Cultured oncogenic osteomalacia tumor cells produce a factor(s) that inhibits osteocalcin production by osteoblastic cells

A 34-year-old patient was diagnosed with oncogenic osteomalacia associated with hypophosphatemia, low levels of serum 1,25-dihydroxyviamin D [1,25(OH)(2)D], and osteocalcin (OC). Resection of the tumor normalized these blood abnormalities. While such tumors produce a humoral factor(s) that affects phosphate reabsorption by the proximal renal tubules, the direct action of such factor(s) on osteoblast function has not been examined previously. We investigated the effect of conditioned medium of cultured osteomalacia tumor cells on OC production by human osteoblastic cell line, MG-63. The conditiond medium inhibited OC production induced by 1,25(OH)(2)D-3. Our results indicate that the humoral factor(s) produced by the tumor has direct effect on osteoblasts and may contribute to development of the characteristic syndrome.