Isolation of high-affinity monomeric human anti-c-erbB-2 single chain Fv using affinity-driven selection

The use of antibodies to target tumor antigens has had limited success, partially due to the large size of IgG molecules, difficulties in constructing smaller single chain Fv (scFv) antibody fragments, and immunogenicity of murine antibodies. These limitations can be overcome by selecting human scFv directly from non-immune or semi-synthetic phage antibody libraries; however, the affinities are typically too low for therapeutic application. For hapten antigens, higher-affinity scFv can be isolated from phage antibody libraries where the VH and VL genes of a binding scFv are replaced with repertoires of V genes (chain shuffling). The applicability of this approach to protein binding scFv is unknown. For this work, chain shuffling was used to increase the affinity of a non-immune human scFv, which binds the glycoprotein tumor antigen c-erbB-2 with an affinity of 1.6 x 10(-8) M. The affinity of the parental scFv was increased sixfold (Kd = 2.5 x 10(-9) M) by light-chain shuffling and fivefold (Kd = 3.1 x 10(-9) M) by heavy-chain shuffling, values comparable to those for antibodies against the same antigen produced by hybridomas. When selections were performed on antigen immobilized on polystyrene, spontaneously dimerizing scFv were isolated, the best of which had only a slightly lower Kd than wild type (Kd = 1.1 x 10(-8) M). These scFv dimerize on phage and are preferentially selected as a result of increased avidity. Compared to scFv which formed only monomer, dimerizing scFv had mutations located at the VH-VL interface, suggesting that VH-VL complementarity determines the extent of dimerization. Higher-affinity monomeric scFv were only obtained by selecting in solution using limiting concentrations of biotinylated antigen, followed by screening mutant scFv from bacterial periplasm by koff in a BIAcore. Using the proper selection and screening conditions, protein binding human scFv with affinities comparable to murine hybridomas can be produced without immunization.

Efficient in vitro affinity maturation of phage antibodies using BIAcore guided selections

Selection of higher affinity mutant phage antibodies has proven less than straightforward due to sequence dependent differences in phage antibody expression, toxicity to Escherichia coli, and difficulty in eluting the highest affinity phage. These differences lead to selection for increased levels of expression or decreased toxicity rather than for higher affinity. In this work, we demonstrate how surface plasmon resonance as employed in the BIAcore can be used to increase the efficiency of phage antibody selections, yielding greater increments in affinity from a single library. A mutant phage antibody library was created by randomizing nine amino acids located in the V(L) CDR3 of C6.5, a human scFv which binds the tumor antigen c-erbB-2 with a Kd of 1.6 x 10-8 M. The library was subjected to five rounds of selection in solution using decreasing concentrations of biotinylated c-erbB-2. After each round of selection, polyclonal phage were prepared and the rate of binding to c-erbB-2 determined in a BIAcore under mass transport limited conditions. Determination of the rate of binding permitted calculation of the concentration, and hence percent, of binding phage present. Results were used to select the antigen concentration for the next round of selection. To determine the optimal eluent, polyclonal phage was injected in a BIAcore and eluted using one of five different solutions (10 mM HCl, 50 mM HCl, 100 mM HCl, 100 mM triethylamine, 2.6 M MgCl2). Differences were observed in eluent efficacy, which was reflected in significant differences in the affinities of phage antibodies isolated from the library after a round of selection using the different eluents. Use of the BIAcore to determine the optimal eluent and guide the antigen concentration used for selection yielded a C6.5 mutant with a 16 fold reduction in Kd (Kd = 1.0 x 10-9 M). This represents at least a twofold greater increment in affinity than previously obtained from a single library of phage antibodies which bind antigens.

Growth inhibition of breast cancer cell lines by combinations of anti-P185HER2 monoclonal antibody and cytokines

The p185HER2 oncogene is associated with poor prognosis in patients with breast cancer. Both anti-p185HER2 MAb and cytokines have been shown to downregulate p185HER2 expression. We investigated the effect of combinations of humanized 4D5, and anti-p185HER2 MAB, and the cytokines IFN-alpha, IFN-gamma or TNF-alpha on the growth of three p185HER2 positive human abreast carcinoma cell lines, SK-BR-3, BT-474, and MDA-MB-453. All three cell lines were treated with IFN-alpha (1000 U/ml) or IFN-gamma (1000 U/ml) or TNF-alpha (100 U/ml) with or without huMAb 4D5 (100 microM), and cell growth was determined on days 3-7. While IFN-alpha, IFN-gamma, TNF-alpha, and huMAb 4D5 all inhibited growth, an apparently additive inhibitory effect occurred using combinations of huMAb 4D5 plus cytokine, with huMAb 4D5 plus TNF-alpha causing the greatest growth inhibition. These results demonstrate the potentiation of growth inhibition of breast cancer cell lines by the combination of anti p185HER2 MAb and cytokines, and suggest that combinations of anti-growth factor receptor MAb and cytokines may be useful in the treatment of breast cancer.

Targeting c-erbB-2 expressing tumors using single-chain Fv monomers and dimers

Single-chain Fv proteins containing a COOH-terminal cysteine (sFv') were constructed by using an antidigoxin 26.10 sFv and an anti-c-erbB-2 741F8 sFv. The fully active sFv' proteins were prepared by expression in Escherichia coli as insoluble inclusion bodies, followed by in vitro refolding using glutathione redox buffers and purification. The COOH-terminal cysteines of the refolded sFv' proteins were protected by a blocking group presumed to be the glutathionyl peptide, which was easily and selectively removed by gentle reduction. Air oxidation of the reduced sFv' monomers resulted in the efficient formation of disulfide-linked sFv' homodimers, designated (sFv')2, which were stable under oxidizing conditions and relatively slow to be disrupted under reducing conditions. The (26-10-1 sFv')-(741F8-1 sFv') heterodimer was prepared and possessed dual-antigen specificity; the active bispecific (sFv')2 dimerized under native conditions, apparently as a manifestation of self-association by the 741F8 sFv' subunit. Biodistribution and imaging studies that were performed on mice bearing human SK-OV-3 tumor xenografts that express the c-erbB-2 as a cell surface antigen were reviewed. Radioiodinated 741F8-2 (sFv')2 homodimer localized to the tumors with high specificity, as evidenced by excellent tumor:normal tissue ratios. Sagittal section autoradiography of whole animals 24 h after administration of antibody species revealed that 741F8 (sFv')2 produced a stronger tumor image than comparable doses of the 741F8 Fab, monomeric sFv', and the 26-10 (sFv')2 control without the high nonspecific background distribution of the 741F8 IgG.

Radioimmunotherapy of breast cancer xenografts with monoclonal antibody ICR12 against c-erbB2 p185: comparison of iodogen and N-succinimidyl 4-methyl-3-(tri-n-butylstannyl)benzoate radioiodination methods

C-erbB2 p185 is a proto-oncogene product expressed in 25-30% of human invasive breast cancers that is associated with poor prognosis and resistance to endocrine therapy and chemotherapy. It is minimally expressed in normal adult tissues (M. F. Press et al., Oncogene, 5: 953-962, 1990). For this reason, it is an attractive target for radioimmunotherapy and other antibody-directed therapies. ICR12 is a rat IgG2a monoclonal antibody directed against a protein epitope of the external domain of the c-erbB2 p185. We performed experiments to optimize the direct iodination of ICR12 with 131I using the IodoGen method, and we found impairment of immunoreactive fraction with increasing specific activity. N-Succinimidyl 4-methyl-3-(tri-n-butylstannyl)benzoate (MATE) is a tin ester that can be radioiodinated easily and then coupled to the epsilon-amino group of lysine residues. This method has been shown to have improved uptake in tumors compared with antibody labeled by direct iodination (P. K. Garg et al., Nucl. Med. Biol., 20: 379-387, 1993). ICR12 could be labeled up to 16 mCi/mg by this technique without loss of immunoreactive fraction. Whole-body retention of MATE-labeled ICR12 was less than IodoGen (P < 0.0001). Radioimmunotherapy experiments in athymic mice bearing established MDA MB 361 human breast cancer xenografts showed growth inhibition for > 24 days at a dose of 600 microCi/mouse (P < 0.0001) when labeled by the IodoGen technique, and 12 days using the MATE method (P < 0.0001).

Targeted tumor killing via an intracellular antibody against erbB-2

Specific killing of erbB-2-overexpressing tumor cells can be achieved using expression of an intracellular antibody directed against the erbB-2 oncoprotein. We have developed a strategy using a recombinant adenovirus encoding an anti-erbB-2 single chain antibody to achieve targeted tumor cell killing in vivo and can show significantly prolonged survival of animals carrying a human ovarian carcinoma tumor burden within their peritoneal cavities. This strategy of gene therapy for ovarian carcinoma offers the potential to achieve highly specific, targeted killing of human tumor cells and thus establishes the rationale to undertake human clinical trials on this basis.

Enhanced tumor specificity of 741F8-1 (sFv')2, an anti-c-erbB-2 single-chain Fv dimer, mediated by stable radioiodine conjugation

The goal of this study was to determine if the stabilization of the radioiodine-protein bond by the N-succinimidyl p-iodobenzoate (PIB) method improved the degree and specificity of tumor localization of 125I-741F8-1 (sFv')2, an anti-c-erbB-2 sFv dimer, in an immunodeficient murine model.

METHODS

Gamma camera images were acquired 21 hr after intravenous administration of 131I-741F8-1 (sFv')2 labeled by the p-iodobenzoate or chloramine T methods. The stability of the radioiodine-protein bond also was assessed in plasma samples after intravenous injection of 125I-741F8-1 (sFv')2 labeled by either the chloramine T or p-iodobenzoate methods.

RESULTS

By 6 hr postinjection, 97% of the activity associated with the 125I-741F8-1 (sFv')2 labeled by the p-iodobenzoate method was protein bound compared with 61% after labeling with the chloramine-T method. These observations indicate that increasing the stability of the conjugation between the radioiodine and the sFv molecule can significantly increase the degree and specificity of tumor targeting. Significantly greater tumor retention (p < 0.005) and lower blood (p < 0.001), spleen (p < 0.001) and stomach (p < 0.005) retention were observed in biodistribution studies when the p-iodobenzoate conjugate was used. This resulted in superior tumor-to-organ ratios for all tissue samples studied.

CONCLUSION

These observations may have clinical relevance for the use of radiolabeled sFv as imaging agents.

Identification of a 140 kDa protein of rat presynaptic terminal membranes encompassing the active zones

A polyclonal antiserum raised against the carboxy-terminal 17 amino acids of the rat p185c-neu (anct) reacted with a 140 kDa polypeptide in membranes of synaptosome fractions from neocortex and hippocampus of 11-day-old and adult rats. The same antiserum reacted with a 185 kDa polypeptide in microsome membranes from rat pheochromocytoma cells (PC12). By light microscopic immunocytochemistry, the anct antibodies against the 140 kDa protein were localized in the neuropile of brain, cerebellum and spinal cord of 11-day-old and adult rats. Especially prominent staining was obtained in the CA2-CA3 zones of the hippocampus, and in the substantia gelatinosa in the spinal cord. The finely granular and diffuse pattern of the immunostain was consistent with synaptic localizations. Interestingly, antibodies against the entire endodomain of p185c-neu (a-Bacneu) were localized in granular structures, probably representing axo-somatic and axo-dendritic synapses, on a subset of pyramidal neurons of the CA3 zone. By immunoelectron terminals in the giant mossy fiber type in the CA3 and CA4 regions. The immunolocalization of the anct antibodies was restricted in segments of the presynaptic membrane facing the synaptic cleft which include the active zone. The identify and function of the 140 kDa membrane protein of rat brain presynaptic terminals, detected by the anct antibodies, is unknown. The 140 kDa protein may be related to p185c-neu, a tyrosine kinase, or to other known or unknown kinases.

Tumor-specific and HLA-A2-restricted cytolysis by tumor-associated lymphocytes in human metastatic breast cancer

A tumor-specific cytotoxic T lymphocyte (CTL) immune response has been well documented in melanoma, renal cell carcinoma, and ovarian cancer. Conflicting evidence exists regarding the existence of tumor-specific CTL populations in breast cancer. Tumor cells and tumor-associated lymphocytes (TAL) were isolated from the pleural effusions of six consecutive patients with metastatic breast cancer. After solid-phase anti-CD3 stimulation, TAL cultures were expanded with weekly autologous tumor stimulation and low-dose IL-2 for 3 wk. T cell populations were characterized using flow cytometric analysis and ranged from 49 to 91% CD8+, > 98% CD3+, and < 3% CD16+. Functionally, tumor-stimulated TAL showed tumor-specific recognition of autologous tumor cells (241 +/- 142 LU20/10(7)) and no detectable lysis of autologous fibroblasts, Daudi or K562. Cytotoxicity of TAL against HLA-A2+ allogeneic targets was significantly higher when compared with HLA-A2- tumor cell lines (127 +/- 76 vs 6 +/- 18 LU, p = 0.0001). This cytotoxicity against autologous and allogeneic tumor cells was blocked by anti-HLA-A2 mAb and cold HLA-A2+ targets in cold-target inhibition assays. TAL from all HLA-A2+ patients recognized GP2, a known, HER2/neu-derived tumor-associated peptide Ag that is HLA-A2 restricted. We have shown that TAL obtained from metastatic effusions of breast cancer patients contain lymphocytes that can recognize and lyse autologous and allogeneic tumor cells in a tumor-specific, HLA-A2-restricted fashion. In addition, tumor-specific TAL derived from breast cancer patients can selectively lyse HLA-A2+ pancreatic and ovarian tumor cell targets, suggesting a common HLA-A2-restricted tumor-associated Ag between these distinct epithelial cancers. Further elucidation of the cell-mediated immune response to breast cancer and the identification of shared TAA could result in the development of broadly applicable vaccine therapies for many cancers.

Lack of expression of c-erbB-2 oncoprotein in human esophageal squamous cell carcinomas

Fifty-one cases of esophageal squamous cell carcinoma were immunohistochemically investigated with monoclonal c-erbB 2 oncoprotein antibody. No tumor showed plasma membrane immunostaining for c-erbB-2 protein. Occasionally, unspecific cytoplasmic staining was found in minor tumor cell populations. The present results show that c-erbB-2 oncoprotein is not overexpressed in esophageal squamous cell carcinomas and does not play a central role in the tumorigenesis.

Changes in an HER-2 peptide upregulating HLA-A2 expression affect both conformational epitopes and CTL recognition: implications for optimization of antigen presentation and tumor-specific CTL induction

The HER-2/neu protooncogene (HER-2) is overexpressed in a significant number of breast and ovarian tumors. Peptides of HER-2 sequence were recently found to reconstitute recognition of cytotoxic T lymphocytes (CTLs) from tumor-associated (TALs) and tumor-infiltrating (TILs) lymphocytes, indicating that they reconstitute natural epitopes recognized by CTLs on HLA-A2+ tumors. Because HER-2 is an important antigen (Ag) for tumor-specific CTL induction and the immunogenicity of peptides for CTL induction is dependent on their presentation as stable complexes with HLA-A2, we identified peptides of high and low stabilizing activity from the sequence of HER-2 and the folate-binding protein (FBP). Distinct sequence patterns in the region positions (P)3-P5 and P1 were found for peptides with high (HSA) and low (LSA) stabilizing ability. A low-HLA-A2-affinity HER-2 peptide, P1 of the CTL epitope, was found to be permissive to substitutions that enhanced HLA-A2-stabilizing ability and conserved CTL recognition. In contrast, the region P3-P5 was not permissive to sequence changes. We conclude that the selective permissivity of P1 and P9 in the tumor epitope sequence may have important implications for optimization of tumor Ag presentation, and "neoantigenicity" of self-antigens, aiming toward induction of tumor-reactive CTLs of defined affinity and specificity for target Ags.

Phase I trial of 2B1, a bispecific monoclonal antibody targeting c-erbB-2 and Fc gamma RIII

2B1 is a bispecific murine monoclonal antibody (BsMAb) with specificity for the c-erbB-2 and Fc gamma RIII extracellular domains. This BsMAb promotes the targeted lysis of malignant cells overexpressing the c-erbB-2 gene product of the HER2/neu proto-oncogene by human natural killer cells and mononuclear phagocytes expressing the Fc gamma RIII A isoform. In a Phase I clinical trial of 2B1, 15 patients with c-erbB-2-overexpressing tumors were treated with 1 h i.v. infusions of 2B1 on days 1, 4, 5, 6, 7, and 8 of a single course of treatment. Three patients were treated with daily doses of 1.0 mg/m2, while six patients each were treated with 2.5 mg/m2 and 5.0 mg/m2, respectively. The principal non-dose-limiting transient toxicities were fevers, rigors, nausea, vomiting, and leukopenia. Thrombocytopenia was dose limiting at the 5.0 mg/m2 dose level in two patients who had received extensive prior myelosuppressive chemotherapy. Murine antibody was detectable in serum following 2B1 administration, and its bispecific binding properties were retained. The pharmacokinetics of this murine antibody were variable and best described by nonlinear kinetics with an average t 1/2 of 20 h. Murine antibody bound extensively to all neutrophils and to a proportion of monocytes and lymphocytes. The initial 2B1 treatment induced more than 100-fold increases in circulating levels of tumor necrosis factor-alpha, interleukin 6, and interleukin 8 and lesser rises in granulocyte-monocyte colony-stimulating factor and IFN-gamma. Brisk human anti-mouse antibody responses were induced in 14 of 15 patients. Several minor clinical responses were observed, with reductions in the thickness of chest wall disease in one patient with disseminated breast cancer. Resolution of pleural effusions and ascites, respectively, were noted in two patients with metastatic colon cancer, and one of two liver metastases resolved in a patient with metastatic colon cancer. Treatment with 2B1 BsMAb has potent immunological consequences. The maximum tolerated dose and Phase II daily dose for patients with extensive prior myelosuppressive chemotherapy was 2.5 mg/m2. Continued dose escalation is required to identify the maximally tolerated dose for patients who have been less heavily pretreated.

Engineering linear F(ab')2 fragments for efficient production in Escherichia coli and enhanced antiproliferative activity

We developed a novel bivalent antibody fragment, the linear (L-) F(ab')2, comprising tandem repeats of a heavy chain fragment VH-CH1-VH-CH1 cosecreted with a light chain. Functional humanized L-F(ab')2 directed against p185HER2 was secreted from Escherichia coli at high titer (> or = 100 mg/l) and purified to homogeneity. The L-F(ab')2 binds two equivalents of antigen with an apparent affinity (Kd = 0.46 nM) that is within 3-fold of the corresponding thioether-linked F(ab')2 fragment. The N-terminal site binds antigen with an affinity (Kd = 1.2 nM) that is approximately 4-fold greater than that for the C-terminal site, as shown by the comparison of L-F(ab')2 variants containing a single functional binding site. L-F(ab')2 has greater antiproliferative activity than the thioether-linked F(ab')2 against the p185HER2-overexpressing tumor cell line BT474. Linear and thioether-linked F(ab')2 have very similar pharmacokinetic properties in normal mice, and their serum permanence times are respectively 7- and 8-fold longer than the corresponding Fab fragment. L-F(ab')2 offers a facile route to bivalent antibody fragments that are potentially suitable for clinical applications, and that may have improved biological activity compared with thioether-linked F(ab')2 fragments.

Clinical trials of bispecific antibody MDX-210 in women with advanced breast or ovarian cancer that overexpresses HER-2/neu

MDX-210 is a bispecific antibody (BsAb) that recognizes Fc gamma R1 on monocytes and macrophages and the cell surface product of the HER-2/neu oncogene, which is overexpressed on some breast and ovarian cancers. Clinical trials have demonstrated that treatment with MDX-210 is well tolerated and that MDX-210 is both immunologically and clinically active. Optimization of the dose and schedule of MDX-210 and development of combination treatments with cytokines that modulate immune effector cells will greatly enhance the efficacy of this novel BsAb construct for treatment of tumours that overexpress HER-2/neu. We envision that MDX-210 will be effective for treating patients with tumors that overexpress HER-2/neu, especially in the minimal disease setting.

Clinical development of 2B1, a bispecific murine monoclonal antibody targeting c-erbB-2 and Fc gamma RIII

Bispecific monoclonal antibodies (BsmAb) can be used to specifically target tumor cells for cytotoxicity mediated by defined effector cells. One such BsmAb, 2B1, targets the extracellular domains of both the c-erbB-2 protein product of the HER-2/neu oncogene and Fc gamma RIII (CD16), the Fc gamma receptor expressed by human natural killer cells, neutrophils, and differentiated mononuclear phagocytes. 2B1 promotes the conjugation of cells expressing these target antigens. It efficiently promotes the specific lysis of tumor cells expressing c-erbB-2 by human NK cells and macrophages over a broad concentration range. 2B1 selectively targets c-erbB-2-positive human tumor xenografts growing in immunodeficient SCID mice. Treatment of such mice with 2B1 plus interleukin 2 (IL-2) inhibits the growth of early, established human tumor xenografts overexpressing c-erbB-2. A phase I clinical trial of 2B1 has been initiated to determine the toxicity profile and maximum tolerated dose (MTD) of this BsmAb and to examine the biodistribution of the antibody and the biologic effects of treatment. Preliminary results of this trial indicate that the dose-limiting toxicity for patients with extensive prior bone marrow-toxic therapy is thrombocytopenia for as yet undetermined reasons. Toxicities of fevers, rigors, and associated constitutional symptoms are explained, in part, by treatment-induced systemic expression of cytokines, such as tumor necrosis factor-alpha. Circulating, functional BsmAb is easily detectible in treatment patients' sera and exhibits complex elimination patterns. HAMA and anti-idiotypic treatment-induced antibodies are induced by 2B1 treatment. Some preliminary indications of clinical activity have been observed. BsmAb therapy targeting tumor antigens and Fc gamma RIII has potent immunologic effects. Future studies will include the development of more relevant animal models for BsmAb therapy targeting human Fc gamma RIII. The ongoing phase I trial will be completed to identify the MTD for patients without extensive prior bone marrow-toxic chemotherapy and radiation. A phase II clinical trial of 2B1 therapy in women with metastatic breast cancer is planned, as is a phase I trial incorporating treatment with both 2B1 and IL-2.

G-CSF-stimulated PMN in immunotherapy of breast cancer with a bispecific antibody to Fc gamma RI and to HER-2/neu (MDX-210)

Myeloid cells can mediate tumor cell cytotoxicity via certain receptors for immunoglobulins. Among the different Fc receptors, the high-affinity IgG receptor (Fc gamma RI, CD64) is a promising trigger molecule because it is selectively expressed on effector cells, including monocytes/macrophages and granulocyte colony-stimulating factor (G-CSF)-primed neutrophils. In vitro, a bispecific antibody (BsAb) (MDX-210, constructed by chemically cross-linking F(ab') fragments of monoclonal antibody (mAb) 520C9 to HER-2/neu and F(ab') fragments of mAb 22 to Fc gamma RI) mediated effective lysis of HER-2/neu overexpressing breast cancer cell lines. HER-2/neu (c-erbB2) is overexpressed in approximately 30% of breast and ovarian carcinomas and is a target for immunotherapy in clinical trials. In vitro assays showed Fc gamma RI-positive neutrophils to constitute a major effector cell population during G-CSF therapy. Based on these preclinical data and a preceding study at Dartmouth (New Hampshire) with a single dose of MDX-210 alone, a combination of G-CSF and MDX-210 is tested in a phase I study in breast cancer patients. In this study, patients receiving G-CSF are treated with escalating single doses of MDX-210. This therapy was generally well tolerated by the treated patients, some of whom reacted with fever and short periods of chills, which were temporally related to elevated plasma levels of IL-6 and TNF-alpha. After MDX-210 application, a transient decrease in the total white blood count and absolute neutrophil count (ANC) was observed. During G-CSF application, isolated neutrophils were highly cytotoxic in the presence of MDX-210 in vitro. These data indicate a potential role for G-CSF and BsAb in immunotherapy.

Immunoselective cell growth inhibition by antibody-adriamycin conjugates targeting c-erbB-2 product on human cancer cells

Monoclonal antibodies targeting c-erbB-2 protooncogene product p185 were conjugated with adriamycin via a pH-sensitive spacer. The resultant antibody-adriamycin conjugates showed immunoselective binding, internalization and cytotoxicity to p185-positive human breast cancer cell SKBr-3 and gastric cancer cell MKN-7, but not to normal human lymphocytes.

Cytotoxicity of anti-c-erbB-2 immunoliposomes containing doxorubicin on human cancer cells

We have examined the selective cytotoxicity of immunoliposomes containing doxorubicin (chemoimmunoliposomes, CILs) targeting the c-erbB-2 gene product (gp185) or gp125. Anti-gp185 and anti-gp125 CILs were prepared by conjugation of doxorubicin-containing liposomes with monoclonal antibodies SER4 (IgG) and HBJ127 (IgG) respectively. Both CILs bound to human SKBr-3 breast cancer cells and MKN-7 human gastric cancer cells, which express both antigens in high density. The IC50 of anti-gp185 CILs on protein synthesis by SKBr-3 cells was respectively 2- and 25-fold lower than that of anti-gp125 CILs and unmodified liposomes. Furthermore, anti-gp185 CILs significantly inhibited neither the phytohaemagglutin response of normal lymphocytes nor protein synthesis of gp185-negative T24 bladder cancer. Quantitative analysis of cell-associated doxorubicin revealed that, compared with anti-gp125 CILs, anti-gp185 CILs required, respectively 4.5 and 4.3 times less doxorubicin association in SKBR-3 and MKN-7 cells, for 50% cytotoxicity. In addition, flow cytometric analysis showed that both SKBr-3 and MKN-7 internalised more anti-gp185 CILs and processed them more efficiently than anti-gp125 CILs. These results suggest that anti-gp185 CILs act selectively against gp185-expressing cancer cells and that gp185 is a more sensitive antigen for CIL cytotoxicity associated with endocytosis activity.

Phase Ia/Ib trial of bispecific antibody MDX-210 in patients with advanced breast or ovarian cancer that overexpresses the proto-oncogene HER-2/neu

PURPOSE

MDX-210 is a bispecific antibody that binds simultaneously to type I Fc receptors for immunoglobulin G (IgG) (Fc gamma RI) and to the HER-2/neu oncogene protein product. MDX-210 effectively directs Fc gamma RI-positive effector cells such as monocytes and macrophages to phagocytose or kill tumor cells that overexpress HER-2/neu. The goals of this phase Ia/Ib trial were to determine the maximum-tolerated dose (MTD) and/or the optimal biologic dose (OBD) of MDX-210.

PATIENTS AND METHODS

Patients with advanced breast or ovarian cancer that overexpressed HER-2/neu were eligible for treatment. Cohorts of three patients received a single intravenous (IV) infusion of MDX-210 at increasing dose levels from 0.35 to 10.0 mg/m2.

RESULTS

Treatment was well tolerated, with most patients experiencing transient grade 1 to 2 fevers, malaise, and hypotension only. Two patients experienced transient grade 3 hypotension at 10.0 mg/m2. Transient monocytopenia and lymphopenia developed at 1 to 2 hours, but no other hematologic changes were observed. Doses of MDX-210 > or = 3.5 mg/m2 saturated > or = 80% of monocyte Fc gamma RI and produced peak plasma concentrations > or = 1 microgram/mL, which is greater than the concentration for optimal monocyte/macrophage activation in vitro. Elevated plasma levels of the monocyte products tumor necrosis factor alpha (TNF alpha), interleukin-6 (IL-6), granulocyte colony-stimulating factor (G-CSF), and neopterin were observed with maximal levels at doses > or = 7.0 mg/m2. Localization of MDX-210 in tumor tissue was demonstrated in two patients. One partial and one mixed tumor response were observed among 10 assessable patients.

CONCLUSION

MDX-210 is immunologically active at well-tolerated doses. The MTD and OBD is 7 to 10 mg/m2.

Engineering high affinity humanized anti-p185HER2/anti-CD3 bispecific F(ab')2 for efficient lysis of p185HER2 overexpressing tumor cells

We previously constructed a humanized anti-p185HER2/anti-CD3 bispecific antibody variant, BsF(ab')2 v1 which retargets the cytotoxic activity of human T cells in vitro against human breast tumor cells which overexpress the p185HER2 product of the HER2/neu (c-erbB-2) protooncogene. Subsequently we identified an improved anti-CD3 variant, v9, which binds to T cells with approx. 100-fold higher affinity than the original variant, v1. Here we demonstrate that BsF(ab')2 v9 is more potent than BsF(ab')2 v1 in stimulating the proliferation of both resting peripheral blood lymphocytes (PBL) and IL-2-activated, long-term cultured T lymphocytes (ATL). In addition, at low concentrations (0.01-1 ng/ml) BsF(ab')2 v9 is much more efficient than BsF(ab')2 v1 in directing lysis of p185HER2-overexpressing tumor cells by IL-2 activated PBL. In contrast, at higher concentration BsF(ab')2 v9 and BsF(ab')2 v1 have similar potency in retargeted cytotoxicity. At BsF(ab')2 v9 concentrations of > or = 1 ng/ml the susceptibility of p185HER2-expressing tumor cells to lysis is apparently independent of the level of p185HER2 expression. At lower concentrations of BsF(ab')2 v9 and/or lower ratios of effector to target cells the extent of lysis is reduced, in some cases improving the selectivity of lysis of high p185HER2 expressors over low expressors. Thus selection of a high affinity anti-CD3 arm is likely important in the design of BsF(ab')2 for retargeting the cytotoxicity of T cells to tumors. The dose of BsF(ab')2 v9 in any future clinical evaluation will require optimization to maximize anti-tumor efficacy whilst minimizing potential toxicity against normal tissue expressing p185HER2.

Preferential detection of catalytically inactive c-erbB-2 by antibodies to unphosphorylated peptides mimicking receptor tyrosine autophosphorylation sites

The c-erbB-2 tyrosine kinase is often overexpressed in human breast cancer, but correlations of receptor expression with tumour behaviour have proven elusive in patients without metastases at diagnosis. To address the possibility that receptor function may be more informative than expression, we previously developed function-specific c-erbB-2 antibodies using synthetic tyrosine-phosphorylated peptide immunogens (Epstein et al., Proc. Natl. Acad. Sci. USA 1992; 89: 10435-10439). Here the converse approach has been taken to determine the functional status of c-erbB-2 receptors detected by antibodies to dephosphorylated (dep) autophosphorylation sequences. In contrast to antiphosphopeptide (apt) antibodies, dep antibodies to the Tyr1248 autophosphorylation site exhibited preferential, but not exclusive, binding to tyrosine-dephosphorylated c-erbB-2. Consistent with this, catalytically active and inactive receptors could not be clearly distinguished by in vitro autophosphorylation experiments in which c-erbB-2 was immunoprecipitated using a monoclonal Tyr1248 dep antibody. A dep antiserum recognizing autophosphorylation sites N-terminal to Tyr1248 exclusively recognized tyrosine-dephosphorylated c-erbB-2 following antibody preabsorption with homologous phosphopeptides. Although indirect, these data are consistent with a model of sequential c-erbB-2 autophosphorylation in which Tyr1248 is the final residue modified. Moreover, since many studies of c-erbB-2 expression have used antibodies to dephosphorylated autophosphorylation sites, these results caution against automatically equating such receptor immunoreactivity with in vivo function or clinical significance.

Construction of a chimeric antibody with therapeutic potential for cancers which overexpress c-erbB-2

We describe the chimerization of a monoclonal antibody directed against the c-erbB-2 protein using a novel PCR method for cloning immunoglobulin variable region genes. We also describe the characterization of the chimera and show its potential use for treating cancers which overexpress the c-erbB-2 protein. The genomic DNA fragments of heavy and light chain variable genes were cloned by PCR using uniquely designed primers which allowed for isolation of genes containing functional promoters, signal and coding sequences. The chimeric genes were then constructed by linking variable regions of murine genes to human constant gamma 1 and kappa genes. Expression of the chimeric immunoglobulin genes resulted in production of properly assembled chimeric antibody with improved biological properties.

Biotechnological and gene therapeutic strategies in cancer treatment

New anti-cancer agents are being developed which incorporate cancer-cell-specific recognition functions and are thus able to distinguish between normal and tumor cells. Recognition is dependent on the enhanced expression of antigenic determinants on the surface of tumor cells. The ErbB-2 receptor (ErbB-2R) is overproduced in a high percentage of adenocarcinomas arising in the breast, ovary, lung and stomach, when compared to normal cells. The tumor-enriched expression and extracellular accessibility make this receptor a suitable target for directed tumor therapy. A gene expressing the single-chain antibody molecule (scFv), specific for the extracellular domain of the ErbB-2R, was constructed by joining cDNAs encoding the light- and heavy-chain variable domains of the monoclonal antibody (mAb) FRP5. This scFv-encoding gene has been used as a targeting domain for two effectors: (i) A recombinant immunotoxin-encoding gene was constructed by adding sequences encoding a modified Pseudomonas aeroginosa exotoxin A (ETA) to the scFv-encoding DNA. (ii) Cytotoxic T-lymphocytes (CTL) with specificity for ErbB-2R-producing tumor cells were generated by retroviral transfer of a chimeric gene which encodes the scFv(FRP5), a hinge region and the zeta-chain of the T-cell receptor (TCR) complex. The bacterially produced recombinant immunotoxin scFv(FRP5)-ETA binds specifically to the ErbB-2R and displays both in vitro and in vivo cytotoxic effects selective for tumor cells producing high levels of the ErbB-2R. Target cells expressing the ErbB-2R gene were lysed in vitro with high specificity by the scFv::hinge::zeta-expressing T-cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Grafting peptides onto polystyrene microplates for ELISA

Three peptides corresponding respectively to two Epstein-Barr viral epitopes and to the c-erbB-2 oncogene product were synthesized with the aim of developing an immunoenzymatic assay. Preliminary experiments indicated that the efficiency of the assay was profoundly affected by the nature of the solid phase for each peptide. In order to optimize the assay the three peptides were covalently coupled to functionalized polystyrene microplates which were used to immobilize both haptens and nucleic acids in a previous study. The results obtained indicate that the use of the carboxylated surfaces permits the linking strategy to be adapted to each peptide. Moreover, high sensitivities (5 x 10(-10)-1 x 10(-13) M) were obtained using amounts of the peptides much lower than those used in the standard system.

Identification of an immunodominant peptide of HER-2/neu protooncogene recognized by ovarian tumor-specific cytotoxic T lymphocyte lines

Synthetic peptide analogues of sequences in the HER-2 protooncogene (HER-2) were selected based on the presence of HLA-A2.1 anchor motifs to identify the epitopes on HER-2 recognized by ovarian tumor-reactive CTL. 19 synthetic peptides were evaluated for recognition by four HLA-A2 ovarian-specific cytotoxic T lymphocyte (CTL) lines obtained from leukocytes associated with ovarian tumors. The nonapeptide E75 (HER-2, 369-377:KIFGSLAFL) was efficient in sensitizing T2 cells for lysis by all four CTL lines. This peptide was specifically recognized by cloned CD8+ CTL isolated from one of the ovarian-specific CTL lines. E75-pulsed T2 cells inhibited lysis by the same CTL clone of both an HLA-A2+ HER-2high ovarian tumor and a HER-2high cloned ovarian tumor line transfected with HLA-A2, suggesting that this or a structurally similar epitope may be specifically recognized by these CTL on ovarian tumors. Several other HER-2 peptides were recognized preferentially by one or two CTL lines, suggesting that both common and private HER-2 epitopes may be immunogenic in patients with ovarian tumors. Since HER-2 is a self-antigen, these peptides may be useful for understanding mechanisms of tumor recognition by T cells, immunological tolerance to tumor, and structural characterization of tumor antigens.

Prolonged survival of mice with human gastric cancer treated with an anti-c-ErbB-2 monoclonal antibody

A monoclonal antibody (MAb), 4D5, specifically recognising an extracellular epitope of the c-ErbB-2 protein, inhibited the growth of human gastric cancer overexpressing c-ErbB-2 severe combined immunodeficient (SCID) mice. This antibody also reduced the mass of established tumours xenografted into SCID mice, whereas gastric cancer not expressing c-ErbB-2 exhibited no regression in response to 4D5 treatment. In addition, administration of 4D5 prevented colonisation of cancer cells and prolonged the survival of host SCID mice inoculated i.v. with c-ErbB-2-overexpressing tumour cells. This is the first reported study to show that treatment with a single antibody specific to c-ErbB-2 prolongs the survival of host SCID mice bearing xenotransplanted tumours.

Optimization of in vivo tumor targeting in SCID mice with divalent forms of 741F8 anti-c-erbB-2 single-chain Fv: effects of dose escalation and repeated i.v. administration

Single-chain Fv molecules in monovalent (sFv) and divalent [(sFv')2] forms exhibit highly specific tumor targeting in mice as a result of their small size and rapid systemic clearance. As a consequence, there is a rapid reversal of the sFv blood/tumor gradient, resulting in diminished retention of sFv species in tumors. In this report we investigate two distinct strategies, dose escalation and repetitive intravenous (i.v.) dosing, aiming to increase the absolute selective retention of radiolabeled anti-c-erbB-2 125I-741F8 (sFv')2 in c-erbB-2-overexpressing SK-OV-3 tumors in mice with severe combined immunodeficiency (SCID). A dose-escalation strategy was applied to single i.v. injections of 125I-741F8 (sFv')2. Doses from 50 micrograms to 1000 micrograms were administered without a significant decrease in tumor targeting or specificity. High doses resulted in large increases in the absolute retention of 125I-741F8 (sFv')2. For example, raising the administered dose from 50 micrograms to 1000 micrograms increased the tumor retention 24 h after injection from 0.46 microgram/g to 9.5 micrograms/g, and resulted in a net increase of greater than 9 micrograms/g. Over the same dose range, the liver retention rose from 0.06 microgram/g to 1 microgram/g, and resulted in a net increase of less than 1 microgram/g. The retention of 9.5 micrograms/g in tumor 24 h following the 1000-micrograms dose of (sFv')2 was comparable to that seen 24 h after a 50-micrograms dose of 125I-741F8 IgG, indicating that the use of large doses of (sFv')2 may partially offset their rapid clearance. When two doses were administered by i.v. injection 24 h apart, the specificity of delivery to tumor observed after the first dose was maintained following the second injection. Tumor retention of 125I-741F8 (sFv')2 was 0.32 microgram/g at 24 h and 0.22 micrograms/g at 48 h following a single injection of 20 micrograms, while 0.04 microgram/ml and 0.03 microgram/ml were retained in blood at the same assay times. After a second 20-micrograms injection at the 24-h assay time, tumor retention increased to 0.49 micrograms/g, and blood retention was 0.06 microgram/ml, at the 48-h point. These results suggest that multiple high-dose administrations of radiolabeled 741F8 (sFv')2 may lead to the selective tumor localization of therapeutic radiation doses.

Activation state-specific monoclonal antibody detects tyrosine phosphorylated p185neu/erbB-2 in a subset of human breast tumors overexpressing this receptor

Amplification of the neu/erbB-2/HER-2 gene and/or overexpression of its receptor tyrosine kinase product, p185neu/erbB-2 (p185), occurs in 15-40% of primary human breast tumors and is variably correlated with poor patient prognosis. Variability in predictive accuracy likely results from activation of p185 by agonist(s) in only a subset of tumors in which it is overexpressed, which may greatly affect outcomes. As a first step toward evaluating this hypothesis, we previously produced a polyclonal antibody that specifically recognizes the activated, tyrosine-phosphorylated forms of p185 and the closely related epidermal growth factor receptor (L. Bangalore et al., Proc. Natl. Acad. Sci. USA, 89: 11637-11641, 1992). We now describe the production of a mAb, PN2A, that specifically recognizes tyrosine-phosphorylated p185 and bears no cross-reactivity with closely related receptors. Furthermore, we demonstrate its reactivity in immunohistochemical staining of paraffin-embedded, formalin-fixed tumor samples. In a series of five p185-overexpressing human tumors examined thus far, PN2A reactivity was detected in two, indicating that p185 is phosphorylated and hence actively signaling in a subset. This reagent will facilitate both clinical and research analyses of p185 activity. Furthermore, this work serves as a prototype for similar analyses of other tyrosine phosphoproteins.

In vitro and in vivo characterization of a human anti-c-erbB-2 single-chain Fv isolated from a filamentous phage antibody library

BACKGROUND

Antibody-based reagents have failed to live up to their anticipated role as highly specific targeting agents for cancer therapy. Targeting with human single-chain Fv (sFv) molecules may overcome some of the limitations of murine IgG, but are difficult to produce with conventional hybridoma technology. Alternatively, phage display of antibody gene repertoires can be used to produce human sFv.

OBJECTIVES

To isolate and characterize human single chain Fvs which bind to c-erbB-2, an oncogene product overexpressed by 30-50% of breast carcinomas and other adenocarcinomas.

STUDY DESIGN

A non-immune human single-chain Fv phage antibody library was selected on human c-erbB extracellular domain and sFv characterized with respect to affinity, binding kinetics, and in vivo pharmacokinetics in tumor-bearing scid mice.

RESULTS

A human single-chain Fv (C6.5) was isolated which binds specifically to c-erbB-2. C6.5 is entirely human in sequence, expresses at high level as native protein in E. coli, and is easily purified in high yield in two steps. C6.5 binds to immobilized c-erbB-2 extracellular domain with a Kd of 1.6 x 10(-8) M and to c-erbB-2 on SK-OV-3 cells with a Kd of 2.0 x 10(-8) M, an affinity that is similar to sFv produced against the same antigen from hybridomas. Biodistribution studies demonstrate 1.47% injected dose/g tumor 24 h after injection of 125I-C6.5 into scid mice bearing SK-OV-3 tumors. Tumor:normal organ ratios range from 8.9:1 for kidney to 283:1 for muscle.

CONCLUSIONS

These results are the first in vivo biodistribution studies using an sFv isolated from a non-immune human repertoire and confirm the specificity of sFv produced in this manner. The use of phage display to produce C6.5 mutants with higher affinity and slower k(off) would permit rigorous evaluation of the role of antibody affinity and binding kinetics in tumor targeting, and could result in the production of a therapeutically useful targeting protein for radioimmunotherapy and other applications.

Suppression and promotion of tumor growth by monoclonal antibodies to ErbB-2 differentially correlate with cellular uptake

Amplification and overexpression of the erbB-2/neu protooncogene are frequently associated with aggressive clinical course of certain human adenocarcinomas, and therefore the encoded surface glycoprotein is considered a candidate target for immunotherapy. We previously generated a series of anti-ErbB-2 monoclonal antibodies (mAbs) that either accelerate or inhibit the tumorigenic growth of erbB-2-transformed murine fibroblasts. The present study extended this observation to a human tumor cell line grown as xenografts in athymic mice and addressed the biochemical differences between the two classes of mAbs. We show that the inhibitory effect is dominant in an antibody mixture, and it depends on antibody bivalency. By using radiolabeled mAbs we found that all of three tumor-inhibitory mAbs became rapidly inaccessible to acid treatment when incubated with tumor cells. However, a tumor-stimulatory mAb remained accessible to extracellular treatments, indicating that it did not undergo endocytosis. In addition, intracellular fragments of the inhibitory mAbs, but not of the stimulatory mAb, were observed. Electron microscopy of colloidal gold-antibody conjugates confirmed the absence of endocytosis of the stimulatory mAb but detected endocytic vesicles containing an inhibitory mAb. We conclude that acceleration of cell growth by ErbB-2 correlates with cell surface localization, whereas inhibition of tumor growth is associated with an intrinsic ability of anti-ErbB-2 mAbs to induce endocytosis. These conclusions are relevant to the selection of optimal mAbs for immunotherapy and may have implications for the mechanism of cellular transformation by an overexpressed erbB-2 gene.

Engineering disulfide-linked single-chain Fv dimers [(sFv')2] with improved solution and targeting properties: anti-digoxin 26-10 (sFv')2 and anti-c-erbB-2 741F8 (sFv')2 made by protein folding and bonded through C-terminal cysteinyl peptides

Single-chain Fv fusions with C-terminal cysteinyl peptides (sFv') have been engineered using model sFv proteins based upon the 26-10 anti-digoxin IgG and 741F8 anti-c-erbB-2 IgG monoclonal antibodies. As part of the 741F8 sFv construction process, the PCR-amplified 741F8 VH gene was modified in an effort to correct possible primer-induced errors. Genetic replacement of the N-terminal beta-strand sequence of 741F8 VH with that from the FR1 of anti-c-erbB-2 520C9 VH resulted in a dramatic improvement of sFv folding yields. Folding in urea-glutathione redox buffers produced active sFv' with a protected C-terminal sulfhydryl, presumably as the mixed disulfide with glutathione. Disulfide-bonded (sFv')2 homodimers were made by disulfide interchange or oxidation after reductive elimination of the blocking group. Both 26-10 (sFv')2 and 741F8 (sFv')2 existed as stable dimers that were well behaved in solution, whereas 741F8 sFv and sFv' exhibited considerable self-association. The 741F8 sFv binds to the extracellular domain (ECD) of the c-erbB-2 oncogene protein, which is often overexpressed in breast cancer and other adenocarcinomas. The recombinant ECD was prepared to facilitate the analysis of 741F8 binding site properties; the cloned ECD gene, modified to encode a C-terminal Ser-Gly-His6 peptide, was transfected into Chinese hamster ovary cells using a vector that also expressed dihydrofolate reductase to facilitate methotrexate amplification. Optimized cell lines expressed ECD-His6 at high levels in a cell bioreactor; after isolation by immobilized metal affinity chromatography, final ECD yields were as high as 47 mg/l. An animal tumor model complemented physicochemical studies of 741F8 species and indicated increased tumor localization of the targeted 741F8 (sFv')2 over other monovalent 741F8 species.

Development of anti-p185HER2 immunoliposomes for cancer therapy

The product of the HER2 protooncogene, p185HER2, represents an attractive target for cancer immunotherapies. We have prepared anti-p185HER2 immunoliposomes in which Fab' fragments of a humanized anti-p185HER2 monoclonal antibody with antiproliferative properties (rhuMAb-HER2) were conjugated to either conventional or sterically stabilized liposomes. These immunoliposomes bind specifically to p185HER2-overexpressing breast cancer cells (SK-BR-3 and BT-474). High-affinity binding of anti-p185HER2 immunoliposomes is comparable to that of free rhuMAbHER2-Fab' or the intact antibody. Empty immunoliposomes inhibit the culture growth of p185HER2-overexpressing breast cancer cells, and this antiproliferative effect is superior to that of free rhuMAbHER2-Fab', indicating that liposomal anchoring of these anti-p185HER2 Fab' fragments enhances their biological activity. Efficient internalization of anti-p185HER2 immunoliposomes, demonstrated by light and electron microscopy, occurs by receptor-mediated endocytosis via the coated pit pathway and also possibly by membrane fusion. Doxorubicin-loaded anti-p185HER2 immunoliposomes are markedly and specifically cytotoxic against p185HER2-overexpressing tumor cells in vitro. Anti-p185HER2 immunoliposomes administered in vivo in Scid mice bearing human breast tumor (BT-474) xenografts can deliver doxorubicin to tumors. These results indicate that anti-p185HER2 immunoliposomes are a promising therapeutic vehicle for the treatment of p185HER2-overexpressing human cancers.

Superantigen-induced human CD4+ helper/killer T cell phenomenon. Selective induction of Th1 helper/killer T cells and application to tumor immunotherapy

Human CD4+ T cells activated with staphylococcal enterotoxin A (SEA) were fractionated by Percoll discontinuous density gradient centrifugation to enrich SEA-reactive CD4+ T cells. The SEA-reactive CD4+ T cells showed significant cytotoxicity, so-called superantigen-dependent cell-mediated cytotoxicity, against SEA-coated class II-positive tumor cells. During lysis of SEA-coated tumor cells, SEA-reactive CD4+ T cells produced high levels of IL-2 and IFN-gamma but not IL-4 in an Ag-specific manner. The skewing of human CD4+ T cells to Th1-type helper/killer T cells was also demonstrated when SEA-reactive CD4+V beta 5.3+ clonal T cells were cultured with SEA, but not with PHA or OKT3 mAb. Interestingly, the generation of SEA-reactive helper/killer T cells was negatively regulated by IL-4, but up-regulated by IL-12. The SEA-reactive CD4+ helper/killer T cells were able to generate from PBMC of tumor patients and could be expanded to 10(9) levels in a 7-day culture. The SEA-reactive CD4+ helper/killer T cells were specifically targeted to c-erbB-2 positive human colon cancer cells using SEA-conjugated-anti-c-erbB-2 mAb. These results initially demonstrated that SEA-activated human CD4+ T cells are a Th1 type of Th cell that has both helper and killer functions which may be useful for adoptive tumor immunotherapy in combination with SEA-conjugated antitumor mAb.

In vitro stimulation of ovarian tumour-associated lymphocytes with a peptide derived from HER2/neu induces cytotoxicity against autologous tumour

The proto-oncogene HER2/neu encodes for a 185 kDa transmembrane protein with extensive homology to the epidermal growth factor (EGF) receptor. We have previously shown a correlation between HER2/neu expression and the level of in vitro cytotoxicity of tumour-associated lymphocytes (TAL) versus autologous tumour. In addition, we have recently demonstrated that tumour-associated cytotoxic T-lymphocytes (CTL) from ovarian and breast cancer patients can recognize a HER2/neu derived peptide epitope when presented in the context of HLA-A2. Since repeated tumour stimulation of CTL enhances both proliferation and cytotoxicity against autologous tumour, we hypothesized that repeated peptide antigen stimulation would have a similar effect. To be therapeutically useful, the peptide antigen must meet the following conditions: (1) the peptide must be immunogenic and cause a proliferation of CTL to adequate therapeutic numbers, and (2) the peptide-specific CTL which are generated must be cytotoxic against autologous tumour. To test our hypothesis, T-lymphocytes isolated from the ascites of four consecutive HER2/neu+ ovarian cancer patients were initially stimulated with solid phase anti-CD3 antibody and divided into three groups: (1) treatment with recombinant interleukin-2 (IL-2) alone, (2) IL-2 plus weekly stimulation with irradiated autologous tumour cells, and (3) IL-2 plus weekly stimulation with a HER2/neu derived peptide. Peptide-stimulated and tumour-stimulated CTL showed similar increases in proliferation with both groups consistently reaching therapeutic numbers. Peptide-stimulated CTL demonstrated significantly enhanced cytotoxicity against autologous tumour in 4-h chromium release assays as compared to the IL-2 alone group.(ABSTRACT TRUNCATED AT 250 WORDS)

Bispecific HER2 x CD3 antibodies enhance T-cell cytotoxicity in vitro and localize to HER2-overexpressing xenografts in nude mice

Recently, we reported the development of fully humanized bispecific F(ab')2 antibodies with dual binding specificities to human T-lymphocytes and to tumor cells overexpressing HER2. These antibodies were shown to effectively mediate targeted HER2-overexpressing tumor cell killing by freshly isolated human T-cells. In this report we extend our studies to describe the interaction of the bispecific antibody with activated T-lymphocytes (ATL) maintained in culture for an extended period of time. A microtiter plate radioreceptor assay was used to elucidate the affinity of bispecific antibody binding to ATL. The data show that ATL maintained in vitro for up to 5 weeks continued to express high-affinity CD3 surface markers that bound to bispecific antibody with a Kd of 2.49 nM and exerted cytolytic activities against targets overexpressing HER2. In addition, we demonstrated the specific localization of HER2 x CD3 bispecific antibody to HER2-overexpressing tumor xenografts in nude mice. Furthermore, HER2 x CD3 bispecific antibody has the ability to inhibit the proliferative activities of breast tumor (SKBR-3) cells in vitro. The clinical implications of these data are discussed.

Breast and ovarian cancer-specific cytotoxic T lymphocytes recognize the same HER2/neu-derived peptide

The identification of antigenic peptides presented on the tumor cell surface by HLA class I molecules and recognized by tumor-specific cytotoxic T lymphocytes may lead to a peptide vaccine capable of inducing protective cellular immunity. We demonstrate that both HLA-A2-restricted breast and ovarian tumor-specific cytotoxic T lymphocytes recognize shared antigenic peptides. At least one of these peptides is derived from the oncogene product of HER2/neu, which is overexpressed in 30-40% of all breast and ovarian cancers. T cells sensitized against this nine-amino acid sequence demonstrate significant recognition of HLA-A2+, HER2/neu+ tumors. Since 50% of the tumor-cell population is HLA-A2+ and many different tumors express HER2/neu, this peptide may be widely recognized and have many clinical applications.

NDF/heregulin activates MAP kinase and p70/p85 S6 kinase during proliferation or differentiation of mammary epithelial cells

Neu differentiation factors (NDF) are a novel family of polypeptide factors which activate sub-class I tyrosine kinase receptors. In all mammary epithelial cells analysed in this study, NDF activates the same signalling pathways while it induces different, cell-specific biological effects. In AU565 cells which are growth inhibited, as well as in T47D or HC11 cells which proliferate in response to NDF, the MAP kinase isoforms p44ERK1 and p42ERK2 and the p70/p85 S6 kinase are activated. NDF stimulates tyrosine phosphorylation and the in vitro kinase activity of ErbB-2. When PKC is activated by TPA, NDF is no longer able to activate ErbB-2 in T47D cells, leading to a blockage of cell proliferation. Activation of ErbB-2 by point mutation, or by monoclonal antibodies, also stimulates both the MAPK and the p70/p85 S6 kinase pathways. The same monoclonal antibodies can induce AU565 cell differentiation. In summary, during growth or differentiation of mammary epithelial cells, NDF stimulates several independent signalling pathways which can also be triggered by ErbB-2 stimulation alone. PKC activation blocks the biological effect induced by NDF through negative modulation of ErbB-2.

EGF receptor and p185erbB-2-specific single-chain antibody toxins differ in their cell-killing activity on tumor cells expressing both receptor proteins

Many human tumors over-express erbB-2 and EGF receptors. The membrane localization of these receptor tyrosine kinases make them appropriate targets for directed tumor therapy. We have used recombinant DNA technology to produce single-chain antibody exotoxin A (scFv-ETA) fusion proteins which specifically bind the erbB-2 and EGF receptors. The scFv portion is composed of the heavy- and light-chain variable domains of monoclonal antibodies which recognize the extracellular portion of each receptor. We have previously described the anti-tumor activity of the bacterially produced scFv(FRP5)-ETA directed to the erbB-2 receptor. In this paper we describe the characteristics of scFv(225)-ETA, a protein which binds the EGF receptor. The bacterially produced recombinant protein binds to the receptor with high affinity and inhibits the in vitro growth of the EGF receptor over-expressing tumor cell lines A431 and MDA-MB468. Combination treatment with scFv-(FRP5)-ETA and scFv(225)-ETA led to an additive inhibitory effect on the in vitro growth of A431 cells. SKBR3 cells expressing low levels of EGF receptor but high levels of p185erbB-2 were not affected by scFv(225)-ETA treatment but were sensitive to scFv(FRP5)-ETA. Stimulation of SKBR3 cells and HCII RI#11 mouse mammary epithelial cells expressing the human erbB-2 with EGF led to an increase in scFv(FRP5)-ETA activity, showing that the EGF-induced activation of erbB-2 can potentiate the action of the erbB-2-directed toxin. Treatment of athymic nude mice with scFv(FRP5)-ETA and the combination of both scFv-ETA proteins led to the transient arrest of growth of established A431 tumors. scFv(225)-ETA treatment alone was the most effective, leading to tumor shrinkage during the course of treatment, whereas treatment with the parental monoclonal antibody 225 led to retarded tumor growth.

Measurement of c-erbB-2 proteins in sera from patients with carcinomas and in breast tumor tissue cytosols: correlation with serum tumor markers and membrane-bound oncoprotein

Using a commercial kit with antibodies against the ectodomain of c-erbB-2 protein, we detected c-erbB-2 immunoreactivity in human serum. We found that the percentages of patients with elevated serum c-erbB-2 immunoreactivities were 35, 21, and 9% in breast, prostate, and ovarian carcinoma, respectively. The majority of the elevated immunoreactivities were associated with sera containing highly elevated tumor markers with the highest in breast carcinoma (35%) and lowest in ovarian cancer (9%). Excellent correlations were also observed between the serum levels of c-erbB-2 immunoreactivity and the dominant tumor markers in serial specimens from individual cancer patients. We could also detect the c-erbB-2 immunoreactivity in the cytosols prepared from the breast tumor tissue for estrogen and progesterone receptor (ER & PgR) measurements using the same commercial kit for serum studies, and the intact c-erbB-2 oncoprotein (p185) in the extracts of the tissue membrane fractions with a different kit designed for tissue extract. The level of c-erbB-2 immunoreactivity in the cytosol from 124 human breast tumor specimens had an excellent correlation with the cell membrane concentrations of p185 (gamma = 0.89). Most of the elevated cytosol c-erbB-2 immunoreactivities were also found to associate with breast tumor specimens containing low concentrations of ER & PgR. It appears that measuring the c-erbB-2 immunoreactivity potentially could be used as a prognostic marker without performing tissue biopsies and also as a serum tumor marker for managing cancer patients.

Development of a humanized disulfide-stabilized anti-p185HER2 Fv-beta-lactamase fusion protein for activation of a cephalosporin doxorubicin prodrug

The humanized anti-p185HER2 antibody, humAb4D5-8, has completed Phase II clinical trials for p185HER2-overexpressing breast cancer. Here, this antibody is used as a building block to engineer a disulfide-linked Fv (dsFv) beta-lactamase fusion protein for use in antibody-dependent enzyme-mediated prodrug therapy using cephalosporin-based prodrugs. Three Fv variants were designed with an interchain disulfide bond buried at the VL/VH interface and secreted from Escherichia coli. One variant, dsFv3 (VL L46C VH D101C0, has similar affinity for antigen (Kd = 0.7 nM) as the wild-type Fv and was used to construct a fusion protein in which beta-lactamase, RTEM-1, is joined to the carboxy terminus of VH. The dsFv3-beta-lactamase fusion protein secreted from E. coli efficiently activates a cephalothin doxorubicin prodrug (PRODOX, kcat/km = 1.5 x 10(5) s-1 M-1). PRODOX is approximately 20-fold less toxic than free doxorubicin against breast tumor cell lines SK-BR-3 and MCF7, which express p185HER2 at elevated and normal levels, respectively. Prebinding the dsFv3-beta-lactamase fusion protein specifically enhances the toxicity level of PRODOX to that of doxorubicin against SK-BR-3 but not MCF7 cells. The fusion protein retains both antigen-binding plus kinetic activity in murine serum and is cleared rapidly as judged by pharmacokinetic analysis in nude mice (initial and terminal half-lives of 0.23 and 1.27 h, respectively). Development and characterization of the dsFv3-beta-lactamase fusion protein is an important step toward targeted prodrug therapy of p185HER2-overexpressing tumors.

Development of resistance to cisplatin is associated with decreased expression of the gp185c-erbB-2 protein and alterations in growth properties and responses to therapy in an ovarian tumor cell line

Overexpression of the c-erbB-2 protein (gp185c-erbB-2) is correlated with a tumorigenic phenotype and may contribute to disease progression. We have reported previously on an anti-gp185c-erbB-2 antibody, TAb 250, that inhibits in vitro and in vivo growth of breast and ovarian cell lines that overexpress the protein and enhances the inhibitory activity of cisplatin (CDDP). To assess whether CDDP resistance is related to gp185c-erbB-2 expression levels, alterations in tumor cell growth characteristics, or efficacy of antibody plus drug combination treatments, an SKOV-3 ovarian tumor cell line was made resistant to escalating doses of CDDP. Parental cells were 12-fold more sensitive to CDDP with 7 times more gp185c-erbB-2 sites than the most resistant variant (SKOV-3/C12). Additionally, the resistant cells demonstrated a longer lag phase for in vivo growth than the parental cells. While TAb 250 enhanced the in vivo inhibitory effect of CDDP against parental SKOV-3 cells, the antibody did not significantly alter the CDDP responsiveness of the resistant population. Growth inhibition by TAb 250 alone of both the parental and the SKOV-3-resistant variants was similar; however, TAb 250 was able to prolong the lag-phase of tumor growth of the resistant variant by up to 25 days. These results indicate that the development of CDDP resistance is associated with lowered levels of gp185c-erbB-2 expression, slower tumor cell growth, and enhanced efficacy of antibody treatment of the resistant cells.

Antigenic and immunogenic mimicry of the HER2/neu oncoprotein by phage-displayed peptides

To recover peptides that antigenically and immunogenically mimic the p185HER2 oncoprotein, we selected the phage-peptide libraries pVIII-9aa and pVIII-9aa. Cys using murine monoclonal antibodies (mAb) MGr2 and MGr6, directed against two distinct epitopes of the p185HER2 extracellular domain. Phage-displayed peptides containing consensus amino acid motifs were recovered and shown to compete specifically for mAb binding on tumor cells that overexpress p185HER2. The deduced amino acid sequence of the peptides suggests that both epitopes defined by the mAb on p185HER2 are discontinuous and that hydrophobic interactions are involved in binding with the mAb. A phage clone displaying the GPLDSLFAQ peptide elicited a specific immune response against the p185HER2 in BALB/c mice, demonstrating that this phage-displayed peptide represents an immunological equivalent of the MGr2 epitope on p185HER2 and might be used as a substitute for this oncoprotein in in vitro and in vivo immunological studies.

Immunotoxins to the HER-2 oncogene product: functional and ultrastructural analysis of their cytotoxic activity

Two immunotoxins were prepared using monoclonal antibodies (mAb) directed towards two distinct epitopes of the gp185HER-2 extracellular domain, and the type I ribosome inactivating protein (RIP) plant toxin saporin 6. Cell protein synthesis inhibition assay reveals that the immunotoxins display a potent and specific cytotoxicity that is characterized by a slow rate, since the time required to inhibit incorporation of radiolabeled leucine completely ranges from 36 h to 60 h depending on the target cell line and the immunotoxin. Because this feature may hamper the immunotherapeutic use of these conjugates we analysed this further by studying the early phases of internalization of immunotoxins by immunoelectron microscopy. The results of this study have demonstrated that the distribution pattern of the immunotoxins and of the unconjugated mAb over the cell surface overlaps. Similarly the mAb and immunotoxins are internalized into the cell by two different pathways: via clathrin-coated pits or via smaller uncoated pits and vesicles. A higher degree of internalization is achieved when the two immunotoxins are used in combination. Unlike the slow kinetics of cell intoxication the process of immunotoxin endocytosis is characterized by a rapid rate of internalization (above 40% at 5 min in the SK-BR-3 cell line). Although these findings provide no clue to explain the mechanisms of the slow rate of cytotoxicity of the two immunotoxins their rapid internalization indicates that these reagents can be exploited in immunotherapeutic approaches to gp185HER-2-expressing malignancies.

The tyrosine kinase activity of the C-erbB-2 gene product (p185) is required for growth inhibition by anti-p185 antibodies but not for the cytotoxicity of an anti-p185-ricin-A chain immunotoxin

Our previous studies have demonstrated that 7 of 10 IgG antibodies against distinct epitopes on the extracellular domain of the c-erbB-2 gene product (p185) inhibit the anchorage-independent growth of SKBr3 human breast-cancer cells that overexpress this transmembrane tyrosine kinase growth-factor receptor. Two of 7 growth-inhibitory antibodies also block the binding and function of the gp30 and p75 c-erbB-2 ligands. In this report we have studied phosphorylation of p185 and different intracellular substrates after binding of antibodies that do or do not inhibit tumor-cell growth. A correlation has been found between antibodies that inhibit growth and the intensity of tyrosine phosphorylation of p185. At late intervals, serine phosphorylation of at least 3 intracellular substrates is increased preferentially by growth-inhibitory antibodies. To test the importance of p185 kinase activity more critically, NIH3T3 cells were transfected with an expression vector containing the full-length human c-erbB-2 gene (cell line 17313), c-erbB-2 with deletion of the kinase region from codons 751-979 (cell line 9309) or c-erbB-2 with deletion of most of the intracellular domain from codons 684-1255 (cell line 9310). Unconjugated antibodies inhibited anchorage-independent growth of 17313 cells as well as SKBr3 cells, but did not inhibit growth of either 9309 or 9310 cells. In contrast, the cytotoxic effect of anti-p185-ricin A chain (RTA) conjugates was comparable for 17313, 9309 and 9310. The tyrosine-kinase activity of p185 is required for growth inhibition mediated by unconjugated anti-p185 antibodies, but not for the cytotoxic activity of anti-p185-RTA immunotoxins.