Improving Localized Radiotherapy for Glioblastoma via Small Molecule Inhibition of KIF11.

Glioblastoma, IDH-wild type (GBM) is the most common and lethal malignant primary brain tumor. Standard of care includes surgery, radiotherapy, and chemotherapy with the DNA alkylating agent temozolomide (TMZ). Despite these intensive efforts, current GBM therapy remains mainly palliative with only modest improvement achieved in overall survival. With regards to radiotherapy, GBM is ranked as one of the most radioresistant tumor types. In this study, we wanted to investigate if enriching cells in the most radiosensitive cell cycle phase, mitosis, could improve localized radiotherapy for GBM. To achieve cell cycle arrest in mitosis we used ispinesib, a small molecule inhibitor to the mitotic kinesin, KIF11. Cell culture studies validated that ispinesib radiosensitized patient-derived GBM cells. In vivo, we validated that ispinesib increased the fraction of tumor cells arrested in mitosis as well as increased apoptosis. Critical for the translation of this approach, we validated that combination therapy with ispinesib and irradiation led to the greatest increase in survival over either monotherapy alone. Our data highlight KIF11 inhibition in combination with radiotherapy as a new combinatorial approach that reduces the overall radioresistance of GBM and which can readily be moved into clinical trials.

A Mesenchymal Tumor Cell State Confers Increased Dependency on the BCL-XL Antiapoptotic Protein in Kidney Cancer.

PURPOSE: Advanced/metastatic forms of clear-cell renal cell carcinomas (ccRCC) have limited therapeutic options. Genome-wide genetic screens have identified cellular dependencies in many cancers. Using the Broad Institute/Novartis combined short hairpin RNA (shRNA) dataset, and cross-validation with the CRISPR/Cas9 DepMap (21Q3) dataset, we sought therapeutically actionable dependencies in kidney lineage cancers. EXPERIMENTAL DESIGN: We identified preferential genetic dependencies in kidney cancer cells versus other lineages. BCL2L1, which encodes the BCL-XL antiapoptotic protein, scored as the top actionable dependency. We validated this finding using genetic and pharmacologic tools in a panel of ccRCC cell lines. Select BCL-XL-dependent (versus independent) cell lines were then transcriptionally profiled to identify biomarkers and mechanistic drivers of BCL-XL dependence. Cell-based studies (in vitro and in vivo) and clinical validations were used to address physiologic relevance. RESULTS: Inactivation of BCL-XL, but not BCL-2, led to fitness defects in renal cancer cells, and sensitized them to chemotherapeutics. Transcriptomic profiling identified a "BCL-XL dependency" signature, including an elevated mesenchymal gene signature. A mesenchymal state was both necessary and sufficient to confer increased BCL-XL dependence. The "BCL-XL dependency" signature was observed in approximately 30% of human ccRCCs, which were also associated with worse clinical outcomes. Finally, an orally bioavailable BCL-XL inhibitor, A-1331852, showed antitumor efficacy in vivo. CONCLUSIONS: Our studies uncovered an unexpected link between cell state and BCL-XL dependence in ccRCC. Therapeutic agents that specifically target BCL-XL are available. Our work justifies testing the utility of BCL-XL blockade to target, likely, a clinically aggressive subset of human kidney cancers. See related commentary by Wang et al., p. 4600.

The small molecule drug CBL0137 increases the level of DNA damage and the efficacy of radiotherapy for glioblastoma.

Glioblastoma (GBM) is an incurable brain tumor with inevitable recurrence. This is in part due to a highly malignant cancer stem cell (CSC) subpopulation of tumor cells that is particularly resistant to conventional treatments, including radiotherapy. Here we show that CBL0137, a small molecule anti-cancer agent, sensitizes GBM CSCs to radiotherapy. CBL0137 sequesters the FACT (facilitates chromatin transcription) complex to chromatin, resulting in cytotoxicity preferentially within tumor cells. We show that when combined with radiotherapy, CBL0137 inhibited GBM CSC growth and resulted in more DNA damage in the CSCs compared to irradiation or drug alone. Using an in vivo subcutaneous model, we showed that the frequency of GBM CSCs was reduced when tumors were pretreated with CBL0137 and then exposed to irradiation. Survival studies with orthotopic GBM models resulted in significantly extended survival for mice treated with combinatorial therapy. As GBM CSCs contribute to the inevitable recurrence in patients, targeting them is imperative. This work establishes a new treatment paradigm for GBM that sensitizes CSCs to irradiation and may ultimately reduce tumor recurrence.

Hyperphosphorylation of CDH1 in Glioblastoma Cancer Stem Cells Attenuates APC/CCDH1 Activity and Pharmacologic Inhibition of APC/CCDH1/CDC20 Compromises Viability.

Glioblastoma (GBM) is the most common and lethal primary brain tumor and remains incurable. This is in part due to the cellular heterogeneity within these tumors, which includes a subpopulation of treatment-resistant cells called cancer stem-like cells (CSC). We previously identified that the anaphase-promoting complex/cylosome (APC/C), a key cell-cycle regulator and tumor suppressor, had attenuated ligase activity in CSCs. Here, we assessed the mechanism of reduced activity, as well as the efficacy of pharmacologically targeting the APC/C in CSCs. We identified hyperphosphorylation of CDH1, but not pseudosubstrate inhibition by early mitotic inhibitor 1 (EMI1), as a major mechanism driving attenuated APC/CCDH1 activity in the G1-phase of the cell cycle in CSCs. Small-molecule inhibition of the APC/C reduced viability of both CSCs and nonstem tumor cells (NSTCs), with the combination of proTAME and apcin having the biggest impact. Combinatorial drug treatment also led to the greatest mitotic arrest and chromosomal abnormalities. IMPLICATIONS: Our findings demonstrate how the activity of the APC/CCDH1 tumor suppressor is reduced in CSCs and also validates small-molecule inhibition of the APC/C as a promising therapeutic target for the treatment of GBM.