Expression of extradomain-B-containing fibronectin in subretinal choroidal neovascular membranes

PURPOSE

To investigate the presence of the fibronectin isoform containing the extradomain B (B-FN), a marker-protein of angiogenesis, in surgically excised human choroidal neovascular membranes (CNVM) to evaluate whether B-FN could be used as a therapeutic target for specific antibody-photosensitizer immunoconjugates.

DESIGN

Laboratory investigation.

METHODS

The setting was an institutional practice. The study population consisted of 15 eyes (15 patients) with CNVM undergoing membrane excision (four eyes with age-related macular degeneration, seven with pathologic myopia and four with multifocal choroiditis). The control group consisted of eight eye bank eyes (four subjects) without choroidal neovascularization. Light microscopic immunohistochemistry on cryostat sections of tissues was obtained. B-FN was detected by a human recombinant antibody, CGS-1, and compared with immunostaining for endothelial cells with factor VIII-related antigen. The main outcome measure was the presence of CGS-1 positively stained cells or areas of the extracellular matrix. Staining of CGS-1 was scored on a scale from 0 to 3.

RESULTS

Fourteen of 15 neovascular membranes stained strongly with CGS-1 (score 2 or 3). One membrane from a patient with pathologic myopia was negatively stained (score 0). CGS-1 positive staining was detected around endothelial cells and in the extracellular matrix of CNVMs. The retina of eyes without choroidal neovascularization was negative with CGS-1 in all eight donor eyes, while the choroid contained some weakly CGS-1 positive cells (score 0 and 1, respectively).

CONCLUSIONS

The extradomain B is abundantly expressed in CNVMs, but its expression is more restricted in eyes harboring no apparent choroidal neovascularization. In the future, B-FN might serve as a target for the delivery of antibody-photosensitizer immunoconjugates to newly developed vessels to enhance the selectivity of photodynamic therapy.

Differentiation between high- and low-grade astrocytoma using a human recombinant antibody to the extra domain-B of fibronectin

Different fibronectin (FN) isoforms are generated by the alternative splicing of the primary FN transcript. We previously demonstrated that the isoform containing the extra domain B sequence of fibronectin (B-FN), a complete type-III-homology repeat, is a marker of angiogenesis that accumulates around neovasculature only during angiogenic processes. We produced a single-chain human recombinant antibody (scFv), L19, which reacts specifically with B-FN and selectively targets tumor vasculature in vivo. We used this scFv and an antibody against a pan-endothelial marker (Factor VIII) in a double-staining procedure on specimens of low- and high-grade astrocytomas to determine the percentage of B-FN-positive vessels, (denominating the resulting value angiogenic index [AI]). Compared to vascular density and proliferative activity (evaluated using antibodies to Factor VIII and Ki67, respectively), AI correlated better with tumor grade (1.6 +/- 2.6% and 92.0 +/- 8.7% of B-FN-positive vessels in low- and high-grade astrocytomas, respectively) and was a more precise diagnostic tool than either of the two conventional methods. In fact, discriminating analysis using these three parameters showed that only AI accurately classified 100% of the cases studied, compared to 64% and 89% correctly diagnosed by vascular density and of proliferating cells, respectively.

Occurrence of a glioblastoma-associated tenascin-C isoform in cerebral cavernomas and neighboring vessels

OBJECTIVE

Regrowth of cerebral cavernomas after apparently complete excision, de novo occurrence, and evidence of proliferation-related patterns raise the question as to their intrinsic growth potential. A particular isoform (Type III repeat c) of the glycoprotein tenascin-C (TN-C), typically associated with the vessels of anaplastic gliomas, is regarded as a marker of vascular proliferation in lesions growing within brain tissue. This study sought to ascertain whether this isoform is expressed in cerebral cavernomas to gain further insight into the growth potential of these lesions.

METHODS

Sixteen cerebral cavernomas and three fragments of normal brain underwent immunohistochemical examinations via two antibody fragments obtained by phage display technology. Previous characterization demonstrated that the fragment TN-12 recognizes the epidermal growth factor-like repeat, common to all TN-C isoforms. On the contrary, the fragment TN-11 was found to be highly specific for the Type III repeat c isoform.

RESULTS

Accumulation of total TN-C was found in the vascular walls and in the interspaces between the blood cavities of all examined cavernomas. When the antibody fragment TN-11 was used, staining of the subendothelial layers occurred in both the bulk of the cavernomas and vessels of the white matter surrounding the lesions, but staining was absent in the control specimens.

CONCLUSION

The distribution of the Type III repeat c isoform of TN-C, a putative marker of vascular proliferation, within cerebral cavernomas is consistent with the hypothesis of a growth potential of cerebral cavernomas. Enlargement of these lesions might involve recruitment of neighboring vasculature, which is possibly dependent on environmental conditions.