More than 50% of patients with aggressive B lymphomas and the majority of patients with low grade lymphomas are not cured by current therapeutic strategies. The lymphomas express the B cell antigen CD20 on the cell surface and this antigen serves as target for antibody-directed therapies. Clinical studies with encouraging results have been underway with the use of a chimeric anti-CD20 antibody (IDEC-C2B8), consisting of human IgG1-6 constant regions and variable regions from the murine monoclonal anti-CD20 antibody IDEC-2B8. This study investigated the potential anti-tumor therapeutic value of combination treatment with anti-C2B8 and cytotoxic drugs. The in vitro study examined the sensitizing effect of C2B8 antibody on the DHL-4 B lymphoma line to various cytotoxic agents. Cytotoxicity was determined by the MTT assay. Surface and cytoplasmic proteins were determined by flow cytometry. Pretreatment of DHL-4 with C2B8 resulted in inhibition of cell proliferation and cell death and a fraction of the cells underwent apoptosis. While the DHL-4 tumor cells were relatively resistant to several cytotoxic drugs, pretreatment with C2B8 rendered the cells sensitive to TNF-alpha, ricin, diphtheria toxin (DTX), adriamycin and cisplatin but not to VP-16. Chemosensitization of DHL-4 tumor cells was not due to downmodulation of either the MDR-1 or bcl-2 gene products. However, treatment of DHL-4 with C2B8 inhibited TNF-alpha secretion. These findings demonstrate that C2B8 antibody potentiates the sensitivity of DHL-4 tumor cells to several cytotoxic agents. Further, the findings suggest that combination treatments with C2B8 antibody and drugs may be of clinical benefit in the treatment of patients with resistant aggressive B lymphomas.

(2011) A stable IgG-like bispecific antibody targeting the epidermal growth factor receptor and the type I insulin-like growth factor receptor demonstrates superior anti-tumor activity, mAbs, 3:3, 273-288,

Therapeutic antibodies directed against the type 1 insulinlike growth factor receptor (IGF-1R) have recently gained significant momentum in the clinic because of preliminary data generated in human patients with cancer. These antibodies inhibit ligand-mediated activation of IGF-1R and the resulting downstream signaling cascade. Here we generated a panel of antibodies against IGF-1R and screened them for their ability to block the binding of both IGF-1 and IGF-2 at escalating ligand concentrations (>1 M) to investigate allosteric versus competitive blocking mechanisms. Four distinct inhibitory classes were found as follows: 1) allosteric IGF-1 blockers, 2) allosteric IGF-2 blockers, 3) allosteric IGF-1 and IGF-2 blockers, and 4) competitive IGF-1 and IGF-2 blockers. The epitopes of representative antibodies from each of these classes were mapped using a purified IGF-1R library containing 64 mutations. Most of these antibodies bound overlapping surfaces on the cysteine-rich repeat and L2 domains. One class of allosteric IGF-1 and IGF-2 blocker was identified that bound a separate epitope on the outer surface of the FnIII-1 domain. Using various biophysical techniques, we show that the dual IGF blockers inhibit ligand binding using a spectrum of mechanisms ranging from highly allosteric to purely competitive. Binding of IGF-1 or the inhibitory antibodies was associated with conformational changes in IGF-1R, linked to the ordering of dynamic or unstructured regions of the receptor. These results suggest IGF-1R uses disorder/order within its polypeptide sequence to regulate its activity. Interestingly, the activity of representative allosteric and competitive inhibitors on H322M tumor cell growth in vitro was reflective of their individual ligand-blocking properties. Many of the antibodies in the clinic likely adopt one of the inhibitory mechanisms described here, and the outcome of future clinical studies may reveal whether a particular inhibitory mechanism leads to optimal clinical efficacy. The type I insulin-like growth factor receptor (IGF-1R)2 is a large transmembrane receptor tyrosine kinase expressed on most somatic cells. IGF-1R is activated by the binding of its constitutive ligands, IGF-1 and IGF-2 (and at a much lower affinity, insulin). Ligand binding to the IGF-1R extracellular domains leads to activation of its cytoplasmic tyrosine kinase domain, receptor autophosphorylation, and phosphorylation of downstream targets such as insulin receptor substrate-1 (IRS-1), the Src homology and collagen domain protein (Shc), and others (1, 2). Phosphorylation of IRS-1 activates the phosphoinositol kinase 3/AKT cellular growth and survival pathways, and Shc phosphorylation leads to the activation of other signal cascades, including the extracellular signal-regulated kinase(Erk)/mitogen-activated protein kinase (MAPK) cellular growth and proliferation pathways (3).Human IGF-1R is synthesized as a 1368-amino acid polypeptide whose primary and tertiary structures have been reviewed (4,5). The N-terminal region (consis...

Purpose: Rituximab [chimeric anti-CD20 monoclonal antibody], alone or combined with chemotherapy, is used in the treatment of non-Hodgkin's lymphoma (NHL). Rituximab binds to CD20 and inhibits intracellular survival/growth pathways leading to chemo/ immunosensitization of tumor cells in vitro. The contribution of rituximab Fc-FcR interaction in signaling is not known. This study examined the role of Fc-FcR interactions in rituximab-induced signaling using rituximab (Fab') 2 fragments as well as rituximab devoid of the CH2 Fc-binding domain (CH2 -). Experimental Design: Rituximab (CH2 -) and rituximab (Fab') 2 were tested for their activity on B-NHL cell lines. Cell signaling and sensitization to chemotherapy and immunotherapy were examined. The in vitro studies were validated in mice bearing tumor xenografts. Results: Although the modified antibodies were defective in antibody-dependent cellular cytotoxicity and complement-dependent cytotoxicity functions, they retained all other biological activities such as inhibition of cell proliferation, induction of cell aggregation, and apoptosis induction. In addition, similar to rituximab, the modified antibodies inhibited the activity of cell survival/growth pathways and their associated transcription factors (e.g., NF-κB, YY1, SP-1), and signal transducers and activators of transcription 3 (STAT-3), and downregulated the expression of antiapoptotic gene products, such as Bcl-2/Bcl XL , which regulate drug resistance. The modified antibodies, similar to rituximab, sensitized resistant B-NHL cells to both CDDP and Fas ligandinduced apoptosis. Furthermore, treatment of nude mice bearing Raji tumor cell xenografts with the combination of rituximab (Fab') 2 or rituximab and CDDP resulted in similar and significant inhibition of tumor growth. Conclusion: These findings reveal that rituximab-mediated inhibition of intracellular signaling pathways and leading to chemo/immuno-sensitization of resistant B-NHL is Fc independent. (Clin Cancer Res 2009;15(21):6582-94) Rituximab (chimeric mouse anti-human CD20 monoclonal antibody) is a genetically engineered monoclonal antibody used for the treatment of patients with relapsed or refractory low-grade or follicular B-cell non-Hodgkin's lymphoma (NHL) and in patients with relapsed stage III/IV follicular lymphoma (1, 2). Rituximab is composed of murine Variable (V) and human IgG1 Constant (C) regions. Rituximab functions by binding to the CD20 antigen expressed on the surface of normal and malignant B cells. The overall response in patients is 50% when it is used as a single agent (3), and the response rate

Lumiliximab is a chimeric macaquehuman monoclonal antibody to CD23, a protein expressed on virtually all chronic lymphocytic leukemia (CLL) cells. We examined the ability of lumiliximab to mediate apoptosis, antibody-dependent cellular cytotoxicity, and complementdependent cytotoxicity against primary CLL cells and CD23-expressing B-cell lines. Our data suggest that lumiliximab kills CLL cells and CD23-expressing B cells predominantly by apoptosis, which occurs through the intrinsic pathway.Lumiliximab-induced apoptosis was accompanied by the down-regulation of antiapoptotic proteins Bcl-2, Bcl-X L , and XIAP, activation of Bax, and release of cytochrome c from the mitochondria. We also found that the addition of lumiliximab to rituximab or fludarabine results in synergistic cytotoxicity of primary CLL cells and CD23-expressing B-cell lines. We investigated the in vivo activity of lumiliximab in a human disseminated CD23 ؉ B-cell lymphoma SCID mouse model and found greater antitumor activity with it than with control antibody. We also found that paralysis-free survival was greater with lumiliximab plus rituximab or fludarabine than with any of those agents alone. These results suggest that lumiliximab may be an effective treatment alone or in combination with rituximab or chemotherapy agents in CLL or other CD23-overexpressing B-cell malignancies. (Blood. 2008;111:1594-1602)