AR-12 Inhibits Chaperone Proteins Preventing Virus Replication and the Accumulation of Toxic Misfolded Proteins

Abstract

CommentaryAlthough originally thought to be an inhibitor of PDK-1, OSU-03012 (AR-12) was shown in 2005 not to primarily act as a PDK-1 inhibitor in its ability to radio-sensitize tumor cells [1,2]. Subsequently it was shown that the primary mechanism by which AR-12 killed tumor cells was via the PKR-like endoplasmic reticulum kinase (PERK) -dependent induction of endoplasmic reticulum stress signaling [1][2][3]. ER stress signaling in turn promoted a toxic form of autophagy resulting in a necroptotic form of cell death.As AR-12 was causing an ER stress signal, the on-going studies became more focused on defining whether the functions and activities of chaperone proteins, particularly HSP90, HSP70 and GRP78, were being altered by the drug [3]. By western immuno-blotting, AR-12 lowered the expression of HSP90 and GRP78 but stimulated HSP70 expression. These findings were independently confirmed [4]. As AR-12 reduced expression of the PERK inhibitory chaperone GRP78, and as the induction of toxic autophagy was PERK dependent, we investigated in more detail the role of altered GRP78 expression in mediating drug toxicity. AR-12 destabilized GRP78 protein, significantly lowering its half-life as assessed by western blotting from >24 hours to 10 hours [5]. Transfection of cells with a plasmid to force over-expression of GRP78 blunted AR-12 induced PERK activation; autophagosome formation, and tumor cell death.Data published in 2014 and 2015 with AR-12 have additionally underlined the prominence of chaperones and especially GRP78 in the cell biology of OSU-03012. Phosphodiesterase 5 inhibitors including sildenafil (Viagra) and tadalafil (Cialis) were shown to interact with OSU-03012 to facilitate killing in a wide variety of tumor cells. The enhanced killing effect of the drug combination was associated with enhanced PERK-dependent ER stress signaling and autophagosome formation, as well as through death receptor activation [6]. Congruent data were obtained using the parent drug of OSU-03012, celecoxib, and also with the multi-kinase inhibitors sorafenib, regorafenib and pazopanib [7,8]. These pre-clinical studies have resulted in two open clinical trials; in all solid tumor patients (NCT02466802) where patients are receiving increasing once daily dosing with regorafenib and sildenafil; in recurrent glioblastoma patients (NCT01817751) where they receive sorafenib, sildenafil and valproate twice daily.From the research of many laboratories it has been defined that multiple chaperone proteins interact to play key roles in preserving protein stability and signaling, most notably in tumor cells which very often express much higher levels of protein than non-transformed cells. Hence some chaperones, e.g. HSP90, have become a target for developmental therapeutic synthetic chemists and also tumor cell biology scientists. In the area of viral reproductive biology, proteins such as HSPA5/ GRP78/ BiP have for almost 30 years been recognized as playing key facilitator roles in the life cycles of both DNA and RNA viruses [9][10][11...

Integrative multi-omics and drug response profiling of childhood acute lymphoblastic leukemia cell lines

“…Previous work has disputed the designation of OSU-03012 as a PDPK1 inhibitor and identified that cell death following treatment with OSU-03012 occurred via induction of ER-stress signaling 77 . Additional studies identified changes in abundance and stability of heat shock proteins (HSPs) following OSU-03012 treatment and suggested that HSPs were targets of OSU-03012 78 . Our dataset identified a significant correlation with HSP90 (HSP90AB1, Fig.…”

Multi-omics molecular phenotyping of childhood acute lymphoblastic leukemia cell lines reveals novel drug vulnerabilities

“…Previous work has disputed the designation of OSU-03012 as a PDPK1 inhibitor, and identified that cell death following treatment with OSU-03012 occurred via induction of ER-stress signaling 71 . Additional studies identified changes in abundance and stability of heat shock proteins (HSPs) following OSU-03012 treatment, and suggested that HSPs were targets of OSU-03012 72 . Our dataset identified significant correlation with HSP90 (HSP90AB1, Figure 5F) in support of this hypothesis.…”

Patent Highlights August–September 2017

“…Additional data demonstrate that the mechanism was autophagy induction, as with bacteria and fungi. For the peer-reviewed companion paper, see Booth et al [38].…”