Suramin is a symmetric polyanionic naphthylurea originally used for the treatment of trypanosomiasis and onchocerciasis. Suramin and diverse analogues exhibit a broad range of biological actions in vitro and in vivo, including, among others, antiproliferative and antiviral activity. Suramin derivatives usually target purinergic binding sites. Class III histone deacetylases (sirtuins) are amidohydrolases that require nicotinamide adenine dinucleotide (NAD(+)) as a cofactor for their catalytic mechanism(.) Deacetylation of the target proteins leads to a change in conformation and alters the activity of the proteins in question. Suramin was reported to inhibit human sirtuin 1 (SIRT1). We tested a diverse set of suramin analogues to elucidate the inhibition of the NAD(+)-dependent histone deacetylases SIRT1 and SIRT2 and discovered selective inhibitors of human sirtuins with potency in the two-digit nanomolar range. In addition, the structural requirements for the binding of suramin derivatives to sirtuins were investigated by molecular docking. The recently published X-ray crystal structure of human SIRT5 in complex with suramin and the human SIRT2 structure were used to analyze the interaction mode of the novel suramin derivatives.

The G protein-coupled P2Y 11 receptor is involved in immune system modulation. In-depth physiological evaluation is hampered, however, by a lack of selective and potent ligands. By screening a library of sulfonic and phosphonic acid derivatives at P2Y 11 receptors recombinantly expressed in human 1321N1 astrocytoma cells (calcium and cAMP assays), the selective non-nucleotide P2Y 11 agonist NF546 [4,4Ј-(carbonylbis(imino-3,1-phenylene-carbonylimino-3,1-(4-methyl-phenylene)carbonylimino))-bis(1,3-xylene-␣,␣Ј-diphosphonic acid) tetrasodium salt] was identified. NF546 had a pEC 50 of 6.27 and is relatively selective for P2Y 11 over P2Y 1 , P2Y 2 , P2Y 4 , P2Y 6 , P2Y 12 , P2X 1 , P2X 2 , and P2X 2 -X 3 . Adenosine-5Ј-O-(3-thio)triphosphate (ATP␥S), a nonhydrolyzable analog of the physiological P2Y 11 agonist ATP, and NF546 use a common binding site as suggested by molecular modeling studies and their competitive behavior toward the nanomolar potency antagonist NF340 [4,4Ј-(carbonylbis(imino-3,1-(4-methyl-phenylene)carbonylimino))bis(naphthalene-2,6-disulfonic acid) tetrasodium salt] in Schild analysis. The pA 2 of NF340 was 8.02 against ATP␥S and 8.04 against NF546 (calcium assays). NF546 was further tested for P2Y 11 -mediated effects in monocyte-derived dendritic cells. Similarly to ATP␥S, NF546 led to thrombospondin-1 secretion and inhibition of lipopolysaccharide-stimulated interleukin-12 release, whereas NF340 inhibited these effects. Further, for the first time, it was shown that ATP␥S or NF546 stimulation promotes interleukin 8 (IL-8) release from dendritic cells, which could be inhibited by NF340. In conclusion, we have described the first selective, non-nucleotide agonist NF546 for P2Y 11 receptors in both recombinant and physiological expression systems and could show a P2Y 11 -stimulated IL-8 release, further supporting the immunomodulatory role of P2Y 11 receptors. Article, publication date, and citation information can be found at http://jpet.aspetjournals.org.

Selective and potent P2Y(11) receptor antagonists have yet to be developed, thus impeding an evaluation of this G protein-coupled receptor mainly expressed on immune cells. Taking suramin with moderate inhibitory potency as a template, 18 ureas with variations of the methyl groups of suramin and their precursors were functionally tested at P2Y(11), P2Y(1), and P2Y(2) receptors. Fluorine substitution of the methyl groups of suramin led to the first nanomolar P2Y(11) antagonist (8f, NF157, pK(i): 7.35). For selectivity, 8f was also tested at various P2X receptors. 8f displayed selectivity for P2Y(11) over P2Y(1) (>650-fold), P2Y(2) (>650-fold), P2X(2) (3-fold), P2X(3) (8-fold), P2X(4) (>22-fold), and P2X(7) (>67-fold) but no selectivity over P2X(1). QSAR studies confirm that residues with favored resonance and size parameters in the aromatic linker region can indeed lead to an increased potency as is the case for 8f. A symmetric structure linking two anionic clusters seems to be required for bioactivity. 8f may be helpful for studies evaluating the physiological role of P2Y(11) receptors.