Preparation of medicaments for treating asthma using (S)-alpha-fluoromethyl histidine and esters thereof

Abstract: (S)-α-fluoromethylhistidine, a potent, selective, mechanism-based inhibitor of mammalian histidine carboxylase, the enzyme responsible for biosynthesis of histamine in mammals, is useful in the treatment of asthma.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is in the field of medicaments for the treatment of asthma. And more particularly, the present invention is in the field of medicaments for treating asthma with pharmaceutical compounds which prevent or inhibit the basic progress of the disease, as opposed to medicaments, the use of which is merely palliative. Bronchial asthma can occur secondarily to a variety of stimuli. The underlying mechanisms are unknown, but inherited or acquired imbalance of adrenergic and cholinergic control of airways diameter has been implicated. Persons manifesting such imbalance have hyperreactive bronchi and, even without symptoms, bronchoconstriction may be present. Overt asthma attacks may occur when such persons are subjected to various stresses, such as viral respiratory infection, exercise, emotional upset, nonspecific factors, e.g., changes in barometric pressure or temperature, inhalation of cold air or irritants, e.g., gasoline fumes, fresh paint and noxious odors, or cigarette smoke, exposure to specific allergens, and ingestion of aspirin™ or sulfites in sensitive individuals. Psychologic factors may aggravate an asthmatic attack but are not assigned a primary etiologic role. Asthmatic attacks are characterized by narrowing of large and small airways due to spasm of bronchial smooth muscle, edema and inflammation of the bronchial mucosa, and production of tenacious mucus. The role of inflammation in the perpetuation of the abnormal airway responses (late-phase reaction) is only now being appreciated. Mechanisms underlying bronchoconstriction are not well defined. However, an imbalance between β-adrenergic and cholinergic control of airways diameter has been proposed. In turn, the observed abnormalities in adrenergic and cholinergic functions in asthma appear to be controlled by the cyclic 3',5'-adenosine monophosphate (cyclic AMP or cAMP) - cyclic 3',5'-guanosine monophosphate (cyclic GMP or cGMP) systems within various tissues, e.g., mast cells, smooth muscle, and mucus-secreting cells. The intracellular concentration of cAMP is a principal determinant of both smooth muscle relaxation and inhibition of IgE-induced release of several mediators, which cause bronchoconstriction either directly or by cholinergic reflex action and increases exocrine secretion. Antigen challenged allergic sheep are a standard animal model for human asthma, having the capability to measure the immediate bronchoconstriction and the important late phase response. Surprisingly, (S)-α-fluoromethylhistidine, in this model, dosed intravenously or by inhaled aerosol, virtually eliminated the late phase response. Since commonly used antiasthma drugs are active in this model, (S)-α-fluoromethylhistidine is expected to have antiasthma activity in man. BRIEF DESCRIPTION OF THE PRIOR ART Drug treatment for asthma includes oral phosphodiesterase inhibitors, oral and inhaled β-adrenergic agonists, oral and inhaled steroids, and inhaled inhibitors of mediator release. British patent specification No. 2,001,626-A discloses α-halomethyl derivatives of amino acids, including α-fluoromethylhistidine, for use as inhibitors of the activity of histidine decarboxylase. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 depicts in bar chart form, the early and late responses of sheep having antigen-induced bronchoconstriction after treatment with (S)-α-fluoromethylhistidine vs. control. Figs. 2 and 3 depict in bar chart form the data from a sheep model of asthma in which (S)-α-fluoromethylhistidine vs. control was given as an aerosol at 1 mg/kg at either 30 minutes before and 4 h after, or as a single dose at 30 minutes before antigen challenge, showing that the acute response was not affected but the average late response was eliminated. SUMMARY OF THE INVENTION In accordance with the present invention there is provided the use of (S)-α-fluoromethylhistidine or a pharmaceutically acceptable salt or ester thereof, for the preparation of a medicament for treating asthma. A therapeutically effective amount is from 10mg to 2g per day, preferably 50mg to 1g per day. The present invention further provides the use of (S)-α-fluoromethylhistidine or a pharmaceutically acceptable salt or ester thereof, for the preparation of a medicament for reducing or preventing late phase reactions of asthma. A therapeutically effective amount is from 10mg to 2g per day, preferably 50mg to 1g per day. In accordance with the present invention it is further provided that the medicaments described above are in the form of an aerosol. The present invention still further provides the combination of (a) a therapeutically effective amount of (S)-α-fluoromethylhistidine or a pharmaceutically acceptable salt or ester thereof, and (b) an anti-asthma agent selected from the group consisting of β₂-agonists, steroids, inhibitors of mediator release, phosphodiesterase inhibitors, and its use for the preparation of a medicament useful for treating asthma. DETAILED DESCRIPTION OF THE INVENTION (S)-α-fluoromethylhistidine and esters thereof may be represented by the following structural formula: where R is H or a pharmaceutically acceptable ester-forming group. Suitable ester forms will be well-known to, and within the skill of the medicinal chemist. For example, R is preferably C₁₋₄ alkyl. Pharmaceutically acceptable salts of the above compound may also be used in the method of the present invention. These include the acid addition salts of the compound of the formula above as base with a suitable organic or inorganic acid. Preferred inorganic acid salts are hydrohalides, e.g., hydrochlorides, hydroiodides, hydrobromides; the sulfates, and the phosphates. The hydrohalides, and especially the hydrochlorides, are preferred. An especially preferred salt is the hydrochloride hemihydrate salt form, also known as MK-453. (S)-α-fluoromethylhistidine may be prepared in accordance with methods of synthesis well known in the art. For example, the fluorodehydroxylation method in which the α-hydroxymethylhistidine is treated with SF₄ in liquid HF may be used. Details of this method is further described in U.S. Pat. No. 4,325,961. In the present invention it is contemplated that the precise unit dosage form and dosage level depend upon the case history of the individual being treated, and that consequently these will be left to the discretion of the therapist. In general, however the (S)-α-fluoromethylhistidine will produce the desired effect of reducing asthmatic symptoms, especially late phase asthmatic symptoms, when given at from about 0.1 to 25 mg/kg of body weight per day. Preferably, this dosage amount will be in the range of from 0.5 to 15 mg/kg. Expressed in other terms, but reflecting the same dosage levels, the amount administered in a single day will be from 10 mg to 2 g, preferably from 50 mg to 1 g per day. Usually, this total daily dosage will be subdivided and given twice a day (b.i.d.), but other dosing regimens may be employed. The preferred form of delivery, i.e., administration of the (S)-α-fluoromethylhistidine for the treatment of asthma, is in the form of an aerosol, since this form of delivery is best calculated to bring the active agent into direct and most effective contact with the bronchia, where the symptoms of asthma are displayed. However, it is possible to also employ any of the usual pharmaceutical oral forms well known in the art, such tablets, elixirs, and aqueous solutions. Thus, e.g., tablets given 1-3 times per day comprising from about 50 mg to about 1g of (S)-α-fluoromethylhistidine are suitable for human treatment. Sterile solutions for injection comprising from about 50 mg to about 1g of (S)-α-fluoromethylhistidine given 1-3 times daily are also suitable means of delivery. It is contemplated that (S)-α-fluoromethylhistidine may be administered alone as the sole therapeutic agent, or that it may be co-administered with any one or more anti-asthma agents, e.g., LTD₄ antagonists, PAF antagonists, phosphodiesterase inhibitors, β₂-agonists, steroids and inhibitors of mediator release. Co-administration may mean that the two therapeutic agents are physically combined and given together. But, the term "co-administration" also contemplates that the two therapeutic agents may be given together simultaneously in the same dosage form where the two agents are physically intact and discrete, but are found together in that dosage form. Sheep Model of Asthma (I.V.) In this study, carried out in accordance with the protocol of W.M. Abraham, published in W.M. Abraham, Arzneimittelforsching/Drug Research, Vol. 39 (II), No. 10a (1989), pages 1328-1331, 2 iv doses of 30 mg/kg were given at 1/2 h before and 4 h post antigen challenge. There was little or no reduction of the early response, but the late phase was virtually eliminated. The data are shown in Fig. 1 of the drawings wherein MK-453 = (S)-α-Fluoromethylhistidine hydrochloride hemihydrate. Sheep Model of Asthma (Aerosol) When (S)-α-Fluoromethylhistidine was given as an aerosol at 1 mg/kg at either 30 minutes before and 4 h after, or as a single dose at 30 minutes before antigen challenge, the early phase was not affected but the late phase was eliminated. The data are shown in Figs. 2 and 3 of the drawings. The aerosol was formed employing a solution prepared by dissolving (S)-α-fluoromethylhistidine hydrochloride hemihydrate (L-641,575 = MK-453) in sterial H₂O-phosphate buffer at pH 7.3.

Claims: The use of (S)-α-fluoromethylhistidine or a pharmaceutically acceptable salt or ester thereof, for the preparation of a medicament useful for treating asthma. The use as claimed in Claim 1 wherein the medicament is useful for reducing or preventing late phase reactions of asthma. The use as claimed in Claim 1 or Claim 2 wherein the medicament is in the form of an aerosol. The use of a combination of (a) a therapeutically effective amount of (S)-α-fluoromethylhistidine or a pharmaceutically acceptable salt or ester thereof, and (b) an anti-asthma agent selected from the group consisting of phosphodiesterase inhibitors, β₂-agonists, steroids, inhibitors of mediator release, LTD₄ antagonists, and PAF antagonists, for the preparation of a medicament useful for treating asthma. A combination of (a) a therapeutically effective amount of (S)-α-fluoromethylhistidine or a pharmaceutically acceptable salt or ester thereof, and (b) an anti-asthma agent selected from the group consisting of phosphodiesterase inhibitors, β₂-agonists, steroids, inhibitors of mediator release, LTD₄ antagonists, and PAF antagonists.

Inventors: KOLLONITSCH JANOS DR, KOLLONITSCH, JANOS, DR.
Applicants: KOLLONITSCH JANOS DR, KOLLONITSCH, JANOS, DR.
Application year: 1991
Main classification: A61K31
IPC codes: A61P11, A61K9, C07D233, A61K31