J. Carlsson

Tumour therapy with radionuclides: assessment of progress and problems

Radionuclide therapy is a promising modality for treatment of tumours of haematopoietic origin while the success for treatment of solid tumours so far has been limited. The authors consider radionuclide therapy mainly as a method to eradicate disseminated tumour cells and small metastases while bulky tumours and large metastases have to be treated surgically or by external radiation therapy. The promising therapeutic results for haematological tumours give hope that radionuclide therapy will have a breakthrough also for treatment of disseminated cells from solid tumours. New knowledge related to this is continuously emerging since new molecular target structures are being characterised and the knowledge on pharmacokinetics and cellular processing of different types of targeting agents increases. There is also improved understanding of the factors of importance for the choice of appropriate radionuclides with respect to their decay properties and the therapeutic applications. Furthermore, new methods to modify the uptake of radionuclides in tumour cells and normal tissues are emerging. However, we still need improvements regarding dosimetry and treatment planning as well as an increased knowledge about the tolerance doses for normal tissues and the radiobiological effects on tumour cells. This is especially important in targeted radionuclide therapy where the dose rates often are lower than 1Gy/h.

EGFR, HER2, and HER3 expression in laryngeal primary tumors and corresponding metastases

BackgroundThere are several substances available to target members of the epidermal growth factor receptor (EGFR) family, both for imaging in nuclear medicine and for various forms of therapy. The level and stability of expression in both primary tumors and corresponding metastases is crucial in the assessment of a receptor as a target in systemic tumor therapy. To date, the expression of EGFR family members has only been determined in primary laryngeal carcinomas, and we have not found published data regarding the receptor status in corresponding metastatic lesions.MethodsExpression of EGFR, HER2, and HER3 was investigated immunohistochemically in both lymph node metastases and corresponding primary laryngeal squamous carcinomas (nxa0=xa040).ResultsEGFR overexpression (2+ or 3+) was found in 87.5% (35/40) of the laryngeal primary tumors and 82.5% (33/40) of the corresponding lymph node metastases. There was a good agreement between the primary tumors and the paired metastases regarding EGFR expression. HER2 overexpression was found in only four cases (10.5%) of the studied primary tumors and in all cases the HER2 expression was retained in the paired metastases. Another two metastases gained HER2 status when compared to the corresponding primary tumors. Strong HER3 staining was found in 26.7% of both the primary tumors and the corresponding metastases.ConclusionsThe high frequency and stability in EGFR expression is encouraging for efforts to use EGFR targeting agents (e.g. Iressa, Tarceva, Erbitux or radiolabeled antibodies) for therapy of laryngeal carcinoma. For a few laryngeal carcinoma patients with HER2 overexpression, anti-HER2 agents could possibly be used.

Comparison of cell survival models for mixed LET radiation

PURPOSEnBiophysical models for predicting survival for mixed LET radiations have been investigated by comparisons with experimental results from heavy ion irradiations. The aim was to choose a model for further theoretical studies on the effects of a variable RBE for protons.nnnMETHODS AND MATERIALSnPredicted survival curves by the Katz track-structure model, the linear quadratic model, LQ model, by Kellerer and Rossi and the lesion additivity model of Lam were compared to experimental survival curves for V79 cells that were irradiated with a mixture of nitrogen ions with an LET of either 78 or 165 keV/microm and 60Co gamma-rays.nnnRESULTSnResults showed that all three models could predict survival within the uncertainty of the measurements for the different mixed radiation schedules used in this study.nnnCONCLUSIONnThe choice of model could be made on other grounds, such as the type of model parameters and the availability of biological data for these parameters. Also, the possibility of including dose-rate effects and repair functions should be considered. For the purpose of carrying out theoretical studies on the effects of a variable RBE for protons, the LQ model was preferred.

Application of the multicellular tumour spheroid model to screen PET tracers for analysis of early response of chemotherapy in breast cancer

IntroductionPositron emission tomography (PET) is suggested for early monitoring of treatment response, assuming that effective anticancer treatment induces metabolic changes that precede morphology alterations and changes in growth. The aim of this study was to introduce multicellular tumour spheroids (MTS) to study the effect of anticancer drugs and suggest an appropriate PET tracer for further studies.MethodsMTS of the breast cancer cell line MCF7 were exposed to doxorubicin, paclitaxel, docetaxel, tamoxifen or imatinib for 7 days for growth pattern studies and for 3 or 5 days for PET tracer studies. The effect on growth was computed using the semi-automated size determination method (SASDM). The effect on the uptake of PET tracers [18F]3-deoxy-3-fluorothymidine (FLT), [1-11C]acetate (ACE), [11C]choline (CHO), [11C]methionine (MET), and 2-[18F]fluoro-2-deoxyglucose (FDG) was calculated in form of uptake/viable volume of the MTS at the end of the drug exposures, and finally the uptake was related to effects on growth rate.ResultsThe drugs paclitaxel, docetaxel and doxorubicin gave severe growth inhibition, which correlated well with inhibition of the FLT uptake. FLT had, compared with ACE, CHO, MET and FDG, higher sensitivity in monitoring the therapy effects.ConclusionSASDM provides an effective, user-friendly, time-saving and accurate method to record the growth pattern of the MTS, and also to calculate the effect of the drug on PET tracer uptake. This study demonstrate the use of MTS and SASDM in combination with PET tracers as a promising approach to probe and select PET tracer for treatment monitoring of anticancer drugs and that can hopefully be applied for optimisation in breast cancer treatment.

Conjugate chemistry and cellular processing of EGF-dextran.

Conjugates with specific binding to the epidermal growth factor receptor, EGFR, of interest for radionuclide based imaging and therapy were prepared using mouse epidermal growth factor, mEGF, and dextran. In one type of conjugate, mEGF was coupled to dextran by reductive amination in which the free amino group on the mEGF N-terminal reacted with the aldehyde group on the reductive end of dextran. The end-end coupled conjugate could be further activated by the cyanopyridinium agent CDAP, thereby introducing tyrosines to the dextran part. In the other type of conjugate, the cyanylating procedure using CDAP was applied, first to activate dextran and then allowing for the amino terminus of mEGF to randomly attach to the dextran. In the latter case, radionuclide-labelled tyrosines or glycines could be added in the same conjugation step. All types of mEGF-dextran conjugates had EGFR-specific binding since the binding could be displaced by an excess of non-radioactive mEGF. The conjugates were to a large extent internalized in the test cells and the associated radioactivity was retained intracellularly for different times depending on both the type of cells and conjugate applied. Different intracellular traffic routes for the radionuclides are discussed as well as applications for both imaging and therapy.

SLT-particles for two-step targeting in boron neutron capture therapy

There are investigations proposing that liposomes, both stabilized and unstabilized, gather at sites of pathology, such as tumors, infections, and inflammations.1, 2, 3, 4 The site-specific uptake of liposomal substances ought to increase with a targeting agent on the liposome. One way to conduct the targeting is to use PEG (polyethylene glycol) as a spacer and conjugate the targeting agent to the terminus of the polymer.5 This conjugated liposome can be named a SLT-particle (stabilized liposome with targeting ligand).