Abstract 3321: Novel therapeutic approaches targeting the transferrin receptor 1 for the treatment of mantle cell lymphoma.

Mantle cell lymphoma (MCL) is an aggressive B-cell malignancy with no defined curative therapy. A hallmark of MCL is the high level of cyclin D1 expression that promotes cell cycle progression with the subsequent increase in proliferation, need for iron, and, thus, overexpression of the transferrin receptor 1 (TfR1). We previously developed an antibody-avidin fusion protein (ch128.1Av) targeting this receptor that shows an enhanced intrinsic in vitro cytotoxicity in malignant hematopoietic cells when compared to the parental antibody without avidin (ch128.1). This cytotoxicity is due to the ability of ch128.1Av to decrease cell surface TfR1 leading to lethal iron deprivation. However, both ch128.1Av and ch128.1 have shown anti-tumor activity in human xenograft models of multiple myeloma. ch128.1Av is also a universal delivery system of biotinylated agents. The main goal of this study is to evaluate the potential use of our anti-TfR1 antibodies alone and as delivery vehicles as possible MCL therapies. Screening of a panel of six human MCL cell lines (Mino, JVM-2, JVM-13, JeKo-1, Z-138, and REC-1) showed high expression of TfR1 but not TfR2, confirming specificity of TfR1 targeted therapy. We found that, when used alone, ch128.1Av exhibits cytotoxicity in MCL cells. In addition, the cytotoxicity dramatically increases when this fusion protein is conjugated to biotinylated saporin, a plant protein synthesis inhibitor. However, a concern with the systemic delivery of potent toxins is their potential side effects. To further enhance the delivery specificity, we explored the potential of dual targeted gene therapy approaches. The first level of targeting occurs through the use of our anti-TfR1 antibodies and takes advantage of the overexpression of the TfR1 on cancer cells. The second level of targeting occurs through transcriptional regulation using the immunoglobulin (Ig) promoter to restrict the expression of the delivered gene to malignant B-cells. Two different approaches were examined: 1) the use of the parental antibody (ch128.1) complexed to lentivirus with a modified, pseudotyped Sindbis virus envelope protein containing the ZZ domain of protein A; and 2) the use of ch128.1Av conjugated to a similar virus containing the biotin acceptor peptide (instead of the ZZ domain) that allows for biotinylation of the virus. We found that the reporter gene encoding enhanced green fluorescent protein (EGFP), under the control of the Ig promoter, was expressed in human malignant B cells U266 (multiple myeloma) and Z-138 (MCL), but not in Jurkat (human T-cell leukemia) cells. As expected, EGFP was expressed in all cell lines when a ubiquitous promoter was used. These results confirm the dual targeted nature of our approaches and suggest the potential use of our anti-TfR1 antibodies alone or as delivery vehicles as therapeutic interventions against incurable B-cell malignancies such as MCL and multiple myeloma. Citation Format: Lai Sum Leoh, Michael A. Erb, Kouki Morizono, Irvin S. Y. Chen, Manuel L. Penichet, Tracy R. Daniels-Wells. Novel therapeutic approaches targeting the transferrin receptor 1 for the treatment of mantle cell lymphoma. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3321. doi:10.1158/1538-7445.AM2013-3321