Phase I-II study of radiolabeled antibody integrated in the treatment of primary hepatic malignancies

Cellular Response to Exponentially Increasing and Decreasing Dose Rates: Implications for Treatment Planning in Targeted Radionuclide Therapy

The treatment of cancer using targeted radionuclide therapy is of interest to nuclear medicine and radiation oncology because of its potential for killing tumor cells while minimizing dose-limiting toxicities to normal tissue. The ionizing radiations emitted by radiopharmaceuticals deliver radiation absorbed doses over protracted periods of time with continuously varying dose rates. As targeted radionuclide therapy becomes a more prominent part of cancer therapy, accurate models for estimating the biologically effective dose (BED) or equieffective dose (EQD2α/β) will become essential for treatment planning. This study examines the radiobiological impact of the dose rate increase half-time during the uptake phase of the radiopharmaceutical. MDA-MB-231 human breast cancer cells and V79 Chinese hamster lung fibroblasts were irradiated chronically with 662 keV γ rays delivered with time-varying dose rates that are clinically relevant. The temporal dose-rate patterns were: 1. acute, 2. exponential decrease with a half-time of 64 h (Td = 64 h), 3. initial exponential increase to a maximum (half time Ti = 2, 8 or 24 h) followed by exponential decrease (Td = 64 h). Cell survival assays were conducted and surviving fractions were determined. There was a marked reduction in biological effect when Ti was increased. Cell survival data were tested against existing dose-response models to assess their capacity to predict response. Currently accepted models that are used in radiation oncology overestimated BED and EQD2α/β at low-dose rates and underestimated them at high-dose rates. This appears to be caused by an adaptive response arising as a consequence of the initial low-dose-rate phase of exposure. An adaptive response function was derived that yields more accurate BED and EQD2α/β values over the spectrum of dose rates and absorbed doses delivered. Our experimental data demonstrate a marked increase in cell survival when the dose-rate-increase half-time is increased, thereby suggesting an adaptive response arising as a consequence of this phase of exposure. We have modified conventional radiobiological models used in the clinic for brachytherapy and external beams of radiation to account for this phenomenon and facilitate their use for treatment planning in targeted radionuclide therapy.

Cancer radioimmunotherapy

Targeting of radionuclides with antibodies, or radioimmunotherapy, has been an active field of research spanning nearly 50 years, evolving with advancing technologies in molecular biology and chemistry, and with many important preclinical and clinical studies illustrating the benefits, but also the challenges, which all forms of targeted therapies face. There are currently two radiolabeled antibodies approved for the treatment of non-Hodgkin lymphoma, but radioimmunotherapy of solid tumors remains a challenge. Novel antibody constructs, focusing on treatment of localized and minimal disease, and pretargeting are all promising new approaches that are currently under investigation.

Recombinant bispecific monoclonal antibodies prepared by the dock-and-lock strategy for pretargeted radioimmunotherapy

The selective delivery of therapeutic radionuclides is a promising approach for treating cancer. Antibody-targeted radionuclides are of particular interest, with 2 products approved for the treatment of certain forms of non-Hodgkin lymphoma. However, for many other cancers, radioimmunotherapy has been ineffective, being limited by prolonged exposure to the highly radiosensitive bone marrow. An alternative approach, known as pretargeting, separates radionuclide from the antibody, allowing the radiation to be delivered on a small molecule that can quickly and efficiently migrate into the tumor, and then rapidly clear from the body with minimal retention in tissues. Several pretargeting methods have been developed that differ in the way they selectively capture the radionuclide. This review focuses on the development of a novel form of bispecific monoclonal antibody (bsMAb) pretargeting that uses a unique radiolabeled hapten-peptide system that can be modified to bind numerous therapeutic and imaging radionuclides. Together with a specialized recombinant humanized bsMAb prepared with by a technique known as the Dock-and-Lock method, this pretargeting procedure has been examined in many different animal models, showing a high level of sensitivity and specificity for localizing tumors, and improved efficacy with less hematologic toxicity associated with directly radiolabeled IgG. The bsMAb is a tri-Fab structure, having 2 binding arms for the tumor antigen and 1 capable of binding a hapten-peptide. Preclinical studies were preformed to support the clinical use of a bsMAb and a hapten-peptide bearing a single DOTA moiety (IMP-288). A phase 0 trial found an (131)I-tri-Fab bsMAb, TF2, that targets carcinoembryonic antigen was stable in vivo, quickly clears from the blood, and localizes known tumors. The first-in-patient pretargeting experience with the (111)In-IMP-288 also observed rapid clearance and low tissue (kidney) retention, as well as localization of tumors, providing initial promising evidence for developing these materials for radioimmunotherapy.

Effect of therapeutic macromolecules in spheroids

Recent advances in biotechnology have allowed the production of new types of macromolecular therapeutic agents (antibodies, immunotoxins, cytokines, extracellular matrix molecule (ECM) proteins, vectors) that may eventually find broad clinical applications in the treatment of human tumors and other diseases. The model of the Multicellular Tumor Spheroids (MTS) represents a valuable tool to test the therapeutic potential of these new pharmacologic agents in a 3-D context. Specific questions pertaining to the behaviour in a 3-D setting of some of the macromolecules under evaluation for in vivo applications can also be addressed in the MTS model (e.g. 'binding site barrier', role of cell-cell and cell-ECM interactions). This paper reviews the most significant contributions regarding the delivery of macromolecules to MTS, the penetration and therapeutic effects of antibodies, radiolabelled antibodies, immunotoxins and other macromolecular compounds.

Proliferation and the advantage of longer-lived radionuclides in radioimmunotherapy

In our previous study we used the linear-quadratic model [J. Nucl. Med. 35, 1861 (1994)] to confirm our initial finding, based on the time-dose-fractionation model [J. Nucl. Med. 34, 1801 (1993)], that longer-lived radionuclides (e.g., 32P, 91Y) can offer a substantial therapeutic advantage over the shorter-lived radionuclides presently used in radioimmunotherapy (e.g., 90Y). The original calculations using the linear-quadratic (LQ) model did not account for proliferation of the tumor and critical bone marrow tissues. It has been suggested that inclusion of a proliferation term in the LQ model can have a substantial impact on the biologically effective dose (BED). With this in mind, we have reexamined the therapeutic efficacy of longer versus short-lived radionuclides using the LQ model replete with proliferation terms for tumor and bone marrow. Relative advantage factors (RAF), which quantify the overall therapeutic advantage of a long-lived compared to short-lived radionuclide, were calculated accordingly. While the extrapolated initial dose rate required to achieve a given BED can be affected by the inclusion of proliferation terms for both the tumor and marrow, the relative advantage factors for the longer-lived radionuclides were not significantly affected. Longer-lived radionuclides such as (114m)In and 91Y are about three times more therapeutically effective than the shorter-lived 90Y which is currently used in RIT. In other words, for a given therapeutic effect in the tumor, a longer-lived radionuclide can result in a lower deleterious effect to the bone marrow than a short-lived radionuclide. Given that bone marrow is generally considered to be the dose-limiting organ, these results have important implications for radioimmunotherapy.

Antibody-targeted photolysis of bacteria in vivo

We have evaluated the efficacy of antibody-targeted photolysis to kill bacteria in vivo using specific antibacterial photosensitizer (PS) immunconjugates. After infecting the dorsal skin in mice with Pseudomonas aeruginosa, both specific and nonspecific tin (IV) chlorin e6-monoclonal antibody conjugates were injected at the infection site. After a 15 min incubation period, the site was exposed to 630 nm light with a power density of 100 mW/cm2 for 1600 seconds. Irradiation resulted in a greater then 75% decrease in the number of viable bacteria at sites treated with a specific conjugate, whereas normal bacterial growth was observed in animals that were untreated or treated with a nonspecific conjugate. Antibody-targeted photolysis may be a selective and versatile tool for treating a variety of infections.

New radiopharmaceuticals and new applications in medicine

All areas of radiology are constantly evolving. At times rapid advances are made because new equipment or pharmaceuticals are introduced. At others the evolution is gradual as established procedures and techniques are refined. The following review of selected areas in nuclear medicine includes both dramatic changes due to new developments and evolutionary changes in established techniques. The first section reviews the development of monoclonal antibodies for use in radioscintigraphy of neoplastic disease. Although many articles have been written about this topic over the years, the clinical applications have suddenly expanded because the Food and Drug Administration (FDA) recently approved one monoclonal antibody for use in the imaging of colorectal and ovarian cancer. It is anticipated that a number of other antibodies will be approved for clinical scintigraphy of both malignant and benign disease and immunotherapy. It is advised that the radiologist performing nuclear medicine procedures become knowledgeable about this expanding area of clinical application. The second section reviews several new radiopharmaceuticals that are being used with increasing frequency for myocardial imaging. The behavior of these tracers is different from that of thallium, and specialized imaging techniques are required. Although the clinical value of these agents is still questioned by some, they are widely used. Familiarity with this topic is recommended. The last section reviews some of the radiopharmaceuticals available for renal imaging and functional evaluation. The relatively new technetium-labeled pharmaceutical that approximates the behavior of hippuran is emphasized. New applications with the renal cortical imaging agent technetium DMSA are also reviewed. A thorough knowledge of the biologic behavior of these tracers and appropriate imaging and measurement techniques is extremely important for their appropriate clinical use.

Sn-chlorin e6 antibacterial immunoconjugates. An in vitro and in vivo analysis

Monoclonal antibody-Sn-chlorin e6 immunoconjugates were prepared by the site-selective covalent modification of the monoclonal oligosaccharide moiety. By carefully controlling the reaction conditions and introducing triethanolamine groups as axial ligands of the Sn moiety, conjugates with in vivo biodistribution properties similar to underivatized IgG were prepared. By varying the reaction conditions, conjugates were reproducibly prepared with a range of photosensitizer to mAb molar ratios from 1.6 to 10. Based on a competitive inhibition radioimmunoassay, conjugates prepared by this method showed selectivity and binding affinity comparable to the unmodified antibody. The immunoconjugates had only slightly lower singlet oxygen yields than that observed with the Sn-chlorin e6 precursor indicating that negligible aggregation or structural modification of the chromophores occurred during the synthesis process. In vitro cell killing experiments demonstrated that all conjugates possessed significant cytotoxic activity. Biodistribution studies in mice showed that conjugates prepared with axial ligands had significant serum retention 24 h after injection while conjugates prepared without the triethanolamine ligand were much more rapidly cleared. In vivo specificity was demonstrated using rats infected with Fisher immunotype I P. aeruginosa at a site in the left posterior thigh muscle. Target to background ratios exceeded 60 at 120 h after conjugate injection of the specific immunoconjugate, compared to a ratio of only 6 for a non-specific mouse IgG conjugate. Biodistribution patterns at 120 h post injection indicate that the conjugates were both biologically active and structurally intact.

Therapeutic aspects of radio-isotopes in hepatobiliary malignancy

Liver tumours frequently present at a late stage and only a minority of patients are likely to benefit from resection or transplantation. Inoperable tumours carry a grave prognosis. External beam irradiation of the liver is dose-limited by the radiosensitivity of hepatocytes, particularly in the presence of cirrhosis, but internal radiation using radio-isotope sources can achieve more selective irradiation of the chosen field. Sealed sources are dose-limited by their effects on surrounding tissues, whereas with unsealed sources the dose of radio-isotope administered is limited by bone marrow suppression. Iridium-192 wires are most frequently employed as a sealed intracavitary source. They may be inserted surgically, transhepatically or endoscopically. Doses of up to 60 Gy can be delivered to a malignant biliary stricture without damage to the surrounding parenchyma. The incidence of cholangitis is low if treatment is administered after insertion of an endoprosthesis. Unsealed radio-isotope sources may be injected directly into the tumour, administered embolically via the hepatic artery in the form of microspheres or lipid droplets, or given via parenteral infusion attached to tumour-specific antibodies. Of these vehicles, the lipid agent Lipiodol appears to be the most effective and can deliver a potentially lethal dose of radiation to small tumours. Host reaction to the injected antibody remains a major drawback to the use of monoclonal antibodies as targeting agents. Iodine-131 is a beta- and gamma-emitter, producing a local tumoricidal effect and allowing accurate dosimetry by means of external scintigraphy. Yttrium-90 is a pure beta-emitter with a greater maximum beta energy and cytotoxic range; however, it is retained in bony tissues, resulting in a dose-related risk of marrow suppression. Bone absorption cannot be measured by external imaging owing to the absence of gamma emission. This lack of accurate dosimetry, coupled with the toxic side-effects of yttrium treatment, make iodine-131 the current isotope of choice.

The curability of tumours of differing size by targeted radiotherapy using 131I or 90Y

A mathematical model has been used to investigate the relationship of curability to tumour size and cell number for spherical tumours treated with targeted 131I or 90Y, assuming uniform uptake of radionuclide throughout the tumour. The analysis shows that, for any given cumulated activity per unit mass of tumour, cure probability is greatest for tumours whose diameter is close to an optimum value which depends on the path length of the emitted beta-particle. Smaller tumours are less curable because of inefficient absorption of radiation energy, and larger tumours are less curable because of greater clonogenic cell number. The lesser curability of very small tumours is a feature of targeted radiotherapy using long-range beta-emitters which does not occur with external beam irradiation. The predicted inefficiency of sterilisation of microscopic tumours poses a problem for targeted radiotherapy which is analogous to "geographic miss" in conventional radiotherapy. The implication is that small micro-metastases could escape sterilisation by radionuclides administered at activity levels sufficient to eradicate larger tumours. It is suggested that single agent targeted radiotherapy should not be used for treatment of disseminated malignancy when multiple tumours of differing size, including micrometastases, may be present. The analysis implies that an advantage might result from the use of a panel of several radionuclides (including short-range emitters) or from combining targeted radiotherapy using long-range beta-emitters with external beam irradiation or some other modality to which microscopic tumours are preferentially vulnerable.

N-(2-hydroxypropyl)methacrylamide copolymers targeted to the hepatocyte galactose-receptor: pharmacokinetics in DBA2 mice

N-(2-Hydroxypropyl)methacrylamide (HPMA) copolymers containing doxorubicin (DOX) and galactosamine can be targeted to the hepatocyte galactose receptor for organ-specific chemotherapy of primary and metastatic liver cancer. Here we report the dose-dependent pharmacokinetics of this macromolecular conjugate. Following intravenous administration to mice most efficient liver targeting was seen at low dose (0.05 mg DOX kg-1), with receptor saturation observed using higher bolus doses. Repeated low dose bolus injections did not cause down-regulation of the galactose receptor and targeted drug delivery rates of greater than or equal to 2 micrograms DOX g-1 liver h-1 were achieved. DOX is released from such conjugates intracellularly via action of lysosomal proteinases. It was shown that isolated rat liver lysosomal enzymes (Tritosomes) can release unmodified DOX from the peptidyl side chain Gly-Phe-Leu-Gly at a rate greater than or equal to 3 micrograms DOX g-1 liver h-1 i.e. the hydrolytic capacity is greater than the observed rate of drug delivery to the liver lysosomes in vivo. Although most conjugate would be captured by normal hepatocytes following intravenous administration, it was shown that the human hepatoma cell line HepG2 retains the galactose receptor, accumulating and processing the conjugate efficiently. Potential dose limiting toxicities of such drug conjugates could include cardio- or hepatotoxicity. Administration of conjugate reduced the 15 min heart level of DOX approximately 100-fold compared with that observed for an equivalent dose of free drug. Preliminary experiments showed that plasma levels of alkaline phosphatase, alanine transaminase and asparate transaminase did not change following administration of HPMA copolymer-daunorubicin (DNR) (10 mg DNR kg-1) indicating no significant heptatoxicity.

The radiobiology of targeted radiotherapy

Targeted radiotherapy consists of biologically selective irradiation of malignant cells by means of radionuclides attached to tumour-seeking molecules. A variety of clinical strategies for targeted radiotherapy may be used, for which different normal tissues will be critical. A large number of radionuclides exist, emitting nuclear particles with a range of path lengths from nanometres to millimetres. An important feature of normal-tissue radiobiology is the dose-rate effect, which is especially marked for late-responding tissues. Radiobiological calculations imply that tolerance dose for targeted radiotherapy using low-LET emitters will depend strongly on the effective half-life of the radionuclide, which will be affected by pharmacokinetics and may vary between patients. Some strategies designed to improve the therapeutic radio (e.g. accelerated clearance of radionuclide) may have modulating effects on the tolerance dose. Tumour response will be governed by the 'four Rs' (repair, repopulation, reoxygenation, redistribution) as well as by mechanisms peculiar to targeted radiotherapy. Analysis based on the extended linear quadratic model predicts that dose-rate effects will be of major importance for only a minority of tumours. Most of the radiation dose to tumour will usually be delivered over a time-scale of a few days. This might give insufficient time for tumour reoxygenation, making the use of hypoxic sensitizers appropriate. A special feature of targeted radiotherapy is the complex relationship between tumour curability and tumour size for different radionuclides. For long-range beta-emitters, microscopic tumours may be operationally resistant because of inefficient absorption of radionuclide disintegration energy in small volumes. Short-range emitters will be more efficient in sterilization of micrometastases but sterilization of larger tumours may require an unattainable degree of homogeneity of radionuclide distribution. Optimal use of targeted radiotherapy may require it to be combined with external-beam irradiation or chemotherapy. Experimental studies will be necessary to investigate those features of targeted radiotherapy which differ from external-beam irradiation. Future directions may include targeted radiotherapy of minimal numbers of tumour cells detected by use of molecular probes. Such applications call for use of short-range alpha-emitters and Auger emitters whose radiobiology will become increasingly important.

Antibody-targeted photolysis: in vitro studies with Sn(IV) chlorin e6 covalently bound to monoclonal antibodies using a modified dextran carrier

A monoclonal antibody-dextran-Sn(IV) chlorin e6 immunoconjugate was prepared by a technique involving the site-specific covalent modification of the monoclonal antibody oligosaccharide moiety. Dextran carriers were synthesized with a single chain-terminal hydrazide group, which was used as the coupling point between the carrier and the monoclonal antibody carbohydrate. Selective in vitro photolysis of SK-MEL-2 human malignant melanoma cells was accomplished using several conjugates prepared from anti-melanoma 2.1 (chromophore:antibody molar ratios, 6.8 and 11.2). Phototoxicity, as measured by clonogenic assay, was dependent on the delivered dose of 634-nm light and was observed only for conjugates that bound SK-MEL-2 cells. As judged by competitive inhibition radioimmunoassay, conjugates prepared in this fashion showed excellent retention of antigen binding activity relative to the unmodified antibody.

Biodegradable emboli and antibody targetting of colorectal and gastric hepatic metastases: a pilot study

The effect of degradable starch microspheres (DSM) on the passage of a low molecular weight marker through the liver of patients with metastases was compared with the passage of an anti-carcinoembryonic antigen monoclonal antibody. In all six patients studied DSM reduced the passage of the marker into the systemic circulation. In three patients who received labelled whole antibody, DSM had no effect. In two of three who received antibody fragments a similar delay to the low molecular weight marker was observed. This delay is likely to be a result of the smaller size of the fragments and may represent accumulation within the extravascular space.

Effect of polarity and differentiation on antibody localization in multicellular tumour spheroid and xenograft models and its potential importance for in vivo immunotargeting

Two monoclonal antibodies (MAbs) AUAI and HMFGI recognize antigens located on different membrane domains of polarized epithelial cells. We have assessed the accessibility of these antigens in multicellular tumour spheroids produced in culture using a well-polarized (HRA-19) and a non-polarized cell line (LoVo) of human large-bowel carcinoma origin. Multicellular spheroids of HRA-19 cells develop polarity, so that the membrane which is in contact with the culture medium (apical) becomes antigenically distinct from the membrane facing the centre of the spheroids (basolateral). This was confirmed by immunostaining sections of spheroids with 2 MAbs, AUAI and HMFGI. AUAI recognizes an antigen located exclusively on the basolateral membranes of polarized epithelial cells, and stained only internal membranes in spheroid sections. Conversely HMFGI, which recognizes an antigen located on the apical membranes, stained only the periphery of the spheroids. These 2MAbs were then radiolabelled with 125I and incubated with live spheroids for 4 hr at 37 degrees C. Autoradiographs of spheroid sections showed a marked difference between the 2 MAbs. 125I-HMFGI-radioantibody localized exclusively on the spheroid surface in a pattern identical to the in vitro immunostaining pattern, while 125I-AUAI radioantibody showed no binding in spite of the uniform presence of antigen on all tumour cells basolaterally. This appeared to be the result of the inaccessibility of basolateral antigenic sites in well-polarized epithelial cells because of the tight junctions connecting these cells at their apical surfaces. In contrast to the HRA-19 cell line LoVo, spheroids do not develop polarity; as a result, when stained with AUAI, variable antigenic expression all over the cell surface was seen. Autoradiographs of these spheroids showed 125I-AUAI binding with a penetration to a depth of about 1-3 cells, while HMFGI which shows no reactivity with this cell line in vitro, did not bind. This phenomenon was further investigated in xenografts of the HRA-19 cell line. It was shown that in a well-differentiated adenocarcinoma where the tumour cells forming acini are arranged in a polarized fashion, the luminal antigenic sites may be inaccessible to the injected MAb. The striking differences in binding of MAbs on polarized and unpolarized tumours indicate the importance of cell polarization and exact location of antigenic sites for in vivo immunotargeting.

Effect of galactose on interaction of N-(2-hydroxypropyl)methacrylamide copolymers with hepatoma cells in culture: preliminary application to an anticancer agent, daunomycin

A series of copolymers were prepared containing 1,2:3,4-di-O-isopropylidene-6-O-methacryloyl-alpha-D-galactopyranose (0 to 99 mol %), methacryoyltyrosinamide and N-(2-hydroxypropyl)methacrylamide (99 to 0 mol %). The effect of galactose content on interaction with hepatoma cells in vitro was studied. Increased galactose content caused increased accumulation of N-(2-hydroxypropyl)methacrylamide copolymers by two human hepatoma cell lines (Hep G2 and SAH), but accumulation by rat and mouse hepatoma (HTC and NCTC) was not galactose dependent. Accumulation of N-(2-hydroxypropyl)methacrylamide copolymers by Hep G2 was shown to be an active process, being inhibited by low temperature and by the metabolic inhibitor 2,4-dinitrophenol. Addition of N-acetylgalactosamine and polymer-galactose to the incubation medium resulted in a concentration-dependent inhibition of accumulation of galactose-containing polymers. Addition of fucose or galactose was without effect at the concentrations used. Polymers bearing galactosamine or fucosylamine residues and, in addition, daunomycin were evaluated for cytotoxicity against Hep G2 and SAH. N-(2-Hydroxypropyl)methacrylamide copolymer-bound daunomycin produced a dose-dependent inhibition of DNA synthesis (measured by incorporation of [3H]thymidine), and the galactose-containing polymer showed greatest inhibition.

Sacral scintigraphy for bone marrow dosimetry in radioimmunotherapy

Myelosuppression has been identified as the dose-limiting toxicity in radioimmunotherapy studies. Accurate bone marrow dosimetry is, therefore, necessary to evaluate bone marrow toxicity which may result from systemic cancer treatment with radiolabeled monoclonal antibodies. Dose to the red marrow was determined in 20 patient studies with 131I labeled anti-carcinoembryonic antigen, anti-alpha-feto-protein, or anti-human chorionic gonadotropin monoclonal antibody for diagnosis or treatment of diverse metastatic carcinomas, using a new technique involving sacral scintigraphy and a previously reported blood-based methodology. For the sacral technique, anterior and posterior gamma camera images of the pelvis were obtained at multiple times. Regions of interest were drawn around the sacrum in order to quantitate activity uptake as a function of time using the conjugate view counting method. Cumulated activity in red marrow was determined by curve integration and division by 0.099, since it has been estimated that 9.9% of the total red marrow is contained in the sacrum of the adult. Red marrow doses were then obtained by multiplying the cumulated activities by the appropriate S factor. These doses were compared to red marrow doses obtained from serial whole blood samples taken from these patients. Cumulated activity in the red marrow was determined from the blood with the assumption that the activity concentration in the blood and red marrow were equal. The mean red marrow dose per injected activity was 2.0 +/- 0.9 rad/mCi using the sacral data and 2.7 +/- 1.3 rad/mCi using the blood data (P less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

A tumour spheroid model for antibody-targeted therapy of micrometastases

Human neuroblastoma cells grown as tumour spheroids were briefly incubated with a conjugate of 131I and an anti-human neuroectodermal monoclonal antibody UJ13A. Unbound 131I was removed by washing and the spheroids observed in culture conditions for up to 4 weeks. Spheroid response to irradiation was evaluated as time to reach 10x treatment volume and proportion of spheroids sterilised. Spheroid growth was found to be affected by both the activity of 131I-UJ13A and the duration of the incubation. Na[131I], 131I-HSA, 131I labelled non-specific antibody and unlabelled antibody were found to be relatively ineffective compared to 131I-UJ13A. The tumour spheroid model has applications in the evaluation of antibodies or antibody fragments and different radionuclides which may be considered for radioimmunotherapy of micrometastases.

Monoclonal antibody-targeted radiotherapy of renal cell carcinoma using a nude mouse model

Radiation dosimetry and monoclonal antibody (MAB)-targeted radiotherapy studies were performed to evaluate the feasibility of using tumor-preferential MAB as targeting agents for internal radiotherapy of renal cell carcinoma (RCC). Two human RCC xenograft lines, TK-177G and TK-82, were established in nude mice and studied using MAB A6H as a targeting agent. This MAB has previously demonstrated excellent in vivo localization to RCC xenografts. Two doses of A6H (13 to 19 micrograms) labeled with iodine 131 (110 to 130 microCi) caused the tumor to regress or arrested the tumor growth in both xenografts. Similar doses (18 to 43 micrograms; 120 microCi) of 131I-labeled control MAB AFP-22 or of unlabeled A6H did not inhibit tumor growth. While most mice in the control groups had tumors greater than 250 mg in weight by day 43, none of the tumors in mice treated with 131I-labeled A6H grew to that size during the 3-month observation period. Sequential computerized scintigraphy was used to calculate the amount of radioisotope localized in tumor versus normal mouse tissue. Therapeutic doses of 131I-labeled A6H delivered a median calculated radiation dose of 38 cGy/microCi (range, 28 to 57) injected dose to RCC xenografts, and a median of 0.9 cGy/microCi to normal mouse tissues. These findings suggest that A6H is able to target radioisotopes highly specifically to RCC and achieve a therapeutic effect in the experimental setting.

A microdosimetric model of astatine-211 labeled antibodies for radioimmunotherapy

Astatine-211 is an alpha-emitter with a short half-life (7.2 hr). This paper discusses the potential of 211At targeted by antibodies for tumor therapy and the possible advantage of 211At over beta- and gamma-emitting radionuclides such as 131I currently employed in the field of radioimmunotherapy. Since the longest range alpha-particle from 211At is only 67 microns and the rate of energy loss is high (track averaged linear energy transfer LT approximately 120 keV/micron), a disintegration of 211At produces a large and extremely localized deposition of energy. A Monte-Carlo model has been developed for studying the stochastic fluctuation of alpha-particle hits and energy deposition in cell nuclei in an attempt to determine the efficacy of 211At-labeled antibodies for tumor cell inactivation. Calculations have been performed for 2 extreme conditions: (a) the case of 211At retained in the capillary, and (b) for a homogeneous distribution of 211At-labeled antibody in the tumor. The results of these two calculations represent the boundary conditions between which any real solution must lie. Finally, developments to the model to include antibody transport across the capillary membrane and through the tumor tissue are discussed.

The diffusion of a tumour-specific monoclonal antibody in lymphoma infiltrated spleen

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Radioimmunotherapy of malignancy using antibody targeted radionuclides

Antibodies directed against tumour associated antigens provide a means for delivering preferentially cytotoxic radionuclides to the cells of primary and secondary tumours. The factors that influence the effectiveness of the radiation in the tumour compared with its effect on the radiosensitive normal tissues include the specificity of the antibody, the distribution of targeted energy within the tumour and the host's response to the injected foreign antibody. Recently some encouraging results from clinical trials of radioimmunotherapy have been reported in the literature. There is a continual search for more avid and specific antibodies, and the techniques of genetic engineering are being applied to the problem of reducing the antigenicity and mass of the carrier antibody. The improved efficiency of the labelled antibody needs to be supplemented by an identification of those tumours most likely to respond to this form of therapy.

Prospects for monoclonal antibody therapy of leukemia and lymphoma

The development of monoclonal antibodies has led to renewed interest in the use of antibodies to treat malignant disease. Unfortunately, treatment with unmodified antibodies has been disappointing. Therapy with unmodified antibodies has been limited by the failure of host effector mechanisms to eliminate antibody-coated tumor cells and by the emergence of variant cells lacking the target antigen. The use of antibodies as carriers of radionuclides has the potential for overcoming both these limitations because the conjugates will be directly cytotoxic and a conjugate bound to a cell surface will deliver radiation to adjacent cells lacking the target antigen. Experimental and clinical therapy trials of radionuclide antibody conjugates have yielded promising results with both tumor-specific antibody and with antibodies against differentiation antigens. Bone marrow toxicity has been dose limiting. Bone marrow support will most likely be required for the treatment of leukemia and lymphoma due to the marrow involvement with malignant cells. In the case of solid tumors, bone marrow infusion may allow administration of curative doses of radionuclide conjugates. Although at an early stage in development, radiolabeled antibodies have the potential for contributing significantly to the therapy of malignant disease.

Detection of specific anti-antibodies in patients treated with radiolabeled antibody

Over 100 patients have received cyclic treatment with polyclonal 131I labeled anti-ferritin and anti-carcinoembryonic antigen (CEA) antibodies from different animal species (rabbit, pig, cynomolgous monkey, bovine, and baboon). Because survival was prolonged from original cyclic treatment, retreatment with original antibodies (recycling) became a necessary consideration. An assay using autoradiography of Ouchterlony gels, with diffusion of patients' sera against the varied radiolabeled antibodies, was developed to detect anti-antibody precipitin bands. Anti-antibody could be detected with a sensitivity to the 60 ng level. Sera from 35 patients given from 1 to 7 separate cycles (2 injections/week, total antibody 6 mg/cycle) of radiolabeled foreign antibody were studied for the production of anti-antibodies. Anti-antibodies were detected in 11 of 22 primary hepatoma patients studied, 3 of 4 intrahepatic biliary cancer patients, and 0 of 9 Hodgkin's disease patients. In all but two of the patients, the anti-antibodies produced were specific for the species used in the treatment of the patient. Eight patients were reinjected (recycled) with previously used antibodies and the presence or absence of precipitin bands correlated with the ability of these antibodies to deposit in the tumor or to be rapidly degraded. The importance of this assay is its simplicity, sensitivity, and the rapid detection of anti-antibody activity for patients requiring treatment with radiolabeled antibodies.

Site-specific covalent modification of monoclonal antibodies: in vitro and in vivo evaluations

A strategy for covalent modification of monoclonal antibodies utilizing the oxidized oligosaccharide moieties on the molecule was evaluated and compared to more conventional methods. As judged by quantitative in vitro measurements, a monoclonal antibody conjugate prepared via the oligosaccharides retained the homogeneous antigen binding property and affinity of the unmodified antibody. In contrast, conjugates of the same antibody, modified to the same degree on either lysines or aspartic and glutamic acid side chains, were heterogeneous in their antigen binding and had lowered affinity. In vivo biodistribution and nuclear-imaging experiments were also performed with a second monoclonal antibody and a tumor xenograft model. Antibodies modified on the oligosaccharides with either a peptide labeled with iodine-125 or a diethylenetriaminepentaacetic acid chelate with indium-111 localize into target tumors more efficiently than the same antibody radiolabeled on either tyrosines or lysines. These in vivo results, when compared to those reported in the literature for conventionally modified antibodies, suggest that oligosaccharide modification of monoclonal antibodies is a preferred method of preparing conjugates.

Detection of colorectal carcinoma by emission-computerized tomography after injection of 123I-labeled Fab or F(ab')2 fragments from monoclonal anti-carcinoembryonic antigen antibodies

This clinical study was based on experimental results obtained in nude mice grafted with human colon carcinoma, showing that injected 131I-labeled F(ab')2 and Fab fragments from high affinity anti-carcinoembryonic antigen (CEA) monoclonal antibodies (MAb) gave markedly higher ratios of tumor to normal tissue localization than intact MAb. 31 patients with known colorectal carcinoma, including 10 primary tumors, 13 local tumor recurrences, and 21 metastatic involvements, were injected with 123I-labeled F(ab')2 (n = 14) or Fab (n = 17) fragments from MAb anti-CEA. The patients were examined by emission-computerized tomography (ECT) at 6, 24, and sometimes 48 h after injection using a rotating dual head scintillation camera. All 23 primary tumors and local recurrences except one were clearly visualized on at least two sections of different tomographic planes. Interestingly, nine of these patients had almost normal circulating CEA levels, and three of the visualized tumors weighed only 3-5 g. Among 19 known metastatic tumor involvements, 14 were correctly localized by ECT. Two additional liver and several bone metastases were discovered by immunoscintigraphy. Altogether, 86% of the tumor sites were detected, 82% with F(ab')2 and 89% with Fab fragments. The contrast of the tumor images obtained with Fab fragments suggests that this improved method of immunoscintigraphy has the potential to detect early tumor recurrences and thus to increase the survival of patients. The results of this retrospective study, however, should be confirmed in a prospective study before this method can be recommended for the routine diagnosis of cancer.

Solid tumor models for the assessment of different treatment modalities: XXIII. A new approach to the more effective utilization of radiotherapy alternated with chemotherapy

This study with the rat hepatoma 3924A demonstrated the marked improvement in tumor cure rates and control of tumor growth that can be achieved by the addition of cyclophosphamide (CP) to multiple fractions of radiation per day (MFD) schedules given intermittently. MFD radiation was delivered over a 2-day period followed by CP (150 mg/kg or 0.9 g/m2) 1 day later; this combined course was repeated at 11-day intervals (to allow for gastrointestinal tract and bone marrow recovery) for a total of 3 courses over a 23-day period. Cure rates of 30, 50 and 60% were achieved with total radiation doses of 4500, 6000 and 7500 rad, respectively, when the MFD radiation was given with CP. No cures and no complete responses were realized when the same intermittent MFD schedules for radiation were employed up to 9000 rad without CP. Other groups of 10 animals each were treated with daily fractions of 100, 150, 188, 250 and 375 rad given on days 0-9, 11-20 and 22-31. A 150 mg/kg or 0.9 g/m2 dose of CP was given after each course of daily radiation on days 10, 21 and 32 in the combined treatment groups. No complete responses or tumor cures occurred with radiation alone given daily for total radiation doses, which were increased from 3000 to 11,250 rad. Only the highest radiation dose given, 375 rad per day to a total of 11,250 rad, resulted in a complete response rate and tumor cure rate of 50% when CP was added. The addition of CP to the daily fractionation schedules reduced the total dose needed to give a growth delay of 100 days by 39% (5600 rad versus 9200 rad). The addition of CP to the intermittent MFD schedules further reduced the total dose needed to give a growth delay of 100 days to 4200 rad. Major improvements in some types of cancer treatment may be realized if we can develop clinical protocols for the alternate use of chemotherapy and radiotherapy as we have done successfully in our experimental program. The finding that intermittent MFD radiation schedules are as effective as daily schedules when given alone suggests that greater flexibility of patient management in clinical radiotherapy may be possible without a major loss of therapeutic effectiveness. These alternated fractionated schedules offer the possibility of optimizing treatment in terms of patient convenience and economy as well as the potential for improving the effectiveness of the interaction of radiotherapy with radiosensitizers, radioprotectors, and hyperthermia in addition to chemotherapy.

A model system that predicts effective half-life for radiolabeled antibody therapy

Radiolabeled antibodies to tumor associated proteins localize in both experimental and clinical cancers. In the therapeutic applications of radiolabeled antibody, tumor effective half-life (composite of biological and physical half-lives), along with the concentration of isotope deposited and energies of the isotope used, determine the tumor dose. Antibodies directed against the same antigenic specificity but derived from different species have varied tumor and whole body effective half-lives and as a result, achieve different tumor doses. In vitro testing does not evaluate the in vivo differences in effective half-life that affect tumor dose. We have developed an animal model to evaluate the effective half-life and biodistribution of radiolabeled immunoglobulin (IgG) from diverse species. To determine the relevance of such a model, the effective half-lives and tissue distributions of the different immunoglobulins in the model were compared to those obtained from the clinical program using the same radiolabeled antibody preparations. In both the experimental model and in the clinical trials, radiolabeled immunospecific and normal IgG derived from monkey, rabbit, and porcine sources had the longest effective half-lives, goat and sheep had intermediate effective half-lives, and chicken and turkey had the shortest effective half-lives. Prescreening of bovine and baboon normal IgG predict long half-lives and similar organ distributions. These species have been immunized for clinical use. Bovine IgG has a long clinical half-life and has been added to our other successful antibodies. Baboon IgG is now ready for clinical testing. The value of this model system is that it appears to be an effective in vivo preclinical screen for tumor effective half-life of antibodies and IgG from diverse species, thus guiding potential clinical use.

CT scanning for radiation therapy treatment planning of hepatoma

One hundred forty-five patients with hepatoma had CT scanning for radiation therapy treatment planning. In order to demonstrate the anatomical distortions that occur with hepatoma and its effect on treatment planning, a control group of 50 colorectal cancer patients with normal livers was analyzed for comparison. The objectives of planning were to deliver as homogeneous a dose to the whole liver as possible and not to treat more than one of two functional kidneys or more than one-half of both functional kidneys. Conventional AP/PA portals were defined by physical examination, intravenous pyelogram, and bowel gas patterns at simulation and were found to be inadequate for the treatment of 76% of patients with hepatoma and 10% of patients with normal livers. Among the control group patients with no hepatoma, only 10% required oblique portals and 6% could not be treated because of left hydronephrosis or a solitary right kidney. Because the distortion of the liver in hepatoma in relationship to the kidneys required portal modification in 76% of hepatoma cases; 39% required oblique planning, 24% AP/PA, 20% PA and left lateral portals, and 17% required 4-field, 3-field or other plans in order to meet the treatment planning objectives. We concluded that all patients receiving radiation therapy to the liver for hepatoma require CT scanning for optimum radiation therapy treatment planning because of the hepatic distortion that occurs in hepatoma and the requirements of renal tolerance.

Antibody-mediated radiotherapy

Antibodies that react with antigens on the surface of tumor cells but not normal cells have great potential for cancer detection and therapy. If radiolabeled without loss of immunologic specificity, such antibodies may be able to deliver cytoxic amounts of radiation. Target-cell specificity and a high extraction coefficient are necessary with any radionuclide in order to minimize normal tissue irradiation. Tumor-cell-retention time and the rate of catabolized radionuclide will also influence ultimate applicability. Among the unanswered questions for choosing a radionuclide is the choice of particle emitter. Although classic beta emitters have been used in a number of clinical situations, they have not had a major impact on disease outcome except in diseases of the thyroid. Unfortunately, Auger emitters such as iodine 125 are cytotoxic only when localized within close proximity to the genome. On the other hand, alpha emitters such as astatine 211 eliminate the need for subcellular sequestration but not cell-specific localization.

Requirements for a treatment planning system for radioimmunotherapy

Cancer-seeking antibodies carrying radionuclides can, in theory, be very powerful agents for the radiotherapy of cancer. However, as with all radiotherapy, the undesired dose to critical normal organs is the limiting factor that determines success or failure. The distribution of radiation dose in cancer and noncancer tissue is highly dependent on choices the therapist can make: choices of the antigens to be targeted, choices of the antibodies or antibody fragments to be used, choices of radionuclides, of amounts, of timing, and other electives. New technologies, especially of monoclonal antibody production, make the options myriad. Optimization of this therapy 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, for particular treatment selections. These tracer techniques can now be implemented by advanced equipment for quantitative, tomographic radionuclide imaging and strengthened by dynamic modeling of the physiological parameters which govern radionuclide distribution, and hence radiation dose distribution.

Radiolabeling of monoclonal antibody against carcinoembryonic antigen with 88Y and biodistribution studies

The biodistribution of the 202 monoclonal antibody against CEA labeled with 88Y by the bicyclic DTPA anhydride method was studied in normal Balb/c mice. The in vitro binding to 1 X 10(7) CO112, LS174T and WiDR colon cancer cells was 21.0, 27.3 and 18.8%, respectively. The binding to an equal number of KM-3 leukemia cells and normal human lymphocytes was 8.9 and 3.2%, respectively. Liver, spleen, kidney and blood were the tissues that showed the highest uptake of radiolabeled antibody in vivo.

Use of specific antibody for rapid clearance of circulating blood background from radiolabeled tumor imaging proteins

A major problem that arises when radiolabeled serum proteins are used for tumor imaging is the presence of a large amount of circulating background activity that persists for several days. This delays imaging for at least 2 days following injection and necessitates computer subtraction of simulated background (second radiopharmaceutical injection) which introduces artifacts that are difficult to control. We propose here the injection of specific antibody immediately before imaging as an alternate way of reducing blood background through clearance of the immune complex by the liver. 111In-alkyl human transferrin and IgG were injected IV in BALB/c tumor mice, and followed in 18 h by anti-human transferrin and anti-human IgG antibody IV. Two hours later, the tumor and organ distribution of activity was compared with control mice not receiving antibody. 111In-transferrin blood activity was reduced to 1/48 of control with no decrease in tumor concentration: as a result, the tumor to blood ratio increased from 1.4:1 to 78:1. 111In-IgG blood activity was reduced to 1/17 of control, again with no decrease in tumor. The tumor to blood ratios increased from 0.7:1 to 17:1. The liver picked up most of the blood activity with none of the complex going to spleen, bone marrow, or kidney. Dog experiments showed clearance of blood was 90% complete in less than 15 min following antibody injection. Simultaneous scintillation images showed complete clearance of activity from the heart and great vessels in the chest and neck, and over the abdomen, with a concomitant increase in liver activity but no increase in spleen, kidney, or bone marrow activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Radioimmunodetection and radioimmunotherapy

The development of monoclonal antibodies that recognize tumor-associated antigens has led to significantly greater practical possibilities for producing highly specific radiolabeled antibodies for diagnosis and therapy of human tumors. A number of problems remain before this technique will be ready for routine clinical application however. Achieving the high target to background ratio that are predicted on theoretical grounds is a major challenge in cancer investigation.

Serum ferritin in relation to the course of Hodgkin's disease

Serum levels of patients with Hodgkin's disease were evaluated during the course of the disease. Significant correlations were seen in relation to the stage of the disease, to sex and to various hematological data. An increase of Fer levels during progression and a decrease during remission was observed. Possible pathogenetic mechanisms are discussed.

Primary hepatocellular cancer--present results and future prospects

Hepatocellular cancer is an enormously difficult clinical problem. This review provides an overview of selected basic and applied aspects of the care of hepatoma patients. Important pathophysiologic and prognostic features are now recognized. Initially, chemotherapy programs focused on the use of those agents commonly employed for gastrointestinal neoplasms (fluoropyrimidines, anthracyclines and alkylators). When employed as a conventional intravenous bolus, only Adriamycin is a reproducibly effective agent. However, because of the unique dual vascular supply of the liver and tumor, the use of intraarterial (IA) infusion chemotherapy has become more popular. In this regard, of promise are the application of IA FUDR and Adriamycin, the use of totally implanted infusion systems, and hepatic artery embolization. Furthermore, combinations of whole liver irradiation with chemotherapy seem efficacious. New directions for the therapy of hepatoma patients will focus on superior drug-radiation combinations, exploration of isotopic immunoglobulin, and hormonal therapy. There is currently no standard therapy for hepatoma patients, but prospects for the future have never been so bright.

The impact of future technology on oncologic diagnosis: oncologic imaging and diagnosis

Over the past few years, the discipline of medical imaging has entered an evolutionary period that reflects primarily the introduction of computers and digital technology into the imaging process. Clinical applications of this evolution realized to date (e.g., transmission computed tomography, ultrasound and quantitative nuclear medicine) are only indicative of future developments that promise to increase the contributions of medical imaging in a very substantial manner. This increase in the area of oncologic diagnosis is one of the more exciting possibilities existing in medicine today.

Hepatocellular carcinoma in young people

The clinical and pathologic features of 23 cases of hepatocellular carcinoma occurring in patients younger than age 35 years (mean age, 17.4 years) were analyzed. Ten of these (43%) were the fibrolamellar oncocytic variant (FLO), characterized by large polygonal neoplastic hepatocytes and lamellar bundles of collagen. The remainder (non-FLO) showed the usual wide range of gross and histologic patterns typical of hepatocellular carcinoma in older age groups. Overall, hepatocellular carcinoma was more common in females than in males. The FLO variant was characterized by a longer duration of symptoms prior to diagnosis, increased frequency of resectability of the tumor, and infrequency of mitoses. Of particular importance is the fact that 5 of 10 patients with the FLO variant are alive and clinically free of disease 1 1/2 to 8 years postoperatively, while none of the 13 patients with non-FLO hepatocellular carcinoma is alive and free of disease. There was no significant difference between the two groups in mean age at diagnosis, presence of single versus multiple hepatic tumors, vascular invasion, or tumor necrosis. Although cirrhosis was present in three non-FLO patients and none of the FLO patients, the difference was not statistically significant. The prognosis of hepatocellular carcinoma in young patients does not appear to differ from that in older patients, with the exception of the fibrolamellar oncocytic variant, a variant which is common in younger patients.

Selective tumor localization in experimental hepatoma by radiolabeled antiferritin antibody

The in vivo localization of 131I-radiolabeled antiferritin and normal IgG in the H-4-II-E rat hepatoma model was investigated by serial necropsy. Groups of 14 to 18 animals were injected with 500 microCi (200 micrograms) of normal and antiferritin IgG. The total dose from the nonpenetrating beta radiation was calculated for tumor and normal tissue, and expressed as a targeting ratio of antiferritin to normal IgG for each organ studied. The results demonstrate 2.9 times greater dose deposition in tumors of animals treated with 131I-antiferritin than with 131I-normal IgG. 131I-antiferritin deposited equivalently in primary tumors and metastatic lesions of similar size. The specific binding in tumors could be competitively inhibited by the addition of unlabeled antiferritin but not unlabeled normal IgG. Specific targeting with 131I-antiferritin comparison to 131I-normal IgG did not occur in any normal tissue. There was considerable variation in the dose deposition in different normal tissues.