8-azaadenosine and 8-chloroadenosine are not selective inhibitors of ADAR

• Published in: bioRxiv
• Main Authors: Cottrell, Kyle A, Luisangely Soto Torres, Weber, Jason D
• Format: Paper
• Language: English
• Published: Cold Spring Harbor Cold Spring Harbor Laboratory Press 14.05.2021
• Subjects: Adenosine; Adenosine deaminase; Cell activation; Cell death; Interferon; RNA editing; Toxicity; Tumor cell lines
• DOI: 10.1101/2021.05.12.443853

The RNA editing enzyme ADAR, is an attractive therapeutic target for multiple cancers. Through its deaminase activity, ADAR edits adenosine to inosine in dsRNAs. Loss of ADAR in some cancer cell lines causes activation of the type I interferon pathway and the PKR translational repressor, leading to inhibition of proliferation and stimulation of cell death. As such, inhibition of ADAR function is a viable therapeutic strategy for many cancers. However, there are no FDA approved inhibitors of ADAR. Two small molecules have been previously described as inhibitors of ADAR: 8-azaadenosine and 8-chloroadenosine. Here we show that neither molecule is a selective inhibitor of ADAR. Both 8-azaadenosine and 8-chloroadenosine show similar toxicity to ADAR-dependent and independent cancer cell lines. Furthermore, the toxicity of both small molecules is comparable between cell lines with knockdown of ADAR and cells with unperturbed ADAR expression. Treatment with neither molecule causes activation of PKR. Finally, treatment with either molecule has no effect on A-to-I editing of an ADAR substrate. Together these data show that 8-azaadenosine and 8-chloroadenosine are not suitable small molecules for therapies that require selective inhibition of ADAR, and neither should be used in preclinical studies as ADAR inhibitors. Competing Interest Statement JDW is a compensated consultant for Ono Pharmaceuticals. The other authors have no competing interest.