Oxidative cytotoxic agent withaferin A resensitizes temozolomide-resistant glioblastomas via MGMT depletion and induces apoptosis through Akt/mTOR pathway inhibitory modulation.
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.
Department of Pharmacology, Toxicology, and Therapeutics, University of Kansas Medical Center, Kansas City, KS, 66160, USA.
Patrick T
PT
Grogan
Jann N
JN
Sarkaria
Barbara N
BN
Timmermann
Mark S
MS
Cohen
D000970:Antineoplastic Agents / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects*; D059447:Cell Cycle Checkpoints / Q000187:drug effects; D016923:Cell Death / Q000187:drug effects; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D015254:DNA Modification Methylases / Q000378:metabolism*; D045643:DNA Repair Enzymes / Q000378:metabolism*; D003606:Dacarbazine / Q000031:analogs & derivatives* / Q000494:pharmacology; D066246:ErbB Receptors / Q000378:metabolism; D059565:G2 Phase Cell Cycle Checkpoints / Q000187:drug effects; D005909:Glioblastoma / Q000188:drug therapy*; D051547:Heme Oxygenase-1 / Q000378:metabolism; D006801:Humans; D020935:MAP Kinase Signaling System / Q000187:drug effects; D019853:O(6)-Methylguanine-DNA Methyltransferase / Q000378:metabolism; D018384:Oxidative Stress / Q000187:drug effects; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D019859:Proto-Oncogene Proteins c-met / Q000378:metabolism; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000378:metabolism; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000378:metabolism; D058570:TOR Serine-Threonine Kinases / Q000378:metabolism*; D000077204:Temozolomide; D025521:Tumor Suppressor Proteins / Q000378:metabolism*; D054358:Withanolides / Q000494:pharmacology*
D000970:Antineoplastic Agents; D015254:DNA Modification Methylases; D045643:DNA Repair Enzymes; D003606:Dacarbazine; D066246:ErbB Receptors; D051547:Heme Oxygenase-1; D019853:O(6)-Methylguanine-DNA Methyltransferase; D051057:Proto-Oncogene Proteins c-akt; D019859:Proto-Oncogene Proteins c-met; D018719:Erb-b2 Receptor Tyrosine Kinases; D038762:Ribosomal Protein S6 Kinases, 70-kDa; D058570:TOR Serine-Threonine Kinases; D000077204:Temozolomide; D025521:Tumor Suppressor Proteins; D054358:Withanolides; C496541:HMOX1 protein, human; C515491:MGMT protein, human; C546842:MTOR protein, human; C512478:EGFR protein, human; C508053:ERBB2 protein, human; C009684:withaferin A