Tumor resection and antibodies to parathyroid hormone-related protein cause similar changes on bone histomorphometry in hypercalcemia of cancer

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.     

The inhibition of RANKL causes greater suppression of bone resorption and hypercalcemia compared with bisphosphonates in two models of humoral hypercalcemia of malignancy

Humoral hypercalcemia of malignancy (HHM) is mediated primarily by skeletal and renal responses to tumor-derived PTHrP. PTHrP mobilizes calcium from bone by inducing the expression of receptor activator for nuclear factor-kappaB ligand (RANKL), a protein that is essential for osteoclast formation, activation, and survival. RANKL does not influence renal calcium reabsorption, so RANKL inhibition is a rational approach to selectively block, and thereby reveal, the relative contribution of bone calcium to HHM. We used the RANKL inhibitor osteoprotegerin (OPG) to evaluate the role of osteoclast-mediated hypercalcemia in two murine models of HHM. Hypercalcemia was induced either by sc inoculation of syngeneic colon (C-26) adenocarcinoma cells or by sc injection of high-dose recombinant PTHrP (0.5 mg/kg, s.c., twice per day). In both models, OPG (0.2-5 mg/kg) caused rapid reversal of established hypercalcemia, and the speed and duration of hypercalcemia suppression were significantly greater with OPG (5 mg/kg) than with high-dose bisphosphonates (pamidronate or zoledronic acid, 5 mg/kg). OPG also caused greater reductions in osteoclast surface and biochemical markers of bone resorption compared with either bisphosphonate. In both models, hypercalcemia gradually returned despite clear evidence of ongoing suppression of bone resorption by OPG. These data demonstrate that osteoclasts and RANKL are important mediators of HHM, particularly in the early stages of the condition. Aggressive antiresorptive therapy with a RANKL inhibitor therefore might be a rational approach to controlling HHM.     

Parathyroid hormone-related protein-(1--36) stimulates renal tubular calcium reabsorption in normal human volunteers: implications for the pathogenesis of humoral hypercalcemia of malignancy

All would agree that hypercalcemia occurs among patients with humoral hypercalcemia of malignancy (HHM) as a result of osteoclastic bone resorption. Some studies suggest that enhanced renal calcium reabsorption, which plays an important pathophysiological role in the hypercalcemia occurring in primary hyperparathyroidism, is also important pathophysiologically in HHM. Other studies have not agreed. In large part, these differences result from the inability to accurately assess creatinine and calcium clearance in critically ill subjects with HHM. To circumvent these issues, we have developed steady state 48-h PTH-related protein (PTHrP) infusion and 8-h hypercalcemic calcium clamp protocols. These techniques allow assessment of the effects of steady state PTHrP and calcium infusions in normal healthy volunteers in a setting in which renal function is stable and measurable and in which the filtered load of calcium can be matched in PTHrP- and calcium-infused subjects. Normal subjects were infused with saline (placebo), PTHrP, or calcium. Subjects receiving PTHrP, as expected, displayed mild hypercalcemia (10.2 mg/dL), suppression of endogenous PTH-(1--84), and phosphaturia. Subjects receiving the hypercalcemic calcium clamp displayed indistinguishable degrees of hypercalcemia and PTH suppression. Despite their matched degrees of hypercalcemia and PTH suppression, the two groups differed importantly with regard to fractional calcium excretion (FECa). The hypercalcemic calcium clamp group was markedly hypercalciuric (FECa averaged 6.5%), whereas FECa in the PTHrP-infused subjects was approximately 50% lower (between 2.5--3.7%), and no different from that in the normal controls, which ranged from 1.5--3.0%. These studies demonstrate that PTHrP is able to stimulate renal calcium reabsorption in healthy volunteers. These studies suggest that PTHrP-induced renal calcium reabsorption, in concert with the well established acceleration of osteoclastic bone resorption, contributes in a significant way to the hypercalcemia observed in patients with HHM.     

A case of pheochromocytoma producing parathyroid hormone-related protein and presenting with hypercalcemia

A 54-yr-old man with a left adrenal pheochromocytoma showed mild hypercalcemia and elevated nephrogenous cAMP. Serum levels of PTH and 1,25-dihydroxyvitamin D3 were not elevated. Postoperatively, serum calcium and nephrogenous cAMP declined to normal ranges. Pathologically, the tumor was a benign pheochromocytoma. The clinical findings resembled those of humoral hypercalcemia of malignancy (HHM), and PTH-related protein (PTHrP) immunoreactivity was detected in the tumor extract at a concentration of 80.7 pmol/g wet wt, which is high compared to levels in malignant tumors causing HHM. Production of PTHrP was further confirmed by the demonstration of PTHrP mRNA with Northern blot hybridization analysis. Gel filtration of the extract revealed the presence of at least two different molecules with both immunological and biological activities. One of the peaks appeared close to PTHrP-(1-34), and the other between cytochrome-c and BSA. The latter showed a higher bioactivity to immunoreactivity ratio. These data indicate the multiplicity of PTHrP molecules in pheochromocytoma and support the idea that PTHrP produced by pheochromocytoma causes hypercalcemia in a similar fashion as HHM.     

Pancreatic neuroendocrine tumor with extensive vascularisation and parathyroid hormone-related protein (PTHrP)--associated hypercalcemia of malignancy.

We report the case of a 34 year old male presenting with symptomatic hypercalcemia due to excessive PTHrP secretion from a pancreatic neuroendocrine carcinoma with extensive hypervascularization and without any evidence for metastatic disease. In the early phase of the disease conventional chemotherapy with streptozocin and doxorubicin was able to control functional activity as well as tumor growth. However, after 2 years tumor escape was indicated by severe therapy-resistant hypercalcemia. Therapeutic options were reduced due to the excessive tumor vascularization and the patient died from his disease after a short period of intensified therapy. The role of PTHrP in hypercalcemia of malignancy (HHM) and its association with neuroendocrine pancreatic tumors as well as possible therapeutic options are reviewed.     

Lung cancer associated with hypercalcemia induced by concurrently elevated parathyroid hormone and parathyroid hormone-related protein levels

In general, many cases of malignancy-associated hypercalcemia are due to HHM. In patients with humoral hypercalcemia of malignancy (HHM), it has been reported that plasma parathyroid hormone-related protein (PTHrP) and cyclic adenosine monophosphate (cAMP) levels were elevated, while plasma PTH and active vitamin D(3) levels were suppressed. Our patient showed hypercalcemia with a concurrent increase in plasma and tumor tissue PTHrP and PTH concentrations and also high cAMP and low 1-25(OH)(2)VD(3) levels in the plasma. These data suggest that the hypercalcemia exhibited by our patient was consistent with HHM due to lung cancer and its liver metastasis. Moreover, diagnostic imaging and autopsy findings showed no appreciable lesions of the parathyroid gland. In addition, histopathologic examination of the primary and metastatic tumors revealed the existence of PTH immunohistochemically stained with anti-PTH antibodies, suggesting an ectopic-PTH-producing lung tumor. From these data, our patient was diagnosed with a rare case of lung cancer, which produced both ectopic PTH and PTHrP.     

The Role of PTHrP in Regulating Mineral Metabolism During Pregnancy,Lactation, and Fetal/Neonatal Development

Parathyroid hormone-related protein (PTHrP) was originally identified as the cause of humoral hypercalcemia of malignancy (HHM), a condition that resembles primary hyperparathyroidism and the effects of excess parathyroid hormone (PTH). But HHM is an unusual situation because PTHrP is normally undetectable in the circulation of the child or adult. Instead, most of PTHrP’s actions are now understood to be paracrine or autocrine, and not humoral. However, PTHrP is present in the circulation at measurable levels during fetal development, pregnancy, and lactation. During these time periods, PTHrP has humoral actions that regulate mineral and bone homeostasis independently of PTH. In fact, the existence of PTHrP was also predicted by the characteristic pattern of serum chemistries and PTH in cord blood of normal newborns, and by the normalization of calcium metabolism that temporarily occurs in hypoparathyroid women who breast-feed. This article reviews our present understanding about PTHrP’s role to control mineral and bone metabolism during pregnancy, lactation, and fetal development. Excess PTHrP can also be produced by the placenta or the breasts during pregnancy, or by the breasts during lactation, and in both situations it can lead to hypercalcemia and other clinical features that are indistinguishable from HHM. The highest concentrations of PTHrP are found in milk, and recent evidence indicates that milk-based PTHrP may reduce mineral accretion by the newborn skeleton, but whether it does this through local actions in the neonatal gut or after absorption into the neonatal circulation is unknown.     

A case of myeloma with hypercalcemia caused by high serum concentrations of both parathyroid hormone-related peptide (PTHrP) and macrophage inflammatory protein-1α (MIP-1α)

A 62-year-old woman was admitted with dry mouth, general fatigue, and severe back pain. Biochemistry examination showed extreme hypercalcemia (21.2 mg/dL). Bone marrow examination was negative, but needle biopsy of a metastatic lung tumor revealed abnormal plasma cells; thus, multiple myeloma stage III-A was finally diagnosed. Serum concentrations of both parathyroid hormone-related peptide (PTHrP) and macrophage inflammatory protein-1α (MIP-1α) were markedly elevated (PTHrP 7.2 pmol/L, normal <1.1 pmol/L; MIP-1α 84.9 pg/mL, normal <46.9 pg/mL). Her myeloma appeared to have simultaneously caused two mechanisms producing hypercalcemia: humoral hypercalcemia of malignancy (HHM) by PTHrP and local osteolytic hypercalcemia (LOH) by MIP-1α. Therefore, the combination of two calcium-modulating abnormalities likely aggravated her hypercalcemia.     

Inhibition by human interleukin-1 alpha of parathyroid hormone-related peptide effects on renal calcium and phosphorus metabolism in the rat.

Humoral hypercalcemia of malignancy (HHM) is at least partly caused by tumor secretion of PTH-related peptide (PTHrP), but there is growing evidence for cosecretion with PTHrP of other bone-resorbing peptides, such as the cytokine interleukin-1 alpha (IL-1 alpha). Administration of PTHrP in vivo and in vitro generally mimics the actions of PTH itself, with increases in both resorption and formation of bone. However, bone in HHM is characterized by uncoupling of bone turnover, with increased resorption and decreased formation. We performed experiments to determine whether IL-1 alpha might alter the effects of PTHrP and produce uncoupling. Thus, we administered to 100-g male rats by sc osmotic minipumps synthetic PTHrP-(1-34) alone (2 micrograms/100 g/day), recombinant IL-1 alpha alone (1.5 micrograms/100 g/day), both peptides together at the previous doses, or vehicle only. We infused 5 groups of 12 rats each (PTHrP, IL-1 alpha, PTHrP plus IL-1 alpha, ad libitum fed control, and controls pair-fed to the PTHrP plus IL-1 alpha group) for 14 days. At the end of the study, blood and urine were taken for chemical measurements, and tibias and femurs were harvested for histomorphometry and extraction of RNA from periosteal cells. As expected, PTHrP induced hypercalcemia, relative hypophosphatemia, phosphaturia, and reduced bone mass. Osteoblast number was increased, but osteoclast number was not. Indices of bone formation were unchanged or reduced. The dose of IL-1 alpha chosen had no statistically significant effect, except for reduced longitudinal bone growth, but when combined with PTHrP, IL-1 alpha reduced hypercalcemia, hypophosphatemia, and phosphaturia. In contrast to the blood and urine effects, IL-1 alpha did not interact significantly with PTHrP's effect on bone measurements. Northern analysis of periosteal cell mRNA showed that PTHrP reduced expression of osteocalcin, but not glyceraldehyde-3-phosphate dehydrogenase; IL-1 alpha had no additional effect. These data suggest that 1) continuously administered PTHrP alone may induce uncoupled bone turnover with decreased cortical bone formation; 2) IL-1 alpha appears to inhibit strongly the renal effects of PTHrP and weakly (if at all) its actions on bone and, thus, to decrease its hypercalcemic, phosphaturic, and hypophosphatemic actions; and 3) cosecretion of IL-1 alpha, and possibly other peptide cytokines, with PTHrP may modify the clinical expression of HHM.     

Conflicting actions of parathyroid hormone-related protein and serum calcium as regulators of 25-hydroxyvitamin D(3)-1 alpha-hydroxylase expression in a nude rat model of humoral hypercalcemia of malignancy.

In patients with humoral hypercalcemia of malignancy (HHM), serum levels of 1,25-dihydroxyvitamin D (1,25(OH)(2)D) are generally low, although the pathophysiology of the impaired vitamin D metabolism is not fully understood. In the present study, we have investigated vitamin D metabolism in our newly developed rat model of HHM in which a human infantile fibrosarcoma producing parathyroid hormone-related protein (PTHrP), named OMC-1, was inoculated s.c. into athymic nude rats. In OMC-1-bearing rats, the serum concentration of 1,25(OH)(2)D was markedly reduced when the animals exhibited severe hypercalcemia (Ca > or =15 mg/dl), while it was rather elevated in those with mild hypercalcemia. To further examine whether serum Ca levels affect 1,25(OH)(2)D concentration, we administered bisphosphonate YM529 to OMC-1-bearing rats when they exhibited severe hypercalcemia. The restoration of the serum Ca level by administration of YM529 was accompanied by a marked increase in the 1,25(OH)(2)D level, suggesting that the serum Ca level itself plays an important role in the regulation of the 1,25(OH)(2)D level in these rats. On the other hand, when the OMC-1-bearing rats were treated with a neutralizing antibody against PTHrP, serum 1,25(OH)(2)D levels remained low despite the reduction in serum Ca levels. Expression of 25-hydroxyvitamin D-1 alpha-hydroxylase (1 alpha-hydroxylase) in kidney was decreased in OMC-1-bearing rats with severe hypercalcemia, and markedly enhanced after treatment with bisphosphonate. This enhancement in 1 alpha-hydroxylase expression was not observed after treatment with the antibody against PTHrP. These results suggest that PTHrP was responsible for the enhanced expression of 1 alpha-hydroxylase in YM529-treated rats, and that hypercalcemia played a role in reducing the serum 1,25(OH)(2)D level in OMC-1-bearing rats by suppressing the PTHrP-induced expression of the 1 alpha-hydroxylase gene.     

Messenger RNA stability of parathyroid hormone-related protein regulated by transforming growth factor-beta1

Humoral hypercalcemia of malignancy (HHM), a paraneoplastic syndrome associated with epithelial cancers, including squamous cell carcinoma (SCC), is due to expression and secretion of parathyroid hormone-related protein (PTHrP). Transforming growth factor-beta1 (TGFbeta1), expressed by many tumors, has been demonstrated in vitro to increase the half-life of PTHrP mRNA. In this study, oral squamous carcinoma cells (SCC2/88) had a two-fold increase in PTHrP mRNA stability (from 45 to 90 min) in response to treatment with TGFbeta1. In order to examine the mechanism of TGFbeta1-mediated PTHrP mRNA stability, a cell-free assay of mRNA degradation was utilized in which the degradation of in vitro-transcribed mRNA incubated with cytoplasmic protein extracts from SCC2/88 treated with vehicle or TGFbeta1 was measured. In this assay, full-length PTHrP mRNA was not significantly stabilized in TGFbeta1-treated samples when compared to vehicle treated samples. However, there was a striking (>5-fold) increase in PTHrP mRNA half-life in TGFbeta1-treated samples when PTHrP mRNA lacked the 3'-untranslated region (3'-UTR). In contrast, the degradation of 3'-UTR-truncated PTHrP mRNA using the cell-free assay was not altered in vehicle-treated samples. UV cross-linking of PTHrP mRNA and cytoplasmic proteins from cells treated with either vehicle or TGFbeta1 revealed numerous mRNA-binding proteins. TGFbeta1 treatment resulting in decreased binding of 33, 31, 27, 20 and 18 kDa binding proteins to the terminal coding region. These studies revealed that TGFbeta1-induced PTHrP mRNA stability might be, in part, the result of cis-acting sequences within the coding region of the PTHrP mRNA.     

Direct comparison of sustained infusion of human parathyroid hormone-related protein-(1-36) [hPTHrP-(1-36)] versus hPTH-(1-34) on serum calcium,plasma 1,25-dihydroxyvitamin D concentrations,and fractional calcium excretion in healthy human volunteers

PTH and PTH-related protein (PTHrP) cause primary hyperparathyroidism and humoral hypercalcemia of malignancy (HHM), respectively. These syndromes are similar in several important ways, but differ in several characteristic, yet unexplained, ways. Two of the unresolved questions in HHM and hyperparathyroidism involve renal physiology. 1) Why does renal proximal tubular production of 1,25-dihydroxyvitamin D [1,25-(OH)(2)D] differ between the two syndromes? 2) Do distal tubular calcium responses to PTH and PTHrP differ in the two syndromes? To address these questions, we compared the two peptides, human PTH-(1-34) and PTHrP-(1-36), in a direct, head to head study using a continuous, steady state infusion of each peptide at the same dose in normal human volunteers for 46 h. We had previously described such methods as applied to PTHrP, but a direct multiday comparison of PTHrP to PTH has not previously been reported. In two groups (seven subjects each) of healthy young (25- to 35-yr-old) normal volunteers, PTH and PTHrP infused at 8 pmol/kg.h displayed similar calcemic effects, although PTH was slightly more potent in this regard. Both peptides also displayed similar phosphaturic effects. In addition, both peptides had similar effects on renal tubular calcium handling, yielding fractional calcium excretion values of approximately 3.5%, some 50% below the values (6.5%) observed in subjects rendered similarly hypercalcemic by the infusion of calcium. In contrast to these several quantitatively similar effects of PTH and PTHrP, PTH tended to be selectively more effective than PTHrP in stimulating renal production of 1,25-(OH)(2)D. These studies indicate that renal tubular calcium reabsorption is likely to contribute to hypercalcemia in patients with HHM. In addition, PTH may be selectively more effective than PTHrP in stimulating 1,25-(OH)(2)D production, in contrast to its phosphaturic, calcemic effects and its effects to stimulate nephrogenous cAMP excretion and renal tubular calcium reabsorption.     

Tumor-induced hypercalcemia. Review of bisphosphonate treatment

INTRODUCTION: The incidence of tumor-induced hypercalcemia is between 10 to 20%. New treatments justify this review article. CURRENT KNOWLEDGE AND KEY POINTS: Tumor-induced hypercalcemia (half of all hypercalcemia) is divided into two groups: hematological tumors (10%), and solid tumors (90%), with osteolytic hypercalcemia and humoral hypercalcemia of malignancy (HHM: mediators include PTHrP). The two most common causes of tumor-induced hypercalcemia are lung cancer and breast cancer. Tumor-induced hypercalcemia most commonly disturbs gastrointestinal, neurological, renal and cardiovascular functions. These symptoms may be erroneously attributed to the underlying malignancy or its therapy. Prognosis of tumor-induced hypercalcemia is very poor, with median survival being about 3 months. Bisphosphonates have emerged as the standard treatment of tumor-induced hypercalcemia. The intravenous administration of isotonic saline is the first step in the management of tumor-induced hypercalcemia. Specific treatment of cancer remains essential to prevent TIH relapse. FUTURE PROSPECTS AND PROJECTS: New bisphosphonates have appeared, the most potent known bisphosphonate today is zoledronate.     

Primary adenosquamous carcinoma of the liver which produces granulocyte-colony-stimulating factor and parathyroid hormone related protein: association with leukocytosis and hypercalcemia

A 55-year-old man was admitted to our hospital with fever and vomiting. Abdominal computed tomography (CT) revealed multiple low density masses in the liver. A diagnosis of primary adenosquamous carcinoma of the liver was confirmed by histological examination of a necropsy specimen. The present case showed leukocytosis and hypercalcemia with high levels of serum granulocyte-colony-stimulating factor (G-CSF) and parathyroid hormone related protein (PTHrP). Recent studies have shown that G-CSF and PTHrP are responsible for the paraneoplastic syndromes with leukocytosis and hypercalcemia. The tumor cells demonstrated positive cytoplasmic immunohistochemistry staining with anti-G-CSF and anti-PTHrP antibodies. This result suggested that the tumor produced G-CSF and PTHrP.     

PTHrP-producing tumor: squamous cell carcinoma of the liver accompanied by humoral hypercalcemia of malignancy,increased IL-6 and leukocytosis

A 77-year-old man was admitted to our hospital showing symptoms of general fatigue and appetite loss. He had leukocytosis, thrombocytosis and hypercalcemia with elevated serum levels of parathyroid hormone related peptide (PTHrP) and interleukin-6 (IL-6). An increase in tumor markers SCC and CYFURA21-1 was observed. The liver contained a huge tumor, which was proved to be PTHrP producing squamous cell carcinoma by immuno-histochemical analysis. Since the tumor did not express IL-6, it was assumed to be induced by PTHrP in osteoblasts. This is the first report of PTHrP producing squamous cell carcinoma of the liver.     

Parathyroid hormone-related peptide producing cholangiocellular carcinoma with a marked psammoma formation

Humoral hypercalcemia caused by parathyroid hormone-related peptide (PTHrP), associated with cholangiocellular carcinoma (CCC), has rarely been documented. There have been no reports of CCC associated with extensive calcification of the tumor with psammoma body formation. A 66-year-old man was admitted with a large calcified tumor in the liver detected on an abdominal X-ray. An ultrasound-guided fine needle biopsy specimen of the liver tumor showed evidence of adenocarcinoma. He had hypercalcemia with an elevated PTHrP level. The patient died because of disseminated intravascular coagulation and progressive hepatic failure. A postmortem examination revealed a large poorly differentiated CCC in the liver. Immunohistochemical examination showed the presence of PTHrP-positive tumor cells. The calcified lesion consisted of a number of accumulated psammoma bodies. We present a case of PTHrP producing CCC with a marked psammoma formation.     

Hypercalcemia and systemic lupus erythematosus

Hypercalcemia is commonly caused by the increased production of parathyroid hormone—related protein (PTHrP) by a malignancy. In fact, the demonstration of increased PTHrP production in a patient with hypercalcemia is virtually pathognomonic of malignancy. We studied a patient with systemic lupus erythematosus (SLE), generalized lymphadenopathy, and hypercalcemia. Immunohistology of 2 biopsied lymph nodes revealed the abundant expression of PTHrP and the absence of malignant transformation. Although apparently rare, PTHrP production by nonmalignant lymphoid tissue may occur in SLE and should be considered in the differential diagnosis of hypercalcemia.