Drug development programs are hindered by the inability to measure intracellular drug concentrations in complex tissues with the high spatial and temporal resolution required to obtain information on key pharmacokinetic aspects of drug behavior. Fast-acquisition Raman methodologies such as Stimulated Raman Scattering (SRS), generate image contrast using the Raman active vibrational frequency of a given chemical, providing information on the biochemical composition of tissues allowing label-free visualisation for a number of biomedical applications, including the study of drug interactions (Cheng & Xie, 2015; Tipping et al, 2016). The fast acquisition speeds, combined with good photostability and lack of phototoxicity associated with SRS, permits real-time imaging of drug distribution within cells with a resolution that allows precise intracellular registration when using dual-modality imaging techniques that employ fluorescent molecular markers (Tipping et al, 2017). The linear relationship between signal intensity and chemical concentration enables quantitative imaging and together with the spatial and temporal resolution afforded by SRS provides a unique opportunity to understand drug distribution within individual cells by delivering single cell pharmacokinetic and pharmacodynamic read-outs.
Spectroscopically bioorthogonal Raman detection in the “cellular silent’ region (1800 – 2800 cm‑1) presents an optimal region for specific drug localisation imaging, as there is minimal contribution from endogenous cellular biomolecules thus improving detection sensitivity. Alkynes, and a number of other functional groups, generate Raman signals within the cellular silent region making them particularly attractive as labels. However, as very few drugs have inherent Raman active groups (only 5% of FDA approved drugs) addition of bioorthogonal tags will be required in the majority of cases. Our data show that some Raman active tags can impact on the biological activity of drugs and improvements in the chemistry are required to optimize bioorthogonal Raman imaging, while minimizing impact on biological activity. The student will synthesize a novel suite of readily conjugated, highly Raman-active tags to give a tunable pallet of vibrational frequencies with well-defined (intra)cellular characteristics, using the Poly (ADP-ribose) polymerase (PARP) inhibitor olaparib as a test platform. The most promising compounds, with minimal impact on biological activity (DNA damage/proliferation/apoptosis) of the parent compound, and with highest Raman activity (measured by spontaneous Raman spectroscopy), will be taken forward for SRS imaging studies. Importantly multimodal imaging will allow correlation of drug uptake and concentration with phenotypic responses on an individual cell basis by using fluorescence reporters. This project will provide evidence that SRS imaging is a powerful tool for the quantitative assessment of intracellular drug concentrations, which will enhance the adoption and widespread use of SRS in drug development programs.
Research Training: this studentship will provide interdisciplinary training in bioorthogonal chemistry, Raman and fluorescence microscopy, and cell biology. The student will be hosted by the Institute of Genetics & Molecular Medicine (IGMM) and the School of Chemistry at the University of Edinburgh and will be integrated into the research teams of Profs Brunton (IGMM) & Hulme (Chemistry).
Cheng JX, Xie XS. Vibrational spectroscopic imaging of living systems: An emerging platform for biology and medicine. Science 2015 350: aaa8870; Tipping WJ, Lee M, Serrels A, Brunton VG, Hulme AN. Stimulated Raman Scattering microscopy: an emerging tool for drug discovery. Chem Soc Rev 2016 45: 2075-2089; Tipping WJ, Lee M, Serrels A, Brunton VG, Hulme AN. Imaging drug uptake by bioorthogonal Stimulated Raman Scattering microscopy. Chemical Sci 8:5606-15 (2017)