Arginine-Based Inhibitors of Nitric Oxide Synthase: Therapeutic Potential and Challenges

Table 1

List of the most important arginine-based inhibitors.

Scaffold	Compound name	Inhibition mechanism	𝐾𝑖/IC50/𝐾𝐼 (μmol/L), 𝑘 (min^−1)			NOS	References
			iNOS	eNOS	nNOS
	R1: CH3, R2: H; L-N^ω-methylarginine (L-NMA)	C	𝐾𝑖 2.6^h	𝐾𝑖 0.7^h	𝐾𝑖 1.7^h	Partially purified recombinant (Sf9 cells)	[59]*
		RBI	𝐾𝐼 2.6^m; 𝑘 0.042^m	No inact.^h	𝐾𝐼 2.0^r; 𝑘 0.022^r	Partially puriffied (iNOS), crude extracts eNOS, nNOS	[20]
	R1: CH3, R2: CH3; L-N^ω,N^′ω-dimethylarginine (ADMA)	C	𝐾𝑖 > 300^r	nd	𝐾𝑖 0.67^r; 𝐾𝑖 > 300^r	Purified recombinant (293 kidney cells); Purified	[49, 50]
	R1: NO2, R2: H; L-N^ω-nitroarginine (L-NNA)	C	𝐾𝑖 1.4^h	𝐾𝑖 0.06^h; Slow on/off	𝐾𝑖 0.09^h; Slow on/off	Partially purified recombinant (Sf9 cells)	[59, 60]*
	R1: CH2CH2CH3, R2: H; L-N^ω-propylarginine	C	𝐾𝑖 180^m	𝐾𝑖 8.5^b	𝐾𝑖 0.057^b	Partially purified	[75]
		RBI	nd	nd	𝐾𝐼 0.02^b; 𝑘 0.0059^b	Partially purified	[76]
	R1: CH2CH=CH2, R2: H; L-N^ω-allylarginine	C	𝐾𝑖 2.1^m	𝐾𝑖 3.1^b	𝐾𝑖 0.2^b	Partially purified	[75]
		RBI	𝐾𝐼 3.4^m; 𝑘 0.026	nd	𝐾𝐼 0.47^b; 𝑘 0.05^b	Desalted crude extract (iNOS), partially purified (nNOS)	[76, 77]
	R1: CH2C≡CH, R2: H; L-N^ω-propargylarginine	C	𝐾𝑖 0.62^m	𝐾𝑖 0.81^b	𝐾𝑖 0.43^b	Partially purified	[75]
	R1: cyclopropyl, R2: H; L-N^ω-cyclopropylarginine	C	𝐾𝑖 7.7^m	nd	nd	Desalted crude extract	[77]
	R1: NH2, R2: H; L-N^ω-aminoarginine	C	𝐾𝑖 0.7^h	𝐾𝑖 0.4^h	𝐾𝑖 0.8^h	Partially purified recombinant (Sf9 cells)	[59]*
		RBI	𝐾𝐼 3^m; 𝑘 0.26	𝐾𝐼 2.5^b; 𝑘 0.53	𝐾𝐼 0.3^r; 𝑘 0.35	Purified	[78]
	R1: NO2, R2: D-Phe, R3: OCH3, X: NH, Y: O, Stereo bond: D; D-Phenylalanine-D-N^ω-nitroarginine methyl ester	C (eNOS, nNOS); U (iNOS)	𝐾𝑖 3600^m	𝐾𝑖 5^b	𝐾𝑖 2^r	Purified recombinant (E. coli)	[79, 80]
	R1: NO2, R2: H, R3: L-2,4-diaminobutyramide, X: NH, Y: O, Stereo bond: L; L-N^ω-nitroarginine-L-2,4-diaminobutyramide	C	𝐾𝑖 25^m	𝐾𝑖 200^b	𝐾𝑖 0.13^r	Purified recombinant (E. coli)	[79]
	R1: NO2, R2: H, R3: trans-3-amino-L-prolineamide, X: NH, Y: O, Stereo bond: L; L- N^ω-nitroarginine-trans-3-amino-L-prolineamide	Not published	𝐾𝑖 5.76^m	𝐾𝑖 200^b	𝐾𝑖 0.087^r	Purified recombinant (E. coli)	[81]
	R1: NO2, R2: H, R3: NHCH2CH2NH2 X: NH, Y: 2H, Stereo bond: L; (4S)-N-(4-amino-5-[aminoethyl]aminopentyl)-N′-nitroguanidine	Not published	𝐾𝑖 39^m	𝐾𝑖 314^b	𝐾𝑖 0.12^r	Purified recombinant (E. coli)	[82]
	R1: NO2, R2: H, R3: 2-(2-aminoethyl)phenylamine, X: NH, Y: 2H, Stereo bond: L; N-(4S)-{4-amino-5-[2-(2-aminoethyl)-; phenylamino]-pentyl}-N′-nitroguanidine	C	𝐾𝑖 3.51^m	𝐾𝑖 105^b	𝐾𝑖 0.05^r	Purified recombinant (E. coli)	[83]
	R1: CH3, R2: H, R3: L-Phe, X: S, Y: O, Stereo bond: L; S-methyl-L-thiocitrulline-L-phenylalanine	C	𝐾𝑖 7.5^h	𝐾𝑖 520^h	𝐾𝑖 27^h	Partially purified recombinant (Sf9 cells),	[84]
	R: H; L-thiocitrulline	C	𝐾𝑖 0.7^h	𝐾𝑖 1^h	𝐾𝑖 1.2^h	Partially purified recombinant (Sf9 cells)	[59]*
	R: CH3; S-methyl-L-thiocitrulline	C	𝐾𝑖 0.04^h	𝐾𝑖 0.011^h	𝐾𝑖 0.001^h; slow off	Purified	[60]
	R: CH2CH3; S-ethyl-L-thiocitrulline	C	𝐾𝑖 0.02^h	𝐾𝑖 0.024^h	𝐾𝑖 0.0005^h; slow off	Purified	[60]
	𝑛=1, R: H; N^5-(1-iminoethyl)-L-ornithine (L-NIO)	C	𝐾𝑖 3.9^m	𝐾𝑖 3.9^b	𝐾𝑖 1.7^r	Purified recombinant (iNOS kidney 293 cells; eNOS, nNOS E.coli)	[85]
		RBI	nd	nd	>20 times less versus vinyl LNIO^r	Purified recombinant (iNOS kidney 293 cells; eNOS, nNOS E. coli)	[85]
	𝑛=1, R: CH2CH3; N^5-(1-iminobutyl)-L-ornithine (ethyl L-NIO)	C	𝐾𝑖 12^m	𝐾𝑖 18^b	Ki 5.3^r	Purified recombinant (iNOS kidney 293 cells; eNOS, nNOS E. coli)	[85]
	𝑛=1, R: CHCH2; N^5-(1-imino-3-butenyl)-L-ornithine; (vinyl L-NIO)	C	𝐾𝑖 60^m	𝐾𝑖 12^b	𝐾𝑖 0.1^r	Purified recombinant (iNOS kidney 293 cells; eNOS, nNOS E. coli)	[85]
		RBI	No inact.^m	Weak^b >20 times less vs. nNOS	𝐾𝐼 0.09^r; 𝑘 0.078^r	Purified recombinant (iNOS kidney 293 cells; eNOS, nNOS E. coli)	[85]
	𝑛=1, R:CH2SCH3; N^5-[2-(methylthio)-1-iminoethyl]-L-ornithine	C	𝐾𝑖 1.17^m	𝐾𝑖 68.7^b	𝐾𝑖 0.37^r	Purified, eNOS and nNOS recombinant (E. coli)	[86]
	𝑛=2, R: H; N^6-(1-iminoethyl)-L-lysine (L-NIL)	C	𝐾𝑖 0.9^h	𝐾𝑖 16^h	𝐾𝑖 10^h	Partially purified recombinant (Sf9 cells)	[59]*
	X: SO2, 𝑛=0; (R)-2-amino-3-{[2-(ethanimidoylamino)ethyl]sulfonyl} propanoic acid (GW273629)	C (eNOS, nNOS) IR, time-dependent (iNOS)	IC50 8^h	IC50 >1000^h	IC50 630^h	Purified recombinant (Sf21 cells)	[87, 88]
	X: S, 𝑛=1; (S)-2-amino-4-{[2-(ethanimidoylamino)ethyl]thio}butanoic acid (GW274150)	C, time dependent and IR for iNOS	IC50 1.4^h	IC50 466^h	IC50 145^h	Purified recombinant (Sf21 cells)	[87, 88]
	R: H; (R)-2-amino-3-[(pyridin-2-ylmethyl)thio]propanoic acid	C	𝐾𝑖 2^h	𝐾𝑖 3.7^h	𝐾𝑖 16^h	Partially purified recombinant (Sf9 cells)	[89]
	R: NH2; (R)-2-amino-3-{[(6-aminopyridin-2-yl)methyl]thio}propanoic acid	C	𝐾𝑖 9.5^h	𝐾𝑖 1.5^h	𝐾𝑖 0.5^h	Partially purified recombinant (Sf9 cells)	[89]
	R: imidazol-1-yl; (S)-2-amino-5-imidazolylpentanoic acid	Not mentioned	IC50 32^r	IC50 13^h	IC50 19^r	Crude extract	[90]
	R: 4,5-Dihydrothiazol-2-yl; (S)-N^δ-(4,5-Dihydrothiazol-2-yl)ornithine	Not mentioned	IC50 8.1^r	IC50 1.3^h	IC50 4.3^r	Crude extract	[91]

Inhibition mechanism: C: competitive, U: uncompetitive, IR: irreversible, RBI: reaction-based inhibitor; Inhibition constants: 𝐾_𝑖: inhibitor affinity constant (competitive inhibition), IC₅₀: concentration at which 50% inhibition is achieved under specific conditions, 𝐾_𝐼: half maximal rate of enzyme inactivation, 𝑘: rate constant of enzyme inactivation, nd: data not available in the referred literature; enzyme origin: ^hhuman, ^mmurine, ^rrat, ^b bovine, *𝐾_𝑖 values were obtained by recalculation using data in [59]. The extent of the inhibition can be estimated in the case of competitive inhibitors using the equation Inhibition(%)=100(𝐼/(𝐼+𝐾_𝑖(1+(Arg/𝐾_𝑚))))   I: inhibitor concentration, Arg: arginine concentration, 𝐾_𝑚: Michaelis constant of the enzyme. 𝐾_𝑚 ranges (μmol/L): iNOS^h 2.2–22, eNOS^h 0.9–4.4, nNOS^h 1.5–6.0, iNOS^m 2.3–14, eNOS^m 1.7–3.6, nNOS^m 1.3-1.4, eNOS^b 3.0–5.0, nNOS^b 2.0–3.3, iNOS^r 19–32, nNOS^r 1.5–14 [59, 79, 89, 92–97].