Effects of a D-Cys6/L-Cys6 interchange in nonselective and selective vasopressin and oxytocin antagonists

Six Decades of History of Hypertension Research at the University of Toledo: Highlighting Pioneering Contributions in Biochemistry, Genetics, and Host-Microbiota Interactions

PURPOSE OF REVIEW

The study aims to capture the history and lineage of hypertension researchers from the University of Toledo in Ohio and showcase their collective scientific contributions dating from their initial discoveries of the physiology of adrenal and renal systems and genetics regulating blood pressure (BP) to its more contemporary contributions including microbiota and metabolomic links to BP regulation.

RECENT FINDINGS

The University of Toledo College of Medicine and Life Sciences (UTCOMLS), previously known as the Medical College of Ohio, has contributed significantly to our understanding of the etiology of hypertension. Two of the scientists, Patrick Mulrow and John Rapp from UTCOMLS, have been recognized with the highest honor, the Excellence in Hypertension award from the American Heart Association for their pioneering work on the physiology and genetics of hypertension, respectively. More recently, Bina Joe has continued their legacy in the basic sciences by uncovering previously unknown novel links between microbiota and metabolites to the etiology of hypertension, work that has been recognized by the American Heart Association with multiple awards. On the clinical research front, Christopher Cooper and colleagues lead the CORAL trials and contributed importantly to the investigations on renal artery stenosis treatment paradigms. Hypertension research at this institution has not only provided these pioneering insights, but also grown careers of scientists as leaders in academia as University Presidents and Deans of Medical Schools. Through the last decade, the university has expanded its commitment to Hypertension research as evident through the development of the Center for Hypertension and Precision Medicine led by Bina Joe as its founding Director. Hypertension being the top risk factor for cardiovascular diseases, which is the leading cause of human mortality, is an important area of research in multiple international universities. The UTCOMLS is one such university which, for the last 6 decades, has made significant contributions to our current understanding of hypertension. This review is a synthesis of this rich history. Additionally, it also serves as a collection of audio archives by more recent faculty who are also prominent leaders in the field of hypertension research, including John Rapp, Bina Joe, and Christopher Cooper, which are cataloged at Interviews .

Design of Oxytocin Analogs

The neurohypophyseal hormone oxytocin (OT) and related modulators of the oxytocin receptor (OTR) have been the subject of intensive research for nearly seven decades. Despite having rather poor drug-like properties, OT is used as a treatment for labor induction, postpartum hemorrhage, and lactation support. The potential use of OT in the treatment of central nervous system (CNS)-related diseases has recently renewed interest in the pharmacology of OT. Oxytocin is one of the most extensively studied cyclic peptides and since the elucidation of its structure in 1953 thousands of peptidic OT analogs with antagonistic and agonistic properties have been synthesized and biologically evaluated. Among them are atosiban, a mixed oxytocin receptor (OTR)/vasopressin 1a receptor (V_1aR) antagonist used as a tocolytic agent approved (in certain countries), and carbetocin, a longer acting OTR agonist on the market for the treatment of postpartum hemorrhage. Many other OT analogs with improved pharmacological properties (e.g., barusiban, Antag III) have been identified. These peptides have been tested in clinical trials and/or used as pharmacological tools. In this chapter, the modifications of the OT molecule that led to the discovery of these compounds are reviewed.

Design of peptide oxytocin antagonists with strikingly higher affinities and selectivities for the human oxytocin receptor than atosiban

The peptide oxytocin (OT) antagonist atosiban, approved for tocolytic use in Europe (under the tradename Tractocile), represents an important new therapeutic advance for the treatment of premature labor. This paper presents some new peptide OT antagonists which offer promise as superior tocolytics. The solid phase synthesis is reported of four pairs of L and D-2-naphthylalanine (L/D-2Nal) position-2 modified analogs of the following four oxytocin (OT) antagonists: des-9-glycinamide [1-(beta-mercapto-beta,beta-pentamethylene propionic acid), 2-O-methyltyrosine, 4-threonine]ornithine-vasotocin (desGly-NH(2),d(CH(2))(5)[Tyr(Me)(2),Thr(4)]OVT) (A); the Tyr-NH(2) (9) analog of (A), d(CH(2))(5)[Tyr(Me)(2),Thr(4),Tyr-NH(2) (9)]OVT (B); the Eda(9) analog of (A), d(CH(2))(5)[Tyr(Me)(2),Thr(4),Eda(9)]OVT (C); and the retro COCH(2)Ph(4-0H)(10) modified analog of (C), d(CH(2))(5)[Tyr(Me)(2),Thr(4),Eda(9)<-- COCH(2)Ph(4-0H)(10)]OVT (D). The eight new analogs of A-D are (1) desGly-NH(2),d(CH(2))(5)[D-2Nal(2),Thr(4)]OVT, (2) desGly-NH(2),d(CH(2))(5)[2-Nal(2),Thr(4)]OVT, (3) d(CH(2))(5)[D-2Nal(2),Thr(4),Tyr-NH(2) (9)]OVT, (4) d(CH(2))(5)[2Nal(2),Thr(4),Tyr-NH(2) (9)]OVT, (5) d(CH(2))(5)[D-2Nal(2),Thr(4),Eda(9)]OVT, (6) d(CH(2))(5)[2Nal(2),Thr(4),Eda(9)]OVT, (7) d(CH(2))(5)[D-2Nal(2),Thr(4),Eda(9)<-- COCH(2)Ph(4-0H)(10)]OVT, (8) d(CH(2))(5)[2Nal(2),Thr(4),Eda(9)<-- COCH(2)Ph(4-OH)(10)]OVT. Peptides 1-8 were evaluated for agonistic and antagonistic activities in in vitro and in vivo rat bioassays, in rat OT receptor (rOTR) binding assays and in human OT receptor (hOTR) and human vasopressin (VP) vasopressor (V(1a)) receptor (hV(1a)R) binding assays. Also reported are the hOTR and hV(1a)R affinity data for atosiban and for B. None of the eight peptides exhibit oxytocic or vasopressor agonism. Peptides 1-8 exhibit weak antidiuretic agonism (activities in the range 0.014-0.21 U/mg). Peptides 1-6 exhibit potent in vitro (no Mg(2+)) OT antagonism (anti-OT pA(2) values range from 7.63 to 8.08). Peptides 7 and 8 are weaker OT antagonists. Peptides 1-6 are all OT antagonists in vivo (estimated in vivo anti-OT pA(2) values in the range 6.94-7.23). Peptides 1-8 exhibit vasopressor antagonism, anti-V(1a) pA(2) values in the range 5.1-7.65. Peptides 1-8 exhibit high affinities for the rOTR (K(i) values = 0.3-7.8 nM). Peptides 1-4 and B exhibit surprisingly very high affinities for the hOTR; their K(i) values are 0.17, 0.29, 0.07, 0.14 and 0.59 nM, respectively. Peptides 1-4 and B exhibit respectively 449, 263, 1091, 546 and 129 times greater affinity for the hOTR than atosiban (K(i) = 76.4 nM). Peptides 1-4 exhibit high affinities for the hV(1a)R (K(i)s = 1.1 nM, 1.3 nM, 0.19 nM and 0.54 nM, all higher than the hV1(a)R affinities exhibited by atosiban (K(i) = 5.1 nM) and by B (K(i) = 5.26 nM). Because of their strikingly higher affinities for the hOTR than atosiban, peptides 1-4 and B exhibit gains in anti hOT/anti hV(1a) receptor selectivity compared with atosiban of 93, 64, 39, 56 and 127, respectively. These OT antagonists are thus promising candidates for development as potential new tocolytic agents.

Synthesis and biological evaluation of oxytocin analogues containing L-alpha-t-butylglycine [Gly(Bu t)] in positions 8 or 9

We report the solid phase synthesis and some pharmacological properties of seventeen new oxytocin (OT) analogues. Basic modification at positions 8 and/or 9 (introduction of L-alpha-t-butylglycine [Gly(Bu(t))]) was combined with D-Cys(6), D-Tyr(Et)(2), Mpa(1) or Pen(1) modifications and their various combinations. We also present properties of two previously reported re-synthesized analogues ([Gly(Bu(t))(8)]OT and [Mpa(1), Gly(Bu(t))(8)]OT). The analogues were tested for rat uterotonic activity in vitro, in the rat pressor assay and for binding affinity to human OTR.

Design of oxytocin antagonists, which are more selective than atosiban

We report the solid phase synthesis of four pairs of L- and D-thienylalanine (Thi/D-Thi) position two modified analogues of the following four oxytocin (OT) antagonists: des-9-glycinamide [1-(beta-mercapto-beta,beta-pentamethylene propionic acid), 2-O-methyltyrosine, 4-threonine]ornithine-vasotocin (desGly(NH2)9,d (CH2)5[Tyr(Me)2,Thr4]OVT) (A); the Tyr-(NH2)9 analogue of (A), d(CH2)5[Tyr(Me)2,Thr4,Tyr-(NH2)9]OVT (B); the Eda9 analogue (where Eda = ethylenediamine) of (A), d(CH2)5[Tyr(Me)2, Thr4, Eda9]OVT (C); and the retro Tyr10 modified analogue of (C), d(CH2)5[Tyr(Me)2, Thr4, Eda9<--Tyr10]OVT (D). The eight new analogues of A-D are (1) desGly(NH2),d(CH2)5[Thi2,Thr4]OVT, (2) desGly(NH2),d(CH2)5[D-Thi2,Thr4]OVT, (3) d(CH2)5[Thi2, Thr4,Tyr-(NH2)9]OVT, (4) d(CH2)5[D-Thi2,Thr4,Tyr-(NH2)9]OVT (5) d(CH2)5[Thi2,Thr4Eda9]OVT, (6) d(CH2)5[D-Thi2,Thr4,Eda9]OVT, (7) d(CH2) [Thi2,Thr4,Eda9<--Tyr10]OVT, (8) d(CH2),[D-Thi2,Thr4,Eda9<--Tyr10]OVT. We also report the synthesis of (C). Peptides 1-8 and C were evaluated for agonistic and antagonistic activities in in vitro and in vivo OT assays, in in vivo vasopressor (V1a receptor) assays and in in vivo antidiuretic (V2 receptor) assays. None of the eight peptides nor C exhibit oxytocic or vasopressor agonism. Peptides 1-8 are extremely weak V2 agonists (antidiuretic activities range from < 0.0005 to 0.20 U/mg). Peptide C is a weak mixed V2 agonist/antagonist. Peptides 1-8 and C exhibit potent in intro (no Mg2+) OT antagonism (anti-OT pA2 values range from 7.76 to 8.05). Peptides 1-8 are all OT antagonists in vivo (estimated in vivo anti-OT pA2 values range from 6.54-7.19). With anti-V1a pA2 values of approximately 5-5.80, peptides 1-8 exhibit marked reductions in anti-V1a potencies relative to those of the parent peptides A-D (anti-V1a pA2 range from 6.48 to 7.10) and to l-deamino[D-Tyr(Et)2, Thr4]OVT (Atosiban, trade name Tractocile) (anti-V1a pA2-6.14). Atosiban has recently been approved in Europe for clinical use for the prevention of premature labour (Pharm. J. 264(7-100): 871). Peptides 1-8 exhibit striking gains in in vitro anti-OT/anti-V1a selectivities with respect to the parent peptides A, B, C and D and to Atosiban. Peptides 1-8 exhibit anti-OT (in vitro)/anti-V1a selectivities of 450, 525, 550, 450, approximately 1080, 116, 355, 227 respectively. The corresponding values for A-D and Atosiban are 30, 4.2, 4.3, 2.6 and 37. With the exception of peptide 6, the remaining seven peptides exhibit 3-18-fold gains in anti-OT (in vivo)/anti-V1a selectivity with respect to Atosiban, peptides 1-8 exhibit anti-OT (in vivo)/anti-V1a selectivities of 22, approximately 82, approximately 82, 147, approximately 83, 11, 31 and 42. By comparison, Atosiban exhibits an anti-OT (in vivo)/anti-V1a selectivity = 8. With an estimated in vivo anti-OT pA2 value = 7.19+/-0.06, peptide 4 is equipotent with Atosiban (pA2 = 7.05+/-0.05). However, with its significantly reduced anti-vasopressor potency, pA2 = approximately 5, it is approximately 18 times more selective for OT receptors with respect to VP V1a receptors than Atosiban. Since we have shown that V1a antagonism could be an unwanted side-effect in tocolytics, peptide 4 and some of the OT antagonists reported here have advantages over Atosiban and thus may be suitable candidates for evaluation as potential tocolytic agents for the treatment of preterm labour.

The influence of steric interactions on the conformation and biology of oxytocin. Synthesis and analysis of penicillamine(6)-oxytocin and penicillamine(6)-5-tert-butylproline(7)-oxytocin analogs

Six [Pen(6)]oxytocin analogs were synthesized by substituting penicillamine for cysteine in oxytocin, [Mpa(1)]oxytocin, [dPen(1)]oxytocin, [5-t-BuPro(7)]oxytocin, [Mpa(1), 5-t-BuPro(7)]oxytocin and [dPen(1), 5-t-BuPro(7)]oxytocin. When tested in the uterotonic test in vitro [Pen(6)]oxytocin, [Pen(6), 5-t-BuPro(7)]oxytocin, [Mpa(1), Pen(6)]oxytocin and [Mpa(1), Pen(6), 5-t-BuPro(7)]oxytocin, all were found to possess both agonistic and antagonistic properties. Their agonistic potency ranged from negligible (0.08 IU/mg) to low (5.85 IU/mg) and their antagonistic potency (pA2) was estimated to range from 6.6 to 7.9. [dPen(1), Pen(6)]Oxytocin and [dPen(1), Pen(6), 5-t-BuPro(7)]oxytocin were found to be pure antagonists with similarly high pA2 values of approximately 8.2. Replacement of proline by 5-tert-butylproline increased binding affinity by a factor of two in [Pen(6)]oxytocin and had no influence on the binding affinity of [Mpa(1), Pen(6)]oxytocin and [dPen(1), Pen(6)]oxytocin. Assignment of the proton signals for prolyl amide cis- and trans-isomers by NMR experiments in water indicated that the Pen(6)-5-tert-BuPro(7) peptide bond cis-isomer population was augmented relative to the prolyl peptides and measured, respectively, at 20, 35 and 35% in the 5-tert-butylproline(7) analogs of [Pen(6)]oxytocin, [Mpa(1), Pen(6)]oxytocin and [dPen(1), Pen(6)]oxytocin. This augmentation in cis-isomer population was correlated with a 21-fold reduction in the agonistic potency and 2-fold augmentation in antagonistic potency for [Pen(6), 5-t-BuPro(7)]oxytocin relative to [Pen(6)]oxytocin. Augmentation of cis-isomer population was also correlated to reduced agonist potency without effect on antagonism on conversion of [Mpa(1), Pen(6)]oxytocin to [Mpa(1), Pen(6), 5-t-BuPro(7)]oxytocin. In the potent oxytocin antagonist, [dPen(1), Pen(6)]oxytocin, substitution of 5-tert-butylproline for proline augmented the cis-isomer population without affecting antagonistic potency. The synthesis and evaluation of [Pen(6)]oxytocin and [Pen(6), 5-t-BuPro(7)]oxytocin analogs 1-6 indicated that steric interactions influenced agonist and antagonist activity by modifying peptide conformation. Augmentations in the prolyl cis-isomer population caused by 5-tert-butylproline occurred concurrently with enhanced or maintained antagonistic potency and binding affinity and reduced agonistic potency.

A study of the relationship between biological activity and prolyl amide isomer geometry in oxytocin using 5-tert-butylproline to augment the Cys(6)-Pro(7) amide cis-isomer population

Three [5-t-BuPro(7)]oxytocin analogues were synthesized by substituting (2S,5R)-5-tert-butylproline for proline in oxytocin, [Mpa(1)]oxytocin, and [dPen(1)]oxytocin. Relative to oxytocin, [5-t-BuPro(7)]oxytocin and [Mpa(1),5-t-BuPro(7)]oxytocin exhibited strongly reduced binding affinity to the receptor; however, both peptides maintained the pharmacophore characteristics responsible for signal transfer evoking the same maximal response as oxytocin in the single-dose procedure and exhibiting partial agonistic activity in the cumulative dose-response procedure. Although [dPen(1)]oxytocin exhibited inhibitory as well as partial agonistic activity, [dPen(1),5-t-BuPro(7)]oxytocin exhibited only inhibitory potency with a similar in vitro pA(2) value of 7.50 in the absence of magnesium. In the presence of magnesium, [dPen(1), 5-t-BuPro(7)]oxytocin exhibited stronger inhibitory potency than [dPen(1)]oxytocin and no partial agonism. Assignment of the proton signals for the 5-tert-butylprolyl amide cis- and trans-isomers by two-dimensional NMR experiments in water indicated that the Cys(6)-Pro(7) peptide bond cis-isomer population was augmented relative to the prolyl peptides and measured respectively at 35%, 33%, and 20% in the 5-tert-butylproline(7) analogues of oxytocin, [Mpa(1)]oxytocin and [dPen(1)]oxytocin. Although caution must be taken when relating the increase in cis-isomer population with an influence on biological activity in [5-t-BuPro(7)]oxytocin analogues, the synthesis and evaluation of analogues 1-3 have provided additional evidence that can be used to support the hypothesis that the prolyl amide cis-isomer may favor antagonism and the trans-isomer is necessary for agonist activity.

Position three in vasopressin antagonist tolerates conformationally restricted and aromatic amino acid substitutions: a striking contrast with vasopressin agonists

We report the solid-phase synthesis and some pharmacological properties of 12 position three modified analogues (peptides 1-12) of the potent non-selective antagonist of the antidiuretic (V2-receptor), vasopressor (V1a-receptor) responses to arginine vasopressin (AVP) and of the uterine contracting (OT-receptor) responses to oxytocin (OT), [1(-beta mercapto-beta,beta-pentamethylenepropionic acid)-2-O-ethyl-D-tyrosine 4-valine] arginine vasopressin [d(CH2)5D-Tyr(Et)2VAVP] (A) and two analogues of (B) (peptides 13,14), the 1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid3 (Tic3) analogue of (A). Peptides 1-12 have the following substituents at position three in (A): (1) Pro; (2) Oic; (3) Atc; (4) D-Atc; (6) D-Phe; (7) Ile; (8) Leu; (9) Tyr; (10) Trp; (11) Hphe; (12) [HO]Tic; Peptide (13) is the Tyr-NH2(9) analogue of (B): Peptide (14) is the D-Cys(6) analogue of (B). All 14 new peptides were evaluated for agonistic and antagonistic activities in in vivo V2 and V1a assays and in vitro (no Mg2+)n oxytocic assays. With the exception of the D-Phe3 peptide (No. 6), which exhibits very weak V2 agonism (approximately 0.0017 U/mg), none of the remaining 13 peptides exhibit any agonistic activities in these assays. In striking contrast to their deleterious effects on agonistic activities in AVP, the Pro3, Oic3, Tyr3 and Hphe3 substitutions in (A) are very well tolerated, leading to excellent retention of V2, V1a and OT antagonistic potencies. All are more potent as V2 antagonists than the Ile3 and Leu3 analogues of (A). The Tyr-NH2(9) and D-Cys(6) substitutions in (B) are also well tolerated. The anti-V2 pA2 values of peptides 1-5 and 7-14 are as follows (1) 7.77 +/- 0.03; (2) 7.41 +/- 0.05; (3) 6.86 +/- 0.02; (4) 5.66 +/- 0.09; (5) approximately 5.2; (7) 7.25 +/- 0.08; (8) 6.82 +/- 0.06; (9) 7.58 +/- 0.05; (10) 7.61 +/- 0.08; (11) 7.59 +/- 0.07; (12) 7.20 +/- 0.05; (13) 7.57 +/- 0.1; (14) 7.52 +/- 0.06. All analogues antagonize the vasopressor responses to AVP, with anti-V1a pA2 values ranging from 5.62 to 7.64, and the in vitro responses to OT, with anti-OT pA2 values ranging from 5.79 to 7.94. With an anti-V2 potency of 7.77 +/- 0.03, the Pro3 analogue of (A) is surprisingly equipotent with (A), (anti-V2 pA2 = 7.81 +/- 0.07). These findings clearly indicate that position three in AVP V2/V1a antagonists, in contrast to position three in AVP agonists, is much more amenable to structural modification than had heretofore been anticipated. Furthermore, the surprising retention of V2 antagonism exhibited by the Pro3, Oic3, Tyr3, Trp3 and Hphe3 analogues of (A), together with the excellent retention of V2 antagonism by the Tyr-NH2(9) and D-Cys6 analogues of (B) are promising new leads to the design of potent and possibly orally active V2 antagonists for use as pharmacological tools and/or as radioiodinatable ligands and for development as potential therapeutic agents for the treatment of the hyponatremia caused by the syndrome of the inappropriate secretion of the antidiuretic hormone (SIADH).