The Humanized Anti-CD40 Antibody, SGN-40, Promotes Apoptosis Signaling and Is Effective in Combination with Standard Therapies in Lymphoma Xenograft Models.

CD40 is a TNF receptor family member that is expressed on B cells and by a wide variety of transformed cells including non-Hodgkin’s lymphoma (NHL), multiple myeloma, and various solid tumors. The humanized anti-CD40 antibody, SGN-40, is a partial agonist that induces apoptosis as well as mediates ADCC against CD40+ NHL B cell lines, contributing to in vivo antitumor activity observed in human lymphoma xenograft models. The current study demonstrates the ability of SGN-40 to initiate multiple signaling cascades upon ligation of CD40 on NHL cell lines. SGN-40 was shown to activate the stress-induced p38 MAP kinase and pro-survival pathways including NF-κB, p42/44 MAP kinase and, to a lesser extent, AKT. Consistent with the apoptosis-inducing activity of SGN-40, cleavage of caspase-3 and its downstream substrate poly (ADP-ribose) polymerase was detected in NHL cell lines. SGN-40 signaling was qualitatively similar to that mediated by trimeric recombinant human CD40 ligand (rhCD40L). However, the overall magnitude of signaling was lower with SGN-40 compared to rhCD40L, consistent with the partial agonistic properties of SGN-40. In addition, constitutive phospho-AKT levels, a key pro-survival signal, were found to be very low in most high-grade lymphoma cell lines and primary NHL specimens, in contrast to the high levels reported in carcinomas. Low AKT activity may bias lymphoma cells toward apoptosis in response to SGN-40 signaling. To augment SGN-40-induced cell killing, in vitro combination studies with chemotherapeutics have been performed using the Ramos, RL, and HT NHL lines. We now report that SGN-40 has additive activity when combined with cisplatin, melphalan, or mitoxantrone and is synergistic with bleomycin. Furthermore, in vivo activity of combination therapy has been demonstrated in a subcutaneous Ramos lymphoma xenograft model. While tumor growth was delayed by either CHOP (cyclophosphamide, adriamycin, vincristine, prednisone) or SGN-40 alone, the combination of SGN-40 and CHOP was significantly more active. Our results suggest that SGN-40 can be combined with standard lymphoma therapies resulting in improved therapeutic efficacy, and provide a rationale for combination clinical trials involving SGN-40. The molecular mechanisms through which standard chemotherapeutic agents enhance SGN-40-mediated cell killing in target lymphoma B cells are currently being investigated.