMA in addition to its androgenic effects (Attardi et al., 2006). The observed decline in LH and T levels at 12 h is unlikely because of diurnal changes, since the magnitude of the changes appear to exceed known circadian variability and persisted at 24 hours. Moreover, no decline in serum T, free T, LH, DHT nor estradiol was observed in the two participants receiving placebo. The suppression of estradiol and DHT in parallel with T is likely because of decreased secretion of T from the testis and/or decreased conversion from the precursor T.

In summary, single escalating doses of DMAU (powder in capsule formulation) up to 800 mg were well tolerated in healthy male volunteers. When DMAU was administered with food, serum DMAU and DMA showed dose-incremental increases. The conversion of DMAU to DMA was limited but was sufficient to have a biological effect, reversibly suppressing LH and endogenous T production. Oral DMAU has promise to act as a single, oral, progestin plus androgen; a prototype ‘male pill’. Oral administration is the preferred method for contraceptive delivery by many men, and thus a single-agent oral medication may offer men and couples an additional, acceptable, contraceptive option that might increase contraceptive use over time (Heinemann et al., 2005). Future studies aimed to optimize bioavailability and test the safety and efficacy of DMAU to suppress gonadotropins and ultimately spermatogenesis in men are warranted.

Acknowledgements

The Los Angeles Center was supported by NICHD contracts HHSN275201100033U and HHSN275201000080U; the Endocrinology, Metabolism and Nutrition training grant (T32 DK007571) and the UCLA Clinical and Translational Science Institute (UL1TR000124) at Harbor-UCLA/LA BioMed. The Seattle center was supported by contract number HHSN275200403370I and 5K12HD053984 from the Eunice Kennedy Shriver National Institute of Child Health and Development, the National Center For Advancing Translational Sciences of the National Institutes of Health under Award Number UL1TR000423, the Center for Research in Reproduction and Contraception U54 HD 04245 (NICHD), and the National Institute of Diabetes and Digestive and Kidney Diseases training grant 5T32 DK007247-35. We thank Peter Christenson, PhD, formerly at LA Biomed for his advice in study design and data analysis plans. We thank our research coordinators Elizabeth Ruiz, Jamie Custodian RN, Marilyn Busher RN, Kathryn Torrez-Duncan and Kathy Winter for their assistance with the study and the technical assistance of Feng Bai and Anne Taylor for DMA and DMAU assay development and validation and the staff of the Endocrine and Metabolic Research Laboratory at Harbor-UCLA/LA Biomed.

Disclosures

The authors have nothing to disclose.

Author contributions

P.S., S.T.P., R.S.S., J.J.N., J.K.A. and C.W. organized and performed this clinical research study; S.T.P., R.S.S., J.K.A., D.L.B., W.J.B. and C.W. designed the study; J.W. monitored the safety of study; P.Y.L. and L.H. managed and analysed the data; L.H. and A.L. significantly contributed to all hormone analyses. P.S., R.S.S., P.Y.L. and C.W. interpreted the data and wrote the manuscript; S.T.P., J.K.A., D.L.B. contributed to the interpretation of the data; S.T.P., J.J.N., J.K.A., A.L., L.H., D.L.B., J.W., W.J.B. critically reviewed many drafts of the manuscript. All authors approved the submitted final version of the manuscript.

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