ED-B fibronectin as a target for antibody-based cancer treatments

Comparative analysis of the membrane proteome of closely related metastatic and nonmetastatic tumor cells

The identification of proteins that are preferentially expressed on the membrane of metastatic tumor cells is of fundamental importance in cancer research. Here, we report the systematic comparison of the membrane proteome of two closely related murine teratocarcinoma cell lines (F9B9 and F9DR), of which only one (F9DR) is capable of forming liver metastases in vivo. The proteomic methodology used in this study featured the surface protein biotinylation on tumor cells followed by protein purification on streptavidin resin and relative quantification of corresponding tryptic peptides by mass spectrometric procedures. The study allowed the identification of 998 proteins and the determination of their relative abundance. Proteins previously known to be associated with metastatic spread were found to be either up-regulated (e.g., synaptojanin-2) or down-regulated (e.g., Ceacam1) in F9DR cells. A dramatic increase in abundance at the cell membrane was observed for a broad variety of proteins (e.g., high-mobility group protein B1), which were mainly thought to reside in intracellular compartments, a finding that was confirmed using confocal laser scanning microscopy and immunochemical analysis of cell cultures. Furthermore, we showed by microautoradiographic analysis that certain target proteins can readily be reached by intravenously administered radiolabeled antibodies. Finally, we showed that the most promising antigens for antibody-based pharmacodelivery approaches are strongly and selectively expressed on the surface of tumor cells in three different syngeneic mouse models of liver metastases. Taken together, our results indicate that the expression of intracellular proteins on the membrane of metastatic cells is a feature much more common than previously expected.

Antibody-mediated delivery of interleukin-2 to the stroma of breast cancer strongly enhances the potency of chemotherapy

PURPOSE

There is an interest in the discovery of biopharmaceuticals, which are well tolerated and which potentiate the action of anthracyclines and taxanes in breast cancer therapy.

EXPERIMENTAL DESIGN

We have produced a recombinant fusion protein, composed of the human antibody fragment scFv(F16) fused to human interleukin-2 (F16-IL2), and tested its therapeutic performance in the MDA-MB-231 xenograft model of human breast cancer. The F16 antibody is specific to the alternatively spliced A1 domain of tenascin-C, which is virtually undetectable in normal tissues but is strongly expressed in the neovasculature and stroma of breast cancer.

RESULTS

When used as monotherapy, F16-IL2 displayed a strikingly superior therapeutic benefit compared with unconjugated recombinant IL-2. The administration of doxorubicin either before (8 days, 24 h, or 2 h) or simultaneously with the injection of F16-IL2 did not decrease the accumulation of immunocytokine in the tumor as measured by quantitative biodistribution analysis. Therapy experiments, featuring five once per week coadministrations of 20 mug F16-IL2 and doxorubicin, showed a statistically significant reduction of tumor growth rate and prolongation of survival at a 4 mg/kg doxorubicin dose but not at a 1 mg/kg dose. By contrast, combination of F16-IL2 with paclitaxel (5 and 1 mg/kg) exhibited a significant therapeutic benefit compared with paclitaxel alone at both dose levels. F16-IL2, alone or in combination with doxorubicin, was well tolerated in cynomolgus monkeys at doses equivalent to the ones now used in clinical studies.

CONCLUSIONS

F16-IL2 may represent a new useful biopharmaceutical for the treatment of breast cancer.

Complete eradication of human B-cell lymphoma xenografts using rituximab in combination with the immunocytokine L19-IL2

The antibody-mediated delivery of therapeutic agents to sites of angiogenesis is an attractive strategy for anticancer therapy, but is largely unexplored in hematologic malignancies. In the present study, we show that the extra domain B (EDB) of fibronectin, a marker of angiogenesis, is expressed in B-cell non-Hodgkin lymphoma (NHL) and that the human monoclonal anti-EDB antibody L19 can selectively localize to the lymphoma-associated subendothelial extracellular matrix. In vivo, the preferential accumulation of the antibody at the tumor site was confirmed by quantitative biodistribution analyses with radioiodinated antibody preparations. The fusion protein L19-IL2, which mediates the delivery of interleukin-2 (IL-2) to the neovasculature, displayed a superior antilymphoma activity compared with unconjugated IL-2 in localized and systemic xenograft models of NHL. When coadministered with rituximab, L19-IL2 induced complete remissions of established localized lymphomas and provided long-lasting protection from disseminated lymphoma. The combined use of rituximab and L19-IL2, which dramatically increases the infiltration of immune effector cells in lymphomas, may deserve clinical investigations, facilitated by the fact that L19-IL2 is currently being studied in phase II clinical trials in patients with solid tumors.

Comparative immunohistochemistry of L19 and F16 in non-small cell lung cancer and mesothelioma: two human antibodies investigated in clinical trials in patients with cancer

The antibody-mediated targeted delivery of therapeutics to tumor sites is an attractive avenue for combating cancer while sparing normal tissues. Indeed, five derivatives of the human monoclonal antibodies L19 and F16, specific to splice isoforms of fibronectin and tenascin-C, are currently being investigated in clinical trials in patients with malignancies. Until now, a comparative immunohistochemical analysis of these antibodies, which recognize components of the modified extracellular matrix, was missing. Here, we report that the majority of NSCLC and mesothelioma specimens are stained with both antibodies in the stroma, while non-tumoral lung and mesothelium samples rarely exhibit reactivity with either L19 or F16. In our analysis, the anti-tenascin F16 antibody was found to generally exhibit a stronger staining of desmoplastic stroma surrounding tumor. This superior performance was found to be particularly striking in the case of low-grade non-small cell lung cancer.

Ligand-based vascular targeting of disease

This review illustrates the basic principles of ligand-based vascular targeting and presents some of the most advanced results obtained in this field, not only in terms of biopharmaceuticals, which are currently being investigated in clinical and preclinical studies, but also in terms of enabling technologies that facilitate target and ligand discovery. Whereas most of the vascular targeting research activities have so far concentrated on tumoral angiogenesis, the development of non-oncological applications has recently gained momentum and is likely to become an important area of modern pharmaceutical research.

A high-affinity human monoclonal antibody specific to the alternatively spliced EDA domain of fibronectin efficiently targets tumor neo-vasculature in vivo

The alternatively spliced extra-domain B of fibronectin is one of the best characterized markers of tumor angiogenesis. Similarly, the extra-domain A (EDA), which can also be inserted in the fibronectin transcript by a mechanism of alternative splicing, has been shown to preferentially accumulate around new blood vessels in certain tumors, but this antigen has not been investigated so far as a target for antibody-based biomolecular intervention. We here describe the generation of 3 human monoclonal antibodies (named F8, B7 and D5), which recognize the same epitope of EDA, but which differ in terms of their dissociation constant to the human antigen (K(D) = 3.1, 16 and 17 nM, measured for monomeric preparations of the F8, B7 and D5 antibodies, respectively, in recombinant scFv format). When the 3 antibody fragments were cloned and expressed with a 5 amino acid linker, the 3 resulting homodimeric antibody preparations displayed comparable tumor: organ ratios in quantitative biodistribution studies, performed in immunocompetent 129SvEv mice, bearing subcutaneous syngeneic F9 murine tumors. The percent injected dose per gram (%ID/g) values in tumors 24 hr after intravenous injection were 9.3, 10.2 and 13 for F8, B7 and D5, respectively. The F8 antibody may serve as useful building block for the development of antibody-based targeted anti-cancer therapeutics. Preclinical and clinical investigations are facilitated by the fact that F8 recognizes the human and mouse antigen with comparable affinity, and by the observation that EDA over-expression is detectable not only in solid tumors, but also in hematological malignancies.

Antibody-cytokine fusion proteins: applications in cancer therapy

BACKGROUND

Antibody-cytokine fusion proteins consist of cytokines fused to an antibody to improve antibody-targeted cancer immunotherapy. These molecules have the capacity to enhance the tumoricidal activity of the antibodies and/or activate a secondary antitumor immune response.

OBJECTIVE

To review the strategies used to develop antibody-cytokine fusion proteins and their in vitro and in vivo properties, including preclinical and clinical studies focusing on IL-2, IL-12 and GM-CSF.

METHODS

Articles were found by searching databases such as PubMed and Clinical Trials of the US National Institutes of Health.

RESULTS/CONCLUSION

Multiple antibody-cytokine fusion proteins have demonstrated significant antitumor activity as direct therapeutics or as adjuvants of cancer vaccines in preclinical studies, paving the way for their clinical evaluation.

Impact of the non-cellular tumor microenvironment on metastasis: potential therapeutic and imaging opportunities

Evidence is accumulating that the malignant phenotype of a given tumor is dependent not only on the intrinsic characteristics of tumor cells, but also on the cooperative interactions of non-neoplastic cells, soluble secreted factors and the non-cellular solid-state ECM network that comprise the tumor microenvironment. Given the ability of the tumor microenvironment to regulate the cellular phenotype, recent efforts have focused on understanding the molecular mechanisms by which cells sense, assimilate, interpret, and ultimately respond to their immediate surroundings. Exciting new studies are beginning to unravel the complex interactions between the numerous cell types and regulatory factors within the tumor microenvironment that function cooperatively to control tumor cell invasion and metastasis. Here, we will focus on studies concerning a common theme, which is the central importance of the non-cellular solid-state compartment as a master regulator of the malignant phenotype. We will highlight the non-cellular solid-state compartment as a relatively untapped source of therapeutic and imaging targets and how cellular interactions with these targets may regulate tumor metastasis.

Generation of a recombinant oncolytic Newcastle disease virus and expression of a full IgG antibody from two transgenes

The most advanced oncolytic Newcastle disease virus (NDV) strains that are used in clinical trials for the treatment of cancer are wild-type mesogenic strains. These virus strains have an inherent, nongenetically engineered, oncolytic activity and selectively replicate in tumor cells but not in normal human cells. To date no investigations have been performed with genetically engineered mesogenic NDV regarding the oncolytic activity. We describe here the generation of recombinant viruses of the mesogenic naturally oncolytic NDV strain MTH68. We show that not only one, but also two additional transgenes coding for amino-acid chains with a molecular weight of 25 and 50 kDa can be inserted into the viral genome without affecting viral growth, oncolytic potency or tumor-selective replication of the virus. Transgenic expression of the heavy and light chains of a monoclonal antibody, as separate additional transcriptional cassettes, leads to the expression of full immunoglobulin G (IgG) monoclonal antibody by recombinant NDV. Infection of tumor cells with antibody-transgenic viruses results in the efficient production and secretion of a functional full size IgG antibody by the tumor cells, that specifically binds to its target-antigen in tumor tissue. This approach will allow to combine the advantages of oncolytic RNA viruses and monoclonal antibodies in a single powerful anticancer agent with improved or even new therapeutic properties.

The extra-domain A of fibronectin is a vascular marker of solid tumors and metastases

One of the most promising new avenues for the development of more selective and efficacious cancer therapies relies on the antibody-mediated targeted delivery of bioactive agents (e.g., cytokines) to the tumor environment. The identification of quantitative differences in the expression of accessible vascular proteins in metastatic lesions and host organs facilitate the development of antibody-based strategies, which should be highly efficient and selective, considering the fact that an over-exuberant neovasculature is a characteristic feature of aggressive cancers, and that tumor blood vessels are readily accessible for i.v. administered therapeutic agents. Metastasis is the main cause of death in cancer. The availability of metastasis-specific antigens accessible from the bloodstream will allow a selective delivery of therapeutic agents to metastatic lesions using antibodies as vehicles. Using a combination of vascular biotinylation of 129Sv mice bearing F9 liver metastases and mass spectrometry, we have identified 435 accessible proteins in metastasis and host organ specimens, of which 117 were exclusively detected in metastases. In particular, we found that the alternatively spliced extra-domain A (EDA) of fibronectin is strongly expressed in the neovasculature of liver metastases, while being undetectable in most normal organs. A human antibody to EDA was used to show EDA expression in the neovasculature of metastases and primary tumors of human cancer patients and to target mouse liver metastases and subcutaneous tumors in vivo. Human antibody fragments specific to the EDA domain of fibronectin promise to serve as general vehicles for the efficient and selective delivery of imaging agents or therapeutic molecules to metastatic sites.

Identification of specific reachable molecular targets in human breast cancer using a versatile ex vivo proteomic method

Targeting of tumoral tissues is one of the most promising approaches to improve both the efficacy and safety of anticancer treatments. The identification of valid targets, including proteins specifically and abundantly expressed in cancer lesions, is of utmost importance. Despite state-of-the-art technologies, the discovery of cancer-associated target proteins still faces the limitation, in human tissues, of antigen accessibility to suitable high-affinity ligands such as human mAb bound to bioactive molecules. Terminal perfusion of tumor-bearing mice or ex vivo perfusion of human cancer-bearing organs with a reactive biotin ester solution has successfully led to the identification of novel accessible biomarkers. This methodology is however restricted to perfusable organs, and excludes most of the tissues of interest to targeted therapies, e.g. primary breast cancer and metastases. Herein, we report on the development of a new chemical proteomic method that bypasses the perfusion step and thus offers the potential to identify accessible molecular targets in virtually all types of animal and human tissues. We have validated our new procedure by identifying biomarkers selectively expressed in human breast carcinoma. Overall, this powerful technology may lay the ground not only for custom-made therapies in cancer, but also for the development of therapies that need to be selectively delivered in a specific tissue.

The antibody-mediated targeted delivery of interleukin-15 and GM-CSF to the tumor neovasculature inhibits tumor growth and metastasis

Tumor-targeting immunocytokines represent a new class of anticancer pharmaceutical agents, which often display a superior therapeutic index compared with the corresponding unconjugated cytokines. In this article, we have studied the anticancer properties of interleukin-15 (IL-15) and granulocyte macrophage colony-stimulating factor (GM-CSF), fused to the human antibody fragment scFv(L19), specific to the EDB domain of fibronectin, a marker of angiogenesis. The immunocytokines L19-IL-15 and L19-GM-CSF were expressed in mammalian cells and purified to homogeneity, revealing no loss of cytokine activity in in vitro assays. Furthermore, the ability of the two immunocytokines to selectively localize to tumors in vivo was confirmed by biodistribution analysis with radioiodinated protein preparations. L19-IL-15 and L19-GM-CSF displayed a potent antitumor activity both in s.c. and in metastatic F9 and C51 murine models of cancer in immunocompetent mice. This therapeutic action was superior compared with IL-15-based and GM-CSF-based fusion proteins, containing antibodies of irrelevant specificity in the mouse, which were used as non-tumor-targeting controls. For both L19-IL-15 and L19-GM-CSF immunocytokines, CD8(+) T cells seemed to mostly contribute to the therapeutic action as shown by in vivo cell depletion experiments. The results presented in this article are of clinical significance, considering the fact that the sequence of EDB is identical in mouse and man and that the tumor-targeting ability of the L19 antibody has been extensively shown in clinical trials in patients with cancer.

In vivo protein biotinylation and sample preparation for the proteomic identification of organ- and disease-specific antigens accessible from the vasculature

Targeted delivery of bioactive molecules to diseased organs or tissues by means of binding molecules specific to markers of diseases represents a promising area of pharmaceutical intervention. The availability of markers of pathology, ideally accessible from the vasculature, is crucial for such strategies. To this aim, here we present a protocol based on terminal perfusion of mice with a reactive ester derivate of biotin that enables the covalent modification of proteins readily accessible from the bloodstream. Biotinylated proteins from total organ or tissue extracts are (i) purified on streptavidin resin in the presence of strong detergents, (ii) digested on the resin and (iii) subjected to proteomic analysis. This technology is applicable to comparative proteomic investigations of differentially expressed, accessible proteins in numerous animal models having different physiological and pathological processes.

Fibronectin as target for tumor therapy

During cancer progression, the extracellular matrix (ECM) of the tissue in which the tumor grows is extensively remodeled, both by degradation of preexisting ECM molecules and by the neosynthesis of ECM components, which in many cases are not present in the ECM of normal tissues. Fibronectin (FN), a class of high-molecular-weight adhesive glycoproteins, plays a prominent role in mediating ECM function, because of its high abundance and its interaction with cellular components. Furthermore, the generation of tumor-associated FN isoforms allows the development of specific ligands (e.g., antibodies), which can be used for the selective delivery of therapeutic agents to the tumor environment. In view of these considerations, it is not surprising that FN is being used as a target for biomolecular intervention, both for the development of inhibitory molecules that block the interaction of FN with integrins and other receptors on the cell surface, and for the development of ligand-based targeted imaging and therapeutic strategies. In this review, we briefly present the essential properties of FN, and we then focus on the therapeutic strategies that are currently in preclinical or clinical development and feature FN as a target, or that are based on FN fragments so as to promote tumor-growth inhibition.

ED-B fibronectin (ED-B) can be targeted using a novel single chain antibody conjugate and is associated with macrophage accumulation in atherosclerotic lesions

It has been shown that ED-B fibronectin (ED-B) is a potential target for plaque imaging. The aim of this study was to test a novel modified single chain anti-ED-B antibody (scFv) conjugated for near infrared fluorescence imaging (NIRF) with tetrasulfonated carbocyanine-maleimide (TSC-scFv) and to examine the association of ED-B with the presence of macrophages in a murine model of atherosclerosis. Expression of ED-B was observed in plaque areas in apolipoprotein E-deficient (apoE(-/-)) mice which increased with age and plaque load. Robust imaging was possible after explantation of the aorta and demonstrated a strong NIRF signal intensity in focal aortic and brachiocephalic plaque lesions, whereas no signals were found in undiseased areas. Plaque lesion ED-B was expressed by smooth muscle cell and was closely associated to macrophage infiltrates. Although not expressed by the same cell type, there was a significant correlation (p<0.01) between ED-B and macrophage immunoreactivity. In vitro human coronary and mouse smooth muscle cells significantly increased ED-B expression after angiotensin II and TNF-alpha treatment. This study demonstrates that plaque NIRF imaging is feasible with a novel single chain antibody and that ED-B expression is closely associated with inflammation in experimental atherosclerosis.

Antibody-mediated delivery of IL-10 inhibits the progression of established collagen-induced arthritis

The antibody-mediated targeted delivery of cytokines to sites of disease is a promising avenue for cancer therapy, but it is largely unexplored for the treatment of chronic inflammatory conditions. Using both radioactive and fluorescent techniques, the human monoclonal antibodies L19 and G11 (specific to two markers of angiogenesis that are virtually undetectable in normal adult tissues) were found to selectively localize at arthritic sites in the murine collagen-induced model of rheumatoid arthritis following intravenous (i.v.) administration. The same animal model was used to study the therapeutic action of the L19 antibody fused to the cytokines IL-2, tumour necrosis factor (TNF) and IL-10. Whereas L19-IL-2 and L19-TNF treatment led to increased arthritic scores and paw swellings, the fusion protein L19-IL-10 displayed a therapeutic activity, which was superior to the activity of IL-10 fused to an antibody of irrelevant specificity in the mouse. The anti-inflammatory cytokine IL-10 has been investigated for the treatment of patients with rheumatoid arthritis, but clinical development plans have been discontinued because of a lack of efficacy. Because the antigen recognised by L19 is strongly expressed at sites of arthritis in humans and identical in both mice and humans, it suggests that the fusion protein L19-IL-10 might help overcome some of the clinical limitations of IL-10 and provide a therapeutic benefit to patients with chronic inflammatory disorders, including arthritis.

A human mAb specific to oncofetal fibronectin selectively targets chronic skin inflammation in vivo

The antibody-based targeted delivery of bioactive agents to sites of angiogenesis is an attractive therapeutic strategy for cancer treatment, but is largely unexplored for chronic inflammatory diseases. In this article, we show that the extra domain B (EDB) domain of fibronectin, a marker of angiogenesis, is expressed in psoriatic lesions, and that the anti-EDB human antibody L19 can selectively localize to chronically inflamed skin in vivo. The L19-based delivery of the cytokines IL10 and IL12 did not improve or worsen inflammation in a mouse model of chronic skin inflammation, which overexpressed vascular endothelial growth factor under the control of the keratin-14 promoter. By contrast, the L19-based targeted delivery of the proinflammatory cytokine IL2 or of the photosensitizer Sn(IV) chlorin e6 resulted in an increased swelling and reddening of inflamed skin. These results indicate that antibodies specific to components of the modified extracellular matrix can selectively accumulate at chronically inflamed sites in vivo. This observation now stimulates the search for bioactive molecules which can be fused to antibodies and which may confer a therapeutic benefit as a result of their preferential accumulation in psoriatic lesions and other sites of inflammation.

A novel, non-immunogenic Fyn SH3-derived binding protein with tumor vascular targeting properties

The generation of novel binding molecules based on protein frameworks ("scaffolds") represents an emerging field in protein engineering, with the potential to replace antibodies for many research and clinical applications. Here, we describe the design, construction, characterization, and use of a novel human Fyn SH3 phage library, containing 1.2 x 10(9) individual clone members. We also present the isolation and in vitro characterization of Fyn SH3-derived proteins binding to the extra-domain B of fibronectin, a marker of angiogenesis. One specific binding clone, named D3, was further evaluated and showed a remarkable ability to stain vascular structures in tumor sections. Furthermore, quantitative biodistribution studies in tumor-bearing mice revealed the ability of D3 to selectively accumulate in the tumor. In contrast to human scFv antibody fragments administered to mice, neither Fyn SH3 WT nor the D3 mutant was immunogenic in mice after four intravenous injections. The extra-domain B binding D3 protein opens new biomedical opportunities for the in vivo imaging of solid tumors and for the delivery of toxic agents to the tumoral vasculature.

An engineered antibody-interleukin-12 fusion protein with enhanced tumor vascular targeting properties

The antibody-mediated targeted delivery of interleukin-12 (IL12) to the EDB domain of fibronectin, a marker of angiogenesis, is a promising avenue for enhancing the therapeutic index of this anti-cancer cytokine. Previous experiments, based on sequential fusion of a single-chain IL12 derivative to the anti-EDB antibody fragment scFv(L19) had yielded a therapeutic fusion protein [IL12-scFv(L19)-FLAG], which displayed an impressive therapeutic activity in murine models of cancer, in spite of a tumor uptake, which was less efficient compared to the parental unmodified scFv(L19). In this article, we describe the comparative analysis of 3 recombinant fusion proteins comprising the scFv(L19) and IL12 moieties. One of them, in which the p40 and p35 form a covalent heterodimer and in which each subunit is fused to a molecule of scFv(L19), displays an excellent tumor targeting performance in vivo, as assessed by quantitative biodistribution analysis, and a potent anti-tumor effect, superior to the one of IL12-scFv(L19)-FLAG. These results may have a clinical impact, considering the fact that the tumor targeting ability of scFv(L19) in patients with cancer has been demonstrated using scintigraphic methods, and that 2 scFv(L19)-based antibody-cytokine fusion are currently entering clinical trials.

Tumor-targeting properties of novel antibodies specific to the large isoform of tenascin-C

BACKGROUND

The targeted delivery of bioactive molecules with antibodies specific to tumor-associated antigens represents a promising strategy for improving the efficacy of tumor therapy. The large isoform of tenascin-C, an abundant glycoprotein of the tumor extracellular matrix, is strongly overexpressed in adult tissue undergoing tissue remodeling, including wound healing and neoplasia, and has been implicated in a variety of different cancers while being virtually undetectable in most normal adult tissues.

EXPERIMENTAL DESIGN

We have used antibody phage technology to generate good-quality human recombinant antibodies (F16 and P12) specific to the alternatively spliced domains A1 and D of the large isoform of tenascin-C. The tumor-targeting properties of F16 and P12 were assessed by biodistribution studies in tumor xenografts using the antibodies in small immunoprotein (SIP) format.

RESULTS

SIP(F16) selectively accumulated at the tumor site with 4.5%ID/g at 24 hours in the U87 glioblastoma model but was rapidly cleared from other organs (tumor-to-organ ratios, approximately 10:1). The accumulation of SIP(P12) in the tumor was lower compared with SIP(F16) and persistent levels of radioactivity were observed in the intestine.

CONCLUSIONS

These data suggest that the F16 antibody, specific to domain A1 of tenascin-C, is a promising building block for the development of antibody-based pharmaceuticals in view of its excellent tumor-targeting performance and the strong expression of the antigen in a variety of primary and metastatic tumors.

A chemical proteomics approach for the identification of accessible antigens expressed in human kidney cancer

A promising avenue toward the development of more selective anticancer drugs consists in the targeted delivery of bioactive molecules to the tumor environment by means of binding molecules specific to tumor-associated markers. We have used a chemical proteomics approach based on the ex vivo perfusion and biotinylation of accessible structures within surgically resected human kidneys with tumor to gain information about accessible and abundant antigens that are overexpressed in human cancer. This procedure led to the selective labeling with biotin of vascular structures. Biotinylated proteins were purified on streptavidin resin and identified using mass spectrometric methodologies, revealing 637 proteins, 184 of which were only found in tumor specimens and 223 of which were only found in portions of normal kidneys. Immunohistochemical and PCR analysis confirmed that several of the putative cancer antigens identified in this study are indeed preferentially expressed in tumors. In conclusion, we have developed a methodology that allows the identification of accessible biomarkers in human tissues. The tumor-associated antigens identified in this study may be suitable targets for antibody-based anticancer therapies. The experimental approach described here should be applicable to other surgical specimens and to other pathologies as well as to the study of basic physiological and immunological processes.

The monoclonal antibody SM5-1 recognizes a fibronectin variant which is widely expressed in melanoma

Background

Previously we have generated the monoclonal antibody SM5-1 by using a subtractive immunization protocol of human melanoma. This antibody exhibits a high sensitivity for primary melanomas of 99% (248/250 tested) and for metastatic melanoma of 96% (146/151 tested) in paraffin embedded sections. This reactivity is superior to the one obtained by HMB-45, anti-MelanA or anti-Tyrosinase and is comparable to anti-S100. However, as compared to anti-S100, the antibody SM5-1 is highly specific for melanocytic lesions since 40 different neoplasms were found to be negative for SM5-1 by immunohistochemistry. The antigen recognized by SM5-1 is unknown.

Methods

In order to characterize the antigen recognized by mAb SM5-1, a cDNA library was constructed from the metastatic human melanoma cell line SMMUpos in the Uni-ZAP lambda phage and screened by mAb SM5-1. The cDNA clones identified by this approach were then sequenced and subsequently analyzed.

Results

Sequence analysis of nine independent overlapping clones (length 3100–5600 bp) represent fibronectin cDNA including the ED-A, but not the ED-B region which are produced by alternative splicing. The 89aa splicing variant of the IIICS region was found in 8/9 clones and the 120aa splicing variant in 1/9 clones, both of which are included in the CS1 region of fibronectin being involved in melanoma cell adhesion and spreading.

Conclusion

The molecule recognized by SM5-1 is a melanoma associated FN variant expressed by virtually all primary and metastatic melanomas and may play an important role in melanoma formation and progression. This antibody is therefore not only of value in immunohistochemistry, but potentially also for diagnostic imaging and immunotherapy.