This article reviews the methods of pretargeting, which involve separating the targeting antibody from the subsequent delivery of an imaging or therapeutic agent that binds to the tumor-localized antibody. This provides enhanced tumor:background ratios and the delivery of a higher therapeutic dose than when antibodies are directly conjugated with radionuclides, as currently practiced in cancer radioimmunotherapy. We describe initial promising clinical results using streptavidin-antibody constructs with biotin-radionuclide conjugates in the treatment of patients with malignant gliomas, and of bispecific antibodies with hapten-radionuclides in the therapy of tumors expressing carcinoembryonic antigen, such as medullary thyroid and small-cell lung cancers.

Calcitonin DT may be superior to initial clinical staging and among the most powerful prognostic indicators in MTC.

Two major points are emphasized in this series: 1) the presence in 7 histologically analyzed streak gonads of a homogeneous 45,X chromosomal complement suggests that the invasion of the primitive genital ridge by a such a cell line may induce abnormal gonadal development; 2) 3 males, apparently normal at birth, developed late onset abnormalities such as dysgenetic testes leading to infertility, Ulrich-Turner stigmata, dysmorphic features, and mild mental retardation. These data indicate the importance of an accurate clinical and histologic evaluation of any patient presenting with 45, X/46,XY mosaicism.

As a first step in the synthesis and the study of DNA polyintercalating drugs, dimers of acridines have been prepared. Their DNA binding properties have been studied. It has been determined that wen the chain separating the two aromatic rings is longer than a critical distance, bisintercalation is actually observed and that the DNA binding affinity becomes quite large (>108-109 M-1). It is shown also that the optical characteristics of these molecules are dependent on the sequences of DNA. The fluorescence intensity of one of these dimers when bound to DNA varies as the fourth power of its A+T content. This derivative could be used as a fluorescent probe of DNA sequence.

Many applications envisioned for liposomes in cell biology and chemotherapy require their direction to specific cellular targets. The ability to use antibody as a means of conferring specificity to liposomes would markedly increase their usefulness. We report here a method for covalently coupling soluble proteins, including monoclonal antibody and Staphylococcus aureus protein A (ref. 4), to small sonicated liposomes, by using the heterobifunctional cross-linking reagent N-hydroxysuccinimidyl 3-(2-pyridyldithio)propionate (SPDP, Pharmacia). Liposomes bearing covalently coupled mouse monoclonal antibody against human beta 2-microglobulin [antibody B1.1G6 (IgG2a, kappa) (B. Malissen et al., in preparation)] bound specifically to human, but not to mouse cells. Liposomes bearing protein A became bound to human cells previously incubated with the B1.1G6 antibody, but not to cells incubated without antibody. The coupling method results in efficient binding of protein to the liposomes without aggregation and without denaturation of the coupled ligand; at least 60% of liposomes bound functional protein. Further, liposomes did not leak encapsulated carboxyfluorescein (CF) as a consequence of the reaction.

An ethidium homodimer and an acridine ethidium heterodimer have been synthesized. The ethidium and the acridine chromophore were introduced in such bifunctional intercalators in order to allow the fluorometric study of the interaction of such molecules with DNA, which is reported in the companion paper (Gaugain, B., Barbet, J., Capelle, N., Roques, B.P., & Le Pecq, J.B.(1978) Biochemistry 17 (following paper in this issue)). In the preparation of the acridine-ethidium dimer, we report the use of acetyl groups as new protecting agents in the phenanthridine series. Conformational studies of these molecules by visible absorption and NMR spectroscopy indicate that these dimers exist in equilibrium between folded and unfolded conformations and that this equilibrium is pH and temperature dependent. Models for the geometry of the folded forms are proposed.

An ethidium homodimer and acridine ethidium heterodimer have been synthesized (Gaugain, B., Barbet, J., Oberlin, R., Roques, B. P., & Le Pecq, J. B. (1978) Biochemistry 17 (preceding paper in this issue)). The binding of these molecules to DNA has been studied. We show that these dimers intercalate only one of their chromophores in DNA. At high salt concentration (Na+ greater than 1 M) only a single type of DNA-binding site exists. Binding affinity constants can then be measured directly using the Mc Ghee& Von Hippel treatment (Mc Ghee, J. D., & Von Hippel, P. H. (1974) J. Mol. Biol. 86, 469). In these conditions the dimers cover four base pairs when bound to DNA. Binding affinities have been deduced from competition experiments in 0.2 M Na+ and are in agreement with the extrapolated values determined from direct DNA-binding measurements at high ionic strength. As expected, the intrinsic binding constant of these dimers is considerably larger than the affinity of the monomer (ethidium dimer K = 2 X 10(8) M-1; ethidium bromide K = 1.5 X 10(5) M-1 in 0.2 M Na+). The fluorescence properties of these molecules have also been studied. The efficiency of the energy transfer from the acridine to the phenanthridinium chromophore, in the acridine ethidium heterodimer when bound to DNA, depends on the square of the AT base pair content. The large increase of fluorescence on binding to DNA combined with a high affinity constant for nucleic acid fluorescent probes. In particular, such molecules can be used in competition experiments to determine the DNA binding constant of ligands of high binding affinity such as bifunctional intercalators.

BackgroundDespite the early theoretical prediction of the 0+-0+ transition of 90Zr, 90Y-PET underwent only recently a growing interest for the development of imaging radioembolization of liver tumors. The aim of this work was to determine the minimum detectable activity (MDA) of 90Y by PET imaging and the impact of time-of-flight (TOF) reconstruction on detectability and quantitative accuracy according to the lesion size.MethodsThe study was conducted using a Siemens Biograph® mCT with a 22 cm large axial field of view. An IEC torso-shaped phantom containing five coplanar spheres was uniformly filled to achieve sphere-to-background ratios of 40:1. The phantom was imaged nine times in 14 days over 30 min. Sinograms were reconstructed with and without TOF information. A contrast-to-noise ratio (CNR) index was calculated using the Rose criterion, taking partial volume effects into account. The impact of reconstruction parameters on quantification accuracy, detectability, and spatial localization of the signal was investigated. Finally, six patients with hepatocellular carcinoma and four patients included in different 90Y-based radioimmunotherapy protocols were enrolled for the evaluation of the imaging parameters in a clinical situation.ResultsThe highest CNR was achieved with one iteration for both TOF and non-TOF reconstructions. The MDA, however, was found to be lower with TOF than with non-TOF reconstruction. There was no gain by adding TOF information in terms of CNR for concentrations higher than 2 to 3 MBq mL−1, except for infra-centimetric lesions. Recovered activity was highly underestimated when a single iteration or non-TOF reconstruction was used (10% to 150% less depending on the lesion size). The MDA was estimated at 1 MBq mL−1 for a TOF reconstruction and infra-centimetric lesions. Images from patients treated with microspheres were clinically relevant, unlike those of patients who received systemic injections of 90Y.ConclusionsOnly one iteration and TOF were necessary to achieve an MDA around 1 MBq mL−1 and the most accurate localization of lesions. For precise quantification, at least three iterations gave the best performance, using TOF reconstruction and keeping an MDA of roughly 1 MBq mL−1. One and three iterations were mandatory to prevent false positive results for quantitative analysis of clinical data.Trial registrationhttp://IDRCB 2011-A00043-38 P101103