Ixonnexin from Tick Saliva Promotes Fibrinolysis by Interacting with Plasminogen and Tissue-Type Plasminogen Activator, and Prevents Arterial Thrombosis

Tick saliva is a rich source of modulators of vascular biology. We have characterized Ixonnexin, a member of the "Basic-tail" family of salivary proteins from the tick Ixodes scapularis. Ixonnexin is a 104 residues (11.8 KDa), non-enzymatic basic protein which contains 3 disulfide bonds and a C-terminal rich in lysine. It is homologous to SALP14, a tick salivary FXa anticoagulant. Ixonnexin was produced by ligation of synthesized fragments (51-104) and (1-50) followed by folding. Ixonnexin, like SALP14, interacts with FXa. Notably, Ixonnexin also modulates fibrinolysis in vitro by a unique salivary mechanism. Accordingly, it accelerates plasminogen activation by tissue-type plasminogen activator (t-PA) with Km 100 nM; however, it does not affect urokinase-mediated fibrinolysis. Additionally, lysine analogue ε-aminocaproic acid inhibits Ixonnexin-mediated plasmin generation implying that lysine-binding sites of Kringle domain(s) of plasminogen or t-PA are involved in this process. Moreover, surface plasmon resonance experiments shows that Ixonnexin binds t-PA, and plasminogen (KD 10 nM), but not urokinase. These results imply that Ixonnexin promotes fibrinolysis by supporting the interaction of plasminogen with t-PA through formation of an enzymatically productive ternary complex. Finally, in vivo experiments demonstrates that Ixonnexin inhibits FeCl3-induced thrombosis in mice. Ixonnexin emerges as novel modulator of fibrinolysis which may also affect parasite-vector-host interactions.

Identification and Mechanistic Analysis of a Novel Tick-Derived Inhibitor of Thrombin

A group of peptides from the salivary gland of the tick Hyalomma marginatum rufipes, a vector of Crimean Congo hemorrhagic fever show weak similarity to the madanins, a group of thrombin-inhibitory peptides from a second tick species, Haemaphysalis longicornis. We have evaluated the anti-serine protease activity of one of these H. marginatum peptides that has been given the name hyalomin-1. Hyalomin-1 was found to be a selective inhibitor of thrombin, blocking coagulation of plasma and inhibiting S2238 hydrolysis in a competitive manner with an inhibition constant (Ki) of 12 nM at an ionic strength of 150 mM. It also blocks the thrombin-mediated activation of coagulation factor XI, thrombin-mediated platelet aggregation, and the activation of coagulation factor V by thrombin. Hyalomin-1 is cleaved at a canonical thrombin cleavage site but the cleaved products do not inhibit coagulation. However, the C-terminal cleavage product showed non-competitive inhibition of S2238 hydrolysis. A peptide combining the N-terminal parts of the molecule with the cleavage region did not interact strongly with thrombin, but a 24-residue fragment containing the cleavage region and the C-terminal fragment inhibited the enzyme in a competitive manner and also inhibited coagulation of plasma. These results suggest that the peptide acts by binding to the active site as well as exosite I or the autolysis loop of thrombin. Injection of 2.5 mg/kg of hyalomin-1 increased arterial occlusion time in a mouse model of thrombosis, suggesting this peptide could be a candidate for clinical use as an antithrombotic.

EPR and ENDOR of Sodium Complexes of Spin Labeled Monoazacrown Ethers

Sodium complexes 3 and 5 of the spin labeled monoazacrown ethers 2,2,15,15-tetramethyl-1-aza- 4,7,10,13-tetraoxacyclopentadecane-1-oxyl (2) and 1,4,7,10-tetraoxa-13-(2′,2′,6′,6′-tetramethyl-piperidine-1′-oxyl-4′-yl)azacyclopentadecane (4) were synthesized and studied by EPR and ENDOR spectroscopies. The hyperfine splitting parameter and the g value of the complex 5, containing the exocyclic nitroxyl moiety, were identical to the parent complexon 4, i.e., aN = 15.6 G. g = 2.0060 ± 0.0001. In contrast, the data for the complex 3, containing the endocyclic nitroxyl moiety were different. Thus, the spectrum of the complex 3 was a triplet of quartets with aN = 15.7 G. aNa = 2.47 G, g = 2.0062 ± 0.0001, whereas the spectrum of the parent complexon 2 was a triplet with aN = 15.5 G, g = 2.0059 ± 0.0001.

The interaction between the sodium cation and the nitroxyl moiety in 3 was further confirmed by the sodium ENDOR transition at 7.27 MHz

In the Search for New Anticancer Drugs, III+ Phosphorylated Diaziridine Derivatives

Several N-diethoxyphosphoryl derivatives 7 of various diaziridines, and compounds 12, 15a, 15b, 18 and 20, structurally related to TEPA (1a) and spin labeled Thio-TEPA (1c) were synthesized.

In the Search for New Anticancer Drugs, XVI Selective Protection and Deprotection of Primary Amino Groups in Spermine, Spermidine and Other Polyamines

Spermidine, spermine and other polyamines 1-5 were selectively protected at the terminal primary amino functions without affecting the secondary amino groups using N-ethoxycarbonyl-phthalimide (15), the Nefkens’ reagent. Three representative products, 17, 18 and 20, readily underwent acylation at the secondary amino nitrogen to give the corresponding compounds 21-26. Selective deprotection of two representative samples 22 and 25 at the primary amino function by hydrazinolysis yielded the corresponding derivatives 27 and 28 with free primary amino groups.

In summary, the application of Nefkens’ reagent for the terminal protection of primary amino groups in various polyamines results in a simple, efficient and selective one-step procedure using commercially available reagents.

Synthesis of Water Soluble Spin Labeled Glucose Derivatives as Potential NMR Contrast Enhancing Agents

Synthetic methodologies for the preparation of nitroxyl labeled derivatives of D -(+)-glucose, α -D -(+)-m ethylglycoside, 2-amino-2-deoxy-D -(+)-glucose, and D -(+)-glucuronic acid are presented. The spin labels in these compounds are attached variably at the 1, 2, 3, and 6 positions of the glucose framework. These new compounds, being water soluble and producing marked en­hancement of spin-lattice (T ,) and spin-spin (T2) proton relaxation in deionized water and human plasma have potential utility as contrast altering pharmaceuticals for magnetic resonance imaging and as spin probes in biomolecular research. These spin labeled carbohydrates may demonstrate in vivo biodistribution characteristics reflecting tissue-specific differences in glucose metabolism .

Synthesis of Cross-Linked Polyamines

Several synthetic approaches are explored for the preparation of polyamines which are cross-linked at the central, secondary nitrogen moiety. Diethylenetriamine, norspermidine and spermidine were used as examples.

Preparation of an Aminoxyl Analog of the Anticancer Agent Miltefosine

The synthesis and a few properties of hexadecyl 2-[N,N-dimethyl-N-(2,2,6.6-tetramethyll- oxyl-piperidin-4-yl)ammonio] ethyl phosphate are described. This compound is a spin labeled analog of the antineoplastic drug hexadecylphosphocholine (Miltefosine)

The epitope of monoclonal antibodies blocking erythrocyte invasion by Plasmodium falciparum map to the dimerization and receptor glycan binding sites of EBA-175

The malaria parasite, Plasmodium falciparum, and related parasites use a variety of proteins with Duffy-Binding Like (DBL) domains to bind glycoproteins on the surface of host cells. Among these proteins, the 175 kDa erythrocyte binding antigen, EBA-175, specifically binds to glycophorin A on the surface of human erythrocytes during the process of merozoite invasion. The domain responsible for glycophorin A binding was identified as region II (RII) which contains two DBL domains, F1 and F2. The crystal structure of this region revealed a dimer that is presumed to represent the glycophorin A binding conformation as sialic acid binding sites and large cavities are observed at the dimer interface. The dimer interface is largely composed of two loops from within each monomer, identified as the F1 and F2 β-fingers that contact depressions in the opposing monomers in a similar manner. Previous studies have identified a panel of five monoclonal antibodies (mAbs) termed R215 to R218 and R256 that bind to RII and inhibit invasion of erythrocytes to varying extents. In this study, we predict the F2 β-finger region as the conformational epitope for mAbs, R215, R217, and R256, and confirm binding for the most effective blocking mAb R217 and R215 to a synthetic peptide mimic of the F2 β-finger. Localization of the epitope to the dimerization and glycan binding sites of EBA-175 RII and site-directed mutagenesis within the predicted epitope are consistent with R215 and R217 blocking erythrocyte invasion by Plasmodium falciparum by preventing formation of the EBA-175– glycophorin A complex.

The scaffolding protein synapse-associated protein 97 is required for enhanced signaling through isotype-switched IgG memory B cell receptors

After their first encounter with a foreign antigen, naïve B cells that have immunoglobulin M (IgM) B cell receptors (BCRs) trigger the primary antibody response and the generation of memory B cells with IgG BCRs. When these memory B cells reencounter the same antigen, the cell surface IgG BCRs stimulate their rapid differentiation into plasma cells that release large amounts of IgG antibodies. We showed that the conserved cytoplasmic tail of the IgG BCR, which contains a putative PDZ (postsynaptic density 95/disc large/zona occludens 1)-binding motif, associated with synapse-associated protein 97 (SAP97), a PDZ domain-containing scaffolding molecule that is involved in controlling receptor density and signal strength at neuronal synapses. SAP97 accumulated and bound to IgG BCRs in the immunological synapses that formed in response to B cell engagement with antigen. Knocking down SAP97 in IgG⁺ B cells or mutating the putative PDZ-binding motif in the BCR tail impaired formation of the immunological synapse, initiation of IgG BCR signaling, and downstream activation of the mitogen-activated protein kinase p38. Thus, heightened B cell memory responses are encoded, in part, by a mechanism that involves SAP97 serving as a scaffolding protein in the IgG BCR immunological synapse.

Cyr61/CCN1 displays high-affinity binding to the somatomedin B(1-44) domain of vitronectin

Background

Cyr61 is a member of the CCN (Cyr61, connective tissue growth, NOV) family of extracellular-associated (matricellular) proteins that present four distinct functional modules, namely insulin-like growth factor binding protein (IGFBP), von Willebrand factor type C (vWF), thrombospondin type 1 (TSP), and C-terminal growth factor cysteine knot (CT) domain. While heparin sulphate proteoglycans reportedly mediate the interaction of Cyr61 with the matrix and cell surface, the role of other extracellular associated proteins has not been revealed.

Methods and Findings

In this report, surface plasmon resonance (SPR) experiments and solid-phase binding assays demonstrate that recombinant Cyr61 interacts with immobilized monomeric or multimeric vitronectin (VTNC) with K_D in the nanomolar range. Notably, the binding site for Cyr61 was identified as the somatomedin B domain (SMTB ^1–44) of VTNC, which mediates its interaction with PAI-1, uPAR, and integrin αvβ3. Accordingly, PAI-1 outcompetes Cyr61 for binding to immobilized SMTB ^1–44, and Cyr61 attenuates uPAR-mediated U937 adhesion to VTNC. In contrast, isothermal titration calorimetry shows that Cyr61 does not display high-affinity binding for SMTB ^1-44 in solution. Nevertheless, competitive ELISA revealed that multimeric VTNC, heat-modified monomeric VTNC, or SMTB ^1–44 at high concentrations attenuate Cyr61 binding to immobilized VTNC, while monomeric VTNC was ineffective. Therefore, immobilization of VTNC exposes cryptic epitopes that recognize Cyr61 with high affinity, as reported for a number of antibodies, β-endorphin, and other molecules.

Conclusions

The finding that Cyr61 interacts with the SMTB ^1–44 domain suggests that VTNC represent a point of anchorage for CCN family members to the matrix. Results are discussed in the context of the role of CCN and VTNC in matrix biology and angiogenesis.

Molecular analysis of CPRalpha, a MATalpha-specific pheromone receptor gene of Cryptococcus neoformans

The putative Cryptococcus neoformans pheromone receptor gene CPRalpha was isolated and studied for its role in mating and filamentation. CPRalpha is MATalpha specific and located adjacent to STE12alpha at the MATalpha locus. It encodes a protein which possesses high sequence similarity to the seven-transmembrane class of G-protein-coupled pheromone receptors reported for other basidiomycetous fungi. Strains containing a deletion of the CPRalpha gene exhibited drastic reductions in mating efficiency but were not completely sterile. Delta cpr alpha cells displayed wild-type mating efficiency when reconstituted with the wild-type CPRalpha gene. Hyphal production on filament agar was not affected in the delta cpr alpha strain, indicating no significant role for CPRalpha in sensing environmental cues during haploid fruiting. The wild-type MATalpha CPRalpha strain produced abundant hyphae in response to synthetic MATa pheromone; however, the hyphal response to pheromone by delta cpr alpha cells was significantly reduced. Exposure of wild-type cells to synthetic MATa pheromone for 2 h induced MFalpha pheromone expression, whereas unexposed cells showed only basal levels of the MFalpha transcript. The delta cpr alpha cells, however, exhibited only basal levels of MFalpha message with or without pheromone exposure, suggesting that CPRalpha and MFalpha are components of the same signaling pathway.

Differential zinc and DNA binding by partial peptides of human protamine HP2

The Zn(II) binding by partial peptides of human protamine HP2: HP2(1-15); HP2(1-25), HP2(26-40), HP2(37-47), and HP2(43-57) was studied by circular dichroism (CD). Precipitation of a 20-mer DNA by these partial peptides and the effects of Zn(II) thereon were investigated using polyacrylamide gel electrophoresis (GE). The results of this study suggest that reduced HP2 (thiol groups intact) can bind Zn(II) at various parts of the molecule. In the absence of DNA, the primary Zn(II) binding site in reduced HP2 is located in the 37-47 sequence (involving Cys-37, His-39, His-43, and Cys-47), while in the presence of DNA, the strongest Zn(II) binding is provided by sequences 12-22 (by His-12, Cys-13, His-19, and His-22) and 43-57 (His-43, Cys-47, Cys-53, and His-57). In its oxidized form, HP2 can bind zinc through His residues of the 7-22 sequence. Zn(II) markedly enhances DNA binding by all partial peptides. These findings suggest that Zn(II) ions may be a regulatory factor for sperm chromatin condensation processes.

Ni(II) specifically cleaves the C-terminal tail of the major variant of histone H2A and forms an oxidative damage-mediating complex with the cleaved-off octapeptide

The acetyl-TESHHK-amide peptide, modeling a part of the C-terminal "tail" of histone H2A, was found previously by us to undergo at pH 7. 4 a Ni(II)-assisted hydrolysis of the E-S peptide bond with formation of a stronger Ni(II) complex with the SHHK-amide product [Bal, W., et al. (1998) Chem. Res. Toxicol. 11, 1014-1023]. To further characterize the hydrolysis and test the resulting Ni(II) complex for redox activity, bovine histone H2A and three peptides were investigated: acetyl-LLGKVTIAQGGVLPNIQAVLLPKKTESHHKAKGK (H2A(34)), modeling the entire "C-tail" of H2A; SHHKAKGK (H2A(8)), modeling the cutoff product of hydrolysis; and acetyl-KTESHKAKGK (H2A(10)), modeling a putative Ni(II) binding site in a minor variant H2A.4 of human histone H2A. The Ni(II)-assisted hydrolysis of H2A and H2A(34) was found to proceed approximately 7-fold faster than that of the Ni(II)-acetyl-TESHHK-amide complex under comparable conditions. In both cases, the Ni(II) complex with H2A(8) was the smaller product of the hydrolysis, indicating a high site specificity of the reaction. Of three other metals tested with H2A(34), only Cu(II) cleaved the E-S bond, although much less efficiently than Ni(II); Co(II) and Zn(II) had no effect whatsoever. The H2A(10) peptide appeared to be fully resistant to hydrolytic cleavage and did not exhibit any redox activity versus H(2)O(2) in the presence of Ni(II) at pH 7.4. Likewise, redox-inactive was the Ni(II)-H2A(34) complex. In contrast, the Ni(II)-H2A(8) complex promoted oxidative damage of pUC19 DNA by H(2)O(2), evidenced by a significant increase in the number of single strand breaks and nucleobase modifications typical for a hydroxyl radical-like species attack on DNA. Interestingly, instead of 8-oxopurines, the corresponding formamidopyrimidines were the major products of the damage. The difference in redox activity between the Ni(II)-H2A(34) and Ni(II)-H2A(8) complexes is most likely associated with their different geometries: octahedral and square planar, respectively. Incubation of the Ni(II)-H2A(8) complex with H(2)O(2) also resulted in degradation of the peptide ligand, especially at its Ser and His residues. Thus, binding of Ni(II) to the ESHHK motif of the histone H2A C-tail is damaging to the histone C-terminal tail and to histone-associated DNA. The results support a dual mechanism of Ni(II)-induced carcinogenesis, including both genotoxic and epigenetic effects.

Interactions of Nickel(II) with histones: interactions of Nickel(II) with CH3CO-Thr-Glu-Ser-His-His-Lys-NH2, a peptide modeling the potential metal binding site in the "C-Tail" region of histone H2A

A combined pH-metric and spectroscopic (UV/vis, CD, NMR) study of the Ni(II) binding to CH3CO-Thr-Glu-Ser-His-His-Lys-NH2 (AcTESHHKam), a blocked hexapeptide modeling a part of the C-terminal sequence of the major variant of histone H2A (residues 120-125), revealed the formation of a pseudo-octahedral NiHL complex in weakly acidic and neutral solutions. Ni(II) is bound to the peptide through imidazole nitrogens on both of its histidine residues and the carboxylate of the side chain of glutamic acid. At higher pH, a series of square-planar complexes are formed. This process is accompanied by hydrolytic degradation of the peptide. At pH 7.4, the peptide hydrolyzes in a Ni(II)-assisted fashion, yielding the square-planar Ni(II) complex of SHHKam as the sole product detected by CD, MALDI-TOF MS, and HPLC. Quantitative analysis of complex stabilities indicates that the -TESHHK- motif is a very likely binding site for carcinogenic Ni(II) ions in the cell nucleus. The Ni(II)-assisted hydrolysis of the C-terminal chain of histone H2A may provide a novel mechanism of genotoxicity combining the damage to the nucleosome with the generation of further toxic Ni(II) species.

Definition of T cell epitopes within the 19 kDa carboxylterminal fragment of Plasmodium yoelii merozoite surface protein 1 (MSP1(19)) and their role in immunity to malaria

MSP1(19) is one of the leading malaria vaccine candidates. However, the mechanism of protection is not clear. To determine whether MSP1(19)-specific effector T cells can control parasitaemia, we analysed the specificity of T cells induced following immunization with recombinant forms of P. yoelii MSP1(19) and asked whether they could protect mice. There was no evidence that effector T cells were capable of protecting since: (1) immunization of mice with yMSP1(19), but not defined epitopes, was able to induce protection; and (2) long term MSP1(19)-specific CD4+ T cell lines were incapable of adoptively transferring protection. In contrast, priming mice with the T cell epitopes resulted in a rapid anamnestic antibody response to MSP1(19) after either challenge with MSP1(19) or parasite. Thus, MSP1(19) contains multiple T cell epitopes but such epitopes are the targets of helper T cells for antibody response but not of identified effector T cells capable of controlling parasitaemia.

Mediation of oxidative DNA damage by nickel(II) and copper(II) complexes with the N-terminal sequence of human protamine HP2

The potential of Ni(II) and Cu(II) complexes with Arg-Thr-His-Gly-Gln-Ser-His-Tyr-Arg-Arg-Arg-His-Cys-Ser-Arg-amide (HP2(1-15)), a peptide modeling the N-terminal amino acid sequence of human protamine HP2, to mediate oxidative DNA damage was studied by measurements of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxo-dG) generation from 2'-deoxyguanosine (dG) and calf thymus DNA and by formation of double-strand breaks in calf thymus DNA. The concentrations of reagents were 0.1 mM dG and the metal-HP2(1-15) complex, 1 mM H2O2, 1.5 mM DNA (per phosphate group), 100 mM phosphate buffer, pH 7.4, ambient O2. Samples were incubated at 37 degrees C for 16-24 h. The Cu(II)-HP2(1-15) complex was found to be an effective promoter of the formation of 8-oxo-dG from both dG and DNA with ambient O2 (approximately 13- and 3-fold increase versus the oxidant alone, respectively) and H2O2 (approximately 25-fold increase in either case). The Ni(II)-HP2(1-15) complex was ineffective with O2 versus 8-oxo-dG production from both substrates but markedly enhanced the attack of H2O2 on dG and DNA (approximately 5-fold increase of 8-oxo-dG production in either case). Both Cu(II)- and Ni(II)-HP2(1-15) equally promoted double-strand scission by H2O2 in calf thymus DNA. The promotion by the complexes of dG and DNA oxidation with H2O2 was accompanied by oxidative damage to the complexes themselves, consisting of decreasing contents of their His (to approximately 50% of control in either complex) and especially Tyr (down to 48% of control in Cu(II)- and 19% in Ni(II)-HP2[1-15]) residues, as well as appearance of aspartic acid, the known oxidation product of His residues in peptides (up to 22% vs Gly for Cu(II)- and 10% for Ni(II)-HP2(1-15)). The above results provide a novel chemical mechanism of Cu(II) and Ni(II) toxicity and may have wide implications for reproductive and transgenerational effects of metal exposure.

Interactions of nickel(II) with histones: enhancement of 2'-deoxyguanosine oxidation by Ni(II) complexes with CH3CO-Cys-Ala-Ile-His-NH2, a putative metal binding sequence of histone H3

Studies of 2'-deoxyguanosine oxidation by hydrogen peroxide in the presence of CH3CO-Cys-Ala-Ile-His-NH2 (CAIH) and/or NiCl2 have been carried out in 100 mM phosphate buffer (pH 7.4) at 37 degrees C. The dimeric CAIH oxidation product, CAIH disulfide, and its weak, octahedral Ni(II) complex, rather than the monomeric CAIH and its strong, square-planar Ni(II) complex, were found to be major catalysts of 8-oxo-2'-deoxyguanosine (8-oxo-dG) formation. The presence of Ni(II) largely enhanced 8-oxo-dG yield, especially at submillimolar concentrations of H2O2. The reaction was found not to involve detectable amounts of free radicals or Ni(III). These results, together with those published previously [Bal, W. et al. (1995) Chem. Res. Toxicol. 8, 683-692], lay a framework for the detailed investigations of the interactions of histone octamer with Ni(II) and other metal ions. They also suggest that molecular mechanisms of nickel carcinogenesis may involve oxidative damage processes catalyzed by weak Ni(II) complexes with cellular components.

Interactions of nickel(II) with histones. Stability and solution structure of complexes with CH3CO-Cys-Ala-Ile-His-NH2, a putative metal binding sequence of histone H3

Nickel(II) compounds are established human carcinogens, but the molecular mechanisms underlying their activity are only partially known. One mechanism may include mediation by nickel of promutagenic oxidative DNA damage that depends on Ni(II) binding to chromatin. To characterize such binding at the histone moiety of chromatin, we synthesized the peptide CH3CO-Cys-Ala-Ile-His-NH2 (L), a model of the evolutionarily conserved motif in histone H3 with expected affinity for transition metals, and evaluated its reactivity toward Ni(II). Combined spectroscopic (UV/vis, CD, NMR) and potentiometric measurements showed that, at physiological pH, mixtures of Ni(II) and L yielded unusual macrochelate complexes, NiL and NiL2, in which the metal cation was bound through Cys and His side chains in a square-planar arrangement. Above pH 9, a NiH-3L complex was formed, structurally analogous to typical square-planar nickel complexes. These complexes are expected to catalyze oxidation reactions, and therefore, coordination of Ni(II) by the L motif in core histone H3 may be a key event in oxidative DNA base damage observed in the process of Ni(II)-induced carcinogenesis.

Effect of TAP on the generation and intracellular trafficking of peptide-receptive major histocompatibility complex class I molecules

Using a fluorescein-conjugated antigenic peptide, peptide-receptive H-2Kb MHC class I molecules were found throughout the secretory pathways of RMA cells and peptide transporter (TAP)-deficient derivative cells (RMA/S). RMA/S cells displayed higher levels of intracellular peptide-receptive molecules, while, surprisingly, RMA cells expressed 3- to 5-fold more cell surface peptide-receptive molecules. Metabolic radiolabeling of Kb-associated oligosaccharides with [1-3H]galactose demonstrated that despite a large difference in the fraction of Kb molecules in native conformation in detergent extracts, Kb transport rates from the trans-Golgi complex to the surfaces of RMA and RMA/S cells were similar. Thus, although considerable numbers of class I alpha chains reach the RMA/S cell surface, they are a less productive source of peptide-receptive molecules than class I molecules synthesized by TAP-expressing RMA cells, suggesting paradoxically that TAP functions to increase the amount of peptide-receptive molecules at the cell surface.

In the search for new anticancer drugs. 26. A comparison of anticancer activities of several TEPA, thio-TEPA, Seleno-TEPA, and azetidine analogs, including congeners containing an aminoxyl moiety

A series of TEPA, Thio-TEPA, Seleno-TEPA, and azetidine analogs, including congeners containing an aminoxyl moiety, were synthesized and evaluated in vivo for anticancer activity against the murine lymphocytic leukemia P388. All aziridine derivatives were found to be active with an increase in life span ranging from 42% to 272%, and all azetidine analogs were rated as inactive with one marginal exception. An attempt was made to rationalize the results on the basis of the lipophilic properties of the compounds. The most active compound (8) possessed the most balanced lipophilic properties, corresponding to a log P value near zero.

Endogenous peptides bound to HLA-A3 possess a specific combination of anchor residues that permit identification of potential antigenic peptides

A motif specific to peptides that bind to the human class I major histocompatibility complex molecule HLA-A3 was identified by sequence analysis of HPLC fractions containing endogenous peptides. Twenty-six different sequences were obtained, 19 of which were nonamers. The majority of these endogenous peptide sequences contained Leu at position (P)2, while most sequences contained Tyr or Lys at P9. In addition, Phe was shared by 16 sequences at P3. Synthetic peptides corresponding to endogenous peptide sequences were shown to bind to HLA-A3. The importance of Leu at P2 and Tyr or Lys at P9 ("anchor" residues) for peptide binding to HLA-A3 was demonstrated by the following results: (i) peptides GLFGGGGGY, GLFGGGGGK, and GLGGGGFGY, but not GLFGGGGGV, specifically bound to HLA-A3 and (ii) six nonapeptides from within the influenza A nucleoprotein, matrix, and polymerase proteins, selected for synthesis based upon their possession of P2 and P9 anchor residues, were shown to bind HLA-A3. In contrast, none of a set of eight peptides that bound to HLA-A2, or six that bound to HLA-B27, bound detectably to HLA-A3. These findings provide a rationale for the design and selection of peptides that can be recognized by HLA-A3-restricted T cells.

In the search for new anticancer drugs. 17. Linear and cyclic polyether analogues of N,N:N',N':N'',N''-tri-1,2-ethanediylphosphoric triamide and N,N:N',N':N'',N''-tri-1,2-ethanediylphosphorothioic triamide

Linear and cyclic polyether derivatives of N,N:N',N':N'',N''-tri-1, 2-ethanediylphosphoric triamide (TEPA) and N,N:N',N':N'',N''-tri-1,2-ethanediylphosphorothioic triamide (thio-TEPA) are synthesized and evaluated for their antineoplastic activity against the murine lymphocytic leukemia P388. All compounds, except for 7d, were active ranging from 42% to 287% increase in life span (% ILS). All CD2F1 male mice treated with the most active compound (7a) at 90 mg/kg per day for 9 days were alive after 30 days, whereas all mice treated with the clinical drug thio-TEPA were dead. The % ILS for compound 7a on day 60 was 525. A correlation is presented between the structural features of compounds and their lipophilicities and antineoplastic activities.

Human erythrocyte membrane permeability and nitroxyl spin-label reduction

Nitroxyl spin labels are paramagnetic compounds that have demonstrated utility as contrast enhancing agents in proton magnetic resonance imaging. The time-course of contrast enhancement depends on distribution and elimination of these agents. Reduction, resulting in formation of the diamagnetic hydroxylamine, is the major metabolic pathway observed in vivo. This bioreduction has implications for the design of contrast agents and for understanding their imaging behavior. Bioreduction has been shown to occur, at least in part, intracellularly. As such, cell membrane permeability to nitroxyl spin labels may influence their bioreduction. In this study, this influence was examined using eight nitroxyl derivatives and the human erythrocyte suspension as a model biomembrane system. Ionizable weak acids and bases were found to equilibrate rapidly across the erythrocyte membrane with half-times of equilibration ranging from less than 10 s to 1.6 min. These derivatives had low octanol:buffer distribution coefficients and were extensively ionized at the pH of the system (7.0). A strong acid, a phosphate ester, and a quaternary amine derivative were excluded by the cell membrane. Reduction of nitroxyl spin labels by the erythrocyte was shown to occur intracellularly. Except for the impermeable probes, the reduction rate was slow in comparison with the membrane penetration rate. The structural dependence of reduction rate was unrelated to penetration rate but correlated well with that observed in other reducing systems, namely, ascorbic acid solution and rat tissue homogenates.

Diradical nitroxyl spin label contrast agents for magnetic resonance imaging. A comparison of relaxation effectiveness

The proton relaxation enhancement characteristics of seven potential MRI contrast agents containing two nitroxyl spin labels per molecule (diradicals) were compared with eight similar agents with only one spin label per molecule (monoradicals). Diradical nitroxyls were evaluated to test the hypothesis that multiple paramagnetic centers in one molecule will result in stronger proton relaxation enhancement characteristics, allowing effective contrast enhancement at lower molar concentrations and thus a reduced osmotic load and greater safety. The acute toxicity of these agents is believed to be largely related to osmotic load. Five of seven diradical nitroxyls tested had spin-lattice relaxivities that were substantially greater than all eight of the monoradicals tested. The spin-spin relaxation properties of these agents and other pertinent characteristics are favorable for contrast enhancement. The results indicate that diradical nitroxyl spin labels may be used advantageously for the design of safer, more effective MRI contrast agents.

Novel Spin Labeled Azacrown Ethers

Four novel spin labeled azacrown ethers contain­ing either endo- or exo-cyclic nitroxyl moieties were synthesized by short and convenient routes. These compounds should be of interest in biological studies of membranes using ESR spectroscopy.

In the search for new anticancer drugs. 13. Phosphonic and phosphinic analogues of ornithine

Phosphonic (4a,b) and phosphinic (5a-d) analogues of ornithine were synthesized and evaluated for their inhibitory activity against ornithine decarboxylase and against the lymphocytic leukemia P388. The title compounds possess a low degree of inhibition against rat liver ornithine decarboxylase as compared to alpha-(difluoromethyl)ornithine. Thus, compounds 4a and 5a inhibit by 40% the ornithine decarboxylase activity at a 5 mM concentration. The other derivatives are less potent. Compounds 4a, 4b, 5b, and 5d are inactive against P388 tumor in CD2F1 mice at doses of 50 and 150 mg/kg.

In the search for new anticancer drugs. VII

Three new diaziridine platinum(II) complexes (4a)-(4c), and a new azetidine platinum(II) complex (3b) were synthesized and tested against the lymphocytic leukemia P388 in mice. (formula; see text) Moderate to good activity was found for all compounds as evidenced by a T/C value of 162 at a dose of 32 mg/kg for (3b), 190 at a dose of 32 mg/kg for (4a), 139 at a dose of 4 mg/kg for (4b), and 142 at a dose of 20 mg/kg for (4c).