Abstract
Previous studies showed that lapatinib and obatoclax interact in a greater-than-additive fashion to cause cell death and do so through a toxic form of autophagy. The present studies sought to extend our analyses. Lapatinib and obatoclax killed multiple tumor cell types, and cells lacking phosphatase and tensin homolog (PTEN) function were relatively resistant to drug combination lethality; expression of PTEN in PTEN-null breast cancer cells restored drug sensitivity. Coadministration of lapatinib with obatoclax elicited autophagic cell death that was attributable to the actions of mitochondrial reactive oxygen species. Wild-type cells but not mitochondria-deficient rho-zero cells were radiosensitized by lapatinib and obatoclax treatment. Activation of p38 mitogen-activated protein kinase (MAPK) and c-Jun NH2-terminal kinase 1/2 (JNK1/2) by the drug combination was enhanced by radiation, and signaling by p38 MAPK and JNK1/2 promoted cell killing. In immunohistochemical analyses, the autophagosome protein p62 was determined to be associated with protein kinase-like endoplasmic reticulum kinase (PERK) and inositol-requiring enzyme 1, as well as with binding immunoglobulin protein/78-kDa glucose-regulated protein, in drug combination-treated cells. Knockdown of PERK suppressed drug-induced autophagy and protected tumor cells from the drug combination. Knockdown of PERK suppressed the reduction in Mcl-1 expression after drug combination exposure, and overexpression of Mcl-1 protected cells. Our data indicate that mitochondrial function plays an essential role in cell killing by lapatinib and obatoclax, as well as radiosensitization by this drug combination.
Footnotes
↵ The online version of this article (available at http://molpharm.aspetjournals.org) contains supplemental material.
This work was supported by the National Institutes of Health National Cancer Institute [Grants R01-CA141704, R01-CA150214], the National Institutes of Health National Institute of Diabetes and Digestive and Kidney Diseases [Grant R01-DK52825], the Department of Defense [Grant W81XWH-10-1-0009], and the Lind-Lawrence Foundation. P.D. is the holder of the Universal Inc. Professorship in Signal Transduction Research.
Article, publication date, and citation information can be found at http://molpharm.aspetjournals.org.
ABBREVIATIONS:
- BAX
- Bcl-2–associated X protein
- S6K
- S6 kinase
- siRNA
- small interfering RNA
- MAPK
- mitogen-activated protein kinase
- JNK
- c-Jun NH2-terminal kinase
- PI3K
- phosphoinositide 3-kinase
- PTEN
- phosphatase and tensin homolog
- PERK
- protein kinase-like endoplasmic reticulum kinase
- ASK1
- apoptosis signaling kinase 1
- BiP
- binding immunoglobulin protein
- GRP78
- 78-kDa glucose-regulated protein
- IRE1
- inositol-requiring enzyme 1
- BAK
- Bcl-2–homologous antagonist/killer
- BH
- Bcl-2 homology
- mTOR
- mammalian target of rapamycin
- DMSO
- dimethylsulfoxide
- ER
- endoplasmic reticulum
- ROS
- reactive oxygen species
- GFP
- green fluorescent protein
- PBS
- phosphate-buffered saline
- PAGE
- polyacrylamide gel electrophoresis
- BEZ235
- 2-methyl-2-{4-[3-methyl-2-oxo-8-(quinolin-3-yl)-2,3-dihydro-1H-imidazo[4,5-c]quinolin-1-yl]phenyl}propanenitrile.
- Received July 25, 2012.
- Accepted September 18, 2012.
- Copyright © 2012 The American Society for Pharmacology and Experimental Therapeutics
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