Synthesis of LJP 993, a multivalent conjugate of the N-terminal domain of beta2GPI and suppression of an anti-beta2GPI immune response

Synthesis of Hydrophilic Aminooxy Linkers and Multivalent Cores for Chemoselective Aldehyde/Ketone Conjugation

A series of three linear and two trivalent aminooxy-containing hydrophilic linkers and cores were synthesized. The five molecules contain from one to three aminooxy groups, and all but one contain an ether for enhanced aqueous solubility. These unique and versatile molecules can be utilized in the chemoselective conjugation of aldehyde/ketone-containing molecules, including reducing sugars, under mild aqueous conditions, and give rise to oxime-containing conjugates useful in a wide variety of applications and studies. The value of these aminooxy-based molecules and the ease and speed of preparation of both monovalent and multivalent oxime-linked molecules is demonstrated in two examples using the disaccharide cellobiose; one with a linear linker, and the second with a trivalent core.

A non-complement-fixing antibody to β2 glycoprotein I as a novel therapy for antiphospholipid syndrome

A single-chain fragment variable (scFv) recognizing β2-glycoprotein 1 (β2GPI) from humans and other species was isolated from a human phage display library and engineered to contain an IgG1 hinge-CH2-CH3 domain. The scFv-Fc directed against β2GPI domain I-induced thrombosis and fetal loss, thus mimicking the effect of antibodies from patients with antiphospholipid syndrome (APS). Complement is involved in the biological effect of anti-β2GPI scFv-Fc, as demonstrated by its ability to promote in vitro and in vivo complement deposition and the failure to induce vascular thrombosis in C6-deficient rats and fetal loss in C5-depleted mice. A critical role for complement was also supported by the inability of the CH2-deleted scFv-Fc to cause vessel occlusion and pregnancy failure. This antibody prevented the pathological effects of anti-β2GPI antibodies from APS patients and displaced β2GPI-bound patient antibodies. The CH2-deleted antibody represents an innovative approach potentially useful to treat APS patients refractory to standard therapy.

Synthesis of site-specific antibody-drug conjugates using unnatural amino acids

Antibody-drug conjugates (ADCs) allow selective targeting of cytotoxic drugs to cancer cells presenting tumor-associated surface markers, thereby minimizing systemic toxicity. Traditionally, the drug is conjugated nonselectively to cysteine or lysine residues in the antibody. However, these strategies often lead to heterogeneous products, which make optimization of the biological, physical, and pharmacological properties of an ADC challenging. Here we demonstrate the use of genetically encoded unnatural amino acids with orthogonal chemical reactivity to synthesize homogeneous ADCs with precise control of conjugation site and stoichiometry. p-Acetylphenylalanine was site-specifically incorporated into an anti-Her2 antibody Fab fragment and full-length IgG in Escherichia coli and mammalian cells, respectively. The mutant protein was selectively and efficiently conjugated to an auristatin derivative through a stable oxime linkage. The resulting conjugates demonstrated excellent pharmacokinetics, potent in vitro cytotoxic activity against Her2(+) cancer cells, and complete tumor regression in rodent xenograft treatment models. The synthesis and characterization of homogeneous ADCs with medicinal chemistry-like control over macromolecular structure should facilitate the optimization of ADCs for a host of therapeutic uses.

N-terminal protein modification using simple aminoacyl transferase substrates

Methods for synthetically manipulating protein structure enable greater flexibility in the study of protein function. Previous characterization of the Escherichia coli aminoacyl tRNA transferase (AaT) has shown that it can modify the N-terminus of a protein with an amino acid from a tRNA or a synthetic oligonucleotide donor. Here, we demonstrate that AaT can efficiently use a minimal adenosine substrate, which can be synthesized in one to two steps from readily available starting materials. We have characterized the enzymatic activity of AaT with aminoacyl adenosyl donors and found that reaction products do not inhibit AaT. The use of adenosyl donors removes the substrate limitations imposed by the use of synthetases for tRNA charging and avoids the complex synthesis of an oligonucleotide donor. Thus, our AaT donors increase the potential substrate scope and reaction scale for N-terminal protein modification under conditions that maintain folding.

Autoantibodies directed against domain I of beta2-glycoprotein I

Patients diagnosed with the antiphospholipid syndrome typically suffer from vascular thrombosis, pregnancy morbidity, or a combination of the two. Due to the high prevalence of these clinical symptoms, the diagnosis of antiphospholipid syndrome is almost completely dependent on the detection of antiphospholipid antibodies in patient plasma. However, not every individual with antiphospholipid antibodies in his or her plasma suffers from thrombosis and/or pregnancy morbidity, which suggests the existence of different populations of antiphospholipid antibodies. Although many antigens have been identified in relation to the antiphospholipid syndrome, β2-glycoprotein I is regarded as clinically most significant. During the past decade, evidence has accumulated to suggest the presence of a dominant epitope on the first domain of β2-glycoprotein I. Several studies have detected a specific population of antibodies recognizing a cryptic epitope on domain I, at least comprising arginine 39 to arginine 43. In contrast to antibodies recognizing other domains of β2-glycoprotein I, anti-domain I antibodies are found to be highly associated with clinical symptoms. This review discusses several studies that have investigated a role for domain I within the antiphospholipid syndrome on a predominantly diagnostic level.

Pathophysiological mechanisms in antiphospholipid syndrome

Antiphospholipid syndrome is a systemic autoimmune disease associated with thrombosis and recurrent fetal loss in the setting of detectable antiphospholipid (aPL) antibodies. The major antigenic target has been identifed as β₂-glycoprotein I (β₂GPI), which mediates binding of aPL antibodies to target cells including endothelial cells, monocytes, platelets and trophoblasts, leading to prothrombotic and proinfammatory changes that ultimately result in thrombosis and fetal loss. This article summarizes recent insights into the role of β₂GPI in normal hemostasis, interactions between aPL antibodies, β₂GPI and cell-surface molecules, molecular prothrombotic and proinfammatory changes induced by aPL antibodies and pathogenic changes leading to fetal loss in antiphospholipid syndrome. New directions in therapy using these insights are examined.

Pharmacokinetics of LJP 993, a tetrameric conjugate of domain 1 of beta2-glycoprotein I for antiphospholipid syndrome

beta2-glycoprotein I is the best-characterized antigenic target for antiphospholipid autoantibodies. We synthesized a tetrameric conjugate of the domain 1 of beta2-glycoprotein I (LJP 993) aimed at developing the conjugate as a Toleragen to suppress antiphospholipid syndrome. The present studies focused on determining the stability, tissue distribution, plasma concentration-time profile and excretion of the LJP 993 in mice. The stability of LJP 993 in mouse plasma was quantitatively evaluated using strong cation-exchange high performance liquid chromatography. ( 125)I-labeled LJP 993 was intravenously injected to mice, and levels of (125)I-labeled LJP 993 in plasma, tissues, urine and feces were determined at known intervals. Incubation of LJP 993 with mouse serum at 37 degrees C for 8 h resulted in a decrease by 34% of LJP 993 concentration. No degradation fragment was observed during the incubation. After a single intravenous administration of (125)I-LJP 993 (0.5 and 5 mg/kg) to mice, both C(max) and area-under-curve values increased in a dose-proportional manner, and blood radioactivity disappeared in a bi-exponential manner with the distribution half-lives equal to 1.7 min, and the elimination half-lives 188 and 281 min, respectively. The (125)I-LJP 993 was moderately distributed into organs and tissues with the exception that brain level of ( 125)I-LJP 993 was negligible. The major sites of (125)I-LJP 993 uptake were the kidney (at 30 min post dosing), and kidney, lung, liver, heart, spleen, skin, muscle and fat tissues (at 4 h post dosing). Cumulative urinary and fecal radioactivity for 0-48 h post dosing accounted for 44.7% and 4.2% of the administered dose, respectively, with the fast rate of urinal excretion occurring within the first 8 h. In summary, LJP 993 was fairly stable in mouse plasma. After administration to mice, (125)I-LJP 993 was taken up mainly by kidney and then distributed extensively to tissues except brain. Both C(max) and area-under-curve values increased in a dose-proportional manner. It was predominantly excreted in the urine with an elimination half-life longer than 3 h. Kidney is a major route to excrete the tetrameric conjugate.

A novel heterobifunctional linker for facile access to bioconjugates

A convenient synthesis of a novel heterobifunctional linker molecule is described. The linker contains a thiol-reactive nitropyridyl disulfide group (Npys) and an aldehyde-reactive aminooxy group with a propensity to form disulfide and oxime linkages. The utility of the linker molecule to cross-link different biomolecules has been demonstrated by employing it in the efficient preparation of a peptide-oligonucleotide conjugate. The linker reported herein could be a useful tool for cross-coupling of different but appropriately functionalised biomolecules.

LJP 1082: a toleragen for Hughes syndrome

A hallmark of systemic lupus erythematosus (SLE) and related autoimmune diseases such as the antiphospholipid syndrome (APL or Hughes syndrome) is an apparent breakdown in tolerance, the process by which the body distinguishes self from nonself in order to maintain a versatile immune defense while protecting itself from self-annihilation. To some extent, loss of tolerance is a desirable feature of host immunity, and is known to occur in healthy individuals. Optimal tolerance then is probably not an all or nothing phenomenon. Autoimmunity should be seen as a breakdown in homeostasis rather than a completely aberrant kind of immunity. This leads to special considerations in the assessment of potentially toleragenic therapies, in which an attempt is made to re-educate the immune system. LJP 1082 is designed as a polyvalent antigenic structure aimed at crosslinking specific surface immunoglobulin and tolerizing B cells to beta2-glycoprotein I. Issues of antigenic selection and multiplex forces influencing tolerance and immunity may have impact on its optimal development and use in patients.

In vivo characterization of bioconjugate B cell toleragens with specificity for autoantibodies in antiphospholipid syndrome

This study investigated the use of well-defined bioconjugate molecules to suppress antigen-specific B cell responses to domain I (DI) of human beta(2)-glycoprotein I (beta(2)GPI) in rats. DI is the dominant target of pathogenic autoimmune antibodies in patients with antiphospholipid syndrome (APS), a disease characterized by antibody-mediated thromboembolic events. Rats primed with DI conjugated to keyhole limpet hemocyanin (DI-KLH) were rendered tolerant to subsequent antigen challenge by treatment with multivalent conjugates of DI. Antibodies to DI were suppressed 89-96% with intravenous doses of 500 micro g, and reductions were paralleled by decreases in splenic antigen-specific antibody-forming cells (AFC). Suppression was achieved with a variety of conjugates having two to four copies of DI and circulating half-lives of 2.6-8.7 h. Antibodies to KLH were not suppressed, indicating the specificity of the approach. These results establish the basis for further development of therapeutic B cell toleragens to suppress pathogenic antibodies in APS and other autoimmune diseases.

Acquired thrombophilias and pregnancy

Acquired thrombophilias are hypercoagulable states secondary to various aetiologies. In particular, during pregnancy the risks are exaggerated due to the underlying physiological changes. The commonest cause of acquired thrombophilia in pregnancy is antiphospholipid syndrome. Antiphospholipid syndrome (APS) is a complex multisystem disorder that has been associated with varied medical and obstetric complications. The pathogenesis of APS has been further elucidated in recent studies. The two most clinically significant antiphospholipid antibodies that are associated with recurrent pregnancy loss and thromboembolism are anticardiolipin antibodies (aCL) and lupus anticoagulant (LA). The laboratory diagnosis is based on the presence of moderate to high positive aCL and/or LA antibodies. It is crucial that APS is not inappropriately diagnosed as this has implications for counselling and management with thromboprophylaxis during pregnancy. Over the last decade there have been significant changes in the laboratory and clinical criteria for the diagnosis of APS. National and international collaborations have made efforts to standardize the laboratory methods. There have been very few randomized placebo-controlled trials of drug therapy and so not all drug treatment strategies have a strong evidence base. With current management strategies, using low-molecular-weight heparin and aspirin, a greater than 70% live birth rate may be achieved in affected pregnancies. A multidisciplinary approach in the management of these women is vital.

Antiphospholipid Antibody Syndrome

Antiphospholipid antibody syndrome (APS) is a recently defined autoimmune disorder characterized by recurrent vascular thromboses or recurrent pregnancy morbidity; these features are linked to the presence in blood of autoantibodies against negatively charged phospholipids or phospholipid-binding proteins. Thrombosis can occur in any tissue, in veins, arteries, or the microvasculature. Pregnancy morbidity in APS includes miscarriages or premature birth. Criteria that define the major clinical and laboratory features of APS were published in 1999. In patients with antiphospholipid antibodies and prior thrombosis or pregnancy morbidity, there is a high risk of recurrence that persists as long as antiphospholipid antibodies occur in blood. This risk for recurrence of thrombosis or pregnancy morbidity is greatly reduced by preventive anticoagulant therapy. Patients presenting with thrombosis in APS are initially managed in much the same way as are patients with vascular thrombosis owing to other causes. However, in patients with APS, high-intensity anticoagulation is usually needed to prevent recurrences of thrombosis. Thrombosis in APS is often multifactorial, as with non-APS thrombosis. Therefore, in all patients with APS, other reversible risk factors for thrombosis should be sought. The pregnancy outcome of women with APS who have had prior miscarriages is greatly improved by treatment during pregnancy with a combination of heparin and low-dose aspirin.

Survey of the year 2001 commercial optical biosensor literature

We have assembled references of 700 articles published in 2001 that describe work performed using commercially available optical biosensors. To illustrate the technology's diversity, the citation list is divided into reviews, methods and specific applications, as well as instrument type. We noted marked improvements in the utilization of biosensors and the presentation of kinetic data over previous years. These advances reflect a maturing of the technology, which has become a standard method for characterizing biomolecular interactions.

Treatment of the antiphospholipid syndrome

Despite increasing knowledge of the immunology and pathophysiology of the antiphospholipid syndrome, treating this condition remains challenging. Because of a paucity of randomized controlled trials, many of the treatment recommendations are not evidence-based. Retrospective case series suggest that a high level of oral anticoagulation is needed to prevent recurrent thrombosis. The combination of heparin and low-dose aspirin is effective in significantly increasing the chances of a successful pregnancy in woman with recurrent pregnancy failure associated with antiphospholipid antibodies. Primary prevention with aspirin is justified in patients with antiphospholipid antibodies but without a prior history of thrombosis. Interesting and controversial issues in the treatment of the antiphospholipid syndrome include the use of less intensive anticoagulation or antiplatelet agents in some patient subsets, anticoagulation for certain nonstroke neurologic conditions, the role of other agents (hydroxychloroquine, antioxidants), and novel immunomodulatory strategies.