Combination of docetaxel and newly synthesized 9-Br-trimethoxybenzyl-noscapine improve tubulin binding and enhances antitumor activity in breast cancer cells.

To strategically design and frame the novel 9-Br-Trimethoxybenzyl noscapine (BTN) with rigorous binding affinity with tubulin, the structure of noscapine (an antitussive plant alkaloid) was amended with a 3,4,5-trimethoxybenzyl group linked at the seventh position on the lower isobenzofuran unit. Molecular modelling and cellular studies were used to assess the single and combined effects of BTN and docetaxel (DOX). Based on MM-GBSA, the individual calculated free energies of binding (ΔGbind, pred) for BTN and DOX with tubulin was found to be -25.69 and -38.17 kcal/mol, respectively, and -29.11 and -36.60 kcal/mol based on MM-PBSA. Furthermore, the ΔGbind,pred of BTN was dramatically reduced (-30.02 and -33.54 kcal/mol using MM-GBSA and MM-PBSA) in presence of DOX on its binding pocket. Parenthetically, the ΔGbind,pred of DOX was substantially decreased (-39.17 and -35.80 kcal/mol using MM-GBSA and MM-PBSA) in the presence of BTN on its binding pocket. The synergistic activity of both compounds on tubulin dimmer was also analysed using purified tubulin, where a combined regimen of BTN and DOX attenuated tubulin intensity to a higher value (50%) particularly in comparison to the single regimen. In comparison to the single regimen, the combination of BTN and DOX effectively prevents cell cycle progression during the G2/M phase and induces breast cancer cell death. Female athymic nude mice were xenografted with MCF-7 cells and the efficacy of (150 mg/kg/day), DOX (1.5 mg/kg/week, i.v.), or in combination (BTN 300 mg/kg/day + DOX 1.0 mg/kg/week, i.v) were evaluated.

Rational design of 9-vinyl-phenyl noscapine as potent tubulin binding anticancer agent and evaluation of the effects of its combination on Docetaxel.

Docetaxel (DOX) based combination therapy is a novel therapeutic strategy that attracts great interest in breast cancer treatment but its clinical utility got limited due to side effects. In contrast, noscapine, an antitussive drug showed antitumor activity against many cancers without any side effects that targets microtubules and attenuates its dynamic instability. In the quest for an increase in the anticancer activity of noscapine, we strategically designed a novel derivative, 9-vinyl phenyl noscapine (VPN), based on our in silico molecular docking and molecular dynamics simulation effort. Molecular docking of VPN and DOX onto microtubule revealed a docking score of -4.82 kcal/mol and -6.67 kcal/mol respectively, while the docking score of VPN was changed to -3.23 kcal/mol when it was docked onto the co-complex of tubulin-DOX. Further, the binding free energy (ΔGbind,PBSA) of VPN and DOX with tubulin showed -24.04 and -18.65 kcal/mol respectively, while the binding free energy of DOX was increased further in combination with VPN (ΔGbind, PBSA was reduced to -21.41 kcal/mol), denoting combination effect of both ligands. The IC50 value amounted to 30.17 µM and 19.92 µM for VPN and 0.621 µM and 0.193 µM for DOX, respectively for 48 h and 72 h. The dose dependent cytotoxicity of DOX has been reduced considerably with the combination dose regimen of VPN. Further, the combine effect of both the agents improved the apoptotic cell death 28.5% compared to single agent treatment 5.71% and 10.5% for VPN and DOX, respectively. Both agents bind effectively to tubulin in single and in combination to interfere with cell cycle progression in G2/M transition. This study provides novel concept of combination treatment of DOX and VPN to amend efficiency in breast cancer treatment.Communicated by Ramaswamy H. Sarma.