A Humanized Anti-VEGF Rabbit Monoclonal Antibody Inhibits Angiogenesis and Blocks Tumor Growth in Xenograft Models

Rabbit antibodies have been widely used in research and diagnostics due to their high antigen specificity and affinity. Though these properties are also highly desirable for therapeutic applications, rabbit antibodies have remained untapped for human disease therapy. To evaluate the therapeutic potential of rabbit monoclonal antibodies (RabMAbs), we generated a panel of neutralizing RabMAbs against human vascular endothelial growth factor-A (VEGF). These neutralizing RabMAbs are specific to VEGF and do not cross-react to other members of the VEGF protein family. Guided by sequence and lineage analysis of a panel of neutralizing RabMAbs, we humanized the lead candidate by substituting non-critical residues with human residues within both the frameworks and the CDR regions. We showed that the humanized RabMAb retained its parental biological properties and showed potent inhibition of the growth of H460 lung carcinoma and A673 rhabdomyosarcoma xenografts in mice. These studies provide proof of principle for the feasibility of developing humanized RabMAbs as therapeutics

Mutational lineage guided humanization of anti-VEGF RabMAb EBV321.

<p>(<b>A–B</b>) Phylogenetic analysis of VK (<b>A</b>) and VH (<b>B</b>) amino acid sequences of 15 neutralizing anti-VEGF RabMAbs by Clustal X. The human antigen-specific clones are underlined. RabMAbs of the same lineage group are boxed and labeled as 1, 2 or 3. (<b>C–D</b>) Alignments of VH (<b>C</b>) and VK (<b>D</b>) protein sequence of the EBV321 lineage group 2 (EBV302, EBV307, EBV320 and EBV321) with human germline and humanized EBV321 sequences. ‘–’ denotes residues that are identical at the corresponding positions. ‘*’ denotes the residues in RabMAb framework regions potentially involved in CDR contacts or inter-chain contacts. ‘$’ denotes the residues considered not critical to the structural activity. ‘#’ denotes the residues humanized in the CDR region. Chothia numbering scheme and Kabat CDR loop definition were used <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0009072#pone.0009072-AlLazikani1" target="_blank">[55]</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0009072#pone.0009072-Kabat1" target="_blank">[56]</a>.</p

Binding affinities of anti-VEGF-A RabMAb EBV321 and its humanized version.

<p><i>k_on</i>, association rate constant; <i>k_off</i>, dissociation rate constant; <i>K_D</i>, equilibrium constant; χ², chi-squared distribution.</p

<i>In vitro</i> characterization of anti-VEGF RabMAbs.

<p>(<b>A</b>) Dose-dependent inhibition of VEGF/VEGFR-2 interaction by 4 representative anti-VEGF RabMAbs. Bevacizumab and a non-relevant anti-human Factor VIII RabMAb were included as controls. Points represent means of three replications and error bars represent standard deviations. The IC₅₀ values are shown in the table below. (<b>B</b>) Inhibition of VEGF-stimulated receptor tyrosine phosphorylation in 293/KDR cells in the presence of neutralizing antibodies against VEGF. Four representative anti-VEGF RabMAbs inhibited VEGF stimulated VEGFR-2 phosphorylation in 293/KDR cells. Bevacizumab and a non-relevant anti-human Factor VIII RabMAb were used as positive and negative controls, respectively. Total VEGFR-2 staining was performed as sample quantitative controls. (<b>C</b>) Specificity and cross-reactivity of anti-VEGF RabMAbs. A panel of seven representative anti-human VEGF antibodies exhibited no reactivity to human VEGF-B, -C, -D. Four of the seven antibodies (EBV302, EBV307, EBV320 and EBV321) were cross-reactive with mouse VEGF.</p

Comparison of hEBV321 and Bevacizumab binding properties to human VEGF.

<p>A. VEGF competition ELISA measuring the binding of hEBV321 to VEGF coated on ELISA plate in the presence of increasing concentration of competitor (hEBV321, Bevacizumab or an irrelevant antibody Humira). B-E. Direct binding of hEBV321 and Bevacizumab to various forms of human VEGF captured on ELISA plate. B. VEGF wild type; C. VEGF I46A; D. VEGF G89A; E. VEGF G88A/Q89A.</p