Glenn Croston

Discovery of the first nonpeptide agonist of the GPR14/urotensin-II receptor: 3-(4-chlorophenyl)-3-(2- (dimethylamino)ethyl)isochroman-1-one (AC-7954).

A functional cell-based screen identified 3-(4-chlorophenyl)-3-(2-(dimethylamino)ethyl)isochroman-1-one hydrochloride (AC-7954, 1) as a nonpeptidic agonist of the urotensin-II receptor. Racemic 1 had an EC50 of 300 nM at the human UII receptor and was highly selective. Testing of the enantiopure (+)- and (-)- 1 revealed that the UII receptor activity of racemic 1 resides primarily in (+)-1. Being a selective nonpeptidic druglike UII receptor agonist, (+)-1 will be useful as a pharmacological research tool and a potential drug lead.

Pharmacological Characterization of FE 202158, a Novel, Potent, Selective, and Short-Acting Peptidic Vasopressin V1a Receptor Full Agonist for the Treatment of Vasodilatory Hypotension

FE 202158, ([Phe2,Ile3,Hgn4,Orn(iPr)8]vasopressin, where Hgn is homoglutamine and iPr is isopropyl), a peptidic analog of the vasoconstrictor hormone [Arg8]vasopressin (AVP), was designed to be a potent, selective, and short-acting vasopressin type 1a receptor (V1aR) agonist. In functional reporter gene assays, FE 202158 was a potent and selective human V1aR agonist [EC50 = 2.4 nM; selectivity ratio of 1:142:1107:440 versus human vasopressin type 1b receptor, vasopressin type 2 receptor (V2R), and oxytocin receptor, respectively] contrasting with AVPs lack of selectivity, especially versus the V2R (selectivity ratio of 1:18:0.2:92; human V1aR EC50 = 0.24 nM). This activity and selectivity profile was confirmed in radioligand binding assays. FE 202158 was a potent vasoconstrictor in the isolated rat common iliac artery ex vivo (EC50 = 3.6 nM versus 0.8 nM for AVP) and reduced rat ear skin blood flow after intravenous infusion in vivo (ED50 = 4.0 versus 3.4 pmol/kg/min for AVP). The duration of its vasopressor effect by intravenous bolus in rats was as short as AVP at submaximally effective doses. FE 202158 had no V2R-mediated antidiuretic activity in rats by intravenous infusion at its ED50 for reduction of ear skin blood flow, in contrast with the pronounced antidiuretic effect of AVP. Thus, FE 202158 seems suitable for treatment of conditions where V1aR activity is desirable but V2R activity is potentially deleterious, such as vasodilatory hypotension in septic shock. In addition to the desirable selectivity profile, its short-acting nature should allow dose titration with rapid onset and offset of action to optimize vasoconstriction efficacy and safety.

New, Potent, Selective, and Short-Acting Peptidic V1a Receptor Agonists

[Arg(8)]vasopressin (AVP) produces vasoconstriction via V(1a) receptor (V(1a)R)-mediated vascular smooth muscle cell contraction and is being used to increase blood pressure in septic shock, a form of vasodilatory hypotension. However, AVP also induces V(2) receptor (V(2)R)-mediated antidiuresis, vasodilation, and coagulation factor release, all deleterious in septic shock. The V(1a)R agonist terlipressin (H-Gly(3)[Lys(8)]VP) also lacks selectivity vs the V(2)R and has sizably longer duration of action than AVP, preventing rapid titration of its vasopressor effect in the clinic. We designed and synthesized new short acting V(1a)R selective analogues of general structure [Xaa(2),Ile(3),Yaa(4),Zaa(8)]VP. The most potent and selective compounds in in vitro functional assays (e.g., [Phe(2),Ile(3),Asn(Me(2))(4),Orn(8)]VP (31), [Phe(2),Ile(3),Asn((CH(2))(3)OH)(4),Orn(8)]VP (34), [Phe(2),Ile(3),Hgn(4),Orn(iPr)(8)]VP (45), [Phe(2),Ile(3),Asn(Et)(4),Dab(8)]VP (49), [Thi(2),Ile(3),Orn(iPr)(8)]VP (59), [Cha(2),Ile(3),Asn(4),Orn(iPr)(8)]VP (68)) were tested by intravenous bolus in rats for duration of vasopressive action. Analogues 31, 34, 45, and 49 were as short-acting as AVP. Compound 45, FE 202158, is currently undergoing clinical trials in septic shock.

Retinoic acid receptor ligands based on the 6-cyclopropyl-2,4-hexadienoic acid

A series of novel cyclopropanyl methyl hexadienoic acid retinoids was designed and prepared. These compounds exhibited either selective activity as RXR agonists or pan-agonists on one or more of each of the RAR and RXR isoforms. The most potent pan-agonist 5a (RARs EC(50)=17-59 nM; RXRs EC(50)=6-14 nM) showed good antiproliferative properties in the in vitro cancer cell lines, ME 180 and RPMI 8226.

Synthesis and structure activity relationships of potent retinoid X receptor ligands

A series of potent retinoid X receptor (RXR) selective ligands was designed and prepared. The lead compound 7a showed good binding (K i ; 20–50 nM) and transactivation (EC 50 ; 40–50 nM) to the RXR subfamily of retinoid receptors. More importantly, small variations in the geometry of the cyclopentane ring moiety led to 9 , one of the most potent RXR agonists to date (K i : 3–8 nM; EC 50 : 3–4 nM).

New, Potent, and Selective Peptidic Oxytocin Receptor Agonists

Mothers of preterm babies frequently have difficulty establishing or maintaining lactation, thought to be due to interference with the milk ejection reflex. Administration of exogenous oxytocin can produce alveolar contraction and adequate breast emptying resulting in establishment of successful lactation. The natural hormone oxytocin is not receptor-selective and may cause hyponatremia via V2 receptor mediated antidiuresis. We have designed a series of potent oxytocin analogues containing N-alkylglycines in position 7 with excellent selectivity versus the related V1a, V1b, and V2 vasopressin receptors and short half-life: agonists 31 ([2-ThiMeGly(7)]dOT), 47 (carba-6-[Phe(2),BuGly(7)]dOT), 55 (carba-6-[3-MeBzlGly(7)]dOT), and 57 (carba-1-[4-FBzlGly(7)]dOT) have EC50 values at hOTR < 0.1 nM, selectivity ratios versus related human vasopressin receptors of >2000, IC50 at hV1aR > 500 nM, and total clearance in rats in the range of 60-80 mL min(-1) kg(-1). Compound 57 (FE 202767) is currently in clinical development for the treatment of preterm mothers requiring lactation support.

Synthesis and structure activity relationships of potent conformationally restricted retinoid X receptor ligands

A series of potent retinoid X receptor (RXR) selective ligands were designed and prepared. The lead compound 6a, showed good binding (Kd; 3–7 nM) and transactivation (EC50; 19–24 nM) to the RXR subfamily of retinoid receptors. More importantly, a small variation on the aromatic ring moiety led to 6b, which had less residual RAR agonist activity with RXR binding and potency of 4–5 nM and 5–13 nM, respectively.

Novel gonadotropin‐releasing hormone antagonists with substitutions at position 5

Gonadotropin‐releasing hormone (GnRH) antagonists with high potency and improved duration of action are needed for potential clinical applications. We synthesized four new antagonists (2–5) of GnRH homologues to Azaline B (1), with a common core sequence of [Aph(X)5, D‐Aph(Cbm)6]Azaline B. In these analogs, (X) contains hydrophobic aromatic moieties (like homoveratoyl in 2, homovanillyl in 3, 2,5‐dimethoxyphenylacetyl in 4, and 3,5‐dimethoxyphenylacetyl in 5) designed to improve the duration of action over that of Azaline B. These analogs were tested in vitro for their ability to antagonize the GnRH receptor and in vivo for duration of action in a castrated male rat assay. Analogs 2, 4, and 5 were potent in vitro, but were found to be short acting in vivo. However, analog 3 [Aph(Hvn)5,D‐Aph(Cbm)6]Azaline B is a potent human GnRH receptor antagonist in vitro (IC50 1.47 nM) and exhibits a longer duration of action than azaline B.

Synthesis and Pharmacological Characterization of Novel Glucagon-like Peptide-2 (GLP-2) Analogues with Low Systemic Clearance

Glucagon-like peptide-2 receptor agonists have therapeutic potential for the treatment of intestinal diseases. The native hGLP-2, a 33 amino acid gastrointestinal peptide, is not a suitable clinical candidate, due to its very short half-life in humans. In search of GLP-2 receptor agonists with better pharmacokinetic characteristics, a series of GLP-2 analogues containing Gly substitution at position 2, norleucine in position 10, and hydrophobic substitutions in positions 11 and/or 16 was designed and synthesized. In vitro receptor potency at the human GLP-2, selectivity vs the human GLP-1 and GCG receptors, and PK profile in rats were determined for the new analogues. A number of compounds more potent at the hGLP-2R than the native hormone, showing excellent receptor selectivity and very low systemic clearance (CL) were discovered. Analogues 69 ([Gly(2),Nle(10),D-Thi(11),Phe(16)]hGLP-2-(1-30)-NH2), 72 ([Gly(2),Nle(10),D-Phe(11),Leu(16)]hGLP-2-(1-33)-OH), 73 ([Gly(2),Nle(10),D-Phe(11),Leu(16)]hGLP-2-(1-33)-NH2), 81 ([Gly(2),Nle(10),D-Phe(11),Leu(16)]hGLP-2-(1-33)-NHEt), and 85 ([Gly(2),Nle(10),D-Phe(11),Leu(16)]hGLP-2-(1-33)-NH-((CH2)2O)4-(CH2)2-CONH2) displayed the desired profiles (EC50 (hGLP-2R) < 100 pM, CL in rat <0.3 mL/min/kg, selective vs hGLP-1R and hGCGR). Compound 73 (FE 203799) was selected as a candidate for clinical development.

Synthesis and Biological Activity of Terlipressin and its Putative Metabolites

Introduction Terlipressin (H-Gly3-LVP, GLYPRESSIN ® [1]), 1, is a peptide drug approved in some European and Asian countries for the treatment of bleeding esophageal varices and in France for hepatorenal syndrome. It presumably acts on the vasopressin 1a receptor (V1a-R), whose endogenous ligand is arginine vasopressin (AVP), to increase peripheral vascular resistance leading to increase in arterial blood pressure (ABP). Although 1 and AVP have both been used clinically to correct syndromes of inappropriate vasodilatation, 1 has much longer onset and duration of action [2,3]. It is hypothesized that 1 acts as a pro-drug and that its onset and duration of action are due to successive cleavage of the glycine N-terminal moieties to ultimately produce lysine vasopressin (LVP, 4). Each of the putative metabolites 2-4 would be biologically active. To determine the biological activity of the metabolites and further investigate the mechanism of action of 1, the peptides 1-4 were synthesized and tested both in vivo and in vitro.