A non-calcemic analog of 1α,25 dihydroxy vitamin D3 (JKF) upregulates the induction of creatine kinase B by 17β estradiol in osteoblast-like ROS 17/2.8 cells and in rat diaphysis

We have reported that multiple treatments with so-called 'non-hypercalcemic',analogs of 1 alpha ,25(OH)(2) vitamin D-3 (1,25(OH)(2)D-3) stimulate the specific activity of creatine kinase BB (CK) in ROS 17/2.8 osteoblast-like cells, and that pretreatment with these analogs upregulates responsiveness and sensitivity to 17 beta estradiol (E-2) for the induction of CK. However, since the analogs showed toxicity in vivo, we have now studied the action of a demonstrably non-calcemic, hybrid analog of vitamin D in ROS 17/2.8 cells, and prepubertal rats. The analog JKF was designed to separate its calcemic activity from other biological activities by combining a calcemic-lowering 1-hydroxymethyl group with a potentiating C, D-ring side chain modification including 24 difluoronation. Treatment with 1 pM JKF alone significantly stimulated CK specific activity at 4 h by 30 +/- 10%. However after three daily pretreatments, JKF upregulated the extent of induction by 30 nM E-2 by 33% at 1 pM and by 97% at 1 nM; the E-2 dose needed for a significant stimulation of CK activity was lowered to 30 pM. The action of the SERMS tamoxifen, tamoxifen methiodide and raloxifene, at 3 muM, was also upregulated by three daily pretreatments with 1 nM JKF; unexpectedly, this pretreatment prevented the inhibition of E-2 stimulation by the SERMS. Upregulation of E-2 action by 1 nM JKF was inhibited by 1 nM ZK159222, an inhibitor of the nuclear action of 1,25(OH)(2)D-3. In vivo, three daily injections of 0.05 ng/g body weight of JKF augmented the response of prepubertal female rat diaphysis and epiphysis to E-2. Therefore, demonstrably non-calcemic analogs of 1,25(OH)(2)D-3 may have potential for use in combination with estrogens or SERMS in the prevention and/or treatment of metabolic bone diseases such as postmenopausal osteoporosis. (C) 2001 Elsevier Science Ltd. All rights reserved.