The novel quinol PMX 290 is an experimental anti‐tumor agent with potent activity against colon, renal and breast tumor cell lines in vitro (GI50 < 200 nM). PMX 290 disrupts thioredoxin/ thioredoxin reductase redox regulation and inhibits HIF‐1 signaling. A pro‐drug of PMX 290 is currently under development at Pharminox Ltd, UK. Here we present data suggesting an additional mechanism of action for PMX 290 highlighting a role for the induction of endoplasmic reticulum stress.

Treatment of HCT116 colon or TK‐10 renal carcinoma cells with PMX 290 leads to the induction of a distinct vacuolar phenotype 4 – 6h after addition of the compound. These perinuclear vacuoles were identified as swollen endoplasmic reticulum (ER) as their membranes stain positively with a fluorescent ER dye. Furthermore when a fluorescent analogue of PMX 290 is added to cells it co‐localized with the ER dye.

Microarray data from HCT116 cells treated with PMX 290 demonstrated the induction of a panel of mRNAs for genes involved in ER stress. These included GADD34, TRIB3, DNAJB9, BiP and CHOP as well as several genes upregulated by ATF4. Uncharacteristically for a quinol there was no increase in thioredoxin reductase mRNA levels although other markers of oxidative stress were upregulated (e.g. heme oxygenase 1).

The gene array results suggest that the PERK‐eIF2alpha ER stress pathway is activated by PMX 290. Upon activation by ER stress PERK phosphorylates eIF2alpha which switches off general translation and allows the expression of the transcription factor ATF4. This switch to reduced protein synthesis and expression of ATF4 transcribed chaperone proteins lowers the load on ER and increases protein folding efficiency thus alleviating ER stress. A transient increase in eIF2aplha phosphorylation and a concurrent increase in BiP levels were detected byWestern blot in response to PMX 290 in HCT116 cells. In conclusion, ER stress appears to play an important role in the anti‐tumor activity of PMX 290 and represents a novel mechanism of action for this class of compound.

Citation Information: Mol Cancer Ther 2009;8(12 Suppl):B164.

Copyright © 2009, American Association for Cancer Research
2009