The hypercalcemic rat leydig cell tumor—A model of the humoral hypercalcemia of malignancy

Abstract

Summary. A transplantable nonmetastasizingLeydig cell tumor, which occurs spontaneously in the aged Fischer rat, was examined both in vitro and in vivo. Animals carrying this tumor were found to have the syndrome recently called the humoral hypercalcemia of malignancy, characterized by hypercalcemia, hypercalciuria, hypophosphatemia, renal phosphate wasting, increased urinary 3'5'-cyclic monophosphate (cyclic AMP) excretion, and suppressed circulating parathyroid hormone (PTH) concentrations. The changes in urinary cyclic adenosine monophosphate (cAMP) excretion occurred simultaneously with hypercalcemia in most animals. In one animal, the primary tumor was excised and this was followed by an immediate fall in serum calcium and urine cAMP excretion. Hypercalcemia was due to increased bone resorption. This was shown by bone histology, which demonstrated an increase in osteoclast number and activity on trabecular bone surfaces associated with bone loss in tumor-bearing animals. No tumor cells were seen adjacent to the osteoclasts. There was no evidence of metastatic disease as assessed by bone-seeking isotopes. Urinary hydroxyproline excretion was increased in tumor-bearing hypercalcemic animals, indicating an increase in bone turnover. The tumor cells were established in culture and found to produce a bone-resorbing factor in vitro using a bioassay for bone resorption based on the release of previously incorporated 4~Ca from fetal rat long bones in culture. This model of the humoral hypercalcemia of malignancy should make it possible to determine the nature of the boneresorbing factor produced by the cultured tumor cells which is responsible for the hypercalcemia, and the relationship of hypercalcemia and the production of the bone-resorbing factor to the other Send offprint requests to G. R. Mundy at the above address.parameters of the syndrome, namely, renal phosphate wasting and increased urinary cAMP excretion.

A vitamin D analogue (EB1089) inhibits parathyroid hormone-related peptide production and prevents the development of malignancy-associated hypercalcemia in vivo.

“…Hypercalcemia may also occur in association with a number of animal neoplasms. Among the best characterized of the animal models, and one which closely mimics the human syndrome, is the male Fischer rat implanted with the Rice 500 Leydig cell tumor (7,8). PTHRP is well documented to cause the hypercalcemia associated with this tumor (9,10).…”

The Tumor Cells (FA-6) Established from a Pancreatic Cancer Associated with Humoral Hypercalcemia of Malignancy: A Simultaneous Production of Parathyroid Hormone-Like Activity and Transforming Growth Factor Activity.

“…Although various animal (Sica et al, 1983;D'Souza et al, 1984;Rosol et al, 1986) and human (Strewler et al, 1983;Bringhurst et al, 1986;Nissenson et al, 1985;Sato et al, 1987a, b) tumor cells associated with HHM have been cultured, cells originating in exocrine pancreatic cancer have not been established in vitro. In the present study, tumor cells were selected from an undifferentiated pleomorphic adenocarcinoma of exocrine pancreas associated with HHM which was injected into nude mice and re- Albumin (66 kDa), carbonic anhydrase (29 kDa), cytochrome C (12.4 kDa), and aprotinin (6.5 kDa) were used as markers of mole;ular size.…”

Failure of parathyroid hormone antagonists to inhibit in vitro bone resorbing activity produced by two animal models of the humoral hypercalcemia of malignancy.

“…Rats that bore tumors developed serum calciums between 13 and 18 mg/dl (6). For collection of conditioned medium, subconfluent cells were cultured in RPMI that contained 1% FCS and 1% horse serum for 48 h and then were treated as described for the Walker cells.…”

“…If this hypothesis is correct, then these PTH antagonists should inhibit the boneresorbing factors produced by these tumors, which are the primary cause of the hypercalcemia. To test the hypothesis, we examined two tumor models of HHM (5,6) which produced both bone-resorbing activity and factors which stimulate adenylate cyclase to determine if the bone-resorbing activity was mediated via PTH receptors.…”