Differentiating responses of lung cancer cell lines to Doxorubicin exposure: in vitro Raman micro spectroscopy, oxidative stress and bcl‐2 protein expression

The potential of Raman micro spectroscopy as an in vitro, non‐invasive tool for clinical applications has been demonstrated in recent years, specifically for cancer research. To further illustrate its potential as a high content and label free technique, it is important to show its capability to elucidate drug mechanisms of action and cellular resistances. In this study, cytotoxicity assays were employed to establish the toxicity profiles for 24 hr exposure of lung cancer cell lines, A549 and Calu‐1, to the commercially available drug, doxorubicin (DOX). Raman spectroscopy, coupled with Confocal Laser Scanning Microscopy and Flow Cytometry, was used to track the DOX mechanism of action, at a subcellular level, and to study the mechanisms of cellular resistance to DOX. Biomarkers related to the drug mechanism of action and cellular resistance to apoptosis, namely reactive oxygen species (ROS) and bcl‐2 protein expression, respectively, were also measured and correlated to Raman spectral profiles. Calu‐1 cells are shown to exhibit spectroscopic signatures of both direct DNA damage due to intercalation in the nucleus and indirect damage due to oxidative stress in the cytoplasm, whereas the A549 cell line only exhibits signatures of the former mechanism of action. PCA of nucleolar, nuclear and cytoplasmic regions of A549 and Calu‐1 with corresponding loadings of PC1 and PC2 Raman microspectroscopy is employed to investigate and compare the in vitro mechanisms of action of Doxorubicin and cellular resistances of cancer cell lines A549 and Calu‐1. Results show the potential of Raman not only to distinguish the different mechanisms of action and subcellular response but also to elucidate drug resistance in the different cell lines.