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[Preparation of hematoporphyrin-herceptin photoimmunoconjugate for photoimmunotherapy].

OBJECTIVE: To prepare photoimmunoconjugate of hematoporphyrin (HP) and herceptin, and study its killing and apoptosis-inducing effect on tumor cells BT-474. METHODS: HP-herceptin photoimmunoconjugate was synthesized with EDCI as the condensator. After exposure of the cells to 630 nm laser, the killing effect of the conjugate and cell apoptosis were evaluated by MTT assay and flow cytometry. RESULTS: Compared with free HP at equivalent dose, the immune reactivity, killing effect and the apoptosis-inducing effect of HP-herceptin immunoconjugate on BT-474 cells was enhanced (P<0.05). CONCLUSION: The killing effect of HP-herceptin immunoconjugate is stronger than free HP on BT-474 cells.

Antibodies, Monoclonal↗

Effects of radiolysis on yttrium-90-labeled Lym-1 antibody preparations.

UNLABELLED: The physical half-life of 2.6 days and 2.2 MeV beta emissions of 90Y provide excellent properties for radioimmunotherapy applications. However, the clinically useful beta particles may be a source of radiation-induced damage of 90Y-labeled immunoconjugate radiopharmaceuticals during preparation or short-term storage. The stability of 90Y-labeled Lym-1 antibody was studied in standard radiopharmacy conditions to establish a formulation at which radiolysis is not a problem. METHODS: Lym-1-21T-BAD immunoconjugate intermediate was prepared according to our standard procedure, then labeled with 90Y at 1, 2, 4 and 9.4 mCi/mg Lym-1 using 0.5 M tetramethylammonium acetate, pH 7, labeling buffer. Each mixture was challenged in diethylenetriaminepentaacetic acid to remove nonspecifically bound 90Y. The 90Y-21T-BAD-Lym-1 products were purified by centrifuged molecular sieving column chromatography. The radiochemical purity and immunoreactivity of each preparation was monitored daily by high-performance liquid chromatography (HPLC) and solid-phase radioimmunoassay, respectively, for 3 days. The preparation at 2 mCi/mg was also formulated in 4% (wt/vol) human serum albumin (HSA) overall and at 9.4 mCi/mg in five-fold water, 4 and 10% (wt/vol) HSA overall; all were monitored as above. RESULTS: The monomeric quality and purity profile of products at 1 and 2 mCi/mg were retained (> or = 80%) as was their immunoreactivity (> or = 75%) over 3 days. The radiochemical purity and immunoreactivity of the product at 4 mCi/mg declined to 65% and 28%, respectively, by 3 days after preparation and in just 48 hr, the product at 9.4 mCi/mg had degraded to 21% in radiochemical purity with only 3% immunoreactivity. The current HPLC data and earlier published chromatographic evidence did not support a compromised radiochemical integrity of 90Y-DOTA complexes by loss of 90Y from the DOTA chelate. CONCLUSION: Radiolysis of 90Y-labeled antibody preparations did not appear to be a problem at 90Y-21T-BAD-Lym-1 products < or = 2 mCi/mg. Human serum albumin proved to be an effective radioprotectant as the initial 100% immunoreactivity of the product at 2 mCi/mg was retained for 72 hr. The results underscore the need for appropriate formulations and dilutions of clinical doses of 90Y immunopharmaceuticals immediately after manufacture.

Antibodies, Monoclonal↗

[Application of monoclonal antibody for drug delivery system--missile therapy for cancer].

Clinical applications of monoclonal antibody for selective delivery of anticancer drug, toxin and radioisotope were reviewed. The difficulties in preparation and clinical application of chemoimmunoconjugate were pointed out. Also the difficulties of immunotoxin in clinical trial due to its high toxicity had been discussed and it is assumed that development of blocked ricin may overcome many problems related to toxicities. Clinically most advanced immunoconjugate seems to be radioimmunoconjugate. Among three types of immunoconjugates preparation of radioimmunoconjugate is easiest and some promising clinical trials were introduced in this review.

Animals↗

Experimental studies on the role of antibody fragments in cancer radio-immunotherapy: Influence of radiation dose and dose rate on toxicity and anti-tumor efficacy.

Whereas bivalent fragments have been widely used for radio-immunotherapy, no systematic study has been published on the therapeutic performance of monovalent conjugates in vivo. The aim of our study was, therefore, to determine the therapeutic performance of (131)I-labeled Fab as compared to bivalent conjugates and to analyze factors that influence dose-limiting organ toxicity and anti-tumor efficacy. The maximum tolerated doses (MTDs) and dose-limiting organ toxicities of the (131)I-labeled anti-CEA antibody MN-14 [IgG, F(ab')2 and Fab] were determined in nude mice bearing s.c. human colon cancer xenografts. Mice were treated with or without bone marrow transplantation (BMT) or inhibition of the renal accretion of antibody fragments by D-lysine or combinations thereof. Toxicity and tumor growth were monitored. Radiation dosimetry was calculated from biodistribution data. With all 3 (131)I-labeled immunoconjugates [IgG, F(ab')2 and Fab], the red marrow was the only dose-limiting organ; MTDs were 260 microCi for IgG, 1,200 microCi for F(ab')2 and 3 mCi for Fab, corresponding to blood doses of 17 Gy, 9 Gy and 4 Gy, respectively. However, initial dose rates were 10 times higher with Fab as compared to IgG and 3 times higher as compared to F(ab')2. The MTD of all 3 immunoconjugates was increased by BMT by approximately 30%. In accordance with renal doses below 10 Gy, no signs of nephrotoxicity were observed. Despite lower absorbed tumor doses, at equitoxic dosing, Fab fragments were more effective at controlling tumor growth than the respective bivalent fragment or IgG, probably due to higher intratumoral dose rates. Our data indicate that the improved anti-tumor effectiveness of antibody fragments as compared to IgG and the higher myelotoxicity at comparably lower red marrow doses are most likely due to the higher initial dose rates observed with antibody fragments.

Animals↗

Lymphokines, monoclonal antibodies, and other biological response modifiers in the treatment of cancer.

Biologicals and biological response modifiers (BRMs) represent a new class of agents for cancer therapy. Historically, there have been many attempts to stimulate the immune response with nonspecific immunomodulators in the form of bacterial extracts, viruses, and chemicals. Although these approaches have occasionally proven useful under defined conditions in experimental models, their extension to the clinic has been largely unsuccessful. Recent advances in molecular biology and hybridoma technology have made available genetically engineered lymphokines and cytokines, as well as monoclonal antibodies, as highly purified biologicals for cancer treatment. These agents may act directly on tumor cells and/or may act on the patient's own biological responses to induce an antitumor response. Selective defects in T-cell function have recently been identified in cancer patients and in patients with acquired immunodeficiency syndrome (AIDS). Simultaneously, the availability of gamma interferon (gamma-IF) and interleukin-2 (IL-2) may allow for the selective correction of these T-cell deficits, leading to restoration of the patient's immune responses and perhaps correction of the clinical syndromes. Preliminary data suggest that gamma-IF and IL-2 have in vitro activity on these T-cell defects, and the preliminary evidence that these agents have activity in vivo will be reviewed. Extensive trials are being conducted at the National Cancer Institute with monoclonal antibodies as anticancer agents. Animal model experiments have demonstrated considerable antitumor activity of immunoconjugates using monoclonal antibodies tied to toxins. Preliminary clinical results suggest that T-101 in leukemia and lymphoma and 9.2.27 in malignant melanoma may prove useful as specific reagents in the treatment of these disorders. While the antitumor effects with these antibodies have not been dramatic, our preliminary data in approximately 30 patients with leukemia, lymphoma, and melanoma clearly demonstrate the ability of intravenous monoclonal antibody to locate and specifically label tumor cells bearing the target antigens. It has been possible to localize antibody on the tumor cells in melanoma deposits that are barely visible in the skin. These data and radioimaging data suggest a future role for immunoconjugates as anticancer agents.

Antibodies, Anti-Idiotypic↗

Selective killing of T cells by immunotoxins directed at distinct V beta epitopes of the T cell receptor.

The potency and specificity of anti-T cell receptor (TcR)-directed immunotoxins were studied in two T cell leukemia lines, HPB-ALL and Jurkat, and in primary T cells. Immunoconjugates were synthesized using anti-CD3, or distinct anti-V beta antibodies cross-linked to CRM9, a binding site-mutant of diphtheria toxin. All TcR-expressing cells display the CD3 complex on the plasma membrane. HPB-ALL cells express the V beta 5 gene product in the beta subunit of the TcR, while Jurkat cells express V beta 8. V beta expression in primary T cells isolated from buffy coats is heterogeneous. Primary T cell populations expressing specific V beta epitopes in the TcR were generated by plating CD3+ T cells on V beta-specific antibody-coated flasks or by positive immunomagnetic selection. Immunotoxins directed against the invariant CD3 epsilon epitope target and kill all T cells. Immunoconjugates targeted at distinct anti-V beta epitopes are specific for cells that express the corresponding gene product in the TcR. The results demonstrate the ability of anti-TcR-based immunotoxins selectively to kill T cells with defined V beta epitopes. These reagents may be clinically useful in disorders mediated by autoreactive T cell populations exhibiting V beta restriction and in the treatment of clonal TcR-expressing lymphomas.

Antibodies, Monoclonal↗

Targeting cancer chemotherapy using a monoclonal antibody (NCC-LU-243) conjugated with mitomycin C.

Two kinds of immunoconjugate (T-3M and T-11M) of murine monoclonal antibody with mitomycin C (MMC) were developed using spacers containing a disulfide (T-3M) or thiocarbamate (T-11M) bond. A murine monoclonal antibody (NCC-LU-243) raised against a human small cell lung carcinoma cell line, Lu-24, in nude mice, is an IgG2a monoclonal antibody that recognizes a 145-kDa protein on the cell surface membrane. T-3M and T-11M showed affinity for the LU-243 antigen-positive H-69 cell line but not for the antigen-negative Lu-65 cell line in vitro. In the in vitro MTT assay, the order of efficacy of these compounds was T-11M > T-3M > MMC against antigen positive H-69 and T-11M = MMC > T-3M against antigen-negative K562. When antigen-positive H-69 was transplanted into nude mice for in vivo assay, the maximum tolerated dose of T-3M was twice as high than that of the parent compound MMC. Furthermore, T-3M showed higher antitumor activity against antigen-positive H-69 than MMC conjugated with a non-specific rabbit IgG in vivo. When the maximum tolerated doses of T-3M and MMC were administered to H-69-bearing nude mice, the effect of T-3M was superior to that of MMC, whereas no differences were observed between the antitumor activity of T-3M and MMC against antigen- negative MX-1, a human breast carcinoma. These two immunoconjugates of monoclonal antibody with mitomycin C are thought to be useful for targeting cancer chemotherapy against human small cell lung carcinomas.

Animals↗

Immunoscintigraphy of prostatic cancer: preliminary results with 111In-labeled monoclonal antibody 7E11-C5.3 (CYT-356).

A phase 1 study was conducted with the investigational immunoscintigraphic agent, 111In-CYT-356, a radiolabeled, site-specific immunoconjugate of monoclonal antibody 7E11-C5.3, in 40 patients with prostatic carcinoma and known distant metastases. Each patient received a single intravenous infusion of CYT-356 (dose range, 0.1-5 mg) radiolabeled with approximately 5 mCi of 111In. None of the patients experienced adverse reactions. One patient who received a 5-mg dose developed antibodies to the CYT-356 immunoconjugate. 111In-CYT-356 immunoscintigraphy detected bony metastases in 21 of 38 patients (55%), including 12 of 14 (86%) receiving concomitant hormonal therapy, and soft tissue lesions in four of six patients (67%). Antibody imaging detected occult lesions in the bony pelvis and lumbar spine, which were confirmed by follow-up imaging tests, in one patient. Higher CYT-356 doses may clear the blood pool more slowly. These results suggest that 111In-CYT-356 can be safely administered to patients with prostatic carcinoma and that further clinical investigation of this agent is warranted.

Aged↗

Highly sensitive time-resolved fluoroimmunoassay of human immunoglobulin E by using a new europium fluorescent chelate as a label.

A new europium fluorescent chelate, 4,4'-bis(1",1",1",2",2",3",3"-heptafluoro-4",6"-hexanedione-6"-yl) - chlorosulfo-o-terphenyl (BHHCT)-Eu3+, was used as a label for highly sensitive time-resolved fluoroimmunoassay of human IgE. Two assay formats were employed in the analysis. In the first format, an immunoconjugate of rabbit anti-human IgE antibody-human IgE-biotinylated goat anti-human IgE antibody-BHHCT-Eu(3+)-labeled SA (or BHHCT-Eu(3+)-labeled BSA-SA; BSA, bovine serum albumin; SA, streptavidin) was used for measurement. The method gives the detection limits of 3.6 x 10(-2) IU/ml (labeled SA) and 1.1 x 10(-2) IU/ml (labeled SA-BSA). In the second format, an immunoconjugate of goat anti-human IgE antibody-human IgE-rabbit anti-human IgE antibody-biotinylated goat anti-rabbit IgG antibody-BHHCT-Eu(3+)-labeled SA (or BHHCT-Eu(3+)-labeled BSA-SA) was used for measurement. The detection limits of these methods are 3.0 x 10(-3) IU/ml (labeled SA) and 1.5 x 10(-3) IU/ml (labeled BSA-SA). The above detection limits are one to two orders of magnitude lower than those of the conventional radioimmunoassay and enzyme immunoassay. The CV of the present method is less than 7%, and the recovery is in the range of 85-105% for serum samples.

Animals↗

Tumor vascular targeting using a tumor-tissue endothelium-specific monoclonal antibody as an effective strategy for cancer chemotherapy.

In this study, we attempted to develop tumor vascular targeting with a tumor tissue endothelium-specific monoclonal antibody. TES-23, which strongly and selectively recognizes tumor tissue endothelial cells, was chemically conjugated with Neocarzinostatin (NCS), and the anti-tumor effect was examined. The immunoconjugate, TES-23-NCS, showed, through the use of tumor hemorrhagic necrosis, a marked anti-tumor effect on KMT-17 tumors in rats at a dosage of 17 micrograms/kg (NCS equivalent) without any side effects, probably due to specific tumor vascular injury. By contrast, TES-23 alone (107 micrograms/kg), NCS alone (17 micrograms/kg), and Mopc-NCS (Mopc, 107 micrograms/kg; NCS, 17 micrograms/kg), the immunoconjugate of control antibody, did not have any anti-tumor activities. By tissue distribution analysis, TES-23 and TES-23-NCS showed high accumulation in KMT-17 tumors 1 h after intravenous administration. Moreover TES-23 also accumulated in Sarcoma-180 tumors in mice 1 h after intravenous administration. These results suggest that TES-23 may be a candidate for a potential tumor vascular targeting agent that is applicable to a wide variety of tumor types.

Animals↗

Control of hypertrophic scar growth using antibody-targeted photolysis.

Hypertrophic scar is marked by excess collagen accumulation secondary to an increased vascularization response in the scar and an increase in fibroblast cell density. It is currently the most debilitating long-term complication of the surviving burn patient, and at present, there is no routinely effective form of therapy. In this study, we investigated the potential use of antibody-targeted photolysis (ATPL) in treating hypertrophic scars. An immunoconjugate consisting of a photosensitizer (Sn-chlorin e6) linked to a monoclonal antibody that binds to human myofibroblasts (PR2D3) was prepared, which in response to photoactivation produces singlet oxygen in close proximity to the target cell surface. The model used for these studies consisted of 1-mm 3 human hypertrophic scar tissue implants in athymic mice. These implants increase approximately 20-fold in volume over a period of 15 days. Four days after implantation immunoconjugate was injected directly into scar implants allowed to diffuse throughout for 24 hr before implants were illuminated with laser light at 630 nm (120 J/cm 2). ATPL treatment caused a significant reduction in total growth compared to the untreated controls (P < 0.05). No effect was observed when an irrelevant conjugate (anti-Pseudomonas aeruginosa) was used. Histological examination of the ATPL-treated implants 24 hr post-ATPL revealed the presence of a large number of lipid droplets indicative of massive cell damage and infiltration by mononuclear cells and neutrophils.

Animals↗

Pharmacokinetics and biodistribution of samarium-153-labelled OC125 antibody coupled to CITCDTPA in a xenograft model of ovarian cancer.

The use of samarium-153 in the context of radioimmunotherapy of cancers has been limited by the instability of antibody labelling, which produces high uptake concentrations in liver and bone. This study compares the pharmacokinetics and biodistribution of 153Sm-labelled OC125 monoclonal antibody, in whole or F(ab')2 fragment form and with diethylene triamine penta-acetic acid (DTPA) or 6-p-isothiocyanatobenzyl diethylene triamine penta-acetic acid (CITCDTPA) coupling, in nude mice grafted subcutaneously with an ovarian adenocarcinoma line (SHIN-3) expressing CA125 antigen. The specific activity of the immunoconjugates was 18.5-55.5 MBq/mg, and their immunoreactivity exceeded 65%. With 153Sm-DTPA-OC125F(ab')2, the stability study in serum indicated that 50% of the metal remained bound to the antibody. The pharmacokinetic study showed a retention half-life of 25.1 h and blood clearance of 0.72 ml/h. The biodistribution study indicated tumour uptake of 4.53%+/-0.49% of injected activity per gram (%ID/g) at 24 h and tumour-to-liver and tumour-to-bone ratios of 0.23+/-0.02 and 1.54+/-0.49 respectively at 24 h. With 153Sm-CITCDTPA-OC125F(ab')2, serum stability was greater (87% of the metal remaining bound to the antibody), retention half-life was 22.25 h and blood clearance was 2.23 ml/h. Tumour was better targeted (8.30%+/-3.56%ID/g at 24 h), and tumour-to-liver and tumour-to-bone ratios were 1.17+/-0.36 and 7.08+/-3.09 respectively at 24 h. However, renal retention remained elevated (29.76%+/-9. 41%ID/g at 24 h). With intact IgG, renal uptake decreased (1.41%+/-0. 49%ID/g at 24 h), but tumour uptake was lower than with fragments (1. 46%+/-0.58%ID/g at 24 h). Liver uptake was higher (tumour-to-liver ratio 0.10+/-0.05), and blood clearance was slower. The stability and distribution of 153Sm-CITCDTPA were more favourable than those of 153Sm-DTPA for application in radioimmunotherapy. Quantitative analysis performed using digitized images obtained by conventional autoradiography and the imaging plate system indicated that the latter system is suitable for biodistribution studies of immunoconjugates.

Animals↗

Pharmacokinetics, tissue distribution, and in vivo antitumor effects of the antimelanoma immunotoxin ZME-gelonin.

Antibody ZME-018 is directed against the gp240 glycoprotein on the surface of more than 80% of human melanoma cell lines and fresh biopsy specimens. Previous studies in our laboratory described the in vitro cytotoxicity and specificity of an immunoconjugate composed of mAb ZME-018 and the plant toxin gelonin. The present study described the in vivo pharmacokinetics and therapeutic effects of ZME-gelonin in human xenograft/nude mouse models. Pharmacokinetic studies of 125I-labeled ZME-018 and ZME-gelonin demonstrated a shorter terminal-phase plasma half-life of the immunoconjugate than native ZME (20.6 h compared to 41.3 h). The initial volume of distribution of the ZME-gelonin was also higher compared to that of ZME alone (2.85 ml compared to 1.94 ml) suggesting an enhanced distribution of the conjugate outside the vasculature. The corresponding area under the concentration/time curve for the ZME-gelonin conjugate was 40% lower than that of ZME alone (80.8 compared to 139.6 microCi.ml-1 x min). In nude mice bearing well-developed human tumor A375 melanoma xenografts, administration of 125I-labeled ZME and ZME-gelonin resulted in tumor-to-blood ratios of 1.9 +/- 0.5 and 1.5 +/- 0.6 respectively by 72 h. Compared with ZME, ZME-gelonin conjugate caused an increase in the content of radiolabel in kidney, spleen and liver. Treatment of nude mice bearing well-developed (150 mm3) s.c. A375-M xenografts with divided doses of ZME-gelonin, ZME, gelonin, or saline resulted in suppression of tumor growth in the immunotoxin group but virtually no retardation of tumor growth in the control groups. Using a murine model for a rapidly growing lethal metastatic human melanoma, treatment with ZME-gelonin resulted in a mean survival of 44 days, 213% increase in mean survival time compared with the saline treatment (14.2 +/- 2 day survival). Given these encouraging results, we are proceeding with further preclinical development of this immunotoxin.

Animals↗

Clinical radioimmunolocalization with a rat monoclonal antibody directed against c-erbB-2.

Lymph node status is still the single most important prognostic factor in breast cancer and surgery remains the only reliable means of providing this information. This study evaluates using a highly specific radiolabeled monoclonal antibody to provide equivalent information. The optimum labeling conditions for radiolabeling a monoclonal antibody against the gene product of the protooncogene c-erbB-2 with Tc99m were established. This immunoconjugate was next evaluated in a mouse model system and averaged 20% localization of the total injected dose per gram of tumor at 24 h. Ten patients have had this immunoconjugate, with planar and tomographic reconstructed images being obtained at 24 h. The resulting images were compared to histopathological examination of the surgical specimens. Three patients acted as normal controls, two patients were selected on the basis of inappropriate sampling of adjacent ductal carcinoma in situ, three patients demonstrated only moderate antigen expression, and two patients demonstrated excellent tumor localization in both breast primary and regional node metastases. The high specificity of this antibody, ease of labeling, and excellent localization performance with a good antigen target encourage the development of this system as a method of localization and a potential means of antibody-guided therapy.

Adult↗

Characterization and In Vitro Cytotoxic Effect of Adriamycin-conjugated Monoclonal Antibody Prepared Against Breast Cancer Cell Line.

We have produced an adriamycin-conjugated monoclonal antibody, AM1, covalently linked by acid-labile cis-aconitic spacer. The immunoconjugate, cis-aconitic adriamycin(cAA)-AM1, was confirmed to retain the binding activity against human breast cancer cell lines by flow cytometry. The immunoconjugate was shown to be internalized into antigen-positive cancer cells by flow cytometry analysis and high performance liquid chromatography. Antitumor effects of cAA-AM1 were assessed on human breast cancer and colon cancer cell lines, with inhibition of (3) H-leucine uptakes to the cells. cAA-AM1 demonstrated a selective cytotoxicity to ZR-75-1 which was reactive with AM1, whereas it showed no antitumor effect on SW1116 cells which did not react with AM1. Free adriamycin demonstrated a non-selective cytotoxicity against both cell lines. AM1 alone and cAA-control IgM did not show any antitumor effect on ZR-75-1. These results suggest that cAA-AM1 retains binding activity and specificity against breast cancer cells in vitro.

Journal Article↗

Progress in the treatment of acute myeloid leukaemia in adults.

There has been important progress in the treatment of Acute Myeloid Leukaemia (AML) in patients under 60 years. A remission rate of 80% can be achieved by several schedules, and 40-45% of patients diagnosed will survive. It may still be possible to improve remission induction treatment eg by intensifying the Ara-C dose although may this only be detectable in an improved disease free survival. The is to reduce relapse. The risk main challenge is pre-determined by a number of powerful risk factors. In the experience of the MRC age, cytogenetics and clearance of blasts from the bone marrow after course 1. Using the later two in combination good risk patients (FAB M3, t(8;21) t(15;17) inv(16)) have a relapse risk of 32%. Poor risk (blasts >15% after course 1 or abnormalities of Chs 5 or 7, 3q- and complex changes have a relapse risk of 82%. All other cases are standard risk and ve a relapse risk of 56%. FLT3 mutations have been detected in about 25% of cases and provide additional negative predictive value overall and within each risk group. The assessment of the most effective consolidation treatment must be made taking into account the heterogeneity of the relapse risk. The MRC investigated the role of allo and autoBMT in addition to intensive chemotherapy. The data was analysis on an intent-to-treat or donor vs no donor basis. Although both types of transplant were able to reduce relapse overall and in all risk groups, there was an overall survival advantage only in standard risk patients. Since chemotherapy has improved since this study, there remains uncertainty about the benefit of transplant in all risk groups. Overall this experience has demonstrated that relapse can be reduced with more therapy. It is probable that the limits of conventional chemotherapy have been reached. The new AML15 trial will assess the value of adding the immunoconjugate (Mylotarg) to induction and/or chemotherapy. Improvements in older patients have been less detectable. MRC trials over the last 20 years show an improvement in remission rate (now 65%) but persistent poor survival (12% at 5 years). In the MRC AML11 Trial three induction schedules were compared (DAT vs ADE vs MAC) with DAT being superior. A comparison of a total of 3 vs 6 courses of treatment or the addition of interferon maintenance did not improve results. Newer approaches currently being assessed include resistance modulation; addition of immunoconjugate and minigrafts. New targets for treatment are emerging of which the most interesting is FLT3 inhibitors.

Acute Disease↗

Copper-67 as a therapeutic nuclide for radioimmunotherapy.

The application of the beta particle-emitting nuclide 67Cu in radioimmunotherapy is reviewed. The production of the nuclide is outlined, and different production modes are discussed with an emphasis on cyclotron production. A short survey of copper chelators currently used for antibody labelling and their impact on the pharmacokinetics of 67Cu-labelled immunoconjugates is provided. Protocols for antibody labelling with 67Cu as well as quality control procedures for 67Cu-labelled antibodies are described. Preclinical data on the biological properties of 67Cu-labelled immunoconjugates are reported and discussed. 67Cu-labelled antibodies show higher and more persistent tumour uptake than their radioiodinated counterparts due to accumulation of labelled metabolites in tumour cells. Biodistribution of 67Cu-labelled antibody fragments has been improved by selection of negatively charged chelators and peptide linkers. Pharmacokinetic analysis of the accumulated dose in tumour and critical organs such as the kidney and liver indicates that, despite this improvement, intact 67Cu-labelled antibodies achieve higher tumour uptake and better therapeutic ratios than 67Cu-labelled antibody fragments and that they are at present the logical choice for clinical studies. Clinical studies using 67Cu-labelled antibodies in lymphoma, colon carcinoma and bladder cancer patients are reviewed. Some of the advantages over radioiodinated antibodies found in the preclinical work, such as higher tumour uptake and better tumour/blood ratios, have also been found with systemic application in lymphoma and colon carcinoma. However, in both lymphoma and colon carcinoma patients, the radiation dose to the liver has been found to be higher from 67Cu- than from 131I-labelled antibodies. The intravesical application of 67Cu-labelled antibody has been shown to be a promising approach for targetting cytotoxic radiation to superficial bladder tumours, without detectable systemic absorption. Given the favourable properties of 67Cu-labelled antibodies, it is the reliable availability of the 67Cu nuclide which is the limiting factor for their more widespread evaluation in radioimmunotherapy trials.

Chelating Agents↗

Monoclonal antibodies in cancer detection and therapy.

Anticancer antibodies have had a long history in the management of cancer, with major applications having been shown in the immunohistochemistry and immunoassay of tumor-associated antigen markers. With the advent of hybridoma-derived monoclonal antibodies, attempts to use these more reproducible reagents in vivo for cancer detection and therapy have intensified. Radiolabeled monoclonal antibodies appear to be gaining a role in the management of cancer by means of imaging methods to detect sites of increased radioactivity, and several products have been developed and tested clinically. In the area of radioimmunotherapy, a number of problems still need to be solved, including low tumor uptake of the radioimmunoconjugate, dose-limiting myelotoxicity, and the induction of an immune response to repeated doses of murine (foreign) immunoglobulins. Similar problems exist for toxin and drug immunoconjugates, but these also fail to benefit from the "bystander" effect of the ionizing radiation delivered with radioimmunoconjugates, and plant and bacterial toxin molecules appear to have additional immunogenicity that restricts repeated injections. Despite these limitations, recombinant engineering and other chemical approaches are making progress in developing second-generation immunoconjugates that may be more efficacious and less immunogenic as cancer-selective therapeutics. Although nonconjugated, "naked", murine monoclonal antibodies have shown limited success in the therapy of human neoplasms, human and "humanized" forms may be more effective, particularly in lymphatic tumors. Some evidence also suggests that anti-idiotype antibodies (antiantibodies) may serve as surrogate antigens in cancer vaccines. Thus, a number of promising immunologic approaches for cancer diagnosis, detection, and therapy have made important progress in recent years.

Animals↗