Wolfgang Maier-Borst

Stereotactically guided fractionated radiotherapy: technical aspects.

A system for high precision radiotherapy in the head and neck region has been developed. The components of the system are a head mask connected to a stereotactic frame, a localization unit that can be used during CT- and MR-imaging and a stereotactic target positioner. Conformal precision radiotherapy is planned with a new treatment planning system (Voxelplan-Heidelberg). Three different multi-leaf collimator systems are used. An evaluation of the precision and accuracy of the head fixation system, which was performed with a photogrammetry system, is presented.

A new 68Ge/68Ga radioisotope generator system for production of 68Ga in dilute HCl

Abstract The synthesis of an ion-exchanger resin produced from pyrogallol and formaldehyde and characterized by a highly efficient adsorption for 68 Ge is described. A 68 Ge/ 68Ga radioisotope generator prepared from this resin and operated with 10 ml of 4.5n HCl as eluant constantly showed a high yield of 68 Ga during a time period of more than 200 days with a contamination of less than 1 ppm 68 Ge. A small column, filled with commercially available anion-exchanger resin and coupled in series with the generator, reduces the volume and HCl concentration of the generator eluate in such a way that 80% of the available 68 Ga appears in 4 ml 0.5 N HCl. The eluate is free of radiolytic products and suitable for human use.

The loading rate determines tumor targeting properties of methotrexate albumin conjugates in rats

Albumin dominates the plasma proteins in man. Following our observation that albumin turnover in rodent tumors is markedly increased, we will present evidence that albumin can be employed as an efficient carrier for targeting cytostatic agents like methotrexate (MTX) into tumors. The considerable discrepancy in the molecular weight of MTX (454 Da) and albumin (about 67 000 Da) tempted researchers to load multiple drug molecules on one carrier molecule. It was supposed that the optimal therapeutic efficacy of MTX protein conjugates could be achieved by increasing the number of the molecules of MTX attached to the carrier. In this paper we will show that only loading rates of close to 1 mol of the cytostatic drug MTX/mol of albumin offer optimal conditions for targeting MTX-albumin conjugates into rodent tumors. Conjugates bearing 5, 7,10 and 20 molecules of MTX on average showed considerable alterations in the HPLC profiles of the conjugates compared to albumin. Conjugates carrying 5-20 mol MTX, tagged with a residualizing radiolabel, were efficiently trapped by the liver before reaching the tumor. The tumor uptake rates of these conjugates declined dramatically with an increasing molecular load of the cytotoxic drug linked to albumin. Competition experiments with maleylated bovine serum albumin and fucoidan revealed that scavenger receptors present on the cells of the liver monocyte macrophage system were involved in this process. For further preclinical and clinical studies, we chose MTX-albumin conjugates, derivatized at a molar ratio of 1:1. These conjugates enjoy the same favorable tumor targeting properties like albumin, e.g. high tumor uptake rates, low liver uptake rates and a very long biological half-life

Evaluation of tumour metabolism and multidrug resistance in patients with treated malignant lymphomas

The management of patients with treated malignant lymphomas requires functional methods to differentiate a residual soft tissue mass. Patients with treated Hodgkins lymphoma (HL,n = 20, 68 malignant lesions, three benign lesions) or non-Hodgkins lymphoma (NHL,n = 26, 46 malignant lesions, one benign lesion) were studied with positron emission tomography (PET) and fluorine-18 deoxyglucose (FDG). Oxygen-15 labelled water was used (n = 14, 25 lesions) in addition to FDG in order to obtain information on the tissue perfusion. Long-term follow-up studies with PET and FDG were performed in nine patients up to 511 days after the initiation of second-line therapy. Fourteen patients underwent single-photon emission tomography (SPET) with technetium-99m sestamibi immediately prior to the first PET examination. PET with FDG displays a high sensitivity for the detection of viable tumour tissue, all the malignant lesions being correctly classified in this study. The possible limitations are inflammatory processes, which may obscure tumour detection due to increased FDG uptake, and malignant lesions with low FDG uptake due to reduced perfusion. Difficulties exist in the prognosis of long-term response, since the change in FDG uptake may be variable. Long-term therapy outcome was correlated with the slope values obtained from the standardized integral uptake (SIU) data, which provides a new approach for the evaluation of PET follow-up studies.99mTc-sestamibi, which should reflect the multidrug resistance, was evaluated with respect to therapy outcome. A high uptake of99m-Tc-sestamibi was observed in patients with stable disease or better. The data support the hypothesis that sestamibi may reflect multidrug resistance. Due to technical limitations of the SPET technique, the use of a positron-labelled compound would be superior to SPET for clinical application.

Pharmacokinetics of methotrexate-albumin conjugates in tumor-bearing rats.

Linking chemotherapeutic drugs to a macromolecular carrier system may enhance tumor targeting, reduce toxicity and overcome drug resistance mechanisms. As an elementary model to evaluate the pharmacological properties of macromolecular drug carrier systems we chose rat serum albumin (RSA) for carrier and methotrexate (MTX) as antineoplastic drug. The conjugation procedure yielded conjugates with an approximate 1:1 molar loading rate (MTX(1)-RSA). In the first part of the study a residualizing [111ln]DTPA protein label was used for mapping in vivo the catabolic sites of the native carrier protein and of the MTX(1)-RSA drug conjugate in Walker 256 carcinosarcoma bearing rats. The tumor accumulation was about 14% of the injected dose for the RSA and MTX(1)-RSA tracers after 24 h. Tracer entrapment by organs with an active mononuclear phagocyte system was low (liver below 7% and spleen below 1.5% of the injected dose after 24 h). The 1:1 conjugation of MTX to RSA did not decisively alter the pharmacokinetic properties nor the tumor or tissue distribution of the native carrier protein RSA. In the second part of the study the different properties of the MTX(1)-RSA conjugate were compared with MTX in vivo. About 2 mg MTX/ kg body weight either of the drug conjugate or of the original drug were injected after being additionally spiked with radiolabeled tracers. Plasma concentrations were simultaneously determined by immunological and radioactive means. After 24 h about 12% MTX(1)-RSA was found in circulation compared to 0.03% MTX. Favorable tumor accumulation rates of about 14% were achieved for MTX(1)-RSA versus 0.04% for MTX. About 45-fold more of the injected dose of [3H]MTX accumulated in the liver as compared to the tumor (1.5 versus 0.03%) after 24 h. Conjugation of MTX to RSA reversed this ratio in favor of the tumor to 1:1.4 (13.6 versus 9.6%). In conclusion, the potential therapeutic benefit of the MTX(1)-RSA conjugate lies in its very long tumor exposure time and its improved tumor accumulation rate compared to conventional MTX. In addition the conjugation to albumin might enhance the therapeutic effects over those achieved by long-term continuous infusion of MTX, as MTX(1)-RSA enters the cells by a different uptake mechanism. This might also help to circumvent MTX resistance mechanisms, such as a reduction in folate receptor numbers or impaired MTX polyglutamylation.

Design of compounds having enhanced tumour uptake, using serum albumin as a carrier—part II. In vivo studies

In the present in vivo study the uptake kinetics of radioiodinated albumin were determined in normal organs, and tumours of rats using sequential scintigraphy. Rat serum (RSA) was radioiodinated either directly at a tyrosine residue (d-RSA), or indirectly at a residualizing marker tagged to the albumin (rm-RSA). These labelling procedures did not alter the kinetics of labelled albumin, as shown by blood disappearance curves. Directly labelled albumin was shown to have tumour uptake. Residualizing markers like tyramine-cellobiose (TCB), tyramine-deoxysorbitol (TDS) and aminonaphthaltyrimide-deoxysorbitol (ANTDS) are metabolically inert. After the intracellular degradation of the albumin carrier the TCB-, TDS- and ATNDS-residues accumulate in the lysosomes, particularly those of tumour cells. It was able to be demonstrated that residualizing-marker tagged albumin-bound radioactivity was five times higher after 72 h than the tumour radioactivity after use of directly labelled RSA. These data found support when whole-body retention of directly labelled RSA, and residualizing marker-RSAs, were determined. After 72 h, 60% of 131I bound to RSA directly had been excreted, compared to only 25% of the activity attached indirectly to RSA with a residualizing marker. Whole-body autoradiography of rats injected with directly labelled RSA, or residualizing marker-RSA, support these results. Most of the radioactivity of directly labelled RSA was excreted within 24 h, whereas labelled residualizing marker-RSAs were also stored in tumour and liver tissue. ANTDS bound to RSA allows fluorescence microscopy. Cryosections of tumours from rats preinjected 10 min and 24 h with ANTDS-RSA before dissection, demonstrated that the fluorescence is localized on and in tumour cells. This indicates that cellular uptake of the marker takes place. Fluorescence was not observed in muscle tissue. This appears to suggest that the albumin uptake is greater in tumours than in normal tissue, and that it is metabolized in the tumour cells.

Regional myocardial nitrogen-13 glutamate uptake in patients with coronary artery disease: inverse post-stress relation to thallium-201 uptake in ischemia.

The purpose of the present study was to evaluate the clinical significance of myocardial scintigraphy with nitrogen-13 (N-13) glutamate as a marker of myocardial metabolism. Within 2 weeks after cardiac catheterization, 25 patients with single vessel left anterior descending coronary artery disease underwent thallium-201 imaging (5 min and 3 h after injection) and N-13 glutamate scintigraphy (10 min after injection). Radionuclide studies were performed in the 30 degrees left anterior oblique projection after symptom-limited bicycle exercise, and regional tracer uptake was quantified by computer-assisted placement of regions of interest within the regions of myocardial activity. Poststenotic tracer uptake in the perfusion bed of the left anterior descending coronary artery (septum) was then normalized to the tracer uptake in the nondiseased left circumflex territory (posterolateral segments = 100%). In 14 patients with a history of previous myocardial infarction (Subgroup A), deficient poststenotic N-13 uptake correlated closely with thallium-201 uptake in both initial (r = 0.82, p less than 0.001) and redistribution (r = 0.74, p less than 0.01) scintigrams. By contrast, in 11 patients with no previous myocardial infarction and normal left ventricular function at rest (Subgroup B), initial uptake of both tracers was inverse: poststenotic N-13 glutamate uptake increased with decreasing thallium-201 uptake during exercise-induced ischemia (r = -0.64, p less than 0.05) and was closely correlated with the percent thallium-201 redistribution (r = 0.74, p less than 0.01). Thus, augmented accumulation of N-13 glutamate in reversibly ischemic (that is, viable) myocardium, and decreased uptake in myocardial scar tissue suggest the clinical usefulness of this metabolic tracer in the differentiation between viable (metabolically active) and irreversibly damaged myocardium.

Antitumor activity of methotrexate-albumin conjugates in rats bearing a Walker-256 carcinoma.

We have recently reported that albumin accumulates in solid tumors and serves there as a source of nitrogen and energy. Methotrexate‐albumin conjugates [MTX(1)‐RSA] derivatized at a molar ratio of 1:1 differ favorably from original MTX in terms of plasma presence and tumor uptake. The purpose of this study was to evaluate the therapeutic efficacy of these novel conjugates in a comparative study with low m.w. MTX in Sprague‐Dawley rats bearing a Walker‐256 carcinoma. The maximum tolerated dose (MTD) for MTX and MTX(1)‐RSA was determined (2 mg/kg based on MTX injected on days 1, 3 and 8). The tumor‐bearing rats received injections of either the MTD or MTD/2 of MTX, MTX‐albumin or mixtures containing the MTD/2 or MTD/4 of both MTX and MTX‐albumin. No toxic side effects were observed. Cure rate and tumor growth retardation were slightly better for the conjugate compared with MTX alone in the MTD group (16 complete remissions vs. 14 of 20 rats). The best results were achieved for the combination treatment with MTX and MTX‐albumin, with complete remission in all 20 rats. In conclusion, MTX‐albumin conjugates show therapeutic activity in vivo without toxic side effects. Additive effects were observed for a combination of MTX‐albumin and MTX. These effects might be caused by the much longer tumor exposition time of the conjugate in conjunction with a different route of uptake (pinocytosis for MTX‐albumin vs. folate receptors for MTX). Int. J. Cancer76:884–890, 1998.© 1998 Wiley‐Liss, Inc.

Synthesis and purification of 2-deoxy-2-[18F]fluoro-d-glucose and 2-deoxy-2-[18F]fluoro-d-mannose: characterization of products by 1H- and 19F-NMR spectroscopy

A procedure has been developed that allows the separation of 2-deoxy-2-[18F]fluoro-D-glucose from 2-deoxy-2-[18F]fluoro-D-mannose employing selectively optimized ion-moderated partition chromatography. Both compounds can be obtained with a greater than 98% chemical and radiochemical purity in about one half-life of 18F. Both the alpha- and beta-anomers of both sugars were completely characterized by high-resolution 1H- and 19F-NMR spectroscopy. Various convenient preparation methods for 2-deoxy-2-[18F]fluoro-D-glucose were compared.

Preparation of a new 18F-labelled precursor: 1-[18F]fluoro-2-pyridone

Abstract The new 18 F-labelled precursor 1-[ 18 F]fluoro-2-pyridone was prepared by reacting [ 18 F]F 2 with 2-(trimethylsiloxy)pyridine. This compound has potential as an easy to use yet selective labelling reagent in preparations, where fluorine carrier may be tolerated. Pure (>92%) 1-[ 18 F]fluoro-2-pyridone is obtained within 35 min from end of bombardment in yields of up to 48%. Quality control consisted of HPLC combined with 19 F-NMR spectroscopy. The mean specific activity of several preparations was 4 MBq/μmol ( ϵ = 16.6). The precursor may be used directly or purified by sublimation.