Detection and localisation of drug molecules in biological samples using Secondary Ion Mass Spectrometry (SIMS)

Abstract

Mass spectrometry imaging (MSI) can be used in the investigation of biological tissue in detecting elements, metabolites, lipids, peptides and proteins. Secondary ion mass spectrometry (SIMS) is the most mature technique used in MSI. SIMS is characterized by its ability to provide high spatial resolution and high-sensitivity imaging of elements (in dynamic mode) and small-medium mass molecules (in static mode), potentially making it a very powerful tool in drug distribution studies that are vital to developing and validating new therapies. Primary malignant brain tumours are universally fatal and glioblastoma multiforme (GBM) is the most frequent and severe type. Boron neutron capture therapy (BNCT) is a form of targeted radiotherapy based on the preferential accumulation of 10B in the tumour core and infiltrating cells relative to contiguous normal cells. Validation of BNCT relies, therefore, on imaging boron at the cellular level within biological tissue. This study focused on assessment of the imaging capabilities of dynamic and static SIMS instruments (CAMECA NanoSIMS 50L and BioToF-SIMS) in detecting the relative concentration and localisation of 10B from the BNCT agent boronophenylalanine (BPA) in primary cell cultures and in imprint samples of tissue biopsies from GBM human brain tumours and the border around the tumours (BAT). The samples received BPA in vitro and, in vivo respectively, and were used for the first time in this project. In addition, the effect of tyrosine preloading and efflux treatment on 10BPA uptake was investigated in primary cell cultures. The performance of both instruments was compared in terms of spatial resolution, sensitivity and quantitative measurement. The results show that the use of the NanoSIMS 50L with a Cs+ beam provided greater spatial resolution in the imaging of 10B distributions at the cellular and sub-cellular levels in the samples and higher sensitivity in the detection of ions of low abundance when compared with BioToF-SIMS with an Au+ beam, whereas the performance of the two instruments was similar in terms of the quantitative measurement. NanoSIMS 50L images also showed that the 10B from BPA accumulated in GBM tumour samples at a higher concentration than for BAT samples. In cell cultures, pre-loading of tyrosine did not improve the BPA uptake while exposure to the efflux process led to a decrease the BPA level in the cells. The images also showed the preferential accumulation of 10B in cell nuclei compared with the cytoplasmic areas in the cell culture samples, which is an important factor in the success of BNCT.

Date of Award	1 Aug 2020
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Nicholas Lockyer (Supervisor) & Katie Moore (Supervisor)