(CANCER RESEARCH (SUPPL.) 50, 820s-827s. Feburary 1, 1990] Innovations That Influence the Pharmacology of Monoclonal Antibody Guided Tumor Targeting1 Jeffrey Schlom,2 Patricia Horan Hand, John W. Greiner, David Colcher, Shashi Shrivastav, Jorge A. Carrasquillo, James C. Reynolds, Steven M. Larson,3 and Andrew Raubitschek Laboratory1of Tumor Immunology and Biology [J. S., P. H. H., J. W. G., D. C., S. S.J, Department of Nuclear Medicine, Clinical Center fJ. A. C., J. C. R., S. M. LJ, and Radiation Oncology Branch [A. R.], National Cancer Institute, and NIH, Bethesda, Maryland 20892 Abstract regulate the expression of specific tumor associated antigens such as carcinoembryonic antigen (CEA) or TAG-72 on the Tumor targeting by monoclonal antibodies (MAbs) can be enhanced surface of carcinoma cells and thus increase MAb tumor bind by (a) increasing the percentage of injected dose taken up by the tumor ing; (b) the intracavitary administration of MAbs. Recent stud and/or (b) increasing the tumor:nontumor ratios. Several groups have demonstrated that one can increase tumor to nontumor ratios by the use ies have demonstrated that when radiolabeled MAb B72.3 is of antibody fragments or the administration of second antibodies. Several administered i.p. to patients with carcinoma of the peritoneal other modalities are also possible: (a) the use of recombinant interferons cavity, it localizes tumor masses with greater efficiency than to up-regulate the expression of specific tumor associated antigens such does concurrent i.v. administered antibody. Studies involving as carcinoembryonic antigen or TAG-72 on the surface of carcinoma cells the comparative pharmacology of intracavitary administration and thus increase MAb tumor binding has proved successful in both in of radiolabeled MAb in patients and several animal models will vitro and in vivo studies; (b) the intracavitary administration of MAbs. be discussed; (c) it has been reported that prior exposure of Recent studies have demonstrated that when radiolabeled B72.3 is ad hepatoma to external beam radiation will increase radiolabeled ministered ¡.p.to patients with carcinoma of the peritoneal cavity, it MAb tumor targeting. We and others have not been able to localizes tumor masses with greater efficiency than does concurrent i.v. duplicate this phenomenon with a human colon cancer xeno administered antibody. Studies involving the comparative pharmacology of intracavitary administration of radiolabeled MAb in patients and graft model and radiolabeled MAbs to two different colon several animal models will be discussed; (c) it has been reported that carcinoma associated antigens. The possible reasons for these prior exposure of hepatoma to external beam radiation will increase differences will be discussed; (d) the cloning and expression of radiolabeled MAb tumor targeting. We and others have not been able to recombinant MAbs with human constant regions and subse duplicate this phenomenon with a human colon cancer xenograft model quent size modification constructs will undoubtedly alter the and radiolabeled MAbs to two different colon carcinoma associated pharmacology of MAb tumor binding. antigens. The possible reasons for these differences will be discussed; (</) the cloning and expression of recombinant MAbs with human constant regions and subsequent size modification constructs will also undoubtedly Augmentation of Tumor Antigen Expression by Recombinant alter the pharmacology of MAb tumor binding in both diagnostic and Human Interferons: Enhanced Tumor Targeting of Monoclonal therapeutic applications. Antibodies Unlike the antigens that constitute the major histocompati- Introduction bility complex and receptor molecules, many carcinoma asso There are numerous parameters that can have an effect on ciated tumor antigens are, for the most part, integral compo the pharmacology of MAb4 guided tumor targeting. Some of nents of the cell membrane and do not undergo internalization, the more obvious parameters are listed in Table 1. Some of capping, etc., after antibody binding. In some cases, the carci these factors are intrinsic, such as the size and location of the noma associated tumor antigens are expressed by a variety of tumor mass, while others can be manipulated. Most of these different tumor types. One example is the B72.3 MAb that was manipulations involve either (a) increasing the percentage of generated in our laboratory using an enriched membrane extract injected dose of MAb taken up by the tumor or (b) increasing prepared from a human carcinoma metastasis to the liver (5, the tumor to nontumor ratios. One of the more widely used 6). B72.3 reacts with a high molecular weight glycoprotein procedures of MAb guided tumor targeting involves the use of antigen, termed TAG-72 (7). The range of reactivity of the immunoglobulin Fab and F(ab')2 fragments (1-3). In general, B72.3 antibody for carcinoma versus normal is selective; i.e., the use of fragments leads to higher tumonblood ratios but a the only normal adult tissue that shows appreciable reactivity lower percentage of injected dose delivered to tumor masses. with the antibody is secretory endometrium (8). Other tissues Similar effects have also been seen with the use of second demonstrate minor reactivities (9). In addition, the range of antibody to clear the blood pool of primary antibody (4); this reactivity of B72.3 among different carcinomas is that of a approach, however, has also led to enhanced liver and spleen pancarcinoma antigen and includes breast, colorectal, ovarian, uptake. stomach, pancreatic, and endometrial cancers (9). This paper will outline and review four of many new and A third characteristic that seems to be shared by many human innovative approaches to enhance MAb guided tumor targeting. carcinoma associated antigens is the existence of antigenic These include: (a) the use of recombinant interferons to up- heterogeneity among the different tumor lesions. This hetero 1Presented at the "Second Conference on Radioimmunodetection and Ra- geneity of tumor antigen expression has been documented both dioimmunotherapy of Cancer," September 8-10, 1988, Princeton, NJ. in experimental models using established human carcinoma cell 2To whom requests for reprints should be addressed, at Laboratory of Tumor lines and in biopsies prepared from in situ carcinoma lesions Immunology and Biology, Bldg. 10, Rm. 8B07, 9000 Rockville Pike, Bethesda, (10, 11). Data are available that demonstrate that, within pri MD 20892. 3Present address: Nuclear Medicine Service, Memorial Sloan Kettering Cancer mary and metastatic human carcinomas, not all of the cells may Center, New York, NY 10021. 4The abbreviations used are: MAb, monoclonal antibody; TAG, tumor asso express a given tumor antigen. Although tumor cell heteroge ciated glycoprotein; rHuIFN, recombinant human interferon; %ID/kg, percentage neity can be defined according to a large number of cellular of injected dose of MAb/kg; RI, radiolocalization index. criteria (i.e., cell size, metastatic ability), the heterogeneity of 820s Downloaded from cancerres.aacrjournals.org on September 24, 2021. © 1990 American Association for Cancer Research. PHARMACOLOGY OF MAßGUIDED TUMOR TARGETING Table 1 Parameters of MAb guided tumor localization and therapy responsiveness of a human tumor Cell line to the ability of rHu- 1. Number of antigen molecules per cell surface IFN-aA to augment surface tumor antigen expression in vivo; 2. Number of cells expressing the reactive antigen in the tumor mass (b) have shown the advantage of a delivery system to administer 3. Size of the tumor mass 4. Fate of antigen-antibody complex rHu-IFN that results in sustained long-term plasma levels; and a. Stability on cell surface also (c) have provided a basis to investigate the relationship b. Internalization c. Capping between in vivo plasma levels and the resultant amount of in d. Shedding vivo localization of a MAb to the tumor site. 5. Degree of vascularization of the tumor Recent studies have demonstrated that recombinant interfer 6. Degree of infiltration and necrosis in the tumor mass 7. Presence and reactivity of circulating antigen in the blood ons a (clone A), 0-ser, and 7 can all up-regulate the expression 8. Duration of MAb binding to cell surface of some (but not all) tumor associated antigens including car- 9. Isotype of immunoglobulin (IgG subtypes or IgM) cinoembryonic antigen and TAG-72 (22). Many of these are 10. Species of immunoglobulin: murine, human, recombinant/chimeric 11. Whole immunoglobulin or fragments: Fab, Fab'. F(ab')2 summarized in Table 2. Recent studies by Rosenblum et al. 12. Clearance of MAb from blood (MAb metabolism) (26) have also shown that interferons can up-regulate tumor a. Excretion b. Reticuloendothelial system targeting of radiolabeled MAbs in a clinical trial. Preclinical c. Administration of second antibody studies have also demonstrated that recombinant interferons 13. Dose of MAb used can both increase the amount of tumor antigen expressed by a 14. Route of inoculation of MAb (i.v., i.p., intralymphatic. intraarterial) 15. Development of a human immune response to the administered MAb given tumor cell and increase the percentage of cells within the a. To constant region tumor cell population that express the antigen. Thus, antigenic b. Antiidiotype heterogeneity of tumor masses can perhaps be dealt with using If radiolabeled MAb is used one or a combination of (a) mixtures of MAbs, (b) radionuclides 16. Ability of MAb to be labeled with specific radionuclide