Quantitative bone scintigraphy. A methodological evaluation in prostate cancer.

PURPOSE: To evaluate a simple method for quantification of focal activity in bone scintigraphy (BS). MATERIAL AND METHODS: The gamma camera was calibrated using a phantom. Quantitative bone scintigraphy (QBS) was performed on 11 men recently diagnosed with prostate cancer (PCa), for whom routine BS showed involvement of the skeleton. Following endocrine therapy for 4 to 8 months, a second QBS was performed. Changes in QBS values were then compared to changes in serum levels of prostate-specific antigen (PSA). RESULTS: PSA response indicating regression of PCa was accompanied by a decrease in the QBS value in 8 of the 11 patients. The overall mean error of the QBS values was 15%. CONCLUSION: QBS according to this method is a relatively simple procedure that might contribute to objective evaluation of therapeutic effects in skeletal metastases, although its validity must be tested in a larger clinical material.

Stability and immunoreactivity of the monoclonal anticytokeratin antibody TS1 after different degrees of iodination.

The immunoreactivity, stability and in vivo kinetics of an anticytokeratin 8 monoclonal antibody, TS1, were investigated following different degrees of labeling with 125I (0.2, 1 and 2-3 125I/TS1 MAb). By testing with ELISA, it was demonstrated that a high degree of iodination, i.e. > 2 125I/TS1, caused a rapid decrease in immunoreactivity to almost zero within 10 days. Furthermore, a complete degradation to low molecular weight fragments and free iodine was seen, as shown by SDS PAGE and autoradiography. The differently labeled radionuclide conjugates were injected into nude mice inoculated with HeLa Hep2 cells and tumor doses (estimated by MIRD formalism), tumor:non-tumor dose ratios, % I.D./gram tissue, Gy/MBq and in vivo kinetics of the differently labeled MAbs were determined. Despite the in vitro instability of the highest iodinated radionuclide conjugate, it was possible to deliver high doses to the tumors if the conjugate was injected into the animal immediately after completion of the iodination procedure. Increases from 1.4 Gy to 15.2 Gy delivered tumor dose were obtained with a tenfold increase in the specific activity, without alterations in the tumor:non-tumor tissue dose ratios. There is room for significant improvements in efficacy at radioimmunotherapy, which can be gained by optimizing the degree of iodination. For therapeutical applications a high degree of iodination may be an advantage.

Methods for estimating uptake and absorbed dose in tumours from 125I labelled monoclonal antibodies, based on scintigraphic imaging of mice.

Monoclonal antibodies for radioimmunotargeting are often tested in tumour bearing nude mice. In vivo determination of the uptake of the monoclonal antibody in the tumour requires quantitative scintigraphy, and this in turn requires an adequate method for subtraction of radiation from the normal tissue. For this reason, two different methods for background subtraction were evaluated, a contralateral background region of interest or an irregular one, surrounding the tumour. A pinhole collimator was used for the scintigraphy and the monoclonal antibodies were labelled with 125I. Furthermore, a method was developed for estimation of the mean absorbed dose in the tumour from these repeated quantitative scintigraphic measurements. This requires that the tumour mass can be accurately estimated in vivo. Finally, the results were compared with in vitro measurements of the uptake.

Serum amyloid P component scintigraphy in familial amyloid polyneuropathy: regression of visceral amyloid following liver transplantation.

Familial amyloid polyneuropathy (FAP) associated with transthyretin (TTR) mutations is the commonest type of hereditary amyloidosis. Plasma TTR is produced almost exclusively in the liver and orthotopic liver transplantation is the only available treatment, although the clinical outcome varies. Serum amyloid P component (SAP) scintigraphy is a method for identifying and quantitatively monitoring amyloid deposits in vivo, but it has not previously been used to study the outcome of visceral amyloid deposits in FAP following liver transplantation. Whole body scintigraphy following injection of iodine-123 labelled SAP was performed in 17 patients with FAP associated with TTR Met30 and in five asymptomatic gene carriers. Follow-up studies were performed in ten patients, eight of whom had undergone orthotopic liver transplantation 1-5 years beforehand. There was abnormal uptake of 123I-SAP in all FAP patients, including the kidneys in each case, the spleen in five cases and the adrenal glands in three cases. Renal amyloid deposits were also present in three of the asymptomatic carriers. Follow-up studies 1-5 years after liver transplantation showed that there had been substantial regression of the visceral amyloid deposits in two patients and modest improvement in three cases. The amyloid deposits were unchanged in two patients. In conclusion, 123I-SAP scintigraphy identified unsuspected visceral amyloid in each patient with FAP due to TTR Met30. The universal presence of renal amyloid probably underlies the high frequency of renal failure that occurs in FAP following liver transplantation. The variable capacity of patients to mobilise amyloid deposits following liver transplantation may contribute to their long-term clinical outcome.

Combinations of nonlabeled, 125I-labeled, and anti-idiotypic antiplacental alkaline phosphatase monoclonal antibodies at experimental radioimmunotargeting.

PURPOSE: Placental alkaline phosphatase (PLAP) is a membrane-bound oncofetal antigen that can be used for radioimmunotargeting. Preinjection of nonlabeled monoclonal anti-PLAP antibody (H7) and postinjection of monoclonal anti-idiotypic anti-PLAP antibody (alpha H7) were used in order to improve the localization efficacy of 125I-labeled H7. MATERIAL AND METHODS: A human cervix adenocarcinoma cell line (HcLa Hep 2) was inoculated subcutaneously in 24 nude mice. Repeated quantitative radioimmunoscintigraphic recordings were performed on 27 occasions in each of the 24 mice during the observation period which lasted for nearly 3 months. The tumor and nontumor doses were calculated according to the Medical International Radiation Dose Committee formula on the basis of the scintigraphic data. RESULTS: All tumors were clearly visualized as early as one day after injection of 125I-labeled H7. The remaining radioactivity was exclusively located in the tumors at days 30-81. As much as 12-16% of the injected dose/g accumulated in the tumors during the first 2 days after injection, and remained stable at this high level for approximately 10 days in all investigated groups. Radioactivity in the whole body was rapidly eliminated during the same time period. The highest tumor/nontumor dose ratio was obtained after a single injection of 125I-labeled H7. CONCLUSION: Neither a preinjection of nonlabeled H7 nor a postinjection of alpha H7 nor a combination of both strategies resulted in improved tumor/nontumor dose ratios compared to a single injection of labeled H7. The monoclonal antibody H7 has a rapid and high uptake, combined with a prolonged retention time in the tumors. The kinetic properties of H7 are different from antibodies targeting intracellular tumor antigens.

Twenty years with monoclonal antibodies: State of the art--Where do we go?

In this review, we have selected some parameters with the potential to improve the efficacy of RIL and RIT. Focus has partially been on the behaviour of radiolabelled antibodies in vivo in relation to properties and amounts of both target antigen and the antibodies used. If, out of the 28 factors listed in Table 1, some should be given preference in future work, it is our opinion that after the initial saturation of the tumour site a rapid decrease in redundant antibody is of significant importance. Furthermore, quantitative aspects of both antigens and antibodies should be more carefully evaluated when possible. By combining several of the listed approaches toward increasing efficiency, a more extensive use of RIL and RIT could be expected in the future.

Secondary antibodies as tools to improve tumor to non tumor ratio at radioimmunolocalisation and radioimmunotherapy.

One way of selectively improving the efficiency of radioimmunolocalization and radioimmunotherapy is to eliminate redundant, circulating, non-targeting radiolabeled antibodies after saturation of the target sites. Secondary antibodies of different types have been proposed as clearing agents for such purposes. The conceptually different approaches of the 'secondary antibody' strategy including its advantages and limitations are discussed. This mini-review also presents a model describing the kinetics of the components (the antigen, the primary and secondary antibodies) and approaches required to improve the efficacy of both radioimmunolocalization and radioimmunotherapy.

Use of anticytokeratin monoclonal anti-idiotypic antibodies to improve tumor:nontumor ratio in experimental radioimmunolocalization.

A syngeneic, high-affinity, anti-idiotypic monoclonal antibody (MAb; alpha TS1) raised against an anticytokeratin monoclonal antibody (TS1) was evaluated as a second antibody to promote the rapid clearance of radiolabeled TS1 from the blood during experimental radioimmunolocalization. By using a novel biosensor technology (BIAcore), association rate dissociation rate, and affinity constants between the idiotype and the anti-idiotype could be determined. The in vivo results in nude mice carrying HeLa Hep 2 tumors demonstrate the possibility of selectively regulating the amount of the idiotypic 125I-labeled circulating MAb by in vivo injection of this high-affinity, anti-idiotypic antibody. Injection of the anti-idiotype in a molar ratio of 0.75 to the idiotype cleared the blood pool from circulating radiolabeled idiotype within 24 h, with a concomitant rapid excretion of 125I in urine. The total amount of remaining radioactivity in the animals decreased to 15-20% during these 24 h, with the tumors still retaining 60-65% of their initial radioactivity. This approach, using syngeneic primary and secondary MAbs with minimized immunogenicity, significantly improves the tumor:nontumor ratio, thus improving efficiency in experimental radioimmunolocalization and radioimmunotherapy, leaving the endogenous antibody repertoire of the host unaffected.

In vivo and in vitro interactions between idiotypic and antiidiotypic monoclonal antibodies against placental alkaline phosphatase.

A monoclonal antiidiotypic antibody alpha H7, was generated against a monoclonal antibody H7 with specificity towards placental alkaline phosphatase. The in vitro and in vivo effects of alpha H7 were investigated. The antiidiotypic antibody was found to generate stable complexes with the radiolabeled idiotypic antibody, visualized both in vivo and in vitro, as revealed by PAGE and autoradiography. Using biosensor technology (BIAcore, Pharmacia) the interactions were followed in real time and the association rate, dissociation rate, and affinity constants between the reactants were determined (KA H7/PLAP 6.7 x 10(9) M-1, KA H7/alpha H7 3.2 x 10(9) M-1). By in vivo injection of the antiidiotype, a rapid dose dependent clearance of circulating radiolabeled idiotypes was demonstrated and a decrease in total body radioactivity was recorded with a concomitant dramatic increase in non-protein-bound 125I excreted in the urine. It is concluded that idiotypic-antiidiotypic interactions offer advantages in the regulation of antibody levels in vivo.

Radioimmunodetection of ovarian cancer.

Radioimmunoscintigraphy (RIS) is a potentially valuable method for the detection of primary, secondary and recurrent malignant tumours. Antigens that have been used for monitoring as well as for RIS of ovarian carcinomas include CA 125, PLAP, HMFG, and CA 19-9. Between 70 and 100% of the tumours have been detected at RIS when these antigens have been used. Conventional methods, e.g., computerized tomography (CT) and ultrasonography (US), demonstrate similar or lower detection rate than RIS for tumour diagnosis. RIS gives additional information to conventional radiological methods (CT and US) for the detection of occult ovarian carcinomas. A review of earlier investigations is given and our own recent results using PLAP as a target antigen are presented. The future potential of the technology is discussed.

Alternative technologies to generate monoclonal antibodies.

Several new technologies to generate and modify established hybridomas that produce monoclonal antibodies have recently been presented and further development should make them more suitable for diagnostic and therapeutic techniques. Different proteolytic procedures have been used for the fragmentation of intact antibodies to Fab2' and Fab fragments and recombinant DNA techniques have made it possible to obtain chimeric, humanized, Fv fragments and single-chain Fvs. A review of the new approaches is presented and the future implications are discussed.