Parathyroid Hormone Analogues Substituted at AA 25, 26, 27, and Use in Osteoporosis Treatment

This invention relates to analogues of parathyroid hormone which, by substitution at the twenty-fifth, twenty-six and twenty-seventh positions of natural parathyroid hormone, have been found to affect calcium change in bone cells without producing the typical effects of parathyroid hormone on systolic and diastolic blood pressure, the effects on smooth muscle relaxation, vascular smooth muscle calcium change as well as positive chronotropic and inotropic effects on the heart.

Parathyroid hormone (hereinafter, PTH) is produced by the parathyroid gland and is involved in the control of calcium levels in blood. It is a hypercalcemic hormone, elevating blood calcium levels. PTH is a polypeptide and the amino acid sequences of bovine and human PTH are closely related. Only the residues at locations one, seven and sixteen differ between the two. Synthetic polypeptides containing the first thirty-four residues of PTH may be prepared using the method disclosed by Erickson and Merrifield, The Proteins, Neurath et al. , Eds., Academic Press, New York, 1976, page 257, preferably as modified by the method of Hodges et al., Peptide Research, 1, 19 (1988).

When serum calcium is reduced to below a "normal" level, the parathyroid gland releases PTH and resorption of bone calcium and increased absorption of calcium from the intestine, as well as renal reabsorption of calcium, occur.

The antagonist of PTH is calcitonin, which acts to reduce the level of circulating calcium. PTH is known to stimulate osteoclasts and its activity requires the presence of derivatives of vitamin D.sub.3, especially 1,25-dihydroxycholecalciferol.

Intracellular calcium, particularly in the cells of the vascular system, has been shown to affect changes in vascular tension, as can be measured by changes in blood pressure. U.S. patent application Ser. No. 603,745 describes one method which has been discovered to regulate calcium uptake in vascular cells.

Osteoporosis is a progressive disease which is particularly characteristic of postmenopausal women, and results in the reduction of total bone mass. The sequelae frequently involve fractures of load-bearing bones and the physical degenerations characteristic of immobilizing injuries. osteoporosis is associated with hyperthyroidism, hyperparathyroidism, Cushings syndrome and the use of certain steroidal drugs. Remedies historically have involved increase in dietary calcium, estrogen therapy and increased doses of vitamin D.

PTH has been used to treat osteoporosis. However, while the use of PTH is effective in the treatment of osteoporosis by diminishing the loss of bone mass, PTH may exhibit other undesired pharmalogical effects, such as hypotension and smooth muscle relaxation (e.g. relaxation of gastrointestinal organs, uterus, tracheal and vas deferens) as well as positive chronotropic and inotropic effects on the heart. The relaxation effects of PTH on smooth muscle as well as positive chronotropic and inotropic effects of PTH are described in Pang et al, Trends in Pharmacological Sciences, Vol. 7, No. 9, pp. 340-341 (September 1986).

U.S. Pat. No. 4,771,124 discloses the property of bovine and human PTH analogues wherein Trp.sup.23 is substituted by amino acids phenylalanine, leucine, norleucine, valine, tyrosine, beta-naphtylalanine and alpha-naphtylalanine as a PTH antagonist. While it was suggested that these analogues might be useful in the treatment of osteoporosis, it was based on the analogues antagonistic action to PTH. Furthermore, there was no data to indicate the effectiveness these analogues on bone or other tissue. In addition, analogues with substituted at Trp.sup.23 with leucine, phenylalanine or tyrosine would produce undesired secondary effects of smooth muscle relaxation, vascular smooth muscle calcium change as well as positive chronotropic and inotropic effects on the heart.

Because PTH is a peptide, topical administration would be the preferred method of administration. However, topical application of PTH or the aforementioned analogues which exhibit vasoactivity would likely produce an undesired local vascular reaction. This reaction could be potentially detrimental if, for example, nasal administration is employed.

It is one object of this invention to ameliorate bone loss while preventing smooth muscle relaxation as well as positive chronotropic and inotropic effects on the heart and without significantly changing blood pressure. It is another object of this invention to identify that portion of PTH which is responsible for calcium regulation and that portion which appears to be primarily related to control of blood pressure and smooth muscle action.

Modification of either bovine or human PTH at each of the twenty-fifth, twenty-sixth and twenty-seventh amino acid positions to substitute for -arginine-lysine-lysine- either alanine, asparagine, aspartic acid, cysteine, glutamine, glutamic acid, glycine, histidine, isoleucine, leucine, methionine, phenylalanine, proline, serine, threonine, tryptophan, tyrosine or valine produces substantially no change in systolic and diastolic blood pressure, substantially no change in muscle tension and substantially no change in the rate of contraction and the force of contraction of the heart as compared to native PTH. It also has been observed that the PTH analogue containing only the first thirty-four amino acids, with substitution at the twenty-fifth, twenty-sixth and twenty-seventh positions, is equally effective in the "osteo effect" without changing blood pressure or causing muscle relaxation or positive chronotropic and inotropic effects on the heart.

The analogues of the present invention should be effective in ameliorating bone loss while preventing smooth muscle relaxation as well as positive chronotropic and inotropic effects on the heart and without significantly changing blood pressure.

FIG. 1a shows the structure of natural bovine PTH (SEQ ID (NO:1).

FIG. 1b shows the structure of natural human PTH (SEQ ID (NO:2).

FIG. 2 shows the structure of BPTH (1-34) with each of positions 25, 26 and 27 substituted with Xaa (SEQ ID NO:3).

FIG. 3 shows the structure of BPTH (1-34) with each of positions 25, 26 and 27 substituted with Ala (SEQ ID NO:4).

FIG. 4 shows the structure of HPTH (1-34) with each of positions 25, 26 and 27 substituted Xaa (SEQ ID NO:5).

FIG. 5 shows the structure of HPTH (1-34) with each of positions 25, 26 and 27 substituted Ala (SEQ ID NO:6).

FIG. 6 shows the structure of BPTH with each of positions 25, 26 and 27 substituted with Xaa (SEQ ID NO:7).

FIG. 7 shows the structure of BPTH with each of positions 25, 26 and 27 substituted with Ala (SEQ ID NO:8).

FIG. 8 shows the structure of HPTH with each of positions 25, 26 and 27 substituted with Xaa (SEQ ID NO:9).

FIG. 9 shows the structure of HPTH with each of positions 25, 26 and 27 substituted with Ala (SEQ ID NO:10).

FIG. 10 shows the effect of bPTH-(1-34) and its analogues on diastolic blood pressure of anesthetized Sprague-Dawley rats. The diastolic blood pressure decreases as the dosage of drugs is increased.

FIG. 11 shows the effect of bPTH-(1-34) and its analogues on systolic blood pressure of anesthetized Sprague-Dawley rats. The systolic blood pressure decreases as the dosage of drugs is increased.

FIG. 12 shows the vasorelaxing effect of bPTH-(1-34) and its analogues on rat tail artery helical strip in vitro. The relaxation of the artery increases as the dosage of drugs is increased.

FIG. 13 shows the depolarizing concentrations of KCl which increased calcium ion levels in cultured osteoblasts. Drug 788 is an anti-osteoporotic agent which inhibits the KCl effect.

FIGS. 14 a-d show the depolarizing concentrations of KCl which increased calcium levels in cultured osteoblasts. Addition of bPTH-(1-34) inhibits the KCl effect.

FIG. 15 shows the effect of Cs88 [bPTH- (1-34)] on the mean arterial blood pressure of anesthetized Sprague-Dawley rats. Blood pressure decreases as the dosage of the drug increases.

FIG. 16 shows the dose-response relationship between Cs88 [BPTH- (1-34) ] and the tension of rat tail artery helical strips precontracted with KCl, norepinephrine and AVP. The tension of the rate tail artery helical strips decreases as the amount of the drug increases.

FIG. 17 shows the effect of Cs88 on [Ca.sup.2+ ].sub.i in cultured UMR osteoblast cells. PTH inhibits intracellular [Ca.sup.2+ ].sub.i increases as stimulated by KCl.

FIG. 18 shows the effect of Cs88 on (Ca.sup.2+ ].sub.i in cultured UMR cells.

FIG. 19 shows a comparison of the effect of Cs221 and Cs99 and BPTH on the mean arterial blood pressure of anesthetized Sprague-Dawley rats. Cs221 with substitutions at positions 25, 26 and 27 shows the least decrease in blood pressure. Cs99 substituted at position 25, shows more of a decrease in blood pressure but still less than the PTH fragment with no substitutions.

FIG. 20 shows the relation between the relaxation curves of Sprague-Dawley rat tail artery helical strips, precontracted with AVP when treated with Cs100, Cs99, Cs88, Cs117 and Cs221. Cs221 shows the least relaxation of the rat tail artery helical strips as compared with Cs99 (substituted at position 25), Cs100 (substituted at position 26), Cs117 (substituted at position 27) and Cs88 (no substitutions).

FIG. 21 shows a comparison between the effect of Cs221 and HPTH on the intracellular calcium uptake in the presence of KCl in UMR cells in culture. The inhibition of intracellular [Ca.sup.2+ ].sub.i increases by Cs221 is comparable to the inhibition of intracellular [Ca.sup.2+ ].sub.i increases by hPTH.

FIG. 22 shows the effect of Cs221 on the intracellular calcium uptake in the presence of KCl in UMR cells in culture. Increasing concentrations of Cs221 produce lower intracellular calcium increments.

FIG. 23 shows the effect of Cs1001 on the intracellular calcium uptake in the presence of KCl in UMR cells in culture. Increasing concentrations of Cs1001 produce lower intracellular calcium increments.

FIG. 24 shows the effect of Cs221 on the contractility and contraction rate of right atrial tissue of Sprague-Dawley rats. Cs221 has minimal effect on the contractility and contraction rate.

FIG. 25 shows the effect of Cs2001 and Cs1001 on the contractility and contraction rate of right atrial tissue of Sprague-Dawley rats. Both Cs1001 and Cs2001 increase the contraction rate.

There are at least two known categories of functions for PTH. PTH is involved in calcium balance in the blood stream and controls both the amount of calcium uptake from the gastrointestinal tract and the deposition and removal of calcium from bone. Calcium also has been found to be effective in the maintenance of blood pressure. Cox, J. Cardiovascular Pharmacology, Vol. 8 (1986), Supp. 8 S48. Control of calcium in the walls of blood vessels is a useful therapeutic regimen for controlling hypertension and calcium channel blockers, which prevent the introduction of calcium into cell walls, is a conventional therapy for hypertension. Needleman et al. in Goodman and Gilman's The Pharmacological Basis of Therapeutics, MacMillan, New York, (1985), page 816 ff.

Administration of therapeutic doses of PTH has been found to be effective for the control of osteoporosis, particularly in individuals who have been subjected to thyroidectomies/parathyroidectomies. Therapeutic dosages of PTH will, in some individuals, result in unacceptable diminution of blood pressure and may result in relaxation of smooth muscles such as gastrointestinal, uterus, tracheal, vas deferens as well as exhibit positive chronotropic and inotropic effects on the heart. To avoid hypotensive effects, smooth muscle relaxation effects and positive chronotropic and inotropic effects on the heart, it was envisaged that the structure of PTH could be modified to decouple the hypotensive, smooth muscle relaxation and positive chronotropic and inotropic function from the bond calcium and bone deposition function. It has now been discovered that a critical site exists at amino acid twenty-five, twenty-six and twenty-seven, which is --Arg--Lys--Lys-- in both bovine and human PTH. Substitution at the --Arg--Lys--Lys--site with --Ala--Ala--Ala-- diminishes the hypotensive as well as smooth muscle relaxation and positive chronotropic and inotropic effects without denigrating from the osteo effect. These results suggest that substitution at the --Arg--Lys--Lys--site with amino acids other than basic amino acids arginine and lysine would also diminish the hypotensive, smooth muscle relaxation and positive chronotropic and inotropic effects without denigrating from the osteo effect.

The procedure of Erickson and Merrifield, as modified by Hodges et al., as described above, may be used to synthesize synthetic PTH or fragments thereof. The procedure enables substitution for the naturally occurring PTH at substantially every location and it is possible to prepare both bovine and human synthetic PTH at full length or in the sequence of the first thirty-four amino acids, which is more facilely performed. Such substitution can also be accomplished by genetic engineering.

Substitution at position twenty-five, twenty-six and twenty-seven invariably alters the observed hypotensive, smooth muscle relaxation and positive chronotropic and inotropic effects, whether the full length PTH or the 1-34 fragment is administered. Substitution of --Ala--Ala--Ala-- for --Arg--Lys--Lys--at position twenty-five, twenty-six and twenty-seven is particularly preferred because the change in blood pressure, smooth muscle relaxation and positive chronotropic and inotropic effects from this substitution are minimal and calcium uptake, as measured in osteoblasts, mimics the results from the administration of native PTH. The 1-34 PTH fragment with --Ala.sup.25 --Ala.sup.26 --Ala.sup.27 -- is particularly preferred because the pharmacological properties are those which are desired and the difficulty of synthesis is minimized. Synthesis of the compounds used in the development of this invention was performed at Alberta Peptide Institute (API) and the cooperation of API is gratefully acknowledged.

The structure of bovine parathyroid hormone (BPTH) and human parathyroid hormone (HPTH) are shown in FIGS. 1a (SEQ ID NO:1) and 1b (SEQ ID NO:2). Representative synthetic analogues are described in Table 1 and are further shown in FIGS. 2-9 and SEQ ID NO:3-SEQ ID NO:10. The hypotensive effects of these analogues is shown in FIGS. 10, 11, 15 and 19. All of the analogues produce either no or less diminution of blood pressure than does native PTH. With only one amino acid at either the 25, 26 or 27 position substituted, the analogue shows less effect than native PTH. With all three positions substituted, it provides almost no change. At the level of 5 .mu.g/kg of PTH, the blood pressure in Sprague-Dawley rats is such that they are essentially moribund.

We have developed a method for modeling the hypotensive effects of natural and synthetic chemical compounds using helically cut tail arteries from Sprague-Dawley rats in a Sawyer-Bartlestone chamber, measuring the change in tension with a force displacement transducer. This method and the effect of bovine PTH-(1-34) in this system is described in Blood Vessels, 22, 57 (1985). It is demonstrated in this paper that bPTH-(1-34) produces dose-dependent relaxation of helical &trips of rat tail artery which have been previously contracted by arginine-vasopressin (AVP). FIGS. 12, 16 and 20 illustrate the effect of the PTH analogues of this invention as measured using this in vitro technique. Alternatively, the strips may be precontracted using other pressor substances such as norepinephrine (NE) or KCl.

We have also developed a method of modeling the chronotropic effects of natural and synthetic chemicals using the right atrium from Sprague-Dawley rats and measuring the change in the force and rate of atrium contraction. This method and the effects of bovine PTH (1-34) in this system are described in Tenner et al, The Canadian Journal of Physiology and Pharmacology, Volume 61, No. 10 (1983) pp. 1162-1167. It is demonstrated in this paper that bPTH (1-34) produces significant dose-dependent chronotropic effects on rat cardiac pacemaker tissue. FIGS. 24-25 illustrate the effect of the PTH analogues of this invention as measured using this in vitro technique.

Because osteoporosis is a progressive syndrome, a model is required and the use of cultured osteoblasts of the UMR-106.rat osteosarcoma cells, ATCC CRL 1661 have been used as the model. Uptake of calcium in these cells has been monitored using the FURA-2 method, wherein a fluorescent dye which is specific for calcium is used as a marker for calcium change into the cells. Cells are incubated with 1-10 .mu.M of the acetomethoxy ester of FURA-2 for 30-60 minutes. Upon uptake, the ester is hydrolyzed to release free FURA-2, which selectively binds free Ca.sup.2+. FURA-2 has a characteristic fluorescence spectrum, which wavelength is shifted when the dye binds to free Ca.sup.2+. According to the method, Ca.sup.2+ which is present in the cell can be quantified by exciting the dye at two different wavelengths, 340 and 380 nm. The emission fluorescence is measured at 510 nm. The calcium concentration is proportional to the ratio of the fluorescent emission when excited at 340 nm to the emission at 380 nm. It is conventional to report the concentration of calcium within the cell in terms of the fluorescence ratio, the 340/380 ratio. This technique is described in Grynkiewicz et al., J. Biol. Chem., 260, 3440 (1985) and Pang et al., P. N. A. S. (USA), 87, 623 (1990).

FIGS. 13, 14 a-d, 17, 18, 21, 22 and 23 illustrate the results of the above-described measurements when inhibitors such as an anti-osteoporotic agent (788) or bPTH-(1-34) or Cs114 were used in the presence of KCl.

As can be readily seen from the figures, the PTH analogues, whether full length or 1-34, which contain anomalous amino acids at positions twenty-five, twenty-six and twenty-seven (most particularly those which contain Ala.sup.25 --Ala.sup.26 --Ala.sup.27), do not effect a hypotensive and smooth muscle relaxation response, including positive chronotropic effects, but do inhibit calcium uptake as stimulated by KCl in osteoblasts, which indicates that these compounds would have the same effect on bone cells as PTH and would be useful in the treatment of osteoporosis in mammals and, particularly, in man, without the aformentioned deleterious side effects in the elderly.

While not being bound by any theory, it is suggested that substitution Arg.sup.25 --Lys.sup.26 --Lys.sup.27 by other amino acids in 1-84 PTH and in the 1-34 analogues removes the vasodepressor, smooth muscle relaxation and positive chronotropic and inotropic effects of either BPTH or HPTH. The effect on KCl induced calcium uptake in osteoblasts, however, is essentially unchanged for 1-84 or 1-34 PTH. In other words, the effect on bone cells is unchanged from PTH.

The physiological significance of an inhibiting effect on the KCl induced calcium uptake in bone cells is not yet understood. One hypothesis is that the analogues interact fully with bone cell receptor activity. The fact that the same effect is seen for both PTH and the analogues disclosed herein suggests that the site of interaction with the osteoblast cell receptor is unchanged by the substitution.

The analogues of the present invention can be used in the treatment of osteoporosis and other bone related diseases and disorders involving bone cell calcium regulation.

The analogues of the present invention may be administered to a warm-blooded mammalian in need thereof, particularly a human, by parental, topical, rectal administration or by inhalation. The analogues may be conventionally formulated in a parenteral dosage form compounding about 1 to about 300 mg per unit of dosage with a conventional vehicle, excipient, binder, preservative, stabilizer, color, agent or the like as called for by accepted pharmaceutical practice.

For parental administration, a 1 to 10 ml intravenous, intramuscular or subcutaneous injection would be given one to four times daily. The injection would contain an analogue of the present invention in an aqueous isotonic sterile solution or suspension optionally with a preservative such as phenol or a solubilizing agent such as ethylenediaminetetraacetic acid (EDTA). Among the acceptable vehicles and solvents that may be employed are water, Ringer's solution and isotonic sodium chloride solution. In addition, sterile, fixed oils are conventionally employed as a solvent or suspending medium. Synthetic monoglycerides, diglycerides, fatty acids (such as oleic acid) find use as fixed oil in the preparation of injectables.

For rectal administration, the analogues of the present invention can be prepared in the form of suppositories by mixing with a suitable non-irritating excipient such as cocoa butter or polyethylene glycols.

For topical use, the analogues of the present invention can be prepared in the form of ointments, jellies, solutions, suspensions or dermal adhesive patches.

In a powdered aerosol, analogues of the present invention may be administered by a spinhaler turbo-inhaler device obtained from Fisons Corporation of Bedford, Mass., at a rate of about 0.1 to 50 mg per capsule, 1 to 8 capsules being administered daily for an average human. In a liquid aerosol, the compounds of the present invention are administered at the rate of about 100 to 1000 micrograms per "puff" or activated release of a standard volume of propellant. The liquid aerosol would be given at the rate of 1 to 8 "puffs" per day with variation in dosages due to the severity of the conditions being treated, the weight of the patient and the particle size distribution of the aerosol. A fluorinated hydrocarbon or isobutane find use as propellants for liquid aerosols.

Daily doses are in the range of about 0.01 to about 200 mg per kg of body weight, depending on the activity of the specific compound, the age, weight, sex and conditions of the subject to be treated, the type and severity of the disease, the frequency and route of administration. As would be well known, the amount of active ingredient that may be combined with the carried materials to produce a single dosage will vary depending upon the host treated and the particular mode of administration.

The following examples demonstrate the utility of applicants' invention. The examples are not limiting, but are illustrative only, and modifications which would be apparent to those skilled in the art are included within the scope of this disclosure.

Sprague-Dawley (S-D) rats were anaesthetized with pentobarbital and a cannula was inserted into the carotid artery. The rats were kept sedated during the procedure and were injected with PTH peptides only when the blood pressure of the rats were stable. Peptides were injected through a cannula in the jugular vein, in amounts of 1, 3 and 5 or more .mu.g/kg and the mean systolic and diastolic blood pressure was monitored continuously throughout the procedure. Results are reported with comparison to bPTH-(1-34).

The assay was performed according to Pang et al., Blood Vessels, 22, 57 (1985). Sprague-Dawley rats were anaesthetized with pentobarbital and the tail artery excised and placed in ice-cold Krebs-Hanseleit solution (KHS) oxygenated with 95% O.sub.2, 5% CO.sub.2. Each artery was cut helically and strips of approximately 1.5 cm were secured in a Sawyer-Bartlestone chamber containing KHS. The force generated by the strips was measured with a Grass FT03 force displacement transducer and recorded on a polygraph. Isolated tail artery helical strips were equilibrated for 1 hour prior to use.

One to two minutes prior to addition of a peptide, the strips were contracted by addition of either arginine vasopressin (AVP), potassium chloride (KCl) or norepinephrine (NE) to the bath. The peptide was then added to the bath and the degree of relaxation measured. Bovine serum albumin was used as a control. Results are reported as percent decrease in tension for each drug and dose used. Drug dose is calculated on the basis of the final concentration in the bath solution.

The assay was performed according to Tenner et al., Canadian Journal of Physiology and Pharmacology, Vol. 61, No. 10 (1983) pp. 1162-1167. Sprague-Dawley rats weighing between 100 and 250 g were treated with heparin (500 IU, i.p.) 15 minutes prior to decapitation. Thoracotomies were performed and the heart rapidly excised and placed in a cold physiological salt solution (PSS) having the following composition (in millimolar): NaCl, 120; KCl, 5.63; CaCl.sub.2, 2.0; MgCl.sub.2, 2.1; NAHCO.sub.3, 25.0; dextrose, 9.7. The solution was continuously aerated by a gas mixture of 95% O.sub.2 -5% CO.sub.2. The right atrium was isolated and suspended in a tissue chamber containing 20 mL of PSS at 37.degree. C., pH 7.4. Atria were allowed to equilibrate for 1 hr under a resting tension of 1 g.

The atrial rate and force were determined from contractions recorded by a Grass FT.03 force-displacement transducer and a Grass model 79 polygraph. The Basial atrial rate f or control atria (as determined by counting the frequency of contractions) was 258.+-.7 bpm (n=29). Basal developed force of the spontaneously beating right atria was 0.33.+-.0.06 g (n=10) . Dose-response curves for the peptides were obtained by cumulative addition of the respective peptides. Drug dose is calculated on the basis of the final concentration in the bath solution.

Intracellular free calcium concentration was measured using the fluorescent dye FURA-2 according to the method of Grynkiewicz et al., J. Biol. Chem., 260, 3440 (1985) and Pang et al., P. N. A. S. (USA), 87, 623 (1990). UMR-106 rat osteosarcoma cells (ATCC CRL-1661) are incubated in 1-10 .mu.M FURA-2 AM (Sigma Chemical Co., St. Louis), the acetomethoxy ester of FURA-2. Upon hydrolysis within the cell, FURA-2 is released which selectively binds to free Ca.sup.2+. Binding to Ca.sup.2+ shifts the fluorescent spectrum of FURA-2. Quantitation is obtained by exciting the dye at two different wavelengths, preferably 340 and 380 nm and measuring the fluorescent emission at 510 nm. The concentration of calcium is proportional to the ratio of the fluorescence emitted at 340 nm to that at 380 nm.

KCl is used in the medium to stimulate (Ca.sup.2+ ].sub.i increase.

After the intracellular (Ca.sup.2+ ].sub.i had been measured, the cells were washed with the original medium and the analogues added and the intracellular (Ca.sup.2+ ].sub.i measured again. KCl was then added without washing to measure the effect of the analogue on KCl induced [Ca.sup.2+ ].sub.i changes. After measurement, the cells were washed with the medium 3-4 times and KCl again added to determine the recovery of the cells after removal of the analogue. Results are shown by actual traces and histograms summarizing the results. As can be seen from FIGS. 14 a-d, PTH inhibits intracellar [Ca.sup.2+ ].sub.i increases as stimulated by KCl and measured by the method. FIGS. 18, 21, 22 and 23 illustrate comparable results for the aa.sup.25,26,27 analogues.

The comparability of the analogues and PTH itself is considered to indicate that the analogues would be as useful as PTH for the treatment of osteoporosis.