Apposition and resorption of bone during oral treatment with (3-amino-1-hydroxypropylidene)-1,1-bisphosphonate (APD)

Precision engineering designed phospholipid-tagged pamidronate complex functionalized SNEDDS for the treatment of postmenopausal osteoporosis

Disodium pamidronate, a second-generation bisphosphonate is a potent drug for the treatment of osteoporosis, which has been very well established by previous literature. It has very low oral permeability, leading to its low oral bioavailability, which restrict this drug to being administered orally. Therefore, the present research work includes the development of an orally effective nanoformulation of pamidronate. In this work, disodium pamidronate was complexed with phospholipon 90G for the enhancement of permeability and to investigate the phospholipon 90G-tagged pamidronate complex-loaded SNEDDS for oral delivery with promises of enhanced bioavailability and anti-osteoporotic activity. The rational design and optimization was employed using Central Composite Design (Design Expert^® 12, software) to optimize nanoformulation parameters. In this work, a commercially potential self nano-emulsifying drug delivery system (SNEDDS) has been developed and evaluated for improved oral bioavailability and better clinical acceptance. The hot micro-emulsification and ultracentrifugation method with vortex mixing was utilized for effective tagging of phospholipon 90G with pamidronate and then loading into the SNEDDS nanocarrier. The optimized Pam-PLc SNEDDS formulation was characterized for particle size, PDI, and zeta potential and found to be 56.38 ± 1.37 nm, 0.218 ± 0.113, and 22.41 ± 1.14 respectively. Also, a 37.9% improved bioavailability of pamidronate compared to marketed tablet was observed. Similarly, in vivo pharmacokinetic studies suggest a 31.77% increased bone density and significant enhanced bone biomarkers compared to marketed tablets. The developed formulation is safe and effectively overcomes anti-osteoporosis promises with improved therapeutic potential. This work provides very significant achievements in postmenopausal osteoporosis treatment and may lead to possible use of nanotherapeutic-driven emerging biodegradable carriers-based drug delivery.

Pamidronate: A model compound of the pharmacology of nitrogen-containing bisphosphonates; A Leiden historical perspective

Pamidronate [3-amino-1-hydroxypropylidene-1,1-bisphosphonate (APD)] was the first nitrogen-containing bisphosphonate (N-BP) investigated in clinical studies. In contrast to other clinically used bisphosphonates, pamidronate was discovered and its properties were initially studied in an Academic Institution. On the occasion of the 50th Anniversary of the first publications on the biological effects of bisphosphonates, I review in this article the contribution of Leiden investigators to the development of pamidronate that led to the recognition of the significance of the Nitrogen atom in the side chain of bisphosphonates for their action on bone resorption and to the formulation of principles for the use of N-BPs in the management of patients with different skeletal disorders.

Mineral density gain in vertebrae of osteoporotic women on oral pamidronate reverts a year after treatment discontinuance

Long-term treatment with 200 mg dry weight/day of pamidronate (APD) by oral route has been proposed to increase bone mineral density (BMD) in postmenopausal osteoporotic women. However, there is widespread concern over the possibility of bone metabolism "freezing" by protracted use of medication liable to inhibit bone resorption. Accordingly, an open population of 39 osteoporotic women was studied in order to determine BMD variations in lumbar vertebrae and femoral neck and to confirm whether given APD doses increase bone mineralization. A parallel group of osteoporotic women was likewise evaluated to determine the potential reversibility of such effect on discontinuing treatment. Results were beneficial at both skeletal sites in subjects on APD therapy, disclosing at 18 months treatment 9.0% mean peak mineral gain versus basal status at lumbar spine. In the few responders completing 4 years of treatment, mean differences versus basal status were +4.9% in vertebrae and +6.2% at femoral neck. In lumbar vertebrae there was a rapid trend in mineral gain up to 18 months on treatment, which declined thereafter to a quarter of its early rate. Concurrently, in the group of 21 baseline-matched women, effects were evaluated after discontinuing daily APD administration one year (n = 11) or two years (n = 7) later. In both subgroups, there was a loss in lumbar (-7.1% and -9.8% respectively; p<0.01) and femoral neck BMD (-2.2% and -4.2% respectively; p: n.s.) on performing measurement one year after APD withdrawal. Furthermore, after three years treatment and subsequent discontinuance, three patients presented bone loss in lumbar vertebrae and minimal changes at femoral neck one year after APD withdrawal. Therefore, APD induces moderate BMD gain which proves reversible on discontinuing therapy, so that it seems unlikely that this compound should "freeze" bone metabolism to a significant extent. However, the precise degree of such reversibility requires evaluation in larger series.

Bisphosphonates: a review of their pharmacokinetic properties

Bisphosphonates are a unique class of drugs. As a family, they are characterized pharmacologically by their ability to inhibit bone resorption, whereas, pharmacokinetically, they are classified by their similarity in absorption, distribution, and elimination. Although all bisphosphonates have similar physicochemical properties, their antiresorbing activities differ substantially. Activity is dramatically increased when the amino group is contained in the aliphatic carbon chain. For example, alendronate, an aminobisphosphonate, is approximately 700-fold more potent than etidronate, both in vitro and in vivo. In general, bisphosphonates are poorly absorbed from the gastrointestinal tract as a result of their poor lipophilicity. In vitro and in vivo studies have shown that bisphosphonates are absorbed from the gastrointestinal tract via paracellular transport. Systemically available bisphosphonates disappear very rapidly from plasma, and are partly taken up by the bone and partly excreted by the kidney. The relative contribution of these two processes to overall plasma elimination differs significantly among bisphosphonates. To date, all bisphosphonates studied show no evidence of metabolism. Renal excretion is the only route of elimination. Studies with alendronate in rats indicate that the drug is actively secreted by an uncharacterized renal transport system, and not by the anionic or cationic renal transport systems. Bisphosphonates bind preferentially to bones which have high turnover rates, and their distribution in bone is not homogeneous. After bone uptake, the bisphosphonates are liberated again only when the bone in which they are deposited is resorbed. Thus, the half-life of bisphosphonates in bone is very long, ranging among different species from 1 to 10 years, depending largely on the rate of bone turnover.

Cytotoxic effects of pamidronate on monolayers of human intestinal epithelial (Caco-2) cells and its epithelial transport

Pamidronate (APD) is a new drug in the treatment of osteolytic bone diseases. Caco-2 cells were used to study the cytotoxic effects of APD on intestinal epithelium and also the transport (mechanism) of APD across the intestinal epithelium. We investigated the cytotoxic effect of APD by combining two spectrophotometric assays [neutral red (NR) uptake and lactate dehydrogenase (LDH) release] with a morphological assay (electron microscopy). The amount of APD transported across the Caco-2 monolayer was measured by HPLC. The permeability of the monolayer was studied by determining the transepithelial electrical resistance (TEER). The results show that after exposing the Caco-2 cells to increasing concentrations of APD [dose range calculated on the basis of relevance to the oral dose administered to patients] the NR uptake decreased while LDH loss increased, which is indicative of a cytotoxic effect of APD. Ultrastructural alterations, including a widening in intercellular spaces and, at higher doses, complete cell death, were observed. The transport percentage of nontoxic doses of APD was low, while the TEER decreased with increasing doses of APD. In conclusion, APD is cytotoxic for Caco-2 cells. As the transport percentage of nontoxic doses of APD is low and APD reduces the TEER, it is hypothesized that APD is transported paracellularly.

Parenteral pamidronate prevents thyroid hormone-induced bone loss in rats

Pamidronate (APD) is a bisphosphonate that prevents bone loss from a variety of causes. We studied the role of APD in preventing thyroid hormone-induced bone loss. A total of 32 rats were assigned to one of four treatment groups: (1) -APD/triiodothyronine (-T3), (2) -APD/+T3, (3) +APD/-T3, or (4) +APD/+T3. In the first of two studies, the rats received APD for the first week and T3 for the second week, and then their blood was analyzed for alkaline phosphatase and osteocalcin. Alkaline phosphatase and osteocalcin were significantly higher (p < 0.05) in hyperthyroid rats (-APD/+T3, 3.9 +/- 0.25 mukat/liter and 23 +/- 1.6 nM, respectively) than in control animals (2.53 +/- 0.28 mukat/liter and 18.3 +/- 1.4 nM, respectively). Hyperthyroid rats pretreated with APD (+APD/+T3) had levels of alkaline phosphatase and osteocalcin no different from controls. In a second study, rats were divided into the same four groups, except they received APD/placebo and T3/placebo concomitantly for 3 weeks. At the end of the study, bone mineral density (BMD) of the femur, spine, and whole body was measured by dual-energy x-ray absorptiometry, and the calcium content of the femora was measured directly. In hyperthyroid rats (-APD/+T3) BMD was significantly lower than in controls in the spine (0.201 +/- 0.004 versus 0.214 +/- 0.002 g/cm2, p < 0.05) and femur (0.204 +/- 0.003 versus 0.218 +/- 0.002, p < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Protective effects of disodium etidronate and pamidronate against the biomechanical repercussion of betamethasone-induced osteopenia in growing rat femurs

To assess the protective effect of bisphosphonates on the biomechanical repercussion of glucocorticoid-induced osteopenia, intraperitoneal doses of 1 or 10 mg/kg/d of disodium etidronate or 1 or 50 mg/kg/day of pamidronate were given to groups of 6 growing rats simultaneously receiving subcutaneous doses of 4.8 mg/kg/day of betamethasone for 20 days. Betamethasone impaired strength and stiffness of femur diaphyses through a reduction of geometric properties, abnormally enhancing bone ability to absorb energy. Both bisphosphonates partially prevented betamethasone effects on diaphyseal stiffness (but not strength) through positive, dose-related effects on material modulus of elasticity and slighter improvements in diaphyseal geometry, avoiding the enhancement of energy-absorbing ability and the subsequent tendency to production of comminute fractures. These results and others obtained treating normal rats with (pamidronate) APD suggest that the sign of bisphosphonate effects on bone biomechanics may depend not only on the type of compound but also on eventual interactions with concomitant treatments.

Pamidronate

OBJECTIVE

The primary objective of this article is to introduce readers to the use of a new agent, pamidronate. The article discusses its use in hypercalcemia of malignancy (HCM), osteolytic lesions, and Paget's disease. Pharmacokinetic data and clinical trials are reviewed, as well as adverse effects and dosage guidelines.

DATA SOURCES

A MEDLINE search was used to identify English-language studies involving pamidronate for the period from 1970 to 1992.

STUDY SELECTION

As comparative trials were few in number, trials using pamidronate as a single agent were also reviewed.

DATA EXTRACTION

Sparse pharmacokinetic data were obtained from clinical trials. All clinical trials available at the time of publication that met the following criteria were reviewed: (1) allowed for adequate rehydration prior to drug therapy; (2) reported standardized and corrected serum calcium concentrations; (3) separated data obtained from patients who received pamidronate alone from those who received pamidronate and concurrent chemotherapy.

RESULTS

Pamidronate has a pharmacologic profile similar to that of etidronate, but pamidronate is more potent and has a longer duration of effect. It has been investigated primarily in the treatment of HCM as well as in the treatment of osteolytic bone metastases and Paget's disease. In hypercalcemia of malignancy it appears to be as effective as established agents with the advantage that a single dose of pamidronate 90 mg iv provides a durable response. In Paget's disease chronic oral administration has also been shown to be effective in relieving bone pain. Adverse reactions with intravenous administration are transient and self-limiting and usually occur with the first dose. The most common adverse effect is a transient and self-limiting fever. Chronic oral administration of doses greater than 600 mg/d is associated with gastrointestinal toxicities.

CONCLUSIONS

Although more well-designed clinical trials comparing pamidronate with standard therapies and other available agents are necessary, initial results indicate that pamidronate is an effective and promising alternative for use in the treatment of HCM.

Bisphosphonates. Pharmacology and use in the treatment of tumour-induced hypercalcaemic and metastatic bone disease

The geminal bisphosphonates are a new class of drugs characterised by a P-C-P bond. Consequently, they are analogues of pyrophosphate, but are resistant to chemical and enzymatic hydrolysis. The bisphosphonates bind strongly to hydroxyapatite crystals and inhibit their formation and dissolution. This physicochemical effect leads in vivo to the prevention of soft tissue calcification and, in some instances, inhibition of normal calcification. The main effect is to inhibit bone resorption, but in contrast to the effect on mineralisation, the mechanism involved is cellular. These various effects vary greatly according to the structure of the individual bisphosphonate. The half-life of circulating bisphosphonates is very brief, in the order of minutes to hours. 20% to 50% of a given dose is taken up by the skeleton, the rest being excreted in the urine. The half-life in bone is far longer and depends upon the turnover rate of the skeleton itself. Bisphosphonates are very well tolerated; the relatively few adverse events that have been associated with their use are specific for each compound. Bisphosphonates have been used to treat various clinical conditions, namely ectopic calcification, ectopic bone formation, Paget's disease, osteoporosis and increased osteolysis of malignant origin. The three compounds commercially available for use in tumour-induced bone disease are in order of increasing potency, etidronate, clodronate and pamidronate. Most data have been obtained with the latter two agents. By inhibiting bone resorption, they correct hypercalcaemia and hypercalciuria, reduce pain, the occurrence of fractures, as well as the development of new osteolytic lesions, and in consequence improve the quality of life. In view of these actions, of their excellent tolerability and of the fact that they are active for relatively long periods, these compounds are, after rehydration, the drugs of choice in tumour-induced bone disease and an excellent auxiliary to the drugs used in oncology.

Sodium EDTA enhances intestinal absorption of two bisphosphonates

Bisphosphonates are poorly absorbed when given orally and their absorption is subject to a large inter- and intraindividual variability. This poor absorbability is thought to result, at least in part, from formation of unabsorbable complexes with calcium. It was therefore investigated whether the calcium chelator EDTA could improve intestinal absorption of two bisphosphonates, 4-amino-1-hydroxybutylidene-1,1-bisphosphonate (AHBuBP), and dichloromethylenebisphosphonate (Cl2MBP). Absorption was assessed indirectly by measuring the suppression of hypercalcemia induced in thyroparathyroidectomized rats by a retinoid. The absorption of AHBuBP was in the range of 1-3%. EDTA increased absorption about tenfold at a AHBuBP dose of 0.6 mg P/kg and about twofold at lower doses, with the minimal effective dose of EDTA being 10 mg/kg. The absorption of Cl2MBP was also increased by EDTA, although to a smaller extent, the lowest effective dose being 100 mg/kg EDTA. Thus, EDTA can, in certain circumstances, increase the intestinal absorption of bisphosphonates. The mechanism might involve an increase in available bisphosphonate and a change in mucosal permeability. The amount of EDTA required is, however, too high for use clinically.

Osteoclast inhibition by pamidronate in metastatic prostate cancer: a preliminary study

Twenty five hormone manipulated patients with prostate cancer and metastatic bone disease, treated at least 6/12 previously by hormone manipulation, were given intravenous infusions of Disodium Pamidronate (APD) over a 6 month period. Patients received 30 mg weekly for 4 weeks then twice monthly for 5 months. No other treatment was administered during study. Eleven of 17 patients with pain at the start of the study were pain free at the end. Fasting morning calcium excretion and serum osteocalcin fell significantly with Pamidronate (P less than 0.0001) and urine hydroxyproline was lowered in 13/20 evaluable patients at 6 months. Alkaline phosphatase fell in a proportion of patients and five of 17 patients with previously progressive bone scans stabilised (4) or regressed (1) on treatment. Rising acid phosphatase levels were also lowered in five patients. It is concluded that Pamidronate may be effective in palliating bone pain in some patients and has a stabilising influence on abnormally high bone turnover in metastatic prostate cancer. Further controlled studies of the compound are now warranted.

Therapeutic efficacy of two different cytostatic-linked phosphonates in combination with razoxane in the transplantable osteosarcoma of the rat

Two new compounds, 4-[4-[bis-(2-chloroethyl)-amino-]phenyl]-1- hydroxybutane-1,1-bisphosphonic acid (BAD) and aminotris-(methylenephosphonato)-diamminoplatinum(II) (ADP) that both have cytostatic and osteotropic properties, have shown good therapeutic efficacy against an osteosarcoma which metastasizes and kills by lung metastases. We therefore combined each of these drugs with the antimetastic agent razoxane. Razoxane (20 mg/kg i.p., 5 days/week for 6 weeks) was administered in combination with either BAD (30 mg/kg i.p.) or ADP (37.5 mg/kg i.v.) twice weekly for 3 weeks. Tumour volumes, body weight, survival time and occurrence of metastases were recorded, in addition to the measurement of the metastasis area compared to the total lung area in serial histological lung samples. In both experiments, razoxane effected a significant increase in life span while being ineffective in tumour inhibition. Razoxane in combination with BAD displayed an enhanced anticancer activity which was not significant. ADP had a good antineoplastic activity and a large increase in survival time (144 per cent ILS). Razoxane used in combination with ADP did not influence antitumour efficacy. Median survivals of both ADP-treated groups were significantly longer than the razoxane-treated group. Analysis of the lung metastasis area showed a maximum of 57 per cent for the controls while all treated groups occupied a lesser area. The lowest metastases area was found with the combination treatment BAD + RAZ (18 per cent). This was considered an antimetastatic effect, while ADP treatment effected a time delay only. No change in metastatic pattern was observed in any of the treatment groups. Histological examination showed no effect on the capillaries in the proliferating region of the tumours that could account for the lower occurrence of metastases.

Anticancer-agent-linked phosphonates with antiosteolytic and antineoplastic properties: a promising perspective in the treatment of bone-related malignancies?

Bisphosphonates are compounds with a high affinity for bone and other calcified tissues. They inhibit tumor-induced bone destruction and the associated hypercalcemia by hindering the activity of the osteoclasts. Owing to a long biological half-life of bisphosphonates in the bone, a treatment using a prophylactic regimen seems possible. This paper summarizes preclinical studies with the bisphosphonate 3-amino-1-hydroxypropylidene-1,1-diphosphonic acid and two methyl derivatives; 3-N,N-dimethylamino-1-hydroxypropylidene-1,1-diphosphonic acid and 4-N,N-dimetyhlamino-1-hydroxybutylidene-1,1-diphosphonic acid with respect to their bone-protecting activity in therapy as well as in prophylaxis. To find substances that are useful for the treatment of primary tumor, as well as bone metastasis, we synthesized and tested cis-diammine[nitrilotris(methylphosphonato)(2-)-O1,N1]platin um(II) and cis-diammine[( bis-(phosphonatomethyl)amino]acetato(2-)-O1,N1)platinum(II), which contain both an osteotropic and an antineoplastic moiety. Experiments were carried out: (a) in the intratibial transplanted Walker carcinosarcoma 256B of the rat, which mimics osteolytic bone metastasis, and (b) in the transplantable osteosarcoma of the rat, which shows a histology and metastatic pattern similar to that found in man. These investigations indicate that it is possible to effect adjuvant therapy of bone metastases by combination of two compounds with different properties into one structure without losing the therapeutic characteristics of the parent compounds. They thus provide evidence that it may be possible to design compounds well suited for the therapeutic or prophylactic treatment of bone-related malignancies.

Prevention of glucocorticoid-induced osteoporosis

There is increasing evidence that pamidronate and related compounds are effective in the prevention and treatment of osteoporosis. It is therefore of relevance to document the time course and mechanism of bisphosphonate action in this condition. To this end, the present study describes the biochemical responses to prophylactic treatment with oral pamidronate (APD, 150 mg/day) in 16 glucocorticoid-treated patients and contrasts them with those in 19 steroid-treated control subjects. Measurements were made over a period of 12 months. The treated patients showed a fall in urine hydroxyproline excretion at 6 weeks associated with a reduction in serum ionized calcium concentration, a rise in serum 1,25-(OH)2D3, and a nonsignificant rise in serum bone gla protein (BGP). In contrast to BGP, serum alkaline phosphatase activity declined at 6 weeks, falling further at 3 months. Between 3 and 12 months, BGP levels paralleled those of alkaline phosphatase and hydroxyproline, all these being significantly below their initial values, and the other parameters returned to baseline. There was a gradual increase in plasma phosphate concentrations in the treated group over the 12 month period. It is concluded that pamidronate produces an acute and sustained inhibition of bone resorption followed by a more gradual reduction in bone formation. This transient dissociation results in a reduction in serum calcium, leading to a rise in serum 1,25-(OH)2D3, which in turn stimulates BGP production. Thereafter, indices of bone turnover remain subnormal but serum calcium and 1,25-(OH)2D3 return to baseline.

3-Amino-1-hydroxypropylidene-1,1-diphosphonate (APD): a novel enhancer of rectal cefoxitin absorption in rats

The promoting action of the calcium chelating compound EDTA on intestinal drug absorption is supposed to be based on Ca2+ depletion, inducing widening of tight junctions. The aim of the present study was to evaluate the effects of the calcium-binding agent 3-amino-1-hydroxypropylidene-1,1-diphosphonate disodium salt (APD) on rectal cefoxitin absorption in rats. The extent of rectal cefoxitin absorption was enhanced by 0.5 to 6% w/v of APD, on rectal infusion as well as on bolus delivery, the latter regimen tending to result in lower bioavailabilities. A maximal cefoxitin bioavailability of 85 +/- 10% was achieved by infusion with 4% w/v of APD, compared with 14 +/- 12% without APD.

Bone loss and bone blood flow in paraplegic rats treated with calcitonin, diphosphonate, and indomethacin

Sham-operated (SO) and paraplegic rats were treated from the day of operation during a period of 4 or 6 weeks with salmon calcitonin 4 IU/kg/day or a diphosphonate (APD) 1mM/kg/day or indomethacin 2.5 mg/kg/day. The consequence of spinal cord section on the femur and tibia is a loss of mineral which affects predominantly trabecular bone (-24 and -13% in calcium content for the tibial metaphysis and the whole bone, respectively, when compared with the SO controls), a twofold increase in bone blood flow as measured by the technique of the microspheres trapping, a moderate decrease of the 72 hour 45Ca accretion rate in the bone shaft, and an increase in the number of metaphyseal osteoclasts in the tibia. In paraplegics, all three drugs inhibit bone loss to some degree, calcitonin and indomethacin being mostly effective on the cortical bone of the shaft, and APD tremendously increasing the trabecular network of the metaphysis. APD is the only drug to exhibit a significant effect on the calcium content of the bones of the SO controls, but some effect is apparent for calcitonin on X-rays and histological preparations. The increase in bone blood flow in paraplegics is unaffected, this point being discussed in view of the hypothesis of the resorptive action of prostaglandins produced by newly formed vessels. 45Ca accretion rate increases in the shaft of calcitonin-treated paraplegics, whereas it decreases in APD-treated controls and paraplegics. The number of osteoclasts decreases in paraplegics treated with calcitonin and indomethacin, and increases in both controls and paraplegics treated with APD.(ABSTRACT TRUNCATED AT 250 WORDS)

Prevention of steroid-induced osteoporosis with (3-amino-1-hydroxypropylidene)-1,1-bisphosphonate (APD)

In a prospective, randomised, placebo-controlled trial comparing the effect of (3-amino-1-hydroxypropylidene)-1,1-bisphosphonate (APD) (150 mg/day) plus calcium (1 g/day) with that of calcium alone on the bone mass of patients receiving long-term glucocorticoid therapy, the mean metacarpal cortical area in patients receiving APD increased by 1.2% between 0 and 6 months (p less than 0.06) and then remained stable between 6 and 12 months. In contrast, this index progressively declined in the placebo group (p less than 0.05 at 12 months). The two groups differed significantly in the changes at both 6 and 12 months (p less than 0.01). Mean vertebral mineral density, as measured by quantitative computed tomography, increased by 19.6% over 12 months in the APD group (p less than 0.02) but showed a non-significant decline of 8.8% in controls. The differences between the changes were again significant (p less than 0.005). Biochemical indices and bone histomorphometry indicated a reduction in bone resorption and bone formation but there was no evidence of osteomalacia. APD may thus prevent bone loss in glucocorticoid-treated patients over a year.

Osteolytic bone metastases in breast carcinoma pathogenesis, morbidity and bisphosphonate treatment

In this review different aspects of osteolytic bone metastasis of breast carcinoma including morbidity, pathogenesis, accompanying hypercalcaemia and treatment, are discussed. Bone metastases occur in many patients with breast cancer (percentages of up to 85% have been reported); although patients seldom die of bone metastases morbidity is pronounced. Literature data point out that humoral factors, such as prostaglandins and the recently described growth factors are of importance beside cell interactions between monocytes, lymphocytes, osteoclasts and tumour cells. Nowadays, no significance is attributed to parathyroid hormone (PTH) overproduction in this respect. The differential diagnosis between primary hyperparathyroidism and tumour-induced hypercalcaemia is not always easy biochemically; combinations of both do occur less frequently than has been assumed in the past. A new and promising line of investigations involves the growth factors, which can increase osteolytic bone resorption and may bind to epidermal growth factor (EGF) or PTH receptors, thus inducing some of the biological effects of PTH (including hypercalcaemia). Until recently it was exceedingly difficult to treat tumour-induced hypercalcaemia (TIH) (the acute condition). Since the availability of the bisphosphonates dichloromethylidene bisphosphonate (Cl2MDP) and 3-amino-1-hydroxypropylidene-1, l-bisphosphonate (APD) this treatment has become very simple. Preliminary results, derived from the literature, point out that bisphosphonate treatment might also be effective in providing long-term control.

Inhibition of bone matrix apposition by (3-amino-1-hydroxypropylidene)-1,1-bisphosphonate (AHPrBP) in the mouse

To elucidate the mechanism of action of (3-amino-1-hydroxypropylidene)-1,1-bisphosphonate (AHPrBP, formerly APD) on bone metabolism, we have studied the influence of low doses of AHPrBP on bone resorption and formation in the mouse. Thirty-five-day-old mice were given daily injections of 0.16, 1.6, or 16 mumol/kg BW per day of AHPrBP for 10 days. At sacrifice biochemical parameters were measured in serum and bone ash, and histomorphometric parameters of bone formation and resorption were determined on undecalcified sections of caudal vertebrae after double 3H-proline and double tetracycline labelings. Serum calcium and 1,25-dihydroxyvitamin D levels remained normal at all dosage levels. Compared to controls, AHPrBP at doses of 1.6 and 16 mumol/kg per day increased the number of osteoclasts and the number of nuclei per osteoclast but markedly decreased the number of acid phosphatase-stained osteoclasts. Thus, AHPrBP appears to inhibit osteoclastic activity in vivo in part through reduction of acid phosphatase activity. At doses of 1.6 and 16 mumol/kg per day AHPrBP reduced serum alkaline phosphatase and the osteoblastic surface and decreased the endosteal osteoid surface and thickness. Both the matrix apposition rate and the mineral apposition rate were progressively reduced at the endosteal level, although they were not significantly changed at the periosteal level. Greater inhibition of bone resorption than bone formation resulted in increased endosteal bone density and bone mineral content. AHPrBP at a dose of 0.16 mumol/kg per day did not alter either the osteoclastic bone resorption or the mineral and matrix apposition rates.

The bisphosphonates HEBP and AHPrBP but not AHBP inhibit mineral mobilization and lysosomal enzyme release from mouse calvarial bones in tissue culture

The effect of 3 bisphosphonates, 1-hydroxyethylidene-1, 1-bisphosphonate (HEBP), 3-amino-1-hydroxy-propylidene-1, 1-bisphosphonate (AHPrBP) and azacycloheptylidene-2, 2-bisphosphonate (AHBP), on the release of minerals (40Ca, 45Ca, Pi) and enzymes from cultured mouse calvaria was investigated in an organ culture system. HEBP and AHPrBP reduced PTH-stimulated mobilization of calcium and inorganic phosphate without affecting the release of lactate dehydrogenase. In contrast, no significant effect by AHBP on mineral mobilization and lysosomal enzyme release could be registered. In parallel with inhibited mineral mobilization, HEBP and AHPrBP inhibited the release of the lysosomal enzyme beta-glucuronidase. A possible cellular mechanism of action of bisphosphonates is discussed in the light of these data.