Structural differences in the cell binding region of human fibronectin molecules isolated from cultured normal and tumor-derived human cells

CAR-T-Cell Therapy for Solid Tumors Positive for Fibronectin Extra Domain B

(1) Background: The lack of specific targets has slowed the progress of CAR-T in treating solid tumors. Recent studies have revealed that EDB-FN (fibronectin extra domain B) may be an effective target for CAR-T treatment of solid tumors; EDB-FN is expressed in tumor and embryonic tissues, and antibody–cytokine fusion proteins targeting EDB-FN have been developed. However, the therapeutic effects of BBz CAR-engineered T-cells targeting EDB-FN in solid tumors have not been evaluated. (2) Results: In this study, we constructed a BBz CAR construct targeting EDB-FN, and the CAR molecule was expressed on the surface of T-cells by lentiviral transduction. In vitro, CAR-T-cells can be activated to express perforin and granzyme and lyse EDB-positive cells (U-87 MG cells, A549 cells, and HUVECs) and have no toxicity to EDB-negative cells (MCF-7). Compared to T-cells, CAR-T-cells can release cytokines after coculture with EDB-positive cell lines. In vivo, CAR-T-cells inhibited the progression of U-87 MG subcutaneous tumors and significantly reduced the blood vessel density in tumor tissue compared to T-cells, without obvious toxicity to mouse tissues and organs. Furthermore, CAR-T-cells overexpressing BiTE targeting EDB-FN can significantly improve their antitumor activity in vitro. (3) Conclusions: These results demonstrate that CAR-T-cells have specific antitumor and angiogenic activities in vivo and in vitro, suggesting that EDB-FN may be a potential solid tumor target for CAR-T therapy.

Human fibronectin extra domain B as a biomarker for targeted therapy in cancer

The extracellular matrix protein fibronectin contains a domain that is rarely found in healthy adults and is almost exclusively expressed by newly formed blood vessels in tumours, particularly in solid tumours, different types of lymphoma and some leukaemias. This domain, called the extra domain B (ED‐B), thus has broad therapeutic potential. The antibody L19 has been developed to specifically target ED‐B and has shown therapeutic potential when combined with cytokines, such as IL‐2. In this review article, we discuss the preclinical research and clinical trials that highlight the potential of ED‐B targeting for the imaging and treatment of various types of cancer. ED‐B‐centred studies also highlight how proper patient stratification is of utmost importance for the successful implementation of novel antibody‐based targeted therapies.

Extracellular matrix of small round cell tumors of childhood: an immunohistochemical study of 67 cases

Sixty-seven childhood tumors were studied immunohistochemically for the extracellular matrix element type IV collagen, laminin, and fibronectin. Tumors included Ewing's sarcoma, primitive neuroectodermal tumor, small cell osteosarcoma, neuroblastoma or ganglioneuroblastoma, rhabdomyosarcoma, and lymphoma. It was found that small cell osteosarcoma was often positive for fibronectin but not type IV collagen or laminin, a new observation. In the lymphomas, matrix proteins were rarely found. Ewing's sarcoma was variably positive for type IV collagen and laminin, but fibronectin was absent. Extracellular laminin and fibronectin were found in one of two cases of primitive neuroectodermal tumor. In neuroblastoma and ganglioneuroblastoma, the matrix components were rarely found. These results, discrepant with findings in cultured cells, may reflect the altered capacity of tumors to produce these proteins in vitro, which suggests that caution should be exercised in drawing conclusions regarding the nature or histogenesis of tumors from data obtained with cultured tumor cells. Embryonal rhabdomyosarcoma frequently contained all matrix elements in the extracellular space and in a dotlike pattern in the cytoplasm; alveolar rhabdomyosarcoma rarely contained these proteins and never exhibited the dotlike pattern. The frequent finding of matrix proteins in embryonal rhabdomyosarcoma but only rarely in alveolar rhabdomyosarcoma and the unique immunostaining pattern in embryonal rhabdomyosarcoma may prove to be a useful adjunct in the diagnosis of childhood tumors.

Myofibroblast and concurrent ED-B fibronectin phenotype in human stromal cells cultured from non-malignant and malignant breast tissue

Primary cultures of stromal cells from non-malignant and malignant breast tissues contained myofibroblasts based on immunoreactivity to alpha-smooth muscle (alpha-sm) actin. The proportions of these cells were variable among cultures from non-malignant origin while consistently high in cultures from carcinomas. High expression of ED-B fibronectin and of type V collagen was observed in myofibroblast-containing cultures. While cells from non-malignant tissues grew relatively steadily, the proliferation of carcinoma-derived cells declined during serial subculturing. In both types of cultures, alpha-sm actin and ED-B fibronectin expression decreased with increasing passage numbers. Epidermal growth factor (EGF), fibroblast growth factor b (FGFb), transforming growth factor alpha (TGF alpha) and platelet-derived growth factor (PDGF) showed consistent mitogenic effects. Addition of FGFb prolonged culture growth and allowed alpha-sm actin and ED-B fibronectin expression to persist. These results demonstrate similar phenotypic modulations in stromal cells from non-malignant and malignant breast tissues that may reflect a common stromal response to various tissue injuries, including neoplasia.

Differential expression of the fibronectin isoform containing the ED-B oncofetal domain in normal human fibroblast cell lines originating from different tissues

Fibronectin (FN) polymorphism is due both to alternative splicing of three sequences (ED-A, ED-B, and IIICS) of the primary transcript and to post-translational modifications. The FN isoform containing the ED-B sequence (B-FN), while having an extremely restricted distribution in normal adult tissues, has a high expression in fetal and tumor tissues. On a panel of non-fetal skin, fetal skin, and fetal lung fibroblast cell lines we have studied, through S1-nuclease protection analysis, the expression of the ED-B containing FN mRNA as well as the expression of the ED-B containing FN isoform through immunoblotting and immunofluorescence techniques, using domain specific monoclonal antibodies. The results show that the expression of B-FN in the different fibroblast cell lines has an extremely great variability depending on the developmental stage of the donor and on the tissue of origin. Moreover, we found that SV-40-transformed fibroblasts present a higher expression of B-FN mRNA with respect to their normal counterparts. An increase in the relative amount of the B-FN isoform in normal human fibroblasts was also obtained by treatment with transforming growth factor-beta.

Fetal myofibroblast-like cells isolated from post-radiation fibrosis in human breast cancer

Cells were isolated from post-radiation fibrosis biopsies of patients with recurrent breast carcinoma. These cells were identified as fibroblasts and compared with fibroblasts from normal breast tissues for their proliferative activities, chromosome number and for the presence of various components of the extracellular matrix and cytoskeleton. The proliferative activity of the fibrosis-derived fibroblasts did not significantly differ from that of normal breast fibroblasts. Both cell types required serum to grow and did not form colonies in soft agar. Cells from 2 of the 3 fibroses analyzed displayed aneuploid karyotypes with multiple structural abnormalities. All of the fibroblastic cells produced types I, III and V collagen, fibronectin and vimentin. However, in contrast to normal breast fibroblasts, fibrosis-derived cells produced high amounts of oncofetal fibronectin. In addition, fibrosis of fibroblasts also expressed the alpha-actin isoform which is specific for smooth-muscle cells. These results suggest that post-radiation fibrosis in malignant breast contains atypical fibroblasts with fetal and myofibroblastic characteristics.

Changes in the subunit composition of laminin during the increased tumorigenesis of mouse A9 cells

We compared the structure and subunit composition of laminin in less tumorigenic mouse A9 and highly tumorigenic mouse A9HT cells by pulse-chase studies. During a 15' pulse, the ratio of laminin B1 to B2 subunits in cell lysates is 1:1 in both the A9 and A9HT cells; however, after a 3 hr chase, this ratio changes to 6:1 and 2:1 in the A9 and A9HT cells, respectively. Analysis of mature laminin subunits in culture media after a 3 hr chase also showed a similar higher ratio of B1 to B2 in the A9 cells as compared to the A9HT cells. The higher ratio of B1 to B2 subunits in A9 cells was evident as early as after a 30' pulse. A comparative analysis of steady-state levels of mRNAs for the laminin subunits B1 and B2 between A9 and A9HT cells showed a ratio of 1:1 for B1 and a ratio of 1:1.65 for B2. The ratio of B1 to B2 mRNAs in A9 cells was 1:1.3 whereas in A9HT cells it was 1:2.5, suggesting changes in the processing of mRNA in the highly tumorigenic A9HT cells. These observations suggest that the processing of laminin B subunits is altered during the process of increased tumorigenicity, thus resulting in the synthesis and secretion of structurally different laminin in tumorigenic A9HT cells as compared to the parent and less tumorigenic A9 cells.

Lack of fibronectin-binding plasma membrane proteins may explain defective pericellular matrix formation in transformed fibroblasts and fibrosarcoma cells

Affinity of iodinated fibronectin (Fn) and its defined proteolytic fragments to electrophoretically separated polypeptides of normal and malignant cells was studied in an overlay assay. Cellular 125I-Fn and a major 125I-Fn fragment (Mr 120,000-140,000), containing the cell-binding site, revealed in fibroblasts Mr 170,000, Mr 140,000, and Mr 47,000 Fn-binding polypeptides of which the first two could also be found in the plasma membrane preparations. Binding of 125I-Fns to Mr 170,000 and Mr 140,000 polypeptides was inhibited by the synthetic peptide Arg-Gly-Asp-Ser and to all 3 polypeptides by Fns and Mr 120,000-140,000 fibronectin fragment. Both fibrosarcoma cells and SV40-virus-transformed fibroblasts appeared to lack the Mr 140,000 Fn-binding polypeptide. Binding was similar when Fn from normal fibroblasts or fibrosarcoma cells was used in the assay, while plasma 125I-Fn had weaker affinity towards the Mr 140,000 polypeptide. Instead, proteolytic Fn-fragments, lacking the cell binding site, did not bind to any proteins in the assay. Radioactive cell-surface labelling showed differences in the corresponding surface polypeptide profiles of normal and malignant cells. The results suggest that the failure of pericellular matrix deposition in malignant cells could be due to either defective surface exposition or defective binding property of the Fn-receptor-like polypeptides.

A family of fibronectin mRNAs in human normal and transformed cells

Previously, two fibronectin mRNAs, generated by alternative splicing of the extra domain (ED) and type III connecting segments (IIICS) sequences, have been described in a human transformed cell line and in human liver, respectively. We now report on a family of fibronectin mRNAs identified by Northern blotting analysis in two normal human fibroblast strains (HEL 299 and Flow 7000) and five transformed cell lines (8387 and HT-1080, fibrosarcomas; G-361, melanoma; JEG-3, choriocarcinoma; and RD, rhabdomyosarcoma). Seven different fibronectin mRNA forms with electrophoretic mobilities ranging between 8.6 and 7.7 kb were identified. Each cell line contains three (HEL 299, Flow 7000 and 8387) or two (HT-1080, G-361, JEG-3 and RD) fibronectin mRNAs species with characteristic size. In all cell lines we detected one fibronectin mRNA form which lacks the ED sequence (ED- fibronectin mRNA) and one or two fibronectin mRNAs containing it (ED+ fibronectin mRNA). These data show that the presence of ED+ and ED- fibronectin mRNAs is a general feature of all cells tested. Moreover, the fibronectin mRNA pattern is characteristic of the cell type analyzed, suggesting the occurrence of specifically programmed splicing mechanisms in each cell line.