PDTC Sensitizes Brain Glioma U251 Cells To Temozolomide Via Downregulating MGMT And BCL-XL

BackgroundBrain glioma is the most common primary tumor in the central nervous system and one of the leading causes of mortality in cancer patients.Despite combined treatment strategies including surgical resection,radio-and chemotherapy(such as TMZ),the total survival remains low.Patients receiving surgery,radiotherapy with concomitant and adjuvant temozolomide(TMZ)show some advances in progression free survival(PFS)and 5-year survival.However,the efficacy of TMZ is limited by the chemoresistance caused by the intracellular activity of O6-methylguanine DNA-methyltransferase(MGMT),a DNA repair enzyme reversing the TMZ effect by specifically removing the methyl group from O6-positions of guanine residues.One regulator of MGMT,the nuclear factor-kappa B(NF-?B),contributes to tumor initiation,progression and resistance to radio-or chemotherapy.High constitutive NF-?B activity is observed in various solid tumors,including glioblastoma.The impact of NF-?B activity on its canonical target genes(such as BCL-XL,survivin,BCL-2,IAP1/IAP2(inhibitor of apoptosis 1/2),TRAF1 /TRAF2(receptor-associated factors),VEGF,MMP9,Cyclin D1)also plays roles in glioma cell survival and chemoresistance.Combination of NF-?B inhibitors and alkylating agents like TMZ maybe a potential potent way to overcome these resistant characters and improve the efficacy of glioma therapy.ObjectiveTo determine whether PDTC,an NF-?B activation inhibitor,can enhance the proliferation-inhibiting,apoptosis-inducing and cell cycle-blocking effects of temozolomide(TMZ)on U251 glioma cell line,and investigate the potential mechanisms.Methods1.After being treated with TMZ,PDTC or combination of TMZ and PDTC,the proliferation and apoptosis/cell cycle distribution of U251 cell lines were respectively measured by MTT assay and flow cytometry.2.The mRNA and protein expression of MGMT,BCL-XL and survivin were determined by q RT-PCR and Western blot.ResultsTreatments of TMZ,PDTC and TMZ+PDTC all significantly suppressed proliferation and induced apoptosis in U251 cells and combination of PDTC and TMZ caused the highest proliferation inhibition rate and apoptosis rate;PDTC treatment markedly reduced the mRNA and protein expression of MGMT,BCL-XL and survivin;While MGMT,BCL-XL and survivin expression were upregulated by TMZ,mRNA and protein expression levels of MGMT,BCL-XL,but not survivin,were significantly reduced in TMZ+PDTC treated cells compared with TMZ treated cells.ConclusionPDTC enhances the sensitivity of U251 cells to temozolomide treatment and this effect can be partly induced by downregulation of MGMT and BCL-XL.