IC50: angiotensin converting enzyme[1]

Spirapril is a non-sulfhydryl angiotensin converting enzyme (ACE) inhibitor pro-drug which is converted to the active metabolite spiraprilat following oral administration, and which has been evaluated primarily for the treatment of hypertension.

In TGM123 mice, spirapril (feeding needle; 10 mg/kg; 3 weeks) reduces alcohol consumption; in TLM mice, it does not. In the brain membranes of treated mice, ACE activity is reduced by 40.2% when treated with spiracillin. In the experiments, it reduces the transgenic effect and passes the blood-brain barrier.[2] In spontaneously hypertensive rats, spiropril can inhibit left ventricular hypertrophy, lessen myocardial damage, and stimulate angiogenesis [3].

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Pharmacodynamic Properties [1]
Spirapril is a prodrug which, when metabolised to its active diacid form spiraprilat, has potent activity against angiotensin converting enzyme (ACE). Inhibition of plasma ACE activity by spirapril has been demonstrated in numerous animal models, through direct measurement of ACE activity or by attenuation of angiotensin I-induced pressor responses. In patients with hypertension, oral spirapril produced short term (measured at 1 or 4 hours) inhibition of plasma ACE activity of between 75 and ≥90%, while longer term assessment (up to 6 months) yielded reductions in ACE activity of between 33 and 86%.
Significant reductions in blood pressure have been achieved with spirapril in numerous clinical trials involving patients with hypertension (see Therapeutic Efficacy section). In addition, spirapril produced reductions in vascular resistance in patients with hypertension or congestive heart failure. Reductions of ≈8 to 17% in a number of structural parameters associated with left ventricular (LV) hypertrophy (posterior wall thickness, LV mass and interventricular septal wall thickness) have been reported for spirapril in humans, confirming favourable findings from animal models of this condition. Limited results suggest that spirapril exerts much of its positive effect on LV hypertrophy by significantly reducing thickening of the LV posterior wall.
In volunteers or patients with normal renal function, spirapril appears to have no significant adverse effects on glomerular filtration rate or renal blood flow. However, the effects of spirapril in patients with renal impairment have yet to be fully characterised, since existing data for this indication are limited and contradictory.

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Therapeutic Efficacy [1]
In several dose-finding studies, spirapril doses of between 6 and 24mg once daily had similar efficacy in reducing blood pressure in patients with mild to severe hypertension. Blood pressure normalisation (24-hour postdose trough reading <90mm Hg at the end of the treatment period) was observed in 29 to 50% of patients in these trials, while approximate mean reductions in trough systolic and diastolic blood pressure at study endpoints were 10 to 18mm Hg and 7 to 13mm Hg, respectively. Spirapril doses of <6mg once daily were generally less effective than higher doses, producing blood pressure normalisation in about 12% of patients and mean reductions in systolic and diastolic blood pressure of approximately 4 to 9mm Hg and 3 to 7mm Hg, respectively. When compared with blood pressure normalisation in 15 and 22% of patients with placebo, spirapril 6 to 24mg once daily yielded normalisation in 35 to 50% of patients.
Results from several clinical studies comparing spirapril with other antihypertensive agents are available, although direct comparisons with other ACE inhibitors are limited in number. Spirapril produced reductions in blood pressure similar to those seen with enalapril (18/17 vs 19/14mm Hg; n = 201) or captopril (10/10 vs 9/9mm Hg; n = 169) in well-controlled studies. Spirapril 12 to 24mg once daily produced a significantly higher rate of blood pressure normalisation (37%) than the calcium antagonist nitrendipine 20 to 40mg once daily (24%) in 213 patients with moderate to severe hypertension who were treated for 8 weeks.
Spirapril 3 to 6mg once daily was effective in reducing hypertension in elderly patients and appeared to have similar efficacy to isradipine in a single comparative study in this indication. Isolated reports of similar antihypertensive efficacy to that seen with isradipine in patients with diabetic nephropathy, and superior efficacy over atenolol, hydrochlorothiazide and isradipine in patients with sleep apnoea require confirmation.

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Dosage and Administration [1]
Clinical trial data suggest that an oral spirapril dosage of 6mg once daily is as effective as higher dosages in reducing blood pressure in patients with hypertension. In elderly patients, spirapril 3 to 6mg once daily has demonstrated significant antihypertensive efficacy. Results from patients with renal impairment [creatinine clearance (CLCR) <80 ml/min] indicate that dosage adjustment is not necessary in this context, in contrast to most other ACE inhibitors. However, spirapril should not be used in patients with severe renal failure (CLCR <30 ml/min), given the absence of definitive information regarding its effects on renal function.

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To test whether angiotensin-converting enzyme (ACE) inhibition may prevent myocardial damage and may affect coronary microvasculature in spontaneously hypertensive rats (SHR), young 5-week-old SHR were treated for 3 months with spirapril and changes in blood pressure (BP) were monitored. Untreated SHR were used as controls. The rats were killed; left ventricular (LV) shape, weight, and wall thickness were examined and the ventricular myocardium was analyzed mor-phometrically to determine the effect of the drug on the relative amount, number per unit area of myocardium, and average dimension of foci of myocardial scarring. Moreover, volume fraction, surface, numerical density, and diffusion distance for oxygen of the coronary capillaries were analyzed. BP remained 20–30% lower in treated SHR with respect to controls, and LV weight and thickness decreased 20 and 21%, respectively. The number and dimension of the foci of fibrosis were reduced, resulting in an overall 68% decrement in the amount of myocardial damage. Finally, a 28% increment in numerical density of capillary profiles associated with a 13% reduction in their cross-sectional area decreased the diffusion distance for oxygen from the capillary wall to the myocytes by 14% in treated SHR. Spirapril decreases BP and LV weight and thickness in the SHR model of hypertension and substantially improves coronary capillary microvasculature, decreasing hypertensive myocardial damage. These results may be attributed to inhibition of the systemic effects of angiotensin II (All) as well as to a local protective action of the drug against possible in-tramyocardial All production. [3]

Animal/Disease Models: TGM123 mice (expressing a rat angiotensinogen transgene) and TLM (deficient the angiotensinogen gene) mice[2]
Doses: 10 mg/kg
Route of Administration: Feeding needle ; 10 mg/kg; 3 weeks
Experimental Results: Alter voluntary alcohol consumption in animals. Crossed the blood-brain barrier and may influence alcohol consumption mainly by decreasing central angiotensin II (AII) levels.

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After a 3-wk period of treatment with spinapril at 10 mg/kg of body weight, the animals were killed by decapitation. The brains were rapidly removed and stored until use at −80°C. Membranes were prepared according to the method of Hulme and Buckley and were stored until use at −80°C in a 50 mM Tris buffer containing 320 mM sucrose. ACE activity was measured via a modified fluorimetric method originally developed by Friedland and Silverstein. In brief, 10 μl of a membrane preparation was incubated for 30 min with 10 μl of 0.025 M hippuryl-histidyl-leucine as substrate in a chloride-containing phosphate buffer at pH 8.3. The reaction was stopped by addition of 1 ml of 0.4 M sodium hydroxide; fluorescence was developed by a reaction of the produced histidyl-leucine with 100 μl of 2% o-phthalaldehyde in methanolic solution. After acidification with 3 M hydrochloric acid and excitement at 365 nm, the fluorescence was measured at 500 nm. We used histidyl-leucine as a standard. Controls of specificity were carried out with 10−6 M of the specific ACE inhibitor lisinopril. The total protein contents of the membrane preparations were determined by a Bradford assay. Statistical calculations were done by applying a t test.

Absorption, Distribution and Excretion
Bioavailability after oral administration is 50%.

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Metabolism/Metabolites
Hepatic metabolism. It is converted to spiroprilat after oral administration.

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Biological Half-Life
30 to 35 hours Pharmacokinetic Characteristics [1]
The mean bioavailability of spiroprilat after oral administration is 50%. Spiraprilat is rapidly converted to its active diacid metabolite, and the maximum plasma concentration (Cmax) of spiroprilat is reached 1.8 to 3.0 hours after oral administration. Spiraprilat is distributed in plasma in a biphasic manner, with an initial phase half-life of 1.5 to 2.2 hours. Spiraprilat binds to angiotensin-converting enzyme (ACE) with a high affinity, resulting in a typical terminal elimination half-life of approximately 30 to 40 hours. Spiraprilat is eliminated primarily through renal and non-renal (hepatic) pathways. No clinically significant accumulation (measured by plasma trough concentration 24 hours after administration) was observed in patients with renal failure after administration of spicalilata, therefore no dose adjustment was required. The pharmacokinetics of spicalilata were altered in elderly patients (with a 30% increase in area under the concentration-time curve (AUC) and Cmax) and in patients with hepatic disease (with a 30% decrease in AUC).

Tolerability [1]
Tolerability of spiropril is generally similar to that of other ACE inhibitors, with the most common adverse events reported in dose-exploration and comparative trials being dizziness (up to 10.7%), headache (up to 13.1%), and fatigue (1.8% to 6.0%) [total n=736]. The incidence of these events in the spiropril and placebo groups was generally similar to that of other common adverse events of other ACE inhibitors. In the few studies that provided cough information, the incidence of cough caused by spiropril (0% to about 4%) appeared to be lower than the reported values of other members of this class of drugs (typical range 1% to 10%, peak incidence between 15% and 25%), but this finding needs to be confirmed by direct prospective comparisons with other ACE inhibitors. No first-dose hypotension has been reported in spiropril studies. In the few direct clinical comparative studies published to date, the incidence of adverse events or patient dropout rates of spiropril was similar to that of captopril, but lower than that of enalapril or nifedipine.

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5311447 Rats, oral LD50 >2500 mg/kg, Toxicologist, 5(98), 1985
5311447 Rats, intraperitoneal LD50 600 mg/kg, Toxicologist, 5(98), 1985
5311447 Mice, oral LD50 >2500 mg/kg, Toxicologist, 5(98), 1985
5311447 Mice, intraperitoneal LD50 400 mg/kg, Toxicologist, 5(98), 1985

[1]. Noble S, Sorkin EM. Spirapril. A preliminary review of its pharmacology and therapeutic efficacy in the treatment of hypertension. Drugs. 1995 May;49(5):750-66.

[2]. Alcohol consumption is controlled by angiotensin II. FASEB J. 2001 Jul;15(9):1640-2.

[3]. Spirapril prevents left ventricular hypertrophy, decreases myocardial damage and promotes angiogenesis in spontaneously hypertensive rats. J Cardiovasc Pharmacol. 1993 Mar;21(3):362-70.

Spirapril hydrochloride is the hydrochloride salt form of spirochene, a prodrug and a non-sulfhydryl angiotensin-converting enzyme (ACE) inhibitor with antihypertensive activity. Spirapril is converted in vivo to its active metabolite, spiroprilat. Spirapril competitively binds to and inhibits ACE, thereby blocking the conversion of angiotensin I to angiotensin II. This prevents the potent vasoconstriction of angiotensin II, leading to vasodilation. Spirapril also reduces adrenal cortex aldosterone secretion for angiotensin II, thereby increasing sodium excretion and consequently increasing water excretion.
See also: Spirapril (its salt form).

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Spiral is a dipeptide, dithioketal, azaspirocyclic compound, dicarboxylic acid monoester, ethyl ester, tertiary amide, secondary amino compound, and pyrrolidine carboxylic acid. It is a prodrug, EC 3.4.15.1 (peptidyl dipeptidase A) inhibitor, and antihypertensive drug. It is functionally related to spiroprilat.
Solapril is an ACE inhibitor used to treat hypertension. After administration, spironolactone is converted to its active form, spironolactone. Angiotensin-converting enzyme inhibitors are primarily used to treat hypertension and congestive heart failure.
Solapril is a prodrug and a non-sulfhydryl angiotensin-converting enzyme (ACE) inhibitor with antihypertensive effects. In the body, spironolactone is converted to its active metabolite, spironolactone. Spiroprilactone competitively binds to and inhibits ACE, thereby blocking the conversion of angiotensin I to angiotensin II. This prevents the potent vasoconstriction of angiotensin II, leading to vasodilation. Spiroprilactone also reduces adrenal cortex aldosterone secretion for angiotensin II, thereby increasing sodium excretion and consequently increasing water excretion.
Drug Indications

Solapril is an angiotensin-converting enzyme inhibitor (ACE inhibitor) used to treat hypertension.
Mechanism of Action Spirapril is the active metabolite of spironolactone. It competitively binds to angiotensin-converting enzyme (ACE) with angiotensin I, thereby blocking the conversion of angiotensin I to angiotensin II. Inhibition of ACE leads to a decrease in plasma angiotensin II levels. Since angiotensin II is a vasoconstrictor and a negative feedback regulator of renin activity, its reduced concentration leads to a drop in blood pressure and stimulates the baroreceptor reflex mechanism, thereby reducing vasopressor activity and aldosterone secretion. Spirapril may also act on kallikrein II, an enzyme identical to angiotensin-converting enzyme (ACE) that degrades the vasodilator bradykinin. Pharmacodynamics Spirapril is an angiotensin-converting enzyme (ACE) inhibitor. ACE is a peptidyl dipeptidase that catalyzes the conversion of angiotensin I to the vasoconstrictor angiotensin II. Spirapril reduces angiotensin II levels by blocking ACE, and angiotensin II is a vasoconstrictor and aldosterone inducer. Therefore, by inhibiting these enzymes, aldosterone secretion decreases (thus reducing sodium reabsorption), and the vasoconstrictive effect is also weakened. Taken together, this leads to a decrease in blood pressure.

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Spiralepide is a non-sulfhydryl angiotensin-converting enzyme (ACE) inhibitor prodrug that is converted to its active metabolite, spiropira, after oral administration and is primarily used to treat hypertension. In dose-exploration studies in patients with mild to severe hypertension, once-daily administration of ≥6 mg of spiropide resulted in a reduction in blood pressure of approximately 10 to 18 mmHg (systolic) and 7 to 13 mmHg (diastolic) [trough reading 24 hours after administration at the end of treatment]. At the end of these studies, 29% to 50% of patients had their blood pressure returned to normal (trough diastolic blood pressure ≤90 mmHg). The dose-response curve for spiropide appears relatively flat in the once-daily dose range of 6 to 24 mg. The number of comparative studies with other ACE inhibitors is limited, and more research is needed before a comprehensive evaluation of the relative antihypertensive efficacy of spiropide can be achieved. However, in single, well-controlled clinical trials, spironolactone has similar blood pressure-lowering effects to enalapril or captopril. When used as monotherapy or in combination with hydrochlorothiazide, spironolactone may be more advantageous than the calcium channel blocker nifedipine. Spiropril is generally well-tolerated, with adverse reactions similar to other ACE inhibitors. Data from small studies suggest that spironolactone can be used in patients with renal impairment without dose adjustment due to its dual renal and hepatic clearance mechanism. This is unlike most ACE inhibitors, which are primarily cleared by the kidneys, leading to the accumulation of active metabolites in patients with impaired renal function. However, its value in patients with renal impairment is not fully established due to controversial data on the effects of spironolactone on renal function. Therefore, spironolactone is a highly effective and well-tolerated antihypertensive drug. More comparative trials are needed to fully determine its efficacy compared to other ACE inhibitors and to better understand its effects on renal function, which will help clarify its role in hypertensive patients with renal failure. [1]

C22H31CLN2O5S2

503.07

502.136

C, 52.53; H, 6.21; Cl, 7.05; N, 5.57; O, 15.90; S, 12.75

94841-17-5

Spirapril;83647-97-6; Spirapril hydrochloride;94841-17-5; 200872-06-6 (HCl hydrate)

6850814

White to off-white solid powder

697.8ºC at 760mmHg

192-194ºC (dec.)

375.8ºC

3.521

3

8

10

32

650

3

CCOC(=O)[C@H](CCC1=CC=CC=C1)N[C@@H](C)C(=O)N2CC3(C[C@H]2C(=O)O)SCCS3.Cl

CLDOLNORSLLQDI-OOAIBONUSA-N

InChI=1S/C22H30N2O5S2.ClH/c1-3-29-21(28)17(10-9-16-7-5-4-6-8-16)23-15(2)19(25)24-14-22(30-11-12-31-22)13-18(24)20(26)27;/h4-8,15,17-18,23H,3,9-14H2,1-2H3,(H,26,27);1H/t15-,17-,18-;/m0./s1

(8S)-7-[(2S)-2-[[(2S)-1-ethoxy-1-oxo-4-phenylbutan-2-yl]amino]propanoyl]-1,4-dithia-7-azaspiro[4.4]nonane-8-carboxylic acid;hydrochloride

Spirapril hydrochloride; 94841-17-5; Spirapril HCl; Spirapril hydrochloride [USAN]; Sch 33844;

2934.99.9001

Powder      -20°C    3 years

                     4°C     2 years

In solvent   -80°C    6 months

                  -20°C    1 month

Note: Please store this product in a sealed and protected environment, avoid exposure to moisture.

Room temperature (This product is stable at ambient temperature for a few days during ordinary shipping and time spent in Customs)

DMSO: 100 mg/mL (198.78 mM)

Note: Listed below are some common formulations that may be used to formulate products with low water solubility (e.g. < 1 mg/mL), you may test these formulations using a minute amount of products to avoid loss of samples.

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Injection Formulation 1: DMSO : Tween 80： Saline = 10 : 5 : 85 (i.e. 100 μL DMSO stock solution → 50 μL Tween 80 → 850 μL Saline)
*Preparation of saline: Dissolve 0.9 g of sodium chloride in 100 mL ddH ₂ O to obtain a clear solution.
Injection Formulation 2: DMSO : PEG300 ：Tween 80 : Saline = 10 : 40 : 5 : 45 (i.e. 100 μL DMSO → 400 μLPEG300 → 50 μL Tween 80 → 450 μL Saline)
Injection Formulation 3: DMSO : Corn oil = 10 : 90 (i.e. 100 μL DMSO → 900 μL Corn oil)
Example: Take the Injection Formulation 3 (DMSO : Corn oil = 10 : 90) as an example, if 1 mL of 2.5 mg/mL working solution is to be prepared, you can take 100 μL 25 mg/mL DMSO stock solution and add to 900 μL corn oil, mix well to obtain a clear or suspension solution (2.5 mg/mL, ready for use in animals).

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Injection Formulation 4: DMSO : 20% SBE-β-CD in saline = 10 : 90 [i.e. 100 μL DMSO → 900 μL (20% SBE-β-CD in saline)]
*Preparation of 20% SBE-β-CD in Saline (4°C，1 week): Dissolve 2 g SBE-β-CD in 10 mL saline to obtain a clear solution.
Injection Formulation 5: 2-Hydroxypropyl-β-cyclodextrin : Saline = 50 : 50 (i.e. 500 μL 2-Hydroxypropyl-β-cyclodextrin → 500 μL Saline)
Injection Formulation 6: DMSO : PEG300 : castor oil : Saline = 5 : 10 : 20 : 65 (i.e. 50 μL DMSO → 100 μLPEG300 → 200 μL castor oil → 650 μL Saline)
Injection Formulation 7: Ethanol : Cremophor : Saline = 10： 10 : 80 (i.e. 100 μL Ethanol → 100 μL Cremophor → 800 μL Saline)
Injection Formulation 8: Dissolve in Cremophor/Ethanol (50 : 50), then diluted by Saline
Injection Formulation 9: EtOH : Corn oil = 10 : 90 (i.e. 100 μL EtOH → 900 μL Corn oil)
Injection Formulation 10: EtOH : PEG300：Tween 80 : Saline = 10 : 40 : 5 : 45 (i.e. 100 μL EtOH → 400 μLPEG300 → 50 μL Tween 80 → 450 μL Saline)

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Oral Formulation 1: Suspend in 0.5% CMC Na (carboxymethylcellulose sodium)
Oral Formulation 2: Suspend in 0.5% Carboxymethyl cellulose
Example: Take the Oral Formulation 1 (Suspend in 0.5% CMC Na) as an example, if 100 mL of 2.5 mg/mL working solution is to be prepared, you can first prepare 0.5% CMC Na solution by measuring 0.5 g CMC Na and dissolve it in 100 mL ddH2O to obtain a clear solution; then add 250 mg of the product to 100 mL 0.5% CMC Na solution, to make the suspension solution (2.5 mg/mL, ready for use in animals).

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Oral Formulation 3: Dissolved in PEG400
Oral Formulation 4: Suspend in 0.2% Carboxymethyl cellulose
Oral Formulation 5: Dissolve in 0.25% Tween 80 and 0.5% Carboxymethyl cellulose
Oral Formulation 6: Mixing with food powders

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Note: Please be aware that the above formulations are for reference only. InvivoChem strongly recommends customers to read literature methods/protocols carefully before determining which formulation you should use for in vivo studies, as different compounds have different solubility properties and have to be formulated differently.

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 (Please use freshly prepared in vivo formulations for optimal results.)