Abrogation of Cellular Senescence Induced by Temozolomide in Glioblastoma Cells: Search for Senolytics

Abstract

A first-line therapeutic for high-grade glioma, notably glioblastoma (GBM), is the DNA methylating drug temozolomide (TMZ). Previously, we showed that TMZ induces not only apoptosis and autophagy, but also cellular senescence (CSEN). We presented the hypothesis that GBM cells may escape from CSEN, giving rise to recurrent tumors. Furthermore, the inflammatory phenotype associated with CSEN may attenuate chemotherapy and drive tumor progression. Therefore, treatments that specifically target senescent cells, i.e., senolytic drugs, may lead to a better outcome of GBM therapy by preventing recurrences and tumor inflammation. Here, we tested Bcl-2 targeting drugs including ABT-737, ABT-263 (navitoclax), several natural substances such as artesunate, fisetin and curcumin as well as lomustine (CCNU) and ionizing radiation (IR) for their senolytic capacity in GBM cells. Additionally, several proteins involved in the DNA damage response (DDR), ATM, ATR, Chk1/2, p53, p21, NF-kB, Rad51, PARP, IAPs and autophagy, a pathway involved in CSEN induction, were tested for their impact in maintaining CSEN. Treatment of GBM cells with a low dose of TMZ for 8–10 days resulted in >80% CSEN, confirming CSEN to be the major trait induced by TMZ. To identify senolytics, we treated the senescent population with the compounds of interest and found that ABT-737, navitoclax, chloroquine, ATMi, ATRi, BV-6, PX-866 and the natural compounds fisetin and artesunate exhibit senolytic activity, inducing death in senescent cells more efficiently than in proliferating cells. Curcumin showed the opposite effect. No specific effect on CSEN cells was observed by inhibition of Chk1/Chk2, p21, NF-kB, Rad51 and PARP. We conclude that these factors neither play a critical role in maintaining TMZ-induced CSEN nor can their inhibitors be considered as senolytics. Since IR and CCNU did not exhibit senolytic activity, radio- and chemotherapy with alkylating drugs is not designed to eliminate TMZ-induced senescent cancer cells.

The Potential of Senescence as a Target for Developing Anticancer Therapy

“…Since TIS involves the increased expression of BCL-2, targeting BCL-2 may exert anticancer effects. BCL2-targeting drugs, including ABT-737 and ABT-263 (navitoclax), natural substances, such as artesunate, fisetin, and curcumin, showed senolytic effects in glioblastoma cells and non-transformed cells [ 83 , 167 ]. ABT-263 eliminated senescent cells and enhanced the efficacy of olaparib, a PARP inhibitor, in both breast and ovarian cancer cell lines [ 168 ].…”

Cell-Free DNA Sequencing Reveals Gene Variants in DNA Damage Repair Genes Associated with Prognosis of Prostate Cancer Patients

“…Another possibility for PCa patients with ATM mutations is the therapeutic application of ATM inhibitors, such as AZD1390, AZD0156, M4076, Ku 60019 or XRD-0394, but these inhibitors are still in clinical phase I studies. However, the combination of the DNA-methylating drug, temozolomide, with the ATM inhibitor, KU60019, has been shown to result in an increased induction of apoptosis in glioblastoma cells in vitro [ 52 ]. Furthermore, Fischer et al showed that PTEN mutant non-small-cell lung cancer requires ATM to suppress proapoptotic signaling and evade radiotherapy.…”

Cellular senescence in cancer: molecular mechanisms and therapeutic targets

“…297 Other well-demonstrated senolytics being tested for cancer treatment are inhibitors of BCL-2 family members. For example, ABT-737 and ABT-263 were shown to selectively kill senescent cells and blunt the recurrent growth and aggressiveness of cancer cells via interference with BCL-2, BCL-XL, and BCL-W. 291,298,299 Other BCL-XL inhibitors, such as A-1331852 and A-1155463, have also exhibited senolytic activity, 300,301 even though their efficacy in tumor therapy has not been confirmed. Using single-cell RNA sequencing, Martina Troiani and her colleagues identified novel senolytic targets that were essential for the survival of senescent tumor cells.…”

“…ABT‐737, navitoclax, chloroquine, ATMi, ATRi, BV‐6, PX‐866 and the natural compounds fisetin and artesunate exhibit senolytic activity, inducing death in senescent cells more efficiently than in proliferating cells. 299 …”