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Prolonged weightlessness affects promyelocytic multidrug resistance
E H Piepmeier1, J E Kalns, K M McIntyre
1College of Pharmacy, University of Texas at Austin 78712, USA.
Abstract:
An immortalized promyelocytic cell line was studied to detect how doxorubicin uptake is affected by microgravity. The purpose of this experiment was to identify the effect that microgravity may have on multidrug resistance in leukocytes. HL60 cells and HL60 cells resistant to anthracycline (HL60/AR) were grown in RPMI and 10% FBS. Upon reaching orbit in the Space Shuttle Endeavour, the cells were robotically mixed with doxorubicin. Three days after mixing, cells were fixed with paraformaldehyde/glutaraldehyde. Ground control experiments were conducted concurrently using a robot identical to the one used on the Shuttle. Fixed cells were analyzed within 2 weeks of launch. Confocal micrographs identified changes in cell structure (transmittance), drug distribution (fluorescence), and microtubule polymerization (fluorescence). Flight cells showed a lack of cytoskeletal polymerization resulting in an overall amorphic globular shape. Doxorubicin distribution in ground cells included a large numbers of vesicles relative to flight cells. There was a greater amount of doxorubicin present in flight cells (85% +/- 9.7) than in ground control cells (43% +/- 26) as determined by image analysis. Differences in microtubule formation between flight cells and ground cells could be partially responsible for the differences in drug distribution. Cytoskeletal interactions are critical to the function of P-glycoprotein as a drug efflux pump responsible for multidrug resistance.
Insights
Microgravity exposure significantly increased doxorubicin uptake in leukemia cells by altering cytoskeletal structure. This finding impacts understanding of multidrug resistance mechanisms in space environments.
Area of Science:
- Cell Biology
- Space Medicine
- Pharmacology
Background:
- Multidrug resistance (MDR) in leukocytes poses challenges for cancer therapy.
- Understanding how environmental factors like microgravity affect drug resistance is crucial for astronaut health and potential extraterrestrial medical treatments.
Purpose of the Study:
- To investigate the impact of microgravity on doxorubicin uptake in HL60 and HL60/AR (anthracycline-resistant) promyelocytic leukemia cells.
- To determine if microgravity influences the mechanisms of multidrug resistance in leukocytes.
Main Methods:
- Cultured HL60 and HL60/AR cells were exposed to microgravity aboard the Space Shuttle Endeavour and compared to ground controls.
- Cells were treated with doxorubicin, fixed, and analyzed using confocal microscopy to assess cell structure, drug distribution, and microtubule polymerization.
- Image analysis quantified doxorubicin presence in flight versus ground control cells.
Main Results:
- Microgravity caused a lack of cytoskeletal polymerization, leading to an amorphic cell shape in flight cells.
- Doxorubicin distribution differed, with fewer vesicles in flight cells compared to ground controls.
- Significantly higher doxorubicin accumulation was observed in microgravity-exposed cells (85%) versus ground controls (43%).
Conclusions:
- Microgravity alters leukocyte cell structure, specifically impacting the cytoskeleton.
- Changes in cytoskeletal polymerization under microgravity may affect P-glycoprotein function, a key efflux pump in multidrug resistance.
- These findings suggest microgravity can enhance doxorubicin uptake, potentially modulating multidrug resistance in leukemia cells.