Oxidative cytotoxic agent withaferin A resensitizes temozolomide-resistant glioblastomas via MGMT depletion and induces apoptosis through Akt/mTOR pathway inhibitory modulation

Abstract

Temozolomide (TMZ) has remained the chemotherapy of choice in patients with glioblastoma multiforme (GBM) primarily due to the lack of more effective drugs. Tumors, however, quickly develop resistance to this line of treatment creating a critical need for alternative approaches and strategies to resensitize the cells. Withaferin A (WA), a steroidal lactone derived from several genera of the Solanaceae plant family has previously demonstrated potent anti-cancer activity in multiple tumor models. Here, we examine the effects of WA against TMZ-resistant GBM cells as a monotherapy and in combination with TMZ. WA prevented GBM cell proliferation by dose-dependent G2/M cell cycle arrest and cell death through both intrinsic and extrinsic apoptotic pathways. This effect correlated with depletion of principle proteins of the Akt/mTOR and MAPK survival and proliferation pathways with diminished phosphorylation of Akt, mTOR, and p70 S6K but compensatory activation of ERK1/2. Depletion of tyrosine kinase cell surface receptors c-Met, EGFR, and Her2 was also observed. WA demonstrated induction of N-acetyl-L-cysteine-repressible oxidative stress as measured directly and through a subsequent heat shock response with HSP32 and HSP70 upregulation and decreased HSF1. Finally, pretreatment of TMZ-resistant GBM cells with WA was associated with O6-methylguanine-DNA methyltransferase (MGMT) depletion which potentiated TMZ-mediated MGMT degradation. Combination treatment with both WA and TMZ resulted in resensitization of MGMT-mediated TMZ-resistance but not resistance through mismatch repair mutations. These studies suggest great clinical potential for the utilization of WA in TMZ-resistant GBM as both a monotherapy and a resensitizer in combination with the standard chemotherapeutic agent TMZ.

Withaferin A suppresses the growth of myelodysplasia and leukemia cell lines by inhibiting cell cycle progression

“…Concentration‐dependent growth‐suppressive effects were confirmed in all cell lines studied, and the IC 50 values ranged from 60 to 200 nM at 72 h (Fig. ), which are lower than the range of IC 50 values reported for other cancer cell lines (300 to 1000 nM at 72 h), suggesting that human leukemia cell lines are comparatively highly susceptible to WA. WA treatment also resulted in an increased number of mitotic cells, and the cell cycle analysis showed that WA induces G2/M arrest (Fig.…”

“…Previous reports have demonstrated that WA affects microtubules or vimentin intermediate filaments and, subsequently, exerts cytotoxicity or inhibition of the epithelial–mesenchymal transition . WA is reported to induce cell cycle arrest at G2/M phase, resulting in apoptosis . Nonetheless, the detailed mechanisms of action remain to be determined and may be different depending on the cells, tissues or experimental systems.…”

“…(7)(8)(9)(10) WA is reported to induce cell cycle arrest at G2/M phase, resulting in apoptosis. (8,(11)(12)(13)(14)(15) Nonetheless, the detailed mechanisms of action remain to be determined and may be different depending on the cells, tissues or experimental systems.…”

Protective HSP70 Induction by Z-Ligustilide against Oxygen–Glucose Deprivation Injury <i>via</i> Activation of the MAPK Pathway but Not of HSF1

“…In support of our results, others' studies also found that HSF1 rises were not followed by enhanced HSP70 expression. 31,32) Recently, cytoprotective functions of HSPs, particularly HSP70, have been connected to MAPKs signaling pathway. 33,34) For this reason, we investigated whether there is involvement of MAPKs in the induction of HSP70 by Z-ligustilide.…”

Treatment of adult and pediatric high-grade gliomas with Withaferin A: antitumor mechanisms and future perspectives

“…Current research looks at combining WA and TMZ, which shows promise by allowing resistant cells to become sensitized and undergo apoptosis [39,40]. WA treatment acts by depleting MGMT, enabling TMZ to cause DNA damage, G2/M cell cycle arrest, and death in cancerous cells [41].…”