Extraction of Chemotherapeutic Agents

The properties of carbon dioxide are especially attractive for extracting compounds from biological materials. This section describes some work carried out on the extraction of antineoplastic agents from plant materials (Krukonis, Branfman, and Broome, 1979). The plant materials tested, which are listed in 

NCI Designation Plant Material (Specific Name, Variety, Origin)  

The extraction tests were exploratory and arbitrary in nature for two reasons relatively little plant material was supplied, with the result that no optimization studies could be carried out and pure material was unavailable for solubility testing. Not only were optimization studies impossible but also the extraction conditions were selected from experience with other complex organic compounds. 

Extraction of the plant materials was performed in a flow apparatus similar to that described in chapter 4. The current National Cancer Institute protocol for extracting new plant materials consists of Soxhlet extraction with 95% ethanol. (For comparison purposes a Soxhlet extraction was also done for this study.) Carbon dioxide conditions of 275 bar and 35°C were chosen to achieve a high density at a temperature reasonably close to ambient temperature. About 20 g of plant material were used for each extraction. The material was contacted with 200 standard liters of carbon dioxide in a flow extractor, and the extract that was collected when the carbon dioxide was expanded to ambient pressure was tested in a bioassay test. 

For the bioassay or cytotoxicity tests the extract (from both the supercritical extraction and 95% ethanol extraction procedures) is dissolved to various concentration levels in 95% ethanol, and the bioactivity is tested in vitro with the 9KB leukemia cell. Samples of cells are treated with various concentration levels of the extract and are then incubated. Cell growth inhibition is determined from protein measurements, which can be correlated to the number of cells. The ED50 value, expressed in mg/1, is defined as the extract concentration at which 50% of the cell growth is inhibited. Obviously, the lower the value, the more cytotoxic the extract. 

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