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

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.

CDK9: A Comprehensive Review of Its Biology, and Its Role as a Potential Target for Anti-Cancer Agents

“…BAY1143572 (atuveciclib), a benzyl sulfoximine, is one of the most selective and potent CDK9 inhibitors (IC 50 = 6 nM) currently being evaluated in clinical trials ( 192 ). The compound inhibited the proliferation of cancer cell lines at sub-micromolar concentrations and suppressed the growth of subcutaneous xenograft models of AML ( 134 , 192 ), TNBC ( 157 ), lymphoma ( 143 , 146 ), and esophageal ( 165 ) cancer. BAY1143572 inhibited the phosphorylation of RNAP II CTD on Ser2, downregulated MCL-1 and MYC, and induced apoptosis.…”

RB expression confers sensitivity to CDK4/6 inhibitor–mediated radiosensitization across breast cancer subtypes

“…Furthermore, specific inhibition of CDK9 may be mediated through suppression of Axl-mediated signaling pathways (44). In our study, abemaciclibwhich inhibits other CDK proteins including CDK9was consistently the most potent and effective radiosensitization agent compared to palbociclib and ribociclib, which are more selective for CDK4/6.…”

Patient-derived xenograft: a developing tool for screening biomarkers and potential therapeutic targets for human esophageal cancers

“…Furthermore, the treatment using a CDK9 inhibitor might enhance the cell-killing effect of radiation on EAC. Synergetic effect of the CDK9 inhibitor, BAY1143572 and radiation were assessed in EAC cell lines and PDX models [ 92 ]. By inhibiting CDK9 activation, BAY1143572 could sensitize EAC cells and PDX of EAC to radiation [ 92 ].…”

“…Synergetic effect of the CDK9 inhibitor, BAY1143572 and radiation were assessed in EAC cell lines and PDX models [ 92 ]. By inhibiting CDK9 activation, BAY1143572 could sensitize EAC cells and PDX of EAC to radiation [ 92 ]. The precise mechanism by which CDK4/6/9 inhibitors suppress EC progression remains unclear and needs further investigation.…”