Monoclonal antibody to fibulin-1 generated by genetic immunization.

Fibulin-1 (Fbln-1) is an extracellular matrix (ECM) and plasma glycoprotein. Considering the growing evidence indicating that Fbln-1 plays a role in cancer we sought to develop monospecific antibodies to better facilitate further studies of the function of Fbln-1 in breast cancer. Using a plasmid expression vector encoding full-length human Fbln-1D as an immunogen and CpG oligodeoxyribonucleotides as adjuvant a monoclonal antibody (MAb) against Fbln-1 was produced. This MAb, designated MEM-2 was of IgM isotype and reacted with bacterially expressed Fbln-1. Furthermore, MEM-2 reacted with Fbln-1 expressed in the ECM released by cultured human breast carcinoma SKBR-3 cells in ELISA, and also with Fbln-1 present in SKBR-3 cell extract in immunoprecipitation and Western blotting. MEM-2 also reacted with Fbln-1 in human breast carcinoma specimens. These findings illustrate the utility of genetic immunization as a means of generating monoclonal antibodies to tumor-related ECM proteins. MEM-2 represents a useful new tool for the study of Fbln-1 in breast cancer.

Prevention of spontaneous neu-expressing mammary tumor development in mice transgenic for rat proto-neu by DNA vaccination.

The HER-2/neu proto-oncogene is overexpressed in 20-30% of human breast cancers and is associated with high recurrence risk. The oncogenic potential of HER-2/neu, together with its elevated expression in tumors, cell surface localization, and immunogenicity in some patients, make this oncoprotein an ideal target for immunotherapeutic approaches. To test the efficacy of immune-based strategies in eliciting an antitumor response, we used the N#202 transgenic mouse model engineered to overexpress the rat neu proto-oncogene under the control of the mouse mammary tumor virus promoter; females of this line develop spontaneous focal mammary tumors by 6 months of age. Transgenic mice immunized intramuscularly with a HER-2 cDNA ligated into the VR1012 (VICAL) expression vector under the control of the cytomegalovirus promoter developed significantly fewer spontaneous tumors as compared with mice injected with the empty vector (P < 0.0001) or not injected (P = 0.0006). However, this protection was observed only when immunization was started in 3-month-old but not in 6-month-old mice. These data suggest that the xenogeneic HER-2 DNA sequence can break immune tolerance to rat neu in transgenic N#202 mice and induce protective immunity that impairs the neu oncogene-driven progression of mammary carcinogenesis. The preventive effect achieved by our immunological approach appeared not to be based on anti-neu specific B and T cell immune attacks but was more possibly based on different mechanisms including aspecific and inflammatory immunological responses.

p185(neu) protein is required for tumor and anchorage-independent growth, not for cell proliferation of transgenic mammary carcinoma.

Transgenic FVB-NeuN mice (N202) bearing the rat neu protooncogene driven by the mouse mammary tumor virus promoter/enhancer develop focal mammary carcinomas overexpressing the neu-encoded p185(neu) protein. In vitro expression of p185(neu) among mammary carcinoma cultures was heterogeneous, and we could establish some cell lines and clones displaying a complete loss of p185(neu) expression, along with others with very high p185(neu) protein level. Upon in vivo injection, p185(neu)-positive cells gave rise to fast-growing tumors with a short latency, while p185(neu)-negative cells required a very long latency time, and the resulting tumors were invariably p185(neu)-positive. The lower growth ability of p185(neu)-negative cells in vivo was also confirmed in athymic nude mice. In vitro, analysis of anchorage-independent growth in soft agar revealed colony formation from p185(neu)-positive but not p185(neu)-negative cells. The direct involvement of p185(neu) in clonogenicity was demonstrated by the inhibition of p185(neu)-positive colony growth in soft agar in the presence of an anti-p185(neu) monoclonal antibody. By contrast, a higher level of anchorage-dependent clonogenic growth and proliferation was observed in p185(neu)-negative cells as compared to p185(neu)-positive cells, thus explaining the relative ease with which p185(neu)-negative cell lines and clones were established in vitro. Together, the results indicate that p185(neu) expression can lead to tumor formation and metastasis through the modification of intrinsic properties of cells related to anchorage-independent growth ability rather than to proliferation or host-dependent mechanisms.

Ectopic expression of pRb2/p130 suppresses the tumorigenicity of the c-erbB-2-overexpressing SKOV3 tumor cell line.

We investigated the in vitro and in vivo effects of the ectopic expression of the pRb2/p130 cell cycle regulator on c-erbB-2-associated tumorigenicity. SKOV3 ovarian cancer cells, which display c-erbB-2 gene amplification and oncoprotein (p185HER2) overexpression, were stably transfected with a plasmid containing the coding sequence for human wild-type pRb2/p130 (wtRb2), or with pcDNA3 empty vector. Three wtRb2-transfected clones (cl. 24, ci. 49, cl. 100) and one empty vector-transfected clone (cl. mock) were randomly picked and further analysed. Western blot analysis revealed high levels of pRb2/p130 in the three clones compared to mock cells. Levels of p185HER2 and the extent of its tyrosine phosphorylation were similar in all transfectant clones, as were levels of pRb1 and p107. In anchorage-independent growth assays, the number of colonies from wtRb2 clone-transfectants was about 90% less than that arising from mock cells (P<0.001). Tumor take rates of the three wtRb2-transfected clones xenografted in nu/nu mice were much lower than those of mock cells, and tumor volume was decreased by 80% (P<0.001). A mutant version of pRb2/p130 deleted of the pocket region (mut-Rb2) was also transfected into SKOV3 cells and studied in parallel with the wtRb2-transfected and pcDNA empty vector-transfected bulk populations. mut-Rb2 transfected cells showed no inhibition of in vitro colony formation and were fully tumorigenic. Together, these findings indicate that Rb2 acts as a tumor suppressor gene in vivo and in vitro in SKOV3 cells and that the intact pocket region is required for the suppressor activity.

Macrophage infiltrate and prognosis in c-erbB-2-overexpressing breast carcinomas.

PURPOSE: Experiments were designed to investigate the association between tumor leukocytic infiltrates with other pathologic and biologic variables in primary tumors and with prognosis, and to define the phenotype of the infiltrating leukocytes. PATIENTS AND METHODS: A retrospective series of 1,207 primary breast carcinomas was studied according to different prognostic variables, including the presence of lymphoplasmacytic infiltrate (LPI). LPI was analyzed in association with other variables and survival. Additionally, a small prospective series of surgical specimens from 75 primary breast carcinomas with infiltrating leukocytes was tested by immunohistochemistry on frozen sections to phenotypically characterize the infiltrate, using anti-CD reagents, and the tumor, using anti-c-erbB-2 oncoprotein monoclonal antibody. RESULTS: In the retrospective series, menopausal status, nodal status, tumor size, stage, grade, and p185HER2 overexpression but not LPI were found to be associated with prognosis and maintained their prognostic significance in a multivariate analysis. LPI was significantly associated with some of these independent prognostic factors, such as tumor size (P = .03), stage (P = .004), grade III carcinomas (P < .000001), and overexpression of the p185HER2 (P < .000001). In some subgroups of patients in whom LPI was found more frequently, such as grade III cases or N- and c-erbB-2-positive cases, LPI was found to be indicative of a good prognosis (P = .008 and P = .03, respectively). Phenotypic analysis of the infiltrating leukocytes revealed a preponderance of macrophages in high-grade (P = .05) or c-erbB-2-positive (P = .008) tumors, whereas T cells constituted most of the infiltrate in the other tumors. CONCLUSION: Our data demonstrate different leukocytic types in the infiltrate of breast tumors with different prognostic significance.