|Roberts, S - UNIVERSITY MASSACHUSETTS|
|Shuler, M - CORNELL UNIVERSITY|
Submitted to: Biotechnology and Bioengineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 17, 2001
Publication Date: N/A
Interpretive Summary: Paclitaxel (Taxol) is a potent chemotherapeutic drug with proven utility against a range of cancers. The very limited supply of this drug from the original source, Pacific yew bark, however, prompted the development of alternative sources of production, including the use of plant cell cultures. For plant cell culture to be an economic production system, however, work is still needed in order to optimize production and release into the cell medium for efficient recovery. This manuscript describes our study into the mechanisms controlling release of paclitaxel from the cells and the specific components in the cell where paclitaxel may reside. Such studies may be beneficial to enhancing overall paclitaxel productivity in plant suspension cultures.
Technical Abstract: Plant cell cultures are utilized to produce valuable plant-derived pharmaceuticals such as paclitaxel. Optimization of such processes involves not only the study of biosynthesis, but also intracellular transport where transport limitations can negatively affect overall productivity. Paclitaxel release from cultures of various Taxus species is sdue to biological mechanisms rather than lysis as demonstrated through the use of viability staining and DNA analysis. Release varied greatly between different Taxus species and cell lines, and was concurrent with paclitaxel accumulation. The use of transport inhibitors (cytochalasin b, brefeldin A and phenylarsineoxide) was used to probe the mechanism of paclitaxel release from Taxus suspension cultures. Cytoclalasin b was the only inhibitor tested that significantly affected the distribution of paclitaxel, consistent with a hypothesis that paclitaxel release involved vesicular transport. Transmission electron micrographs confirmed the presence of vesicles in paclitaxel accumulating cell cultures. The addition of exogenous calcium to cell suspension cultures induced a significant increase in the amount of cell-associated paclitaxel with a corresponding decrease in the amount of paclitaxel released to the extracellular medium. This result was supported through data obtained using the calcium channel blocker verapamil. The optimization of medium calcium levels may be beneficial to enhancing release of paclitaxel with improvements in overall productivity in cell suspension cultures.