Investigation of the biological effectiveness of Boron Neutron Capture Therapy for Head and Neck Cancer
Final Report Abstract
This project was carried out with the major aim to assess the applicability of Boron Neutron Capture Therapy for Head & Neck malignancies. In order to do this, uptake of p-boronophenylalanine and protein expression of amino acid transporter 4F2hc/LAT1 were to be linked through immuno-histochemical analysis with their combined potential to induce specific lethal radiation damage to tumour tissue upon neutron irradiation. In order to support the findings from irradiation experiments, visualisation and quantification of cellular boron was to be carried out with the intention to be used for the creation of a microdosimetrical calculation and prediction model, an approach that was successful in the past for brain tumours in animal models. Enhancement of BPA uptake through pre-loading with tyrosine and methionine could be demonstrated for different types of tissue retrieved from H&N and glioma biopsies. The greater and more systematic effect was found for glioma, though due to the limited amount of H&N biospies available, the assessment remains somewhat incomplete and requires more detailed studies. However, it was not possible to influence the retention of BPA or the efflux at all. Nonetheless, the results hint at a possibility for a simple and effective improvement of BNCT in clinical trials by the mere administration of tyrosine or methionine before giving BPA. So far, it remains to be shown why especially tyrosine was effective and whether the effect is connected to more than just 4F2hc/LAT1 expression and activity. While single staining of biomarkers LAT1 - representing the amino acid transporter responsible for the uptake of BNCT agent BPA - and γH2AX - representing the damage dealt by ionising radiation - in glioma and H&N crysections could be established, double staining of the two biomarkers and staining of tissue imprints altogether could not be achieved. Therefore, it has not yet been possible to link the findings of the incubation experiments to the expression of 4F2hc/LAT1 in the time given. For technical reasons, only a single irradiation experiment could be performed, which proved the feasibility of similar experiments. The effect of ionising radiation on H&N tumours generated through neutron capture could therefore not be investigated in detail. For an improved visualisation of boron at a cellular level, Quantitative Neutron Capture Radiography protocols were successfully improved to meet the requirements for boron quantification at a high spatial resolution in cryosections, however, they could not be transferred to fresh tissue imprints. Promising results were achieved for cytospin samples, which are unfortunately only usable in cell culture studies. For technical reasons, no analysis with SIMS could be carried out. Since from both SIMS and QNCR no data on the microdistribution of boron in tissue could be generated, it was not yet possible to contribute to the creation of a microdosimetrical model. Even though the original aim to gain a better understanding of the effectiveness of BNCT for H&N malignancies was not met, the results gathered are very valuable as they show that the understanding and the use of the uptake mechanism by 4F2hc/LAT1 in BPA-based BNCT is not as profound as the related literature indicates. Especially the pre-loading effect might lead to more effective treatment of glioma and H&N tumours in the future. Hopefully the results will stimulate more biological and medical research, which will lead to further investigation of the detailed processes of cell kill in BNCT and to a detailed evaluation of 4F2hc/LAT1 as transport route for targeted tumour therapy and its value in disease progression prognosis.
