THE USE OF GALLIUM SALTS FOR THE MANUFACTURE OF PHARMACEUTICAL COMPOSITIONS FOR THE TREATMENT OF DISORDERS OF CALCIUM HOMEOSTASIS

Abstract: The use of gallium salts for preventing or treating disorders associated with excessive loss of calcium from bone in an individual is disclosed. More particularly the use of gallium salts in the prevention or treatment of hypercalce­ mia associated with cancer or hyperthyroidism and the use of gallium salts to prevent osteoporosis is given.

Description: THE USE OF GALLIUM SALTS TO TREAT DISORDERS OF CALCIUM HOMEOSTASIS Background of the Invention This invention concerns the use of gallium salts to regulate calcium resorption from bone. Strict regulation of calcium ion concentration is necessary for normal cell functioning. In addition to maintaining cell membrane structure and excitability, calcium acts as a key second messenger to modulate critical biochemical pathways. Though intracellular levels of calcium are orders of magnitude less than extracellular levels, they reflect and depend on extracellular levels. The calcium reservoir in the body is maintained in dynamic equilibrium between various tissues by a complex system of interrelated factors. Calcium is deposited in the bone but it can also be resorbed from bone and enter the mobile calcium pool in blood where it is carried to and from individual cells that require calcium. Ingested calcium replaces that lost by excretion, so that the amount of calcium in the pool normally remains constant. However, when one of the factors maintaining equilibrium fails, abnormalities in the concentration of calcium in specific tissues may result. Hypercalcemia is one such abnormal state. Hypercalcemia raises intracellular levels of calcium which results in profound disruption of physiological processes within all cells. In the earliest phases, few signs or symptoms are present. With rising serum calcium levels-{-11 to--13-mg%) polyuria and nocturia associated with nausea, anorexia, fatigue, constipation, and mental dull ness may develop. With higher serum calcium levels ( > 13 mg%), decreased mentation progresses to obtundation and ileus develops. Furthermore, complete cardiovascular collapse can result from several factors: dehydration caused by water loss associated with calciuresis, the renal tubular defect in conserving waster, chronic emesis, and decreased fluid intake. In rare instances, the positive inotropic effect of calcium on the cardiac muscle has even been reported to trigger serious arrhythmias. Diseases associated with hypercalcemia include a wide variety of human cancers as well as primary hyperparathyroidism. Both of the latter diseases are extremely prevalent and thus provide the urgency to develop an effective form of therapy. Cancer-associated hypercalcemia is being recognized as one of the most commonly occurring paraneoplastic syndromes. This morbidity of cancer may arise suddenly and can progress rapidly, resulting in a life-threatening metabolic disturbance requiring prompt and effective treatment. Unfortunately, most therapies in current use are non-specific and are not directed at the underlying pathophysiological processes that cause increased bone resorption and calcium release. Among the recommended treatment choices in hypercalcemia are calciuretic diuretics such as ethacrynic acid or furosemide (Lasix), glucocorticoid steroids or, in the case of patients with predictable and progressive hypercalcemia IV infusion of mithramycin. (Bockman, R., Your Patients and Cancer, March, 1-5 (1981)). Accordingly, a search has been undertaken to discover agents which inhibit calcium resorption from bone. It has been unexpectedly observed that gallium salts are effective regulators of calcium resorption from bone and are effective in the treatment of hypercalcemia associated with cancers. SUMMARY OF THE INVENTION Accordingly, it is a principal object of the present invention to provide a method for regulating resorption of calcium from bone. It is another principal object of the present invention to provide a method of treating disorders associated with excessive loss of calcium from bone. It is another object of the present invention to provide a method of preventing and treating hypercalcemia associated with cancer or hyperparathyroidism, the two most common causes. It is an important object of the present invention to provide a method of preventing osteopenia due to calcium resorption from bone. It is further object of the present invention to provide a method of inhibiting release of calcium from cultured bone cells. It is a further object of the present invention to provide a method of administering gallium salts in anti hypercalcemic effective amounts. In accordance with these objectives, the present invention comprises a method of administering gallium salts in non-nephrotoxic amounts to inhibit resorption of calcium from bone in patients with hypercalcemia, bone fragility or other disorders associated with abnormally increased calcium resorption. Gallium is a metal belonging to the group IIIa elements of the periodic table. In 1950, gallium-72 was found to accumulate in neoplastic tissues (Dudley, H.C. et al, Radiology, 50, 571 (1950), and shortly thereafter, the therapeutic use of radioactive gallium was first reported by King et vl, for the treatment of patients with malignant bone tumors. (King, E.R., et awl., Arch Int. Med., 90, 785 (1952)). In 1969, Edwards and Hays observed that carrierfree gallium-67 localized at sites of tumors in cancer patients (Edwards, C.L., et al., J. Nuc. Med., 10, 103 (1969)). Since then, gallium-67 citrate has been widely used as an oncophilic agent for the diagnostic evaluation of patients with a variety of neoplastic diseases, particularly malignant lymphoma (McCaffrey, J.A. et al., Am. J. Med., 60, 523 (1976); Hoffer, P., J. Nuc. Med. 21, 394 (1980)). While conducting clinical trials with gallium nitrate as an anti-cancer agent, we observed that blood calcium levels frequently dropped to sub-normal levels. Previously it had been reported that gallium nitrate caused excess urinary excretion of calcium (hypercalciuria ),when administered with mannitol (Krakoff, et al., Cancer, 44, 1722 (1979)). However, our later carefully controlled metabolic studies showed that this observation was an artifact probably caused by the diuretic effect of mannitol. In our metabolic studies, the net amount of calcium was calculated from measurements of intake and excretion. This monitoring of calcium showed that gallium nitrate did not cause any change in calcium excretion even though it reduced blood levels of calcium. This suggests that gallium ion is exerting its hypocalcemic effect by inhibiting an inçortont factor which maintains the normal dynamic equilibrium of the calcium pool i.e., bone resorption. That the equilibrium involved that of bone resorption was confirmed by later experiments with bone cell cultures wherein it was shown that loss of calcium from bone tissue of fetal rats was inhibited by gallium nitrate even in the presence of a potent calcium-releasing agent, OAF. DETAILED DESCRIPTION OF THE INVENTION The present invention comprises a method of administering gallium salts, preferably gallium nitrate, along with a pharmaceutically acceptable carrier in non-nephrotoxic amounts to patients with hypercalcemia due to resorption of calcium from bone. Gallium salts which may be employed are those which are physiologically acceptable including nitrate, citrate, halide, preferably chloride, carbonate, acetate, tartrate, oxalate, oxide or hydrated oxide. It is to be understood that the active therapeutic agent is the gallium ion and, that therefore the choice of anion may be determined by such factors as commercial accessibility, solubility characteristics, and mode of administration. The gallium salt may be administered orally or intravenously. In the preferred embodiment of the present invention, gallium nitrate is administered by continuous infusion. The hypocalcemic effect of gallium salts is strictly schedule related. Previous clinical trials of gallium nitrate demonstrated that bolus administration produced dose limiting nephrotoxicity. In an effort to increase the therapeutic index of this compound and to establish -a satisfactory out-patient schedule which avoided the use of parenteral hydration, the therapeutic and toxic effects of gallium nitrate administered as a continuous infusion were evaluated. It was found that gallium nitrate administered as a continuous infusion for seven days at 200 to 400 mg/sqm/day is well tolerated and is an effective treatment for patients with hypercalcmia. Ovt-patient administration using portable infusion pumps is safe and practical. It is expected that oral administration of gallium salts will also be effective especially when used in conjunction with time release coatings which allow a controlled supply of gallium to the bloodstreom. Initial Clinical Studies of Gallium Nitrate as an Anticancer Agent Results of both the Phase I (Warrell R.P. et al, Clinical Research 29, 684A, (1981)) and Phase II (Warrell R.P. et al., Proc Am Soc Clin Oncol. 1, 160, (1982)) studies showed that gallium nitrate possessed moderate antitumor activity in patients with advance malignant lymphoma. We also observed that two-thirds of patients who received gallium nitrate as a continuous infusion (300 mg/sqm/day x 7 days) developed hypocalcemia as a result of this therapy. Metabolic Studies on Patients Receiving Gallium Studies of calcium homeostasis require an assessment of multiple factors including dietary intake, excretion of calcium into urine and stool, and analysis of calcium mobilization from body stores (chiefy bone). A series of patients who participated in a careful study of the effects of gallium nitrate upon calcium metabolism were thus assessed. Patients were hospitalized and received. a diet of defined calcium, sodium, and fluid intake. Measurements of calcium excretion into urine and stool (along with multiple other laboratory tests) were made daily during a 6-day baseline period and during a subsequent treatment period using gallium nitrate. The drug was administered as a continuous infusion at a dose of 300 mg/sq m/day/ for durations ranging from 4-7 days. Despite the finding that the total serum calcium concentration was reduced by the gallium infusion, we found no significant increase in calcium excretion during the infusion relative to the baseline observation period. These data suggested that gallium nitrate might exert its hypocalcemic effect by directly affecting calcium resorption from bone. In Vitro Effects of Gallium Nitrate Upon Bone Resorption Using an in vitro assay of fetal rat bones (Bockman, R.S. and Repo, MA., J Exp Med 154 529 (1981)), the effects of gallium nitrate upon calcium release from bone were measured after exposure to a tumor-derived factor (osteoclast activating factor, OAF). Simultaneous addition of gallium and OAF did not reduce calcium release relative to the use of OAF alone. However, pre-incubation of bones with gallium for 48 hours preceding the addition of OAF caused a marked reduction in calcium release. Moreover, at the doses of gallium nitrate employed in these tests (1-10 mcg/ml), no toxic effect on bone metabolism was observed. These data suggested a unique mechanism of gallium-nitrate induced hypocalcemia, namely a direct inhibition of calcium resorption from bone which was independent of any cytotoxic effect. This mechanism also indicates that gallium might prove useful for the treatment of diseases associated with increased losses of calcium from bone. Treatment of Cancer-Related Hypercalcemia With Gallium Nitrate Infusions Gallium nitrate was used for the treatment of seven patients with cancer-related hypercalcemia. The daily dose of drug was 200 mg/sqm administered as a continuous infusion for durations ranging from 5-7 days. The diagnoses of this patient population and the change in total serum calcium concentration in response to this therapy are presented in Table 1. Note that all patients responded to this treatment by a reduction in serum calcium concentration to normal (and frequently sub-normal) values. With the single exception of Patient 5 (Table 1), the hypocalcemic effect was not associated with any anti-cancer effect. Patient 5 demonstrated a transient decrease in the size of a lymphomatous mass followed shortly thereafter by progression of her disease and death. The subsequent increase of her disease was not accompanied by an increase in serum calcium which indicates a persistent control of the metabolic problem by the previous treatment with gallium nitrate. All other patients who received the drug manifested progressive cancer despite control of the hypercalcemia. This finding indicates that the hypocalcemic effects is not produced by a direct cytotoxic effect of gallium nitrate upon tumor cells. Table 1 Response of patients with cancer-related hypercalcemia to continuous infusion of gallium nitrate. 1 Total Serum Calcium Patient Cancer Pre- Post- Daily Dose of Di agnosi s Treatment Treatment Gallium Nitrate (mg/sqm) x days 1 Breast 13.6 8.9 200 x 5 2 Lymphoma 14.0 6.7 200 x 6 3 Head & Neck 12.3 8.5 200 x 5 4 Breast 14.4 7.7 200 x 6 5 Lymphoma 15.6 8.6 200 x 7 6 Lung 12.5 7.0 200 x 5 7 Lung 12.7 9.4 200 x 5 Serum concentration expressed in mgjdl (formal range, 9.0X10.8 mg/dl). recent studies (Warrell R.P., et al., Cancer 51:1982-87, 1983) have strongly suggested that administration of gallium nitrate by continuous intravenous infusion produces a substantial increase in the drug's therapeutic index as a cytotoxic agent, relative to administration as a bolus injection (i.e. more effective, less toxic). The infusion method avoids large, peak plasma drug concentrations and it achieves prolonged exposure to low, constont plasma drug levels. An oral method of administration would provide not only a convenient route of drug delivery but it would also allow one to achieve constant, low-level plasma drug concentrations and avoid large peak levels. Prolonged exposure (greater than 48 hours) to gallium nitrate concentrations which ranged from 1-1O,ugiml is necessary to inhibit stimulated bone resorption in vitro. As previous pharmocokinetic studies (Kelsen, D.P. et al., Cancer 46:2009-13, 1980) have shown, gallium nitrate administration 2 by continuous infusion at a daily dose of 200 mg/m iday achieves a steady state plasma gallium concentration which ranges from 0.9-2.0 sg/ml. This dose is extremely effective in controlling cancer related hypercalcemia (see Table 1 of this application). Therefore, an orally administered gallium salt which achieves a plasma gallium concentration of approximately 0.9-2.0 sg/ml should also be effective in controlling cancer related hypercalcemia as well as other disorders associated with accelerated loss of calcium from bone. In order to evaluate oral absorption of gollium salts, a concentrated solution of gallium nitrate was administered by oral gavage to a dog. The total oral dose was 1.200 mg. The next 24 hour urine specimen was then collected from the dog and assayed for gallium concentrations by atomic absorption spectrophotometry of the urine as well as of sequentially drown plasma samples. The 24 hour urine volume was 183 ml, and it contained a total amount of 1.13 mg of gallium. The blood levels achieved at vqvious times after drug administration are noted in table 2. Importantly, the animal who received this oral dose of gallium nitrate experienced no toxic reactions whatsoever. Table 2: Plasma gallium concentrations achieved in a dog after cdministration of 1.200 mg gallium nitrate by oral gavage time gilium concentration (#g/ml) O 0 15" 0.5 32'' 1.25 60il 1.37 120" 2.75 240'' 2.0 24 hrs 0.75 Approximatély two-thirds of an intravenously injected dose of gallium nitrate is excreted into the urine within the A first 24 hours (Kelsen, D.P., et al., Cancer 46:2009-13, 1980). Based on the reasonable assumption that excretion of gallium is similar in dogs and humans, one can conclude from the urinary data that approximately 1-2 percent of an orally administered dose of gallium nitrate is absorbed and subsequently excreted into urine. Moreover, oral administration of a 1200 mg dose of gallium nitrate achieved a sustained plasma gallium concentration at a level known to be effective in inhibiting bone resorption in vitro and in controlling cancer-related hypercolcemia in vivo. Administration of daily or twice daily oral doses would reasonably be expected to maintain a constant, low level plasma gallium concentration. If a 1200 mg dose of gallium nitrate achieves a pharmacologically active concentration of gallium in the plasma of a 10 kg dog, it is estimated that 0.5-20 gms of gallium nitrate administered orally to a 70 kg human would achieve similarly therapeutic concentrations of gallium in plasma. Depending upon differences in possible pharmacodynamic behavior between species. An oral dose in humans of this magnitude administered 1-4 times/day is anticipated.

Claims: CLAIMS 1. A method of preventing or treating a disorder associated with excessive loss of calcium from bone in an individual comprising administering to the individual a phormnceuticolly acceptable gallium salt. 2. The method of Claim 1 wherein said disorder is hypercalcemia. 3. The method of Claim 1 wherein said disorder is osteopenia. 4. A method of inhibiting release of calcium from cultured bone cells comprising contacting said cultured cells with a gallium salt. 5. The method of Claim 1 wherein said gallium salt is administered by intravenous injection. - 6. The method of Claim 5 wherein intravenous injection comprises continuous infusion. 7. Thp method of Claim 6 comprising continuous infusion at a dose rate of up to 400 mg/sqm/day. 8. The method of Claim 1 wherein said gallium salt is administered orally. 9. The method of Claim 8 wherein said oral dose comprises 0.5 to 20 gm per day. 10. The method of Claim 1 wherein said gallium salt is gallium nitrate. 11. A composition for treatment of hypercalcemia associated with excessive loss of calcium from bone comprising an anti-hypercalcemic effective amount of a gallium salt in a pharmaceutically acceptable carrier.

Inventors: BOCKMAN, RICHARD, WARRELL, RAYMOND P.
Applicants: SLOAN-KETTERING INSTITUTE FOR CANCER RESEARCH
Application year: 1983
Main classification: A61K33
IPC codes: A61P43, A61K33, A61P3