Deciphering Pharmacological Targets of Plumbagin in Cisplatin-resistant Ovarian Cancer Model using in vitro and in silico Approaches.

Introduction: Ovarian cancer (OC) is a malignancy of the female reproductive system for which cisplatin chemotherapy is one of the first-line treatments. Despite the initial response to chemotherapy, such patients eventually develop resistance, which poses a major obstacle to treatment, along with potential side effects. Phytochemicals function as chemosensitizers, offering novel therapies in OC patients by targeting drug resistance, and are perceived to be less toxic. Plumbagin has emerged as an anticancer compound, with some findings suggesting its anti-ovarian cancer activity. However, there is no study on the potential of plumbagin to target cisplatin resistance in non-high-grade OC. The current study aimed to determine the antitumor activity of plumbagin for cisplatin resistance in OC cells in vitro, and to identify its potential molecular target for therapeutic benefit using in silico studies.

Methods: Plumbagin was used for in vitro cytotoxic effects on cisplatin-resistant (A2780-CR) and sensitive (A2780-CS) isogenic cell lines using a crystal violet cell viability assay. The binding of plumbagin to the nine selected molecular targets was estimated by molecular docking, and their binding energies were compared. The stabilities of the selected docked complexes were confirmed by molecular dynamics simulation (MDS) and molecular mechanics generalized born surface area (MM-GBSA) calculations, and conclusions were drawn to predict the inhibition potential of plumbagin to its best targets.

Results: Plumbagin demonstrated the potential to kill A2780-CR cells, and, expectedly, the cell death effect on A2780-CS ovarian cancer cells demonstrated its anti-tumor activity in vitro. It was found to be noneffective in killing normal non-tumorigenic RPE cells, even at higher doses. Docking analysis suggested that it potentially inhibits ovarian cancer cells through various pharmacological targets with high affinity for binding to Chk1 (PDB ID=1ia8) and Aurora Kinase (PDB ID=5ORL). Molecular dynamic simulation data revealed strong and stable protein-ligand complex formation, which was measured in terms of root mean square deviation (RMSD), root mean square fluctuation (RMSF), and radius of gyration (Rg). On the other hand, the MM-GBSA study revealed that the binding free energy of the CT1019-1ia8 complex (-84.26 ± 2.99 Kcal/mol) and CT1019-5ORL (-67.04 ± 2.63 Kcal/mol) was better when compared to other complexes.

Discussion: Plumbagin showed the anti-ovarian cancer benefits of plumbagin in cisplatin-resistant ovarian cells, and the potential pharmacological targets identified were Chk1 and Aurora kinase.

Conclusion: Our study offers promising insights into plumbagin, particularly in combating cisplatin-resistant OC. However, further in vivo and mechanistic studies are required to validate plumbagin's potential as a therapeutic candidate for OC.