PT  - JOURNAL ARTICLE
AU  - Robert Trondl
AU  - Lea S. Flocke
AU  - Christian R. Kowol
AU  - Petra Heffeter
AU  - Ute Jungwirth
AU  - Georg E. Mair
AU  - Ralf Steinborn
AU  - Éva A. Enyedy
AU  - Michael A. Jakupec
AU  - Walter Berger
AU  - Bernhard K. Keppler
TI  - Triapine and a More Potent Dimethyl Derivative Induce Endoplasmic Reticulum Stress in Cancer Cells
AID  - 10.1124/mol.113.090605
DP  - 2014 Mar 01
TA  - Molecular Pharmacology
PG  - 451--459
VI  - 85
IP  - 3
4099  - http://molpharm.aspetjournals.org/content/85/3/451.short
4100  - http://molpharm.aspetjournals.org/content/85/3/451.full
SO  - Mol Pharmacol2014 Mar 01; 85
AB  - Triapine (3-AP; 3-aminopyridine-2-carboxaldehyde thiosemicarbazone), a ribonucleotide reductase inhibitor, has been extensively evaluated in clinical trials in the last decade. This study addresses the role of endoplasmic reticulum (ER) stress in the anticancer activity of 3-AP and the derivative N4,N4-dimethyl-triapine (3-AP-Me), differing from 3-AP only by dimethylation of the terminal nitrogen. Treatment of colon cancer cells with 3-AP or 3-AP-Me activated all three ER stress pathways (PERK, IRE1a, ATF6) by phosphorylation of eIF2α and upregulation of gene expression of activating transcription factors ATF4 and ATF6. In particular, 3-AP-Me led to an upregulation of the alternatively spliced mRNA variant XBP1 (16-fold). Moreover, 3-AP and 3-AP-Me activated the cellular stress kinases c-Jun N-terminal kinase (JNK) and p38 mitogen-activated protein kinases, and inhibition of JNK activity antagonized the cytotoxic effect of both compounds. Subsequent to induction of the unfolded protein response, a significant upregulation of proapoptotic proteins was detected, including the transcription factor CHOP and Bim, an essential factor for ER stress–related apoptosis. In correlation with the higher degree of ER stress after 3-AP-Me treatment, also a more potent depolarization of mitochondrial membranes was found. These data suggest that 3-AP and 3-AP-Me induce apoptosis via ER stress. This was further corroborated by showing that inhibition of protein biosynthesis with cycloheximide prior to 3-AP and 3-AP-Me treatment leads to a significant reduction of the antiproliferative properties of both compounds. Taken together, this study demonstrates that induction of ER stress contributes to the mode of action of 3-AP and that terminal dimethylation leads to an even more pronounced manifestation of this effect.