Abstract:
This invention relates to a method of treating patients afflicted with osteoporosis. The method includes administering to a patient in need of treatment an effective amount of a thiol or reducible disulfide compound according to the formula set forth in the specification.

Description:
FIELD OF THE INVENTION 
     This invention relates to a method for reducing or preventing osteoporosis in patients at risk. The method involves administering an effective amount of a disulfide or thiol-containing compound to a patient at risk of developing osteoporosis. 
     BACKGROUND OF THE INVENTION 
     Osteoporosis is by definition a loss of bone material, and results in a progressive weakening of bones. It predominantly occurs in post-menopausal women, but there are numerous other factors that can mediate the loss of bone tissue, in both men and women. The exact cause of the disease is not clear and is thought to be multifaceted. 
     Current treatments for both regression and prevention of osteoporosis include calcium and hormonal therapy, as well as administration of hormonal blockers. Many of these treatments involve highly undesirable side effects, namely increased risk of certain cancers, dyspnea, venous thrombosis, hot flashes, night sweats, leg cramps, and others. Many of these treatments are not indicated for premenopausal women. 
     Mesna (sodium 2-mercaptoethene sulfonate) and dimesna (disodium 2,2′-dithiobis ethane sulfonate) are known therapeutic compounds that have heretofore demonstrated a wide variety of therapeutic uses. Both mesna and dimesna have been shown to be effective protective agents against certain specific types of toxicity associated with the administration of cytotoxic drugs used to treat patients for various types of cancer. 
     In particular, mesna has been used with some success in mitigating the toxic effects of cytotoxic agents such as ifosfamide, oxazaphosphorine, melphalane, cyclophosphamide, trofosfamide, sulfosfamide, chlorambucil, busulfan, triethylene thiophosphamide, triaziquone, and others, as disclosed in U.S. Pat. No. 4,220,660, issued Sep. 2, 1980. 
     The near absence of toxicity of dimesna further underscores the usefulness of this compound, as large doses can be given to a patient without increasing the risk of adverse effects from the protective agent itself. 
     Further, pharmacological profiles of each compound indicate that, if proper conditions are maintained, mesna and dimesna do not prematurely inactivate primary therapeutic drugs to a significant degree. Thus, neither compound will significantly reduce activity of the chemotherapeutic agent, and in many cases, act to potentiate the effect of the main drug on targeted cancer cells. 
     The structures of both mesna and dimesna are shown below as Formula I and Formula II respectively. 
     
       
         HS—CH 2 —CH 2 —SO 3 Na  (I) 
       
     
     
       
         NaO 3 S—CH 2 —CH 2 —S—S—CH 2 —CH 2 —SO 3 Na  (II) 
       
     
     As is well known, dimesna is a dimer of mesna, with the optimum conditions for oxidation occurring in the slightly basic (pH ˜7.3), oxygen rich environment found in blood plasma. In mildly acidic, low oxygen conditions, in the presence of a reducing agent such as glutathione reductase, conditions prevalent in the kidneys, the primary constituent is mesna. 
     Mesna acts as a protective agent for a number of cytotoxic agents by substituting a nontoxic sulfhydryl moiety for a toxic hydroxy (or aquo) moiety. This action is particularly evidenced in the coadministration of mesna and oxazaphosphorine, and in the administration of dimesna along with cisplatin or carboplatin. 
     Mesna and dimesna, as well as some analogues of these compounds, have excellent toxicity profiles in mammalian species. In fact, dimesna has been administered intravenously to mice and dogs in doses higher than the accepted oral LD 50  for common table salt (3750 mg/kg), with no adverse effects. Dimesna has also been administered to humans in doses exceeding 40 g/m 2 , with no adverse effects. 
     Mesna, and other analogues with free thiol moieties, constitute the more physiologically active form of the two types of compounds described in this specification. These compounds manifest their activity by providing free thiol moieties for terminal substitution at locations where a terminal leaving group of appropriate configuration is located. 
     Dimesna and other disulfides can be activated intracellularly by glutathione reductase, a ubiquitous enzyme, thereby generating high concentrations of intracellular free thiols. These free thiols act to scavenge the free radicals and other nucleophilic compounds often responsible for causing cell damage. 
     This profile is especially significant in explaining the success of dimesna in controlling and mitigating the toxic effects of platinum complex antitumor drugs. The mechanism for action in the case of cisplatin (cis-diammine dichloro platinum) is explained in U.S. Pat. No. 5,789,000, which is incorporated herein by reference. 
     Mesna, dimesna, and analogues of these compounds have been the subject of several prior pharmaceutical uses described in the literature and in prior patents, both in the United States and around the world. In addition to the cytotoxic agent protection uses, one or more of these compounds have proven effective, in vitro, against a multiplicity of biological targets, and have been effective, in vivo, in the treatment of sickle cell disease, radiation exposure, chemical agent exposure, and other uses. 
     Mesna, dimesna, and analogues thereof are synthesized from commonly available starting materials, using acceptable routes well known in the art. One such method involves the two-step, single pot synthetic process for making dimesna and like compounds of the following formula: 
     
       
         R 1 —S—R 2 ; 
       
     
     wherein: 
     R 1  is hydrogen, X-lower alkyl, or X-lower alkyl-R 3 ; 
     R 2  is -lower alkyl-R 4 ; 
     R 3  and R 4  are each individually SO 3 M or PO 3 M 2 ; 
     X is absent or X is sulfur; and 
     M is an alkali metal. 
     The process essentially involves a one or two step single pot synthetic process that results in the conversion of an alkenyl sulfonate salt or acid to the desired formula I compound. The process in the case of mesna is a single step process that converts the alkenyl sulfonate salt to mesna or a mesna derivative by reacting with an alkali metal sulfide or with hydrogen sulfide. 
     If the desired end product is dimesna or a dimesna analogue, a two-step single pot process is involved. Step 1 is as described above. Step 2 of the process is performed in the same reaction vessel as Step 1 without the need to purify or isolate the mesna formed during that step. Step 2 includes the introduction of oxygen gas into the vessel, along with an increase in pressure and temperature above ambient values, at least 20 pounds per square inch (psi) and at least 60° C. Dimesna or a derivative thereof is formed in essentially quantitative yield. 
     Other processes, well known and documented in the prior art, may be employed to make either mesna or dimesna, or derivatives and analogues thereof. 
     SUMMARY OF THE INVENTION 
     This invention involves the administration of an effective amount of compounds of formula I, below, for treating patients suffering from osteoporosis.                           
     wherein: 
     R 1  is hydrogen, lower alkyl or                           
     R 2  and R 4  are each individually SO 3   − M + , PO 3   2− M 2   2+ , or PO 2 S 2− M 2   2+ ; 
     R 3  and R 5  are each individually hydrogen, hydroxy or sulfhydryl; 
     m and n are individually 0, 1, 2, 3 or 4, with the proviso that if m or n is 0, then R 3  is hydrogen; and 
     M is hydrogen or an alkali metal ion; or 
     a pharmaceutically acceptable salt thereof. 
     Effective amounts of the formula I compounds to be administered according to the method of this invention vary, and depend on the severity of the patient&#39;s risk of developing osteoporosis. 
     Accordingly, it is an object of this invention to provide for a method of safely and effectively reducing the occurrence of or preventing osteoporosis. 
     Other objects will become apparent upon a reading of the following description. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The preferred embodiments herein described are not intended to be exhaustive nor to limit the invention to the precise form disclosed. They are chosen and described to explain the principles of the invention, and its application and practical use to best enable others skilled in the art to follow its teachings. 
     The method of this invention involves the administration of an effective amount of a formula I compound to a patient at risk of developing osteoporosis. Administration may be either oral or parenteral. 
     The effective amount of the formula I compound will necessarily depend upon the severity of the risk of the patient&#39;s developing osteoporosis or the severity of the condition if the patient ahs already been diagnosed. Since the formula I compounds are essentially nontoxic, large amounts can be safely administered. 
     The preferred dosage to reduce the risk osteoporosis may be as low as 0.1 mg/kg up to 1,000 mg/kg. The more severe the risk of disease or occurrence thereof, the more formula I compound should be administered to provide an effective response. The patient at risk should replenish the plasma supply of formula I compound frequently to obtain maximum benefits of the agent. 
     Administration is preferably through parenteral or oral routes, most preferably oral. For parenteral administration, the formula I compound is dissolved in a suitable solvent, most preferably water, to produce a solution that may be injected or infused. One or more pharmaceutically acceptable excipients may also be added to provide for an elegant formulation. 
     For oral administration, the formula I compound is preferably combined with one or more pharmaceutically acceptable excipients, fillers and/or diluents. Oral dosage forms may include pills, caplets, tablets, and others. Alternatively, the formula I compound may be contained in a swallowable container such as a gelatin capsule or the like. 
     Administration of the formula I compound should be prescribed as soon as possible after determining the patient&#39;s risk of developing osteoporosis or as soon after diagnosis as possible. Preferred initial dose is between 20 mg/kg and 500 mg/kg per day, usually in split or multiple doses. Persons with the highest risk of developing osteoporosis are those who spend large amounts of time exposed to the rays of the sun. 
     Other accepted methods for preventing or treating osteoporosis may also be combined with the administration of the formula I compound. Due to the excellent safety profile and the rapid clearance rate, additional doses of the formula I compound may be administered with relative safety. 
     It is understood that the above description is in no way limiting of the invention, which may be modified within the scope of the following claims.