ASGSB 1998 Annual Meeting Abstracts

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GRAVISENSING, APOPTOSIS, AND DRUG RECOVERY FROM TAXUS CELL SUSPENSIONS.   D.J. Durzan. Environmental Horticulture, University of California, One Shields Ave., Davis, CA.

Haploid and diploid cell suspensions of Taxus sp. were examined for their adaptive plasticity in response to simulated microgravity, unit gravity, and hypergravity (3 to 150 x g in a centrifuge). Microgravity was simulated in rotating wall vessels (Synthecon, TX) and in liter vessels on a clinostat having significant Coriolis mixing. Cell suspensions produced the taxane, paclitaxel (Taxol^TM), used in the treatment of ovarian, lung, and breast cancer.

Immunocytochemical results showed that amyloplasts contributed to taxane ring biosynthesis and to drug release at the cell wall. Drug-producing cells reacted as gravisensing osmotic tensiometers. In stressed cells, amyloplasts docked and fused in clusters to sites on the plasmalemma before taxane release into the culture medium. In simulated microgravity and compared to all other treatments, taxane production was reduced nearly 100-fold. However, the percent paclitaxel of total taxanes was 3-to 6-fold greater, and biomass doubled. When p53-independent programmed cell death was induced, taxanes were released into the culture medium as free molecules (soluble and insoluble) or bound to membranes, nuclear fragments, hemicellulose and other particulate materials.

Unit gravity and especially hypergravity to 150 x g promoted terminal differentiation (xylogenesis) and significant drug overproduction. Low levels of bound taxanes were removed from cell walls by xylanase treatment after solvent extraction of the biomass.

A model relating the expression of families of ‘touch’ (TCH), nuclear cycling, and apoptosis-regulating genes to gravisensing, cell wall modifications, and to taxane recovery accounted for most but not all of the observations.

(Supported by NASA: NAG-9-825)

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