Synthesis of phosphonate 3-phthalidyl esters as prodrugs for potential intracellular delivery of phosphonates.

A new prodrug approach for intracellular delivery of phosphonates was developed via the synthesis of 3-phthalidyl esters of 1-naphthalenemethylphosphonate. This approach is advantageous over the traditional acyloxymethyl phosphonate prodrugs, because these prodrugs do not generate formaldehyde and have improved plasma half-lives.

The solution structure of melanoma growth stimulating activity.

The solution structure of melanoma growth stimulating activity (MGSA), a dimeric chemokine consisting of 73 residues per monomer, has been determined using two-dimensional homonuclear and three-dimensional heteronuclear NMR spectroscopy. Structure calculations were carried out using a hybrid distance geometry-simulated annealing approach with the programs DGII and X-PLOR. The structure is based on a total of 2362 experimental restraints, comprising 2150 NOE-derived distance restraints (2076 unambiguous intrasubunit restraints, 60 unambiguous intersubunit restraints, and 14 ambiguous restraints with potential contributions from both intra- and intersubunit NOEs), 84 distance restraints for 42 backbone hydrogen bonds, and 128 torsion angle restraints. The ambiguous distance restraints were treated using a target function which accounts for both intra- and intermolecular contributions to the NOE intensity. A total of 25 structures were calculated, with the backbone (N, C alpha, C) atomic r.m.s. distribution about the mean coordinates for residues 8 to 69 being 0.44(+/- 0.10) A for the dimer and 0.34(+/- 0.07) A for the individual monomers. The N- and C-terminal residues (1 to 7 and 70 to 73, respectively) are disordered. The overall structure of the MGSA dimer is similar to that reported previously for the NMR and X-ray structures of interleukin-8 (IL-8), and consists of a six-stranded antiparallel beta-sheet packed against two C-terminal antiparallel alpha-helices. A best fit superposition of the NMR structure of MGSA on the X-ray and NMR structures of IL-8 yields backbone atomic r.m.s. differences of 0.99 and 1.28 A, respectively for individual monomers, and 1.08 and 1.82 A, respectively for the dimers (using MGSA residues 8 to 14 and 19 to 69). In general, the MGSA structure resembles the IL-8 X-ray structure more than it does the IL-8 NMR structure. At the tertiary (monomer) level the two main differences between the MGSA solution structure and IL-8 NMR structure involve the loops between residues 14 to 19 and between residues 30 to 38. At the quaternary (dimer) level the difference results from differing angles between the beta-strands which form the dimer interface, and is manifest as a different interhelical separation (distance of closest approach between the two helices is 15.3 A in the IL-8 NMR structure and 11.7 (+/- 0.4) A in the MGSA structure).

A receptor for the malarial parasite Plasmodium vivax: the erythrocyte chemokine receptor.

Plasmodium vivax and P. falciparum are the major causes of human malaria, except in sub-Saharan Africa where people lack the Duffy blood group antigen, the erythrocyte receptor for P. vivax. Duffy negative human erythrocytes are resistant to invasion by P. vivax and the related monkey malaria, P. knowlesi. Several lines of evidence in the present study indicate that the Duffy blood group antigen is the erythrocyte receptor for the chemokines interleukin-8 (IL-8) and melanoma growth stimulatory activity (MGSA). First, IL-8 binds minimally to Duffy negative erythrocytes. Second, a monoclonal antibody to the Duffy blood group antigen blocked binding of IL-8 and other chemokines to Duffy positive erythrocytes. Third, both MGSA and IL-8 blocked the binding of the parasite ligand and the invasion of human erythrocytes by P. knowlesi, suggesting the possibility of receptor blockade for anti-malarial therapy.

The human erythrocyte inflammatory peptide (chemokine) receptor. Biochemical characterization, solubilization, and development of a binding assay for the soluble receptor.

In addition to the two human interleukin-8 (IL-8) receptors that have been cloned, IL-8RA and IL-8RB, we recently described a binding protein in human erythrocytes that binds IL-8 and monocyte chemotactic peptide-1 (MCP-1), which we have termed the chemokine (CK) receptor. This communication describes the biochemical characterization, detergent solubilization, and development of a solubilized receptor binding assay for the erythrocyte CK receptor. Competitive 125I-IL-8 binding studies in cells transfected with IL-8RA and IL-8RB revealed that only IL-8 and MGSA were able to displace the radiolabeled IL-8 from these cells. In contrast, a whole array of chemokines were able to cross-compete with 125I-IL-8 for binding to the CK receptor in erythrocyte ghosts. Scatchard analysis of 125I-IL-8 binding to erythrocyte membranes and to dodecyl beta-maltoside solubilized CK receptors revealed a single class of high affinity binding sites in both cases with KD values of 9.5 nM +/- 3.6 and 15.4 nM +/- 5.0, respectively. Chemical cross-linking studies with erythrocyte membranes and with solubilized CK receptors indicated that the CK receptor has a lower molecular mass than the cloned IL-8 receptors (39 kDa compared to 57-69 kDa). Treatment of the cross-linked 47-kDA protein with N-glycanase reduced its molecular mass to 42 kDa.

Analysis of fibrinogen A alpha-fusion proteins. Mutants which inhibit thrombin equivalently are not equally good substrates.

We have examined the interaction of thrombin with fibrinogen A alpha chain residues 7-16. Using genetically engineered constructions, we have synthesized in Escherichia coli a fibrinogen A alpha 1-50 fusion protein and seven mutant proteins with single amino acid substitutions. These are: Asp7----Ala, Phe8----Tyr, Glu11----Ala, Gly12----Val, Gly13----Val, Gly14----Val, and Arg16----Leu. Competitive immunoassay of cell lysates showed that all the mutations but one, Arg16----Leu, altered the structure of the protein such that cross-reactivity with the A alpha-specific monoclonal antibody, Y18, was significantly reduced. The fusion proteins were purified and analyzed as thrombin inhibitors and substrates. All the fusion proteins are competitive inhibitors of the amidolytic hydrolysis of Spectrozyme TH, a thrombin-specific chromogenic substrate, with inhibition constants corresponding to that for fibrinogen. We conclude that these 7 amino acid substitutions do not alter thrombin binding to the fusion proteins. The fusion proteins were tested as substrates by monitoring thrombin-dependent peptide release. The natural sequence and three mutants, Asp7----Ala, Glu11----Ala, and Gly14----Val, are good substrates. The other mutants are either poor substrates or are not cleaved by thrombin within A alpha 1-50. These results indicate that residues between Asp7 and Arg16 are critical to efficient peptide hydrolysis, whereas residues outside this region are critical to thrombin binding.