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The Targeting of RNA Polymerase I Transcription Using CX-5461 in Combination with Radiation Enhances Tumour Cell Killing Effects in Human Solid Cancers.

ABSTRACT: An increased rate of cellular proliferation is a hallmark of cancer and may be accompanied by an increase in ribosome biogenesis and dysregulation in rRNA synthesis. In this regard, CX-5461 has been developed as a novel RNA polymerase I inhibitor and is currently in Phase I/II clinical trials for solid and hematological malignancies. In the present study, interactions between CX-5461 and single-dose X-ray exposure were assessed using isobologram analysis using MTS assay and drug-induced cell death was assessed using flow cytometric, confocal microscopy and Western blot analysis. Combination treatments involving CX-5461 and single-dose X-ray exposure highlighted increased effectiveness compared to individual treatment alone in the CaSki cervical cancer line, with marked synergistic interaction occurring within the low-drug (50 nM) and low-dose radiation range (2-6 Gy). Cell lines challenged with CX-5461 demonstrated the presence of DNA damage, induction of apoptosis, autophagy and senescence alongside high percentages of G2/M cell cycle arrest. In addition, we report preferential sensitivity of ovarian cancer cells with BRCA2 mutation to this novel agent. Taken together, CX-5461 displayed a broad spectrum of activity in a panel of solid cancer cell lines with IC50 values ranging from 35 nM to >1 µM. The work described herein identifies the synergistic effects of CX-5461 in combination with X-rays in solid cancers and may also aid in the design of clinical trials involving this novel agent.

SUBMITTER: Ismael M

PROVIDER: S-EPMC6826960 | biostudies-literature | 2019 Sep

REPOSITORIES: biostudies-literature

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The Targeting of RNA Polymerase I Transcription Using CX-5461 in Combination with Radiation Enhances Tumour Cell Killing Effects in Human Solid Cancers.

Ismael Mohammed M Webb Roger R Ajaz Mazhar M Kirkby Karen J KJ Coley Helen M HM

Cancers 20190925 10

An increased rate of cellular proliferation is a hallmark of cancer and may be accompanied by an increase in ribosome biogenesis and dysregulation in rRNA synthesis. In this regard, CX-5461 has been developed as a novel RNA polymerase I inhibitor and is currently in Phase I/II clinical trials for solid and hematological malignancies. In the present study, interactions between CX-5461 and single-dose X-ray exposure were assessed using isobologram analysis using MTS assay and drug-induced cell dea ...[more]

PMID: 31557908

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Project description:Hyperactivation of RNA polymerase I (Pol I) transcription of ribosomal RNA (rRNA) genes (rDNA) is a key determinant of growth and proliferation and a consistent feature of cancer cells. We have demonstrated that inhibition of rDNA transcription by the Pol I transcription inhibitor CX-5461 selectively kills tumor cells in vivo. Moreover, the first-in human trial of CX-5461 has demonstrated CX-5461 is well-tolerated in patients and has single-agent anti-tumor activity in hematologic malignancies. However, the mechanisms underlying tumor cell sensitivity to CX-5461 remain unclear. Understanding these mechanisms is crucial for the development of predictive biomarkers of response that can be utilized for stratifying patients who may benefit from CX-5461. The rDNA repeats exist in four different and dynamic chromatin states: inactive rDNA can be either methylated silent or unmethylated pseudo-silent; while active rDNA repeats are described as either transcriptionally competent but non-transcribed or actively transcribed, depending on the level of rDNA promoter methylation, loading of the essential rDNA chromatin remodeler UBF and histone marks status. In addition, the number of rDNA repeats per human cell can reach hundreds of copies. Here, we tested the hypothesis that the number and/or chromatin status of the rDNA repeats, is a critical determinant of tumor cell sensitivity to Pol I therapy. We systematically examined a panel of ovarian cancer (OVCA) cell lines to identify rDNA chromatin associated biomarkers that might predict sensitivity to CX-5461. We demonstrated that an increased proportion of active to inactive rDNA repeats, independent of rDNA copy number, determines OVCA cell line sensitivity to CX-5461. Further, using zinc finger nuclease genome editing we identified that reducing rDNA copy number leads to an increase in the proportion of active rDNA repeats and confers sensitivity to CX-5461 but also induces genome-wide instability and sensitivity to DNA damage. We propose that the proportion of active to inactive rDNA repeats may serve as a biomarker to identify cancer patients who will benefit from CX-5461 therapy in future clinical trials. The data also reinforces the notion that rDNA instability is a threat to genomic integrity and cellular homeostasis.

Dataset Information

The Targeting of RNA Polymerase I Transcription Using CX-5461 in Combination with Radiation Enhances Tumour Cell Killing Effects in Human Solid Cancers.

Publications

The Targeting of RNA Polymerase I Transcription Using CX-5461 in Combination with Radiation Enhances Tumour Cell Killing Effects in Human Solid Cancers.

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