An ErbB-3 antibody, MP-RM-1, inhibits tumor growth by blocking ligand-dependent and independent activation of ErbB-3/Akt signaling.

The ErbB receptors, such as ErbB-1 and ErbB-2, have been intensely pursued as targets for cancer therapeutics. Although initially efficacious in a subset of patients, drugs targeting these receptors led invariably to resistance, which is often associated with reactivation of the ErbB-3-PI3K-Akt signaling. This may be overcome by an ErbB-3 ligand that abrogates receptor-mediated signaling. Toward this end, we have generated a mouse monoclonal antibody, MP-RM-1, against the extracellular domain (ECD) of ErbB-3 receptor. Assessment of human tumor cell lines, as well as early passage tumor cells revealed that MP-RM-1 effectively inhibited both NRG-1ß-dependent and -independent ErbB-3 activation. The antagonizing effect of MP-RM-1 was of non-competitive type, as binding of [(125)I]-labeled NRG-1ß to ErbB-3 was not influenced by the antibody. MP-RM-1 treatment led, in most instances, to decreased ErbB-3 expression. In addition, MP-RM-1 was able to inhibit the colony formation ability of tumor cells and tumor growth in two human tumor xenograft nude mouse models. Treatment with the antibody was associated with a decreased ErbB-3 and Akt phosphorylation and ErbB-3 expression in the excised tumor tissue. Collectively, these results indicate that MP-RM-1 has the potential to interfere with signaling by ErbB-3 and reinforce the notion that ErbB-3 could be a key target in cancer-drug design.

Characterization of mouse ALCAM (CD166): the CD6-binding domain is conserved in different homologs and mediates cross-species binding.

Activated leukocyte cell adhesion molecule (ALCAM; CD166) is a member of the immunoglobulin gene superfamily (IgSF) which is expressed by activated leukocytes and thymic epithelial cells and is a ligand for the lymphocyte antigen CD6. Herein, we report on the isolation and characterization of cDNA clones encoding mouse ALCAM (mALCAM). Comparison of the predicted amino acid sequence of mALCAM and human ALCAM (hALCAM) showed an overall identity of 93%. Binding studies with truncated forms of the extracellular region of mALCAM showed that the CD6 binding site is located in the N-terminal Ig-like domain and that mALCAM is capable of binding both human and mouse CD6. Mutagenesis studies on hALCAM suggested that residues critical for CD6 binding map to the predicted A'GFCC'C" beta-sheet of ALCAM's N-terminal binding domain. Residue differences in the N-terminal domains of mALCAM and hALCAM were analyzed with the aid of a molecular model of ALCAM. All residues critical for CD6 binding are conserved in both mALCAM and hALCAM, whereas residue differences map to the predicted BED face which is opposite the CD6 binding site on hALCAM. These findings provide a molecular rationale for the observed cross-species CD6/ALCAM interaction and the apparent inability to generate monoclonal antibodies (mAb) against the CD6 binding site. RNA blot analysis showed that mRNA transcripts encoding mALCAM are expressed in the brain, lung, liver, and the kidney, as well as by activated leukocytes and a number of cell lines. A rat mAb specific for mALCAM was produced and by two-color immunofluorescence studies was shown to bind to both activated CD4+ and CD8+ T cells.

Identification of the tumor antigen 90K domains recognized by monoclonal antibodies SP2 and L3 and preparation and characterization of novel anti-90K monoclonal antibodies.

The tumor antigen 90K (Mac-2BP, L3 antigen), which has been shown to have T cell costimulatory activity, is a approximately 90 kDa secreted protein found in high levels in plasma, saliva, breast milk and other human fluids. The 90K antigen can be divided into three domains: an amino terminal scavenger receptor cysteine-rich (SRCR)-like domain (D1), followed by a heavily glycosylated mucin-like domain (D2) and a approximately 27 kDa carboxy-terminal domain (D3). In this study we report on the construction of six different 90K immunoglobulin (Ig) fusion proteins containing different 90K domain combinations. Initially these fusion proteins were used to identify which 90K domain contains the epitopes recognized by the anti-90K monoclonal antibodies (mAb) SP2 and L3. Both of these mAbs were found to recognize 90K-D2. A new panel of anti-90K mAb was then generated by immunizing mice with ascites derived 90K protein. The 90K domain specific fusion proteins were then used to identify novel anti-90K mAbs which recognize the amino terminal SRCR domain and the carboxy terminal approximately 27 kDa domain of 90K. Two novel anti-90K SRCR (D1) and one anti-90 27 kDa domain (D3) mAbs were obtained. These 90K-Ig fusion proteins, as well as the novel and existing anti-90K mAbs, provide a set of tools which will allow further dissection of the structure and function of this immune modulatory protein.

Elevated serum levels of 90K/MAC-2 BP predict unresponsiveness to alpha-interferon therapy in chronic HCV hepatitis patients.

BACKGROUND: The clinical outcome of hepatitis virus infections is though to depend on the complex interplay between the host immune response profile and virus factors. 90K/MAC-2 BP is a novel member of the Scavenger Receptor Cysteine Rich protein superfamily that functions as a molecular alarm signal for the cellular immune system against both cancer cells and virus infections. METHODS: To assess the significance and the potential clinical usefulness of testing for serum levels of 90K/MAC-2 BP in chronic viral hepatitis patients we studied 115 consecutive patients with chronic HCV hepatitis, 28 HBsAg chronic hepatitis patients, 12 asymptomatic HCV carriers and 11 asymptomatic HBV carriers. 103 out of the 115 HCV patients have been treated with recombinant alpha 2a-interferon at the dose of 3 Mega Units (MU) t.i.w. for 6 months followed by 1.5 MU t.i.w. for 6 months, and have been followed up for a further 12 months. Serum levels of 90K/MAC-2 BP were measured by an immunoradiometric assay based on the specific SP-2 monoclonal antibody. RESULTS AND CONCLUSIONS: Serum 90K/MAC-2 BP levels are increased in chronic viral hepatitis patients, being significantly higher in HCV than in HBV patients. In chronic HCV hepatitis, serum 90K/MAC-2 BP levels are related to both the degree of disease severity and duration of infection. Moreover, elevated 90K/MAC-2 BP serum levels are an independent predictor of failure to respond to alpha-interferon treatment in a cohort of community-acquired chronic hepatitis C patients.

The 90K tumor-associated antigen and clinical progression in human immunodeficiency virus infection.

We investigated the possibility that a secreted glycoprotein of approximately 90,000 daltons, termed 90K and identified as a member of the protein superfamily characterized by the scavenger receptor cysteine-rich (SRCR) domain, might have value as a predictor of progression to acquired immunodeficiency syndrome (AIDS) in subjects infected with the human immunodeficiency virus (HIV). Among 488 HIV-seropositive intravenous drug users with a median follow-up of 32.5 months, high levels of serum 90K at baseline proved to be a significant predictor of faster progression to AIDS, either as a continuous variable (log 90K; p < 0.0001) or as a dichotomous variable with an optimized cutoff point of 30 U/ml (p < 0.00001). Analysis of 90K in relation to known prognostic factors found an association with CD4 count, beta 2-microglobulin, and p24 antigen but none with neopterin. In multivariate analysis, the baseline 90K level was an independent predictor of AIDS. As compared with subjects with low levels of 90K, the relative risk of developing AIDS was 3.5 (95% CI 1.9-6.5) among those with high levels of 90K. The predictive value of 90K was maintained after stratification by baseline CD4 count: among subjects with > or = 500 x 10(6)/L CD4 cells, the proportion in whom AIDS developed was 10.5% for those with 90K levels < or = 30 U/ml as compared with 20% for those with 90K above the cutoff point (p = 0.006). Serum 90K is an independent predictor of the risk for progression to AIDS in HIV-infected subjects, including those whose CD4 counts have not fallen.

The secreted tumor-associated antigen 90K is a potent immune stimulator.

Immunization of mice with conditioned media from human breast cancer cells yielded the monoclonal antibody SP-2, which recognized an antigen of approximately 90-95 kDa. This protein, designated 90K, was found to be present in the serum of healthy individuals and at elevated levels in the serum of subpopulations of patients with various types of cancer and AIDS. Here we report the primary structure of the SP-2 antigen and demonstrate its relationship to a family of proteins which carry a scavenger receptor cysteine-rich domain. Northern blot analysis of normal tissues, primary tumors, and tumor-derived cell lines indicates a broad expression spectrum of the 90K gene at widely varying levels. Functional characterization reveals stimulatory effects of 90K on host defense systems, such as natural killer cell and lymphokine-activated killer cell activity, and indicates that its immunostimulatory effects may be mediated through the induction of interleukin-2 and possibly other cytokines.

Elevated serum levels of a 90,000 daltons tumor-associated antigen in cancer and in infection by human immunodeficiency virus (HIV).

Levels of a 90,000 daltons monoclonal antibody-defined tumor-associated antigen, termed 90K, were measured in the serum from 649 patients with various types of cancer and 1215 patients infected by the human immunodeficiency virus (HIV). Significantly increased 90K serum levels (12.1 +/- 0.5 U/ml) were found in cancer patients with respect to healthy controls (5.7 +/- 0.3 U/ml), with the highest levels in neoplasms of the breast, lung and gastrointestinal tract. In 355 patients with breast cancer, the elevation of serum 90K levels was more pronounced at advanced stages of disease. Mean levels of 90K for 1215 HIV-infected subjects (21.2 +/- 0.8 U/ml) were significantly higher than controls and cancer patients, and the levels progressively increased with disease worsening from asymptomatic infection to full blown AIDS. These data suggest that 90K is not merely a tumor-associated antigen and lead us to postulate it to be a signalling molecule whose production might be related to the immune deficit caused by pathogenetic events such as neoplastic progression and virus infection.

Prognostic value of a novel circulating serum 90K antigen in breast cancer.

Monoclonal antibody SP-2 to the tumour-associated antigen 90K was generated by immunisation with conditioned medium of human breast cancer cells. We investigated whether circulating levels of 90K can influence the prognosis of patients with breast cancer. Serum samples were obtained from 425 patients with histologically proven breast cancer with no clinical evidence of disease after surgery (NED) and in 310 patients with metastatic disease. Serum 90K was determined by a new immunoradiometric assay (IRMA). Antigen levels in NED patients were elevated in 18.5% of cases, mean levels being higher than in healthy controls (P = 0.001). Among 375 evaluable patients, the 75-month overall survival for 90K-negative (< or = 11 U ml-1) and 90K-positive (> 11 U ml-1) patients was 78% and 53% respectively (P = 0.004). The prognostic value of 90K appeared to be limited to patients with node-positive disease. Number of metastatic axillary lymph nodes and level of 90K antigen were the only independent variables for predicting overall survival. Patients with metastatic breast cancer had elevated 90K in 51.3% of cases. High 90K levels were significantly associated with the presence of metastases to liver, shorter disease-free interval and younger age. We conclude that an elevated 90K antigen level in serum is a predictor of poor prognosis in breast cancer.

A 90-kDa protein serum marker for the prediction of progression to AIDS in a cohort of HIV-1+ homosexual men.

Levels of a 90-kDa protein (90K), recently reported as a possible marker of HIV-1 infection, were serially examined in a group of HIV-1-infected (HIV-1+) and uninfected (HIV-1-) subjects drawn from the same cohort of homosexual men. The first phase of the study included 61 HIV-1+ AIDS-free subjects 4 years (+/- 6 months) postseroconversion and 75 contemporaneous unifected subjects. Two years later, a subset of 35 HIV-1+ AIDS-free subjects and 72 HIV-1- controls was examined. Mean 90K levels for HIV-1+ subjects were significantly higher than for contemporaneous HIV-1- subjects both 4 and 6 years postseroconversion (p < 0.0001). A significantly more rapid progression to AIDS was seen in HIV-1+ subjects with high 90K levels both 4 years (p = 0.01) and 6 years (p = 0.003) postseroconversion. Four years postseroconversion, 90K was significantly correlated with CD8 cell percent, interferon, neopterin, and beta 2-microglobulin (p < 0.05). Two years later, significant correlations were seen between 90K levels and CD4 cell percent, CD4 cell number, and beta 2-microglobulin (p < 0.05). Stepwise-stepdown regression modeling using 90K, CD4 cell percent, interferon, and beta 2-microglobulin levels 4 years postseroconversion showed that the predictive value of a trivariate model of 90K-interferon-CD4 percent was better than any univariate or bivariate model. We conclude that the 90K protein may be a useful predictor of progression to AIDS in HIV-1+ patients, particularly in combination with the established markers of CD4 cell percent and interferon.

Purification and characterization of a 90 kDa protein released from human tumors and tumor cell lines.

A novel tumor-associated protein, termed 90K, and recognized by mAb SP-2 was purified from serum of breast cancer patients, ovarian cancer ascitic fluid and conditioned medium of human breast cancer cells. In these three sources, native 90K is present as a high molecular weight complex that was dissociated by SDS-PAGE into a major band of approximately 90,000 Da. On the basis of electrophoretic mobility, buoyant density value, amino acid composition, and immunoreactivity, the 90K from the different sources appeared to be identical. NH2-terminal amino acid sequence revealed no homology to known protein.

Dynamic test with recombinant interferon-alpha-2b: effect on 90K and other tumour-associated antigens in cancer patients without evidence of disease.

We have previously shown that a short course of recombinant interferon-alpha-2b (rIFN-alpha-2b) (3 million units day for 5 days) for patients with primary gynaecologic malignancies was able to increase the circulating levels of a newly discovered tumour associated antigen, termed 90K. In this study, we have investigated the effects of the same modality of administration of rIFN-alpha-2b in 62 patients with breast and colorectal cancer whose primary tumour was surgically removed 1 month before and who were without evidence of disease (NED) at the time of the study. A significant increase of 90K serum concentration was already observed 24 h after the first r-IFN-alpha-2b injection and persisted throughout the investigational period. The increase was more pronounced in patients with a basal 90K-negative than a 90K-positive assay. Of 54 patients who started the test with a 90K negative assay, 17 (31%) shifted to a positive assay after rIFN-alpha-2b. Twenty-eight of 62 (45%) patients exhibited a 90K value above the mean increment of the whole population. The serum levels of CEA, CA-15-3, CA 19-9, and alpha-fetoprotein measured in the same serum samples were not modified. After 2 years of follow-up, ten patients relapsed. Six of them showed a 90K increase above the mean increment of the whole population. As with ovarian cancer, the increase of 90K following r-IFN-alpha-2b administration might be of importance for the early detection of disease recurrence in clinically NED breast and colon cancer patients.