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5-Lipoxygenase inhibitors reduce PC-3 cell proliferation and initiate nonnecrotic cell death
1Department of Medicine, Rush Medical College, Chicago, Illinois 60612, USA.
Background:
Products of the arachidonic acid-metabolizing enzyme, 5-lipoxygenase, stimulate the growth of several cell types. Selective inhibitors of the enzyme, including SC41661A and MK886, reduce PC-3 prostate cell proliferation. With continued culture, cells die, but the mode of death, necrotic or nonnecrotic, has not been established.
Methods:
Flow cytometry, laddering after agarose electrophoresis of DNA from inhibitor-treated cells, and light and electron microscopy were employed to examine the type of death in PC-3 prostate cells cultured with either 5-lipoxygenase inhibitor.
Results:
The inhibitors induced nonnecrotic, programmed cell death. SC41661A-treated cells exhibited "foamy," vacuolated cytoplasm and mitochondria with disrupted cristae and limiting membranes, while some cells contained numerous polysomes and extended hypertrophic Golgi and secretory cisternal networks. A proportion of the treated cells detached and the nuclei of these cells were characteristic of type 1 "apoptotic" programmed cell death. MK886, a 5-lipoxygenase-inhibitor with a different mechanism of action, induced nonnecrotic changes largely confined to the cytoplasm, most consistent with type 2 "autophagic" programmed cell death. In preliminary studies of mechanism, we demonstrated that PC-3 cells express mRNA for 5-lipoxygenase and for 5-lipoxygenase-activating protein. The less active inhibitor, SC45662 neither reduced proliferation nor induced DNA laddering. The antioxidant, N-acetyl-l-cysteine but not butylated hydroxy toluene or alpha tocopherol, partially reduced the inhibition of proliferation from SC41661A.
Conclusions:
SC41661A and MK886 inhibit PC-3 cell proliferation and induce a form of type 1 or type 2 programmed cell death, respectively. PC-3 cells contain messenger RNA for 5-lipoxygenase and 5-lipoxygenase-activating proteins. Drug-induced changes included altered redox potential, inferred from the increased survival due to the antioxidant and glutathione precursor, N-acetyl-l-cysteine. PC-3 cells are an appropriate model for studying the mechanism responsible for 5-lipoxygenase inhibitor-induced cellular suicide.
Insights
Selective 5-lipoxygenase inhibitors, SC41661A and MK886, halt prostate cancer cell growth. These compounds trigger programmed cell death, offering new insights into cancer therapy mechanisms.
Area of Science:
- Biochemistry
- Cell Biology
- Cancer Research
Background:
- 5-lipoxygenase enzyme products stimulate cell growth.
- Inhibitors SC41661A and MK886 decrease PC-3 prostate cell proliferation.
- The specific mode of cell death induced by these inhibitors was previously unestablished.
Purpose of the Study:
- To investigate the mechanism of cell death in PC-3 prostate cancer cells treated with 5-lipoxygenase inhibitors.
- To determine whether the cell death is necrotic or nonnecrotic.
- To characterize the morphological and molecular changes associated with inhibitor-induced cell death.
Main Methods:
- Flow cytometry was used to analyze cell death.
- DNA laddering assessed apoptosis.
- Light and electron microscopy examined cellular morphology.
- RT-PCR confirmed gene expression of 5-lipoxygenase and FLAP.
Main Results:
- SC41661A induced type 1 programmed cell death (apoptosis) with characteristic nuclear changes and cytoplasmic vacuolization.
- MK886 induced type 2 programmed cell death (autophagy) with cytoplasmic alterations.
- PC-3 cells express mRNA for 5-lipoxygenase and 5-lipoxygenase-activating protein.
- N-acetyl-l-cysteine partially rescued cells from SC41661A-induced proliferation inhibition, suggesting altered redox potential.
Conclusions:
- SC41661A and MK886 inhibit PC-3 cell proliferation via distinct programmed cell death pathways (apoptosis and autophagy, respectively).
- PC-3 cells express key components of the 5-lipoxygenase pathway.
- The findings suggest a role for altered redox potential in inhibitor-induced cell death.
- PC-3 cells serve as a suitable model for studying 5-lipoxygenase inhibitor mechanisms.