66. Identification and Characterization of a B Cell Aptamer That Targets Diffuse Large B Cell Lymphoma (DLBCL) and Chronic Myelogenous Leukemia (CML)

Diffuse large B cell lymphoma (DLBCL) is a heterogenous group of non-Hodgkin's lymphoma (NHL) constituting ~40% of all NHL diagnoses in the United States of America. Alternative therapies for DLBCL are required, since only 30-50% of patients respond to current therapy regimens of either chemotherapeutic drugs (CHOP) alone or CHOP with Rituxan (R-CHOP). The high incidence of relapse/refractory lymphoma following treatment with R-CHOP and Rituxan's non-specific binding to normal CD20+ B cell demonstrates the clinical need for alternative therapies that specifically target malignant B cells. Majority of lymphoma patients suffer from the adverse side-effects associated with aggressive therapies like radiation and chemotherapy such as nausea, hair loss, and organ damage in severe cases.In recent years, aptamers or nucleic acid ligands have been explored as novel therapeutics, since aptamers are highly specific, not immunogenic, and amenable for conjugation of therapeutic molecules such as toxins, chemotherapeutic agents, and siRNAs. Aptamers, both antagonists and agonists, can be used to target receptors on cells with high affinity and specificity. We describe the identification and characterization of an RNA aptamer against a biomarker expressed on certain types of GCB diffuse large B cell lymphoma and chonic myelogenous leukemias (CML). Aptamer appears to be specific to cancerous B cells and does not interact with healthy B cells. We are currently conducting experiments to identify the unique biomarker expressed on these GCB DLBCL cells of origin BJAB, HT, and OCI-Ly1, and of CML origin. We have performed a proof of concept study conjugating saporin to a novel aptamer that specifically targets DLBCL specific B cells and does not bind to healthy B cells. We have developed an aptamer to deliver toxic agents and other cargoes to a subset of leukemia and lymphoma cells. This aptamer is engineered into a chimeric molecule possessing two levels of specificity: the binding domain (aptamer), and the agent domain (saporin) that specifically targets and kills cancerous cells in vitro.The creation of a novel in vivo targeted therapeutic platform could result in a significant advance over the existing technology because the aptamer-drug chimera can potentially lower the amount of drug required to achieve efficacy by specifically targeting circulating, malignant B cells. In addition, this novel DLBCL-specific therapeutic will have the advantage of being more potent and cause less nonspecific damage to surrounding tissue, which are the current side-effects associated with standard treatment of care for DLBCL. Hematological malignancies are optimal for toxin conjugated therapeutics because malignant lymphocytes are intravascular and will be accessible to an intravenously administered aptamer-drug toxin. Our goal is to develop a novel aptamer-toxin chimera therapeutic that specifically targets and eliminates diffuse large B cell lymphomas. Once developed, such aptamer-drug chimeras can be evaluated in animal models of DLBCL for safety and efficacy and then be translated into first-in-human clinical studies to treat patients with DLBCL.