Authors:

Derek B. Sisbarro

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About Paper:

Glioblastoma (GBM) is a deadly cancer where the standard of care treatment is the guanine-targeted chemotherapy — temozolomide (TMZ) [1]. Post-TMZ treatment, gross nuclear and chromosomal abnormalities are observed. To protect chromosome integrity, the shelterin complex binds G-quadruplexes (G4s), guanine-rich structures that can be found in telomeres [2]. Disrupted shelterin binding can cause telomere crisis, nuclear envelope rupture, and ultimately the DNA damage phenomenon chromothripsis (CT) [3]. Here we show that TMZ disrupts shelterin binding and increases both nuclear envelope rupturing and chromothripsis. We investigate the hypothesis that TMZ treatment increases cell reliance on nuclear import-export machinery, making TMZ-resistant cells more sensitive to the nuclear export protein (XPO1) inhibitor KPT-330. To study telomeric mechanisms and interactions with KPT-330 in drug sensitive and resistant GBM, we used PacBio HIFI sequencing, immunofluorescence and cell-proliferation assays for in vitro mechanistic studies. We also used KPT-330 (Selinexor) treated clinical trial samples to determine the clinical efficacy of targeting a nuclear export protein in combination with TMZ in a real world setting. We show that TMZ-resistant GBM cells display shortened telomeres, and the canonical chromothripsis markers of nuclear envelope rupturing and protein mislocalization in vitro. We show that chromothripsis-positive TMZ-resistant cells have significantly increased sensitivity to the XPO1 inhibitor KPT-330, as compared with TMZ-sensitive cells. We also find that CT is sufficient for KPT-330 induced cell death, and that G-targeted chemotherapies specifically can increase KPT-330 sensitivity. Finally, we observe that patients treated with KPT-330 (Selinexor) see a decrease in CT markers, where higher baseline CT markers led to longer overall survival. Overall, our findings show that G-targeted chemotherapy can increase chromothripsis which leads to increased nuclear envelope rupturing and protein mislocalization. These changes affect telomere integrity, leading to increased dependence on import/export machinery and increased sensitivity to KPT-330 both in vitro and in patients.

Source:

Northwestern University

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Co-authors:

Derek B. Sisbarro