Validation of 17beta-HSD2 inhibition as potential approach for the prevention of osteoporosis: comparison of in vivo efficacy and safety between a 17beta-HSD2 inhibitor and a specifically targeting bone 17beta-HSD2 inhibitor
Pharmacy
Final Report Abstract
Osteoporosis is a disease characterized by the loss of bone mass and density, which ultimately results in an increased risk of bone fractures. Osteoporosis is distributed worldwide and has a high socio-economic impact, which will increase due to demographic reasons. Postmenopausal women are a high-risk group for osteoporosis because of the cessation of ovarian hormone production, in particular of estrogens. Within this study, we evaluated a novel approach to prevent postmenopausal bone loss. Experimentally we used the well-established pharmacological model for osteoporosis, namely castration (ovariectomy) induced bone loss in female rats. The overall aims of this project were twofold. First, we aimed to test whether specific inhibitors for the estradiol converting enzyme 17β-hydroxysteroid dehydrogenase 2 (17βHSD2) provide a therapeutic option for the prevention of osteoporosis. Second, we aimed to optimize bone specific inhibition of 17βHSD2 by developing and testing a new strategy of selectively targeting 17βHSD2 inhibitors to bone thereby improving bone specific effectiveness of inhibition. For the proof of principle study, three candidate molecules of 17βHSD2 inhibitors, namely C15, C22, C24, were provided by the Medicinal Chemistry group (Prof. Dr. R.W. Hartmann). These inhibitors were characterized for their inhibitory efficiency in vitro and it turned out that they showed higher potency toward human and rodent 17βHSD2, lower cell toxicity, high aqueous water solubility and high metabolic stability. Following pharmacokinetic profiling of the inhibitors and exclusion of potential interaction of the compounds with the estrogen receptors, C24 was identified as the most suitable inhibitor to be used in the proof of principle study. This study was performed in the Molecular Cell Physiology group (Prof. G. Vollmer) in a dose/response setting using the experimental model mentioned above. Bone protective effects were detectable for the dose group of 2 mg/kg bodyweight per day of C24. In addition and irrespective of the dose group, unwanted, estrogenic side effects were not detectable in the uterus. These results clearly demonstrate that inhibition of 17βHSD2 represents a potential target for the prevention of osteoporosis. However, 2 mg/kg bodyweight per day was the lowest dose investigated in the dose response analysis. No effects on bone were seen following the application of the higher doses of 10 and 50 mg/kg bodyweight per day. This is presumably due to the very high bioavailability of C24, which results in high serum levels of C24. The observed levels are capable to inhibit both 17βHSD2 and its counterpart 17β-hydroxysteroid dehydrogenase 1 (17βHSD1). In other words, the effective treatment window had to be characterized in more detail. This was attempted in a dose dependent follow up experiment centered around the effective dose level of 2 mg/kg bodyweight per day. This experiment disclosed, that the unexpected high bioavailability of C24 is also associated with a high variability of achievable serum levels rendering the precise dosing difficult. In continuation of the aims of the project and based on the chemical structure of C24, an optimized 17βHSD2 inhibitor which carries a diphosphonate (C24DP) moiety was successfully synthesized. This diphosphonate moiety is intended to be used to target the inhibitor specifically to the bone. In the frame of this project, C24DP was successfully characterized in a pharmacokinetic experiment. This experiment showed that subcutaneous application was the most efficient path of application to deliver the modified inhibitor C24DP. In conclusion, we showed that inhibition of 17βHSD2 is a potential target for the prevention of osteoporosis. In addition, we could exclude potential estrogenic side effects. Matters of optimization comprise verification of bone targeting of the tagged inhibitor, degree of dissociation between inhibition of 17βHSD2 and 17βHSD1, as well as optimization of the potential therapeutic window.
Publications
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(2018) Structure-based design and profiling of novel 17β-HSD14 inhibitors. Eur J Med Chem 155: 61-76
Braun F, Bertoletti N, Möller G, Adamski J, Frotscher M, Guragossian N, Madeira Girio PA, Le Borgne M, Ettouati L, Falson P, Müller ST, Vollmer G, Heine A, Klebe G, Marchais-Oberwinkler S
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(2019) Effects of 17β-HSD2 inhibition in bones on osteoporosis based on an animal rat model. J Steroid Biochem Mol Biol. 2019 Jun 8; 192: 105405
Müller ST, Pählig S, Merabet A, Abdelsamie AS, van Koppen CJ, Marchais-Oberwinkler S, Hartmann RW, Zierau O, Vollmer G
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(2019). Design, synthesis, and biological characterization of orally active 17β-hydroxysteroid dehydrogenase type 2 inhibitors targeting the prevention of osteoporosis. J. Med. Chem. 62: 7289 – 7301
Abdelsamie AS, Salah M, Siebenbürger L, Merabet A, Scheuer C, Frotscher M, Müller ST, Zierau O, Vollmer G, Menger MD, Laschke MW, van Koppen CJ, Marchais-Oberwinkler S, Hartmann RW
