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].

---

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.

---

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.

---

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.

---

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.

---

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 is 50% following oral administration.

---

Metabolism / Metabolites
Hepatic. Converted to spiraprilat following oral administration.

---

Biological Half-Life
30 to 35 hours

---

Pharmacokinetic Properties [1]
Following oral administration, the mean bioavailability of spirapril is 50%. Conversion of spirapril to its active diacid metabolite occurs rapidly, with maximum plasma concentrations (Cmax) of spiraprilat reached 1.8 to 3.0 hours after an oral spirapril dose. The disposition of spiraprilat in plasma is biphasic, with an initial phase half-life of 1.5 to 2.2 hours. High affinity binding of spiraprilat to ACE is responsible for a typical terminal elimination half-life of ~t30 to 40 hours. Elimination of spiraprilat occurs by both renal and nonrenal (hepatic) mechanisms. Spiraprilat does not exhibit any clinically significant accumulation (as measured by trough plasma concentrations 24 hours postdose) in patients with renal failure and dosage adjustment is not required. The pharmacokinetics of spiraprilat are altered in the elderly [30% increase in area under the concentration-time curve (AUC) and Cmax] and in patients with liver disease (30% decrease in AUC).

Tolerability [1]
Spirapril has a tolerability profile which is broadly similar to that of other ACE inhibitors, the most common adverse events reported in dose-finding and comparative trials being dizziness (up to 10.7%), headache (up to 13.1%) and fatigue (1.8 to 6.0%) [pooled n = 736]. The rates of these events, and of others commonly reported with ACE inhibitors, were generally similar for spirapril and placebo. The incidence of cough with spirapril (0 to ~t4%) in the few studies which provided this information appeared to be lower than values reported for other members of this drug class (typical range 1 to 10%, with peak incidences of between 15 and 25%), although direct prospective comparisons with other ACE inhibitors are required to confirm this finding. First-dose hypotension has not been reported in studies of spirapril. In the few direct clinical comparisons published to date, rates for adverse events or patient withdrawals with spirapril were similar to those with captopril and lower than those with enalapril or nitrendipine.

---

5311447 rat LD50 oral >2500 mg/kg Toxicologist., 5(98), 1985
5311447 rat LD50 intraperitoneal 600 mg/kg Toxicologist., 5(98), 1985
5311447 mouse LD50 oral >2500 mg/kg Toxicologist., 5(98), 1985
5311447 mouse LD50 intraperitoneal 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 spirapril, a prodrug and non-sulfhydryl angiotensin converting enzyme (ACE) inhibitor with antihypertensive activity. Spirapril is converted in the body to its active metabolite spiraprilat. Spiraprilat competitively binds to and inhibits ACE, thereby blocking the conversion of angiotensin I to angiotensin II. This prevents the potent vasoconstrictive actions of angiotensin II and results in vasodilation. Spirapril also decreases angiotensin II-induced aldosterone secretion by the adrenal cortex, which leads to an increase in sodium excretion and subsequently increases water outflow.
See also: Spirapril (is salt form of).

---

Spirapril is a dipeptide, a dithioketal, an azaspiro compound, a dicarboxylic acid monoester, an ethyl ester, a tertiary carboxamide, a secondary amino compound and a pyrrolidinecarboxylic acid. It has a role as a prodrug, an EC 3.4.15.1 (peptidyl-dipeptidase A) inhibitor and an antihypertensive agent. It is functionally related to a spiraprilat.
Spirapril is an ACE inhibitor antihypertensive drug used to treat hypertension. Spirapril is converted to the active spiraprilat after administration. ACE inhibitors are used primarily in treatment of hypertension and congestive heart failure.
Spirapril is a prodrug and non-sulfhydryl angiotensin converting enzyme (ACE) inhibitor with antihypertensive activity. Spirapril is converted in the body to its active metabolite spiraprilat. Spiraprilat competitively binds to and inhibits ACE, thereby blocking the conversion of angiotensin I to angiotensin II. This prevents the potent vasoconstrictive actions of angiotensin II and results in vasodilation. Spiraprilat also decreases angiotensin II-induced aldosterone secretion by the adrenal cortex, which leads to an increase in sodium excretion and subsequently increases water outflow.

---

Drug Indication
Spirapril is an ACE inhibitor class drug used to treat hypertension.

---

Mechanism of Action
Spiraprilat, the active metabolite of spirapril, competes with angiotensin I for binding at the angiotensin-converting enzyme, blocking the conversion of angiotensin I to angiotensin II. Inhibition of ACE results in decreased plasma angiotensin II. As angiotensin II is a vasoconstrictor and a negative-feedback mediator for renin activity, lower concentrations result in a decrease in blood pressure and stimulation of baroreceptor reflex mechanisms, which leads to decreased vasopressor activity and to decreased aldosterone secretion. Spiraprilat may also act on kininase II, an enzyme identical to 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 substance, angiotensin II. By blocking ACE, spirapril decreases angiotensin II which is a vasoconstrictor and inducer of aldosterone. So by inhibiting the enzymes, aldosterone secreation is decreased (so less sodium is reabsorbed) and there is a decrease in vasoconstriction. Combined, this leades to a decrease in blood pressure.

---

Spirapril is a non-sulfhydryl angiotensin converting enzyme (ACE) inhibitor prodrug which is converted to the active metabolite spiraprilat following oral administration, and which has been evaluated primarily for the treatment of hypertension. In dose-finding studies of patients with mild to severe hypertension, spirapril > or = 6 mg once daily produced reductions in blood pressure of approximately 10 to 18 mm Hg (systolic) and 7 to 13 mm Hg (diastolic) [24-hour postdose trough readings at the end of the treatment period]. Blood pressure normalisation (trough diastolic blood pressure < or = 90 mm Hg) had occurred in 29 to 50% of patients at the end of these investigations. The dose-response curve for spirapril appears to be flat for doses of 6 to 24 mg once daily. Comparisons with other ACE inhibitors are limited in number, and further studies are required before the relative antihypertensive efficacy of spirapril can be fully evaluated. However, in single, well controlled clinical trials, spirapril produced similar reductions in blood pressure to those seen with enalapril or captopril. When given as monotherapy or in combination with hydrochlorothiazide, spirapril may offer potential advantages over the calcium antagonist nitrendipine. Spirapril is generally well tolerated and produces an adverse event profile similar to that of other ACE inhibitors. Data from small studies suggest that spirapril can be used without dosage adjustment in patients with renal impairment, as a consequence of its dual renal and hepatic clearance mechanisms. This is in contrast to most ACE inhibitors, which are eliminated by a predominantly renal mechanism that results in accumulation of the active metabolite when renal function is impaired. However, the utility of spirapril in this patient group has yet to be fully determined because of conflicting data regarding its effects on renal function. Thus, spirapril is an effective antihypertensive agent which is well tolerated. Further comparative trials are needed to fully determine its efficacy with respect to other ACE inhibitors, and a better understanding of its effects on renal function will 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.

---

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).

View More

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)

---

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).

View More

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

---

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.

---

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