Optimization and evaluation of MALDI TOF mass spectrometric imaging for quantification of orally dosed octreotide in mouse tissues.

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry imaging (MALDI-TOF-MSI) has received considerable attention in recent years since it allows molecular mapping of diverse bimolecular in animal/plant tissue sections, although some barriers still exist in absolute pixel-to-pixel quantification. Octreotide, a synthetic somatostatin analogue, has been widely used to prevent gastrointestine bleeding in the clinic. The aim of the present study is to develop a MALDI-TOF-MSI method for quantitatively visualizing spatial distribution of octreotide in mouse tissues. In this process, a structurally similar internal standard was spotted onto tissue section together with matrix solution to minimize signal variation and give excellent quantitative results. The 2,5-dihydroxybenzoic acid was chosen as the most suitable matrix via comparing the signal/noise generated by MALDI-TOF-MSI after cocrystallization of octreotide with different matrix candidates. The reliability of MALDI-TOF-MSI, with respect to linearity, sensitivity and precision, was tested via measuring octreotide in fresh tissue slices at different concentrations. The validated method was then successfully applied to visualize the distribution of octreotide in mouse tissues after oral administration of octreotide at 20mg/kg. The results demonstrated that MALDI-TOF-MSI could not only clearly visualize the spatial distribution of octreotide, but also make the calculation of the key pharmacokinetic parameters (Tmax and t1/2) possible. More importantly, the tissue concentration-time curves of octreotide determined by MALDI-TOF-MSI agreed well with those measured based on LC-MS/MS.These findings illustrate the potential of MALDI-TOF-MSI in pharmacokinetic profiling during drug development.