Bauss F, Esswein A, Reiff K, Sponer G, Müller-Beckmann B
Department of Preclinical Research and Development, Bone Metabolism, Boehringer Mannheim GmbH, Sandhoferstrasse 116, D-68305 Mannheim, Germany.
Calcif Tissue Int. 1996 Sep;59(3):168-73. doi: 10.1007/s002239900104.
In order to target 17beta-estradiol directly at bone we synthesized three 17beta-estradiol-bisphosphonate conjugates (E2-BPs) with different esterase-sensitive linkers between both molecular moieties. The systemic administration of these compounds should result primarily in local estrogenic effects on bone with no or negligible systemic hormonal effects. Only if a considerable margin exists between the doses required for inhibition of bone loss and those for systemic hormonal effects can such a pro-drug be considered acceptable for patients refusing systemic estrogen replacement therapy for several reasons. The conjugates were tested in vitro for their 17beta-estradiol release in rat serum and in vivo for their local and systemic effects in rats: in vitro, the conjugates expressed cleavage resistance, low cleavage (4.8%), or high cleavage (33.1%) within 48 hours of incubation. The conjugate with the low-cleavage doubled 17beta-estradiol serum half-life (3.78 hours) whereas the high-cleavage conjugate resulted in approximately four times higher serum half-life (8.36 hours) when compared with free 17beta-estradiol. In ovariectomized rats, bone loss was optimally prevented by 50 nmol/kg/day of 17beta-estradiol when administered S. C. over a period of 5 weeks, and protection against uterine atrophy was achieved at doses as low as 5 nmol/kg/day. The cleavage-resistant conjugate was ineffective in preserving bone and uterus in doses ranging from 5 to 150 nmol/kg/day. The other two E2-BPs revealed a dose-dependent inhibition of bone loss which was paralleled by the respective uterus weight with a dose range of 1.5-150 nmol/kg/day being fully effective in a range similar to 17beta-estradiol alone. The higher sensitivity of the uterus versus bone to protective estrogenic effects (1:10) was abolished by the conjugates. We conclude that E2-BPs containing esterase-sensitive linkers failed to act as bone-seeking pro-drugs expressing primarily local effects on bone without systemic effects.
为了使17β-雌二醇直接作用于骨骼，我们合成了三种17β-雌二醇-双膦酸盐偶联物（E2-BPs），两个分子部分之间带有不同的酯酶敏感连接子。这些化合物的全身给药应主要产生对骨骼的局部雌激素作用，而无全身激素作用或全身激素作用可忽略不计。只有当抑制骨质流失所需剂量与全身激素作用所需剂量之间存在相当大的差距时，对于因多种原因拒绝全身雌激素替代疗法的患者而言，这种前体药物才会被认为是可接受的。这些偶联物在体外进行大鼠血清中17β-雌二醇释放测试，在体内进行大鼠局部和全身效应测试：在体外，偶联物在孵育48小时内表现出抗裂解性、低裂解率（4.8%）或高裂解率（33.1%）。与游离17β-雌二醇相比，低裂解率的偶联物使17β-雌二醇血清半衰期加倍（3.78小时），而高裂解率的偶联物导致血清半衰期大约高出四倍（8.36小时）。在去卵巢大鼠中，当以50 nmol/kg/天的剂量皮下给药5周时，17β-雌二醇能最佳地预防骨质流失，而低至5 nmol/kg/天的剂量就能实现对子宫萎缩的保护作用。抗裂解偶联物在5至150 nmol/kg/天的剂量范围内对骨骼和子宫均无保护作用。另外两种E2-BPs显示出剂量依赖性的骨质流失抑制作用，相应地子宫重量也呈现剂量依赖性变化，在1.5 - 150 nmol/kg/天的剂量范围内具有与单独使用17β-雌二醇相似的完全有效性。偶联物消除了子宫与骨骼对雌激素保护作用的敏感性差异（1:10）。我们得出结论，含有酯酶敏感连接子的E2-BPs未能作为靶向骨骼的前体药物发挥作用，无法主要对骨骼产生局部作用而无全身作用。
