Curcumin and Plumbagin Synergistically Target the PI3K/Akt/mTOR Pathway: A Prospective Role in Cancer Treatment

Abstract

Cancer development is associated with the deregulation of various cell signaling pathways brought on by certain genetic and epigenetic alterations. Therefore, novel therapeutic strategies have been developed to target those pathways. The phosphoinositide 3-kinase (PI3K)/protein kinase B (Akt)/mammalian target of rapamycin (mTOR) (PI3K/Akt/mTOR) pathway is one major deregulated pathway in various types of cancer. Several anticancer drug candidates are currently being investigated in preclinical and/or clinical studies to target this pathway. Natural bioactive compounds provide an excellent source for anticancer drug development. Curcumin and plumbagin are two potential anticancer compounds that have been shown to target the PI3K/Akt/mTOR pathway individually. However, their combinatorial effect on cancer cells is still unknown. This study aims to investigate the synergistic effect of these two compounds on the PI3K/Akt/mTOR pathway by employing a sequential molecular docking and molecular dynamics (MD) analysis. An increase in binding affinity and a decrease in inhibition constant have been observed when curcumin and plumbagin were subjected to sequential docking against the key proteins PI3K, Akt, and mTOR. The MD simulations and molecular mechanics combined with generalized Born surface area (MM-GBSA) analyses validated the target proteins' more stable conformation when interacting with the curcumin and plumbagin combination. This indicates the synergistic role of curcumin and plumbagin against cancer cells and the possible dose advantage when used in combination. The findings of this study pave the way for further investigation of their combinatorial effect on cancer cells in vitro and in vivo models.

Keywords: MD simulation; cancer therapy; curcumin; molecular docking; plumbagin; synergism.

Figure 1

Chemical structures of (A) curcumin and (B) plumbagin.

Figure 2

Sequential binding of curcumin and plumbagin after docking against PI3K protein. The red arrows indicate the position of bound ligand on the target protein.

Figure 3

Sequential binding of curcumin and plumbagin after docking against Akt protein. The red arrows indicate the position of bound ligand on the target protein.

Figure 4

Sequential binding of curcumin and plumbagin after docking against mTOR protein. The red arrows indicate the position of bound ligand on the target protein.

Figure 5

Analysis of MD simulation trajectories with a 100 ns time scale for the interaction of curcumin and plumbagin with PI3K. (A) Root means square deviation (RMSD) plot displaying the molecular vibration of Cα backbone of PI3K-P (blue), PI3K-C (orange), and PI3K-C-P (red). (B) Root mean square fluctuation (RMSF) plot showing the fluctuations in respective amino acids throughout the simulation time of 100 ns for PI3K-P (blue), PI3K-C (orange), and PI3K-C-P (red). (C) Radius of gyration (Rg) plot for the deduction of compactness of PI3K-P (blue), PI3K-C (orange), and PI3K-C-P (red). (D) Number of H-bonds formed between PI3K and plumbagin (blue), PI3K and curcumin (orange), and PI3K and curcumin–plumbagin combination (red). (E) The free energy landscape (FEL) displaying the progression of global minima (ΔG, kJ/mol) of PI3K in presence of (1) plumbagin, (2) curcumin, and (3) curcumin–plumbagin combination with respect to their RMSD (Å) and Rg (Å). The lower right panel displays the energy scale used in the measurement of FEL.

Figure 6

Analysis of MD simulation trajectories with a 100 ns time scale for the interaction of curcumin and plumbagin with Akt. (A) RMSD plot displaying the molecular vibration of Cα backbone of Akt-P (blue), Akt-C (orange), and Akt-C-P (red). (B) RMSF plot showing the fluctuations of respective amino acids throughout the simulation time of 100 ns for Akt-P (blue), Akt-C (orange), and Akt-C-P (red). (C) Rg plot for the deduction of compactness of Akt-P (blue), Akt-C (orange), and Akt-C-P (red). (D) Number of H-bonds formed between Akt and plumbagin (blue), Akt and curcumin (orange), and Akt and curcumin–plumbagin combination (red). (E) The FEL displays the progression of global minima (ΔG, kJ/mol) of Akt in presence of (1) plumbagin, (2) curcumin, and (3) curcumin–plumbagin combination with respect to their RMSD (Å) and Rg (Å). The lower right panel displays the energy scale used in the measurement of FEL.

Figure 7

Analysis of MD simulation trajectories of 100 ns time scale for the interaction of curcumin and plumbagin with mTOR. (A) RMSD plot displaying the molecular vibration of Cα backbone of mTOR-P (blue), mTOR-C (orange), and mTOR-C-P (red). (B) RMSF plot showing the fluctuations of respective amino acids throughout the simulation time of 100 ns for mTOR-P (blue), mTOR-C (orange), and mTOR-C-P (red). (C) Rg plot for the deduction of compactness of mTOR-P (blue), mTOR-C (orange), and mTOR-C-P (red). (D) Number of H-bonds formed between mTOR and plumbagin (blue), mTOR and curcumin (orange), and mTOR and curcumin–plumbagin combination (red). (E) The FEL displays the progression of global minima (ΔG, kJ/mol) of mTOR in presence of (1) plumbagin, (2) curcumin, and (3) curcumin–plumbagin combination with respect to their RMSD (Å) and Rg (Å). The lower right panel displays the energy scale used in the measurement of FEL.