Lovastatin Induces Multiple Stress Pathways Including LKB1/AMPK Activation That Regulate Its Cytotoxic Effects in Squamous Cell Carcinoma Cells

Abstract

BackgroundCellular stress responses trigger signaling cascades that inhibit proliferation and protein translation to help alleviate the stress or if the stress cannot be overcome induce apoptosis. In recent studies, we demonstrated the ability of lovastatin, an inhibitor of mevalonate synthesis, to induce the Integrated Stress Response as well as inhibiting epidermal growth factor receptor (EGFR) activation.Methodology/Principal FindingsIn this study, we evaluated the effects of lovastatin on the activity of the LKB1/AMPK pathway that is activated upon cellular energy shortage and can interact with the above pathways. In the squamous cell carcinoma (SCC) cell lines SCC9 and SCC25, lovastatin treatment (1–25 µM, 24 hrs) induced LKB1 and AMPK activation similar to metformin (1–10 mM, 24 hrs), a known inducer of this pathway. Lovastatin treatment impaired mitochondrial function and also decreased cellular ADP/ATP ratios, common triggers of LKB1/AMPK activation. The cytotoxic effects of lovastatin were attenuated in LKB1 null MEFs indicating a role for this pathway in regulating lovastatin-induced cytotoxicity. Of clinical relevance, lovastatin induces synergistic cytotoxicity in combination with the EGFR inhibitor gefitinib. In LKB1 deficient (A549, HeLa) and expressing (SCC9, SCC25) cell lines, metformin enhanced gefitinib cytotoxicity only in LKB1 expressing cell lines while both groups showed synergistic cytotoxic effects with lovastatin treatments. Furthermore, the combination of lovastatin with gefitinib induced a potent apoptotic response without significant induction of autophagy that is often induced during metabolic stress inhibiting cell death.Conclusion/SignificanceThus, targeting multiple metabolic stress pathways including the LKB1/AMPK pathway enhances lovastatin’s ability to synergize with gefitinib in SCC cells.

Metabolic stress and cancer: is autophagy the common denominator and a feasible target?

“…On further examination, the mechanisms utilised were identified to involve the depletion of ATP through the inhibition of mitochondrial function or more specifically complex I. [16,49] This feature is attributed to the structural design of the drug, namely tetrahydrofuran rings, which were replaced in this study by ethylene glycol ether units, and as a consequence, there was enhanced efficacy. It was illustrated that the ATP depletion was responsible for the activation of AMPK and inhibition of mTOR with a concomitant autophagic response.…”

“…[15] This was supported by another group that showed that STRAD induced the relocation of LKB1 to the cytoplasm from the nucleus where it is active and is aided by MO25, which stabilises the interaction between LKB1 and AMPK. [16] To date, these findings suggest that SIRT1 could be a plausible key regulator in numerous cancer cell lines given that the tumour microenvironment is akin to that represented in a caloric-restricted model.…”

“…[13][14][15][16] It is significantly overexpressed in HeLa cells when caloric restriction is incurred, and as a consequence, there is an increase in autophagic activity. As the maintenance and biogenesis of mitochondria is the target of its action, it has been speculated that the role of SIRT1 is not only to facilitate autophagic activity but more importantly to regulate the mitochondrial dynamics of the cell.…”

“…This sequence of molecular events, however, did not lead to autophagic induction. [16,67] Even though there was AMPK activation and mTORC1 inhibition following treatment, the exact rationale for this is yet to be determined. It is postulated that the increase in the PAR levels over-ride the cytoprotective activation of the AMPK-MTORC1 pathway and autophagic induction.…”

Reactivation of latently infected HIV-1 viral reservoirs and correction of aberrant alternative splicing in the LMNA gene via AMPK activation: Common mechanism of action linking HIV-1 latency and Hutchinson–Gilford progeria syndrome

“…1). Indeed, various members of the statin class of cholesterol-lowering medications have been shown to activate AMPK, correct mitochondrial dysfunction and extend longevity in HGPS (Zmpste24 À/À ) mouse models, and increase HIV-1 LTR-driven promoter activity and viral transcription [169,173,174]. Interestingly, HDACs have been shown to modulate alternative splicing by influencing splice site selection and the HDAC inhibitors belinostat, trichostatin A, and vorinostat have each been shown to activate AMPK and reactivate (albeit inefficiently) latent HIV-1 viral reservoirs [175][176][177][178].…”