Intraperitoneal radioimmunotherapy for ovarian cancer: pharmacokinetics, toxicity, and efficacy of I-131 labeled monoclonal antibodies

Calcium Carbonate Microparticles as Carriers of 224Ra: Impact of Specific Activity in Mice with Intraperitoneal Ovarian Cancer

BACKGROUND

Patients with advanced-stage ovarian cancer face a poor prognosis because of recurrent peritoneal cavity metastases following surgery and chemotherapy. Alpha-emitters may enable the efficient treatment of such disseminated diseases because of their short range and highly energetic radiation. Radium-224 is a candidate α-emitter due to its convenient 3.6-day half-life, with more than 90% of the decay energy originating from α-particles. However, its inherent skeletal accumulation must be overcome to facilitate intraperitoneal delivery of the radiation dose. Therefore, ²²⁴Ra-labeled CaCO₃ microparticles have been developed.

OBJECTIVE

The antitumor effect of CaCO₃ microparticles as a carrier for ²²⁴Ra was investigated, with an emphasis on the ratio of activity to mass dose of CaCO₃, that is, specific activity.

METHODS

Nude athymic mice were inoculated intraperitoneally with human ovarian cancer cells (ES-2) and treated with a single intraperitoneal injection of ²²⁴Ra-labeled CaCO₃ microparticles with varying combinations of mass and activity dose, or cationic ²²⁴Ra in solution. Survival and ascites volume at sacrifice were evaluated.

RESULTS

Significant therapeutic effect was achieved for all tested specific activities ranging from 0.4 to 4.6 kBq/mg. Although treatment with a mean activity dose of 1305 kBq/kg of cationic ²²⁴Ra prolonged the survival compared with the control, equivalent median survival could be achieved with ²²⁴Ra-labeled microparticles with a mean dose of only 420 kBq/kg. The best outcome was achieved with the highest specific activities (2.6 and 4.6 kBq/mg).

CONCLUSION

Radium-224-labeled CaCO₃ microparticles present a promising therapy against cancer dissemination in body cavities.

Radiopharmaceutical therapy in cancer: clinical advances and challenges

Radiopharmaceutical therapy (RPT) is emerging as a safe and effective targeted approach to treating many types of cancer. In RPT, radiation is systemically or locally delivered using pharmaceuticals that either bind preferentially to cancer cells or accumulate by physiological mechanisms. Almost all radionuclides used in RPT emit photons that can be imaged, enabling non-invasive visualization of the biodistribution of the therapeutic agent. Compared with almost all other systemic cancer treatment options, RPT has shown efficacy with minimal toxicity. With the recent FDA approval of several RPT agents, the remarkable potential of this treatment is now being recognized. This Review covers the fundamental properties, clinical development and associated challenges of RPT.

Development of 131I-ixolaris as a theranostic agent: metastatic melanoma preclinical studies

Tissue factor (TF), a blood coagulation protein, plays an important role in tumor growth, invasion, and metastasis. Ixolaris, a tick-derived non-immunogenic molecule that binds to TF, has demonstrated in vivo inhibitory effect on murine models of melanoma, including primary growth and metastasis. This work aimed to: I) develop an efficient and stable labeling technique of ixolaris with Iodine-131(¹³¹I); II) compare the biodistribution of ¹³¹I and ¹³¹I-ixolaris in tumor-free and melanoma-bearing mice; III) evaluate whether ¹³¹I-ixolaris could serve as an antimetastatic agent. Ixolaris radioiodination was performed using iodogen, followed by liquid paper chromatography. Labeling stability and anticoagulant activity were measured. Imaging studies were performed after intravenous administration of free ¹³¹I or ¹³¹I-ixolaris in a murine melanoma model employing the B16-F10 cell line. Animals were divided in three experimental groups: the first experimental group, D0, received a single-dose of 9.25 MBq of ¹³¹I-ixolaris at the same day the animals were inoculated with melanoma cells. In the second group, D15, a single-dose of 9.25 MBq of ¹³¹I-ixolaris or free ¹³¹I was applied into mice on the fifteenth day after the tumor induction. The third group, D1-D15, received two therapeutic doses of 9.25 MBq of ¹³¹I-ixolaris or ¹³¹I. In vitro studies demonstrated that ¹³¹I-ixolaris is stable for up to 24 h and retains its inhibitory activity on blood coagulation. Biodistribution analysis and metastasis assays showed that all treatment regimens with ¹³¹I-ixolaris were effective, being the double-treatment (D1/D15) the most effective one. Remarkably, treatment with free ¹³¹I showed no anti-metastatic effect. ¹³¹I-ixolaris is a promising theranostic agent for metastatic melanoma.

Ra-224 labeling of calcium carbonate microparticles for internal α-therapy: Preparation, stability, and biodistribution in mice

Internal therapy with α‐emitters should be well suited for micrometastatic disease. Radium‐224 emits multiple α‐particles through its decay and has a convenient 3.6 days of half‐life. Despite its attractive properties, the use of ²²⁴Ra has been limited to bone‐seeking applications because it cannot be stably bound to a targeting molecule. Alternative delivery systems for ²²⁴Ra are therefore of considerable interest. In this study, calcium carbonate microparticles are proposed as carriers for ²²⁴Ra, designed for local therapy of disseminated cancers in cavitary regions, such as peritoneal carcinomatosis. Calcium carbonate microparticles were radiolabeled by precipitation of ²²⁴Ra on the particle surface, resulting in high labeling efficiencies for both ²²⁴Ra and daughter ²¹²Pb and retention of more than 95% of these nuclides for up to 1 week in vitro. The biodistribution after intraperitoneal administration of the ²²⁴Ra‐labeled CaCO₃ microparticles in immunodeficient mice revealed that the radioactivity mainly remained in the peritoneal cavity. In addition, the systemic distribution of ²²⁴Ra was found to be strongly dependent on the amount of administered microparticles, with a reduced skeletal uptake of ²²⁴Ra with increasing dose. The results altogether suggest that the ²²⁴Ra‐labeled CaCO₃ microparticles have promising properties for use as a localized internal α‐therapy of cavitary cancers.

Targeted Cancer Therapy Using Radiolabeled Monoclonal Antibodies

Radioimmunotherapy (RIT) combines the advantages of targeted radiation therapy and specific immunotherapy using monoclonal antibodies. RIT can be used either to target tumor cells or to specifically suppress immunocompetent host cells in the setting of allogeneic transplantation. The choice of radionuclide used for RIT depends on its distinct radiation characteristics and the type of malignancy or cells targeted. Beta-emitters with their lower energy and longer path length are more suitable to target bulky, solid tumors whereas α-emitters with their high linear energy transfer and short path length are better suited to target hematopoietic cells (normal or malignant). Different approaches of RIT such as the use of stable radioimmunoconjugates or of pretargeting strategies are available. Encouraging results have been obtained with RIT in patients with hematologic malignancies. The results in solid tumors are somewhat less favorable but new strategies for patients with minimal residual disease using adjuvant and locoregional treatment are evolving. This report outlines basic principles of RIT, gives an overview of available radionuclides and radioimmunoconjugates, and discusses clinical results with special emphasis on their use in hematologic malignancies including use in conditioning regimens for bone marrow transplantation.

Dose escalation and dosimetry of first-in-human α radioimmunotherapy with 212Pb-TCMC-trastuzumab

Our purpose was to study the safety, distribution, pharmacokinetics, immunogenicity, and tumor response of intraperitoneal (212)Pb-TCMC-trastuzumab (TCMC is S-2-(4-isothiocyanatobenzyl)-1,4,7,10-tetraaza-1,4,7,10-tetra(2-carbamoylmethyl)cyclododecane) in patients with human epidermal growth factor receptor type 2 (HER-2)-expressing malignancy.

METHODS

In a standard 3 + 3 phase 1 design for dose escalation, (212)Pb-TCMC-trastuzumab was delivered intraperitoneally less than 4 h after administration of trastuzumab (4 mg/kg intravenously) to patients with peritoneal carcinomatosis who had failed standard therapies.

RESULTS

Five dosage levels (7.4, 9.6, 12.6, 16.3, and 21.1 MBq/m(2)) showed minimal toxicity at more than 1 y for the first group and more than 4 mo for others. The lack of substantial toxicity was consistent with the dosimetry assessments (mean equivalent dose to marrow, 0.18 mSv/MBq). Radiation dosimetry assessment was performed using pharmacokinetics data obtained in the initial cohort (n = 3). Limited redistribution of radioactivity out of the peritoneal cavity to circulating blood, which cleared via urinary excretion, and no specific uptake in major organs were observed in 24 h. Maximum serum concentration of the radiolabeled antibody was 22.9% at 24 h (decay-corrected to injection time) and 500 Bq/mL (decay-corrected to collection time). Non-decay-corrected cumulative urinary excretion was 6% or less in 24 h (2.3 half-lives). Dose rate measurements performed at 1 m from the patient registered less than 5μSv/h (using portable detectors) in the latest cohort, significantly less than what is normally observed using nuclear medicine imaging agents. Antidrug antibody assays performed on serum from the first 4 cohorts were all negative.

CONCLUSION

Five dose levels of intraperitoneal (212)Pb-TCMC-trastuzumab treatment of patients with peritoneal carcinomatosis showed little agent-related toxicity, consistent with the dosimetry calculations.

Dose escalation and dosimetry of first-in-human α radioimmunotherapy with 212Pb-TCMC-trastuzumab

Our purpose was to study the safety, distribution, pharmacokinetics, immunogenicity, and tumor response of intraperitoneal (212)Pb-TCMC-trastuzumab (TCMC is S-2-(4-isothiocyanatobenzyl)-1,4,7,10-tetraaza-1,4,7,10-tetra(2-carbamoylmethyl)cyclododecane) in patients with human epidermal growth factor receptor type 2 (HER-2)-expressing malignancy.

METHODS

In a standard 3 + 3 phase 1 design for dose escalation, (212)Pb-TCMC-trastuzumab was delivered intraperitoneally less than 4 h after administration of trastuzumab (4 mg/kg intravenously) to patients with peritoneal carcinomatosis who had failed standard therapies.

RESULTS

Five dosage levels (7.4, 9.6, 12.6, 16.3, and 21.1 MBq/m(2)) showed minimal toxicity at more than 1 y for the first group and more than 4 mo for others. The lack of substantial toxicity was consistent with the dosimetry assessments (mean equivalent dose to marrow, 0.18 mSv/MBq). Radiation dosimetry assessment was performed using pharmacokinetics data obtained in the initial cohort (n = 3). Limited redistribution of radioactivity out of the peritoneal cavity to circulating blood, which cleared via urinary excretion, and no specific uptake in major organs were observed in 24 h. Maximum serum concentration of the radiolabeled antibody was 22.9% at 24 h (decay-corrected to injection time) and 500 Bq/mL (decay-corrected to collection time). Non-decay-corrected cumulative urinary excretion was 6% or less in 24 h (2.3 half-lives). Dose rate measurements performed at 1 m from the patient registered less than 5μSv/h (using portable detectors) in the latest cohort, significantly less than what is normally observed using nuclear medicine imaging agents. Antidrug antibody assays performed on serum from the first 4 cohorts were all negative.

CONCLUSION

Five dose levels of intraperitoneal (212)Pb-TCMC-trastuzumab treatment of patients with peritoneal carcinomatosis showed little agent-related toxicity, consistent with the dosimetry calculations.

General overview of radioimmunotherapy of solid tumors

Radioimmunotherapy (RIT) represents an attractive tool for the treatment of local and/or diffuse tumors with radiation. In RIT, cytotoxic radionuclides are delivered by monoclonal antibodies that specifically target tumor-associated antigens or the tumor microenvironment. While RIT has been successfully employed for the treatment of lymphoma, mostly with radiolabeled antibodies against CD20 (Bexxar(®); Corixa Corp., WA, USA and Zevalin(®); Biogen Idec Inc., CA, USA and Schering AG, Berlin, Germany), its use in solid tumors is more challenging and, so far, few trials have progressed beyond Phase II. This review provides an update on antibody-radionuclide conjugates and their use in RIT. It also discusses possible optimization strategies to improve the clinical response by considering biological, radiobiological and physical features.

Emerging trends for radioimmunotherapy in solid tumors

Due to its ability to target both known and occult lesions, radioimmunotherapy (RIT) is an attractive therapeutic modality for solid tumors. Poor tumor uptake and undesirable pharmacokinetics, however, have precluded the administration of radioimmunoconjugates at therapeutically relevant doses thereby limiting the clinical utility of RIT. In solid tumors, efficacy of RIT is further compromised by heterogeneities in blood flow, tumor stroma, expression of target antigens and radioresistance. As a result significant efforts have been invested toward developing strategies to overcome these impediments. Further, there is an emerging interest in exploiting short-range, high energy α-particle emitting radionuclides for the eradication of minimal residual and micrometastatic disease. As a result several modalities for localized therapy and models of minimal disease have been developed for preclinical evaluation. This review provides a brief update on the recent efforts toward improving the efficacy of RIT for solid tumors, and development of RIT strategies for minimal disease associated with solid tumors. Further, some of promising approaches to improve tumor targeting, which showed promise in the past, but have now been ignored are also discussed.

Evaluation of effects on the peritoneum after intraperitoneal α-radioimmunotherapy with (211)At

The introduction of the short-lived α-emitter (211)At to intraperitoneal radioimmunotherapy has raised the issue of the tolerance dose of the peritoneum. The short range of the α-particles (70 μm) and the short half-life (7.21 h) of the nuclide yield a dose distribution in which the peritoneum is highly irradiated compared with other normal tissues. To address this issue, mice were injected with (211)At-trastuzumab to irradiate the peritoneum to absorbed doses ranging between 0 and 50 Gy and followed for up to 34 weeks. The peritoneum-to-plasma clearance of a small tracer, (51)Cr-ethylenediamine tetraacetic acid, was measured for evaluation of the small solute transport capacity of the peritoneal membrane. The macroscopic status of the peritoneum and the mesenteric windows was documented when the mice were sacrificed. Biopsies of the peritoneum were taken for morphology and immunohistochemical staining against plasminogen activator inhibitor-1 and calprotectin. Peritoneum-to-plasma clearance measurements indicated a dose-dependent decrease in peritoneal transport capacity in irradiated mice. However, macroscopic and microscopic evaluations of the peritoneal membrane showed no difference between irradiated mice versus controls. The results imply that the peritoneal membrane tolerates absorbed doses as high as 30-50 Gy from α-particle irradiation with limited response.

Clinical radioimmunotherapy--the role of radiobiology

Conventional external-beam radiation therapy is dedicated to the treatment of localized disease, whereas radioimmunotherapy represents an innovative tool for the treatment of local or diffuse tumors. Radioimmunotherapy involves the administration of radiolabeled monoclonal antibodies that are directed specifically against tumor-associated antigens or against the tumor microenvironment. Although many tumor-associated antigens have been identified as possible targets for radioimmunotherapy of patients with hematological or solid tumors, clinical success has so far been achieved mostly with radiolabeled antibodies against CD20 ((131)I-tositumomab and (90)Y-ibritumomab tiuxetan) for the treatment of lymphoma. In this Review, we provide an update on the current challenges aimed to improve the efficacy of radioimmunotherapy and discuss the main radiobiological issues associated with clinical radioimmunotherapy.

(124)I-huA33 antibody PET of colorectal cancer

Humanized A33 (huA33) is a promising monoclonal antibody that recognizes A33 antigen, which is present in more than 95% of colorectal cancers and in normal bowel. In this study, we took advantage of quantitative PET to evaluate (124)I huA33 targeting, biodistribution, and safety in patients with colorectal cancer. We also determined the biodistribution of (124)I-huA33 when a large dose of human intravenous IgG (IVIG) was administered to manipulate the Fc receptor or when (124)I-huA33 was given via hepatic arterial infusion (HAI).

METHODS

We studied 25 patients with primary or metastatic colorectal cancer; 19 patients had surgical exploration or resection. Patients received a median of 343 MBq (44.4-396 MBq) and 10 mg of (124)I-huA33. Nineteen patients received the antibody intravenously and 6 patients via HAI, and 5 patients also received IVIG.

RESULTS

Ten of 12 primary tumors were visualized in 11 patients. The median concentration in primary colon tumors was 0.016% injected dose per gram, compared with 0.004% in normal colon. The PET-based median ratio of hepatic tumor uptake to normal-liver uptake was 3.9 (range, 1.8-22.2). Quantitation using PET, compared with well counting of serum and tissue, showed little difference. Prominent uptake in bowel hindered tumor identification in some patients. Pharmacokinetics showed that patients receiving IVIG had a significantly shorter serum half-time (41.6 ± 14.0 h) than those without (65.2 ± 9.8 h). There were no differences in clearance rates among the intravenous group, IVIG group, and HAI group, nor was there any difference in serum area under the curve, maximum serum concentration, or volume of distribution. Weak titers of human-antihuman antibodies were observed in 6 of 25 patients. No acute side effects or significant toxicities were associated with huA33.

CONCLUSION

Good localization of (124)I-huA33 in colorectal cancer with no significant toxicity has been observed. PET-derived (124)I concentrations agreed well with those obtained by well counting of surgically resected tissue and blood, confirming the quantitative accuracy of (124)I-huA33 PET. The HAI route had no advantage over the intravenous route. No clinically significant changes in blood clearance were induced by IVIG.

Intraperitoneal radioimmunotherapy: Auger electron emitters for solid tumors

Evaluation of: Boudousq V, Ricaud S, Garambois V et al.: Brief intraperitoneal radioimmunotherapy of small peritoneal carcinomatosis using high activities of noninternalizing 125I-labeled monoclonal antibodies. J. Nucl. Med. 51, 1748–1755 (2010). Mesothelioma, pseudomyxoma peritonei, ovarian and colon cancers, and several other malignancies produce peritoneal carcinomatosis in their advanced stages. This condition is typically managed with curative intention by means of a radical cytoreductive surgery and intraperitoneal hyperthermic chemotherapy. The method has been shown to improve the survival of some patients with peritoneal dissemination. However, the intracavitary instillation of chemotherapy results in a nonuniform drug distribution and allows penetration of the drug only into the outermost layer of the cancer nodule. Authors of the current study demonstrate that 125I-radiolabeled monoclonal antibody, 35A7, which recognizes anti-carcinoembryonic antigen, can be used effectively and safely with low toxicity in the therapy of small volume peritoneal carcinomatosis after cytoreductive surgery.

Intraperitoneal alpha-particle radioimmunotherapy of ovarian cancer patients: pharmacokinetics and dosimetry of (211)At-MX35 F(ab')2--a phase I study

The alpha-emitter (211)At labeled to a monoclonal antibody has proven safe and effective in treating microscopic ovarian cancer in the abdominal cavity of mice. Women in complete clinical remission after second-line chemotherapy for recurrent ovarian carcinoma were enrolled in a phase I study. The aim was to determine the pharmacokinetics for assessing absorbed dose to normal tissues and investigating toxicity.

METHODS

Nine patients underwent laparoscopy 2-5 d before the therapy; a peritoneal catheter was inserted, and the abdominal cavity was inspected to exclude the presence of macroscopic tumor growth or major adhesions. (211)At was labeled to MX35 F(ab')(2) using the reagent N-succinimidyl-3-(trimethylstannyl)-benzoate. Patients were infused with (211)At-MX35 F(ab')(2) (22.4-101 MBq/L) in dialysis solution via the peritoneal catheter. gamma-Camera scans were acquired on 3-5 occasions after infusion, and a SPECT scan was acquired at 6 h. Samples of blood, urine, and peritoneal fluid were collected at 1-48 h. Hematology and renal and thyroid function were followed for a median of 23 mo.

RESULTS

Pharmacokinetics and dosimetric results were related to the initial activity concentration (IC) of the infused solution. The decay-corrected activity concentration decreased with time in the peritoneal fluid to 50% IC at 24 h, increased in serum to 6% IC at 45 h, and increased in the thyroid to 127% +/- 63% IC at 20 h without blocking and less than 20% IC with blocking. No other organ uptakes could be detected. The cumulative urinary excretion was 40 kBq/(MBq/L) at 24 h. The estimated absorbed dose to the peritoneum was 15.6 +/- 1.0 mGy/(MBq/L), to red bone marrow it was 0.14 +/- 0.04 mGy/(MBq/L), to the urinary bladder wall it was 0.77 +/- 0.19 mGy/(MBq/L), to the unblocked thyroid it was 24.7 +/- 11.1 mGy/(MBq/L), and to the blocked thyroid it was 1.4 +/- 1.6 mGy/(MBq/L) (mean +/- SD). No adverse effects were observed either subjectively or in laboratory parameters.

CONCLUSION

This study indicates that by intraperitoneal administration of (211)At-MX35 F(ab')(2) it is possible to achieve therapeutic absorbed doses in microscopic tumor clusters without significant toxicity.

Brief overview of preclinical and clinical studies in the development of intraperitoneal radioimmunotherapy for ovarian cancer

Due to the generally slow and incomplete transit of i.p. infused agents into the circulation, treating disease confined to the peritoneal cavity with chemotherapy, biologics, and/or radionuclides provides a pharmacologic advantage. A higher i.p. concentration can be achieved than could be tolerated by systemic administration. An advantage of i.p. versus i.v. administration for localization of radiolabeled antibodies to small peritoneal surface disease has been shown in animal model and human biopsy studies (1, 2). A recent phase III Gynecologic Oncology Group chemotherapy trial has confirmed a survival advantage for i.p. delivery among women undergoing initial therapy for advanced ovarian cancer (3). Although the therapy was more difficult to tolerate such that 60% of patients randomized to the i.p. arm did not complete the entire regimen, there was a 16-month survival advantage. I.p. radionuclide therapy has been used in treatment of ovarian cancer for more than three decades, but side effects have been problematic in non-tumor-targeted 32P therapy (4). Efforts to improve specificity have used a number of antigens expressed on ovarian cancer cells as targets for selective delivery of radionuclide-conjugates. Mouse models and cell culture have been prominent for preclinical study of agents and strategies in the development of i.p. targeted radionuclide therapy for ovarian cancer. Animal studies, which have directed clinical trials, have shown clear improvement in survival with various modifications including combination chemotherapy, pretargeting, and combination of antibodies over simply delivery of a radiolabeled antibody via i.p. route.

A phase I trial of (90)Y-DOTA-anti-CEA chimeric T84.66 (cT84.66) radioimmunotherapy in patients with metastatic CEA-producing malignancies

PURPOSE/OBJECTIVE

Previous radioimmunotherapy (RIT) clinical trials at this institution with (90)Y-labeled cT84.66 anti-CEA (carcinoembryonic antigen) evaluated the antibody conjugated to diethylenetriaminepentaacetic acid (DTPA). The aim of this phase I therapy trial was to evaluate cT84.66 conjugated to the macrocyclic chelate (90)Y-DOTA and labeled with (90)Y in a comparable patient population.

EXPERIMENTAL DESIGN

Patients with metastatic CEA-producing cancers were entered in this trial. If antibody targeting to tumor was observed after the administration of (111)In-DTPA cT84.66, the patient then received the therapy infusion of (90)Y-DOTA-cT84.66 1 week later. Serial nuclear scans, blood and urine collections, and computed tomography (CT) scans were performed to assess antibody biodistribution, pharmacokinetics, toxicities, and antitumor effects.

RESULTS

Thirteen (13) patients were treated in this study. Dose-limiting hematologic toxicity was experienced at initial starting activity levels of 12 and 8 mCi/m(2). Subsequent patients received systemic Ca-DTPA at 125 mg/m(2) every 12 hours for 3 days post-therapy to allow for a dose escalation to 16 mCi/m(2), where hematologic toxicity was observed with an associated maximum tolerated dose (MTD) of 13.4 mCi/m(2). Tumor doses ranged from 4.4 to 569 cGy/mCi, which translated to 97-12,500 cGy after a single infusion of (90)Y-DOTA-cT84.66. Human anti-chimeric antibody (HACA) response developed in 8 of 13 patients and prevented additional therapy in 4 patients.

CONCLUSIONS

This study demonstrates the feasibility of using (90)Y-DOTA-cT84.66 for antibody-guided radiation therapy. Immunogenicity of the DOTA-conjugated cT84.66 antibody was not appreciably greater than that observed with (90)Y-DTPA-cT84.66 in previous trials. Dose-limiting hematopoietic toxicity with (90)Y-DOTA-cT84.66 decreased with Ca-DTPA infusions post-therapy and appears to be comparable to previously published results for (90)Y-DTPA-cT84.66. The highest antibody uptake and tumor doses were to small nodal lesions, which supports the predictions from preclinical and clinical data that RIT may be best applied in the minimal tumor burden setting.

Phase III Trial of Intraperitoneal Therapy With Yttrium-90–Labeled HMFG1 Murine Monoclonal Antibody in Patients With Epithelial Ovarian Cancer After a Surgically Defined Complete Remission

Purpose

This was a multinational, open-label, randomized phase III trial comparing yttrium-90–labeled murine HMFG1 (90Y-muHMFG1) plus standard treatment versus standard treatment alone in patients with epithelial ovarian cancer (EOC) who had attained a complete clinical remission after cytoreductive surgery and platinum-based chemotherapy.

Patients and Methods

In total, 844 International Federation of Gynecology and Obstetrics stage Ic to IV patients were initially screened, of whom 447 patients with a negative second-look laparoscopy (SLL) were randomly assigned to receive either a single dose of 90Y-muHMFG1 plus standard treatment (224 patients) or standard treatment alone (223 patients). Patients in the active treatment arm received a single intraperitoneal dose of 25 mg of 90Y-muHMFG1 (target dose 666 MBq/m2). The primary end point was length of survival; secondary end points included time to relapse and safety. The study had an 80% power to detect a 15% change in survival.

Results

After a median follow-up of 3.5 years (range, 1 to 6 years), 70 patients had died in the active treatment arm compared with 61 patients in the control arm. Cox proportional hazards analysis of survival demonstrated no difference between treatment arms. In the study drug arm, 104 patients experienced relapse compared with 98 patients in the standard treatment arm. No difference in time to relapse was observed between the two study arms. Active therapy was associated with occasional grade 3 or 4 thrombocytopenia and neutropenia and grade 1 or 2 GI symptoms, abdominal discomfort, arthralgia, and myalgia.

Conclusion

A single IP administration of 90Y-muHMFG1 to patients with EOC who had a negative SLL after primary therapy did not extend survival or time to relapse.

Targeted cancer therapy and immunosuppression using radiolabeled monoclonal antibodies

Radioimmunotherapy (RIT) as a means to target radiation therapy to tumor cells or to specifically suppress host immunity specifically in the setting of allogeneic transplantation is a promising new strategy in the armory of today's oncologist. Different approaches of RIT such as injection of a stable radioimmunoconjugate or the use of pretargeting are available. The choice of the radionuclide used for RIT depends on its radiation characteristics with respect to the malignancy or cells targeted. beta-Emitters with their lower energy and longer path length are more suitable for targeting bulky, solid tumors, whereas alpha-emitters with their high linear energy transfer and short path length are better suited to target cells or tumors of the hematologic system. Encouraging results have been obtained using these approaches treating patients with hematologic malignancies. While the results in solid tumors are somewhat less favorable, new strategies for patients with minimal residual disease (MRD), using adjuvant and locoregional treatment, are currently being investigated. In this report, we outline basic principles of RIT, give an overview of available radioimmunoconjugates and their clinical applications with special emphasis on their use in hematologic malignancies, including use in conditioning regimens for stem cell transplantation (SCT).

Hematologic toxicity in radioimmunotherapy: dose-response relationships for I-131 labeled antibody therapy

Bone marrow toxicity is generally dose-limiting for radioimmunotherapy (RIT) with beta-emitting radionuclides. Treatment may be prescribed on the basis of administered activity or absorbed dose. An optimal definition of maximum tolerated dose will enable the clinical benefits of RIT to be maximized.

METHODS

We examined data from six clinical studies of RIT with various 131-I labeled antibodies and antibody fragments that treated a total of 114 patients. We also examined a sub-set of 36 patients with minimal prior chemotherapy who were treated with 131I-labeled intact murine IgG at a single institution. For both these groups the ability of absorbed dose-based methods to predict bone marrow tolerance was compared with that of activity-based methods.

RESULTS

Marrow toxicity was more accurately predicted by absorbed dose than by activity in the general case where a variety of different antibodies and antibody fragments were used. For the more homogeneous smaller group, well defined "dose-response" relationships were observed for both absorbed dose and administered activity. However, absorbed dose-based definitions of maximally tolerated dose yielded a better stratification of patients than activity-based definitions (including per meter squared) such that fewer patients had major toxicity when treated below "tolerance", and fewer patients had minor toxicity when treated above "tolerance".

CONCLUSIONS

Absorbed dose-based definitions of maximum tolerated dose and escalation variables are optimal for 131I-labeled antibody therapy. The ability of pre-therapy dosimetry studies to predict the behavior of therapeutic administrations must be validated for prospective clinical applications.

Radiation dosimetry for radionuclide therapy in a nonmyeloablative strategy

Radionuclide therapy extends the usefulness of radiation from localized disease of multifocal disease by combining radionuclides with disease-seeking drugs, such as antibodies or custom-designed synthetic agents. Like conventional radiotherapy, the effectiveness of targeted radionuclides is ultimately limited by the amount of undesired radiation given to a critical, dose-limiting normal tissue, most often the bone marrow. Because radionuclide therapy relies on biological delivery of radiation, its optimization and characterization are necessarily different than for conventional radiation therapy. However, the principals of radiobiology and of absorbed radiation dose remain important for predicting radiation effects. Fortunately, most radionuclides emit gamma rays that allow the measurement of isotope concentrations in both tumor and normal tissues in the body. By administering a small "test dose" of the intended therapeutic drug, the clinician can predict the radiation dose distribution in the patient. This can serve as a basis to predict therapy effectiveness, optimize drug selection, and select the appropriate drug dose, in order to provide the safest, most effective treatment for each patient. Although treatment planning for individual patients based upon tracer radiation dosimetry is an attractive concept and opportunity, practical considerations may dictate simpler solutions under some circumstances. There is agreement that radiation dosimetry (radiation absorbed dose distribution, cGy) should be utilized to establish the safety of a specific radionuclide drug during drug development, but it is less generally accepted that absorbed radiation dose should be used to determine the dose of radionuclide (radioactivity, GBq) to be administered to a specific patient (i.e., radiation dose-based therapy). However, radiation dosimetry can always be utilized as a tool for developing drugs, assessing clinical results, and establishing the safety of a specific radionuclide drug. Bone marrow dosimetry continues to be a "work in progress." Blood-derived and/or body-derived marrow dosimetry may be acceptable under specific conditions but clearly do not account for marrow and skeletal targeting of radionuclide. Marrow dosimetry can be expected to improve significantly but no method for marrow dosimetry seems likely to account for decreased bone marrow reserve.

Clinical trial design and scoring of radionuclide therapy endpoints: normal organ toxicity and tumor response

Like other cancer therapy agents under development, radionuclide therapies are usually evaluated in a progressive series of clinical trials after basic science, human cell culture and animal model studies. Toxicities during these trials are graded using common scoring systems that are in widespread use such as the Common Toxicity Criteria from the National Cancer Institute. Information on normal tissue toxicity from radionuclides is more limited than that from external beam radiation and is more variable. Variability is likely due to many biologic factors as well as less precise dose quantitation than those used in external beam radiation practice. As expected based on known radiobiologic effects, tolerance to radionuclide therapy appears to exceed that from high dose rate external beam radiation in most organs. Although the correlation between reported dose estimates and toxicity has progressively and substantially improved over the past two decades, further progress is needed to establish optimal toxicity predictive relationships. Continued refinement of dosimetry techniques and standardization is expected to increase the accuracy and comparability of radiation dose reports between institutions as well as improve dose/response correlation.

Intraperitoneal radioimmunochemotherapy of ovarian cancer: a phase I study

A phase I trial was designed to examine the feasibility of combining interferon and Taxol with intraperitoneal radioimmunotherapy (177Lu-CC49). Patients with recurrent or persistent ovarian cancer confined to the abdominal cavity after first line therapy, Karnofsky performance status > 60, adequate liver, renal and hematologic function, and tumor that reacted with CC49 antibody were enrolled. Human recombinant alpha interferon (IFN) was administered as 4 subcutaneous injections of 3 x 10(6) U on alternate days beginning 5 days before RIT to increase the expression of the tumor-associated antigen, TAG-72. The addition of IFN increased hematologic toxicity such that the maximum tolerated dose (MTD) of the combination was 40 mCi/m2 compared to 177Lu-CC49 alone (45 mCi/m2). Taxol, which has radiosensitizing effects as well as antitumor activity against ovarian cancer, was given intraperitoneally (i.p.) 48 hrs before RIT. It was initiated at 25 mg/m2 and escalated at 25 mg/m2 increments to 100 mg/m2. Subsequent groups of patients were treated with IFN + 100 mg/m2 Taxol + escalating doses of 177Lu-CC49. Three or more patients were treated in each dose group and 34 patients were treated with the 3-agent combination. Therapy was well tolerated with the expected reversible hematologic toxicity. The MTD for 177Lu-CC49 was 40 mCi/m2 when given with IFN + 100 mg/m2 Taxol. Interferon increased the effective whole body half-time of radioactivity and the whole body radiation dose. Taxol did not have a significant effect on pharmacokinetic or dosimetry parameters. Four of 17 patients with CT measurable disease had a partial response (PR) and 4 of 27 patients with non-measurable disease have progression-free intervals of 18+, 21+, 21+, and 37+ months. The combination of intraperitoneal Taxol chemotherapy (100 mg/m2) with RIT using 177Lu-CC49 and interferon was well tolerated, with bone marrow suppression as the dose-limiting toxicity.

Role of radiation dosimetry in radioimmunotherapy planning and treatment dosing

Cancer-seeking antibodies (Abs) carrying radionuclides can be powerful drugs for delivering radiotherapy to cancer. As with all radiotherapy, undesired radiation dose to critical organs is the limiting factor. It has been proposed that optimization of radioimmunotherapy (RIT), that is, maximization of therapeutic efficacy and minimization of normal tissue toxicity, depends on a foreknowledge of the radiation dose distributions to be expected. The necessary data can be acquired by established tracer techniques, in individual patients, using quantitative radionuclide imaging. Object-oriented software systems for estimating internal emitter radiation doses to the tissues of individual patients (patient-specific radiation dosimetry), using computer modules, are available for RIT, as well as for other radionuclide therapies. There is general agreement that radiation dosimetry (radiation absorbed dose distribution, cGy) should be utilized to establish the safety of RIT with a specific radiolabeled Ab in the early stages (i.e. phase I or II) of drug evaluation. However, it is less well established that radiation dose should be used to determine the radionuclide dose (amount of radioactivity, GBq) to be administered to a specific patient (i.e. radiation dose-based therapy). Although treatment planning for individual patients based upon tracer radiation dosimetry is an attractive concept and opportunity, particularly for multimodality RIT with intent to cure, practical considerations may dictate simpler solutions under some circumstances.

Clinical radioimmunotherapy

Radioimmunotherapy (RIT) is a promising new therapy for the treatment of a variety of malignancies. General principles of RIT are discussed, including important considerations in the selection of monoclonal antibodies (MAb) and radionuclides for RIT. Results of clinical trials using RIT for the treatment of lymphoma, leukemia, and solid tumors are summarized. The results from many of these trials are promising, especially for the treatment of lymphohematopoietic malignancies, in which a variety of MAb, radionuclides, and study designs have resulted in high response rates with a number of durable responses. Encouraging results have also been obtained using RIT to treat some solid tumors, primarily in patients with relatively low tumor burdens. RIT is generally well tolerated, with the primary toxicity being transient reversible myelosuppression in most nonmyeloablative studies. Nonhematologic toxicity, especially at nonmyeloablative doses, has been minimal in most studies. Approaches for increasing the therapeutic index of RIT are reviewed, which may further potentiate the efficacy and decrease the toxicity of RIT.

Targeted radiotherapy of multicell neuroblastoma spheroids with high specific activity [125I]meta-iodobenzylguanidine

PURPOSE

Iodine-125 induces cell death by a mechanism similar to that of high linear energy transfer (high-LET) radiation. This study investigates the cytotoxicity of high-specific-activity [125I]meta-iodobenzylguanidine (125I-mIBG) in human SK-N-MC neuroblastoma cells grown as three-dimensional multicellular spheroids.

MATERIALS AND METHODS

Spheroids were incubated with high-specific-activity 125I-mIBG (6 mCi/microg, 1000 times that of the conventional specific activity used for autoradiography). Cytotoxicity was assessed by fluorescence viability markers and confocal microscopy for intact spheroids, fluorescence-activated cell sorting and clonogenic assay, and clonogenic assays for dispersed whole spheroids. Distribution of radioactive mIBG was determined by quantitative light-microscope autoradiography of spheroid cryostat sections. Dose estimation was based on temporal knowledge of the retained radioactivity inside spheroids, and of the radiolabel's emission characteristics. Findings were compared with those of spheroids treated under the same conditions with 131I-mIBG, cold mIBG, and free iodine-125.

RESULTS

125I-mIBG exerted significant cell killing. Complete spheroids were eradicated when they were treated with 500 microCi of 125I-mIBG, while those treated with 500 microCi or 1000 microCi of 131I-mIBG were not. The observed difference in cytotoxicity between treatments with 125I- and 131I-mIBG could not be accounted for by the absorbed dose of spheroid alone. The peripheral, proliferating cell layer of the spheroids remained viable at the moderate radioactivity of 100 microCi for both isotopes. Cytotoxicity induced by 125I-mIBG was quantitatively comparable by the peripheral rim thickness to that of 131I-mIBG at the dose of 100 microCi. The peripheral rim thickness decreased most significantly in the first 17 hours after initial treatment. There was no statistical decrease in the rim thickness identified afterwards for the second, third, and fourth days of incubation.

CONCLUSION

The cytotoxic effect of high-specific-activity 125I-mIBG appears to be comparable to, if not more efficient than that of conventionally used 131I-mIBG at the same level of total radioactivity. 125I-mIBG may improve the therapeutic index over that of 131I-mIBG in the clinical management of metastatic neuroblastoma due to the short range of Auger electrons.

A model to estimate the dose to tumour following intracavity administration of radioimmunoconjugates to patients with malignant gliomas

Patients who have relapsed following primary treatment for malignant glioma and have undergone further surgical debulking have been treated with an anti-human neural cell adhesion molecule (NCAM) MoAb linked to either Iodine-131 or Yttrium-90. These reagents are introduced into the tumour resection cavity via an Ommaya reservoir. Pharmacokinetic and imaging studies indicate that the radioimmunoconjugate remains within the cavity for a protracted period of time. In this manuscript we develop a dosimetric model to predict the dose delivered to the rim of tissue surrounding the resection cavity. The model takes into account variables such as the diameter of the cavity and the degree of antibody binding which is achieved. Whilst the calculated doses to the wall of the cavity are relatively inaccurate due to our inability to measure factors such as diffusion and heterogeneity in antibody uptake, the model illustrates the potential benefits and pitfalls that can result from targeting the two radionuclides. It is hoped that as increasing interest is shown in this type of "liquid brachytherapy" other groups will find it useful to apply the model to allow comparisons to be made between our targeting strategy and those developed by other individuals.

Comparison of the biodistribution and the efficacy of monoclonal antibody 323/A3 labeled with either 131I or 186Re in human ovarian cancer xenografts

PURPOSE

The radionuclide 186Re has favorable physical characteristics for use in radioimmunotherapy, including the emission of beta-particles of a high-energy and a low-abundance of gamma-emission. The gamma-emission, in particular, is ideal for tumor imaging and poses less hazards to the patient and the medical personnel when compared with the gamma-emission of the widely used radionuclide 131I. In the present study, we determined whether 186Re-labeled monoclonal antibody 323/A3 may be better suited for the treatment of ovarian cancer than 131I-323/A3.

METHODS AND MATERIALS

We compared the biodistribution and the efficacy of 186Re- and 131I-labeled 323/A3 in nude mice bearing s.c. the human ovarian cancer xenografts FMa, OVCAR-3 and Ov.Pe. 186Re was conjugated to 323/A3 with the use of the S-benzoylmercaptoacetyltriglycine (S-benzoyl-MAG3) chelate.

RESULTS

A molar ratio of Re-MAG3:323/A3 of 3:1 did not affect the integrity and the pharmacokinetic behaviour of the MAb. The tumor uptake and the retention of 186Re- and 131I-labeled 323/A3 were comparable, but the cumulative absorbed radiation dose in the tumor delivered by 186Re-323/A3 was 1.3-fold higher than that of 131I-323/A3. When mice were treated with equivalent radionuclide doses, the tumor growth inhibition induced by 186Re-323/A3 was similar or slightly better when compared with the efficacy of 131I-323/A3. When mice were treated with radionuclide doses that were adjusted to obtain equal cumulative absorbed radiation doses in the tumor for both conjugates, 131I-323/A3 was slightly more effective in the inhibition of the growth of FMa and OVCAR-3 xenografts.

CONCLUSIONS

The favorable physical characteristics of 186Re as well as its efficacy when conjugated to a MAb indicate 186Re as an attractive radionuclide in radioimmunotherapy of ovarian cancer patients.

Radioimmunodetection with 111In-labeled monoclonal antibody Nd2 in patients with pancreatic cancer

This report summarizes results from an initial clinical evaluation of radioimmunodetection (RAID) in patients with pancreatic cancer using murine monoclonal antibody Nd2, directed against mucins from pancreatic cancer. Nd2 (2 mg) was labeled with 111In (2 mCi) and injected into 19 patients suspected of having pancreatic cancer. Planar scintigrams were taken 3 days post-infusion. As for final diagnoses after surgery, 14 cases were pancreatic cancer, and one case each was chronic pancreatitis, neurilemmoma, islet cell carcinoma, cholangioma, and apparent absence of suspected recurrent lesion of pancreatic cancer. Of 14 patients with pancreatic cancer, RAID was positive in 10 cases (71.4%). Cases other than pancreatic cancer were all negative, so the specificity was 100%. These results demonstrate that RAID using 111In-Nd2 can be useful in differentiating exocrine pancreatic cancer from benign conditions and other types of carcinomas in the pancreatoduodenal regions.

Reproducibility of operator processing for radiation dosimetry

Reproducibility of operator processing for radiation dose and biological half-life was assessed for radioimmunotherapy. Mean coefficient of variation for intra-operator consecutive processing and for inter-operator processing was less than 15% for all tissues. The mean coefficient of variation for intraoperator processing over 2 wk or inter-operator processing comparing an experienced and less experienced operator was generally greater, and particularly so for tumors. Satisfactory reproducibility was achievable using visual determination of regions of interests after 80 h of training.

The current status of targeted radiotherapy in clinical practice

Biologically targeted radiotherapy in clinical practice requires a molecule which has a relative specificity for tumour tissue--the missile--coupled to a radionuclide with appropriate physical characteristics--the warhead. When administered to a patient this combination should result in selective irradiation of the target tumour cells with relative sparing of normal tissues. Simple ions and small molecules which follow physiological pathways as either the natural substrates or analogues form the best examples of biological targeting. Clinically valuable results are seen with, for instance, iodine uptake by normal and malignant thyroid cells, incorporation of the calci-mimetic element strontium in areas of increased bone metabolism and accumulation of the catecholamine analogue meta-iodobenzylguanidine in neuroblastoma. The use of monoclonal antibodies as targeting vehicles has not proved to be a panacea, yet some patients with lymphoma, hepatoma and ovarian carcinoma have obtained benefit. Current clinical studies in targeted radiotherapy focus on the integration of radionuclide treatment with conventional treatments, and the optimization of such combined approaches. The development of modifications to offset the limitations inherent in the use of crude antibodies also offers an opportunity for improved clinical outcomes.

Radioimmunotherapy of solid cancers: A review

Depending on radionuclide characteristics, radioimmunotherapy (RIT) relies on radioactivity to destroy cells distant from immunotargeted cells. Therefore, even heterogeneous tumors (for antigen recognition) can be treated, because not all cells have to be targeted. Substantial complete response rates have been reported in patients with non-Hodgkin's lymphoma. Much more modest results have been reported for patients with bulky solid tumors, e.g. adenocarcinomas. The radiation doses delivered by targeting antibodies are generally too low to achieve major therapeutic responses. Dose escalation is limited by myelotoxicity, and higher doses need to be delivered to neoplasms less radiosensitive than lymphomas. Various trials for both systemic and regional RIT have been reported on. Intraperitoneal administration has been applied for colorectal and ovarian carcinomas. Our own results indicate that, e.g., intraperitoneal pseudomyxoma can be treated with RIT. Myelotoxicity can be reduced by anti-antibody-enhancement, 2- and 3-step strategies, bispecific monoclonal antibodies (MAbs), and extracorporeal immunoadsorption. The radionuclide has to be selected properly for each purpose; it can be a beta-emitter, e.g. I-131, Y-90, Re-188, Re-186, Lu-177 or Sm-153, an alpha-emitter At-211 or Bi-212 or an Auger-emitter, e.g. I-125, I-123. One major problem with RIT, besides slow penetration rate into tumor tissue and low tumor-to-normal tissue ratio, is the HAMA response, which can be partly avoided by the use of humanized MAbs and immunosuppression. However, RIT will be, because of all the recent developments, an important form of cancer management.

Monoclonal antibodies used in the detection and treatment of epithelial ovarian cancer

Conventional therapy for epithelial ovarian cancer, including aggressive cytoreductive surgery followed by combination chemotherapy regimens, has failed to reduce the number of deaths caused by this disease, which remains the most lethal of gynecologic malignancies. Monoclonal antibodies, which offer the promise of high selectivity for detection and therapy, may be targeted to tumor-associated antigens, growth factors, receptors, or oncogenes. They may be used alone as immunotherapeutic agents or conjugated to chemotherapeutic drugs, toxins, or radionuclides. Radioimmunoconjugates may also be used for preoperative or intraoperative tumor localization. The authors focused on the clinical utility, technical limitations, and potential of monoclonal antibodies in the detection and treatment of epithelial ovarian cancer with emphasis on radioimmunodetection and radioimmunotherapy.

Radioimmunotherapy of ovarian cancer

Despite the advances in the management of ovarian cancer, the disease remains the leading cause of death from gynecological malignancies. As it generally remains confined to the peritoneal cavity, ovarian cancer is an attractive target for radioimmunotherapy via the intraperitoneal route of administration. Several clinical trials have been carried out investigating radiolabeled monoclonal antibodies and the results seem promising, especially in patients with small-volume residual disease after conventional therapy. Intraperitoneal radioimmunotherapy has yet to prove itself as an important part of the treatment of ovarian cancer.

Characterization and biodistribution of a mouse/human chimeric antibody directed against pancreatic cancer mucin

BACKGROUND

Nd2 is a murine monoclonal antibody (MoAb) directed against purified mucins of the human pancreatic cancer cell line SW1990. The authors previously reported promising results with Nd2 for immunotargeting pancreatic cancer. However, murine MoAbs induce human anti-mouse antibodies (HAMAs), a serious problem for clinical use. Mouse/human chimeric antibodies may be less immunogenic and therefore reduce the incidence of HAMAs. In this study, the binding affinity, tumor specificity, biodistribution, and immunoimaging of chimeric Nd2 were evaluated.

METHODS

The affinity of chimeric Nd2 was evaluated by competition radioimmunoassay and Scatchard analysis using 125I-chimeric Nd2, 125I-murine Nd2, and SW1990 mucin. Immunoreactivity against pancreatic cancer tissues was examined histochemically by the avidin-biotin peroxidase complex method. The biodistribution of the MoAbs was examined in athymic nude mice bearing SW1990 xenografts that were administered intravenous 125I-labeled chimeric or murine Nd2. 111In-chimeric Nd2 was injected into the same xenograft models, and scintigrams were obtained on day 3.

RESULTS

Affinity analysis and immunohistochemical studies showed that chimeric Nd2 had the same affinity to SW1990 mucin and the same specificity for pancreas cancer tissues as murine Nd2. Intravenous administration of 125I-chimeric Nd2 resulted in a maximum tumor accumulation of 43% of the initial dose/gram of tumor, which was almost identical to the accumulation of 125I-murine Nd2. Distinct immunoscintigrams of tumors in nude mice were obtained with 111In-chimeric Nd2.

CONCLUSION

Chimeric Nd2 may have clinical potential in the radioimmunodetection and immunotherapy of pancreatic cancer.

Pharmacokinetics and dose estimates following intrathecal administration of 131I-monoclonal antibodies for the treatment of central nervous system malignancies

PURPOSE

Treatment of malignant disease in the central nervous system (CNS) with systemic radiolabeled monoclonal antibodies (MoAbs) is compromised by poor penetration into the cerebrospinal fluid (CSF), limited diffusion into solid tumors, and the generation of anti-mouse antibodies. To attempt to avoid these problems we have treated patients with diffuse neoplastic meningitis with radioimmunoconjugates injected directly into the intrathecal space.

METHODS AND MATERIALS

Tumor-specific MoAbs were conjugated to Iodine-131 (131I) (629-3331 MBq) by the Iodogen technique, and administered via an intraventricular reservoir. A clinical response rate of approximately 33% was achieved, with better results in more radiosensitive tumors. Here, we present detailed pharmacodynamic data on patients receiving this intracompartmental targeted therapy.

RESULTS

Elimination from the ventricular CSF appeared biphasic, with more rapid clearance occurring in the first 24 h. Radioimmunoconjugate entered the subarachnoid space and subsequently the vascular compartment. From this information, the areas under the effective activity curves for ventricular CSF, blood, and subarachnoid CSF were calculated to permit dosimetry. Critical organ doses were calculated using conventional medical internal radiation dose (MIRD) formalism. Where available, S-values were taken from standard tables. To calculate the doses to CSF, brain, and spinal cord, S-values were evaluated using the models described in the text.

CONCLUSION

A marked advantage could be demonstrated for the dose delivered to tumor cells within the CSF as compared to other neural elements.

A pilot study of the treatment of patients with recurrent malignant gliomas with intratumoral yttrium-90 radioimmunoconjugates

A pilot study of the treatment of patients with relapsed malignant gliomas with direct intratumoral injections of yttrium-90 (90Y) radioimmunoconjugates has been completed. Patients were recruited following maximal tumour resection, and received 1-3 injections of 90Y conjugated to a monoclonal antibody designated ERIC-1, which binds the neural cell-adhesion molecule. Data were collected to establish clinical toxicity, pharmacokinetics and radiation doses to the cavity wall and critical body organs. Twenty-three injections were completed in 15 patients, with a mean injected activity of 675 MBq (range 399-921). Early toxicity manifested as cerebral oedema and was readily controlled with dexamethasone. Delayed myelosuppression was observed but no intervention was required. Pharmacokinetic analysis confirmed prolonged retention of isotope in the cavity with correspondingly low activity in the bloodstream. These data were translated into estimates of absorbed radiation dose using the Medical Internal Radiation Dosimetry (MIRD) scheme. Mean doses, and dose rates, to the wall of the cavity, i.e. 'tumour,' were very high in comparison to normal tissue doses, with a further advantage if targeting was achieved.

Cancer therapy with radiolabeled antibodies. An overview

Considerable progress has been achieved during the last two decades in the use of radiolabeled tumor-selective monoclonal antibodies in the diagnosis and therapy of cancer. The concept of localizing the cytotoxic radionuclide to the cancer cell is an important supplement to conventional forms of radiotherapy. In theory the intimate contract between a radioactive antibody conjugate and a target cell enables the absorbed radiation dose to be concentrated at the site of abnormality with minimal injury to the normal surrounding cells and tissues. A variety of approaches and combinations of this strategy are now being pursued. This synopsis attempts to summarize the theoretical and biological basis for radio-immuno-therapy (RIT), and to review present efforts to further develop this treatment. Some of the critical issues in RIT are highlighted, and novel ways of improving the therapeutic indices of these radiopharmaceuticals are outlined. The attention is focused on the results obtained in clinical trials employing RIT. Encouraging complete response rates have recently been reported in patients with non-Hodgkin's lymphoma resistant to combination chemotherapy. More modest results have been obtained in patients with solid cancers. The promises and hurdles in creating tumor-selective radiolabeled antibodies for cancer therapy are discussed, and prospects for further improvements are presented.

Clinical pharmacology and tissue disposition studies of 131I-labeled anticolorectal carcinoma human monoclonal antibody LiCO 16.88

Antibody LiCO 16.88 is a human IgM recognizing a 30- to 45-kDa intracytoplasmic antigen present in human adenocarcinoma cells. An 8-mg sample of antibody labeled with 5 mCi 131I was co-administered i.v. with 120 mg (three patients), 240 mg (three patients) or 480 mg (four patients) unlabeled antibody as a 4-h infusion. The plasma half-life was 24 +/- 1.2 h and the immediate apparent volume of distribution was 5.2 +/- 0.2 l at the 28-mg dose level. The plasma half-lives and the cumulative urinary excretion of radiolabel did not seem to vary significantly with increasing doses of unlabeled antibody. However, both the volume of distribution and the clearance rate from plasma increased significantly with increasing antibody dose. Uptake of antibody into tumor tissues obtained during laparotomy 8-9 days after administration varied between 0.00002% ID/g and 0.00127% ID/g. In five of seven patients, the tumor content of antibody was higher than that in adjacent normal tissue. Tumor-to-normal tissue ratios ranged from 0.8 to 10 (mean = 3.8 +/- 1.0). In general, the higher radioactivity(cpm)/g tumor was confirmed by both immunoperoxidase and autoradiography. Antibody 16.88 localizes in tumors after administration and may be considered for use in radioimmunotherapy trials.

Will immunogenicity limit the use, efficacy, and future development of therapeutic monoclonal antibodies?

While monoclonal antibodies show promise for use in the treatment of a variety of disease states, including cancer, autoimmune disease, and allograft rejection, generation of anti-antibody responses still remains a problem. For example, 50% of the patients who receive OKT3 produce blocking antibodies that interfere with its binding to T cells, thus decreasing the therapeutic effect (51). HAMA responses have also interfered with tumor imaging (39,40) and radioimmunotherapy (56). The generation of an anti-antibody response is dependent on many factors. These include the dose of antibody, the number of injections of antibody, the immunogenicity of the antibody, the form of the antibody, and the immunocompetence of the recipient. Predictably, both the number of injections of antibody and the dosage are influential in the generation of an anti-antibody response. It is apparent that human antibodies, chimeric antibodies, and mouse Fab fragments are much less likely to induce anti-antibody responses than intact mouse monoclonal antibodies or mouse F(ab')2 fragments when one injection is administered. Injections of human or chimeric antibodies appears to reduce immunogenicity, but the probability that anti-antibody responses can still be induced on multiple injections must be considered and appropriately evaluated. Several areas demand extensive investigation to enhance the clinical utility of monoclonal antibodies. First, results of thorough clinical trials with human or chimeric antibodies need to be evaluated for the induction of anti-antibodies after multiple injections of antibodies. Second, less immunogenic forms of antibodies (Fab, Fv) need to be studied for their clinical efficacies and for their abilities to induce anti-antibody responses.

Overview of radiation myelotoxicity secondary to radioimmunotherapy using 131I-Lym-1 as a model

The radiation dose-limiting toxicity from radioimmunotherapy has been myelotoxicity in the absence of bone marrow reconstitution (transplantation). Myelotoxicity can be assessed directly by biopsy examination of the bone marrow and indirectly by peripheral blood counts. In patients with B-cell malignancies, thrombocytopenia has been the initial and most severe manifestation of 131I-Lym-1 radiation toxicity from treatment. Manifestations of myelotoxicity varied greatly among the patients and from one treatment dose to another in the same patient, suggesting that additional factors were present. There was an increased likelihood of Grade 3-4 hematopoietic toxicity after 131I-Lym-1 treatment if the patient had peripheral blood cell abnormalities before undergoing 131I-Lym-1 treatment. Fractionation of the total 131I-Lym-1 dose was associated with less toxicity. In many patients, myelotoxicity could not be explained by marrow radiation dose (0.36 +/- 0.13 rads per administered mCi) from 131I-Lym-1 in the blood and body alone. Bone marrow examination and 131I-Lym-1 imaging usually provided evidence for additional marrow radiation from 131I-Lym-1-targeting of marrow malignancy and also for residual toxic effects from prior treatment in these patients. Immunohistologic and imaging examination of the bone marrow performed with the intended treatment antibody allowed assessment of extent of marrow malignancy and prediction of degree of myelotoxicity from subsequent treatment. Treatment programs (and protocols) for radioimmunotherapy should incorporate these methods into the decision process. Larger amounts of 131I-Lym-1 can be used in patients selected to have relatively normal peripheral blood cell counts and normocellular bone marrows uninvolved by the malignancy. These observations appear to be relevant to the maximum tolerated dose in radioimmunotherapy for other malignancies as well.

Recent developments in radioimmunotherapy

With the advent of monoclonal antibody techniques, there has been renewed interest in RIT as a treatment modality in patients with a variety of tumour types. There has been a considerable research effort to increase understanding of the scientific basis of such therapy at all levels. Antibody, chelator and radioisotope factors are all the subject of research aimed at producing a potent effector system capable of maximal target cell kill with acceptable normal tissue toxicity. Improved knowledge of the host and tumour factors which limit access to the target cell offers the possibility of optimizing targeting and increasing the therapeutic index. Target cell factors that influence response to low dose rate RIT have been elucidated and provide an opportunity to integrate the treatment modality into radical therapy regimens. A number of Phase I and II trials have now been performed in various tumour types. The results have been promising but, as yet, the prospect of radical RIT remains a research goal. Before it can be achieved it will be necessary to improve specific tumour cell targeting and to increase both the initial dose rates and the total dose delivered to tumour deposits. Until such time, it is likely that RIT will be incorporated into multimodality protocols to deliver a moderate (10-20 Gy) tumour boost, or in an adjuvant setting in patients with minimal residual disease.

Complete ablation of small squamous cell carcinoma xenografts with 186Re-labeled monoclonal antibody E48

In previous studies we have shown that in mice bearing head and neck squamous cell carcinoma (HNSCC) xenografts, radioimmunotherapy (RIT) with 186Re-labeled MAb E48 resulted in complete regressions in one-third of the tumors (followup > 150 d). MAb E48 was labeled with 186Re following a novel labeling procedure developed at our institute. The injected dose was 600 microCi, which was the maximum tolerated dose (MTD; < 15% wt loss) in these studies. The mean size of the tumors was 140 +/- 60 mm3. To investigate whether the therapeutic efficacy of RIT in our xenograft model would be improved when treating smaller xenografts, mice bearing 2 HNSCC xenografts with a vol of 75 +/- 17 mm3 (number of mice, n = 6; number of tumors, t = 12) were treated with 600 microCi of 186Re-labeled MAb E48 IgG. All tumors completely regressed and did not regrow during followup (> 150 d). In all mice, weight loss did not exceed 10%. To obtain biodistribution data, mice bearing two xenografts with a vol of 58 +/- 31 mm3 were injected with 100 microCi of 186Re-labeled MAb E48 IgG. The maximum uptake in blood was 26.4% injected dose/g (%ID.g-1) at 2 h pi and was 53.1%ID.g-1 in the tumor at d 7 pi. In normal tissues, no nonspecific accumulation was observed. Based on these biodistribution data, the absorbed cumulative radiation dose was calculated. The accumulated dose in blood and tumor was 2004 cGy and 8580 cGy, respectively. In other tissues, the dose was less than 8.1% of the dose delivered to tumor.(ABSTRACT TRUNCATED AT 250 WORDS)

Construction, characterisation and kinetics of a single chain antibody recognising the tumour associated antigen placental alkaline phosphatase

The murine monoclonal antibody H17E2 recognises placental alkaline phosphatase (PLAP), an antigen present in the human term placenta and also expressed by many tumours. The antibody is of value in both immunoscintigraphy and radioimmunotherapy in testicular and ovarian cancer. The small size of genetically engineered single chain antibodies (SCAs) should give diagnostic and therapeutic advantages of improved tumour penetration and increased blood clearance compared to IgG. Employing recombinant DNA techniques a SCA based on H17E2 has been expressed in Escherichia coli and has been shown to bind placental alkaline phosphatase specifically. When administered to nude mice bearing human tumour xenografts, the H17E2 SCA effectively localised to tumour whilst a co-administered non-specific SCA did not. H17E2 SCA achieves tumour: blood ratios that are superior to those achieved with whole IgG, probably owing to its rapid blood clearance. We conclude that the H17E2 SCA is suitable for further investigation as an agent for clinical imaging and therapy. Additionally, the SCA can also be used for the construction of antibody based fusion proteins to target other effector functions to tumour cells.

Adjuvant therapy of ovarian cancer with radioactive monoclonal antibody

Fifty-two patients with epithelial ovarian cancer were treated with yttrium-90-labelled monoclonal antibody HMFG1 administered intraperitoneally following conventional surgery and chemotherapy as part of an extended phase I-II trial. The treatment was well tolerated and the only significant toxicity observed was reversible myelosuppression as previously described. Following conventional surgery and chemotherapy, 21 out of the 52 patients had no evidence of residual disease and were regarded as receiving treatment in an adjuvant setting. To date, two of these patients have died of their disease (follow-up 3-62 months, median follow-up 35 months). This extended phase I-II study suggests that patients with advanced ovarian cancer who achieve a complete remission following conventional therapy may benefit from further treatment with intraperitoneal radioactive monoclonal antibody.