Abstract
BackgroundOnconase represents a new class of RNA-damaging drugs. Mechanistically, Onconase is thought to internalize, where it degrades intracellular RNAs such as tRNA and double-stranded RNA, and thereby suppresses protein synthesis. However, there may be additional or alternative mechanism(s) of action.MethodsIn this study, microarray analysis was used to compare gene expression profiles in untreated human malignant mesothelioma (MM) cell lines and cells exposed to 5 μg/ml Onconase for 24 h. A total of 155 genes were found to be regulated by Onconase that were common to both epithelial and biphasic MM cell lines. Some of these genes are known to significantly affect apoptosis (IL-24, TNFAIP3), transcription (ATF3, DDIT3, MAFF, HDAC9, SNAPC1) or inflammation and the immune response (IL-6, COX-2). RT-PCR analysis of selected up- or down-regulated genes treated with varying doses and times of Onconase generally confirmed the expression array findings in four MM cell lines.ResultsOnconase treatment consistently resulted in up-regulation of IL-24, previously shown to have tumor suppressive activity, as well as ATF3 and IL-6. Induction of ATF3 and the pro-apoptotic factor IL-24 by Onconase was highest in the two most responsive MM cell lines, as defined by DNA fragmentation analysis. In addition to apoptosis, gene ontology analysis indicated that pathways impacted by Onconase include MAPK signaling, cytokine-cytokine-receptor interactions, and Jak-STAT signaling.ConclusionsThese results provide a broad picture of gene activity after treatment with a drug that targets small non-coding RNAs and contribute to our overall understanding of MM cell response to Onconase as a therapeutic strategy. The findings provide insights regarding mechanisms that may contribute to the efficacy of this novel drug in clinical trials of MM patients who have failed first line chemotherapy or radiation treatment.
Highlights
Onconase represents a new class of RNA-damaging drugs
RNases [5], inhibition of protein synthesis due to transfer RNA (tRNA) damage cannot explain many activities of Onconase [2,6]. Another postulated Onconase mechanism is that it acts as an intracellular catalyst for the generation of interfering RNAs (RNAi) which could trigger apoptosis depending upon the microenvironment of the cell [6]
Onconase inhibits MM cell viability Similar to previous studies [10], cell viability assays showed that some MM cell lines are more responsive to Onconase than others
Summary
Onconase represents a new class of RNA-damaging drugs. Onconase damage to tRNA [1,2,3] causes activation of the caspase cascade in mammalian cells and results in apoptosis [2,4]. RNases [5], inhibition of protein synthesis due to tRNA damage cannot explain many activities of Onconase [2,6]. Another postulated Onconase mechanism is that it acts as an intracellular catalyst for the generation of interfering RNAs (RNAi) which could trigger apoptosis depending upon the microenvironment of the cell [6]. Further information on the structure and therapeutic potential of Onconase is found in several recent reviews [7,8,9]
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