Antibody guided irradiation of brain glioma by arterial infusion of radioactive monoclonal antibody against epidermal growth factor receptor and blood group A antigen

Targeted intraarterial anti-VEGF therapy for medically refractory radiation necrosis in the brain

Radiation necrosis (RN) is a serious complication that can occur in up to 10% of brain radiotherapy cases, with the incidence dependent on both dose and brain location. Available medical treatment for RN includes steroids, vitamin E, pentoxifylline, and hyperbaric oxygen. In a significant number of patients, however, RN is medically refractory and the patients experience progressive neurological decline, disabling headaches, and decreased quality of life. Vascular endothelial growth factor (VEGF) is a known mediator of cerebral edema in RN. Recent reports have shown successful treatment of RN with intravenous bevacizumab, a monoclonal antibody for VEGF. Bevacizumab, however, is associated with significant systemic complications including sinus thrombosis, pulmonary embolus, gastrointestinal tract perforation, wound dehiscence, and severe hypertension. Using lower drug doses may decrease systemic exposure and reduce complication rates. By using an intraarterial route for drug administration following blood-brain barrier disruption (BBBD), the authors aim to lower the bevacizumab dose while increasing target delivery. In the present report, the authors present the cases of 2 pediatric patients with cerebral arteriovenous malformations, who presented with medically intractable RN following stereotactic radiosurgery. They received a single intraarterial infusion of 2.5 mg/kg bevacizumab after hyperosmotic BBBD. At mean follow-up duration of 8.5 months, the patients had significant and durable clinical and radiographic response. Both patients experienced resolution of their previously intractable headaches and reversal of cushingoid features as they were successfully weaned off steroids. One of the patients regained significant motor strength. There was an associated greater than 70% reduction in cerebral edema. Intraarterial administration of a single low dose of bevacizumab after BBBD was safe and resulted in durable clinical and radiographic improvements at concentrations well below those required for the typical systemic intravenous route. Advantages over the intravenous route may include higher concentration of drug delivery to the affected brain, decreased systemic toxicity, and a significantly lower cost.

Construction of an immunotoxin, D2C7-(scdsFv)-PE38KDEL, targeting EGFRwt and EGFRvIII for brain tumor therapy

PURPOSE

The EGF receptor gene (EGFR) is most frequently amplified and overexpressed, along with its deletion mutant, EGFRvIII, in glioblastoma. We tested the preclinical efficacy of the recombinant immunotoxin, D2C7-(scdsFv)-PE38KDEL, which is reactive with a 55-amino acid (AA) region present in the extracellular domain of both EGFRwt (583-637 AAs) and EGFRvIII (292-346 AAs) proteins.

EXPERIMENTAL DESIGN

The binding affinity and specificity of D2C7-(scdsFv)-PE38KDEL for EGFRwt and EGFRvIII were measured by surface-plasmon resonance and flow cytometry. In vitro cytotoxicity of D2C7-(scdsFv)-PE38KDEL was measured by inhibition of protein synthesis in human EGFRwt-transfected NR6 (NR6W), human EGFRvIII-transfected NR6 (NR6M), EGFRwt-overexpressing A431-epidermoid-carcinoma, and glioblastoma xenograft cells (43, D08-0493MG, D2159MG, and D270MG). In vivo antitumor efficacy of D2C7-(scdsFv)-PE38KDEL was evaluated using 43, NR6M, and D270MG orthotopic tumor models.

RESULTS

The KD of D2C7-(scdsFv)-PE38KDEL for EGFRwt and EGFRvIII was 1.6×10(-9) mol/L and 1.3×10(-9) mol/L, respectively. Flow cytometry with NR6W and NR6M cells confirmed the specificity of D2C7-(scdsFv)-PE38KDEL for EGFRwt and EGFRvIII. The D2C7-(scdsFv)-PE38KDEL IC50 was 0.18 to 2.5 ng/mL on cells expressing EGFRwt (NR6W, A431, 43, and D08-0493MG). The D2C7-(scdsFv)-PE38KDEL IC50 was approximately 0.25 ng/mL on EGFRvIII-expressing cells (NR6M) and on EGFRwt- and EGFRvIII-expressing glioblastoma xenograft cells (D2159MG and D270MG). Significantly, in intracranial tumor models of 43, NR6M, and D270MG, treatment with D2C7-(scdsFv)-PE38KDEL by convection-enhanced delivery prolonged survival by 310% (P=0.006), 28% (P=0.002), and 166% (P=0.001), respectively.

CONCLUSIONS

In preclinical studies, the D2C7-(scdsFv)-PE38KDEL immunotoxin exhibited significant potential for treating brain tumors expressing EGFRwt, EGFRvIII, or both.

Radioimmunotargeting of malignant glioma by monoclonal antibody D2C7 reactive against both wild-type and variant III mutant epidermal growth factor receptors

INTRODUCTION

Malignant glioma remains a significant therapeutic challenge, and immunotherapeutics might be a beneficial approach for these patients. A monoclonal antibody (MAb) specific for multiple molecular targets could expand the treatable patient population and the fraction of tumor cells targeted, with potentially increased efficacy. This motivated the generation of MAb D2C7, which recognizes both wild-type epidermal growth factor receptor (EGFRwt) and a tumor-specific mutant, EGFRvIII.

METHODS

D2C7 binding affinity was determined by surface plasmon resonance and its specificity characterized through comparison to EGFRwt-specific EGFR.1 and EGFRvIII-specific L8A4 MAbs by flow cytometry and immunohistochemical analysis. The three MAbs were labeled with (125)I or (131)I using Iodogen, and paired-label internalization assays and biodistribution experiments in athymic mice with human tumor xenografts were performed.

RESULTS

The affinity of D2C7 for EGFRwt and EGFRvIII was 5.2×10(9) M(-1) and 3.6×10(9) M(-1), and cell-surface reactivity with both receptors was documented by flow cytometry. Immunohistochemical analyses revealed D2C7 reactivity with malignant glioma tissue from 90 of 101 patients. Internalization assays performed on EGFRwt-expressing WTT cells and EGFRvIII-expressing NR6M cells indicated a threefold lower degradation of (125)I-labeled D2C7 compared with (131)I-labeled EGFR.1. Uptake of (125)I-labeled D2C7 in NR6M xenografts (52.45±13.97 %ID g(-1) on Day 3) was more than twice that of (131)I-labeled L8A4; a threefold to fivefold tumor delivery advantage was seen when compared to (131)I-labeled EGFR.1 in mice with WTT xenografts.

CONCLUSIONS

These results suggest that D2C7 warrants further evaluation for the development of MAb-based therapeutics against cancers expressing EGFRwt and EGFRvIII.

Planning for intracavitary anti-EGFR radionuclide therapy of gliomas. Literature review and data on EGFR expression

Targeting with radionuclide labelled substances that bind specifically to the epidermal growth factor receptor, EGFR, is considered for intracavitary therapy of EGFR-positive glioblastoma multiforme, GBM. Relevant literature is reviewed and examples of EGFR expression in GBM are given. The therapeutical efforts made so far using intracavitary anti-tenascin radionuclide therapy of GBM have given limited effects, probably due to low radiation doses to the migrating glioma cells in the brain. Low radiation doses might be due to limited penetration of the targeting agents or heterogeneity in the expression of the target structure. In this article we focus on the possibilities to target EGFR on the tumour cells instead of an extracellular matrix component. There seems to be a lack of knowledge on the degree of intratumoral variation of EGFR expression in GBM, although the expression seemed rather homogeneous over large areas in most of the examples (n=16) presented from our laboratory. The observed homogeneity was surprising considering the genomic instability and heterogeneity that generally characterises highly malignant tumours. However, overexpression of EGFR is, at least in primary GBMs, one of the steps in the development of malignancy, and tumour cells that lose or downregulate EGFR will probably be outgrown in an expanding tumour cell population. Thus, loss of EGFR expression might not be the critical factor for successful intracavitary radionuclide therapy. Instead, it is likely that the penetration properties of the targeting agents are critical, and detailed studies on this are urgent.

Monoclonal antibodies for brain tumour treatment

Conventional treatment of brain tumours includes surgical, radiotherapeutic and chemotherapeutic modalities. Nonetheless, the outcome of patients with brain tumours, in particular glioblastoma, remains poor. Immunotherapy with armed or unarmed monoclonal antibodies targeting tumour-specific antigens has emerged in the last two decades as a novel potential adjuvant treatment for all types of neoplasia. Many challenges to its implementation as a safe and viable therapy for brain tumours still need to be addressed; nevertheless, results from ongoing Phase I/II clinical trials are encouraging, as disease stabilisation and patient survival prolongation have been observed. Advances in preclinical and clinical research indicate that treatment of brain tumours with monoclonal antibodies can be increasingly adjusted to the characteristics of the targeted tumour and its environment. This aspect relies on the careful selection of the target antigen and corresponding specific monoclonal antibody, and antibody format (size, class, affinity), conjugation to the appropriate toxin or radioactive isotope (half-life, range), and proper compartmental administration.

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.

Status of radioimmunotherapy in the new millennium

This synopsis attempts to summarize progress made in radioimmunotherapy (RIT) by the end of the 20th century addressing the problems, possible solutions, and recent developments. The reduction of minimal residual disease in an adjuvant setting appears to be a feasible goal for RIT utilizing short-range alpha-emitters. RIT has been more successful in the radiosensitive hematologic malignancies, for example lymphomas and leukemias as compared with small solid tumors. Several radiopharmaceuticals seem near approval for RIT in patients with non-Hodgkin's lymphoma (NHL) as therapeutic responses, including complete responses, are common. Obstacles to successful RIT have been recognized and strategies to overcome these hurdles and to improve efficacy are continuously being developed resulting in encouraging outcome particularly with locoregional routes of administration in solid tumors. Systemic RIT for solid tumors will need manipulating the tumor-host to improve the tumor uptake and retention of radioimmunoconjugates (RICs). The utilization of radiometals, stable chelators, biodegradable linkers and bone marrow transplantation should be able to deliver the radiation dose required for successful treatment. In conjunction with additional synergistic agents, RIT is likely to have a great impact on the treatment of solid tumors. The ability to generate new constructs, such as bivalent antibodies or fusion proteins incorporating two different functional proteins opens exciting opportunities for new therapeutic modalities. These developments will hopefully offset the impediments to the successful use of RIT.

Phase I clinical evaluation of a neutralizing monoclonal antibody against epidermal growth factor receptor in advanced brain tumor patients: preliminary study

High levels of growth factors and their receptors have been demonstrated in human tumors. Gliomas and meningiomas are characterized by overexpression of epidermal growth factor receptor (EGF-R). Ior egf/r3, is a neutralizing murine monoclonal antibody (MAb) against EGF-R, and was generated at the Cuban Institute of Oncology. The antibody recognizes EGF-R with high affinity, inhibiting tyrosine kinase activation. A clinical trial was conducted in brain tumor patients to evaluate toxicity, immunogenicity, and clinical benefit of escalating doses of the antibody. Nine patients with histologically confirmed gliomas or meningiomas, who had active or recurrent disease after receiving conventional treatment, received four intravenous doses of ior egf/r3. Total dosages ranged from 160 to 480 mg. As inclusion criteria, radioimmunoscintigraphy with the same MAb labeled with 99mTechnetium (99mTc) was performed. Immune response against the murine antibody was also evaluated. After four doses of ior egf/r3 MAb, no significant toxicity was found, except in one patient who developed a grade 4 allergic adverse event. This reaction was probably related with previous sensitization to the same MAb and the development of human anti-mouse antibodies (HAMA) response. Despite no major objective antitumor responses, eight patients had stable disease on the 6-month evaluation, and two patients remain alive after four years of MAb therapy.

Technetium-99m labeled epidermal growth factor-tumor imaging in mice

We have shown previously that the epidermal growth factor peptide (EGF) may be radiolabeled with 99mTc at room temperature and neutral pH by using the N-hydroxysuccinimide ester of S-acetyl mercaptoacetyltriglycine (MAG3) as a bifunctional chelator. By a competition binding assay, we found that MAG3-conjugated EGF retained biological activity. Furthermore, the labeled peptide exhibited saturation binding to EGF receptor-positive tumor cell lines which could be inhibited by presaturation of the cells with unlabeled, native EGF. Biodistribution in normal mice at 3 h postadministration showed rapid clearance with minimal retention of the label in sampled organs. We have now investigated the tumor localization properties in mice of this labeled peptide. Nude mice implanted with the EGF receptor-positive tumors A431 and LS-174T were administered labeled EGF and a labeled control peptide (BPTI, aprotinin). Tumor uptake at 12 h postadministration was 0.44% injected dose/g for EGF/g vs. 0.09 for the control. Pretreatment of tumored mice with unlabeled EGF blocked about half the tumor uptake. Animals were also administered an anti-EGF receptor antibody labeled with 99mTc via MAG3. Relative to the antibody, tumor-to-muscle ratios were improved from 6 to 15 and tumor-to-blood ratios from 0.4 to 7 with EGF. These favorable results along with documented evidence of overexpression of the EGF receptor in many human tumors suggest that 99mTc-EGF should be considered further for tumor detection.

Importance of pre-treatment radiation absorbed dose estimation for radioimmunotherapy of non-Hodgkin's lymphoma

Non-Hodgkin's lymphoma I-131 radioimmunotherapy data were analyzed to determine whether a predictive relationship exists between radiation absorbed doses calculated from biodistribution studies and doses derived from patient size. Radioactivity treatment administrations scaled to patient size (MBq/kg or MBq/m2) or fixed MBq doses do not produce consistent radiation absorbed dose to critical organs. Treatment trials that do not provide dose estimates for critical normal organs are less likely to succeed in identifying a clinical role for radioimmunotherapy.

Radiolabeling of epidermal growth factor with 99mTc and in vivo localization following intracerebral injection into normal and glioma-bearing rats

High grade gliomas may have amplified expression of the epidermal growth factor receptor (EGFR) gene c-erb-B, which often is associated with increased expression of transmembrane EGFR. The purpose of the present study was to develop a method for labeling EGF with 99mTc and to determine whether the resulting radioligand would localize, following intracerebral injection, in rats bearing EGFR-positive gliomas. EGF has a relatively low molecular mass (approximately 6 kDa) compared to monoclonal antibodies, and this has allowed smaller bioconjugates, which should diffuse more rapidly within the brain and more effectively target disseminated glioma cells, to be constructed. In the present study, EGF has been labeled with either 131I or 99mTc, and in vitro uptake of the resulting radioligand has been investigated using C6EGFR rat glioma cells, which had been transfected with the EGFR gene. Cellular uptake of 131I radioactivity peaked after approximately 30 min of incubation with [131I]EGF, following which time it declined, while 99mTc radioactivity continued to increase over a 6 h incubation with [99mTc]-EGF. To determine if radiolabeled EGF had in vivo tumor-localizing properties, C6EGFR glioma cells were implanted stereotactically into the brains of Fischer rats. Four weeks later, either 99mTc- or 131I-labeled EGF was injected intracerebrally into normal or glioma-bearing animals using the same stereotactic coordinates. External gamma scintigraphy revealed that 131I radioactivity disappeared rapidly from the brain regions of tumor-bearing animals compared to 99mTc, approximately 50% of which remained in the tumor for up to 12 h. In contrast, only approximately 20% remained in the brains of non-tumor-bearing animals after 6 h. These studies are the first to describe a method for radiolabeling EGF with 99mTc and to detect it by external scintigraphy in the brains of tumor-bearing animals.

Epidermal growth factor receptor expression by acoustic neuromas

Antibodies directed against epidermal growth factor receptor (EGFr) impede proliferation and induce differentiation of EGFr-positive cancers. To explore the effectiveness of anti-EGFr monoclonal antibodies on acoustic neuromas (ANs), we first sought to evaluate EGFr expression by ANs. The records of all patients with the diagnosis of AN at our institution from January 1989 to July 1994 were reviewed. Immunohistochemical analysis for EGFr was performed on formalin-fixed, paraffin-embedded archival surgical specimens. Skin, liver, and placenta were used as positive tissue controls. Purified rabbit immunoglobulin G replacing the experimental antibody acted as a negative control, and normal eighth cranial nerve was evaluated for background staining. Slides were scored as 0, +, ++, or and for percentage of positive cells by two pathologists, with Antoni A and Antoni B areas scored separately. Results demonstrate that most tumors are revealed to be EGFr positive with a mild degree of staining. Antoni A areas generally have greater staining than Antoni B regions, while normal eighth cranial nerves demonstrate minimal background staining. These results suggest that ANs express low levels of EGFr, with Antoni A areas having the highest levels. While further studies may more accurately quantitate EGFr levels in these tumors, the clinical efficacy of anti-EGFr-based therapies for ANs seems doubtful.

Boron neutron capture therapy of brain tumors: past history, current status, and future potential

Boron neutron capture therapy (BNCT) is based on the nuclear reaction that occurs when boron-10 is irradiated with low-energy thermal neutrons to yield alpha particles and recoiling lithium-7 nuclei. High-grade astrocytomas, glioblastoma multiforme, and metastatic brain tumors constitute a major group of neoplasms for which there is no effective treatment. There is growing interest in using BNCT in combination with surgery to treat patients with primary, and possibly metastatic brain tumors. For BNCT to be successful, a large number of 10B atoms must be localized on or preferably within neoplastic cells, and a sufficient number of thermal neutrons must reach and be absorbed by the 10B atoms to sustain a lethal 10B(n, alpha)7 Li reaction. Two major questions will be addressed in this review. First, how can a large number of 10B atoms be delivered selectively to cancer cells? Second, how can a high fluence of neutrons be delivered to the tumor? Two boron compounds currently are being used clinically, sodium borocaptate (BSH) and boronophenylalanine (BPA), and a number of new delivery agents are under investigation, including boronated porphyrins, nucleosides, amino acids, polyamines, monoclonal and bispecific antibodies, liposomes, and epidermal growth factor. These will be discussed, and potential problems associated with their use as boron delivery agents will be considered. Nuclear reactors, currently, are the only source of neutrons for BNCT, and the fission process within the core produces a mixture of lower-energy thermal and epithermal neutrons, fast or high (> 10,000 eV) energy neutrons, and gamma rays. Although thermal neutron beams have been used clinically in Japan to treat patients with brain tumors and cutaneous melanomas, epithermal neutron beams should be more useful because of their superior tissue-penetrating properties. Beam sources and characteristics will be discussed in the context of current and future BNCT trials. Finally, the past and present clinical trials on BNCT for brain tumors will be reviewed and the future potential of BNCT will be assessed.

Boronated epidermal growth factor as a potential targeting agent for boron neutron capture therapy of brain tumors

In order for boron neutron capture therapy (BNCT) to be successful, a large number (approximately 10(9)) of 10B atoms must be delivered to each cancer cell in order to sustain a lethal 10B(n, alpha)7Li reaction. The majority of high grade gliomas express an amplified epidermal growth factor receptor (EGFR) gene, and increased numbers of EGFR are found on the cell surface. If a sufficiently large number of 10B atoms could be attached to EGF, the resulting bioconjugates might be useful for targeting brain tumors. In order to accomplish this, we have boronated a fourth-generation starburst dendrimer (SD) using an isocyanato polyhedral borane, Na(CH3)3NB10H8NCO. For conjugation, reactive thiol groups were introduced into the boronated SD using N-succinimidyl 3-(2-pyridyldithio)propionate (SPDP), and EGF was derivatized with m-maleimidobenzoyl-N-hydroxysulfosuccinimide ester (sMBS). Subsequent reaction of thiol groups of derivatized BSD with maleimide groups of derivatized EGF produced stable BSD-EGF bioconjugates containing approximately 960 atoms of boron per molecule of EGF. As determined by electron spectroscopic imaging, the BSD-EGF initially was bound to the cell surface membrane and then was endocytosed, which resulted in accumulation of boron in lysosomes. The favorable in vitro properties of these bioconjugates suggest that they may be useful for the in vivo targeting of EGFR positive brain tumors.

Intralesional administration of I-131 labelled monoclonal antibodies in the treatment of malignant gliomas

The authors report their preliminary experience with the use of radiolabelled monoclonal antibodies (MAb) as an adjuvant treatment for 33 malignant gliomas. MAbs employed in this study are raised against Tenascin (TN) which is an antigen of the extracellular matrix of the tumour. It has also been found in neoplastic cells but never in normal brain tissue. This therapy is aimed to give a local high dose radiation (boost) while sparing healthy brain structures. This treatment has always been well tolerated and no adverse reactions at the level of CNS or major extraneural organs has been observed. Significant improvement of median survival has been obtained but this result should be cautiously evaluate since the study is non-randomized. Comparison with other current adjuvant technique is briefly discussed.

Production and evaluation of syngeneic antibodies showing specificity for the A15 A5 transplantable rat glioma

Antibodies have been raised which show specificity for the A15 A5 transplantable rat glioma model. Viable, irradiated, colcemid-treated and microwave-fixed A15 A5 cells were each used to hyperimmunize BDIX rats by subcutaneous inoculation, while viable cells were also injected intracerebrally into syngeneic animals. Specific anti-A15 A5 antibodies were detected in serum by a modified enzyme-linked immunoabsorbent assay (ELISA). Immunoperoxidase and immunofluorescence cytochemistry revealed the presence of antigen in paraffin-wax and frozen sections, respectively, of A15 A5 gliomas. The different methods of immunogen denaturation were found to affect the degree of immunological potency of the cells. This study has shown that A15 A5 cells are immunogenic in a syngeneic host. Intracerebrally transplanted, viable cells produced antibodies of higher titre than subcutaneously-injected, denatured cells. The anti-A15 A5 antisera may be used for detection of neoplastic rat astrocytes using immunocytochemistry. These antibodies will prove to be of value in discriminating between neoplastic and normal cells at the tumor/brain interface.

Strategy for boron neutron capture therapy against tumor cells with over-expression of the epidermal growth factor-receptor

PURPOSE

Gliomas, squamous carcinomas and different adenocarcinomas from breast, colon and prostate might have an increased number of epidermal growth factor (EGF) receptors. The receptors are, in these cases, candidates for binding of receptor specific toxic conjugates that might inactivate cellular proliferation. The purpose of this study was to evaluate whether it is reasonable to try ligand-dextran based conjugates for therapy.

METHODS AND MATERIALS

EGF or TGF alpha were conjugated to dextran and binding, internalization, retention and degradation of eight types of such conjugates were analyzed in EGF-receptor amplified glioma cells. The conjugates were labelled with radioactive nuclides to allow detection and two of the conjugates were carrying boron in the form of carboranyl amino acids or aminoalkyl-carboranes. Comparative binding tests, applying 125I-EGF, were made with cultured breast, colon and prostate adenocarcinoma, glioma and squamous carcinoma cells. Some introductory tests to label with 76Br for positron emission tomography and with 131I for radionuclide therapy were also made.

RESULTS

The dextran part of the conjugates did not prevent receptor specific binding. The amount of receptor specific binding varied between the different types of conjugates and between the tested cell types. The dextran part improved intracellular retention and radioactive nuclides were retained for at least 20-24 h. The therapeutical effect improved when 131I was attached to EGF-dextran instead of native EGF.

CONCLUSION

The improved cellular retention of the ligand-dextran conjugates is an important property since it gives extended exposure time when radionuclides are applied and flexibility in the choice of time for application of neutrons in boron neutron capture therapy (BNCT). It is possible that ligand-dextran mediated BNCT might allow, if the applied neutron fields covers rather wide areas around the primary tumor, locally spread cells that otherwise would escape treatment to be inactivated.

Radiation dose heterogeneity in receptor and antigen mediated boron neutron capture therapy

Boron neutron capture therapy, BNCT, might be a valuable tumour therapeutical modality for the treatment of cells that are difficult to handle with conventional methods such as surgery or external radiotherapy. The principle is that tumour associated 10B atoms capture thermal neutrons and thereby forms high-LET helium and lithium ions as reaction products. An interesting development is to conjugate 10B atoms to macromolecules that bind to tumour cells with over-expressed receptors or specific antigens. The targeting macromolecules might be receptor-ligands, antibodies or antibody-fragments containing 10B. The present study deals with the limitations of such an approach. One problem is the background dose from capture of neutrons in physiologically occurring elements, especially nitrogen. We showed, with computer simulations, that the background specific energy (the stochastic analogy of dose) in the cell nuclei, due to captures in nitrogen, had a wide spread and could be rather high, up to 3 Gy in some cells, when relevant neutron fluencies were applied. The maximal amount of 10B that can be delivered to single tumour cells due to receptor-ligand, receptor-antibody or antigen-antibody mediated binding is probably in the range 10(8)-10(10) atoms/cell. Our calculations showed that the tumour cells had to contain about 10(9) 10B/cell to give a therapeutically interesting dose to the nuclei of the targeted cells. The doses were highest when the boron was in the cell nucleus. There was also a wide spread of specific energy absorbed by the nuclei after neutron capture in 10B. When, for example, 10(8) 10(10)B/nucleus were applied the specific energy to the analysed nuclei varied from 0 Gy up to about 7 Gy. These variations were due to the stochastic nature of the capture processes. Some helium or lithium ion tracks passed through the centre of the cell nuclei delivering a lot of energy, some passed through only a smaller part delivering small amounts of energy and sometimes the nuclei escaped without any hits at all. The results were obtained when relevant neutron fluencies (2-5 x 10(12) n/cm2) were applied. Increased neutron fluencies gave higher doses both due to capture in boron and in nitrogen but in order to improve the ratio between the dose to targeted tumour cells and the dose to normal cells, the number of 10B atoms in the targeted cells had to be increased and/or the boron placed in the cell nuclei.

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.

Antibody-targeted drugs for the therapy of cancer

The advent of monoclonal antibodies has revitalised the concept of magic bullets and various agents (eg. drugs, toxins and isotopes) have been conjugated to monoclonal antibodies for selective delivery to tumours. Preclinical studies in mouse tumour models have been impressive and have lead to several clinical trials. These phase I trials have been less impressive. However, keeping in mind the aim of Phase I trials, the safety of using these conjugates in humans have been established. Several, major problems still remain to be overcome before these agents may be useful for the treatment of cancer. These problems stem from the nature of tumour vasculature, cytotoxic activity of the moiety linked to antibody and the targeted tumour antigen expressed on the cell surface. This review will deal with these various aspects described above and possible approaches to overcome these obstacles with a definite bias towards drug-monoclonal antibody conjugates. However, these concepts are equally applicable for improved targeting of other agents.

Dose enhancement in fast neutron tumour therapy due to neutron captures in 10B

High energy neutrons, applied in fast neutron tumour therapy, lose energy when passing through tissue and are at the end of their trajectories captured in nitrogen, hydrogen or other normally occurring elements. If the tissue contains 10B, which has a very high cross section for capture of thermal neutrons, then disintegration products of this process, helium and lithium ions, give a dose enhancement which, if the boron is targeted to tumour cells, may be beneficial. The dose enhancement was in the present study calculated as a function of the 10B concentration in the cells and as a function of different thermal neutron fluencies. If the tumour cells contained 10 or 100 microns 10B/g the average dose enhancement was about 20 or 200 mGy respectively. This was obtained with the thermal neutron fluency 2.0 x 10(10) n/cm2. The relative biological effectiveness of the neutron capture process is unknown but assuming the factor 2, these doses correspond to 0.04 or 0.4 CGE (cobolt-60 gray equivalent) respectively, which could directly be compared to the 2-3 Gy of low-LET radiation that is daily applied in conventional radiotherapy. However, if thermal or epithermal neutron fields are directly applied to the patients a hundred times higher thermal neutron fluency can be used. This gives, in the cases with 10 or 100 micrograms 10B/g, about a hundred times higher average doses so that 2-20 Gy, corresponding to about 4-40 CGE, can be given to the patients. Thus, a successful targeting with high amounts of 10B in the tumour cells gives a significant dose enhancement when applied in fast neutron therapy but it is then more reasonable to treat the patient directly with thermal or epithermal neutrons since the average dose enhancement in the latter case is about a hundred times higher and curable doses might be obtained by the tumour specific capture processes alone.

Inhibitory effect of bombesin/gastrin-releasing peptide (GRP) antagonists RC-3950-II and RC-3095 on MCF-7 MIII human breast cancer xenografts in nude mice

Bombesin/gastrin-releasing peptide (GRP) may be involved in the growth of human breast cancers. Nude mice bearing xenografts of MCF-7 MIII human breast cancer cell line were treated for 7 weeks with bombesin/GRP antagonists RC-3950-II and RC-3095. RC-3950-II, administered sc twice daily at a dose of 10 micrograms, produced significant inhibitory effects on tumor growth after 2 weeks of administration. RC-3095 acetate (D 22213), injected sc twice daily at the same dose of 10 micrograms, suppressed tumor growth after 4 weeks. Both RC-3950-II and RC-3095 significantly decreased the final tumor volume and tumor weights. RC-3950-II appeared to be somewhat more efficacious than RC-3095 in inhibiting the growth of MCF-7 MIII breast cancers. Chronic treatment with either bombesin/GRP antagonist caused down-regulation of receptors for epidermal growth factor (EGF) in tumor cell membranes, which might be related to inhibition of tumor growth. These findings suggest that bombesin/GRP antagonists should be considered for a new endocrine therapy of breast cancer.

Intraportal injection of monoclonal antibody in nude mice bearing hepatic metastases

Using a model for hepatic human colorectal carcinoma metastases in athymic mice, we compared the selective [intraportal (ip)] and systemic [intravenous (iv)] injection of radiolabeled monoclonal antibody (mAb) strongly reactive against the cell line. Percent injected dose of radiolabeled antibody per gram (%id/g) of tumor or normal tissues was measured at selected time points (up to 5 days postinjection) within 3 dose levels: 0.1, 1.0, and 2.0 micrograms (micrograms). At each dose level, 3-9 animals were studied in each of 3 groups: animals receiving ip injection (group HT-29-15 ip), those receiving intravenous injection (group HT-29-15 iv), and those receiving isotype-matched control antibody via the intraportal route (group BL-3 ip). Significantly greater (P < 0.005) %id/g in tumor was seen in group HT-29-15 ip at all time points and dose levels compared to those in groups HT-29-15 iv or BL-3 ip. However, immediately after injection of mAb, there was no difference in tumor %id/g between groups HT-29-15 ip and HT-29-15 iv at the highest dose level. There was no increase in %id/g of mAb in normal liver and blood after ip injection compared to iv injection beyond day 1. Therefore ip injection resulted in higher tumor to liver and tumor to blood ratios compared to iv (P < 0.005). We conclude that delivery of mAb to hepatic metastases can be enhanced by selective injection; this has important implications in the design of future clinical trials utilizing radiolabeled mAb in the diagnosis and treatment of hepatic metastases.

Development of a method to measure kinetics of radiolabelled monoclonal antibody in human tumour with applications to microdosimetry: positron emission tomography studies of iodine-124 labelled 3F8 monoclonal antibody in glioma

We present a method to assess quantitatively the immunological characteristics of tumours using radiolabelled monoclonal antibody and positron emission tomography (PET) to improve dosimetry for radioimmunotherapy. This method is illustrated with a glioma patient who was injected with 96.2 MBq of iodine-124 labelled 3F8, a murine antibody (IgG3) specific against the ganglioside GD2. Serial PET scans and plasma samples were taken over 11 days. A three-compartment model was used to estimate the plasma to tumour transfer constant (K1), the tumour to plasma transfer constant k2, the association and dissociation constants (k3, k4) of antibody binding, and the binding potential. Tumour radioactivity peaked at 18 h at 0.0045% ID/g. The kinetic parameters were estimated to be: K1 = 0.048 ml h-1 g-1, k2 = 0.16 h-1, k3 = 0.03 h-1, k4 = 0.015 h-1 and BP = 2.25. Based on these kinetic parameters, the amount of tumour-bound radiolabelled monoclonal antibody was calculated. This method permits estimates of both macrodosimetry and microdosimetry at the cellular level based on in vivo non-invasive measurement.

Penetration and binding of epidermal growth factor-dextran conjugates in spheroids of human glioma origin

Targeting with toxic EGF-based conjugates against tumour cells with amplified EGF-receptors might be a possible approach towards improved therapy of certain malignancies such as gliomas and squamous carcinomas. In this study, the penetration and binding of 125I delivered by EGF-dextran conjugates were analysed in cultured spheroids applied as a tumour nodule model. The spheroids consisted of human glioma cells, U-343MGaCl2:6, with large amounts of EGF-receptors. The penetration and binding patterns of 125I delivered by 125I-EGF and 125I-dextran were analysed for comparison. The EGF-dextran associated 125I-activity showed a rather slow penetration but after some hours significant amounts of radioactivity had reached the deeper regions and good penetration was obtained within 5 hours. The penetration seemed somewhat faster when the 125I-activity was delivered with EGF possibly dependent on the lower molecular weight allowing for faster diffusion. Furthermore, EGF-dextran associated 125I seemed to penetrate somewhat faster after the EGF-receptors were blocked with non-radioactive EGF, probably due to the lack of binding preventing free diffusion. After administration of 125I-EGF-dextran or 125I-EGF, the binding patterns were superimposed on the penetration patterns. In the penetration studies, the superimposed accumulations due to binding were removed by presaturation of the receptors with non-radioactive EGF. After a 1 hour incubation, binding of EGF-dextran associated 125I-activity could be seen only in an outer region, with an approximative thickness of 50 microns, of the viable cell layer. Extensive receptor specific binding in the deeper regions, at a depth of 100-200 microns, was seen after several hours incubation. In addition, low levels of non-specific binding in the central regions were seen when the 125I-activity was delivered with dextran without EGF. A similar low background binding was seen also in the centre of spheroids incubated with 125I-EGF-dextran or 125I-EGF after saturation of the receptors with non-radioactive EGF. However, the major amount of radioactivity delivered as 125I-EGF-dextran or 125I-EGF had a receptor specific binding and, also in inner regions, it could be displaced by non-radioactive EGF. Thus, EGF-dextran, which is a candidate compound for targeted therapy, allowed penetration of the applied radioactivity and binding could be observed, after some hours, also in the inner regions of the spheroids.

Animal models for radiolabeled monoclonal antibodies in cancer research

A review of the different animal tumor model systems used for radiolabeled monoclonal antibody research is given. Problems within the field of radioimmunotargeting are presented, and the tumor models are discussed in relation to the types of problems which can be investigated, and the ability of the models to answer different questions.

Effects of EGF-dextran-tyrosine-131I conjugates on the clonogenic survival of cultured glioma cells

Epidermal growth factor, EGF, and 131I or 125I-labelled tyrosine were conjugated to the sugar polymer dextran. The conjugates bound to EGF-receptor rich human glioma cells in culture and the binding was mainly receptor specific because cells presaturated with nonradioactive EGF gave strongly reduced binding. The 131I labelled conjugates were used in tests on cellular retention and therapeutical effects. 131I activity delivered to the cells as EGF-dextran-tyrosine-131I remained cell-associated for much longer periods of time than 131I activity delivered by only EGF. The amount of cell-associated 131I activity was nearly constant for up to 25 hours. The 131I labelled conjugate gave, after a one hour incubation period for binding followed by a 25 hour incubation in nonradioactive medium, a good therapeutical effect. This effect, which corresponded to about 3.0 Gy of external 60Co radiation, was due to the specifically bound 131I. The comparatively small effects of nonbound 131I in the culture medium, present only during the first incubation hour, were measured in control experiments with presaturated receptors and were corrected for in the evaluation of the EGF-receptor mediated effects. Control experiments showed that neither nonradioactive EGF nor non-radioactive EGF-dextran conjugates gave measurable effects on clonogenic growth. The results obtained were promising and the possibilities to use EGF-dextran conjugates for therapy should be further examined.

Clinical effect of intra-arterial tumor necrosis factor-alpha for malignant glioma

Recombinant human tumor necrosis factor-alpha was administered intra-arterially to treat 20 cases of malignant gliomas, mostly progressive or recurrent. The optimum dosage was determined to be 1 x 10(5) U/sq m/day. Among the 10 evaluable patients treated at this dosage, two responded (one completely and one partially), resulting in a 20% response rate. Side effects were mild and easily controllable. Improvement of neurological symptoms was noted in 47% of the patients a few days after treatment, even when computerized tomography showed no tumor regression. This might have been due to the pleiotypic biological activity of tumor necrosis factor-alpha. Neuroradiographic observations revealed narrowing of the tumor-feeding artery, a decrease in tumor staining ability, and necrosis in the central part of a tumor. The authors suggest that intra-arterial administration of tumor necrosis factor-alpha may be an effective treatment for malignant glioma, including recurrent cases.

Radioimmunotherapy: clinical results and dosimetric considerations

Radiolabeled antibodies for cancer therapy are being investigated in clinical trials in more than 30 centers. 131Iodine-labeled antibody (Ab) therapy of solid tumors has produced few responses when given alone. When given in conjunction with chemotherapy and external beam therapy in hepatoma patients, objective responses have occurred. Because of the short range of 131I, 90Y and 186Re are being studied and objective responses have occurred in patients without the addition of other therapies. 131I-labeled Ab therapy of lymphoma, a radioresponsive tumor, has produced a much higher objective response rate than in other solid tumors. Regional RIT has not been shown to offer a definite advantage over the intravenous route. Tumor doses have generally been less than 2000 cGy per treatment with some tumors receiving higher doses. The bone marrow is the dose-limiting organ for RIT and marrow cryopreservation with subsequent reinfusion may prove useful.

Malignant astrocytomas treated with iodine-125 labeled monoclonal antibody 425 against epidermal growth factor receptor: a phase II trial

Twenty-five patients with primary presentation of malignant astrocytoma, astrocytoma with anaplastic foci, and glioblastoma multiforme were treated with surgical resection and definitive radiation therapy followed by intravenous or intra-arterial administration of Iodine-125 labeled monoclonal antibody-425, which binds specifically to human epidermal growth factor receptor. The patients presented with primary untreated disease, positive contrast enhanced computed tomography scans of the brain, and compatible clinical symptoms. In this Phase II clinical trial, the patients had surgical debulking or biopsy followed by definitively administered external beam radiation therapy and one or multiple doses (35 to 90 mCi per infusion) of radiolabeled antibody. The total cumulative doses ranged from 40 to 224 mCi. The administrations of the radiolabeled antibody were performed in most cases 4-6 weeks following completion of the primary surgery and radiation therapy. Ten patients had astrocytoma with anaplastic foci and 15 had glioblastoma multiforme. No significant life-threatening toxicities were observed during this trial. At 1 year 60% of the patients with astrocytoma with anaplastic foci or glioblastoma multiforme are alive. The median survival for both groups was 15.6 months.

Strategy for planned radiotherapy of malignant gliomas: postoperative treatment with combinations of high dose proton irradiation and tumor seeking radionuclides

A strategy for improved treatment of malignant gliomas grade III-IV is presented. The strategy can briefly be described as surgical removal of the bulky tumor, high precision external irradiation of small brain volumes over and near the primary tumor area with high doses from proton beams, and thereafter treatment of spread cells with toxic radionuclides. Proton beams suitable for this are under development. The clinical effects of high single doses on malignant gliomas grade III-IV are presently tested with conventional gamma radiation. Targeting of spread glioma cells with toxic radionuclides tagged to epidermal growth factor, EGF, or to EGF-dextran is presently tested in experimental systems and can, in the near future, be tested in combination with local high doses of external proton radiation. The possibilities to combine proton beams with EGF-guided neutron capture therapy will be considered in a longer perspective.

Response of low-passage human malignant gliomas in vitro to stimulation and selective inhibition of growth factor-mediated pathways

The proliferation of many nonglial tumors in vitro depends on the presence of nanomolar concentrations of one or more growth factors. To define the growth factor requirements of malignant glial tumors, the authors examined the response properties of four low-passage human malignant glioma lines to the following mitogens: epidermal growth factor (EGF), acidic and basic fibroblast growth factors (FGF's), insulin-like growth factor I (IGF-I), nerve growth factor (NGF), platelet-derived growth factor (PDGF), 12-O-tetradecanoyl-13-phorbol acetate (TPA), and serum. Each of the tumors showed increased deoxyribonucleic acid (DNA) synthesis (assessed by acid-precipitable [3H]-thymidine incorporation) in response to PDGF with a maximum effect at 50 ng/ml. Three tumors responded to EGF, three to IGF-I, two to acidic FGF, two to basic FGF, and two to TPA with maximum effects at 10, 50, 1, 1, and 10 ng/ml, respectively. None of the tumors responded to NGF. In the responsive tumors, optimum concentrations of EGF, IGF, TPA, acidic FGF, and basic FGF induced, at most, a two- to fourfold increase in [3H]-thymidine incorporation, which was only 30% to 50% of the response seen in 10% serum. In contrast, PDGF increased DNA synthesis eight- to 10-fold, equaling the effect of 10% serum. Measurements of cell proliferation also demonstrated a significant response to PDGF in each of the tumors. Appropriate concentrations of an anti-PDGF neutralizing antibody inhibited baseline DNA synthesis and proliferation in the absence of added growth factors, suggesting the possible role of PDGF in autocrine stimulation of these cells. However, this antibody produced only slight inhibition of serum-induced mitogenesis. Trapidil, an agent reported to inhibit the effects of PDGF, and polymyxin B, an inhibitor of protein kinase C, strongly inhibited baseline as well as PDGF- and serum-induced mitogenesis. It is concluded that, in the malignant gliomas studied, PDGF may be acting as a dominant mitogen to enhance DNA synthesis, and may function in autocrine stimulation. However, other factors contained in serum can also contribute to cell division.

Morphological, immunocytochemical and growth characteristics of three human glioblastomas established in vitro

The human glioblastoma-derived cell lines 86HG-39, 87HG-28 and 87HG-31, used for the production of monoclonal antibodies (mAbs) against glioma-associated antigens (GAA), were characterized in terms of morphology, growth behaviour, chromosomes and antigen expression. In the primary tumours, differential expression of glial fibrillary acidic protein, S100 protein, Leu-7 and GAA as defined by mAbs MUC 2-39, MUC 2-63 and MUC 8-22 was demonstrated. Receptors for epidermal growth factor (EGFr) and nerve growth factor (NGFr) were found in many cells in short-term cultures, but the transferrin receptor (Tr) was found in only a few cells of 87HG-28. In permanent cell lines, differentiation antigens and EGFr decreased and Tr increased markedly. NGFr and GAA remained stable. Transplantation tumours of 86HG-39 were partly positive for Tr and GAA. Chromosomal analysis revealed that the 86HG-39 and 87HG-28 cell lines had a hypodiploid or diploid stem line with lines in the hypotetraploid to tetraploid region for 50 in vitro passages. The 87HG-31 cell line had chromosomal patterns in the hypotriploid to triploid region. A gain of chromosomes was seen in the groups C7, C8, C10, D14, F19, F20, G21, G22. The variability of antigens in these tumours and especially during long-term cultivation probably reveals an ability to influence the growth of malignant glioma cells via the respective effector molecules.

Epidermal growth factor receptors in intracranial and breast tumours: their clinical significance

A method to determine the binding of epidermal growth factor (EGF) to the particulate fraction of the cell has been established and evaluated using rat liver, human placenta, and tumours of human breast and brain. Little EGF receptor (EGFR) activity was detected in normal or benign tumour tissues except for meningioma (positive in 95% samples), but EGFR were present in 43% of 131 breast tumours and 75% of 55 primary cerebral tumours. Despite the strong inverse correlation between EGFR activity and oestrogen receptors in breast tumours and a tendency for high levels of EGFR activity to be associated with glioblastoma multiforme, analysis showed that EGFR was of little prognostic significance in patients with tumours of either breast or brain.

Lymphoscintigraphy with 123I-labelled epidermal growth factor

We have used 123I-labelled epidermal growth factor (EGF) scans to study 14 patients with advanced cervical cancer. Abnormal lymph node imaging was seen most clearly 6-8 h after the injection and revealed abnormal uptake by pelvic lymph nodes in 11 patients. 4 of these 11 had abnormal computerised tomographic and ultrasound scans; in the other 7 conventional radiology did not confirm the presence of disease.

Expression of growth factor receptors in human brain tumours

The expression of the EGF receptor, c-erbB-2 and PDGF receptor proteins has been studied in a series of human brain tumour biopsies and cell lines. Western blotting was used to determine the amount of protein present and their intrinsic and ligand promoted enzyme activities were studied by immunoprecipitation followed by autophosphorylation. EGF receptors were found to be expressed at very high levels in 40% of primary tumour biopsies, but at uniformly low levels in tumour derived cell lines. The c-erbB-2 protein was not detected in tumour biopsies, but was present at variable, but low levels in extracts of tumour cell lines. PDGF receptors were also found at moderate to low levels in both primary tumours and cell lines. The EGF receptor gene was amplified in four out of 14 primary tumours and this generally correlated with high levels of protein expression. The c-erbB-2 gene was not amplified. Employing the polymerase chain reaction and sequence specific oligonucleotides as probes there was no evidence of mutations in the c-erbB-2 gene transmembrane region. These results suggest that alterations of expression of the EGF receptor may play a role in human brain tumours. There was however no evidence for aberrant expression of the c-erbB-2 protein. Additional experiments are required to assess the influence of PDGF receptor expression in brain tumour cells.

Binding of epidermal growth factor-dextran conjugates to cultured glioma cells

Some gliomas, melanomas and squamous carcinomas have large numbers of EGF receptors which could, in these cases, be used for targeting with toxic agents. We investigated whether EGF could be conjugated to dextran, which is a suitable carrier for toxic agents, without losing its ability to bind to the receptor. Dextran of 20 kDa molecular weight was activated with I-cyano-4-dimethylamino pyridinium tetrafluoroborate (CDAP) yielding highly active pyridinium-isourea derivatives. EGF was coupled to the activated dextran through the amino terminus and glycine was added to block residual activity. The EGF-dextran conjugate was, after purification on Sephadex G25 and Sephacryl 200 columns, tested for its receptor binding properties on human malignant glioma, U343MGaC12:6, cells. The conjugate inhibited binding of 125I-EGF in a competitive assay, showing that the binding was receptor-specific. Dextran conjugated with glycine, without EGF, had no inhibitory effect. The conjugate was radio-labelled either on the EGF part with 125I or on the dextran part with 3H-glycine, and the internalization patterns were compared to the internalization of 125I-EGF. The radioactivity of the conjugates remained cell-associated for more than 20 hr, regardless of whether the radioactivity was on the EGF or on the dextran part, while the radioactivity of unconjugated EGF rapidly disappeared from the cells. Most of the cell-associated radioactivity was, at all analysed time intervals, located intracellularly. Thus, it seems promising to use dextran, conjugated with EGF, as a carrier of, for example, toxic radioactive nuclides.

Epidermal growth factor receptor expression in human gliomas

The expression of epidermal growth factor receptor (EGFR) was determined in cryosections of 42 human gliomas using biotinylated epidermal growth factor (B-EGF) and two monoclonal antibodies (mAb) against EGFR. All gliomas were found to express EGFR when examined with B-EGF, whereas 33 expressed EGFR when examined with the two mAbs. The highly malignant gliomas (glioblastomas and anaplastic astrocytomas) had a more heterogeneous staining strongly with B-EGF than did the low-grade gliomas (astrocytomas, oligodendrogliomas, mixed gliomas, and ependymomas). This indicates that high-grade gliomas contain more tumour cells rich in EGFR than do the low-grade gliomas. Reactive astrocytes, ependymal cells, and many types of nerve cells (cerebral cortical pyramidal cells, pyramidal and granular hippocampal cells, Purkinje cells, cerebellar granular cells and neurons in the molecular layer of the cerebellum) expressed EGFR, whereas small neurons and normal glial cells were not found to express EGFR.

Distribution and stability in the rat of a 76Br/125I-labelled polypeptide, epidermal growth factor

A positron-emitting isotope of bromine, 76Br, with a half-life of 16.2 h, was produced using the reaction natBr(p, xn)76Kr. Labelling of mouse epidermal growth factor (EGF) with 76Br was optimized, using the chloramine-T method, obtaining a maximal radiochemical yield of 53%. In tests with receptor-rich, cultured glioma cells, [76Br]EGF and [125I]EGF bound equally well. A study of the distribution and stability of [76Br]EGF and [125I]EGF in normal rat was carried out. The distribution of both radioisotopes was similar, however, the percentage of 76Br bound to the high molecular weight fraction in the plasma, liver and kidney was greater than that of 125I.

Fundamentals of radioimmunotherapy

Design of a radioimmunotherapy trial is a complex process. This involves antibody selection, choice of radioisotope, and labeling method. Observation of the behavior of the new radiopharmaceutical involves determination of normal organ and tumor uptake, as well as residence time. Calculation of external radiation absorbed dose must also be performed, and criteria set for therapy. Once treatment has taken place, mechanisms for patient follow-up must be implemented. This contribution discusses important considerations in the design and implementation of a clinical trial in radioimmunotherapy.

Effects of 131I-EGF on cultured human glioma cells

Malignant glioma cells often have more epidermal growth factor (EGF) receptors than normal cells and targeting of toxic substances to the receptor might therefore be an attractive therapeutical approach. Radiation effects were analysed on human glioma cells growing as monolayers after exposure to 131I-EGF. Unspecific effects were analysed with 131I-BSA or after presaturation with nonradioactive EGF. The radiation effects were compared to the effects obtained by external 60Co gamma irradiation. Administration of the highest radioactive concentrations, 0.2-0.5 MBq/ml in the culture medium, corresponded, after 20 min incubation, to a binding of about 1.0-2.5 dpm/cell. Such an exposure to 131I decays gave effects on cell survival corresponding to about 2.5 Gy of external gamma irradiation. Somewhat less than half of this effect came from the specific bound radioactivity and the rest from nonbound radioactivity. When administrating lower concentrations of radioactivity both the binding and the radiation effects were smaller. The observations showed that it is possible to inactivate cell-proliferation of glioma cells with specific bound 131I-EGF. The possibilities to fractionate the treatments and of binding also other toxic agents than 131I to the EGF receptor are discussed.

Response of malignant glioma cell lines to epidermal growth factor and platelet-derived growth factor in a serum-free medium

The use of a serum-free culture system for assessing the growth factor responsiveness of malignant glial cells is described. The mitogenic properties of epidermal growth factor (EGF) and platelet-derived growth factor (PDGF) were examined in three human malignant glioma cell lines (T98G, U87, and U138). Each of the three had high-affinity EGF receptors and all responded in a dose-dependent fashion to physiological concentrations of EGF. These cell lines also showed a pronounced mitogenic response to PDGF which equaled or exceeded that achieved with EGF. Simultaneous stimulation with both factors produced an additive response, which approximated that obtained in medium supplemented with 10% fetal calf serum. The authors conclude that functional EGF and PDGF receptors were present in the human malignant glial tumors studied. The response of the human glioma lines to these growth factors in many respects parallels the response seen in fetal astrocytes tested under similar conditions. In contrast, the behavior of two chemically induced rat gliomas (9L and C6) differed significantly from that seen in the human lines, suggesting that the rat lines may not be entirely acceptable as models for studying the growth characteristics of human malignant glial tumors.