Pure compound libraries; a new perspective for natural product based drug discovery.

What often distinguishes the leaders in drug discovery and development from the rest is the quality of their compound libraries and the ease of access that they have to the information within those libraries. The screening of natural products can provide greater structural diversity than standard synthetic chemistry and offers significant opportunities for finding novel low molecular weight lead compounds. However, which strategy is the best for natural-product-based drug discovery? Two well established but relatively time consuming approaches are the screening of crude extracts and pre-fractionated extracts. This case study describes a third, pure-compound-screening approach, and discusses its benefits and pitfalls.

The naphtosultam derivative RP 62203 (fananserin) has high affinity for the dopamine D4 receptor.

The dopamine D4 receptor is a potential target for novel antipsychotic drugs. Most available compounds with affinity for the dopamine D4 receptor also bind to dopamine D2 receptors. This report describe the affinity of the 5-HT2A receptor antagonist RP 62203 (fananserin) for the human dopamine D4 receptor. Fananserin displaces [3H]spiperone binding to recombinant human dopamine D4 receptors with a Ki of 2.93 nM. This compares with an affinity (Ki) of 0.37 nM for the rat 5-HT2A receptor and of 726 mM for the rat dopamine D2 receptor. [3H]Fananserin can be used to label the recombinant dopamine D4 receptor expressed in Chinese hamster ovary cells with a KD of 0.725 nM. Fananserin is, thus, the first compound to be reported that distinguishes between dopamine D4 and D2 receptors.

Naturally occurring somatostatin and vasoactive intestinal peptide inhibitors. Isolation of alkaloids from two marine sponges.

The vasoactive intestinal peptide (VIP) and somatostatin (somatotropin release inhibiting factor, SRIF) are important neurotransmitters in a number of basic physiological events. Their disturbances have been reported in many diseases such as cystic fibrosis, impotent man (VIP), Alzheimer's disease, and some tumours (SRIF). Xestospongine B (1), sceptrine (2), and ageliferine (3), three alkaloids isolated from Xestospongia sp. and Agelas novaecaledoniae are reported as somatostatin and VIP inhibitors. The natural products 1, 2 and 3 exhibited a high affinity for somatostatin (IC50 = 12 microM, 0.27 microM, and 2.2 microM, respectively), 2 and 3 showed an affinity for VIP (19.8 microM and 19.2 microM, respectively). Due to the interaction between non-peptidic compounds and somatostatin/VIP receptors, these three alkaloids could be promising agents in the research on natural non-peptidic compounds for therapeutical interventions.

Further brominated bis- and tris-indole alkaloids from the deep-water New Caledonian marine sponge Orina Sp.

Two tris-indole alkaloids, (+/-) gelliusines A and B [1], have been isolated for the first time from a marine source, the New Caledonian sponge, Orina sp. (or Gellius sp.), along with five further indole constituents [2-6]. Compound 6 has been identified as 2,2-bis-(6'-bromo-3'-indolyl(-ethylamine, previously isolated from the tunicate Didemnum candidum, but the remaining four indoles [2-5] are novel compounds. These showed anti-serotonin activity and a strong affinity for somatostatin and neuropeptide Y receptors in receptor-binding assays.

The human galanin receptor: ligand-binding and functional characteristics in the Bowes melanoma cell line.

The human galanin receptor has been characterized pharmacologically from the Bowes melanoma cell line. Using porcine [125I]galanin as the radioligand, a single population of non-interacting high-affinity binding sites (KD = 0.05 +/- 0.01 nM; Bmax = 135 +/- 7 fmol/mg protein) was demonstrated. Human galanin peptide competitively inhibited the specific binding of [125I]galanin (IC50 = 0.35 +/- 0.13 nM) and decreased the forskolin-stimulated cAMP production (EC50 = 0.46 +/- 0.05 nM) with a maximal inhibition of 63 +/- 2% at 10(-7) M. Rat and porcine galanin peptides and the chimeric peptides M15, M35, M32, M40 and C7 also dose-dependently inhibited the forskolin-stimulated cAMP production, while the fragment porcine galanin-(3-29) and [D-Trp2]galanin were found to be inactive. The specific binding of [125I]galanin was decreased in a dose-dependent manner by GTP and the cAMP response was inhibited by the pertussis toxin, suggesting the activation of a G-protein dependent process. The Bowes cell line thus appears to be a relevant tool for the study of human galanin receptor.

Stereospecific hydrolysis by soluble and immobilized lipases.

Stereospecific hydrolysis of insoluble monoesters by lipases are reported. Among the lipases tested, porcine pancreatic lipase was the most stereospecific when acting on 3-chloro-2-methyl propanol propionate. When the chain length of the acid was enhanced, the stereospecificity decreased. Initial rate measurements analysis concluded that the observed stereospecificity was the result of different catalytic constants rather than different Michaelis constants. From these results, methods were derived for the preparation of l- or d-3-chloro-2-methylpropanol (an intermediary in the synthesis of levomepromasine) based on the hydrolysis of esters by soluble or immobilized lipases.

Purification and specificity of antibodies to adenosine.

Antibodies to adenosine were elicited in rabbits by immunization with bovine serum albumin-adenosine conjugate. The antibodies were purified and fractionated on two affinity columns (Sepharose-oligo(A) and Sepharose-AMP). Two families of antibodies have been obtained. The antibodies purified on the Sepharose-oligo(A) column react with poly(A) while those purified on the Sepharose-AMP column do not, as shown by gel diffusion. The association constants for the binding of Fab fragments or IgG purified on the Sepharose-oligo(A) column and several haptens were deduced from dialysis equilibrium, fluorescence quenching and displacement of AMP-fluorescein conjugate. The antibodies mainly recognize adenine, and the ribose or the phosphate group of (or AMP derivatives) do not play a critical role in the interaction. Thermodynamic parameters for adenosine-Fab fragments complexes have been determined deltaH degrees = 16 kcal/mole and deltaS degrees = - 15 cal. degree-1 mole-1. Circular dichroism studies indicate that about three nucleotide residues penetrate the binding site of Fab fragments.

[Specificity of anti-ApA antibodies]. / Spécificité des anticorps anti-ApA

Antibodies to ApA elicited in Rabbits by immunization with bovine serum albumin-ApA conjugate have been purified by affinity chromatography. These purified antibodies react with bovine serum albumin-AMP, 8 bromo AMP, ApA conjugates as shown by gel diffusion. The association constants for the binding of antibodies and several haptens were deduced from dialysis equilibrium. The number of bound hapten molecules per antibody binding site depends upon the nature of the hapten.