Enhancement of apoptotic activities on brain cancer cells via the combination of γ-tocotrienol and jerantinine A

Background: gamma-Tocotrienol, a vitamin E isomer possesses pronounced in vitro anticancer activities. However, the in vivo potency has been limited by hardly achievable therapeutic levels owing to inefficient high-dose oral delivery which leads to subsequent metabolic degradation. Jerantinine A, an Aspidosperma alkaloid, originally isolated from Tabernaemontana corymbosa, has proved to possess interesting anticancer activities. However, jerantinine A also induces toxicity to non-cancerous cells. Purpose: We adopted a combinatorial approach with the joint application of gamma-tocotrienol and jerantinine A at lower concentrations in order to minimize toxicity towards non-cancerous cells while improving the potency on brain cancer cells. Methods: The antiproliferative potency of individual gamma-tocotrienol and jerantinine A as well as combined in low-concentration was firstly evaluated on U87MG cancer and MRC5 normal cells. Morphological changes, DNA damage patterns, cell cycle arrests and the effects of individual and combined low-concentration compounds on microtubules were then investigated. Finally, the potential roles of caspase enzymes and apoptosis-related proteins in mediating the apoptotic mechanisms were investigated using apoptosis antibody array, ELISA and Western blotting analysis. Results: Combinatorial study between gamma-tocotrienol at a concentration range (0-24 mu g/ml) and fixed IC20 concentration of jerantinine A (0.16 mu g/ml) induced a potent antiproliferative effect on U87MG cells and led to a reduction on the new half maximal inhibitory concentration of gamma-tocotrienol (i.e. tIC50 = 1.29 mu g/ml) as compared to that of individual gamma-tocotrienol (i.e. IC50 = 3.17 mu g/ml). A reduction on undesirable toxicity to MRC5 normal cells was also observed. G0/G1 cell cycle arrest was evident on U87MG cells receiving IC50 of individual.-tocotrienol and combined low-concentration compounds (1.29 mu g/ml gamma-tocotrienol + 0.16 mu g/ml jerantinine A), whereas, a profound G2/M arrest was evident on cells treated with IC50 of individual jerantinine A. Additionally, individual jerantinine A and combined compounds (except individual gamma-tocotrienol) caused a disruption of microtubule networks triggering Fas-and p53-induced apoptosis mediated via the death receptor and mitochondrial pathways. Conclusions: These findings demonstrated that the combined use of lower concentrations of gamma-tocotrienol and jerantinine A induced potent cytotoxic effects on U87MG cancer cells resulting in a reduction on the required individual concentrations and thereby minimizing toxicity of jerantinine A towards non-cancerous MRC5 cells as well as probably overcoming the high-dose limiting application of gamma-tocotrienol. The multi-targeted mechanisms of action of the combination approach have shown a therapeutic potential against brain cancer in vitro and therefore, further in vivo investigations using a suitable animal model should be the way forward. (C) 2017 Elsevier GmbH. All rights reserved.