Seocalcitol (EB 1089): A vitamin D analogue of anti-cancer potential. Background, design, synthesis, pre-clinical and clinical evaluation

It is well established that the metabolically active form of vitamin D, 1 alpha,25-dihydroxyvitamin D-3 (1 alpha,25(OH)(2)D-3) plays a key role in the establishment and maintenance of the calcium metabolism in the body. In addition to this classic effect of 1 alpha,25(OH)(2)D-3, substantial evidence has emerged demonstrating that 1 alpha,25(OH)(2)D-3 is able to regulate cell growth and differentiation in a number of different cell types, including cancer cells. However, the clinical usefulness of 1 alpha 25(OH)(2)D-3 is limited by its tendency to cause hypercalcaemia. Much effort has therefore been directed to identifying new vitamin D analogues with potent cell regulatory effects, but with weaker effects on the calcium metabolism than those of 1 alpha,25(OH)(2)D-3. One of these new synthetic analogues is Seocalcitol (EB 1089). Despite being 50-200 times more potent than 1 alpha,25(OH)(2)D-3 with respect to regulation of cell growth and differentiation in vitro as well as in vivo, EB 1089 displays a reduced calcaemic activity in vivo compared to that of 1 alpha,25(OH)(2)D-3. These characteristics make EB 1089 a potentially useful compound for the treatment of cancer. Recent clinical evaluation of EB 1089 has focused mainly on establishing a maximum tolerated dose in cancer patients. Early results confirm that the low calcaemic activity observed in animals can be reproduced in the clinic. Furthermore, EB 1089 has been shown to induce regression of tumours, especially in hepatocellular carcinoma where complete remission has been obtained. In conclusion, the development of EB 1089 as an anti-cancer drug holds promise. However, its final evaluation must await the completion of ongoing controlled clinical trials.