Proapoptotic signaling activity of the anti-CD40 monoclonal antibody dacetuzumab circumvents multiple oncogenic transformation events and chemosensitizes NHL cells

Abstract

Non-Hodgkin lymphoma (NHL) is a genetically heterogeneous disease with several oncogenic events implicated in the transformation of normal developing B lymphocytes. The objective of this study was to elucidate the signal transduction-based antitumor mechanism(s) of action for the anti-CD40 monoclonal antibody dacetuzumab (SGN-40) in NHL. We report that dacetuzumab activates two distinct proapoptotic signaling pathways, overcoming transformation events key to the pathogenesis of NHL. Dacetuzumab-mediated CD40 signaling constitutively activated the nuclear factor-jB and mitogenactivated protein kinase signaling pathways producing the sustained downregulation of B-cell lymphoma 6 (BCL-6), an oncoprotein implicated in lymphomagenesis. Loss of BCL-6 resulted in c-Myc downregulation and activation of a transcriptional program characteristic of early B-cell maturation, concomitant with reduced proliferation and cell death. In a second mechanism, dacetuzumab signaling induced the expression of the proapoptotic p53 family member TAp63a and downstream proteins associated with the intrinsic and extrinsic apoptotic machinery. Dacetuzumab was synergistic in combination with DNA-damaging chemotherapeutic drugs, correlating with TAp63a upregulation. Furthermore, dacetuzumab augmented the activity of rituximab in combination with multiple chemotherapies in the xenograft models of NHL. The ability of dacetuzumab signaling to circumvent oncogenic events and potentiate the activity of chemotherapy regimens provides a unique therapeutic approach to NHL.

Distinct Apoptotic Signaling Characteristics of the Anti-CD40 Monoclonal Antibody Dacetuzumab and Rituximab Produce Enhanced Antitumor Activity in Non-Hodgkin Lymphoma

“…We have previously shown that activation of the NF-kB and MAP kinase pathways is important to the cytotoxicity of dacetuzumab in cultured NHL cell lines (24). Therefore, we contrasted the relative ability of dacetuzumab to activate signal transduction through these signaling cascades with that of rituximab (Fig.…”

“…Our group has previously reported that dacetuzumab causes a sustained downregulation of the BCL-6 oncoprotein and upregulates the proapoptotic p53 family member TAp63a in NHL cell lines (24). Because rituximab and dacetuzumab activate similar signaling pathways in 2/3 cell lines, we evaluated the ability of rituximab to affect BCL-6 and TAp63a expression (Fig.…”

“…Dacetuzumab initiates signaling in lymphoma cells following binding to CD40, activating the ERK1/2, JNK, p38 MAP kinase, and NF-kB signal transduction pathways (24). Constitutive activation of these pathways downregulates B-cell lymphoma 6 (BCL-6) and c-Myc oncoproteins in lymphoma cell lines, whereas the proapoptotic p53 family member TAp63a, Fas, and Bim are upregulated (24).…”

“…Dacetuzumab initiates signaling in lymphoma cells following binding to CD40, activating the ERK1/2, JNK, p38 MAP kinase, and NF-kB signal transduction pathways (24). Constitutive activation of these pathways downregulates B-cell lymphoma 6 (BCL-6) and c-Myc oncoproteins in lymphoma cell lines, whereas the proapoptotic p53 family member TAp63a, Fas, and Bim are upregulated (24). In addition, dacetuzumab is an IgG 1 antibody capable of mediating antibody-dependent cellular cytotoxicity (ADCC) and antibody-dependent cellular phagocytosis (ADCP) effector function activities (23,25).…”

To respond or not to respond to CD40 agonism: That is the prediction

“…models 8 and SGN-40 in combination with Rituximab and gemcitabine in a SGN-40 phase Ib trial where 54% (15 out of 28) of patients with DLBCL experienced an objective response. 9 Similarly, CP-870,893, another anti-CD40 agonist antibody, combined with gemcitabine elicited potent tumor shrinkage in a subset of pancreatic cancers, although in this case macrophages were reported to be responsible for the efficacy.…”