Development of Quantitative Raman
Imaging Techniques to Study
Inclusive Dates: 10/01/00 - 07/01/02
Background - The determination of drug mechanisms at the cellular level is a problem of great importance to the evaluation and development of new anticancer agents. Recently, the implementation of rational drug designs, combinatorial chemistry techniques, and high throughput screening have led to large numbers of new candidate drugs. Currently, few cost-effective and efficient methods exist to understand the details of how these candidate drugs work at the cellular level. This lack of methodologies requires pharmaceutical companies to spend millions of dollars in animal and clinical studies to assess a candidate drug.
Approach - The objective of this project is to develop direct Raman imaging as a cost-effective tool to study drug mechanisms at the cellular level. The application of direct Raman imaging was studied to determine drug distribution in single living cells. To extract useful information from a recorded Raman image, a model was developed to describe the degradation of Raman signals during imaging. Factors such as the nonuniform illumination of the laser excitation source, blurring by the microscope system, the influence of the fluorescence background, and the disturbance of additive signal-dependent Gaussian noise were included in the model. Using this model, special-purpose image-processing algorithms were developed to restore the Raman images. Taxol, an important anticancer agent whose mechanisms at the cellular level have been well-studied, was used to evaluate the capabilities of direct Raman imaging. Raman images were obtained from a MDA-435 cancer cell before, during, and after the drug treatment.
Accomplishments - The Raman images show how the distribution of Taxol in a living tumor cell changes with time. It was found that Taxol does not enter the cell nucleus, but concentrates around the cell centrosome and near the cell membrane (refer to the illustrations below). This finding is well explained by the binding characteristics of Taxol and its molecular target, the microtubules. This result demonstrated the feasibility of using direct Raman imaging to determine the intracellular distribution of a drug. From the drug distribution, its mechanism and intracellular pharmacokinetics can be studied.