MGMT inhibition in ER positive breast cancer leads to CDC2, TOP2A, AURKB, CDC20, KIF20A, Cyclin A2, Cyclin B2, Cyclin D1, ERα and Survivin inhibition and enhances response to temozolomide
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George C. Bobustuc1,2, Amin B. Kassam1,2, Richard A. Rovin1,2, Sheila Jeudy3, Joshua S. Smith3, Beth Isley3, Maharaj Singh1,2, Ameya Paranjpe4, Kalkunte S. Srivenugopal4 and Santhi D. Konduri1,2
1Aurora Research Institute, Milwaukee, WI, USA
2Aurora Neurosciences Innovation Institute, Milwaukee, WI, USA
3Florida Hospital, Orlando, FL, USA
4Texas Tech University Health Sciences Center, Amarillo, TX, USA
George C. Bobustuc, email: George.Bobustuc@aurora.org
Santhi D. Konduri, email: Santhi.Konduri@aurora.org
Keywords: MGMT; BG; temozolomide; ER-positive breast cancer
Abbreviations MGMT: O6 methylguanine DNA methyltransferase; BG: O6 Benzylguanine; TMZ: Temozolomide; qRT-PCR: Quantitative Reverse Transcriptase Polymerase Chain Reaction (real-time PCR)
Received: September 04, 2017 Accepted: June 13, 2018 Published: July 03, 2018
The DNA damage repair enzyme, O6-methylguanine DNA methyltransferase (MGMT) is overexpressed in breast cancer, correlating directly with estrogen receptor (ER) expression and function. In ER negative breast cancer the MGMT promoter is frequently methylated. In ER positive breast cancer MGMT is upregulated and modulates ER function. Here, we evaluate MGMT’s role in control of other clinically relevant targets involved in cell cycle regulation during breast cancer oncogenesis. We show that O6-benzylguanine (BG), an MGMT inhibitor decreases CDC2, CDC20, TOP2A, AURKB, KIF20A, cyclin B2, A2, D1, ERα and survivin and induces c-PARP and p21 and sensitizes ER positive breast cancer to temozolomide (TMZ). Further, siRNA inhibition of MGMT inhibits CDC2, TOP2A, AURKB, KIF20A, Cyclin B2, A2 and survivin and induces p21. Combination of BG+TMZ decreases CDC2, CDC20, TOP2A, AURKB, KIF20A, Cyclin A2, B2, D1, ERα and survivin. Temozolomide alone inhibits MGMT expression in a dose and time dependent manner and increases p21 and cytochrome c. Temozolomide inhibits transcription of TOP2A, AURKB, KIF20A and does not have any effect on CDC2 and CDC20 and induces p21. BG+/-TMZ inhibits breast cancer growth. In our orthotopic ER positive breast cancer xenografts, BG+/-TMZ decreases ki-67, CDC2, CDC20, TOP2A, AURKB and induces p21 expression. In the same model, BG+TMZ combination inhibits breast tumor growth in vivo compared to single agent (TMZ or BG) or control. Our results show that MGMT inhibition is relevant for inhibition of multiple downstream targets involved in tumorigenesis. We also show that MGMT inhibition increases ER positive breast cancer sensitivity to alkylator based chemotherapy.
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