Abstract
While pharmacological inhibition of Akt kinase has been regarded as a promising anti-cancer strategy, most of the Akt inhibitors that have been developed are enzymatic inhibitors that target the kinase active site of Akt. Another key cellular regulatory event for Akt activation is the translocation of Akt kinase to the cell membrane from the cytoplasm, which is accomplished through the pleckstrin homology (PH) domain of Akt. However, compounds specifically interacting with the PH domain of Akt to inhibit Akt activation are currently limited. Here we identified a compound, lancemaside A (LAN-A), which specifically binds to the PH domain of Akt kinase. First, our mass spectra analysis of cellular Akt kinase isolated from cells treated with LAN-A revealed that LAN-A specifically binds to the PH domain of cellular Akt kinase. Second, we observed that LAN-A inhibits the translocation of Akt kinase to the membrane and thus Akt activation, as examined by the phosphorylation of various downstream targets of Akt such as GSK3β, mTOR and BAD. Third, in a co-cultured cell model containing human lung epithelial cancer cells (A549) and normal human primary lung fibroblasts, LAN-A specifically restricts the growth of the A549 cells. LAN-A also displayed anti-proliferative effects on various human cancer cell lines. Finally, in the A549-luciferase mouse transplant model, LAN-A effectively inhibited A549 cell growth with little evident cytotoxicity. Indeed, the therapeutic index of LAN-A in this mouse model was >250, supporting that LAN-A is a potential lead compound for PH domain targeting as a safe anti-cancer Akt inhibitor.
Highlights
A long-term cell survival phenotype is established by the sensing of various cellular events, and the mechanisms involved in recognition and delivery of stress signals are highly conserved among mammalian cells
At 20 mM lancemaside A (LAN-A), the highest concentration used, greater than 60% reduction in viability was detected for all three cell lines
The A549-luc-c8 cells were used for this study and we confirmed that LAN-A treatment caused a comparable reduction in cell viability (Figure 1B)
Summary
A long-term cell survival phenotype is established by the sensing of various cellular events, and the mechanisms involved in recognition and delivery of stress signals are highly conserved among mammalian cells. The PI3K/Akt pathway is a central regulatory network that governs the cellular events essential for transcription, cell survival [1], growth [2], differentiation [3], migration [4], metabolism [5], and angiogenesis [6]. The dysregulation of the PI3K/Akt pathway is commonly observed in many human cancers, allowing for long-term survival and outgrowth [7,8,9]. Pharmacological inhibitors targeting this pro-survival pathway have been extensively investigated as potential anti-cancer agents [10]. Since Akt is a central regulator that controls the activity of numerous downstream targets through its kinase activity, Akt inhibitors have been the focus of several studies [10,11,12]. Most of the Akt inhibitors that have been tested mainly target the kinase active site or ATP binding site of Akt [13,14,15,16] and exhibit potential unwanted off-target effects for numerous other cellular kinases
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