Targeting cyclin-dependent kinase 9 by a novel inhibitor enhances radiosensitization and identifies Axl as a novel downstream target in esophageal adenocarcinoma.

Omkara Veeranki ,Riham Katkhuda,Sunil Krishnan,Michael Tetzlaff,Barbara Mino,Jaime Rodriguez Canales,Alicia Mejia,Rashmi Dokey,Ramesh Tailor,Ji Yuan Wu,Mariela Blum,Yawei Qiao,Zhimin Tong,Scott Kopetz,Pankaj Kumar Singh,Steven H Lin,Wayne L Hofstetter ,Zhang Jian-Hu ,Jaffer A Ajani ,Roland L Bassett ,Dipen M Maru

doi:10.18632/oncotarget.27095

Omkara Veeranki , Riham Katkhuda + Show 19 more

Open Access

https://doi.org/10.18632/oncotarget.27095

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Abstract

Cyclin-dependent kinase 9 (CDK9) transcriptionally regulates several proteins and cellular pathways central to radiation induced tissue injury. We investigated a role of BAY1143572, a new highly specific CDK9 inhibitor, as a sensitizer to radiation in esophageal adenocarcinoma. In vitro synergy between the CDK9 inhibitor and radiation was evaluated by clonogenic assay. In vivo synergy between the CDK9 inhibitor and radiation was assessed in multiple xenograft models including a patient’s tumor derived xenograft (PDX). Reverse phase protein array (RPPA), western blotting, immunohistochemistry, and qPCR were utilized to identify and validate targets of the CDK9 inhibitor. The CDK9 inhibitor plus radiation significantly reduced growth of FLO-1, SKGT4, OE33, and radiation resistant OE33R xenografts and PDXs as compared to the cohorts treated with either single agent CDK9 inhibitor or radiation alone. RPPA identified Axl as a candidate target of CDK9 inhibition. Western blot and qPCR demonstrated reduced Axl mRNA (p = 0.02) and protein levels after treatment with CDK9 inhibitor with or without radiation in FLO-1 and SKGT4 cells. Axl protein expression in FLO-1 xenografts treated with combination of CDK9 inhibitor and radiation was significantly lower than the xenografts treated with radiation alone (p = 0.003). Clonogenic assay performed after overexpression of Axl in FLO-1 and SKGT4 cells enhanced radiosensitization by the CDK9 inhibitor, suggesting dependency of radiosensitization effects of the CDK9 inhibitor on Axl. In conclusion, these findings indicate that targeting CDK9 by BAY1143572 significantly enhances the effects of radiation and Axl is a novel downstream target of CDK9 in esophageal adenocarcinoma.

Highlights

The incidence of adenocarcinoma of the esophagus and gastro esophageal junction has rapidly increased in the USA and other western countries over past 30 years [1, 2]
Radioresistant OE33R cells were established by exposing radiosensitive OE33 cells to weekly doses of 2 Gy radiation and radiation resistance was achieved after 45 fractions of 2 Gy radiation
This study provides strong evidence of efficacy of a novel Cyclin-dependent kinase 9 (CDK9) inhibitor in preclinical models of esophageal adenocarcinoma, supporting a role of targeted inhibition of CDK9 as sensitizer to the radiation in a clinical trial of esophageal adenocarcinoma

Summary

Introduction

The incidence of adenocarcinoma of the esophagus and gastro esophageal junction has rapidly increased in the USA and other western countries over past 30 years [1, 2]. Advent of preoperative chemoradiation in neoadjuvant setting has improved patients’ survival and likelihood of complete surgical resection [3, 4]. In spite of such aggressive therapeutic approach, 5-year survival for these patients is 20–30% [5, 6]; primarily because of development of chemoradiation resistance and inability of chemoradiation to kill all tumor cells to achieve complete pathologic response. Molecular targeted therapy is yet to show efficacy in enhancing chemoradiation efficacy in neoadjuvant setting in esophageal adenocarcinoma. Enhancing radiosenstization by a targeted agent has an advantage of reducing the required dose and toxicity of radiotherapy to the vital organs like heart and lungs

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Conclusion