Antitumor Efficacy of a Combination of CMC-544 (Inotuzumab Ozogamicin), a CD22-Targeted Cytotoxic Immunoconjugate of Calicheamicin, and Rituximab against Non-Hodgkin’s B-Cell Lymphoma John F. DiJoseph, 1 Maureen M. Dougher, 1 Lyka B. Kalyandrug, 1 Douglas C. Armellino, 1 Erwin R. Boghaert, 1 Philip R. Hamann, 2 Justin K. Moran, 3 and Nitin K. Damle 1 Abstract Purpose: CMC-544 is a CD22-targeted cytotoxic immunoconjugate, currently being evaluated in B-cell non-Hodgkin’s lymphoma (B-NHL) patients. Rituximab is a CD20-targeted antibody commonly used in B-NHL therapy. Here, we describe antitumor efficacy of a combination of CMC-544 and rituximab against B-cell lymphoma (BCL) in preclinical models. Experimental Design: BCLs were cultured in vitro with CMC-544, rituximab, or their combina- tion. BCLs were injected either s.c. or i.v. to establish localized s.c. BCL in nude mice or dissemi- nated BCL in severe combined immunodeficient mice, respectively. I.p. treatment with CMC-544 or rituximab was initiated at various times either alone or in combination and its effect on s.c. BCL growth or survival of mice with disseminated BCL was monitored. Results: In vitro growth-inhibitory activity of CMC-544 combined with rituximab was additive. Rituximab but not CMC-544 exhibited effector functions, such as antibody-dependent cellular cytotoxicity and complement-dependent cytotoxicity. Rituximab was less effective in inhibiting growth of established BCL xenografts than developing xenografts. In contrast, CMC-544 was equally effective against both developing and established BCL xenografts. Although CMC-544 and rituximab individually caused partial inhibition of the growth of BCL xenografts at suboptimal doses examined, their combination suppressed xenograft growth by >90%. In a disseminated BCL model, 60% of CMC-544-treated mice and 20% of rituximab-treated mice survived for 125 days. In contrast, 90% of mice treated with the combination of CMC-544 and rituximab survived for longer than 125 days. Conclusion: The demonstration of superior antitumor activity of a combination of CMC-544 and rituximab described here provides the preclinical basis for its clinical evaluation as a treatment option for B-NHL. CMC-544 (inotuzumab ozogamicin) is a CD22-targeted cytotoxic agent composed of a humanized IgG4 anti-CD22 antibody covalently linked to N-acetyl-g-calicheamicin dimeth- yl hydrazide (CalichDMH) via the acid-labile 4-(4V -acetylphe- noxy)butanoic acid linker (1 – 3). CD22 is a B-lymphoid lineage – specific differentiation antigen expressed on both normal and malignant B cells. CMC-544 binds CD22 with subnanomolar affinity, and, upon binding, is rapidly internal- ized delivering the conjugated CalichDMH inside the cells. This preferential intracellular delivery of CalichDMH causes DNA damage resulting in B-cellular apoptosis. CalichDMH is a derivative of g-calicheamicin, a natural product produced by Micromonospora echinospora and is significantly more potent than cytotoxic chemotherapeutic agents used in cancer therapy. It binds in the minor groove of DNA and causes double- strand DNA breaks in a relatively sequence-specific and thiol- dependent manner leading to apoptotic response in cells (4 – 6). CMC-544 exerts potent and CD22-selective growth inhibito- ry activity against CD22 + B-cell lymphoma (BCL) cell lines in vitro and causes regression of developing (minimal disease), small established (palpable disease), and large BCL xenografts, with a high therapeutic index (1). In addition, CMC-544 protects severe combined immunodeficient (SCID) mice against hind limb paralysis and death caused by systemically disseminated BCL (7). In the absence of the conjugated CalichDMH, G5/44, the targeting monoclonal antibody (mAb) in CMC-544, is ineffective in vivo as an antitumor agent in various preclinical models (1, 7) and, thus, CMC-544 is regarded as an antibody-targeted chemotherapy agent rather than an immunotherapeutic agent like rituximab. Largely due Cancer Therapy: Preclinical Authors’Affiliations: 1 Oncology Discovery Research, 2 Chemical and Screening Sciences, and 3 Chemical and Process Development, Wyeth Research, Pearl River, NewYork Received 8/30/05; revised 10/14/05; accepted 10/20/05. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact. Note: All authors are employed by Wyeth Research whose investigational agent, CMC-544, was studied in the present work. CMC-544 is being jointly developed by Wyeth Research and UCB Celltech (Slough, United Kingdom). Requests for reprints: Nitin K. Damle, Oncology Discovery Research,Wyeth Research, 200/4604, 401North Middletown Road, Pearl River, NY 10965. Phone: 845-602-3984; Fax: 845-602-5557; E-mail: damlen@wyeth.com. F 2006 American Association for Cancer Research. doi:10.1158/1078-0432.CCR-05-1905 www.aacrjournals.org Clin Cancer Res 2006;12(1) January 1, 2006 242 Cancer Research. on February 13, 2022. © 2006 American Association for clincancerres.aacrjournals.org Downloaded from