ZSTK474 Sensitizes Glioblastoma to Temozolomide by Blocking Homologous Recombination Repair

Abstract

Glioblastoma (GBM) is the most common primary malignant brain tumor in adults. Temozolomide (TMZ) is used as the standard chemotherapeutic agent for GBM but with limited success, and treatment failure is mainly due to tumor resistance. One of the leading causes of TMZ resistance is the upregulation of the DNA repair mechanism. Therefore, targeting the DNA damage response (DDR) is proposed to be an effective strategy to sensitize tumor cells to TMZ. In the present study, we demonstrated that the combined use of the PI3K inhibitor ZSTK474 and TMZ showed synergetic anticancer effects on human GBM cells in vitro and in vivo. The combination treatment led to significantly increased cell apoptosis and DNA double strand breaks (DSBs). In addition, a mechanistic study indicated that TMZ enhanced the homologous recombination (HR) repair efficiency in GBM cells, while ZSTK474 impaired HR repair by blocking the phosphorylation of ATM and the expression of BRCA1/2 and Rad51, thereby sensitizing GBM cells to TMZ. Moreover, TMZ activated the PI3K signaling pathway through upregulation of the PI3K catalytic subunits p110α and p110β and the phosphorylation of Akt. Meanwhile, ZSTK474 blocked the activity of the PI3K/Akt pathway. Taken together, our findings suggested that the combination of ZSTK474 and TMZ might be a potential therapeutic option for GBM.

Multiplex single-cell chemical genomics reveals the kinase dependence of the response to targeted therapy

“…Knockdown of CDK18 , recently described as a co-factor for ATR-driven homologous recombination repair in GBM, 48 led to a significant increase in proliferation in response to the PI3K inhibitor zstk474 ( Figure 3 F). zstk474, like other PI3K inhibitors, targets other DNA damage response kinases such as DNA-PKc and ATM 49 , 50 and was shown to generate strand breaks in GBM cells. 50 Therefore, the effect of CDK18 loss on the proliferative response to zstk474 exposure may result from an additive increase in genotoxic stress.…”

“…zstk474, like other PI3K inhibitors, targets other DNA damage response kinases such as DNA-PKc and ATM 49 , 50 and was shown to generate strand breaks in GBM cells. 50 Therefore, the effect of CDK18 loss on the proliferative response to zstk474 exposure may result from an additive increase in genotoxic stress. Our analysis demonstrates that our multiplex chemical genomic screen identifies significant interactions between genotype and exposure, including kinase perturbations that sensitize or resist the effect of RTK-pathway-targeting inhibitors on proliferative gene expression.…”

Multiplex single-cell chemical genomics reveals the kinase dependence of the response to targeted therapy

“…Knockdown of CDK18 , recently described as a co-factor for ATR-driven homologous recombination repair in GBM 48 , led to a significant increase in proliferation in response to the PI3K inhibitor zstk474 ( Fig 3F ). Zstk474, like other PI3K inhibitors, targets other DNA damage response kinases such as DNA-PKc and ATM 49, 50 and was shown to generate strand breaks in GBM cells 50 . Therefore, the effect of CDK18 loss on the proliferative response to zstk474 exposure may result from an additive increase in genotoxic stress.…”