No abstract

There is a growing interest for screening antitumor drugs for their mechanism of action on cancer cells. Yet, screening for "modes of action" presents a technical challenge that is beyond the capability of conventional methods used in cellular or molecular biology. Several studies have highlighted the advantages of using infrared spectroscopy for diagnostic purposes at the clinical level for identifying cell types. In the present work, we suggest that the Fourier Transform Infrared (FTIR) spectrum of cells exposed to anti-cancer drugs could offer a unique opportunity to obtain a fingerprint of all molecules present in the cells and to observe, with a high sensitivity, the metabolic changes induced by potential anti-cancer drugs. Ouabain is one of the most potent cardenolides, which acts by inhibiting sodium pump activity. Cardenolides represent a class of compounds that are intended to soon enter clinical trials in oncology. In order to evaluate the potential of infrared spectroscopy to yield a signature for ouabain action on cancer cells, human prostate cancer PC-3 cells were treated with 36 nM ouabain, a sub-lethal concentration. Using ouabain as a model, we have thus demonstrated the possibility of using IR spectroscopy in the assessment of the global effects of an investigational compound on the cell constituents, thus contributing to setting up a new method for screening for novel anti-cancer agents in general, and potential anti-cancer cardenolides in particular. The most spectacular data obtained strongly suggest a modification in the nature of the cell lipids.

The number of anticancer agents that fail in the clinic far outweighs those considered effective, suggesting that the selection procedure for progression of drug molecules into the clinic requires improvement. Traditionally, new drugs are evaluated for their potential to kill cancer cell lines. This approach is obviously not sufficient, and molecules with new modes of action are required. We suggest here that the infrared spectrum of cells exposed to anticancer drugs could offer an opportunity to obtain a fingerprint of the metabolic changes induced by the drugs. Because the infrared spectrum of cells yields a precise image of all the chemical bonds present in the sample, different drug targets are likely to yield different infrared fingerprints characteristic of the 'mode of action' of the therapeutic agent under investigation. In turn, drug-induced metabolic disorders should be amenable to classification in the same way that bacteria gender, species, and strains can be classified. We examined here a human prostate cancer PC-3 cell line exposed to 7 well described antimitotics. In a first step the IC(50) values were determined. For FTIR imaging, PC-3 cells were exposed to the IC(50) concentration of each drug for 48 h. About one hundred images of 4096 IR spectra at 8 cm(-1) spectral resolution were acquired. We show with a Student t-test that the different molecules tested induced different infrared spectral modifications. Furthermore, drugs known to induce similar types of metabolic disturbances appear to cluster when spectrum shapes are analyzed. Finally, supervised statistical methods allowed the building of an efficient and discriminant model. When the discriminant model was applied to a full infrared image a good sorting was generally obtained and misclassified spectra generally belonged to a small number of specific cells. Taken all together these data suggest that FTIR could be used for the classification of drug action.

We show in the present work that the infrared (IR) spectrum of human PC-3 prostate cancer cells exposed to anticancer drugs could offer a unique opportunity to get a fingerprint of all the major biochemical components (DNA, RNA, proteins, lipids, etc.) present in the cells and to identify with high sensitivity the signature of the metabolic changes induced by anticancer drugs. We investigated here the FTIR-related signatures of the effect of 4 structurally-related cardiotonic steroids (CS), i.e. ouabain, 19-hydroxy-2″-oxovoruscharin, hellebrin and 19-hydroxy-hellebrin on PC-3 cancer cells incubated between 0 and 36 h in the absence (control) or the presence of the CS. For each molecule a single spectral signature described the largest part of the time dependent modifications with a possible very minor second component. The spectral signatures characterizing the effects of each of the four CS were unique but very similar when compared to the signature of the effect of an intercalating anticancer drug, i.e. doxorubicin, selected as a positive reference compound in our study, suggesting a fully distinct set of cellular perturbations. The current study thus illustrates that Fourier Transform Infrared (FTIR) analyses can be used to identify, among the perturbations induced on a given cancer cell line, the features common to a group of anticancer compounds as well as features specific to every single drug.