Biom-32. Endoplasmic Reticulum Protein Ssr3 Determines and Predicts Response to Paclitaxel in Breast Cancer and Glioblastoma

Abstract

Paclitaxel (PTX) is one the most potent and commonly used chemotherapies for breast and pancreatic cancer. Given the potency of this drug for glioblastomas (GBM) several ongoing clinical trials are investigating means of enhancing delivery of PTX across the blood-brain barrier for this disease. In spite of the efficacy of PTX, individual tumors exhibit variable susceptibility to this drug, with response rate in the range of 30%-60%. To identify predictive biomarkers for response to PTX, we performed a genome-wide CRISPR knock-out screen using human glioma cells. The most enriched genes in the CRISPR screen underwent further selection based on their correlation with survival in the breast cancer patient cohorts treated with PTX and not in patients treated with other chemotherapies, a finding that was validated on a second independent patient cohort. This led to the discovery of endoplasmic reticulum (ER) protein SSR3 as a putative predictive biomarker for PTX. SSR3 protein levels showed positive correlation with response to PTX in breast cancer cells, glioma cells, in multiple intracranial glioma xenografts and in GBM patient derived explant cultures. Knockout of SSR3 turned the cells resistant to PTX while its overexpression sensitized the cells to PTX. In gliomas, SSR3-mediated susceptibility to PTX relates to modulation of phosphorylation of ER stress sensor IRE1α. Thus, by using genome-wide screen combined with patient response data, we discovered a biomarker that demonstrates causal and correlative relationship with response to PTX in breast cancer and GBM. Prospective validation of this biomarker is warranted for its broad implementation for precision oncology.

Unveiling immune checkpoint regulation: exploring the power of in vivo CRISPR screenings in cancer immunotherapy

“…As kinases are a major drug target and a major control point in cell behavior, the kinase has also been the target of large-scale functional genomics with CRISPRko screenings and drug discovery efforts, especially in cancer therapeutics (Workman, 2005). To investigate the contribution of glioma cell-intrinsic kinases in T cell recognition, GL261 cells were intracranially implanted into WT and CD8 deficient C57BL/6 mice after they had been transfected with a CRISPRko library for all 713 known kinases (Dmello et al, 2023). Among the kinase KO clones depleted in WT mice relative to the CD8 deficient mice, which contributed towards resistance to CD8 T-cell-mediated killing, checkpoint kinase 2 (Chek2) had the most depleted sgRNA.…”

“…Among the kinase KO clones depleted in WT mice relative to the CD8 deficient mice, which contributed towards resistance to CD8 T-cell-mediated killing, checkpoint kinase 2 (Chek2) had the most depleted sgRNA. Mechanistically, loss of Chek2 enhances antigen presentation, STING pathway activation, and PD-L1 expression in mouse gliomas, supporting Chek2 as a promising target for enhancement of response to immune checkpoint blockade therapy in glioblastoma (GBM) (Dmello et al, 2023).…”