Ratiometric imaging of minor groove binders in mammalian cells using Raman microscopy

Quantitative drug imaging in live cells is a major challenge in drug discovery and development. Many drug screening techniques are performed in solution, and therefore do not consider the impact of the complex cellular environment in their result. As such, important features of drug-cell interactions may be overlooked. In this study, Raman microscopy is used as a powerful technique for quantitative imaging of Strathclyde-minor groove binders (S-MGBs) in mammalian cells under biocompatible imaging conditions. Raman imaging determined the influence of the tail group of two novel minor groove binders (S-MGB-528 and S-MGB-529) in mammalian cell models. These novel S-MGBs contained alkyne moieties which enabled analysis in the cell-silent region of the Raman spectrum. The intracellular uptake concentration, distribution and mechanism were evaluated as a function of the pKa of the tail group, morpholine and amidine, for S-MGB-528 and S-MGB-529, respectively. Although S-MGB-529 had a higher binding affinity to the minor groove of DNA in solution phase measurements, the Raman imaging data indicated that S-MGB-528 showed a greater degree of intracellular accumulation. Furthermore, using high resolution stimulated Raman scattering (SRS) microscopy the initial localisation of S-MGB-528 was shown to be in the nucleus before accumulation in the lysosome, which was demonstrated using a multimodal imaging approach. This study highlights the potential of Raman spectroscopy for quantitative drug imaging studies and highlights the importance of imaging techniques to investigate drug-cell interactions, to better inform the drug design process

Quantitative drug imaging of minor groove binders using Raman microscopy

Quantitative drug imaging in live cells is a major challenge in drug discovery and development. The application of analytical techniques to study drug uptake, retention and mechanism of action thus facilitate the understanding of biological dynamics in cellulo, with accordant potential to improve drug discovery. Of great interest is the class of compounds known as Strathclyde-minor groove binders that were proved active against tumour growth and microbials. The molecular bulk of these compounds includes the head, the core and the tail fragment, which are associated with different activity profiles. However, little is known about how minor structural changes within these fragments affect the intracellular drug uptake, subcellular distribution and DNA binding in mammalian cells. To address this lack of knowledge, Raman microscopy was used to investigate Strathclyde-minor groove binders in mammalian cells upon the insertion of minor structural changes within the tail of the core fragment. Alkyne tags that minimally impact on the pharmacokinetics and pharmacodynamics of the drugs, were inserted within the head fragment to improve the sensitivity of detection, and the drug properties were investigated following the insertion of minor structural changes within the tail fragment, morpholine vs amidine. The insertion of a morpholine tail resulted in greater intracellular uptake, with either molecule having the nucleus as the preferential site of accumulation and minor groove binding detected through a redshift of the alkyne tags. Furthermore, the pKa of the morpholine tail was shown to head the lysosomal localisation of the molecule at later time points. The pharmacokinetics and pharmacodynamics of the Strathclyde-minor groove binders in absence of Raman active tags were also investigated, resulting in the investigation of minor structural changes within the core fragment. The replacement of an alkyl-pyrrole with an alkyl-thiazole was shown to affect the intracellular uptake and the cytotoxicity of the compounds, with DNA binding being the putative mechanism through which the alkyl-thiazole analogue exerts its cytotoxicity against mammalian cells. Overall, this study utilised Raman microscopy to establish a structure-activity uptake distribution model for the core and the tail fragment of Strathclyde-minor groove binders, suggesting the early use of Raman microscopy for the characterisation of the pharmacokinetics and pharmacodynamics of the drugs with the aim to achieve the desired drug activity.Quantitative drug imaging in live cells is a major challenge in drug discovery and development. The application of analytical techniques to study drug uptake, retention and mechanism of action thus facilitate the understanding of biological dynamics in cellulo, with accordant potential to improve drug discovery. Of great interest is the class of compounds known as Strathclyde-minor groove binders that were proved active against tumour growth and microbials. The molecular bulk of these compounds includes the head, the core and the tail fragment, which are associated with different activity profiles. However, little is known about how minor structural changes within these fragments affect the intracellular drug uptake, subcellular distribution and DNA binding in mammalian cells. To address this lack of knowledge, Raman microscopy was used to investigate Strathclyde-minor groove binders in mammalian cells upon the insertion of minor structural changes within the tail of the core fragment. Alkyne tags that minimally impact on the pharmacokinetics and pharmacodynamics of the drugs, were inserted within the head fragment to improve the sensitivity of detection, and the drug properties were investigated following the insertion of minor structural changes within the tail fragment, morpholine vs amidine. The insertion of a morpholine tail resulted in greater intracellular uptake, with either molecule having the nucleus as the preferential site of accumulation and minor groove binding detected through a redshift of the alkyne tags. Furthermore, the pKa of the morpholine tail was shown to head the lysosomal localisation of the molecule at later time points. The pharmacokinetics and pharmacodynamics of the Strathclyde-minor groove binders in absence of Raman active tags were also investigated, resulting in the investigation of minor structural changes within the core fragment. The replacement of an alkyl-pyrrole with an alkyl-thiazole was shown to affect the intracellular uptake and the cytotoxicity of the compounds, with DNA binding being the putative mechanism through which the alkyl-thiazole analogue exerts its cytotoxicity against mammalian cells. Overall, this study utilised Raman microscopy to establish a structure-activity uptake distribution model for the core and the tail fragment of Strathclyde-minor groove binders, suggesting the early use of Raman microscopy for the characterisation of the pharmacokinetics and pharmacodynamics of the drugs with the aim to achieve the desired drug activity