Effect of several bicyclic peptide and cyclic pseudopeptide tachykinin NK2 receptor antagonists in the human isolated urinary bladder

The Neurokinins: Peptidomimetic Ligand Design and Therapeutic Applications

The neurokinins are indisputably essential neurotransmitters in numerous pathoand physiological events. Being widely distributed in the Central Nervous System (CNS) and peripheral tissues, their discovery rapidly promoted them to drugs targets. As a necessity for molecular tools to understand the biological role of this class, endogenous peptides and their receptors prompted the scientific community to design ligands displaying either agonist and antagonist activity at the three main neurokinin receptors, called NK1, NK2 and NK3. Several strategies were implemented for this purpose. With a preference to small non-peptidic ligands, many research groups invested efforts in synthesizing and evaluating a wide range of scaffolds, but only the NK1 antagonist Aprepitant (EMENDT) and its prodrug Fosaprepitant (IVEMENDT) have been approved by the Food Drug Administration (FDA) for the treatment of Chemotherapy-Induced and Post-Operative Nausea and Vomiting (CINV and PONV, respectively). While non-peptidic drugs showed limitations, especially in side effect control, peptidic and pseudopeptidic compounds progressively regained attention. Various strategies were implemented to modulate affinity, selectivity and activity of the newly designed ligands. Replacement of canonical amino acids, incorporation of conformational constraints, and fusion with non-peptidic moieties gave rise to families of ligands displaying individual or dual NK1, NK2 and NK3 antagonism, that ultimately were combined with non-neurokinin ligands (such as opioids) to target enhanced biological impact.

Bladder cancer and urothelial impairment: the role of TRPV1 as potential drug target

Urothelium, in addition to its primary function of barrier, is now understood to act as a complex system of cell communication that exhibits specialized sensory properties in the regulation of physiological or pathological stimuli. Furthermore, it has been hypothesized that bladder inflammation and neoplastic cell growth, the two most representative pathological conditions of the lower urinary tract, may arise from a primary defective urothelial lining. Transient receptor potential vanilloid channel 1 (TRPV1), a receptor widely distributed in lower urinary tract structures and involved in the physiological micturition reflex, was described to have a pathophysiological role in inflammatory conditions and in the genesis and development of urothelial cancer. In our opinion new compounds, such as curcumin, the major component of turmeric Curcuma longa, reported to potentiate the effects of the chemotherapeutic agents used in the management of recurrent urothelial cancer in vitro and also identified as one of several compounds to own the vanillyl structure required to work like a TRPV1 agonist, could be thought as complementary in the clinical management of both the recurrences and the inflammatory effects caused by the endoscopic resection or intravesical chemotherapy administration or could be combined with adjuvant agents to potentiate their antitumoral effect.

Effect of nepadutant at tachykinin NK(2) receptors in human intestine and urinary bladder

We have characterized the action of the tachykinin NK(2) receptor antagonist nepadutant (c¿[(beta-D-GlcNAc)Asn-Asp-Trp-Phe-Dpr-Leu]c(2 beta-5 beta)¿) in the human isolated ileum, colon and urinary bladder. Nepadutant (30-1000 nM) competitively antagonized neurokinin A- or [beta Ala(8)]neurokinin A-(4-10)-induced contractions in all tissues, with pK(B)=8.3 (ileum and colon) and pK(B)=8.5 (bladder). In contrast, the nonpeptide tachykinin NK(2) receptor antagonist SR 48968 (or (S)-N-methyl-N [4-acetylamino-4-phenylpiperidino)-2-(3, 4-dichlorophenyl) butyl] benzamide) (30-1000 nM) produced insurmountable antagonism in all preparations. The tachykinin NK(2) receptor blockade produced by nepadutant in the colon was fully reversed by washout, whereas that produced by SR 48968 was not. Nepadutant (1 microM) greatly reduced (by 70-80%) the nonadrenergic noncholinergic (NANC) contractile off-response evoked by electrical field stimulation in the human ileum, and almost abolished it in the presence of the tachykinin NK(1) receptor antagonist GR 82334 (or: [[(S,S) Pro-Leu (spiro-gamma-lactam)](9,10),Trp(11)]Physalaemin (1-11)) (1 microM). The present results show that nepadutant is a potent, competitive and reversible antagonist at human tachykinin NK(2) receptors and provide further evidence that tachykinins act as excitatory NANC neurotransmitters in the human small intestine.