Inhibition of the development of morphine tolerance by a potent dual mu- / delta-opioid antagonist, H-Dmt-Tic-Lys-NH-CH2-Ph

Three analogues of the dual mu-/delta-antagonist, H-Dmt-Tic-R-NH-CH2-Ph (R = 1, Lys-Z; 2, Lys-Ac; 3, Lys) were examined in vivo: 1 and 2 exhibited weak bioactivity, while 3 injected intracerebroventricularly was a potent dual antagonist for morphine- and deltorphin C-induced antinociception comparable to naltrindole (delta-antagonist), but 93% as effective as naloxone (nonspecific opioid receptor antagonist) and 4% as active as CTOP, a mu antagonist. Subcutaneous or oral administration of 3 antagonized morphine-induced antinociception indicating passage across epithelial and blood-brain barriers. Mice pretreated with 3 before morphine did not develop morphine tolerance indicative of a potential clinical role to inhibit development of drug tolerance

From the potent and selective mu opioid receptor agonist H-Dmt-D-Arg-Phe-Lys-NH2 to the potent delta antagonist H-Dmt-Tic-Phe-Lys(Z)-OH

H-Dmt-D-Arg-Phe-Lys-NH2 ([Dmt1]DALDA) binds with high affinity and selectivity to the í opioid receptor and is a potent and long-acting analgesic. Substitution of D-Arg in position 2 with Tic and masking of the lysine amine side chain by Z protection and of the C-terminal carboxylic function instead of the amide function transform a potent and selective í agonist into a potent and selective ä antagonist H-Dmt-Tic-Phe-Lys(Z)-OH. Such a ä antagonist could be used as a pharmacological tool

Direct influence of C-terminally substituted amino acids in the Dmt-Tic pharmacophore on delta-opioid receptor selectivity and antagonism.

A series of 17 analogues were developed on the basis of the general formula H-Dmt-Tic-NH-CH(R)-R' (denotes chirality; R = charged, neutral, or aromatic functional group; R' = -OH or -NH(2)). These compounds were designed to test the following hypothesis: the physicochemical properties of third-residue substitutions C-terminal to Tic in the Dmt-Tic pharmacophore modify delta-opioid receptor selectivity and delta-opioid receptor antagonism through enhanced interactions with the mu-opioid receptor. The data substantiate the following conclusions: (i) all compounds had high receptor affinity [K(i)(delta) = 0.034-1.1 nM], while that for the mu-opioid receptor fluctuated by orders of magnitude [K(i)(mu) = 15.1-3966 nM]; (ii) delta-opioid receptor selectivity [K(i)(mu)/K(i)(delta)] declined 1000-fold from 22,600 to 21; (iii) a C-terminal carboxyl group enhanced selectivity but only as a consequence of the specific residue; (iv) amidated, positive charged residues [Lys-NH(2) (6), Arg-NH(2) (7)], and a negatively charged aromatic residue [Trp-OH (11)] enhanced mu-opioid affinity [K(i)(mu) = 17.0, 15.1, and 15.7 nM, respectively], while Gly-NH(2) (8), Ser-NH(2) (10), and His-OH (12) were nearly one-tenth as active; and (v) D-isomers exhibited mixed effects on mu-opioid receptor affinity (2' 1 microM) except H-Dmt-Tic-Glu-NH(2) (3), which was a partial delta-opioid receptor agonist (IC(50) = 2.5 nM). Thus, these C-terminally extended analogues indicated that an amino acid residue containing a single charge, amino or guanidino functionality, or aromatic group substantially altered the delta-opioid receptor activity profile (selectivity and antagonism) of the Dmt-Tic pharmacophore, which suggests that the C-terminal constituent plays a major role in determining opioid receptor activity as an "address domain"

Synthesis and opioid activity of N,N-dimethyl-Dmt-Tic-NH-CH(R)-R ' analogues: Acquisition of potent delta antagonism

N,N-Dimethylation of the H-Dmt-Tic-NH-CH(R)-R0 series of compounds produced no significant affect on the high d-opioid receptor affinity (Ki=0.035–0.454 nM), but dramatically decreased that for the m-opioid receptor. The effect of N-methylation was independent of the length of the linker (R); however, the bioactivities were affected by the chemical composition of the third aromatic group (R0): phenyl (Ph) (50–80) elicited a greater reduction in m-affinity (40–70-fold) compared to analogues containing 1H-benzimidazole-2-yl (Bid) (9-fold). The major consequences of N,N-dimethylation on in vitro bioactivity were: (i) a loss of d-agonism coupled with the appearance of potent d antagonism (40–70) (pA2=8.14–9.47), while 1 exhibited only a 160-fold decreased d agonism (10) and the d antagonism of 8 enhanced >10-fold (pA2=10.62, 80); and (ii) a consistent loss of m-affinity resulted in enhanced d-opioid receptor selectivity. With the exception of compound 10, the change in the hydrophobic environment at the N-terminus and formation of a tertiary amine by N,N-dimethylation in analogues of the Dmt-Tic pharmacophore produced potent d-selective antagonists

Conversion of the potent delta-opioid agonist H-Dmt-Tic-NH-CH2-Bid into delta-opioid antagonists by N-1-benzimidazole alkylation

N1-Alkylation of 1H-benzimidizole of the ä agonist H-Dmt-Tic-NH-CH2-Bid with hydrophobic, aromatic, olefinic, acid, ethyl ester, or amide (1-6) became ä antagonists (pA2 ) 8.52-10.14). ä- and í-Opioid receptor affinities were high (Kiä ) 0.12-0.36 nM and Kií ) 0.44-1.42 nM). Only ä antagonism (pA2 ) 8.52-10.14) was observed; í agonism (IC50 ) 30-450 nM) was not correlated with changes in alkylating agent or ä antagonism, and some compounds yielded mixed ä antagonism/ í agonism

Potent delta opioid receptor agonists containing the Dmt-Tic pharmacophore

Conversion of delta-opioid receptor antagonists containing the 2',6'-dimethyl-L-tyrosine (Dmt)-1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid (Tic) pharmacophore into potent delta-agonists required a third heteroaromatic nucleus, such as 1H-benzimidazole-2-yl (Bid) and a linker of specified length both located C-terminally to Tic in the general formula H-Dmt-Tic-NH-CH(R)-R'. The distance between Tic and Bid is a determining factor responsible for the acquisition of delta agonism (2, 2', 3, 4, 6) or delta antagonism (8). Compounds containing a C-terminal Ala (1, 1'), Asp (5), or Asn (7) with an amide (1, 1', 5) or free acid group (7) served as delta-antagonist controls lacking the third heteroaromatic ring. A change in chirality of the spacer (2, 2') or inclusion of a negative charge via derivatives of Asp (4, 6) resulted in potent delta agonism and moderatey agonism, although delta-receptor affinity decreased about 10-fold for 4 while mu affinity fell by over 2 orders of magnitude. Repositioning of the negative charge in the linker altered activity: H-Dmt-Tic-NH-CH(CH2-Bid)COOH (6) maintained high delta affinity (K-i = 0.042 nM) and delta agonism (IC50 = 0.015 nM), but attachment of the free acid group to Bid [H-Dmt-Tic-NH-CH2-Bid(CH2-COOH) (9)] reconstituted delta antagonism (K-e = 0.27 nM). The data demonstrate that a linker separating the Dmt-Tic pharmacophore and Bid, regardless of the presence of a negative charge, is important in the acquisition of opioids exhibiting potent delta agonism and weaky agonism from a parent delta antagonist

From the potent and selective mu opioid receptor agonist H-Dmt-D-Arg-Phe-Lys-NH2 to the potent delta antagonist H-Dmt-Tic-Phe-Lys(Z)-OH

H-Dmt-d-Arg-Phe-Lys-NH(2) ([Dmt(1)]DALDA) binds with high affinity and selectivity to the mu opioid receptor and is a potent and long-acting analgesic. Substitution of d-Arg in position 2 with Tic and masking of the lysine amine side chain by Z protection and of the C-terminal carboxylic function instead of the amide function transform a potent and selective mu agonist into a potent and selective delta antagonist H-Dmt-Tic-Phe-Lys(Z)-OH. Such a delta antagonist could be used as a pharmacological tool

Potent delta-opioid receptor agonists containing the Dmt-Tic pharmacophore

Conversion of ä-opioid receptor antagonists containing the 2¢,6¢-dimethyl-L-tyrosine (Dmt)- 1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid (Tic) pharmacophore into potent ä-agonists required a third heteroaromatic nucleus, such as 1H-benzimidazole-2-yl (Bid) and a linker of specified length both located C-terminally to Tic in the general formula H-Dmt-Tic-NHCH( R)-R¢. The distance between Tic and Bid is a determining factor responsible for the acquisition of ä agonism (2, 2¢, 3, 4, 6) or ä antagonism (8). Compounds containing a C-terminal Ala (1, 1¢), Asp (5), or Asn (7) with an amide (1, 1¢, 5) or free acid group (7) served as ä-antagonist controls lacking the third heteroaromatic ring. A change in chirality of the spacer (2, 2¢) or inclusion of a negative charge via derivatives of Asp (4, 6) resulted in potent ä agonism and moderate í agonism, although ä-receptor affinity decreased about 10-fold for 4 while í affinity fell by over 2 orders of magnitude. Repositioning of the negative charge in the linker altered activity: H-Dmt-Tic-NH-CH(CH2-Bid)COOH (6) maintained high ä affinity (Ki ) 0.042 nM) and ä agonism (IC50 ) 0.015 nM), but attachment of the free acid group to Bid [H-Dmt- Tic-NH-CH2-Bid(CH2-COOH) (9)] reconstituted ä antagonism (Ke ) 0.27 nM). The data demonstrate that a linker separating the Dmt-Tic pharmacophore and Bid, regardless of the presence of a negative charge, is important in the acquisition of opioids exhibiting potent ä agonism and weak í agonism from a parent ä antagonist

Orally administered H-Dmt-Tic-Lys-NH-CH2-Ph (MZ-2), a potent mu/delta-opioid receptor antagonist, regulates obese-related factors in mice

Orally active dual mu-/delta-opioid receptor antagonist, H-Dmt-Tic-Lys-NH-CH(2)-Ph (MZ-2) was applied to study body weight gain, fat content, bone mineral density, serum insulin, cholesterol and glucose levels in female ob/ob (B6.V-Lep/J homozygous) and lean wild mice with or without voluntary exercise on wheels for three weeks, and during a two week post-treatment period under the same conditions. MZ-2 (10mg/kg/day, p.o.) exhibited the following actions: (1) reduced body weight gain in sedentary obese mice that persisted beyond the treatment period without effect on lean mice; (2) stimulated voluntary running on exercise wheels of both groups of mice; (3) decreased fat content, enhanced bone mineral density (BMD), and decreased serum insulin and glucose levels in obese mice; and (4) MZ-2 (30 microM) increased BMD in human osteoblast cells (MG-63) comparable to naltrexone, while morphine inhibited mineral nodule formation. Thus, MZ-2 has potential application in the clinical management of obesity, insulin and glucose levels, and the amelioration of osteoporosis