Antibody therapy is a core component of treatment regimens for B cell lymphoma, yet a subset of these malignancies are refractory to front-line therapy. Nearly 10% of aggressive B-cell lymphomas harbor chromosome rearrangements involving the MYC and BCL2 (or BCL6) oncogenes. These so called ?double-hit lymphoma (DHLs)? are associated with very poor prognosis with standard chemo-immunotherapy. In addition, 25-30% of DLBCLs without MYC rearrangements have protein over-expression of MYC and BCL2. These lymphomas (so-called ?double overexpressing lymphomas (DOL)?) also have very high rates of primary treatment failure. Combined, these tumors represent a significant fraction of currently incurable DLBCL. The Hemann laboratory recently developed a treatment refractory humanized mouse model of DHL amenable to treatment with therapeutic antibodies. Specifically, B-cell-specific co-expression of the oncogenes MYC and BCL2 in human hematopoietic stem cells and adoptive transferred to NSG mice resulted in the rapid development of an aggressive human malignancy that effectively recapitulated the pathological and clinical characteristics of DHL. Like human DHL, the model lymphomas had low/no expression of CD20, suggesting that rituximab (a core component of current lymphoma treatment regimes) would have minimal effects. However, the cells highly expressed surface CD52, the target of alemtuzumab. The combination of alemtuzumab and cyclophosphamide (CTX) yielded a strikingly synergistic (~160-fold) therapeutic effect, leading to near-complete elimination of disease in all sites. The synergy of alemtuzumab and CTX was very specific to this drug combination, as co-dosing alemtuzumab with other chemotherapies failed to produce a synergistic effect. CTX induced the expression of the pro-phagocytic factor calreticulin and reduced expression of the ?don't eat me? signal CD47 on tumor cells. To confirm that the same effects occur in human DHL, we xenografted specimens obtained from patients with relapsed/refractory DHL. In both models (which also express high levels of CD52), treatment with the combination was markedly synergistic, with near or complete eradication of disease after a single cycle of treatment with the combination, but not with either single agent. While this work represents a significant first step in the development of effective treatment for DHL, very little is known about the mechanism of this drug-antibody synergy. The focus of this proposal is to understand the molecular basis by which CTX promotes the efficacy of therapeutic antibodies and to identify basic principles of antibody/drug combination therapy that will expand and enhance their clinical use. Together, these studies will define the mechanisms and broader applicability of CTX/antibody combinations that could be immediately applied in patients with relapsed/refractory lymphomas or other conditions dependent upon antibody-mediated cytotoxicity.
We propose studies relevant to the action of cyclophosphamide in promoting antibody efficacy in lymphoma. Specifically, we will perform in vivo and in vitro studies that assay the effects of cyclophosphamide and other agents on phagocytosis, tumor burden, and molecular mechanisms of synergistic activity. These studies depend on preclinical models developed in the Hemann lab, as well as PDX models obtained from collaborators.
