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In vivo diagnosis and therapy of human tumors with monoclonal antibodies: Overview of the symposium
Nuci. Med. Biol. Vol. 16, No. 2, pp. VII-VIII, 1989 ht. J. Radial. Appl. In.wum. Part B Printed in Great Britain
0883-2897/89
$3.00 + 0.00
Pergamon Press
plc
PREFACE
In I/ivo Diagnosis and Therapy of Human Tumors with Monoclonal Antibodies: Overview of the Symposium It has been nearly a decade since the first studies with monoclonal antibodies were performed in humans by Mach et al. (1980), and in that time numerous investigations have reconfirmed the principal benefits of the monoclonal source of antibody for radioimmunodetection and radioimmunotherapy in human tumors. In comparison to radiolabelled heterosera, which were used in the earliest human studies (Goldenberg er ai., 1978), the monoclonal antibody preparations are more easily characterized as to specificity, affinity, and immunoreactivity after labelling, and availability for clinical studies is significantly better. The international symposium held in Naples, Italy, in March 1988, In Vivo Diagnosis and Therapy of Human Tumors with Monoclonal Antibodies, brought together scientists from Western Europe, the U.S.A., and Japan. The tone of this meeting was marked by an emerging scientific maturity, which is characterized by a continuing enthusiasm for the potential advantages of immunotherapy and immunodiagnosis, tempered by the technical and biologic realities that limit selectivity for tumor localization of radioisotopes, drugs and toxins, when antibodies are used as carriers (immunoconjugates). The current status of immunodiagnosis as reported in the large Italian trial of antimelanoma antibody preparations and anticolon cancer antibody is that a significant fraction of occult lesions (IS-20%) were detected first by radiolabelled monoclonal antibody imaging (RIS) and that, in comparison to CT examination, RIS was clearly superior for detecting recurrence in the pelvis. Occult tumor from colon and ovary in the peritoneal cavity was detected in about l/3 of cases after intraperitoneal injection of the antibody preparation ‘3’I-labelled B72.3, and lymphomatous involvement by T-cell was first detected by RIS in the lymph nodes of patients with cutaneous T-Cell lymphoma in over 40% of patients, when other tests were negative. Similar findings were observed in neuroblastoma, using the 3F8 antibody, and RIS was suggested as the standard for staging of malignant involvement in this disorder. Thus, in a variety of tumor types, a sine qua non for clinical utility, namely the demonstration of occult tumor by RIS, appears to be well documented for diverse tumor types. The current status of immunotherapy was also reported in this symposium and can be summarized as slow but steady progress, with documented cures in animal tumor systems, e.g. the use of ‘311-labelled B72.3 to cure established human tumors in nude mice, with doses delivered in the range of 8000 rad. In humans, the marrow appears to be the target organ for toxicity in most of the clinical trials reported to date, and marrow suppression occurs in a dose dependent manner which has so far heen readily managed without life-threatening consequences. Dramatic responses were observed with ‘3’I-labelled TlOl and immunoconjugates that target T-cells. Although nodes and skin lesions responded these did not result in cures, but were nonetheless encouraging confirmation of the potential for use of these reagents in human tumors. More long term responses have been achieved in human lymphomas by the use of 13’I- labelled B-l antibody, at tumor and normal tissue doses which are tolerated without marrow transplant. Although solid tumors, as expected, have been more difficult to treat with the immunoconjugate approach, injecting the radiolahelled antibody into closed spaces, such as the peritoneum and pleural spaces, has resulted in encouraging early clinical results, with some initial responses, and favorable dosimetry. Perhaps most important, these initial clinical trials have pointed out potential areas of improvement, for example, the substitution of the metal ion q for the halogen “‘I as a therapeutic label for T-101, in treatment of T-cell lymphomas, is predicted to have much greater in uivo stability and resulting improvement in therapeutic ratios between tumor and marrow. This was a meeting in which several recently discovered promising new antibodies were discussed that appear to have in vivo properties that are especially noteworthy. Among these were antibodies with reactivity for lung cancer, such as L-6 and P-80. Lung cancer has not been extensively studied by these immunoconjugate techniques, apparently because of difficulty in finding sufficiently selective monoclonal antibodies. Also, an antibody with unusually good properties for in vivo localization, the 3F8 (neuroblastoma) was described at this meeting, and represents the unusual combination of an antibody which has activity against tumor in the unconjugated state, is highly selective for diagnosis in radiolabelled form, and has sufficient concentration in tumor after iv. injection, to show promise for radioimmunotherapy. VII
VIII
Preface
Advances of a technical and biologic nature were described that address some of the problem areas for selectivity of immunoconjugates when used in vivo. A major advance was presented in the initial results using chimeric antibodies in a therapeutic trial against colon cancer. In comparison to the use of murine antibody of the same specificity (17-lA), the human antibody response was much reduced, and no anti-idiotypic antibody was observed. Such studies support the concept that the anti-tumor specificity of valuable murine antibodies can be utilized in the form of chimeric antibodies which are predominantly human in composition, but which retain the murine active binding site. Such chimeric reagents would have great advantages for repeated in vivo use either in therapy or diagnostic applications, in human cancer. The microscopic distribution of radiolabelled antibodies within tumor and normal tissues has important implications for this field, in terms of developing a better understanding of the biologic factors which determine the selectivity of immune proteins with tumors. Such factors as heterogeneity of antigen expression, the role of tissue permeability and blood flow, the differences of regional uptake within tumors between immune proteins of various molecular weights, have been much discussed, but hard data are limited. A technical innovation was reviewed at this meeting which promises to permit study of these matters. The method utilizes quantitative autoradiography, a way of mapping the microscopic quantitative distribution of radioactivity in tissue sections, and has been used successfully to measure the regional antigen density distributions in tumors, as well as the microdistribution of radiolabelled monoclonal antibodies after in vivo injection, in absolute concentration terms. The relatively slow uptake of antibody into tumor, and the fact that optimum concentration gradients between tumor and normal tissues may take days to develop, is a biologic limitation that imposes harsh constraints on half-life of the radionuclide and the stability of the radioconjugates used for in vivo studies. A new approach which offers promise in overcoming this problem depends on anti-hapten chimeric antibodies, which have dual specificities: to the tumor, and also, to a small radioactive carrier molecule. In this method, also called the “two-step” technique, the large unlabelled chimeric antibody is injected and the slow kinetic steps of uptake into tumor and slow clearance of the unreacted antibody from normal tissues and body compartments is allowed to proceed, over days or even weeks if necessary. The radioactivity is introduced in a form which rapidly diffuses throughout the tissues and achieves maximum ratios of tumor to normal tissues within a few hours, through binding to the bifunctional antibody which is retained on the tumor. Numerous variants of this method have been proposed, and appear to offer the potential for improved practicality of use of radionuclides of shorter half-life, including those like 99”rc, which is available in every nuclear medicine laboratory; and positron labels for use with positron emission tomography. Undoubtedly, two step methods will have major implications for future research in this field. Technical limitations have been more important in reducing the quality of immunoconjugates for in vivo targeting than has been generally recognized. In particular, the fact that for many radiolabelled preparations in clinical use, the immunoreactivity (fraction of radiolabelled molecules which can react with antigen) has been low, in the 3040% range. In this symposium, a new method was described that improved immunoreactivity of radiolabelled preparations, based on anti-idiotypic antibody-affinity chromatography. Such purified preparations are likely to result in greatly improved tumor to normal tissue ratios. One abstract received attention as the recipient of a prize of U.S. $5000, for special merit (Ritter et al., 1988). The presentation described the discovery of a unique antibody against breast carcinoma, and novel chemistry for linking metal ions to this antibody while retaining immunoreactivity. The excellence of this paper depended on an interdisciplinary collaboration of the highest order. We congratulate the co-authors on this work, and wish them continuing success in applications to patient trials. The organizing committee wishes to thank the participants for their excellent efforts in making this meeting a success. STEVENh'i.hRSON KEITH E. BRI~WN E. PORTA M. SALVAMRE
References Goldenberg, D. M.; DeLand, F. H.; Rim, E. et al. Use of radiolabelled antibodies to carcinoembryonic antigen for the detection and localization of diverse cancers by external photoscanning. N. Engl. J. Med. 298: 1384-1386, 1978. Mach, J. P.; Carrel, S.; Fomi, M.; R&hard, J.; Donath, A.; Alberta, P. Tumor localization of radiolabelled antibodies against carcinoembryonic antigen in Patients with carcinoma: a critical evaluation. N. Engl. J. Med. 303: S-10, 1980. Ritter W.; Gudat F.; Stahl, C.; Macke, H. A new monoclonal antibody (b-12) directed against a cancer associated antigen. Symposium abstract. Nucl. Med. Biol. 16: 177485; 1989.
0883-2897/89
$3.00 + 0.00
Pergamon Press
plc
PREFACE
In I/ivo Diagnosis and Therapy of Human Tumors with Monoclonal Antibodies: Overview of the Symposium It has been nearly a decade since the first studies with monoclonal antibodies were performed in humans by Mach et al. (1980), and in that time numerous investigations have reconfirmed the principal benefits of the monoclonal source of antibody for radioimmunodetection and radioimmunotherapy in human tumors. In comparison to radiolabelled heterosera, which were used in the earliest human studies (Goldenberg er ai., 1978), the monoclonal antibody preparations are more easily characterized as to specificity, affinity, and immunoreactivity after labelling, and availability for clinical studies is significantly better. The international symposium held in Naples, Italy, in March 1988, In Vivo Diagnosis and Therapy of Human Tumors with Monoclonal Antibodies, brought together scientists from Western Europe, the U.S.A., and Japan. The tone of this meeting was marked by an emerging scientific maturity, which is characterized by a continuing enthusiasm for the potential advantages of immunotherapy and immunodiagnosis, tempered by the technical and biologic realities that limit selectivity for tumor localization of radioisotopes, drugs and toxins, when antibodies are used as carriers (immunoconjugates). The current status of immunodiagnosis as reported in the large Italian trial of antimelanoma antibody preparations and anticolon cancer antibody is that a significant fraction of occult lesions (IS-20%) were detected first by radiolabelled monoclonal antibody imaging (RIS) and that, in comparison to CT examination, RIS was clearly superior for detecting recurrence in the pelvis. Occult tumor from colon and ovary in the peritoneal cavity was detected in about l/3 of cases after intraperitoneal injection of the antibody preparation ‘3’I-labelled B72.3, and lymphomatous involvement by T-cell was first detected by RIS in the lymph nodes of patients with cutaneous T-Cell lymphoma in over 40% of patients, when other tests were negative. Similar findings were observed in neuroblastoma, using the 3F8 antibody, and RIS was suggested as the standard for staging of malignant involvement in this disorder. Thus, in a variety of tumor types, a sine qua non for clinical utility, namely the demonstration of occult tumor by RIS, appears to be well documented for diverse tumor types. The current status of immunotherapy was also reported in this symposium and can be summarized as slow but steady progress, with documented cures in animal tumor systems, e.g. the use of ‘311-labelled B72.3 to cure established human tumors in nude mice, with doses delivered in the range of 8000 rad. In humans, the marrow appears to be the target organ for toxicity in most of the clinical trials reported to date, and marrow suppression occurs in a dose dependent manner which has so far heen readily managed without life-threatening consequences. Dramatic responses were observed with ‘3’I-labelled TlOl and immunoconjugates that target T-cells. Although nodes and skin lesions responded these did not result in cures, but were nonetheless encouraging confirmation of the potential for use of these reagents in human tumors. More long term responses have been achieved in human lymphomas by the use of 13’I- labelled B-l antibody, at tumor and normal tissue doses which are tolerated without marrow transplant. Although solid tumors, as expected, have been more difficult to treat with the immunoconjugate approach, injecting the radiolahelled antibody into closed spaces, such as the peritoneum and pleural spaces, has resulted in encouraging early clinical results, with some initial responses, and favorable dosimetry. Perhaps most important, these initial clinical trials have pointed out potential areas of improvement, for example, the substitution of the metal ion q for the halogen “‘I as a therapeutic label for T-101, in treatment of T-cell lymphomas, is predicted to have much greater in uivo stability and resulting improvement in therapeutic ratios between tumor and marrow. This was a meeting in which several recently discovered promising new antibodies were discussed that appear to have in vivo properties that are especially noteworthy. Among these were antibodies with reactivity for lung cancer, such as L-6 and P-80. Lung cancer has not been extensively studied by these immunoconjugate techniques, apparently because of difficulty in finding sufficiently selective monoclonal antibodies. Also, an antibody with unusually good properties for in vivo localization, the 3F8 (neuroblastoma) was described at this meeting, and represents the unusual combination of an antibody which has activity against tumor in the unconjugated state, is highly selective for diagnosis in radiolabelled form, and has sufficient concentration in tumor after iv. injection, to show promise for radioimmunotherapy. VII
VIII
Preface
Advances of a technical and biologic nature were described that address some of the problem areas for selectivity of immunoconjugates when used in vivo. A major advance was presented in the initial results using chimeric antibodies in a therapeutic trial against colon cancer. In comparison to the use of murine antibody of the same specificity (17-lA), the human antibody response was much reduced, and no anti-idiotypic antibody was observed. Such studies support the concept that the anti-tumor specificity of valuable murine antibodies can be utilized in the form of chimeric antibodies which are predominantly human in composition, but which retain the murine active binding site. Such chimeric reagents would have great advantages for repeated in vivo use either in therapy or diagnostic applications, in human cancer. The microscopic distribution of radiolabelled antibodies within tumor and normal tissues has important implications for this field, in terms of developing a better understanding of the biologic factors which determine the selectivity of immune proteins with tumors. Such factors as heterogeneity of antigen expression, the role of tissue permeability and blood flow, the differences of regional uptake within tumors between immune proteins of various molecular weights, have been much discussed, but hard data are limited. A technical innovation was reviewed at this meeting which promises to permit study of these matters. The method utilizes quantitative autoradiography, a way of mapping the microscopic quantitative distribution of radioactivity in tissue sections, and has been used successfully to measure the regional antigen density distributions in tumors, as well as the microdistribution of radiolabelled monoclonal antibodies after in vivo injection, in absolute concentration terms. The relatively slow uptake of antibody into tumor, and the fact that optimum concentration gradients between tumor and normal tissues may take days to develop, is a biologic limitation that imposes harsh constraints on half-life of the radionuclide and the stability of the radioconjugates used for in vivo studies. A new approach which offers promise in overcoming this problem depends on anti-hapten chimeric antibodies, which have dual specificities: to the tumor, and also, to a small radioactive carrier molecule. In this method, also called the “two-step” technique, the large unlabelled chimeric antibody is injected and the slow kinetic steps of uptake into tumor and slow clearance of the unreacted antibody from normal tissues and body compartments is allowed to proceed, over days or even weeks if necessary. The radioactivity is introduced in a form which rapidly diffuses throughout the tissues and achieves maximum ratios of tumor to normal tissues within a few hours, through binding to the bifunctional antibody which is retained on the tumor. Numerous variants of this method have been proposed, and appear to offer the potential for improved practicality of use of radionuclides of shorter half-life, including those like 99”rc, which is available in every nuclear medicine laboratory; and positron labels for use with positron emission tomography. Undoubtedly, two step methods will have major implications for future research in this field. Technical limitations have been more important in reducing the quality of immunoconjugates for in vivo targeting than has been generally recognized. In particular, the fact that for many radiolabelled preparations in clinical use, the immunoreactivity (fraction of radiolabelled molecules which can react with antigen) has been low, in the 3040% range. In this symposium, a new method was described that improved immunoreactivity of radiolabelled preparations, based on anti-idiotypic antibody-affinity chromatography. Such purified preparations are likely to result in greatly improved tumor to normal tissue ratios. One abstract received attention as the recipient of a prize of U.S. $5000, for special merit (Ritter et al., 1988). The presentation described the discovery of a unique antibody against breast carcinoma, and novel chemistry for linking metal ions to this antibody while retaining immunoreactivity. The excellence of this paper depended on an interdisciplinary collaboration of the highest order. We congratulate the co-authors on this work, and wish them continuing success in applications to patient trials. The organizing committee wishes to thank the participants for their excellent efforts in making this meeting a success. STEVENh'i.hRSON KEITH E. BRI~WN E. PORTA M. SALVAMRE
References Goldenberg, D. M.; DeLand, F. H.; Rim, E. et al. Use of radiolabelled antibodies to carcinoembryonic antigen for the detection and localization of diverse cancers by external photoscanning. N. Engl. J. Med. 298: 1384-1386, 1978. Mach, J. P.; Carrel, S.; Fomi, M.; R&hard, J.; Donath, A.; Alberta, P. Tumor localization of radiolabelled antibodies against carcinoembryonic antigen in Patients with carcinoma: a critical evaluation. N. Engl. J. Med. 303: S-10, 1980. Ritter W.; Gudat F.; Stahl, C.; Macke, H. A new monoclonal antibody (b-12) directed against a cancer associated antigen. Symposium abstract. Nucl. Med. Biol. 16: 177485; 1989.