History of the development of new vitamin D analogs: studies on 22-oxacalcitriol (OCT) and 2beta-(3-hydroxypropoxy)calcitriol (ED-71).

In 1981 Suda and his colleagues first reported the new activity of calcitriol namely its ability to differentiate the myeloid leukemia cells into normal monocytes-macrophages. However, the possibility of using calcitriol as an antileukemic drug was not feasible because of its potent calcemic effects. Based on these observations, several pharmaceutical companies initiated the synthesis of vitamin D analogs with the aim to separate the calcemic actions of calcitriol from its actions on regulating the cell growth and differentiation. As a result, numerous noncalcemic analogs with a potential for the treatment of leukemia and other cancers were synthesized. The group at Chugai introduced two characteristic analogs of opposite type namely, 22-oxacalcitriol (OCT) and 2beta-(3-hydroxypropoxy)calcitriol (ED-71) which have been shown to have therapeutic value and are already being used clinically. The work on OCT and ED-71 together with the work on calcipotriol and KH-1060 by Leo Laboratories, and 1alpha,25(OH)(2)-16-ene-23-yne-D(3) by Hoffmann-La Roche, vigorously stimulated research world-wide in the development of vitamin D analogs into pharmaceutical products. More recently new impressive vitamin D analogs such as 3-epi analogs, 19-nor analogs, 18-nor analogs, 2-methyl-20-epi-calcitriol, non-steroidal vitamin D analogs are being developed. The authors are convinced that various vitamin D analogs will become highly effective therapeutic agents at the clinical level in the new century, and also that a new theory on the mechanism of vitamin D action will be generated.