Selection of reagents for human radioimmunotherapy

Radioimmunotherapy of refractory or relapsed Hodgkin's lymphoma with 90Y-labelled antiferritin antibody

The aim of this study was to evaluate the safety and efficacy of radiolabelled rabbit polyclonal antiferritin antibody in relapsed or refractory Hodgkin's lymphoma. The protocol included a first intravenous injection of In-labelled antiferritin antibody, followed by immunoscintigraphy at 4, 48 and 72 h, and an intravenous injection of Y-labelled antiferritin antibody in the case of tumour targeting. Ten patients were included in the study: median number of chemotherapy regimens: 3; number of autografted patients: 8; number of previously irradiated patients: 9; response to last chemotherapy: six partial response and four progressions. All immunoscintigraphies showed tumour targeting. Nine patients were treated, as the last patient died from progressive Hodgkin's lymphoma before therapeutic injection. Median injected activity was 12 MBq/kg (0.32 mCi/kg). Among the 10 patients who were included in the study, one complete response and six partial responses were observed (overall response rate 70%) with a median duration of response of 8 months (range: 7-12 months). Toxicity was mainly haematological, with grade 1 or 2 neutropenia and anaemia, and grade 2 and 3 thrombocytopenia. The pharmacokinetic study showed that the half-lives of In and Y were almost identical. These results confirm those previously reported and show the therapeutic potential of rabbit polyclonal antiferritin antibody in relapsed or refractory Hodgkin's lymphoma. They therefore justify further multicentre prospective trials.

Comparative animal models for the study of lymphohematopoietic tumors: strengths and limitations of present approaches

The lymphomas probably represent the most complex and heterogenous set of malignancies known to cancer medicine. Underneath the single term lymphoma exist some of the fastest growing cancers known to science (i.e Burkitt's and lymphoblastic lymphoma), as well as some of the slowest growing (i.e. small lymphocytic lymphoma [SLL] and follicular lymphoma). It is this very biology that can dictate the selection of drugs and treatment approaches for managing these patients, strategies that can range from very aggressive combination chemotherapy administered in an intensive care unit (for example, patients with Burkitt's lymphoma), to watch and wait approaches that may go on for years in patients with SLL. This impressive spectrum of biology emerges from a relatively restricted number of molecular defects. The importance of these different molecular defects is of course greatly influenced by the intrinsic biology that defines the lymphocyte at its different stages of differentiation and maturation. It is precisely this molecular understanding that is beginning to form the basis for a new approach to thinking about lymphoma, and novel approaches to its management. Unfortunately, while our understanding of human lymphoma has blossomed, our ability to generate appropriate animal models reflective of this biology has not. Most preclinical models of these diseases still rely upon sub-cutaneous xenograft models of only the most aggressive lymphomas like Burkitt's lymphoma. While these models clearly serve an important role in understanding biology, and perhaps more importantly, in identifying promising new drugs for these diseases, they fall short in truly representing the broader, more heterogenous biology found in patients. Clearly, depending upon the questions being posed, or the types of drugs being studied, the best model to employ may vary from situation to situation. In this article, we will review the numerous complexities associated with various animal models of lymphoma, and will try to explore several alternative models which might serve as better in vivo.

The experimental study on the radioimmunotherapy of the nasopharyngeal carcinoma overexpressing HER2/neu in nude mice model with intratumoral injection of 188Re-herceptin

The therapeutic efficacy of radioimmunotherapy (RIT) of 188Re-labeled herceptin, which is a humanized anti-p185-HER2/neu monoclonal antibody (mAb), was studied. The nude mice bearing nasopharyngeal carcinoma (NPC) expressing HER2/neu protooncogene were injected with 188Re-herceptin intratumorally and intravenously. The biodistribution was observed on day 2 (n = 3). The tumor growth inhibition rate (IR) was determined by measurement of tumor volume. In the intratumorally treated mice, tumor uptake of 188Re-herceptin was significantly greater than in the intravenously treated mice [11.53% injected dose (ID)/g vs. 2.79% ID/g at 48 h], and lower normal organ uptake was also seen. The intratumoral administration of 188Re-herceptin caused greater inhibition of tumor growth at the fourth week as compared to the intravenous administration. It is concluded that intratumoral administration of 188Re-herceptin makes high level of radioactivity retained in tumor with significantly lower radioactivity retained in normal tissues, and provides a more effective regional therapy for NPC overexpressing HER2/neu.

Antibody therapy of non-Hodgkin's B-cell lymphoma

Engineering antibodies with reduced immunogenicity and enhanced effector functions, and selecting antigen targets with the appropriate specificity, density, and/or functionality, have contributed to the recent clinical successes in using unconjugated "naked" antibody therapies of B-cell lymphoma (rituximab) and breast carcinoma (Herceptin). The non-overlapping toxicities of naked antibodies and chemotherapy, together with their potential synergy, which is based on unique and complementary mechanisms of action, have contributed to the creation of new standards of care in cancer therapy and management. Clinical trial results supporting these concepts are presented. Furthermore, the exquisite specificity of antibodies renders them ideal vehicles for selective delivery of toxic payloads such as drugs or radionuclides. Although successful in therapy of hematological cancers (Zevalin, Mylotarg), the broader application of these technologies to carcinomas still remains to be proven in clinical testing. Engineering of antibody constructs with optimal blood clearance and tumor-targeting kinetics, and selecting the radionuclide that may deliver sufficient radiation energy to kill the more radio-resistant carcinomas, are discussed. With the advent of genomics and proteomics, new membrane-associated tumor antigens are being discovered and will provide novel targets for future antibody therapy of cancer.

Distribution of monoclonal antiferritin antibody in Kaposi's sarcoma, Hodgkin's disease, and hepatocellular carcinoma

The immunotherapeutic treatment of cancers using antibodies (naked or conjugated to a drug, toxin, or radionuclide) relies upon the preferential expression of a targeted antigen on the cancer cell compared to normal tissues. Polyclonal antiferritin antisera have shown selective distribution and therapeutic efficacy when radiolabeled in Hodgkin's disease and hepatoma. In this immunohistochemical study, we investigated the distribution of ferritin in tumors from 6 patients with Kaposi's sarcoma, 12 patients with Hodkgin's disease, and 9 patients with hepatoma, as well as in selected normal tissues. We found that the monoclonal antiferritin antibody binds primarily to histiocytes in samples from Kaposi's sarcoma and Hodgkin's disease. One hepatocellular carcinoma showed diffuse cytoplasmic staining with ferritin. Deposition of the monoclonal antibody was not detectable in the remaining hepatocellular carcinoma samples.

A review of the intravenous administration of radiolabeled immunoglobulin G to cancer patients. High or low protein dose?

This retrospective analysis of preclinical and clinical radiolabeled immunoglobulin studies focuses on three well-known observations: (1) IV tumor reactive IgG provides higher response rates in patients with hematological malignancies than in patients with solid tumors. (2) Patients with CD20 positive B cell lymphoma require a high IV IgG protein dose for effective tumor targeting. (3) Most patients experience high uptake of IV administered radiolabeled IgG in normal liver. This review supports the following new hypotheses: (1) The blood-tumor barrier in most solid tumors is higher than in most hematological malignancies. (2) The blood-tumor barrier in CD20 positive B cell lymphomas is lowered by the IV administration of high doses [> 100 mg] of anti-CD20 IgG, presumably due to IgG induced intra-tumoral production of vaso-active biological response modifiers. (3) The blood-tumor barrier is low in Hodgkin's disease, presumably due to the continuous and innate production of biological response modifiers in tissues containing Hodgkin's disease. (4) The uptake of tumor reactive IgG in the normal liver is controlled by the Fc portion of the IgG. The radioimmunoconjugate is not catabolized in the liver. This appears to indicate that the F(c) portion of the IgG binds to the MHC class I like, F(c)gammaRn receptors in liver endothelium and hepatocytes and not to F(c)gamma RI, RII or RIII receptors The new hypotheses require verification and can be instrumental in the design of new more effective clinical RIT studies.

Experimental radioimmunotherapy

Experimental radioimmunotherapy (RIT) studies in animal models have contributed significantly to the design of clinical RIT protocols, although the results have not always been directly translated. Reviewed in this article are current areas of active research in experimental RIT to increase the therapeutic ratio that are likely to have a significant impact on the design of future clinical studies. Approaches for increasing the therapeutic efficacy of RIT include the development of new targeting molecules (genetically engineered monoclonal antibodies, antibody fragments, single-chain antibodies, diabodies and minibodies, fusion toxins, or peptides); improved labeling chemistry; novel radionuclide use and fractionation; locoregional administration; pretargeting; use of biological response modifiers or gene transfer techniques to increase target receptor expression; bone marrow transplantation; and combined modality therapy with external-beam radiation therapy, chemotherapy, or gene therapy. Further research with these new experimental approaches in preclinical animal models is necessary to contribute to advances in the treatment of cancer patients using radiolabeled antibodies and peptides.

Proposal for translational analysis and development of clinical radiolabeled immunoglobulin therapy

BACKGROUND AND PURPOSE

Radiolabeled immunoglobulin therapy (RIT) can be a selective, effective, low-toxicity outpatient cancer therapy. A consensus on the best approach for the preclinical and clinical development of RIT reagents needs to be developed. We report the M.D. Anderson Cancer Center prior experience in translating RIT from laboratory to clinic for the treatment of Hodgkin's disease and propose a flow diagram for the development of RIT for other malignancies.

MATERIAL AND METHODS

Three different animal models are described: nude mice bearing human tumor xenografts, normal beagle dogs, and normal rhesus monkeys. We produced and purified antibodies and prepared chelate-immunoconjugates reactive with six different human tumor-associated antigens. The Igs used were derived from rabbits, mice, and humans (human-derived RIT reagents being less immunogenic in human patients). Eighty patients with refractory Hodgkin's disease were treated with radiolabeled antiferritin.

RESULTS

We recommend a two-injection scheme using, (1) an indium-111-labeled radioimmunoconjugate for diagnosis, pharmacokinetic studies, and dosimetry, and (2) a yttrium-90-labeled radioimmunoconjugate for therapy. The animal models provide useful data on tumor targeting, radiotoxicology, and undesirable biodistributions. A 70% response rate is obtained in patients with advanced recurrent Hodgkin's disease. More extensive preclinical testing allows for safer and more effective clinical RIT studies.

CONCLUSIONS

We recommend, (1) preclinical optimization of chelation chemistry, Ig size, Ig origin, route of administration, and fractionation, (2) new clinical Phase I-III studies more appropriate for RIT development than the classical Phase I-III studies used for the development of chemotherapeutic agents, and (3) more extensive preclinical testing of RIT reagents.

Hodgkin's disease. Future treatment strategies: fact or fiction?

Many new approaches involving biological agents have given promising results in experimental HD models. Clinical trials with immunotoxins, IL-2, Bi-Moabs or radioimmunoconjugates have demonstrated some clinical efficacy in patients with advanced refractory HD. Although it looks very unlikely to cure patients with larger tumour masses by either of these approaches, it might be feasible to treat bulky disease by conventional therapy first and then administer biological drugs to kill residual H-RS cells. Future phase-III trials will have to prove a possible superior effect of this combined immuno-/chemotherapy. In the meantime, the search for the most promising approach continues.

Preclinical evaluation and PET imaging of 18F-labeled Mel-14 F(ab')2 fragment in normal dogs

The F(ab')2 fragment of monoclonal antibody Mel-14, reactive with human melanomas and gliomas, was labeled with 18F using two acylation agents, N-succinimidyl 8-[(4'-[18F]fluorobenzyl)amino]suberate (SFBS) and N-succinimidyl 4-[18F]fluorobenzoate (SFB). The immunoreactivity and affinity for Mel-14 F(ab')2 labeled using the two methods were similar. As a prelude to human clinical evaluation, PET imaging, tissue distribution and pharmacokinetic measurements were performed in two groups of normal foxhounds. Similar in vivo behavior was seen for Mel-14 F(ab')2 labeled using SFBS and SFB. Radiation dosimetry calculations suggest that a 10 mCi dose could be used for this F(ab')2 fragment labeled using either acylation agent.

Pharmacokinetics and toxicity of an yttrium-90-CITC-DTPA-HMFG1 radioimmunoconjugate for intraperitoneal radioimmunotherapy of ovarian cancer

BACKGROUND

The intracavitary route for the administration of monoclonal antibodies is used in a variety of locally spreading cancers. The authors have been treating patients with ovarian cancer in Phase I and II studies assessing toxicity and response to improved radioimmunoconjugates.

METHODS

Nineteen patients, 34-65 years of age, were treated with a new radioimmunoconjugate, 90Y-CITC-DTPA-HMFG1, instilled in the peritoneal cavity after second-look laparoscopy. Activity was increased in a stepwise fashion.

RESULTS

Following the intraperitoneal administration of 90Y-CITC-DTPA-HMFG1, levels of the radioimmunoconjugate in the blood increased, reaching a peak of about 30% of injected activity at around 54 hours posttreatment. Approximately 18% of the radiolabel was excreted in the urine within 96 hours. Bone-marrow toxicity was the dose-limiting factor. Grade III platelet and granulocyte toxicity was observed at 19.3 mCi/m2. A type III immunologic response was observed in a number of patients.

CONCLUSIONS

A dose of 18.5 mCi/m2 for subsequent treatments is recommended, based on a linear correlation of activity dose-to-body surface area. The clinical profile of a mild to moderate hypersensitivity syndrome is presented and hypotheses regarding its etiology are suggested.

Cytokine intervention permits dose escalation of radioantibody. An analysis of myelostimulation by bolus versus continuous infusion of IL-1/GM-CSF

BACKGROUND

The authors recently reported that a 12-day schedule (beginning 3 days before radioantibody treatment) of twice-daily dosing of rH-IL-1 (1 x 10(3) U/dose) and rM-GM-CSF (0.5 micrograms/dose) can reduce the magnitude and duration of radioantibody-induced myelosuppression, thereby permitting a 25-30% increase in the dose of radioantibody that can be administered without the dose proving lethal. In an effort to further reduce toxicity and escalate the tolerated dose, the authors altered the method of administration of cytokines from daily bolus dosing to continuous infusion by implantable osmotic pumps.

METHODS

A control group of mice was compared to five groups of mice that either did or did not receive a 340 microCi dose of radioantibody, and received no cytokines, cytokines by bolus dosing, or cytokines by continuous infusion. For 4 weeks, peripheral white blood cell and thrombocyte counts and thymus and spleen weights were taken, marrow cell number was monitored, and marrow colony-forming unit activity was evaluated weekly in the untreated control mice and the treated mice.

RESULTS

These studies demonstrated that after a dose of radioantibody, continuous dosing of cytokines resulted in higher white blood cell (WBC) and platelet values than if bolus delivery was used (day 7, WBC: 110% vs. 59%; day 14, WBC: 85% vs. 62%; day 21, WBC: 98% vs. 42%; day 7, platelets: 122% vs. 51%; day 14, platelets: 159% vs. 72%; day 21, platelets: 239% vs. 171%). A comparison of bolus versus continuous dosing in the absence of radioantibody indicated that spleen weight increased by 40-60% after continuous infusion of cytokines and by 20-25% after bolus dosing. The 20-30% decrease in thymus weight was similar with both dosing regimens. Colony-forming units (CFUs) in marrow increased from 30-35 in untreated mice to 50-55 in mice given cytokines by bolus injection, and to 150-180 in mice given continuous infusion of cytokines. Spleen CFUs exhibited an insignificant increase after bolus dosing of cytokines but increased almost fourfold after continuous dosing. Peak stimulation of marrow and spleen CFUs occurred 28 days after initiation of cytokine administration (2 weeks after cytokines administration was stopped). The probability of survival for 6 weeks after further dose escalation to 360 microCi I-131-MN-14 immunoglobulin G was 16.4% +/- 8.6% after bolus dosing and 58.1% +/- 11.3% after continuous infusion of cytokines.

CONCLUSIONS

Although continuous infusion of cytokines proved to be a better method of reducing hematopoietic toxicity, further dose escalation of radioimmunotherapy using the "pump" method of cytokine delivery was not possible. Cytokine intervention by either mode of delivery permits a 25% dose intensification without the dose becoming lethal. Further escalation is not feasible, possibly because of other end organ toxicity.

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.

Preclinical evaluation of intravenously administered 111In- and 90Y-labeled B72.3 immunoconjugate (GYK-DTPA) in beagle dogs

B72.3, a monoclonal antibody with reactivity against human adenocarcinomas was obtained from the Cytogen Corporation in the form of an immunoconjugate coupled with linker-chelator GYK-DTPA by using proprietary carbohydrate directed site specific chemistry. The immunoconjugate was radiolabeled with indium-111 or yttrium-90. A preclinical analysis was performed in 10 normal beagle dogs. The pharmacokinetics of intravenously administered indium- and yttrium-labeled immunoconjugates were compared serially in blood, bone marrow and urine samples. Compared to 90Y less of the 111In label ended up in urine and more was found in blood and bone marrow. Indium-labeled B72.3 GYK-DTPA had relatively higher uptake in most glandular tissues than 111In-labeled antiferritin immunoconjugate. Bone marrow toxicity was the dose limiting side effect after intravenous infusion of 90Y-labeled B72.3 GYK-DTPA. Toxicity was also observed in the liver but not in other organ systems. Recently other investigators obtained similar results with these immunoconjugates in human patients. A preclinical pharmacokinetic analysis of radioimmunoconjugates in beagle dogs provided useful information regarding bone marrow toxicity, liver toxicity and in vivo instability of the immunoconjugate. Data suggest that for future trials in human patients, a more stable chelated immunoconjugate for yttrium is needed to achieve less liver uptake and a better correlation with the 111In-labeled product than the 90Y-labeled B72.3 GYK-DTPA used in this investigation.

Fractionated intravenous administration of 90Y-labeled B72.3 GYK-DTPA immunoconjugate in beagle dogs

B72.3, a monoclonal antibody with reactivity against human adenocarcinomas, was coupled with linker-chelator GYK-DTPA using carbohydrate mediated conjugation chemistry and radiolabeled with yttrium-90. Single and double intravenous injections of radioimmunoconjugate were compared for acute and late normal tissue toxicity in 15 beagle dogs. The second injection was given 4 or 8 days after the first. Pharmacokinetics of the radioimmunoconjugate in blood, bone marrow and urine were similar for first and second injections. Only bone marrow (acute) and liver (late) toxicity were observed. Both liver and bone marrow toxicity were decreased by fractionation of the injections. After double injections, the total equitoxic dose was 15 and 60% higher for bone marrow and liver toxicity, respectively. The mechanisms of normal tissue protection offered by fractionated radioimmunoglobulin therapy (RIT) remain to be defined. Fractionated RIT will have a better therapeutic ratio than single injection RIT, if antitumor effects appear to be less susceptible to fractionation than normal tissues.

Sensitization processes in human tumor cells during protracted irradiation: possible exploitation in the clinic

Recent studies documenting the response of several human tumor cell lines to protracted, continuous irradiation and to acutely delivered radiation, suggest that tumor control may be enhanced with a tumor therapy combining external beam fractionated therapy and protracted irradiation from radiolabeled antibodies. We have evaluated the cytotoxic effect of continuous, protracted irradiation (0.005 Gy/hr to 0.50 Gy/hr) and acutely delivered high-dose-rate irradiation (1.0 Gy/min) on monolayer cultures of human tumor cell lines. Colony formation in these studies was analyzed by the seven-parameter simulation model of Dillehay. Additionally, for some cell lines, cultures were challenged during irradiation with an acute dose of 2.5, 5.0, 7.5 or 10.0 Gy at high-dose-rate. Results from these various studies indicate an altered cellular radiosensitivity occurs for some cell lines during protracted irradiation. At least two mechanisms have been identified that underlie this altered radiosensitivity. One mechanism, G2B, associated with redistribution within the cell cycle, has been previously described by Mitchell and others, and is associated with the phenomenon termed "the inverse dose-rate effect". The other mechanism is only observable following a challenge by acute high-dose-rate irradiation. We have termed this phenomenon "protracted-exposure-sensitization." The characteristics of these two mechanisms are discussed from the perspective of clinical therapeutic exploitation of combined external beam fractionated therapy and radiolabeled immunoglobulin therapy.