A series of digitalis-like compounds with a 17-aminoalkoxyiminoalkyl or -alkenyl substituent was synthesized and evaluated for inhibition of Na(+),K(+)-ATPase and for inotropic activity. The highest inhibition was found with compounds having the substituent in configuration 17beta and the amino group at a distance of 6 or 7 bonds from C(17) of the digitoxigenin skeleton. The presence of the oxime function strengthens the interaction with the receptor, more if alpha,beta-unsaturated, thus mimicking the electronic situation of the unsaturated lactone in natural digitalis compounds. The most active compounds showed Na(+),K(+)-ATPase inhibitory potencies (IC(50)) 17-25 times higher than the standards digitoxigenin and digoxin and 3-11 times higher inotropic potencies (EC(50)) in isolated guinea pig left atria. These features are supported by a molecular model suggesting the possible interactions of the groups described above with particular amino acid residues in the H1-H2 domains of Na(+),K(+)-ATPase. Some interactions are the classical ones already described in the literature; a new, very strong interaction of the basic group with the Cys138 was found and adds new possibilities to design compounds interacting with this region of the receptor. The most interesting compounds were also studied in vivo in the anesthetized guinea pig for evaluating their inotropic effect versus the lethal dose. Compounds 9 and 12 showed a slightly higher safety ratio than digoxin and deserve further evaluation.

The design, synthesis, and biological properties of novel inhibitors of the Na(+),K(+)-ATPase as potential positive inotropic compounds are reported. Following our model of superposition between cassaine and digitoxigenin, digitalis-like activity has been elicited from a non-digitalis steroidal structure by suitable modifications of the 5alpha,14alpha-androstane skeleton. The strong hydrophobic interaction of the digitalis or cassaine polycyclic cores can be effectively obtained with the androstane skeleton taken in a reversed orientation. Thus, oxidation of C-6 and introduction in the C-3 position of the potent pharmacophoric group recently introduced by us, in the 17 position of the digitalis skeleton, namely, O-(omega-aminoalkyl)oxime, led to a series of substituted androstanes able to inhibit the Na(+),K(+)-ATPase, most of them with an IC(50) in the low micromolar level, and to induce a positive inotropic effect in guinea pig. Within this series, androstane-3,6,17-trione (E,Z)-3-(2-aminoethyl)oxime (22b, PST 2744) induced a strong positive inotropic effect while being less arrhythmogenic than digoxin, when the two compounds were compared at equiinotropic doses.

In patients with ocular hypertension or glaucoma, all treatments aim to lower intraocular pressure (IOP) by modulating aqueous humour (AH) production and/or uveoscleral and trabecular meshwork/Schlemm's canal AH drainage. PG analogues are considered to be the 'gold standard' treatment and are the most frequently used IOP-lowering agents. Recent data support an important role for NO in regulating IOP. Thus, novel PG analogues carrying a NO-donating moiety were recently advanced. Latanoprostene bunod (LBN) and NCX 470, NO-donating derivatives of latanoprost and bimatoprost, respectively, are examples of such compounds. LBN ophthalmic solution, 0.024% (Vyzulta™), showed greater IOP-lowering efficacy compared with that of Xalatan (latanoprost ophthalmic solution, 0.005%) or 0.5% timolol maleate in clinical settings. NCX 470 was found to be more effective than bimatoprost in animal models of ocular hypertension and glaucoma. Selective EP receptor agonists (i.e. taprenepag isopropyl, omidenepag isopropyl and aganepag isopropyl) and non-selective prostanoid receptor agonists (i.e. ONO-9054, sepetaprost isopropyl) that concomitantly stimulate FP and EP receptors have also been shown to hold promise as effective IOP-lowering agents.

Organic nitrates, such as nitroglycerin, have been used in clinical practice for more than one century for the treatment of angina, even before the identification of Nitric Oxide (NO) as the so-called Endothelium Derived Relaxing Factor (EDRF). Recently, multiple functions of this molecule in biology and pathophysiology have been discovered and alterations in the NO signalling pathway have often been associated with disease progression in mammals, providing a strong rationale for the use of NO as a potential drug. To have a therapeutic benefit from NO properties, an elegant approach has been designed coupling well-known existing drugs with moieties able to slowly release NO following enzymatic metabolism. "Hybrid nitrates", in which activities of both the native drug and NO are present, have been obtained with the aim of originating safer and more active drugs. The technology consists in the choice of the appropriate chemical spacer arm carrying the nitric ester in order to obtain the best pharmacodynamic and pharmacokinetic profile. The connecting linkers already explored are of different chemical structure, ranging from aliphatic chains to heteroaromatic rings. The molecules so far obtained have already demonstrated their potential therapeutic interest in both pharmacological tests and clinical trials. In this review, we describe the approach and the possibility of generating new chemical entities, combining well-known drugs with an NO-donating moiety in order to increase activity and safety, along with examples of their activity and potential therapeutic application in different pathologies. A few significant examples of molecules in the early preclinical stage, as well as in advanced clinical development will be described.