Endoplasmic reticulum-targeting doxorubicin: a new tool effective against doxorubicin-resistant osteosarcoma

Abstract

Doxorubicin is one of the most effective drugs for the first-line treatment of high-grade osteosarcoma. Several studies have demonstrated that the major cause for doxorubicin resistance in osteosarcoma is the increased expression of the drug efflux transporter ABCB1/P-glycoprotein (Pgp).We recently identified a library of H 2 S-releasing doxorubicins (Sdox) that were more effective than doxorubicin against resistant osteosarcoma cells. Here we investigated the molecular mechanisms of the higher efficacy of Sdox in human osteosarcoma cells with increasing resistance to doxorubicin.Differently from doxorubicin, Sdox preferentially accumulated within the endoplasmic reticulum (ER), and its accumulation was only modestly reduced in Pgp-expressing osteosarcoma cells. The increase in doxorubicin resistance was paralleled by the progressive down-regulation of genes of ER-associated protein degradation/ER-quality control (ERAD/ERQC), two processes that remove misfolded proteins and protect cell from ER stress-triggered apoptosis. Sdox, that sulfhydrated ERassociated proteins and promoted their subsequent ubiquitination, up-regulated ERAD/ERQC genes. This up-regulation, however, was insufficient to protect cells, since Sdox activated ER stress-dependent apoptotic pathways, e.g. the C/EBP-β LIP/CHOP/PUMA/caspases 12-7-3 axis. Sdox also promoted the sulfhydration of Pgp, that was subsequently ubiquitinated: this process further enhanced Sdox retention and toxicity in resistant cells.Our work suggests that Sdox overcomes doxorubicin resistance in osteosarcoma cells by at least two mechanisms: it induces the degradation of Pgp following its sulfhydration and produces a huge misfolding of ER-associated proteins, triggering ERdependent apoptosis. Sdox may represent the prototype of innovative anthracyclines, effective against doxorubicinresistant/Pgp-expressing osteosarcoma cells by perturbing the ER functions.

Ciclopirox activates PERK-dependent endoplasmic reticulum stress to drive cell death in colorectal cancer

“…Under certain circumstances, unfolded and/or misfolded proteins can accumulate within ER due to the limitation of the degradation capabilities of proteasomes, which leads to the activation of ER stress and UPR ER to promote cell survival 31,32 . However, under conditions of severe and sustained ER stress, when the UPR ER is unable to restore homeostasis of ER protein, the upregulation of CHOP expression results in apoptosis 33,34 . Thus, ER stress and UPR ER signaling can be viewed as a double-edged sword; supporting cancer cell survival in an adverse environment, while promoting cancer cell death under severe and prolonged stress conditions 35,36 .…”

Pleiotropic activities of nitric oxide-releasing doxorubicin on P-glycoprotein/ABCB1

“…2B). P-gp is synthesized and folded within ER, then it undergoes glycosylation in the Golgi apparatus and migrates to the plasma membrane [19,32]. Notably, the same pattern of nitrotyrosines observed in whole cell lysates was detected in ER ( Fig.…”

Insights into P-Glycoprotein Inhibitors: New Inducers of Immunogenic Cell Death

“…Until now, few agents are described as inducers of Pgp ubiquitination. Among them, there are sulfhydrating agents such as hydrogen disulfide-releasing doxorubicin [42] or disulfiram [43] that destabilize disulfide bonds and alter the proper folding of nascent Pgp. Curiously, the tetrandrine derivative H1, an inhibitor of Pgp ATPase activity, has been reported to be a strong inducer of Pgp ubiquitination [44].…”