Synergistic Effect of 1,3,6-Trihydroxy-4,5,7-Trichloroxanthone in Combination with Doxorubicin on B-Cell Lymphoma Cells and Its Mechanism of Action Through Molecular Docking

Background: The increasing rate of cancer chemoresistance and adverse side effects of therapy have led
to the wide use of various chemotherapeutic combinations in cancer management, including lymphoid
malignancy.
Objective: We investigated the effects of a combination of 1,3,6-trihydroxy-4,5,7-trichloroxanthone (TTX)
and doxorubicin on the Raji lymphoma cell line.
Methods: Raji cells were treated with different concentrations of TTX, doxorubicin, or combinations
thereof. Cancer cell growth inhibition was evaluated using 3-(4,5-dimethyltiazol-2-yl)-2,5- diphenyltetra-
zolium bromide/MTT assay to determine the half-maximal inhibitory concentration. Combination index
values were calculated using CompuSyn (ComboSyn, Inc, Paramus, NJ). Molecular docking was conducted
using a Protein-Ligand ANT System.
Results: The mean (SD) half-maximal inhibitory concentration values of TTX and doxorubicin were 15.948
(3.101) μM and 25.432 (1.417) μM, respectively. The combination index values of the different combina-
tions ranged from 0.057 to 0.285, indicating strong to very strong synergistic effects. The docking study
results reveal that TTX docks at the active site of Raf-1 and c-Jun N-kinase receptors with predicted free
energies of binding of −79.37 and −75.42 kcal/mol, respectively.
Conclusions: The xanthone-doxorubicin combination showed promising in vitro activity against lym-
phoma cells. The results also indicate that the TTX and doxorubicin combination’s effect was due to the
interaction between TTX with Raf-1 and c-Jun N-kinase receptors, 2 determinants of doxorubicin resis-
tance progression.