LAUSR

9‐[(3‐chloro)phenylamine]‐2‐[3‐(diethylamine)propylamine]thiazolo[5,4‐b]quinolone (D3ClP) is a bioisostere of N‐(4‐(acridin‐9‐ylamino)‐3‐methoxyphenyl)methanesulfonamide (m‐AMSA) a DNA topoisomerase II inhibitor with proven cytotoxic activity and known to induce DNA damage and apoptotic cell death in K562 cells. However, recent evidence is not consistent with DNA topoisomerase II (DNA TOP2) as the primary target of D3ClP, in contrast to m‐AMSA. We provide evidence of histone γH2AX phosphorylation at Ser135 in HeLa cells treated with D3ClP, a marker of DNA double strand repair through Mre11‐Rad50‐Nbs1 (MRN) pathway. Using two‐dimensional gel electrophoresis and mass spectrometry, the upregulation of the protein GRP78, the cleavage of Cytokeratin 18, and the downregulation of prothymosine, calumenin, and the α chain of the nascent polypeptide associated complex were observed in HeLa cells treated with D3ClP. An increase in GRP78 has been related with the onset and progression of the unfolded protein response (UPR), a process aimed to reduce endoplasmic reticulum (ER) stress and protein misfolding. The IRE1‐α dependent splicing of mRNA encoding X‐box binding protein 1 was detected. Microtubule‐associated Proteins 1A/1B, Light Chain 3‐II (LC3b‐II) accumulation was observed, and suggest some involvement of autophagy. The production of the pro‐apoptotic protein DNA‐damage‐inducible protein 153 (GADD‐153) was also detected. These results, are consistent with the induction of the UPR and the DNA‐Damage Response in D3ClP‐treated HeLa cells, and are also consistent with a concurrent apoptotic cell death. J. Cell. Biochem. 118: 1164–1173, 2017. © 2016 Wiley Periodicals, Inc.