ABSTRACT
PTH-related protein (PTHrP) has been shown to be a major factor responsible for hypercalcemia of malignancy. PTHrP acts via the PTH/PTHrP receptor, and therefore, PTH antagonists might be expected to reverse the hypercalcemia in malignancy. In the present studies, the PTH antagonists [Tyr34]bovine (b) PTH-(7-34)NH2, [D-Trp12,Tyr34]-bPTH-(7-34)NH2, or PTHrP-(7-34)NH2, were administered to hypercalcemic athymic nude mice bearing a human squamous cell carcinoma of the lung in 60- to 500-fold molar excess of a dose of PTHrP-(1-34) known to produce hypercalcemia. The antagonists had no significant effect on serum calcium levels. In an adenylyl cyclase assay using the ROS 17/2.8 cells, a potent PTH antagonist, [Leu11,D-Trp12]PTHrP-(7-34)NH2 was rapidly inactivated in the presence of rat or human plasma. This inactivation by plasma was not blocked by common inhibitors of proteolysis (aprotinin, soybean trypsin inhibitor, and leupeptin). Preliminary studies demonstrated that inactivation of the PTHrP antagonist was caused by a plasma component with an apparent mol wt of 230,000 daltons. The knowledge of the structure of the PTH/PTHrP receptor combined with the identification of a hormone-inactivating plasma factor should facilitate the design of PTH-antagonists that are effective in vivo.
Subject(s)
Blood , Carcinoma, Squamous Cell/complications , Hypercalcemia/etiology , Parathyroid Hormone/antagonists & inhibitors , Animals , Calcium/blood , Humans , Hypercalcemia/metabolism , Mice , Mice, Nude , Neoplasm Transplantation , Parathyroid Hormone/pharmacology , Peptide Fragments/pharmacology , Protease Inhibitors/pharmacology , Proteins/pharmacologyABSTRACT
Transforming growth factor alpha (TGF alpha) has been implicated in the pathogenesis of inhibited bone formation in hypercalcemia of malignancy. We evaluated the effects of infusions of vehicle or TGF alpha (0.25 microgram/h), or parathyroid hormone-related protein (1-34) (PTHrP) (0.025 microgram/h) alone, or a combination of TGF alpha and PTHrP on bone histomorphometry in mice. The peptides were infused for 6 days via Alzet osmotic minipumps. TGF alpha alone, PTHrP alone, or a combination of the two resulted in an increase in bone resorption as well as bone formation parameters. The increase in bone formation with the combination of TGF alpha and PTHrP was significantly greater than that seen with either peptide alone. Therefore, it is unlikely that TGF alpha is the factor responsible for inhibited bone formation in hypercalcemia of malignancy.
Subject(s)
Bone and Bones/pathology , Proteins/pharmacology , Transforming Growth Factor alpha/pharmacology , Animals , Bone Resorption , Bone and Bones/drug effects , Drug Synergism , Infusion Pumps, Implantable , Male , Mice , Mice, Inbred BALB C , Parathyroid Hormone-Related Protein , Proteins/administration & dosage , Transforming Growth Factor alpha/administration & dosageABSTRACT
Large quantities of parathyroid hormone-related protein (PTHrP) are present in the milk of various species. It has been suggested that PTHrP may play a role in neonatal calcium homeostasis. In the present study we evaluated the effect of neutralization of amino-terminal PTHrP activity by passive immunization in 1-day-old mouse pups. Neutralization of amino-terminal PTHrP activity had no significant effect on serum calcium or whole-body calcium content in the neonatal mice. In additional studies, we demonstrated that subcutaneous administration of PTHrP-(1-34) increased serum calcium, whereas oral administration had no significant effect in 3-day-old pups. The studies therefore demonstrate that the amino terminus of PTHrP may not play a significant role in neonatal calcium homeostasis. Local effects of PTHrP cannot be excluded by the results of the present study.
Subject(s)
Calcium/blood , Neoplasm Proteins/pharmacology , Parathyroid Hormone-Related Protein , Peptide Fragments/pharmacology , Proteins , Administration, Oral , Animals , Animals, Newborn , Calcium/analysis , Calcium/metabolism , Enzyme-Linked Immunosorbent Assay , Homeostasis , Immune Sera/metabolism , Immunization, Passive , Injections, Subcutaneous , Mice , Mice, Inbred Strains , Neoplasm Proteins/administration & dosage , Neoplasm Proteins/metabolism , Neoplasm Proteins/physiology , Peptide Fragments/administration & dosage , Peptide Fragments/metabolism , Peptide Fragments/physiologyABSTRACT
Parathyroid hormone (PTH)-related protein has been shown to be a factor responsible for hypercalcemia of malignancy. Recent studies have shown the presence of mRNA for PTH-related protein in lactating breast tissue, suggesting a physiological role for this peptide during lactation. In the present study, we evaluated the effect of neutralization of PTH-related protein activity in lactating mice (by passive immunization) on various parameters of maternal and neonatal calcium homeostasis. PTH-related protein bioactivity, as tested in the adenylate cyclase assay, was present in mouse milk, and this activity was completely neutralized by the antisera used in the present study. In lactating mice, the effects of injection of PTH-related protein antisera on maternal serum calcium concentrations, milk calcium and phosphorus concentration, pup growth, dam femur calcium content, and pup calcium content were similar to those of the injection of normal rabbit serum. Therefore, maternal PTH-related protein does not appear to have a role in calcium homeostasis during lactation.
Subject(s)
Calcium/metabolism , Lactation/physiology , Proteins/metabolism , Animals , Antibodies , Female , Homeostasis , Mice , Mice, Inbred Strains , Neutralization Tests , Parathyroid Hormone/metabolism , Parathyroid Hormone-Related ProteinABSTRACT
Bone resorption is increased in both humoral hypercalcemia of malignancy (HHM) and primary hyperparathyroidism. On the other hand, bone formation parameters are increased in primary hyperparathyroidism and decreased in HHM. Recently, a PTH-related protein (PTHrP) has been shown to be responsible for the hypercalcemia in the syndrome of HHM. In the present study we evaluated the effects of a neutralizing antiserum to PTHrP on bone histomorphometric parameters in hypercalcemic athymic mice bearing a human squamous cell lung cancer. These effects were compared to those of tumor resection. Similar to the effects of tumor resection, the antiserum to PTHrP resulted in a decrease in serum Ca levels, a decrease in bone resorption, and an increase in bone formation parameters. The studies, therefore, indicate that PTHrP is the major factor responsible for all of the features, including the decreased bone formation seen in HHM.
Subject(s)
Antibodies/pharmacology , Bone and Bones/pathology , Carcinoma, Squamous Cell/complications , Hypercalcemia/pathology , Lung Neoplasms/complications , Proteins/immunology , Animals , Bone Resorption/pathology , Carcinoma, Squamous Cell/pathology , Carcinoma, Squamous Cell/surgery , Hypercalcemia/etiology , Lung Neoplasms/pathology , Lung Neoplasms/surgery , Mice , Mice, Inbred BALB C , Mice, Nude , Neoplasm Transplantation , Osteoblasts/pathology , Osteoclasts/pathology , Parathyroid Hormone-Related ProteinABSTRACT
A parathyroid hormone-related protein (PTHrP) has recently been isolated from tumors associated with hypercalcemia. In the present study, we tested the effects of neutralizing antisera to the PTHrP on serum calcium and urine cAMP in two animal models of malignancy-associated hypercalcemia. The animal models consisted of (a) a human squamous cell lung cancer and (b) a human laryngeal cancer, both serially carried in athymic mice. The antisera specifically reduced the elevated serum calcium and urinary cAMP levels in the tumor-bearing animals. We conclude that PTHrP plays a major role in the pathogenesis of malignancy-associated hypercalcemia.
