Ovarian Carcinoma Patients Fragments in 2 ) ′ Monoclonal Antibody MOv 18 IgG and F ( ab Kinetics and Tissue Distribution of the Radiolabeled Chimeric

Twenty-four patients suspected of having ovarian carcinoma received i.v. injection with a combination of radiolabeled intact IgG (1 mg) and F(ab')2 fragments (1 mg) of the chimeric monoclonal antibody MOvlS, each form labeled with 1.85 MBq I3II or I25I. Laparotomy was performed either 2 or 6 days after injection, and the uptake of radioactivity was determined in a total of 329 biopsies of normal and malignant tissues. The mean elimination half life in plasma of cMOvlS IgG and F(ab')2 was 70 ±8 (SD) and 20 ±5 h, respectively. The mean uptake of IgG in tumor biopsies was 3.6-fold higher two days after injection and 6.9-fold higher than the uptake of F(ab')2 6 days after injection. Uptake in normal tissues was 3.3 and 5.5 times higher for IgG at 2 and 6 days, respectively. Two days after injection, the mean ratio of the uptake in tumonnormal tissue/patient was 3.8 ±1.5 and 4.0 ±1.8 for radiolabeled cMOvl8 IgG and F(ab')2, respectively. Six days after injection, this was 6.7 ±4.7 for Ig G and 5.7 ±4.1 for F(ab')2. cMOvl8 IgG has a longer circulation time in blood, a higher uptake in tumor and normal tissues, and a longer retention time compared to the F(ab')2 fragments. However, the tumor:normal tissue ratios are similar. The results do not warrant a definite conclusion as to which antibody form is most suitable for therapeutic application of antibodies but provide a more firm basis for rational design of therapeutic targeting studies using immunoconjugates. INTRODUCTION The clinical application of MAb3 conjugates for therapy of cancer is mainly limited by the relatively low antibody uptake in tumor compared with the uptake in normal tissues. A second obstacle for efficient tumor therapy could be the development of a human antimurine antibody immune response. The latter limitation might be overcome using a chimeric mouse/human antibody construct in which the epitope-specific variable region of a murine MAb is combined with the constant region of a human immunoglobulin (1, 2). To date, no studies have been reported regarding the in vivo tissue distribution of chimeric MAbs in ovarian cancer patients. In the present study, cMOvlS was used for radioimmunotargeting of ovarian cancer. MOvlS is a MAb with restricted reactivity with an antigen frequently expressed on ovarian carcinoma cells (3). The murine MOvlS anti body has been used in a clinical study (4), whereas both murine and chimeric MOvlSs have been investigated in vitro in human ovarian cancer-bearing nude mice (5). Antibody size is one of the factors that influence the accumulation of MAbs in tumor tissue. Smaller fragments clear more rapidly from Received 4/5/93; accepted 9/8/93. 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. ' This study was supported by Clinical Research Gran! NWO 900-715-020 of the Netherlands Organization for Scientific Research and by Grant 92-05 from the Biocare Foundation. 2 To whom requests for reprints should be addressed, at Department of Obstetrics and Gynecology, Free University Hospital, De Boelelaan 1117, 1081 HV Amsterdam, The Netherlands. 'The abbreviations used are: MAb, monoclonal antibody; cMOvlS, chimeric mono clonal antibody MOvlS; %ID. percentage of the injected dose; T:NT, tumonnormal tissue ratio; T;B, tumorblood ratio; HPLC, high performance liquid chromatography. the circulation in comparison to intact immunoglobulins, resulting in an increased tumonnormal tissue ratio (6-8). A disadvantage of using fragments for therapeutic purposes might be the lower absolute tumor uptake in comparison with whole IgG (8-10). For the application of (radiolabeled) antibodies for cancer treatment, it is important to study whether the intact antibody or its fragments should be applied. In the present study, 24 patients received a single i.v. injection with a combination of IgG and F(ab')2 fragments of cMOvlS, labeled with a low tracer dose of ml and I25I, allowing the assessment in the same patient of the kinetics and tissue distribution of both antibody forms. In addition, for immunoscintigraphic purposes, 8 patients received cMOvlS Fab' indirectly labeled with WmTc and 16 patients received cMOvlS IgG or F(ab')2 labeled with 1231, simultaneously injected with the low tracer doses of radiolabeled MAbs. All patients were suspected of having primary or recurrent/residual epithelial ovarian cancer. Patients underwent extensive laparotomy either 2 or 6 days after injection of the immunoconjugates, allowing the evaluation of the radioactivity uptakes at two different time points. MATERIALS AND METHODS Patients and Study Design. Twenty-four patients (mean age, 58.5 years; range, 32-78 years) entered the study after giving informed consent. All patients were suspected of having primary or recurrent/residual epithelial ovar ian cancer and were referred to the oncological gynecology department of the Free University Hospital or of the Netherlands Cancer Institute. The study was approved by the Dutch Health Council and the Medical Review Board of both hospitals. Inclusion criteria were: Karnofsky performance score of 70 or higher; life expectancy of at least 3 months; and age between 30 and 80 years. Exclusion criteria were: previous administration of MAbs; serious organ fail ure; iodine sensitivity; and chemo-/radiotherapy within 3 weeks prior to ad ministration of the immunoconjugates. Reactivity of tumor tissue with the MAb was not assessed prior to injection of the immunoconjugates. Eligible patients received a single i.v. injection with a mixture of immunoconjugates. Prior to injection, history, physical examination, performance status, vital signs, and hematological and biochemical serum profiles were recorded. Pa tients received sodium perchlorate from I day before until 5 days after admin istration of the immunoconjugates in order to block thyroid uptake of radio active iodine. Following immunoconjugate infusion, vital signs and serum profiles were frequently monitored. The patients' characteristics, the final diagnosis, and the combination of radiolabeled antibodies administered are listed in Table 1. Due to inefficient labeling, one patient (Table 1, patient 12) was excluded from further evaluation. Extensive explorative laparotomy was performed in all 23 évaluablepatients, either 2 (n = 11) or 6 days (n = 12) after injection of the immunoconjugates. Eight of the 11 patients who under went surgery 2 days after injection did have ovarian carcinoma (6 patients had primary ovarian carcinoma and 2 had residual ovarian cancer after initial treatment with debulking surgery and combination chemotherapy), 2 patients had a benign ovarian tumor, and in 1 patient there was no evidence of residual ovarian carcinoma. In the group of 12 patients who underwent surgery 6 days after injection, 9 patients did have ovarian carcinoma (3 primary and 6 recurrent/residual ovarian cancer), 1 had a benign ovarian tumor, 1 had a tumor of borderline malignancy, and in 1 patient there was no evidence of residual disease. All patients received i.v. injections of a combination of cMOvl8 IgG and cMOvlS F(ab')2 labeled with a low tracer dose of '•"! and 125I.The first 8