Direct Raman imaging techniques for study of the subcellular distribution of a drug

Abstract

Direct Raman imaging techniques are demonstrated to study the drug distribution in living cells. The advantage of Raman imaging is that no external markers are required, which simplifies the sample preparation and minimally disturbs the drug mechanism during imaging. The major challenge in Raman imaging is the weak Raman signal. In this study, we present a Raman image model to describe the degradation of Raman signals by imaging processes. Using this model, we demonstrate special-purpose image-processing algorithms to restore the Raman images. The processing techniques are then applied to visualize the anticancer agent paclitaxel in living MDA-435 breast cancer cells. Raman images were obtained from a cancer cell before, during, and after drug treatment. The paclitaxel distribution illustrated in these images is explained by means of the binding characteristics of the paclitaxel and its molecular target-the microtubules. This result demonstrates that direct Raman imaging is a promising tool to study the distribution of a drug in living cells.

Cellular discrimination using in vitro Raman micro spectroscopy: the role of the nucleolus

“…PCA allows the reduction of the number of variables in a multidimensional dataset, the order of the PCs denoting their importance in the dataset where PC1 describes the highest amount of variation. 18,20 While PCA identifies differences between the data sets, LDA maximizes these differences so as to group similar spectral sets. PCA performs a feature reduction of the data and LDA classifies the data into one of two or more classes.…”

Paclitaxel distribution in poly(ethylene glycol)/poly(lactide-co-glycolic acid) blends and its release visualized by coherent anti-Stokes Raman scattering microscopy

“…While this method provides chemical selectivity, the long excitation wavelength used in FT-IR microscopy offers the spatial resolution of several to tens micrometer, which does not allow the visualization of 3D distribution of drug molecules in thin polymer films or microparticles. Raman microscopy [16][17][18] provides better spatial resolution by using a shorter excitation wavelength, but the weak Raman scattering necessitates a long image acquisition time from minutes to hours. A recently developed nonlinear optical imaging technique that is based on coherent anti-Stokes Raman scattering (CARS) circumvents these difficulties.…”

Label-free detection of anticancer drug paclitaxel in living cells by confocal Raman microscopy

“…21 By direct Raman microscopy, Raman images of MDA-435 breast cancer cells treated with highly concentrated (350 lM) paclitaxel have been acquired at a single selected Raman peak (1000 cm À1 ) with 0.54 lm resolution. 22 In this work we provide data on paclitaxel distribution at close to clinical concentrations (%10lM) in live cancerous MCF-7 (Michigan Cancer Foundation-7) cells based on a set of Raman spectral lines of paclitaxel, using a higher resolution (300 Â 300 Â 800 nm) confocal Raman spectroscopy. For better image contrast we complete the experimental work with cluster analysis and correlation map calculations.…”

“…2(a) and 2(b) shows that most of Raman peaks appearing in the spectra of cells overlap with the vibrational peaks of the paclitaxel. Moreover, the previously used peak by Ling et al 22 at 1002 cm À1 which is due to sp 3 hybridized carbon-carbon (C-C) vibration in the paclitaxel occurs also in the cell's spectra. Therefore in our work the peak at 1740 cm À1 (the C¼O stretching band marked in the red spectrum of Fig.…”

“…22 This might lead to different interpretation due to different cell physiology and difficulty to identify the different cytoplasmic compartments. We have not observed drug localization around bundles of stabilized microtubules that would have been expected according the classical picture of paclitaxel's pharmaceutical action.…”