Ciclopirox olamine inhibits mTORC1 signaling by activation of AMPK

Abstract

Ciclopirox olamine (CPX), an off-patent antifungal agent, has recently been identified as a potential anticancer agent. The mammalian target of rapamycin (mTOR) is a central controller of cell growth, proliferation and survival. Little is known about whether and how CPX executes its anticancer action by inhibiting mTOR. Here we show that CPX inhibited the phosphorylation of p70 S6 kinase 1 (S6K1) and eukaryotic initiation factor 4E binding protein 1 (4E-BP1), two downstream effector molecules of mTOR complex 1 (mTORC1), in a spectrum of human tumor cells, indicating that CPX inhibits mTORC1 signaling. Using rhabdomyosarcoma cells as an experimental model, we found that expression of constitutively active mTOR (E2419K) conferred resistance to CPX inhibition of cell proliferation, suggesting that CPX inhibition of mTORC1 contributed to its anticancer effect. In line with this, treatment with CPX inhibited tumor growth and concurrently suppressed mTORC1 signaling in RD xenografts. Mechanistically, CPX inhibition of mTORC1 was neither via inhibition of IGF-I receptor or phosphoinositide 3-kinase (PI3K), nor by activation of phosphatase and tensin homolog (PTEN). Instead, CPX inhibition of mTORC1 was attributed to activation of AMP-activated protein kinase (AMPK)-tuberous sclerosis complexes (TSC)/raptor pathways. This is supported by the findings that CPX activated AMPK; inhibition of AMPK with Compound C or ectopic expression of dominant negative AMPKα partially prevented CPX from inhibiting mTORC1; silencing TSC2 attenuated CPX inhibition of mTORC1; and CPX also increased AMPK-mediated phosphorylation of raptor (S792). Therefore, the results indicate that CPX exerts the anticancer effect by activating AMPK, resulting in inhibition of mTORC1 signaling.

Effects of the antifungal agent ciclopirox in HPV‐positive cancer cells: Repression of viral E6/E7 oncogene expression and induction of senescence and apoptosis

“…In addition to the strong downregulation of the HPV oncogenes, the antiproliferative, prosenescent and proapoptotic effects of CPX in HPV‐positive cancer cells are further supported by the reported potential of CPX to interfere with cellular pathways linked to tumorigenesis. For example, CPX has been reported to block growth‐promoting signaling cascades, such as Wnt or mTOR signaling, and to inhibit specific iron‐dependent enzymes, including ribonucleotide reductase which is required for DNA synthesis . Moreover, CPX has been shown to inhibit the iron‐dependent activity of deoxyhypusine hydroxylase (DOHH), an enzyme which is required for the synthesis of the eukaryotic translation initiation factor 5A‐1 (eIF5A1) .…”

Iron chelation inhibits mTORC1 signaling involving activation of AMPK and REDD1/Bnip3 pathways

“…6a and S5D). In addition, ectopic expression of dominant-negative AMPK (AMPK-DN) by infection with a recombinant adenovirus expressing AMPKα-DN [48] successfully attenuated iron chelation-induced dephosphorylation of S6K1 and 4E-BP1 (Fig. 6b).…”

“…The effect of iron chelation on mTORC1 inhibition is not related to ROS production, copper chelation, or PP2A activation mTOR can be inhibited or activated in response to certain oxidative stresses depending on experimental conditions and cell lines [47]. CPX and Dp44mT have ROS generating feature [48,49]. To determine whether iron chelationinduced mTORC1 inhibition is the consequence of ROS induction, N-acetyl-L-cysteine (NAC), a general ROS scavenger and antioxidant, was used.…”

Sorafenib and 2-Deoxyglucose Synergistically Inhibit Proliferation of Both Sorafenib-Sensitive and -Resistant HCC Cells by Inhibiting ATP Production

“…The mechanism behind this growth inhibition was attributed to the inhibition of ATP and macromolecule synthesis 19 . Moreover, there is a strong correlation between cellular ATP levels and AMPK activation resulting in inhibition of mTOR 16,18,20 , a kinase that responds to altered energy levels to regulate cell cycle progression 21 . We hypothesized that the depletion of cellular ATP together with reduced mTOR activation could be the mechanism driving the combination therapy induced cell cycle arrest observed in our studies.…”