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Sequential events of apoptosis involving docetaxel, a microtubule-interfering agent: a cytometric study
Francesco Fabbri1, Silvia Carloni, Giovanni Brigliadori
1Department of Medical Oncology, Morgagni-Pierantoni Hospital, Via Forlanini 34, 47100 Forlì, Italy. francesco.fabbri@ausl.fo.it
Background:
Despite the great advances in the understanding of programmed cell death, little attention has been paid to the sequence of the events that characterise it. In particular, the course of apoptotic events induced by microtubule-interfering agents such as taxanes is poorly understood. In order to increase such knowledge, we studied a number of independent biochemical and cytological modifications using cytometric methods in a bladder cancer cell line treated with the second generation taxane, docetaxel.
Results:
Within a few hours, drug treatment had induced mitochondrial membrane transition, cell shrinkage and a decrease in granularity. Cell cycle was almost completely blocked in G2/M phase within 24 hours. The hypodiploid peak started to become prominent 48 hours after the treatment. At the same time, the appearance of a DNA ladder demonstrated caspase-dependent chromatin fragmentation. Concurrently, specific cell surface modifications took place, involving at first glycoprotein syalilation and later phospholipid asymmetry. DNA fragmentation was subsequently detected by TUNEL assay. Over time, cell membranes became permeable to propidium iodide. A very similar time-course of apoptotic events was found after treatment of a myelomonocytic cell line with the same drug.
Conclusion:
After discussing some characteristics of the methods employed and their limitations, a succession of apoptotic events over time is suggested, in which the collapse of mitochondrial transmembrane potential (Deltapsim) is the earliest sign of apoptosis.
Insights
The collapse of mitochondrial membrane potential is the first sign of programmed cell death (apoptosis) induced by docetaxel. This study details the sequence of apoptotic events in cancer cells following taxane treatment.
Area of Science:
- Cell Biology
- Cancer Research
- Pharmacology
Background:
- Understanding programmed cell death (apoptosis) is crucial, yet the specific event sequence induced by microtubule-interfering agents like taxanes remains unclear.
- Docetaxel, a second-generation taxane, is widely used in cancer therapy, necessitating a detailed understanding of its apoptotic mechanisms.
Purpose of the Study:
- To elucidate the temporal sequence of biochemical and cytological events during docetaxel-induced apoptosis.
- To characterize the early and late markers of apoptosis in a bladder cancer cell line.
Main Methods:
- Utilized cytometric methods to analyze various cellular modifications.
- Monitored mitochondrial membrane potential, cell size, granularity, cell cycle progression, DNA fragmentation (DNA ladder, TUNEL assay), cell surface changes (glycoprotein sialylation, phospholipid asymmetry), and membrane permeability (propidium iodide uptake).
Main Results:
- Docetaxel rapidly induced mitochondrial membrane potential collapse, cell shrinkage, and decreased granularity.
- Cell cycle arrest at G2/M phase occurred within 24 hours, followed by hypodiploid peak formation and DNA fragmentation by 48 hours.
- Early cell surface changes included glycoprotein sialylation, followed by phospholipid asymmetry, with membrane permeability to propidium iodide occurring later.
Conclusions:
- The collapse of mitochondrial transmembrane potential (ΔΨm) is identified as the earliest indicator of docetaxel-induced apoptosis.
- A distinct temporal cascade of apoptotic events was established, providing insights into taxane-mediated cell death pathways.
- Similar apoptotic event sequences were observed in both bladder cancer and myelomonocytic cell lines, suggesting a conserved response to docetaxel.
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