The Effect of Molecular Weight,PK, and Valency on Tumor Biodistribution and Efficacy of Antibody-Based Drugs

Poor drug delivery and penetration of antibody-mediated therapies pose significant obstacles to effective treatment of solid tumors. This study explored the role of pharmacokinetics, valency, and molecular weight in maximizing drug delivery. Biodistribution of a fibroblast growth factor receptor 4 (FGFR4) targeting CovX-body (an FGFR4-binding peptide covalently linked to a nontargeting IgG scaffold; 150 kDa) and enzymatically generated FGFR4 targeting F(ab)₂ (100 kDa) and Fab (50 kDa) fragments was measured. Peak tumor levels were achieved in 1 to 2 hours for Fab and F(ab)₂versus 8 hours for IgG, and the percentage injected dose in tumors was 0.45%, 0.5%, and 2.5%, respectively, compared to 0.3%, 2%, and 6% of their nontargeting controls. To explore the contribution of multivalent binding, homodimeric peptides were conjugated to the different sized scaffolds, creating FGFR4 targeting IgG and F(ab)₂ with four peptides and Fab with two peptides. Increased valency resulted in an increase in cell surface binding of the bivalent constructs. There was an inverse relationship between valency and intratumoral drug concentration, consistent with targeted consumption. Immunohistochemical analysis demonstrated increased size and increased cell binding decreased tumor penetration. The binding site barrier hypothesis suggests that limited tumor penetration, as a result of high-affinity binding, could result in decreased efficacy. In our studies, increased target binding translated into superior efficacy of the IgG instead, because of superior inhibition of FGFR4 proliferation pathways and dosing through the binding site barrier. Increasing valency is therefore an effective way to increase the efficacy of antibody-based drugs.     

Atypical Antigen Recognition Mode of a Shark Immunoglobulin New Antigen Receptor (IgNAR) Variable Domain Characterized by Humanization and Structural Analysis

The immunoglobulin new antigen receptors (IgNARs) are a class of Ig-like molecules of the shark immune system that exist as heavy chain-only homodimers and bind antigens by their single domain variable regions (V-NARs). Following shark immunization and/or in vitro selection, V-NARs can be generated as soluble, stable, and specific high affinity monomeric binding proteins of ∼12 kDa. We have previously isolated a V-NAR from an immunized spiny dogfish shark, named E06, that binds specifically and with high affinity to human, mouse, and rat serum albumins. Humanization of E06 was carried out by converting over 60% of non-complementarity-determining region residues to those of a human germ line Vκ1 sequence, DPK9. The resulting huE06 molecules have largely retained the specificity and affinity of antigen binding of the parental V-NAR. Crystal structures of the shark E06 and its humanized variant (huE06 v1.1) in complex with human serum albumin (HSA) were determined at 3- and 2.3-Å resolution, respectively. The huE06 v1.1 molecule retained all but one amino acid residues involved in the binding site for HSA. Structural analysis of these V-NARs has revealed an unusual variable domain-antigen interaction. E06 interacts with HSA in an atypical mode that utilizes extensive framework contacts in addition to complementarity-determining regions that has not been seen previously in V-NARs. On the basis of the structure, the roles of various elements of the molecule are described with respect to antigen binding and V-NAR stability. This information broadens the general understanding of antigen recognition and provides a framework for further design and humanization of shark IgNARs.     

Evolutionary implications of substitution patterns in prolamin genes of Oryza glaberrima (African rice, Poaceae) and related species

Patterns of sequence variation of nuclear genes encoding 10-kDa and 16-kDa prolamin seed storage proteins were examined in Oryza glaberrima (African rice, Poaceae) and O. barthii and compared to available sequences for the genus to assess potential application of these gene families in evolutionary studies. Sequence variation among species in 10-kDa genes was very low. In contrast, the 16-kDa genes have undergone rapid evolution, displaying a larger number of length and point mutations that in some cases result in frame shift or produce truncated protein or pseudogenes. The proportion of nonsynonymous substitution is high in both genes. Although nonsynonymous mutations did not alter the overall profile of the protein, pronounced shifts in proportions of some amino acids were evident and could have systematic application. The data provide support for a proposed direct evolution of the Asian (O. sativa) and African rice from O. rufipogon and O. barthii, respectively. Patterns of amino acid frequencies of the 10-kDa genes show the distinctness of O. rufipogon and O. longistaminata from the other species. The study underscores the potential application of the prolamin genes as markers from the nuclear genome for evolutionary studies in grasses at different taxonomic levels.     

Use of dual affinity tags for expression and purification of functional peripheral cannabinoid receptor

The human peripheral cannabinoid receptor (CB2) was expressed as a fusion with the maltose-binding protein (at the N-terminus), thioredoxin A (at the C-terminus) and two small affinity tags (a Strep-tag and a polyhistidine tag). Expression levels of the recombinant receptor in Escherichia coli BL21(DE3) cells were dependent on location and type of tags in the expression construct, and were as high as 1-2mg per liter of bacterial culture. The recombinant receptor was ligand binding-competent, and activated cognate G-proteins in an in vitro coupled assay. The fusion CB2-125 protein was purified by immobilized metal affinity chromatography on a Ni-NTA resin. Maltose-binding protein, thioredoxin and a decahistidine tag were removed from the fusion by treatment with Tobacco etch virus (Tev) protease. Purification to over 90% homogeneity of the resulting CB2, containing an N-terminal Strep-tag was achieved by affinity chromatography on a StrepTactin resin. Circular dichroism spectroscopy indicated an alpha-helical content of the purified recombinant protein of approximately 54%. The expression and purification protocol allows for production of large (milligram) quantities of functional peripheral cannabinoid receptor, suitable for subsequent structural characterization. Preliminary results of reconstitution experiments indicate that the CB2 has retained its ligand-binding properties.     

Brain MR Imaging and Proton MR Spectroscopy in Female Mice with Pyruvate Dehydrogenase Complex Deficiency

Pyruvate dehydrogenase complex (PDC) deficiency is an inborn metabolic disorder that causes neurological abnormalities. In this report, a murine model of PDC deficiency was analyzed using histology, magnetic resonance (MR) imaging and MR spectroscopy (MRS) and the results compared to PDC-deficient female patients. Histological analysis of brains from PDC-deficient mice revealed defects in neuronal cytoarchitecture in grey matter and reduced size of white matter structures. MR results were comparable to previously published clinical MR findings obtained from PDC-deficient female patients. Specifically, a 15.4% increase in relative lactate concentration, 64.4% loss of N-acetylaspartate concentration and a near complete loss of discernable glutamine plus glutamate concentration were observed in a PDC deficient mouse compared to wild-type control. Lower apparent diffusion coefficients (ADCs) were observed within the brain consistent with atrophy. These results demonstrate the usefulness of this murine model to systematically evaluate the beneficial effects of dietary and pharmacological interventions. Special issue dedicated to John P. Blass. Lioudmila Pliss and Richard Mazurchuk are two investigators who contributed equally.     

The physiological homeostasis of human populations in variable environments

A close evolutionary relationship of physiology and ecology of organisms determines the dynamic dependence of the population physiological status in man on ecological factors. For the explanation of the stability and variability of population physiological status the concept of physiological homeostasis was applied. The investigation of physiological status in several populations of Middle Asia, Kazakhstan, North-East Asia and Khakassia has shown that reversible changes in the environment may temporarily destabilize the equilibrium in the "population-environment" system and prolonged stresses may cause a state of disadaptation. For estimation of population physiological homeostasis dependent on the environment, generalized dispersion, correlation and factor analyses are very informative. They not only mark the violation of population homeostasis, but also indicate changes in the environment.     

Pharmacological modulation and differential regulation of the cardiac gap junction proteins connexin 43 and connexin 40

Gap junction channels provide the basis for the electrical syncytial properties of the heart as a communicating electrical network. Cardiac gap junction channels are predominantly composed of connexin 40 or connexin 43. The conductance of these channels (g(j)) can be regulated pharmacologically: substances which activate protein kinase C, protein kinase A or protein kinase G may alter Cx43 gap junction conductance. However, for PKC, this seems to be subtype specific. Thus, antiarrhythmic peptides can enhance g(j) via activation of PKCepsilon, while FGF-2 reduces g(j) via PKCepsilon. Lipophilic drugs can uncouple the channels. Besides an acute regulation of g(j), the expression of the cardiac connexins can also be regulated. A decrease in Cx43 with a concomitant increase in Cx40 has been found in end-stage failing hearts, while in renovascular hypertension, an increase in Cx43 has been described. Mediators like endothelin-1, angiotensin-II, TGF-beta, VEGF, and cAMP have been shown to increase Cx43. Interestingly, endothelin-1 and angiotensin-II increased Cx43 but did not affect Cx40 expression. In contrast, in humans suffering from atrial fibrillation (AF), the content in Cx40 can be enhanced while Cx43 was unaltered, although in several other studies, other changes of the cardiac connexins were found, which might be related to the type of AF. Regarding the role of calcium, the content in both Cx40 and Cx43 was decreased in cultured neonatal rat cardiomyocytes after 24 h administration of 100 nM verapamil. Thus, gap junctional channels can be affected pharmacologically either acutely by modulating gap junction conductance or chronically by altering gap junction protein expression. Interestingly, it appears that the expression of Cx43 and Cx40 can be differentially regulated.     

Improving the pharmacokinetic properties of biologics by fusion to an anti-HSA shark VNAR domain

Advances in recombinant antibody technology and protein engineering have provided the opportunity to reduce antibodies to their smallest binding domain components and have concomitantly driven the requirement for devising strategies to increase serum half-life to optimise drug exposure, thereby increasing therapeutic efficacy. In this study, we adopted an immunization route to raise picomolar affinity shark immunoglobulin new antigen receptors (IgNARs) to target human serum albumin (HSA). From our model shark species, Squalus acanthias, a phage display library encompassing the variable binding domain of IgNAR (VNAR) was constructed, screened against target, and positive clones were characterized for affinity and specificity. N-terminal and C-terminal molecular fusions of our lead hit in complex with a naïve VNAR domain were expressed, purified and exhibited the retention of high affinity binding to HSA, but also cross-selectivity to mouse, rat and monkey serum albumin both in vitro and in vivo. Furthermore, the naïve VNAR had enhanced pharmacokinetic (PK) characteristics in both N- and C-terminal orientations and when tested as a three domain construct with naïve VNAR flanking the HSA binding domain at both the N and C termini. Molecules derived from this platform technology also demonstrated the potential for clinical utility by being available via the subcutaneous route of delivery. This study thus demonstrates the first in vivo functional efficacy of a VNAR binding domain with the ability to enhance PK properties and support delivery of multifunctional therapies.