Cure of Metastatic Human Colonic Cancer in Mice with Radiolabeled Monoclonal Antibody Fragments 1 Thomas M. Behr, Rosalyn D. Blumenthal, Stavros Memtsoudis, Robert M. Sharkey, Stefan Gratz, Wolfgang Becker, and David M. Goldenberg 2 Department of Nuclear Medicine of the Georg-August-University, Go ¨ttingen, Germany [T. M. B., S. M., S. G., W. B.], and Garden State Cancer Center, Belleville, New Jersey 07109 [R. D. B., R. M. S., D. M. G.] ABSTRACT There is currently no method to cure patients with disseminated colorectal cancer, which is the third leading cancer killer in the Western World. This report shows that the GW-39 intrapulmonary micrometastatic human colonic cancer model in nude mice can be cured with radiolabeled antibodies against carcinoembryonic antigen, and that this approach of radioimmunotherapy is superior to conven- tional chemotherapy with 5-fluorouracil and leucovorin (5- FU/LV). Monovalent Fab fragments labeled with 131 I are superior to intact IgG when survival was evaluated 3, 7, and 14 days after implantation, leading to cures in up to 90% of the mice. Histological results provide support for the differ- ences in therapeutic efficacy observed. Microautoradiogra- phy was used to evaluate the intratumoral distribution of each form of antibody. The enhanced tumor control by Fab compared with IgG could be explained in part by the ho- mogeneity of radioantibody distribution of Fab. Biodistri- bution analysis and initial dose rate calculations for all three forms of antibody also help explain the ability of 131 I-labeled Fab to provide better tumor growth control than seen with 131 I-labeled IgG. Thus, radioimmunotherapy may be a new modality to treat metastatic disease, particularly when using small antibody fragments. INTRODUCTION Despite improvements in the surgical management of can- cer, the prognosis of patients with solid tumors has not improved significantly over the past decades (1). For example, in colorec- tal cancer, which is the third most frequent malignancy in both sexes, 60% of patients will develop local tumor recurrence or distant metastases (2, 3). At the time of primary surgery, tumor cells have been found in the bone marrow of 30% of colorec- tal cancer patients (4 – 6). Although the skeleton is not a pre- ferred site of overt metastasis in this disease, the presence of tumor cells here is interpreted as evidence of the tumor’s general disseminative capacity and a strong predictor of later clinical relapse (7). Adjuvant therapeutic strategies aim at killing these residual cancer cells to increase the relapse-free survival period. Indeed, Moertel et al. (8) showed that a combination regimen of 5-fluorouracil and levamisole increases the relapse-free 5-year survival by 30%. Similar results have been reported for 5- fluorouracil-folinic acid combinations (9, 10), which are most frequently used for treating clinically apparent metastatic dis- ease as well (11, 12). More recently, an immunotherapeutic approach with the monoclonal antibody CO17-1A, which is a murine intact IgG 2a directed against a cell surface-associated M r 41,000 glycoprotein of colorectal cancer cells, but which is also expressed on normal epithelia (13, 14), has yielded results comparable with those of adjuvant chemotherapy (15). Interest- ingly, however, although CO17-1A decreased the incidence of distant metastases, it was not able to reduce the incidence rate of local recurrences (15), which was interpreted on the basis that single tumor cells, which are the progenitors of future distant metastases, may be more susceptible to antibody-mediated im- munological effector mechanisms than larger cell clusters. These tumor cell clusters, which were left in the surroundings of the previous primary tumor and from which local recurrences arise, may be less amenable to penetration by the intact antibody or infiltrating host effector cells (16, 17). In this context, radioimmunotherapy, involving the use of anticancer antibodies conjugated with therapeutic radionuclides, appears as an attractive alternative, because cross-fire radiation from cells targeted by the radiolabeled antibody may deliver tumoricidal doses to surrounding cells as well (18). Although results have been disappointing in bulky disease of solid tumors (19), the potential of radiolabeled antibodies to treat microme- tastases or minimal residual disease has been observed (20, 21). The advantages of smaller immunoconjugates, such as F(ab) 2 fragments, with respect to faster and more homogeneous tumor uptake (because of their higher diffusion capacity and more rapid background clearance), has been recognized for many years (22). Even smaller molecular recognition units, such as Fab fragments or peptides, are generally believed not to be suitable for therapeutic purposes. There are two major reasons for this assumption: (a) their tumor uptake is lower than with bivalent IgG or F(ab) 2 , possibly resulting in lower radiation doses to the tumor (23); and (b) because of the high renal accretion of small fragments and peptides, below the glomeru- larly filtrable size (M r 60,000), radiation nephrotoxicity may become an important limitation in the therapeutic application of such agents (24, 25). Received 6/16/00; revised 10/12/00; accepted 10/26/00. 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. 1 This work was supported in part by Outstanding Investigator Grant CA39841 from the National Cancer Institute, National Institutes of Health (to D. M. G.), and Grants Be 1689/1-1/2 and Be 1689/4-1/2 from the Deutsche Forschungsgemeinschaft (to T. M. B.). 2 To whom requests for reprints should be addressed, at Garden State Cancer Center, 520 Belleville Avenue, Belleville, NJ 07109. Phone: (973) 844-7010; Fax: (973) 844-7020; E-mail: dmg.gscancer@att.net. 4900 Vol. 6, 4900 – 4907, December 2000 Clinical Cancer Research Research. on July 13, 2021. © 2000 American Association for Cancer clincancerres.aacrjournals.org Downloaded from